The invention of Nylon-6/clay nanocomposites by the Toyota Research Group of Japan heralded a new chapter in the field of polymer composites. This article highlights the work done in the field of rubber/clay nanocomposites. The preparations of rubber/clay nanocomposites by solution blending, latex compounding, and melt intercalation are covered and a thorough discussion of the mechanical properties of the various rubber/clay nanocomposite systems is presented. Other properties such as barrier, dynamic mechanical behavior, and thermal properties are also discussed. Finally, the future trends in the rubber/clay nanocomposites are mentioned. POLYM. ENG. SCI., 47:1956–1974, 2007. © 2007 Society of Plastics Engineers

A short review on rubber/clay nanocomposites with emphasis on mechanical properties

Effects of epoxidized natural rubber as a compatibilizer in melt compounded natural rubber–organoclay nanocomposites

Oils, fats, carbohydrates, lignin, and amino acids are all important raw materials for the production of biorenewables. These compounds already play an important role in everyday life in the form of wood, fabrics, starch, paper and rubber. Enzymatic reactions do, in principle, allow the transformation of these raw materials into biorenewables under mild and sustainable conditions. There are a few examples of processes using immobilised enzymes that are already applied on an industrial scale, such as the production of High-Fructose Corn Syrup, but these are still rather rare. Fortunately, there is a rapid expansion in the research efforts that try to improve this, driven by a combination of economic and ecological reasons. This review focusses on those efforts, by looking at attempts to use fatty acids, carbohydrates, proteins and lignin (and their building blocks), as substrates in the synthesis of biorenewables using immobilised enzymes. Therefore, many examples (390 references) from the recent literature are discussed, in which we look both at the specific reactions as well as to the methods of immobilisation of the enzymes, as the latter are shown to be a crucial factor with respect to stability and reuse. The applications of the renewables produced in this way range from building blocks for the pharmaceutical and polymer industry, transport fuels, to additives for the food industry. A critical evaluation of the relevant factors that need to be improved for large-scale use of these examples is presented in the outlook of this review.

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Immobilised enzymes in biorenewables production

Morphology/behaviour relationship of nanocomposites based on natural rubber/epoxidized natural rubber blends

Preparation, microstructure, and microstructure-properties relationship of thermoplastic vulcanizates (TPVs): A review

Thermoplastic elastomers, prepared by melt blending of natural rubber (NR) and isotactic polypropylene (PP) through a dynamic vulcanization technique, were developed during the later 1970s. However, they have certain drawbacks due to thermal degradation and higher molecular weight of NR. In the study reported here, NR was masticated to different levels prior its addition to isotactic polypropylene to improve the flow properties and to reduce the incompatibility resulting from molecular weight mismatch of NR/PP thermoplastic blends. Mixing energy curves of uncrosslinked blends and those of dynamically vulcanized blends crosslinked using different cure systems were compared. The mixing energy curves of blends containing NR of different molecular weight (Mn) and two grades of PP (injection and film grades) were also compared. Technological and processing properties of the dynamically vulcanized (sulphur and peroxide cure systems) and unvulcanized blends were compared with those of the samples containing unmasticated NR. The results indicated that a number average molecular weight in the range 4 × 105 for NR increased the procoessability without significantly affecting the technological properties of NR/PP thermoplastic blends. Among the three cure systems studied Luperox 101 and dicumyl peroxide gave better technological properties than the sulphur-cured samples. Two antioxidants, viz. quinoline (TDQ) and imidazole (MBI) type, were tried in NR/PP blends. It was found that TDQ imparts better aging resistance compared to MBI. The improvement in processability due to the reduction in molecular weight of natural rubber by mastication is more noticeable in the case of peroxide vulcanized blends compared to sulphur vulcanized samples. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2063–2068, 2004

Natural rubber–isotactic polypropylene thermoplastic blends

This paper focused on the comparative evaluation of cure characteristics and mechanical properties of blends of natural rubber with dichlorocarbene modified styrene–butadiene rubber and chloroprene rubber with different blend composition. It was found that the Mooney scorch time and cure index shows a negative deviation from the calculated value based on the interpolation between the two component elastomers. However for the blends, modulus and hardness show a positive deviation. The mechanical properties of NR/DCSBR blend are higher than that of NR/CR blends. Flammability, oil and ozone resistance of the blend showed that as the NR content in the blend increases these properties were decreases and also NR/DCSBR blend showed excellent thermal, oil and ozone resistance than that of NR/CR in entire blend ratios. The mechanical properties, modulus and hardness were also investigated after oil immersion. The changes in mechanical properties were correlated with variation in cross-link density estimated from stress–strain and swelling behavior.

Studies on the cure and mechanical properties of blends of natural rubber with dichlorocarbene modified styrene–butadiene rubber and chloroprene rubber

Flow behavior of latices is industrially important for the manufacturing of various latex goods. Rheology of latices having fillers can assist in the understanding and quantification of the matrix–filler interaction. The impact of layered silicates such as sodium bentonite and sodium fluorohectorite on the rheological behavior of natural rubber, carboxylated styrene butadiene rubber latices, and their blends was analyzed with special reference to shear rate, temperature, and filler loading. The layered silicates-reinforced latex samples were characterized by X-ray diffraction technique to analyze the extent of intercalation and exfoliation. In the presence of layered silicates, latex systems exhibited enhancement in viscosity due to the network formation. Because of the breaking of networks at higher temperature, the viscosity of all systems decreased with increase in temperature. Layered silicates-reinforced latex systems showed pseudoplastic flow behavior and possesses enhanced zero shear viscosity and yield stress. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2355–2362, 2006

Rheological behavior of nanocomposites of natural rubber and carboxylated styrene butadiene rubber latices and their blends

Role of dichlorocarbene modified styrene butadiene rubber in compatibilisation of styrene butadiene rubber and chloroprene rubber blends

Skim natural rubber latex (SNRL) is a protein rich by-product obtained during the centrifugal concentration of natural rubber (NR) latex. A new method to recover rubber hydrocarbon and to obtain nanocomposites with organoclay (OC) was investigated. The approach involved treatment of SNRL with alkali and surfactant, leading to creaming of skim latex and removal of clear aqueous phase before addition of OC dispersion. Clay mixed latex was then coagulated to a consolidated mass by formic acid, followed by drying and vulcanization like a conventional rubber vulcanizate. X-ray diffraction (XRD) studies revealed that NR nanocomposites exhibited a highly intercalated structure up to a loading of 15 phr (parts per hundred rubber) of OC. Transmission electron microscopy studies showed a highly exfoliated and intercalated structure for the NR nanocomposites at loadings of 3-5 phr organically modified montmorillonite (OMMT). The presence of clay resulted in a faster onset of cure and higher rheometric torque. The rubber recovered from skim latex had a high gum strength, and a low amount of OC (5 phr) improved the modulus and tensile strength of NR. The high tensile strength was supported by the tensile fractography from scanning electron microscopy. Thermal ageing at 70°C for 6 days resulted in an improvement in the modulus of the samples; the effect was greater for unfilled NR vulcanizate. The maximum degradation temperature was found to be independent of the presence and concentration of OC. The increased restriction to swelling with the loading of OC suggested a higher level of crosslinking and reinforcement in its presence.

Rosamma Alex

Papers

Natural rubber–isotactic polypropylene thermoplastic blends

Studies on the cure and mechanical properties of blends of natural rubber with dichlorocarbene modified styrene–butadiene rubber and chloroprene rubber

Rheological behavior of nanocomposites of natural rubber and carboxylated styrene butadiene rubber latices and their blends

Role of dichlorocarbene modified styrene butadiene rubber in compatibilisation of styrene butadiene rubber and chloroprene rubber blends

Preparation and characterization of organoclay‐rubber nanocomposites via a new route with skim natural rubber latex