The thermal properties of the composite blends containing different reinforcement (rice, wood and DDGS) measured by DSC are shown in Table 12.2.

Figure 12.5 presents the thermograms of the second heating of the PP/reinforce — ment flour blends subjected to the same rate flow. Only one endothermic peak corre­sponding to PP can be observed in these figures. All the composites regardless have invariably exhibited a slightly higher Tm compared to the Tm of neat PP. Figure 12.5 shows DSC curves corresponding to the cooling scan for PP and its composites. All curves show exothermic peaks corresponding to the crystallization of the polymeric matrix. A shift of Tc towards higher temperatures in the presence of MAPP and rein­forcement was observed in the composites. This indicated that the phenomenon of crystallization during the cooling occurred more rapidly in composites containing MAPP than in the pure PP. The effect of rising crystallization rates was clear for all of the composites containing MAPP. The results imply that MAPP acted as a pre­cursor and increased crystallization. The presence of reinforcement (wood, rice or DDGS) decreases the thermal stability, heat in turn causes scissions of chains and all these phenomena generate an early fusion and it is more pronounced whit samples with reinforcement agent.

Figure 12.6 shows DSC curves corresponding to the cooling scan for PP and its composites. All curves show exothermic peaks corresponding to the crystallization of the polymeric matrix. Every bio-filler affects the thermal properties of the com­posite differently4950. The cooling characteristics have shown very interesting be­havior. The temperatures corresponding to onset of crystallization and peak crystal­lization have increased due to presence of filler reinforcement. These temperatures have further increased due to chemical treatment of rice husk and DDGS. Thus it seems that addition of reinforcement is causing early crystallization of PP. This indi­cates that reinforcement is influencing the degree of super cooling of PP. Hattotuwa et al.51 also have reported similar results. The presence of MAPP does not signifi­cantly modify the crystallization temperature but leads to an increase in the degree
of crystallinity. It is recognized that wood and MAPP act as nucleating agents52,16. The presence of these two elements generates the formation of more crystals. Tm, Tc,

ЛHm and xcor are reported in Table 12.2 for composites of PP matrix and differ­ent reinforcements of wood, rice and DDGS. An increase in T was observed when reinforcement was loaded into the polymer matrix. The addition of reinforcement had the effect of shifting Tm to higher values. This increase was accompanied by an increase of the composites’ degree of crystallinityX(%) which was corrected as Xcor (%) by taking into account there enforcement concentration53 54. These results suggest that crystallization occurred earlier with the incorporation of reinforcement, which played the role of a nucleating agent. Reinforcement provided sites for het­erogeneous nucleation; this induced crystallization of the polymeric matrix. This was ascribed to the poor thermal conductivity of reinforcement. In the composite, reinforcement acted as an insulating material, hindering the heat conductivity. As a result, the composites compounds needed more heat to melt. Similar findings were previously reported by Matuana and Kim55 for PVC based wood-plastic composites. They found that the addition of wood flour to the PVC resin caused significant in­creases in the temperature and energy at which fusion between the particles started. The delayed fusion time observed in rigid PVC/wood flour composites was attrib­uted to the poor thermal conductivity of the wood flour; this decreased the transfer of heat and shear throughout the PVC grains. These phenomena were consistent with the results of this study. For a composite, the impact strength depends on the composition and structure as well as the testing method. Adding reinforcement in all cases was shown to increase both the crystallization temperature and extent of crystallization of polymer matrix in WPC systems as compared to controls.

FIGURE 12.6

The thermal stability of the composites was investigated using DSC analysis under nitrogen atmosphere. The results have shown a spectacular improvement of thermal stability of the composites and an increase of the degree of crystallinity. Although the properties of some blends are acceptable for some applications, further improvement will be necessary, mainly by optimizing fiber-polymer.