Preparation of skim natural rubber and polypropylene blends via melt blending: A study on processability

Abstract

Processability of thermoplastic natural rubber (TPNR) blends is a vital aspect in the preparation of blends for industrial applications and is assessed using different techniques. In this study, skim natural rubber/Polypropylene (SNR/PP) blends were prepared using melt mixing and their processability was examined in terms of mixing torque development, long-term processability, moving die rheometer (MDR) torque, thermo-gravimetric analysis (TGA), melt flow index (MFI) and morphological studies. A series of unvulcanized (UV) and dynamically vulcanized (DV) blends having 70/30, 60/40, 50/50, 40/60, and 30/70 SNR/PP compositions were prepared. Standard Lanka Rubber (SLR) and PP blends having corresponding ratios were also studied for the purpose of comparison. The study reveals that a high percentage of non-rubbers present in the SNR has positively influenced the processability of both UV and DV SNR/PP blends compared to SLR/PP blends as assessed by the mixing torque values. As suggested by the mixing torque development and long-term processability, natural rubber dominant both DV blends cannot be processed. However, they can be processed under low shear rates as shown in the MDR studies irrespective of the rubber type. Therefore, it can be inferred that these rubber dominant blends can be processed into molded products via compression molding technique. TGA studies revealed that a similar degree of protection has been offered to the blends against thermal degradation by SNR and SLR. MFI studies showed that there is no significant difference in flowability between UV SNR/PP blends and SLR/PP blends. However, for DV blends, SNR/PP blends showed a higher flowability than SLR/PP blends. In addition, increase in PP percentage in the blend enhances the flowability while dynamic vulcanization reduces the flowability irrespective of the type of rubber used in the blends. Morphological studies suggest continuous or co-continuous phase structures for UV blends and two-phase structures for DV blends where the plastic phase acts as the continuous phase.

Preparation of skim natural rubber and polypropylene blends via melt blending: A study on physico-mechanical properties

“…The melt mixing was carried out at the melt temperature of 180°C and a rotor speed of 70 rpm following the same procedure adopted in an earlier study. 32 Both unvulcanized (UV) and their dynamically vulcanized (DV) counterparts were prepared. The formulation used for the preparation of DV blends is shown in Table 1.…”

“…[29][30][31] However, no much information on mechanical properties and dynamic mechanical properties of SNR/PP blends are available in literature except the study carried out on the processability of SNR/PP blends prepared via melt mixing. 32 The influence of the high content of non-rubbers on the morphology of these blends, modifications of the rubber phase, and properties of SNR/PP blends covering a wide range of NR/PP blend ratios has not yet been reported. In fact, the high non-rubber content and different molecular characteristics of SNR could directly affect the properties of the blends.…”