Determination of modified polyamide 6's foaming windows by bubble growth simulations based on rheological measurements

Abstract

Reactive extrusion was used to modify virgin polyamides 6 (v-PA6) and to prepare chain extended PA6 (CE-PA6) and longchain branched PA6 (LCB-PA6) for the melt foaming process. This was done using a twin-screw extruder and the following modifiers: a chain extender ADR-4368 and a branching agent maleic anhydride grafted polypropylene. A reaction mechanism was proposed to explain the chain extension and long-chain branching reactions and was verified by the Fourier transform infrared spectroscopy data. The analysis of the gel permeation chromatography data showed that LCB-PA6 presented a strong increase in the molecular weight and in the dispersity index. Moreover, the rheological properties of the v-PA6 and modified PA6 resins were characterized by a dynamic shear test. The LCB-PA6 compared with CE-PA6 showed much higher shear viscosity and longer characteristic relaxation times, indicating the presence of an LCB structure. A uniaxial elongation test showed that the LCB-PA6 had the highest melt viscosity and melt strength as well as most obvious strain-hardening behavior. A high-pressure differential scanning calorimeter under compressed CO 2 was used to investigate the PA6's crystallization properties so as to analyze its minimum temperature of foaming windows. The melt foamability of the CE-PA6 and the LCB-PA6 was verified by batch melt foaming experiments with CO 2 as the blowing agent and maximum temperature of foaming windows was also quantitatively determined by numerical simulation of bubble growth based on the rheological measurements. The results showed that the LCB-PA6 foams had a smaller cell diameter, a larger cell density, a greater expansion ratio, and wider foaming temperature window than the CE-PA6.

Polypropylene/thermoplastic polyester elastomer blend: Crystallization properties, rheological behavior, and foaming performance

“…In contrast, the strain hardening behavior is caused by the LCB structure. Xu et al 42 obtained the long‐chain structure and LCB structure through grafted modification of PA6 and then confirmed through uniaxial tensile rheology that the long‐chain structure did not produce strain hardening behavior, which is caused by the LCB structure. Therefore, tensile rheology can effectively distinguish the existence of LCB structures.…”

“…Thus, it is not clear whether the | η *| and G′ of modified composites are increased compared with PPC, and whether these changes are caused by the long chain or branched molecular structure. Shear rheology analysis provides sufficient information of molecular weight and molecular weight distribution, but uniaxial tensile rheology is more sensitive to the branched molecular structure than dynamic shear rheology 42 . The best way to prove the existence of branched structure is to observe the occurrence of strain hardening through tensile rheological measurements.…”

Enhancement of the Processability and Properties of Nylon 6 by Blending with Polyketone

“…The loss tangent shown in Figure 8 b also decreased with the formation of long chain branches in the presence of chain extender. The loss tangent has an inverse relationship with the melt strength, which affects the melt processing properties [ 32 ]. That is, the melt processability of PA6 was enhanced by the addition of ADR due to the formation of long chain branches.…”

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.…”