Composite Materials Journal of Thermoplastic - LSU School of ...

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Thermal and Mechanical Properties of WF/Talc-filled PLA Composites 215 composite and PLA70/WF20/talc10 composite were 348.0 and 340.58C, respectively. The thermal decomposition temperatures of PLA/WF/talc composites with 1 wt% silane were higher, compared to those of the composites with 3 wt% silane. At higher levels of WF, the DT p values of the composites with 1 wt% silane were 2–48C higher than those with 3 wt% silane. The incorporation of silane to PLA/WF/talc decreased the DT p by 27–398C compared to that of neat PLA. 3.1.2. DSC DATA The glass transition temperature, T g as function of WF loading for various systems are shown in Figure 2(a). The T g of neat PLA was 63.48C. As the WF loading increased, double peaks were observed in DSC thermograms, and the T g decreased slightly (Figure 2(a)). For example, the T g of the composite with WF (40 wt%) to PLA (60 wt%) decreased about 2.58C from that of pure PLA. The use of talc (10 wt%) in PLA50%/ WF40% composites largely lowered the T g of the hybrids (4.08C), compared to that of PLA60%/WF40% hybrid. At the WF loading of 10, 20, and 30 wt%, the addition of 1 wt% silane to the PLA/WF/talc combinations led to higher T g values than those of the combinations with 3 wt% silane. Similar to DT p data, higher T g of the composites with 1 wt% silane could be ascribed to an improved interfacial adhesion between two materials (i.e., polymer matrix and fillers). This result also indicated that the T g depends on molecular characteristics, composition, and compatibility of the components in the amorphous matrix [19]. The melting temperature, T m , as a function of WF loading is shown in Figure 2(b). The T m of the PLA was 164.58C. The loading of WF (10–40 wt%) to the PLA decreased the T m by 1.5–1.78C. A decrease in the melting temperature might be due to the presence of voids in the composites. The enthalpy H m of the PLA was 41.7 J/g (Figure 3(a)). The H m values for composites with increased WF loading from 10 to 40 wt% significantly decreased (as low as 11.4 J/g), indicating that less energy was required to melt the composites (Figure 3(a)). This phenomenon implies that thermal degradation of the polymer became easier upon the hybridization with WF. The addition of talc (10 wt%) and silane (1 and 3 wt%) to PLA/WF composites showed no significant effect on the T m and H m of composites. This result suggested that the addition of talc had resulted in tertiary interfaces in the composites and the added silane acted as a dispersing agent in the interfaces. Figure 3(b) shows the T c , representing an exothermic peak due to the crystallization of the polymer matrix. The T c of neat PLA was 113.18C, and the incorporation of WF to the neat PLA slightly decreased the T c by Downloaded from http://jtc.sagepub.com at KAIST GRADUATE SCHOOL OF MGMT on April 27, 2008 © 2008 SAGE Publications. All rights reserved. Not for commercial use or unauthorized distribution.
216 S.-Y. LEE ET AL. (a) Glass transition temp. (T g , °C) 70 65 60 55 PLA/WF PLA/WF/Talc10% PLA/WF/Talc10%/Silane1% PLA/WF/Talc10%/Silane3% 50 0 10 20 30 40 Wood flour (%) (b) 170 Melting temp. (˚C) 168 166 164 162 160 158 156 154 152 PLA/WF PLA/WF/Talc10% PLA/WF/Talc10%/Silane1% PLA/WF/Talc10%/Silane3% 150 0 10 20 30 40 Wood flour (%) Figure 2. Differential scanning calorimetric properties of the composites (I): (a) Glass transition temperature of PLA/wood flour/talc/silane composites; and (b) Melting temperature of PLA/wood flour/talc/silane composites. about 2.0–4.28C for the resultant composites. However, the loading of 10 wt% talc to the PLA/WF composites had no significant effect on the T c . The addition of silane (1 and 3 wt%) to the PLA/WF/talc composites gave slightly lower T c values than those of other composites without silane. Downloaded from http://jtc.sagepub.com at KAIST GRADUATE SCHOOL OF MGMT on April 27, 2008 © 2008 SAGE Publications. All rights reserved. Not for commercial use or unauthorized distribution.
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