Rubber Curing Research Articles

Grafting hydroxy‐terminated polybutadiene onto nanosilica surface for styrene butadiene rubber compounds

AbstractHydroxy teminated polybutadiene (HTPB) was grafted onto the surface of nanosilica particles via toluene di‐isocyanate (TDI) bridging to reduce filler–filler interactions and improve dispersion of nanosilica in rubber. Also, this prepolymer as modifier contains double bonds which participate in sulfur curing of styrene butadiene rubber (SBR) matrix to enhance filler/polymer interaction and reinforcement effects of silica. The reactions were characterized by titration and Fourier transforms infrared spectroscopy. Thermogravimetric analysis was utilized to evaluate the weight percentage of grafted TDI and HTPB. About 60% of the hydroxyl sites of silica were reacted with excess TDI in the first reaction. In the second reaction, HTPB as desired reactive coating was grafted on the functionalized nanosilica to constitute about 24 wt % of the final modified silica. The sedimentation experiments showed good suspension stability for the modified nanosilica in the organic media. Scanning electron microscopy revealed nanoscale dispersion of modified silica aggregates in the SBR matrix at concentration of about 14 phr. Also, vulcanization characteristics and mechanical properties of compounds demonstrated that HTPB grafting improved dispersion of nanosilica as well as its interaction to the rubber matrix as an efficient reinforcement. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

FACTORS INFLUENCING REINFORCEMENT OF NR AND EPDM RUBBERS WITH SHORT ARAMID FIBERS

Abstract Among short fiber reinforced composites, those with rubbery matrices have gained great importance due to the advantages they have in processing and low cost, coupled with high strength. These composites combine the elastic behavior of rubbers with strength and stiffness of fibers. Aramid fibers have been chosen because of their significantly higher modulus and strength, compared to other commercial fibers. Compounds based on NR and EPDM are prepared. Short aramid fibers with different kinds of surface treatments, standard finish, and resorcinol formaldehyde latex (RFL)-coating result in different rubber–fiber interfaces. The reinforcing effect of these short aramid fibers is characterized by mechanical and viscoelastic experiments, and by studying the fracture surfaces with electron microscopy techniques. Related to the fiber coating and rubber curing system, sulfur- or peroxide-based, different reinforcement mechanisms are observed, where the combination of peroxide-cured EPDM with RFL-treated fibers is the only case showing clear signs of chemical adhesion. In all other combinations there are only indications of mechanical interactions of the fibers with the rubber matrices, due to bending/buckling of fibers, dog-bone shaped fiber ends, and surface roughness due to the RFL-coating.

Numerical Investigation of Curing Process in Reaction Injection Molding of Rubber for Quality Improvements

A large number of rubber products are formed into their final shape by vulcanization. In particular, curing process of rubber is the final step in manufacturing many rubber products and determines both the quality of the resulting product as well as production costs. This paper is devoted to the simulation of rubber curing process in a three-dimensional model. The effects of final temperature of mold are investigated on curing process and quality of final product. The results were compared with the experimentally measured data, which confirmed the accuracy and applicability of the method.

T2 distribution mapping profiles with phase-encode MRI

Two 1-D phase-encode sequences for T 2 mapping, namely CPMG-prepared SPRITE and spin-echo SPI, are presented and compared in terms of image quality, accuracy of T 2 measurements and the measurement time. The sequences implement two different approaches to acquiring T 2-weighted images: in the CPMG-prepared SPRITE, the T 2-weighting of magnetization precedes the spatial encoding, while in the spin-echo SPI, the T 2-weighting follows the spatial encoding. The sequences are intended primarily for T 2 mapping of fluids in porous solids, where using frequency encode techniques may be problematic either due to local gradient distortions or too short T 2. Their possible applications include monitoring fluid-flow processes in rocks, cement paste hydration, curing of rubber, filtering paramagnetic impurities and other processes accomplished by changing site-specific T 2.

Tris(triorganosilyl)phosphites—New ligands controlling catalytic activity of Pt(0) complex in curing of silicone rubber

Applying novel and efficient method, new tris(triorganosilyl)phosphites were synthesized and further used for the preparation of new well-defined platinum complexes [Pt(DVTMDS){P(OSiR 3) 3}] (DVTMDS = (H 2C CHSiMe 2) 2O, R 3 = Si 7O 9( i Oct) 7, i Pr 3, MePh 2, Ph 3, (O t Bu) 3, (OSiMe 3) 3) which were well characterized by spectroscopic methods. Structures of two platinum(0) complexes, [Pt{η 4-(H 2C CHSiMe 2) 2O}{P(OSiPh 3) 3}] ( 10) and [Pt{η 4-(H 2C CHSiMe 2) 2O}{P(OSi(O t Bu 3) 3}] ( 11) were determined by X-ray analysis. The new complexes proved to be very effective catalysts of a cross-linking of silicones via hydrosilylation at elevated temperature with relatively short cure time and the enthalpy of network formation similar to that of Pt-Karstedt's/DAM (DAM = diallyl maleate) catalytic system. Additionally, the catalyzed silicone formulation had sufficiently long pot-life at room temperature.

Optimization of thick rubber part curing cycles

Thick rubber part moulding is a process, during which coupling between heat and chemical kinetic equations is strong. Automatic tooling control, therefore, is the guarantee of achieving proper curing within the mould. This article initially presents a detailed method for curing optimization. With this aim in view, the optimum temperature cycle for the desired curing state is examined. The use, here, of the conjugate gradient method implies to determine the solution of both adjoin and sensitivity equations. A sensitivity study is also conducted in order to improve the kinetic model. Finally, some optimization examples are discussed.

Koagenty sieciowania nadtlenkowego uwodornionego elastomeru butadienowo-akrylonitrylowego

Peroxide curing of acrylonitrile-butadiene rubber (HNBR/DCP), assisted with monoallyl maleate (MM) or itaconic acid (KI) in the presence of neutralizing substances: metal alkoxides [EtONa, (EtO)2Mg, (i-PrO)3Al, (t-BuO)4Ti] and magnesium hydroxide (Table 1, 2), was carried out. The effects of types of coagent and neutralizing substance on the kinetics of elastomer blend vulcanization (Table 3), on curing yield and density (Table 4) as well as on tensile strength of vulcanizates (Table 5) were investigated. It was found that coagents' application shortens vulcanization time, increases the process yield and improves tensile strength of cured products due to increase in vulcanizate relaxation ability being the result of a formation of additional ionic crosslinking points in its structure (Fig. 1). The most effective systems assisting the peroxide curing were: MM/(EtO)2Mg and KI/EtONa+Mg(OH)2.

Development of an advanced computer simulation technique for the modeling of rubber curing process

This research work is devoted to the development of an advanced computational technique for the simulation of the rubber curing process. The main novelty of the work is to cover the most important features that have not been addressed in the previous works. These include the use of incompatible meshes, thermal contact between rubber and mold, more accurate models for the description of the variation of rubber thermal properties with temperature and state-of-cure, use of a modified kinetic model and development of more robust auxiliary computer code. The general purpose finite element code ABAQUS has been used in conjunction with an in-house written subroutine (UMATHT) to solve the heat conduction equation and the rubber cure kinetics, simultaneously. It is used to simulate the curing process of a thick rubber article in the mold and the post-cure stage. The results were compared with experimentally measured data (temperature and state-of-cure) which confirmed the accuracy and applicability of the method.

Effect of triorganophosphites on platinum catalyzed curing of silicon rubber

Triorganophosphites containing substituents with different electronic and steric properties have been synthesized and tested as inhibitors of Karstedt's catalyst (complex Pt(0) with divinyltetramethyldisiloxane) in cross-linking of silicones via hydrosilylation. Relatively bulky or electron-withdrawing substituents in phosphite appeared to be the most efficient inhibitors of hydrosilylation showing sufficiently long pot-life at room temperature and short curing time at high temperature. New molecular complexes of Pt(DVTMDS)–selected phosphites have been synthesized and characterized. The new complexes proved to be effective catalysts of the curing process. The free phosphites as well as the phosphite–Pt complexes have been found resistant to oxidation and hydrolysis.

Comparing the dynamic behaviour of several rubbers filled with silanized silica nanofiller

AbstractBACKGROUND: The effect of the same amount of precipitated silica nanofiller on the curing and dynamic properties of different rubbers, including natural rubber (NR) without and with the addition of elemental sulfur (NR with S), synthetic polyisoprene (IR), polybutadiene (BR) and poly(styrene‐co‐butadiene) copolymer (SBR), was investigated. The silica surfaces were pre‐treated with bis(3‐triethoxysilylpropyl)tetrasulfane (TESPT) to chemically bond the silica to the rubber. The rubbers were primarily cured by using sulfur in TESPT with the addition of optimum accelerator (TBBS) and activator (ZnO), which helped to form sulfur chemical bonds between the rubber and filler.RESULTS: Cure properties, Mooney viscosity, glass transition temperature, bound rubber and crosslink density along with dynamic properties of the filled rubbers, including tan δ, loss modulus (G″) and storage modulus (G′), were measured as a function of double oscillation amplitude (DSA) from 15 to 1000 µm, temperature from −130 to 100 °C and frequency from 1 to 100 Hz. The results with emphasis on potential for tyre tread applications are discussed. It emerged that SBR along with BR filled rubbers had the highest rolling resistance while IR filled rubber had the least. Moreover, it was found that SBR filled rubber had the best skid resistance and BR filled rubber the worst.CONCLUSION: Interestingly, the variation of G′ with DSA showed a complicated behaviour for different filled rubbers. It emerged that in some DSA ranges the Payne effect was observed, and in the remaining ranges increments of G′ with DSA were seen. Because the bound rubber of most of the filled rubbers was more than 92%, there should be another predominant mechanism in the systems studied rather than simply de‐agglomeration or filler network breakdown, which is proposed by the Payne model. In addition, the nanoscale of the filler may be effective for this behaviour. Copyright © 2008 Society of Chemical Industry

The behavior of dithiocarbimate derivative as safety accelerator of natural rubber compounds

AbstractA conventional vulcanization system containing tetrabutylammonium bis(4‐methylphenyldithiocarbimato)zincate(II) (ZNIBU) was used for curing of natural rubber (NR) compounds. Rheometric (ts1, t90, and CRI) and mechanical properties, such as tensile and tear strengths and modulus at 300%, were measured to evaluate the acceleration potential of ZNIBU. Commercial accelerators (TMTD, MBTS, and CBS) and a binary system CBS/ZNIBU were also tested for comparison purposes. It was observed that ZNIBU alone does not give either safe scorch time or cure rates appropriate for industrial applications. Nevertheless, mechanical properties are comparable to those given by the other accelerators used. As for the binary system, positive synergistic effects can be found in tear strength and modulus of NR vulcanizates. Besides, ZNIBU does not contribute for the formation of nitrosamines in the vulcanization process. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Low-molecular-weight model study of peroxide cross-linking of ethylene–propylene–diene rubber using gas chromatography and mass spectrometry: II. Addition and combination reactions

The dicumyl-peroxide-initiated addition and combination reactions of mixtures of alkanes ( n-octane, n-decane) and alkenes [5,6-dihydrodicyclopentadiene (DCPDH), 5-ethylidene-2-norbornane (ENBH) and 5-vinylidene-2-norbornane (VNBH)] were studied to mimic the peroxide cross-linking reactions of terpolymerised ethylene, propylene and a diene monomer (EPDM). The reaction products of the mixtures were separated by both gas chromatography (GC) and comprehensive two-dimensional gas chromatography (GC × GC). The separated compounds were identified from their mass spectra and their GC and GC × GC elution pattern. Quantification of the various alkyl/alkyl, alkyl/allyl and allyl/allyl combination products shows that allylic-radicals comprise approximately 60% of the substrate radicals formed. The total concentration of the products formed by combination is found to be independent of the concentration and the type of alkene. The total concentration of the products formed by addition to the alkene increases with increasing concentration of alkene. In addition, the total concentration of the formed addition products depends strongly on the type of the alkene used, viz. VNBH > ENBH ≈ DCPDH, which is a consequence of differences in steric hindrance of the unsaturation. The peroxide curing efficiency, defined as the number of moles of cross-linked products formed per mol of peroxide, is 173% using 9% (w/w) 5-vinylidene-2-norbornane (VNBH). This indicates that the addition reaction is recurrent. All these findings are consistent with experimental studies on peroxide curing of EPDM rubber. In addition, the present results provide more-detailed structural information, increasing the understanding of the mechanism of peroxide curing of EPDM. The described approach to use low-molecular-weight model compounds followed by GC–mass spectrometry (MS) and GC × GC–MS analysis is proven to be a very powerful tool to study the cross-linking of EPDM.

Comparing effects of silanized silica nanofiller on the crosslinking and mechanical properties of natural rubber and synthetic polyisoprene

AbstractThe effect of the same amount of precipitated silica nanofiller on the curing and mechanical properties of natural rubber and synthetic polyisoprene was investigated. The silica surfaces were pretreated with bis(3‐triethoxysilylpropyl) tetrasulfide (TESPT) to chemically bond silica to rubber. The rubbers were primarily cured by using sulfur in TESPT, and the cure was optimized by the addition of accelerator and activator, which helped to form sulfur chemical bonds between the rubber and filler. Different amounts of accelerator and activator were needed to fully crosslink the filled rubbers. The hardness, tensile strength, elongation at break, stored energy density at break, tearing energy, and modulus of the vulcanizates improved substantially by the incorporation of the filler in the rubber. This was due to high level of rubber‐filler adhesion and formation of chemical bonds between the rubber and TESPT. Interestingly, natural rubber benefited more from the filler than did synthetic polyisoprene. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effects of rubber curing ingredients and phenolic‐resin on mechanical, thermal, and morphological characteristics of rubber/phenolic‐resin blends

AbstractThis article examines the physical and mechanical characteristics of mixtures of two different synthetic rubbers, namely styrene‐butadiene rubber (SBR) and nitril‐butadiene rubber (NBR), with novolac type phenolic‐resin (PH). According to Taguchi experimental design method, it is shown that the addition of PH increases the crosslinking density of rubber phase probably due to its curative effects. Thermal analysis of the blends indicates that, contrary to NBR/PH blend, thermal stability of SBR/PH blend is dependent on sulfur content due to predominant polysulfidic crosslinks formed in SBR. Slight shift in glass‐transition temperature (Tg) of pure SBR and NBR vulcanizates by the addition of PH suggests that both SBR/PH and NBR/PH are incompatible blends with a partially soluble PH in the rubber phase. Two‐phase morphology of the mixtures is also evidenced by scanning electron microscopy. Correlation of the rubber/PH modulus versus PH concentration by Halpin‐Tsai model shows a deviation from the model. Presence of PH in the rubber phase is thought to vary the mechanical properties of the rubber phase by changing both the crosslinking density and rigidity of the molecular network of the rubber, leading to misuse of modulus of pure rubber in Halpin‐Tsai equation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Hybrids of HNBR and in situ polymerizable cyclic butylene terephthalate (CBT) oligomers: properties and dry sliding behavior

A peroxide curable hydrogenated nitrile rubber (HNBR) was modified by cyclic butylene terephthalate oligomer (CBT), added in 100 parts per hundred rubber (phr). CBT polymerization was expected to occur simultaneously with that of the curing of the HNBR rubber (T = 190°C, t =2 5 min). Differential scanning calorimetry (DSC) indicated that only a minor part of CBT has been polymerized (pCBT) in the hybrid. Dynamic mechanical thermal analysis (DMTA) revealed that HNBR formed the continuous whereas (p)CBT the dispersed phase. Mechanical properties (hardness, tensile modulus, ultimate tensile strength and strain, tear strength) of the HNBR and HNBR/CBT were determined and collated. Tribological properties were investigated with pin(steel)-on- plate(rubber) (POP), with roller(steel)-on-plate (rubber) (ROP), with oscillating steel cylinder on rubber plate (Fretting) test configurations. Coefficient of friction (COF) and specific wear rate of the HNBR-based systems were determined. It was found that the resistance to wear increases with CBT hybridization. On the other hand, COF did not change much with CBT content. The friction and wear characteristics strongly depended on the test configurations. The worn surface of the HNBR systems was inspected in scanning electron microscope (SEM) to conclude the typical wear mechanisms. SEM investiga- tion showed that the CBT was predominantly recrystallized from its molten state under the curing conditions set. The well developed prism- and platy-like, micron-scaled CBT crystals were made responsible for the reinforcing effect observed.

Screening of EPDM Cure States Using Depth-Sensing Indentation

The applicability of depth-sensing indentation as a characterization tool for high throughput experimentation (HTE) in the field of rubber curing was investigated. Depth-sensing indentation is a suitable candidate for HTE as small amounts of material per sample suffice and large numbers of samples can be automatically measured sequentially. The applicability of this technique to characterize rubber crosslinking was studied using a set of peroxide cured EPDM vulcanizates. Depth-sensing indentation results were correlated with state of cure, Shore A hardness and macroscopic mechanical properties such as modulus and compression set.

Modyfikacja kauczuku butadienowo-styrenowego polimetylosiloksanami. Cz. I. Oddzialywania modyfikatora z kauczukiem

The results of investigations on structural aspects of styrene-butadiene rubber (SBR) modification with polymethylhydrosiloxanes (PMHS) or polydimethylsiloxanes (PDMS) were presented. The modifiers varied in reactivity, measured as a ratio of methylhydrosiloxane and dimethylsiloxane units (Table 1). The effects of modifier reactivity on the kinetics of radical reaction of rubber curing in the presence of dicumyl peroxide (DCP) as well as on the sulfur-induced vulcanization were determined (Table 2-5, Fig. 2 and 3). In case of DCP use the curing rate and efficiency increase with increasing reactivity of modifier used. However, in case of sulfur-induced vulcanization the systems containing less active PMHS showed the highest reaction rate. No modifier effect on the efficiency of sulfur-induced vulcanization was observed. It can be the result of active complex blocking by polysiloxanes, wetting the surface of ZnO being an activator of sulfur curing system. The curing in the presence of DCP is accompanied with the reactions of PMHS grafting onto elastomer and its polymerization in the rubber matrix. Organosilicon modifiers show the tendency to surface migration and segregation in the rubber. Together with the change in system morphology (Fig. 1) it influences mechanical (Table 6) and tribological properties (Table 8) of cured SBR. Namely, the introduction of a modifier into the rubber caused decrease in tensile strength, especially in case of the rubber cured in the presence of DCP. Macroscopic coefficient of friction for modified sulfur vulcanizates increases. However, in the case of SBR cured in the presence of DCP this coefficient can be lowered when low reactive PDMS or PMHS are used for modification.

Rubber curing chemistry governing the orientation of layered silicate

The effect of curing systems on the orientation and the dispersion of the layered silicates in acrylonitrile butadi- ene rubber nanocomposite is reported. Significant differences in X-ray diffraction pattern between peroxide curing and sul- fur curing was observed. Intense X-ray scattering values in the XRD experiments from peroxide cured vulcanizates indicate an orientation of the layers in a preferred direction as evinced by transmission electron micrographs. However, sulfur cured vulcanizates show no preferential orientation of the silicate particles. Nevertheless, a closer inspection of transmission elec- tron microscopy (TEM) images of peroxide and sulfur cured samples shows exfoliated silicate layers in the acrylonitrile butadiene rubber (NBR) matrix. It was revealed in the prevailing study that the use of an excess amount of stearic acid in the formulation of the sulfur curing package leads to almost exfoliated type X-ray scattering pattern.

407 発泡ゴムの架橋プロセスに関する研究(機械材料・材料加工IV)

407 発泡ゴムの架橋プロセスに関する研究(機械材料・材料加工IV)

Three-dimensional Finite Element Modeling of Rubber Curing Process

This paper describes the development of a finite element model for the simulation of the rubber curing process in a mold. Thermal conductivity and heat capacity of the rubber are assumed to be dependent on temperature. The cure kinetic behavior of the rubber is also assumed to be described by an empirical model proposed by Kamal and Sourour. The governing equation is solved using the finite element method in a three-dimensional Cartesian coordinate system. The applicability of the model is verified by a comparison between the results of the simulation of the vulcanization of a rubber part in the mold with experimentally measured temperature profile. It has been shown that there is very good agreement between the model predictions and the actual data.