Selective Decomposition of Waste Rubber from the Shoe Industry by the Combination of Thermal Process and Mechanical Grinding.

Qiao Xiao,Xiaoli Sun,Lingxing Zeng,Changlin Cao,Qingrong Qian,Qinghua Chen,Baoquan Huang,Longshan Bai,Dandan Lei,Huibin Cheng,Liren Xiao

doi:10.3390/polym14051057

Abstract

A major challenge in waste rubber (WR) industry is achieving a high sol fraction and high molecular weight of recycled rubber at the same time. Herein, the WR from the shoe industry was thermo-mechanically ground via the torque rheometer. The effect of grinding temperature and filling rate were systematically investigated. The particle size distribution, structure evolution, and morphology of the recycled rubber were explored by laser particle size analyzer, Fourier transform infrared spectroscopy (FTIR), sol fraction analysis, gel permeation chromatography (GPC), differential scanning calorimeter (DSC), and scanning electron microscope (SEM). The results indicate that the thermo-mechanical method could reduce the particle size of WR. Moreover, the particle size distribution of WR after being ground can be described by Rosin’s equation. The oxidation reaction occurs during thermal-mechanical grinding. With the increase of the grinding temperature and filling rate, the sol fraction of the recycled WR increases. It is also found that a high sol fraction (43.7%) and high molecular weight (35,284 g/mol) of reclaimed rubber could be achieved at 80 °C with a filling rate of 85%. Moreover, the obtained recycled rubber compound with SBR show a similar vulcanization characteristics to pure SBR. Our selective decomposition of waste rubber strategy opens up a new way for upgrading WR in shoe industry.

Highlights

Introduction iationsThe rubber industry makes remarkable contribution to the world economy, and the production of rubber from the footwear and tire industries grows annually, but it results in a large amount of waste [1–3]
The torque values related to the resistance of the waste rubber (WR) face can be measured during grinding, which can evaluate the grinding effect
The influence of different temperatures and filling rates on the structure and properties of the waste rubber from the shoe industry was investigated by means of thermo-mechanical grinding technology

Summary

Introduction

The rubber industry makes remarkable contribution to the world economy, and the production of rubber from the footwear and tire industries grows annually, but it results in a large amount of waste [1–3]. Despite decades of research in this field, the disposal of waste rubber remains an economic, social, and environmental issue [4]. The improper disposal of waste rubber results in a large amount of waste discarded or incinerated, which causes environmental damage and even has the risk of spreading diseases, affecting dramatically the quality of human life [5]. Waste tire and footwear rubber are usually vulcanized, which is mainly composed of complex mixtures such as inorganic fillers, activators, accelerators, pigments, and stabilizers. When substances with low molar mass are discarded randomly in the natural environment, they may permeate the soil and the groundwater over time and seriously harm human.

Methods

Results

Discussion

Conclusion