Differences between polyether TPU and polyester TPU
1. Differences in raw materials and formulations
(1) The main raw materials for the production of polyether TPU are 4-4'-diphenylmethane diisocyanate (MDI), polytetrahydrofuran (PTMEG), 1,4-butanediol (BDO). The amount of MDI is about 40%, PTMEG is about 40%, BDO is about 20%.
(2) The main raw materials for polyester TPU production are 4-4'-diphenylmethane diisocyanate (MDI), 1,4-butanediol (BDO), adipic acid (AA). The amount of MDI is about 40%, AA is about 35%, and BDO is about 25%.
2. Molecular mass distribution and its influence
The relative molecular mass distribution of polyether follows Poisson's probability equation, and the relative molecular mass distribution of polyester diols follows Flory's probability distribution, while the relative molecular mass distribution of polyester diols follows Flory's probability distribution.
The molecular weight of soft segment has an effect on the mechanical properties of polyurethane. Generally speaking, assuming that the molecular weight of polyurethane is the same, if the soft segment is polyester, the strength of polyurethane increases with the increase of molecular weight of polyester glycol; if the soft segment is polyether, the strength of polyurethane decreases with the increase of molecular weight of polyether glycol, but the elongation increases. This is because the polarity of polyester soft segment is stronger, and the structure regularity is higher when the molecular weight is large, which is beneficial to improving the strength, while the polarity of polyether soft segment is weaker. If the molecular weight is increased, the relative content of hard segment in polyurethane decreases and the strength decreases.
3. Mechanical properties comparison:
Oligomeric polyols such as polyether and polyester form soft segments. Soft segment accounts for the majority of polyurethane, and the properties of polyurethane prepared by different oligomer polyols and diisocyanates are different. The mechanical properties of polyurethane elastomers and foams obtained by using polar polyester as soft segment are better. Because the polyurethane made of polyester contains ester groups with high polarity, the polyurethane can not only form hydrogen bonds between hard segments, but also form hydrogen bonds between the polar groups on soft segments and the polar groups on hard segments, so that the hard phase can be more evenly distributed in soft phases and play the role of elastic crosslinking point. Some polyesters can form soft segment crystallization at room temperature, which affects the properties of polyurethane. The strength, oil resistance and thermal oxidation stability of polyester polyurethane are higher than those of PPG polyether, but the hydrolysis resistance of polyester polyurethane is worse than that of polyether polyurethane.
4. Hydrolysis stability comparison:
The hydrolysis resistance of polyester thermoplastic polyurethane was improved after it was protected by carbodiimide. Polyether ester thermoplastic polyurethane and polyether thermoplastic polyurethane have the best hydrolysis resistance at high temperature.
Polyester is vulnerable to water molecule invasion and breakage, and hydrolysis acid can catalyze the further hydrolysis of polyester. The types of polyesters have certain effects on the physical properties and water resistance of elastomers. The water resistance of polyester polyurethane elastomer was improved with the increase of methylene content in polyester glycol. The content of ester group is small and its water resistance is good. Similarly, the water resistance of polyurethane elastomer synthesized by long-chain dicarboxylic acid is better than that of polyester polyurethane synthesized by short-chain dicarboxylic acid.
5. Comparison of microbial resistance:
Polyester-type soft thermoplastic polyurethane can be eroded by microorganisms when it is in contact with moist soil for a long time, while polyether-type soft or rigid thermoplastic polyurethane and polyether-type thermoplastic polyurethane or rigid thermoplastic polyurethane are usually not eroded by microorganisms.