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The Effect of Type of Filler on Microphase Separation and Reinforcement in Polyurethane Based Composites

Abstract In order to investigate the effect of hydrophilicity and size of a filler on the reinforcement and supramolecular structure of polyurethane (PU) based composites, a sequence of polymer composites based upon oligomeric 4,4'-diphenylmethane diisocyanate (MDI) and propylene diol with molecular weight equal to 1000 were prepared via a simple in-situ method. Titanium (IV) dioxide (TO) was used as a microsized filler and an aerosol silica (AS) was used as a nanosized filler, both with hydrophilic surfaces. Carbon black (CB) was used as a microsized filler with a hydrophobic surface. The maximal degree of filling was varied from 5 wt% for AS, 25 wt% for CB, and up to 50 wt% for TO. It was shown that maximal reinforcement of the PU composites (up to one order of magnitude in improvement) could be obtained if the filler increases the microphase separation in the PU matrix. This effect was maximal for CB filler, although this filler was not active in the formation of hydrogen bonds. Thus, the neutral filler also changed the supramolecular structure of the polymer matrix. The strong reinforcement by the CB was connected with their nucleating ability, i.e. the possibility to produce a maximal number of rigid domains by CB/PU interactions in the PU matrix.