Correlation Between Monomers And Enzymatic Hydrolysis Of Aliphatic Polyesters

Poly（butylene succinate）（PBS）is a synthetic aliphatic polyester with good biodegradability and processability.Thus,it is used in various fields,such as food packaging,agricultural film and other fields.In this study,two kinds of hydroxy monomers and carboxyl monomers were used to replace1,4-butanediol or succinic acid in PBS,and three kinds of succinic-polyesters and three kinds butylene-polyesters were synthesized by melt-solution polymerization,respectively.And the effect of different monomer on the enzymatic degradation was also investigated.Three butylene-polyesters,Poly（butylene succinate）（PBS）,Poly（butylene adipate）（PBA）and Poly（butylene suberate）（PBSub）,were synthesized by melt-solution polymerization using 1,4-butanediol as hydroxyl monomers,three kinds of dicarboxylic acids as carboxyl monomers,respectively.The chemical structure,thermal properties,mechanical properties,hydrophilicity and cutinase enzymatic degradation behavior of the three butanediol-polyesters were compared.All the three different polyesters exhibit good mechanical properties and thermal stability performance.The results showed that with increase the methylene groups number in the carboxyl monomer,the tensile strength decrease,but the elongation at break increase.At the same time,the weight loss of the three polyesters was more than 90%after 24 h degradation,and the biodegradability was excellent,and the degradation rates was in the order of PBSub>PBA>PBS.The degradation behavior of the three polyesters depends on their CH₂/CO ratio,morphology,and thermal characteristics.Among them,CH₂/CO is the major factor.Gel permeation chromatography and end-group analysis confirmed that the mechanism of enzymatic hydrolysis changed from endo-type to exo-type.The analyses of differential scanning calorimetry,powder X-ray diffraction,and Fourier transform infrared spectroscopy indicated that the cutinase could simultaneously degrade the crystalline and amorphous regions of polyester films,and destroyed the crystal structure.Three succinate-polyesters,Poly（ethylene succinate）（PES）,poly（butylene succinate）（PBS）,and poly（hexylene succinate）（PHS）,were synthesized by melt-solution polymerization using succinic acid and three kinds of different dihydric alcohols as material.The synthesized polyesters were characterized by DSC,TG,and mechanical assay.The results show that the tensile strength of the three aliphatic polyesters is above 30 MPa and the elongation break is more than 300%.The thermal decomposition temperature of the three polyesters are all higher than 294℃,and the thermal stability was well.At the same time,the enzymatic degradation rate of the three succinate-polyesters was more than 95%at 12 h,and the biodegradability was excellent.There are many factors affecting the degradation behavior of polyester,such as CH₂/CO,melting point,crystallinity,hydrophilicity and glass transition temperature.The cutinase is more prefer to erosion the polyester containing more methylene groups,melting point close to the hydrolysis temperature,low crystallinity,good hydrophobicity,and low glass transition temperature.