Vinyl acetate ethylene copolymer and nanosilica reinforced epoxidized natural rubber: Effects of sulfur curing systems on cure characteristics,tensile properties,thermal stability,dynamic mechanical properties and oil resistance

This study aimed at preparing nanocomposite from epoxidized natural rubber with about 40 mol% epoxidation (ENR40), vinyl acetate ethylene copolymer (VAE) contained about 70 wt% acetate groups and nanosilica (nSiO₂). Two parts by weight per hundred parts of rubber/resin of nSiO₂ were assembled to 80/20 (w/w) ENR40/VAE blend via latex blending. The resulting nanocomposite latex was coagulated before compounding with curing agents in an internal mixer. Tetrabenzylthiuram disulphide was used as a non‐carcinogenic accelerator in three sulfur vulcanization/curing systems, namely conventional (CV), semi‐efficient (semi‐EV) and efficient (EV) systems. The rubber compounds were sheeted on a two‐roll mill and press‐cured using a compression molding machine. Influence of curing systems on cure characteristics, tensile properties, thermal stability, dynamic mechanical properties and oil resistance of the nanocomposites was investigated. The results revealed that the CV system exhibited the highest crosslink density, tensile properties and storage modulus, while the EV system exhibited the longest scorch and cure time and the highest thermal stability and oil resistance. Moreover, the percentage retention of the tensile properties after thermal aging for CV system was lower than that of semi‐EV and EV systems. However, the pristine ENR40 and 80/20 (w/w) ENR40/VAE blend were also prepared for comparison. J. VINYL ADDIT. TECHNOL., 25:E28–E38, 2019. © 2018 Society of Plastics Engineers     

Influence of Additives in Adhesion of UV Radiation Surface-Treated SBS Rubber

In this study, the effect of additives (oils, lubricants) included in the formulations of different block styrene–butadiene–styrene (SBS) rubbers on the effectiveness of the ultraviolet (UV) radiation treatment to improve adhesion to polyurethane adhesive was analyzed. The modifications on the UV-treated rubber surfaces for different lengths of treatment have been characterized by contact-angle measurements (ethylene glycol, 25°C), Attenuated Total Reflectance-Infrared (ATR-IR) spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and Scanning Electron Microscopy (SEM). The adhesion properties have been evaluated from T-peel strengths of treated rubber/polyurethane adhesive/leather joints. The UV-radiation treatment on all rubber surfaces produced an increase in wettability, carbon–oxygen polar moieties, and ablation. The oxidation degree produced on the rubber surface treated with UV radiation was less when oils and lubricants were included in the formulation, likely due to competition of the oxidation process with the migration of low-molecular-weight additives to the rubber surface. On the SBS2 rubber surface (rubber containing carbon black and calcium carbonate fillers), the migration of oils and lubricants was also produced during the UV-radiation treatment, but a decrease in adhesion occured likely due to the lower tensile strength and higher extent of oxidation produced by the UV radiation treatment.     

Mechanical Properties and Morphology of Nitrile Rubber Toughened Polystyrene

Mechanical properties and morphology of blends of polystyrene and finely powdered (uncrosslinked and crosslinked) nitrile rubber were studied with special reference to the effect of blend ratio. Blends were prepared by melt mixing polystyrene and nitrile rubber in an internal mixer at 180°C in the composition range of 0–20 wt% nitrile rubber. The tensile stress/strain properties and impact strength of the polystyrene/nitrile rubber blends were determined using injection molded test specimens. In comparison to the blends with uncrosslinked nitrile rubber, blends with crosslinked nitrile rubber showed higher tensile strength, elongation at break, Young's modulus, impact strength, flexural strength, and flexural modulus. The enhanced adhesion between the dispersed nitrile rubber phase and the polystyrene matrix results in an increase in mechanical properties. Scanning electron micrographs of the fractured surfaces confirm the enhancement in mechanical properties.     

Improvement of Physicochemical Properties of Rubber Blends Between Nonirradiated and Irradiated Rubber Latexes by Radiation Vulcanization

Abstract

Nonirradiated natural rubber latex (NRL) and irradiated (12 kGy) rubber latex were blended in ratios of 100:0, 85:15, 65:35, 50:50, 35:65, 15:85, and 0:100 (v/v) to improve properties of the rubber latex. The blends were irradiated using different irradiation doses (0–20 kGy) in the presence of a radiation vulcanization accelerator (RVA), normal butyl acrylate (n-BA). The physicochemical properties of the nonirradiated latex, irradiated latex, and blend films were determined after leaching with distilled water. It was observed that the tensile strengths of the blend films increases with an increase in the content of the irradiated proportion and radiation doses. The composition of the blends and the doses of radiation were optimized. The maximum tensile strength (31.41 MPa) was found for the 50:50 composition of the blend with a 5 kGy radiation dose. The 100:0 blends, when irradiated, give the highest tensile strength (27.69 MPa) with 12 kGy but a 15:85 nonirradiated blend gives the tensile strength of 26.18 MPa.     

The viscoelastic properties of rubber–resin blends. I. The effect of resin structure

Blends of elastomers with the proper concentration of appropriate low molecular weight resins exhibit performance as pressure sensitive adhesives. Viscoelastic properties, which may be related to adhesive performance, were measured on 1:l blends of rubber and resin using a mechanical spectrometer. Significant differences in viscoelastic properties were observed depending upon the resin structure. On plots of G′ and tan δ vs. temperature, the addition of a compatible resin produces a pronounced shift of the tan δ peak to a higher temperature and reduces the modulus in the rubbery plateau. An incompatible resin results in a minor shift in the tan δ peak of the elastomer along with the appearance of a second peak at higher temperature, attributed to a second phase which is predominantly resin. Also, the modulus is increased in the rubbery plateau. A polystyrene resin, M_w about 900, is shown to be incompatible with natural rubber but compatible with styrene–butadiene rubber. A cycloaliphatic poly(viny1 cyclohexane) resin, M_w about 650, prepared by hydrogenating the polystyrene resin, is compatible with natural rubber, but incompatible with styrene-butadiene rubber. An alkyl-aromatic poly(tert-butylstyrene) resin, M_w about 850, which is intermediate in aromaticity between the aromatic polystyrene resin and the cycloaliphatic poly(viny1 cyclohexane) resin, is compatible with both natural rubber and styrene-butadiene rubber. Therefore, the structure of the resin is very important in adjusting the viscoelastic properties of a rubber–resin blend to achieve pressure sensitive adhesive performance.     

ABS modified with hydrogenated polystyrene‐grafted‐natural rubber

Natural rubber (NR) latex was grafted by emulsion polymerization with styrene monomer, using cumene hydroperoxide/tetraethylene pentamene as redox initiator system. The polystyrene‐grafted NR (PS‐g‐NR) was hydrogenated by diimide reduction in the latex form using hydrazine and hydrogen peroxide with boric acid as a promoter. At the optimum condition for graft copolymerization, a grafting efficiency of 81.5% was obtained. In addition, the highest hydrogenation level of 47.2% was achieved using a hydrazine:hydrogen peroxide molar ratio of 1:1.1. Hydrogenation of the PS‐g‐NR (H(PS‐g‐NR)) increased the thermal stability. Transmission electron microscopy analysis of the H(PS‐g‐NR) particles revealed a nonhydrogenated rubber core and hydrogenated outer rubber layer, in accordance with the layer model. The addition of H(PS‐g‐NR) at 10 wt % as modifier in an acrylonitrile–butadiene–styrene (ABS) copolymer increased the tensile and impact strengths and the thermal resistance of the ABS blends, and to a greater extent than that provided by blending with NR or PS‐g‐NR. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Study on the Properties of Blend Rubber Between Grafted Rubber Latex and Natural Rubber Latex by Gamma Radiation

Blend rubber films were prepared by mixing styrene grafted rubber latex and natural rubber latex (NRL) with varying proportions by gamma radiation from Co-60 source at room temperature. Tensile strength, modulus at 500% elongation, elongation at break, permanent set, and swelling ratio were measured. Tensile strength and modulus at 500% elongation attain maximum at 8 kGy radiation dose for blend rubber films. The increase in tensile strength is insignificant, but modulus increases from 5.61 to 7.46 MPa with increased proportion of grafted rubber latex from 40 to 70% in the blend at this radiation dose. Elongation at break, permanent set, and swelling ratio of blend rubber decreases with increase in radiation dose as well as proportion of grafted rubber.     

Latex influence on the mechanical behavior and durability of cementitious materials

The results of an experimental program conducted on latex-modified mortars are presented in this article. These mortars have become of growing interest in the field of construction. They were used as superplasticizers, or water reducers, for finishing work applications and for repairs, coatings, and waterproofing. This study is about using two polymers (latex), i.e. styrene–butadiene rubber and styrene–acrylic, in order to assess their performance in replacing cement in mortars. A series of mortar mixtures, containing 0, 2.5, 5, 10, 15, and 20% of solid polymer latex (by weight), were prepared and tested in the fresh and hardened states. The test parameters include the fluidity, compressive and flexural strengths, porosity accessible to water, adhesion to clay bricks, and cementitious substrates. The experimental results showed that substituting cement into modified mortars improves their fluidity and adhesion. In the case of clay substrates, a cohesive failure occurs within the substrate layer beyond 10% of substitution, while the rupture takes place at the interface for all formulations tested on cementitious substrates. It was also noted that the flexural tensile strength improved beyond 60 days. However, the compressive strength of polymer mortars decreased with the substitution rate of cement, for all maturities considered. However, for porosity accessible to water, the results follow a linear function, with an inflection at 5% of latex substitution.     

Adhesion of RFL-coated aramid fibres to elastomers: The role of elastomer–latex compatibility

The performance of fibre-reinforced composites is strongly dependent on the nature and the strength of the fibre–matrix interface. Good interfacial bonding is required to ensure load transfer from matrix to reinforcing fibres. For rubber-reinforced composites, resorcinol formaldehyde latex (RFL) is known as a fibre surface coating which is able to provide good adhesion between rubber and fibres. In the present study, aramid fibres are investigated, because of their significantly higher modulus and strength, compared to other commercial fibres. Their adhesion after being coated with RFL, in compounds based on natural rubber (NR) and in NR blended with a small amount of styrene butadiene rubber (SBR) is investigated. It is shown that though having very similar tensile properties, the latter compound has much better adhesion to RFL which is also less sensitive to RFL ageing, compared to the pure NR compound. It is argued that an interphase region is formed between RFL and the elastomer, which is stronger for the compound containing SBR due to its enhanced compatibility with the latex part of the RFL.     

Highly grafted polystyrene‐modified natural rubber as toughener for polystyrene

A polystyrene‐modified natural rubber (SNR) with 80% degree of grafting was evaluated against natural rubber (NR) in their blends with polystyrene (PS). The rubber loading of the PS‐SNR and PS‐NR blends was varied from 5 to 20% by volume. At 10–15% rubber loading, the PS‐SNR blends were found to be approximately 8–10% higher in tensile strength and 7–13% higher in Young's modulus than the PS‐NR blends. Over the range of rubber loading investigated, it was also observed that the PS‐SNR blends were 5–42 and 14–36% higher in flexural strength and flexural modulus, respectively. The most pronounced difference between the two blend systems is in their impact strength, where the former is about 55–230% higher than the latter. Relative to the pure PS, the PS‐NR and PS‐SNR blends are approximately 50–250 and 140‐1050% higher, respectively, in impact strength. Morphological observations, which are consistent with the relative tensile, flexural, and impact properties of the two systems, indicate that SNR is more compatible with PS than NR and more homogeneously dispersed in the PS matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1660–1665, 2004     

Synthesis and mechanical properties of high impact polystyrene with in situ bulk polymerization toughened by one‐pot Nd‐based styrene–isoprene–butadiene terpolymer rubber

High impact polystyrene (HIPS) resins were obtained with in situ bulk polymerization toughened by styrene–isoprene–butadiene terpolymer rubber (SIBR). SIBR prepolymer was prepared through selective polymerization of styrene (St), isoprene (Ip), and butadiene (Bd) in St with [Nd]/[Al]/[Cl] catalyst. Nd‐based catalyst exhibited more favorable activity toward conjugated diene other than St, resulting in St solution of random SIBR with high cis‐1,4 stereoregularity and low St content, which was directly exposed to the free radical polymerization of St to generate HIPS. Effect of toughened rubber and the initiators [difunctional (D2) and trifunctional (T3)] were examined to attain HIPS possessing mechanical properties as follow: impact strength, 0.9–24.8 kJ/m²; tensile strength, 16.0–27.5 MPa; and elongation at break, 7.4–107.0%. Increasing SIBR matrix in HIPS improved the impact strength and decreased tensile strength. The fracture surface morphologies of HIPS specimens were studied by notched impact tests and scanning electron microscopy (SEM), illustrating that the incremental SIBR matrix presented synergistic toughening effect of crazing to enhance the ductile fracture behavior. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43979.     

Relationship Among Thermal Ageing Degradation,Dynamic Properties,Cure Systems,and Antioxidants in Natural Rubber Vulcanisates

The present work aims to study the relationship among the thermal ageing stability, dynamic properties, cure systems, and antioxidants in natural rubber (NR) vulcanisates. Thermal degradation behavior of NR vulcanisates has been investigated and correlated to the changes in cross-link density, tensile and dynamic mechanical properties. The results obtained show that thermal ageing properties of NR vulcanisates depend strongly on cross-link density, which changes during thermal oxidative ageing or the so-called postcuring effect. In addition, the increases in ageing temperature and time lead dominantly to the postcuring and linkages scission phenomena in vulcanisates cured with CV and EV systems, respectively. With increasing ageing temperature, the tensile strength shows sharp drop at ageing temperature higher than 70°C and 100°C for the specimens cured with CV and EV systems, respectively. The sharp drop of tensile strength of vulcanisates cured with CV system is attributed to the too high cross-link density, which is caused by the postcuring effect. In the case of the vulcanisates cured with EV system, the linkage scission causes the sharp drop of tensile strength. The addition of amine-based antioxidant appears to improve ageing properties. However, the excessive antioxidant reduces tensile properties via a decrease in cross-link density.     

The viscoelastic properties of rubber–resin blends. II. The effect of resin molecular weight

In blends of rubber and low molecular weight resins, the compatibility of the system controls the viscoelastic properties and ultimately the performance of the composition as a pressure sensitive adhesive. The effect of the resin molecular weight on compatibility was examined by studying rubber–resin blends prepared from resins which represent a range of molecular weights. Viscoelastic properties were measured using a mechanical spectrometer on 1:1 blends of rubber and a series of polystyrene resins and poly(vinylcyclohexane) resins. Based on plots of G′ and tan δ vs. temperature, blends of natural rubber and polystyrene resin show incompatibility at resin M_w of about 600 and above. Blends of natural rubber and poly(vinyl cyclohexane) are incompatible at resin M_w of about 1800, but are compatible at M_w of about 650. Blends of styrene–butadiene rubber and polystyrene resins are compatible at resin M_w of about 650 but appear to contain a low volume incompatible phase at M_w of about 900. Therefore, the compatibility of a rubber–resin blend depends upon the molecular weight of the resin. Even systems expected to be compatible will show evidence of incompatibility as the molecular weight of the resin is raised above some limiting value.     

Effects of heat and moisture on characteristics,tensile properties of RFL‐coated rayon cords,and their adhesion with NR/SBR matrix

The objective of this study was to evaluate the effects of heat and moisture on the characteristics and tensile properties of resorcinol‐formaldehyde‐latex (RFL)‐coated rayon cords and their adhesion to the natural rubber (NR)/styrene‐butadiene rubber (SBR) matrix. The water absorption ratio, shrinking percentage, breaking force, and elongation at break of the cords, which were treated under various temperature‐humidity conditions, were tested, and an attenuated total reflection (ATR)‐Fourier transform infrared (FTIR) spectroscopy was used to investigate the chemical changes of the outer RFL layer. The static adhesion was investigated by an H pull‐out test, and the evolution of the adhesive properties of the RFL‐coated rayon cord/rubber matrix was tracked by an elastomer testing system. A scanning electron microscope (SEM) was employed to observe the interfacial fracture caused by both H pull out and fatigue. The results of this investigation show that the moisture absorption significantly affects the characteristics and the mechanical properties of rayon cords. The chemical state of the RFL layer and the static adhesion of the cord/rubber matrix were not obviously affected, but the interfacial fatigue life was extended due to the decrease of the load in the second of three fatigue stages, which was caused by a reduction in the modulus of the rayon cords. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45559.     

Novel method for toughening of polystyrene based on natural rubber latex

γ‐Radiation vulcanized natural rubber latex/phase transfer/bulk polymerization is a novel process for the preparation of toughened polystyrene based on natural rubber latex. The negatively charged γ‐radiation vulcanized natural rubber latex was first titrated with benzyldimethylhexadecylammonium chloride in the presence of a styrene monomer. At a critical transfer concentration, the crosslinked rubber particles transferred from the aqueous phase into the styrene phase in which they swelled, depending on the irradiation dose used. By bulk polymerization of the styrene phase containing transferred particles, the polymer blends exhibited two‐phase morphology similar to that of commercial high‐impact polystyrene that was microscopically obtained. The final product showed an increase in the unnotched Izod impact energy over the unmodified polystyrene. The effect of irradiation dose, rubber content, and initiator concentration on the impact property and morphology of toughened polystyrene prepared was investigated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1333–1345, 1999     

硫化体系对溶聚丁苯橡胶T2000R基本性能的影响

考察了传统、半有效、有效硫化体系对溶聚丁苯橡胶T2000R基本物理性能的影响。并且对T2000R和乳聚丁苯橡胶ESBR1502胶料的基本性能进行了对比。结果表明,各硫化体系下T2000R的加工安全性均优于ESBR1502。且T2000R半有效硫化体系的加工性能较好;采用半有效硫化体系的T2000R硫化胶的交联密度、拉伸强度和100％定伸应力均高于传统和有效硫化体系;T2000R有效硫化体系硫化胶的耐裂口增长能力最好。     

Effect of plasticizer and curing system on freezing resistance of rubbers

At glass transition temperature, T_g the rubber compound becomes stiff and brittle and it loses all its rubbery characteristics. This article deals with the changes in T_g of rubber blends based on natural rubber and polybutadiene rubber of varying vinyl content having different types and content of plasticizers, different curing systems and its effect on physico‐mechanical properties to improve its freezing resistance. The plasticizers used were dioctylphthalate (DOP), tricrecylphosphate (TCP), dioctyladipate (DOA), and oil type plasticizers like parafinic oil (P#2) and aromatic oil (A#2). Among the plasticizers, when DOP and DOA content was high, an appreciable decrease of T_g was found compared to TCP. Moreover, there was a remarkable decrease of T_g using DOA plasticizer, which shows more effective on freezing resistance. However, there was not much change in T_g with oil‐type plasticizers with high oil content compared to TCP plasticizer. The effect of cross‐linking systems such as conventional sulfur vulcanization (CV), efficient sulfur vulcanization (EV), and dicumyl peroxide (DCP) and rubber blends with varying vinyl content in polybutadiene rubber were also carried out. It was found that T_g in different cross‐linking system decreased in this order: CV < EV < DCP. It reveals that DCP cross‐linking system affect more for improving freezing resistance. Physico‐mechanical properties such as tensile strength, tear strength, hardness were also measured. The ratio of initial slope (M₀) to steady‐state slope (M₁), M₀/M₁ in tensile curves of different blends were verified, which in turn related to the physico‐mechanical properties and freezing resistance of rubber compounds. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39795.     

Energetic Material/Polymer Interaction Studied by Atomic Force Microscopy

The interactions of energetic materials and polymers have important implications in safety, long‐term storage, and performance of explosives and explosive mixtures. Atomic force microscopy was used to investigate adhesion forces at the molecular scale of nine energetic materials, organic explosives and energetic salts, on eleven common polymers (polyethylene, polyvinylalcohol, poly(vinyl chloride), polycarbonate, polystyrene, poly(methyl methacrylate), styrene‐butadiene rubber, poly(4‐vinyl phenol), poly(2,6‐dimethylphenylene oxide), poly(2,6‐diphenyl‐p‐phenylene oxide) (Tenax®), and polytetrafluoroethylene (Teflon®)). Teflon was the least adhesive polymer to all energetic materials, while no distinct trend could be elucidated among the other polymers or energetic materials.     

Synthesis and characterization of ABS resin using in situ transferring from emulsion to suspension polymerization

A novel approach based on an emulsion in situ suspension polymerization process for synthesizing poly(acrylonitrile–butadiene–styrene) (ABS) resin is reported. Experimental results show that the reaction system can be transformed from an emulsion state to a suspension polymerization state steadily with the content of polybutadiene (PB) in the range 0–15 wt% in ABS resin. When PB is replaced by poly(styrene‐co‐butadiene) with the content of rubber particles being kept below 20 wt%, the emulsion system can be easily transferred to the suspension polymerization state through a process of latex coagulation in the forward direction, which means that the emulsion solution was dripped slowly into the suspension reaction system in the presence of coagulating agent. The dispersion status of the rubber particles in the ABS resin was studied using transmission electron microscopy, which indicated that the rubber particles were in a dispersed state in a continuous matrix of poly(styrene‐co‐acrylonitrile) when the content of rubber particles was below 20 wt%. The mechanical properties of the ABS resins obtained are as follows: elongation at break, 9.4–45.7%; yield tensile strength, 35.1–42.2 MPa; impact strength, 98.2–116.3 J m^?1. Copyright © 2006 Society of Chemical Industry     

Factors influencing resorcinol–formaldehyde–latex‐coated continuous basalt fiber cord/rubber interfacial fatigue behavior: Loading direction and RFL formula

In this study, samples were prepared with resorcinol–formaldehyde–latex (RFL)‐coated continuous basalt fiber (CBF) cords and a natural rubber (NR)/styrene–butadiene rubber (SBR) matrix for interfacial fatigue tests under periodic radial loading conducted using a De Mattia Rubber Flexometer. The effects of the RFL formula on the interfacial fatigue behavior, including the fatigue life and the evolution of residual adhesion strength, were the focus of this work. The fatigue behavior was compared with that under axial loading. The results showed that under radial loading, the residual adhesion strength of the samples remained higher than that under axial loading, and the evolution of adhesion was divided into three stages. The adhesion improvement in the second stage was due to further cocrosslinking between the rubber matrix and the latex in the RFL layer, and the duration of the second stage was determined by the amount of reactive latex in the RFL layer. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46619.