Study On Structure And Properties Of Palygorskite-modified Poly (Lactic Acid)

Poly（lactic acid）（PLA） is a potential substiute of common petrol-based nondegradable plastics. In order to overcome slow crystallization rates, brittleness, low viscosity, and poor heat stability, the PLA and palygorskite（PA） nano-composites are prepared through melt blending by using natural PA as heterogeneous nucleating agent and filler to improve the properties of PLA matrix. The mechanism of PA reinforcement is also studied to reveal the interactions between the PA surface and PLA matrix.The dispersion of PA in PLA matrix is super when the concent of the PA is 3wt%, which is confirmed by SEM and TEM results. FT-IR results indicate that interaction in form of hydrogen bond exists between PA and PLA molecules. Such results are further confirmed by XPS analysis, which leads to the binding of PLA chains on the PA surfaces. Thus,the mechanical properties of PLA/PA nanocomposite are better than those of neat PLA. Here it is noted that the complex viscosity increases with the addition of PA. All the zero-shear-rate viscosity of the PLA-PA nano-composites is higher than that of the neat PLA and this reinforcement effect is more significant at low frequency than at high frequency. Also, there is an improvement of storge module over the whole frequency range, and it is more pronounced at low frequency region. The values of the storage module of all PLA-PA nano-composites increase at low frequency which indicates that the addition of clay has effect on the linear dynamic viscoeleastic response.The onset decomposition temperature of the PLA/PA nano-composite is 11 °C, and it is higher than that of the neat PLA. The significant finding by DSC is that PA acts as the nucleating-agent and it accelerates the crystallization process of neat PLA. The neat PLA shows a very slow crystallization rate and the minimum crystallization t_1/2 is 18.54 min at 130 °C. The addition of PA increases the crystallization rate effectively, thus the t_1/2 decreases to 4.73 min for PLA/PA nano-composite with 3wt% of PLA.As compared to neat PLA, the PLA/PA nano-composites show several enhanced properties, which is expected to be used as a potential food packing materials to replace the use of general plastics.