Urea-formaldehyde resins foams

Urea.—Forma.IdehydeResins. Cellular urea—formaldehyde resins can be prepared in the following manner an aqueous solution containing surfactant and catalyst is made into a low density, fine-celled foam by dispersing air into it mechanically. A second aqueous solution consisting of partially cured urea—formaldehyde resin is then mixed into the foam by mechanical agitation. The catalyst in the initial foam causes the dispersed resin to cure in the cellular state. The resultant hardened foam is dried at elevated temperatures. Densities as low as 8 kg/m can be obtained by this method (117). 

Syntactic Cellular Polymers. Syntactic cellular polymer is produced by dispersing rigid, foamed, microscopic particles in a fluid polymer and then stabilizing the system. The particles are generally spheres or microhalloons of phenoHc resin, urea—formaldehyde resin, glass, or siUca, ranging 30—120 lm dia. Commercial microhalloons have densities of approximately 144 kg/m (9 lbs/fT). The fluid polymers used are the usual coating resins, eg, epoxy resin, polyesters, and urea—formaldehyde resin. 

Foams prepared from phenol—formaldehyde and urea—formaldehyde resins are the only commercial foams that are significantly affected by water (22). Polyurethane foams exhibit a deterioration of properties when subjected to a combination of light, moisture, and heat aging polyester-based foam shows much less hydrolytic stabUity than polyether-based foam (50,199). 

For the preparation of the foam, a solution of 1 g technical sodium diisobutyl naphthalene sulfonate in 50 ml of 3% orthophosphoric acid is prepared. 20 ml of this solution are poured into a 11 beaker and air is stirred in with a fast running mixer until the cream-like dispersion has reached a volume of 300-400 ml.Then,20 ml of the prepared urea/formaldehyde resin are mixed in, whereby the resin must be evenly distributed. After 3-4 min the introduced resin gellifies into a molded article permeated with many water/air pores under the influence of the acidic catalyst. After 24 h,the crosslinking is completed. Drying for 12 h at 40 °C in a circulating air dryer yields a brittle thermoset foam.The foamed plastic obtained is hydrophobic and has a large internal surface. It can take up about 30 times its own weight of petroleum ether. 

Foaming of urea - formaldehyde resins for cavity wall insulation Alkylbenzene sulphonic acids and salts Foaming agents... 

The physicochemical features of the processes of formation, stabilisation and solidification of foams are best studied for a polymer foam from urea-formaldehyde resins. That is why the urea polymer foams are used here below to exemplify the principles of optimisation of the technology for production of polymer foam materials. 

Molded articles from cellular polysulfone, coated with polystyrene, epoxy resin, or vinyl resin, are reported to have improved hardness and surface rigidity. They can also be used as insulating or packaging materials, or, when modified with urea-formaldehyde resin, as flowerpots that are permeable to air and water. These foams have excellent selfextinguishing and low anoke-generating properties (21). 

The principal end use of urea is to provide combined nitrogen for solid fertilizer formulations. Some urea is also converted to biuret (H2NCONHCONH2, also called carbamoyl urea) and to a sulfur derivative, which are sold as Kedlor [65] and Urasil [66] cattle feed supplements, respectively. Urea is also used to a lesser extent in the manufacture of plastics components, such as melamine, and as a component of urea-formaldehyde resins used as adhesives. It is also used as a component of foam-in-place formulations as a rigid insulating material [67], and as an ingredient in noncorrosive aircraft deicing solutions [67a]. 

Basopor . [BASF AG] Urea-formaldehyde resin precondensate for prod of synthetic urea-formaldehyde resin foam, diermal insulation in construction, protection t ainst explosions in mining. 

Ammonia and methanol are starting points for amino-resins, which are therefore syngas derivatives. Urea-formaldehyde resins are used in particle board (chipboard) and plywood manufacture UF-foam is also widely used for cavity wall insulation in the U.K. Melamine-formaldehyde resins are possibly more familar from the dinnerware and heat-resistant wood finishes produced. 

Hygromull Urea-formaldehyde resin (foam) BASF, Germany... 

Urea-formaldehyde resins are applied in the field of electronics. They possess superior electrical insulation properties compared to phenolic resins and are used in the production of mainly sockets, plugs and switches. A special application of urea-formaldehyde resins consists in the obtaining of foams for placing on airport... 

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