Blowing or Foaming Agents

Blowing agents (foaming agents) are used to generate gas bubbles in a liquid polymer or compoimd, at approximately the same time as the polymer is made to solidify, whether because of a chemical reaction or by cooling. 

The use of foamed plastics instead of solid is growing because foamed products have a very low density compared with the original, use less polymer for a given volume, and offer improved insulation characteristics. Foams can contain fillers, including wood flour, or reinforcing fibres. 

Foam production is compatible with injection and compression moulding, extrusion, thermoforming, rotational and blow moulding, and with the spread coating of PVC. 

A wide variety of polymers can be foamed, including the polymethanes, polyisocyanurates, PVC, polystyrene, ABS, polycarbonate, PET, PBT, polyamides, PPO, EVA and the polyolefins. Other additives required for the foaming process besides blowing agents may include foam nucleating agents, stabilisers, surfactants, plasticisers, colourants, flame retardants and particulate fillers. 

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Uses. As a refrigerant solvent extractant as a blowing or foaming agent... 

A plastic foam can be defined as a plastic material with a cellular structure. Generally, it consists of a minimum of two phases a gas phase dispersed in a solid plastic matrix phase. The gaseous phase is contained in voids or cells and is often referred to as the blowing or foaming agent. The solid plastic component may be neat resin, polymer blends, alloys, or contain fillers, either fibrous or other shapes [17-19]. 

Blends of poly (ethylene terephthalate) (PETP) and polypropylene (PP) with different rheological properties were dry blended or compounded, and extrusion foamed using both physical blowing and chemical agents, and the foam properties compared with those of foam produced from the individual components in the absence of compatibilisers and rheology modifiers. The foams were characterised by measurement of density, cell size and thermal properties. Low density foam with a fine cell size was obtained by addition of a compatibiliser and a co-agent, and foamed using carbon dioxide. The presence of PP or a polyolefin-based compatibiliser did not effect... 

Blowing (foaming) agent — A substance that alone or in combination with other substances can produce a cellular structure in a plastic or elastomeric mass. It can be a compressed gas, a volatile liquid, or a solid that decomposes into a gas upon heating. 

Composites can be created in which the core optimizes desired physical properties such as modulus, whereas the outer layer optimizes surface considerations not inherent in the core material. Solid outer—foam core can provide composites with significant reductions in specific gravity7 (0.7). Dry blowing agents can be "dusted" onto the pellets or liquid agents injected into the first transition section of the extruder. 

OBSH is one of the best blowing agents of the sulfonyUiydrazide class. Its gas hberation characteristics (no stepwise change up to 140°C) makes it possible to obtain foams with small, uniform cells. It is nontoxic and does not impart color and smell to articles. OBSH is used for foaming PVC, polyolefins, polysulfides, microporous rubber, or foamed materials based on mixtures of polymers with rubbers. In the last case, OBSH acts additionally as a cross-linking agent. 

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