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Silane Dispersing Agents: Techno Brief

Dispersing agents are used to facilitate and stabilize the dispersion of solid compounding materials such as fillers or pigments in a polymeric (or a liquid resin) matrix. Better dispersion leads to better processability and improved material properties!

Silane is one such agent that helps in easier processing and/or better product performances along with cost advantages. Want to know more about Silane Dispersing Agents?

Get an overview on how silanes can improve the dispersability of pigments & fillers in plastics and how they can help in better material processability and performances.

Silane Dispersants


TAGS:  Surface Modification      Dispersing Agents    

Silane as Dispersing AgentA silane is a molecule containing a central silicon atom bonded to two types of groups: Alkoxy groups and organofunctional groups.

These two types of group exhibit different reactivity and allow sequential reactions. In the case of dispersing agents, the alkoxy groups provide reactivity with mineral or filler surface. This reaction is common to all alkoxysilanes. The organofunctional group is typically non-reactive. The type of group is chosen to provide the needed compatibility with the polymer.



Dispersing Mechanism


During silane treatment of a filler or pigment a reaction takes place between the functional groups of the filler or pigment (such as OH groups) and the alkoxy groups of the silane to create a silane functionalized surface.

The surface of the filler can be functionalized to improve compatibility with the polymer matrix via specific interactions or chemical reaction between the polymer and silane organo functional group. The functionality of the silane should be chosen to match the polymer matrix.

Silane treatment also creates a "protective layer" preventing re-agglomeration of the particles.

The figure below shows the treatment of mineral surface by organosilane.

Surface Treatment with Silane
Source: www.azom.com
Treatment of a mineral surface by an organosilane


Continue Reading to Know More about:

 » Benefits of using silane dispersing agents
 » Various filler treatments with silane for improving surface of a material


Why Use Silane Dispersing Agents?


The use of a silane dispersing agent in a filled thermoplastic, rubber or thermoset formulation results in a number of benefits which ultimately translate into easier processing and/or better product performances. During masterbatch production, the use of Silane treated pigments allows higher pigment loadings or higher production rates.

The use of silane as dispersing agent provides significant performances and cost advantages.

Learn the various benefits of silane dispersing agents provide to a material or click on the specific benefit to address a specific issue:


Benefits of Silane Dispersing Agent


#1. Better Dispersion and Wet-out with Silane


Using silane dispersing agents leads to a significant improvement of filler and pigment dispersion in a polymer system.

The polymers can be thermoset, thermoplastic or even rubber elastomer networks.

This improvement is due to surface modification of the filler making it more compatible with the polymeric matrix and improving the wettability of the filler. Silanes such as Dow Corning® Z-6070 Silane also create a "protective layer" minimizing re-agglomeration of the particles and sealing off the effects of the surface on resin cure and electrical properties.

Comparison between Filler treated silane and Untreated Silane
Comparison between Filler treated silane and Untreated Silane


For thermoplastics systems, an improved dispersion results in:

  • Easier filler or pigment incorporation (higher loading, wider processing window)
  • Lower material viscosity
  • Lower surface defects
  • Better mechanical properties
  • Better opacity for pigments (ex: TiO2)

For liquid resin systems, improved dispersion often results in less air occlusion and reduced slurry viscosity, allowing easier flow during molding and the possibility of using increased proportions of inexpensive filler.

#2. Lower Viscosity with Silane


Introducing filler into a molten polymer tends to increase the melt viscosity of the mixture. The viscosity increase depends on numerous parameters like:

  • Viscosity of the molten polymer
  • Filler concentration
  • Quality of the wetting between the polymer and the filler
  • Particle size distribution

Treating filler particles with silanes enables better wetting of the filler by the polymer, helps the filler remain well dispersed and gives a lower viscosity compound than with untreated fillers. This leads to easier processability, higher throughput, better surface quality and higher filler loading in masterbatches.

Silane treated fillers and pigments allow higher throughput,
better surface quality and higher loadings


The figure below shows the influence of silane treatment on the melt temperature and torque percent during the production of a PE/TiO2 masterbatch at 80 weight percent TiO2.

Silane Treated TiO<sub>2</sub>
Silane Treated TiO2 allowing low torque and higher throughput


#3. Reduced Cure Inhibition


Fillers are known to have varying degress of effect on the cure systems of thermoset resins that can inhibit their cure. Using silanes as dispersing agents can lead to reduced cure inhibition. Silane treatment of fillers in both polyesters and epoxies often overcomes cure inhibition as measured by cure exotherms (see the figure below). Silanes that were generally the most effective dispersing agents often enabled the highest exotherms.

Using Silanes as Dispersing Agent can Lead to a Reduced Cure Inhibition


Most Effective Silane Dispersing Agents
Silanes that allowed maximum exotherms were generally the most effective dispersing agents


#4. Improved Electrical Properties


The ability of silane dispersing agents to impart improved electrical properties is shown in the table below with an epoxy resin reinforced with quartz filler.

The table below shows an improvement in electrical properties with silane dispersing agents in quartz-reinforced epoxy resins

System
Dielectric Constant
Dissipation Factor
Dry
Wet*
Dry
Wet*
Unfilled resin
3.44
3.43
0.007
0.005
Quartz, no silane
3.39
14.60
0.017
0.305
Quartz, Z-6040
3.40
3.44
0.016
0.024
Quartz, Z-6011
3.46
3.47
0.013
0.023
* After 72 hours immersion in boiling water

Without filler, the epoxy resin showed good electrical properties, dielectric constant and dissipation factor, even after aging for 72 hours in boiling water. However, once quartz filler was added, the hydrophilic surface of the quartz led to severe loss of electrical properties during the water boil test. With either Z-6040 epoxysilane, Z-6011 aminosilane or the Z-6070 alkoxysilane, the quartz-filled composite exhibited a dramatic retention of electrical properties.


Filler Treatment with Silanes


Mineral fillers have become increasingly important additives and modifiers for organic polymer. Silanes are a natural fit to treat the surface of the mineral to make the mineral more dispersible in the polymer.

The different applications of silane dispersing agents in mineral treatment:

Filler Treatment with Silanes


The table below lists some benefits of silane treated filler:

Benefits of Silane Treated Filler

Processing benefits

Better dispersion leads to:
  • Higher filler loading
  • Lower die build-up
  • Higher production rates
  • Wider processing window


Products benefits
Better dispersion leads to:
  • Better color stability
  • Higher gloss and optical quality
  • Better mechanical properties



TiO2 Treatment


TiO2 is the most commonly used white pigment for plastics. It exhibits excellent whiteness, excellent opacity and good UV resistance.

Most compounders and masterbatchers process TiO2 and all require the following attricutes to maintain high quality standards and competitive prices.

The table below shows the Key requirements for materials or masterbaches containing TiO2:

Process requirements
Product requirements
  • Low torque, low pressure (high rates)
  • Excellent dispersion
  • High filler loadings for masterbatch
  • Lacing resistance
  • Low abrasion
  • Low die build-up
  • Good color stability and whiteness
  • High opacity
  • Cost effectiveness
  • Excellent mechanical retention
  • Good surface quality (for films, sheets...)


To achieve this, TiO2 is treated with silane dispersing agents such as Z-6070.

The use of silane treated TiO2 improves TiO2 dispersabiliy
as well as performance of the TiO2-filled plastic.


The figure below shows how a silane treatment reduces the melt temperature and the torque required in the compounding machine during production of a PE/TiO2 masterbatch at 80 percent TiO2 loading.

Silane Treatment to Fillers
Reduction of the melt temperature and torque of a compounding machine with the addition of silanes


Talc Treatment with Silane


Talc is platty filler commonly used as reinforcer in polyolefins (PE, PP, EVA), styrenics and occasionally in engineering polymers. Talc is used to increase HDT and stiffness and can reduce creep, shrinkage and coefficient of linear thermal expansion (CLTE).

To achieve this, Talc is treated with silane dispersing agents such as Z-6070.

The use of silane treated talc improves talc dispersability
as well as performance of the talc-filled plastic.


Wollastonite Treatment with Silane


Wollastonite is white acicular filler imparting good dimensional stability, good scratch resistance and excellent stiffness to thermoplastics such as PP or PA. Main applications are automotives parts such as trims, bumpers or instrument panels.

Using silane dispersing agents such as Z-6070 to treat Wollastonite provide these performances.

The use of silane treated wollastonite improves wollastonite dispersability
as well as the performance of the wollastonite-filled plastic.



Commercially Available Dispersing Agents


Find out all dispersing agent grades available in market today!



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