Phenol-formaldehyde moulding powder

It is thus seen that a phenol-formaldehyde moulding powder will contain the following ingredients ... 

Today the phenol-formaldehyde moulding compositions do not have the eminent position they held until about 1950. In some, important applications they have been replaced by other materials, thermosetting and thermoplastic, whilst they have in the past two decades found use in few new outlets. However, the general increase in standards of living for much of this period has increased the sales of many products which use phenolics and consequently the overall use of phenol-formaldehyde moulding powders has been well maintained. 

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. 

This includes wire enamels on a base of polyvinyl formal, polyurethane or epoxy resins as well as moulding powder plastics on phenol-formaldehyde and similar binders, with cellulose fillers, laminated plastics on paper and cotton cloth base, triacetate cellulose films, films and fibres of polyethylene terephthalate. 

The term aminoplastics has been coined to cover a range of resinous polymers produced by interaction of amines or amides with aldehydes. Of the various polymers of this type that have been produced there are two of current commercial importance in the field of plastics, the urea-formaldehyde and the melamine-formaldehyde resins. There has in the past also been some commercial interest in aniline-formaldehyde resins and in systems containing thiourea but today these are of little or no importance. Melamine-phenol-formaldehyde resins have also been introduced for use in moulding powders, and benzoguanamine-based resins are used for surface coating applications. 

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 (phenolic) plastics The chemical resistance is affected by the phenol used, cresols giving the best acid resistance whilst xylenols are often used to obtain the best alkali resistance. For chemical-resistant applications the fillers used in moulding powder and reinforcing material in laminates should be inorganic, e.g. asbestos or glass. The resins are usually dark in colour. 

Phenol-formaldehyde (PF) was the first fully synthetic macromolecular material ( Bakelite , 1907). In a slightly precured condition and provided with fillers, it is, as a moulding powder, available for processing into end-use articles such as bulb fittings, switch housings, coils, laminated wood and foam for thermal insulation. 

Phenolic plastics. Collective designation for phenolic resin-based plastics. Phenolic resins are produced by condensation of phenol and/or its homologues, such as cresol, with an aldehyde, such as formaldehyde or with an aldehyde-releasing material such as hexamethylenetetramine. Phenol/formaldehyde and/or cresol/formaldehyde resins are used as binding materials in fibre board, laminated paper and fabrics. In phenolic moulding compounds, the proportion of filler (such as wood flour, rock flour, asbestos, stone powder, mica, glass fibre) can be equal to that of the resin. These thermosets can be processed by compression or injection moulding into black or dark-coloured products mainly for the electric industry. 

Phenol-formaldehyde was reported as the first commercially synthetic polymer (1899) which was introduced as BakeliteT by Baekeland in 1909. This was the period which marked the dawn for the production of commercial synthetic thermosetting polymers. Other advances in the field included the discovery of urea-formaldehyde resins in 1884 and the beginning of their commercialization as Beetle moldable resin in 1928, followed by thiourea-formaldehyde (1920), aniline-formaldehyde (Cibatine by Ciba, 1935) and melamine-formaldehyde (1937) moulding powders. The year 1909 marked the discovery of epoxy compounds by Prileschaiev, which were not used until World War 2. The first thermoset polyesters, invented by Ellis, date back to 1934 and in 1938 was reported their first use in the forms of glass-reinforced materials [1]. 

The most commonly known phenolic composite group is phenol formaldehyde polymers (phenoplasts). They are produced by polycondensation of a phenol and a mixture of phenols (phenol and phenol derivatives like cresol-resorcinol or para tertiary butyl phenol) with an aldehyde, usually formaldehyde and hexamethylene tetramine. Reaction of formaldehyde with phenol (up to 3 moles of formaldehyde can react with one mole of phenol - phenol acts as a three functional monomer) yields methylol groups in the ortho and para positions of the phenol molecule. In a further reaction, the methylol groups condenses with another molecule of phenol to form a methylene bridge. In practice, a prepolymer (usually a powder) is prepared first which is then cured later to the shape of the article in the mould. 

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

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