Cast polyurethane elastomers based on 1,4-butanediol (BDO)-extended MDI systems using PTMEG as the soft segment are among the most useful polyurethane materials, offering cost and performance advantages. We see these elastomers used in a myriad of diverse cast urethane applications including wheels, heavy duty casters and tires for lift trucks, mowers; and all-terrain vehicles; industrial belts, wiper blades, and chute liners; pipe, hose, pump components, and tank liners used in abrasive service; mining, power, and oil-field equipment such as gaskets, valves, hydro cyclones, screens, and flotation parts; athletic shoes, boots and recreational equipment; and medical devices.
Advantages of the PTMEG/MDI/BDO polyurethane elastomers include superior hydrolysis resistance, maintenance of flexibility and other mechanical properties at low temperatures, high resiliency and rebound properties, superior resistance to impingement abrasion, good sliding abrasion resistance, impact resistance, and low dynamic heat build-up (low hysteresis).
The molecular weight grades of PTMEG diols range from 210 to 3000. By varying the hard block (MDI/BDO) and soft block (PTMEG) concentration and the molecular weight of the PTMEG segment, formulators can produce hot-cast elastomers with hardness ranges from the low Shore A range to the high Shore D range. The soft and hard segment contents also influence other properties such as tensile strength and modulus, low and high temperature performance, dynamic properties, resiliency, tear strength, and abrasion resistance.
When it comes to MDI systems, 1,4-BDO is the chain extender of choice for most processors.
BDO is hygroscopic, so formulators must take precautions to keep BDO sufficiently dry to avoid moisture reactions with MDI.
The influence of the molecular weight of the PTMEG polyol and the weight percent of the PTMEG soft segment in the PTMEG/MDI/BDO polyurethane has been studied. As the % soft-to-hard block ratio increases in a polyurethane, the Shore A hardness decreases as does the tensile modulus, tensile strength, tear strength and compression set. The elongation at break and hydrolysis resistance increases with an increase in the PTMEG content.