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Odourless Natural Rubber (ONR)
Abstract
Unpleasant odour produced by natural rubber, in particular during mastication of Standard Malaysian Rubber (SMR 20) is objectionable to some workers. The issue of unpleasant odour of natural rubber has long been raised both by the rubber industry and the public. However, until today there seems to be no effective solution to overcome the problem. In view of this situation, work was initiated to develop Odourless Natural Rubber (ONR). This paper discusses the work to investigate and identify microorganisms that are responsible for unpleasant odour. Samples ofodourous cuplumps were taken from the SMR factory of Malaysian Rubber Board in Sungai Buloh. Microorganisms isolated from cuplumps were identified by means of VITEK® 2 System. The odourous compounds produced were collected using solid-phase microextraction (SPME) before being subjected to Gas Chromatography Mass Spectrometry (GCMS) to analyse the odour. Samples were analysed on a day to day basis for six days to determine the most odourous compounds. The volatile compounds detected at early incubation period were mainly hydrocarbons. Other volatile compounds produced throughout the incubation were low molecular weight compounds such as volatile fatty acids, sulphurous compounds, amino compounds, esters and alcohols. Three different antimicrobial agents were used to suppress the growth of odourous microorganisms during storage of cuplumps before processing. The SPME/ GCMS analysis provided experimental evidence that sodium hypochlorite and formaldehyde were able to inhibit the growth of microbes and suppressed the unpleasant odour of rubber. This rubber is now called Odourless Natural Rubber (ONR). Mixing was conducted on ONR to evaluate cure characteristics and physical properties of the vulcanised rubber based on ACS 1 mix formulation. ONR enhanced the cure rate and physical properties such as tensile strength, hardness and resilience which were higher than the control (SMR L).
... e offensive odor from raw natural rubber (NR) has been a long-standing problem of manufacturers [1]. e obnoxious odor released during processing and mastication of NR is undesirable to workers and a nuisance to the public residing near rubber manufacturing facilities [2,3]. e volatile compounds produced during microbial degradation of carbohydrates, proteins, and other nonrubber components of NR generate the offensive odor [2][3][4][5]. ...
... e obnoxious odor released during processing and mastication of NR is undesirable to workers and a nuisance to the public residing near rubber manufacturing facilities [2,3]. e volatile compounds produced during microbial degradation of carbohydrates, proteins, and other nonrubber components of NR generate the offensive odor [2][3][4][5]. Currently, water scrubbers are used to control the offensive odor from NR [1,5,6], but the expense of installation and maintenance makes it unattractive to rubber manufacturers. ...
... Cylinder-plate assays were performed for antimicrobial analysis of natural and zincmodified bentonite against selected microorganisms known to degrade or produce offensive odor from raw NR. Micrococcus luteus is a Gram-positive microorganism previously classified by Nornanysya et al. [3] to produce foul smell from coagulated NR latex. Xanthomonas oryzae is a Gram-negative microorganism known to degrade NR [21]. ...
Natural bentonite was modified with zinc ions and was used as a filler to reduce the offensive odor from raw natural rubber (NR). Characterization of filler shows the limited exchange of inherent calcium ions and the preferred adsorption of zinc ions on the surface of natural bentonite during modification. The modification process was also accompanied by bassanite formation due to sulfate ions brought by the zinc salt. Zinc-modified bentonite demonstrates an antimicrobial effect against microorganisms that are known to degrade or produce offensive odor from raw NR. Due to its antimicrobial and adsorption properties, zinc-modified bentonite significantly reduces the offensive odor from raw NR at loadings of 2.5–7.5 phr as shown by the olfactometry test. In terms of vulcanization characteristics, the loading of zinc-modified bentonite at 7.5 phr caused a slight decrease in elastic torque and increase in scorch and curing times of NR. The hardness and tensile properties of vulcanized NR are maintained after compounding with zinc-modified bentonite at 7.5 phr.
Understanding and managing the generation of odour nuisances throughout the raw rubber processing industry are vital to reduce the impact on the community. This paper aims to review literature on odour studies and management in the raw rubber processing industry. The generation of odour is typically associated with microbial reactions occurring in non-rubber components. The most offensive compound groups commonly discussed in the literature are sulfur derivatives and volatile fatty acids due to their unpleasant characteristics and low-odour threshold. Major sources of these odorants are from effluent treatment of the latex processing plant and exhaust gas from the drying process at the block rubber processing plant, respectively. However, studies performed on the composition of rubber emissions also reported the presence of other compound groups such as aldehyde, ester, amine and aromatic, which could potentially contribute to the odour emissions. Single or multiple odour assessment methods can be applied based on the objective of the odour assessment. Olfactory and chemical testings were generally applied to evaluate the odour concentration, offensiveness and identification of potential odorants, while odour wheel and dispersion modelling were employed to assess the impact on the community. Odour legislations mainly used olfactory techniques and dispersion modelling to control the odour emissions by limiting the odour release at a tolerable limit. Numerous mitigation measures have been studied and performed upstream and downstream of rubber processing, such as utilising biological methods and aerated effluent treatment that produces less odour, chemical substitution and installation of wet scrubber to reduce the odour emissions from drying process. Nevertheless, the literature is lacking studies conducted at the industrial scale on odour generation and mitigation where knowledge can be applied to develop an appropriate odour management strategy in the current industrial scenario to mitigate the odour effectively.
Different extraction procedures were evaluated to assess their potential for measuring volatile organic compounds (VOCs) from raw rubber materials. Four headspace sampling techniques (SHS, DHS, HS-SPME and µ-CTE) were studied. Each method was firstly optimised to ensure their reliability in performance. Passive sampling was also compared as a rapid identification of background VOCs. 352 VOCs were identified, 71 from passive sampling and 281 from active headspace sampling, with 62 not previously reported (hexanenitrile, octanone, decanal, indole, aniline, anisole, alpha-pinene as well as pentanol and butanol). The volatiles belonged to a broad range of chemical classes (ketones, aldehydes, aromatics, acids, alkanes, alcohol and cyclic) with their thermal effects (lower boiling points) greatly affecting their abundance at a higher temperature. Micro-chamber (µ-CTE) was found to be the most suitability for routine assessments due to its operational efficiency (rapidity, simplicity and repeatability), identifying 115 compounds from both temperatures (30 °C and 60 °C). Whereas, HS-SPME a widely applied headspace technique, only identified 75 compounds and DHS identified 74 VOCs and SHS only 17 VOCs. Regardless of the extraction technique, the highest extraction efficiency corresponded to aromatics and acids, and the lowest compound extraction were aldehyde and hydrocarbon. The interaction between techniques and temperature for all chemical groups were evaluated using two-way ANOVA (p-value is 0.000197) explaining the highly significant interactions between factors.
Natural rubber latex is produced by over 2,000 plant species, and its main constituent is poly(cis-1,4-isoprene), a highly un- saturated hydrocarbon. Since 1914 there have been efforts to investigate microbial rubber degradation; however, only re- cently have the first proteins involved in this process been identified and characterized and have the corresponding genes been cloned. Analyses of the degradation products of natural and synthetic rubbers isolated from various bacterial cultures indicated without exception that there was oxidative cleavage of the double bond in the polymer backbone. A similar deg- radation mechanism was postulated for the cleavage of squalene, which is a triterpene intermediate and precursor of steroids and triterpenoids. Aldehyde and/or carbonyl groups were detected in most of the analyzed degradation products isolated from cultures of various rubber-degrading strains. The transient formation of intermediate degradation products with molecular masses of about 104 Da from poly(cis-1,4 isoprene) having a molecular mass of about 106 Da by nearly all rubber- degrading bacteria investigated without detection of other in- termediates requires an explanation. Knowledge of rubber deg- radation at the protein and gene levels and detailed analyses of detectable degradation products should result in a detailed un- derstanding of these obviously new enzymatic reactions.
Nowadays, increasing use of latex products in the healthcare area has also led to an increase in new scientific controls of raw material and manufactured products in order to maintain higher standards in quality control. Since field latex is a rich environment for microbial growth, in the absence of adequate preservation, the carbohydrates that it contains become microbiologically oxidised to the so-called volatile fatty acids (VFAs). Samples of natural rubber latex coming from different countries and processed in different ways have been tested by applying a capillary electrophoresis method for the measurement of the short-chain organic acids present in sera. The separation was performed with phosphate buffer at pH 6.25 and cetyltrimethylammonium bromide (CTAB) as background electrolyte in an uncoated fused-silica capillary with -10 kV of applied potential. The sample needs no other pre-treatment more than coagulation to obtain the serum. In the assayed samples, it has been shown that poorly-preserved latex presented higher amounts of succinic acid and lower amounts of malic acid. The succinic to malic acid ratio may be an important parameter because it cannot be altered by dilution or similar processes such as the traditional VFA index, used to determine the quality of latex. Ratios for succinic to malic acid <0.6 have been found for well-preserved latex and >0.6 for poorly-preserved latex.