Supercritical CO₂ Mold Foaming To Prepare Polyamide 6 Foam And Research On The Mechanical Properties

Polyamide 6(PA6) is currently the most widely used nylon material,which has the characteristics of light weight,good toughness,acid and alkali resistance,and abrasion resistance.With the rise of microcellular foam materials,there are more and more researches on high performance PA6 and its microcellular foaming materials.Linear PA6 was modified with chain extender KL-E4370 and antioxidant pentaerythritol ester(1010)to prepare modified PA6 materials with high melt strength.The foamability of the modified materials was characterized by differential scanning calorimeter and rheometer.The foaming was carried out under different process conditions,and the effects of different process conditions,such as temperature,pressure and saturation time,on the cell structure were explored with the foaming methods of solid-state foaming and melt-cooling foaming.The results show that the temperature range of PA6 solid-state foaming is narrow.With the increase of CO2 saturation pressure,the bubble diameter of PA6 foam gradually decreases,but the cell density and expansion ratio increase.If the saturation time is too long,the thermal degradation of PA6 leads to a decrease in its expansion ratio.The foaming temperature window of the melt-cooling method is wider.The cell diameter and foaming ratio of the foams were similar to the results of solid-state foaming,but the phenomenon of cell rupture increased.The PA6 foams with bubble diameter ranging from 18.3μm-143.6μm,cell density ranging from 7.42×106-1.75×109 cells/cm3,and expansion ratio ranging from 5.6-22.4 were prepared by controlling the saturation pressure in the range of 10 to 20 MPa and foaming temperature 223-231℃.The range of the tensile strength of the PA6 foams was 0.72-5.8 MPa,the range of the elongation at break was 22%-51%,and the range of the compressive strength was 0.03-2.47 MPa.Compared with the melt-cooling foaming method,the tensile strength of the PA6 foam prepared by the solid-foaming method are similar,and the compression strength decreases slightly.The finite element simulation software COMSOL Multiphysics V5.4 was used to simulate the tensile and compressive properties,and the influence of cell diameter on the mechanical properties of PA6 foam was researched.The simulation results show that small cells were beneficial to enhance the tensile and compressive properties of the foams.The test results of the mechanical properties of the foams basically agree with the simulation results,and the tensile strength and compression strength of PA6 foams with smaller bubble diameter are higher.