Water as blowing agent

Alternative blowing agents for CFCs are HCFCs, e.g., HCFC-141b, HCFC-123 and HCFC-22. The combined use of HCFCs and water as blowing agent was also proposed (153g). The sole use of HCFC-22 as... 

These phosphorus polyols with ortho-phosphoric ester structure are not used at the moment because, the formulated polyols containing water as blowing agent are not resistant to hydrolysis. Due to hydrolysis, acidic groups appear which decrease markedly the reactivity of the formulated polyol. The resulting acidity inhibits the activity of the tertiary amine used as a catalyst in the foaming process. 

Studies of the processing behaviour of thermoplastic elastomers carried out by Berstorff are reported, and developments by the Company in processing methods and machinety for these materials are examined. These include extmsion compounding machinery, extmders for the production of solid profiles and for the coextrusion of profiles combining solid and foamed thermoplastic elastomers with mbbers, and a process for the extmsion of foamed profiles using water as blowing agent. 

A review is presented of developments by Berstorff in machinery for the processing of thermoplastic elastomers, including co-rotating twin-screw extruders for continuous compounding and extrusion and coextrasion lines for the production of solid and foamed profiles. Reference is also made to the development by Berstorff and Advanced Elastomer Systems of a process for the extrusion of foamed profiles using water as blowing agent. 

The major commercial applications of hydrazine solutions are as blowing agents ( 40%), agricultural chemicals ( 25%), medicinals ( 5%), and — increasingly — in boiler water treatment now as much as 20%. The detailed pattern of usage, of course, depends to some extent on the country concerned. 

Carbon Dioxide (COj) Until 1958 when halocarbons were first used as blowing agents for urethane foams carbon dioxide (COj) was the blowing agent used. The COj was liberated by the isocyanate-water reaction shown below (13). 

In addition to water, auxiliary blowing agents may be included in the foam formulation to further reduce the foam density (16) (17). These agents can be used in addition to, or as part replacement for the water in developing special foam properties. An example is the use of methylene chloride or CFC-11 in either polyether- or polyester-based systems for softening the resulting foam. A number of other volatile solvents are known to have been used also. 

As a general rule, castor oil and its derivatives confer on the resulting PU hydrophobicity and water repellency. These polyols have an excellent compatibility with the pentanes that are used as blowing agents and the resulting PU foams have excellent resistance to humid ageing degradation. 

Rigid insulation foams are usually hydrocarbon blown to produce a closed-cell foam with excellent insulation properties. High-density foams are water blown where structural and screw-holding strength is needed, and halocarbons are used as blowing agents when high-quality, decorative surfaces are required. A compromise between these two aims can be achieved by the addition of water to halocarbon-blown formulations. 

The substances used as blowing agents are also used in refrigeration systems and aerosols. When used to foam plastics, water is often added for various reasons. 

Both water and fluorocarbons are used as blowing agents, sometimes in combination. Water is used mainly in preparation of the conventional, high density. 

Hydrazine and its derivates are used as blowing agents for plastic foams, boiler water treatment, polymerization initiators, pesticides, pharmaceuticals, and dyes. 

Polyurethanes are manufactured by addition of polyols (polyether or polyester) with polyvalent isocyanates. Polyether-polyols are sensitive to oxygen. Thermal-oxidative degradation typically occurs during the manufacture of flexible foams when water is used to form carbon dioxide as blowing agent. Large PUR slab stock... 

---