Transition of phase continuity induced by crosslinking and interfacial reaction during reactive processing of compatibilized PVC/SBR blends

Blends of 50 wt% of poly(vinyl chloride) (PVC) and 40 wt% of styrene butadiene rubber (SBR) with 10 wt% of acrylonitrile butadiene rubber (NBR) as the compatibilizer were prepared in a Haake mixer. An inversion of phase continuity was observed when the sulfur concentration was changed from 0.0 to 2.0 parts per hundred parts of resins (phr) in the blends containing an NBR with an acrylonitrile content of 29.5 wt% (NBR-29). The SBR phase, which is continuous in the unvulcanized blend, changes progressively into the dispersed phase as sulfur concentration increases. This is explained by the viscosity increase of the rubber caused by crosslinking. There is no phase inversion as a result of increasing sulfur concentration when the compatibilizer NBR-29 was replaced by an NBR with an acrylonitrile content of 40 wt% (NBR-40). The SBR phase is discrete in the unvulcanized blend with NBR-40 as the compatibilizer.

A change in phase continuity occurs during processing of the vulcanized PVC/NBR-29/SBR (50/10/40) blends. A torque peak in the torque curve during processing is correlated to the transition of the PVC phase continuity. There is a gradual increase in the torque curve after the torque peak. The rubber particle size decreases as a result of such a post-peak increase in the torque. The torque peak and the post-peak increase in the torque are absent in the case of the binary blends (PVC/NBR and PVC/SBR). The post-peak increase in the torque is attributed to the interfacial reaction between SBR and NBR that resides in the PVC phase.

A novel method developed recently was applied to study the interface development during processing. An interface with a higher rubber concentration develops during processing of the compatibilized blends.     

A Study of FTIR,Thermal Properties and Natural Weathering Test on NBRVirgin/Recycled with SBR Blends

The effects of styrene butadiene rubber/virgin acrylonitrile butadiene rubber (SBR/NBRv) blends and styrene butadiene rubber/recycled acrylonitrile butadiene rubber (SBR/NBRr) blends on properties such Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) were carried out. Results indicated that, based on intensity of amine peak from FTIR at 85/15 blend ratio (R15) revealed optimum formation of crosslink between SBR and NBR either using virgin or NBRr. TG thermograms of SBR/NBRv blends of all ratios showed better onset thermal stability than SBR/NBRr blends. The change in the horizontal baseline from high to low energy level occurred in virgin NBR blends because the amount of reactive sites available in virgin NBR is higher compared to NBRr. Meanwhile NBRr blends showed T_c because the amount of crosslink occurred in these blends were slightly lower than NBRv blends. Up to 25 phr of NBRr, the tensile strength and elongation at break (E_b) retention of SBR/NBRv blends was better than SBR/NBRr blends after 6 months' weathering test except for M100. The scanning electron microscopy on the surface of both blends after 6 months exposure indicated that the severity of the crack was minimal for SBR/NBRr blends compared to SBR/NBRv particularly at 50/50 blend ratio designated the SBR/NBRr blends that contained more NBRr particles could reduce the degradation towards natural weathering.     

Poly(vinyl chloride)/styrene-butadiene rubber blends prepared by dynamic vulcanization with nitrile rubber as the compatibilizer

A new kind of thermoplastic elastomer is obtained by dynamic curing of PVC/SBR blends. A compatibilizer is necessary, and of three tested—NBR and two ABSs—NBR-18 is the best. Sulfur and Dicumyl peroxide were chosen as the two different curing agents for the blends. The curing agent and its concentration have a dramatic effect on the mechanical properties. Di(2-ethyl hexyl)phthalate was used as the plasticizer for PVC. Variations in the PVC and di(2-ethyl hexyl)phthalate concentrations can produce materials having a wide range of hardness and strength to meet the needs of different applications. The effects of processing parameters such as blending time and processing temperature and the effect of filler in the blend on the mechanical properties were also investigated. The material, after processing five times, showed no significant changes in physical properties. © 1995 John Wiley & Sons, Inc.     

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

This 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 (T_g) 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     

Improvement of the homogeneity of SBR/NBR blends using polyglycidylmethacrylate‐g‐butadiene rubber

Polyglycidylmethacrylate grafted butadiene rubber (PGMA‐g‐BR) was synthesized by a graft solution copolymerization technique. The PGMA content was determined through titration against HBr. The PGMA‐g‐BR was blended with styrene butadiene rubber/butadiene acrylonitrile rubber (SBR/NBR) blends with different blend ratios. The SBR/NBR (50/50) blend was selected to examine the compatibility of such blends. Compatibility was examined using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and viscosity measurements. The scanning electron micrographs illustrate the change of morphology of the SBR/NBR rubber blend as a result of the incorporation of PGMA‐g‐BR onto that blend. The T_gs of SBR and NBR in the blend get closer upon incorporation of PGMA‐g‐BR 10 phr, which indicates improvement in blend homogeneity. The intrinsic viscosity (η) versus blend ratio graph shows a straight‐line relationship, indicating some degree of compatibility. Thermal stability of the compatibilized and uncompatibilized rubber blend vulcanizates was investigated by determination of the physicomechanical properties before and after accelerated thermal aging. Of all the vulcanizates with different blend ratios under investigation, the SBR/NBR (25/75) compatibilized blend possessed the best thermal stability. However, the SBR/NBR (75/25) compatibilized blend possessed the best swelling performance in brake fluid. The effect of various combinations of inorganic fillers on the physicomechanical properties of that blend, before and after accelerated thermal aging, was studied in the presence and absence of PGMA‐g‐BR. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1559–1567, 2006     

PVC/TPU/NBR三元共混物的制备及性能研究

对PVC／热塑性聚氨酯（TPU）／SR三元共混物的性能进行研究，重点讨论NBR品种、TPU／NBR并用比、PVC聚合度、增塑剂DOP和硫化剂DCP用量对PVC／TPU／NBR三元共混物性能的影响。结果表明。PVC／TPU／NBR-3604三元共混物的物理性能较优；PVC／TPU／NBR-3604三元共混物的拉断伸长率和拉断永久变形均随着PVC聚合度的增大基本呈上升趋势；随着增塑剂DOP用量的增大，共混物的邵尔A型硬度、拉伸强度、撕裂强度和拉断永久变形均基本呈下降趋势，拉断伸长率增大；随着硫化剂DCP用量的增大。共混物的拉伸强度和拉断伸长率变化不大，撕裂强度基本呈逐渐减小的趋势。不同PVC／TPU／SR三元共混物的扫描电子显微镜照片表明，NBR与PVC和TPU的相容性较好。     

Mechanical Properties and Thermooxidative Aging of a Ternary Blend,Pvc/Enr/Nbr,Compared with the Binary Blends of Pvc

In the quest to improve the thermooxidative aging of the poly(vinyl chloride)/epoxidized natural rubber (PVC/ENR) blend, nitrile rubber (NBR) was incorporated into the blend to yield a ternary blend of PVC/ENR/NBR. A Brabender Plasticorder with a mixing attachment was used to perform the melt mixing at 150°C and 50 rpm followed by compression molding. The mechanical properties, dynamic mechanical properties, and thermooxidative aging behavior of the ternary blend were compared with those of the binary blends (i.e., PVC/ENR and PVC/NBR). It was found that the ternary blend exhibits mechanical properties which are superior to those of PVC/ENR. A single glass transition temperature (T _g) obtained from dynamic mechanical analysis coupled with synergism in the modulus and some other mechanical properties indicate that PVC, ENR, and NBR form a single phase (miscible system) in the ternary blend. Di-2-ethyl hexylphthalate (DOP) plasti-cizer improves the aging resistance of the blends generally, whereas the presence of CaCO₃ as a filler only imparts minor influences on the properties and aging resistance of the blends.     

DMA analysis of the damping of ethylene–vinyl acetate/acrylonitrile butadiene rubber blends

The mechanical and damping properties of blends of ethylene–vinyl acetate rubber (VA content > 40% wt) (EVM)/acrylonitrile butadiene rubber (NBR), with 1.4 phr BIPB [bis (tert‐butyl peroxy isopropyl) benzene] as curing agent, were investigated by DMA and DSC. The effect of chlorinated polyvinyl chloride (CPVC), silica, carbon black, and phenolic resin (PF) as a substitute curing agent, on the damping and mechanical properties of EVM/NBR blends were studied. The results showed that 10 phr CPVC did not contribute to the damping of EVM700/NBR blends; Silica could dramatically improve the damping of EVM700/NBR blends because of the formation of bound rubber between EVM700/NBR and silica, which appeared as a shoulder tan δ peak between 20 and 70°C proved by DMA and DSC. This shoulder tan δ peak increased as the increase of the content of EVM in EVM/NBR blends. The tensile strength, modulus at 100% and tear strength of the blend with SiO₂ increased while the elongation at break and hardness decreased comparing with the blend with CB. PF, partly replacing BIPB as the curing agent, could significantly improve the damping of EVM700/NBR to have an effective damping temperature range of over 100°C and reasonable mechanical properties. Among EVM600, EVM700, and EVM800/NBR/silica blend system, EVM800/NBR/silica blend had the best damping properties. The EVM700/NBR = 80/10 blend had a better damping property than EVM700/NBR = 70/20. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Micromechanical properties on the surface of PVC/SBR blends spatially resolved by a nanoindentation technique

The microhardness and micromodulus on the surface of poly(vinyl chloride) (PVC)/styrene‐butadiene rubber (SBR) blends were determined using a nanoindenter. A flat surface was obtained by microtoming the sample at ?100°C in liquid nitrogen. Dozens of indents along a line with a spatial interval of 0.5 μm were performed. From the loading and unloading curves of each indentation, the stiffnesses of the unloading curve and the contact area between the sample and the indenter were evaluated, and the local modulus and hardness were calculated. Profiles of the local hardness and modulus were obtained from the lines of indents. Pure PVC and a miscible PVC/acrylonitrile‐butadiene rubber (NBR) (40/10) blend showed constant modulus and hardness values. In the case of an immiscible PVC/SBR (50/50) blend, which has a morphology of elongated PVC droplets in the SBR matrix, the hardness and modulus profiles showed regions of the different phases. At the interface between the SBR and PVC phases, a step change in the modulus and hardness profiles was observed. The force required to deform the material at the same displacement increased systematically across the interface from the SBR to the PVC phase because of the increasing contribution of the PVC phase. Polym. Eng. Sci. 44:609–614, 2004. © 2004 Society of Plastics Engineers.     

Homogeneous Styrene Butadiene/Acrylonitrile Butadiene Rubber Blends

The graft copolymerization of acrylonitrile (AN) onto butadiene rubber (BR) was carried out in toluene at 80°C, using dibenzoyl-peroxide (BPO) as initiator. The synthesized poly acrylonitrile-grafted-butadiene rubber (AN-g-BR) was characterized by N% elemental analysis and Fourier-transform infrared (FT-IR) spectroscopy. Styrene butadiene rubber/acrylonitrile butadiene rubber (SBR/NBR) blends were prepared with different blend ratios in presence and absence of AN-g-BR, where the homogeneity of such blends were examined with intrinsic viscosity (η) measurements, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The scanning electron micrographs illustrate disappearance of the macro-scale phase separation of SBR/NBR rubber blend as a result of the incorporation of AN-g-BR into that blend. Viscosity measurements confirm homogeneity of that blend. Differential Scanning Calorimetry traces exhibit shifts in glass transition temperatures (T _g's) of SBR and NBR in their blend, indicating some degree of homogeneity. Physico-mechanical properties of the rubber blend vulcanizates with different blend ratios, in presence and absence of AN-g-BR, were investigated before and after accelerated thermal aging. The SBR/NBR (25/75) homogeneous blend possessed the best physico-mechanical properties after thermal aging, together with the best swelling behavior in motor oil. The physico-mechanical properties of SBR/NBR (25/75) filled blend with different types of inorganic fillers during thermal aging were studied.     

动态硫化PVC/SBR共混体系的研究

采用动态硫化法制备了ＰＶＣ／ＳＢＲ共混物，考察了橡塑比、硫化体系、相容剂及ＰＶＣ交联对共混物性能的影响。结果表明，当ＰＶＣ／ＳＢＲ并用比为７５／２５，相容剂ＮＢＲ／氯化聚乙烯并用比为２．５／２．５，采用半有效或半有效加２份交联剂ＤＣＰ的硫化体系时，共混物综合性能较好。在ＰＶＣ中加入０．４份促进剂ＮＡ－２２可明显改善共混物的压缩永久变形。     

Electrical and Mechanical Properties of Some Butadiene Rubber Composites in the Vicinity of the Percolation Threshold

The electrical and mechanical properties of NBR/SBR blends with different compositions were studied before the addition of carbon black. The increase in permittivity ε′ and dielectric loss ε″ noticed by increasing NBR content is due to the increase in C ≡ N dipoles. The mechanical properties which include tensile and elongation at yield and rupture are also found to be increased. This work also includes the compatibility study, which was carried out using different tools and techniques (Heat of mixing, dielectric and scanning electron microscope). This study led to a conclusion that both blends are incompatible.

The electrical as well as the mechanical properties were carried out on NBR, SBR and NBR/SBR blend (50/50) to be loaded with different concentrations of high abrasion furnace black (HAF) in order to find out the percolation thresholds in relation to the net work formation.

The electrical conductivity of carbon-black-filled composites is increased from pure polymer to that of pure carbon, through the change in the different composites. Up till certain concentration of HAF (30 phr for both NBR and SBR) and 20 phr for NBR/SBR blends the conductivities of the composites are approximately the same and closed to that of the pure, electrically insulating polymer matrix. These concentrations are called percolation thresholds. Above such concentrations, the conductivity increases many orders of magnitude with very little increase in the filler amount. With this increase the tendency of conductivity chain formation increases through the aggregation of the carbon black particles network. The change in conductivity beyond the percolation threshold is expressed according to the percolation theory with straight line when plotted graphically versus P-P_c; P_c is the volume fraction of carbon black at the percolation threshold.

In addition to the conductivity term, the data of permittivity ε′ and dielectric loss ε″ given at different frequencies from 100 Hz up to 100 kHz show an abrupt increase at 30 phr HAF for NBR & SBR and 20 phr HAF for NBR/SBR. More over, the relaxation times obtained from the analyses of these data using Fröhlich and Havriliak-Nagami functions, which ascribe the orientation of the large aggregates caused by the movement of the main chain also show an abrupt increase at the same concentration of HAF.

The mechanical properties, which investigated through the measurements of tensile and elongation at yield and rupture indicate an abrupt increase at the same concentration of HAF found in the case of electrical measurements. This result gives evidence to the good applicability between both mechanical and electrical investigations through the network formations.

Any how, the percolation threshold found in case of NBR/SBR blend is less than that for NBR itself. This result is attributed to the uneven distribution of the filler in the incompatible blend matrix.     

Mechanical and thermo-oxidative properties of blends of poly(vinyl chloride) with epoxidized natural rubber and acrylonitrile butadiene rubber in the presence of an antioxidant and a base

Being polar and compatible with poly(vinyl chloride), epoxidized natural rubber (ENR) is similar in behaviour to acrylonitrile butadiene rubber (NBR). To assess the extent of this similarity, the mechanical properties of 50/50 blends of PVC with these two rubbers were compared. Their response to thermo-oxidative ageing in the presence of an antioxidant and a base was also investigated by ageing the blends at 100°C for 7 days. Studies involving mechanical properties and FTIR were used to evaluate the extent of thermal degradation. The results revealed that blends of ENR show mechanical properties which are as good as, and in some instances better than, those of the NBR blends. However, the ENR blends with PVC are very prone to oxidative ageing. This might be attributed to the susceptibility of the oxirane group to ring-opening reactions, particularly in the presence of PVC, which yields HCl as it degrades. The amine-type antioxidant 2,24-trimethyl-1,2-dihydroquinoline (TMQ) improved the oxidative stability of both blends. This was more significant in the ENR blend, which in some cases attained stability comparable with that of NBR. The addition of a base, calcium stearate [Ca(St)₂], did not show any influence in the PVC/ENR blend, even though it was expected to curb acid-catalysed degradation. Ca(St)₂, however, improved the oxidative stability of the PVC/NBR blend. The combination of optimum amounts of TMQ and Ca(St)₂ effectively improved the tensile strength of both unaged blends, without appreciable adverse effect on elongation at break. This combination also imparted stability better than that of TMQ alone.     

Compatibility studies on some polymer blend systems by electrical and mechanical techniques

Systematic electrical and mechanical studies were carried out on natural rubber (NR) blended with different types of synthetic rubber such as styrene‐butadiene rubber (SBR), polybutadiene rubber (BR), and ethylene‐propylene‐diene monomer (EPDM) as nonpolar rubbers and nitrile‐butadiene rubber (NBR) and chloroprene rubber (CR) as polar rubbers. The NR/SBR, NR/BR, NR/EPDM, NR/NBR, and NR/CR blends were prepared with different ratios (100/0, 75/25, 50/50, 25/75, and 0/100). The permittivity (ε′) and dielectric loss (ε″) of these blends were measured over a wide range of frequencies (100 Hz–100 kHz) and at room temperature (∼ 27°C). The compatibility results obtained from the dielectric measurements were comparable with those obtained from the calculation of the heat of mixing. These results were confirmed by scanning electron microscopy and showed that NR/SBR and NR/BR blends were compatible while NR/EPDM, NR/NBR, and NR/CR blends were incompatible. To overcome the problem of phase separation (incompatibility) between NR and EPDM, NBR, or CR, a third component such as SBR or poly(vinyl chloride) (PVC) was added as a compatibilizing agent to these blends. The experimental data of dielectric and mechanical measurements showed that the addition of either SBR or PVC could improve the compatibility of such blends to some extent. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 60–71, 2001     

Curing Characteristics and Mechanical and Morphological Properties of Styrene Butadiene Rubber/Virgin Acrylonitrile-Butadiene Rubber (SBR/vNBR) and Styrene Butadiene Rubber/Recycled Acrylonitrile-Butadiene Rubber (SBR/rNBR) Blends

Curing characteristics and mechanical and morphological properties of styrene butadiene rubber/virgin acrylonitrile-butadiene rubber (SBR/vNBR) and styrene butadiene rubber/recycled acrylonitrile-butadiene rubber (SBR/rNBR) were investigated. Results indicated that the curing characteristics, such as scorch time, t₂, and cure time, t₉₀, of SBR/vNBR and SBR/rNBR blends decreased with increasing vNBR and rNBR content. At similar blend ratios, particularly up to 15 phr, SBR/rNBR blends exhibited higher t₂ and t₉₀ compared with SBR/vNBR blends. Minimum torque (ML) and maximum torque (MH) of SBR/vNBR blends significantly increased with increasing vNBR content. For SBR/rNBR blends, ML increased with increasing rNBR content, but MH exhibited the opposite trend. Tensile strength, elongation at break (E_b), resilience, and fatigue decreased with increasing virgin and recycled NBR content in both blends. Up to 15 phr, the tensile strength, E_b and fatigue life (Kc) of SBR/rNBR blends were higher than in SBR/vNBR blends. The M100 (stress at 100% elongation), hardness, and cross-linking density of both blends also showed an increasing trend with increasing vNBR and rNBR content. The scanning electron microscopy study indicates that rNBR exhibited a weak rNBR-SBR matrix interaction particularly when more than 15 phr of rNBR was used, thus decreasing the mechanical properties of SBR/rNBR blends.     

The Effect of Epoxidized Sunflower Oil on the Miscibility of Plasticized PVC/NBR Blends

Blends of plasticized poly(vinyl chloride) (PVC) with several ratios of nitrile rubber (NBR) were studied. The effects of epoxidized sunflower oil (ESO) in combination with di-(2-ethylhexyl)phthalate (DEHP) in the PVC blends on the tensile strength, elongation, hardness, and dynamical mechanical analysis (DMA) were studied. The modulus and hardness results revealed that the addition of ESO to the blend favors the miscibility of PVC and NBR. The PVC/NBR/(DEHP-ESO) blends behave as a compatible system as is evident from the single T _g observed in DMA. The moderate level broadening of the T _g zone in blends is due to the presence of ESO in the plasticizer system. Blends of plasticized PVC and nitrile rubber showed promising properties. The ESO is suitable to partially replace DEHP in PVC/NBR blends.     

丁腈橡胶－40／三元共聚型氯醚橡胶并用的研究

对丁腈橡胶－４０（ＮＢＲ－４０）与三元共聚型氯醚橡胶（ＣＨＣ）进行了并用研究．发现二者之间的相容性良好。ＮＢＲ－４０／ＣＨＣ并用比为８０／２０时，胶料的综合物理性能较好；为７０／３０时．胶料耐４０＃机油的性能最好；耐四氯化碳溶剂的性能随并用比的减小（ＣＨＣ用量增加）而提高。胶料硫化体系以过氧化物硫化体系［过氧化二异丙苯（ＤＣＰ）／硫黄／四氧化三铅／促进剂ＮＡ－２２］最佳，补强剂选用中超耐磨炭黑。