engleski

Mechanical Properties and Hydrogen Bonding in Polyurethanes

Morphology, mechanical and FTIR investigations were performed on neat PU polymer matrix and PU+CaCO3 composite thin films in order to understand how the nanofiller influenced mechanical properties. The measurements were performed on the strips that were cut from the prepared films in parallel and perpendicular direction with respect to the direction of film preparation. PU and PU+CaCO3 thin films are evaluated by microscopy techniques in order to determine their structure. Optical micrograph of neat PU polymer imaged in polarized light reveals continuous spherulites morphology with impinging polygonal radial spherulites. A substantial decrease of the spherulites size into fine grain spherulitic structure is observed by the addition of nano-CaCO3 in PU polymer matrix. Polarized micrograph of neat PU polymer stretched to 100 % of strain shows deformation of spherulites to a fiber-like structure aligned parallel to the strain direction. Further increase of strain to 300% resulted in denser and higher oriented fibrils. Optical microscopy of PU+CaCO3 composite during the stretching exhibits finer fibrilar morphology with filler particles oriented toward fibril orientation. It seems that nano- particles inhibited the fibrillization of PU matrix. The orientation of hard and soft segments was studied by FTIR linear dichroic measurements performed on stretched PU and PU+CaCO3 composite films. The analysis of NH and C=O stretching vibrations yielded information about the hydrogen bonding between different segments in PU polymers. The analysis has indicated that NH groups in PU were nearly completely hydrogen bonded (97 %).Even 80% of hydrogen bonded NH groups participate in hard- hard segment interaction, while the rest are included in hard-soft segment interaction. The consideration of hydrogen bonding with carbonyl groups has shown that about 10 % of them in soft segment is hydrogen bonded to hard segment.

polyurethane ; IR dichroism

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