Regrind (flake/chips) from cross-linked, rotationally molded parts can be successfully added to injection molding resins. That's the word according to a recent study sponsored by the Association of Rotational Molders (ARM, Oak Brook, IL). Researchers looked at combinations of flake or powder in two typical polyethylene resins, HDPE and LMDPE. Regrind content varied from 15 to 75%. Some of the findings: Although the amount of shrinkage depended on the base polyethylene, shrinkage decreased as recycle content increased. In HDPE, there was a decrease in tensile modulus, but an increase in flex modulus of almost one-third. LMDPE showed a significant increase in both the tensile and flexural moduli. Also, a 50% regrind flake in HDPE resulted in 10-to-30 fold Izod improvement. In LMDPE, no breaks occurred. Elongation at yield did not change significantly with regrind in HDPE, but decreased sharply with at least 15% regrind in LMDPE. For most applications, representatives of ARM say, it should now be possible to select the important properties from the study and determine the appropriate blend with which to begin trials for potential products. Users are cautioned to note that this study was conducted using post-industrial scrap, i.e. the regrind came from molded parts not shipped to the marketplace. The report costs $25. Call: (630) 571-0611, www.rotomolding.org on the Internet.
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