| In recent years,the demand for environmentally friendly products has surged due to concerns over non-renewable resources and environmental issues such as plastic waste pollution.Consequently,the development of high-performance biodegradable materials has gained significant attention.Polyvinyl alcohol(PVA),a water-soluble polymer,possesses excellent mechanical and barrier properties.It can be synthesized from biomass ethanol and is biodegradable by microorganisms.Despite its advantages,PVA faces limitations such as slow degradation and high cost compared to petroleumbased plastics like polypropylene and polyethylene.Thus,research focused on accelerating PVA’s biodegradation and reducing its cost is crucial.Blending PVA with rapid-degrading,low-cost biomass fillers effectively addresses PVA’s limitations.Starch(ST),a renewable polysaccharide found in plants,is an ideal candidate due to its affordability,biodegradability,and water solubility.However,ST’s semi-crystalline nature hampers gelatinization and leads to uneven dispersion within the PVA matrix,negatively impacting mechanical properties.The high hydroxyl content in PVA and ST also compromises water resistance.Our study thoroughly investigates methods to regulate the structure and properties of PVA/ST composites,focusing on the PVA/ST ratio,plasticizers,alkalis,and composite process.The primary research objectives are as follows:In the first part,we investigated the structural differences between two types of PVA with varying degrees of alcoholysis.PVA1788,with lower crystallinity and a faster degradation rate,is chosen as the raw material.Furthermore,studying the structure and properties of composites with different PVA and ST ratios to determine the optimal ratio.In the second part,the influences of three plasticizers represented by glycerin,calcium chloride,and urea on the mechanical properties and water resistance of PVA/ST composites were discussed.The optimal addition amount of three plasticizers was studied when the composite films achieved the best mechanical properties,and the best plasticizing effect was determined by adding 20% glycerin content.In addition,it was found that plasticizers had no positive effect on the water resistance.In the third part,using glycerol as a plasticizer,the influence of different alkali concentrations on the structure and properties of PVA/ST composites was studied,and the ability of alkali to improve the water resistance of the materials was speculated and verified by experiments.In addition,it was found that the alkali added later caused damage to the previously formed more uniform structure,thus reducing the mechanical properties.In the fourth part,we employed advanced composite technology to prepare PVA/ST composites with outstanding overall properties by leveraging the dual effects of alkali on PVA and ST.Conducting in-depth characterization of the structure and properties of the composites.Discovering that alkali treatment not only promotes ST gelatinization and inhibits regeneration but also enhances PVA crystallization.This approach achieves improvements in mechanical properties and water resistance without sacrificing biodegradability.The resulting composite film exhibits a tensile strength of 23 MPa and an elongation at a break of 390%,with the ability to maintain mechanical properties when exposed to water.Moreover,the composite film demonstrates excellent flame retardancy,as evidenced by a limited oxygen index(LOI)of 30%.Furthermore,in a 60-d soil degradation test,the composite film exhibited a degradation rate exceeding 40%.Through the above research,we successfully develop PVA/ST composite films with desirable strength,water resistance,and biodegradability.We elucidate the influence of the PVA/ST ratio,plasticizers,and alkalis on the formation of a multilevel structure within the composite film.These findings provide valuable theoretical guidance for the development of biodegradable products based on the PVA/ST system. |
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