Microcellular polymers based on concentrated emulsions (PolyHIPE)

Cellular materials can be defined as materials containing gaseous voids called cells (this term derives from the Latin cella meaning chamber), surrounded by a dense solid matrix. Cellular materials are widely used in a wide range of applications such as thermal and sound insulation, liquid absorbents and low-density structures.

Depending on their composition, cell morphology and physical properties, cellular polymers can be considered rigid or flexible. Depending on cell size, cellular polymers can be classified as macrocellular (>100 µm), microcellular (1 to 100 µm), ultramicrocellular (0.1 to 1 µm) or nanocellular (0.1 to 100 nm).

Cellular materials can be distinguished according to whether their cells are open or closed. In closed-cell materials, the voids are isolated from each other and the cavities are surrounded by a continuous polymer wall. In open-cell materials, the walls are pierced by openings of varying sizes.

Cellular structures are very common in nature: cork, wood, sponges and corals are examples of such structures. Mankind has used these natural cellular materials for centuries, and has recently developed its own synthetic cellular materials: polymers are the most common, but techniques have also been developed to shape metals and ceramics in cellular form. Cellular polymers are generally prepared by chemical or physical foaming. In this case, control of cell size and morphology is difficult to achieve. It is also difficult to obtain fully interconnected structures.

The approach of using highly concentrated emulsions to prepare microcellular polymers with controlled, fully interconnected porosity may therefore represent an attractive alternative for many applications. The resulting materials, known by the acronym polyHIPE, are attracting a great deal of interest from academic and industrial researchers alike, thanks to their ease of preparation and high application potential.

AIBN

azobisisobutyronitrile

BET

Brunauer, Emmett and Teller theory

BPO

benzoyl peroxide

DVB

divinylbenzene

E/H

water-in-oil

H/E

oil-in-water

HIPE

High Internal Phase Emulsion

HLB

hydrophilic-lipophilic balance

KPS

potassium...