additives | Clarifi ers & nucleators
provides the desired and perceived level of quality,” King says.
New Japan Chemical claims its Rikafast EDX clarifi er combines excellent clarity with a wider processing window than some alternatives
points out that PP copolymers have made signifi cant inroads into the health science fi elds, especially for single-use items that must be pre-sterilized. Such articles need to be able to withstand the
necessary sterilization techniques before their intended use, even if they are stored for prolonged timeframes. They also need to function without cracking, bending, breaking, shredding or tearing during their use; the retention of physical properties is related to maintaining the molecular weight (MW) of the polymer. But second- ary requirements, such as the maintenance of aesthetic features, can be equally important. “Initial low colour, good maintenance of that low colour, and good clarity (low haze) are key to assuring that the plastics article
The sterilization of some types of plastic articles has proven to be challenging in terms of being able to maintain the original strength and aesthetics, he says. “Sterilization via gamma or electron beam radiation, while timely and effi cient, can be destructive to the physical and aesthetic properties of the plastic. Consequently, there has been an ongoing challenge to the industry to provide fully formulated plastic feed- stocks that can resist the damaging effects of the high energy radiation; again, not only in terms of maintaining physicals (molecular weight, molecular weight distribu- tion), but also the aesthetics (colour and clarity).” King and his team examined the relative effective- ness of three stabilization systems in a clarifi ed random polypropylene copolymer designed for injection moulded articles intended for use in the health science industry. The formulations, which included various BASF additives and also Milliken’s Millad 3988 DMDBS third-generation sorbitol clarifi er, were compared in regard to their resistance to increasing doses of gamma radiation. They also examined the retention of those properties as a function of accelerated aging of inventory storage stability at 60oC for 21 days. “We ran this project to see if we could make
incremental improvements versus the traditional benchmark stabilization system for gamma irradiated polypropylene copolymers,” says King. “It is clear that we have a competitive advantage with Irgaclear XT 386, which is a non-sorbitol based high performance clarifi er [it is an aromatic trisamide]. This alternative approach to higher loadings of conventional sorbitol
Figure 1A (left) shows the yellowness index (YI) colour of gamma irradiated samples, denoted as Benchmark-1 (which dates back to the mid-1990s), Modifi ed Benchmark-2 and BASF’s New System-3. New System-3 offers a competitive advantage in terms of lower colour. Figure 1B (right) shows that after 21 days of oven aging the same trends are maintained
68 COMPOUNDING WORLD | May 2016
www.compoundingworld.com
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