Short fibers thermoplastic systems

A correlation between Kq and UTS has been shown by others, also for short fiber reinforced thermoplastics [69], and more generally for a variet of composite systems, embracing unidirectional. 0 90 woven and nonwoven, and random chopped fiber arrangements [118]. 

As one might expect, any fiber-polymer system is unique, not only because of the differences in the respective properties of the components, but also because the fiber surface properties and the polymer chemistry have important effects. Not all aspects are yet understood and any generalization would indeed be abusive. A clear demonstration of this fact is offered when comparing the effect of a given type of short glass fiber (E-glass), at constant loading (30%) in different thermoplastics (Table 7.2). 

Whilst finely grinding wood material may considerably hide the fiber aspect of wood particles, WPC exhibit properties which are typical of systems filled with short fibers of natural origin. As WPC is a rich subject in itself, only a few basic aspects will be discussed hereafter. It is obvious that not all thermoplastics can be used to prepare WPC. Indeed the polymer component melts or at least softens at or below the degradation point of the wood component, normally 200-220°C but must be rigid at normal usage temperatures (i.e., up to around 65°C). Practically, this reduces the choice to polypropylene, low-and high-density polyethylenes, polystyrene, and vinylics (essentially PVC). 

Extensive reviews on short fibers-reinforced elastomers have been published by Goettler and Shen, ° and more recently by Rajeev. Table 7.11 is a list of selected published works on natural fiber-filled rubber composites, sorted by rubber type. Only vulcanizable rubbers were considered in preparing the table thermoplastic rubber and rubber-plastics blends were omitted. As can be seen most grades of conventional elastomers have been considered with quite a large variety of natural fibers. Natural Rubber, SBR, and EPDM compounds have received much attention, as expected with respect to their industrial importance. A bonding system is us in most cases, with resin types (i.e. resorcinol-formaldehyde, resorcinol-hexamethylenetetramine, sil-ica-resorcinol-hexamethylenetetramine) the most frequent ones. 

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