Replacement of CFCs

There is no direct alternative blowing agent for polyurethane foams that combines the advantageous properties of CFCs and the trend has been to develop replacements specific to individual applications. Much has been achieved but the present blowing systems are widely regarded as interim solutions in the longer term, the solution is seen in pentane-based compounds. 

The main CFC to be replaced is CFC Rll (trichlorofluoromethane), which offers high molecular weight and therefore low thermal conductivity, low boiling point and therefore good blowing action, high chemical stability, non-toxicity, non-flammability, and low price. 

In addition to ozone depletion, the greenhouse effect is important. Greenhouse warming potential (GWP) of a compound depends primarily on its reactivity towards hydroxyl free radicals, which in turn determines their concentration in the stratosphere. A second factor is their absorption capacity for infra-red radiation, primarily determined by bonds between carbon and 

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New products stereo-selective production of pharmaceuticals and agrochemicals, new oil products and energy carriers, replacement of CFCs ... 

Matters Relating to the Replacement of CFCs in Medicinal Products CPMP and DGIII Guidehne III/5462/93, Commission of the European Communities, Brussels, Adopted December 1993. 

Infer why the replacement of CFCs with HFCs helps protects the ozone layer. 

There are increasing pressures on the pharmaceutical industry to use environmentally friendly materials in products, which are biodegradable or recyclable and do no harm to the environment. Examples are the replacement of CFCs in pressurised metered dose aerosols and the replacement of polyvinyl chloride (PVC) for alternative packaging materials in some countries. Any special restrictions on the use of materials in the product need to be identified at the product design stage. The choice of appropriate materials to suit product, customer and environment may also have cost implications. 

Figure 4 Replacement of CFC propellants with non-CFC propellants within an MDI is far from a simple matter of direct substitution. For use in humans, toxicity testing is clearly essential, and use of new propellants necessitates redesign of aerosols to accommodate the propellants differing physicochemical characteristics, followed by extensive testing when reformulation with each of the medicines involved has been done. The time scale of this process is shown here. (Redrawn from material originally supplied by the International Pharmaceutical Aerosols Consortium.)...

Chapter 7 is a new chapter on the relationship between GFGs and the ozone hole, expanded from the four pages in the previous edition. The mechanisms by which oxygen and ozone protect us are discussed in the context of the Chapman Cycle. Scientific responses to the issue and the replacement of CFCs are considered. There is also discussion addressing the relationship between UV exposure and skin cancer. 

New developments Replacement of CFC blowing agents (in polyurethane and polystyrene foams). 

Replacement of CFCs in rigid polyurethane foams has been a much more serious problem, since the main use of these foams is as heat insulators and the main property required is therefore low thermal conductivity. Blowing gases of high... 

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