Man-made cellulose short fiber reinforced oil and bio-based thermoplastics
The present chapter considers the possibilities of reinforcing thermoplastic matrix materials with cellulose man-made fibers, in particular high performance rayon tire cord yarn. Mechanical properties of the composites such as tensile strength, stiffness, and impact properties are in the focus of interest. Composite and fracture surface morphology is accessed by scanning electron microscopy (SEM) and the quality of fiber-matrix adhesion is revealed. Advantages and disadvantages of using coupling agents are discussed. Thermoplastics both from fossil and from renewable resources are used as matrix materials. From the first group, polypropylene is the most important example and is considered in detail while polyethylene, polybutene-1, impact modified polystyrene, ABS are briefly sketched. On the bio-based side, the emphasis is on poly(lactic acid) (PLA) as the most easily commercially accessible inexpensive bioplastic. Polyhydroxyalkanoates (PHA) are also considered but in less detail. Composites are manufactured by a specially developed melt compounding method on twin screw extruders and shaped by injection molding. In general, rayon reinforcement proves to be superior to natural fiber reinforcement, in particular in terms of impact strength. For PP-rayon the properties are even comparable to those of short glass fiber reinforced polypropylene (GFPP) and PC/ABS with advantages in terms of impact strength compared to GFPP. With 30% rayon in PP, tensile strength is tripled, modulus is doubled, and notched impact strength is doubled at room temperature and quadrupled at -18°C. For the bio-based thermoplastics, rayon is an ideal reinforcement since the bio-based character is preserved. Strength and modulus always increase, and at the same time, impact strength is increased dramatically for brittle products such as PLA. This is true in particular for a specially designed fiber-matrix interphase using a decoupling agent.