聚乳酸/低密度聚乙烯共混聚合物的制备及表征

Poly(lactic acid)/Low Density Polyethylene Polymer Blends:Preparation and Characterization

聚乳酸（PLA）是一种来源于玉米及甜菜根的脂肪类聚合物，可被降解为无毒的化合物。目前，常用的PLA合成方法为直接由乳酸或丙交酯开环聚合制得PLA。首先用乳酸合成低分子量的PLA，随后使其解聚成丙交酯（不稳定的二聚物），最后经催化剂开环聚合成可控的高分子聚合物，其制备过程免溶剂处理。该方法能够以低成本生产高分子量的PLA，故在市场上得到了广泛的应用。

Poly （lactic acid） （PLA） was melt blended with low density polyethylene （LDPE） with the aim of replacing com- modity polymers in future applications. Because cost of PLA is quite high, it is not economically feasible to use it alone for day to day use as a packaging material without blending. In this work, PLA was blended with LDPE in different ratios by using a laboratory scale single screw extruder, The prepared blends were characterized in terms of rheological and mechanical properties. Rheological properties were studied using a capillary rheometer, and the Bagley＇s correction was performed. True shear rate （ γr ） ＇ true shear stress （ τr ） , true viscosity （ ηr ） and non-Newtonian index （n） were determined. The relation- ship between true viscosity and temperature was also studied, and the flow activation energy at a constant shear stress （E） was determined. The mechanical properties of the blends were investigated on dog bone-shaped samples obtained by injection molding, tensile tests were performed using Testometric M350-10KN, stress at break, strain at break and Young＇s modulus were determined. Rheological results show incompatibility between the two polymers where the true viscosity of the blend decreased with increasing PLA content below the line of mixing rule, also it was found that the blend exhibits shear-thinning behavior over the range of the studied shear rates. The mechanical results also showed incompatibility between PLA and LDPE in the blend, where stress at break and Young＇s modulus of the blend increasedwith increasing PLA content,whereas strain at break of the blends was similar to that of neat PLA.