Amorphous Polymers’ Foaming and Blends with Organic Foaming-Aid Structured Additives in Supercritical CO2, a Way to Fabricate Porous Polymers from Macro to Nano Porosities in Batch or Continuous Processes

Abstract

Organic polymers can be made porous via continuous or discontinuous expansion processes in scCO2. The resulting foams properties are controlled by the interplay of three groups of parameters: (i) Chemical, (ii) physico-chemical, and (iii) technological/process that are explained in this paper. The advantages and drawbacks of continuous (extrusion, injection foaming) or discontinuous (batch foaming) foaming processes in scCO2, will be discussed in this article; especially for micro or nano cellular polymers. Indeed, a challenge is to reduce both specific mass (e.g., ρ < 100 kg·m−3) and cell size (e.g., average pore diameter ϕaveragepores < 100 nm). Then a particular system where small “objects” (coreshells CS, block copolymer MAM) are perfectly dispersed at a micrometric to nanometric scale in poly(methyl methacrylate) (PMMA) will be presented. Such “additives”, considered as foaming aids, are aimed at “regulating” the foaming and lowering the pore size and/or density of PMMA based foams. Differences between these additives will be shown. Finally, in a PMMA/20 wt% MAM blend, via a quasi one-step batch foaming, a “porous to nonporous” transition is observed in thick samples. A lower limit of pore size (around 50 nm) seems to arise.

Thermoplastic Starch with Poly(butylene adipate-co-terephthalate) Blends Foamed by Supercritical Carbon Dioxide

“…There are many works associated with TPS, such as the study of starch-based films [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ], the production of innovative biodegradable products [ 29 ], the additives used to strengthen TPS [ 30 ], water or azodicarbonamide used as foaming agents to develop starch-based foams [ 18 , 26 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ], and evaluating the performance of starch loose-fill foams and expanded polystyrene [ 39 ]. Foam products are often used in packing goods, which can easily become plastic garbage.…”

“…Starches with high amylose content are able to produce TPS foams [ 18 , 26 , 31 , 32 , 35 , 36 , 38 ]. Starch grafting by poly(methyl acrylate) [ 34 ], or grafting polystyrene [ 37 ] using water as a foaming agent to make foams, has been studied.…”

Self-foaming polymers: Opportunities for the next generation of personal protective equipment

“…It was also exploited for designing nonisocyanate polyurethanes (NIPUs) foams as promising alternatives to conventional PU foams for thermal insulation. [52] Despite the numerous advantages of this method used for foaming many polymer matrices, [39,40,53,54] it does require intricate equipment to maintain CO2polymer melt under pressure. Moreover, the method is hardly transferrable to crosslinked polymers, i.e., thermosetting polymers.…”

SEBS as an Effective Nucleating Agent for Polystyrene Foams

“…On the other hand, in a PMMA/20 wt.% MAM blend, through a quasi-one-step batch foaming, a "porous to nonporous" transition was observed on thick samples. Such a sharp porosity gradient (from nonporous transparent areas to porous opaque areas within the same sample) revealed a lower pore size limit of around 50 nm in a classical batch process in "mild conditions" [10]. Qingfeng et al reported a remarkable increase in the cell density of PP foams with the inclusion of a 5.2 wt.% of PDMS [5].…”