Formaldehyde powder

Urea-formaldehyde powders have a limited shelf-life but some improvement is made by incorporating a stabiliser such as hexamine into the moulding power. In some formulations the cure rate and the related time for flow are controlled by keeping the latent acid catalyst fixed and adjusting the stabiliser. 

Mouldings from melamine-formaldehyde powders are superior to the urea-formaldehyde plastics in a number of respects. 

Carbonized materials based on para-alkylphenols (50-53) had an unusually high degree of microporosity when compared with conventional phenol-formaldehyde resins. It was possible to generate high surface area materials from conventional phenol-formaldehyde resins by grinding the cured resin prior to carbonization. Carbonization of four phenol-formaldehyde powders containing a narrow particle size distribution showed that surface area increased rapidly as the resin particle size fell. The effect is extremely pronounced, and has not been previously reported. 

Waferboard is a structural board made of wood wafers cut to predetermined dimensions randomly distributed and bonded with phenolic adhesives." It is estimated that by 1981, 80 million pounds of adhesives on a solid basis will be used in waferboard and other types of particleboard bonding. Currently either solid or liquid phenolic resins are being used in these applications. Formaldehyde and phenol fumes and phenol formaldehyde powder dust,... 

Place 1 g of formaldehyde powder, together with a few drops of distilled water, into a vessel (e.g., a desiccator) that can be closed (see Note 12). 

Humbrol Cascamite Urea/formaldehyde powder, mix with water. 

To the remainder of the gelatin solution, add 0 5 to o 8 g. of finely powdered commercial trypsin and incubate at 40 . Carry out the formaldehyde titration on 25 ml. samples at intervals as above. 

Prepare a solution of 41 g. of anhydrous palladium chloride (1) in 10 ml. of concentrated hydrochloric acid and 25 ml. of water (as in A). Add all at once 60 ml. of 6iV-sulphuric acid to a rapidly stirred, hot (80°) solution of 63 1 g. of A.R. crystallised barium hydroxide in 600 ml. of water contained in a 2-htre beaker. Add more 6iV-sulphuric acid to render the suspension just acid to htmus (5). Introduce the palladium chloride solution and 4 ml. of 37 per cent, formaldehyde solution into the hot mechanically stirred suspension of barium sulphate. Render the suspension slightly alkaline with 30 per cent, sodium hydroxide solution, continue the stirring for 5 minutes longer, and allow the catalyst to settle. Decant the clear supernatant hquid, replace it by water and resuspend the catalyst. Wash the catalyst by decantation 8-10 times and then collect it on a medium - porosity sintered glass funnel, wash it with five 25 ml. portions of water and suck as dry as possible. Dry the funnel and contents at 80°, powder the catalyst (48 g.), and store it in a tightly stoppered bottle. 

Urea reacts with formaldehyde compounds such as monomethylolurea, NH2CONHCH2OH, dimethylolurea, HOCH2NHCONHCH2OH, and others, depending on the mol ratio of formaldehyde, to urea and upon the pH of the solution. Hydrogen peroxide and urea give a white crystalline powder, urea peroxide, CO(NH2 (2 -H2 02, known under the trade name of Hypersol, an oxidizing agent. 

Phenol—formaldehyde (PF) was the first of the synthetic adhesives developed. By combining phenol with formaldehyde, which has exceptional cross-linking abiHties with many chemicals and materials, and a small amount of sodium hydroxide, a resin was obtained. The first resins soHdified as they cooled, and it was discovered that if it was ground to a powder with a small amount of additional formaldehyde and the appHcation of more heat, the mixture would Hquify and then convert to a permanently hard material. Upon combination of the powdered resin mixture with a filler material such as wood flour, the result then being placed in a mold and pressed under heat and pressure, a hard, durable, black plastic material was found to result. For many years these resulting products were called BakeHte, the trade name of the inventor. BakeHte products are still produced today, but this use accounts for only a small portion of the PF resins used. 

Hexamethylenetetramine. Hexa, a complex molecule with an adamantane-type stmcture, is prepared from formaldehyde and ammonia, and can be considered a latent source of formaldehyde. When used either as a catalyst or a curative, hexa contributes formaldehyde-residue-type units as well as benzylamines. Hexa [100-97-0] is an infusible powder that decomposes and sublimes above 275°C. It is highly soluble in water, up to ca 45 wt % with a small negative temperature solubiUty coefficient. The aqueous solutions are mildly alkaline at pH 8—8.5 and reasonably stable to reverse hydrolysis. 

Paraformaldehyde [30525-89-4] is a mixture of polyoxymethylene glycols, H0(CH20) H, with n from 8 to as much as 100. It is commercially available as a powder (95%) and as flake (91%). The remainder is a mixture of water and methanol. Paraformaldehyde is an unstable polymer that easily regenerates formaldehyde in solution. Under alkaline conditions, the chains depolymerize from the ends, whereas in acid solution the chains are randomly cleaved (17). Paraformaldehyde is often used when the presence of a large amount of water should be avoided as in the preparation of alkylated amino resins for coatings. Formaldehyde may also exist in the form of the cycHc trimer trioxane [110-88-3]. This is a fairly stable compound that does not easily release formaldehyde, hence it is not used as a source of formaldehyde for making amino resins. 

Urea and melamine adhesives represent products of very mature and overaged technologies. Essentially, they are simple reaction products of urea or melamine with formaldehyde they may be Hquids or powders. Liquids are converted to dry powders by "spray drying." Melamine-urea combinations generally are spray-dried powders of co-reacted Hquid melamine and area-formaldehyde resias. 

Bonechar, Vh in and under 27-40 B27 Phenol-formaldehyde molding powder. 30-40 A36... 

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. 

Fillers are often employed to reduce the surface tack of the final product. Examples are talc and china clay. If powdered materials are added directly to a latex they compete for the emulsion stabiliser present and tend to coagulate the latex. They are therefore added as an aqueous dispersion prepared by ball milling the filler with water and a dispersing agent, for example a naphthalene formaldehyde sulphonate at a concentration of about 1% of the water content. Heat and light stabilisers which are solids must be added in the same way. 

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. 

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. 

A moulding powder based on urea-formaldehyde will contain a number of ingredients. Those most commonly employed include the following ... 

From the above discussion it will be recognised that in addition to differences in colour, commercial urea-formaldehyde moulding powders may differ in the following respects ... 

Urea-formaldehyde moulding powders may be moulded without difficulty on conventional compression and transfer moulding equipment. The powders, however, have limited storage life. They should thus be stored in a cool place and, where possible, used within a few months of manufacture. 

Urea-formaldehyde moulding powders may be transfer moulded. Pressures of 4-10 ton/in (60-150 MPa), calculated on the area of the transfer pot, are generally recommended. 

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