Structure Of Vulcanizates Research Articles

Effect of organosilane agents on the vulcanizate structure and physical properties of silica-filled solution styrene butadiene rubber compounds

Physical properties of rubber compounds are affected by the filler-rubber interaction, filler dispersion in the rubber matrix, and crosslink structure formed during vulcanization. Organosilane agents are essentially used in silica-rubber compounds to inhibit the formation of silica agglomerates and increase the formation of silica-rubber networks. Generally, organosilane agents have an alkoxysilyl alkyl sulfide structure and are classified into silane coupling and covering agents depending upon the presence of sulfur. Coupling agents have a sulfur moiety and serve as a sulfur donor during the vulcanization process, thus increasing the formation of filler-rubber and chemical crosslink networks. On the other hand, covering agents promote the hydrophobation of silica surfaces, decreasing the adsorption loss of vulcanization additives, which increases the formation of chemical crosslink networks. This implies that organosilane agents can affect the vulcanizate structure, which causes a variation in the properties of silica compounds. Therefore, in this study, the effect of coupling (bis(3-triethoxysilylpropyl)disulfide (TESPD) and bis(3-triethoxysilylpropyl)tetrasulfide (TESPT)) agents and a covering (triethoxy(octyl)silane) agent on the vulcanizate structure and properties of silica compounds was investigated and compared. In the comparative study of coupling and covering agents, the influence of sulfur donors on the formation of vulcanizate structures was investigated. In the case of the coupling agents, the effect of sulfur rank on the vulcanizate structure and properties of silica-rubber compounds was quantitatively analyzed through various characterization techniques.

The effect of percent hydrogenation and vulcanization system on ozone stability of hydrogenated natural rubber vulcanizates using Raman spectroscopy

The ozone stability of partially hydrogenated natural rubbers (HNRs) was evaluated. HNRs with the hydrogenation levels of 14, 33 and 65 mol% including with vulcanization systems of peroxide and sulfur on ozone stability comparing with natural rubber (NR) and ethylene-propylene-diene-rubber (EPDM) vulcanizates were studied. The chemical structures of rubber vulcanizates were characterized by Raman spectroscopy. The surface cracks were observed by Raman optical microscopy. The results clearly exhibited that the ozone stability of HNRs vulcanizates was much greater than that of the NR vulcanizates. The difference between the integral intensities of C=C bonds of isoprene units in rubber chains by Raman spectroscopy before and after ozone exposed was minimized with the degree of hydrogenation. The depth of cracking observed by three-dimensional (3D) modes clearly decreased with an increase in the degree of hydrogenation, while no cracks on the surface of EPDM were found. These findings indicated that ozone stability increased with the degree of hydrogenation. Regarding the effect of vulcanizing systems, sulfur cure showed greater resistance to ozone degradation than peroxide cure.

Improvement of hardness and compression set properties of EPDM seals with alternating multilayered structure for PEM fuel cells

In Proton Electrolyte Membrane (PEM) fuel cells, seals are used to keep intimate contact between all components as well as to keep the reactant gases and liquid within their respective regions. Suitable seal materials should be chosen and designed to sustain the long term operation. In this paper, EPDM seal materials with soft and hard alternating multilayered structure are fabricated through the multilayered co-extrusion system. The structure and morphology of multilayered and blended EPDM vulcanizates were observed by Scanning electron microscopy (SEM). The results of tensile, hardness, compression set and compression stress relaxation test show that multilayered vulcanizates have lower tensile strength and compression set but higher hardness than blended one. The hardness of multilayered vulcanizates increases with the increase of the layer number, leading to higher sealing force and better dimensional stability. The compression set of multilayered vulcanizates decreases with the increase of the layer number, indicating better sealing capacity and longer working life. The permeability test shows that multilayered materials have nearly same gas permeability property as blended one. The results of aging test reveal that the mechanical properties of EPDM seal materials decrease with time, but multilayered vulcanizates still have lower compression set than blended one after aging.

The effect of accelerator contents on the vulcanizate structures of SSBR/silica vulcanizates

Physical properties of rubber compounds are affected by the filler–rubber interaction, filler dispersion in the rubber matrix, and cross-link structure formed during vulcanization. In particular, the cross-link structure is closely related to the physical properties of vulcanizates and has been analyzed using the swelling test and Flory-Rehner equation. However, the relationship between the structure and physical properties of vulcanizates cannot be explained by the cross-link density obtained using these methods. The cross-link density obtained from the swelling test is a complex result of the filler–rubber interaction occurring during the compounding as well as the chemical cross-link structure formed by sulfur during the vulcanization. Moreover, the rubber vulcanizates that use silica need to be separately analyzed for each factor as its physical properties are affected more by the filler–rubber interaction than by carbon black. Therefore, this study determines the factors that contribute to the total cross-link density of vulcanizates into chemical cross-link density and filler–rubber interaction via quantitative analysis using the swelling test results and Flory-Rehner and Kraus equations. The vulcanizates used for the analysis were carbon black-filled and silica-filled non-functionalized SSBR compounds with varying cure accelerator for each filler loading. Their chemical cross-link density was measured and the effect of the filler–rubber interactions on their mechanical and dynamic viscoelastic properties was investigated. Furthermore, the relationship between the structure and physical properties of rubber vulcanizates was elucidated.

Impacts of filler covalent and non‐covalent modification on the network structure and mechanical properties of carbon–silica dual phase filler/natural rubber

The carbon–silica dual phase filler (CSDPF) was modified by bis (3‐triethoxy‐silylpropyl) tetrasulphane (Si69) and 1‐allyl‐3‐methyl‐imidazolium chloride (AMI), respectively. The natural rubber (NR) vulcanizates filled with modified CSDPF were fabricated through mechanical mixing followed by a high‐temperature cure process. The impacts of filler surface modification on the curing characters, crosslinked junctions, network structure, and mechanical properties of NR vulcanizates were investigated. The results showed that the Si69 interacted with CSDPF through covalent bond, while the interaction between AMI and CSDPF was hydrogen bond. Both modifications increased the cure rate of CSDPF/NR compounds as well as the crosslinked degree, compared with those of pristine CSDPF/NR compound. The modifications improved the dispersion of CSDPF in NR matrix. The covalent modification by Si69 caused a limited movement of NR chains in the CSDPF surface, which contributed to a greater tensile modulus of Si69‐modified CSDPF/NR. However, the higher content of mono‐sulfidic crosslink and the poorer content of strain‐induced crystallization in the NR matrix led to a slight increase of tensile strength and tear strength of Si69‐modified CSDPF/NR, compared with those of CSDPF/NR. The tensile modulus of AMI‐modified CSDPF/NR had a lower value due to a faster polymer chain motion on the CSDPF surface. However, the tensile and tear strength of AMI‐modified CSDPF/NR increased significantly because of the increase of mono‐sulfidic crosslink, strain‐induced crystallization, and the existed hydrogen bond between CSDPF and NR. Copyright © 2015 John Wiley & Sons, Ltd.

EFFECT OF IN SITU SURFACE-MODIFIED NANO–ZINC OXIDE ON THE STRUCTURE AND PROPERTIES OF CONVENTIONAL VULCANIZATION IN NATURAL RUBBER

ABSTRACT In situ surface-modified nano–zinc oxide (ZnO) had been prepared by the sol-gel method. The microscopic structure of the ZnO particles was characterized by X-ray diffraction and transmission electron microscopy. Scanning electron microscopy with energy-dispersed X-ray spectroscopy was used to observe the dispersal of ZnO in conventional vulcanization of natural rubber (NR). Properties such as cure and tensile characteristics as well as heat-resistance oxygen aging properties were researched and compared. The vulcanized structure of vulcanizate was studied by the balance-swelling method and chemical-detecting process. Results demonstrated that the dispersal of in situ surface-modified nano-ZnO in NR vulcanizate was better than that of ordinary ZnO. Compared with the addition of 5 phr of ordinary ZnO in NR, the tensile strength and elongation of NR vulcanizate filled with 2 phr of in situ surface-modified nano-ZnO increased by 0.55% and 10.34%, respectively. Meanwhile, the retention of tensile strength and elongation of vulcanizate increased by 35.85% and 19.36%, respectively.

Determination of Crosslink Density and Network Structure of NR Vulcanizates by Means of TSSR

Unfilled vulcanizates based on natural rubber (NR) were investigated by temperature scanning stress relaxation (TSSR) measurements. Different sulfur based cure systems, i.e. conventional (CV), semi-efficient (SEV) and efficient (EV) vulcanization system, were used to prepare the vulcanizates. It was found that sulfur/accelerator - ratio has a strong impact on the shape of the relaxation spectrum, deduced from TSSR measurements. By deconvolution of the relaxation spectra, peak separation was performed and 3 different peaks were found in case of CV - cured samples. In contrast, only a single peak was found, in case of the EV-cured sample. After thiolamine treatment the shape of the relaxation spectra altered significantly in case of the CV-cured sample whereas the spectra of the SEV-and EV-cured sample exhibited only slight differences. Additionally, the crosslink density of the samples decreased after thiolamine treatment. This is due to selective cleavage of polysulfidic crosslinks. It has been concluded, that the significant peak in the relaxation spectrum at about 120 °C can be attributed to the cleavage of polysulfidic crosslinks. Furthermore, a linear relationship between the percentage of polysulfidic crosslinks and the sulfur/accelerator - ratio is assumed.

Effect of neodymium stearate on cure and mechanical properties of epoxidized natural rubber

The effect of neodymium stearate (NdSt) on cure and mechanical properties of expoxidized natural rubber with 25 mol.% epoxidation (ENR25) was studied in the concentration range of 0 to 2 phr, and the relationship between structure and mechanical properties of ENR25 vulcanizates was also discussed. Neodymium sterate was synthesized by saponification of stearic acid with newly formed rare earth hydroxide in water medium, and the structure of NdSt was investigated by Fourier transform infrared spectroscopy (FTIR). Crosslinking density of vulcanized natural rubber was studied by equilibrium swelling method. The results indicated that the interaction force between carboxylic ion of NdSt prepared in the lab and Nd ion was mainly ionic bond through FTIR analysis. NdSt could accelerate the vulcanization of ENR25 and influence the network structure of ENR25 vulcanizates. The incorporation of 1 phr NdSt for ENR25 vulcanizates showed the optimal aging resistance.

Application of Electron Beam Radiation to Modify Crosslink Structure in Rubber Vulcanizates and Its Tribological Consequences

The aim of this work was the modification of crosslink density and structure of rubber vulcanizates in order to control surface energy, mechanical strength under static as well as dynamic conditions and in consequence, tribological properties of the materials. Sulphur vulcanizates of styrene-butadiene rubber, filled with carbon black, were subjected to electron beam radiation in the range from 150 to 200 kGy. Changes in crosslink density and structure were determined applying the method of selective swelling of rubber in “hard” and “soft” solvents. The modification influences the ability of material of energy dissipation and its surface wettability. The changes are discussed from the friction and abrasion of rubber point of view.

Changes in the Network Structure of Vulcanizates during Tensile Deformation

Changes in the Network Structure of Vulcanizates during Tensile Deformation

Phase separation and thermal aging behavior of styrene‐butadiene rubber vulcanizates using liquid polymers as plasticizers studied by differential scanning calorimetry and dynamic mechanical spectroscopy

AbstractStyrene–butadiene rubber (SBR) vulcanizates were prepared using plasticizers including the four liquid types of styrene–butadiene copolymers (LPSB), polybutadiene (LPB), polyisoprene (LPI), and the hydrogenated polyisoprene (LHPI) as well as the conventional process oil, and their phase‐separated structures and mechanical properties were investigated by differential scanning calorimetry and dynamic mechanical spectroscopy. The phase separation was observed for the SBR vulcanizates when LPI and LHPI were used as the plasticizers, while the LPSB and LPB gave homogeneous structures because of the good miscibility with the SBR. The phase‐separated structure of the SBR vulcanizate prepared using LPI changed to the homogeneous during the thermal aging. We revealed the role of the liquid polymers as the plasticizers in maintaining the physical and mechanical properties of the SBR vulcanizates during the thermal aging process when the plasticizers were miscible to the SBR. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Influences of Accelerators on the Properties of Nitrile Butadiene Rubber and Attenuated Total Reflectance (ATR)-Fourier Transform Infrared (FTIR) Investigation.

The effect of incorporation of different types of accelerators i.e. TMTD, TMTM, DOTG and NPV/C on properties of NBR rubber was investigated. Without any organic accelerator it required long time to cure; tensile properties showed the least value but elasticity was the highest one and ageing properties were poor. Thiuram accelerators gave very fast cure; good tensile properties; high crosslinking density reflected on its resistance to organic solvents and gave the best ageing characteristics. Di -o- tolyl guanidine and vulcacit NPV/C thiourea gave slow onset of cure; long scorch time; high tensile; resilience properties, DOTG gave better ageing properties than NPV/C accelerator. The effect of accelerator type on compounds viscosity corresponded well with the melting point of the accelerators. NBR had high resistance to oil, in toluene and benzene TMTD and TMTM gave the best resistance. Elucidation of the structure of vulcanizates was determined by ATR- FTIR techniqueKey words: acrylo nitrile butadiene rubber, accelerators, mechanical properties, ageing, ATR- FTIR.

Effects of hot‐air aging and dynamic fatigue on the structure and dynamic viscoelastic properties of unfilled natural rubber vulcanizates

AbstractThe effects of hot‐air aging and dynamic tensile fatigue on the network structure and dynamic viscoelastic properties of unfilled natural rubber (NR) vulcanizates were investigated with magnetic resonance crosslink density spectrometry, Fourier transform infrared spectroscopy/attenuated total reflection (FTIR–ATR), and dynamic mechanical analysis. The results showed that there was a carbonyl weak absorption peak at 1723 cm−1 in the FTIR–ATR spectra of unfilled NR vulcanizates after hot‐air aging; The crosslink density decreased continuously as the aging time increased. The dynamic modulus of an aged specimen declined considerably, and the value of tan δ after 72 h of aging greatly increased. There was a large difference in the FTIR–ATR spectra of unfilled NR vulcanizates before and after tensile fatigue. The peaks at 1597, 1415, and 1015 cm−1 increased concurrently with the tensile fatigue time. Initial analysis suggested that structures such as conjugated dienes appeared in the network structure. The modulus declined sharply, whereas the value of tan δ increased noticeably, after tensile fatigue. The effects of hot‐air aging and tensile fatigue on the crosslink density and FTIR–ATR spectra of unfilled NR vulcanizates were different, but both affected the viscoelastic properties dramatically. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Ultrasound devulcanization: comparison of synthetic isoprene and natural rubbers

Sulfur-cured vulcanizates of unfilled synthetic isoprene rubber (IR) were prepared and successfully devulcanized in a continuous co-axial ultrasonic reactor. Die pressure characteristics and ultrasonic power consumptions were measured. Network structures of the virgin vulcanizates, devulcanizates and revulcanizates were characterized by gel fraction and crosslink density according to the classic swelling method. The molecular characteristics of the sol generated by ultrasound treatment were determined by GPC. Kinetics of revulcanization, rheological properties of the devulcanizates and mechanical properties of the revulcanizates were compared with those of virgin uncured IR and their vulcanizates. In addition, a comparison of the cure behavior, devulcanization characteristics, network structures and the mechanical properties was made between IR and the natural rubber (NR) reported earlier. Simulations on the correlation of the normalized gel fraction and the normalized crosslink density show that these two rubbers have almost equivalent probability of main chain scission and crosslink rupture ratio, which is probably determined by the main chain structure of both rubbers consisting of cis-1,4-isoprene.

Effect of plasticizer nature on the cure rheokinetics and structure of Thiokol sealant vulcanizates

The influence of the nature and concentration of plasticizers on the curing rate of compositions and the structure of vulcanizates of the sealant U-30M was studied. It was shown that a proper choice of the nature and amount of plasticizer makes it possible to control the pot life of compositions and to prepare material structures with a crosslink density that ensures an acceptable level of their properties.

Structural characterization of sulfur vulcanized deproteinized natural rubber by solid-state13C NMR spectroscopy

The structural changes in unfilled and filled vulcanized deproteinized natural rubber (DPNR), which is a highly purified natural rubber (NR), were investigated by solid-state 13C NMR spectroscopy. The chemical shifts of new signal were assigned by calculation and compared with those observed by Koenig et al. for conventional vulcanized NR. The crosslink structure of sulfur vulcanized DPNR were similar to that of sulfur-vulcanized NR for CV system assigned by Koenig et al. The increase in the relative intensities of signals between 45 and 58 ppm, which was assigned to monosulfidic and polysulfidic bonds, was concerned with the increase in crosslink density. In this case, the crosslink density was increased after aging, which might be due to incomplete curing. Furthermore, the solid-state 13C NMR spectrum of the aged sulfur vulcanizate DPNR showed new signals at around 73 ppm, which is assignable to carbon attached to hydroxyl group because of thermal oxidation. It can provide more complete understanding of the final vulcanizate crosslink structure of DPNR vulcanizates. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1875–1880, 2006

ゴムの科学技術の展望 促進イオウ加硫のメカニズム

The reactivities of hydrocarbon, the radical reactions through the allylic radicals, the results of model compound vulcanization, and the cross-link structures of vulcanizates are comprehensively reviewed and discussed to understand the main reaction for accelerated sulfur vulcanization. Through this review, the author's view on the main mechanism and cross-linking structure for accelerated sulfur vulcanization are discussed.

The Main Mechanism and Cross-Linking Structure for Accelerated Sulfur Vulcanization

The reactivities of hydrocarbon, the radical reactions through the allylic radicals, the results of model compound vulcanization, and the cross-link structures of vulcanizates are comprehensively discussed to understand the main reaction for accelerated sulfur vulcanization. Through this review, the author's view on the main mechanism and cross-linking structure for accelerated sulfur vulcanization are discussed.

ゴムのカーボンブラック補強 その８（最終回）エラストマーの弱さと補強の原点

The author proposes the universal model for the cross-linked structure of real rubber vulcanizates, characterized by the heterogeneous networks of a densely cross-linked and a on-cross-linked phase, the volume fraction being 75-80% in the former and 20-25% in the latter. Fundamentally, the densely ross-linked phase is discontinuously structured in the system, surrounded by the continuous non-cross-linked phase.If we will accept the above concept, we should carefully reconsider the applicability of the rubber elasticity theory (Gaussian or non-Gaussian) based on the assumption of homogeneous cross-linking to real rubber vulcanizates, concerning the affine deformation, the stress-strain relation, the visco-elasticity and the fracture of rubbers.In this final report, we would like to summarize the origin of the strength and weakness of rubbers, spreading rubber species to thermoplastic and thermosetting elastomers and polyurethane.

Models for the Investigation of the Structure of Vulcanizates

AbstractFor the investigation of vulcanizates structure, new models have been developed relating the modulus of vulcanizates and the volume fraction of filler. The parameters of the models are the filler distribution and the properties of the shell surrounding the filler particles. Three functions of filler distribution have been assumed. Dynamic mechanical properties of a series of vulcanizates were tested and the parameters of the models were computed. The obtained data allows estimating the properties of the shell formed around filler particles in vulcanizates and to distinguish the functions of filler distribution.