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Polymer Additives

Selection of Light Stabilizers for Polymers

Degradation is an undesirable process in most polymeric applications. It generally leads to changes in the chemical and physical structure of the polymer resulting in the loss of many useful properties. UV degradation of polymers can negatively affect molecular weight, impact resistance, elongation at break, gloss and color. By incorporating weathering stabilizers, the occurrence of such damages can slow down considerably. Explore, in detail, about basics of light stabilizers/UV absorbers and degradation mechanism in different polymers. Also, get tips to select the best suitable light stabilizers/UV absorbers & formulation examples for your polymer applications.

Overview

Need for Light Stabilizers & UV Absorbers in Polymers

Need for Light Stabilizers & UV Absorbers in Polymers

The service life of polymers is limited by their degradation. Degradation can be caused by a number of environmental factors, e.g. temperature, humidity, impurities, mechanical load, irradiation, microorganisms, chemicals and air.

Light stabilizers and UV absorbers combat the degradation that polymers can undergo under the effects of:
  • Sunlight
  • UV rays
  • Heat
  • Reaction with oxygen

For example, several engineering thermoplastics like polyamides being majorly used for outdoor applications require long time U.V stabilization. Polybutylene terephthalate (PBT) finds uses in pigmented automotive exterior applications. Polyurethane based end products like automotive door trims, instrument panels, steering wheels, window sealants, head and arm rests and shoe soles, degrade when exposed to heat and light. Such degradation causes discoloration and formation of cracks.

Addition of light stabilizers and UV absorbers into the polymer mix, improves the appearance/aesthetics and the overall life of the product. Selection of a light stabilizer/UV absorber largely depends upon the substrate to be protected, its envisioned functional life and its sensitivity to photodegradation.



UV Degradation Effects in Polymers

UV Degradation Effects in Polymers

Effects of UV degradation on polymers may be assessed from the factors discussed below.

Effect of UV Degradation on Polymers

  • Change in chemical structure - Natural weathering is normally an oxidative degradation which produces hydroperoxy, hydroxy, carbonyl groups and cross-linking, which can be detected by IR, UV and NMR spectroscopy.

  • Change on surface - Most of the oxidative degradation takes place at the surface of polymeric material because oxidative processes are more intense at surface due to greater availability of oxygen and high temperature. Thus, a brittle outer layer is formed on polymer surface due to weathering and with the help of SEM or optical microscopy it can be observed.

  • Embrittlement - Many oxidative degradation processes cause embrittlement in polymers, which can be easily examined manually.

  • Generation of free radicals - Almost all the degradation processes are free radical reactions and generation of various types of free radicals can be detected by electron spin resonance spectroscopy.

  • Change in molecular weight - Reduction in molecular weight due to chain scission processes is commonly observed phenomenon during polymer degradation. Viscosity measurements and GPC are the commonly used techniques to study this aspect of polymer degradation.

  • Loss in mechanical properties - Change in chemical structure and chain scission processes are reflected in the loss in mechanical properties of a degraded polymeric material.

  • Impairment of transparency - This can be observed even manually that transparent polymeric material loses its transparency upon degradation. This is due to formation of different morphology on polymer degradation. This results in heterogeneity in bulk of a polymeric material, which scatters incident light rather than transmitting it. Eventually polymeric material loses its transparency.

The understanding of degradation mechanisms is further complicated by factors such as morphology, diffusion processes and interactions of additives.

In this guide, you will get familiarize to various UV stabilizers used with these engineering plastics. You would be able to find out the functionalities of different UV stabilizers for different engineering plastics, such as polyamides, polyesters, polycarbonate and more in demand. Let's begin with one of the popular materials - polyamides.

Learn how to prevent polymer degradation with BASF Light Stabilizers.

BASF Light Stabilizers


Mechanism of Oxidation in Aliphatic Polyamides (PA-6, 66, 11, etc.)

Mechanism of Oxidation in Aliphatic Polyamides (PA-6, 66, 11, etc.)

Aliphatic polyamides (PA), also referred as nylons, are the class of thermoplastic polymers which contain the amide repeat linkage in the polymer backbone.

Examples of aliphatic polyamides are PA6, PA66, PA11, PA12 and more. These polyamides are versatile engineering plastic and excellent fiber materials. As per their application, aliphatic polyamides are categorized in two divisions: Polyamide Fibers and Polyamide Thermoplastics.


Polyamide Fibers


Polyamide Fibers for TiresPolyamide fibers are generally manufactured by melt-spun process.

Nylon filaments are mainly used in carpets, apparel, tire reinforcement and in other industrial applications. Polyamide fibers are used in racing car tires and airplane tires owing to their:

  • Excellent strength
  • Adhesion to rubber and
  • Fatigue resistance in these demanding applications

Aliphatic polyamides are used extensively in fiber applications, e.g., for textiles, carpets, and for technical applications. Long term thermal stability is of prime importance.


Polyamide Thermoplastics


Polyamides are important engineering plastics because of their toughness over wide range of temperatures. They have good resistance to impact and abrasion, organic solvents and petroleum products.

Polyamides can be processed by processing techniques like injection molding, extrusion, blow molding etc. Due to their hygroscopic nature and hydrolytically unstable properties, polyamides are well dried before melt processing.

  • Thermoplastic polyamides are used in many automotive applications such as gears, bearings etc. Reinforced nylons are used for exterior body compartments such as fender extensions, decorative louvers, filler plates, head lamp housings, cross-over panels and many other applications.
  • In electrical and electronic area, polyamides are used in making plugs, sockets, switches, connectors.
  • It is commonly co-extruded with polyethylene for food packaging where the oxygen barrier characteristics of nylon and moisture barrier capabilities of PE are required.
  • Other applications include shoes, ski boots, combs, bicycle wheels, cigarette lighters, racket frames, propellers, fans and toys.
Polyamide Thermoplastic Applications
Thick sections glass fiber reinforced polyamides also need to confer long term thermal stability in demanding automotive applications such as engine fans, radiator headers and grills, power steering fluid reservoirs, air brake contacts.


Oxidation Process in Aliphatic Polyamides


Oxidation* is one of the most important of all degradation processes. The initial studies into the oxidation of aliphatic polyamides have been credited to Sharkley & Mochel, Levantovskaya, and Lock & Sagar. These investigations showed there were three principal overall reactions mentioned in the image.
Oxidation of Aliphatic polyamides  
The results also showed that products from the thermo-oxidation of aliphatic polyamides agreed with the mechanistic study of model amides. Their conclusion was that either thermal oxidation or photooxidation is initiated by abstraction of a hydrogen atom from an N-vicinal methylene group and propagates by oxidation of the formed macro-radical.

Primary Site of Attack of Oxygen


Support for the N-vicinal methylene group as the primary site of attack of oxygen on the polymer chain came from hydrolysis experiments on PA6. Homologous aliphatic normal monocarboxylic, dicarboxylic, valeric acid and adipic acid were the main products. There was also simultaneous production of N-alkylamines which indicates a parallel mechanism of degradation.

A revised mechanism for the thermo-oxidation of aliphatic polyamides was produced by Karstens and Rossbach and is supported by many other authors.

  • The mechanism is again based on the primary attack on the N-vicinal methylene group.
  • The radical in the initial step forms at the N-vicinal methylene group then combines with oxygen to give a new radical.
  • This new radical may isomerize or follow various reaction pathways (each involving chain scission) resulting in formation of carbonyl and carboxy end-groups.

Any other methylene group can be oxidized in aliphatic polyamides. This can lead to β-scission, which results in an aldehyde and a free macroradical.

N-acylamides (imides) formed during thermal oxidation of aliphatic polyamides are unstable. They cannot accumulate in the polymer but dissociate into two radicals. Saturated aldehydes are formed by hydrogen abstraction, which then undergo crotonization.

The formation of the nitroxide can occur. It is attributed to a deamination reaction followed by oxidation of the secondary amine.

Oxidation of Methylene Groups


Further, oxidation of methylene groups after formation of N-acylamides has been supported by a number of research groups. However, it has been noted that preferential attack by oxygen is likely to occur at the α-positioned methylene group.
Oxidation of Methylene Groups
The N-acylamide group may be further degraded to acid and cyano groups or subjected to continuing oxidation. Unsaturated N-acylamide can consequently become an α, β-unsaturated carbonyl.

UV/vis active chromophores in aliphatic polyamides result from the consecutive reactions of azomethines and account for the yellowing of polyamides


Thermal Oxidation of Polyamides


Thermal Oxidation of PolyamidesDuring thermal oxidation of polyamides, oxidation products formed are associated with the successive decomposition of hydro-peroxides. PA that contained a high initial concentration of hydro-peroxides show rapid chain scission from the commencement of oxidation, possibly due to the hydro-peroxides inducing β-scission.

The content and ratio of carboxylic and amine end groups can have a significant effect on the rate of thermo-oxidation of polyamides.

A higher ratio of carboxylic end groups to amine end groups makes the polymer more sensitive to oxidation

This can be attributed to the catalytic effect of carboxylic groups on the decomposition of hydro-peroxides.

Conversely, amine end groups can stabilize polyamides. This is attributed to the ability of amine end groups to react with hydro-peroxides and peroxy radicals by a similar mechanism to that of hindered amine stabilizers.

  • Amine end groups also condense with aldehydes and ketones, generated by oxidation, to form aldimines and azomethines respectively.
  • Additional oxidative stability is attributed to this removal of oxidation products and higher tendency for crosslinking by amine end groups.

However, it has been suggested that the consecutive reaction of azomethines results in sequences of conjugated double bonds, which gives rise to the chromophore that accounts for the observed yellowing of polyamides during oxidation.


Heat Stabilizers for Aliphatic Polyamides

Heat Stabilizers for Aliphatic Polyamides

In the processing and manufacture of thermoplastic polyamide (PA6, PA 66, PA 4-6, PA 11, and PA 12) semi-finished products and end products, heat stabilizers have to be added to the plastics to prevent:

  • Prevent discoloring
  • Maintain mechanical properties (being impaired by the decomposition processes that occur)

The same applies to the storage and use of the end products. To prevent the decomposition, stabilizers are added.


Copper salts/Iodide systems


Copper salts/Iodide systemsTraditionally, aliphatic polyamides are stabilized with small amounts of copper salts up to 50 ppm in combination with halogen ions such as iodine and bromine. Copper salts/Iodide systems are very effective at low concentrations.

The mechanism for the stabilization of polyamides is in 2 steps. The first step is the reduction of a hydroperoxide group by iodine (I-) in the presence of an acid to give an alcohol. The alcohol is receptive to chain scission, which is possibly catalyzed by the presence of the transition metal, to give an amine end-group and an aldehyde. Chain scission does occur however autocatalytic initiation of new chains is prevented.

Retardation of the free radical chain oxidation in Polyamides by copper/iodine salts is further supported by the chemiluminescence studies of Cerruti.

They confer good contribution to long term thermal stability at aging temperatures above 150°C. However, their dispersability in substrate can be critical and leaching in contact with water or water/solvent.

Addition of copper salts causes coloring of nylon, incurring serious restrictions on the utility of such nylon.


Aromatic amines


Aromatic amines are classical stabilizers for long term thermal stability applications but need to be used at high concentrations from 0.5 to 2% and can lead to discoloration in nylon after light exposure.

Aromatic amine antioxidants such as 4,4’-Bis(α,α-dimethylbenzyl) diphenylamine are effective to confer good long term thermal stability to aliphatic polyamides.

Phenolic & Secondary Antioxidants


Antioxidants provide good contribution to long term thermal stability. They are more effective than copper salts systems at lower aging temperatures below 150°C with respect to the retention of physical properties. As an additional benefit, initial color prior to thermal aging is better with the antioxidants than with copper salt stabilization. Antioxidants can be split into two groups:

  • Primary phenolic antioxidants which, on the one hand, trap radicals by transferring a hydrogen radical, which causes the formation of a stabilized phenol radical from the phenol, and, on the other hand, also trap a second radical through addition of this stabilized phenol radical to the second radical.
  • Secondary antioxidants which directly decompose hydroperoxide groups by reduction without producing new radicals. Typical for this group are phosphites.


Recommended Heat Stabilizer Package for Aliphatic Polyamides


A very effective heat stabilizer package for aliphatic polyamides can consist of the synergistic combination of the two following additives:

  • 0.25% of the phenolic antioxidant N,N’-hexane-1,6-diylbis(3-(3,5-di-tert.-butyl-4- hydroxyphenylpropionamide) or Triethylene glycol bis(3-tert-butyl-4-hydroxy-5- methylphenyl)propionate.
  • 0.25% of the hydrolytically stable secondary antioxidant Tris(2,4-ditert-butylphenyl) phosphite.


Antioxidant package Advantages Drawbacks
Cu salts/Iodide
  • Good contribution to long term thermal stability at aging T > 150°C
  • Very affective at low dosage levels
  • Leaching in contact with water and solvents.
  • May cause discoloration
  • Dispersability in substrate is critical
  • Copper plate-out
  • Corrosion
Aromatic amines
  • Good contribution to long term thermal stability
  • Strong discoloring properties
  • Need to be used at high concentrations
Phenolic Antioxidants-

N,N’-hexane-1,6-diylbis
(3- (3,5-di-tert.-butyl-4-hydroxyphenylpropionamide)
OR Triethylene glycol bis
(3-tertbutyl-4-hydroxy-methylphenyl)propionate

Secondary Antioxidant-

Tris(2,4-ditert-butylphenyl) phosphite
  • Good contribution to long term thermal stability at T < 150°C
  • Good color performance
  • Inferior long-term thermal stability at T > 150°C compared to Cu salts/Iodide system


Light Stabilizers for Aliphatic Polyamides

Light Stabilizers for Aliphatic Polyamides

One drawback of polyamides is their inadequate weathering resistance for many applications. UV degradation of polyamides can negatively affect impact resistance, elongation at break, gloss and color. By incorporating weathering stabilizers, the occurrence of such damages can slow down considerably.

Mechanism of Photo Oxidation of Aliphatic Polyamides


Spectral ranges causing Photo-oxidationThe absorption** in the short wavelength region of sunlight is attributed to impurities present in polyamides.

Direct chain scissions at wavelengths below 300 nm and photosensitized oxidation above 300 nm were believed to be responsible for photo-oxidation for many years.

The rate of free radical formation in polyamide is probably function of the formation and photochemical transformation of alpha-keto imide groups which is believed to be responsible for photo-initiation of polyamide oxidation by UV light of wavelengths above 360 nm.

It has also been found that photo-oxidation of polyamide PA6 is caused by light in the wavelength range between 260 and 480 nm. 2 distinct spectral regions causing photo-oxidation were detected, one below 300 nm and the other in the range of 340 to 400 nm.

Lemaire et al. carried out much of the work to elucidate the various aspects of the polyamide photo-oxidation which has been discussed below:

  • Direct excitation of the NH-CO chromophore leads to photo-initiation up to wavelengths of 340 nm. Above 340 nm, photo-initiation is due to excitation of chromophores present as impurities in the polymer. Consequently, a dual initiation mechanism is involved under sunlight at wavelengths above 295 nm.
  • The hydro-peroxides formed in polyamides do not show any photo-inductive effect.
  • Even under dry conditions, the main route of disappearance of the imide groups with polyamide photo-oxidation results from hydrolysis with water formed in-situ in close proximity to the imide groups. Imides formed in PA6 are hydrolyzed faster at 60°C than the corresponding imides in PA11 and PA12.

The main photo-oxidation products formed are hydro-peroxides, imides, aldehydes, carboxylic acids, monoxide. Scission of the polymer chain may result from direct photolysis with radiation of wavelengths below 340 nm or from hydrolysis of the imide groups.


Recommended Light Stabilizer Packages for Aliphatic Polyamides


Injection Molded and Extrusion Grades


The addition of free radical acceptors reduces the photo-oxidation rate because the chain oxidation reaction is suppressed. The combination of the phenolic antioxidant N,N’-hexane-1,6-diylbis(3-(3,5-ditert.- butyl-4-hydroxyphenylpropionamide with Tris(2,4-ditert-butylphenyl) phosphite can improve the light stability of polyamides by a factor of 3 to 4.

The ternary combination of the phenolic antioxidant N,N’-hexane-1,6-diylbis(3-(3,5-di-tert.-butyl-4- hydroxyphenylpropionamide with Tris(2,4-ditert-butylphenyl) phosphite and a hindered amine light stabilizer (HALS) is synergistic and confers excellent light stability to polyamides. The addition of a UV absorber UVA to the ternary package further boosts the performance.

Less volatile high Mw UVAs of the hydroxyphenyl-benzotriazole class such as Phenol, 2-(2H-benzotriazol- 2-yl)-4,6-bis(1-methyl-1-phenylethyl) and a High molecular weight HALS such as Poly[[6-[(1,1,3,3- tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6- hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]] are preferred to cope with polyamide processing conditions at high temperatures.

A very effective light stabilizer package for aliphatic polyamides injection molded grades can consist of the synergistic combination of the 4 following additives:

  • 0.25% of the phenolic antioxidant N,N’-hexane-1,6-diylbis(3-(3,5-di-tert.-butyl-4- hydroxyphenylpropionamide) or Triethylene glycol bis(3-tert-butyl-4-hydroxy-5- methylphenyl)propionate.
  • 0.25% of the hydrolytically stable secondary antioxidant Tris(2,4-ditert-butylphenyl) phosphite.
  • 0.25% of the low volatile UV absorber Phenol, 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1- phenylethyl) or Ethanediamide, N-(2-ethoxyphenyl)-N'-(2-ethylphenyl).
  • 0.25% of the high molecular weight hindered amine light stabilizer Poly[[6-[(1,1,3,3- tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6- hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]]).

Injection Molded Polyamide 6/PA6 Grade Formulation


  • Applicable type: 1mm thick injection molded PA6 plaques
  • Applicable base polymer: PA6
  • Applicable industrial sectors: Automotive parts, sport equipments, tool housings

Ingredients Parts by weight
PA6 99.0%
Benzotriazole UV absorber Phenol, 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl) 0.25%
High Mw HALS Poly[[6-[(1,1,3,3-tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl]
[(2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6-hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]])
0.25%
Phenolic AO N,N’-hexane-1,6-diylbis(3-(3,5-di-tert.-butyl-4-hydroxyphenylpropionamide) 0.25%
Phosphite PS Tris(2,4-ditert-butylphenyl) phosphite 0.25%

Injection Molded Polyamide 12/PA12 Grade Formulation


  • Applicable type: 1mm thick injection molded PA12 dumbbells
  • Applicable base polymer: Nylon 12/PA12
  • Applicable industrial sectors: Sport shoe soles

Ingredients Parts by weight
PA12 99.0%
Benzotriazole UV absorber Phenol, 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl) 0.25%
High Mw HALS Poly[[6-[(1,1,3,3-tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl]
[(2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6-hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]])
0.25%
Phenolic AO Triethylene glycol bis(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate 0.25%
Phosphite PS Tris(2,4-ditert-butylphenyl) phosphite 0.25%

Polyamide 11/PA11 Extrusion Grade Formulation


  • Applicable type: Polyamide 11/PA11 extrusion grade
  • Applicable base polymer: Nylon 11/PA11
  • Applicable industrial sectors: Flexible tubes

Ingredients Parts by weight
PA11 99.0%
Oxanilide UV absorber Ethanediamide, N-(2- ethoxyphenyl)-N'-(2-ethylphenyl) 0.25%
High Mw HALS Poly[[6-[(1,1,3,3-tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl]
[(2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6-hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]])
0.25%
Phenolic AO Triethylene glycol bis(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate 0.25%
Phosphite PS Tris(2,4-ditert-butylphenyl) phosphite 0.25%

Fiber Grades


UV absorbers confer some improvement to UV stability of polyamide fibers. However, a high Mw HALS is more effective than UVAs. The ternary combination of a high Mw HALS with a low volatile phenolic antioxidant and a low volatile phosphite provides the best protection with respect to physical properties and color retention.

Light stability
Discoloration
Light stability
Tensile strength
Volatility Profile
No stabilizers Poor Poor N.A
Antioxidant AO Passable Passable Very Good
Antioxidant AO + phosphite PS Average Average Very Good
AO + PS + high Mw UVA Good Good Very Good
AO + PS + low Mw HALS Very Good Good Average
AO + PS + high Mw HALS Excellent Excellent Very Good

A very effective light stabilizer package for aliphatic polyamides fiber grades can consist of the synergistic combination of the 3 following additives:

  • 0.25% of the phenolic antioxidant N,N'-hexane-1,6-diylbis(3-(3,5-di-tert.-butyl-4- hydroxyphenylpropionamide)
  • 0.25% of the hydrolytically stable secondary antioxidant Tris(2,4-ditert-butylphenyl) phosphite
  • 0.25% of the high molecular weight hindered amine light stabilizer Poly[[6-[(1,1,3,3- tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6- hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]])

Polyamide Fiber Grade Formulation


  • Applicable type: PA6 fibers 420/17 technical grade (24.7 dtex / filament), stretch ratio 1:4.2
  • Applicable base polymer: Unpigmented PA6
  • Applicable industrial sectors: Fishing nets

Ingredients Parts by weight
PA6 99.35%
HALS stabilizer- Poly[[6-[(1,1,3,3-tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl]
[(2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6-hexanediyl[(2,2,6,6-tetramethyl-4- piperidinyl)imino]])
0.5%
Phenolic AO- N,N’-hexane-1,6-diylbis(3-(3,5-di-tert.-butyl-4-hydroxyphenylpropionamide) 0.75%
Phosphite PS- Tris(2,4-ditert-butylphenyl) phosphite 0.75%


Aromatic Polyamides - Oxidation Mechanism & Stabilizers

Aromatic Polyamides - Oxidation Mechanism & Stabilizers

Wholly aromatic polyamides (aramids) are high-performance organic materials due to their outstanding mechanical and thermal resistance. Their properties arise from their aromatic structure and amide linkages, which result in stiff rod-like macromolecular chains that interact with each other via strong and highly directional hydrogen bonds. These bonds create effective crystalline micro-domains, resulting in a high-level intermolecular packing and cohesive energy.

The better-known commercial aramids are:

  • Poly(p-phenylene terephthalamide)
  • Poly(m-phenylene isophthalamide)

They are used in advanced technologies and have been transformed into high-strength and flame-resistant fibers and coatings, with applications in the:
Aromatic Polyamide Applications
  • Aerospace and armament industry
  • Bullet-proof body armor
  • Protective clothing
  • Sport fabrics
  • Electrical insulation
  • Asbestos substitutes
  • Industrial filters, among others

Heat Stabilization of Aromatic Polyamides


The synthetic aromatic polyamides differ from the aliphatic polyamides (nylons) on the highly aromatic nature of the polymer backbone. Both nylons and aromatic polyamides are considered engineering materials, but the aromatic structure of the main chain of the aramids endow these polymers with specialty characteristics making them:

  • Less sensitive to oxidation
  • Higher solvent resistant

…and conferring the materials with superior mechanical and thermal resistance, thus being classified as high performance materials. As these materials have relatively high inherent thermal stability, antioxidant additives are not generally necessary.

Light Stabilization of Aromatic Polyamides


Aromatic polyamides are sensitive to UV light.

  • Unprotected yarns tend to discolor from yellow to brown after prolonged exposure. However, discoloration of fresh yarn after exposure to ordinary room light is normal and is not indicative of degradation.
  • Loss of mechanical properties can occur after extended exposure to UV.
  • Degradation occurs in the presence of oxygen, and is not enhanced by moisture or other atmospheric contaminants such as sulfur dioxide.
Unprotected yarns before & after UV exposure
For effective protection of yarn from UV degradation, the wavelength region between 300 to 450 nm is critical and must be excluded. Only small amount of this light occurs in artificial light sources such as fluorescent bulbs or in sunlight filtered by window glass. However, to avoid potential damage yarn should not be stored one foot of fluorescent lamps or near windows.

Aromatic aramid yarns are intrinsically self-screening. External fibers form a protective barrier, which shields interior fibers in a filament bundle or fabric. UV stability increases with size, the denier of the yarn, the thickness of the fabric, or the diameter of a rope.

Extra UV protection can be provided by encapsulation by over braiding with other fiber or by applying an extruded jacket over ropes and cables. Whenever a coating, extrudate or film is used, it should not be UV transparent, but should rather be pigmented to absorb in the 300-450 nm.

UV-resistant additives can also be incorporated into the fibers to increase the fibers' resistance to UV radiation.

One type of UV-resistant additive is UV light absorbers. UV light absorbers are materials that absorb UV radiation to reduce the deleterious effects of that radiation on the medium (fibers in this case) in which the absorber is incorporated. Such UV light absorbers include, for example:

UV Light Absorbers
Another type of UV-resistant additive that can be incorporated into the fibers is hindered amine light stabilizers HALS. HALS stabilizers include, for example, amide compounds and piperidine compounds.

UV light absorbers are particularly effective in improving fabric strength retention, while HALS stabilizers are particularly effective in improving fabric colorfastness

Although they can be used separately, incorporation of both a UV light absorber and a HALS stabilizer into a given fabric can yield improved results in terms of strength retention and/or colorfastness.

The UV-resistant additives can be incorporated into the fibers of the fabric at nearly any stage in the production process. Given that carriers that may be used as dye assistants in the dyeing process, it may be desirable to add the UV-resistant additives to the fibers during the dyeing process, assuming dyeing is performed. In such a case:

  • The UV light absorber(s) can, for example, be provided in the mixture in a concentration of about 2 to 4% on weight of fabric, and
  • HALS stabilizers can be provided in the dye bath in a concentration of about 2 to 3% on weight of fabric.


Recommended Light Stabilizer Package for Aromatic Polyamides/Dyed Fiber Grades


A very effective light stabilizer package for aromatic polyamides can consist of the synergistic combination of the following additives added during the dyeing process:

  • UV absorbers such as 2,4-dihydroxy-benzophenone) or 2,2'-dihydroxy-4,4'- dimethoxybenzophenone), or 2,2'-4,4'-tetrahydroxybenzophenone), or (2-propenoic acid,3- (4Omethoxyphenyl)-,2-ethylhexylester), or 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-lphenylethyl) phenol), or 2-(3,5,Di-(tert)-butyl-2-hydoxyphenyl)-5-chlorobenzotriazole, or 2-hydroxy- 3,5-di-(ter)-amylphenyl)benzotriazole at dosage levels of 2 to 4% on weight of fabric.
  • HALS stabilizers such as (N,N'-1,6-hexanediylbis(N-(2,2,6,6-tetramethyl-piperidinyl-formamide), or Butanedioicacid,dimethylester polymer with 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol, or the liquid stabilizer (1-acetyl-4-(3-dodecyl-2,5-dioxo-l-pyrrolidinyl)-2,2,6,6-tetramethyl-piperidine at dosage levels of 2 to 3% on weight of fabric.

 »  Click here, to know about the FAQ's regarding UV Stabilizers for Polyamides!


UV Stabilizers for Polypropylene (PP)

UV Stabilizers for Polypropylene (PP)

Polypropylene is especially sensitive to UV radiation. It degrades when exposed to light by an oxidative mechanism in which chain scission predominates over cross-linking.

Chain scission leads to an increase in crystallinity which in turn results in surface cracking. The formation of cracks leads to changes in appearance (color and gloss) as well as mechanical failure of parts. Articles for use both outdoors and indoors must be stabilized against UV light.

UV Stabilizers for PP Tapes


PP tapes are usually used in the form of woven or knitted fabrics such as shadow nets, soil covers, or different types of bags and sacks for packing. A different but growing application of tapes is artificial grass flooring for decoration and sport. Tapes are usually made from cut and drawn films and one consequence of the stretching is the increased UV stability of the substrate.

Combining two HALS stabilizers yields the most synergistic effectHowever, only with the addition of appropriate light stabilizers, a very high life span for such thin walled final articles can be achieved. In tapes applications, a good retention of physical properties after light and heat exposure is mostly required. Light stabilizers are also used to improve light fastness of certain organic pigments. Blooming which could be caused by the migration of light stabilizers should be avoided.

In thin-section parts such as tapes, UV absorbers provide little protective benefit. In addition, because of environmental concerns regarding heavy metals, some UV absorbers such as nickel organics are not used anymore. UV absorbers have been largely replaced by HALS. However, the use of UV absorbers such as benzophenones or benzotriazoles is recommended to confer light fastness improvement of certain organic pigments.

The use of derivatives of benzoates as light stabilizers for polyolefins predates that of hindered amines. Like other hindered phenols, the benzoates inhibit the oxidative degradation process by scavenging free radicals. The downside of this mechanism is that it is sacrificial in nature and the benzoates are consumed, unlike the hindered amines which act by a regenerative mechanism. When compared directly, the hindered amines HALS provide superior weatherability versus benzoates.

In polypropylene tape applications, combining two HALS stabilizers yields the most synergistic effect

Using combination of a low molecular mass HALS with a high molecular mass HALS leads to a significant improvement in PP tape applications.

The combination of two high molecular mass HALS comes very close to the low molecular mass HALS. An additional advantage of the combination of two high molecular mass HALS resides in its contribution to the long-term thermal stability of the PP tapes.

Hence, the combination of the two high molecular mass HALS combines the best of the low molecular mass HALS, i.e superior contribution to light stability, with the best of the high molecular mass HALS, i.e, superior contribution to long-term thermal stability.

With respect to pigmented tapes containing organic pigments with limited light fastness, the use of UV absorber as part of the formulation can be beneficial. Here the UV absorber may be acting to improve the light fastness of the organic pigments by quenching of their excited states.

Light stability 
Mechanical properties retention
Light stability Pigments Light fastness Resistance to Migration
Heat stability
Mechanical properties
Impact on formulation costs
UV absorber benzotriazole ++ +++ + + ++
UV absorber benzophenone + +++ + + ++++
UV absorber benzoates ++ + + +++ ++
UV absorber nickel organics + +++ +++ + +
Low Mw HALS +++++ + + ++ +++++
High Mw HALS +++ + +++++ +++++ +++
Combination low HALS + High Mw HALS +++++ + +++ ++++ +++++
Combination polymeric secondary HALS + polymeric tertiary HALS +++++ + +++++ +++++ +++
Combination polymeric secondary HALS + polymeric tertiary HALS + UVA benzotriazole +++++ +++ +++++ +++++ ++

Polypropylene Tapes Formulation


  • Applicable type: PP tape
  • Applicable base polymer: PP homo-polymer, MFI 230/2.16 = 3g/10 min, 8800 dtex tapes.
  • Applicable industrial sectors: Artificial lawn

Ingredients Parts by weight
Green pigmented PP homopolymer 99.4%
Processing aid Ca-Stearate 0.1%
Primary Antioxidant 0.05%
Processing stabilizer 0.05%
High Molecular Mass polymeric secondary HALS 0.15%
High Molecular Mass polymeric tertiary HALS2 0.15%
UVA benzotriazole 0.1%


UV Stabilizers for PP Fibers


UV stabilized used in Geo-membranes There is a wide variety of fiber applications which require a good light stability such as:

  • PP fibers and staple fibers (e.g., geo-membranes and packaging),
  • PP fibers & yarns for automotive interiors and carpets,
  • PP spun-bond nonwovens for colored, outdoor and high-temperature applications.

Very often, PP fibers undergo a thermal treatment, e.g. on crimping or latexing. These thermal treatments can be simulated in an oven. Typically, PP fibers or fabrics are exposed for 20 minutes at 120°C. Such a "simulated tentering" can have an effect on the performance of different light stabilizers. In such conditions, the measurement of physical properties (retention of tensile strength) after light exposure of not heat treated and heat-treated fibers is the criterion of choice.

UV stability of PP fibers provided by benzophenone type UV absorber and a nickel organics is considerably inferior to a low molecular mass HALS.

  • The performance of a high molecular mass HALS is somewhat inferior to that of a low molecular mass HALS, but still superior to UV absorbers. The comparison refers to PP multi-filaments that have not received special thermal treatment.
  • The effect of thermal treatment at 120°C can affect performance of the light stabilizers that have a marked tendency to migrate such as a low molecular weight UV absorber and the low molecular mass HALS. No such a reduction in performance is observed with nickel organics and the high molecular mass HALS.
  • Synergistic performance effects can be achieved with the combinations of high molecular mass HALS.

With respect to pigmented fibers containing organic pigments with limited light fastness, the use of UV absorbers as part of the formulation can be beneficial. Here the UV absorber may be acting to improve the light fastness of the organic pigments by quenching of their excited states.

Light stability of untreated fibers
Mechanical properties retention
Light stability of heat treated fibers
Mechanical properties retention
Light stability Pigments Light fastness Resistance to Migration Impact on formulation costs
UV absorber benzotriazole + + +++ + ++
UV absorber benzophenone + + +++ + ++++
UV absorber nickel organics ++ +++ +++ +++ +
Low Mw HALS +++++ ++ + + +++++
High Mw HALS +++ ++++ + +++++ +++
Combination polymeric secondary HALS + polymeric tertiary HALS ++++ +++++ + +++++ +++
Combination polymeric secondary HALS + polymeric tertiary HALS + UVA benzotriazole ++++ +++++ +++ +++++ ++

Polypropylene Fiber Starting Point Formulation


  • Applicable type: PP fiber
  • Applicable base polymer: PP fiber grade, multifilaments 130/17 dtex, stretch ratio 1 :3.2, 100 % elongation
  • Applicable industrial sectors: Automotive, packaging, carpet

Ingredients Parts by weight
Not pigmented PP fiber grade 99.3%
Processing aid Ca Stearate 0.1%
Primary Antioxidant 0.05%
Processing stabilizer 0.05%
High Molecular Mass polymeric secondary HALS 0.15%
High Molecular Mass polymeric tertiary HALS2 0.15%

UV Stabilizers for PP Thick Sections


For the deeper layers (> 1mm below the surface) of thick section parts, all the UV radiation can be blocked with incorporation of a UV absorber to prevent photo degradation. This serves to improve retention of mechanical properties after exposure.

The superiority of HALS products over UV absorbers is significant.

  • A low molecular mass HALS is considered better than a high molecular mass HALS, especially if retention of impact strength and visual appearance are considered.
  • The light stabilization performance of the HALS mixture is not significantly better than that of the low-molecular weight HALS used alone.
  • The high molecular weight HALS may provide other benefits in the formulation such as improved thermal oxidative stability at moderate temperatures.
  • The use of such combinations is most appropriate when the benefits provided by both components are required in the final application.

The combinations of a low molecular mass HALS and UV absorbers provide some improvement in physical property retention after exposure but no improvement in surface protection (exposure time to cracking) versus the HALS alone. Low molecular weight additives such as benzoates are able to migrate from protected deeper layers to layers closer to the surface in which photo degradation is taking place.

The use of the three components formulation containing HALS, benzoate & UV absorber gives better performance than the two component formulations based on the HALS & benzoate or HALS & UV absorber


Light stability 
Mechanical properties retention
Light stability
Surface aspect
Heat stability
Mechanical properties
Impact on initial color of transparent PP molded grades Impact on formulation costs
UV benzotriazole + + + -- ++
UV benzophenone + + + -- ++++
UV benzoate + + +++ (0) ++
Low Mw HALS +++ ++++ ++ (0) +++++
High Mw HALS ++ +++ +++++ (0) +++
Low Mw HALS + High Mw polymeric HALS ++++ +++++ ++++ (0) ++++
Low Mw HALS + UV benzotriazole +++++ +++ ++ - +++
Low Mw HALS + UV benzophenone ++++ ++++ ++ - +++++
Low Mw HALS + UV Benzotriazoles + UV benzoates +++++ +++++ +++ - +++

PP Thick Section Starting Point Formulation


  • Applicable type: PP injection molding grade, 3.5 mm thick.
  • Applicable base polymer: PP block-copolymer, MFI 190/2.16 = 20 g/10 min.
  • Applicable industrial sectors: Grey pigmented bumpers

Ingredients Parts by weight
PP /EPDM blend 1:1 98.9%
Carbon black 0.15%
White pigment 0.30%
Processing aid Ca Stearate 0.1%
Primary Antioxidant 0.05%
Processing stabilizer 0.1%
High Molecular Mass polymeric HALS 0.2%
Low Molecular Mass HALS 0.2%

 »  Check Out the Light Stabilizers/UV Absorbers Grades for Polypropylene!


UV Stabilizers for Polyethylene (PE)

UV Stabilizers for Polyethylene (PE)

As all polyolefins, the different polyethylene grades are sensitive to UV radiation, although less than PP. For outdoor use, they need special stabilization against UV light. The light stabilizers are in principle the same as for polypropylene. However, there are special technical challenges to be taken into account with films for agriculture.

UV Stabilizers for HDPE Tapes


HDPE tapes are usually used in the form of woven or fabrics such as sacks, knitted bags, carpet backing, wrapping fabrics and many other applications.

In HDPE tapes applications, a good retention of physical properties after light exposure is mostly required. Blooming which could be caused by the migration of light stabilizers should be avoided.

In HDPE tape applications, combining two HALS stabilizers yields the most synergistic effect. Using combination of a low molecular mass HALS with a high molecular mass HALS leads to a significant improvement in HDPE tape applications.

The combination of two high molecular mass polymeric HALS confers the best performance.

Light stability 
Mechanical properties
Resistance to Migration Impact on formulation costs
UV absorber benzotriazole + + ++
UV absorber benzophenone ++ ++ ++++
UV absorber benzoates + + ++
Low Mw HALS ++++ + +++++
High Mw HALS +++ +++++ +++
Combination low Mw HALS + High Mw HALS +++++ +++ ++++
Combination polymeric secondary HALS +  polymeric tertiary HALS ++++++ +++++ +++

HDPE Tapes Formulation


  • Applicable type: HDPE tape, 50 microns thick, stretch ratio 1:6
  • Applicable base polymer: HDPE (Ti-catalyst, d=0.95)
  • Applicable industrial sectors: Sacs, bags

Ingredients Parts by weight
HDPE 99.55%
Processing aid Ca-Stearate 0.1%
Primary Antioxidant 0.05%
Processing stabilizer 0.1%
High Mw polymeric secondary HALS 0.1%
High Mw polymeric tertiary HALS 0.1%

UV Stabilizers for HDPE Injection Molding Grades


Injection molding grades can be applied to a wide range of products from housewares, food containers and ice cream tubs to more demanding applications such as pallets and crates.

Special requirements must be considered to stabilize HDPE thick sections against UV light. Preservation of the mechanical properties of the articles is of considerable importance. Moreover, deterioration of the visible appearance of the articles should be minimized. In this respect, chalking, loss of gloss, and the formation of surface cracks should be avoided. Light stabilizers are also used to improve light fastness of certain organic pigments.

Light stability 
Mechanical properties

Light stability
Pigments light fastness

Impact on initial color
 of
transparent PP molded grades
Impact on formulation costs
UV benzotriazole + +++ - ++
UV benzophenone ++ +++ -- ++++
Low Mw HALS ++++ + (0) +++++
High Mw HALS +++ + (0) +++
Low Mw HALS + UV benzotriazole +++++ +++ - ++++
High Mw HALS + UV benzotraizole ++++ +++ - +++
Combination High Mw secondary HALS +
High Mw tertiary HALS
+++++ + (0) +++
Combination High Mw secondary HALS +
High Mw tertiary HALS + UV benzotriazole 
+++++ +++ - +++

The effectiveness of the benzophenone-type UV absorber is higher than a benzotriazole UV absorber. However, it is still surpassed by low Mw HALS. The low Mw Hindered amine light stabilizer confers better performance than a high Mw polymeric HALS. The effectiveness of Hindered amine light stabilizers can still be improved by combining it with an UV absorber.

In addition, the lightfastness of the pigment can be improved by the addition of small amount of benzotriazole type UV absorber. Performance of high Mw polymeric secondary HALS and high Mw polymeric tertiary Hindered amine light stabilizers is comparable. However, the combination of both polymeric HALS is superior to the best of the components.

HDPE Injection Molding Grades Formulation


  • Applicable type: HDPE pigmented plaques, 2 mm thickness
  • Applicable base polymer: HDPE (Ti catalyst, d=0.96)
  • Applicable industrial sectors: Crates

Ingredients Parts by weight
HDPE 99.45%
Organic red 0.1%
Processing aid Ca-Stearate 0.1%
Primary Antioxidant 0.05%
Processing stabilizer 0.10%
High Mw polymeric secondary HALS 0.05%
High Mw polymeric tertiary HALS 0.05%
UV benzotriazole 0.1%

 »  Check Out the Light Stabilizers/UV Absorbers Grades Designed for HDPE!

UV Stabilizers for LDPE Blown Films


UV stabilizers in AgricultureLow density PE (LDPE) is used mainly for film manufacturing. Applications for LDPE films are in construction (covers) and in agriculture (film tunnels, greenhouses).

Light stabilizers are required to increase the service life of the films. However, the chemical nature of pesticides influences the useful lifetime of greenhouse films. Pesticides used inside greenhouses are mostly sulfur- and/or halogen-based compounds. Hence, they can affect the light stability of greenhouse films in general.

Only a few light stabilizers are suitable for LDPE, because lot of light stabilizers are not compatible at the concentrations necessary for the required protection. They can bloom rather rapidly. Initially, benzophenones and benzotriazoles were used to protect LDPE materials. The development of nickel organics improved the service life of films. However, the use of nickel organics decreased because of their negative impact on the environment and on the initial color of films.

The development of polymeric HALS contributed to overcome many of these problems. The combination of a high Mw polymeric HALS with a UVA is synergistic and leads to an outstanding performance.

However, acidic species from chlorine or and sulfur containing pesticides can reduce the lifetime of greenhouse covers, especially of HALS stabilized greenhouse films. For these reasons, it is necessary to add basic compounds to the stabilizer formulations to preferentially intercept the acidic species formed. The solution is based on combining an efficient High Mw HALS with a metal oxide and a stearate.

In applications where the sulfur concentration in the film of covers is particularly very high up to 3000 ppm, a hydroxylamine ethers derived from HALS exhibits the best performance.

The different light stabilizers considered so far for LDPE homopolymers show the same ranking of performance in an EVA copolymer (10 to 15% vinyl acetate) used for the manufacture of "thermal films" or "Infra Red barriers films".

Light stability 
Mechanical properties
Resistance to Migration
Impact
on
initial color of films
Light stability after pesticide treatment Impact on formulation costs
UV absorber benzotriazole + + - + ++
UV absorber benzophenone + ++ -- ++ ++++
UV absorber Nickel organics ++ ++ --- ++ +
High Mw polymeric HALS ++++ +++++ (0) + +++
High Mw polymeric HALS + UVA +++++ +++ - + ++++
High Mw HALS/oxides/stearates ++++ ++++ (0) ++++ +++
Hydroxylamine ethers derived from HALS ++++ ++++ (0) +++++ ++

LDPE Blown Films Formulation


Applicable type: LDPE homo-polymer, film grade, 200 microns

Applicable base polymer: LDPE homo-polymer

Applicable industrial sectors: Agriculture films exposed to permethrin, chlorine containing pesticide

Ingredients Parts by weight
LDPE 98.77%
Primary Antioxidant 0.03%
High Mw HALS/oxides/stearates 1.2%

 »  Check Out the Light Stabilizers/UV Absorbers Grades for LDPE!

UV Stabilizers for Linear Low Density PE


Linear low density PE (LLDPE) is used for film manufacturing, injection molding, roto molding, blow molding.

A number of grades serve a variety of applications, including stretch films, flexible and general packaging, carrier bags, electrical, housewares, containers, toys, doormats, dust bins, hardware, caps, water pipes and threaded closures. The UV-stabilized grades are ideally suited for applications that require excellent dimensional control, minimal warping, retention of physical properties and color.

The performance of the benzophenone is higher than a benzotriazole type UVA. However, a high Mw polymeric HALS confers a better protection. A combination of a High Mw polymeric tertiary HALS and a high Mw polymeric secondary HALS shows a pronounced synergistic effect in LLDPE.

Light stability 
Mechanical properties
Resistance to Migration
Impact on initial color
of
 transparent m-PE molded grades
Impact on formulation costs
UV absorber benzotriazole + + - ++
UV absorber benzophenone ++ ++ -- ++++
High Mw polymeric secondary HALS ++++ +++++ (0) ++++
High Mw polymeric tertiary HALS ++++ +++++ (0) +++
Combination High Mw secondary HALS + High Mw tertiary HALS +++++ +++++ (0) +++

Linear Low Density Polyethylene Formulation


  • Applicable type: LLDPE rotomolding grade
  • Applicable base polymer: LLDPE
  • Applicable industrial sectors: Non-black water tanks

Ingredients Parts by weight
LLDPE 99.50%
Primary Antioxidant 0.02%
Processing stabilizer 0.08%
Processing aid Ca-Stearate 0.1%
High Mw polymeric secondary HALS 0.15%
High Mw polymeric tertiary HALS 0.15%

 »  Check Out the Light Stabilizers/UV Absorbers Grades for LLDPE!


Explore about the need for antioxidants, and how they impact the processing & long term thermal stability of polyolefins (PP, PE).

Antioxidants  Selection for Polyolefins (PP, PE)


UV Stabilizers for Polyvinyl Chloride (PVC)

UV Stabilizers for Polyvinyl Chloride (PVC)

The low production cost, good processability, easy modification, and excellent chemical resistance of poly(vinyl chloride) (PVC) make it a very attractive and most suitable plastic for a wide variety of outdoor applications, such as house siding panels, exterior claddings, and window profiles.

However, the ultimate user acceptance of the PVC products for outdoor building applications will depend on their ability to resist deterioration of their mechanical and aesthetic properties over long periods of exposure. This is because PVC materials undergo serious chemical and physical modifications, when they are exposed for a long time to natural weathering, especially sunlight.

UV Stabilizers for White Pigmented Flexible PVC


There are many flexible PVC applications which require appropriate light stabilizers. Indeed, such additives can help extend the durability and life expectancy of flexible PVC end-use products such as:

UV Stabilizers for PVC Roofing Membranes
  • PVC roofing membranes
  • PVC pond, pool
  • Irrigation and waste disposal liners
  • PVC coated fabrics for tents, tarps, canopies and awnings
  • Flexible PVC wall coverings and decorative foils
  • PVC flooring and exterior carpeting
  • Exterior and interior automotive trim
  • Outdoor signs and banners

Light stabilizers can protect white pigmented PVC products from the harmful effects of light exposure and helps it maintain physical properties during long-term weathering. Roofing membranes is one of the most demanding flexible PVC applications.

Light stability
Discoloration
White pigmented PVC
Light Stability
Mechanical properties
White pigmented PVC
Impact on formulation costs
No stabilizers +++ + ++++
UV absorber benzotriazoles (0) + ++
UV absorber benzophenone (0) + ++++
Low Mw HALS ++++ ++++ ++++
High Mw HALS ++++ ++++ +++
Non-basic NOR HALS +++++ +++++ +++

When enough light scattering pigment is used, it is usually unnecessary to add UV absorbers to these systems to enhance weatherability. However, HALS used alone confer some color stability and a good retention of physical properties. As PVC degrades it releases hydrochloric acid which neutralizes and deactivates the HALS stabilizer, thus severely reducing the effectiveness of HALS. Non-basic light stabilizers NOR HALS perform very well in an acidic environment and give better durability than traditional HALS.

White Pigmented Flexible PVC Starting Point Formulation


  • Applicable type: Flexible PVC
  • Applicable base polymer: Flexible PVC, white pigmented, containing Ba/Zn heat stabilizer
  • Applicable industrial sectors: Roofing membranes with top ply 0.5 mm thick.

Ingredients Parts by weight
PVC stabilized Ba/Zn stabilizer, white 100%
Plasticizer 70%
CaCO3 15%
NOR HALS 1%

UV Stabilizers for Clear and Transparent Flexible PVC


Usually the appropriate light stabilizers system can extend the useful lifetime of a good flexible WC compound three to four times that of an unstabilized system. This is most evident with clear or transparent flexible PVC articles.

Impact on initial color
Clear flexible PVC
Light stability
Discoloration
Clear flexible PVC
Light Stability
Mechanical properties
Impact on formulation costs
UV absorber benzotriazoles + +++ +++ ++
UV absorber benzophenone ++ ++ ++ ++++
Low Mw HALS +++ + + ++++
High Mw HALS +++ + + +++
UV absorber benzotriazole + Basic low Mw HALS ++ ++++ ++++ +++
Non-basic NOR HALS +++ ++++ +++++ +++
Non basic NOR HALS + Benzophenone +++ +++++ +++++ ++++

The most commonly used UV stabilizers in clear flexible PVC are benzophenone UV absorbers. Conventional hindered amine light stabilizers (HALS) cannot well perform in an acidic environment due to their basicity. As PVC degrades it releases hydrochloric acid which neutralizes and deactivates the HALS stabilizer, thus severely reducing the effectiveness of HALS.

Non-basic light stabilizers NOR HALS perform very well in an acidic environment and give better durability than traditional HALS. However, the synergistic combination of a UV absorber and a NOR HALS confers a good light stability to clear flexible PVC.

Clear Flexible PVC Starting Point Formulation


  • Applicable type: clear PVC system
  • Applicable base polymer: S-PVC
  • Applicable industrial sectors: Calendered floor coverings

Ingredients Parts by weight
SPVC 100%
Plasticizer 50%
Epoxidized soya bean oil 3%
Tin carboxylate 3%
Lubricants 0.5%
NOR HALS 0.5%
UVA 0.5%

 »  Check Out the Light Stabilizers/UV Absorbers Grades for Flexible Polyvinyl Chloride (PVC)!


UV Stabilizers for Rigid PVC


Rigid and semi rigid PVC compounds are materials that typically contain from 0 to 15 phr of plasticizer. They are processed at higher temperatures and require highly effective thermal stabilizers for this reason. Alkyl tin mercaptides are the most efficient heat stabilizers for PVC and are most often the thermal stabilizer of choice for rigid PVC compounds. However, they are known to provide only marginal light stability. Since they are widely used in building products such as sidings, window profiles where UV stability is critical, effective light stabilizers have to be applied.

White Pigmented


The most common way to enhance the weatherability of a tin mercaptide stabilized compound is through the use of a UV light screening pigment, such as titanium dioxide. PVC compounders typically incorporate 8 to 15 phr of a rutile or anatase grade of TiO2, for PVC compounds used in building products. Other inorganic pigments can also function in a similar manner and thus protect the PVC polymer from photo degradation by screening or scattering the incident UV light.

Light stability
Discoloration
White pigmented PVC
Light Stability
Physical properties
White pigmented PVC
Impact on formulation costs
No UV or HALS stabilizers ++++ + +++++
UV absorber benzotriazoles (0) + ++
UV absorber benzophenone (0) + +++
UV absorber Oxanilide (0) + ++
Low Mw HALS +++++ +++++ +++

When enough light scattering pigment is used, it is usually unnecessary to add UV absorbers to these systems to enhance weatherability. However, a low Mw HALS used alone confer some color stability and a good retention of physical properties.

Related Read: PVC Plasticizers and Stabilizers Following Safer Sustainable Path!

White Pigmented Rigid PVC Starting Point Formulation


  • Applicable type: White PVC systems
  • Applicable base polymer: SPVC
  • Applicable industrial sectors: Weatherable Siding, Window Profile Formulations

Ingredients Parts by weight
SPVC 100%
Acrylic impact modifier 5.0-7.0%
Processing aid 1.0-1.5%
Tin mercaptide 1.5-2.0%
Wax 0.3-1.0%
Calcium stearate 0.5 -1.5%
TiO2 white pigment 8.0-15.0%
Fillers 3.5-5.0%

Pastel and Dark Colored


The weatherability of pastel and dark colored rigid PVC compound can be achieved by substituting the more light stable tin carboxylate thermal stabilizers for the tin mercaptides. Although one must adjust the PVC formulation to match the processing stability of the more efficient tin mercaptide systems, the tin carboxylates in combination with a mixture of ultraviolet absorber and hindered amine light stabilizers can provide color-hold and retention of mechanical properties.

Light stability
Pigment light fastness
Light Stability
Physical properties
Impact on formulation costs
UV absorber benzotriazoles ++++ +++ ++
UV absorber benzophenone +++ +++ ++++
UV absorber Oxanilide ++ +++ ++
Low Mw HALS + +++++ ++++
UV absorber benzotriazoles + Low Mw HALS +++++ ++++ +++

The benzotriazole-type UV stabilizers are superior to the hydroxyl-benzophenones and to the oxanilides. The sterically hindered amine light stabilizer HALS has positive effect on the retention of physical properties. However the combination of HALS with a benzotriazole-type UV absorber outperforms the UV absorbers and HALS used alone at the same concentrations.

Pastel Pigmented Rigid PVC Starting Point Formulation


  • Applicable type: Pastel PVC systems
  • Applicable base polymer: SPVC
  • Applicable industrial sectors: Weatherable Siding, Window Profile Formulations

Ingredients Parts by weight
SPVC 100%
Acrylic impact modifier 5.0-7.0%
Processing aid 1.0-1.5%
Tin carboxylate 2.5-3.0%
Wax 0.1-0.6%
Lubricants 0.1-1.0%
Pigments inorganic 1.0-3.0%
TiO2 white pigment (rutile) 5.0-12%
UVA 0.5%
Low Mw HALS 0.5%

Clear Rigid PVC


Since clear rigid PVC is used to package foodstuffs and cosmetics, the light stabilizer selected should be approved for use by the FDA (U.S.A.) or other applicable authority. Usually it is used to protect the contents of packaging by screening out the deleterious UV light.

Impact on initial color
Clear flexible PVC
Light stability
Protection of content
In clear rigid PVC
Regulatory
Impact on formulation costs
Impact on formulation costs
UV absorber benzotriazoles + ++++ ++++ ++
UV absorber benzophenone ++ +++ (0) ++++
UV absorber Oxanilide + ++ (0) ++

The benzotriazole-type UV stabilizer such as 2-(2'-hydroxy-5'-methylphenyl) benzotriazole has the required FDA approvals. It also exhibits a UV performance which is superior to the hydroxyl-benzophenones and oxanilides.

Clear Rigid PVC Starting Point Formulation


  • Applicable type: Rigid PVC film
  • Applicable base polymer: SPVC
  • Applicable industrial sectors: Packaging formulations

Ingredients Parts by weight
SPVC 100%
Modifier MBS 0.0-5.0%
Ca/Zn stabilizer 2.0-3.0%
Epoxidized soybean oil 1.0-1.5%
Wax 0.2-0.4%
Lubricants 0.2-0.5%
Processing aids 0.5-1.0%
UVA 0.25-1.0%

 »  Check Out the Light Stabilizers/UV Absorbers Grades for Rigid Polyvinyl Chloride (PVC)!


UV Stabilizers for Polycarbonate (PC)

UV Stabilizers for Polycarbonate (PC)

Polycarbonate (PC) is one of the most versatile and widely used thermoplastics. It shows excellent mechanical properties and are thermally stable up to 135°C. Polycarbonate is primarily used in applications where high impact resistance and transparency and UV resistance are required. Typical examples are windows for transportation vehicles, globes for streetlights, extruded lighting canopy, etc.

Exposure of PC to UV light leads to surface degradation. This in turn affects various properties of the polymer, particularly impact strength and clarity (yellowing). To reduce yellowing and loss of mechanical properties, in exterior applications, protection of polycarbonate/ stabilization of polycarbonate becomes mandatory.

UV Stabilizers for Polycarbonate Injection Molded Grades


UV exposure of stabilized Polycarbonate leads first to a decrease in discoloration. The time to reach the original yellow shade again (yellowing induction time) is a function of the nature and the concentration of the additive.

Stabilizer Light stability
Discoloration
Tensile elongation Volatility Impact on formulation costs
No stabilizers - - (o) +++++
Low Mw UV Absorber hydroxyphenyl-benzotriazole class +++ +++ ++ +++
High Mw UV Absorber hydroxyphenyl-benzotriazole class +++ +++ ++++ ++
UV Stabilizers for Polycarbonate injection molded grades 

Injection Molded Polycarbonate Grades - Starting Point Formulation


  • Applicable type: 2 mm injection molded grades
  • Applicable base polymer: polycarbonate
  • Applicable industrial sectors: globe lights fixtures

Ingredients Parts by weight
Polycarbonate polymer 99.43%
Processing stabilizer PS 0.07%
High Mw UV Absorber of the hydroxyphenyl- benzotriazole class 0.5%
Ingredients for Injection Molded Polycarbonate Grades 

UV Stabilizers for Polycarbonate Coextruded Grades


Weatherable polycarbonate sheet can be produced by coextruding a cap layer containing a UV absorber over a minimally stabilized bulk layer. Stabilization of thin Polycarbonate grades is difficult because protection by UV absorption is related to sample thickness and absorber concentration according to the Lambert-Beer law.

Nevertheless, it is possible to achieve good UV protection by using hydroxyphenyl-triazine type UV absorbers. They are significantly more efficient than benzotriazole type UV absorbers. The product provides superior long term weatherability because of its strong UV absorbance and its excellent photostability. It is also relatively nonvolatile and has only a minimal effect on melt viscosity. High concentrations of UV Absorbers are recommended in thin films formed on top of Polycarbonate by coextrusion.

Stabilizer Light stability
Discoloration
Tensile elongation Volatility Impact on formulation costs
No stabilizers - - (o) +++++
High Mw UV Absorber hydroxyphenyl-benzotriazole class +++ ++ ++++ ++
UV Absorber of hydroxyphenyl-triazine class +++++ +++++ +++++ +
UV Stabilizers for Polycarbonate coextruded grade

Coexrudetd Polycarbonate twin wall grade - Starting point formulation


  • Applicable type: coextruded layer thickness 25 microns, Polycarbonate sheet 10mm sheet
  • Applicable base polymer: polycarbonate
  • Applicable industrial sectors: coextruded Polycarbonate twin wall sheet

Ingredients Parts by weight
Polycarbonate film 93%
UV Absorber of hydroxyphenyl-triazine class 7.0%
Ingredients for Coextruded Polycarbonate Grades 

Select the Right UV Stabilizer for High Performance


The best performance is achieved with ultraviolet light absorbers (UV Absorber) of the hydroxyphenyl-benzotriazole class. Similar conclusions are reached if test elongation is the test criterion. Usually choosing the right benzotriazoles depends on the application. For extrusion of plates and profiles, low volatility is required to minimize deposits of the light stabilizer on chill rolls and gauging rolls. High molecular weight UV Absorbers of the hydroxyphenyl-benzotriazole class are therefore recommended.

It needs to be pointed out that hindered amine light stabilizers (HALS) are not recommended in Polycarbonate because these basic amine compounds accelerate Polycarbonate hydrolysis.


UV Stabilizers for Polyurethanes (PU)

UV Stabilizers for Polyurethanes (PU)

Polyurethane are among the most versatile polymers. They are used in a wide variety of applications including:

  • Adhesives & sealants
  • Coatings
  • Fibers
  • Reaction-injection molded components
  • Thermoplastic parts
  • Elastomers and
  • Both rigid and flexible foams

Polyurethane offer an impressive range of performance characteristics. The use of appropriate stabilizers can extend the service life of polyurethane products. Selecting the best stabilization system depends on:

  • Specific production conditions
  • End-use environment and
  • Understanding of the fundamental degradation mechanisms of the polyurethane components.

Degradation of both the polyol and urethane components will cause changes in the physical or mechanical properties of the polyurethane. Urethanes are susceptible to degradation by free radical pathways induced by exposure to heat or ultraviolet light. The use of UV absorbers and hindered amine stabilizers protects polyurethane from UV light-induced oxidation.

This selection guide will enable you to select the right light/UV Stabilizer for aromatic & aliphatic TPU, Polyurethane Reaction Injection Molded Foam, Polyurethane fibers and adhesives & sealants. It will also acquaint you with polyurethane processing and the possible applications of polyurethane.

UV Stabilization of Aromatic TPU


Aromatic TPU based on isocyanates like MDI are workhorse products and can be used in applications that require flexibility, strength and toughness. There are also applications which require good light stability such as shoe soles for example. The poor light stability of aromatic TPU requires the use of robust light stabilizers packages.

Light stability
Discoloration
Aromatic PUR
Light stability
Physical properties
Aromatic PUR
Handling
Impact
on
formulation costs
No stabilizers - - (0) +++++
UVA benzotriazole solid + + + ++
UVA benzotriazole liquid + + +++++ +
UVA Benzotriazole solid + AO ++ ++ + ++
Low Mw HALS solid ++++ ++++ + ++++
Low Mw HALS liquid ++++ ++++ +++++ +++
High Mw HALS +++ +++ + +++
Ternary liquid LS package: Liquid UVA benzotriazole +
Liquid Low Mw HALS + Liquid AO
+++++ +++++ +++++ ++

Light stabilizers do provide some improvement in light stability for aromatic polyurethane. Low molecular weight hindered amine light stabilizers are somehow effective to confer a reasonable light protection & good light stability to aromatic TPU. However a ternary liquid package composed of a liquid phenolic antioxidant, a liquid UV absorber and a liquid low Mw HALS provides the best long term light stability whilst conferring ease of handing.
Ternary Liquid Package

Aromatic TPU/Starting Point Formulation


  • Applicable type: Aromatic TPU film
  • Applicable base polymer: Aromatic polyester urethane cast film
  • Applicable industrial sectors: Laminated film 60 microns.

Ingredients Parts by weight
Aromatic TPU 99%
Liquid Antioxidant 0.2%
Liquid Benotriazole UVA 0.4%
Liquid Low Mw HALS 0.4%

UV Stabilization of Aliphatic TPU


Aliphatic TPU based on isocyanates like H12 MDI, HDI and IPDI are inherently light stable and offer excellent optical clarity. They are commonly employed in automotive interior and exterior applications and as laminating films to bond glass and polycarbonate together in the glazing industry. They are also used in projects where attributes like optical clarity, adhesion and surface protection are required.

Light stability
Discoloration
Aliphatic PUR
Light stability
Physical properties
Aliphatic PUR
Handling
Impact
on
formulation costs
No stabilizers + + (0) +++++
UVA benzotriazole powder ++ ++ + ++
UVA benzotriazole liquid ++ ++ +++++ +
UVA Benzotriazole solid + AO powder +++ +++ + ++
Low Mw HALS powder ++++ +++++ + ++++
Low Mw HALS liquid ++++ +++++ +++++ +++
High Mw HALS powder ++ ++++ + +++
Ternary liquid LS package: Liquid UVA benzotriazole + Liquid Low Mw HALS + Liquid AO
+++++ +++++ +++++ ++

Light stabilizers are particularly effective in aliphatic polyurethanes. Their protection effect in aliphatic TPU is much more pronounced than in aromatic TPU. Benzotriazole UV absorbers and hindered amine light stabilizers provide an outstanding light stability to aliphatic polyurethanes. However, the liquid synergistic package composed of a liquid UV absorber, a liquid low Mw HALS and a liquid antioxidant provides the best protection after UV exposure whilst conferring ease of handling.

Aliphatic TPU/Starting Point Formulation


  • Applicable type: Aliphatic TPU film
  • Applicable base polymer: Polyester urethane cast film based on aliphatic polyisocyanates
  • Applicable industrial sectors: Laminated film 60 microns.

Ingredients Parts by weight
Aliphatic TPU 99%
Liquid Antioxidant 0.2%
Liquid Benotriazole UVA 0.4%
Liquid Low Mw HALS 0.4%

UV Stabilization of Polyurethane Reaction Injection Molded Foam


Polyurethane parts can be made by the RIM (reaction injection molding) process. Raw materials are injected into a mold where the polymerization occurs. Depending on the end use of the product, enhanced light stability may be required. In particular, automotive parts and closed cell expanded PUR for shoe sole compounds have stringent performance requirements for which light stabilizers are used.

Light stability
Discoloration
Reaction Injection Molded Polyurethane
Light stability
Surface microcracks
Reaction Injection Molded Polyurethane
Handling
Impact
on
formulation costs
No stabilizers + + (0) +++++
UVA benzotriazole powder ++ ++ + ++
UVA benzotriazole liquid ++ ++ +++++ +
Low Mw HALS powder + +++ + ++++
Low Mw HALS powder + UVA benzotriazole powder +++ +++ + +++
Low Mw HALS (powder)+ UVA (powder)
+ Antioxidant (powder)
++++ +++++ + +++
Ternary liquid LS package: UVA benzotriazole (liquid) +
Low Mw HALS (liquid) + Antioxidant (liquid)
+++++ +++++ +++++ ++

In RIM applications, the use of HALS alone is inferior to the UV absorbers. The combination of a low Mw hindered amine light stabilizer HALS with a benzotriazole UV absorber yields an increase in performance. The best protection is conferred with the three component stabilization system based on a liquid low molecular HALS, a liquid UVA and a liquid antioxidant.

Polyurethane Reaction Injection Molded Foam Starting Point Formulation


  • Applicable type: White pigmented polyurethane integral foam
  • Applicable base polymer: Polyester polyurethane
  • Applicable industrial sectors: Shoe soles

Ingredients Parts by weight
White RIM 98.5%
Liquid Antioxidant 0.3%
Liquid Benotriazole UVA 0.6%
Liquid Low Mw HALS 0.6%

UV Stabilization of Polyurethane Fiber


Polyurethane fiber, commonly known as spandex, is a synthetic elastomeric fiber. It is strong with very high extensibility and elasticity making it ideal for such textile applications as swimsuits, hosiery and fitness garments. For enhanced performance demanded by consumers, light stability for exterior exposure is required.

Light stability
Discoloration
PUR Fiber
Light stability
Degree of Crazing
PUR Fiber
Handling
Impact on formulation costs
No stabilizers + + (0) +++++
UVA1 benzotriazole +++ ++ + ++
UVA2 benzotriazole liquid +++ +++ ++++ +
Low Mw HALS1 ++ ++ + ++++
High Mw HALS2 ++ ++++ ++++ +++
UA1 + Low Mw HALS1 ++++ ++ + +++
UA2 + High Mw HALS2 ++++ ++++ ++++ +++
UA2 + High Mw HALS2 + AO +++++ +++++ +++++ +++

Benzotriazole UV absorbers used alone or in combination with a HALS confer a good color retention to PUR fibers after UV exposure. However, the use of two volatile UVA and HALS lots during fiber processing can lead to a premature failure of physical properties after light exposure. Low volatile light stabilizers are therefore recommended. The ternary combination of a low volatile phenolic antioxidant with a low volatile benzotriazole UV absorber and a low volatile HALS provides the best light stability in PUR fibers applications.

Polyurethane Fiber Starting Point Formulation


  • Applicable type: Polyurethane fibers
  • Applicable base polymer: Polyurethane
  • Applicable industrial sectors: Textiles

Ingredients Parts by weight
PUR Fibers 98.5%
Low volatile Antioxidant 0.5%
Low volatile Benotriazole UVA 0.5%
Low volatile High Mw HALS 0.5%

Polyurethane Adhesives and Sealants UV Stabilization


Polyurethanes are widely used for formulating adhesives and sealants. Polyurethane adhesive formulations include both solvent-based as well as hot-melt. In some cases, high-performance adhesives can replace standard mechanical bonding methods such as nuts and bolts, screws and welding. Appropriate stabilizers are important in retarding degradation and maintaining physical properties for production of high quality adhesives.

Light stability
Discoloration
PUR sealants
Light stability
 Degree of Crazing
 PUR sealants
Handling
Impact
on
formulation costs
No stabilizers + + (0) +++++
UVA benzotriazole powder ++ ++ + ++
UVA benzotriazole liquid +++ ++ +++++ +
Low Mw HALS powder + +++ + ++++
Low Mw HALS powder + UVA benzotriazole powder +++ +++ + +++
Low Mw HALS (powder)+ UVA (powder)
+ Antioxidant (powder)
++++ +++++ + +++
Ternary liquid LS package: UVA benzotriazole (liquid) + Low Mw HALS (liquid) + Antioxidant (liquid)
+++++ +++++ +++++ ++

All the stabilization systems confer good stability to Polyurethane sealants. The combination of a liquid phenolic antioxidant with a liquid benzotriazole UV absorber and a liquid HALS provides the best light stability in Polyurethane used as a sealant. The discoloration and crazing formation can be significantly reduced through such a liquid package.

Polyurethane Sealant Starting Point Formulation


  • Applicable type: Polyurethane sealant
  • Applicable base polymer: Polyurethane
  • Applicable industrial sectors: Adhesives

Ingredients Parts by weight
Polyurethane sealant 98.75%
Liquid Antioxidant 0.25%
Liquid Benotriazole UVA 0.5%
Liquid Low Mw HALS 0.5%

 »  Check Out the Light Stabilizers/UV Absorbers Grades for Polyurethane!


UV Stabilizers for Polyoxymethylene (POM)

UV Stabilizers for Polyoxymethylene (POM)

Polyoxymethylene (POM), also known as polyacetal is an engineering thermoplastic which offers many excellent properties including high stiffness, low wear, good resilience, low water absorption. The most common forming processes for polyacetal are injection molding and extrusion (sheets and rods), but also blow molding and rotational molding are possible.

Polyoxymethylene is mainly used for technical parts where the mentioned mechanical properties give it an advantage over other plastics. Typical polyoxymethylene applications are gears, springs, chains, screws, handles, zippers, clips, fuel pumps, Inhalers, furniture sliders.

UV stabilization is mandatory for outdoor use of POM articles. In particular, the properties of exterior parts of automobiles and parts of electrical appliances and business machines are likely to deteriorate when subjected to ambient conditions of use, such as solar rays, rain, fluorescent lamps and air. Thus, parts formed of polyacetal resins may, during use, become discolored, lose their surface smoothness resulting in a reduction of gloss, and/or experience crack formation on the parts' surfaces. Such deterioration may thus impair the parts' appearance and/or mechanical properties.

The matrix below will inform you about the various UV stabilizers that can be used with POM resins and what are their other impacts on the resin.

Stabilizer Discoloration after light exposure Time to chalking after light exposure Loss of gloss after exposure Impact on formulation costs
No stabilizers ++++ - - +++++
UVA hydroxyl-benzophenone type + ++ ++ ++++
Low Mw UV Absorber of hydroxyphenyl -benzotriazole class + +++ +++ +++
High Mw UV Absorber of hydroxyphenyl-benzotriazole class + ++++ ++++ ++
High Mw HALS ++++ +++ + +++
High Mw UV Absorber of hydroxy phenyl-benzotriazole class + High Mw HALS + +++++ +++++ +++
UV Stabilizers for POM Grades

It is possible to significantly retard formation of chalking and maintain gloss after UV exposure by using UV absorbers of the 2-hydroxybenzophenone and 3-hydroxyphenyl-benzotriazole type. A low volatile high Mw UV Absorber of the hydroxyphenyl-benzotriazole class is preferred to cope with processing conditions at high temperatures.

A low volatile polymeric HALS is also effective in POM resins and retard formation of chalking in a comparable way to that obtained with UV absorbers. However, if ancillary properties are also considered, e.g yellowing on thermal treatment, there is a definite advantage in favor of HALS.

POM chalking is usually seen only after long exposure. By then a considerable number of surface cracks may be apparent and the samples may have lost most of their gloss. Therefore both crack formation and loss of gloss become test criteria for stabilizer effectiveness. The combination HALS/UV Absorber confers the best effect on the loss of gloss and surface cracking.

Injection-molded Polyoxymethylene Starting point formulation

  • Applicable type: 2mm thick injection molded Polyoxymethylene copolymer plaques
  • Applicable base polymer: Polyoxymethylene copolymer
  • Applicable industrial sectors: automotive exterior molded parts, molded parts of electrical appliances

Ingredients Parts by weight
POM copolymer 98.85 %
Ca-stearate 0.3%
Phenolic antioxidant 0.15%
High Mw UV Absorber of the hydroxyphenyl-benzotriazole class 0.3%
Polymeric HALS 0.4%


UV Stabilizers for Polyesters (PET, PBT...)

UV Stabilizers for Polyesters (PET, PBT...)

Linear polyesters or thermoplastic polyesters include polyethylene terephthalate (PET) and polybutylene terephthalate (PBT).

  • PET fibers have been used for a long time for clothing, carpeting, upholstery, and tire cords.
  • PET and PBT have many applications in films, coatings, beverage bottles, appliances, plumbing, and transportation.

On exposure to UV radiation, polyethylene terephthalate fibers tend to lose their elasticity, elongation, and tensile strength. Polyester films discolor, show surface crazing, and become brittle. UV protection is therefore required in applications sensitive to UV radiation.

Polybutylene terephthalate easily absorbs UV radiation below 300nm. Therefore, impact can only be found on the exposed surface of the plastic. Though it is known that PBT and PET have superior UV resistance when compared to polyolefins, still prolonged exposure can lead to yellowing of the surface and other defects. This calls for the addition of UV stabilizers for these engineering plastics.

UV Stabilization of Polybutylene Terephthalate


Polybutylene Terephthalate end products tend to crack, lose their gloss, turn yellow and are not able to retain their tensile strength when exposed to UV light for longer durations. It therefore becomes necessary to add a UV stabilizer to combat the negative effects UV light may have on their surfaces. The matrix below would help you find the ideal UV stabilizer for Polybutylene Terephthalate. It would also inform you about the other add on properties of these UV stabilizers when used with PBT products.

Stabilizers Light Stability
Initial color
Light stability
Discoloration after exposure
Light stability
Mechanical properties
Volatility Impact on formulation costs
No stabilizers +++++ - - (0) +++++
Low Mw UV Absorber of hydroxyphenyl- benzotriazole class ++ + +++ ++ +++
High Mw UV Absorber of hydroxyphenyl- benzotriazole class ++ ++ ++++ ++++ ++
UV Absorber of hydroxyphenyl- triazine class +++ ++++ +++++ +++++ +

The benzotriazole-type UV stabilizers are generally the first choice because they exhibit low initial color and good color stability. High Mw UV absorbers of the hydroxyphenyl-benzotriazole class are preferred because of their lower volatility. However, UV stabilizers of the hydroxyphenyl-triazine class give the best protection, whether test criterion is initial color, yellowing after exposure, or mechanical properties.

Injection-molded Polybutylene terephthalate - Starting point formulation


  • Applicable type: 1mm thick injection molded Polybutylene terephthalate plaques
  • Applicable base polymer: Polybutylene terephthalate
  • Applicable industrial sectors: exterior mirror housing

Ingredients Parts by weight
Polybutylene terephthalate 99 %
Phenolic antioxidant 0.1%
Phosphite processing stabilizer 0.4%
UV Absorber of  hydroxyphenyl-triazine class 0.5%

UV Stabilization of Polyethylene Terephthalate Injection Molded Grades


Stabilizers Light Stability
Initial color
Light stability
Discoloration after exposure
Light stability
Gloss Retention
Volatility Impact on formulation costs
No stabilizers +++++ - - (0) +++++
Low Mw UV Absorber of hydroxyphenyl- benzotriazole class ++ + + ++ +++
High Mw UV Absorber of hydroxyphenyl- benzotriazole class +++ ++ + ++++ ++
UV Absorber of hydroxyphenyl- triazine class +++ +++ +++++ +++++ +

The UVAs of the hydroxyphenyl-triazine class give the best protection, whether test criterion is initial color, yellowing after exposure, or gloss retention.

Injection molded Polyethylene Terephthalate - Starting point formulation

  • Applicable type: 2mm thick injection molded Polyethylene terephthalate plaques
  • Applicable base polymer: Polyethylene terephthalate (PET-G)
  • Applicable industrial sectors: food containers used outdoor

Ingredients Parts by weight
Polyethylene terephthalate (PET-G) 99.8 %
UVA of the hydroxyphenyl-triazine class 0.2%

UV Stabilization of PET Fiber Grades

It is more difficult to stabilize PET fibers than PET sheets because UV absorbers are less efficient in thin articles. Light stability improvements are however possible in fibers by adding UV absorbers.

Stabilizers Light stability Mechanical properties Volatility Polyester hydrolysis Impact on formulation costs
No stabilizers - (0) (0) +++++
Low Mw UV Absorber of hydroxyphenyl- benzotriazole class ++ ++ (0) +++
High Mw UV Absorber of hydroxyphenyl- benzotriazole class +++ ++++ (0) ++
Low Mw HALS +++ ++ - ++++
UV Absorber of hydroxyphenyl- benzotriazole class + low Mw HALS +++++ +++ - +++
UV Absorber of hydroxyphenyl- triazine class ++++ +++++ (0) +

The benzotriazole-type UV absorbers are generally the first choice because they exhibit good retention of mechanical properties (tensile strength). Low volatile high Mw UVAs of the hydroxyphenyl-benzotriazole class are preferred to cope with processing conditions at high temperatures.

Hindered amine light stabilizers HALS, like other amines, may catalyze polyester hydrolysis. However, the performance of a low Mw HALS is comparable of a UV Absorber benzotriazole. Though the combination of a HALS with a UV absorber shows a very good performance, the use of an UV Absorber alone of the hydroxyphenyl-triazine class exhibits the best protection with respect to retention of mechanical properties after UV exposure without conferring any risk for polyester hydrolysis.

PET Fibers Starting point formulation

  • Applicable type: PET fiber grade multi-filaments 110/24
  • Applicable base polymer: PET
  • Applicable industrial sectors: textiles

Ingredients Parts by weight
Polyethylene terephthalate (PET) 99.3 %
UVA of the hydroxyphenyl-triazine class 0.7%
UV Stabilizers for Styrenic Polymers

UV Stabilizers for Styrenic Polymers

Preventing yellowing after light exposure is especially important in crystal PS and styrene acrylonitrile copolymers SAN. Hence, light stabilization is necessary for articles to be exposed to UV light, e.g covers for fluorescent lights.

Styrenic plastics such as Acrylonitrile Butadiene Styrene graft copolymers ABS and impact resistant PS are very sensitive to oxidation, essentially because of their polybutadiene content. Degradation of weathering starts on the surface and results in fast loss of mechanical properties such as impact strength.

UV Stabilizers for Crystal Polystyrene (PS)


General purpose polystyrene resins are transparent polymers suitable for injection molding or extrusion applications. Uses for these products vary from foodservice and food packaging to refrigerator components to healthcare and diagnostic labware to XPS insulation. Preventing yellowing after light exposure is important in some applications such as covers for fluorescent lights.
Applications of Crystal Polystyrene
UV absorbers can improve significantly the light stability of crystal polystyrene. UV absorber of the 2(2'-hydroxyphenyl) benzotriazole type are used almost exclusively in crystal PS. The benzotriazole-type UV absorber confers a much better light stability than the benzophenone-type UV absorber.

The system composed of a UV benzotriazole absorber and a low Mw HALS performs better than the UV absorber alone or the low Mw HALS alone.

Impact on initial color

Light stability
Discoloration

Light Stability
Color fastness
Impact on formulation costs
UV absorber benzotriazole (0) +++ ++++ ++
UV absorber benzophenone (0) + + ++++
Low Mw HALS -- ++++ ++++ +++++
Combination UV absorber Benzotriazole + Low Mw HALS -- +++++ ++++ ++

Crystal Polystyrene Formulation


  • Applicable type: Crystal Polystyrene, 2 mm injection molded polystyrene plaques
  • Applicable base polymer: Crystal Polystyrene
  • Applicable industrial sectors: Covers for fluorescent lights

Ingredients Parts by weight
Crystal Polystyrene 99.50%
UV benzotriazole absorber 0.25%
Low Mw HALS 0.25%

 »  Check Out the Light Stabilizers/UV Absorbers Grades for Polystyrene (PS)!

UV Stabilizers for High Impact Polystyrene (HIPS)


HIPS is a low-cost plastic material that is easy to machine and fabricate. HIPS is often specified for low strength structural applications when impact resistance, machinability, and low cost are required. It is frequently used machining pre-production prototypes since it has excellent dimensional stability and is easy to fabricate, paint and glue. There are applications such as covers, housings, signage, display items which require effective light stabilizers to retard their yellowing and maintain their physical properties after light exposure.

Impact on initial color

Light stability
Discoloration
Light Stability
Mechanical properties
Impact on formulation costs
UV absorber benzotriazole (0) ++ ++ ++
Low Mw HALS (0) ++ ++ +++++
Liquid low Mw HALS (0) +++ +++ ++++
Combination UV absorber Benzotriazole + Low Mw HALS (0) ++++ ++++ +++
Combination UV absorber Benzotriazole + liquid low Mw HALS (0) +++++ +++++ ++++

High Impact Polystyrene Formulation


  • Applicable type: HIPS, 2 mm injection molded polystyrene plaques
  • Applicable base polymer: HIPS
  • Applicable industrial sectors: Signage, housings

Ingredients Parts by weight
HIPS 99.5%
UV benzotriazole absorber 0.25%
Low Mw HALS 0.25%

 »  Check Out the Light Stabilizers/UV Absorbers Grades for High Impact Polystyrene (HIPS)!

UV Stabilizers for Styrene Acrylonitrile Copolymers (SAN)


Styrene acrylonitrile copolymers (SAN) feature a very well-balanced property profile ranging from excellent transparency and good chemical resistance to high stiffness, extraordinary heat resistance as well as very good dimensional stability. These polymers comprise a broad selection of grades designed for injection molding and extrusion applications.

The combination of transparency and resistance to oils, fats and cleaning agents make SAN very suitable for use in the kitchen as mixing bowls and basins and fittings for refrigerators. It is also used for the outer casings of thermally insulated jugs, for tableware, cutlery, coffee filters, jars and beakers as well as storage containers for all kinds of foods. An additional application is in multi-trip tableware for the catering sector. The pleasing appearance especially when colored and the ease of printing on SAN have allowed a number of applications in the bathroom (toothbrushes and bathroom fittings) and cosmetic packaging.

Applications which require light stability protection to retard yellowing after light exposure include advertising signs, garage door window, industrial door glazing.

Impact on initial color

Light stability 
Yellowness Index
Light Stability
Color fastness
Impact on formulation costs
UV absorber benzotriazole (0) ++++ ++++ ++
UV absorber benzophenone (0) + + ++++
Low Mw HALS (0) ++ ++ ++++++
Combination UV absorber Benzotriazole + Low Mw HALS (0) +++++ ++++++ +++

Styrene Acrylonitrile Formulation


  • Applicable type: SAN, 2 mm injection molded polystyrene plaques
  • Applicable base polymer: SAN copolymer 75% styrene + 25% acrylonitrile
  • Applicable industrial sectors: Fittings for shops and exhibitions, industrial door glazing

Ingredients Parts by weight
SAN 99.5%
UV benzotriazole absorber 0.25%
Low Mw HALS 0.25%

For the light stabilization of SAN the same conclusions are valid in principle as for crystal PS. UV absorbers can improve significantly the light stability of SAN. UV absorber of the 2(2'-hydroxyphenyl) benzotriazole type is widely used in crystal PS.

The benzotriazole-type UV absorber confers a much better light stability than the benzophenone-type UV absorber. However, the best protection is achieved with the synergistic combination of a UV benzotriazole absorber and a low Mw HALS.

 »  Check Out the Light Stabilizers/UV Absorbers Grades for Styrene Acrylonitrile Copolymers (SAN)!

UV Stabilizers for Acrylonitrile Butadiene Styrene Graft Copolymer (ABS)


Acrylonitrile Butadiene Styrene is an ideal material wherever surface quality, colorfastness and luster are required.

Because of its good balance of properties, toughness/strength/temperature resistance coupled with its ease of molding and high quality surface finish, ABS has a very wide range of applications.

These include domestic appliances, telephone handsets computer and other office equipment housings, lawn mower covers, safety helmets, luggage shells, pipes and fittings, automotive interior and exterior trim components. There are applications such as automotive trim components, protective carrying cases which require effective light stabilizers to retard their yellowing and maintain their physical properties after light exposure.

Impact
on
initial color

Light stability
Discoloration

Light Stability
Mechanical properties
Light stability
followed by storage
in the dark
Discoloration
Impact on formulation costs
UV absorber benzotriazole - ++ ++ + ++
Low Mw HALS (0) ++ ++ ++ +++++
Liquid low Mw HALS (0) ++ ++ +++ ++++
Combination UV absorber Benzotriazole + Low Mw HALS - +++++ +++++ +++ +++
Combination UV absorber Benzotriazole + liquid low Mw HALS - ++++ +++++ +++++ ++++

Acrylonitrile Butadiene Styrene Formulation


  • Applicable type: Acrylonitrile Butadiene Styrene, 2 mm injection molded polystyrene plaques
  • Applicable base polymer: Acrylonitrile Butadiene Styrene
  • Applicable industrial sectors: Automotive trim components, luggage, protecting carrying cases

Ingredients Parts by weight
Acrylonitrile Butadiene Styrene (ABS) 98.8%
Primary antioxidant 0.2%
UV benzotriazole absorber 0.50%
Liquid Low Mw HALS 0.5%

UV degradation of Acrylonitrile Butadiene Styrene results in fast loss of mechanical properties such as impact strength. A benzotriazole-type UV absorber can contribute to weathering stability of ABS. The use of a low Mw HALS confers a better physical retention of physical properties than UV absorbers. However, the combination of a low Mw HALS with a UV benzotriazole type absorber provides the best effect on the impact strength of Acrylonitrile Butadiene Styrene. The UV absorber protects the deeper layers, and the low Mw HALS provides surface protection. At the same time, discoloration is reduced significantly.

The liquid HALS (Mixture of Bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate and methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebecate) is better than the solid low Mw HALS (Bis(2,2,6,6,-tetramethyl-4-piperidyl)sebacate) if subsequent discoloration on storage in the dark is also taken into account. The combination of the liquid HALS and a UV absorber also provides a slightly better retention of impact strength than the combination of a solid low Mw HALS and a UV absorber.

For very demanding outdoor applications, ABS can be capped with a very weatherable polymer such as ASA (Acrylonitrile Styrene Acrylate). ASA cap protects Acrylonitrile Butadiene Styrene from the damaging effects of sunlight. ABS capped with ASA is used in many applications exposed to UV light including camper tops, swimming pool steps, SUV running boards, boat decks and hulls, golf carts, surf boards, outdoor equipment covers.

 »  Check Out the Light Stabilizers/UV Absorbers Grades for Styrene Acrylonitrile Polymers (SAN)!


FAQ

FAQ

Question 1. Why do aromatic polyamides need light stabilization?

Answer: Aromatic polyamides are sensitive to UV light. Unprotected yarns tend to discolor from yellow to brown after prolonged exposure. Loss of mechanical properties can occur after extended exposure to UV. Find out more about aromatic polyamides light stabilization here.

Question 2. Which environmental factors affect the service life of polymers?

Answer
: The service life of polymers is limited by their degradation, which can be caused by a number of environmental factors, e.g. temperature, humidity, impurities, mechanical load, irradiation, microorganisms, chemicals and air.

Question 3. How are aliphatic polyamides stabilized?

Answer
: Traditionally, aliphatic polyamides are stabilized with small amounts of copper salts up to 50 ppm in combination with halogen ions such as iodine and bromine. Copper salts/Iodide systems are very effective at low concentrations. The two step mechanism for stabilization of polyamides can be found here.

Question 4. Which light stabilizers/UV Absorbers are recommended for aliphatic polyamides fiber grades?

Answer
: UV absorbers confer some improvement to UV stability of polyamide fibers. However, a high Mw HALS is more effective than UV Absorbers. The ternary combination of a high Mw HALS with a low volatile phenolic antioxidant and a low volatile phosphite provides the best protection with respect to physical properties and color retention. Check out the recommended light stabilizer package for aliphatic polyamides fiber grades here!

Question 5. Where can I find some products related to light stabilizers for polymers?

Answer
: You can find and select a wide range of Light Stabilizer products for polymers and their technical data sheets in our selector.

*Oxidation can occur in every stage of the life cycle of a polymer: during manufacture and storage of the polymer resin, as well as during processing and end use of the plastic article produced. Numerous oxidation products are formed as the result of the degradation of polymers, such as peroxides, alcohols, ketones, aldehydes, acids, peracids, peresters and γ-lactones. Elevated temperatures, irradiation (e.g. UV) and catalysts such as metal ions increase oxidation rates. Also, most polymers have structural elements that are particularly prone to oxidative degradation reactions.

**Absorption of UV radiation is governed by the Beer-Lambert Law: A = Ebc where A is the absorbance, E is the molar absorptivity of the UV absorber, b is the path length, and c is the concentration. Because the absorbance is directly dependent on the path length, UV absorbers provide little or no protection at the surface of a part where the path length is very short.


Light Stabilizers & UV Absorbers for Polymers and Elastomers


View a wide range of Light Stabilizers & UV Absorbers available today, analyze technical data of each product, get technical assistance or request samples.


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3 Comments on "Selection of Light Stabilizers for Polymers"
ch c Sep 18, 2021
一篇关于紫外线稳定剂的优秀论文。
Andres C Oct 30, 2019
Really, very useful.
David R Oct 30, 2019
What an excellent paper on UV stabilisers.

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