Preparation And Mechanical Properties Optimization Design Of Three-dimensional Denim Waste Fiber Needle-punching Composites

A large number of waste textiles have been disposed through incineration and burial,which cause serious environmental pollution.Therefore,recycling textile wastes into valuable products with eco-friendly method is an urgent issue.The recycling and reuse of waste denim is one of challenges towards sustainable disposal of waste textiles.The waste denim is the study object,which is opened into recycled denim fibers(abbreviation:waste denim fibers)firstly,and then adopting the needle-punching process and vacuum assisted resin transfer molding method to prepare high mechanical performance and low-cost three-dimensional denim waste fiber needle-punching composites.In this thesis,the change law and mechanism of the mono-layer fiber web areal density,fiber volume content,and needle-punching density on mechanical properties,dynamic mechanical analysis,pore size distributions,and fiber/resin interfaces of composites with different process parameters were studied.The three-dimensional denim waste fiber needle-punching composite with a mono-layer fiber web areal density of 557 g/m~2 has excellent mechanical properties.This is because the appropriate areal density of the mono-layer fiber web introduces more flat short fibers into the thickness direction,which strengthens the entanglement between the fibers in the vertical directions of the fiber web.The compactness of denim waste fiber needle-punching felt is enhanced,and the mechanical properties of the composite are improved effectively.The storage modulus and glass transition temperature of the composite are better than those of the epoxy resin.This is because the reinforcement denim waste fiber needle-punching felt increases the stiffness and thermal stability of the composite.The mechanical performance of the three-dimensional denim waste fiber needle-punching composite is optimal with the fiber volume fraction of 27.16%and the needle-punching density of 373 needles/cm~2.This is because an appropriate fiber volume fraction establishes a good mechanical interlocking between the denim waste fibers and the epoxy resin,and enhances the adhesion of the fiber/resin interface.The appropriate needle-punching density makes the average pore size of denim waste fiber needle-punching felt smaller.The distribution of needle-punching holes is more uniform,which is conducive to the impregnation of epoxy resin into the denim waste fiber needle-punching felt.As a result,the mechanical properties of composites are improved.The bending modulus and 24 h thickness swelling rate of the three-dimensional denim waste fiber needle-punching composite are superior according to the standard of particle boards,thus showing enormous potential as alternative raw materials to make furniture products such as particle boards,plywood,and desks.Besides,the small-size model of the three-dimensional denim waste fiber needle-punching composite was established by using the finite element method,and its tensile strength was predicted.The error between the prediction value and the experimental result is less than 12%, which proves the accuracy of the model.Therefore,the small-size finite element models can be used to predict the tensile properties of the staple fiber needle-punching composites effectively with lower time and economic costs.