**4. Conclusions**

peak of decomposition of olefinic products or their oxidation degradation products containing functional groups such as C=O, O–H, and C–O–C which formed in the first stage of polyethylene degradation appears at 438°C. This second main peak of PE degradation is in superposition with the second main peak of the bio-fillers due to degradation of char (**Figure 15a**). Therefore, the second-stage degradation of both polyethylene and the bio-fillers is competitive at above 438°C, that can also lead to retard the degradation of the composite. However, there is a one-step degradation of polypropylene in air atmosphere and PP fully degraded at 380°C.

Therefore, RH char did not affect the degradation of polypropylene.

20 Composites from Renewable and Sustainable Materials

**Figure 16.** Effect of compatibilizers on TGA of 50% filler composites in nitrogen atmosphere.

due to a wick effect.

anhydride functional groups of compatibilizers.

The RH-filled PE leaves a bigger residue than the SD-filled PE, as expected from the TGA analysis of the fillers. The residues of rice husk composites (10.9–18.8% in nitrogen and 5.5– 9.4% in air atmosphere) were much higher than those of saw dust composites (4.5–8.8% in nitrogen and 1.0–1.3% in air atmosphere) due to high ash content of rice husk compared to saw dust. The residue is in all cases 0–10% smaller than the value calculated from the residues of the separate components, and only in the saw dust composites in air, it is a third of the expected value. The filler/matrix interaction leads to a more profound decomposition maybe

**Figure 16** shows the TGA curves of the composites at 50 wt.% filler without and with compatibilizers (2 wt.% for PP matrix composites and 4 wt.% for PE matrix composites). The thermal stability and degradation temperature of the composites with compatibilizers [PP/RH (MA), PE/RH (MA), and PE/SD (MA)] were slightly higher than those of the composites without compatibilizers (PP/RH, PE/RH, and PE/SD). The improved thermal stability of the composites with compatibilizers is due to enhanced interfacial interaction and additional intermolecular bonding (ester and hydrogen bonds) between hydroxyl groups of rice husk, saw dust and the

The performance of rice husk and saw dust fillers, used as low ecological footprint reinforcement of PE and PP, was investigated. SEM micrographs show the different morphology of rice husk platelets and fibrous saw dust fillers. Rice husk has the higher stiffness and the higher density of the two fillers considered. In a PE or PP matrix, the fillers increase the bending moduli. In composites without compatibilizer, an increase in filler load leads to decreased tensile, bending, and impact strengths.

Here, PE matrix composites with saw dust have smaller moduli but higher strengths than those with rice husk filler. The tensile, bending, and impact strengths of bio-filler/polyolefine composites increase with increasing compatibilizer content, due to the improvement in interfacial bonding strength between filler and matrix. The coefficient of thermal expansion of PP and PE decreased upon adding rice husk and saw dust fillers.

The thermal stability of the fillers or natural fibers in general is not as high as that of highperformance fibers. This limits the matrices of thermoplastic composites with bio-fillers to those materials processable below 200°C, such as PP, PE, or polylactic acid (PLA).

Rice husk and saw dust can be used as fillers in manufacturing inexpensive polyolefine composites for furniture and household articles as well as construction materials, generating economic development for rural areas and reducing environmental pollution caused by these bio-wastes if unused.
