Blends of poly(L-lactic acid) (PLLA) and poly (butylene terephthalate-co-adipate) (PBTA) were prepared at ratios of 50 : 50, 60 : 40, and 80 : 20 by melt blending in a Laboplastomill. Improved mechanical properties were observed in PLLA when it was blended with PBTA, a biodegradable flexible polymer. Irradiation of these blends with an electron beam (EB) in the presence of triallyl isocyanurate (TAIC), a polyfunctional monomer, did not cause any significant improvement in the mechanical properties, although the gel fraction increased with the TAIC level and dose level. Irradiation of the blends without TAIC led to a reduction in the elongation at break (E b ) but did not show a significant effect on the tensile strength. E b of PBTA was unaffected by EB radiation in the absence of TAIC.
Latex crepe rubber is the purest form of natural rubber and contamination of crepe rubber with metal ions should be avoided to maintain the quality of the rubber, especially to prevent the oxidative aging during storage. The influence of iron in processing water on raw rubber properties of crepe rubber has been investigated. Our research has shown that most of the iron ions contaminated from the processing water were leached out during the production process. The remaining iron ions in the crepe rubber catalyse the thermo-oxidative degradation and thereby significantly affect the oxidative stability of the rubber. Combination effect of Fe 3+ ions and aromatic thiol, which adds into natural rubber (NR) latex to bleach the yellow pigments in fractionated bleached (FB) crepe rubber, further reduced its resistance to thermal oxidation, measured by Plasticity Retention Index (PRI). Therefore, fractionated unbleached (FUB) crepe rubber has a better oxidative stability than fractionated bleached (FB) crepe rubber. Further investigations carried out to study the effect of oxidation state of iron showed that not only Fe 3+ ions but also Fe 2+ ions catalyses the oxidative degradation process of natural rubber (NR). Based on our experimental results, new specifications for total iron concentration in the processing water and maximum allowable iron concentration in latex crepe rubber have been proposed.
A dryer consisting of a saw dust fed furnace and a drying chamber was designed and fabricated for drying of skim natural rubber laces using hot smoke. Uninterrupted drying of laces was carried out in warm smoke in three different temperature ranges. Drying performance was evaluated in terms of raw rubber properties and drying period to achieve complete dryness. Quality of laces was assessed by visual appearance. The best temperature range for drying of skim natural rubber laces was found to be 30-34 0 C. Drying efficiency of laces was accelerated by more than 60% without affecting its raw rubber properties when laces were dried at this temperature range. The resistance to mould growth of dried laces was also improved. However, the dried product was downgraded according to the visual quality assessment in terms of colour which is commonly practiced in the trade for grading of rubber. Therefore, heating mechanism was modified to provide a draft of clean warm air into the drying chambers where the laces were hung for drying. The drying temperature inside the chambers was maintained at the selected temperature range (30-34 0 C) and drying of laces was completed within twenty-four hours. It was able to obtain skim laces with improved colour. Drying curve for skim laces dried using accelerated drying system was derived. Results of tests carried out to determine the raw rubber properties of laces showed that raw rubber properties of skim laces were not affected due to accelerated drying within the selected temperature range. Mechanical and physical properties of 80/20 (w/w) blends of Technically Specified Rubber (TSR 20)/ambient air dried skim laces and the blends of TSR (20)/warm air dried skim laces were also compared. The properties studied were tensile properties, hardness, compression set and resilience. The results suggest that warm air drying of skim laces has no significant effect on the mechanical and physical properties of the blends of TSR/skim laces.
Objective of this study was to investigate the effect of different preservative systems used in the concentrated latex manufacturing industry on physical properties of the latex crepe made out of them. Unfractionated and unbleached (UFUB) crepe rubber manufactured from latices preserved with ammonia, tetramethylthiuram disulphide, zinc oxide and a 1:1 mixture of tetramethylthiuram disulphide (TMTD) and zinc oxide (LATZ) were subjected to examine their raw rubber properties. It was observed that UFUB crepe rubber manufactured out of either ammonia preserved, ZnO preserved or chemically untreated latices have better resistance to thermo-oxidative degradation compared to UFUB crepe rubber made out of both TMTD and LATZ preserved latex. Further, it was observed that neither ammonia nor ZnO has any effect on the thermal degradation of crepes made out of ammonia or ZnO preserved latex. It was clear from the results that the TMTD added as a component of the preservative system adversely affects the resistance to thermooxidative degradation as judged by PRI of crepe produced. Crepe rubber manufactured from TMTD preserved latex exhibits unusually lower PRI and a nitrogen content comparable with the normal UFUB crepe rubber. Skim crepe rubber which is considered a by-product of the latex centrifuging industry, usually records higher nitrogen percentages and lower PRI values. Therefore, evaluation of these two parameters could be used to differentiate skim crepe rubber from normal UFUB crepe rubber. It was also observed that TMTD has a strong negative impact on PRI of crepe rubber even at very low concentrations. It could be proposed that dimethylthiuram monosulphide (DMTMS) free radicals generated by thermal decomposition of TMTD are responsible for this PRI reduction.
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