Kinetics of sulfur-free thiuram vulcanization

Sulfur-free thiuram vulcanization has been investigated at temperatures from 160° to 190°C over 0.5 to 600 min. Continuous measurements in a VUREMO curemeter were used to estimate the extent of crosslinking, which was plotted against cure time. Simultaneously the values of the network chain density were calculated from swelling measurements on the vulcanizates. The cure curves show clearly an induction period (t_i), then fast crosslinking, a partial degradation, a “long-time” crosslinking, and finally a slow, limited degradation. Apart from the induction period, the kinetic graphs are satisfactory represented by a rate equation assuming three independent first-order reactions: fast crosslinking, degradation, and slow crosslinking. The rate equation contains seven kinetic parameters. Over the temperature range studied, there is no difference between the values of activation energy for fast crosslinking, for degradation, for slow crosslinking, and for t. Due to the presence of thiourea, the values of the induction period, the rate constant, and the extent of slow crosslinking are decreased. Simultaneously the activation energies calculated from degradation and slow crosslinking are significantly increased. On the basis of the above results, the mechanism of the sulfur-free thiuram vulcanization, in which ionic and radical reactions take place, is discussed.     

Prevulcanization inhibitor of sulfur-free thiuram vulcanization

On the basis of Mooney scorch measurements at 120°C and of continuous measurements of vulcanization in a Vuremo curemeter at 145°C, sulfenamides which function as inhibitors of the sulfur-free thiuram vulcanization have been investigated. It was found that the actual prevulcanization inhibitor is 2-mercaptobenzothiazole. Its formation from sulfenamides is activated by zinc dimethyldithiocarbamate since the vulcanization of rubber by thiuram disulfides in the presence of zinc oxide is always accompanied by the formation of zinc dithiocarbamate. It seems probable that the inhibition effect of 2-mercaptobenzothiazole is attributable to the formation of a complex with zinc dimethyldithiocarbamate which decreases the reaction rate in the initial steps of the sulfur-free thiuram vulcanization and thus causes the scorch delay.     

Thiuram vulcanization of natural rubber in the presence of hydrofuramide and ethanolamines

Influence of hydrofuramide and ethanolamines on efficient vulcanization (EV), semi-EV, and conventional sulfur vulcanization accelerated by tetramethyl thiuram disulfide is reported. In the case of thiuram vulcanization, the amines increase the cure rate but reduce the crosslink density. The interaction of tetramethyl thiuram disulfide with amines has been studied. The amines interact with thiuram disulfide (TMTD) giving rise to the formation of gaseous products. Thermogravimetric analysis shows weight loss of about 50% in case of TMTD–ethanolamine system and 25% in case of TMTD–hydrofuramide system. Gas chromatographic studies of the gaseous products indicate that it consists mainly of H₂S. The other constituents in the gaseous product are CO₂ and a thiol. A possible reaction based on these observations to account for decrease in crosslink density in thiuram vulcanization caused by amines is reported.     

Effect of aerosil on the course of thiuram accelerated sulfur vulcanization

Tetramethylthiuram disulfide (TMTD)-accelerated sulfur vulcanization of natural rubber has been investigated at temperatures from 100°C to 145°C. Continuous measurements in a Vuremo curemeter were used to estimate the extent of crosslinking, which was plotted against cure time. The cure curves as well as their linearized forms (dependences of the logarithm of the extent of vulcanization on the cure time) clearly show that at lower cure temperatures the course of the vulcanization differs significantly from the first-order rate law. These digressions have been removed by the addition of a highly dispersed silica gel, Aerosil, which simultaneously speeds up the course of the vulcanization up to the value corresponding to the rate of zinc dimethyldithiocarbamate (ZnDMDC)-accelerated sulfur vulcanization. These results are in accordance with our recent theory supposing that ZnDMDC is the actual accelerator in TMTD-accelerated sulfur systems. In the presence of Aerosil, the formation of ZnDMDC from TMTD is catalyzed via dispersed silica gel. Support for this view derives from the temperature dependences of vulcanization reactions. The activation energies of TMTD-accelerated sulfur vulcanizations in the absence (31 kcal/mole) and in the presence of Aerosil (23.5 kcal/mole) correspond exactly to the values calculated from the rate constants of the thiuram decrease in TMTD-accelerated vulcanization (30 kcal/mole) and from the rate constants of crosslinking in the dithiocarbamate-accelerated sulfur vulcanization (23 kcal/mole), respectively.     

Influence of clay on the vulcanization kinetics of fluoroelastomer nanocomposites

The vulcanization kinetics of gum and montmorillonite (Na-MMT) clay filled fluoroelatomer (FKM) nanocomposite was studied using both oscillating disc rheometer and differential scanning calorimetry under isothermal and dynamic conditions. The X-ray diffraction pattern of clay filled FKM showed a shift in d-spacing toward higher values indicating the formation of intercalated silicate layer. The cure characterization showed higher rate and state of vulcanization of modified clay filled compound than that of gum and unmodified clay filled FKM indicating the accelerating effect of quaternary ammonium salt modified clay. Although the unmodified clay slowed down the cure reaction, there was marked increase in cure rate at higher level of curative. Higher loading of clay decreased the cure rate with lowering of maximum torque values. The presence of organoclay increased the torque value through the formation of confined elastomer network within the silicate galleries. The experimental data obtained provided the evidence that the curing behavior illustrated autocatalytic characteristics. The kinetic parameters determined from the model equation had good agreement with the experimental results. The calculated activation energy of the gum and clay filled systems indicated the ease of cure process with respect to the type of clay. The cure kinetics measured by different methods was well correlated with each other.     

Effect of mineral filler sepiolite on sulphur-free thiuram vulcanization of natural rubber

The effect of sepiolite on the sulphurless vulcanization of NR by tetramethylthiuram disulphide, with and without activator (triethanolamine) was studied. The influence on: a) kinetic vulcanization parameters, b) crosslinking density, c) crosslinking types, d) efficiency factor E and e) zinc sulphide formation was considered. The vulcanization rate increases with increasing sepiolite level but crosslinking density is reduced. Based on these results a vulcanization mechanism is proposed and discussed.     

Studies on the effect of thiuram disulfide on NR vulcanization accelerated by thiazole-based accelerator systems

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.     

Influence of prolonging vulcanization on the structure and properties of hard rubber

This research on vulcanization illuminates the structure–property relationship of hard rubber with prolonging vulcanization. At the early stage of curing, polysulfur reacts with styrene–butadiene rubber (SBR) macromolecules to form chemical crosslink, as evidenced by the significant increase of modulus during vulcanization. The chemical crosslink is followed by a large amount of interchain attraction, which is due to the modification of SBR macromolecules by combined sulfur. The combined sulfur is formed by the reaction of sulfur atom with SBR backbone, which improves the polarity of SBR macromolecules since sulfur is polar. The influences of chemical crosslink and interchain attraction on the mechanical properties, thermal properties, dynamic mechanical properties, and fracture morphology were analyzed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

橡胶硫化反应动力学研究概况

综述橡胶硫化反应的各种动力学机理和硫化反应动力学的研究方法和手段。介绍各种不同的硫化反应机理及其相应的动力学模型方程．列举了等温和不等温条件下的橡胶硫化反应动力学方程。硫化反应动力学的研究方法有物理化学法、硫化仪法和热分析法等．这些方法各有利弊．研究中应将它们结合起来，并对结果进行综合分析。     

硫化树脂对EPDM性能的影响

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。     

蛋白质对天然橡胶硫化动力学的影响

选用与天然胶乳中的d球朊结构类似的牛白蛋白,将其加入到经Alcalase蛋白酶处理得到的低蛋白天然橡胶中,通过硫化仪法研究了蛋白质对胶料硫化动力学的影响。结果表明：各胶样的硫化反应可按一级反应处理;在相同温度条件下,随着蛋白质用量的增加,焦烧时间（t10）和正硫化时间（t90）缩短,硫化反应速率提高,说明牛白蛋白能够提高天然橡胶的硫化速度;硫化速率随着温度的升高而显著提高,且都能很好地符合阿伦尼乌斯方程;反应活化能随着蛋白质用量的增加而提高。     

天然橡胶硫化动力学研究

采用硫化仪测定了2种不同凝固工艺的天然橡胶（NR）的硫化过程,探讨了制胶工艺、配方和温度对硫化动力学参数的影响。研究结果发现,随着温度的上升,硫化速率常数迅速上升。在纯胶体系中,微生物凝固胶的活化能高于酸凝固胶。当加入炭黑后,酸凝固胶的活化能升高,而微生物凝固胶的活化能下降。     

Effect of vulcanization temperature and vulcanization systems on the structure and properties of natural rubber vulcanizates

The effect of vulcanization temperature (150°–180°C) on the structure and technical properties of gum natural rubber vulcanizates with four different 2-(morpholinodithio)-benzothiazole: sulphur ratios (A, 0.6:2.4; B, 1.5:1.5; C, 2.4:0.6; D, 3.0:0.0) at the respective optimum cure times has been determined. The influence of cure temperature on (a) the chemical crosslink density; (b) the distribution of crosslink types; (c) the extent of sulphidic main chain modifications and (d) the zinc sulphide formation was investigated. Results show that elevated cure temperatures produce a network with lower crosslink density, in particular a lower polysulphidic crosslink density. The formation of intramolecular sulphidic groups and zinc sulphide increase with increasing cure temperatures. The possibility of chain scission during vulcanization, as examined by a quantitative analysis of the sol—gel data, was found to be negligible. The network results have been correlated with the technical properties.     

Effect of the temperature on the kinetic of natural rubber vulcanization with the sulfur donor agent dipentamethylene thiuram tetrasulphide

The effect of the temperature on the kinetics of vulcanization of natural rubber with the sulfur donor agent dipentamethylene thiuram tetrasulphide (DPTT) was investigated. The oscillatory disk rheometer and differential scanning calorimetry under dynamic and isothermal conditions were used. The Coran's model was applied to set the kinetic constants within each distinct step of the vulcanization process using the obtained values of the rheometer curves. During the curing period it was observed that there were two stages. Either the torque increment (ΔS) or the crosslink density arise a maximum value at 130°C. The dynamic and isothermal thermograms showed two overlapped peaks during the curing reaction. These results were in concordance with those obtained by curemeter testing. In addition, the activation energy of the vulcanization process was also calculated by means of both techniques. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

超临界二氧化碳对硅橡胶硫化动力学的影响

采用差示扫描量热法考察了超临界二氧化碳（scCO2）的饱和时间、饱和温度（Ts）、饱和压力（Ps）和过氧化二异丙苯（DCP）用量对甲基乙烯基硅橡胶（MVQ）非等温硫化动力学的影响,并根据Kissinger法计算得到MVQ的硫化表观活化能（Ea）,通过Málek法和?eatak-Berggren自催化模型确定了可用于描述MVQ硫化动力学行为的参数。结果表明,随着DCP用量增加,Ea增大。MVQ在scCO2中饱和12 h后Ea减少至117.0 kJ/mol。当Ts为70 ℃,Ps为20 MPa时Ea分别降至110.6 kJ/mol和109.4 kJ/mol。scCO2饱和前后MVQ的硫化反应级数均约为1,硫化过程均表现出自催化反应的特征。     

Structural characterization of vulcanizates. XII. Efficient vulcanization using a sulfenamide–thiuram disulfide accelerator system

Vulcanizates obtained from the sulfur vulcanization of natural rubber using a combination of the accelerators N-cyclohexylbenzothiazole-2-sulfenamide (CBS) and tetramethylthiuram disulfide (TMTD) have been analyzed in terms of the numbers of poly-, di-, and monosulfide crosslinks, network-bound accelerator residues, and cyclic sulfide chain modifications as a function of cure time. The vulcanization system produced mainly monosulfide crosslinks at optimum cure, although there were differences in detail between this mixed system and a previously reported efficient sulfur vulcanization (EV) system using a high ratio of CBS to sulfur.     

基于CAN总线的橡胶硫化监控网络系统

采用CAN总线技术设计基于CAN的控制模块对硫化机硫化进行监控.控制模块由微控制器C8051F040、CAN总线收发器TJA1050T、仪表放大器INA128、液晶显示器与触摸屏等组成.其数据采集采用测量3次取中间值的方法,并对所采集的数据进行兼容算术平均值和中值滤波的复合滤波方式进行防脉冲干扰滤波,温度控制则采用模糊PID的方法.     

Effect of iron oxide on vulcanization kinetics and electrical conductance of butyl rubber composites

This paper investigates the effect of iron oxide concentration on the vulcanization process, electrical conductance during swelling in kerosene, and sheds some light on the possible mechanism of vulcanization kinetics. The rate and degree of crosslinking have been evaluated as a function of Fe₂O₃ concentration. It was found that the characteristic time constant during vulcanization decreases as the Fe₂O₃ concentration increases. The activation energy of the crosslinking reaction is calculated. An abrupt decrease in electrical conductance appears after a characteristic time of swelling. A modified model is suggested to calculate the separation distance in the conductive rubber matrix. The effect of microwave irradiation on electrical conductance and separation distance between conductive aggregate of butyl rubber (IIR) composites is also studied. Fe₂O₃ inhibits the degradation of IIR composites and microwave irradiation enhances the texturing microstructure of rubber matrix. © 2000 Society of Chemical Industry     

Reaction mechanism,kinetics and network structure of the DGEBA-DDS system

Different techniques were used to analyse the reaction mechanisms and kinetics of the system 2,2-[4-(2,3-epoxypropyl)phenyl]propane polycondensed with 4,4′-sulphonyl-dianiline in the temperature range 100?185°C. The results show the role of catalysts, of stoichiometry and of curing cycles in the reaction mechanisms and paths. Based on chemical balances of residual epoxy groups, and of hydroxy and ether groups formed, we have shown the effect of these functions on the thermal properties of the material.