The mechanical properties and low-profile characteristic of unsaturated polyester/polyurethane (UPE-PU) interpeneatrating polymer network (IPN) materials as the matrix of fiber-reinforced composites were studied for application of sheet molding compound (SMC) process. The molded parts were prepared by compression molding at 130°C under 35atm pressure. The mechanical properties were tested according to ASTM procedure and the low-profile characteristic was obserbed by taking the photographs of the surface lines of the molded part observed by microscope (x75).
Improved impact strength was observed with increasing the content of polyurethane and lowering the crosslink density of the polyurethane crosslinked site($\overline{Mc}$), but these gave poor tensile strength of the composite. Polyurethane content of 20wt% with $\overline{Mc}$ of 2840 was observed to be the optimum condition of impact modifier with increase of the impact strength (22%) with slight decrease of the tensile strength (13%). Polyurethane using PTMG(Poly (tetramethylene ether glycol)) showed better impact strength than using PPG (Polypropylene glycol).
The increase of the content and $\overline{Mc}$ of polyurethane improved the low-profile characteristic of the IPN matrices. But, the differences of the low-profile characteristic of polyurethane contents using PTMG or PPG were not observed.
