常见塑料薄膜在大气环境下的老化特征研究

Aging characteristics of commonly used plastics under natural environment

塑料垃圾的老化降解是环境微塑料的重要来源之一。本文选取生活中常用的快递包装袋、外卖包装袋、垃圾包装袋等聚乙烯塑料袋、生物基环保塑料袋和全生物降解塑料袋在室外开展为期16周的暴露实验,通过力学性能测试,结合红外光谱和扫描电镜分析,探究它们在老化降解过程中的特征变化。结果显示,快递包装袋薄膜和外卖包装袋薄膜的断裂伸长率在第5周时迅速降低,垃圾包装袋薄膜和全生物降解塑料袋薄膜的断裂伸长率在第2周迅速降低,垃圾包装袋薄膜第7周之后无法进行力学性能测试,生物基环保塑料袋薄膜的断裂伸长率在实验期间变化不大;5种塑料薄膜的拉伸强度均随老化时间增加而逐渐降低。在老化过程中聚合物与氧气和水发生氧化反应产生羰基、乙烯基和羟基等降解产物,各塑料薄膜的羰基指数、乙烯基指数和羟基指数的变化基本相同,随老化时间增加均呈增加或先增加后降低的变化趋势,而结晶指数变化趋势不明显。经过大气老化后,快递包装袋薄膜和外卖包装袋薄膜表面变得粗糙,出现孔洞和裂纹;垃圾包装袋薄膜表面划痕增加,出现细小白色颗粒;生物基环保塑料袋薄膜表面的淀粉微球剥落并出现分层;全生物降解塑料袋薄膜表面裂纹坑洞变多,颗粒剥落。该结果可为研究包装用塑料袋薄膜的环境行为过程、微塑料来源及其环境风险评估等提供基础数据。

Microplastics from plastic debris broken after they entered environment is considered as one of the important sources of microplastics.In this study,plastic films from 5 kinds of packaging bag commonly used in our daily life,including express packing bag,takeaway packing bag,trash bag,bio-based environmentally-friendly bag,and biodegradable plastic bag,were selected to carry out aging-degradation experiment under the natural environment condition.The characteristics of plastic films were analyzed according to tensile test,fourier transform infrared spectrometry(FT-IR)and scanning electron microscope during the experiment period.The elongation-at-break of films from express packing bag and takeaway bag decreased rapidly after 5 weeks of aging period,those from trash bag and biodegradable plastic bag showed a rapid decline at the 2nd week.The mechanical performance testing was not applicable after 7 weeks for the film from trash bag.The elongation-at-break of biodegradable plastic bag varied in a little range during the aging process.The tensile strength of all the films from 5 kinds of packing bag showed a general decreasing trend with increase of exposure time.FT-IR spectra indicated that the aging and degradation products contained carbonyl,vinyl,and hydroxyl group.The index of carbonyl,vinyl,and hydroxyl for the films from the 5 kinds of bag showed an increase trend or an increase-decrease trend with the increase of exposure time,while the index of crystal changed little during the experiment period.At the end of aging exposure experiment,the microstructure of the film from express packing bag and takeaway bag became rough and showed many small pits and cracks.There were many scratches and granules on the surface of film from trash bag,and starch particles peeled from the surface of the film from the bio-based environmental friendly bag.More cracks,potholes,and particle peeling were observed in the surface of film from biodegradable plastic bag.These results provide basic data for the study of environmental behavior processes of packing plastic debris and source of microplastics,assessment of environmental risk,etc.