Journal articles: 'Sulfur cured'

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Ansarifar, A., N. Ibrahim, and M. Bennett. "Reinforcement of Natural Rubber with Silanized Precipitated Silica Nanofiller." Rubber Chemistry and Technology 78, no. 5 (2005): 793–805. http://dx.doi.org/10.5254/1.3547914.

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Abstract The effect of a large amount of precipitated amorphous white silica nanofiller, pre-treated with bis[3-triethoxysilylpropyl-)tetrasulfide (TESPT), on the mechanical properties of a sulfur-cured natural rubber (NR) was studied. TESPT chemically adheres silica to rubber and also prevents silica from interfering with the reaction mechanism of sulfur-cure. The silica particles were fully dispersed in the rubber, which was cured primarily by using sulfur in TESPT, or, by adding a small amount of elemental sulfur to the cure system. The cure was also optimized by incorporating sulphenamide accelerator and zinc oxide into the rubber. The hardness, tear strength, tensile strength, and stored energy density at break of the vulcanizate were substantially improved when the filler was added. Interestingly, these properties were also enhanced when the rubber was cured primarily by using sulfur in TESPT.

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Wang, Hua Dong, Rui Wang, Mao Fang Huang, and Qi Yang. "Effect of Curing System on Morphological, Rheological, Thermal and Mechanical Properties of Thermoplastic Vulcanizates Based on Epoxidized Natural Rubber and Polypropylene." Advanced Materials Research 602-604 (December 2012): 690–95. http://dx.doi.org/10.4028/www.scientific.net/amr.602-604.690.

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Thermoplastic vulcanizates (TPVs) based on epoxidized natural rubber (ENR) and polypropylene (PP) were prepared in an internal mixer at 180°C. The effects of curing systems (i.e., sulfur and peroxide) on morphological, rheological, thermal and mechanical properties were studied. It is found that the sulfur cured TPVs show higher tensile strength, tear strength and elongation at break than those cured with the DCP systems. The rheological analysis indicates that TPVs cured with DCP system show lower apparent shear viscosity than those with sulfur system. SEM studies show that TPVs vulcanized with DCP system exhibit smaller and finely dispersed rubber domains, which provides it higher thermal stability than sulfur cured TPVs.

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Vennemann, Norbert, Christina Schwarze, and Claudia Kummerlöwe. "Determination of Crosslink Density and Network Structure of NR Vulcanizates by Means of TSSR." Advanced Materials Research 844 (November 2013): 482–85. http://dx.doi.org/10.4028/www.scientific.net/amr.844.482.

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Unfilled vulcanizates based on natural rubber (NR) were investigated by temperature scanning stress relaxation (TSSR) measurements. Different sulfur based cure systems, i.e. conventional (CV), semi-efficient (SEV) and efficient (EV) vulcanization system, were used to prepare the vulcanizates. It was found that sulfur/accelerator - ratio has a strong impact on the shape of the relaxation spectrum, deduced from TSSR measurements. By deconvolution of the relaxation spectra, peak separation was performed and 3 different peaks were found in case of CV - cured samples. In contrast, only a single peak was found, in case of the EV-cured sample. After thiolamine treatment the shape of the relaxation spectra altered significantly in case of the CV-cured sample whereas the spectra of the SEV-and EV-cured sample exhibited only slight differences. Additionally, the crosslink density of the samples decreased after thiolamine treatment. This is due to selective cleavage of polysulfidic crosslinks. It has been concluded, that the significant peak in the relaxation spectrum at about 120 °C can be attributed to the cleavage of polysulfidic crosslinks. Furthermore, a linear relationship between the percentage of polysulfidic crosslinks and the sulfur/accelerator - ratio is assumed.

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Joseph, Anu Mary, Benny George, K. N. Madhusoodanan, and Rosamma Alex. "CURE CHARACTERISTICS OF DEVULCANIZED RUBBER:THE ISSUE OF LOW SCORCH." Rubber Chemistry and Technology 90, no. 3 (2017): 536–49. http://dx.doi.org/10.5254/rct.17.83737.

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ABSTRACT We investigate the reasons behind the observed low scorch during the revulcanization of devulcanized rubber. Mechanically devulcanized carbon black filled natural rubber vulcanizates originally cured by conventional vulcanization (CV), semiefficient vulcanization (semi EV), efficient vulcanization (EV), and peroxide systems as well as buffing dust obtained from pre-cured tread with known formulation were used. Revulcanization of these devulcanized samples using sulfur/sulfonamide system led to the following observations; irrespective of the type of sulfur cure system used for the initial vulcanization of the rubber, (i) the devulcanized samples cured without pre-vulcanization induction time and (ii) devulcanized samples prepared from peroxide vulcanized rubber cured with scorch safety. Based on the earlier reports that solvent extraction of devulcanized rubber did not improve the scorch time during revulcanization, the role of zinc bound non-extractable moieties was investigated using devulcanized rubber prepared from activator-free vulcanizates, which disproved the role of such moieties. This confirmed that the scorch reducing moieties should be attached to the rubber main chain, which can be unreacted crosslink precursors and cyclic sulfides left after the initial accelerated sulfur vulcanization of the original sample. The ability of pre-vulcanization inhibitor to induce scorch safety when devulcanized rubber is revulcanized as such, without adding any virgin rubber, proved that mercaptobenzothiazole (MBT) generated from crosslink precursors is the cause of low scorch. Acetone extracted devulcanized rubber samples prepared from tetramethyl thiuramdisulfide (TMTD) cured natural rubber, which does not follow the MBT pathway when revulcanized, cured with scorch safety, which further proved the role of MBT. Based on the previous reports and our results, it is obvious that powdering of rubber vulcanizate and devulcanization processes have no role on the low process safety of these materials, but it is inherent to the initial accelerated sulfur vulcanization chemistry undergone by these materials.

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Ansarifar, A., L. Wang, R. J. Ellis, and S. P. Kirtley. "The Reinforcement and Crosslinking of Styrene Butadiene Rubber with Silanized Precipitated Silica Nanofiller." Rubber Chemistry and Technology 79, no. 1 (2006): 39–54. http://dx.doi.org/10.5254/1.3547928.

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Abstract Synthetic precipitated amorphous white silica nanofiller was used to reinforce and crosslink styrene-butadiene rubber (SBR). The silica surfaces were pre-treated with bis[3-triethoxysilylpropyl-)tetrasulfide (TESPT) bifunctional organosilane. TESPT chemically adheres silica to rubber and also prevents silica from interfering with the reaction mechanism of sulfur-cure. The silica particles were fully dispersed in the rubber, which was cured primarily by using sulfur in TESPT, or, by adding elemental sulfur to the cure system. The cure was also optimized by incorporating different accelerators and activators in the rubber. This study showed that the silica particles could be used both as crosslinking and reinforcing filler in the rubber.

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Yang, Liu, Kaikai Liu, and Aihua Du. "The Effect of Network Structure on Compressive Fatigue Behavior of Unfilled Styrene-Butadiene Rubber." Advances in Materials Science and Engineering 2020 (April 20, 2020): 1–9. http://dx.doi.org/10.1155/2020/6729754.

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The effect of network structure on dynamic compressive fatigue behavior and static compressive mechanical properties of styrene-butadiene rubber (SBR) were investigated. A series of SBR compounds with different amounts of sulfur and dicumyl peroxide (DCP) were prepared, and their crosslinking densities were calculated using the Flory–Rehner equation. Compressive fatigue resistance and creep behavior of the vulcanizates were performed on a mechanical testing and simulation (MTS) machine. The fatigue damage surface of SBR vulcanizates before and after a dynamic compressive fatigue test was observed with a scanning electron microscopy (SEM). The results suggested that the surface of the samples was badly damaged as the number of compressive cycles increased. By comparison, compressive fatigue caused less surface damage to sulfur-cured SBR than to peroxide-cured SBR. The peroxide-cured SBR samples showed higher energy dissipation than sulfur-cured SBR during cyclic compression. The peroxide-cured SBR showed lower creep strain and compression set than the sulfur-cured SBR. The -Sx- linkages provided by the sulfur curing system allow dynamic compressive deformation but suffer from poor static compressive resistance. However, the carbon-carbon linkages from DCP are irreversible and provide higher resistance to static compressive stress, but they do not show obvious dynamic compressive fatigue resistance.

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Tuampoemsab, Surakit, Apaipan Rattanapan, and Pornsri Pakeyangkoon. "Antagonism of Natural Anti- and Pro-Oxidants in Synthetic Polyisoprene Rubber Vulcanizates." Advanced Materials Research 979 (June 2014): 159–62. http://dx.doi.org/10.4028/www.scientific.net/amr.979.159.

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This research was to elucidate the antagonism of natural anti-and pro-oxidants in synthetic polyisoprene rubber (IR) grade 2200 as a model system. Alanine and linoleic acid was chosen as natural anti-and pro-oxidants, respectively. These two amino acids were directly added into the rubber by mixing in two-roll mill. Peroxide vulcanization and three types of the sulfur curing system, i.e., conventional vulcanization (C.V.), efficient vulcanization (E.V.) and semi-E.V. have been studied. Cure properties of the rubber compounds were characterized with moving die rheometer (MDR) at 150 and 170°C for sulfur and peroxide vulcanizing systems, respectively. The compounded rubbers were divided into two parts. The former was pressed on a hydraulic hot press machine and cut to a dumbbell specimen according to ASTM D412 type C. Then, the rubber specimens were subjecting to accelerate the thermal oxidative degradation at 100°C under air-circulating oven with various times. The deterioration of the aged rubber specimens was determined by tensile test. The latter was shaped and characterized by ozone resistance in accordance with ISO 1431/1. For tensile test, the results showed that only the C.V. system of the sulfur cure, the tensile stress at 200% strain of IR comprised alanine and linoleic acid with the ratio of 1:1 was higher predominantly than that of the cured IR control. In addition, the peroxide cured IR mixed with alanine and linoleic acid cannot be passed the heat aging for 96 h. For the ozone resistance, the results exhibited that all specimens appeared uncountable number of crack but only the IR cured by peroxide presented the length of crack less than 1 mm (C-3). It might be concluded from the experiment that anti-oxidative activity of the alanine plays a vital role in the rubber vulcanizate only for C.V. system. However, the existing of both alanine and linoleic acid in the sulfur cured IR was not outstandingly changed for the ozone resistance but not that for the peroxide cured IR.

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Walton, Kim L., Morgan M. Hughes, and Deepak R. Parikh. "A New Class of Ethylene—Propylene—Diene Terpolymers Produced from Constrained Geometry Metallocene Catalysts." Rubber Chemistry and Technology 74, no. 4 (2001): 688–700. http://dx.doi.org/10.5254/1.3544967.

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Abstract Until recently, ethylene/propylene/diene (EPDM) terpolymers have been manufactured exclusively using vanadium based Ziegler—Natta catalyst systems. The vanadium based catalysts are known to have both product and process limitations. These limitations are due to a complex combination of factors including monomer reactivity, catalyst activity, reactor temperatures and pressures. Single-site metallocene constrained geometry catalyst (CGC) technology enables the manufacture of EPDM terpolymers at higher reactor temperature and catalyst efficiency than standard Ziegler—Natta catalyst systems. The unique combination of monomer, catalyst and process technology enables the manufacture of highly crystalline EPDMs having ethylene contents over 90 wt %. This study investigated these new highly crystalline EPDM terpolymers and their differentiation from commercially available EPDMs. The results indicated that these new EPDMs had very high green strength and barrier properties, yet could be cured by conventional vulcanization techniques. The cure response of these EPDMs to either peroxide or sulfur increased with increasing ethylene content. Sulfur cured vulcanizates had much higher tensile strength than peroxide cured vulcanizates. These new EPDMs demonstrated utility as additives to enhance the abrasion, hot tear, and tensile properties of natural rubber compounds. Sponge compounds, having the unique combination of polyethylene physical properties and the utility of sulfur vulcanization were developed from these new polymers.

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Gopisathi, Shibulal, Changsin Park, Yang Il Huh, et al. "ENHANCING THE REVERSION RESISTANCE, CROSSLINKING DENSITY AND THERMO-MECHANICAL PROPERTIES OF ACCELERATED SULFUR CURED CHLOROBUTYL RUBBER USING 4,4′-BIS (MALEIMIDO) DIPHENYL METHANE." Rubber Chemistry and Technology 92, no. 1 (2019): 110–28. http://dx.doi.org/10.5254/rct.18.82605.

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ABSTRACT Vulcanizates of chlorobutyl rubber (CIIR) with the accelerated sulfur generally exhibit poor crosslinking density owing to the low level of unsaturation in the backbone of CIIR. Therefore, the sulfur cured CIIR shows inferior thermo-mechanical properties at elevated temperature. In addition to this, the vulcanization of CIIR with accelerated sulfur is limited at higher temperature due to reversion. To solve these problems, 4,4′-bis (maleimido) diphenyl methane (BMDM) was applied as a crosslinking additive along with the accelerated sulfur. The detailed curing studies have proved that the presence of BMDM greatly enhanced the rheometric torque and the reversion resistance while curing CIIR with accelerated sulfur even at higher vulcanization temperature. Moreover, the crosslinking densities of the sulfur cured CIIR have increased by 109% with the use of 1 phr BMDM and further rose to 380% with 5 phr BMDM. The improved crosslink density could enable reduction of the compression set of the sulfur cured CIIR to around 40% at 100 °C when it was vulcanized in the presence of 5 phr BMDM. The kinetic studies revealed that incorporation of this additive does not adversely affect the original vulcanization behavior of CIIR with accelerated sulfur, instead it marginally improved the speed of the vulcanization.

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10

Gibala, David, and Gary R. Hamed. "Cure and Mechanical Behavior of Rubber Compounds Containing Ground Vulcanizates. Part I—Cure Behavior." Rubber Chemistry and Technology 67, no. 4 (1994): 636–48. http://dx.doi.org/10.5254/1.3538699.

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Abstract SBR compounds containing ground vulcanizates of known composition and cure state were prepared and the cure behavior studied. Decreases in scorch times and maximum rheometer torques were observed when ground vulcanizates were added to the SBR compounds. Two primary phenomena are proposed to explain these findings: (1) migration of sulfur from the matrix rubber to the ground vulcanizate (causing torque reduction) and (2) migration of accelerator fragments from the ground vulcanizate to the matrix (causing decreased scorch time). The first proposal is based on direct measurement of sulfur concentrations in both ground particles and the matrix. The second is based on the detection, by high performance liquid chromatography, of mercaptobenzothiazole in the extract from ground vulcanizates. The second also is inferred from the fact that ground vulcanizate particles cured with peroxide do not alter scorch time. Moreover, a compound containing sulfur and ground (accelerated-sulfur vulcanized) rubber, but no added accelerator, nonetheless exhibits acceleration of cure.

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Tsou, Andy H., Alistair D. Westwood, Jonathan S. Schulze, and Erik G. Herbert. "Cure State Distributions in Rubbers by Dynamic Nano-Indentation." Rubber Chemistry and Technology 77, no. 4 (2004): 678–90. http://dx.doi.org/10.5254/1.3547844.

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Abstract A depth-sensing and frequency-specific dynamic indentation technique was used to determine the spatial distributions of dynamic moduli, including storage (E′) and loss moduli (E″), in poly-cis-1,4-butadiene (BR) and brominated poly(isobutylene-co-p-methylstyrene) (BIMS) rubbers with varying degrees of cure and with or without carbon black fillers as a function of penetration depth. The BR rubbers were cured with sulfur and a sulfur accelerator and the BIMS rubbers were cured using zinc oxide and stearic acid. The dynamic modulus reached a constant bulk value after the Berkovich indentor penetrated into rubbers far beyond the surface. Spatially averaged bulk dynamic moduli thus determined using the nano-indentation technique were compared with the tensile extensional moduli and the frequency-dependent dynamic tensile moduli both measured from the bulk rubbers. Spatial distributions of cure and its dependence on penetration depth were evaluated as functions of cure level, filler loading, and sample surface preparation. The ultimate goal is to provide quantitative cure distribution maps in rubber blends and compounds through a combination of Atomic Force Microscopy (AFM) and dynamic nano-indentation characterization.

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Kim, Ji-Han, Go-Eun Hong, Chang-Won Pyun, Woojoon Park, and Chi-Ho Lee. "Enhancement of physicochemical, microbiological and sensory properties of dry-cured loin by using processed sulfur-fed pigs." Animal Production Science 56, no. 11 (2016): 1936. http://dx.doi.org/10.1071/an14680.

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The present study showed that processed sulfur supplementation and processing condition affected changes in physicochemical, microbial and sensory properties of dry-cured loin. The pigs were divided into two groups at the fattening phase: non-sulfur-fed pigs (NSFP) and 0.3% processed sulfur-fed pigs (SFP) in fattening phase. The crude fat content of SFP was lower than that of NSFP in raw meat and dry-cured loin. Lipid and pigment oxidation were suppressed in SFP compared with NSFP during whole process. Lightness of SFP was significantly higher than that of NSFP during storage. SFP showed higher colour stability than did NSFP during storage. Moreover, microbial spoilage of dry-cured loin was greatly prevented in SFP compared with NSFP. Free amino acids related to taste in SFP were significantly higher than those in NSFP. Polyunsaturated fatty acid of dry-cured loin from SFP group was higher than that of NSFP, while saturated fatty acid of NSFP was significantly higher than that of SFP. SFP had higher preference and flavour scores than did NSFP in a sensory test. Feeding processed sulfur improved the meat-quality characteristics and extended the shelf-life of meat products.

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Manleh, Chanida, Charoen Nakason, Natinee Lopattananon, and Azizon Kaesaman. "Effect of Sulfur Donor on Properties of Thermoplastic Vulcanizates Based on NR/PP." Advanced Materials Research 626 (December 2012): 54–57. http://dx.doi.org/10.4028/www.scientific.net/amr.626.54.

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Thermoplastic vulcanizates based on natural rubber and polypropylene blend (NR/PP) was prepared via dynamic vulcanization by melt mixing process at 180°C and a rotor speed of 60 rpm. Three types of vulcanizing agent (i.e., Tetramethyl thiuram disulfide (TMTD), 4,4 Dithiodimorpholine (DTDM) and Dipentamethylene thiuram tetrasulfide (Tetrone A)) were used to cure the rubber phase of NR/PP blends. Influence loading levels of sulfur donor at 1, 2 and 3 phr on dynamic properties and crosslink density were studied. The result showed that the dynamically cured NR/PP blends with Tetrone A gave higher mechanical properties, storage modulus, complex viscosity, and crosslink density with the lower value of tanδ than those of the blends with TMTD and DTDM. Furthermore, the storage modulus, complex viscosity and crosslink density of TPVs increased with increasing loading levels for all types of sulfur donor. It was also found that thermal stability of dynamically cured NR/PP blends is higher than that of the pure NR.

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Chokcharoenchai, Bandith, Nontawate Kraitape, Thanapon Kattiyaboot, Rattiya Rodsantia, and Chanchai Thongpin. "Cure Characteristics, Morphology and Mechanical Properties of Partially Cured NBR Blended with NR." Advanced Materials Research 747 (August 2013): 463–66. http://dx.doi.org/10.4028/www.scientific.net/amr.747.463.

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This research is aimed to study the effect of partially cured acrylonitrile butadiene styrene rubber (NBR) blended with natural rubber (NR) and vulcanized with sulfur system. The research started with compounding NBR with zinc chloride, ZnCl2 in an internal mixer. The cure characteristic of the NBR compound was investigated using moving die rheometer (MDR). The compound NBR is then blended in NR at 160 °C. The temperature was then lowered to 50 °C before the addition of sulfur cure additives. Cure characteristic of the rubber blends were investigated and found that the increasing of NBR caused shortened in scorch time. Rubber blends morphology was investigated using SEM. NBR was found dispersed in NR phase. The particle size of dispersed NBR was increased with its content. This is due to high viscosity of NBR and hence larger particles will be obtained. The de-bonding at the interface was shown in SEM micrograph. The compound is then filled with fragrance absorbed fumed silica. The fragrance silica was added during milling of NBR and NR. The releasing behavior of fragrance was found dependent upon NBR/NR ratio.

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Kako, Yasuhiko, Shigetaka Watanabe, Yutaka Higashimura, and Kenji Matsunobu. "Internal Partial Discharge Resistance of Sulfur Cured Rubber." IEEJ Transactions on Fundamentals and Materials 113, no. 10 (1993): 696–702. http://dx.doi.org/10.1541/ieejfms1990.113.10_696.

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JANA, GOUTAM K., RAM N. MAHALING, TANMOY RATH, ANNA KOZLOWSKA, MAREK KOZLOWSKI, and CHAPAL K. DAS. "Mechano-chemical recycling of sulfur cured natural rubber." Polimery 52, no. 02 (2007): 131–36. http://dx.doi.org/10.14314/polimery.2007.131.

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Tajamul Basha, Sanha Kaizer, R. Divya, Ashwini U. Menon, Neelesh Ashok, and Meera Balachandran. "Cure and Degradation Kinetics of Sulfur Cured Nanocomposites of EPDM-NBR Rubber Blends." Materials Today: Proceedings 5, no. 11 (2018): 23586–95. http://dx.doi.org/10.1016/j.matpr.2018.10.147.

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Ibrahim, Siti Zulaikha, Che Mohd Som Said, Mohamad Asri Ahmad, and Azemi Samsuri. "Preliminary Study on Curing of Thick Rubber Article." Advanced Materials Research 1134 (December 2015): 23–27. http://dx.doi.org/10.4028/www.scientific.net/amr.1134.23.

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In this study, several batches of natural rubber (SMR L) were compounded with three different types of accelerators, which were N-cyclohexylbenzothiazole-2-sulphenamide (CBS), diphenylguanidine (DPG) and zinc diethyldithiocarbamate (ZDEC). ZDEC is known as an ultrafast accelerator. The rubber compounds were cured at 140°C, 130°C, 120°C, 110°C and 100°C in accordance with the temperature gradients observed within the thick rubber block. The main aim of this study is to cure the rubber at each temperature region to the same cure time as that of the outermost region (20 minutes at 140°C). The amount of sulfur and accelerator were adjusted accordingly at each curing temperature to match the state of cure at 140°C. The state of cure of of the vulcanized rubbers were measured using hardness and tensile strength. The same state of cure is achieved if the hardness and tensile strength value are within ±2 IRHD and ±3 MPa, respectively with that of the control vulcanized rubber (hardness and tensile strength cured at 140°C). The results shows that the hardness and tensile strength of the vulcanized rubber at each temperature region are within the expected margins. The results clearly indicated that the type and amount of accelerators, and the amount of sulfur were correctly chosen at each temperature.

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Boonkerd, Kanoktip, and Wanwisa Limphirat. "The Influence of Chemical Compounds on the Sulfur K-Edge X-Ray Absorption near Edge Spectrum of the Vulcanized Rubber." Advanced Materials Research 905 (April 2014): 128–31. http://dx.doi.org/10.4028/www.scientific.net/amr.905.128.

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The vulcanized styrene-butadiene rubber (SBR) was studied using X-ray absorption near edge spectroscopy (XANES). The effect of the sulfur containing molecules left over in the sample on the precision of the sulfur K-edge XANES spectrum was focused. The six rubber compounds used here were vulcanized with different curing systems including convention, semi-efficiency and efficiency. For each compound, the measurements were preformed on two different samples which were the untreated and treated chloroform samples. The results showed when compounds were cured with conventional or semi-efficient vulcanization system, the XANES spectra between the untreated and treated sample was changed with very high sulfur to accelerator ratio. On the other hand, the tremendous dissimilarity was observed when compounds were cured with the efficient vulcanization system. Thus the sample treatment was necessary when using XANES to identify sulfur crosslink.

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Liu, Zhigang, Ru Wang, Chaohui Zhang, Shanshan Guo, and Peijie Chen. "A case of vitiligo cured with cucumber and sulfur." Phytotherapy Research 33, no. 4 (2019): 1241–42. http://dx.doi.org/10.1002/ptr.6309.

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Klueppel, M., and G. Heinrich. "Network structure and mechanical properties of sulfur-cured rubbers." Macromolecules 27, no. 13 (1994): 3596–603. http://dx.doi.org/10.1021/ma00091a022.

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Oikawa, Hidetoshi. "Dynamic light scattering study on sulfur-cured natural rubber." Journal of Macromolecular Science, Part B 31, no. 1 (1992): 49–63. http://dx.doi.org/10.1080/00222349208215457.

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Grima, M. M. Alvarez, A. G. Talma, R. N. Datta, and J. W. M. Noordermeer. "New Concept of Co-Agents for Scorch Delay and Property Improvement in Peroxide Vulcanization." Rubber Chemistry and Technology 79, no. 4 (2006): 694–711. http://dx.doi.org/10.5254/1.3547961.

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Abstract Peroxide cure is an important and widely used cure system for rubber. Several properties obtained via peroxide vulcanization are superior and not achievable with sulfur vulcanization, e.g.: aging resistance, no reversion and low compression set. However, other properties such as tensile strength and dynamic properties, are inferior to those of sulfur vulcanizates. The use of co-agents in peroxide cure leads to a certain extent to improvement in mechanical properties such as tensile strength. Nevertheless the properties are still inferior with respect to mechanical/dynamical properties of sulfur-cured articles. If these properties can be improved, the range of applications of peroxide cure in the rubber industry can be significantly broadened. Scorch is a common problem in peroxide cure, especially for injection molding and extrusion applications. Several additives can help to improve scorch safety, however, they always result in a lower peroxide efficiency, thus inferior vulcanizate properties. In the present study a new concept of co-agents for peroxide vulcanization is introduced. This new concept consists of the use of a combination of a bismaleimide type co-agent, like N,N′-m-phenylenedimaleimide (BMI-MP), and a sulfur containing compound, like dipentamethylenethiuram tetrasulfide (DPTT). This combination provides scorch safety and at the same time improves the mechanical properties of the vulcanizates. Within the bismaleimide type co-agents N,N′-p-phenylenedimaleimide (BMI-PP) provides better mechanical properties than BMI-MP. The concentration of co-agent and sulfur containing compound have a big influence on the scorch time and on the mechanical properties. Optimal properties are reached with 4 phr of co-agent and 0.7 to 0.96 phr of sulfur containing compound.

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Rajesh, C., K. C. Manoj, G. Unnikrishnan, and E. Purushothaman. "Investigation on Ageing Characteristics of Short Nylon-6 Fibre Reinforced NBR Composites." Progress in Rubber, Plastics and Recycling Technology 24, no. 4 (2008): 239–53. http://dx.doi.org/10.1177/147776060802400402.

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The ageing characteristics of nylon 6 fibre reinforced NBR composites have been analysed by exposing them to degrading agents such as heat and gamma (γ) radiation. The effects of fibre loading, curing systems and bonding agents on the retention of tensile properties of the composite samples which were exposed to these degrading agents have been studied. The addition of fibres improves the ageing resistance of NBR. The DCP cured composites exhibit a reduction in their ability to retain the elastic modulus as the thermal ageing period increases from 7 to 14 days, whereas sulfur cured composites show a reverse trend. The efficiency for the retention of modulus of sulfur cured samples increases as the dosage of γ-radiation increases from 5 to 10 Mrad whereas a higher dose of 15 Mrad lowers it. However, the DCP cured samples show a continuous reduction in their ability to retain modulus. The composite system containing hexa-resorcinol as the bonding agent has better resistance to heat and γ-radiation than the unbonded one.

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Hamed, Gary R., and Kanoktip Boonkerd. "EFFECT OF CURE EFFICIENCY ON PROPERTIES OF GUM AND BLACK FILLED NATURAL RUBBER VULCANIZATES." Rubber Chemistry and Technology 84, no. 2 (2011): 229–42. http://dx.doi.org/10.5254/1.3577535.

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Abstract Effects of the sulfur cure efficiency on the reversion behavior and the normal and edge-cut tensile strength of gum and black filled natural rubber (NR) vulcanizates were studied. N, N-dicyclohexyl-2-benzothiazole sulfenamide (DCBS) was used as an accelerator. A series of five vulcanizates with high to low cure efficiencies was prepared by increasing the sulfur (S) to DCBS ratios within the range of 0.26–6.66. All vulcanizates were formulated to have the same crosslink density. The degree of reversion (%) calculated from cure curves of gum and black filled NR at 20 min above the cure time (tc100) passed through maximum with decreasing cure efficiencies. For both gum and black filled NR, the highest degree of reversion (%) was observed at the S/DCBS ratio of 1.17. The normal tensile strengths of gum and black filled NR were directly proportional to the cure efficiency. For gum NR vulcanizates, the edge-cut tensile strength was markedly influenced by cure efficiency. Similar to the normal tensile strength, the gum NR vulcanizates cured with the lowest cure efficiency showed the lowest edge-cut tensile strength. Effect of the cure efficiency on the edge-cut tensile strength was less in the case of black filled NR vulcanizates. However, the black filled NR vulcanizates cured with the lowest cure efficiency also showed the lowest edge-cut tensile strength. The cut tip characteristics of the fracture specimens were investigated using scanning electron microscopy. The gum specimens showed only the simple lateral cracking pattern, while all black filled specimens showed the longitudinal cracking pattern. Four different cracking patterns of the black filled specimens were identified. The distribution of cracking patterns depended strongly on the size of precut and the cure efficiency.

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Kim, Ji-Han, Ha-Young Noh, Gyum-Heon Kim, et al. "Physicochemical and sensory properties of dry-cured ham with dietary processed-sulfur supplementation." Animal Production Science 57, no. 1 (2017): 191. http://dx.doi.org/10.1071/an14556.

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The aim of the present study was to explore the changes in physicochemical and sensory properties of dry-cured ham (from pigs that received a dietary supplement of processed sulfur, PS), as a function of the level of dietary PS. The following three groups were tested: (1) commercial basal feed (control, CON); (2) 0.1% of PS in the control diet (T1); and (3) 0.3% of PS in the control diet (T2). Dry-cured ham from T2 pigs had a higher moisture content and lower fat concentration than did that from the control pigs. Dry-cured ham T1 and T2 samples showed excellent lipid oxidation stability during storage and showed positive aroma scores in comparison with CON samples. Nonetheless, the total microbial plate count of dry-cured ham T1 (or T2) samples was significantly lower than that of CON samples, and volatile basic nitrogen of T1 (or T2) samples was higher than that of CON samples (P < 0.05). Concentrations of total free amino acids and sulfur-containing amino acids of ham T1 or T2 samples were significantly (P < 0.05) higher than those of control samples. Concentrations of polyunsaturated fatty acids of ham T1 and T2 samples were significantly higher than that of CON samples, whereas concentration of saturated fatty acids of CON samples was significantly higher. Thus, dry-cured ham from pigs receiving 0.3% PS in the diet showed the lowest fat concentration, increased nutrient quality and extended shelf life.

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Tang, Zhenghai, Yingjun Liu, Qingyi Huang, Jinshan Zhao, Baochun Guo, and Liqun Zhang. "A real recycling loop of sulfur-cured rubber through transalkylation exchange of C–S bonds." Green Chemistry 20, no. 24 (2018): 5454–58. http://dx.doi.org/10.1039/c8gc02932f.

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Wręczycki, Jakub, Dariusz Bieliński, and Rafał Anyszka. "Sulfur/Organic Copolymers as Curing Agents for Rubber." Polymers 10, no. 8 (2018): 870. http://dx.doi.org/10.3390/polym10080870.

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It is widely acknowledged that waste sulfur generated from the petroleum industry creates huge storage and ecological problems. Therefore, the various methods of utilization are becoming increasingly attractive research topics worldwide. The thermal ability of elemental sulfur to homolytic cleavage of S8 rings enables its free radical copolymerization with unsaturated organic species and the obtaining of chemically stable polymeric materials. Here we report a novel possibility to use sulfur/organic copolymers obtained via “inverse vulcanization” as curatives for rubber. For this purpose, several various sulfur/organic copolymers were synthesized and analyzed from the point of view of their performance as rubber crosslinking agents. Solvent extraction was used to purify sulfur/organic copolymers from unreacted (elemental) sulfur. Thermal properties of the prepared copolymers were characterized by thermogravimetric analysis and differential scanning calorimetry (TGA–DSC). Crosslink density and structure of cured elastomers was studied by equilibrium swelling, thiol-amine analysis and freezing point depression. Mechanical properties of the vulcanizates were determined under static and dynamic conditions (DMA—dynamic mechanical analysis). It is proved that the utilization of sulfur/organic copolymers as curatives enables an effective crosslinking process of rubbers. Taking into account the results of a crosslink density analysis and mechanical properties of the vulcanizates cured with purified copolymers, it is evident that relatively long copolymer macromolecules are also involved in the formation of chemical bonds between unsaturated rubber macromolecules.

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Kojima, M., K. Ogawa, H. Mizoshima, M. Tosaka, S. Kohjiya, and Y. Ikeda. "Devulcanization of Sulfur-Cured Isoprene Rubber in Supercritical Carbon Dioxide." Rubber Chemistry and Technology 76, no. 4 (2003): 957–68. http://dx.doi.org/10.5254/1.3547784.

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Abstract A new devulcanization process that utilizes supercritical CO2 (scCO2) along with devulcanizing reagents was studied. Unfilled polyisoprene rubber samples (vulcanizates) with different crosslink distributions were prepared by controlling the cure time and the curatives. Each of the vulcanizates was subjected to the Soxhlet extraction using azeotropic acetone/chloroform to remove residual curatives. The devulcanization was performed at various temperatures (140–200 °C) in the presence of scCO2 for 60 min. The product was fractionated into sol and gel components, and molecular weight of the sol component and the crosslink density of the gel component were determined. Thiol-amine reagent was found to be effective among several devulcanizing reagents; the molecular weight of the resulted sol component was about tens of thousands and the crosslink density of gel component decreased substantially from the initial ones. Yield of the sol component increased with the increase in the CO2 pressure. In the supercritical fluid state of CO2, the vulcanizate was more efficiently devulcanized than in an ordinary gaseous state of CO2. The sol fraction depended considerably on the crosslink distribution in the vulcanizate. These results suggest that the devulcanizing reagents penetrate and diffuse into the vulcanizate in the presence of scCO2.

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Ding, R., and A. I. Leonov. "An Approach to Chemorheology of a Filled SBR Compound." Rubber Chemistry and Technology 72, no. 2 (1999): 361–83. http://dx.doi.org/10.5254/1.3538808.

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Abstract Three steps in complex chemorheological studies are necessary for complete rheological characterization of filled rubbers during cross-linking reaction. They include: (i) kinetic studies of cross-linking reaction, (ii) rheological studies of green rubber compounds, and (iii) correlation between the rheological parameters and the degree of cure. Basic experiments in the steps (i)–(iii) and their modeling are presented in this paper on the example of a filled SBR compound with sulfur accelerated vulcanization. The approach provides a unique possibility to trace therheological properties of rubber compounds from the green to completely cured states.

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Bakar, Rohani Abu, Rosiyah Yahya, and Seng Neon Gan. "COMPARISON BETWEEN RICE HUSK SILICA-FILLED EPOXIDIZED NR CROSS-LINKED WITH FUMARIC ACID AND VULCANIZED WITH SULFUR." Rubber Chemistry and Technology 92, no. 2 (2018): 286–97. http://dx.doi.org/10.5254/rct.18.81554.

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ABSTRACT A wide variety of fillers are used in the rubber industry to modify the properties of rubber compounds and reduce the cost of products in different applications. Silica produced from rice husk could be an alternative filler to commercial precipitated silica widely used in sulfur-vulcanized rubber formulations. High purity amorphous silica (&gt;99% SiO2) was produced after pretreatment of rice husk with dilute sulfuric acid before combustion at 600 °C. Epoxidized NR (ENR) with 50 mol% epoxide groups (ENR50) containing various silica loadings was cured with fumaric acid via reactions of the epoxide group with –COOH, whereas sulfur vulcanization used the carbon–carbon double bonds, as confirmed by Fourier transform infrared spectroscopy (FTIR) analysis. Increasing silica loading in both of types of samples led to an increase in rheometer torque and a decrease in percentage of solvent swelling due to the stiffening effect of silica, with no change in glass-transition temperature, which presumably was due to no chemical reaction between silica and ENR. The tensile strength of fumaric acid–cured ENR50 slightly increased with increasing silica loading and remained unchanged upon aging. The sulfur-vulcanized ENR50 containing 30 phr silica exhibited higher tensile strength, but further increase of silica weakened these properties. After aging, the tensile strength reduced by 5–7 MPa. Fumaric acid–cured rubbers have shown superior aging properties.

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Zhang, Bowen, Samuel Petcher, and Tom Hasell. "A ternary system for delayed curing inverse vulcanisation." Chemical Communications 55, no. 72 (2019): 10681–84. http://dx.doi.org/10.1039/c9cc04380b.

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Unreacted sulfur and crosslinkers readily separate without mixing, but the final product is a crosslinked solid. We report a stable pre-polymer solution that can be later cured to the final form as needed.

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Zheng, Sijia, Mengchen Liao, Yang Chen, and Michael A. Brook. "Dissolving used rubber tires." Green Chemistry 22, no. 1 (2020): 94–102. http://dx.doi.org/10.1039/c9gc03545a.

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Reductive silylation cleaves S–S crosslinks in used automotive rubbers, allowing recovery of polymeric oils in up to 93% yield. The oils can undergo oxidative crosslinking to give new elastomers, closing the loop for sulfur-cured rubbers.

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34

Dziemidkiewicz, Anna, Magdalena Maciejewska, and Martyna Pingot. "Thermal analysis of halogenated rubber cured with a new cross-linking system." Journal of Thermal Analysis and Calorimetry 138, no. 6 (2019): 4395–405. http://dx.doi.org/10.1007/s10973-019-08881-7.

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Abstract The aim of this work was to examine the influence of new curing agents proposed for brominated butyl rubber (BIIR) on the cross-linking process of rubber compounds and the thermal behavior of the vulcanizates. Rubber blends that were filled with carbon black and contained acetylacetonates of different transition metals in the presence of triethanolamine (TEOA) as new cross-linking agents were prepared. The performed studies showed that metal acetylacetonates (Me(acac)) are effective cross-linking agents for BIIR, which was confirmed by high values of the torque increment (∆M) and significant cross-linking degree of the vulcanizates (α(T)). The most active curing agent seems to be iron acetylacetonate (Fe(acac)). Its application results in a shorter optimal vulcanization time, lower onset vulcanization temperature and similar vulcanization enthalpy compared to the BIIR cured with a sulfur curing system. The BIIR vulcanizates cured with Me(acac) reveal good mechanical properties with tensile strengths in the range of 9–14 MPa and better damping properties comparing to the sulfur-cured rubber. The proposed curing agents do not significantly affect the thermal stability of the BIIR vulcanizates.

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35

Kojima, Masaaki, Masatoshi Tosaka, and Yuko Ikeda. "Chemical recycling of sulfur-cured natural rubber using supercritical carbon dioxide." Green Chemistry 6, no. 2 (2004): 84. http://dx.doi.org/10.1039/b314137c.

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Loo, Kheng‐Hooi, Lee Tin Sin, Soo‐Tueen Bee, et al. "Electron Beam Irradiation to Recrosslink Devulcanized Sulfur Cured Rubber Blended Polypropylene." Polymer Engineering & Science 59, no. 5 (2019): 1017–27. http://dx.doi.org/10.1002/pen.25057.

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37

Zedler, Łukasz, Xavier Colom, Javier Cañavate, Mohammad Reza Saeb, Józef T. Haponiuk, and Krzysztof Formela. "Investigating the Impact of Curing System on Structure-Property Relationship of Natural Rubber Modified with Brewery By-Product and Ground Tire Rubber." Polymers 12, no. 3 (2020): 545. http://dx.doi.org/10.3390/polym12030545.

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The application of wastes as a filler/reinforcement phase in polymers is a new strategy to modify the performance properties and reduce the price of biocomposites. The use of these fillers, coming from agricultural waste (cellulose/lignocellulose-based fillers) and waste rubbers, constitutes a method for the management of post-consumer waste. In this paper, highly-filled biocomposites based on natural rubber (NR) and ground tire rubber (GTR)/brewers’ spent grain (BSG) hybrid reinforcements, were prepared using two different curing systems: (i) sulfur-based and (ii) dicumyl peroxide (DCP). The influence of the amount of fillers (in 100/0, 50/50, and 0/100 ratios in parts per hundred of rubber) and type of curing system on the final properties of biocomposites was evaluated by the oscillating disc rheometer, Fourier-transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, swelling behavior, tensile testing, and impedance tube measurements. The results show, that the scorch time and the optimum curing time values of sulfur cured biocomposites are affected by the change of the hybrid filler ratio while using the DCP curing system, and the obtained values do not show significant variations. The results conclude that the biocomposites cured with sulfur have better physico-mechanical and acoustic absorption, and that the type of curing system does not influence their thermal stability. The overall analysis indicates that the difference in final properties of highly filled biocomposites cured with two different systems is mainly affected by the: (i) cross-linking efficiency, (ii) partial absorption and reactions between fillers and used additives, and (iii) affinity of additives to applied fillers.

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38

Ferradino, Anthony G. "Antioxidant Selection for Peroxide Cure Elastomer Applications." Rubber Chemistry and Technology 76, no. 3 (2003): 694–718. http://dx.doi.org/10.5254/1.3547763.

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Abstract For applications demanding the best high temperature aging performance with lowest compression set, polymers are crosslinked with peroxides. The carbon-carbon bonds that are formed are more thermally stable than crosslinks containing sulfur atoms generated by conventional vulcanization by sulfur- and sulfur based cure systems. However, peroxide crosslinking requires special attention to the selection of compounding ingredients. Materials such as plasticizers, oils, and acidic materials such as silicas and air-floated clays detract from crosslinking efficiency by competing with the polymer for the free radicals produced by peroxides. Antioxidants, as a class, are free-radical scavengers and inhibit peroxide crosslinking. This paper discusses selecting the best antioxidant systems for peroxide cured elastomers by comparing various classes of antidegradants: peroxy and alkoxy radical traps (amines and hindered phenols), hydroperoxide decomposers, and synergists. Among the most effective include: 1) a quinoline polymerized 1,2-dihydro-2,2,4-trimethylquinoline 2) an amine, p-dicumyl-diphenylamine, 3) a hindered phenol, tetrakis (metylene (3,5-di-t-butyl-4-hydroxy-hydrocinnamate)) methane, and 4) a dithiocarbamate, nickel dimethyl-dithiocarbamate. For optimum performance, these are used in combination with the synergist, zinc-2-mercaptotoluimidazole. Also presented is an antioxidant system optimization study using a statistically designed experiment.

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39

Mousa, Ahmad. "Cure Characteristics and Thermal Properties of Sulfur-Cured EPDM-Based Composites by Compounding with Layered Nano-Organoclays." Polymer-Plastics Technology and Engineering 45, no. 8 (2006): 911–15. http://dx.doi.org/10.1080/00986440600724344.

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40

Lee, Shirley, Henry Pawlowski, and A. Y. Coran. "Method for Estimating the Chemical Crosslink Densities of Cured Natural Rubber and Styrene-Butadiene Rubber." Rubber Chemistry and Technology 67, no. 5 (1994): 854–64. http://dx.doi.org/10.5254/1.3538716.

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Abstract Chemical crosslink densities of gum and carbon black-filled natural rubber (NR) and styrene-butadiene rubber (SBR) were estimated by using a newly developed rheometer. The rheometer is the Rubber Process Analyzer (RPA 2000) which is designed specifically to measure dynamic properties such as shear storage modulus G′ and shear loss modulus G″ in cured and uncured rubber. It was found that the differences between the G′ values of dicumyl peroxide-cured NR and those of uncured samples yielded estimates of the crosslink densities which were nearly the same as the values inferred by chemical analysis. For TMTD-cured SBR, the same procedure yielded estimates of chemical crosslinks very close to those estimated by a tensile stress-strain method and by NMR. In addition, accelerated sulfur-cured natural rubber was also investigated. The agreement between the crosslink densities of these stocks determined from G′ values and from a solvent-swelling method was very good.

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41

Chun, H., and A. N. Gent. "Strength of Sulfur-Linked Elastomers." Rubber Chemistry and Technology 69, no. 4 (1996): 577–90. http://dx.doi.org/10.5254/1.3538385.

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Abstract Fracture energies have been determined for tearing through a sheet of a polysulfide elastomer, and for peeling apart two sheets bonded together with sulfur interlinks. Measurements were made over wide ranges of rate of crack propagation and test temperature. By shifting curves at various temperatures along the rate axis, using shift factors aT calculated from the “universal” form of the WLF equation, master curves were obtained for tear and peel energy vs. rate of tear or peel at the glass transition temperature Tg about −55°C. These master curves of strength vs. effective rate of crack propagation at Tg were closely similar to those obtained previously for several hydrocarbon elastomers: BR, SBR and EPR; interlinked with C-C bonds. Thus, under comparable test conditions the strength of the present polysulfide elastomer with sulfur crosslinks is similar to that for hydrocarbon elastomers with C-C crosslinks. The question then arises: Why are sulfur-vulcanized elastomers stronger in common experience than peroxide-cured ones? Possible reasons are discussed.

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42

Sabzekar, Malihe, Mahdi Pourafshari Chenar, Seyed Mohammadmahdi Mortazavi, Majid Kariminejad, Said Asadi, and Gholamhossein Zohuri. "Influence of process variables on chemical devulcanization of sulfur-cured natural rubber." Polymer Degradation and Stability 118 (August 2015): 88–95. http://dx.doi.org/10.1016/j.polymdegradstab.2015.04.013.

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43

Klüppel, M., H. Menge, H. Schmidt, H. Schneider, and R. H. Schuster. "Influence of Preparation Conditions on Network Parameters of Sulfur-Cured Natural Rubber." Macromolecules 34, no. 23 (2001): 8107–16. http://dx.doi.org/10.1021/ma010490v.

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44

Sirisinha, Chakrit, Pongdhorn Saeoui, and Sirichai Pattanawanidchai. "Rheological properties, oil, and thermal resistance in sulfur-cured CPE/NR blends." Journal of Applied Polymer Science 93, no. 3 (2004): 1129–35. http://dx.doi.org/10.1002/app.20555.

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45

Jiang, Kuan, Jinwei Shi, Youyong Ge, et al. "Complete devulcanization of sulfur-cured butyl rubber by using supercritical carbon dioxide." Journal of Applied Polymer Science 127, no. 4 (2012): 2397–406. http://dx.doi.org/10.1002/app.37542.

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46

Dijkhuis, K. A. J., W. K. Dierkes, J. W. M. Noordermeer, and P. Sutanto. "Improved Aging Performance of Virgin EPDM Roof-Sheeting Compounds with Amine-Devulcanized EPDM Weatherstrip Material." Rubber Chemistry and Technology 81, no. 5 (2008): 865–80. http://dx.doi.org/10.5254/1.3548237.

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Abstract Sulfur-cured EPDM building-profile material was reclaimed in a co-rotating twin-screw extruder using hexadecylamine as reclaiming aid. This reclaim was blended with increasing amounts of a virgin EPDM roof-sheeting masterbatch and cured at temperatures allowing for a reversion-free vulcanization. The trends in cure characteristics showed that increasing amounts of reclaim employed in the blends lowered the reversion-free cure temperature and the maximum torque values, while the vulcanization speed was increased. The insoluble fraction and crosslink density both decreased, while the ratio of mono- to di- and polysulfidic crosslinks increased with growing reclaim contents. A SEM-EDX morphology study of the blends, in order to evaluate the dispersion of the reclaim into the virgin rubber matrix showed, that even large amounts of reclaimed material resulted in homogeneous and smooth compounds. Tensile strength, modulus at 300% strain and hardness decreased, while elongation at break, tear strength and compression set at 70 °C increased with increasing reclaim ratios. Irrespective of the blend ratios, the mechanical properties all fulfilled the most stringent UEAtc specifications for EPDM roof-sheeting. Increasing reclaim contents improve the aging resistance and prolong the time before a practical limiting value for elongation at break of 250% for EPDM roof-sheeting purposes is reached.

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47

Kruželák, Ján, Richard Sýkora, Rastislav Dosoudil, and Ivan Hudec. "Relationship between the cross-link structure and properties of peroxide and sulfur-cured magnetic composites based on NR and NBR." Journal of Elastomers & Plastics 49, no. 6 (2016): 459–80. http://dx.doi.org/10.1177/0095244316672094.

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In the present work, rubber magnetic composites were prepared by incorporation of strontium ferrite into rubber matrices based on natural rubber (NR) and acrylonitrile butadiene rubber (NBR). The sulfur and peroxide curing systems were introduced in cross-linking of rubber matrices. The research was aimed at the evaluation of magnetic filler content and type of curing system on the cross-link density, physical–mechanical and magnetic properties of prepared composites. The relationship between the composition of elastomers and cross-link structure within the rubber matrices, formed by applying different curing systems, was under investigation through strain–stress behavior of tested materials. The achieved results showed that ferrite behaves as a reinforcing filler in peroxide-cured composites based on NR, and in both, sulfur as well as peroxide-cured composites based on NBR. The results also demonstrated that the cross-linking degree and the type of cross-link structure as well as the composition of rubber matrices, to a large extent, influence the property spectrum of tested composite systems.

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48

Smith, S. R., and J. L. Koenig. "Solid-State Carbon-13 NMR Studies of Vulcanized Elastomers. IX. TMTD-Vulcanized cis-1,4-Polybutadiene at 75.5 MHz." Rubber Chemistry and Technology 65, no. 1 (1992): 176–200. http://dx.doi.org/10.5254/1.3538598.

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Abstract The results of the present study indicate that, for the most part, the variety of C-S bonded structures formed in TMTD-vulcanized cis-BR qualitatively parallel those found in sulfur-cured vulcanizates of the material. Key exceptions include the demonstrated existence of stable rubber-bound accelerator fragments, and the possible elimination of select intramolecular cyclic species. Cis-to-trans isomerization has again been shown to be the predominant feature of the vulcanization reaction sequence and seems to obey first-order kinetics with respect to the concentration of accelerator. While the kinetic rate of conversion among all intermediate species was too rapid to permit a full account of the process, the spectral data demonstrate further that, subsequent to the formation of rubber-bound accelerator residues, sulfur becomes quickly redistributed to form crosslink structures of low average sulfur rank. In contrast to results obtained from elemental sulfur-cured BR vulcanizates, relatively high concentrations of monosulfidic crosslink structures were found in the TMTD vulcanizates at even the shortest reaction times. Similar to the results of the sulfur study, on the other hand, comparison between chemical and physical crosslink densities of the samples indicate the reaction sequence to have been highly localized, producing spatially inhomogeneous networks of elastically inefficient, clustered crosslinks. This latter result can be taken to imply that network morphology in TMTD-vulcanized BR is critically influenced by the solubility of the active accelerator complex in the rubber matrix. The effect was exaggerated in the present study by the omission of a compatible chelating agent for the zinc ions. From the standpoint of efforts aimed at optimization and control of the performance properties of vulcanized rubber articles, systematic investigation of the dependence of this effect on a wider range of formulation variables is warranted.

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Jana, G. K., and C. K. Das. "Mechanochemical Devulcanization of Vulcanized Gum Natural Rubber." Progress in Rubber, Plastics and Recycling Technology 21, no. 3 (2005): 183–99. http://dx.doi.org/10.1177/147776060502100302.

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De-vulcanization of vulcanized elastomers represents a great challenge because of their three-dimensional network structure. Sulfur-cured gum natural rubbers containing three different sulfur/accelerator ratios were de-vulcanized by thio-acids. The process was carried out at 90 °C for 10 minutes in an open two-roll cracker-cum-mixing mill. Two concentrations of de-vulcanizing agent were tried in order to study the cleavage of the sulfidic bonds. The mechanical properties of the re-vulcanized rubber (like tensile strength, modulus, tear strength and elongation at break) were improved with increasing concentrations of de-vulcanizing agent, because the crosslink density increased. A decrease in scorch time and in optimum cure time and an increase in the state of cure were observed when vulcanized rubber was treated with high amounts of de-vulcanizing agent. The temperature of onset of degradation was also increased with increasing concentration of thio-acid. DMA analysis revealed that the storage modulus increased on re-vulcanization. From IR spectroscopy it was observed that oxidation of the main polymeric chains did not occur at the time of high temperature milling. Over 80% retention of the original mechanical properties (like tensile strength, modulus, tear strength and elongation at break) of the vulcanized natural rubber was achieved by this mechanochemical process.

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Nillawong, Manuchet, Pongdhorn Sae-Oui, and Chakrit Sirisinha. "Influences of Coagent Hybrid Ratios and Silanes on Viscoelastic Properties of Silica-Filled HNBR." Advanced Materials Research 747 (August 2013): 564–67. http://dx.doi.org/10.4028/www.scientific.net/amr.747.564.

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Silica filled HNBR compounds were prepared, and modified with 2 different silanes, namely, mercapto silane (TESPT) and vinyl silane (VTEO). Because the HNBR was cured with peroxide, the 2 coagents (TRIM and ZDA) were used simultaneously as a hybrid system for a purpose of cure efficiency enhancement. Various composition ratios of TRIM to ZDA were used in association with 2 different silanes. Results of viscoelastic properties, as investigated by RPA2000 via oscillatory shear flow, suggest the different suitability of coagent hybrid ratio in the system with different silanes. Due to the released sulfur molecules from TESPT, a cure retardation phenomenon is resulted. The use of high ZDA composition leads to improved viscoelastic and cure properties in TESPT filled system. On the other hand, the system modified with VTEO reveals the synergistic effect of VTEO and TRIM, probably via a co-crosslink, resulting in the enhanced crosslink density, especially at high composition ratio of TRIM.

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Journal articles on the topic 'Sulfur cured'

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