土壤环境中LLDPE地膜残余物的高温索氏提取及堆肥降解评价

Extraction and Compost Degradation of LLDPE Residue by High-temperature Soxhlet Apparatus in Soil

可降解LLDPE地膜降解后以粉末形式进入土壤的"降解"存在很大的争议,为了探究进入土壤的高分子残余物是否继续降解,通过高温索式提取法采用混合溶剂(V(正庚烷)∶V(二甲苯)=1∶4)对土壤中的LLDPE(Mw=120 000)残余物进行分离提取,分别考察提取时间和土壤类型对LLDPE提取率及结构和热性质的影响,同时做堆肥实验并进行相对分子质量的测定.结果表明,对LLDPE的提取率随提取时间的增加而增大,最佳提取时间为4 h,提取率75%;提取时间对LLDPE的分子结构、结晶及平均重均相对分子质量均无明显影响,但会导致相对分子质量分布略微变窄;土壤类型对LLDPE的提取率基本没有影响;将普通LLDPE和光降解LLDPE样品分别做堆肥实验,采用高温索氏分别提取样品进行GPC测定,结果表明该提取方法可以用于实际土壤中LLDPE及其残余物的降解测试评价,长期跟踪下去还可以评估LLDPE完全降解所需时间.

There is some controversy of the ＂degradation＂ form of the degradable PE film decomposed into the powder in soil after degradation.It is necessary to establish the method of separation and recovery PE residues from soil to elucidate that whether the poly-mer powder can continue degrade after it into the soil.LLDPE powders （Mw =120 000） were taken as the simulated PE residue and then,they were extracted in soil through the soxhlet apparatus extraction method at high-temperature with mixed solvent （V（heptane） ∶ V（（xylene） =1∶ 4）.The LLDPE samples were characterized by FT-IR-,HT-GPC-and DSC-after the separation.The effect of the extraction time and soil types on the molecular structure and thermal properties of LLDPE were studied.At the same time,the molecular weight of the composted LLDPE after 1 ～ 6 months were investigated by the outdoor compost experiment.The results show that the extraction rate increased with extraction time and it reached the rnaximtun after 4 h （75％）.The FT-IR spectra illustrates that the molecular structure of LLDPE was not destroyed during the extraction and the crystallization of LLDPE was unchanged basically.Without too much influence on average molecular of LLDPE＇ the extraction time slightly narrow the molecular weight distribution.The LL-DPE recovery is independent of soil type.The outdoor compost experiments of normal LLDPE and light degraded LLDPE had been carried out for 6 months by this method.Results show that there is a certain degradation of light degraded LLDPE samples during 4-6 months while scarce degradation of the normal LLDPE samples within 6 months.Experiment results indicate that the extraction and detection method can be used to evaluate the degradation of actual LLDPE in soil.The method can also assess the totally degradation time of LLDPE after long-term tracking down.