From gas release to foam synthesis, the second breath of blowing agents

Abstract

The increasing concern about the environmental impact of physical blowing agents (PBAs) favours the use of chemical blowing agents (CBAs) to replace controversial PBAs. Blowing agents are key compounds in order to obtain polymer foams. Indeed, blowing agents are crucial additives that release gas needed to blow polymer foams. CBA compounds have been widely studied in recent decades, and today if new CBA are studied, one of the challenges remains to adapt the use of CBA to new polymers or new formulations. Only a handful of books present different CBAs commercially available but in these documents, the presentation of CBAs is not enough complete to understand potential or limits. Thus, our work is focused on the most common, both inorganic and organic chemical blowing agents and highlights the specifications of these CBAs, with their advantages and drawbacks, and finally presents promising perspectives.

Chemistry, Processing, Properties, and Applications of Rubber Foams

“…Figure 2 presents a list of typical organic CFA and their gas produced depending on the temperature. The information is mainly based on the work of Coste and coworkers [ 85 ].…”

“…Figure 2 presents a list of typical organic CFA and their gas produced depending on the temperature. The information is mainly based on the work of Coste and coworkers [85]. For CFA, the molecules breakdown via a series of reactions after reaching the decomposing temperature and the heat released can activate adjacent particles.…”

Biobased composites from agro-industrial wastes and by-products

“…During thermoforming, the porous structure of the foam is formed by insufflation of gas in the molten polymer blend, which expands as pressure is reduced, or by gas formation within the batter due to the use of chemical blowing agents that produce gas by thermal decomposition or chemical reaction. Carbon dioxide is currently the most widely used gas for physical blowing of polymer foams as an eco-friendlier alternative to hydrochlorofluorocarbons (HCFCs), due to its low toxicity, high stability, and low-cost [384]. Some foams are obtained by air diffusion into the battery by whipping before curing [385].…”

“…Supercritical inert gases, like carbon dioxide and nitrogen, are used as more environmentally friendly alternatives to blowing foams [373,381,[386][387][388]. Yet these blowing agents require specific and expensive equipment to work under high-pressure conditions, thus chemical blowing agents that are easily incorporated during mixing in the polymer matrix are sometimes preferred [384]. The latter leads to highly diffusing gas molecules (CO 2 , N 2, and H 2 ) resulting in open-cell structures that limit the foam's fields of application.…”

“…Urea was also studied as a blowing agent in biocomposite starch foams considering both its plasticizing and cross-linking properties in starch matrices [126]. A vast variety of chemical blowing agents have been reviewed by Coste et al [384], yet the authors highlighted that unreacted blowing agent and by-products can compromise the material's properties and toxicity due to migration throughout their life cycle. Consequently, various parameters and reaction conditions should be determined for each blowing agent/polymer system to meet the final material requirements with no side effects.…”