Tuning The Morphology And Property Of Polylactide/elastomer Immiscible Blends Via OMMT

Poly(lactic acid)(PLA) is a biodegradable polymer which can be decomposed into water and carbon dioxid. PLA has excellent mechanical and transparency properties, but its poor toughness and flexibility restricts its application scope in packing and film fields. Three different elastomeric polymer:linear low-density polyethylene (LLDPE), ethylene vinyl acetate copolymer (EVA) and poly(butylene adipate-co-terephthalate)(PBAT) were used to modify PLA in order to improve its toughness. However, as we know, these PLA blending systems are immiscible. Then organic montmorillonite (OMMT) as a kind of compatibilizer was used to improve the compatibility of above-mentioned immiscible blends. The selective distribution effect of OMMT on the interface of dispersed phase was used to reduce the interfacial surface energy, leading to a size refinement in the dispersed phase and an improvement in compatibility of these PLA blending systems. The effects of OMMT content on microstructure, tensile toughness, crystallization-melting behavior and thermal stability of these blends were studied, respectively. Moreover, the compatibilizing mechanism on these immiscible blends is detailed presented according to the selective distribution effect of OMMT.SEM results for the three PLA blends showed similar phenomena that two-phase interface become blurred with addition of OMMT. A size reduction of the dispersed phases and a simultaneous improvement in size distribution can be seen with addition of OMMT compared with binary blends. SEM result indeed suggests a remarkable compatibilization of immiscible binary blends by using OMMT. TEM micrographs of PLA/LLDPE/OMMT ternary nanocomposites with different magnifications show that the main part of OMMT is localized in the LLDPE phase and the interface of PLA and LLDPE. The magnified photographs shows that montmorillonite formed an intercalated structure which consistent with the result of XRD.The results of surface tension show that the selective distribution of OMMT at phase interface and internal of dispersed phase during melt mixing can decrease the total surface energy of the ternary blends. The compatibilization mechanism of nanoparticles in these PLA blending systems has been proposed based on thermodynamics consideration. A size reduction of the dispersed phases was achieved when OMMT selectively distriuted at phase interface.The effects of OMMT on tensile property of PLA/LLDPE, PLA/EVA and PLA/PBAT blends were studied, respectively. With adding OMMT into these binary blends, the elongation at break increased significantly while the strength decreased slightly. In the PLA/LLDPE/OMMT blending system, with the addition of3phr OMMT, elongation at break increased from80.8%for the binary blend to maxium vaule of249.6%. In the PLA/EVA/OMMT blending system, elongation at break increased from176.9%for the binary blend to maxium vaule of376.6%when5phr OMMT was introduced In particular, comparing with the PLA/PBAT binary blend, elongation at break reached to the maximum value of294.3%when OMMT addition was3phr, increased nearly600%. However, further increasing OMMT content induced an obvious decrease in elongation at break due to the serious aggregation of OMMT particles.The melt crystallization and melting process of the blend was studied by DSC testing. It showed that OMMT and three elastomeric polymers did not effectively improve the melt-crystallization ability of PLA matrix. But from the subsequently second heating DCS thermograms for these specimens, it can be pointed that OMMT played a role of nucleating agents to improve the cold crystallization ability of PLA matrix. However, it was interestingly found that cold crystallization ability of PLA matrix was became worse and Tcc of PLA matrix increased when to OMMT and elastomer was added to PLA matrix together. This result was in contradiction with improving the crystallization ability of PLA when OMMT was added to PLA matrix alone. It suggests that there was a noticeable negative factor to restrain the nucleating effect when OMMT and elastomer were introduced into PLA matrix together. It can be explained by the morphological change of PLA blend. From the SEM figures, it can be seen that dispersed phase size drastically reduced when nanoparticles selective distribution on dispersed phase interface. This led to an obvious decrease in the distance of dispersed phase particles. Apparently, the decrease in the distance of dispersed phase would largely retrain the mobility of chain segments and cold crystallization ability of PLA matrix, with the performance of the cold crystallization temperature increased.TGA analysis showed that the addition of OMMT can greatly improve the heat decomposition temperature of these blends. In the PLA/LLDPE/OMMT blending system, with the addition of3phr OMMT, heat decomposition temperature increased from316.3?of binary blend to329.3?of the ternary blend. Similarly, in the PLA/EVA/OMMT and PLA/PBAT/OMMT blends, thermal decomposition temperature of ternary blends were increased by about8?and3?(OMMT=3phr), respectively.