Utilization of limestone dust waste as filler in natural rubber

The possibility of using limestone dust waste (LDW) as a filler in natural rubber (NR) was investigated. First, the basic properties of LDW were characterized; LDW was then incorporated into NR and the compound properties were determined. Comparison of the reinforcing effect of LDW and other commercial fillers such as light-precipitated calcium carbonate (PCC) and nanoprecipitated calcium carbonate (NPCC) was made. The results revealed that even though the addition of LDW has little effect on compound processability, it has a negative effect on most mechanical properties, e.g., tensile strength, tear strength, and abrasion resistance, of the vulcanizate. Among the three fillers, the degree of reinforcement could be placed in the following order: NPCC > PCC > LDW. Due to their relatively low specific surface area and thus low reinforcement ability, both LDW and PCC can be grouped as nonreinforcing fillers, whereas NPCC, the specific surface area of which is relatively high, could be grouped as a semi-reinforcing filler for rubber.     

Possible use of sludge ash as filler in natural rubber

Potential use of sludge ash as a filler in NR was studied. In this study, two grades of sludge ash namely SA-300 and SA-700 were prepared by sintering sludge waste obtained from concentrated natural rubber (NR) latex production at 300 and 700 °C, respectively. Properties of NR filled with various contents of SA-300 and SA-700 were then investigated and compared with those of NR filled with precipitated calcium carbonate (CaCO₃). The results reveal that, regardless of the filler type, both scorch time (t _s1) and optimum cure time (t _c90) decrease whereas hardness and modulus increase with increasing filler loading. At a given loading, both SA-300 and SA-700 give shorter scorch time and cure time with higher hardness and modulus than CaCO₃. Due to their higher specific surface area and greater cure activation efficiency, SA-300 and SA-700 provide better reinforcement, i.e., greater tensile strength; tear strength and abrasion resistance than CaCO₃. Taken as a whole, it could be said that the two grades of sludge ash could be utilized as rubber fillers with economic advantage.