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1.
A detailed study of the vulcanization of polybutadiene with various combinations of sulphur, tetramethylthiuram disuphide, ZnO, stearic acid, and zinc dimethyldithiocarbamate is reported. Vulcanization was conducted by heating samples at 2.5°C/min in a differential scanning calorimeter. The reaction was stopped at various points along the vulcanization exotherm, the soluble reaction products and residual curatives were extracted and analyzed, and the crosslink density and percentage polysulphidic crosslinks were determined. The overall reaction mechanism was found to be similar to that for polyisoprene, but the reaction, once initiated, was faster than in polyisoprene, the crosslink density was higher, and the percentage polysulphidic crosslinks was lower. These differences are discussed. © 1993 John Wiley & Sons, Inc.  相似文献   

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The effect of high-abrasion furnace (HAF) carbon black on the course of the tetra-methylthiuram disulfide-accelerated sulfur vulcanization of natural rubber has been investigated at temperatures from 100°C to 140°C. Continuous measurements in a Vuremo curemeter were used to estimate the extent of crosslinking, which was plotted against cure time. Results now available show (1) HAF carbon black does not alter the mechanism of the thiuram-accelerated sulfur cure; it also has no qualitative effect on the kinetics of the vulcanization reactions involved. (2) Quantitatively speaking, essential differences take place. The rate constants of vulcanization rise considerably when HAF carbon black is used; there is a dependence on the HAF carbon black content of the rubber compound. Yet the activation energies of vulcanizations are practically the same as in carbon black-free mixture, amounting to about 31 kcal/mole. (3) Measurements of the course of vulcanizations prove the reinforcing effect of HAF carbon black.  相似文献   

4.
The sulfur vulcanization of NR by a MBT-TMTD mixed accelerator system both in the presence and absence of ZnO and stearic acid with or without DCP has been studied. The rate of decomposition of DCP in the presence of both MBT and TMTD is quite similar to that in the MBT system alone. The reduction in crosslinking due to DCP is dependent mainly on MBT. The decomposition product of TMTD may contribute to it only at the later stage of vulcanization. Though TMTD has no influence on the decomposition rate, it reacts with MBT at least in the initial stage of vulcanization and suppresses the retardation caused by MBT on DCP vulcanization in accordance with the free sulfur decrease, the nature of crosslinking formation both in the presence and absence of DCP, and the methyl iodide treatment of the vulcanizates. The vulcanization process of the MBT-TMTD-S-NR system has been interpreted in terms of both free radical and polar mechanisms. The domination of either of these depends on the dominant amount of either MBT or TMTD in the acclerator ratio. According to the initial high rate of crosslink formation, free sulfur decrease and also the initial additiveness of crosslinking in stocks containing DCP, the vulcanization process of MBT-TMTD-ZnO-St. acid-S-NR system has been explained in terms of an ionic mechanism. The pronounced synergistic nature of such systems has been interpreted by the enhanced activation of MBT-S-ZnO-St. acid complex due to the dithiodicarbamate ion formed in the initial stages of vulcanization, and also by the activation of TMTD accelerated vulcanization due to the mercaptobenzothiazylion.  相似文献   

5.
Thiuram disulfides form synergistic combinations with thiazole and thiazole-based accelerators, namely, N-cyclohexy-2-benzothiazole sulfenamide (CBS), 2-mercaptobenzothiazole(MBT), and 2-mercaptobenzothiazyl disulfide (MBTS). Unfortunately, widely used thiuram disulfides (TD) generate carcinogenic N-nitrosoamine. It is reported that the nitrosamines from N-methylpiperazine and dibenzylamine are free from this menace. So, some investigations were carried out with the binary combinations of each of bis(N-methylpiperazino)thiuram disulfide (MPTD), tetrabenzylthiuram disulnde (TBzTD), and tetramethyl-thiuram disulfide (TMTD) separately with CBS, MBT, and MBTS. It was observed that all the TD are activated by the CBS, MBT, or MBTS in the combinations studied. The intensity of activation is manifested in the enhancement of torque, modulus, tensile strength, cure rate, hardness, and decrease of elongation at break values and is very much dependent upon the ratio of the accelerators used. Considering the torque, modulus, tensile strength, and the elongation at break values, it apears that MPTD and TBzTD are capable of competing with the hitherto unbeaten TMTD as suitable accelerators for the vulcanization of rubber. Some investigations in respect to heat- and age-resistance behavior have also been carried out and the observed differences in the activities of various binary combinations have been explained through a mechanism. The results obtained with filled vulcanizates indicate that the binary systems comprising TD and MBTS provide fruitful results of which the TBzTD–MBTS combination seems to give the best cure and physical data for practical vulcanizates. © 1996 John Wiley & Sons, Inc.  相似文献   

6.
The induction periods and maximum cure rates of an EPDM gum rubber were determined by using the Monsanto oscillating disk rheometer and correlated against the initial concentrations of curing ingredients. Sulfur curing systems accelerated by TMTM and TMTD were used. The maximum cure rates of the TMTM-accelerated and the TMTD-accelerated EPDM terpolymer compounds differed significantly only at low sulfur concentrations where the TMTM-accelerated compounds had slower maximum cure rates. Above approximately the 1% concentration level, TMTM and TMTD were found increasingly to retard the maximum cure rates of the EPDM terpolymer compounds as the initial concentrations of the thiuram accelerators were increased. The maximum cure rates of the TMTM-and TMTD-accelerated terpolymer compounds were found to be variable order in initial accelerator concentration, second-order in initial cure site concentration, approximately half-order in initial sulfur concentration above 0.3% sulfur, and of a positive variable order in initial zinc oxide concentration.  相似文献   

7.
Polyisoprene was vulcanized with binary accelerator systems comprising mixtures of the zinc salts of tetramethylthiuram disulfide (TMTD) and 2-mercaptobenzothiazole (MBT). Samples were heated in a DSC at a programmed rate, the reaction was stopped at points along the thermal curve, and the system was analyzed. Extractable curatives and reaction intermediates were analyzed by HPLC and the crosslink density of samples measured by swelling. DSC curves for the different systems displayed similar characteristics and their similarity to the curve obtained with the zinc salt of TMTD rather than to the curve obtained with the zinc salt of MBT suggested that the reaction was dominated by the former accelerator. This conclusion was supported by HPLC analyses of extractable curatives. A reaction mechanism for the binary system is discussed. © 1996 John Wiley & Sons, Inc.  相似文献   

8.
Polyisoprene was vulcanized with the binary accelerator system tetramethylthiuram disulfide–2-mercaptobenzothiazole (TMTD–MBT) in the absence of ZnO. Samples were heated in a DSC at a programmed rate, the reaction was stopped at points along the thermal curve, and the system was analyzed. Extractable curatives and reaction intermediates were analyzed by HPLC and the crosslink density of samples measured by swelling. Two cross-linking reaction sequences were identified, the first being initiated by polysulfides of the mixed accelerator N,N-dimethyldithiocarbamylbenzothiazole disulfide, and the second by MBT. All the TMTD is consumed in the first reaction sequence. Synergism of the reaction is discussed in terms of recent work detailing a reaction mechanism for TMTD-accelerated vulcanization. © 1996 John Wiley & Sons, Inc.  相似文献   

9.
Polyisoprene was vulcanized with N-cyclohexylbenzothiazole sulfenamide (CBS), sulfur, and zinc oxide by heating in a Differential Scanning Calorimeter (DSC) at a programmed rate to given temperatures. The reaction was quenched and the product analyzed. Soluble curatives and reaction intermediates were analyzed by high-performance liquid chomatography (HPLC) and the crosslink density of the network determined by swelling. The delayed action of the CBS accelerator is explained in terms of an exchange reaction between benzothiazole terminated polysulfidic pendent groups on the polymer chain and CBS to yield unreactive amine terminated pendent groups and 2-bisbenzothiazole-2,2′-disulfide (MBTS). MBTS reacts with sulfur to form 2-bisbenzothiazole-2,2′-polysulfides (MBTPs), which also form pendent groups. Crosslinking does not commence until all of the CBS has been consumed and pendent groups are no longer deactivated. 2-Mercaptobenzothiazole (MBT) is released only on crosslinking. When MBT is present in the formulation at the outset of the reaction it traps cyclohexylamine released when CBS adds to the chain as a pendent group. The MBT-amine salt participates in a reaction that regenerates MBTS, which is, thus, not consumed in the vulcanization process. ZnO does not react with CBS, and its role in increasing the crosslink density is attributed to its promoting crosslinking reactions between pendent groups and neighboring chains rather than intramolecular reactions, which lead to cyclization. © 1996 John Wiley & Sons, Inc.  相似文献   

10.
Vulcanization of latex products are usually carried out at lower temperatures compared to dry rubber products. It has been suggested that, in latex vulcanization systems where thiourea is used as a secondary accelerator, it acts as a nucleophilic reagent facilitating the cleavage of the sulfur bonds in the primary accelerator like TMTD or CBS at lower temperature. But no conclusive proof is given to such a postulate. In the present study 1-phenyl-2,4-thiobiuret (DTB II) and 1,5-diphenyl-2,4-dithiobiuret (DTB III), which are more nucleophilic than thiourea and which vary in their nucleophilic reactivity, were studied as secondary accelerators along with tetramethyl thiuram disulphide (TMTD) and N-cyclohexylbenzothiazyl sulphenamide (CBS) in the vulcanization of natural rubber latex. These binary systems were found to be very effective in reducing the optimum vulcanization time. Also it was noted that 1-phenyl-2,4-dithiobiuret, which is more nucleophilic, is more reactive (as observed from the reduction in optimum cure time) as a secondary accelerator, indicating a nucleophilic reaction mechanism in the vulcanization reactions under review. The optimum dosages of the secondary accelerators required were derived. Physical properties like tensile strength, 300% modulus, and elongation at break of the latex vulcanizates were also studied. There is a definite advantage with respect to many of these properties for dithiobiuret systems compared to the systems containing TMTD alone or TMTD/thiourea. DTB III gives higher values in many of these physical properties than DTB II. Chemical characterization of the vulcanizates was also carried out to correlate the physical properties with the type of chemical crosslinks formed. © 1993 John Wiley & Sons, Inc.  相似文献   

11.
The reactions of tetraethylthiuram di‐ and monosulfide (TETD and TETM, respectively) were investigated in the absence of rubber and compared with those reported previously for tetramethylthiuram compounds. The reactions of TETM, TETD, and zinc diethyldithiocarbamic acid with zinc oxide and sulfur were investigated by differential scanning calorimetry, and the reaction products analyzed by high performance liquid chromatography. TETM was shown to be more stable at vulcanization temperatures (±150°C), but also less reactive with sulfur than tetramethylthiuram disulfide (TMTD). The reactions of TETD are very similar to those of TMTD, the TETD reacting slower than the TMTD to form analogous products. In the presence of zinc oxide, the formation of the zinc compound of TETD, zinc diethyldithiocarbamic acid, occurred readily. TMTD does not react readily with zinc oxide. The reaction of TETD with sulfur lead to the formation of polysulfidic accelerator species, although the concentrations formed in the absence of rubber were considerably less than that formed by the corresponding TMTD system. These differences in reactivity would affect the vulcanization reactions that take place in the rubber. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2292–2299, 2001  相似文献   

12.
为节约一氧化碳耐硫变换催化剂硫化费用、缩短一氧化碳变换工段开车时间,贵州天福化工有限责任公司采用外购氢气和硫化剂——二硫化碳对一氧化碳耐硫变换催化剂进行硫化,达到了目的,节约了耐硫变换催化剂硫化费用,缩短了一氧化碳变换工段开车时间,为类似装置耐硫变换催化剂升温硫化提供借鉴和参考。  相似文献   

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The sulfur vulcanization of polyisoprene accelerated by 2-bisbenzothiazole-2,2′-disulfide (MBTS) was investigated. Rubber compounds were heated in a DSC and removed at various temperatures along the DSC thermal curve. The rubber vulcanizate was analyzed for crosslink density and for residual reactants and extractable reaction products. MBTS reacts readily with sulfur, and the polysulfidic accelerator complexes react with the rubber chain to form pendent groups. Crosslinking results from hydrogen abstraction, by the benzothiazole pendent group, from a neighboring chain. 2-Mercaptobenzothiazole, a product of crosslinking, also acts as an accelerator in the later stages of the reaction. MBTS has been shown not to react with ZnO and the higher crosslink densities obtained when ZnO is present are attributed to ZnO aiding the abstraction of the benzothiazole pendent group to give zinc mercaptobenzothiazole. A mechanism for the MBTS acceleration of sulfur vulcanization is proposed. © 1996 John Wiley & Sons, Inc.  相似文献   

15.
文中通过对三元乙丙橡胶化学结构的分析,探讨了多种硫化树脂与EPDM分子中的双键、巯基进行的交联反应,旨在提高EPDM制品的物理机械性能,减少其他配合剂的用量,防止硫化产品喷霜。实验证明,树脂硫化EPDM体系效果良好,在性价比方面国产WS硫化树脂具有较大的市场发展空间。  相似文献   

16.
Compounds of polyisoprene with sulfur and bis(2-mercaptobenzothiazole)zinc(II) (Zn(mbt)2) or ZnO and 2-mercaptobenzothiazole (MBT) were vulcanized by heating in a differential scanning calorimeter. The reaction was stopped at points along the thermogram and the product analyzed. ZnO and MBT readily react, the reaction going to completion during compounding. The presence of Zn(mbt)2 delays the onset of crosslinking compared to compounds without zinc. It is suggested that the induction period prior to crosslinking is occasioned by the inactivity of Zn(mbt)2, which must breakdown to MBT before it can participate in the vulcanization process. Such decomposition results from attack by anions generated when polysulfidic crosslinks, formed in the unaccelerated sulfur that occurs in the early stages of crosslinking, undergo scission. The effect of MBT, not bound to zinc, on the mechanism of the reaction is discussed. © 1995 John Wiley & Sons, Inc.  相似文献   

17.
陈玉涌  扈广法 《应用化工》2007,36(8):761-763,766
炭黑是三元乙丙橡胶(EPDM)主要填充剂,对其硫化动力学有重要的影响。探讨了炭黑的比表面积、填充量及结构与硫化反应级数、硫化反应表观速度常数、诱导时间、硫化反应表观活化能之间的关系。结果表明,快压出炭黑550对硫化反应表观反应级数基本上没有影响,对诱导时间及反应速度常数有不同程度的影响,填充量对表现活化能有较大影响。  相似文献   

18.
It is well known that the use of binary accelerator systems in rubber vulcanization provide better physical and chemical properties to the vulcanizates. The present work reports the results obtained on the study of amidinothiourea as a secondary accelerator along with tetramethyl thiuram disulfide (TMTD) in the sulfur vulcanization of natural rubber. Vulcanizates containing amidinothiourea have an appreciable increase in mechanical properties and better retention of these properties after aging compared to the reference mixes used. These mixes containing amidinothiourea showed appreciable reduction in optimum cure time as well. This suggests a nucleophilic reaction mechanism in the vulcanization reactions under review. Mixes with varying concentrations of amidinothiourea were tried; and the optimum level of amidinothiourea required has been derived based on the cure characteristics of the mixes and physical properties of the vulcanizates. © 1994 John Wiley & Sons, Inc.  相似文献   

19.
采用液相化学沉积法和凝聚共沉法制备稀土镝掺杂炭黑填充型粉末NR[P(NR/HAF.Dy)],在分析P(NR/HAF-Dy)硫化曲线的基础上,建立了不同稀土铺用量下胶料在硫化延迟阶段、硫化及硫化返原阶段的动力学模型.采用该动力学模型计算得到的拟合值与实测值吻合较好,说明该模型可以用来很好地模拟P(NR/HAF-Dy)在各个硫化温度下的硫化反应过程.  相似文献   

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