Melt pump manufacturer overview of the difference between polymer melt viscosity and strength
Polymer melt strength refers to the ability of polymer to support its own mass in the melting state. Or when the melt breaks under certain conditions under the action of a force (such as traction or tensile force), which is defined as the melt strength of the polymer. For the difference between polymer melt viscosity and strength, zhengzhou Butt melt pump manufacturers from the following three aspects.
1, Polymer Melt strength is ultimately determined by the degree of polymer chain Entanglement at melt, high Entanglement mean high melt strength.
2. There are many factors affecting polymer melt viscosity, including processing temperature, pressure, shear rate, relative molecular weight and distribution of materials. The higher the processing temperature is, the lower the melt viscosity is. The higher the pressure, the higher the melt viscosity; The higher the shear rate, the lower the melt viscosity. The role of the force has shear force, such as injection processing, and tensile force, such as extrusion, blow molding processing. Molecular weigh and molecular chain compliance is flexible and generally shown as shear sensitivity, and it is also rigid, shown as temperature sensitivity.
3. Analyze why PA is not easy to draw, but PP is easy? PA in the processing temperature range, good fluidity, viscosity is relatively low, but because the molecular weight of PA itself is not large, and the molecular weight is wide, and THE relative molecular weight of PP PA is large, the distribution is narrow, chain tangles more, by external force after the melt strength is high, it is easy to wire. From the perspective of crystallinity and crystallization speed, due to the polar bond between the molecular chains of PA, orientation crystallization is relatively slow, while PP has fast orientation and high crystallinity. The crystallization point can be used as a physical cross-linking point to improve the melt strength, which is conducive to wire drawing.
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