Reactive extrusion of polystyrene/polyethylene blends

The feasibility of inducing beneficial changes to polystyrene/polyethylene (PS/PE) blends via reactive extrusion processes is considered. Experiments have been conducted on 50:50 wt.% PS/PE blends that were treated with different levels of dicumyl peroxide and triallyl isocyanurate coupling agent. Both a low molecular weight and a high molecular weight blend series have been investigated. A “more reactive” polystyrene was synthesized by incorporation of a minor amount of ortho-vinylbenzaldehyde. Blends containing this modified polystyrene were subjected to identical processing' conditions on a counter-rotating twin screw extruder. Examination of the tensile properties of the extrusion products suggested that a judicious level of peroxide and coupling agent additives would be beneficial to the ultimate physical properties. The quantity of styrenic phase becoming chemically grafted to the polyethylene matrix was influenced most strongly by the level of the chosen coupling agent. As determined by scanning electron microscopy, the phase morphologies of the tensile test fracture surfaces were strongly dependent upon the reaction extrusion process; those extruded blends that had been exposed to the additive pre-treatment displayed substantially finer microstructure. The enthalpy of fusion of the polyethylene melting endotherm was likewise influenced by both the presence or absence of the additives as well as the molecular weight nature of the blend series.     

Reactive extrusion of polyolefin ternary blends

Reactive extrusion of polypropylene (PP)/ethylene–propylene–diene terpolymer (EPDM)/high-density polyethylene (PE) (80/10/10 by weight) blends were carried out using a corotating twin-screw extruder. The effects of peroxide and coagent concentrations and extruder rpm were studied in terms of rheological, morphological, thermal, and mechanical properties of the blends. Melt viscosity of the peroxide-treated blend increased and decreased over the untreated one depending on the amount of a coagent. Morphologically, interfaces blur with only a peroxide treatment, and significant domain reduction was obtained when peroxide and a coagent were used together. Both T_m (crystalline melting temperature) and T_g (glass transition temperature) of PP increased in the blend, whereas those of PE slightly decreased. © 1996 John Wiley & Sons, Inc.     

活性预处理三元乙丙橡胶/天然橡胶并用胶的性能

采用硫载体硫化剂4,4′-二硫化二吗啉(DTDM)对三元乙丙橡胶(EPDM)进行活性预处理,研究了活性预处理EPDM/天然橡胶(NR)并用胶的性能,并探讨了活性预处理EPDM对并用胶力学性能影响的机理。结果表明,预处理EPDM/NR并用胶的共硫化程度得到改善,并用硫化胶的力学性能提高;并用硫化胶的耐老化性能优于NR硫化胶,但比未处理EPDM/NR并用硫化胶差;并用胶只存在1个玻璃化温度的转变区,两相的相容性得到改善;在高温动态条件下,EPDM与DTDM发生活性反应,但未生成大量凝胶。     

Cure characteristics and mechanical properties of hydrogenated natural rubber/natural rubber blends

The cure characteristics and mechanical properties of blends consisting of hydrogenated natural rubber (HNR) and natural rubber (NR) blends were investigated. The HNR/NR blends at 50/50 wt ratio were vulcanized using various cure systems: peroxide vulcanization, conventional vulcanization with peroxide, and efficient vulcanization with peroxide. The HNR/NR vulcanizates cured by the combination of peroxide and sulfur donor (tetramethylthiuram disulfide, TMTD) in the efficient vulcanization with peroxide exhibited the best mechanical properties. It was also found that the hydrogenation level of HNR did not affect the tensile strength of the vulcanizates. The tensile strength of the blends decreased with increasing HNR content because of the higher incompatibility to cause the noncoherency behavior between NR and HNR. However, the HNR/NR vulcanizate at 50/50 wt ratio showed the maximum ultimate elongation corresponding to a co‐continuous morphology as attested to by scanning electron micrographs. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Microhardness studies of PMMA/natural rubber blends

The microhardness, H, of PMMA/natural rubber blends, prepared following the solution method has been investigated by means of the microindentation technique. Hardness changes are correlated with the variation of the glass transition temperature. The influence of temperature and degree of deformation on H were additionally examined. The inclusion of rubber particles in the PMMA matrix is shown to soften the blends. The variation of the micromechanical property at the phase boundary of polymer/rubber particle has been studied. Results reveal that H drastically drops at the interphase. In the case of the drawn materials, the indentation anisotropy (ΔH) is shown to gradually increase with the draw ratio, where ΔH is found to be higher for the PMMA/rubber blend than for the original PMMA. This result is explained by the higher orientation of the PMMA molecules near the periphery of stretched rubber particles. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 205–210, 2004     

Distribution of carbon black in natural rubber/acrylic rubber blends

Distributions of carbon black in 30/70% (w/w) natural rubber (NR)/acrylic rubber (ACM) blends were investigated as a function of the carbon black content and type using a dynamic mechanical thermal analysis (DMTA) technique. Two different types of carbon black (N220 and N330) were used, and 10–50 phr carbon black was compounded to the rubber blends. From the DMTA thermograms of various blends, the weight fractions of carbon black in the NR and ACM phases were calculated. Carbon black was unevenly distributed in the rubber blend. It preferred to migrate into the NR phase, regardless of the amount of carbon black that was used. By increasing the carbon black content, the weight fraction of carbon black in the NR phase decreased whereas that in the ACM phase increased. A change in the type of carbon black from N220 to N330 significantly decreased the weight fraction of carbon black in the NR phase, but it was not sufficiently strong to affect the tensile properties and hardness of the rubber blend. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:248–256, 2006     

Epoxidized natural rubber/dicarboxylic acid self-vulcanized blends

Curing behaviour as well as mechanical properties of binary blends of epoxidized natural rubber (ENR) and dodecanedioic acid (DA) were investigated for development of self-vulcanizable elastomer blends. Cross-linking reaction at 180 °C of reactive functional rubber containing 25 and 10 mol% epoxide groups was followed by rheology. The properties of the cured materials were studied by dynamic mechanical analysis, stress-strain experiments, and DSC measurements. It was shown that a specific ratio ENR/DA gave rise to optimum mechanical properties. This ratio decreases together with the epoxidation level of the rubber. DSC measurements revealed that the glass transition temperature of the cured material increases nonlinearly at high concentrations of cross-linking agent. By comparing cross-linking with DA and reaction with monofunctional lauric acid, this behaviour was attributed to polar interactions due to free carboxylic groups of pending diacid grafts.     

In situ compatibilization of PP/EPDM blends during ultrasound aided extrusion

Blends of isotactic polypropylene (iPP) and uncured ethylene-propylene diene rubber (EPDM) of various concentrations were treated by high power ultrasonic waves during extrusion. Die pressure and power consumption were measured. The effects of different gap sizes, blend ratios and number of ultrasonic horns were investigated. The rheological properties, morphology and mechanical properties of the blends with and without ultrasonic treatment were studied. In situ compatibilization of the blends was observed as evident by their more stable morphology after annealing, improved mechanical properties and IR spectra. The obtained results indicated that ultrasonic treatment induced the thermo-mechanical degradations and led to the possibility of enhanced molecular transport and chemical reactions at the interfaces. Processing conditions were established for enhanced in situ compatibilization of the PP/EPDM blends.     

Grafting of natural rubber for preparation of natural rubber/unsaturated polyester resin miscible blends

Graft copolymers of natural rubber and polystyrene were synthesized by free‐radical grafting of styrene monomer onto natural rubber in latex form. The obtained graft copolymers and unsaturated polyester (UPE) resin were mixed and cast at room temperature using methyl ethyl ketone peroxide as an initiator and Co‐octoate as an accelerator. The samples prepared from ungrafted natural rubbers exhibited the aggregation of the rubber component, whereas the samples prepared from grafted natural rubbers showed good dispersion of the rubber component in a glassy matrix of UPE resin. It was found that the amount of polystyrene grafted onto natural rubber and the graft copolymer content in polymer blend significantly affect the mechanical properties of the blend samples. An increase in the amount of hard and brittle polystyrene in glassy matrix of UPE resin overshadowed the impact‐absorbing ability of the rubber component, causing the impact strength of the blend samples to be lower than that of pure UPE resin. On the other hand, an increase in easily elongated uncrosslinked rubber molecules, as the graft copolymer content in blend samples increased, resulted in a decrease in their flexural strength. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1496–1503, 2004     

白炭黑用量对氯丁橡胶/天然橡胶共混物性能的影响

研究了不同用量的沉淀法白炭黑填充质量比75/25的氯丁橡胶/天然橡胶共混物的物理机械性能、耐热老化性能和耐油性能,并用扫描电镜研究了共混物的结构。结果显示,白炭黑的加入改善了共混硫化物的拉伸强度、100%定伸应力和邵尔A硬度。压缩永久变形减小,黏度增大,从而导致在形变的过程中天然橡胶分散相占有率相对减少。相关性能也证明随着白炭黑用量的增加,硫化胶的耐热和耐油性能显著提高。     

Effect of compatibilizers on the miscibility of natural rubber/silicone rubber blends

In this study, the blending system of natural rubber (NR) and silicone rubber (SR) at 70/30 ratio was investigated. Two kinds of graft polymers, polysiloxane‐g‐octane with different grafted ratios (polymers A, B, and C) and polysiloxane‐g‐(3,7‐dimethyl‐6‐octylene) (polymer D), were designed and synthesized to serve as compatibilizers. Dynamic mechanical analysis and scanning electron microscopy analyses showed that the compatibilizers improved the compatibility between NR and SR, and resulted in improved mechanical properties. For example, the tensile strength of the blends with compatibilizer C was 11.7 MPa, whereas that of the blends without any compatibilizer was only 7.86 MPa. The larger the grafted ratios, the better the compatibilization effect of the graft polymer. The differences in compatibilization effects between non‐reactive (polysiloxane‐g‐octane) and reactive [polysiloxane‐g‐(3,7‐dimethyl‐6‐octylene)] compatibilizers can be attributed to their different chemical compositions. The crosslink density obtained from solid‐state nuclear magnetic resonance indicated that the reactive compatibilizer (polymer D) engaged in the crosslink reaction through the active vinyl at the side chains, which effectively inhibited the decreasing trend of the crosslink density caused by the addition of compatibilizers. POLYM. ENG. SCI., 54:355–363, 2014. © 2013 Society of Plastics Engineers     

New oligomer‐bound antioxidants in natural rubber/polybutadiene rubber and natural rubber/styrene–butadiene rubber blends

New paraphenylene diamine antioxidants were prepared. The efficiency and permanence of these oligomer‐bound paraphenylene diamines were compared with those of conventional amine‐type antioxidants in elastomer blends such as natural rubber/styrene–butadiene rubber and natural rubber/polybutadiene rubber. These oligomer‐bound antioxidants showed improved aging resistance and ozone resistance in comparison with the blends containing conventional antioxidants. The liquid oligomer‐bound paraphenylene diamine could replace the plasticizer required for compounding. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 437–443, 2004     

环氧化天然橡胶共交联改性EPDM/NR共混物的性能

将三元乙丙橡胶(EPDM)与环氧化天然橡胶(ENR)共交联改性后,再与天然橡胶(NR)共混,考察了ENR共交联改性EPDM/NR共混胶的硫化特性、硫化胶的物理机械性能、溶胀指数和耐热空气老化性能,并对该硫化胶进行了差示扫描量热分析。结果表明,EPDM经过ENR共交联改性后与NR共混,ENR共交联改性EPDM/NR共混胶的交联程度明显提高,各相达到了同步交联,硫化胶的综合性能得到了显著改善。     

Thermal behavior of natural rubber and chlorinated rubber blends

A solid-state chemical reaction occurs when a solvent cast film of a blend of masticated natural rubber and chlorinated natural rubber is heated in the presence of air at 150°C. The thermal behavior of solvent cast films of chlorinated natural rubber, masticated natural rubber, and a 1 : 1 w/w blend (2% w/v in xylene) of these two polymers has been studied using differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy, and nuclear magnetic spectroscopy. The results suggest that carbonyl groups are incorporated into the blend on heating and that the vinyl functionality of the isoprene units is modified during this apparent oxidation. Heating for 2 h at 150°C results in a material that no longer contains the rubber-like cis-1,4-polyisoprene units. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1379–1384, 1997     

聚乙烯醇/天然橡胶共混物的制备及其性能研究

利用环氧化天然胶乳作为界面改性剂,采用胶乳共混法将聚乙烯醇（PVA）溶液同天然胶乳进行混溶,制备了PVA/天然橡胶（NR）的共混物,通过电子万能材料试验机、动态热机械分析仪、热老化箱和臭氧老化箱,研究了共混物力学性能、玻璃化转变温度、老化性能以及耐溶剂抽出性。结果表明,PVA的加入明显提高了NR的撕裂强度和硬度,而共混物的拉伸强度和断裂伸长率随着PVA含量的增加都出现下降的趋势;随着PVA含量的增加,NR的玻璃化转变温度呈现先增加后降低的趋势;随着PVA含量增加,共混物各试样对乙醇的耐抽出能力相差不大,对水的耐抽出能力逐步变弱。热空气老化对材料的力学性能影响明显,而臭氧老化由于时间较短,对材料的力学性能影响不明显。老化实验对材料的性能变化率影响显著。     

液体异戊橡胶对顺丁橡胶/天然橡胶共混胶性能的影响

考察了分别用自制的液体异戊橡胶和液体异戊橡胶LIR-50等量取代顺丁橡胶/天然橡胶共混胶中的天然橡胶部分时对共混胶性能的影响。结果表明,液体异戊橡胶的加入对于共混胶料的抗湿滑性能有所改善,但同时也增大滚动阻力。随着液体异戊橡胶用量(5~15份)的增加,共混硫化胶的拉伸强度、撕裂强度和扯断伸长率稍有下降,磨耗量和生热有所增大。2种液体异戊橡胶的使用效果相当。     

改性炭黑对天然橡胶/顺丁橡胶并用胶性能的影响

采用3种方法对传统炭黑进行表面改性,考察了改性前后炭黑表面形貌及结构的变化,并采用改性炭黑填充天然橡胶（NR）/顺丁橡胶（BR）并用胶,考察了改性炭黑对并用胶力学性能、硫化特性及动态力学性能等的影响。结果表明,与未改性炭黑相比,细化粒径、调高pH值及木质素改性处理后,炭黑表面的粗糙程度增加;且细化改性炭黑具有更高的比表面积,调高pH值改性炭黑具有更多疏松的二次结构,木质素改性炭黑粒径略有增加。对于炭黑填充NR/BR,用细化粒径及调高pH值方法处理的炭黑进行填充,NR/BR硫化胶的力学性能、耐磨性能及抗湿滑性均得到明显改善,但硫化延迟效应明显;木质素改性后,炭黑填充胶的力学性能、耐磨性能均出现不同程度的降低。     

Improvement of the compatibility of natural rubber/ethylene–propylene diene monomer rubber blends via natural rubber epoxidation

The longitudinal ultrasonic velocity, longitudinal ultrasonic absorption (attenuation coefficient), glass‐transition temperature, and Mooney viscosity for epoxidized natural rubber/ethylene–propylene diene monomer blends were measured. The variation of the longitudinal ultrasonic velocity with the blend ratios was linear, indicating a compatible system in comparison with the same system without epoxidation (natural rubber/ethylene–propylene diene monomer), which was incompatible. Also, the behavior was confirmed by heat of mixing calculations as well as Mooney viscosity measurements. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2816–2819, 2002     

环氧树脂增强天然橡胶/顺丁橡胶并用胶的性能

采用低相对分子质量的液体环氧树脂(EP)与固化剂混合作为增强体的前驱体,比较了其填充天然橡胶(NR)、顺丁橡胶(BR)及两者并用胶的物理机械性能,考察了EP用量对并用胶及炭黑增强并用胶物理机械性能的影响,并通过扫描电子显微镜表征了填充后的NR、BR及并用胶的微观相态结构。结果表明,EP的加入均可提高NR、BR、NR/BR并用胶的物理机械性能,其中并用胶的拉伸强度提高幅度最大;当EP用量约为24份时,NR/BR并用胶的综合性能最佳;EP可以提高炭黑增强NR/BR并用胶的物理机械性能,但提高幅度不大;EP在NR/BR并用胶中呈现规整的圆球形状,直径为1.0～2.5μm。