Morphological, thermo-mechanical, and thermal conductivity properties of halloysite nanotube-filled polypropylene nanocomposite foam

Studies about polypropylene nanocomposite foams are receiving attention because nanoparticles can change physical and mechanical properties, as well as improve foaming behavior in terms of homogeneous cell structure, cell density, and void fraction. In this research, the foaming behavior of polypropylene, polypropylene/long-chain branched polypropylene (LCBPP) 100/20 blend, and polypropylene/LCBPP/halloysite nanocomposites with 0.5 and 3 parts per hundred of resin (phr) is studied. The LCBPP was used to improve the rheological properties of polypropylene/LCBPP blend, namely the degree of strain-hardening. Transmission electron microscopy observation indicated that halloysite nanotube particles are well distributed in the matrix by aggregates. Subsequent foaming experiments were conducted using chemical blowing agent in injection-molding processing. Polypropylene foam exhibited high cell density and cell size as well as a collapsing effect, whereas the polypropylene/LCBPP blend showed a reduction of the void fraction and cell density compared to expanded polypropylene. Also, the blend showed reduction of the collapsing effect and increase of homogeneous cell size distribution. The introduction of a small amount of halloysite nanotube in the polypropylene/LCBPP blend improved the foaming behavior of the polypropylene, with a uniform cell structure distribution in the resultant foams. In addition, the cell density of the composite sample was higher than the polypropylene/LCBPP sample, having increased 82% and 136% for 0.5 and 3 phr of loaded halloysite nanotube, respectively. Furthermore, the presence of halloysite nanotube increased crystallization temperature (Tc) and slightly increased dynamic-mechanical properties measured by dynamic-mechanical thermal analysis. By increasing halloysite nanotube content to 3 phr, the insulating effect increased by 13% compared to polypropylene/LCBPP blend. For comparative purposes, the effect on foaming behavior of polypropylene/LCBPP was also investigated using talc microparticles.

A study on the fabrication of plasticized polystyrene-carbon nanotube nanocomposites for foaming

The impregnation of carbon nanotubes within fiber-reinforced polymers (FRPs) is a sought after capability for the advancement of composite systems. This study evaluates the novel processing of a carbon nanotube nanocomposite that has been developed to incorporate varying carbon nanotube loadings within final composite foams. This material is manufactured through a melt mix process of carbon nanotubes and polystyrene at ∼2.0–13.0 wt.% that further underwent a plasticization process in an acetone solvent. The chemical foaming agent 2.2′-Azobi(isobutyronitrile) is used to facilitate foaming at a constant 3.0 wt.% concentration. The foamed nanocomposite results in a carbon nanotube-loaded micro-porous structure showing capabilities of delivering localized carbon nanotube placement within fiber composite laminate systems. This report’s aim is to illustrate the effects of plasticizing polystyrene-carbon nanotube nanocomposite and calendaring the softened material to form foams imbedded with carbon nanotubes (carbon nanotubes). Scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and Fourier transform infrared spectroscopy were the tools that are used to characterize the materials at the various morphologies with their findings inclusive.

Polystyrene/multi-wall carbon nanotube composite and its foam assisted by ultrasound vibration

Polystyrene/multi-wall carbon nanotube composite with an interconnected honeycomb-like structure was prepared by firstly coating the surface of the polystyrene pellets with multi-wall carbon nanotube, and sequentially welded through an ultrasound vibration technique. The mechanical and morphological properties of as-prepared composite were investigated in various measurements. It was found that an aggregative and honeycomb-like morphology of multi-wall carbon nanotube existed in the polystyrene/multi-wall carbon nanotube composite according to the polarized optical microscopic and scanning electron microscopic results; the ultrasound vibration could benefit to the performance of flexural strength. Furthermore, different composite foams were studied in this work, employing supercritical carbon dioxide as a blowing agent. Compared to other foams prepared by the conventional methods, the compressive strength of the foams derived from as-described novel method, was significantly improved. Also, being ascribed to this interconnected structure by coating carbon nanotube on polystyrene pellets, good electrical conductivity of 0.05–0.11 S/m was achieved in the novel composite foams.