Dispersibility of Kaolinite-Rich Coal Gangue in Rubber Matrix and the Mechanical Properties and Thermal Stability of the Composites

Kenan Zhang,Yongjie Yang,Hao Zhang,Linsong Liu,Qinfu Liu,Lihui Liu

doi:10.3390/min11121388

Abstract

The aim of this work was to investigate the dispersibility of kaolinite-rich coal gangue in rubber matrix, the mechanical properties and thermal stability of coal gangue/styrene butadiene rubber (SBR) composites, and to compare these properties to those of the same coal gangue but had undergone thermal activation and modification. Several experimental techniques, such as X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric-differential scanning calorimetry (TG-DSC), laser-scattering particle analyzer were adopted to characterize the coal gangue particles and then the obtained composites. The results demonstrated the raw coal gangue (RCG) was mainly composed of kaolinite. Calcination led to amorphization of thermal activated coal gangue (ACG), increased hydrophilicity and void volume, and decreased pH. The grain size of ACG became coarser than RCG, but ACG turned loose confirmed by higher degree of refinement after grinding. Modification enhanced the hydrophobicity of the coal gangue and improved its dispersibility than fillers without modification. Calcined samples had better dispersibility than uncalcined fillers. Additionally, the coal gangue treated by calcinating, grinding and modifying (MGA) had the best dispersion in rubber matrix. Either calcination or modification could improve the mechanical properties and thermal stability of coal gangue filled rubber, while the performance of MGA reinforced SBR (MGA-SBR) was the best. The enhanced performance of the MGA-SBR was owed to better dispersion of particles as well as stronger interactions between particles and rubber macromolecules.

Highlights

Nowadays, coal gangue has been the largest industrial solid wastes in China with the accumulative amount of exceeding 5 billion tons and an annual stockpile increasing at a rate of 0.3 billion tons [1,2]
Most peaks in the X-ray diffraction pattern of raw coal gangue (RCG) (Figure 1) can be attributed to kaolinite, except for two weak peaks labeled by the solid downward triangle and solid diamond, which represent boehmite and negligible quartz, correspondingly
All peaks of kaolinite vanished and a diffuse band located between 15 and 30◦ appeared in the pattern of activated coal gangue (ACG) (Figure 1), indicating the conversion of kaolinite in coal gangue to amorphous metakaolinite [37]

Summary

Introduction

Coal gangue has been the largest industrial solid wastes in China with the accumulative amount of exceeding 5 billion tons and an annual stockpile increasing at a rate of 0.3 billion tons [1,2]. Coal gangue has the potential to be used as polymer filler [5,6,7]. Coal gangue is composed of inorganic and organic components with some unsaturated points and polar functional groups, including hydroxyl and carboxyl groups, etc., locate on. Organic composition in coal gangue may augment the inter-attraction of this particle and the matrix [5]. Coal gangue shows different properties when used as rubber filler relative to carbon black or white carbon black (silica). The activation methods of coal gangue mainly include mechanical activation, chemical activation, thermal activation, microwave activation, and composite activation [8,9,10,11]

Objectives

Methods

Results

Conclusion