INVESTIGATION OF THE EFFECT OF NOZZLE TEMPERATURE ON THE PROPERTIES OF POLYETHYLENE SAMPLES OBTAINED BY FDM PRINTING

The influence of the nozzle temperature of a 3-D printer on the warping and physical and mechanical properties of high-density polyethylene (HDPE) extruded on a "cold" table has been studied. It has been established that an increase in nozzle temperature from 200° to 260°C leads to a decrease in HDPE warpage. In addition, with almost the same stress at break (σb), an increase in strain at break (εb) by more than 20% is observed. Methods of thermophysical, rheological, microstructural studies have proved the change in the structure of samples of thin films obtained by FDM printing with a change in extrusion temperature. An increase in the temperature of the nozzle leads to an increase in the relaxation time of the material structure, which, under conditions of rapid cooling, contributes to the realization of a metastable state characterized by a lower density of nodes of the physical network of entanglements in the amorphous part of the HDPE. A relationship is shown between the change in the free volume, which determines the shrinkage of the material during the FDM process, the change in viscosity during cooling of the melt, and its relaxation time. Increasing the relaxation time leads to a decrease in shrinkage and its dependence on temperature, which explains the decrease in warping of samples obtained at a higher nozzle temperature.