黑曲霉菌对废旧电缆聚乙烯降解效果及反应机理研究

Degradation Effect and Degradation Mechanism of Aspergillus Niger on Polyethylene Components of Waste Cables

近年来,随着电缆批量退役,有机固体废物大量堆积,严重威胁环境清洁和人类生命健康。微生物降解废旧电缆比传统的焚烧填埋更为清洁、经济,因此可以采用菌群降解手段实现废旧电缆环保处理。为了研究微生物降解废弃聚乙烯(PE)组分的过程,该文选取黑曲霉菌对聚乙烯粉末进行降解处理,利用傅里叶红外光谱(FTIR)和X射线光电子能谱(XPS)进行官能团分析及样品表面碳、氧元素的含量分析,使用X射线衍射实验(XRD)进行样品的晶体结构分析,采用差示扫描量热-热重分析(DSC-TGA)联用热分析方法开展样品的变温热性能分析,同时基于扫描电子显微镜(SEM)进行10 000~50 000倍下样品的微观形貌观测。实验结果表明,在黑曲霉菌降解低密度聚乙烯的过程中发生了氧化反应,产生了羟基、羰基等亲水基团,在菌群处理聚乙烯天数为14天时,氧元素含量从1.38%增加至13.60%,同时聚乙烯结晶度从53.4%下降到34.18%,起始热解温度降低200℃,最终热解温度降低10℃,熔融峰降低0.87 mW/mg,表面形貌出现明显的孔隙和沟壑。该文解析了黑曲霉菌降解低密度聚乙烯的化学机制为醇化、羰基化以及酶促氧化反应。

In recent years,the accumulation of organic solid waste,particularly from the retirement of extensive cable systems,poses a significant threat to environmental cleanliness and human health.However,traditional incineration methods only exacerbate environmental pollution.Therefore,there is an urgent need for a safe and environmentally friendly degradation method to address the challenge of managing discarded cables.To investigate the process of microbial degradation of discarded polyethylene(PE)components,this study selected Aspergillus niger to treat polyethylene powder.The study examined the effects and reaction mechanisms of Aspergillus niger on the degradation of polyethylene in discarded cables by analyzing changes in functional groups,crystallinity,elemental composition,and the microscopic morphology of the samples.First,Fourier-transform infrared analysis(FTIR)was used to detect changes in the functional groups of the samples after treatment with Aspergillus niger.New functional groups,such as hydroxyl and carbonyl groups,were observed.Subsequently,the possible degradation products,such as alcohols and aldehydes,were analyzed through the newly formed chemical bonds.X-ray photoelectron spectroscopy(XPS)was employed to scan and analyze the changes in the carbon-oxygen elements on the sample's surface.After two weeks of treatment,the atomic ratio of oxygen elements on the surface increased from 1.38%to 13.6%.Further analysis of the sample's crystalline structure through X-ray diffraction(XRD)experiments revealed a decrease in crystallinity from 53.4%to 34.18%,indicating the disruption of the regularity of polymer molecular chains.In addition to these findings,a combined differential scanning calorimetry-thermogravimetric analysis(DSC-TGA)method was used to analyze the sample's thermal properties at different temperatures.The initial decomposition temperature decreased by 200℃,and the final decomposition temperature declined by 10℃.This phenomenon suggested the presence of lower-energy carbon-oxygen bonds during the degradation process,corresponding to the new functional groups observed in the FTIR analysis.Finally,scanning electron microscopy(SEM)was employed to observe the microscopic morphology of the samples at magnifications ranging from 10000 to 50000 times,revealing the presence of pores,grooves,cross-linking fractures,and other features on the sample's surface.This led to the inference that the samples had been attacked by extracellular enzymes produced by the Aspergillus niger.From the experimental results,the following conclusions can be drawn:(1)Aspergillus niger produces hydroxyl groups during the degradation of low-density polyethylene cable material.Subsequently,under the action of enzymes such as alcohol dehydrogenase and monooxygenase,these hydroxyl groups are converted into carbonyl and C—O—C groups,promoting the degradation process.(2)With increasing treatment time by Aspergillus niger,thermal decomposition and melting experiments indicate the presence of lower-energy carbon-oxygen bonds during the degradation process.This is consistent with the appearance of new functional groups in FTIR analysis and the increase in the atomic ratio of oxygen elements in XPS.(3)After being attacked by Aspergillus niger,the relative crystallinity of polyethylene samples decreased from 53.4%to 34.18%with prolonged treatment time.This phenomenon indicates that Aspergillus niger.can attack the polymer chains of polyethylene,disrupting their regularity and symmetry,leading to a reduction in crystallinity.(4)Microscopic observations of the sample's morphology revealed the presence of clear pores,grooves,and cross-linking fractures.This suggests that Aspergillus niger.can secrete extracellular enzymes to attack the polyethylene molecular chains,causing long-chain molecules to break into smaller chains and promoting degradation.