Effect on Mechanical Properties of the Composite Material

Cellulose fiber is a good reinforcing tiller. In fact, this is one of the two major factors of the very existence of WPC materials (a) to make the composite material less expensive and (b) to obtain material with overall better properties compared to neat plastic, on the one hand, and wood, on the other. For example, tensile modulus of a particular sample of neat polypropylene was 203,000 psi, whereas for the same polypropylene filled with 40% of jute it was 1,030,000 psi. For a comparison, for the same polypropylene filled with 40% glass fiber it was 1,100,000 psi. Tensile modulus for natural fiber itself is in the range of 3,800,000-17,400,000 psi [135]. Table 3.4 shows data in more detail. 

Effect of a different hller, wood flour, on mechanical properties of polypropylene is shown in Table 3.5. 

Comparison of Tables 3.4 and 3.5 shows that hemp as a filler results in a much higher flexural strength increase compared to wood flour (57% compared to 12-15%) however, increase of flexural modulus is about the same with the two Filers (2.2 times with 33% of hemp, compared to 1.6 and 2.5 times with 20 and 40% of wood flour, respectively). 

Another set of data, obtained in a wider range of wood flour content as polypropylene filler (Table 3.6), shows that flexural strength of the composite reached maximum at 40% tiller, and then decreases. Apparently, there is not enough plastic to provide good adhesion for all tiller particles. Flexural modulus, however, is increased 

TABLE 3.4 Mechanical properties of filled polypropylene composites [135] 

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