Establishment Of Bacterial System For The Rapid Biodegradation Of Polylactic Acid (PLA) Nonwovens

Polylactic acid?PLA?is a biodegradable aliphatic polyester that can be produced byfermentation of renewable resources such ascorn,cassava,potato and sugarcane.PLA can be completely degraded into CO₂ and H₂O in microbial environment.However,the degradation rate is slow in the natural environment.How to improve the degradation rate has become one of the hotspots in the current research.If rapid degradation is not achieved,seriousenvironmental pollution problems such as soil acidification will be caused.Therefore,it will also affect the healthy development of the industry.The process of polylactic acid material biodegradation is a very complex one,whicheffect is not enough good treated by a single strain.It maybe possible to achieve a short time and high efficiency degradation under the synergistic action of several enzymes or mixedbacteria.To obtain a strengthening system which can accelerate the degradation of polymer materials,the biodegradable bacteria were enriched and isolated from soil of orchard in the natural environment.The communitic structure and the diversities of this bacterial mixed suspension have also been analyzed.After being purified and domesticated,these mixedbacterial strains were used to construct a stengthening system to degrade PLA materials rapidly.The results in this study maybe provide an effective way to solve the increasingly serious environmental pollution of organic polymers in modern society.The conclusions in this study were as follows:1.Polylactic acid?PLA?materials could be rapidly biodegraded by microorganisms innative orchard soil around Guangzhou University Mega City.And thesemicroorganisms could be enriched,collected,subcultured and acclimated for biodegrade treatment of PLA.2.With DGGE gel fingerprint analysis,the dominant bacterial communities in enrichedbacterial suspension from orchard soil was mainly composed by four families ofmicrobes,which were respectively to Enterobacteriaceae,Vibrionaceae,Aeruginosa,Bacillaceae.Among these subculturable bacterial strains,they accounted respectivelyfor 27.79%,10.45%,4.98%and 15.88%.3.A strengthening system to degrade PLA material rapidly could be suscessfullyconstructed by 9 isolated strains.They were Citrobacter sp.Strain8,Citrobacter sp.Strain15 and Citrobacter freundii Strain12,Bacillus sp.Strain6,Bacillus cereusStrain9 and Bacillus cereus Strain 18;Lysinibacillus fusiformis Strain10 andAeromonas hydrophila Strain16.4.Under strengthening system,polylactic acid?PLA?materials could be degradedrapidly with a higher bacterial concentration condiction.Up to 11th day of biologicaltreatment,the release value of CO₂ from PLA degrading substrates was 352 mg,whichwas 3.78 times of the normal control group.Comparing with the theoretical releasevalue,the efficiency of degradation of PLA materials reached 21.5%.