What is the difference between polyester TPU and polyether TPU processing?

TPU as a thermoplastic polyurethane elastomer, also known as PU thermoplastic, is a linear block copolymer composed of soft segments of oligomer polyols and hard segments of diisocyanate chain extenders
.
So is there any difference between polyester TPU and polyether TPU processing? Next, the editor of Dingzhi will give you a detailed introduction to this problem
.
1.
Drying As we know, polyurethane is a polar polymer, which will slowly absorb moisture when exposed to the air
.
It is formed by melt processing with hygroscopic TPU pellets.
The water vaporizes at the processing temperature, which makes the surface of the product not smooth, generates bubbles inside, and reduces physical properties.
Therefore, in order to ensure the performance of the product and prevent the bubbles caused by the vaporization of moisture during melt processing, Before TPU processing, it is generally necessary to dry the pellets
.
Since polyester is susceptible to breakage by the attack of water molecules, the acid generated by hydrolysis can catalyze the further hydrolysis of polyester.
Under normal circumstances, under the same conditions, polyester TPU has a higher water content than polyether TPU.
There are many, so special attention should be paid to polyester TPU during the drying process, and it should be thoroughly dried and the drying conditions should be strictly controlled
.
2.
Pressure Due to the greater cohesive energy of polyester TPU molecules, the nitrogen-oxygen bonds in its molecular structure are also more difficult to break, so higher temperatures and pressures are required for its processing, that is, to destroy its molecular bonds
.
3.
Cooling Because polyester TPU has relatively large internal friction and high molecular cohesive energy, it is difficult to cool it even if it returns to its normal state, so a long cooling time is required
.
4.
Fluidity Because the cohesive energy of the polyether TPU ether bond is low, and the rotation barrier of the bond is small, as the relative molecular weight of the polyether increases, the chain is more flexible, and its molecular chain has a high degree of flexibility, so it is performance It has good fluidity, while polyester TPU is slightly inferior
.
5.
Processing time.
Under normal circumstances, the increase in molecular weight will lengthen the molecular chain, the slower the center of gravity of the molecular chain moves, the more opportunities for offsetting the relative displacement between the chain segments, the greater the flexibility of the long molecular chain, and the increase in entanglement points.
It is difficult to release and slip, so that the resistance of the flow process increases, and the time and energy required also increase, showing the sensitivity of viscosity to shear
.
Under normal circumstances, polyester TPU has a larger molecular weight than polyether TPU, so it takes longer to process and shape
.
6.
Processing temperature Because polyester TPU generally has a wider molecular mass distribution than polyether TPU, the temperature required during processing is higher
.
Since the nitrogen-oxygen bond of polyether TPU is easier to break, relatively low temperature is required to realize its processing
.
7.
In the pressure-holding stage, when the polymer melt is being injected, whether it is the pre-molding stage or the injection stage, the melt must undergo the combined action of internal static pressure and external dynamic pressure
.
In the pressure-holding stage, the polymer melt will be subjected to high pressure.
Under this pressure, the free volume between the molecular chains is compressed.
As the free volume between the molecular chains is reduced, the close of the macromolecular chains will strengthen the intermolecular force.
The apparent viscosity is improved.
In addition, because the cohesive energy of the ether bond of the polyether TPU is lower, the rotation barrier of the bond is smaller, which leads to the smaller effect of strengthening the close segment of the molecular chain.
Therefore, when the molecular chain is compressed, the molecular chain The relative displacement is large, so the viscosity appears to be able to change in a large range
.
In addition, since the molecular chain of polyether TPU is much softer than polyester TPU, permanent deformation of polyether TPU is more difficult to form.
Therefore, when the pressure is maintained during the processing of polyether TPU, it is more flexible than polyester TPU.
In comparison with TPU, polyether TPU needs to control a longer holding time
.
The above differences between polyester TPU and polyether TPU processing are shared here.
In general, polyester TPU is mainly mechanically resistant and suitable for mechanical parts.
Polyether TPU is mainly resistant to hydrolysis.
Good performance, mainly used in wire and cable products
.