Polymer matrices, natural fiber

Many research efforts to enhance the interfacial properties of biocomposites and ultimately to improve the mechanical and thermal properties and so forth have been performed more extensively by treating or modifying natural fibers before composite processing than by modifying polymer matrices. Natural fibers can be treated by chemical and physical approaches. 

In a natural fiber polymer composite, natural fiber is incorporated in a definite volume in the polymer matrix. Mechanical properties can be enhanced by increasing the fiber volume in a composite, but after a certain level, it may start decreasing due to the poor bonding between fiber and matrix. Oksman et al. [9] studied the effect of fiber loading with epoxy polymer. As shown in the Table 22.5, sisal fiber... 

Naturally, fibers and whiskers are of little use unless they are bonded together to take the form of a structural element that can carry loads. The binder material is usually called a matrix (not to be confused with the mathematical concept of a matrix). The purpose of the matrix is manifold support of the fibers or whiskers, protection of the fibers or whiskers, stress transfer between broken fibers or whiskers, etc. Typically, the matrix is of considerably lower density, stiffness, and strength than the fibers or whiskers. However, the combination of fibers or whiskers and a matrix can have very high strength and stiffness, yet still have low density. Matrix materials can be polymers, metals, ceramics, or carbon. The cost of each matrix escalates in that order as does the temperature resistance. 

Ultra-high modulus fibers such as aramid and carbon fibers have been currently utilized for composite material fabrication. Ultra-high modulus polyethylene (UHMPE) fiber is also applicable for composite fabrication because of the light weight in addition to its high modulus, vibration damping, and resistance to chemicals. However, this fiber has drawbacks such as poor interfacial adhesion with the polymer matrix of the composite because of highly hydrophobic nature of the fiber surface. 

The infiltration of carbonaceous structures by liquid silicon or silicon vapor is also an interesting technique to produce SiC components. Especially the Si-inhltration of C-structures coining from natural materials like wood offers the possibility for low cost fabrication of SiC, and has already been described in Sect. 4. Infiltration of polymer-matrix derived carbon fiber reinforced carbon is schematically drawn in Fig. 14 [255, 256]. The production of complex SiC-composite parts and components as well as big parts is possible by this route. 

Completely biodegradable Here the polymer matrix is derived from natural sources (such as starch or microbially grown polymers), and the fiber reinforcements are produced from common crops such as flax or hemp. Microorganisms are able to consume these materials in their entirety, eventually leaving carbon dioxide and water as by-products (Katarzyna et al., 2010). 

Improved fiber matrbc adhesion and thereby improved mechanical properties can be accomplished by engineering a superior processing condition in preparing the bio-composites, by altering the polymer architecture of the matrix or by the surface treatment on the fiber [47]. Table 23.1 showed mechanical properties of natural fiber-reinforced PLA composites. 

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