What are the Reasons for Differences to ether TPU and ester TPU?
1. Polyether Polyols
Polyether polyols are polymers or oligomers with ether bonds in the main molecular chain structure and hydroxyl groups at the terminals. Because the ether bonds in their structure have lower cohesive energy and are more easily rotated, polyurethane materials prepared from them have good low - temperature flexibility and excellent hydrolysis resistance. Although their mechanical properties are not as good as those of polyester polyol - based polyurethane, they have a better feel. The system has low viscosity, is easily miscible with isocyanates and additives, and has excellent processing properties.
2. Polyester Polyols
Polyester polyols are mainly produced by the condensation reaction of dicarboxylic acids and alcohols with two or more hydroxyl groups. Their structural characteristics include ester groups in the main molecular chain and hydroxyl groups at the terminals, with a molecular weight generally ranging from 500 to 3000.
Polyurethane materials based on polyester polyols typically have good mechanical properties, excellent oil resistance, and superior wear resistance. However, they have poorer hydrolysis resistance and low - temperature flexibility. The feel of their products, especially at low temperatures, is not as soft as that of polyether polyol - based polyurethane. Polyester polyols have high cohesive energy and are mostly waxy solids at room temperature. Their viscosity after heating and melting is relatively high, and their miscibility with other raw materials used in polyurethane synthesis is far inferior to that of polyether polyols.
3. Flexible Chain Segments
When the chemical ratio of raw materials is constant, changing the length of the flexible chain segments has different effects on the properties of elastomers with different soft segments. Increasing the molecular weight of the soft segment means reducing the proportion of hard segments. Because the ether bonds have lower cohesive energy and smaller bond - rotation barriers, as the relative molecular weight of polyether increases, the chains become more flexible. With an increased proportion of soft segments, the strength decreases, the elasticity increases, and the permanent deformation increases. For polyester diols, the effect of soft segment length on strength is not very obvious. This is because the presence of polar ester groups in the molecules means that as the molecular weight of the polyester soft segments increases, the ester groups also increase, offsetting the negative impact of the increased soft segments and reduced hard segments on strength. Additionally, the hydrolysis resistance of polyester - type polyurethane decreases with increasing polyester chain segment length due to the increased number of ester groups. In contrast, the hydrolysis resistance of polyether - type polyurethane increases with increasing polyether chain segment length.