Supercritical CO2 Foaming of Radiation Cross-Linked Isotactic Polypropylene in the Presence of TAIC

Abstract

Abstract:Since the maximum foaming temperature window is only about 4 • C for supercritical CO 2 (scCO 2 ) foaming of pristine polypropylene, it is important to raise the melt strength of polypropylene in order to more easily achieve scCO 2 foaming. In this work, radiation cross-linked isotactic polypropylene, assisted by the addition of a polyfunctional monomer (triallylisocyanurate, TAIC), was employed in the scCO 2 foaming process in order to understand the benefits of radiation cross-linking. Due to significantly enhanced melt strength and the decreased degree of crystallinity caused by cross-linking, the scCO 2 foaming behavior of polypropylene was dramatically changed. The cell size distribution, cell diameter, cell density, volume expansion ratio, and foaming rate of radiation-cross-linked polypropylene under different foaming conditions were analyzed and compared. It was found that radiation cross-linking favors the foamability and formation of well-defined cell structures. The optimal absorbed dose with the addition of 2 wt % TAIC was 30 kGy. Additionally, the foaming temperature window was expanded to about 8 • C, making the handling of scCO 2 foaming of isotactic polypropylene much easier.

A strategy for the preparation of closed‐cell and crosslinked polypropylene foam by supercritical CO2 foaming

“…Pristine PP undergoes degradation upon high‐energy irradiation and the gel content of irradiated PP is nearly zero . The decrease of crystallinity of the blends indicated the radiation degradation, as shown in Supporting Information Table SI.…”

“…The foaming process in this work consists of the following steps: (1) blending, (2) sheet molding, (3) γ‐ray irradiation, (4) scCO 2 foaming, and (5) stable microporous structure formation. The detailed foaming process is reported in our previous papers …”

“…prepared closed‐cell PP foam with a large cell diameter by using high melt strength PP. Triallylisocyanurate (TAIC) was added to improve the γ‐ray radiation crosslinking of PP, which increased the melt strength greatly in our previous study . However, the cell density was low, cell size was large, and the cell wall was thin, which was not obvious to improve the mechanical property of PP foam.…”

“…Polymer foams with a closed‐cell structure exhibit high mechanical properties and excellent heat, sound, and water insulation properties . Hence, polymer foams with closed‐cell microstructures have been used in a variety of applications such as in automotive, ship building and aerospace industry, insulation, food, and electronic packaging, as well as in sports and traffic equipments . The use of supercritical carbon dioxide (scCO 2 ) as a physical blowing agent to create microporous structure materials has attracted increasing attention, since CO 2 is less harmful than traditional organic blowing agents and is much easier to be dissolved in melt polymers …”

A developed, eco-friendly, and flexible thermoplastic elastomeric foam from SEBS for footwear application

“…There are plenty of articles in the literature regarding crosslinked TPE foams from polymer or polymer blend [15,[33][34][35][36][37], such as EVA, PU/EVA blend, PVC/TPU blend, NR/EVA blend, etc. During the processing of polymeric foams, irradiation crosslinking can broaden the temperature window for the SCF foaming, and improve cell morphology of the foams with high volume expansion ratio [38][39][40]. Taking these advantages into account, the combination of SCF foaming and irradiation can be applied for continuous manufacturing of TPE foams.…”