| Poly(lactic acid) (PLA) is a kind of commercially available and biodegradable thermoplastic with high strength (50-70 MPa), excellent transparency, relatively good processability, and biocompatibility. Nevertheless, the shortcomings involving brittleness, slow crystallization rate and high-cost limit its practical application. In this study, use of multiepoxy compound (ADR) as an in-situ compatibilizer for PLA,poly(butylene adipate-co-terephthalate) (PBAT) and starch was researched to obtain a sort of composite material with high toughness and low cost. Before the preparation of PLA/PBAT/starch/ADR blends, three types of PLA blends embracing PLA/starch/ADR,PBAT/starch/ADR and PLA/PBAT/ADR blends were studied respectively. The mechanical properties of PLA blends were increased with addition of ADR. The main research contents are as follows:(1) The influence of ADR on rheological properties, microstructure and tensile properties of PLA/starch and PBAT/starch samples were studied. The results of torque and melt flow index tests indicated that the chain extension has occurred between PLA,ADR and starch, the same as the one for PBAT, ADR and starch. SEM photograghs show that the addition of ADR strengthened the interfacial adhesion and improved the interfacial compatibility. Tensile properties were also enhanced at the presence of ADR.For PLA/starch blends, with 1 phr ADR added, tensile strength up to 55.04 MPa from 44.41 MPa and the elongation at break up to 3.31 % from a vaule of 2.26%. On the other hand, tensile strength increased from 7.23 MPa to 8.73 MPa and elongation at break enhanced from 725.42% to 809.47% with 1 phr ADR adding into PBAT/starch blends.(2) Effect of ADR on rheological properties, microstructure, mechanical properties and isothermal crystallization kinetics for PLA/PBAT(60/40) with different feeding method(one-step method and two-step method) was researched in detail. As a result,the torque increased and the values of MFR decreased due to the addition of ADR. As is vividly depicted from the above SEM pictures, the incorporation of ADR can improve the compatibilization between PLA and PBAT. Furthermore, the domain size of PBAT made further diminution through the changing the feeding sequence which we called two-step method. The mechanical properties tests showed that both tensile properties and impact properties enhanced with the existence of ADR. The samples made by two-step method showed better mechanical performance than the one made by one-step method. For example, when adding 1 phr ADR, the notched impact strength increased from 6.75 KJ/m2 to 42.49 KJ/m2 and the value of two-step further improved to 74.48 KJ/m2 while elongation at break had the same change. Hence, samples made by two-step method had more excellent performance.Moreover, melt isothermal crystallization kinetics of PLA/PBAT/ADR blends were studied. t1/2 increased as Tc rised from 115? to 125?. However, with ADR added,t1/2 of PLA/PBAT/ADR blends became shorter. Alternatively, t1/2 of two-step samples was shorter than one-step samples at the same temperature and the same proportion.(3) PLA/PBAT/starch/ADR(60/40/25/X) blends were prepared to research rheological properties, microstructure and tensile properties. The results of the increasing torque and diminishing melt flow index indicated that the chain extension has occurred between PLA, PBAT, starch and ADR. According to SEM pictures, the incorporation of ADR reduced the dispersed phase size of PB AT obviously and two-step method made interface more compatible. The elongation at break of PLA/PBAT/starch/ADR blends had a great improvement with ADR addation owing to the enhancement of interface bonding force. When the content of ADR was 2 phr, the elongation at break up to 42.08% from 5.58%, and the vaule further ascended to 65.16%for the sample made by two-step method. |
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