Polyamide (PA), is used worldwide in fiber, film, packaging, and molding applications. It is one of the most important commercial engineering plastics because it offers an attractive combination of good processability, excellent mechanical properties, and desirable chemical resistance. However, due to its molecular weight and molecular weight distribution limitations, industrially produced PA6 is unsuitable for use in the melt foaming process. Chemical modification for virgin PA6 have been verified as a practical option to require high melt viscosity/and melt strength. In this study, modified PA6 with high melt strength by screening out excellent chain extenders was successfully fabricated and then was used for foaming with CO2 as the foaming agent. We used the reactive extrusion method to modify virgin polyamides 6 (PA6) for melt foaming. The reactive extrusion was performed with a Haake melt mixer, and the following modifiers were used: 1,1'-isophthaloyl-bis-caprolactam (IBC), 2,2'-bis(2-oxazoline) (BOZ) and an epoxy-type chain extender KL-E4370 (EP) as well as an IBC and BOZ combination. The chain extender’s effects on the reactive modification were characterized through the PA6 chain’s rheological properties, including the storage modulus, the loss modulus, and the dynamic complex viscosity. The EP-modified PA6 was shown to have the highest viscoelasticity; that is, the highest melt strength. Furthermore, we used a high-pressure DSC to measure the effects of CO2 on the crystallization kinetics of PA6. We found that high CO2 pressures led to lower half-crystallization times (t1/2) and the high non-isothermal crystallization rate of the modified PA6 under compressed CO2 seemed to be related to the small cell diameters in the PA6’s foams. With the presence of developed crystals, the cell density would increase and the cell size would become smaller. We also studied the PA6’s batch melt foaming with various modifiers using CO2 as the foaming agent. And the EP-modified PA6 with the highest melt strength had the widest foaming window and the biggest expansion ratio.

Chain extension of polyamide 6 using multifunctional chain extenders and reactive extrusion for melt foaming

255th National Meeting (2018)

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