Materials
Fig. 1. SMA improves thermal performance, surface polarity and miscibility.
SMA as additive for amorphous thermoplastics
Styrene maleic anhydride (SMA) boosting thermal performance, paintability and compatibility in multi-material systems. Patrick Muezers reports.
S
tyrene maleic anhydride (SMA) compounds have long been used as moulding resins in the automotive, packaging, and building and construction industries, and maleic anhydride itself is a well-known coupling agent between
glass or natural fibres and resin matrices. However, a lesser known but growing use for neat
(unreinforced, non-impact modified) SMA grades is as an additive/compatibiliser in amorphous thermoplastics and copolymers to improve thermal performance, surface polarity, and miscibility with other resins in blends and alloys. XIRAN SMA additives can boost performance and value of recycled or virgin resins such as acrylonitrile butadiene styrene (ABS), and polymethyl methacrylate (PMMA), and extending thermal stability, improving the processing window, and making parts moulded from these resins easier to bond, paint, print on, or plate at a modest cost vs. other additives and proprietary polymer-modification techniques for these same resin families. Expanding the use of SMA as a performance enhancer
for thermoplastics is Polyscope Polymers BV. Sold under the tradename XIRAN, the company claims to have the broadest offering of SMA resin additives and moulding compounds in terms of both range of molecular weights and percent maleic
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anhydride – two variables that can be manipulated to change final molded-part properties. SMA has unique functional properties due to the combination of polar maleic anhydride (which also contributes stiffness, thermal stability, and chemical reactivity) and non-polar styrene (which also provides processing ease). Manipulation of the ratio of styrene to maleic anhydride allows polarity to be adjusted. This copolymer is miscible in a wide range of plastics, which enables it to be used as a compatibilizer in multi-polymer systems. Thanks to XIRAN SMA’s high glass-transition temperature
(Tg) range of 145–175˚C (293–347˚F) , it is a cost-effective way to boost thermal performance in PMMA and ABS resins. Properties like heat-deflection temperature (HDT), continuous- use temperature (CUT), Vicat softening, and heat aging can all be improved. Incidentally, the base resin’s processing window also is broadened, and its dimensional stability and ability to hold tight tolerances after moulding are increased coincident with improvements in its thermal performance. Depending on the starting ABS copolymer and the
grade of XIRAN SMA used, generally for every 1 per cent of SMA added to the compound, the thermal performance of the base resin is shifted upward by 0.7°C (1.2°F). This means that compounders and recyclers can take lower value,
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