Patent GB-574382-A (GB)
Title: Improvements in or relating to the manufacture of cellular material of low density
IPC: C08J9/30
Filed: 1943-03-16
Abstract: In the manufacture of set-foam cellular material from foamed alginate solution, a chromium salt is employed as a setting agent. The solution of alginate, which may be an alkali metal, ammonium or magnesium alginate or an amine alginate such as triethanolamine alginate or a mixture of these, is converted into a foam by aeration and while in the foamed state is converted into an insoluble form by addition of the chromium salt and thereafter dried.  The chromium salt may be basic chromium sulphate or acetate, chrome-alum or normal chromium sulphate.  The basic sulphate should be added in the form of a freshly boiled solution. A frothing agent such as sodium isopropyl naphthalene sulphonate or saponin may be present in the alginate solution.  Hard foams are obtained when sodium or ammonium alginate is employed and resilient foams when triethanolamine alginate is used; tough set foams are obtained when fibre such as wood pulp is incorporated in the alginate solution prior to foaming.  A more rigid set foam is produced by using a mixture of basic or normal chromium sulphate and calcium sulphate or zinc sulphite as setting agent. Also, a foam of ammonium alginate can be mixed with calcium carbonate or sulphite and thereafter set with a mixture of a complex chromium salt, such as the normal sulphate and formaldehyde to give a hard set foam; the chromium salt in this case gives rigidity to the gelled foam during drying while the setting reaction between alginate, calcium compound and formaldehyde goes to completion. Another method of preparing hard foams comprises dissolving casein in alginate solution, foaming the solution, setting by addition of chromium salt and using sufficient formaldehyde or calcium compound or both to harden the casein; the proportion of casein may range up to 100 per cent of the weight of alginate.  In examples: (1) a foamed solution of sodium alginate containing sodium isopropyl naphthalene as sulphonate as frothing agent was set by addition of a freshly boiled solution of basic chromium sulphate and a resilient material obtained upon drying; (2) a foamed solution containing ammonium and triethanolamine alginate, sodium isopropyl naphthalene sulphonate and kraft paper fibre was set by addition of freshly boiled basic chromium sulphate solution and after drying gave a tough slab resembling cork of density approximately 0.15; (3) as in example (2) above, but using triethanolamine alginate only; (4) to a stirred foamed solution of sodium alginate containing sodium isopropyl naphthalene sulphonate and sodium hexametaphosphate was added a quantity of anhydrite and the foam set by addition of chromium sulphate solution; a hard material was obtained on drying; (5) a foamed solution containing ammonium alginate, kraft paper pulp, calcium carbonate and saponin was set by the simultaneous addition of both a solution of formaldehyde and sodium hexametaphosphate and a solution of normal chromium sulphate; drying gave a hard slab of density 0.13; (6) a foamed solution containing ammonium alginate, kraft paper fibre, sodium isopropyl naphthalene sulphonate and calcium sulphite was set by the simultaneous addition of both a solution containing formaldehyde and paraformaldehyde, and a solution of normal chromium sulphate; (7) a foamed solution comprising ammonium alginate, kraft paper fibre, casein (dissolved in sodium carbonate solution), saponin and calcium sulphite was set by the simultaneous addition of both a solution of formaldehyde and sodium hexametaphosphate and a solution of normal chromium sulphate; a very hard product, density 0.25, was obtained on drying.  Specification 560,317 is referred to.ALSO:In the manufacture of set-foam cellular material from foamed alginate solutions, a chromium salt is employed as a setting agent.  The solution of alginate which may be an alkali metal, ammonium or magnesium alginate or an amine alginate such as triethanolamine alginate or a mixture of these, is converted into a foam by aeration and while in the foamed state is converted into an insoluble form by addition of the chromium salt and thereafter dried. The chromium salt may be basic chromium sulphate or acetate, chrome-alum, or normal chromium sulphate; the basic sulphate should be added in the form of a freshly boiled solution.  A frothing agent such as sodium isopropyl naphthalene sulphonate or saponin may be present in the alginate solution. Hard foams are obtained when sodium or ammonium alginate is used; triethanolamine alginate forms resilient material: tough set-foams are obtained by incorporating fibre such as wood pulp in the alginate solution prior to foaming.  A more rigid set-foam is produced by using a mixture of basic or normal chromium sulphate and calcium or zinc sulphite as setting agent.  A hard set-foam is obtained by mixing calcium carbonate or sulphite with a foamed ammonium alginate solution and setting the foam by means of a mixture of a complex chromium salt such as the normal sulphate and formaldehyde.  Another hard set-foamed alginate is prepared by dissolving casein in an alginate solution, foaming the solution, and setting by addition of a chromium salt and using sufficient formaldehyde or calcium compound or both to harden the casein; the proportion of casein may range up to 100 per cent of the weight of alginate.  In examples: (1) a foamed solution of sodium alginate containing sodium isopropyl naphthalene sulphonate as frothing agent, was set by addition of a freshly boiled solution of basic chromium alginate and dried to give a resilient material; (2) a foamed solution of ammonium and triethanolamine alginates, sodium isopropyl naphthalene sulphonate and containing kraft paper fibre was set by addition of freshly boiled basic chromium sulphate and after drying, a tough slab resembling cork was obtained of density 0.15; (3) a set foam was prepared and set as in (2) above using however triethanolamine alginate only; (4) to a foamed sodium alginate solution containing sodium isopropyl naphthalene sulphonate and sodium hexametaphosphate, was added a quantity of anhydrite and the stirred foam, set by means of chromium sulphate solution, gave a hard material on drying; (5) a foamed solution containing ammonium alginate, kraft paper fibre, calcium carbonate and saponin was set by simultaneous addition of both a solution of formaldehyde and sodium hexametaphosphate and a solution of normal chromium sulphate; drying gave a hard slab of density 0.13; (6) a foamed alginate solution containing ammonium alginate, kraft paper fibre, calcium sulphite and sodium isopropyl naphthalene sulphonate was set by the simultaneous addition of both a solution of normal chromium sulphate and a solution of formaldehyde and para-formaldehyde; (7) a foamed solution of ammonium alginate, kraft paper fibre, casein (dissolved in sodium carbonate solution), calcium sulphite and saponin was set by simultaneous addition of a both normal chromium sulphate solution and a solution of formaldehyde and sodium hexametaphosphate; a very hard product, density 0.25, was obtained on drying.  Specification 560,317 is referred to.