A process for producing a polyvinyl alcohol foam, closed-cell from an aqueous polyvinyl alcohol solution.

摘要

A dry closed cell foam having an average cell-size of 0.06-0.4 inches, an apparent density of 0.01-0.5 lbs./cu. ft. and a pneumatic compressive strength of at least 4 inches of mercury is prepared from polyvinyl alcohol and a gelling agent. Polyvinyl alcohol is defined as the product obtained when 75-100% of the acetated groups in polyvinyl acetate are hydrolysed. The gelling agent may be a thermally reversible one, e.g. Congo red. The foam may also contain 20-70% of an infra-red transmission control agent which absorbs or reflects radiation of 5-25m wave-length, e.g. aluminium powder or carbon black, a foam stabilizing agent, e.g. sodium lauryl sulphate, a thickening agent, e.g. a poly-saccharide, a flame-retardant, e.g. 10% boric acid, a rodent repellant, bactericide or fungicide and fibrous material. The foam may be produced by mixing the solid materials in particulate form, adding to this water and optionally an acetate buffer and foaming the dispersion so formed. Foaming may be effected by a gas through an orifice into the aqueous mixture. If a thermally reversible gelling agent is used the aqueous mixture will be a gel which must be melted before foaming. The gas used must be less than 10% soluble in water at 25 DEG C. The wet foam is allowed to drain before solidification and a suitable apparatus for foaming and draining consists of a cylinder of approximately equal diameter and length disposed with its axis vertical and closed at the top and bottom by frusto-conical caps. The air enters at the bottom of the lower cap, the foamable mixture enters horizontally further up the lower cap and the foam passes out at the top of the upper cap. The wet foam may contains 0.5-5% polyvinyl alcohol and may have an apparent density of 1-5 lbs./cu. ft. It may dry by natural evaporation or by cooling in the case of a thermally reversible gelling agent and may be used for insulating, acoustic and packing materials.