| 摘要 |
Porous polyvinyl acetal filter elements having a pore size of 2-200 m are prepared by dissolving a mixture of polyvinyl alcohol and starch of appropriate grain size in water to which formalin and a mineral acid are added, allowing acetalization to occur at 40-45 DEG C., raising the temperature to about 70 DEG C. to hydrolyse the starch and then washing out the resultant glucose with water and drying. Reference is also made to acetalating a porous mass of polyvinyl alcohol with an aldehyde and to treating an aqueous solution of polyvinyl alcohol with aldehyde while aerating the solution.ALSO:A filter for removing micro-organisms from air used in the aerobical production of micro-organisms comprise a porous structure of polyvinyl acetal, or polyvinyl acetal or polyvinyl alcohol impregnated with a thermosetting synthetic resin, said structure having pores of a diameter of from 2 to 200m and being capable of withstanding a temperature of from 100 to 300 DEG C. A porous structure of polyvinyl alcohol or polyvinyl acetal having pores of a diameter of from 2 to 200m is dipped into a 5-50% solution of a thermosetting resin (e.g. an aqueous or alcoholic solution of a melamine, phenolic or furan resin), the solvent evaporated and the coated structure heat treated to cure the resin.
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