Nano ZnO as cure activator and reinforcing filler in natural rubber

Zinc oxide (ZnO) nanoparticles of size 20–90 nm and surface area 9.56 m²/g were synthesized from ZnCl₂ and Chitosan and characterized by X‐ray diffraction, high resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM). Natural rubber (NR) vulcanizates containing nano ZnO was prepared by mill mixing and characterized by SEM, energy dispersive X‐ray analysis (EDAX), and HRTEM. Cure characteristics, free volume studies, bound rubber, crosslink density, and dynamic mechanical properties were evaluated and compared with that of NR vulcanizate containing conventional micro ZnO. Considering the cure characteristics, it was found that NR vulcanizate with 0.5 phr (parts per 100 g rubber) of nano ZnO showed low values of optimum cure time (t₉₀) and very high cure rate index compared with 5 phr of conventional micro ZnO. The study shows that micro ZnO can be successfully replaced with nano ZnO for accelerated sulfur vulcanization process in NR, and preparation of vulcanizate containing nano ZnO with better properties as that of micro ZnO. The optimum dosage of nano ZnO as a cure activator in NR vulcanization was found to be 0.5 phr compared with conventional grade micro ZnO. This will lead to substantial cost reduction in the manufacture of rubber products and alleviate environmental pollution due to excess ZnO in rubber compounds. POLYM. ENG. SCI., 2013 © 2013 Society of Plastics Engineers     

Preparation of zinc‐oxide‐free natural rubber nanocomposites using nanostructured magnesium oxide as cure activator

The effect of sol–gel synthesized magnesium oxide (MgO) nanoparticles as cure activator is studied for the first time in the vulcanization of natural rubber (NR) and compared with conventional zinc oxide (ZnO) in terms of cure, mechanical, and thermal properties. The NR vulcanizate with 1 phr (Parts per hundred parts of rubber) nano MgO shows an excellent improvement in the curing characteristics and the value of cure rate index is about 400% greater for NR vulcanizate containing 1 phr nano MgO in comparison to the NR vulcanizate with 5 phr conventional ZnO. Both mechanical and thermal properties of NR vulcanizate are found to be satisfactory in the presence of 1 phr nano MgO as cure activator in comparison to conventional NR vulcanizate. This study shows that only 1 phr nano MgO can successfully replace 5 phr conventional ZnO with better resulting properties in the sulfur vulcanization of NR. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42705.     

Understanding the role of ZnO as activator in SBR vulcanizates: Performance evaluation with active,nano, and functionalized ZnO

This study investigates (ZnO)s with different surface features as vulcanization activators in unfilled SBR vulcanizates. ZnO is termed the best activator due to its fast reaction kinetics. A high release of ZnO into the environment harms marine ecosystems, and most ZnO production goes to the rubber sector; therefore, reducing ZnO amount is essential. Active, nano and functionalized ZnO compared to conventional ZnO in SBR matrix; concentration optimized based on curing, mechanical, physical, and dispersion analyses. The Arrhenius equation approximated the cure curve's kinetic constant and activation energy. Crosslink density measured by swelling experiment and solvent freezing point depression. Nano ZnO was used from 0.5 to 2phr, active ZnO from 1 to 4phr, and functionalized ZnO from 1 to 3phr compared to 5phr of conventional ZnO. The tensile strength of N1.5, F1.5, and A2 SBR increased by 5%, 26%, and 18% compared to C5SBR, whose elongation at break improved by 30%, 7%, and 23%. The data were analyzed using tukey HSD post hoc test. Regarding mechanical properties and curing characteristics, 2phr active, functionalized, and 1.5phr nano ZnO is analogous to 5phr conventional ZnO in an unfilled SBR matrix. The quantity of ZnO in rubber vulcanizates decreased successively by 60%, 60%, and 70%.     

Influence of zinc oxide during different stages of sulfur vulcanization. Elucidated by model compound studies

The addition of zinc oxide (ZnO) as an activator for the sulfur vulcanization of rubbers enhances the vulcanization efficiency and vulcanizate properties and reduces the vulcanization time. The first part of this article deals with the reduction and optimization of the amount of ZnO. Two different rubbers, solution‐styrene‐butadiene rubber and ethylene–propylene–diene rubber, have been selected for this study. The results demonstrate that the curing and physical properties can be retained when the level of ZnO (Red Seal) is reduced to 1 or 2 phr, respectively. Of particular interest is nano‐ZnO, characterized by a nanoscale particle distribution. The cure characteristics indicate that with nano‐ZnO, a reduction of zinc by a factor of 10 can be obtained. In the second part, model compound vulcanization is introduced to investigate the effects of ZnO during the different stages of vulcanization. Experiments are described with two models, squalene and 2,3‐dimethyl‐2‐butene, both with benzothiazolesulfenamide‐accelerated vulcanization systems. The results demonstrate the influence of ZnO during the different stages of the vulcanization. With ZnO present, a marked decrease can be observed in the sulfur concentration during an early stage of vulcanization, along with a slight delay in the disappearance of the crosslink precursor. The crosslinked product distribution is influenced as well. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1388–1404, 2005     

Safe amine based zinc dithiocarbamates for the vulcanization of carbon black reinforced natural rubber

Binary combination of three safe amine based synthesized zinc dithiocarbamates (ZDC), namely zinc (N‐benzyl piperazino) dithiocarbamate (ZBPDC), zinc (N‐ethyl piperazino) dithiocarbamate (ZEPDC), and zinc (N‐phenyl piperazino) dithiocarbamate (ZPPDC) with mercapto benzothiazole disulfide (MBTS) as an effective accelerator system for the vulcanization of carbon black (N330, N550, and N774) filled natural rubber (NR) composites are studied. A comparison between the safe amine based zinc dithiocarbamates with the unsafe zinc dimethyl dithiocarbamate (ZDMC) in the light of mechanical and aging resistance behavior, introduces the non carcinogenic rubber additives in the filled vulcanization of rubber. Both accelerator and filler have the major importance for improving the mechanical as well as aging resistance behavior of the resultant vulcanizate. Variation in the filler and also filler to oil ratio are done to optimize the mechanical properties. SEM studies of different types of filler with different amounts show that N330 at 30 phr loading composites forms more homogeneity and less aggregated structures. Natural rubber systems with N330 carbon black show the best results with respect to tensile strength, but after the aging N774 carbon black filled system indicates better retention in the tensile strength. ZPPDC‐MBTS accelerated vulcanizate shows the better age resistance behavior than ZDMC‐MBTS accelerated vulcanizate. From both the points of age resistance and mechanical properties, ZBPDC‐MBTS accelerator system is the suitable substitute for ZDMC‐MBTS accelerated system in the filled vulcanization of natural rubber composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39988.     

New approach for preparation of dry natural rubber nanocomposites through acid‐free co‐coagulation: Effect of organoclay content

Natural rubber (NR) vulcanizates exhibit good mechanical properties compared to vulcanizates of synthetic rubbers. Incorporation of a conventional filler at higher loadings to NR enhances its modulus, while reduction in tensile strength and elongation. This paper presents a new strategy for development of a NR‐clay nanocomposite with enhanced mechanical properties by incorporation of lower loadings (2–8 phr) of cetyl trimethyl ammonium bromide modified montmorillonite clay (OMMT‐C) under acid‐free environment. The effect of OMMT‐C loading on cure characteristics, rubber‐filler interactions, crosslink density, dynamic mechanical thermal properties, and mechanical properties were evaluated. Incorporation of OMMT‐C accelerated the vulcanization process and enhanced mechanical properties. X‐ray diffraction analysis and scanning electron microscopy images revealed that the formation of intercalated clay structures at lower OMMT‐C loadings, and clay aggregates at higher loadings. A nanocomposite at OMMT‐C loading of 2 phr exhibited the best balanced mechanical properties, and was associated with highest crosslink density and rubber–filler interactions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46502.     

Rheological characterization and modeling of vulcanization kinetics of natural rubber/starch blends

Vulcanization kinetics of natural rubber/starch (NR/ST) blends was investigated by oscillating disc rheometer. The scorch and cure times are significantly reduced with the loading of starch in all blends from 1.15 and 2.22 to 0.91 and 1.88 min, respectively, to improve curing rate. Meanwhile, the maximum torque values and the maximum vulcanization rate of NR/ST blend increase with the starch loading from 1.51 N m and 0.387 min^?1 to 2.224 N m and 0.492 min^?1 respectively. The results of vulcanization kinetics of NR and its blends revealed that it is controlled by two‐stages, chemical and diffusion. The experimental data of the vulcanization rate of NR/ST blends did not fit with autocatalytic kinetic model except the pure natural rubber. Therefore, the Criado method was used and it was observed that the reaction kinetic model of pure NR and its blends with starch is best described by the D diffusion model (D2). © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46347.     

Understanding the influence of anti-reversion agent and metal oxide dose on natural rubber–carbon black system

Sulfidic linkages that are formed during the vulcanization process of natural rubber (NR) are unstable at a higher temperature and can be reversed into conjugated diene. To overcome such issue and to build a compound that is hostile to inversion and with increasing service life, anti-reversion agent (ARA), for example, N,N′-4,4′-diphenylmethyene bismaleimide (BMDM), is added into the formulation. This work explains the conjugation reaction mechanism of conjugated diene and BMDM by means of gas chromatography–mass spectrometry and Fourier transform infrared spectroscopy. The first phase of this study is associated with the change in ARA dosage keeping ZnO dosage the same. It is observed that 5 phr of BMDM and 2 phr ZnO combination (ARA4) shows lowest reversion at 160°C. The modulus value at 300% elongation increased 12% by the incorporation of BMDM as compared to the compound of no BMDM (ARA1). The second part is all about keeping BMDM dosage the same at 5 phr level and varying ZnO phr by 3, 4, and 5. From the overall results, it is observed that at a suitable dosage of BMDM and ZnO (5 phr BMDM and 3 phr ZnO combination [ARA5]), least reversion can be achieved and vulcanizates containing optimized BMDM and ZnO show better retention properties after aerobic aging as compared to ARA1.     

Synthesis and effect of surface modified nano ZnO in natural rubber vulcanization

It is well known that surface of ZnO acts both as a reactant and a catalytic reaction template in rubber vulcanization by activating and bringing together reactants. The particles of accelerators, fatty acid, and sulfur diffuse through the polymer matrix and get adsorbed on the surface of ZnO, forming intermediate complexes. Hence dispersion of ZnO in the elastomer matrix is a determining parameter. Capping is one of the novel techniques for increasing ZnO‐stearic acid/accelerator interaction, thereby enhancing their activities. During the sol–gel precipitation of nano ZnO, if a suitable capping agent is added, agglomeration of ZnO particles gets reduced, leading to the formation of nano particles. Since only very few studies are found reported on synthesis of accelerator‐capped ZnO and its application in rubber vulcanization, attempts have been made in this study to synthesize our novel accelerator N‐benzylimine aminothioformamide (BIAT)‐capped‐stearic acid‐coated nano ZnO (ZOBS), and BIAT‐capped ZnO (ZOB) to investigate their effects in natural rubber (NR) vulcanization. Efforts have also been made to synthesize stearic acid‐coated nano zinc phosphate (ZPS) with an aim to find an alternative to conventional ZnO in vulcanization. Mechanical properties like tensile strength, tear resistance, abrasion resistance, and compression set were found out. Swelling values of the vulcanizates as a measure of crosslink densities were also determined. Optimum dosage of ZOBS and a combination of ZOB and ZPS were also derived and found that capped ZnO is superior in NR vulcanization to conventional ZnO in improving cure properties including scorch safety and mechanical properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Rubber composite materials with the effects of electromagnetic shielding

This work deals with the preparation and properties evaluation of magnetic composites with acrylonitrile butadiene rubber matrix, which are able to shield electromagnetic radiation. In addition to the rubber matrix, these materials contained soft magnetic filler (Li or H40) and ingredients necessary for vulcanization process of prepared rubber compounds (sulfur, accelerator N‐cyclohexyl‐2‐benzothiazole sulfenamide, activators ZnO, and stearin). This study was aimed at the preparation of elastomeric composite materials and evaluation of the influence of ferrite weight fraction on curing characteristics, physical–mechanical, and magnetic properties. The results showed that with increasing content of filler, the moduli, and tensile strength decline. Conversely, elongation at break increased with increasing amount of filler. All composites containing 200 and more phr of ferrite showed sufficient absorption shielding properties, whereas lithium ferrite shows better shielding properties compared with manganese–zinc ferrite H40. POLYM. COMPOS., 37:2933–2939, 2016. © 2015 Society of Plastics Engineers     

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     

Effect of carbon nanotubes content on the vulcanization kinetic in styrene–butadiene rubber compounds

Styrene–butadiene rubber compounds reinforced with commercial multiwall carbon nanotubes (MWCNT) in amounts between 0.5 and 10 parts per hundred of rubber (phr) were mixed in a two‐roll mill. A compound with 40 phr of carbon black (CB) was prepared as reference. From rheometric curves at five different temperatures (between 140°C and 180°C), a similar maximum torque and vulcanization time values in the samples reinforced with 10 phr of MWCNT and 40 phr of CB were obtained. The Kamal–Sourour model was used to analyze the influence of the MWCNT content and the vulcanization temperature on the cure rate and induction time. Then, through an Arrhenius plot, it became evident the effect of the reinforcement content on the activation energy of the vulcanization process. Mechanical properties of normalized sheets vulcanized at 160°C indicate that content between 5 and 10 phr of MWCNT are enough to reach a similar performance to that sample with 40 phr of CB. SEM analysis exhibits a good dispersion of MWCNT. Swelling experiments point out a similar absorption degree of toluene in the compounds with 5 phr of MWCNT and 40 phr of CB. POLYM. ENG. SCI., 59:E327–E336, 2019. © 2019 Society of Plastics Engineers     

Mooney scorch time and cure index of epoxidized natural rubber in presence of sodium carbonate

The effect of sodium carbonate on the Mooney scorch time and cure index of epoxidized natural rubber (ENR 50) was studied with concentrations of 0–2 phr and 100–160°C temperatures. A conventional vulcanization system based on an ASTM formulation was used throughout the investigation on the gum and carbon black filled rubber compound. The results indicated that the scorch time and cure index for the gum and filled compounds increased to a maximum value at 0.15 phr of sodium carbonate, and further loading of sodium carbonate caused it to decrease. This observation was attributed to the neutralization of the residual acid in ENR 50 in the initial stage, thus reducing the formation of ether crosslinks via an acid‐catalyzed ring‐opening reaction with the epoxide group in ENR 50. However, as the sodium carbonate was increased beyond 0.15 phr, the excess sodium carbonate enhanced the vulcanization rate as shown by the drop of the scorch time and cure index. The peak maximum was more evident at lower temperature and its peak height decreased with increasing temperature, suggesting that the neutralization effect by sodium carbonate was overshadowed by the faster cure rate resulting from the availability of thermal energy to overcome the activation energy of vulcanization as the temperature was elevated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1352–1355, 2001     

纳米级高反应界面活性氧化锌替代间接法氧化锌应用于橡胶制品的可行性分析

对纳米级高反应界面活性氧化锌进行了理化指标比表面积和粒径的测定，同时进行了三种氧化锌变量实验，最后得出以下四个结论：活性氧化锌具有特别低的变价金属含量，有利于它改进在胶料中的老化性能；活性氧化锌的最大特点在于它具有高的反应界面，并通过高达51m^2／g反应界面保证了它在橡胶中具有较高的硫化活化作用；活性氧化锌在胶料中具有与普通间接法氧化锌完全相同的硫化活化作用，随硫化温度升高，活性氧化锌的硫化活性甚至超过普通间接法氧化锌；从不同硫化温度的硫化物理机械性能对比证实，纳米级高反应界面活性氧化锌与司接法氧化锌具有完全相同的物理机械性能；因此，纳米级高反应界面活性氧化锌可以完全等量取代间接法氧化锌，而对胶料性能没有影响。     

尿素衍生物对硅橡胶海绵性能的影响

以硅橡胶海绵的孔隙率、口模膨胀率、密度和硬度为测评参数，研究了尿素衍生物及其与氧化锌并用作发泡助剂对以发泡剂H发泡的硅橡胶海绵性能的影响。结果显示：在用发泡剂H制备硅橡胶海绵中，尿素衍生物作发泡助剂可有效提高发泡效果，当其用量为0．3份时．硅橡胶海绵的孔隙率达到70%，口模膨胀率达到325％，其密度为0.33g／cm^3，硬度为22；当以尿素衍生物为第一发泡助剂，ZnO为第二发泡助剂时，发泡效果进一步改善，当ZnO用量为0.6份时，硅橡胶海绵的孔隙率达到75％，口模膨胀率达到400%，其密度为0.31g／cm^3，硬度为22，且质地均匀美观，泡孔结构更为理想。SIEM电镜分析表明，当发泡剂H与氧化锌配合尿素衍生物并用时，可得到较理想的硅橡胶海绵。     

膨润土对SBR无促进剂硫磺硫化的影响

在无促进剂的ＳＢＲ／硫磺（１００／６,质量比）胶料中加入小于或等于２０份的膨润土,可降低焦烧,用量超过２０份则对焦烧无影响;加入润土对硫化速度的影响不大。经红外光谱表征,膨润土既有促进橡胶离子生成的作用,又有吸附橡胶离子的作用,这两种作用能相互抵消。     

Rice husk ash filled natural rubber. III. Role of metal oxides in kinetics of sulfur vulcanization

In preceding investigations the overall rate and apparent activation energy for the vulcanization process were calculated for natural rubber compounds, assuming that vulcanization follows first‐order kinetics. It was observed that the addition of white rice husk ash (WRHA) increased the rate of crosslinking and lowered the apparent activation energy more profoundly than commercial fillers, precipitated silica (Zeosil‐175) and carbon black (N762), with a conventional vulcanization system. In this work, a specific model for the vulcanization process accelerated by N‐cyclohexylbenzothiazole sulfenamide was used to investigate the real role of WRHA in crosslink formation. Cure studies were carried out at 150°C, and the kinetics constants were evaluated. In relation to the other fillers, WRHA seems to develop catalytic activity, resulting in a positive effect on the specific rate of crosslink formation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1519–1531, 2003     

Cure behavior and antimicrobial performance of sulfur‐cured natural rubber vulcanizates containing 2‐hydroxypropyl‐3‐piperazinylquinolinecarboxylic acid methacrylate or silver‐substituted zeolite

This work used 2‐hydroxypropyl‐3‐piperazinylquinolinecarboxylic acid methacrylate (HPQM) or silver‐substituted zeolite (SSZ) as antibacterial agents for natural rubber (NR) compounds vulcanized by conventional vulcanization (CV), semi‐efficient vulcanization, and efficient vulcanization (EV) systems. The cure behavior and antibacterial performance of the NR vulcanizates were studied by varying the loadings of HPQM or SSZ, contact times, and vulcanization systems. The antibacterial performance of the rubber compounds was examined by halo test and plate‐count‐agar methods against Escherichia coli (E. coli, ATCC 25922) and Staphylococcus aureus (S. aureus, ATCC 25923) as the testing bacteria. The cure time and crosslink density were dependent on the vulcanization recipe used but were not affected by the addition of HPQM or SSZ. Diphenylguanidine at the level of 1.0 phr (parts by weight per hundred parts of resin) in NR vulcanized by the EV system had the ability to kill the E. coli and S. aureus bacteria. The NR vulcanized by the CV system showed the most pronounced antibacterial performance, as compared with the other two vulcanization systems, via migration and diffusion of HPQM or SSZ onto the NR surfaces, this being identified by the relatively large reduction of contact angle values. The HPQM showed the most preference for NR compounds vulcanized with the CV system with a contact time of 120 min or longer to achieve a bacteria‐killing efficacy of 99.0–99.9%, the efficacy being more pronounced for E. coli bacteria. J. VINYL ADDIT. TECHNOL., 19:123–131, 2013. © 2013 Society of Plastics Engineers     

Rheological and curing behavior of reactive blending. II. Natural rubber‐g‐poly(methyl methacrylate)–cassava starch

Graft copolymers of natural rubber (NR) and methyl methacrylate (MMA) were prepared using cumene hydroperoxide and tetraethylene pentamine as redox initiators via the semibatch emulsion polymerization technique. Various molar percentage ratios of NR/MMA were studied in the grafting reaction (i.e., 95/5, 90/10, 80/20, 70/30, and 60/40). The graft copolymer with a 70/30 molar ratio was selected and used to prepare rubber blends with cassava starch. The starch was used at levels of 0, 20, 40, and 60 phr. Another set of rubber blends was prepared for comparison purposes. The NR‐g‐poly(MMA) (PMMA, 75 phr) was blended with 25 phr of NR air dried sheets (ADS) and a given level of the cassava starch. We found that the Mooney viscosity, shear stress, and shear viscosity increased with an increasing concentration of cassava starch. This may be attributed to the chemical interactions between the polar groups of the NR‐g‐PMMA and the cassava starch. The blends were later compounded using a compounding formulation according to ASTM D 3184‐89. A similar short delay onset of vulcanization (i.e., approximately 1 min) was observed for the whole set of compounds under study. However, different curing characteristics were observed for the blends of NR‐g‐PMMA–cassava starch and NR‐g‐PMMA–ADS–cassava starch. The NR‐g‐PMMA–cassava starch compounds exhibited two‐stage curing characteristics. The curing curve had a slight reversion at a testing time of approximately 8 min. The shear modulus then abruptly increased with an increasing testing time in the range of 20–60 min. The curing curves for NR‐g‐PMMA–ADS–cassava starch blends exhibited a single curing stage with a shear modulus that increased slightly with the testing time was increased from 20 to 60 min. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1453–1463, 2003     

New binary systems containing TMTD‐amidino phenyl thiourea and CBS–amidinophenyl thiourea for the vulcanization and rheological behavior of natural rubber latex

The use of accelerators in rubber latex is basically different from their use in dry rubber. In the present study, N amidino N'phenyl thiourea (APT) which is more nucleophilic than thiourea was studied as a secondary accelerator along with tetra methyl 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 vulcanization time. The optimum dosages for this non‐toxic secondary accelerator required were derived. Rheological studies of the compounded latex show that the introduction of APT in these systems does not have adverse effect in processing in comparison with the thiourea systems. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010