At present, a large number of waste textiles are disposed through incineration and burial, which cause serious environmental pollution. Therefore, recycling textile wastes into high mechanical products with eco-friendly method is an urgent issue. Based on the above status quo, three kinds of 3D waste denim fiber needled felts/epoxy composites (3DWECs) with different areal densities of the mono-layer fiber web were designed and fabricated, and the effect of the areal density of the mono-layer fiber web on its mechanical properties was studied in this work. The cross-section morphologies of 3DWECs were also examined. Tensile, bending and compressive test results revealed that 2# 3DWECs (the planar density of mono-layer fiber webs was 557 g/m2) possessed better mechanical properties than 1# 3DWECs and 3# 3DWECs. Both the static and dynamic mechanical testing results showed that 3D waste denim fiber needled felts acting as the reinforcement played an essential role in the bearing function. Moreover, the peel tests indicated that the peel strengths of the 3DWECs were above the limits of the Chinese National Standard for particle board. The composites have the potential as a substitute for some particle boards.

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The small-size microstructure models of the 3D needled waste cotton fiber/epoxy composites (3DNWCFCs) were brought out to predict their key vibration parameters (natural frequency and mode shapes) with the finite element analysis method. Six kinds of 3DNWCFCs with different parameters were prepared and tested by the experimental modal analysis method to verify the accuracy of the prediction of the natural frequencies and mode shapes with the finite element method. The effects of the fiber volume content and needling density of the composites on the modal behavior were investigated. The natural frequency of the cantilever beams of the composites increased with the increase of the fiber volume content and increased at first then decreased with the increasing needling density. The effect of needling density on the vibration properties of the composite depended on the degree of damage and entanglement of Z-direction fibers. The comparative analysis of the finite element analysis and the experimental results showed that the small-size microstructure models of the 3DNWCFCs were effective to predict their vibration parameters. Therefore, the small-size finite element models can be used to predict the modal properties of the staple fiber reinforced composites effectively with less time and lower economic costs.

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