Materials
SMA, with a maximum of 60 per cent used depending on the application requirements.
Compounding can be done on
Fig. 4. A detail of an automotive door handle created with the held of SMA additives.
thermoplastic elastomers (TPEs) and vulcanizates (TPVs) like styrene-ethylene/butylene-styrene (SEBS), and polymers that normally are immiscible with PMMA and ABS, such as nylon (polyamide (PA). Several different grades of SMA additive are commercially
available in the XIRAN product line to provide broad flexibility in adjusting base resin properties for ABS and PMMA. Grades are available for either injection moulding or extrusion and are offered granulate form. A liquid form factor is also available for fibre-coating treatments. These can be let down at the rate a processor requires to achieve specific molded-part properties. Typical letdown per centages range from 20–40 wt-per cent
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most conventional equipment with good temperature control. The best mixing will be achieved with a twin- screw extruder (TSE), although a single-screw extruder (SSE) may also be used where lower per centages of SMA are being compounded into the base resin. For typical extrusion- compounding conditions, feed-zone temperature should be around 120˚C (248˚F) and the die should be around 220˚C (428˚F), with an optimum melt temperature between 240–260˚C (464–500˚F). Other additives (eg, release agents, antistatic agents, fillers
Patrick Muezers, Managing Director, Polyscope Polymers.
and reinforcements, UV stabilisers, pigments, etc) may either be dry-blended at the start or introduced via side or top feeders during compounding. Ironically, SMA also is a very effective purging compound due to its inherent polarity, so compounding or moulding with it helps ensure clean equipment. In Japan, SMA is used as the preferred purging compound rather than polyethylene (PE) as is more common in Europe and North
America. ❒
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Patrick Muezers is managing director, Polyscope Polymers BV, Geleen, The Netherlands.
www.polyscope.eu
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