Apart from textile applications, man-made cellulose fibers play an important role for the reinforcement of rubber goods, first of all tires. In accord with current sustainability concepts, possibilities are sought to find “green” solutions also in the field of short fiber reinforced thermoplastics. Here mainly glass fibers are used today with market volumes of 1 million tons of reinforced PP and PA in Europe alone. The potential of cellulose man-made fibers to substitute glass fibers in these applications was proven by extensive investigations carried out at Fraunhofer IAP. In the present paper, on overview will be given with emphasis on the combination of rayon (man-made fiber manufactured via the viscose process) and bio-based plastics, in particular poly(lactic acid) (PLA), a biodegradable and bio-based aliphatic polyester available on the market in amounts exceeding 150 kt and representing a possible future green commodity polymer. In more detail, rayon fibers with three different diameters and practically the same tensile properties were used to study the effect of fiber thickness on mechanical properties including impact behavior. For the latter property it turned out that thicker fibers are more appropriate due to less fiber breakage during the manufacturing process and thus higher fiber length. Moreover, a tailored interphase modification (weak coupling) was carried out in order to facilitate an energy absorbing fiber pull out mechanism leading to extraordinary notched Charpy impact strengths. With the thickest fibers (17 µm) in these tests, notched Charpy values as high as 27 kJ/m2 could be found while un-notched values reached 95 kJ/m2, compared to 2.5 kJ/m2 and 25 kJ/m2 for the unreinforced PLA, respectively. While all rayon types investigated gave considerable improvements in the mechanical and fracture mechanical characteristics of the composites, properties can be fine-tuned by the choice of the fiber diameter with advantages of thicker fibers for processing stability and notched impact properties. Weak coupling was established as a method to generate extraordinary high impact properties without sacrificing composite strength and modulus.

Cellulose man-made fibers reinforcing bio-based thermoplastics – the role of fiber diameter and fiber-matrix interphase

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.