Preparation And Properties Of UP/PU Blends

Liquid composite molding(LCM) process has a strict requirement for the matrix,requiring the resin not only with a low viscosity,but also with high strengh,high toughness and high elongation at break after cured.The UP resin is well-known for its low price and curing convenient,if its properties can be improved to satisfy the requirement of the process,there will be a new way to develop high performance UPR.Low viscosity UPR was prepareted by lowering the molecular weight at synthesization.It was modified by isocyanate or PU prepolymer to improve the mechanical properties which were greatly lowered by its low molucular weight.In the system of UP/PU blends,the crosslinking reaction of UP and the extender reation between isocyanate group and hydroxyl group happened at the same time.Then,the IPNs between UP and PU were formed,which was helpful to improve the mechanical strengh and modular of the low viscosity UP resin.In this way, the UP resin with great process performance and excellent mechanical properties was prepared.When the molar percentages of excess dihydric alcohol were limited to 25%-33%, the viscosity of the resins were 190-140mPa.s,which were almost 1/3-1/5 of that general UPRs.Low molucular weight PU prepolymers synthesised by TDI and PEG200 with the molar percentage of 4:1 were proved to be with proper viscosity and storage time. UP/PU blends formed when blengding the low viscosity UPR and PU together.The result showed that the bending strength,the tensile strength,the toughness of the blends expressed the same trend, first increased then decreased with the increase of the PU amount. The UPRs had better mechanical performance when modified by PU perpolymer than the isocyanate.The elongation at break of the blends depended on the competition between the the molar percentage of adipic acid and the PU amount.The add of the adipic acid in UPR improved the elongationat break.The PU decreased the elongation at break at low amount,whlie improved it at high amount.Controlling the two factors,the UP/PU blends with high strength and high elongation at break were prepared with tensile strength 67.5MPa and elongation at break 6.0%.The UP/PU blends had excellent infiltration and interface effects to the glass fiber,especially to the blends modified by PU prepolymer.The composite materials preparated by it had better mechanical performance the the 191-# UPR,with the tensile strength 398MPa,the bending strength 449MPa and the elongration at break 2.7%.