Biodegradable High-density Polyvinyl Agricultural Mulching Film And Research On Degradation Mechanism

In recent years,increasingly serious plastic pollution has become a major threat to public health,and more and more people have put forward higher requirements for environmental remediation.Microbial environmental remediation is cleaner and more economical than traditional incineration landfills,which will cause subsequent environmental pollution.Using microbial communities to degrade various plastic contaminants into non-toxic or less toxic compounds is a better choice.At present,bioremediation of microbial communities has practical significance and has been applied in some cases.Polyethylene can be used as the sole carbon source for the survival of microbial communities.Microorganisms can form biofilms on the surface of polyethylene or form a region called plastic spheres,which interact to produce acids or enzymes to degrade polyethylene.The degradation of polyethylene by microorganisms depends on the microstructure,surface characteristics,molecular weight and molecular weight distribution of the polymer.In this paper,different methods were used to screen bacteria from three different sites,and different degrees of degradation of polyethylene plastics were studied in different ways :1.Discarded polyethylene(PE)mulch film has led to persistent agricultural pollution.Biodegradation of plastic waste is considered a promising solution that can potentially overcome environmental and economic problems.In this study,a novel bacterium(Bacillus paramycoides)was isolated from a waste mulch recycling plant and showed an extraordinary ability to customize polyethylene film.It was observed by scanning electron microscopy that a large number of pits and wrinkle cracks existed on the polyethylene,indicating that the strain used PE film as the sole carbon source.Meanwhile,the loss of weight of the film was tested continuously,and approximately 12% of the initial weight of the film was found to be lost within 45 days after coincubation with TW-2.The surface hydrophobicity of the polyethylene film decreased while the surface tension increased from 9.755 to 31.013.Fourier transform infrared(FTIR)analysis indicated that absorption peaks near 1740 cm-1and 2760 cm-1 were attributed to the stretching vibrations of aldehyde and carboxyl groups,respectively,suggesting that hydrophilic groups were produced.This was also confirmed by XPS spectroscopy analysis.X-ray diffraction(XRD)analysis also showed that the relative crystallinity decreased from 33% to 11.51%.In addition,GPC analysis showed that the molecular weight decreased,while the proportion of low molecular weight fragments increased.These results strongly indicated that the PE film was able to be degraded to some extent by the strain.Finally,a new biodegradable mechanism for polyethylene was proposed.2.The microbial degradation of polyethylene(PE)mulch has attracted a lot of attention,but current research on the degradation of polymers by pure strains is limited by the fact that the metabolic pathways of its degradation can be studied using pure strains,ignoring the fact that PE mulch films Degradation in the environment is the result of the synergistic interaction of different microorganisms.This limitation can be overcome by using microbial consortia,in which toxic metabolites produced by one microorganism can often be used as substrates for the growth of another.In this study,three Bacillus species,Bacillus cereus,mold and Bacillus megaterium,were isolated and purified.The crude enzyme mixture MCE produced by NLJ-1 was co-cultured for 60 days in a medium with PE membrane as the sole carbon source.The removal rate of PE membrane of NLJ-1 was as high as 31.3 %.The MCE removal rate was 24.5 %.The samples were characterized by SEM,GPC,FTIR,XPS,XRD and GC-MS.It was found that the surface of PE was broken,the low molecular weight PE chain was first degraded,and new oxygen-containing functional groups appeared.Its chemical inertness is also greatly reduced.Finally,the mechanism of enzymatic degradation of polyethylene was revealed.This study enriched the biological resources of PE degradation and provided a paradigm for species interaction to promote PE degradation.3.Plastics are widely used in daily production and life due to their ease of processing,transportation,storage and chemical stability,and are also increasing due to their long-term potential in the environment.Biodegradation is one of the inevitable environmental behaviors of plastics,and it is also an environmentally friendly plastic waste treatment method.Therefore,the study of plastic biodegradation is more targeted and ecological.In this study,polyethylene(PE)degrading strains were isolated and screened with PE plastic film as the sole carbon source.The strains were identified as Rhizobium by morphological observation,physiological and biochemical analysis and 16 S r RNA analysis.Strain BM grew best at PH 7.0 and30℃.The mass loss of PE mulch was 26.9%±0.03% after co-culture with BM for 60 days.In addition,many pits and folds on PE were observed by SEM.A new stretching vibration peak of oxygen-containing functional groups(hydroxyl,aldehyde and carboxyl)was detected by Fourier transform infrared spectroscopy(FTIR),which was also confirmed by XPS.Biodegradation led to the formation of extractable oxygenated compounds and unoxidized low molecular weight hydrocarbons,which was confirmed by GC-MS studies.X-ray diffraction(XRD)analysis also showed that the relative crystallinity decreased from 63.91 % to 47.2 %.In addition,GPC analysis showed that the molecular weight decreased,while the proportion of low molecular weight fragments increased.These results indicated that strain BM had a certain degradation effect on polyethylene film.The good degradation performance of BM strain provides a theoretical basis for further study on the degradation and metabolism mechanism of waste PE in the environment.