TPU materials have various properties such as high wear resistance, bending fatigue resistance, processability, oil resistance, water resistance, mold resistance, recyclability, high elasticity, and various other properties. It can be used for various automotive parts and can be combined with other plastics or rubbers to create automotive bumpers, airbags, dust covers, and other parts.
TPU contains many polar functional groups, which can easily absorb moisture from the air. On the one hand, the absorbed water acts as a plasticizer, which will lower the physical properties of TPU, but this effect is reversible. If the TPU material is completely dried, the absorbed water can be removed from the TPU, and its physical properties can still be restored to the level before water absorption.
Increasing the carbon chain length of polyester can improve its hydrolytic stability. Introducing branching or rigid ring structures into the polyester structure also improves its hydrolytic stability. For adipate polyester, polyester synthesized from hexanediol or neopentyl glycol has better water resistance than polyester synthesized from ethylene glycol or butanediol.
Since the polyolefin-ethylene glycol soft segment cannot provide the strong electronegative element required for forming hydrogen bonds, the synthesized TPU materials have excellent hydrolysis resistance, but poor oxidation resistance due to the presence of double bonds in the molecule. TPU synthesized from polycarbonate diol and polycarbonate diol has better water resistance than the polycarbonate series, but it is much more expensive.
Polyester synthesized by mixing adipic acid and terephthalic acid in a certain proportion has good water resistance;
Introducing a certain proportion of polyether into the polyester structure can be random copolymerization or block copolymerization. The synthesized polyether ester can significantly improve its water resistance;
Controlling the acid value of the synthesized polyester to below 0.1 can also maintain its basic stability.
Adding polycarbonate diimide (PCD) to polyester TPU can improve its water resistance. The mechanism is that the carboxyl group in polyester and the carboxyl group produced by hydrolysis react with PCD to form urea derivatives, thereby preventing the self-catalysis of carboxyl groups.
Since each PCD molecule contains multiple carbon diimide groups, it can reconnect end carboxyl functional polymer formed by chain scission, thereby repairing the chain. The commonly used hydrolysis stabilizer is stabaxol P200 (Bayer), with a dosage of 0.5-2.5wt% of polyols.