Inclusion of Mechanically Refined Douglas-Fir Bark Fiber in Plastic Moldings

Fibers (sclereids) recovered by sedimentation and screening of pressurized-disk-refined bark of Douglas-fir were added to polypropylene and high-density polyethylene used to make injection moldings. Randomly oriented fibers (20 % by weight of the blend) generally lowered impact strength, but stiffness of moldings increased 1.9 to 2.9 times. Reduction of impact strength is contrary to earlier findings, and the cause is not clear. Yield of fiber, 16 percent of dry bark weight, was not increased by reprocessing flotage or modifying the refining process.

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