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Nanocomposites based on natural rubber latex as the matrix and naturally occurring tubular shaped nanoclay, halloysite nanotubes (HNTs) as the reinforcing phase were prepared through co-coagulation method. XRD, morphology, mechanical, and solvent transport properties of the nanocomposites with special reference to weight percentage of nanoclay were analyzed and discussed in detail. Matrix-filler interaction was estimated from Kraus, Cunneen-Russell, and Lorentz-Park plots. Theoretical estimation of reinforcement effect revealed a better interaction between rubber and filler at lower concentration of filler. At higher loading properties decreased due to the formation of filler-filler networks than polymer-filler networks resulting in the reduction of aspect ratio of fillers. Properties of nanocomposites depend on the aspect ratio and volume fraction of reinforcing filler. Morphological analyses of the nanocomposites were done in detail from scanning electron micrographs. Theoretical modulus of nanocomposites was computed using different composite theories by varying the aspect ratio of filler and compared with experimental data. A good agreement between experimental and theoretical values was observed at lower concentration of filler. Solvent transport properties of nanocomposites were found to decrease at lower concentration of HNT because of the tortuosity of the path. POLYM. COMPOS., 37:602-611, 2016. © 2014 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Abstract: Transport properties of aromatic solvents such as benzene, toluene and p-xylene through micron sized fillers reinforced natural rubber, carboxylated styrene butadiene rubber and their 70/30 blend latex membranes were investigated. The effect of penetrant size, filler loading and temperature on the diffusion properties were studied. The dispersion of filler in the matrix were analysed from scanning electron micrographs. Due to the lack of polymer/filler interaction aggregation of filler was higher in NR. The filled samples showed reduced swelling rate owing to the tortuosity of the path. A dramatic decrease in diffusion coefficient of filled samples was observed. However, blend system exhibited unexpected diffusion behaviour because of the immiscibility of the two components. The activation energies for diffusion of the penetrant were computed from the Arrhenius plots. The activation energy needed for diffusion of penetrant was found to be higher for filled virgin polymers. The transport mechanism was investigated and found that all systems exhibited non-Fickian anomalous behaviour. [Copyright &y& Elsevier]

Abstract: Solvent resistance properties of nano-structured layered silicates filled natural rubber (NR), carboxylated styrene butadiene rubber (XSBR) and their 70/30 latex blend were investigated by equilibrium swelling method using benzene, toluene and p-xylene. The layered nano-structured sodium bentonite and sodium fluorohectorite were used in the present study. The impact of concentration of filler, temperature and penetrant size on the transport properties of aromatic solvents through layered silicates reinforced latex membranes were analysed. The transport properties of filled latex membranes was analysed as a function of extent of exfoliation of the layered silicate in the rubber matrix. The morphology of filler dispersion in the rubber matrix was analysed from transmission electron micrographs. More exfoliated structure was found in sodium-fluorohectorite filled latex membrane. The extent of intercalation of polymer chain into the layers of silicates was estimated using X-ray diffraction technique. The enhanced d-spacing in latex nanocomposite indicated the intercalated structure. Nanocomposite of natural rubber (NR), carboxylated styrene butadiene rubber (XSBR) and their blends showed reduced swelling rate due to the tortuosity of the path and the reduced transport area in polymeric membrane. [Copyright &y& Elsevier]

Abstract: The thermal stability of natural rubber (NR) and carboxylated styrene butadiene rubber (XSBR) latices and their blends was studied by thermogravimetric methods. Ageing characteristics of these latex blends were studied by applying hot air oven thermal ageing for seven days at 70°C. The mechanical properties of the aged samples were studied. Thermal degradation and ageing properties of these individual latices and their blends were investigated with special reference to blend ratio and vulcanization techniques. As the XSBR content in the blends increased their thermal stability was also found to increase. Among sulphur and radiation-vulcanized samples, radiation cured possesses higher thermal stability due to the higher thermal stability of carbon–carbon crosslinks. DTG curves were used for the determination of different stages involved in the degradation. Activation energy for degradation was determined from Coats–Redfern plot. The properties of aged samples were found to decrease due to chain depletion. However, the moduli of XSBR and NR/XSBR blends were found to increase owing to the formation of crosslinks upon ageing. [Copyright &y& Elsevier]

Abstract: The gas permeability coefficient of nano and micro composites of natural rubber, carboxylated styrene butadiene rubber and 70:30 natural rubber/carboxylated styrene butadiene rubber blend membranes has been investigated with special reference to type of filler, gases, filler loading and pressure. The layered silicates such as sodium bentonite and sodium fluorohectorite were the nanofillers used and the conventional micro fillers were clay and silica. Latex nanocomposites were characterized by X-ray diffraction technique. The dispersion of layered silicates in the polymer matrix was analysed using transmission electron microscopy. The fluorohectorite silicate showed excellent dispersion in natural rubber matrix. The effect of free volume on the gas barrier properties was investigated by positron annihilation lifetime spectroscopy. It was observed that due to the platelet like morphology and high aspect ratio of layered silicates, the gas barrier properties of nano filled latex membranes were very high. The crosslink density values and extent of reinforcement were estimated in order to correlate with the gas barrier properties. The oxygen/nitrogen selectivity of these membranes were investigated. The diffusion of gas molecules through the polymer was determined by time-lag method and diffusion selectivity of the membranes was computed. [Copyright &y& Elsevier]

Conductive carbon black (CCB), carbon nanotubes (CNT) and its hybrids are introduced into the natural rubber (NR) matrix aiming to explore the effect of filler ratio on the transport properties. Solvent transport of NR is found to decrease for hybrid filler systems as compared to single filler incorporated systems. Kinetic parameters of solvent transport behavior of filled NR systems are analyzed using various kinetic models. Upon the computation of kinetic parameters of transport data, it is found that the Peppas-Sahlin model is in good agreement with experimental observations, which suggests that the transport mechanism is diffusion controlled. Rubber-filler interaction parameters are computed and analyzed from the swelling experiments using Kraus, Cunneen-Russel, and Lorenz-Park equations. [ABSTRACT FROM AUTHOR]

A series of interpenetrating polymer network membranes have been synthesised from natural rubber and polystyrene by the sequential polymerisation technique. The transport of aromatic hydrocarbons through semi- and full-interpenetrating polymer network membranes (IPNs) have been studied in detail by tracing the solvent uptake up to equilibrium. The sorption was carried out in a series of aromatic solvents viz. benzene, toluene and xylene. The effect of temperature on swelling is studied by carrying out the experiments in toluene in the temperature range of 30–75 °C. The effects of blend ratio, crosslinker content and nature of initiator on the diffusion of various solvents were analysed. It was found that in all cases, the uptake value increased by about 50% as the PS content decreased from 70–30%. The diffusion, sorption and permeation coefficients were evaluated. As the crosslink density was increased, the uptake decreased by 40%. Kinetic and thermodynamic parameters were evaluated from diffusion experiments. The diffusion profiles were compared with theoretical predictions. The influence of swelling on the mechanical performance of the membranes has been investigated by conducting tensile testing of swollen specimens. [Copyright &y& Elsevier]

The versatility and potential have framed natural rubber (NR) nanocomposites as the focal point in the polymer research field and industry. Currently, NR nanocomposites filled with hybrid nanostructures is an interesting area than single filler or conventional filler systems. Halloysite nanotube (HNT) and bentonite clay are well-studied potential fillers of polymers. This work is an attempt to study the effect of hybrid filler system of HNT and organically modified bentonite nanoclay (NC) in the properties of NR. NR/HNT-NC systems with varied filler concentrations were prepared in a two-roll mixing mill. Properties such as cure characteristics, morphology, mechanical, thermal, and transport behavior were analyzed in detail. The prepared composites had better wear properties than gum vulcanizates. Improvement in physical properties was observed due to the increased contact surface area between the filler and the matrix. The nanocomposite with 2 wt% hybrid filler shows a 31% decrease in abrasion loss compared to neat NR composite. Apparently, 4 wt% of hybrid filler could improve modulus at 300% strain and tear by approximately 57% and 14%, respectively. The ability to withstand high strain was evident from the improved crack growth resistance as observed in micrographs. Lorenz–Park plots were employed to analyze the rubber–filler interaction. The activation energy of thermal degradation was calculated using Coats–Redfern equation. [ABSTRACT FROM AUTHOR]

Permselective polymeric membranes are important materials for the efficient separation of organic solvents and azeotropic mixtures. In this work, we address an effective strategy to the fabrication of novel high-performance membranes of crosslinked poly(vinyl alcohol) (PVA) by incorporating chemically modified cage-structured polyhedral oligomeric silsesquioxane (m-POSS) through solution casting method. The fabricated PVA/m-POSS system showed excellent mechanical stability as well as good pervaporation performance for the separation of isopropanol (IPA)-water azeotropic mixture. Scanning electron micrographs and atomic force microscopy analysis revealed the homogeneous dispersion of m-POSS in PVA matrix. Differential scanning calorimetric studies showed the rigidification of crosslinked PVA matrix by the incorporation of m-POSS. Tensile strength and Young's modulus of PVA matrix were increased remarkably to 200% and 740%, respectively, in the presence of 5 wt% of m-POSS. Moreover, the membranes exhibited excellent water selectivity, hydrophilicity and excellent anti-fouling properties compared to traditional hydrophilic membranes. At lower filler loading (1.0 wt%), 300% and 200% increase in selectivity and permeance were observed for PVA/m-POSS system over crosslinked PVA. The excellent mechanical properties and other comprehensive properties revealed the potential of the PVA/m-POSS system for the effective separation of azeotropic IPA-water mixture. Modified Maxwell-Stefan model was applied for the theoretical estimation of permeation flux and it was in good agreement with the experimental findings. [ABSTRACT FROM AUTHOR]

Organically modified halloysite nanotube (HNT) containing polysulfone (PSU) membranes were fabricated by the wet phase inversion method. Organic modification of HNT was carried out using telehelic polyetheramine inorder to overcome the poor dispersion of HNT in PSU matrix. Telehelic polyetheramine acts as a dispersing agent and a hydrophilic modifier. FTIR results revealed the hydrogen bond formation between -SO2 of PSU and -NH2 of modified HNT. Based on the obtained results of contact angle measurements, the wettability of membranes were found to increase with the weight percentage of HNT in the presence of polyetheramine. At higher loading of filler the water uptake was found to be increasing due to the aggregation of nanotubes. Porosity values substantiate the results obtained for contact angle and water uptake measurements. Thermogravimetric results showed that the thermal stability of polysulfone (PSU)/HNT nanocomposite membranes decreased when compared to neat PSU due to the presence of aliphatic chain of polyetheramine. [ABSTRACT FROM AUTHOR]