摘要传统聚氯乙烯（PVC）保鲜膜存在着严重的安全问题，而其他聚乙烯（PE） 和聚偏二氯乙烯（PVDC）等石油基保鲜膜的大量使用会造成对能源的浪费，且这些保鲜膜废弃后可残存于自然界中长达上百年不会降解，从而带来严重的“白 色污染”问题。聚乳酸（PLA）是一种新型的，对环境友好，性能优良的生物降解材料，通过天然产物乳酸合成，在包装、医疗卫生、农业、纺织、日常生活用品等领域都 有着广泛应用。本文主要研究 PLA 保鲜膜与传统保鲜膜的力学性能、透光、透湿、防雾防霉等性能，并考察了对水果实物的保鲜效果，综合评估 PLA 保鲜膜 代替传统保鲜膜的可行性。此次实验采用吹膜法将 PLA 吹塑成膜，用来代替传统的石油基 PE 保鲜膜，并将不同薄膜制成保鲜袋，分别在室内与恒温恒湿箱内 保鲜苹果与香蕉，最终通过硬度，失重率，可滴定酸，外观变化等实验测得的具 体数据来综合评估实际的保鲜效果。83367

实验显示，PLA 保鲜膜的拉伸强度远远高于 PE 保鲜膜，为 40MPa 以上， 断裂伸长率虽稍逊 PE 保鲜膜，但也可以达到 300%上下。PE 保鲜膜的水蒸气只 有 6。4g/m2*24h，而本实验所制得的两种 PLA 保鲜膜的水蒸气透过率均远大于 PE 保鲜膜，达到 35 g/m2*24h 左右。随着波长增加，三种保鲜膜的透光率逐渐增加，其中 2 号 PLA 保鲜膜的透光性能最好，达到 80%左右，1 号 PLA 保鲜膜和 PE保鲜膜的透光性能相差不大，均在 70%左右，同时 2 号 PLA 保鲜膜对紫外光的 吸收率远远高于 PE 保鲜膜。PE 保鲜膜的接触角较大，润湿效果较差，所以防雾 性能不好；相对于 PE 保鲜膜，1 号和 2 号 PLA 保鲜膜的防雾性能较好。吹膜法 制得的聚乳酸保鲜膜的实际保鲜效果是比传统 PE 膜稍差的，但确实有一定的保 鲜效果。

毕业论文关键词：可降解；聚乳酸；保鲜膜

Abstract The traditional Polyvinyl chloride (PVC) cling films have the serious security problems, the polyethylene (PE) and the polyvinylidene chloride (PVDC) cling films are made from petroleum, large use of them may lead to the waste of our energy。 Meanwhile, these cling films can’t be degraded in the natural even after 100 years, so it  can cause  serious   “White pollution”。。

Poly lactic acid is a new type of biodegradable material, which is friendly to the environment and has good performance。 It is widely used in  packaging, medical, health, agriculture, textile, daily necessities and so on。 In this paper, we mainly study PLA cling film and traditional fresh-keeping film, moisture permeability, anti fog and anti mildew properties, and the effects of the preservation effect of real fruit, then we will consider the comprehensive evaluation of PLA fresh-keeping film to instead of the traditional cling film feasibility。 The experiment produces PLA   film   by  blown to replace the traditional petroleum based PE cling film and make different film fresh-keeping bag, respectively in the interior and a constant temperature and humidity box fresh apple and banana。 Finally, the hardness, weight loss rate, appearance change experiment measured the specific data to assess the actual effect of preservation。

Experiments showed that The tensile strength of PLA cling film is much higher than that of PE cling film, which is more than 40MPa, while the elongation at break is slightly less than that of PE, but it can reach up to 300%。The water vapor of PE preservative film was only 6。4g/m2*24h, and the water vapor transmission rate of the two kinds of PLA films prepared by this experiment was much greater than that of PE plastic film, reaching about 35 g/m2*24h。With the increase of wavelength, the light transmission rate of the three fresh-keeping films increased, and the  light transmittance of No。 2 PLA cling film was the best, it was about 80%, while the permeability of the No。1 PLA cling film and PE cling film differ were not quite, they were  in  about  70%,  and  2  PLA cling  film's  ultraviolet  light  absorption rate  is far