Analysis of components, additives and compounding ingredients

Many coating polymers contain additives and compounding ingredients to improve the physical durability, flexibility and performance. Rubber coatings in particular usually include carbon black and inorganic fillers to improve physical properties or reduce costs. 

1 Determination of carbon black in rubbers and plastic coatings. 

The method involves the pyrolysis of a weighed amount of the polymer in a stream of nitrogen in an electric furnace at 300-500 °C and is very reproducible (Haslam et al., 1983). The carbon residue after heating is cooled, desiccated and weighed. The percentage of carbon is determined from the original polymer sample weight. 

Coatings, especially PVC, contain plasticisers to render the film coating flexible over a range of utility temperatures. There are a wide variety of plasticisers available in the form of aliphatic and aromatic phthalates, sebacates, ricinoleates, adipates, phosphates, oleates, stearates, pahnitates, lactates andglycollates. Dioctyl phthalate is typically known for its use in PVC coatings. 

Qualitative analysis of common plasticisers is complicated by the fact that there may be other fillers and additives in the coating polymer. It is important to dissolve out the plasticiser in a reflux apparatus with suitable solvent such as ether, methanol or carbon tetrachloride. 

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