Auras Rafael, Harte Bruce, Selke Susan
The School of Packaging, Michigan State University, East Lansing, MI 48824-1223, USA.
Macromol Biosci. 2004 Sep 16;4(9):835-64. doi: 10.1002/mabi.200400043.
Polylactide polymers have gained enormous attention as a replacement for conventional synthetic packaging materials in the last decade. By being truly biodegradable, derived from renewable resources and by providing consumers with extra end-use benefits such as avoiding paying the "green tax" in Germany or meeting environmental regulations in Japan, polylactides (PLAs) are a growing alternative as a packaging material for demanding markets. The aim of this paper is to review the production techniques for PLAs, summarize the main properties of PLA and to delineate the main advantages and disadvantages of PLA as a polymeric packaging material. PLA films have better ultraviolet light barrier properties than low density polyethylene (LDPE), but they are slightly worse than those of cellophane, polystyrene (PS) and poly(ethylene terephthalate) (PET). PLA films have mechanical properties comparable to those of PET and better than those of PS. PLA also has lower melting and glass transition temperatures than PET and PS. The glass transition temperature of PLA changes with time. Humidity between 10 and 95% and storage temperatures of 5 to 40 degrees C do not have an effect on the transition temperature of PLA, which can be explained by its low water sorption values (i.e. <100 ppm at Aw = 1). PLA seals well at temperatures below the melting temperature but an appreciable shrinking of the films has been noted when the material is sealed near its melting temperature. Solubility parameter predictions indicate that PLA will interact with nitrogen compounds, anhydrides and some alcohols and that it will not interact with aromatic hydrocarbons, ketones, esters, sulfur compounds or water. The CO2, O2 and water permeability coefficients of PLA are lower than those of PS and higher than those of PET. Its barrier to ethyl acetate and D-limonene is comparable to PET. The amount of lactic acid and its derivatives that migrate to food simulant solutions from PLA is much lower than any of the current average dietary lactic acid intake values allowed by several governmental agencies. Thus, PLA is safe for use in fabricating articles for contact with food.
在过去十年中，聚乳酸聚合物作为传统合成包装材料的替代品受到了广泛关注。聚乳酸（PLA）具有真正的生物可降解性，源自可再生资源，并为消费者提供额外的最终使用优势，例如在德国避免支付“绿色税”或符合日本的环境法规，因此作为一种适用于高端市场的包装材料，其应用日益广泛。本文旨在综述PLA的生产技术，总结PLA的主要性能，并阐述PLA作为聚合物包装材料的主要优缺点。PLA薄膜的紫外线阻隔性能优于低密度聚乙烯（LDPE），但略逊于玻璃纸、聚苯乙烯（PS）和聚对苯二甲酸乙二酯（PET）。PLA薄膜的机械性能与PET相当，优于PS。PLA的熔点和玻璃化转变温度也低于PET和PS。PLA的玻璃化转变温度会随时间变化。湿度在10%至95%之间以及储存温度在5至40摄氏度时，对PLA的转变温度没有影响，这可以用其低吸水率来解释（即水分活度Aw = 1时<100 ppm）。PLA在低于熔点的温度下密封良好，但当材料在接近其熔点的温度下密封时，会观察到薄膜有明显收缩。溶解度参数预测表明，PLA会与氮化合物、酸酐和一些醇类相互作用，而不会与芳烃、酮类、酯类、硫化合物或水相互作用。PLA的二氧化碳、氧气和水的渗透系数低于PS，高于PET。其对乙酸乙酯和D - 柠檬烯的阻隔性能与PET相当。从PLA迁移到食品模拟溶液中的乳酸及其衍生物的量远低于几个政府机构允许的当前平均膳食乳酸摄入量值。因此，PLA用于制造与食品接触的制品是安全的。
