Tetramethylthiuram Disulphide Research Articles

Cross‐reactivity between thiurams

Retesting with an allergen at a site with previous allergic contact dermatitis has been shown to enhance reactivity. It has been suggested that retesting with a cross-reactive allergen will also induce hyperreactivity. Concurrent sensitization to more than 1 thiuram is common, but whether this is due to concomitant primary sensitization or cross-reactivity is uncertain. The aim of this study was to investigate the use of retesting to distinguish between concomitant sensitization and cross-reactivity in the rubber chemicals tetraethylthiuram disulphide (TETD) and tetramethylthiuram disulphide (TMTD). There was a non-significant trend towards enhanced reactivity for both TETD and TMTD when testing in an area with previous allergic contact dermatitis due to TETD. Cross-reactivity between the 2 chemicals is likely, but a definite conclusion from this pilot study is not possible.

Effect of vulcanizing system on the crosslink density of nitrile rubber compounds

The synergistic activity of binary accelerator systems in rubber vulcanization is well known. Binary accelerator systems are being widely used in industry and are becoming increasingly popular because of the fact that such mixed systems can produce a vulcanizate with superior mechanical properties compared to those of stock cured with a single accelerator. The authors have studied the performance of a binary accelerator system based on cyclohexyl benzothiazole sulfenamide (CBS), tetramethyl thiuram disulphide (TMTD) in the sulfur vulcanization of nitrile rubber. The amount of sulfur and accelerator was varied to change the network crosslink density of vulcanizates. The observed mutual activity has been discussed based on the mechanical properties and crosslink density. The physical crosslink density of the various nitrile rubber mixes was estimated using the Kinetic Theory of Elasticity. The mechanical properties of the various rubber compounds were related to the corresponding crosslink density estimated for each compound. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2440–2445, 2005

New binary accelerator systems for sulphur vulcanisation of styrene butadiene rubber

It is suggested that binary systems of rubber vulcanisation containing thiourea proceed by a nucleophilic reaction mechanism. The exact mechanism of the chemical reactions involved when binary accelerator systems are used in rubber vulcanisation is not fully understood even now. It differs with the systems and the nature of the elastomer used. In the present work, a derivative of thiourea, N-amidino N'-phenyl thiourea (APT), was studied as a secondary accelerator along with tetramethyl thiuram disulphide (TMTD)/mercaptobenzothiazyl disulphide (MBTS) in the sulphur vulcanisation of styrene butadiene rubber. Thiourea binary systems were used as controls. The binary systems containing APT are very effective in reducing the optimum vulcanisation time. APT being more nucleophilic than thiourea, is more reactive here (as observed by the reduction in cure time). A nucleophilic reaction mechanism is indicated in the vulcanisation reaction under review. Different concentrations of APT were tried in various mixes using standard recipes, and reference mixes were also evaluated. The optimum dosage of APT required has been derived based on the cure characteristics of the mixes and the physical properties of the vulcanisates.

Fungicide control of Stenocarpella Maydis in the Nigerian Savanna

A survey of farmers' fields in the Savanna zone of Nigeria in 1999 indicated the presence of stalk and cob rots of maize at incidence rates of 15 – 43% and disease severity of 2.0 – 6.7. The causal organism was identified as Stenocarpella maydis ( = Diplodia maydis). S. maydis was found to reduce seed germination by up to 29.2%. Laboratory and screen house experiments were used to evaluate the efficacy of six seed treatment fungicides indicated that Luxan (a local fungicide of unknown composition), benomyl (Benlate) and mancozeb (Dithane M-45) were more effective than metalaxyl + carboxin + furathiocarp (Apron-plus), carbendazin + maneb (Delsene M) and tetramethylthiuram disulphide + hexachlorobenzene (thiram + HCB) in controlling S. maydis. Stalk rot severity increased with increasing fertilization rates.

Effect of common pesticides used in the Niger Delta basin of southern Nigeria on soil microbial populations.

The effects of eleven pesticides on the populations of bacteria, actinomycetes, fungi and protozoa was investigated by treating a garden soil with their recommended rates. The microbial populations were estimated using the standard plate-count technique. Of the 11 pesticides investigated, phenylmercuric acetate (agrosan) at 50 microg g(-1) inhibited bacterial density the most, i.e. from 4,600,000 to 220 cells g(-1). The pesticides were Pentachloronitrobenzene (PCNB), tetramethylmethylthiuram disulphide (thiram), 1-naphthylmethylcarbamate (Vetox 85), 1,2,3,4,5,6-hexachlorocyclohexane (Gammalin 20), phenylmercuric acetate (Agrosan), tetrachloroterephthalic acid (Dacthal), 4-nitrophenyl-2-nitro-4-trifluoromethylphenyl ether (Preforan), 2-ethyl-6-methyl-N-2-methoxy-1-methyl ethyl-chloroacetanide (Dual), Benlate, Brestan and Gramoxone. Pentachloronitrobenzene (PCNB) at 240,000 microg g(-1) reduced bacterial population from 4,600,000 to 2,100 cells g(-1), whereas tetramethylthiuram disulphide (thiram) at 100 microg g(-1) suppressed it by 2 log orders of magnitude. Soil application of 1-naphthylmethylcarbamate (Vetox 85) at 100 microg g(-1) and 1,2,3,4,5,6,-hexachlorocyclohexane (Gamalin 20) at 1,300 microg g(-1) repressed the bacterial numbers by 2 log orders of magnitude each. Pentachloronitrobenzene reduced the actinomycetes density from 340,000 to 320 cells g(-1) and completely eliminated all fungal and protozoan propagules from the soil. The Gammalin 20 completely wiped out all the fungi, whereas phenylmercuric acetate totally eliminated all the protozoa and reduced the fungal population from 34,000 to 60 cells g(-1). In general, protozoa and fungi were more susceptible to fungicides than bacteria and actinomycetes. Pentachloronitrobenzene, 1,2,3,4,5,6,-hexachlorocyclohexane and phenylmercuric acetate were toxic particularly to soil microorganisms, whereas the herbicides dacthal, Preforan and Dual were quite harmless in soil at application rates of 0.1, 0.06 and 0.02 microg g(-1) respectively.

The Effect of the Vulcanizing System on Cure and Mechanical Properties of Nbr/Epdm Blends

The effect of the curing system and curing parameters, mechanical properties, ageing resistance, and crosslink density of NBR/EPDM blends has been investigated. The curing characteristics of the blends were affected by the accelerator type and the sulphur concentration. The sulphur/benzothiazyl-disulphide (S/MBTS) vulcanizing system offered the best scorch safety, whereas those single and binary accelerator systems based on tetramethyl thiuram disulphide (TMTD) provided faster cure. The MBTS single accelerator system was able to crosslink the EPDM phase better and consequently displayed better mechanical performance than the other systems based on tetramethyl thiuram disulphide (TMTD). Higher thermal stability was also achieved in blends containing higher levels of sulphur, probably because of increased crosslinking in the EPDM phase. The results of dynamic mechanical investigations showed differences in the glass transition temperatures, which increased with increasing of the sulphur content in both S/MBTS and S/MBTS/TMTD vulcanizing systems. Formulations based on S/TMTD single accelerator systems gave the lowest values of Tg, and the amount of sulphur did not affect this property.

Studies on sulphur vulcanisation of natural rubber using amidino thiourea

Binary accelerator systems are widely used in vulcanisation of rubbers, providing more effective vulcanisation than using single accelerator systems. It has been reported previously that when thiourea is used in binary systems, it favours the cleavage of S–S, S–C, or S–N bonds in primary accelerators such as tetramethylthiuram disulphide (TMTD), mercaptobenzothiazyl disulphide (MBTS), and cyclohexylbenzthiazylsulphenamide (CBS), indicating a nucleophilic reaction mechanism in these vulcanisation reactions. However, there is no conclusive proof for this mechanism. In the present work the results obtained when a derivative of thiourea, namely amidino thiourea (ATU), is used as a secondary accelerator together with TMTD, MBTS, or CBS in the sulphur vulcanisation of natural rubber (NR) are discussed. There is appreciable reduction in the optimum cure time of the different experimental mixes compared with the reference formulations. This study also supports a nucleophilic reaction mechanism in such vulcanisation. Binary systems with varying concentrations of ATU with different primary accelerators have been examined and the optimum quantity of ATU required has been derived. The cure characteristics and tensile and other physical properties of the different mixes are studied in detail. In order to correlate these physical properties with the chemical crosslinks formed, chemical characterisation of the different vulcanisates has also been carried out.

Covulcanisation of natural rubber and chlorobutyl rubber. Effect of curative diffusion between phases and ZnCl2 addition

Natural rubber (NR) and chlorobutyl rubber (CIIR) were compounded with various formulations containing tetramethylthiuram disulphide (TMTD), sulphur, and ZnO, and masterbatches of these compounds were blended in a 70 : 30 NR/CIIR ratio and vulcanised in a press at 150°C. Crosslink densities of vulcanisates were determined by swelling and tensile properties measured. In formulations in which the concentration gradient permitted the diffusion of TMTD and sulphur to a CIIR phase containing ZnO, tensile strengths were slightly better than 70% of the values of NR compounds of similar crosslink densities. In formulations in which TMTD and sulphur diffused to the faster curing NR phase, blend properties were also better than 70% of those of NR compounds, but at higher crosslink densities, tensile strengths and elongation at break decreased in parallel. This was attributed to failure in a layer of more highly crosslinked material formed within the NR phase close to the interface. Although ZnCl2 can crosslink CIIR to NR, thus ensuring good interfacial bonding, the addition of ZnCl2 to the CIIR masterbatch led to attack on the TMTD accelerator and a significant reduction in crosslink density and tensile properties of blends.

The Effect of Accelerator/Sulphur Ratio on the Cure Time and Torque Maximum of Epoxidized Natural Rubber

The cure time of accelerated sulphur vulcanization of Epoxidized Natural Rubber (ENR 25) was studied while one grade of unmodified natural rubber– Standard Malaysian Rubber Light (SMR L) was used as a control. Five accelerators, viz. 2-mercaptoben-zothiazole (MBT), tetramethylthiuram disulphide (TMTD), zinc dimethyldithiocarbamate (ZDMC), N-tert-butyl-2-benzothiazylsulphenamide (TBBS) and diphenylguanidine (DPG) were used in the study and the vulcanization systems used were conventional vulcanization (CV), semi-efficient vulcanization (semi-EV) and efficient vulcanization (EV). Monsanto Moving-Die Rheometer (MDR 2000) was used to determined the cure time in the temperature range of 100-180°C. The results indicate that cure time decreases exponentially with increasing temperature for the two rubbers studied. At a fixed curing temperature, ENR 25 shows shorter cure time compared to that of SMR L. This has been attributed to the activation of the double bond by the adjacent epoxide group in ENR 25. Studies of the effect of varying amounts of M Bata a fixed sulphur concentration show that cure time decreases as the accelerator concentration increases. ENR 25 shows higher torque maximum than SMR L. This observation can be related to the oxirane group which is bulky and thus accounts for increased glass; transition temperature with increase in the level of epoxidation. Of the vulcanization systems, CV shows the highest torque maximum followed by semi-EV and than EV. This trend can be attributed to the amount of active sulphurating agent which increases with increasing accelerator concentration. It was also found that the influence of accelerator/sulphur ratio becomes less significant as vulcanization temperature increases.

Effect of tetramethylthiuram disulphide on bis(triethoxysilylpropyl)tetrasulphane as coupling agent for silica in polyisoprene

Polyisoprene was compounded with 30 phr unmodified silica and with silica in the presence of modifiers bis(triethoxysilylpropyl)tetrasulphane (TESPT) and the unsymmetric polysulphide formed on reaction of TESPT with tetramethylthiuram disulphide. The modifiers improved bound rubber formation and the green strength characteristics of compounds compared with compounds with unmodified silica. However, the use of the unsymmetric polysulphide, part of which could react with hydroxy groups on the silica surface and part of which contains an accelerator moiety, gave only a marginal improvement in bound rubber formation and green strength, compared with compounds in which silica is modified with TESPT alone. Heating at 150°C is essential to improve bound rubber formation and it ensures that essentially all of the bound rubber, formed in the presence of modifiers, is firmly held to the surface, swelling in an ammonia atmosphere giving no further solublisation of rubber compared with normal swelling. Chain end radicals, formed during mixing, play no role in bound rubber formation.

Capillary Electrophoretic Determination of Tetramethylthiuram Disulphide (Thiram)

SUMMARY A simple and sensitive capillary electrophoretic method was developed for the separation and determination of Thiram in boric acid buffer by direct UV absorbance detection at λ = 254 nm. The separation behaviour of Thiram from Nabam was studied and it is dependent on pH and the nature of the buffer. The detection limit (S/N = 3) is 0.5 μg/ml for Thiram. The method was successfully applied to the analysis of wheat samples spiked with Thiram.

Cure index and activation energy of ENR 25 compared with SMR L in various vulcanization systems

Cure index of standard Malaysian rubber (SMR L) and epoxidized natural rubber (ENR 25) was determined in the temperature range from 100 to 180°C using a Monsanto Automatic Mooney Viscometer MV2000. Five accelerators, viz. 2-mercaptobenzothiazole (MBT), tetramethylthiuram disulphide (TMTD), zinc dimethyldithiocarbamate (ZDMC), N- tert-butyl-2-benzothiazyl sulphenamide (TBBS) and diphenylguanidine (DPG) were used in the study and the vulcanization systems used were conventional vulcanization (CV), semi-efficient vulcanization (semi-EV) and efficient vulcanization (EV). Results indicate that the cure index and apparent activation energy for SMR L is greater than that of ENR 25 and it decreases exponentially with increasing temperature. The lower values of the cure index and apparent activation energy in ENR 25 is attributed to the activation of a double bond by the adjacent epoxide group in ENR 25. The cure index also depends on the accelerator and vulcanization systems. Highly substituted accelerators (e.g. TBBS) tend to give a higher cure index and apparent activation energy which suggests that steric hindrance plays an important role in accelerated sulphur vulcanization of rubbers.

Effects of tetramethylthiuram disulphide (thiram) on adenine nucleotide (ATP, ADP, AMP) levels in the ciliate Tetrahymena pyriformis

Axenic cultures of Tetrahymena pyriformis GL populations were exposed to 0.40 μg/mL of tetra methylthiuram disulphide (TMTD). Doubling times and ATP, ADP and AMP levels were followed on control and treated populations at various cell densities during the exponential growth phase. For the control populations, the average generation time was 171.9 min and ATP levels were 2–8×10−14 mol/cell. For the treated populations, growth was reduced and the populations with the highest densities were more sensitive than populations treated with TMTD at the early stage of the exponential growth phase. For treated populations, ATP and ADP concentrations showed significant differences compared to the control populations. Mechanisms compensating the action of the TMTD have been observed with treated populations at 25,000 cells/mL density. Unfortunately AMP levels were unstable within control populations showing no differences with those from treated populations. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 409–413, 1999

Effects of tetramethylthiuram disulphide (thiram) on adenine nucleotide (ATP, ADP, AMP) levels in the ciliateTetrahymena pyriformis

Axenic cultures of Tetrahymena pyriformis GL populations were exposed to 0.40 μg/mL of tetra methylthiuram disulphide (TMTD). Doubling times and ATP, ADP and AMP levels were followed on control and treated populations at various cell densities during the exponential growth phase. For the control populations, the average generation time was 171.9 min and ATP levels were 2–8×10−14 mol/cell. For the treated populations, growth was reduced and the populations with the highest densities were more sensitive than populations treated with TMTD at the early stage of the exponential growth phase. For treated populations, ATP and ADP concentrations showed significant differences compared to the control populations. Mechanisms compensating the action of the TMTD have been observed with treated populations at 25,000 cells/mL density. Unfortunately AMP levels were unstable within control populations showing no differences with those from treated populations. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 409–413, 1999

Simple and sensitive method for determination of tetramethylthiuram disulphide (thiram)

A rapid, simple, direct and sensitive method has been developed for the determination of thiram (tetramethylthiuram disulphide) based on the formation of copper dimethyldithiocarbamate complex, which is rendered water-soluble by a cationic surfactant, cetytrimethylammonium bromide (CTAB). The method has been applied to the determination of thiram in synthetic mixtures, grain (wheat) samples and vegetables. © 1998 SCI

Simple and sensitive method for determination of tetramethylthiuram disulphide (thiram)

Simple and sensitive method for determination of tetramethylthiuram disulphide (thiram)

The effect of accelerator/sulphur ratio on the scorch time of epoxidized natural rubber

The Mooney scorch time of epoxidized natural rubber (ENR) was studied with natural rubber (SMR L) as a reference. The effect of sulphur to accelerator ratio on scorch behaviour in the presence of the more common types of accelerators was investigated. Mooney scorch time was studied by using the Mooney Shearing Disk Viscometer in the temperature range 100–180 °C. The results indicate that Mooney scorch time decreases exponentially with increasing temperature for ENR and SMR L. At a fixed temperature, ENR with 25 mol % epoxidation shows shorter scorch time compared with SMR L. This has been attributed to the activation of the double bond by the oxirane group. The investigation involving different types of accelerators shows that Mooney scorch time decreases in the order; N-tert-butyl-2-benzothiazylsulphenamide (TBSS) > tetramethylthiuram disulphide (TMTD) > diphenylguanidine (DPG) > 2-mercaptobenzothiazole (MBT) > zinc dimethyldithiocarbamate (ZDMC). This accelerator dependence becomes less significant as temperature increases. Studies of the effect of varying amounts of MBT at a fixed sulphur concentration show that scorch time decreases as the accelerator concentration increases. Thus, scorch time was observed to decrease in the order; conventional vulcanization system > semi-efficient vulcanization system > efficient vulcanization system for MBT accelerated compounds. However, no such predictable patterns were shown by the other types of accelerators. It was also found that the influence of accelerator/sulfur ratio becomes less significant as vulcanization temperature increases.

Pulse polarographic determination of tetramethylthiuram disulphide in commercial fungicides and rubber accelerators

A convenient and accurate analytical procedure has been developed for the trace determination of tetramethylthiuram disulphide in commercial fungicides and rubber accelerators for the purpose of quality control. Thiuram disulphide gives a well defined, diffusion controlled cathodic wave in 0.01 m pyridinium perchlorate in dimethylformamide with half-wave potential -0.36 V against a saturated calomel electrode. Determination has been made by normal pulse and differential pulse polarography using linear calibration plots.

Effects of advancement on nucleic acids in sugarbeet (Beta vulgaris) seeds

AbstractSugarbeet (Beta vulgaris) seeds which had undergone an advancement treatment germinated more quickly and showed greater germination in a standard test at 9°C than seeds which had been steeped in water. Both treatments included the fungicide, thiram (tetramethyl thiuram disulphide). Advanced seeds also emerged more quickly and showed higher establishment in the field. The levels of extractable high molecular weight (HMW) RNA and DNA from advanced, thiram-steeped and untreated seeds were compared. Advanced seeds contained significantly (P > 0.05) more HMW RNA and DNA than thiram-steeped or untreated seeds. Extractable DNA levels were higher from thiram-steeped seeds than untreated seeds but not significantly so. Cell-cycle studies on advanced seeds demonstrated an increase from 2% to 24% of root-tip nuclei with DNA contents of 4C and above. This indicates that DNA replication occurred during the advancement treatment. There was no evidence of cell division occurring, indicating that: (1) advanced seeds were arrested post-S-phase and (2) the period following DNA synthesis in sugarbeet seeds is desiccation tolerant.

Studies on clastogenic and carcinogenic potency of tetramethyl thiuram disulphide.

Tetramethyl thiuram disulphide (Thiram, TMTD), a mutagen, is analysed for its clastogenic property by using micronuclei induction studies in the bone marrow of erythrocytes of male Swiss albino mice. Three concentrations of TMTD, i.e. 100, 150 and 200 mg/kg body wt did not significantly increase the micronuclei in polychromatic erythrocytes or the ratio of poly-to normochromatic erythrocytes. The tumour initiating (10 mg and 1 mg each in 0.2 ml DMSO) and promoting (1 mg in 0.2 ml DMSO) potency of TMTD were tested in female Swiss mice by two stage skin carcinogenic model. There was no significant increase in tumours in the TMTD treated groups, either as initiator or promoter. The results indicated nonclastogenicity and non-carcinogenicity of TMTD under these experimental conditions.