Biobased composites

Biobased thermoplastics, such as poly(lactic acid), have attracted much attention in recent years as an alternative to oil-based plastics both in academia and industry. Based on renewable raw materials these polymers offer advantages in terms of decreased dependence on fossil resources and reduced CO2 footprint in accord with sustainability ideas and climate protection. In order to improve the properties of these materials, reinforcement with biobased fibers represents a promising option. An alternative route to glass and natural fiber reinforcement was taken and intensively investigated. The novel approach is based on the use of cellulose man-made fibers, in particular rayon tire cord yarn, as a biogenic reinforcing component. It was demonstrated that short fiber rayon reinforcement leads to dramatic improvements in the mechanical properties of various biobased and partially biobased matrix materials. While stiffness is easily enhanced also with natural fibers, the use of rayon results in considerable improvements in strength and impact properties in contrast to natural fiber reinforcement. For example, an enhancement of more than 500 % was observed in notched Charpy impact strength of poly(lactic acid). In the present contribution results concerning composite mechanical properties will be presented for various biobased matrix materials with special emphasis on the role of the fiber-matrix interphase. By reactive extrusion this interphase can be tailored from being weak (anti-coupling), intermediate (no modification) or strong (covalent coupling). Implications for the composite properties as a function of matrix stiffness will be discussed. Other factors influencing the composite properties such as fiber length and fiber diameter will be considered as well. Finally, some general conclusions will be drawn concerning future work and industrial prospects