Abstract:

Objective In order to study the force change of fibers in the process of mechanical recycling of waste textiles and to improve the recycling efficiency, a mesoscopic model composed of fiber assemblies is established on the basis of the existing macroscopic model of woven fabrics. The twist parameter is added to this mesoscopic model and the influence of twist on elastic modulus is considered.

Method Abaqus was adopted to simulate the shredding process of the macroscopic model and the mesoscopic model, and a relevant experiment was designed to validate the accuracy of the models. The force of the sawtooth shredder at different rotational speeds and yarns with different twists were taken into consideration.

Results From the simulation results of the two models, it was observed that as the rotational speed of the sawtooth shredder decreased, the force exerted by the sawtooth shredder became smaller. It was found that the shredder force provided at a speed of 40 rad/s, and the cotton fabric was not be ripped up due to the low speed, indicating that that a suitably high speed should be selected in practical production. From the above finite element analysis, it was learnt that the force characteristics of the two models are basically the same, but the force values of the mesoscopic model are lower than those of the macroscopic model, which may be due to the fact that the material parameters of the yarn and fiber assembly are not fully mapped in the mesoscopic mode. In order to map the characteristic of yarn twist in the macroscopic model, the levels of yarn twist in the mesoscopic model were taken into consideration to study the influence of twist variation on the shredding process, of which twist levels of 60, 70 and 80 twist/(10 cm) were considered in the analysis. The results demonstrated that the change in twist affected the elastic modulus of yarns in the mesoscopic model. From the simulation analysis results, it was seen that the force on the sawtooth shredder of the mesoscopic model is the smallest when the yarn twist was assumed to be 60 twist/(10 cm). The relationship between the yarn twist level and the maximum force offered by the sawtooth shredder exhibited positive correlation.

Conclusion The mesoscopic model composed of fiber assemblies was established on the basis of the macroscopic model. Combined with Abaqus software, the finite element simulation of the shredding process of waste cotton cloth was carried out for two models. By simulating the influences of different sawtooth shedder speeds on the shredding process, it was learnt that the speed should not be lower than 573 r/min (60 rad/s) so as to provide the lowest shredding force. Between 60 twist/(10 cm) and 80 twist/(10 cm), the maximum force on the sawtooth shredder decreases as the twist decreases. The macroscopic model was found difficult to represent the force characteristics of the fibers and the way they move, and the mesoscopic model was established to refine the structure of the macroscopic model and can describe the variation of twist. Suitable mesh sizes and simple contacts between yarns were adopted to reduce the computational cost of the simulation.

Key words: mechanical recycling, waste cotton fabric, cotton fbric mesoscopic model, shredding process simulation, twist