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

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

Environmentally safe preservation and stabilization of natural rubber latex in an acidic environment

“…The onset of putrefaction triggers an unwanted coagulation process, which renders the latex challenging to handle and process. [ 4,5 ] Hence, the natural rubber producer is forced to use chemicals, such as ammonia, tetramethylthiuram disulfide (TMTD), and zinc oxide (ZnO) to stabilise and preserve the liquid natural rubber latex. Once these chemicals are added, the latex no longer decomposes, and it remains in a stable flowable condition.…”

“…[ 9 ] Like ammonia, zinc oxide is also a category 1 environmentally damaging substance that creates an acute hazard to aquatic environments. [ 5 ]…”

“…But not until 2008 was a wastewater treatment plant built, almost seventy years after the factory began processing latex .” Such treatment plants include aerobic, anaerobic, and facultative ponds, which require large areas to expose wastewater to sunlight and oxygen. [ 4–7,9 ]…”

“…[9] Like ammonia, zinc oxide is also a category 1 environmentally damaging substance that creates an acute hazard to aquatic environments. [5] The stabilising effect of the chemicals inside the liquid latex that keep it from coagulating wanes over time, forcing the producer to process the latex into solid rubber or rubber products within a few months; at most, a stabilised latex has a shelf life of 6 months. The waste material that is left after extracting the solid rubber, which needs to be disposed of, contains ammonia, as well as sugars, proteins, amino acids, and lipids, which due to their contact with ammonia and TMTD, have been rendered useless.…”

“…Such treatment plants include aerobic, anaerobic, and facultative ponds, which require large areas to expose wastewater to sunlight and oxygen. [4][5][6][7]9] Today, many countries recognise the need to regulate the amount of chemicals present in wastewater discharged from their processing plants. For example, in 2015, Colombia established stringent limits on chemical concentrations in effluents discharged by processing facilities such as the ones from the natural rubber industry.…”