Thermally expandable microcapsules for polymer foaming-Relationship between expandability and viscoelasticity

Abstract

A new thermally expandable microcapsule was developed for use with foaming polypropylene (PP) by injection molding and extrusion processes at operating temperatures above 2008C. The microcapsule consists of a blowing agent as the core and a shell polymer. The rheological properties of the shell polymer were controlled by a crosslinking agent to design the expandability and shrinkage. The effects of rheological properties on the expandability and the surface appearance of foam products were thoroughly investigated. It was found that storage modulus G 0 and tan d significantly affected the expandability and shrinkage and were controllable through crosslinking polymerization. Visual observation of batch foaming, rheological measurement, and experiments of foam injection molding and extrusion elucidated the existence of the optimal degree of crosslinking that could realize more than 30% density reduction while maintaining a smooth surface at PP foam injection molding and extrusion. POLYM. ENG. SCI., 50:835-842,

Facile and rapid preparation of ultramicrocellular polystyrene using voided nanoparticles

“…Depending on the parameters of the polymerisation, the VNPs with various morphologies have been obtained. The particle size of 100-400 nm of the VNPs is significantly smaller than commonly reported expandable microspheres in the literature [13,14]. The structure of the VNP is of a well-defined encapsulation type with a shell thickness of 10 -50 nm.…”

“…Thermally expandable microspheres [13,14] seem to be a preferred choice for the enhancement of surface quality, but the size of the expandable microspheres, typically 10 -50 mm, is too large for ultramicrocellular or even microcellular foaming, and besides the microspheres could be expanded dozens of times in diameter compared with their original sizes after applying heat. It is desirable to fabricate ultramicrocellular polymers with a fine cell structure and good surface quality by facile and rapid processing.…”

Increased onset temperature of expansion in thermally expandable microspheres through combination of crosslinking agents

“…Kawaguchi and Oishi with coworkers 13 have also been able to improve the thermal properties of TEMS, by altering the monomer composition of the polymer shell. A paper from Kawaguchi in collaboration with Ohshima and coworkers 14 investigates the correlation between the viscoelastic properties of the polymer shell and the expansion properties of the TEMS. Recently, Hu et al 10 published a paper on the synthesis of TEMS utilizing nitrogen from the decomposition of encapsulated p-toluenesulphonylhydrazide to expand the microspheres.…”

Effect of viscoelastic properties of the base polymer on extrusion foaming with thermally expandable microcapsules

“…One of solutions for the foaming of PP is to use MCs. MCs are core–shell structured capsules with diameters of several tens of micrometers and which are composed of a thermoplastic resin shell and a hydrocarbon core . When an MC is heated, it expands to several tens or several hundreds of micrometers in diameter due to vaporization expansion of the core component.…”