Preparation And Properties Cage-type Of Sesquisiloxane Copolymers/Bone Gelatin Composite Mulch Film

As one of the four major means of agricultural production,plastic film has greatly promoted the transformation of traditional agriculture to modernization in China.However,polyethylene(PE)plastic film,which is widely used,is non-degradable and harmful to the environment and human health.Developing biodegradable plastic film is a fundamental solution to PE film pollution.Natural macromolecular bone gelatin(BG)is derived from waste animal bones and their by-products are non-toxic and pollution-free.It has good film-forming properties,biocompatibility,and microbial degradation.After degradation,it can be used as a soil amendment to increase crop yield,but the flexibility of the BG film still needs to be improved.Cage-type sesquisiloxane polymers(POSS)is a kind of organic-inorganic hybrid nanomaterial at the molecular level,with highly stable Si-O-Si core and peripheral group designable characteristics.This study proposes the design and synthesis of POSS copolymers containing epoxy and ester groups,which are used to modify bone gelatin through two-step and one-step methods,respectively,to prepare POSS copolymer/bone gelatin composite.Amino-polydimethylsiloxane(PDMS-NH2)was selected for hydrophobic modification of modified BG,and a composite film was prepared by solution casting method.The properties of insulation and moisture retention were investigated.The main research work is as follows:(1)The POSS copolymers(PAAB)was prepared by free radical polymerization with octavinylsilsesquioxane(POSS-Vi),allyl glycidyl ether(AGE),butyl acrylate(BA)and acrylic acid as raw materials.The reaction temperature and initiator dosage were optimized with monomer conversion rate as the main indicator,and PAAB was characterized by FTIR,XRD and TEM.The results showed that when the reaction temperature was 80℃ and the amount of initiator was 14%,the monomer conversion rate was 91%.Preparation of POSS copolymers/bone gelatin(PAAB/BG)composite by modifying BG with PAAB.Using the mechanical properties of the thin film as the main indicator,optimize the dosage of AGE:BA,PAAB,and reaction pH.Characterization of PAAB/BG using FTIR,XRD,and SEM.The results showed that when AGE:BA was 1:1,PAAB dosage was 25%,and reaction pH was 9.The tensile strength(TS)of PAAB/BG composite film was 13.91±0.14 MPa,and the elongation at break(EAB)was 107.29±19.44%,which was lower than the standard requirements of GB/T 35795-2017 Biodegradable mulching film for agricultural uses(EAB≥200%)and still needs to be improved.The ring opening reaction between the epoxy group of PAAB and the amino group of BG changed the amorphous structure of BG.After covering the soil with PAAB/BG film,the moisture content of the upper,middle,and bottom layers increased by 0.94%,2.55%,and 4.26%,respectively,and the average soil temperature increased by 0.37℃.The film could degrade 82.98%within 60 days of burial in natural soil.(2)The POSS copolymers/bone gelatin(PAH/BG)composite was prepared by a one-step polymerization method with POSS-Vi,AGE,hydroxyethyl acrylate(HEA)and BG as raw materials.Taking the mechanical property of the film as the evaluation index,PAH the dosage,AGE:HEA and reaction pH were optimized,and the PAH/BG was characterized by FTIR,XRD and TEM.The results showed that when the amount of PAH was 30%,AGE:HEA was 3:1,and the reaction pH was 6.The TS of PAH/BG composite film was 7.27±0.14 MPa,and the EAB was 300.86 ± 17.22%,meeting the requirements of GB/T 35795-2017 standard.The WVT was 1105.61 ± 4.99 g/(m2·24 h),which meets the Class B film standard(800-1600 g/(m2·24 h)).The epoxy group of PAH can form covalent bonds with the carboxyl group and amino group of BG,which changes the triple helix structure of BG.The multi-side chains of PAH are interwoven with BG and there are a lot of hydrogen bonds,which increases the energy dissipation during the stretching process.After covering the soil with PAH/BG film,the moisture content of the upper,middle,and bottom layers increased by 3.29%,5.29%,and 5.51%,respectively.The average soil temperature increased by 0.75℃,and its insulation effect was more prominent than that of PE film under sufficient sunlight(16:00).The film could degrade 77.60%within 60 days of burial in natural soil.(3)PDMS-NH2 was prepared by the hydrolysis and condensation reaction of dimethyldimethoxysilane and γ-aminopropyltriethoxysilane.Then PDMS-NH2/PAH/BG film was prepared by modifying PAH/BG with PDMS-NH2.The effects of different contents of PDMS-NH2 on the mechanical properties,contact angle,light transmittance,and moisture permeability of films were studied.The results showed that when the introduction amount of PDMS-NH2 was 4%,the EAB of PDMS-NH2/PAH/BG film was 361.38±25.04%,TS was 5.93±0.81%,WVT was 1060.98±13.07 g/(m2·24 h),and the water contact angle was 128°.The transmittance in the visible light range increased by 9.27%on average.The enrichment of a large amount of low surface energy Si elements in the upper layer of the film was caused by the formation of a hydrophobic layer on the surface by PDMS-NH2.After covering the soil with PDMS-NH2/PAH/BG film,the moisture content of the upper,middle,and bottom layers increased by 16.06%,18.35%,and 16.06%,respectively.And the soil temperature increased by 1.09℃ on average.The film could degrade 77.91%within 60 days of burial in natural soil.The biodegradable plastic film prepared in this study has excellent flexibility,surface hydrophobicity,and insulation and moisture retention properties,which is expected to solve the "white pollution" problem of plastic films and promote the high-value utilization of discarded bones.