Xanthate accelerators for low temperature curing of natural rubber

Zinc salts of ethyl, isopropyl, and butyl xanthates were prepared in the laboratory. They were purified by reprecipitation and were characterized by IR, NMR, and thermogravimetric analysis techniques. The melting points were also determined. The rubber compounds with different xanthate accelerators were cured at temperatures from 30 to 150°C. The sheets were molded and properties such as tensile strength, tear strength, crosslink density, elongation at break, and modulus at 300% elongation were evaluated. The properties showed that all three xanthate accelerators are effective for room temperature curing. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1769–1775, 2000     

Behavior of zinc complex of bis(N-phenylsulfonyldithiocarbimate) as accelerator in the vulcanization of nitrile rubber compounds

Chemical complexes containing N-R-sulfonyldithiocarbimates have been looked at as potential substitutes for N-R-dithiocarbamates as accelerators for the vulcanization process, especially due to their structural similarities and, most importantly, for the capability of this last compound to not form nitrosamines during the vulcanization process. The zinc complex bis(N-phenylsulfonyldithiocarbimate)zincate(II) (n-PSC) of tetrabutylammonium was tested in nitrile rubber compositions and its performance compared with bis(4-methylphenylsulfonyldithiocarbimate)zincate(II) (MPSC) of tetrabutylammonium and also with commercial accelerators. The complex n-PSC imparted values of cure times intermediate between those given by ultrafast and moderate commercial accelerators. Nitrile rubber compounded with n-PSC also presented similar mechanical properties as compared with the commercial accelerators except for an inferior aging resistance. Concerning the two complexes, n-PSC was found to promote better properties such as optimum cure time, crosslink density, and elongation at break as compared with MPSC. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47211.     

Effect of nano zinc oxide on the cure characteristics and mechanical properties of the silica‐filled natural rubber/butadiene rubber compounds

With the increasing interest in environmental and health issues, legal restrictions, such as European Union (EU) End of Life Vehicle Directives, were strengthened. This led us to incorporate nano zinc oxide (nano‐ZnO), with particle sizes of 30–40 nm and specific surface areas of 25.0–50.0 m²/g, instead of conventional ZnO into natural rubber (NR)/butadiene rubber (BR) compounds to decrease the content of zinc in the formulation. In the unfilled system, only a 20 wt % nano‐ZnO content, compared to conventional zinc oxide content, showed the cure characteristics and mechanical properties of the same level. This was because the increase in the specific surface area of the nano‐ZnO led to an increase in the degree of crosslinking. The effect of nano‐ZnO on the cure characteristics and mechanical properties was more pronounced in the silica‐filled system than in the unfilled system. This was mainly because of the dispersing agent used in the silica‐filled system, which also improved the dispersion of nano‐ZnO. The silica‐filled NR/BR compounds containing 0.3–3.0 phr of nano‐ZnO showed improved curing characteristics and mechanical properties, such as optimum cure time, 100 and 300% modulus, tensile strength, and tear strength compared to the compound with 5 phr of conventional ZnO. The optimum amounts of nano‐ZnO and stearic acid were only 1.0 and 0.1 phr, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

HNBR/NBR共混物的动态硫化

以硫黄（１．５份）、促进剂ＤＭ９１．５份）作为ＮＢ交联剂,在１００℃下动态硫化８ｍｉｎ,制得ＨＮＢＲ／ＮＢＲ共混物。考察了不同硫化体系及并用比对动态硫化共混物性能的影响。对比了动态硫化和静态硫化共混物在性能上的差异,并对其加工流动性和微观结构作了探讨。结果表明,随着ＨＮＢＲ含量的增加,动态硫化共混物性能提高,尤其是动态硫化共混物的耐热空气第化性能要优于静态硫化共混物,ＴＥＭ分析表明,ＨＮＢＲ／ＮＮ     

Epoxidized natural rubber as a reinforcement modifier for silica‐filled nitrile rubber

Hydrated silicas impart better physical properties to polar rubbers, compared to those of hydrocarbon rubbers. However, to achieve optimum properties silane coupling agents are crucial in such formulations. Epoxidized natural rubber (ENR) in small proportions is used as a reinforcement modifier for silica‐filled nitrile rubber (NBR). Two systems of cure were used: N‐cyclohexyl‐ 2‐benzthiazyl sulfenamide (CBS) alone and in combination with diphenyl guanidine (DPG). In the CBS accelerated system, incorporation of an optimum concentration of about 15% of ENR on total rubber was found to improve technological properties. Addition of a secondary accelerator further improves these properties. Comparable results are obtained with those containing coupling agent and NBR–ISAF. High bound rubber and volume fraction values indicate a high polymer–filler interaction and gel content resulting from the NBR–ENR interaction. Results of this study reveal that ENR could be used as a reinforcement modifier for the NBR–silica system. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 292–306, 2002     

Effect of silane coupling agent on the fatigue crack propagation of silica‐filled natural rubber

Based on the real‐time crack tip morphology monitoring, the influence of silane coupling agent (SCA) on the crack‐growth behavior of silica‐filled natural rubber (NR) was analyzed. By using SCA, silica particles can be well dispersed and a filler–matrix network can be formed, which leads to lower crack‐growth rate. Results indicate that a dosage of 5 wt % (with respect to silica loading) is the optimal content. The real‐time observation and scanning electron microscopy (SEM) analysis proved that thin ligaments and dimples with homogeneous distribution appear on the crack tip. These crack tip morphologies reflect the low crack‐growth rate. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41980.     

HNBR/NBR共混物的静态硫化

研究了混炼工艺、硫化体系、氢化丁腈橡胶（ＨＮＢＲ）的饱和度及并用比对ＨＮＢＲ／丁腈橡胶（ＮＢＲ）共混物性能的影响,并通过ＴＥＭ和ＤＭＡ考察了共混物的结构和相容性。结果表明,混炼工艺对性能的影响水大;采用质量份分别为过氧化二异丙苯４、硫黄０．３和促进剂ＣＺ１．５的硫化体系,选择饱和度为９５％的ＨＮＢＲ与ＮＢＲ共混,共混物有较好的物理机械性能和热空气老化性能;共混物物理机械性能随ＨＮＢＲ用量的增加面提     

Resin‐vulcanized NBR: Suitability of rheometric parameters for the calculation of cure kinetic constants

Several mechanisms can be used to describe the vulcanization process, and study of the reactions that actually take place can be done through different techniques. In this work, two methods that used rheometric parameters to calculate the kinetic constant were compared for the cure of nitrile rubber with a system of phenolic resin, polychloroprene, and zinc oxide. The formulations and data analysis were based on a complete factorial experiment design. The results enabled the identification of the influence of each parameter involved in the vulcanization process and the suitability of the two methods used. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 505–513, 2002; DOI 10.1002/app.2354     

Studies on novel binary accelerator system in sulfur vulcanization of natural rubber

The synergistic activity of binary accelerator systems in rubber vulcanization is well known. Binary accelerator systems are being widely used in industry and are becoming increasingly popular because of the fact that such mixed systems can effectively prevent prevulcanization, permit the vulcanization to be carried out at a lower temperature in a shorter time, and produce a vulcanizate with superior mechanical properties compared to those of a stock cured with a single accelerator. Thiourea and its derivatives are important secondary accelerators in this context. It is suggested that thiourea containing binary accelerator systems cause rubber vulcanization to proceed by a nucleophilic reaction mechanism. In the present study 1‐phenyl‐5‐ortho, ‐meta, and ‐para‐tolyl derivatives of 2,4‐dithiobiurets, which are more nucleophilic than thiourea and vary in their nucleophilic reactivity, are used as secondary accelerators along with 2‐morpholinothiobenzothiazole in the vulcanization of natural rubber. The results show an appreciable reduction in the cure time for the mixes containing the dithiobiurets compared to the reference mix. These results are indicative of a nucleophilic reaction mechanism in the vulcanization reaction under consideration. These vulcanizates also demonstrate comparatively better tensile properties and good retention of these properties after aging. An attempt is also made to correlate the variation in physical properties to chemical crosslink formation in the various vulcanizates. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3173–3182, 2003     

NB R / Zn (MAA) 2合金的硫化与交联

用硫化仪研究了NBR／Zn(MAA)2合金的硫化特性,结果表明,随着Zn(MAA)2用量的增大,合金的硫化速度提高,焦烧时间缩短,表现活化能下降,平衡溶胀及平衡应力一应变实验表明,NBR／Zn(MAA)2合金的交联密度随Zn(MAA)2用量的增大而增大。差示扫描量热分析表明合金内部发生了复杂的化学交联,同时Zn(MAA)2均聚物与NBR交联网络互相贯穿缠结,起到了强迫相容的作用。     

Effects of silanization temperature and silica type on properties of silica‐filled solution styrene butadiene rubber (SSBR) for passenger car tire tread compounds

Influence of silanization temperature on properties of silica‐filled solution polymerized styrene butadiene rubber was investigated. Two types of silica, i.e., highly dispersible silica (HDSi) and conventional silica (CSi), were compared. Results show that the increased silanization temperature leads to the enhanced rubber–filler interaction, filler dispersion, and cross‐link density giving rise to the improvement in vulcanizate properties such as modulus, heat build‐up (HBU), and dynamic set, as well as tire performance, e.g., wet grip (WG), rolling resistance (RR), and abrasion resistance. Great care, however, must be taken to avoid the scorching phenomenon during the mixing process at too high temperature. Taken as a whole, the balanced properties are found at the silanization temperature of 140°C. Surprisingly, HDSi provides insignificant differences in degree of filler dispersion, WG, and RR, compared to CSi, despite its claimed greater dispersability. Probably, the relatively long mixing time used in this experiment may override the influence of silica type. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43342.     

Vulcanization characteristics and mechanical properties of nitrile rubber filled with short leather fibres

Leather shavings have been used as filler in short fibre form for nitrile rubber reinforcement. Shavings neutralized with sodium bicarbonate and ammonia showed improved vulcanization characteristics and mechanical properties, whereas sodium hydroxide neutralized shavings exhibited poor properties. Swelling of the vulcanizates in water and 1% NaOH was found to increase with leather loading, whereas in MEK a reversed trend was observed. Thermogravimetric analysis indicates that the thermal stabilities of the vulcanizates fall between those of pure leather and gum nitrile rubber vulcanizate.     

Some interesting phenomena in silica‐filled HNBR with the addition of silane coupling agent

Hydrogenated nitrile rubber (HNBR)/silica nanocomposites were prepared by in‐situ modification dispersion technology, and the silane coupling agent γ‐methacryloxypropyl trimethoxy silane (KH570) was chosen to promote the interfacial strength between silica particles and HNBR matrix and further improve the dispersion of silica particles. Rubber Process Analyzer (RPA2000) was used to test the Payne effect of HNBR/silica compounds, from which some interesting phenomena were found: the Payne effect became stronger after KH570 was added to HNBR/silica compound at room temperature, which was a contrary result compared to SBR/silica system. However, after stored for a month at room temperature, the Payne effect weakened, which was contrary to the traditional phenomenon of storage hardening of filled rubber. All these results are related to filler–filler interaction and filler–rubber interaction. The modulus at small strain amplitude of HNBR/silica compound with KH570 gradually decreased with the increase of times of circulatory strain sweep but that of compound without KH570 had almost no change, which was explained by Fourier Transform Infrared (FTIR) results that the reaction between silica and KH570 almost completed at the test condition: 80°C and about 1 h. The effects of silane amount, heat‐treated temperature and time on the Payne effect of compounds and the mechanical properties of vulcanizates were also investigated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

N‐benzoyl‐N′N′‐disubstituted thioureas—A new binary accelerator system and its effect of nucleophilicity in sulfur vulcanization of natural rubber

The effect of several new binary accelerator systems were studied with special emphasis to the relationship of nucleophilicity to their rheological and mechanical properties. In this study, dialkyl/azacycloalkyl substituted benzoylthioureas (BTU 1‐5) were used as secondary accelerators (SA) along with three different primary accelerators (PA) viz., Cyclohexylbenzthiazylsulfonamide (CBS), Mercaptobenzothiazole (MBT) or Zincdithiocarbamate(ZDC) in the sulfur vulcanization of natural rubber. The effect of these secondary accelerators on the rheological and mechanical properties was found to be improved when compared to the reference mixes. It is noted that the N‐benzoyl‐N′N′‐piperidinylthiourea (BTU 4) is more effective as a secondary accelerator due to the higher nucleophilicity of the same when compared with the test compounds. The ZDC‐BTU gives the best result as binary accelerator system in natural rubber. Chemical characterization was carried out by determining the total crosslink density. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Comparison of cure characteristics and mechanical properties of nano and micro silica‐filled CSM elastomers

In this study, the effect of micro and nano silica and their combination on mechanical and thermal properties of Chlorosulfonated Polyethylene compounds were investigated. Cure characteristics were studied using a Monsanto Moving Die Rheometer at 155°C. Incorporation of nano silica accelerated the vulcanization whereas the micro silica particles decelerated the curing process. Both micro and nano silica increased the crosslink density as evidenced by swelling test. However, this value has been more improved in CSM/nano silica composites. The physico‐mechanical properties of CSM/nano silica are superior compared to CSM/micro silica. Nano silica provided reinforcing efficiency which is not only because of higher specific surface area but also because of various interactions and especially physical interactions which are discussed in the text. Nano silica particles also improved the thermal properties more efficiently. Incorporation of 15 phr (part per hundred) nano and 5 phr micro silica to polymer improved the initial decomposition temperature for about 51°C and 16°C, respectively, using a TGA. The combination of micro and nano silica, showed that by coupling nano and micro fillers, the loading of fillers can be minimized. In other words, the hybrid samples with a lower filler loading behave as efficient as their separate counterpart with higher loading. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42668.     

Studies on xanthate/dithiocarbamate accelerator combination in NR/BR blends

Zinc butyl xanthate [Zn(bxt)₂] was prepared in the laboratory. The effect of this xanthate with zinc diethyl dithiocarbamate (ZDC) on the vulcanization of natural rubber (NR), polybutadiene rubber (BR), and NR/BR blend has been studied at different temperatures. The amounts of Zn (bxt)₂ and ZDC in the compounds were optimized by varying the amount of ZDC from 0.75 to 1.5 phr and Zn (bxt)₂ from 0.75 to 1.5 phr. The cure characteristics were also studied. HAF filled NR, BR, and NR/BR blend compounds were cured at different temperatures from 60 to 150°C. The sheets were molded and properties such as tensile strength, tear strength, crosslink density and elongation at break, compression set, abrasion resistance, etc. were evaluated. The results show that the mechanical properties of 80NR/20BR blends are closer to that of NR vulcanizates, properties of 60NR/40BR blends are closer to BR vulcanizates, while the 70NR/30BR blends show an intermediate property. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3516–3520, 2007     

Synergic effect of N‐benzylimine aminothioformamide secondary accelerator during sulfur vulcanization of a styrene‐butadiene‐natural rubber blend

In this study we reported synergic activity of a novel secondary accelerator N‐Benzylimine aminothioformamide (BIAT) along with tetramethylthiuram disulfide (TMTD) in improving cure and mechanical properties of gum and filled mixes of Styrene‐Butadiene Rubber (SBR). The feasibility of application of BIAT in sulfur vulcanization of an ideal blend of SBR and natural rubber (NR) has also been investigated. The mechanical properties like t ensile strength, tear resistance, hardness, compression set, and abrasion loss were measured. Swelling values were also determined as a measure of crosslink densities of the vulcanizates. The binary accelerator system BIAT‐TMTD was found very effective in improving cure properties of the mixes of pure SBR and a 50/50 blend of SBR and NR.There was also found simultaneous improvement in mechanical properties of vulcanizates of both pure and blend. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A comparative study of cardanol and aromatic oil as plasticizers for carbon‐black‐filled natural rubber

Cardanol is the main ingredient of cashew nut shell liquid, an agro‐byproduct. Its comparative merits vis‐a‐vis aromatic oil for plasticizing HAF‐black‐filled natural rubber (NR) is the subject of this article. Aromatic oil is the conventional plasticizer employed for such compounding requirements. The mechanical properties, ageing behavior, and torque time curves during cure of NR plasticized by both these materials are compared under identical conditions. It has been established that cardanol, when used as plasticizer, gives rise to similar tensile properties, shorter cure times, and superior ageing behavior compared to aromatic oil. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4835–4841, 2006     

Properties of a new synthetic rubber: High‐trans 1,4‐poly(butadiene‐co‐isoprene) rubber

A high‐trans 1,4‐butadiene/isoprene copolymer (TBIP) was synthesized in a 5‐L autoclave with hydrogen as an effective molecular weight modifier. The effects of hydrogen on the catalyst efficiency and molecular weight of the copolymers were investigated. The processability and physicomechanical properties of TBIP and their relationship to the composition, composition distribution, and molecular weight of TBIP were examined in detail. Increasing the H₂ pressure effectively reduced the molecular weight of TBIP. The optimum Mooney viscosity of TBIP and the 1,4‐butadiene molar content in the feed were 30–50 and 5–25%, respectively. No cis–trans isomerization was observed during the roll processing procedure for TBIP. The vulcanization characteristics of TBIP were similar to those of general rubbers, and no reverse vulcanization was observed for TBIP. A high green strength was the typical characteristic of TBIP. Vulcanized TBIP (TBIR) with an optimum composition and molecular weight presented outstanding antifatigue properties and low heat buildup in comparison with general rubbers. Compared with general sidewall stock [natural rubber (NR)/butadiene rubber (BR) = 50/50], TBIR exhibited a greater than 15‐fold increase in its crack‐initiation resistance. The other mechanical properties of TBIR were similar to those of 50/50 NR/BR. The heat‐aging mechanism of TBIR was crosslinking aging. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2941‐2948, 2004     

Experimental analysis of viscoelastic properties in carbon black‐filled natural rubber compounds

Processability and viscoelastic properties of natural rubber (NR) compounds filled with different carbon black loadings and types were investigated with the use of a steady shear rheometer, namely, the Mooney viscometer, and an oscillatory rheometer, namely, the Rubber Process Analyser (RPA2000). It was found that the type and amount of carbon black strongly influence the viscoelastic properties of rubber compounds. Both the dilution effect and filler transient network are responsible for the viscoelastic properties, depending on the vulcanization state. In the case of uncured compounds, the damping factor of the uncured NR decreases with increasing black loading. This is attributed to the reduction of mobilized rubber content in the compound (or the dilution effect). However, in the case of the cured NR vulcanizates, the filler transient network is the dominant factor governing the damping factor of the vulcanizate. With increasing black loading, the damping factor of the vulcanizate clearly increases. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2197–2203, 2005