additives feature | Coupling agents & dispersants
says that the increased use of liquid organic colorants in place of heavy metal versions has hastened the adoption of liquid metering equipment in many shops. As a result, most compounders have become more comfortable working with liquid additives. The grades were developed in partnership with
major compounders, he notes, and the technology has been licensed for use in North America, China and elsewhere, an indication, perhaps, that it will soon be applied to automotive part production.
Dow Corning offers a range of silane-based coupling agents and disper- sants
developed a form of silane chemistry that improves the ability of a polypropylene (PP) resin matrix to bond with reinforcing fibres – Grade 32-441 is optimised for glass fibre, while Grade 32-440 is for natural fibre applications. Christophe Paulo, global sales manager for plastic
additives, says that the products can take PP reinforced with 30 to 35% glass or natural fibres to the perfor- mance level of a 30% glass-reinforced grade of polyamide 6 (PA 6).
The obvious benefit is higher performance in a
low-cost resin, which is a particularly important requirement for one potential application – automotive under-the-hood parts. Paulo adds that the improve- ment in PP performance includes a “nice boost” in heat deflection temperature of 10 to 15°C. Both materials are liquids and act in compounds as in-situ modifiers. They are injected right before the addition of fibre reinforcements, at average loadings of 1 to 1.3%. Five years ago, the use of liquid coupling agents might have been daunting to many compounders. Paulo
Fully dispersed Dow Corning also recently commercialized its Grade 11-100 liquid dispersant for use with ATH (alumina trihydrate) and MDH (magnesium hydroxide) flame retardants (FRs) in polyolefin compounds. The silane additive is engineered for compatibility with polyolefins and to improve the dispersion of these materials in compounds. The advantages to this include more effective flame retardant properties along with im- proved aging properties in finished parts. The main application target is wire and cable compounds. Paulo adds that the dispersion of FRs is efficient
enough to reduce the torque level of compounding operations by 5 to 10%, which speeds production, reduces energy use and minimizes wear and tear on process lines. Grade 11-100 has other application benefits. Paulo says that its silicon bonding mechanism is strong enough to resist high-heat processing in the 300 to 500°C range. This means that it outperforms organic additives used as processing aids, which typically drop off in performance at around 250°C. The dispersant can also be used to maintain a
relatively high degree of whiteness in formulations where high-heat resins such as PA, polyimide and polyetheretherketone are compounded with titanium dioxide. Paulo says a processor will not get a deep white in a high-heat resin with Grade 11-100 and TiO2
, but will
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