Additives | polyamides
Additive producers are developing a range of additive technologies to allow polyamides to take on ever more challenging requirements. Peter Mapleston reviews some of the latest introductions
Adding performance to PA
Polyamides are well known for their ease of processing, high temperature resistance, good mechanical and barrier properties. But as applications change and develop, especially in automotive and electronics markets, more is being demanded of them. Additives suppliers, however, are warming to the task with the development of a number of new products designed to enhance polyamide performance, most notably targeting impact resistance, hydrolysis resistance, high temperature performance and fl ow. “The use of impact modifi ers is an effi cient way to
tailor performance and fulfi l stringent specifi cations, thus avoiding the costly development of new resin grades. For example, low temperature impact perfor- mance can be achieved in polyamide 6 or 66 by the addi- tion of functionalised polyolefi n backbones,” says Yannick Saint-Gérard, Sales Development Manager for Additives in Engineering Plastics Applications with Dow subsidiary Rohm and Haas Europe Services, who cites Dow’s Paraloid EXL-3808D as a suitable choice. “Other requirements like enhanced elongation at break in highly reinforced glass fi bre-containing compounds can be obtained via the use of acrylic core-shell rubbers such as Paraloid EXL-2300.”
High fl ow solutions However, newer challenges are emerging today, such as the need for very high fl ow compounds for use in thin gauge applications where light-weighting is a must, Saint-Gérard says. To this end, Dow Plastics Additives has developed a new generation of impact modifi er, Paraloid EXL-3815, which is a copolymer of ethylene and octene grafted with maleic anhydride (MAh). This typically yields a notched Izod impact resistance higher than 500J/m at -30°C in a polyamide 6 at a 20% loading (by weight) – around 10 times more than a neat polymer – while maintaining fl ow (MVI) largely above 20 cm3
/10
min. Measurements performed in actual moulding conditions using a spiral mould also show the benefi t in fl ow properties versus standard impact modifi ers (Figure 1). Paraloid EXL-3815 exhibits low temperature impact
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performance in polyamide 66 as well, Saint-Gérard says. It is also used in glass fi bre reinforced compounds where better impact and fl ow can be obtained without impairing modulus and defl ection temperature under load (DTUL). Vertellus Specialties is also developing additives
containing copolymers grafted with maleic anhydride, but for slightly different purposes. At the Compounding World Forum in Philadelphia in December last year, Ashok Adur, Global Commercial Development Director for Plastics, discussed ZeMac, a group of alternating (1:1) copolymers of ethylene and maleic anhydride with 78% MAh content and more than 200 reactive groups per chain. The products can be used to modify polyam- ides (and other engineering plastics) to increase molecular weight and branching at low dosages. Adur highlighted target applications in upgrading
recycled polyamides, increasing relative viscosity, and mitigating some of the negative effects of impact modifi ers in polyamides (examples shown in Table 1).
February 2016 | COMPOUNDING WORLD 19
Main image: Increasing
demands in the engine
compartment
are a key driver behind
developments in polyamide additives. (Image: Clariant)
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