Abstract:

The preparation of nanosilica/polyurethane composites via in situ polymerization is reported. Nanosilica particles were first dispersed into polymer diols by high pressure shearing homogenizer(HPSH), then polymerization was carried out with the addition of the 4,4′-diphenylmethane diisocyanate(MDI) and the polymer diols containing ethylene glycol(EG) as the chain extender. Effects of the nanosilica content and dispersion method on the thermal and mechanical properties of nanosilica/polyurethane composites were investigated by thermogravimetric analysis(TGA), scanning electron microscopy(SEM), and dynamic mechanical thermal analysis(DMTA). The results indicated that the —NCO groups in reaction mixture had reacted with the hydroxy on the surface of nanosilica particles during the in situ polymerization, and the chemical encapsulating ratio of the surface for nanosilica was 7%. Nanosilica particles(HPSH treated) in the nanocomposites were homogenously dispersed in the polyurethane matrix at the size of 30~40 nm, while the nanosilica treated by ultrasonic method aggregated so seriously that the diameter of the agglomerate size reached about 200 nm. Meanwhile, the tensile strength and elongation of the nanocomposites(HPSH treated) increased with increasing the nanosilica mass fraction(＜3%). When the mass fraction of silica was 3%, the tensile strength and enlongation reached the maximal values, and were 84.3 MPa and 438.7% respectively. Moreover, the polyurethane/nanosilica composites（HPSH treated） obtained by in situ polymerization had better thermal stability than pure polyurethane resins. Compared with the pure PU, the Tg, Td and T-50% of the nanocomposites samples（4% nanosilica） were increased by 17.2, 9 and 21 ℃, respectively.

Key words: polyurethane resin, nano-silica, high pressure shearing homogenizer, In situ polymerization, thermal stability, tensile strength, dynamic mechanical properties