No abstract

Interpenetrating polymer networks of vinyl ester (VE) resin and polyurethane (PU) were synthesized using blend ratio of 93:7(w/w). Two sets of nanocomposites based on i) pure vinyl ester and ii)VE/PU IPN(93VE), were prepared with organically modified silica nanoparticle (OMS) as filler by 1, 2, 3 and 5% weight of the matrix resin. All the nanocomposites were characterized in terms of mechanical and thermomechanical properties.VE/silica nanocomposite with 2% filler (VES2) showed improvement in ultimate tensile strength by 83.5% and toughness by 42% compared to that of VE resin itself. The IPN based nanocomposite, 93VES2, exhibited 31.14%, 10.8% and 18%greater tensile strength, Young’s modulus and toughness respectively in comparison to that of the base 93VE IPN. IPN based nanocomposites were tougher than VE based nanocomposites. Storage modulus of nanocomposites was lower than that of 93VE and VE matrix system. Higher tanδmax of the 93VE/OMS nanocomposites than that of the 93VE matrix was indication of more elastic nature of the later. Smaller size of dispersed domains was found in SEM micrographs for IPN based nanocomposites than that in micrographs of VE based nanocomposites of corresponding composition.

Kenaf fibre-reinforced vinyl ester (VE)/polyurethane (PU) interpenetrating polymer network (IPN)-based composites were made by hand lay-up technique. The kenaf bast fibre was chemically treated with 3, 6 and 9% vinyl silane. Treated fibres were characterized in terms of crystallinity, mechanical strength, density, thermal property and morphology. In comparison with the untreated fibre, 6% silane-treated fibres showed 25.4% higher % crystallinity, 66.9% increase in modulus elasticity and 604.2% increase in tenacity. Comparison of the pure VE with VE/PU IPN showed that the IPN had 3.3% lower modulus but 26.4% higher toughness than the former. Composites based on pure VE matrix and VE/PU IPN matrix were manufactured with the variation of untreated and treated fibre loading as 15, 20, 25, 30, 35 and 40 wt%. Novelty of this work lies in the modification of both the fibre surface and the matrix system simultaneously with the aim of increasing the adhesion between the fibre surface and matrix material of the composite. Composites with untreated fibres showed poor strength compared to that with modified fibres having corresponding compositions. IPN-based composites, with 35 wt% silane-treated fibre, showed improvement in tensile modulus by 16.61% and flexural modulus by 6.35% than pure VE-based composites with corresponding fibre loading.

Interpenetrating polymer networks based on vinyl ester resin and polyurethane were synthesized using different blend ratio, for example, 93:7, 90:10, and 80:20 (w/w). The samples were subjected to thermogravimetric analysis under non-isothermal conditions in presence of an inert atmosphere within the temperature range of 303–773K. Determination of distributed activation energy at various stages of degradation process and its implication in the reaction mechanism was investigated by using various isoconversional models and Kissinger’s model fitting approaches. It was observed that IPNs showed higher thermal stability and also possessed higher activation energy for degradation than pure VE in the selected range of temperature when heated at a specific rate.

Vinyl ester resin networks formed by using mixture of diluents were prepared. Methyl methacrylate (MMA) diluent was mixed in various proportions with vinyl ester resin which was already premixed with styrene diluent (45 wt. %). Weight ratios e.g. 80:20, 70:30 and 60:40 of VE resin: MMA diluents were studied. Viscoelastic properties of the cross-linked resin were studied by dynamic mechanical analyzer in terms of storage modulus and tanδ. Thermal analysis was performed using non-isothermal mode of Differential scanning calorimetry. The samples with mixed diluents, showed higher modulus, and glass transition temperature in comparison to that of the pure vinyl ester-styrene resin cross-linked in presence of styrene only. The difference in thermal stability between vinyl ester-styrene and vinyl ester-MMA-styrene was checked. Vinyl Ester -20 wt. % MMA-Styrene samples have the best thermal property among all other prepared samples. Multiphase morphology was formed for the thermoset crosslinked with mixed diluents in contrast to that formed with single diluent. With increase in MMA content in the resin dispersed domain size increased.