Modification of natural rubber (SIR 10) with maleic anhydride as binder for sand aggregate

The modification of natural rubber (NR) using grafting method with maleic anhydride (MA) is intended to improve adhesion of the matrix as a binder on sand aggregate surface. In this work, natural rubber (Standard Indonesian Rubber: SIR 10) was modified using reflux technique, for 60 minutes, in toluene solution with various concentration of MA (i.e.,1,3,5,7,10phr) in the presence of constant concentration of benzoyl peroxide (BPO: 0.5 phr) as initiator. The reaction mixture were then evaporated and dried under vacuum oven at 60°C to constant weight. Amount of grafted MA in NR matrices were determined by titration method using potassium hydroxide in ethanol solution after exhaustive washing in acetone-methanol solvents. It was found that the optimum grafting degree of MA in NR matrix was 7.6%,when used 7 phr of MA, and this was confirmed by FTIR spectra analysis which showed the presence of NR-grafted MA (NR-g-MA) at absorption peak of carbonyl (>C=O) group number 1712.58 cm-1. The NR-g-MA matrices were then mixed with various weight ratio of the matrices to sand aggregate (3:7, 4:6, and 5:5) using mechanical stirrer in toluene solution. After drying, the mixtures were compression moulded to specimens, according to ASTM D 790-02. Results of 3-point bending tests of the specimens with optimum weight ratio (5:5) were: modulus of elasticity MoE) 969.82 MPa and modulus of rupture (MoR) of 4.42 MPa. Further testing according to SNI 03-2105-2006, showed water absorption ability of 3.76%. Characterization of the optimum sample using differential scanning calorimetry (DSC) showed decomposition on peak at higher temperature but lower heat capacity when compared to sample without sand aggregate.