The soil degradation of OBF, PFR and their composites is measured in the function of weight loss with every 20 days of soil-burial time. The percentage weight loss with time is shown in Table 10.6. It can be noted that weight loss of PFR is very low, maybe due to antibacterial activities of formaldehyde. However, the degradation of OBF is faster than that of composites; hence, cellulose possesses the tendency to be degraded when buried in soil by the action of microorganism. Weight loss increased with the increase in burial time for all the specimens, and after 60 days, OBF is completely degraded in soil. It is also observed that up to 29 wt% OBF-PFR composites weight loss is not so prominent. This may be due to stronger interaction of fibre and PFR matrix beyond this percentage of fibre. Again, OBF is a natural biodegradable fibre which instantly absorbs water due to strong hydrophilic character. During soil degradation test, water penetrates from the cutting edges of the compos­ites and degradation occurred in presence of microorganism. So, higher fibre faction composite shows higher tendency of biodegradation.

10.2 Conclusion

In this chapter, the properties of OBF-PFR composites including density, bulk

content, mechanical properties, thermal and soil degradation properties are also

discussed. The following conclusions can be drawn:

1. Enhancement of the content of OBF will improve the mechanical properties of OBF-PFR composites. Results suggested that the appropriate percentage of OBF in composite is 29 wt%, but a larger amount of OBF would decrease the tensile strength and flexural strength of OBF-PFR composites. However, 38 wt% OBF containing composite is given higher modulus than other composites.

2. The presence of hydroxyl groups of the OBF also increases water absorption and resultant poor compatibility between the OBF and the hydrophobic PFR. AN-grafting gives hydrophobic character of OBF and hence increases compatibility with PFR. On the other hand, the surface area is increased by alkali treatment and bleaching which is well distributed in PFR and hence gives higher mechanical properties.

3. It is also indicated that the initial degradation temperature and final degradation temperature of OBF is increased after composite fabrication. Higher fibre — containing composite has lesser thermal stability.

4. OBF is readily degraded when buried in soil. PFR restricted the biodegradation of OBF-PFR composites.