The use of 1,2-benzisothiazolin-3-one (BIT) in preparation of low-ammonia and zinc-free natural rubber latex concentrate

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.