The preparation and characterization of white fly ash filled natural rubber compounds / Mohd Norhisyam Mohd Mokhtar

The preparation and characterization on natural rubber (NR) using ‘Standard Malaysian Rubber’ (SMR 10) grade with white fly ash (WFA) was undertaken. SMR 10 compounds were prepared by melt mixing on a two roll mill and followed by compression moulding. Carbon black (CB) and silica filled natural rubber compounds were used as a comparison. The effect of WFA with at filler loading up to 30 phr on curing characteristics, mechanical properties, hardness, swelling behavior of natural rubber compounds were studied. WFA was grinded with pulveriser and sieved to 45-75 μm. The size of CB and silica that was used is 80-90 nm and 120-150 nm. The main elemental composition (wt%) of WFA was analyzed by X-Ray flourescence (XRF) spectrometry as follows: SiO2 (60.7%), Fe2O3 (14.8%), CaO (13.7%), K2O (3.7%), P2O3 (1.5%) and other elements (5.6%). Both scorch and cure time were reduced whereas the maximum and minimum torque increased with the increased loading of WFA in NR. For carbon black, the scorch time and cure time was decreased with increasing filler loading whereas the scorch time of silica decreased with increasing filler loading. The tensile strength of NR increased up to 5 phr loading and then decreased with increasing WFA loading. For CB, the tensile strength was increased whereas the tensile strength for silica decrease with increasing filler loading. Elongation at break continuously decreased with increased WFA loading same as with carbon black and silica trend. As expected, the hardness and tensile modulus increased with increasing WFA loading. Swelling test indicated that WFA had the higher filler-rubber interaction. The dispersion of WFA filled natural rubber compounds shows the surface h.as many tear line with branching that indicates higher tensile strength whereas deeper matrix tearing are noticed for CB, that indicated high stress was needed. For silica, the tensile fracture is brittle and rough with many tear lines. It shows that the tensile strength of silica decreased with increasing filler loading. The effect of WFA loading with the presence of 3 aminopropyltrimethoxysilane (APTMS) in NR compounds was studied using two different method, insitu addition and surface treatment. The optimum content of APTMS is at 1.0 phr. Shorter scorch and cure time was achieved with the presence of APTMS when compared to NR without APTMS. Tensile strength of the WFA/NR compounds with APTMS content increased with filler loading until 5 phr and then started decrease with further increase in filler loading. Improvements of mechanical properties such as elongation at break and tensile modulus was also observed with APTMS content. Thermal aging was carried out on 2, 4 and 7 days at 100 °C and tensile testing was performed in order to determine the aging properties. It shows that, tensile strength of WFA increased after 2 days aging and further decreased after 4 days aging process.