| Abstract: | The effect of impingement mixing on the microstructures developed during a reaction injection molding process in a thermoplastic urethane system was investigated. The polyurethane studied was a 4,4′-diphenylmethane diisocyanate/l,4-butane diol/poly(propyleneoxide) end-capped with poly(ethy1eneoxide) polyol system with a 5/4/1 molar ratio. Three different impingement mixing levels ranging from Re = 80 to Re = 210 were implemented by a laboratory RIM machine. The samples were characterized by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), optical microscopy, and transmission electron microscopy (TEM). Morphologies of hard-segment globules, hard-segment spherulites, and soft-segment rich matrix were observed. The multiple DSC endotherms were related to different crystalline structures. A higher level of mixing was found to increase the molecular weight and produce more paracrystalline structures. A lower mixing level produced better phase separation and spherulitic structures. High temperature annealing caused transurethanization, which may allow molecular rearrangement and change the crystalline structures. |
