Effect of γ-radiation on the dynamic mechanical properties of silicone rubbers

Dimethyl-, trifluoropropyl-, and high phenyl content polysiloxanes were irradiated in a ⁶⁰Co source to doses of 100 Mrad. The hardness of the specimens increased with dose. Crosslink density changes did not directly reflect the hardness changes. The crosslink density of the dimethyl polymer increased significantly and that of the trifluoropropyl polymer increased only slightly. There was a slight decrease in the crosslink density of the aromatic material. The storage moduli reflected the changes in crosslink density. Loss moduli of the dimethyl- and trifluoropropylpolysiloxanes initially decreased and then increased on continuing irradiation. Dynamic moduli of the high aromatic content polymer were essentially unchanged by the radiation. All the dynamic data were correlated by the WLF time–temperature relationship.     

Physicomechanical properties of α‐cellulose–filled styrene–butadiene rubber composites

In this research, the influence of adding α‐cellulose powder to styrene–butadiene rubber (SBR) compounds was investigated. Physicomechanical properties of SBR–α‐cellulose composites, including tensile strength, elongation, Young's modulus, tear strength, hardness, abrasion, resilience, and compression set, before and after ageing, were determined and analyzed. Young's modulus, hardness, and compression set increased and elongation and resilience decreased with increasing α‐cellulose loading in the composites, whereas tensile strength, tear strength, and abrasion resistance initially increased at low α‐cellulose concentration (5 phr), after which these properties decreased with increasing α‐cellulose content. Lower loadings of α‐cellulose (5 phr) showed better results than higher loadings, given that tensile strength, tear strength, and abrasion resistance increased at low α‐cellulose concentration. Theoretical prediction of elastic modulus was carried out using rule of mixtures, Hashin, Kerner, and Halpin–Tsai equations. Calculated results show that these equations are not suitable for accurate prediction for the work carried out. However, these models can be used with confidence for the prediction of elastic modulus because experimental results are higher than the calculated values. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2203–2211, 2005     

Flammability and degradation characteristics of styrene–butadiene rubbers

Uncured styrene–butadiene gum, a known cured composition, and four SBR beltings used in underground coal mining were subjected to thermal oxidative degradation in static and dynamic systems. The room temperature volatiles produced under the static conditions at 370°C were identified and quantitated. Monomers and their interaction products were liberated by the raw gum; the cured composition formed together with the above products materials traceable to the curing ingredients. The four beltings gave a large spectrum of products; an attempt was made to correlate these with possible components used in belts manufacture. In the dynamic system, the occurrence of glow, the rate of smoke generation, and char yields were determined at 400°C and 500°C. None of the materials glowed at 400°C. At 500°C, the raw gum volatilized completely, and the cured rubber and two beltings glowed. One of the beltings, which failed to glow, liberated the smallest quantity of toxic products.     

Some considerations concerning the dynamic mechanical properties of cured styrene–butadiene rubber/polybutadiene blends

The dynamic mechanical response of several binary mixtures of a styrene–butadiene copolymer and high cis‐polybutadiene has been studied. The loss tangent and shear modulus were measured with a free damping torsion pendulum at temperatures between 143 and 343 K in argon atmosphere. From the loss tangent data the glass transition temperature of each sample was evaluated. The results can be represented by the Fox equation that relates the glass transition temperature of the blend with that of constituent polymers. The influence in the loss tangent data of the crystallization of the high cis BR used in the blend is discussed. A study of the separation of the crystalline and amorphous parts in the polybutadiene using the storage modulus data is presented. Finally, the loss of crystallinity at different contents of SBR in the blend is analysed using the dynamic mechanical data. © 2000 Society of Chemical Industry     

Effect of new additives on the ultrasonic attenuation and mechanical properties of styrene–butadiene rubber

The change in attenuation of longitudinal ultrasonic waves has been measured as a function of frequency and temperature for styrene–butadiene-rubber (SBR) mixed with Ismacorr 141 as plasticizer and antioxidant. Analysis of the results showed relaxation processes and the activation energies for these processes were calculated and found to be related to the plasticization of samples. Also the velocity of the ultrasonic longitudinal waves through different samples was measured. The effect of Ismacorr 141 on the physical and mechanical properties of SBR was also studied.     

Characterization of sulfur-cured styrene–butadiene copolymer rubbers and their polybutadiene blends

Dissolution of sulfur-cured, carbon black-loaded copolymers and their blends with cis-1,4-polybutadiene (PBD) are brought about by boiling with o-dichlorobenzene which contains a small amount of 2,2′-dibenzamidodiphenyl disulfide. The resulting slurries are subjected to a sequence of separations which include high-speed centrifugation to remove solids, and solvent precipitation followed by filtration to isolate the precipitates. The precipitates are washed with solvent to remove soluble organic materials followed by carbon disulfide washing to dissolve the polymers. Cast films of the polymers are obtained by evaporating the carbon disulfide washings onto sodium chloride discs. The infrared spectra of the cast films of these preparations are very similar to those of their respective polymers prior to loading and curing. Calculations for relative concentrations of bound styrene and PBD microstructures permit nominal identification of the kinds of styrene–butadiene rubber and the amounts of cis-1,4-PBD used in a cured rubber formulation. Absorption bands used are near 3.35 μ for cis-1,4-PBD, 6.65μ for bound styrene, 10.35 μ for trans-1,4-PBD; and 11.0 μ for vinyl-1,2-PBD. Efforts are being made to improve the data by using a grafting infrared instrument and also to extend the calibrations to include other rubber blends.     

Effect of γ-radiation on synthetic fibres–III electrical properties and electron microscope studies

The effect of irradiation on the electrical properties of the synthetic fibres has been studied. The electron photomicrographs have been taken to investigate the structural changes occuring due to irradiation on the surface of the yarn. The results indicate that under optimum conditions of irradiation antistatic properties could be imparted to synthetic fibres without affecting the desirable properties.     

Effect of the microstructure parameters on the mullins softening in carbon‐black filled styrene–butadiene rubbers

A quantitative estimate of the Mullins softening is proposed and tested on various carbon‐black filled styrene–butadiene rubbers. To model the behavior of elastomeric materials, some constitutive equations reported in the literature are based on the account of a strain amplification factor, which evolves with the maximum strain history. The amplification factor is grounded on the representation of filled rubbers as heterogeneous materials made of hard rigid domains and soft deformable domains. In this work, this factor is split into two parts with opposite effects that account for the Mullins softening and for the filler reinforcement, respectively. Evolutions of both parts are obtained through a direct analysis of cyclic uniaxial tensile tests performed on a series of materials. The Mullins softening part is shown to linearly depend on the filler volume fraction and on the maximum strain applied, when defined as the first invariant of the Hencky tensor. Its changes with the gum cross‐link density parameter are insignificant. The reinforcement part of the amplification factor shows quadratic dependence on the filler volume fraction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Cut growth properties of styrene–butadiene copolymers

The cut growth properties of styrene–butadiene block and random copolymers are considered in terms of the tearing energy theory. It is found that the value of T₀ (the minimum value of tearing energy below which no cut growth takes place in the absence of chemical effects) is far higher for a styrene–butadiene resin copolymer system with a high amount of bound styrene resin than for a conventionally vulcanized SBR elastomer. Similarly, it is shown that the value of T₀ for a butadiene–styrene block copolymer (thermoplastic rubber) is considerably reduced when the material is crosslinked. It is proposed that the value of T₀ is influenced by the hystersial properties of the rubber.     

Curing behaviour and mechanical properties of dicarboxylated telechelic poly(ε-caprolactone)s/styrene–(epoxidized butadiene)–styrene triblock copolymer reactive blends

End-carboxylated telechelic poly(ε-caprolactone)s (XPCLs) with different molecular weights were blended into a triblock copolymer of styrene–(epoxidized butadiene)–styrene (ESBS) to investigate the curing behaviour and the mechanical properties of the XPCL/ESBS binary reactive blend. It was found that the time–torque cure curve showed a significant torque increase after a very short induction period, in which the degree of the torque increase depended on the molecular weight of XPCL. This indicates that substantial crosslinking reaction takes place between the XPCLs and the epoxidized polybutadiene of the ESBS. Stress–strain curves of the blends after cure depended on the molecular weight of XPCL and the blend ratio. The XPCL/ESBS blends had sufficient thermal stability to show elastomeric behaviour at elevated temperature above the glass transition of the styrene domains of ESBS because of formation of crosslinking points between unlike polymer components by the reactive blending. © 1999 Society of Chemical Industry     

Preparation and dynamic mechanical properties of poly(styrene‐b‐butadiene)‐modified clay nanocomposites

Polybutyl acrylate (PBA) was intercalated into clay by the method of multistep exchange reactions and diffusion polymerization. The clay interlayer surface is modified, and obtaining the modified clay. The structures of the clay‐PBA, clay‐GA (glutamic acid), and the clay‐DMSO (dimethyl sulfoxide) were characterized using X‐ray diffraction (XRD). The new hybrid nanocomposite thermoplastic elastomers were prepared by the clay‐PBA with poly(styrene‐b‐butadiene) block copolymer (SBS) through direct melt intercalation. The dynamic mechanical analysis (DMA) curves of the SBS/modified clay nanocomposites show that partial polystyrene segments of the SBS have intercalated into the modified clay interlayer and exhibited a new glass transition at about 157°C (T_g3). The glass transition temperature of polybutadiene segments (T_g1) and polystyrene segments out of the modified clay interlayer (T_g2) are about ?76 and 94°C, respectively, comparied with about ?79 and 100°C of the neat SBS, and they are basically unchanged. The T_g2 intensity of the SBS‐modified clay decreases with increasing the amounts of the modified clay, and the T_g3 intensity of the SBS‐modified clay decreases with increasing the amounts of the modified clay up to about 8.0 wt %. When the contents of the modified clay are less than about 8.0 wt %, the SBS‐modified clay nanocomposites are homogeneous and transparent. The T_gb and T_gs of the SBS‐clay (mass ratio = 98.0/2.0) are ?78.39 and 98.29°C, respectively. This result shows that the unmodified clay does not essentially affect the T_gb and T_gs of the SBS, and no interactions occur between the SBS and the unmodified clay. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1499–1503, 2002; DOI 10.1002/app.10353     

Structural morphology and properties of star styrene–isoprene–butadiene rubber and natural rubber/star styrene–butadiene rubber blends

Star styrene–isoprene–butadiene rubber (SIBR) was synthesized with a new kind of star anionic initiator made from naphthalene lithium and an SnCl₄ coupled agent. The relationship between the structure and properties of star SIBR was studied. Star block styrene–isoprene–butadiene rubber (SB‐SIBR), having low hysteresis, high road‐hugging, and excellent mechanical properties, was closer to meeting the overall performance requirements of ideal tire‐tread rubber according to a comparison of the morphology and various properties of SB‐SIBR with those of star random SIBR and natural rubber/star styrene–butadiene rubber blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 336–341, 2004     

Effect of 60Co γ-radiation on the properties of poly(hydroxybutyrate-co-hydroxyvalerate)

The effects of ⁶⁰Co γ-radiation on the properties of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), including the chemical, mechanical, and thermal properties, were investigated. Molecular weight of the irradiated PHBV as measured using a Ubbelohde-type capillary viscometer decreased significantly. Fourier transform infrared–attenuated total reflection (FTIR–ATR) and ¹H nuclear magnetic resonance (NMR) spectra show that chain scission was the predominant reaction in the PHBV irradiated with 10 and 25 MRad doses. The G(S) value for the chain scission was 0.9, and the number of bond cleavages per molecule was 0.22 MRad⁻¹. Thermal and tensile properties of control and irradiated PHBV were examined using a differential scanning calorimeter (DSC) and an Instron tensile testing machine, respectively. Results indicate that ⁶⁰Co γ-radiation significantly affected the thermal and tensile properties of PHBV. The melting temperatures of the irradiated PHBV decreased. Tensile strength and fracture strain of the irradiated PHBV decreased dramatically, indicating increased brittleness. The fracture surfaces studied using a scanning electron microscope (SEM) showed some voids and a brittle fracture surface. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1059–1067, 1999     

Effect of γ-radiation on the thermal conductivity of polypropylene

The effect of ⁶⁰Co γ-radiation on the thermal conductivity of polypropylene (PP) has been studied over the temperature range 0–160°C. for radiation doses of 600 and 1800 Mrad. The conductivity of unirradiated specimens rises from 4.5 × 10^?4 cgs units (cal./cm.-sec.-°C.) at 0°C. to 4.8 × 10^?4cgs units at 80°C. and subsequently decreases with temperature to a value of about 3.1 × 10^?4cgs units at 160°C. Upon irradiation to 600 Mrad the thermal conductivity is lowered over the 0–150°C. temperature range. Above 90°C. the conductivity decreases with temperature and becomes relatively constant at 3.4 × 10^?4 cgs units from 120 to 160°C. Differential scanning calorimeter (DCS) measurements from 30 to 200°C. show that irradiation to 600 Mrad lowers the energy associated with crystalline melting and shifts the endotherm melting peak from about 160 to 105°C. Irradiation to 1800 Mrad results in additional lowering of the thermal conductivity over the 50–160°C. range, a further decrease in area of the endothermic peak and a shift of its maximum peak position to about 75°C. The effects of radiation on the thermal conductivity of polypropylene are compared and correlated with the observed effects of radiation on the dynamic mechanical behavior.     

Curing characteristics and mechanical properties of vinyltriethoxysilane-coupled carbon black/styrene–butadiene rubber vulcanizates

Styrene–butadiene rubber (SBR) vulcanizates containing 0 to 2.73 parts of vinyltriethoxysilane (VTEOS) per hundred parts of rubber (phr) were prepared, keeping the other ingredients weight constant. The mixes were tested for their curing behavior by a curemeter. The vulcanizates were analyzed through a Universal tensile tester, fatigue-to-failure tester, and scanning electron microscope mainly for mechanical properties and correlation. An increase in induction time and decrease in cure time, each by 10%, was noticed by the incorporation of 2.73 phr of VTEOS. The tensile strength and elongation at break improved significantly up to 0.5 phr of VTEOS and either a small improvement or deterioration of these properties was observed beyond this concentration of VTEOS. The fatigue-to-failure cycle at four extension ratios showed a gradual and appreciable improvement. It is noteworthy to mention that the vulcanizate containing 2.73 phr VTEOS possessed about a threefold increase in the fatigue-to-failure cycle compared to its non-VTEOS vulcanizate. However, this distinction of the fatigue-to-failure cycle progressively decreased with increase in the extension ratios. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1719–1725, 1998     

Anisotropy of styrene–butadiene rubber

Anisotropy of styrene–butadiene rubber (SBR) was investigated. The anisotropy of the copolymer varies linearly with the styrene content and the ultimate value coincides with that of polystyrene at elevated temperature. From these facts, the transverse configuration of the pendant phenyl group is estimated irrespective of the styrene content of SBR.     

Effect of organoclay reinforcement on the curing characteristics and technological properties of styrene–butadiene rubber

Rubber nanocomposites based on styrene–butadiene rubber (SBR) and organophilic layered silicate were prepared. Clay structures based on dodecyl benzene sulfonic acid (DBSA), nonyl phenol ethoxylate (NPE), and DBSA/NPE (50/50%) were prepared and characterized. The results indicate the intercalation of the used surfactants within the clay layers. Varying amount of organoclay, 2, 4, 6, 8, and 10 (phr), was added to the SBR matrix. X‐ray diffraction revealed exfoliated structure for the modified clay–SBR composites. No new component in the rubber was found by fourier transform infrared measurements (FTIR). Scanning electron microscopy showed a uniform distribution of the modified clay with mixed DBSA/NPE (6 phr) in the matrix. The rheometric characteristics and physicomechanical properties of the SBR compounds were analyzed. The effect of DBSA/NPE clay loading on aging resistance of SBR nanocomposites at 90 ± 1°C for 4 and 7 days was also investigated. Rubber nanocomposites displayed an increase in the minimum and maximum torques, acceleration of the vulcanization process, and improved mechanical properties, with organoclay content up to 6 phr. This effect was more noticeable in the presence of the treated clay with DBSA/NPE. Also incorporation of DBSA/NPE‐clay (6 phr) resulted in significant improvement of the degradation profile of the nanocomposites at 90 ± 1°C for 4 days. POLYM. COMPOS., 36:1293–1302, 2015. © 2014 Society of Plastics Engineers     

Preparation and properties of carbon nanotube composites with nitrile‐ and styrene‐butadiene rubbers

The work deals with the preparation and characterization of elastomer/multiwalled carbon nanotube (CNT) composites. Nitrile‐butadiene‐rubber (NBR), emulsion styrene‐butadiene‐rubber (E‐SBR) with random segment distribution, and solution styrene‐butadiene‐rubber (S‐SBR) having a blocked styrene content were used as elastomer matrix. The preparation of composites by a masterbatch process was compared to the direct melt‐mixing process using two different types of multiwalled CNT. It turned out that extremely low‐percolation thresholds of ～0.2 and 1 wt% CNT can be reached by direct melt mixing of Nanocyl 7000 CNT with S‐SBR and NBR, respectively. The effect of CNT on the vulcanization reaction was studied by application of a first‐order kinetic model. It can be shown that the rate constants are decreasing with increasing CNT content especially at higher reaction temperatures and that CNT cause a decrease in activation energies. Temperature scanning stress‐relaxation measurements were used to prove the reinforcing effect of the CNT, to verify the phase structure of the S‐SBR, and to estimate the effect of CNT on crosslink density. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Short-fiber-reinforced styrene–butadiene rubber composites

Processing characteristics, anistropic swelling, and mechanical properties of short-jute-fiber-and short-glass-fiber-reinforced styrene–butadiene rubber (SBR) composites have been studied both in the presence and absence of carbon black. Tensile and tear fracture surfaces of the composites have been studied using scanning electron microscopy (SEM) in order to assess the failure criteria. The effects of bonding agent. carbon black, jute fiber, and glass fiber on the fracture mode of the composites have also been studied. It has been found that jute fiber offers good reinforcement to SBR as compared to glass fibers. The poor performance of glass fibers as reinforcing agent is found to be mainly due to fiber breakage and poor bonding between fiber and rubber. Tensile strength of the fiber–SBR composites increases with the increase in fiber loading in the absence of carbon black. However, in the presence of carbon black a minimum was observed in the variation of strength against fiber loading. SEM studies indicate that fracture mode depends not on the nature of the fiber but on the adhesion between the fiber and the matrix.     

The characterization of styrene–β-pinene polymers

Styrene was polymerized with β-pinene at 30°C and ?50°C in methylene dichloride and in m-xylene solvents. The styrene-to-terpene ratio on pyrolysis suggests that the polymers made at 30°C are copolymers, whereas most of the polymers made at ?50°C are not copolymers. On the other hand, ethylene, ethane, and propylene analysis suggests that more of the polymers made at ?50°C are copolymers.