Preparation And Application Of High Strength And High Modulus Polyethylene Fiber Functional Paper-based Materials

The raw material synthesis and spinning and molding technology of high-strength and high-modulus polyethylene fiber（UHMWPE）in China have made substantial progress and reached the international advanced level,and the promotion and application of this kind of fiber has gradually received wide attention.As filament fibers,UHMWPE fibers have been used in three major fields,namely aerospace,military and civil,for their excellent properties such as high strength,high modulus and good resistance to acid and alkali corrosion.Therefore,how to enrich and broaden the applications of UHMWPE staple fibers is the goal we want to achieve.In this paper,we firstly investigate the process and performance of UHMWPE fiber paper matrix composites prepared with UHMWPE staple fibers and coniferous wood pulp,in order to have a deeper understanding of the main factors and their mechanism of action affecting the preparation of paper by wet nonwoven method of UHMWPE staple fibers.Based on the above research results of UHMWPE fiber wet process paper formation,UHMWPE fiber was used as the base raw material to prepare lithium-ion battery separator by wet nonwoven technology based on its excellent chemical stability,good thermal stability and good insulation properties,and the separation membrane support body by wet nonwoven technology based on its high strength and good chemical stability properties.The factors influencing the forming of these two functional paper-based materials and their mechanisms of action are discussed and analyzed,and their properties are characterized.The studies are summarized as follows:UHMWPE fiber paper matrix composites were prepared from UHMWPE staple fibers and coniferous wood pulp by wet copying process.The effects of UHMWPE fiber to conifer wood pulp fiber mass ratio,conifer wood pulp beating degree,quantification and different UHMWPE fiber length on the strength,pore size distribution and porosity of UHMWPE fiber paper matrix composites were investigated.The results show that when the pulping degree of coniferous wood pulp is gradually increased,the swelling and fine fibrillation of coniferous wood pulp fibers gradually deepen,thus the specific surface area of coniferous wood pulp fibers increases rapidly and more chemical groups are released,which promotes the chemical bonding between fibers and strengthens the inter-fiber bonding,and the tensile index and tear index of UHMWPE fiber paper matrix composites show an increasing trend,the tightness keeps increasing,the air permeability and porosity show a decreasing trend,the pore size distribution is more concentrated and the pore size becomes smaller;when the mass ratio of coniferous wood pulp gradually increases,the number of polar groups keeps increasing,so that the tightness,tensile index and tear index of UHMWPE fiber paper matrix composites gradually increase,the pore size distribution is more concentrated and the pore size becomes smaller,and the air permeability and porosity keep decreasing;when the quantity keeps increasing,the tightness and tensile index of UHMWPE fiber paper matrix showed a trend of first increasing and then decreasing,the tear index gradually increased,the pore size distribution became more concentrated and smaller,and the air permeability and porosity continuously decreased;compared with the UHMWPE fiber paper matrix composite prepared by 6 mm UHMWPE fiber,the tightness and tensile index of 3 mm UHMWPE fiber paper matrix composite were greater,and the air permeability,tear index,porosity and pore size were more smaller and the pore size distribution was more concentrated.The effects of fiber mass ratio and conifer wood pulp beating degree on the performance of wet copying of UHMWPE fiber paper-based diaphragm were investigated.Since the pore size of the paper base prepared by the wet copying process is large,it is difficult to meet the requirements of lithium-ion battery diaphragm,so the pore size and other properties of UHMWPE fiber paper-based diaphragm were improved by adding nanofibrillated cellulose（NFC）and polyvinyl alcohol/silicon dioxide（PVA/Si O₂）coating.The results showed that under the experimental conditions of quantification of 30 g/m²,mass ratio of UHMWPE fiber and coniferous wood pulp of 5:5,beating degree of coniferous wood pulp of 93°SR,NFC addition amount of 12%（relative to absolute dry fiber）,and coating solution of PVA/Si O₂with mass fraction of 6%for UHMWPE fiber paper base paper,compared with the paper-based diaphragm base paper,the mechanical properties of UHMWPE fiber paper-based diaphragm improved by about 4.5 times,the pore size became smaller,the porosity and liquid absorption increased by 7.01%and 4.69%,respectively,and the thermal stability performance became better.Compared with commercial Celgard 2500,the UHMWPE fiber paper-based diaphragm has a stable electrochemical window,higher liquid absorption and porosity,better thermal stability,higher ionic conductivity(1.059 m S·cm^-1)and lower interfacial impedance value（140Ω）.Since UHMWPE fibers have excellent properties such as good solvent resistance and high strength,UHMWPE staple fibers and low melting point PVA fibers were copied and combined with wet copying and hot pressing processes to prepare wet nonwoven UHMWPE fiber supports.The results showed that when the mass ratio of UHMWPE fiber to PVA fiber was 6:4,the amount of dispersant PEO was 0.9%,and the amount of reinforcing agent CPAM was 0.6%（all relative to the absolute dry fiber）,the performance of the prepared wet nonwoven UHMWPE fiber separation film support body was better.The best performance was achieved when the hot pressing time was 6 min,the hot pressing pressure was 20 MPa,and the hot pressing temperature was 110℃.In addition,the comparison of the data shows that the differences in mechanical properties,porosity and pore size between the prepared wet nonwoven UHMWPE fiber separation membrane support and commercial separation membrane support are not significant and can meet the requirements of practical applications.