Engineering Thermoplastics Blends?
The timeline of appearance of materials for the plastics industry can be viewed as several overlapping phases. The industry started with natural materials such as horn and bone, which can be thermoformed. Next came chemical modification of natural polymers, producing cellulose nitrate and cellulose acetate from cotton and also wood fibre. The 20th century saw the appearance of wholly synthetic polymers (PVC, polystyrene, polyethylene etc). The era of seeking monomers to convert into useful polymers was followed by a period of creating copolymers to extend the choice of thermoplastics and the range of properties. This quest for new polymers and copolymers became curtailed because of the massive capital investment required.
The less expensive route of blending two existing polymers has become an attractive method of widening the properties profiles to satisfy diverse applications. Some polymers mix well with each other (miscible or compatible blends). However, most pairs result in blends that literally fall apart or delaminate. The addition of a few percent of special polymers (compatibilisers) can encourage the two engineering thermoplastics to stick together and generate some interesting blends. These blends bring out the best properties of the two components in a synergistic way.
In PC/ABS, the most common blend, the polycarbonate adds fire performance to the properties of ABS. In return, ABS contributes processability. Acrylonitrile-styrene-acrylic (ASA) and polymethylmethacylate (PMMA) improve weathering resistance in blends with polycarbonate or polyesters. Polycarbonate adds dimensional stability and flame resistance in blends with polyesters. Some blends, such as polypropylene/polyamide, give good mould detail for matt, scratch resistant finishes, obviating the cost of painting, while acrylics in blends with polycarbonate can achieve high quality, gloss, piano black finishes.
So what will be the next development in thermoplastic blends in providing designers with broader palettes in matching thermoplastics with design requirements?
Trade names: ‘Bayblend’, ‘Cycoloy’, ‘Makroblend’, ‘Schulblend’ and also ‘Xenoy’.
This Engineering Thermoplastics Blends article was written by Dr. Charlie Geddes for Hardie Polymers
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Finally, more information on this topic may be available on the excellent British Plastics Federation website.
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