Epoxy resin was modified with polyurethane having different isocyanate index. Impact strength, tensile strength, elongation at break and flexural strength were estimated as functions of polyurethane content and isocyanate index. Hardness, linear expansion coefficient and the deflection temperature under load were estimated for selected compositions. Infrared spectroscopy was carried out for unmodified epoxy resin and compositions with improved mechanical properties. Maximum improvement in the fracture toughness was reached with polyurethane with highest content of isocyanate. Hardness was not affected but elastic modulus decreased, implying a softening of epoxy-based compositions. The infrared spectra indicated that an excess of isocyanate groups leads to a grafting process between the modifier and the matrix, explaining the toughening of the latter.

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The present study investigates the biodegradation of synthesized condensation nonisocyanate polyurethanes (NIPUs). It was prepared by reacting phenol sulphonic acid and oligooxypropylene diol and formaldehyde and contained different amounts of hard segments (HSs). Polyurethane samples were submitted to biodegradation with microorganisms R-14 and in garden soil. The tensile strength (TS), relative elongation at break and weight loss of the prepared samples were evaluated and their structure and morphology analysed. It was found that maximum decrease of the TS of all tested NIPU samples occurred only after 7 days of biodegradation. Maximum TS decrease attained was approximately 70% and 75%, respectively, for NIPU based on 0.8-mol and 1-mol HS. Moreover, significant decrease of relative elongation at break and weight loss values after biodegradation in culture R-14 for NIPU samples based on 0.9-mol HS and 1-mol HS was observed. Fourier transform infrared and scanning electron microscopic results confirmed that biodegradation occurred in urea or urethane groups. The glass transition of HSs decreased by at least 20°C due to biodegradation, suggesting that this later took place almost only in the crystalline region of NIPU samples.

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