Structure and properties of strain‐induced crystallization rubber–clay nanocomposites by co‐coagulating the rubber latex and clay aqueous suspension

Natural rubber (NR)–clay (clay is montmorillonite) and chloroprene rubber (CR)–clay nanocomposites were prepared by co‐coagulating the rubber latex and clay aqueous suspension. Transmission electron microscopy showed that the layers of clay were dispersed in the NR matrix at a nano level, and the aspect ratio (width/thickness) of the platelet inclusions was reduced and clay layers aligned more orderly during the compounding operation on an open mill. However, X‐ray diffraction indicated that there were some nonexfoliated clay layers in the NR matrix. Stress–strain curves showed that the moduli of NR were significantly improved with the increase of the amount of clay. At the same time, the clay layers inhibited the crystallization of NR on stretch, especially clay content of more than 10 phr. Compared with the carbon‐black‐filled NR composites, NR–clay nanocomposites exhibited high hardness, high modulus, high tear strength, and excellent antiaging and gas barrier properties. Similar to NR–clay nanocomposites, CR–clay nanocomposites also exhibited high hardness, high modulus, and high tear strength. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 318–323, 2005     

Phenolic resin‐crosslinked natural rubber/clay nanocomposites: Influence of clay loading and interfacial adhesion on strain‐induced crystallization behavior

Nanocomposites of natural rubber (NR) and pristine clay (clay) were prepared by latex mixing, then crosslinked with phenolic resin (PhOH). For comparative study, the PhOH‐crosslinked neat NR was also prepared. Influence of clay loading (i.e., 1, 3, 5, and 10 phr) on mechanical properties and structural change of PhOH‐crosslinked NR/clay nanocomposites was studied through X‐ray diffraction (XRD), transmission electron microscopic (TEM), wide‐angle X‐ray diffraction (WAXD), tensile property measurement, and Fourier transform infrared spectroscopy (FTIR). XRD and TEM showed that the clay was partly intercalated and aggregated, and that the dispersion state of clay was non‐uniform at higher clay loading (>5 phr). From tensile test measurement, it was found that the pronounced upturn of tensile stress was observed when the clay loading was increased and a maximum tensile strength of the PhOH‐crosslinked NR/clay nanocomposites was obtained at 5 phr clay. WAXD observations showed that an increased addition of clay induced more orientation and alignment of NR chains, thereby lowering onset strain of strain‐induced crystallization and promoting crystallinity of the NR matrix during tensile deformation. FTIR investigation indicated a strong interfacial adhesion between NR matrix and clay filler through a phenolic resin bridge. This suggested that the PhOH did not only act as curative agent for crosslinking of NR, but it also worked as coupling agent for promoting interfacial reaction between NR and clay. The presence of strong interfacial adhesion was found to play an important role in the crystallization process, leading to promotion of mechanical properties of the PhOH‐crosslinked NR/clay nanocomposites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43214.     

Strain‐induced crystallization behavior of polychloroprene rubber

The crystallization behavior of polychloroprene rubber (CR) has been studied in this work. Differential scanning calorimetry (DSC) was applied to characterize the crystallization behavior. And X‐ray diffraction was applied to determine the impact of crosslinking on the crystallization of CR. Synchrotron X‐ray diffraction (SXRD) method was applied to study the dynamic crystalline behavior. On the basis of the experimental results, it is found that crosslinking will hamper the crystallization of CR while large strain can restore this course. And this is in accord with the Mooney‐Rivlin analysis result. Detailed discussion was offered circling around this phenomenon. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of norbornyl modified soybean oil on CB‐filled chloroprene rubber

Carbon black (CB)‐filled chloroprene rubber (CR) compounds and vulcanizates containing naphthenic oil (NO), soybean oil (SO), and two different levels of norbornyl modified soybean oil (MSO) were prepared and investigated. The MSO was prepared through the reaction of SO and dicyclopentadiene (DCPD) at different ratios. Various properties including gel fraction, crosslink density, bound rubber fraction, curing behavior, thermal, mechanical, and aging properties of CB‐filled CR containing different oils were compared. It was observed that the addition of SO and MSO could benefit the dispersion of the filler, lower the glass transition temperature, and increase the thermal stability of the CB‐filled CR/MSO compounds and vulcanizates, and also slightly decrease the crosslink density of the CB‐filled CR/MSO vulcanizates compared to that of the CR/NO vulcanizate. With the increase of the modification level of the MSO, the curing time of the CB‐filled CR/MSO compounds was found to be decreased, the tensile property, tear strength, abrasion resistance, and aging resistance of the CB‐filled CR/MSO vulcanizates were improved compared with those of the CB‐filled CR/NO vulcanizate. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43809.     

Possible use of ultra‐fine acrylonitrile butadiene rubber powder as filler in natural rubber vulcanizates

Possible use of ultra‐fine acrylonitrile butadiene rubber powder (UFNBRP) as a filler for natural rubber (NR) was investigated. The UFNBRP was added into NR at various concentrations, and the compound properties were determined. It is found that, with increasing UFNBRP loading, the compound viscosity is increased, whereas both scorch time and optimum curing time are significantly reduced. The results also reveal that UFNBRP has negative effect not only on crosslink density but also on most mechanical properties of the vulcanizate, such as tensile strength, tear strength, compression set, and abrasion resistance. The deterioration of these mechanical properties is thought to arise mainly from the combined effect of large phase size of the dispersed UFNBRP and low interfacial adhesion taking place from the polarity difference between UFNBRP and NR. Interestingly, it is found that, after aging, UFNBRP could promote postcuring phenomenon leading to increases of both relative 100% modulus and relative tensile strength. Oil resistance is also found to improve considerably with increasing UFNBRP loading. This improvement is mainly attributed to the dilution effect, i.e., the higher the UFNBRP loading, the lower the NR portion and, thus, the greater the oil resistance of the vulcanizate. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Physical and mechanical properties of poly(methyl methacrylate)‐grafted natural rubber synthesized by methyl methacrylate photopolymerization initiated by N,N‐diethyldithiocarbamate functions previously created on natural rubber chains

Well‐defined poly(methyl methacrylate) (PMMA)‐grafted natural rubbers (NRs) were prepared to study the structure–property relationships. Syntheses were achieved by the photopolymerization of methyl methacrylate initiated by N,N‐diethyldithiocarbamate groups created beforehand in side positions on the NR chains. With this procedure, good control of the graft density and PMMA content could be obtained. Thermal, morphological, and mechanical properties of NR‐g‐PMMA copolymers were studied as a function of the NR/PMMA composition and graft density. NR‐g‐PMMAs containing 15–80% grafted PMMA showed characteristics of heterogeneous materials (characterized by two glass‐transition temperatures, those of PMMA and NR, in differential scanning calorimetry). Under these conditions, they developed the morphology of thermoplastic elastomers with PMMA nodules dispersed in the rubber matrix when the PMMA content was near 20%; conversely, they developed the morphology of softened thermoplastics with rubber nodules dispersed in PMMA when the PMMA content was near 80%. Graft copolymers containing about 20% PMMA remained essentially rubbery, but they were already different from pure NR. On the other hand, the thermal stability of NR wash improved after the introduction of PMMA grafts onto NR chains. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal aging properties and chemical resistance of blends of natural rubber and epoxidized low molecular weight natural rubber

Studies into solvent resistance and aging properties of blends of natural rubber and epoxidized low molecular weight natural rubber were carried out. Vulcanization of the blends using the semi‐efficient vulcanization (semi‐EV) system was found to have curing advantages over conventional vulcanization (CV) and efficient vulcanization (EV) systems. The rheological properties (cure time, t₉₀, and scorch time, t₂), solvent resistances, and aging properties of the vulcanizates were found to improve as the level of epoxidized low molecular weight natural rubber in the blends increases. The mechanical properties of the blends were also found to be within the accepted level for NR vulcanizates. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1733–1739, 2005     

Effect of a natural magnesium silicate treated with a new coupling agent on the properties of ethylene–propylene–diene rubber compounds

The behavior of sepiolite (magnesium silicate with a microfibrillar morphology) as a filler in ethylene–propylene–diene compounds was studied. A new coupling agent, meta‐isopropenyl dimethyl benzyl isocyanate, was used. The effect of the filler modified by meta‐isopropenyl dimethyl benzyl isocyanate on the physical properties was improved with respect to other fillers and commercial silane coupling agents under the same conditions. In addition to a smoother surface, the flow behavior of compounds filled with sepiolite, on account of its fibrous morphology, was better than that obtained with other fillers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1489–1493, 2004     

Strain‐induced crystallization behavior of phenolic resin crosslinked natural rubber/clay nanocomposites

Nanocomposites of natural rubber (NR) and unmodified clay were prepared by latex compounding method. Phenolic resin (PhOH) was used to crosslink NR. Crosslinked neat NR was also prepared for comparison. The structure–property relationship of uncrosslinked and crosslinked NR/clay nanocomposites was examined to verify the reinforcement mechanism. Microstructure of NR/clay nanocomposites was studied by using transmission electron microscopic (TEM), X‐ray diffraction (XRD), wide angle X‐ray diffraction (WAXD), and small angle X‐ray scattering (SAXS) analyses. The results showed the evidence of intercalated clay together with clay tactoids for the nanocomposite samples. The highest tensile strength was achieved for the crosslinked NR/clay nanocomposite. The onset strain of deformation induced the crystallization of NR for nanocomposites was found at almost the same strain, and furthermore their crystallization was developed at lower strain than that of the crosslinked neat NR because of the clay orientation and alignment. However, at high strain region, the collaborative crystallization process related to the clay dispersion and conventional crosslink points in the NR was responsible to considerably high tensile strength of the crosslinked NR/clay nanocomposite. Based on these analyses, a mechanistic model for the strain‐induced crystallization and orientational evolution of a network structure of PhOH‐crosslinked NR/clay nanocomposite was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42580.     

Torrefied agro-industrial residue as filler in natural rubber compounds

This study explored the feasibility of using torrefied biomass as a reinforcing filler in natural rubber compounds. Carbon black was then replaced with the torrefied biomass in elastomer formulations for concentrations varying from 0% to 100% (60 parts per hundred rubber or phr total). Their influence on the curing process, dynamic properties, and mechanical properties was investigated. Results were compared with the properties of vulcanizates containing solely carbon black fillers. Time to cure (t₉₀) for compounds with torrefied biomass fillers increased, while filler-filler interactions (ΔG') decreased, compared to carbon black controls. At low strains, the tan δ values of the torrefied fillers vulcanizates were similar to the controls. Incorporation of torrefied biomass into natural rubber decreased compound tensile strength and modulus but increased elongation. Replacement with torrefied fillers resulted in a weaker filler network in the matrix. Still, results showed that moderate substitution concentrations (~20 phr) could be feasible for some natural rubber applications.     

Effect of silane coupling agent on the fatigue crack propagation of silica‐filled natural rubber

Based on the real‐time crack tip morphology monitoring, the influence of silane coupling agent (SCA) on the crack‐growth behavior of silica‐filled natural rubber (NR) was analyzed. By using SCA, silica particles can be well dispersed and a filler–matrix network can be formed, which leads to lower crack‐growth rate. Results indicate that a dosage of 5 wt % (with respect to silica loading) is the optimal content. The real‐time observation and scanning electron microscopy (SEM) analysis proved that thin ligaments and dimples with homogeneous distribution appear on the crack tip. These crack tip morphologies reflect the low crack‐growth rate. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41980.     

Effects of palm ash loading and maleated natural rubber as a coupling agent on the properties of palm‐ash‐filled natural rubber composites

Natural rubber composites were prepared by the incorporation of palm ash at different loadings into a natural rubber matrix with a laboratory‐size two‐roll mill (160 × 320 mm²) maintained at 70 ± 5°C in accordance with the method described by ASTM D 3184–89. A coupling agent, maleated natural rubber (MANR), was used to improve the mechanical properties of the natural rubber composites. The results indicated that the scorch time and cure time decreased with increasing filler loading, whereas the maximum torque exhibited an increasing trend. Increasing the palm ash loading increased the tensile modulus, but the tensile strength, fatigue life, and elongation at break decreased. The rubber–filler interactions of the composites decreased with increasing filler loading. Scanning electron microscopy of the tensile fracture surfaces of the composites and rubber–filler interaction studies showed that the presence of MANR enhanced the interfacial interaction of the palm ash filler and natural rubber matrix. The presence of MANR also enhanced the tensile properties and fatigue life of palm‐ash‐filled natural rubber composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of core‐shell morphology evolution on the rheology,crystallization, and mechanical properties of PA6/EPDM‐g‐MA/HDPE ternary blend

In this article, polyamide 6 (PA6), maleic anhydride grafted ethylene‐propylene‐diene monomer (EPDM‐g‐MA), high‐density polyethylene (HDPE) were simultaneously added into an internal mixer to melt‐mixing for different periods. The relationship between morphology and rheological behaviors, crystallization, mechanical properties of PA6/EPDM‐g‐MA/HDPE blends were studied. The phase morphology observation revealed that PA6/EPDM‐g‐MA/HDPE (70/15/15 wt %) blend is constituted from PA6 matrix in which is dispersed core‐shell droplets of HDPE core encapsulated by EPDM‐g‐MA phase and indicated that the mixing time played a crucial role on the evolution of the core‐shell morphology. Rheological measurement manifested that the complex viscosity and storage modulus of ternary blends were notable higher than the pure polymer blends and binary blends which ascribed different phase morphology. Moreover, the maximum notched impact strength of PA6/EPDM‐g‐MA/HDPE blend was 80.7 KJ/m² and this value was 10–11 times higher than that of pure PA6. Particularly, differential scanning calorimetry results indicated that the bulk crystallization temperature of HDPE (114.6°C) was partly weakened and a new crystallization peak appeared at a lower temperature of around 102.2°C as a result of co‐crystal of HDPE and EPDM‐g‐MA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of quasi‐nanogel particles on the rheological and mechanical properties of natural rubber: A new insight

The influence of sulfur‐crosslinked, quasi‐nanosized gels on the rheological and mechanical properties of raw natural rubber (NR) was investigated. Latex gels with different crosslink densities were prepared through the variation of the sulfur‐to‐accelerator ratio. These gels were characterized by dynamic light scattering, solvent swelling, and mechanical properties. The gels were mixed with raw NR latex at concentrations of 2, 4, 8, and 16 phr, and their effect on the rheological properties of NR was studied by Monsanto processability tester. The presence of gel in raw NR reduced the apparent shear viscosity and die swell considerably. Initially, the viscosity decreased up to a 8 phr gel loading and then increased with an increase in the gel loading. However, the change in the viscosity was related to the crosslink density of the gels. A new empirical equation relating the viscosity, volume fraction of the gels, and crosslink density was proposed. The die swell of gel‐filled raw NR was at least 10% lower than that of unfilled raw NR and decreased with an increase in the gel loading. The effect of the gels on the die swell properties was explained through the calculation of the principal normal stress difference of gel‐filled NR systems. Scanning electron photomicrographs of the extrudates revealed much better surface smoothness for the gel‐filled virgin rubber systems than for the unfilled rubber. The addition of the gels to raw NR increased the modulus and tensile strength, whereas the elongation at break decreased. The effect of the gels on the dynamic mechanical properties of NR was also investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nanomodified fillers in chloroprene‐rubber‐compatibilized natural rubber/acrylonitrile–butadiene rubber blends

Because of the structural dissimilarity, natural rubber (NR) and acrylonitrile–butadiene rubber (NBR) are immiscible, and compatibilizers are used during their blending. Neoprene or chloroprene rubber (CR) has a polar chlorine part and a nonpolar hydrocarbon part. Also, it has many advantageous properties, such as oil resistance, toughness, a dynamic flex life, and adhesion capacity. Hence, it is not less scientific to use CR as a compatibilizer in the blending of NBR with NR. Because many fewer studies on the use of neoprene as a compatibilizer in NR–NBR blend preparation are available, efforts were made to prepare 20:80 NR–NBR blends with CR with the aim of studying the effect of poly(ethylene oxide) (PEO)‐coated nano calcium silicate along with nano N‐benzylimine aminothioformamide and stearic acid coated nano zinc oxide in the sulfur vulcanization of the blends. The optimum dosage of the compatibilizer was derived by the determination of the tensile properties, tear resistance, abrasion resistance, compressions set, and swelling values. The tensile strength, tear resistance, and abrasion resistance of the gum vulcanizates of the blend were improved by the compatibilizing action of CR up to 5 parts per hundred parts of rubber (phr). In the case of the filled vulcanizates, the tear resistance, 300% modulus, hardness, and abrasion resistance increased with increasing dosage of nano calcium silicate. The elongation at break percentage decreased as expected when there was an increase in the modulus. Scanning electron microscopy was used to study the phase morphology of the blends. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of coagulation processes on properties of epoxidized natural rubber

The epoxidized natural rubber (ENR) with epoxy group contents of 48.4% were coagulated with ethanol and steam and the structures, processing performances, antioxidative behaviors, cure characteristics, and dynamic mechanical properties were analyzed using infrared spectroscopy, rubber processing analyzer, thermogravimetric analyzer, rheometer, and dynamic thermomechanical analyzer, respectively. The results indicate that the ENR coagulated with ethanol (ENR‐e) exhibits a compact structure and the contents of residual low‐molecular‐weight matters are higher than those of unconsolidated ENR coagulated with steam (ENR‐s). Therefore, the processing performance and antioxidative behavior as well as the curing characteristics of ENR‐e compound are poorer than those of ENR‐s. Although the mechanical properties and wet skid resistance of ENR‐s vulcanizate are poorer than those of ENR‐e, the heat build‐up or rolling resistance of ENR‐s is better than that of ENR‐e. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Strain‐induced crystallization behavior of natural rubber and trans‐1,4‐polyisoprene crosslinked blends

The strain‐induced crystallization (SIC) behaviors of crosslinked blends based on natural rubber (NR) and trans‐1,4‐polyisoprene (TPI) with different content of TPI were probed explored by using synchrotron two‐dimensional wide angle X‐ray diffraction and dynamic mechanical analysis. The results showed that when TPI content is less than 70% no reflection peak of TPI but NR crystallite diffractions can be observed and the diffractions of TPI βform appear when TPI content is 70 wt % in the cocured blend. SIC of cocured blends started at smaller strain ratio than the pure NR. By calculating ΔS_def, it is found that the drop in entropy upon strain decreased when TPI is incorporated into NR due to the reduction of molecular mobility of NR. The degree of SIC and crystallization rate index in crosslinked blends monotonously decreased with the increase of TPI content. The apparent crystallite size exhibited some surprising variations. L₂₀₀ and L₁₂₀ decreased with the increase of TPI content in the cocured blends. These observations were usually caused by two factors: (i) Less number of polymer chains could involve in crystal growth due to the lower mobility of polymer chains in the cocured blends which is proved by dynamic mechanical analysis results; (ii) The mean distance between nuclei decreases, which was caused by the fluctuation of crosslink density in NR phase derived from the heterogeneous distribution of curatives in two phases supported by the varying tendency of curing degree and crosslink density. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of zinc‐oxide‐free natural rubber nanocomposites using nanostructured magnesium oxide as cure activator

The effect of sol–gel synthesized magnesium oxide (MgO) nanoparticles as cure activator is studied for the first time in the vulcanization of natural rubber (NR) and compared with conventional zinc oxide (ZnO) in terms of cure, mechanical, and thermal properties. The NR vulcanizate with 1 phr (Parts per hundred parts of rubber) nano MgO shows an excellent improvement in the curing characteristics and the value of cure rate index is about 400% greater for NR vulcanizate containing 1 phr nano MgO in comparison to the NR vulcanizate with 5 phr conventional ZnO. Both mechanical and thermal properties of NR vulcanizate are found to be satisfactory in the presence of 1 phr nano MgO as cure activator in comparison to conventional NR vulcanizate. This study shows that only 1 phr nano MgO can successfully replace 5 phr conventional ZnO with better resulting properties in the sulfur vulcanization of NR. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42705.     

Polymer blends of epoxy resin and epoxidized natural rubber

The aim of this research was to investigate the behaviors of epoxy resin blended with epoxidized natural rubber (ENR). ENRs were prepared via in situ epoxidation method so that the obtained ENRs contained epoxide groups 25, 40, 50, 60, 70, and 80 mol %. The amounts of ENRs in the blends were 2, 5, 7, and 10 parts per hundred of epoxy resin (phr). From the results, it was found that the impact strength of epoxy resin can be improved by blending with ENRs. Tensile strength and Young's modulus were found to be decreased with an increasing amount of epoxide groups in ENR and also with an increasing amount of ENR in the blends. Meanwhile, percent elongation at break slightly increased when ENR content was not over 5 phr. In addition, flexural strength and flexural modulus of the blends were mostly lower than the epoxy resin. Scanning electron microscope micrograph of fracture surface suggested that the toughening of epoxy resin was induced by the presence of ENR globular nodules attached to the epoxy matrix. TGA and DSC analysis revealed that thermal decomposition temperature and glass transition temperature of the samples were slightly different. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 452–459, 2006     

Strain-induced crystallization of peroxide-crosslinked natural rubber

Effect of network-chain density (ν) on the strain-induced crystallization of peroxide-crosslinked natural rubber was studied by fast time-resolved synchrotron wide-angle X-ray diffraction. It was observed that the elongation ratio at the onset of strain-induced crystallization (α_c) became smaller with the increase of ν. The difference of the entropy between the undeformed and deformed states at each α_c was nearly equal in spite of the variation of ν. The calculated melting temperature at α_c of the samples was also almost the same regardless of their ν. These observations mean that the strain-induced crystallization occurred when the deformation brought about a definite entropic state for peroxide-crosslinked natural rubber. They agreed with the prediction by Flory and were consistent with the classical theory of rubber elasticity.