Effect of Modification Conditions of Coal Gangue on Properties of Natural Rubber Composites

The purpose of this work is to study the reinforcement effect of modified coal gangue (CG) on natural rubber (NR); carbon black (CB) was taken as reference filler. The addition of CG and CB to NR with the total filler loading fixed at 35 phr. The orthogonal experiment was employed to reveal the modification conditions on reinforcing properties. The results show that modification conditions such as weight ratio of coupling agent (CA), calcining temperature (CT), and calcining time (CM) affect the strengthening properties of CG, and CA is the most important factor influencing the tensile strength of NR, the order of influence can be expressed as CA > CT > CM. The optimum modification conditions are CT 800 degrees C, CM 1 hr, and CA 2%. 300% modulus of NR composites filled with modified CG (17.5 phr)/CB (17.5phr) hybrid filler is similar to NR filled with CB alone at same filler loading, while elongation at break increases significantly for existent of CG. The effect of heat treatment and modification conditions of CG were tested by particle size distribution, scanning electron microscopy, Fourier transform infrared spectra, and X-ray diffraction. The results show that the specific surface area of CG increased and hydroxyl group in crystal structure of CG removed under heat treatment. Dynamic mechanical analysis results show that the storage modulus and tan delta of CG filled NR composites are higher while T-g is less than that of CB, indicating the existence of a strong and stiff interface between filler and NR matrix. (C) 2014 Society of Plastics Engineers