Effect Of Orderly Orientation And Interface Modification Of Polyvinyl Alcohol Fiber On Properties Of Thermoplastic Starch

With the increasing pollution of petroleum-based plastics like PE and PP to the environment,the dependence on fossil resources has led to continuous research on biodegradable polymers,especially on renewable resources.However,the development of biopolymers with properties comparable to general synthetic polymers is still an open challenge.Starch is a widely used biopolymer material,which attracts much attention due to its low cost and good biodegradability.Since natural starch has strong intermolecular and intramolecular bonds,its melting point is higher than the degradation temperature,which limits its processing performance and application,so natural starch is not a true thermoplastic.However,with proper plasticizer,temperature and shearing,starch granules will break,swell and melt,and hydrogen bonds between starch molecules will be broken.Therefore,thermoplastic starch(TPS)can be produced and processed as a thermoplastic material,and has the similar applications as traditional thermoplastics.However,TPS still has obvious shortcomings,which limits its application in industry,such as high moisture sensitivity and poor mechanical properties.In addition,these properties are largely dependent on changes in storage time and humidity.Our research is to add eco-friendly reinforcing materials to the TPS to improve the final properties of the TPS composite without affecting the biodegradability of the material.Polyvinyl alcohol fiber has the characteristics of high strength and high modulus.In addition,it has good acid and alkali resistance,is safe and non-toxic without causing environmental pollution,and a large number of hydroxyl groups on the surface can form strong hydrogen bonds with starch macromolecules.To a certain extent,it promotes the compatibility between the starch matrix and the polyvinyl alcohol fiber.A small amount of PVA fiber added to the thermoplastic starch system can play a role in enhancing performance.On this basis,by orderly arranging fibers in the matrix,the reinforcing effect in the orientation direction can be improved,while reducing the water absorption of the material.performance.Therefore,it is of great significance for biodegradable materials to prepare polyvinyl alcohol fiber orderly reinforced thermoplastic starch composite material and modify it on this basis.In this paper PVAF/TPS composite film with ordered orientation was prepared by pre-fixing evenly distributed polyvinyl alcohol fibers on the rollers by hot-press forming.To enhance the effect of TPS,we focused on the effects on the mechanical properties,dynamic mechanical properties,thermal stability and hygroscopicity of PVAF/TPS composite membranes.Finally,the finite element commercial software ABAQUS was used to simulate the moisture diffusion behavior of the composite membrane,reducing the material's moisture absorption process,in order to deeply understand its internal mechanism,and provide a theoretical basis for improving the water resistance of thermoplastic starch composites in the future.The specific work was as follows:(1)In the randomly oriented PVAF reinforced TPS system,when the addition of PVAF increases to 4.5 vt%,the tensile strength of the PVAF/TPS composite film increases to a maximum value of about 5.34 MPa;thermal stability analysis shows that when the addition of PVAF increases to 4.5 vt%,the peak temperature of PVAF/TPS rises to the highest value,about336.3°C;DMA test shows that when the addition of PVAF increases to 4.5 vt%,PVAF/TPS The storage modulus of the composite film is the largest,and the glass transition temperature at this time reaches the maximum,which is 63.5 k J°C,and the activation energy reaches 315.667 k J/mol;the addition of 4.5 vt%of PVAF makes the PVAF/TPS moisture absorption rate significantly decrease,the equilibrium moisture absorption of PVAF/TPS decreases to the lowest31.83%.(2)Highly oriented PVAF reinforced TPS composite film is prepared by fiber orientation winding.Optical microscope can observe that PVAF in the composite film is highly oriented and uniformly distributed;the high orientation of PVAF can significantly improve the tensile strength of PVAF/TPS,But at the same time,the flexibility of the composite film decreases.With the increase of the amount of PVAF,the tensile strength of the PVAF/TPS composite film continues to increase.The maximum value increased from 2.13 MPa for pure TPS to 13.13 MPa,which is close to the tensile strength Traditional petroleum-based plastic PE.Thermal stability analysis shows that the addition of PVAF can improve the thermal stability of TPS.When the amount of PVAF increased to 4.5 vt%,the peak temperature of PVAF/TPS rose to the highest 336.3°C,which was significantly improved;DMA test It shows that the order of PVAF makes the storage modulus value of the composite film in the initial stage of stretching larger than TPS,and as the PVAF content increases,the storage modulus of the composite film also gradually increases;hygroscopicity experiments show the addition of ordered PVAF The increase of the amount makes the hygroscopicity of the PVAF/TPS composite membrane continuously decrease,which limits the diffusion behavior of water molecules inside the composite membrane to a certain extent.(3)PVAF/TPS composite membrane was prepared by modifying PVAF with SHMP.The study found that the hydroxyl group of PVAF interacted with the phosphate group of SHMP,thus enhancing the interaction force between TPS and PVAF.The mechanical performance test results show that when the amount of SHMP added increases,the tensile strength of the PVAF/TPS composite film increases first and then decreases.When the amount of addition is 1.0%,the tensile strength reaches the maximum value,about 12.25 MPa;thermal stability analysis shows that the composite film obtained by 1.5 vt%PVAF modified by 1.0%SHMP exhibits the best thermal stability,and the peak temperature corresponding to the maximum decomposition rate increases from 331.2°C to 338.9°C;DMA test shows the storage modulus,glass transition temperature and activation energy of the PVAF/TPS composite membrane were all improved.The glass transition temperature increased to 77.65°C,and the activation energy increased to the maximum value of 370.12 k J/mol;the hygroscopicity experiment showed that 1.0%SHMP changed The hygroscopicity of the PVAF/TPS composite membrane under the highest temperature is the most significant,and the equilibrium moisture absorption has been reduced from 33.72%to 29.21%when not modified by SHMP.(4)The surface of PVAF was modified by esterification in different degrees by the same modification method.The results showed that the infrared spectrum indicates that CA and PVAF or TPS had undergone an esterification reaction,which increased the compatibility between the components;mechanical property tests showed that the lower content of CA-modified PVAF/TPS composite film can improve the tensile Strength,but its tensile strength gradually decreased as the added amount continues to increase.When the added amount of CA was 0.3%,the strength of the obtained PVAF/TPS composite film reach the maximum value,which was 9.15 MPa;thermal stability analysis showed that the addition of citric acid can improve the thermal stability of the material,0.3%content of citric acid improved the thermal stability of the composite film relatively the most,but the amount of modifier added was small,resulting in the insignificant thermal stability enhancement effect;DMA test showed that when the CA content was only 0.3%,the glass transition temperature of the composite film was the highest.With the increase of CA content,the glass transition temperature gradually decreased,and the storage modulus gradually increased;hygroscopicity experiments showed that a small amount of CA modification can reduce the hygroscopicity of the composite film,when the CA content was 0.3%,PVAF/TPS composite membrane had the lowest equilibrium moisture absorption of 29.2%.(5)The ABAQUS finite element software was used to simulate the hygroscopic behavior of the thermoplastic starch matrix material and ordered PVAF with different contents to enhance the hygroscopic behavior of the TPS composite film.The finite element simulation data and the actual experimental data were in good agreement,so that it played a guiding role in our experimental process.The moisture diffusion behavior of the composite membrane was basically in accordance with Fick diffusion,that is,in the initial stage of moisture absorption,the moisture absorption rate was linearly related to t^1/2,and then the moisture absorption rate gradually decreased until the internal moisture of the material was isaturated and reach hygroscopic balance.