Influence of Crosslink Density on Mechanical Properties of Natural Rubber Vulcanizates

Crosslink density is an important structural parameter for cured rubber. Natural rubber (NR) vulcanizates with different crosslink densities were obtained through using different sulfur and accelerator amounts and different accelerator types. The crosslink density was characterized by an ¹ H-NMR technique and its influence on mechanical properties, such as Shore A hardness, 300% modulus, tensile strength, and elongation at break, of NR vulcanizates was investigated. The results showed that both the sulfur amount and the accelerator type and amount had an influence on the crosslink density of the NR networks. The relationship between total crosslink density and mechanical properties was also studied. The results, by changing either the sulfur or the accelerator amount, showed that tensile strength of NR vulcanizates reached maximum value when the total crosslink density was around 13.5 × 10^?5 mol/cm³, equivalently the average molecular weight of the intercrosslink chains (Mc) was around 7000 g/mol. The maximum value of tensile strength came from the balance between contributions of crosslink joints and stretch-induced orientation and/or crystallization of intercrosslink chains. The study on influence of total crosslink density on Shore A hardness and 300% modulus of NR vulcanizates showed that they both increased linearly with the crosslink density, the slopes were 2.7 ～ 3.0 cm³/10^?5 mol and 0.27 ～ 0.31 MPa cm³/10^?5 mol for Shore A hardness and 300% modulus, respectively, whether the crosslink density was varied by sulfur or accelerator.     

Ecofriendly latex films from cassava starch-filled radiation pre-vulcanized natural rubber latex

ABSTRACT

The demands of the usage of hazardous ingredients for sulfur curing system in latex industries decrease with an increase in health-conscious and environmental awareness. This work demonstrates the incorporation of cassava starch (CS) as biodegradable fillers with natural rubber latex (NRL) through a sulfur-free crosslinking technique using radiation pre-vulcanization natural rubber latex (RVNRL) in comparison to sulfur pre-vulcanized natural rubber latex (PvNRL). The 20% CS dispersion was prepared, and 5–25?phr of dispersed CS content were compounded with NRL and formed into films by the coagulant dipping method. Microstructures and crystallinity of the films were analyzed by scanning electron microscopy (SEM) and X-ray diffraction, and their mechanical properties of NRL/CS films were characterized by tensile and tear tests. The result revealed that the crystallinity of RVNRL films was lower than PvNRL films. The total bond of S?C from PvNRL contributes to high tensile strength compared to C?C intermolecular rubber bond from radiation vulcanization system. The trend of decrement of tensile properties from sulfur crosslinking was larger than radiation crosslinking, and both systems gave similar tensile behavior at 25?phr of CS content. This attributed to the better dispersion of CS in RVNRL as confirmed by SEM micrographs. It was found that the optimum tear strength of RVNRL/CS and PvNRL/CS films was obtained at 10 and 5?phr of filler content, respectively. The result presented in this study may facilitate a contribution to the current literature on the development of latex film by radiation pre-vulcanization for rubber industry in the future.     

Synthesis of nanoparticles and its effect on properties of elastomeric nanocomposites

Calcium carbonate (CaCO₃) nanoparticles (9, 15, and 21 nm) were synthesized by solution spray of CaCl₂ and NH₄HCO₃ with sodium lauryl sulfate (SLS) as a stabilizing agent, and their effect was studied on polybutadiene rubber (PBR) with variations in wt% loading (4, 8, and 12%). The results of PBR nanocomposites were compared with commercial CaCO₃ (40 μm) and fly ash (75 μm) filled PBR microcomposites. Properties such as tensile strength, young modulus, elongation at break, glass transition temperature, decomposition temperature, and abrasion resistances were determined. Profound effect in properties was observed, because nanometric size of CaCO₃ particles synthesized using solution spray technique. Maximum improvement in mechanical and flame retarding properties was observed at 8 wt% of filler loading. This increment in properties was more pronounced in 9-nm size CaCO₃. The results were not appreciable above 8 wt% of nanofillers because of agglomeration of nanoparticles. In addition, an attempt was made to consider modeling Young’s modulus of PBR–nano CaCO₃ which was predicted by modified Halpin–Tsai equation. It was observed that the predication by the Guth equation and modified Halpin–Tsai equation agreed very well with experimental, whereas the Halpin–Tsai equation can only applied to predict the modulus of rubber nanocomposites in the range of low addition of nanofiller, which agrees the Nielsen equation.     

Effect of Surface Structure of Nano-CaCO3 Particles on Mechanical and Rheological Properties of PVC Composites

To study the effect of different surface structures on resultant mechanical and rheological properties, nano-CaCO₃ particles were treated with isopropyl tri-stearyl titanate (H928), isopropyl tri-(dodecylbenz-enesulfonyl) titanate (JN198), and isopropyl tri-(dioctylpyrophosphato) titanate (JN114). Scanning electron microscopy (SEM) and dynamic mechanic analysis (DMA), carried out to characterize the effective interfacial interaction between the nano-CaCO₃ particles and a poly(vinyl chloride) (PVC) matrix, indicated that JN114 treated nano-CaCO₃ particles had the strongest interfacial interaction with a PVC matrix, while H928 treated nano-CaCO₃ had the weakest. The rheological and mechanical properties of PVC/nano-CaCO₃ composites were investigated as a function of surface structure and filler volume fraction. The tensile yield stress and elongation at break decreased with the increasing of calcium carbonate content while tensile modulus increased. PVC filled with JN114 treated nano-CaCO₃ had the highest tensile modulus and tensile yield stress, while those filled with H928 treated nano-CaCO₃ had the highest elongation at break at the same filler content. The impact strength of PVC/nano-CaCO₃ composites increased with the increasing of CaCO₃ content, and PVC composites filled with JN198 treated nano-CaCO₃ particle had a higher impact strength than those with JN114 or H928 treated, with the value reaching 23.9 ± 0.7 kJ/m² at 11 vol% CaCO₃, four times as high as that of pure PVC. Rheological properties indicated that a suitable interfacial interaction and a good dispersion of inorganic filler in a PVC matrix could reduce the viscosity of PVC/nano-CaCO₃ composites. The interfacial interaction was quantitatively characterized by semiempirical parameters calculated from the tensile strength of PVC/nano-CaCO₃ composites to confirm the results from the SEM and DMA experiments.     

Enhancing mechanical properties of prevulcanized natural rubber latex via hybrid radiation and peroxidation vulcanizations at various irradiation doses

At present, there are three popular vulcanization processes being used in natural rubber latex industries, which are sulfur, radiation and peroxide vulcanization. Sulfur vulcanization produced products with superior mechanical properties compared to radiation and peroxide vulcanization. This paper discussed the effect of gamma irradiation dose on hybrid radiation and peroxidation vulcanizations in improving the mechanical properties of radiation vulcanized natural rubber latex (RVNRL). Latex compounding formulations are developed based on 2.5?parts per hundred rubber (phr) of hexanediol diacrylate (HDDA) as the sensitizer, 0.1?phr of tert-butyl hydroperoxide (t-BHPO) as the co-sensitizer and 2.5?phr of Aquanox LP antioxidant. The RVNRL was prepared and irradiated at various gamma radiation doses of 2, 4, 6, 8, 10 and 12?kiloGray (kGy). The rubber film obtained from irradiation at 6?kGy had tensile strength, modulus @ 500% and modulus @ 700% of 27.0, 3.0 and 11.0?MPa, respectively, which is more than 37% increment compared to the control film. Besides, the crosslink percentage of the rubber film showed 4% increment from 90% to 94%.     

Morphology, mechanical, cross-linking, thermal, and tribological properties of nitrile and hydrogenated nitrile rubber/multi-walled carbon nanotubes composites prepared by melt compounding: The effect of acrylonitrile content and hydrogenation

The purpose of this work was to prepare nanocomposites by mixing multi-walled carbon nanotubes (MWCNT) with nitrile and hydrogenated nitrile elastomers (NBR and HNBR). Utilization of transmission electronic microscopy (TEM), scanning electron microscopy (SEM), and small- and wide-angle X-ray scattering techniques (SAXS and WAXS) for advanced morphology observation of conducting filler-reinforced nitrile and hydrogenated nitrile rubber composites is reported. Principal results were increases in hardness (maximally 97 Shore, type A), elastic modulus (maximally 981 MPa), tensile strength (maximally 27.7 MPa), elongation at break (maximally 216%), cross-link density (maximally 7.94 × 10²⁸ m⁻³), density (maximally 1.16 g cm⁻³), and tear strength (11.2 kN m⁻¹), which were clearly visible at particular acrylonitrile contents both for unhydrogenated and hydrogenated polymers due to enhanced distribution of carbon nanotubes (CNT) and their aggregated particles in the applied rubber matrix. Conclusion was that multi-walled carbon nanotubes improved the performance of nitrile and hydrogenated nitrile rubber nanocomposites prepared by melt compounding.     

Nanocomposites Prepared by Solution Blending: Microstructure and Mechanical Properties

Composites of poly(vinyl chloride) (PVC) filled with micron‐ and nanosized calcium carbonate (CaCO₃) particles were prepared by solution blending. The influences of particle size and CaCO₃ content on the microstructure and mechanical properties of the PVC composites were investigated by means of polarized optical microscopy and mechanical testing. The polarized optical microscope images revealed that nanosized CaCO₃ particles were more agglomerated than micron‐sized CaCO₃ particles and the amount of agglomerates increased with increasing particle content. PVC/CaCO₃‐0.22 composites (PVC nanocomposite filled with 220‐nm‐particle‐sized CaCO₃) 5 phr CaCO₃ content had the maximum tensile strength. The Young's modulus of all composites increased with increasing particle content. The energy at break of all composites showed a decreasing trend as a function of CaCO₃ content and varied with particle size.     

The Effect of Oil‐Extension on the Properties of TPI and TPI/SBR Vulcanizates

Trans‐1,4‐polyisoprene (TPI) with a Mooney viscosity of 120 was filled with 37.5 phr aromatic oil to prepare oil‐extended trans‐1,4‐polyisoprene (OETPI) by a dry oil‐extending process. The curing characteristics of TPI gum, OETPI gum, and TPI/SBR compounds were studied and the mechanical properties of vulcanizates were also investigated. The experimental results showed that the Shore A hardness, Mooney viscosity, and mechanical properties of OETPI gum decreased, compared with that of TPI gum. The modulus at 100% elongation, Shore A hardness, and tensile strength of OETPI vulcanizates also decreased, while the abrasion loss, compression heat build‐up, and compression set increased. Compared with TPI/SBR, the dispersibility of carbon black in OETPI/SBR compounds was improved. The mechanical properties of OETPI/SBR vulcanizates changed little, while the wet skid resistance and fatigue resistance was greatly improved.     

Investigation of the Morphological and Mechanical Properties of Polyethylene Terephthalate (PET)/Ethylene Propylene Diene Rubber (EPDM) Blends in the Presence of Multi-Walled Carbon Nanotubes

In this study the blends of polyethylene terephthalate (PET)/ethylene propylene diene rubber (EPDM) in the presence of multi-walled carbon nanotubes (MWCNT) (1 and 3?wt %) were prepared by melt compounding in an internal mixer. Mechanical and morphological properties of the nanocomposites were investigated. The thermal behaviors of the PET/EPDM nanocomposites were also investigated, by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results of the mechanical tests showed that the tensile strength, elastic modulus and the hardness of the blends were increased with increasing CNT, while the impact strength and elongation at break decreased. The DSC and TGA results showed an increase of melting temperature (T_m) and degradation temperature of the nanocomposites with the addition of the carbon nanotubes, because the carbon nanotubes serve both as nucleating agents to increase T_m and prevent the composite from degradation to increase the thermal stability. The microstructure of the composites was evaluated through field emission scanning electron microscopy (FESEM) and the results showed a good distribution of the MWCNT within the polymer blend.     

Thermal and mechanical properties of gamma-irradiated prevulcanized natural rubber latex/low nitrosamines latex blends

Thermal and mechanical properties of blended radiation prevulcanized natural rubber latex (RVNRL) and low nitrosamines latex (LNL) were studied. RVNRL was blended with LNL at various composition ratios. From the tensile test, it was found that the optimum tensile value was attained at a total blending ratio of 70% RVNRL and 30% LNL. Latex blending with optimum tensile strength was then subjected to gamma irradiation at various doses with the presence and absence of methyl methacrylate (MMA) at 10?pphr. It was found that the gamma irradiation of latex blend with the presence of MMA could help increase further the tensile value. Composition of blending at a specific ratio and gamma irradiation at a specific dose has led to a significant improvement in the mechanical properties of the latex blend. The formation of grafting in the latex blend was characterized by Fourier transform infrared spectra (FTIR) spectroscopy and differential scanning calorimetry (DSC). FTIR spectroscopy confirmed that MMA could be grafted onto blended latex effectively under appropriate irradiation conditions. Two new peaks at 1731 and 1149?cm^?1 were observed after irradiation, indicating the presence of an ester group from poly(methyl methacrylate) (PMMA), which was grafted onto rubber chains. This finding was proved by the presence of new T_g in DSC analysis. The increase in new T_g indicates the movement of grafting chains, which are tightly bound onto rubber chains.     

Comparative Properties of Styrene-Butadiene Rubbers (SBR) Containing Pyrolytic Carbon Black,Conventional Carbon Black,and Organoclay

To evaluate the reinforcing potential of pyrolytic carbon black, styrene-butadiene rubber (SBR) was filled with pelletized pyrolytic carbon black (pCB_p), N660 industrial CB, their blend in a 1/1 ratio, and the latter also in the absence and presence of additional organoclay (OC). The Shore A hardness of the filled SBR gums was 65 ± 2°. Effects of the compositions on the filler dispersion, cure behavior, dynamic mechanical thermal parameters (including the Payne effect), tensile mechanical (including the Mullins effect), and fracture mechanical (making use of the J-integral concept) properties were studied and discussed. Though pCB_p had a higher specific surface weight than CB, the latter proved to be a more active filler with respect to the tensile strength. The opposite tendency was found for the tear strength and fracture mechanics characteristics (J-integral at crack tip opening, tearing modulus, and trouser tear strength). This was traced to an enlargement in the crack tip damage zone supported by the dispersion characteristics of the pCB_p. The performance of pCB_p was similar to that of CB with respect to some other properties. OC supported the filler networking which positively affected the resistance to crack initiation.     

Mechanical Properties of Rubber Sheets Produced by Direct Molding of Ground Rubber Tire Powder

The so called “direct powder molding” is a compressions molding process which can be directly applied to ground rubber tire (GRT). This study shows that the GRT can be re-used to produce medium-size parts with good mechanical properties without any addition of virgin rubber. For rubber sheets prepared from the mechanically ground rubber tire (MGRT) and the cryogenically ground rubber tire (CGRT), the densities and crosslink densities of the rubber sheets increased with a decrease of the particle size of the waste tire powder. The tensile strength of the rubber sheets increased with the decreasing of the particle size for the two types of waste tire powder to 250 μm and 120 μm, respectively, and then became level. The moulding pressure had no effect on the densities, tensile strength or elongation at break of the rubber sheets. These results suggested that the effect of the particle size is important and is correlated with the mechanical properties of the rubber sheets produced by direct powder moulding technology. In general, the best mechanical properties were obtained with waste tire rubber with a size of about 250 μm for the rubber particles obtained from the mechanical grinding method of waste tire powdering.     

Natural rubber nanocomposites using polystyrene-encapsulated nanosilica prepared by differential microemulsion polymerization

In this study, nanocomposites of natural rubber (NR) and polystyrene (PS)-encapsulated nanosilica were prepared by latex compounding method. The nanolatex of PS-encapsulated silica was synthesized via in situ differential microemulsion polymerization. The resulted hybrid nanoparticles showed core-shell morphology with an average diameter of 40 nm. The silica hybrid nanoparticles were subsequently used as filler for the NR nanocomposite. The properties of NR were found to be improved as a result of the incorporation of PS-encapsulated nanosilica at 3 and 3-9 parts per hundred rubber (phr) for tensile strength and modulus at 300% strain, respectively, except the elongation at break, and up to 9 phr for flammability. The results from dynamic mechanical analyzer showed that the elastic properties of NR near the glass transition temperature increased with the inclusion of increasing concentration of the PS-encapsulated nanosilica, causing by the semi-interpenetrating nanostructure in the NR nanocomposites.     

甲基苯基乙烯基硅橡胶电离总剂量效应

甲基苯基乙烯硅橡胶具有耐高低温、防震等独特优势,在航天器的减震、密封等领域具有广泛应用前景。研究了甲基苯基乙烯基硅橡胶的电离总剂量效应。结果表明,随着辐射剂量的增加,甲基苯基乙烯基硅橡胶的力学性能出现了不同程度的退化。拉伸强度和撕裂强度变化规律以1×106 Gy(Si)剂量点为分界点。低于该剂量,拉伸和撕裂随剂量增加快速下降;高于该剂量时,随辐照剂量增加,拉伸强度出现一定程度反弹,呈现出宽"U"形,而撕裂强度则是先增加后下降。拉断伸长率和邵氏硬度A随辐照剂量增加分别出现快速下降和增加,最终接近饱和。最后,从辐射交联和裂解方面讨论了甲基苯基乙烯基硅橡胶电离总剂量效应的潜在物理机制。     

Preparation and characterization of a novel antistatic poly(vinyl chloride)/quaternary ammonium based ion-conductive acrylate copolymer composites

Antistatic poly(vinyl chloride)/quaternary ammonium salt based ion-conductive acrylate copolymer (PVC/QASI) composites were successfully prepared in a Haake torque rheometer. The surface resistivity of the PVC/QASI composites could be reduced to 10⁷ Ω sq^?1 order of magnitude when the QASI content reached 20 phr (parts per hundreds of resin). The surface resistivity of the composites was slightly sensitive to the relative humidity (RH), showing a good antistatic ability under an RH of 12%. Mechanical properties tests, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were also used to investigate the tensile strength, elongation at break, thermal properties, and morphology of the PVC/QASI composites, respectively.     

Studies on interface in polyester/fly-ash particulate composites

Fly ash (FA)-general purpose unsaturated polyester resin (GPR) particulate composites have been made. The effect of surface treatment of FA with two different silane coupling agents (CAs) on the mechanical properties like tensile, flexural, impact strength and hardness, thermal properties like thermal stability and morphological properties (SEM) of FA-GPR composites are studied. The properties of FA-CA-GPR are also compared with that of GPR and CaCO₃ -GPR. An enhancement in the tensile, flexural, and impact strength and moduli are observed when FA is surface treated with CA. Hardness is also found to increase with CA-treated FA-filled GPR. A suitable mechanism for the chemical reaction taking place at the interface in the presence of CAs is proposed.     

Surface treatment of CaCO3 with a mixture of amino- and mercapto-functional silane coupling agents and tensile properties of the rubber composites

In order to reinforce the composite consisting of isoprene rubber (IR) and calcium carbonate (CaCO₃) particles, the surface treatment of CaCO₃ particles with a mixture of amino- and mercapto-functional silane coupling agents was investigated. The quantity of chemisorbed silanes in treated CaCO₃ measured using thermogravimetry was greater for amino- than for mercapto-silane and for the tri- than for the dialkoxy structure. Second, the molecular mobility of polycondensate of the mixtures with the trialkoxy structure measured using ¹H pulse nuclear magnetic resonance had the least molecular mobility, i.e., formed the highest density network. The greater values of stress at 500% strain, fracture stress, and elongation at break were determined for the treatment with amino- and mercapto-functional silanes having a trialkoxy structure from the stress-strain curves of composite. The mixture treatment with dialkoxy structure and with amino- or mercapto-functional silane only did not improve the mechanical properties sufficiently. Interactions between the amino group and the CaCO₃ surface, covalent bonding between the mercapto group and the IR, and high density network formation of trialkoxy silane were important for improving the mechanical properties of the composite.     

凹凸棒石/硅橡胶复合材料的热氧化降解和老化性能研究

本文采用高压均质结合对辊挤压工艺对天然凹凸棒石进行棒晶解离得到了纯度较高和比表面积较大(133.7 m²/g)的纳米解离凹凸棒石. 进一步通过机械共混法分别将天然凹凸棒石和纳米解离凹凸棒石与硅橡胶生胶复合制备了天然凹凸棒石-硅橡胶和纳米解离凹凸棒石-硅橡胶材料,研究了天然凹凸棒石和纳米解离凹凸棒石对凹凸棒石/硅橡胶复合材料热氧化降解和老化性能的影响. 结果表明,天然凹凸棒石-硅橡胶和纳米解离凹凸棒石-硅橡胶在300 oC热氧老化处理0.5 h后,相比于纯硅橡胶,初始5%失重温度从385 oC提高至396∽399 oC. 系列表征结果表明,天然凹凸棒石和纳米解离凹凸棒石增强了纳米粒子与硅橡胶之间的相互作用从而抑制了纳米颗粒聚集,并且可显著提高硅橡胶侧链Si-CH₃的保存率,从而提高了该复合材料的热氧化降解和老化性能. 此外,纳米解离凹凸棒石可大大抑制纳米粒子的长大;因此老化后,纳米解离凹凸棒石-硅橡胶表现出了比硅橡胶(10.6%、7.4%和5.0%)更高的拉伸强度、断裂伸长率和撕裂强度保留率(40.6%、34.9% 和30.1%).     

Improved Dispersion of Carbon Nanoparticles Modified by Poly(Sodium 4-Styrenesulfonate) and Its Influence on the Properties of Natural Rubber Latex

A novel strategy of radical polymerization of sodium 4-styrenesulfonate on the surface of carbon black (CB) in the solid state was developed to prepare hydrophilic carbon nanoparticles (PNASS-CB). A high performance natural rubber latex (NRL)/PNASS-CB composite was produced by the latex compounding technique. Scanning electron microscope shows considerable improvement in the dispersion of PNASS-CB in rubber matrix. The lower degree of filler–filler networks and the stronger filler–rubber interaction of PNASS-CB in rubber matrix were confirmed by dynamic mechanical thermal analysis. Rheometric properties of NRL/PNASS-CB, like scorch time and optimum cure time, decreased. Tensile strength, tear strength, and elongation at break increased due to stronger interaction between the PNASS-CB and rubber matrix. Dynamic mechanical properties of the modified carbon nanoparticles further corroborated a significant contribution from the better dispersion and efficient load transfer of PNASS-CB on the static and dynamic mechanical properties of composites.     

Effect of Compression Pressure on the Ethylene Propylene Diene Terpolymer (EPDM)/Acrylonitrile Butadiene Copolymer (NBR) Rubber Blends Filled with Different Types of Carbon Black

Blends of ethylene-propylene diene terpolymer/acrylonitrile butadiene copolymer (EPDM/NBR) loaded with different types [(N326-HAF) and (N774-SRF)] and ratios of carbon black (CB) fillers were prepared. The mechanical properties of the EPDM/NBR rubber blends unloaded and loaded with different ratios of CB were investigated. Among the blends, the one with 75% EPDM and 25% NBR, both loaded and unloaded with CB, were found to exhibit the highest tensile strength and elongation at break. The observed changes in the mechanical properties of the blends were correlated to the morphology as observed by scanning electron microscopy. The changes of the electrical resistivity of the rubber blend composites during compression were investigated. The experimental results were explained from the position that an external pressure induces either an increase or decrease of the resistivity of the blend composites according to whether annihilation or creation of effective conductive paths occurs, respectively.