The blending of different rubbers is one of the effective methods to achieve required performance properties in their final products. This article reviews the thermodynamic considerations of rubber–rubber blends and their filled systems. Factors affecting the rubber blend morphology (i.e. distribution mechanism of fillers, curatives and other compounding ingredients) and preparation techniques for rubber–rubber blends emphasizing their advantages and disadvantages are well discussed in this review. Microscopy is the field of interest to all material scientists. In the case of rubber blends, microscopy is an essential tool in order to understand the morphology, that is, size, shape and distribution of phases and filler particles in the rubber–rubber blend. In this review, selected scientific reports based on optical microscopy, electron microscopy and atomic force microscopy in rubber–rubber blends are discussed. Rubber material is a complex macromolecule; it has significant proportion of fillers, processing aids and curing agents; therefore, only a very few studies have been reported on the microscopic aspects of filled rubber–rubber blends. In particular, influence of rubber blend composition, fillers (micro and nano length scales) and processing additives on the morphology of rubber blends systems has not been systematically reviewed and discussed in the scientific literature. Therefore, in the present scenario, this review was thought of, which deals with the essential background to rubber–rubber blends, miscibility and morphological characterization of various rubber blend systems by microscopy. It is very important to add that although there is scattered information on these aspects in the scientific literature, to date a comprehensive review has not been published. The pros, cons, artefacts and the new challenges on the use of microscopy for the characterization of rubber–rubber blends are also discussed here.
Polymer membrane based gas transport and pervaporation processes are fast growing areas in separation technology and have received wide attention as areas of 'clean technology'. Mechanically stable novel polyhedral oligomeric silsesquioxane (POSS) embedded poly(vinyl alcohol) (PVA)/poly(ethylene oxide) (PEO) blend membranes were prepared by solution blending followed by casting. The addition of carboxymethyl cellulose enhanced the interfacial activities of the PVA and PEO blends. The peripheral organic substituent on POSS plays a key role in achieving compatibility with polymers whereas the rigid Si-O-Si core of POSS imparts high mechanical strength. Compared to PVA membrane, poly(ethylene glycol) and octa(tetramethylammonium) functionalized POSS embedded PVA/PEO membranes exhibit 680% and 580% enhancement in Young's modulus as well as 130% and 140% improvement in tensile strength respectively. The Einstein, Kerner and Frankel-Acrivos models were applied to compare the experimental and theoretical Young's modulus of PVA-PEO/POSS membranes. The presence of an ethylene oxide tail on POSS as well as PEO in the blend membrane enhances the CO 2 affinity of the membrane. The presence of a hydrophilic functional group on the POSS improves the hydrophilicity of the membrane and produces more binding sites for water molecules in the membrane during the pervaporation separation of a tetrahydrofuran-water azeotropic mixture. The transport properties of the membrane are further elucidated by means of free volume defect analysis carried out by positron annihilation lifetime spectroscopy and coincidence Doppler broadening spectroscopy.
Knowledge of solvent effect on the polymer is a need, for a large number of industrial and laboratory purposes. It is well known that swelling is a serious drawback for rubber products such as seals and O‐rings. The flexible rubber chains are highly prone to diffusion and allow easy penetration of solvent molecules through it, which causes swelling in rubber products. The flexibility and molecular mobility of rubber chains are reduced by either cross‐linking/blending/ adding inclusions. This reduces the swelling of rubber products. In the present work, blending rubbers and adding inclusions are experimented and reported. Various compositions of natural rubber (NR) / butadiene rubber (BR) i.e., 70NR/30BR, 50NR/50BR,30NR/70BR with and without carbon black (CB) were compounded, cured and characterized for diffusion analysis using benzene, toluene, and xylene. To determine the effect of varying filler concentration, 70NR/30BR blend was filled with 10, 20, 30, 40, and 50phr of CB and analyzed for diffusion characteristics. Loading of CB into rubbers reduces the chain flexibility as a result of rubber/filler interactions and this leads to a dramatic reduction in the diffusion of the solvent into rubber compounds. Diffusion characteristics of CB filled rubber blends were compared with their neat counterparts and CB filled blends showed less solvent uptake. Swelling characteristics for the neat and filled rubbers and their blends were calculated to determine coefficients and index of swelling. The experimental diffusion data obtained were fitted with mathematical models for predicting the diffusion behavior through the rubber vulcanisates to understand the mechanism of transport phenomena.
Smart materials are much discussed in the current research scenario. The shape memory effect is one of the most fascinating occurrences in smart materials, both in terms of the phenomenon and its applications. Many metal alloys and polymers exhibit the shape memory effect (SME). Shape memory properties of elastomers, such as rubbers, polyurethanes, and other elastomers, are discussed in depth in this paper. The theory, factors impacting, and key uses of SME elastomers are all covered in this article. SME has been observed in a variety of elastomers and composites. Shape fixity and recovery rate are normally analysed through thermomechanical cycle studies to understand the effectiveness of SMEs. Polymer properties such as chain length, and the inclusion of fillers, such as clays, nanoparticles, and second phase polymers, will have a direct influence on the shape memory effect. The article discusses these aspects in a simple and concise manner.
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