Structures and Mechanical Properties of Polyurethane/Clay Composites Prepared by Different Pre-mixing Procedures

A novel method for preparing polyurethane/nano-clay composites was used in this study. The nano-clay was pre-mixed with the various components, such as diphenylmethane diisocyanate (MDI), 2,2-bis(hydroxymethyl) propionic acid (DMPA) or polytetramethyleneglycol (PTMG), of polyurethane (PU) polymer to prepare the composites. The PU/clay composites prepared by this method revealed that the values of the tensile strength at break, the elongation at break, the modulus and the surface roughness for the composite prepared from the pre-mixture of clay and PTMG (PU/clay-PTMG composite) were higher than those for the composite prepared from the pre-mixture of clay and MDI (PU/clay-MDI composite), the composite prepared from the pre-mixture of clay and DMPA (PU/clay-DMPA composite) and PU. The thickness of the crystals for PU/clay-MDI and PU/clay-DMPA composites was larger than that for PU and PU/clay-PTMG; whereas the layer distance of the crystals for PU/clay-MDI and PU/clay-DMPA composites was smaller than those for PU and PU/clay-PTMG. The values of glass transition temperature (Tg) of soft and hard segments were in the order of PU/clay-MDI > PU/clay-DMPA > PU > PU/clay-PTMG. Among the three PU/clay composites prepared by the pre-mixing procedure, PU/clay-MDI and PU/clay-DMPA composites showed significant gathering of the nano-clay in the PU matrix. A possible mechanism of the structural changes under tensile stress was speculated to explain the reason for the higher tensile strength and elongation at break of PU/clay-PTMG composite. The pre-mixing of clay-PTMG was a good procedure for the manufacture of the PU/clay composite, which had higher values of tensile strength and elongation at break.