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Multifunctional branched/hyperbranched copolymers from poly(vinyl alcohol) (PVA) and citric acid (CA) are synthesized by varying the mole compositions of PVA and CA and are used as a prospective vehicle for encapsulation and release of bioactive molecules and as a potential scaffold for cell adhesion and growth. The branched architecture is established from spectroscopy and rheological measurements. All the copolymers have shown a lower hydrodynamic size and viscosity than the linear, high molecular weight PVA because of spherical and more compact architecture. Importantly, the size of the highly branched copolymer is found independent of pH which proved that the branch ends are capped with OH groups. Lower viscosity at equivalent solid content, biocompatibility, high antibacterial property, and presence of adequate macromolecular voids make the branched/hyperbranched copolymers a potential platform for encapsulation and release of gentamicin and other bioactive molecules. The macromolecular voids and chain end functionality also promote adhesion and growth of differentiated primary cells as well as undifferentiated stem cells implying that the copolyester can also be used as a potential 2D/3D scaffold for tissue engineering applications. [ABSTRACT FROM AUTHOR]

Process parameters of poly (ethylene- co-vinyl acetate) (EVA)-modified poly (ethylene- co-1-octene) (POE)-interpenetrating, double network blend was designed through Taguchi L9 orthogonal array as a novel approach for complete optimization of engineering and solvent-swelling properties. Influence of different factors like EVA and peroxide concentrations, blending temperature, and blending time on gel content, tensile modulus, tensile strength, ultimate elongation were statistically calculated. Results showed good correlation between mathematical and physical inferences. Stress relaxation, hysteresis and other physico-mechanicals like total elongation, solvent-swelling, etc., were interestingly depended upon the nature of dominantly crosslinked phase instead of net crosslinking of the network hybrids. Sorption, on the other hand, depended on the hydrophobic-hydrophilic property of the surfaces. The series of data produced finally helped to select the best process parameters under which a particular POE-EVA blend composition yielded most balanced physico-mechanicals. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

Polar modification of poly(ethylene- co-octene) (POE) elastomer was carried out with a relatively new approach. Poly(ethylene- co-acrylic acid) (EAA) was taken as the modifier and POE with a calculated amount of EAA were coextruded with dicumyl peroxide (DCP; used as a crosslinker). The majority of the compositions showed the existence of a crosslinked EAA phase inside POE, although increasing DCP concentrations and extrusion temperatures were possibly capable of crosslinking either of the phases, as observed with a model composition. All of the samples were soft and light in nature. The best composition was the one that contained 13.3 wt % EAA; that composition showed excellent surface polarity and superior mechanical properties. Detailed solvent swelling experiments also yielded the best results for that particular composition. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 [ABSTRACT FROM AUTHOR]

The mechanism of active stress generation in tension wood is still not fully understood. To characterize the functional interdependency between the G-layer and the secondary cell wall, nanostructural characterization and mechanical tests were performed on native tension wood tissues of poplar (Populus nigra × Populus deltoids) and on tissues in which the G-layer was removed by an enzymatic treatment. In addition to the well-known axial orientation of the cellulose fibrils in the G-layer, it was shown that the microfibril angle of the S2-layer was very large (about 36°). The removal of the G-layer resulted in an axial extension and a tangential contraction of the tissues. The tensile stress–strain curves of native tension wood slices showed a jagged appearance after yield that could not be seen in the enzyme-treated samples. The behaviour of the native tissue was modelled by assuming that cells deform elastically up to a critical strain at which the G-layer slips, causing a drop in stress. The results suggest that tensile stresses in poplar are generated in the living plant by a lateral swelling of the G-layer which forces the surrounding secondary cell wall to contract in the axial direction. [ABSTRACT FROM AUTHOR]