Influence of crystallization on microcellular foaming behavior of polyamide 6 in a supercritical CO₂‐assisted route

Abstract

Supercritical CO2 as a blowing agent has attracted increasing interest in the preparation of microcellular polyamide 6 (PA6) foams. In this work, we developed the supercritical CO2‐assisted method to prepare a series of different microcellular PA6 foams by controlling its crystallization properties in two steps and carefully investigated the corresponding crystallization properties of modified PA6 and foams using various techniques. Initially, a multifunctional epoxy‐based chain extender (CE) was used to produce high‐melt strength‐modified PA6 with improved foaming ability; then, the resulting PA6 was foamed to prepare the microcellular foams of PA6 using supercritical CO2 as a blowing agent in a batch foaming route. The CE effectively enhanced the melt strength of PA6, and CE usage was optimized to obtain a threshold of high branching without crosslinking. The number of crystals was also adjusted by the saturation temperature. Furthermore, these crystals that formed during the saturation process served as high‐efficiency bubble nucleating agents and then limited the growth of bubbles at the same time. The microcellular foams of PA6 were successfully obtained with a cell size of 10.0 μm, and cell density of 2.0 × 109 cells/cm3 at the saturation temperature of 225°C.

Microstructure and Properties of Glass Fiber-Reinforced Polyamide/Nylon Microcellular Foamed Composites

“…In recent years, the microcellular foaming composites are increasingly recognized as an important component for improving the structure and properties of polymeric materials due to their remarkable effects such as lightweight [ 1 , 2 , 3 ] and low dielectric constant [ 4 , 5 ]. The microcellular foaming process can generate large numerous of micron-sized cells inside the polymer matrix, forming a unique dense surface and core foamed structure [ 6 , 7 , 8 ]. This structure could reduce the weight of the material, and it endows the material with higher toughness, impact strength, and dimensional accuracy [ 9 , 10 , 11 , 12 , 13 ], which is meaningful to the requirement of lightweight.…”

Influence of fibrillated poly(tetrafluoroethylene) on microcellular foaming of polyamide 6 in the presence of supercriticalCO2

“…They found that the PTFE nanofibrils network was effective cell nucleating agent. However, according to our knowledge, only a few reports on polyamide 6 foam using batch foaming method assist by scCO 2 were reported 14,15,35,36 . The influence of PTFE in PA6 foams was unclear.…”

“…The low melt strength of the pure PA6 with linear molecular chain structure limit its foaming ability 14–16 . To improve the PA6 melt strength, the chain extending modification usually was used 15,17–21 .…”

“…The low melt strength of the pure PA6 with linear molecular chain structure limit its foaming ability 14–16 . To improve the PA6 melt strength, the chain extending modification usually was used 15,17–21 . Lu et al 19 used chain extension modification of PA6 by terephthaloyl‐biscaprolactam (TBC), and found the improvement of intrinsic viscosity of PA6.…”

“…In our previous work, the multifunctional epoxy‐based chain extender was added in the PA6 to form branched structure 15 . The microcellular PA6 foams were obtained by the crystals that formed during the saturation process served as cell nucleating agents.…”