| 摘要 |
A process for gelling an aqueous polyvinyl alcohol solution comprises reacting therein (1) a first compound which does not cross-link the polyvinyl alcohol by which is convertible into a second compound which supplies ions which do cross-link the polyvinyl alcohol; and (2) a reagent which accomplishes the conversion in situ to obtain the ions which cross-link the polyvinyl alcohol. Suitable ions to effect crosslinking are Cr 3 +, Ti 4 + and V less than 5 +, which ions may be provided by reduction of hexavalent chromium or pentavalent vanadium compounds, oxidation of trivalent titanium compounds, or release of the ions from complexes. Sodium and potassium chromates and dichromates may be reduced with sodium bisulphite, sulphide, hyposulphite or hydrosulphite or ethanethiolic acid, optionally in the presence of copper ions which may be provided by cupric sulphate, chloride, acetate or nitrate; sodium, potassium and ammonium vanadates may be reduced with sodium sulphite, sodium hydrosulphite, hydroxylamine hydrochloride or hydrazine; titanium trihalides and titanous sulphate may be oxidized with oxygen, nitric acid, alkali metal nitrates, acetoxime, sodium sulphite, sodium bisulphite or sodium thiosulphate; and titanium 4 + ions may be released from complexes, e.g. potassium titanium oxalate, with ammonia, amines, basic salts and buffers such as carbonic acid/bicarbonate buffers. Gelled foams may be prepared by foaming the polyvinyl alcohol solution. In examples aqueous polyvinyl alcohol solutions are gelled with (1) sodium chromate and sodium bisulphite in the presence of copper sulphate; (2) sodium dichromate and sodium sulphide; titanium trichloride and (3) potassium nitrate and optionally sodium molybdate, and (4) sodium thiosulphate; ammonium vanadate and (5) sodium sulphide, (6) sodium hydrosulphide and (7) hydroxylamine hydrochloride and copper sulphate; and potassium titanium oxalate and (8) sodium bicarbonate together with (9) sodium oxalate and (10) sodium oxalate, boric acid and glycerol. A gelled foam is prepared by blowing the solution of Example 10 with air. |
