Phenol-formaldehyde moulding powder properties

Resins prepared from melamine, phenol and formaldehyde have found some use in the preparation of moulding powders. These materials have properties which are intermediate between those of melamine-formaldehyde and phenol-formaldehyde moulding powders. In particular, mouldings have better dry-heat dimensional stability than those based on straight melamine-formaldehyde and they may be produced in a much wider range of colours than phenol-formaldehyde mouldings. Typical applications of melamine-phenol-formaldehyde materials include domestic mouldings such as iron handles where a combination of heat resistance and decorative appeal is required. 

Moulding powders based on melamine-phenol-formaldehyde resins were introduced by Bakelite Ltd, in the early 1960s. Some of the principal physical properties of mouldings from these materials are given in Table 24.1. 

Phenol/formaldehyde Good properties at elevated temperature good chemical resistance good hardness/flexibility Solid poor weather reistance Powder coatings, moulding compounds... 

More important polymers of furfural are based on its ability to react with phenols to form thermosetting resins. The most common resins of this kind are of the novolak type made by reaction of a slight molar excess of phenol with furfural in the presence of an alkaline catalyst (cf. Chapter 12). Usually, blends of phenol-furfural novolaks and phenol-formaldehyde novolaks are used in the production of moulding powders with enhanced flow properties. 

As with resins, moulding powders based on melamine are used for specialised applications. The two main areas of application are tableware, where their improved water and scratch resistance compared to urea based materials makes them ideally suitable for this purpose, and for high performance electrical goods. Their electrical properties are superior to urea formaldehyde based materials under conditions of high temperature and humidity. They can be made in more attractive colours than phenolic moulding powders and have superior track resistance. 

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