Research On The Poly (Lactic Acid) Biodegradable Composites Reinforced With Plant Fibers And Their Derivatives

Green degradable packaging materials,which have inherent properties such as biodegradability and environmental friendliness,are gradually replacing traditional packaging materials based on petroleum.Polylactic Acid（PLA）,an environment-friendly material with completely biodegradability,owes the advantages of good transparency,biodegrad-ability and processability when applied in packaging field.However,the extensive application of PLA in packaging material is limited due to its disadvantages such as slow crystallization rate,high brittleness,poor thermal stability and low gas barrier.In this paper,according to the above disadvantages of PLA,natural plant fiber and its derivative nano-cellulose were added into PLA matrix as nucleating agent and toughening agent in order to improve the crystallization rate,crystallinity,and mechanical properties of the materials.Silane coupling agent and anhydride were used to modify the surface of reed fiber and nano-cellulose to improve the compatibility of the two phases.Then nano-cellulose with high strength and crystallinity was added in order to enhance the toughness and barrier property.And silver nanoparticles and polypyrrole were added to the matrix,endowing PLA film with excellent antibacterial and fresh-keeping properties.The main contents and results of this paper are as follows:Preparation and properties of reed fiber/PLA composites.Silane coupling agent was used for surface alkylation treatment of reed fiber.The FT-IR results showed that the coupling agent reacted with cellulose surface after silane alkylation treatment and the hydroxyl group on the fiber surface decreased obviously.When the modified reed fiber was added to the PLA matrix,it played a role of heterogeneous nucleation,which accelerated the crystallization rate of the PLA matrix.Compared with the unmodified reed fiber,the modified one improved the mechanical properties and crystallization properties of the composites.Preparation and properties of nano-cellulose/PLA composites.High pressure homogenization method was used to treat reed stem and acid-hydrolysis method was used to treat camellia oleifera husk respectively,preparing the cellulose nano-fiber（CNF）with lengths of700²000 nm and cellulose nano-whisker（CNC）with lengths of100⁵00 nm.Then modified nano-fiber（BCNF）and modified nano-whisker（BCNC）were prepared by butyric anhydride,and BCNF/PLA and BCNC/PLA composite films were produced by solution casting.The results showed that BCNF and BCNC dispersed uniformly in PLA matrix and had good interfacial interaction with PLA substrate.The tensile strength and barrier property of the composite films were also improved significantly,which could be applied in food packaging.Preparation and antibacterial properties of BCNC/PLA-polypyrrole（PPy）multi-layer composite film（CPP）.Fe³⁺was used as evocating agent to lead the polymerization of pyrrole on BCNC/PLA composite film to prepare CPP multi-layer composite film.The results showed that the mechanical properties and transparency of BCNC/PLA film decreased slightly,but its thermal stability was improved after the surface was coated with PPy layer.The composite films showed good antibacterial effect on Escherichia coli and the antibacterial effect enhanced with the increasing of the amount of PPy.Preparation and antibacterial properties of silver-loaded BCNF/PLA composite film（Ag-BCNF/PLA）.Silver loaded nanofilament（Ag-BCNF）was prepared under rapid reaction system of microwave radiation by using glucose as reducing agent and BCNF as substrate.Then Ag-BCNF/PLA composite film was prepared by solution casting.The results showed that the diameter of silver nanoparticles was 5-10 nm and it could be loaded on the network structure of BCNF.Escherichia coli,Staphylococcus aureus and Aspergillus Niger were used as typical pathogenic bacteria models.The results showed that the antibacterial rate of Ag-BCNF/PLA was over 99%.In addition,the composite films owed excellent fresh-keeping effect on raspberry.The decay rate and weight loss rate were significantly reduced and quality of raspberry were maintained.The shelf life of raspberry can be extended from 2days to 8 days under the open storage environment of 4℃,which proved that the antibacterial film had application potential in packaging.