Study on process-induced degradation of cellulose fibers in thermoplastic composites

Cellulose based natural fibers have high potential to find application as reinforcement in thermoplastic composite materials. Especially pulp and paper fibers show suitably high mechanical properties due to their high cellulose content and homogenous quality. In this work, the process-induced degradation of cellulose fibers was investigated. Polypropylene composites, which were reinforced with paper fibers, were produced by twin-screw extrusion and injection molding. Different fiber volume fractions and multiple reprocessing steps were carried out in order to observe the influence on the composites mechanical properties and fiber degradation. The increase of fiber fraction had no significant effect on the resulting fiber length distribution. However composite recycling led to a gradual degradation of the cellulose fiber length. Even though the fiber length decreased with every processing cycle, the mechanical properties increased from the first to the second cycle and also stayed at a high level after third and fourth processing.