Chemical-biological Cascade Degradation Of Low Density Polyethylene Plastics

Plastic products which are widely used in various industries have the advantages of good quality,stable physical,chemical properties,and low manufacturing costs.While plastics bring convenience,they also bring serious pollution problems to the natural environment.Among them,a large number of waste polyethylene plastics still lack a strong recycling method due to the high hydrophobicity and good chemical and biological corrosion resistance of polyethylene(PE).To address the key issues of poor biodegradation and long biodegradation cycles of polyethylene,a novel green and low-energy chemicalbiological cascade approach to degrade polyethylene plastics is carried out in this thesis.Rational optimization and cascade of chemical oxidation treatment process and microbial degradation process are carried out to provide technical support for efficient degradation pathways of polyethylene from scratch.The main findings of this thesis are as follows:(1)Chemical oxidative degradation of LDPE.We prefer the treatment method of catalytic oxidation of peroxynitrite and cobalt acetylacetonate.The effects of reaction time,temperature and catalyst type on the interface properties and degradation characteristics of LDPE were investigated.The functional groups,surface structure,and molecular weight changes of LDPE powder were analyzed and examined by Fourier infrared spectroscopy(FT-IR),atomic scanning electron microscopy(SEM),and high-temperature gel chromatography(HT-GPC).The oxygen-containing active functional groups of the LDPE powder treated with chemical oxidation increased significantly,forming carbonyl functional groups with hydroxyl functional groups.Within 24 h,the carbonyl index increased from 0 to 2.99,the oxygen content could reach7.92%,the molecular weight curve shifted to the lower left,and the Mw decreased by 8.58%.The results indicate that chemical oxidation treatment can improve the interface properties and degradation characteristics of LDPE powder.(2)Enhanced oxidative degradation of LDPE under oxygen pressure.On the basis of chemical oxidation of LDPE powder,the interface hydrophilic properties and degradation properties of LDPE were further enhanced by oxygen regulation.The effects of reaction time,temperature,stirring speed and oxygen pressure on the interface properties and degradation characteristics of LDPE were investigated in depth by the conditions of reaction time,temperature,stirring speed and oxygen pressure.The functional groups,surface structure and molecular weight changes of LDPE powder were analyzed and examined by FT-IR,SEM and HT-GPC.Within 24 h,the carbonyl index increased from 0 to6.21,which was twice as high as that of the atmospheric pressure group,and the oxygen content could reach 10.86%,which greatly improved the oxygen content of LDPE.The molecular weight curve undergoes a more obvious shift to the lower left,and the intermediate product analysis reveals that many oligomers are produced,releasing C12-C30 short chain length intermediates,such as alkanes and carboxylic acids of different lengths.The results suggest that the interface oxidation state and degradation of the treated LDPE powder can be further enhanced under oxygen pressure environment.(3)Chemical-biological cascade degradation of LDPE.The biodegradation process of LDPE powder after chemical oxidation treatment was investigated using B.velezensis C5 with degradation ability.The results showed that after chemical pretreatment,the degradation ability of B.velezensis C5 on LDPE powder could be enhanced and the oxidized LDPE powder was more hydrophilic.B.velezensis C5 adhered to the LDPE surface better and faster,and the degradation enzymes interacted with the LDPE powder to continuously promote the biodegradation of LDPE.The mass loss of LDPE powder could reach 23.91% after 90 days,which was three times higher than that of the blank control group.The results show that the biodegradation effect of LDPE powder can be effectively improved after the treatment by chemical bio-cascade method.In response to the current problem of high energy consumption required for traditional chemical treatment of polyethylene and the poor biodegradation and slow degradation rate of polyethylene during biological treatment,this thesis innovatively proposes a novel green and low energy consumption chemical-biological cascade method to degrade polyethylene plastics.The optimal oxidation experimental group after oxidation treatment was constructed with B.velezensis C5 in a co-culture system,which successfully achieved 18-24% of polyethylene degradation mass within 90 days,which was 2-3 times of the control group.With this method,green and mild,rapid and efficient degradation of polyethylene can be achieved.Meanwhile,this strategic new method of degrading plastics by chemical-biological cascade will play an important role in environmental protection and recycling treatment.