Design, Preparation And Application Of PgP/OMCC/PLA Biodegradable Films For Fruit And Vegetable Preservation

The design and development of degradable packaging materials not only addresses the problems of plastic pollution and natural resource depletion,but also promotes the harmonious coexistence of humans and nature while implementing plastic reduction policies.It has been deemed as a critical starting point for exploring green transformations of packaging industry and promoting the development path of double carbon.This study utilized microcrystalline cellulose（MCC）extracted from waste cotton fabric as reinforcing materials for polylactic acid（PLA）.Inspired by the entanglement characteristics of Xanthium and linear fibers,we modified the MCC by constructing a long-chain hydrophobic interface on its surface and studied the preparation of degradable OMCC/PLA films,aiming at significantly improving the mechanical properties of the composite film.Additionally,a PgP/OMCC/PLA functional degradable film was prepared after introducing Punica granatum peel polyphenols（PgP）,and its fresh-keeping packaging performance for Cherry tomatoes was tested as well.Finally,the degradation properties of as-obtained film were analyzed with degradation rate,morphological changes during degradation,and degradation performance in soil environment.The main research contents include:（1）Design,preparation and properties of OMCC/PLA degradable filmThe microcrystalline cellulose（MCC）extracted from waste cotton fabric by acid hydrolysis was hydrophobically modified to obtain DMCC and OMCC.OMCC was involved in the preparation of OMCC/PLA degradable films as a reinforcing material for the polylactic acid（PLA）matrix.The results showed that the optimum addition amount of OMCC was 3%,and the 3%OMCC/PLA degradable films were endowed with advantages of high transparency,excellent mechanical properties,good thermal stability and strong water absorption.Through the bionic construction of MCC surface,it was the entanglement between the long chain on the surface of OMCC and the linear molecules of PLA that modifies the interfacial compatibility between OMCC and PLA matrix and therefore improved the mechanical properties of the composite films.（2）Preparation of PgP/OMCC/PLA degradable films and their application in Cherry tomato packagingThe microwave-assisted extract polyphenols（PgP）from Punica granatum peel was introduced into the 3%OMCC/PLA composite film to prepare a PgP/OMCC/PLA degradable film with fresh-keeping property.The morphology,mechanical properties,water vapor permeability,wettability and oxidation resistance of PgP/OMCC/PLA degradable films under different PgP dosages were tested and analyzed by means of ultra-depth-of-field microscope,SEM and universal testing machine.The results showed that when the addition amount of PgP was 3%,the mechanical properties of the composite film were not only better than those of pure PLA films,but also of good water vapor permeability and antioxidant activity.Therefore,3%PgP/OMCC/PLA degradable film was selected for the preservation packaging experiment of Cherry tomatoes.The results showed that 3%PgP/OMCC/PLA degradable film packaging improved the freshness preservation and nutritional quality of Cherry tomatoes effectively.The PgP particles contributed to reducing the impact of oxidative stress on Cherry tomatoes,and thereby delaying fruit aging and deterioration process.The film was believed of important application value in the field of fruit and vegetable preservation.（3）Degradation behavior of PgP/OMCC/PLA film in soil environmentWe carried out both in-soil and on-soil degradation experiments for 3%PgP/OMCC/PLA films.The degradation performance of the 3%PgP/OMCC/PLA films was described with film morphology,degradation rate and soil structure after film degradation.The experimental results showed that the degradation of 3%PgP/OMCC/PLA film was enhanced significantly under in-soil degradation condition,and the degradation rate reached 100%in 35 days.Moreover,the FT-IR characterization results indicated that the 3%PgP/OMCC/PLA film broke down into small molecules during in-soil degradation process,as results of which new functional groups such as-CH₂,-CH₃,C=O and C-O were detected in the degradation soil.On this basis,the change of soil enzyme activity and soil microbial diversity after degradation were further studied.The results showed that the in-soil degradation of 3%PgP/OMCC/PLA film promoted the activities of urease,protease and catalase of soil significantly,and increased the richness of microbial community in soil.With the correlation analysis results of soil microbial community composition and enzyme activity,it was concluded that the increase of soil enzyme activity had a significant correlation with the increase of microbial species abundance such as Proteobacteria and Bacteroidetes in soil after film degradation.In summary,the 3%PgP/OMCC/PLA film showed remarkable degradation performance under in-soil degradation conditions,and had a positive impact on soil structure and soil micro-ecological environment.