Odours, catalyst residues

For objects produced by RIM, it is desirable to have as high a conversion of monomer as possible, since this will affect both the mechanical properties of the product and the extent of residual odour. With many catalyst systems the conversion is often only 90-95%, but with the use of certain additives such as CCI4 and C6H5CCI3, conversions as high as 99.9% have been claimed (Newburg 1984). It is not clear how such additives work but presumably the propagating species is protected in such a way as to make it less vulnerable to destruction. 

The main requirements for contact with food are that the article must not impart odour or taste to the food and should be suitable for the intended application. Additives, monomers, catalyst residues, polymer degradation products and so on can migrate into any food in contact if the concentration of these substances is lower in the food than in the plastic. The migration is dependent on temperature and time the rate of migration is inversely proportional to molecular weight. The migration of these species could produce toxicity or the formation of undesirable flavours or odours, known as organoleptic problems. 

Utilities using post-combustion SCR-supported ammonia injection for NOx control as well as those using ammonia conditioning to improve electrostatic precipitator performance will produce fly ash that contains ammonia compounds. The ammonia is primarily physically adsorbed onto the fly ash particles as sulphate and bisulphate species. In many cases, the residual ammonia levels are quite low (<50ppm) however, elevated concentrations can occur as the catalyst ages or due to mechanical problems with the ammonia injection system. While elevated ammonia concentrations in fly ash do not negatively impact pozzolanic properties, it can reduce ash marketability due to odour concerns. For this reason, several processes have been developed to remove or reduce the amount of ammonia in fly ash. 

Crompton s carboxylic acid based nucleating agent, Moldpro 931 is said to cost only a third as much as benzylidene sorbitol varieties or the organophosphate salts, and is also claimed to have exceptionally low effects on odour and taste. Moldpro 931 is designed to reduce the cycle time in making polypropylene water bottles. Its action depends on the presence of a small quantity of residual aluminium catalyst, and it does not work if the antistatic additive, glycerol monostearate, is present. 

Odour resulting from residual catalyst cannot usually be tolerated in foams and this has to be considered in any choice of amine catalysts. A number of amines having low volatility have been proposed to decrease or eliminate obnoxious amine odour. Among those claimed are arylene dicarbamic acid esters, V,V-dialkyl-3-(dialkylamino)-propylamine, V-acetamido-propylmorpholine or piperidine, and 3-dialkylaminopropion-amides. 

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