Construction And Properties Of Starch Modified Poly(4-Hydroxybutyrate) Biodegradable Films

Development of all creatures and biodegradable green film is an effective way to solve the white pollution.Poly（4-hydroxybutyrate）（P4HB）is a new fully degradable aliphatic polyester with high strength and toughness.It has excellent biocompatibility,good processing performance and low melting point.At present,our research group has achieved batch preparation of high molecular weight poly（4-hydroxybutyrate）through chemical synthesis on the basis of self-designed binary catalytic system.Compared with biological fermentation,chemical synthesis can greatly reduce the cost of P4HB and expand the application of P4HB in traditional plastic products.Starch is a kind of natural polymer material with a wide range of sources.Starch,a cheap polysaccharide with a wide range of sources,is easy to cause the growth and aggregation of microorganisms under natural conditions.When filling polyester as a filler,it is more likely to cause the degradation of polyester,and can further reduce the cost of degradable materials.In this study,P4HB was used as matrix and natural starch（St）as filler to prepare biodegradable films.The effects of annealing conditions,blending methods and starch content on the properties of P4HB films were studied.In order to improve the compatibility between P4HB and starch,two different compatibency enhancing methods were used to modify P4HB.One is to graft polycaprolactone（PCL）onto the surface of starch,and blend the modified starch with P4HB,the other is to prepare compatibant P4HB-g-GMA by melting method,and directly blend with P4HB and starch.Through this study,the problem of poor compatibility between P4HB and starch was solved,and the application of natural polymer materials in the field of degradable plastics was expanded.The research content mainly includes:1.First,optimize the membrane process.By comparing the tensile properties of the films prepared by different methods and the micromorphology of the films,the film-making process was established:The P4HB/St composite material was prepared by melting method,and then the composite material was dissolved in methylene chloride and cast in the mold by solution film forming method.After film forming,the P4HB/St film was obtained by annealing treatment at 70℃for 1 h to eliminate bubble holes.The results show that the tensile properties and water vapor barrier properties of P4HB/St films decrease with the increase of starch content.The biodegradability of the films increased with the increase of starch content.When the starch content was 70 Phr,the tensile strength remained at 18.6 MPa,the elongation at break reached 141.8%,and the yield strength was 13.1 MPa.P4HB film was degraded to 60 days in the compost soil environment,and the quality retention rate was 40.2%.The degradation rate was accelerated after adding starch,and the quality retention rate of P4HB/St-70 film degraded to 60 days was 17.7%.2.In order to improve the compatibility of P4HB and starch,the bulk grafting method was used to initiate ring-opening polymerization of caprolactone monomer on the surface of ball milling starch（BSt）,and the high grafting rate of starch grafted polycaprolactone copolymer（BSt-g-PCL）was prepared.Then,different dosage of BSt-g-PCL were fused with P4HB,and the films were prepared by solution method.The physical and mechanical properties,biodegradability and barrier properties of the films were characterized.The results showed that ball milling pretreatment could activate starch and effectively improve the grafting rate of BSt-g-PCL.At the same time,under the condition of adding 1%catalyst,the mass grafting rate of BSt-g-PCL reached the highest,reaching 49.5%.Compared with ordinary starch,the interface compatibility,tensile strength and deformation resistance of the blend film with high grafting rate BSt-g-PCL are significantly improved,and the film has good toughness.The degradation rate of P4HB film increased after the addition of BSt-g-PCL,and the mass retention rate of P4HB/BSt-g-PCL_1.0-70 film was 19.8%.Pure P4HB film has better water vapor barrier,and the water vapor barrier performance decreases after adding BSt-g-PCL.3.The compatibility between starch and P4HB was improved by adding compatibilizer.Using BIBP as initiator,GMA was grafted onto P4HB by melting method to prepare poly（4-hydroxybutyrate）grafted glycidyl methacrylate（P4HB-g-GMA）,which was fused with P4HB and starch to prepare thin films.The mechanical and thermodynamic properties were characterized.The results show that the interfacial compatibility,tensile strength and toughness of the blend films with high graft rate P4HB-g-GMA are significantly improved.When the addition amount of P4HB-g-GMA was 6%of the total mass,the compatibilizing effect was the best.When the starch content is 70Phr,the tensile strength is 18.8 MPa,the elongation at break is276.5%,and the yield strength is 10.1 MPa.While the amount of starch is much higher than the commercial film,it still maintains excellent tensile properties and is stronger than the commercial film.