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.
Nowadays starch based natural polymers have been received tremendous attention owing to their non-toxicity, biodegradability, and biocompatibility. However, the applications of starch-based films are restricted due to water sensitivity and bacterial contaminations. To overcome these issues, a polymer composite film was produced by solution casting using cassava starch and silver vein graphite composite. The incorporation of silver vein graphite composite into cassava starch showed a reduction in water absorption capacity of the film. Polymer composite film from cassava starch and SVG (SVG/C.St film) showed excellent antibacterial activity against Staphylococcus aureus (diameter of the inhibition zone, ±22 mm; positive control, ±24 mm) and moderate activity against Escherichia coli (diameter of the inhibition zone, ±8 mm; positive control, ±23 mm). Inhibition zones were not observed for any of those bacteria species when C.St films were used. Therefore, SVG/C.St film could be a promising material for many antibacterial applications.
Lactic acid is used in pharmaceutical, cosmetic and polymer industries. Lactic acid can be synthesized by fermenting glucose obtained from the hydrolysis of starch. In the present study, powdered corn kernels were hydrolyzed by α-amylase under optimized stirring time (1.5 hrs.), temperature (47 ℃) and corn starch concentration (0.75% w/v) to obtain the glucose. The glucose concentration was measured by 3, 5-Dinitrosalicylic acid method. Resulted glucose was fermented (37 ℃) using Streptococcus thermophilus and the highest concentration of lactic acid was obtained after four days. The lactic acid yield was determined using UV visible spectrophotometer and calculated as 128.4 g/L. Lactic acid was purified by centrifugation followed by fractional distillation and characterized by Fourier Transform Infrared spectroscopy. Therefore, lactic acid could be successfully extracted from Sri Lankan corn starch using Streptococcus thermophilus.
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