Synergistic Enhancing And Toughening Of Biopolvester With Functionalized Cellulose Nanocrystals

Nowadays,due to environmental pollution and resource shortage,biodegradable nanocomposites have attracted extensive attention as a new type of plastic compared to the petroleum based non-degradable traditional plastics with serious environmental pollution.Compared with traditional plastics,PHBV has been extensively studied for its biodegradability and biocompatibility.However,it has defects such as large spherulite size,poor toughness,and no antibacterial property.In this study,cellulose nanocrystals?CNC?were prepared by a green and sustainable method,and the PHBV nanocomposite films were prepared by incorporating of CNC and graphene oxide?GO?as reinforcing materials for the PHBV matrix.To investigate the effects of different contents on PHBV nanocomposite film,thermal stability,crystallization,mechanical,barrier properties,and overall migration and antibacterial properties were investigated.The main results are summarized as follows:???High yield?up to 87.8%?of carboxylated and sulfated CNC were produced using a recoverable citric acid/hydrochloric acid and H₂SO₄,respectively.The use of fresh and recycled citric acid/hydrochloric acid and H₂SO₄ mixtures during the hydrolysis process hardly affects the chemical structure,crystallinity and thermal stability of CNCh and CNCs.Importantly,CNCh-3 has the best thermal stability,T₀,T_5%and T_maxax values increased by 64.2,65.1 and112.3 ^oC,compared to CNCs-3,respectively.Surface carboxylation functionalization provides a green and sustainable process for the production of thermally stable CNC.Further,the prepared CNC was used to prepare a Pickering emulsion,and a smaller size emulsion droplet and a long-term stable emulsion system were obtained as the concentration of the CNC was increased,which provided an economical and reduced pollution of acidic waste.The method of preparing the CNC has potential application in the preparation of Pickering emulsion for the food system.???The PHBV nanocomposite films with different CNC and GO contents and their grafting products?CNC-GO?were prepared by solution coating method.Field emission scanning electron microscopy?FE-SEM?,FT-IR,DSC,etc.were used to investigate the effects of?CNC-GO?on the chemical structure,thermal,crystallization,and mechanical properties of PHBV.It has been found that uniformly dispersed CNC,GO and CNC-GO can be used as heterogeneous nucleating agents in the PHBV matrix to accelerate the crystallization of PHBV.Compared with pure PHBV,PHBV/1%CNC-GO had the highest thermal stability?starting degradation temperature increased by 14.3°C?,crystallization temperature(melting temperature T_m33 increased by 7.1°C)and mechanical properties?tensile strength increased by170.2%?,the Young's modulus and elongation at break increased by 137.5%and 52.1%,respectively.The addition of CNC,GO and CNC-GO can significantly improve the barrier propertiesof PHBV nanocomposite films and the migration performance in food simulating liquid.As the content of CNC or GO increased,the barrier property became stronger and the overall migration amount decreases.Simultaneous addition of CNC and GO had a stronger barrier effect and lower migration than the addition of CNC or GO alone.Among all PHBV nanocomposite films,PHBV/1%CNC-GO had the best performance.Compared with pure PHBV and PHBV/CNC nanocomposite films,nanocomposite films with a small amount of GO exhibited excellent antibacterial properties against E.coli and S.aureus,which can greatly limit the growth of bacteria and organisms in food packaging.The quality and safety of the items are guaranteed during the process.