Selection of Impact Modifiers for Polymers

Impact modifiers are added to plastic compounded materials to improve the durability and toughness of a variety of plastic resins. The amount of impact modifier added depends upon the level of impact resistance needed for end-use applications.

Explore what are impact modifiers, the different types of impact modification, and how impact modifiers improve the properties of several engineering plastics while retaining the cost/performance balance. Check out:

Let’s start by understanding the levels of impact resistance desired by end-users…

Need for Impact Modifiers

TAGS:  Impact Modifiers     Surface Modification    

Impact Modifiers for PolymersImpact modifiers are added to plastic compounded materials to improve the durability and toughness of a variety of plastic resins.

According to end-use applications and polymer intrinsic resistance, formulators need to achieve a very different level of impact resistance, from general-purpose to super toughness.

General-purpose Impact Modification

General-purpose impact modification is a very low level of impact modification which is, for instance, applied to avoid conditioning of molded PA parts.

  • It translates to reasonable room temperature impact strength but does not take into account any requirements for low-temperature (below 0°C) impact strength.
  • For most of this type of applications only low levels of impact modifier will be required (<10%) and the impact modifier does not necessarily have to contain reactive groups to be acceptable for the application.

Low-temperature Impact Modification

Low-temperature impact strength is needed for applications that require a certain level of low-temperature flexibility and resistance to break.

This is, for example, the case for many applications in the appliance area. For this purpose, modifier levels between 5-15% of mostly reactive modifiers will be necessary.

Levels of Toughness

Super Toughness

Super-tough impact strength will be required for applications that should not lead to a failure of the part even if hit at low temperatures (-30 to -40°C) under high speed. This requirement can only be fulfilled with high levels (20-25%) of reactive impact modifier with low Tg.

In addition to the impact performance, impact modifiers can further help improve other characteristics of the material such as:

  • Optical and tensile properties 
  • Weatherability
  • Processability
  • Flammability
  • Heat distortion 

 »  View All the Commercially Available Impact Modifier in Market Today!

After understanding the levels of impact resistance, let's focus on how do impact modifiers work and explore their technology categorization in detail...

How do Impact Modifiers Work?

The elastomeric and rubbery nature of impact modifiers absorbs or dissipates the energy of impact. Impact modifiers can be incorporated through polymerization in the reactor, or may also be incorporated as additives in the compounding step. The two mechanisms are:

Craze Propagation

The principle is to disperse impact modifiers into the brittle matrix, a dampening phase capable to absorb energy and stop craze propagation.

Craze Propagation

Shear Band/Cavitation

A second mechanism is the formation of shear bands around the elastomeric particle absorbing deformation energy. This mechanism is always accompanied by the cavitation of the dampening particle (apparition of voids) absorbing also the energy. However, the apparition of shear bands absorbs most of the energy. 

Mechanism of Shear Band/Cavitation
Mechanism of Shear Band/Cavitation

To be efficient the dispersed phase needs to have the following properties:

  • Dampening capability: The elastomeric phase is recommended. Generally, low glass transition materials and low crystallinity polymers are used. Low Tg is absolutely required for low-temperature toughening. Polyolefin copolymers are excellent candidates.

  • Good cohesion with the continuous phase: This parameter is really key for an efficient toughening. Lack of cohesion can initiate numerous crazes that can then propagate until failure. Good cohesion can be obtained by specific interaction at the surface or by reactivity. The compatibilization occurs by formation, at the interface, of "amphiphilic" copolymers reducing surface tension and increasing adhesion.

Polymer compatibility will also impact the size, the regularity and the stability of the dispersion affecting positively the mechanical performance of the finished part.

Impact Modifier Technologies Categorization

#1. Modification with Functionalized Polyolefins

In order to fulfill the industry requirements, polymers, such as polyamide, polyester, PVC or bioplastics, need improved impact resistance.

Among the impact modification technologies available in the market, polymeric impact modifiers, also known as functionalized polyolefins, offer a full range of toughening performance – from general-purpose to super toughening in various polymer systems.

Click here and learn about the modification with different polymers such as:

Polyamide (PA)

A broad range of impact modifiers, based on functionalized or non-functionalized ethylene copolymers or ionomers, are available to meet unique needs for your PA 6, PA 6,6 or glass-reinforced PA compounds.

Industry-leading Impact Resistance Performance:

  • Super-tough impact resistance
  • Low-temperature toughness
  • Intermediate toughness at reduced cost

Additional Benefits:

  • Improved flow for higher productivity
  • Aesthetic properties (Class A surface finish, excellent colorability)
  • Higher graft level to improve efficiency for cost reduction
  • FDA compliance for direct food contact

Polyester (PBT, PET)

Either in engineering polymer or cast sheet applications, polymeric impact modifiers offer a wide range of performance levels that allow tailored solutions to meet your unique needs.

  • Engineering Polymers: For applications with the most demanding requirements, some polymeric impact modifiers provide super-tough impact resistance in virgin and glass fiber reinforced compounds. However, when compounding PBT engineering polymers, the challenge is increasing impact strength while maintaining original properties.

    Among the wide range of offerings, these impact modifying solutions give compounders a valuable new tool for tailoring the properties of PBT resins to the requirements of electrical and electronic connectors, as well as a wide range of other industrial and consumer products.

  • Cast Sheet Applications: Increasing productivity while achieving the right impact strength properties is a highly complex challenge when it comes to PET-based cast sheet applications.

Benefits in Engineering Polymer Applications Benefits in Cast Sheet Applications
  • Toughening and the retention of original properties
  • Higher melt flow
  • Improved processability
  • Better thermo-stability
  • Higher-strength retention (tensile strength and flexural modulus)
  • Enhanced hydrolysis resistance
  • Improved productivity (cycle time, process stability, regrind utilization)
  • Material cost reduction (lower viscosity PET) (CPET)
  • Food regulations compliant (FDA, European) (APET)

Polyvinyl Chloride (PVC)

Depending on the end-use, different types of PVC resins require different impact modification additives to achieve the right performance goals.

Flexible PVC Rigid PVC
  • Durable strength and flexibility
  • Better low-temperature properties
  • Greater property retention after heat aging
  • Better flexibility after chemical exposure
  • Improved flow and fusion characteristics of the compound
  • Enhanced filler compatibility
  • Lower processing temperature
  • Higher throughput
  • Higher filler loading
  • Lower stabilizer content

Polypropylene (PP)

Polypropylene is a semi-crystalline polymer exhibiting a very attractive cost-performance balance and easy processability. However, to fulfill some industry needs, PP requires improved impact resistance at ambient or low temperatures.

Impact modifiers improve the toughness obtained for polypropylene (PP) at room or low temperatures.

A broad portfolio of products is available in order to offer a unique and customized solution for each situation.

Additional Benefits:

  • Enhanced the dispersion of pigments, glass-fibers or mineral loads
  • Improved compatibility for PP alloys

Acrylonitrile Butadiene Styrene (ABS)

ABS resins perform at a level between engineering plastics, such as polycarbonate, and commodity materials, such as polystyrene. They are widely used in applications such as computer and printer housings, consumer electronics, appliances, garden equipment, automotive parts and toys.

While producing ABS compounds, whether standard, recycled or filled, poor toughness can be encountered.

Impact modification is a highly complex challenge for which one specific solution exists depending on the temperature required for general-purpose strength performance.

Additional Benefits:

  • High compatibility
  • High dispersibility (allows in-line modification during processing)

 »  View All the Impact Modifiers for Acrylonitrile Butadiene Styrene (ABS)!

PC Blends (PC/ABS, PC/PBT)

Actual requirements concerning polycarbonates are connected with superior low-temperature impact strength while maintaining good processability, allowing efficient production of highly specific parts and profiles such as automotive applications by injection molding.

A specific additive is required depending on the polymer used to blend the PC-based resin and the level of toughness needed.

Compared to alternative technology, additional benefits can be found within the following:

  • Better processability of the compound thanks to reduced melt viscosity
  • Better UV and thermo-stability
  • Higher elongation
  • Easier handling & processing due to pellet form instead of powder

#2. Modification with Core-shell

A representation of a typical core-shell impact modifier is provided below.

Typical Core-Shell Impact Modifier

These materials usually have a low Tg rubber core, such as butyl acrylate or butadiene, with a poly (methyl methacrylate) PMMA shell. Examples of commercially available core-shell impact modifiers include Paraloid from Dow Chemical and ClearStrength from Arkema.

One of the primary advantages offered by the core-shell impact modifier approach is that a pre-determined particle size is provided. However, the impact modifier must be appropriately dispersed in and coupled to the matrix polymer in order to be effective for toughening engineering plastics.

This coupling can result from the physical interaction of the shell matrix with the matrix or by chemical reaction. The most obvious route to achieve that is to combine reactive moieties into the shell chains during fabrication by emulsion polymerization. Those reactive moieties, then, subsequently react with the matrix during melt processing.

MBS Impact Modifiers vs. Acrylic Impact Modifiers

Methacrylate Butadiene Styrene (MBS) Acrylic Impact Modifiers (AIM)
MBS acrylic AIM
  • Excellent low-temperature impact
  • Excellent colorability
  • Excellent dispersion in most engineering plastics matrices
  • Excellent low-temperature impact
  • Excellent UV stability
  • Excellent thermal stability
  • Good colorability
  • Outdoor (painted), interior
  • Outdoor (UV & Thermal), interior (Neat Heat Sources)

 »  View All the Commercially Available Arcylic Impact Modifiers!

  • MBS Core-shell impact modifiers are designed to provide exceptional cold-temperature impact in a wide range of Engineering Plastics such as polycarbonate, polycarbonate alloys (PC/ABS, PC/PBT), and polyesters.

  • Core-shell impact modifier imparts better low-temperature impact strength, mold-in colorability, and thermal stability to polycarbonate than any other acrylic available in the market.

Click here or continue reading about the benefits of MBS Impact Modifiers in:

MBS Impact Modifiers in Polycarbonate

Polycarbonate (PC) is known for its transparency, its excellent resistance to impact and its ability to withstand high temperatures during the lifespan of the final article.

However, PC's low chemical resistance (gasoline) is an issue for automotive applications. The injection molding of high viscosity grades is another limitation, especially when high impact resistance is required.

Moreover inherent performances of PC, such as impact, are also seriously compromised when colored pigments, fillers or flame retardant additives are used in the compound.

Recycled PC's are a cost-effective solution for compounders. However, the recycling steps reduce PC's mechanical performance, making the use of impact modifiers necessary in recycled PC, in order to reach the desired level of performance.

Benefits of MBS Impact Modifiers in Polycarbonate

Benefits Description
Exceptional Low-temperature Impact Performance
  • MBS Impact modifiers allow PC and particularly high flow PC to achieve high impact performance at very low-temperatures.
  • High-performance impact modifiers based on butadiene rubber (ABS or MBS) are detrimental to the inherent UV and heat stability performances of polycarbonate.
  • In weatherable outdoor applications or high heat environments, it will be critical to use a very stable impact modifier that will still provide high impact performances. Impact modifiers are designed to respond to this technical challenge.
Excellent Weatherability & Heat Aging
  • MBS Impact modifiers provide excellent weatherability expected of an all-acrylic impact modifier.
  • This allows impact modifiers to be used in applications that demand good color hold and retention of mechanical properties upon typical outdoor exposure, yielding products that retain long-term performance under severe conditions.
Exceptional Mold-in Colorability
  • MBS Impact modifiers provide far more superior colorability than most of the acrylic modifiers available on the market, which are known to lower color intensity thus making dark color parts difficult if not impossible to achieve.
  • Based on a patented technology, they have opened the door for applications that demand good color hold and unique mechanical properties retention upon exposure to the elements.

 »  View All the MBS Impact Modifiers for Polycarbonate (PC)!

MBS Impact Modifiers in Polycarbonate Blends (PC/ABS, PC/PBT)

To meet new market requirements, including technical performances but also cost, compounders have designed polymer blends that balance the excellent inherent benefits of polycarbonate with the unique cost-performance characteristics of other matrices such as ABS or polyesters (PBT).

These polymer blends offer high performance as compared to traditional PC. These blends help:

  • Overcome poor flow behavior and embrittlement – In order to improve flow behavior in opaque applications of high impact grade PC, a rubbery phase, such as Acrylonitrile-Butadiene-Styrene (ABS), may be added into the PC matrix.

    PC/ABS is the fastest-growing PC alloy today in which ABS allows to balance the high impact strength, surface finish and high flow for better processing. As a drawback, PC/ABS blends often do not meet the new flame retardancy standards.

    The most common end uses for PC/ABS are automotive parts, office equipment housings, computers, and mobile phones.

  • Overcome low chemical resistance – Polycarbonate is known to have very low chemical resistance, which is a critical performance in automotive application when contact with oil and gasoline.

    In order to overcome this weakness, Polycarbonate and Polyesters such as PBT as blended to obtain high chemical resistance alloy, with unfortunately the consequent poor impact performance characteristics of PBT.

    But when it comes to recycling, adding fillers, color pigments or flame retardants, all these blends lose their primary critical toughness performance.

Benefits of MBS Impact Modifiers in Polycarbonate Blends

Benefits Description
Better Compatibility
  • The high impact performance of PC/ABS alloys will greatly depend on the ability to well disperse the various polymer phases (PC, PB, SAN), typically achieved through technical compounds.
Superior Low-temperature Impact
  • The low glass transition temperature (Tg < -80°C) of impact allows them to be used for demanding low-temperature applications to create products that can withstand temperatures as low as - 50°C and still maintain their structural integrity.
Good Dispersion
  • Impact modifiers are easily dispersed using conventional compounding techniques.
  • The resulting engineering plastics compounds flow readily in molding equipment and have exceptional impact strength resistance.

MBS Impact Modifiers in Polyesters

Polyesters like polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) are semi-crystalline polymers exhibiting very attractive performance such as high heat stability and chemical resistance.

On the other hand, polyesters exhibit poor low-temperature impact performances, therefore impact modifiers are needed.

Polyesters are often used in automotive applications such as drive housing for electric window lift and light-conducting housing. They are also used for many appliances, electrical and medical applications.

However, to fulfill some industry requirements, these resins require improved impact performance at ambient or low temperatures. For these applications, the use of impact modifiers is critical.

Benefits of MBS Impact Modifiers in Polyesters

Benefits Description
Superior Low-temperature Impact
  • The low glass transition temperature (Tg < -80°C) of impact modifiers allow them to be used for demanding low-temperature applications, in order to create products that can withstand temperatures as low as - 50°C while remaining ductile.
Good Dispersion
  • Impact modifiers are easily dispersed using conventional compounding techniques.
  • The resulting engineering plastics compounds flow readily in molding equipment and have an exceptional impact strength resistance.

Excellent dispersion of MBS Impact modifiers
Excellent Dispersion of MBS Impact Modifiers

 »  View All the MBS Impact Modifiers for Polybutylene Terephthalate (PBT)!

#3. Modification with TPEs

A thermoplastic elastomer is generally defined as a polymer that can be processed as a thermoplastic material but also possesses the properties of a conventional thermoset rubber.

Some of the general classes of commercial TPE’s include:

  • Styrenic block copolymers
  • Thermoplastic polyurethanes
  • Thermoplastic copolyesters
  • Thermoplastic polyamides

In order to be classified as a thermoplastic elastomer, a material needs to have the following features:

  • The ability to be stretched to moderate elongations and, upon the removal of the stress, returning to something close to its original shape
  • Processability as a melt at elevated temperatures
  • Absence of significant creep

Some examples of TPE products that have been recently developed and extensively used include:

  • Arnitel® from DSM
  • Engage™ from Dow Chemical
  • Hytrel® from DuPont, and
  • KRATON™ from Kraton Polymers

TPE's – Advantages and Disadvantages

Advantages Disadvantages
  • Recyclable. They have typical elastic properties of rubbers which are not recyclable
  • Require little or no compounding, with no need to add reinforcing agents, stabilizers or cure systems
  • Consume less energy
  • They melt at elevated temperatures and this can limit their utility with certain engineering plastics
  • May require drying before processing
  • There are a limited number of low modulus materials that can be used in TPE’s

TPE's are often used when conventional elastomer materials cannot provide the range of physical properties needed in the product. Thus, their use in applications is end-use driven and specific TPE’s are used based on the final need.

This is another example of the requirement to achieve the appropriate balance of modulus and impact properties with the impact modification of engineering plastics. This is a feature that is relevant and important to all of the described approaches.

Impact Modification Strategies for Engineering Polymers

#4. Modification with Bulk Elastomeric Compounds

The approach of using bulk elastomeric compounds as impact modifiers is different from the use of core-shell materials because the size of the dispersed rubber phase is dependent on the processing conditions that are utilized. This does allow for the control of the particle size in the final impact-modified product.

Disadvantages of Using Elastomers as Impact Modifiers

One of the biggest drawbacks of the approach is that the stiffness decrease that is observed with the addition of an elastomer is typically larger than is observed with the use of core-shell modifiers.

This means that if the retention of the stiffness that is offered by the engineering plastic is critical to the application, the concentration of elastomer must be adjusted appropriately.

Example: PBT Modification Using Elastomeric Compound

In that case, processing conditions of the PBT/elastomer mixtures affect the size of the elastomer particles and, hence, the impact modification that is achieved. In addition, the relative viscosities of the components will affect the morphology in the final blend.

Since the melt viscosities are directly related to the molecular weights of the polymers, it follows that the molecular weights are important factors in defining the observed impact modifications.

Commercially Available Impact Modifiers

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2 Comments on "Selection of Impact Modifiers for Polymers"
adrian o Dec 12, 2019
GOOD DAY could you please let me know what impact modifier we can use in isothalic gelcoats and polyester resins. we make fibreglass products for the trucking and tank container industries thank you kindly Adrian Oberholzer Cape Composite adrian@capecomposite.co.za +27414016700 +27836566180
Dr.P.L. M Feb 1, 2017
Impact Modifiers are one of the most important ingredient of the Engineering Plastics.The knowledge of Impact Modifiers chemistry and their Application in desired end product will be the heart of future revolution in the Plastics world.

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