1.Effect of molecular weight:

The larger the molecular weight, and the narrower the molecular weight distribution, the higher the viscosity.

2.Effect of low molecular additives:
Low molecular additives can reduce the intermolecular forces between large molecules, thereby reducing viscosity. Some plastics add solvents or plasticizers during processing to reduce viscosity and facilitate mold forming.

3.Effect of temperature on viscosity:
Temperature has a significant impact on the viscosity of most molten plastics. Generally, as the temperature increases, the viscosity decreases. However, the extent to which the viscosity of different plastics decreases varies:

For PE/PP plastics, increasing the temperature has little effect on improving fluidity and reducing melt viscosity. If the temperature is too high, it can result in increased consumption without much benefit.
For plastics such as PMMA/PC/PA, increasing the temperature significantly reduces viscosity. For PS and ABS, increasing the temperature has a significant advantage in reducing viscosity and improving moldability.

4.Effect of shear rate:
Increasing the shear rate of plastic effectively reduces viscosity. However, there are some exceptions, such as PC, which is not significantly affected by screw speed.

5.Effect of pressure:
The effect of pressure on viscosity is more complex. Generally, the viscosity of PP and PE plastics is not greatly affected by pressure, but the pressure has a significant impact on PS. In actual production, on machines with well-equipped equipment, it is important to take advantage of high-speed injection, that is, the action of high shear rate, rather than blindly increasing pressure.