Differences in processing of the hottest polyester

2022-10-23
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Differences in processing of polyester TPU and polyether TPU

as we know, polyurethane is a polar polymer, which will slowly absorb moisture when exposed to air. The hygroscopic TPU particles are melted and processed into shape, and the water is vaporized at the processing temperature, making the surface of the product not smooth, generating bubbles inside, and reducing the physical properties. Therefore, in order to ensure the properties of the product and remove the frost (FOG) to avoid the generation of water and ice energy, and prevent bubbles caused by moisture gasification during melting processing, the particles generally need to be dried before TPU processing

because polyester is easily broken by water molecules, and the acid generated by hydrolysis can catalyze the further hydrolysis of polyester. Generally, under the same conditions, the water content of polyester TPU is much higher than that of polyether TPU. Therefore, pay special attention to polyester TPU in the drying process, pay attention to its thorough drying, and strictly control the drying conditions

pressure maintaining stage

when polymer melt is injected, whether in 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 maintaining stage, the polymer melt will be subjected to high pressure. Under this pressure, the excellent improvement of the experimental machine by Jinan new era Gold Testing Instrument Co., Ltd. in 2017 has been satisfactorily completed. Market Research and consulting company marketsandmarkets predicts that the free volume between segments will be compressed. Due to the reduction of the free volume between molecular chains, the proximity of macromolecular segments will strengthen the intermolecular force, that is, the viscosity will increase. In addition, Due to the low cohesion energy of ether bond and the small rotation barrier of the bond of polyether TPU, the effect of strengthening the tight chain segments of the molecular chain is small. Therefore, the relative displacement of the molecular chain is large during compression, so the viscosity can change in a large range. In addition, because the molecular chain of polyether TPU is much more flexible than polyester TPU, it is difficult to form permanent deformation of polyether TPU. Therefore, when maintaining the pressure during the processing of polyether TPU, compared with polyester TPU, the development status and spatial analysis of polyether TPU plastic extruder should control a longer holding time

processing time

in general, the increase of molecular weight lengthens the molecular chain segment, the slower the movement of the center of gravity of the molecular chain, the more opportunities for the relative displacement offset between the chain segments, the greater the flexibility of the long molecular chain, the more entangled nodes, and the difficulty of chain release and slip, which increases the resistance of the flow process and the time and energy required, showing the sensitivity of viscosity to shear. Generally, the molecular weight of polyester TPU is larger than that of polyether TPU, so the processing time will be longer

processing temperature

generally, polyester TPU has a wider molecular weight distribution than polyether TPU, so the temperature required in the processing process is higher. Because the nitrogen oxygen bond of polyether TPU is easy to break, it needs relatively low temperature to process it

because polyester TPU has large molecular cohesion energy, and the nitrogen oxygen bond in its molecular structure is also difficult to break, it also requires higher temperature and pressure to destroy its molecular bond

due to the large internal friction and molecular cohesion of polyester TPU, it is difficult to cool it even if it returns to normal state, so it needs a long cooling time

because polyether TPU has low cohesion energy of ether bond and small rotation barrier of bond, with the increase of relative molecular weight of polyether, the chain is more flexible, and its molecular chain has high flexibility, so it shows good fluidity, while polyester TPU is slightly inferior

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