Study on the Nonlinear Behavior of Melt in Dynamic Molding of Polymer Materials

The relationship between the apparent viscosity of the melt and the vibration frequency under the relationship of the wall shear stress and the shear rate of the capillary wall at d = 0.05 mm. The three curves in each figure are the three set amplitudes A = 0, 0.05 mm. And 0.15mm with the / change (A = 0mm steady state extrusion). The constant melt temperature 7 = 165C, 1/0 = 20. From the, can be seen: Compared with the steady-state extrusion, the apparent viscosity of the melt after the introduction of the vibration force field in the case of other parameters consistent Significantly reduced; in each figure, it is also found that the apparent viscosity of the melt decreases with the increase of the vibration frequency at the same amplitude; at the same vibration frequency, the apparent viscosity of the melt also increases with the amplitude. Non-linear decreasing trend.

It can be considered that after superimposed vibration in the flow process of the polymer melt, a pulsating shear stress is superimposed on the original shear stress in the flow field, and the pulsating shear stress continuously generates instantaneous extrusion and release of the flow field. The effect is that this action effectively promotes the orientation process of the molecular chain along the flow direction; at the same time, due to the instantaneous increase of the shear stress, the instantaneous destruction rate of the large molecular chain entanglement point will be greater than the instantaneous generation rate, making the moment of the entanglement point. The decrease in density favors the unwrapping of macromolecular chains; the unwrapping and orientation of macromolecular chains reduces the resistance of the polymer melt, and the macroscopic manifestation is the decrease of the apparent viscosity of the melt.

5 Concluding remarks Under the premise of appropriate assumptions, this paper does not rely on any existing constitutive relations, and has established a formula for calculating the apparent viscosity of the polymer melt during the dynamic forming process. Dynamic rheological experiments on LDPE were carried out using a self-developed constant-velocity capillary dynamic rheological device. By measuring the instantaneous value of capillary inlet pressure and volume flow at a certain vibration frequency and amplitude, the change law of melt shear stress, shear rate and apparent viscosity at different frequencies and amplitudes can be obtained. It was found that dynamic extrusion of LDPE melts at different amplitudes and frequencies, as with steady-state extrusion, also has a nonlinear proportional relationship between wall shear stress and wall shear rate; compared with steady-state extrusion, When the vibration force field is introduced, the apparent viscosity of the melt decreases significantly; moreover, the apparent viscosity of the melt at different amplitudes and frequencies tends to change nonlinearly.