凝聚态结构对PLA/PPC共混物结构及水蒸气阻隔性的影响

Effect of Condensed Structures on the Structure and Water Vapor Barrier Properties of Polylactic Acid/Poly Propylene Carbonate Blends

目的研究不同聚集态结构聚乳酸(PLA)/聚甲基乙撑碳酸酯(PPC)的相容性、晶体学结构特征及其水蒸气阻隔性能的演化,拓宽其在包装领域的应用范围。方法采用共混法并配合不同的热处理工艺,获得了3种不同凝聚态结构(非晶态、α’晶型、α晶型)的PLA/PPC共混物,并通过FT-IR、DSC、OM、SEM、XRD、DSC、水蒸气透过率测试进行分析和表征。结果分析结果表明,虽然PLA与PPC之间有一定的相容性,但整体上表现为热力学不相容。当热处理温度由80℃升高到130℃时,结晶态共混物PLA/PPC的晶体结构将由α’转变为α晶型。水蒸气透过率测试结果表明,具有α晶型的结晶态共混物对水蒸气具有最优的阻隔性能。不同凝聚态结构共混物的水蒸气渗透系数为非晶态>α’晶型>α晶型。结论不同聚集态共混物具有不同的结构及水蒸气阻隔性,α晶型优良的水蒸气阻隔性能主要归因于大分子链排列规整度更高,链与链之间产生更强的范德华力,进而延长了水蒸气的扩散路径,通过控制PLA/PPC共混物的聚集态,调整其结构及性能是一种有效的方法。

The work aims to study the compatibility,crystallographic characteristics and evolution of water vapor barrier properties of polylactic acid/poly propylene carbonate(PLA/PPC)blends with different condensed structures and broaden the application scope of blends in the packaging field.Three kinds of PLA/PPC blends with different condensed structures(amorphous form,α’crystalline form andαcrystalline form)were prepared by blending method and different heat treatment processes and then characterized and tested by FT-IR,DSC,OM,SEM,XRD,DSC and water vapor permeability test.Although there was certain compatibility,PLA and PPC showed thermodynamic incompatibility on the whole.The crystal structure of the crystalline PLA/PPC blends changed fromα’toαcrystalline form when the heat treatment temperature increased from 80℃to 130℃.The results of water vapor permeability test showed that the crystalline blends withαcrystalline form had the best barrier performance to water vapor.At the same time,the water vapor permeability coefficients of the blends with three different condensed structures were qualitatively given in the order of amorphous form>α’crystalline form>αcrystalline form.Blends with different condensed structures have different structures and water vapor barrier properties.The excellent water vapor barrier properties ofαcrystalline form are mainly attributed to the higher regularity of macromolecular chains,stronger van der Waals force between chains and longer path of water vapor diffusion.It is an effective method to adjust the structure and properties of PLA/PPC blends by controlling the condensed structures.