What are the differences between polyester TPU and polyether TPU in processing?

Thermoplastic polyurethane elastomers called TPU, also known as PU thermal plastics, if according to the soft segment structure can be divided into polyester type, polyether type and butylene type, they contain ester-, ether-based and butene-based, then polyester-type TPU and polyether TPU in the processing of those differences? Let's analyze it next.
dry
as we know, polyurethane is a polar polymer that slowly absorbs moisture when exposed to air. With moisture-absorbing TPU particles melting molding, water in the processing temperature gasification, so that the surface of the product is not smooth, internal bubbles, material reduction, so in order to ensure the performance of the product, to prevent melting processing caused by moisture gasification bubbles, before TPU processing, generally need to dry the particles
Chin china
.
Because polyester is susceptible to water molecules and break, hydrolytic acids can catalytic the further hydrolysis of polyester, usually, in the same conditions, polyester TPU than polyether TPU water content is much higher, so in the drying process to pay special attention to polyester TPU, pay attention to its thorough drying, strict drying conditions to control.
the pressure protection phase
the polymer melt in injection molding, whether in the pre-molding stage or injection stage, the melt has to withstand the internal static pressure and external dynamic pressure of the joint action.
the pressure-keeping phase, the polymer melt will be subjected to high pressure, under which the free volume between the molecular chain segments is compressed, due to the reduction of the free volume between the molecular chains, the proximity of the large molecular chain segment makes the intermolecules strengthen the force i.e. the performance viscosity is increased, in addition, Because the ether-like TPU has a lower ether bond cohesion energy and a smaller rotational base of the key, which results in a smaller role between the tight chain segments of the enhanced molecular chain, the molecular chain has a large relative displacement during compression, so the viscosity can be changed in a larger range. In addition, because the polyether-type TPU molecular chain is much softer than the polyester-type TPU, the permanent deformation of polyether-type TPU is more difficult to form, so when the polyether-type TPU processing process is pressurized, compared with the polyester-type TPU, the polyether-type TPU to control a longer pressure-keeping time.
Processing time
because in general, the increase in molecular weight makes the molecular chain segment longer, the slower the center of gravity of the molecular chain moves, the more opportunities for relative displacement between the chain segments to cancel, the more flexible the molecular long chain, the more tangled points, the chain release and slip difficulties, so that the flow process resistance increases, the time and energy required also increase, showing viscosity sensitivity to shearing. In general, polyester TPU is longer than the molecular mass of polyether TPU, so its processing and molding time will be longer.
processing temperature
because the general polyester TPU compared to the molecular mass distribution of polyether TPU is wider, so the processing process requires a higher temperature. Because the nitrogen and oxygen bonds of the polyether TPU are more easily broken, it is necessary to process them at a relatively low temperature.
pressure
Because polyester-type TPU molecules have large internal energy, nitrogen and oxygen bonds in their molecular structure are also more difficult to break, so its processing is to destroy its molecular bonds also need higher temperature and pressure.
cooling
due to the polyester TPU friction is large, molecular cohesion energy is larger, so it is difficult to cool even if it is difficult to return to normal state, so it requires a longer cooling time.
Liquidity
Due to the low cohesion energy of the polyether-like TPU ether bond, the rotational position of the key is smaller, with the increase of the relative molecular mass of the polyether, the chain is more gentle, its molecular chain has a high degree of flexibility, so it shows good fluidity, while the polyester-type TPU is slightly less.