Effect Of Molecular Structure And Heterogeneous Nucleating Agent On The Foaming Properties Of PA6 Microcellular Injection Molding And The Mechanical Properties Of Foamed Products

In this article,linear(L-)PA6 and long-chain branched(LCB-)PA6 foaming material with dense and uniform cells were prepared by adding several different nucleating agents in the long-chain branching modification process of L-PA6,using MuCell(?)supercritical N2 assisted microcellular injection foaming process.The effects of cell morphology and nucleating agents on the mechanical properties of PA6 were analyzed.It was shown that LCB-PA6 had higher complex viscosity and more pronounced shear thinning than linear PA6.It also had a lower crystallization temperature,and the LCB molecular structure can increase the crystallization rate and crystallinity and refine the crystal grains at a high cooling rate.As the injection temperature increased,the cell density of the PA6 foaming splines decreased,and the average cell diameter increased.In addition,the cell density of LCB-PA6 was higher than that of L-PA6 under various process conditions,but LCB-PA6 could not foam because the amount of scN2 dissolved in the homogeneous system was too low at 260?.The high SCN2 content system was beneficial to the formation of denser cell morphology in the low temperature range,while it tended to form larger cell size in the high temperature range.This work also showed that nucleating agents in the polymer matrix can increase the polymer's melt strength and provide a large number of nucleation sites,which can promote heterogeneous nucleation during the foaming process,and accelerate the nucleation rate.Also,the nucleating agent can induce and accelerate the formation of crystal nuclei during the crystallization process,and increase the crystallization temperature,resulting in an increase in cell density,a decrease in cell size,and a narrower cell size distribution.Among them,Nanographite had the greatest improvement in the foaming performance of L-PA6,with a cell density of 1.66×107 cm-3 and an average cell diameter of 35?m at 250?.MWCNTs and MWCNTs-OH improved the cell morphology of LCB-PA6 most obviously,the cell density of which can reach 1.84×108 cm-3 and 1.51×108 cm-3 respectively when the average cell diameter decreased from 95 ?m to 22?m.In addition,adding different nucleating agents can make PA6 show different mechanical properties.MWCNTs can significantly increase the tensile elongation at break of LCB-PA6,while MWCNTs-OH can increase the tensile modulus and flexural modulus of LCB-PA6.With the addition of Nanographite,the flexural modulus and flexural strength of L-PA6 even exceeded that of unfoamed L-PA6.