Inorganic Reinforcing Fibers

The final properties depend not only on unstaturated polyester structure but also on a number of other parameters, such as the nature and proportion of unsaturated comonomer, the nature of the initiator, and the experimental conditions of the crosslinking reaction. Moreover, since polyester resins are mainly used as matrices for composite materials, the nature and amount of inorganic fillers and of reinforcing fibers are also of considerable importance. These aspects have been discussed in many reviews and book chapters and are beyond the scope of this chapter.7-9... 

The organofunctional portion bonds with the resin in the adhesive or the organic medium, and the silane portion bonds to the inorganic or substrate surface. Silane coupling agents are commonly used between the adhesive and the adherend, between resin matrix and reinforcing fibers in composites, and between resin matrix and mineral fillers in compounds. The resulting interface provides... 

Another important distinction is based on (1) filled and reinforced plastics, and (2) foams. (1) When any family of polymers is combined with particulate inorganic fillers, this produces major increase in density, modulus, dimensional stability, heat transfer, dielectric constant, and opacity, and frequently a decrease in cost. When the fillers are reinforcing fibers, they can further produce a great increase in strength, impact resistance, and dimensional stability. Thus, these properties may depend more upon the use of fillers and fibers, than upon the choice of the particular polymer in which they are used. 

Fillers are particulate, organic or, for the most part, inorganic substances in solid form. Their incompatibility with the basic material (matrix) results in a multiphase system, the compatibility of which can, however, be increased by means of coupling additives (coatings) - similarly to the process with reinforcing fibers leading, at the least, to bridge formation. 

Natural fiber-reinforced PLA composites are attractive because both the reinforcement (natural fiber) and matrix (PLA) are obtained from renewable resources. Natural fibers are considered as environment friendly alternatives to conventional reinforcing fibers such as glass, carbon, aramid, and so on. Natural fibers can be subdivided into three categories plant (cotton, jute, flax, hemp, etc.), animal (wool, silk, etc.), and mineral fibers (asbestos, inorganic whiskers, etc.). Generally, plant fibers are more popularly used as natural fiber reinforcements. Of these fibers, the most used are flax, jute, sisal, ramie, hemp, kenaf, and cotton. Plant fibers can generally be classified as nonwood (vegetable fibers) and wood fibers [20]. 

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