No abstract

No abstract

Natural rubber (NR) contains cis-1,4-polyisoprene as well as a small quantity of non-rubber components, affecting the physical properties of NR, especially the storage hardening via gel formation. The free and/or linked non-rubber components were removed from NR by various treatments. The origin of gel formation in NR mainly resulted from proteins, which could be removed by enzymatic deproteinisation, surfactant washing or saponification treatment, and partly from phospholipids linked to NR molecule via H-bonding, which were decomposed by saponification or polar solvent treatment. The effect of the nonrubber components in NR on storage hardening was investigated by an accelerated storage hardening test (ASHT). The crude NR (CNR) containing proteins and lipids clearly showed the increase of gel content, suggesting the formation of crosslink structure during storage, resulting in the high plasticity number and Mooney viscosity after the ASHT. The gel content in protein-free NR did not change significantly only in washed NR (WSNR), but increased in the enzymatic deproteinised NR (DPNR). This resulted from the presence of residual proteins, such as oligopeptides. Interestingly, the gel content also reduced in the acetone extracted CNR (AE-CNR) and there was no significant effect on the storage hardening after ASHT, like WSNR. These were supposed to be due to the interaction or the participation of proteins and free fatty acids in the branching formation. Although the saponification could be decomposed branching at both terminal ends of the NR molecule, the protein and lipid residues occluded in the saponified NR (SPNR) affected the storage hardening. However, the flocculant remaining in the SPNR coagulated with acid and flocculant (AF-SPNR) would obstruct both gel formation and storage hardening.

No abstract

Ammonia is a well-established preservative for natural rubber latex (NRL). It functions not only as an effective biocide but also imparts stability to latex. Owing to its pungent and toxic nature, there is an increasing effort in searching for a less obnoxious alternative to its use as the sole preservative for commercial high ammonia (HA) latex concentrate. Another NRL concentrate containing low ammonia, known commercially as LA-TZ, is preserved with added tetramethylthiuram disulfide (TMTD) and zinc oxide in addition to ammonia. However, TMTD can generate carcinogenic nitrosamines during the processing of rubber products. This study shows that an alternative preservative, 1,2-benzisothiazolin-3-one (BIT), in combination with or without EMAL E27 or Levenol WX as a stabiliser in the presence of an ammonia, can inhibit bacteria proliferation and putrefaction while maintaining the stability of the latex for more than 30 days. Supporting evidence on bacteria count, volatile fatty acid number, mechanical stability time, zeta potential, particle size, and scanning electron micrograph were presented to establish the effectiveness of preservation and the state of colloid stability of the concentrated natural rubber latex. Among the various preservative systems investigated, it was found that the system: 0.025% BIT in the presence of 0.075% ammonium laurate and 0.3% ammonia is a suitable alternative for the LA-TZ latex. It was further found that the tensile properties of the vulcanised film obtained using this latex are comparable to those of LA-TZ latex. Hevea latex, a renewable plant-based largest source of commercial elastomer preserved with a TMTD-and zinc-free preservative, possesses attributes of a green and sustainable feedstock for the latex dipping industries. KeywordsNatural rubber latex • Preservatives • Putrefaction • Colloidal stability • Alternative green preservative system • TMTD-free and zinc-free preservative for Hevea latex * Porntip Rojruthai