IMPACT MODIFIERS | ADDITIVES Compounds toughen up
Whether to meet more demanding specifications or to upcycle recycled resins, impact modifiers play an important role in compound development today. Peter Mapleston reports on the latest introductions
The drive to lighter parts, together with increas- ingly demanding performance specifications, is calling for polymer materials that display improved levels of toughness. Meanwhile, increasing de- mand for compounds containing recycled poly- mers means taking steps to upgrade performance to near-virgin specification. Impact modifier technology can help in both scenarios; this article takes a look at some of the latest introductions. Polyamides such as PA6 are the first choice for many demanding engineering parts for their inherent resistance to abrasion, heat, chemicals, and weathering, as well as their aging stability. However, some applications require more in terms of toughness and amine-terminated butadiene- acrylonitrile copolymers (ATBNs) can increase the impact strength of polyamide through co-polymer- isation at concentrations of 10%-to-20%. CVC Thermoset Specialties, part of Emerald
Materials, markets ATBN polymers under the Hypro banner. These ATBNs are low-molecular-weight, liquid butadiene-acrylonitrile copolymers that contain secondary amines at the terminal positions of the polymer chains. Acrylonitrile content ranges from 0 to 26% and the nitrile content influences polymer compatibility, surface chemistry, and the ultimate polymer properties.
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ATBN polymers can be incorporated into the synthesis of the polyamide through the reaction with caprolactam using various strategies, all resulting in phase-separated rubber domains with a typical size of around a micron in diameter. These rubbery inclusions can increase the impact strength of the polyamide by orders of magnitude over a wide temperature range, with little sacrifice in other properties such as modulus and glass transition temperature (see Figure 1). Jeremy Pasatta, Technology Manager Specialty
Polymers, at CVC Thermoset Specialties, says ATBN can also improve the wetting behaviour of glass fibres in polyamides, allowing an increase not only in the amount of glass fibre that can be incorpo- rated but also the length of the glass fibres. ATBN also increases the adhesion between the glass fibres and the polyamide matrix. Because of these enhanced properties, the polyamide/ATBN – glass fibre composite has significantly increased tensile strength, tensile modulus, flexural strength, and flexural modulus, as well as improved heat distor- tion temperature (HDT).
Also working on ways to modify polyamides – but in this case mostly PA recyclates – is Brügge- mann Chemical. It says its new Bruggolen TP- M1417 additive provides compounders and
July 2018 | COMPOUNDING WORLD 65
Main image: Purell KT MR 07 PB-1
plastomer from LyondellBasell enhances low temperature toughness and impact resistance of PP medical tubing
PHOTO: LYONDELLBASELL
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