GB1101203A - Cementing compositions - Google Patents

Abstract

An aqueous dispersion of a copolymer, for use in cement compositions, comprises at least 70% by wt. of units derived from vinylidene chloride and 4 to 30% of units derived from a monomeric component (i) comprising at least one monoethylenically unsaturated compound that is soluble in water to the extent of at least 0.5 gm. per 100 ml. of water at 50 DEG C. and contains no non-ionic surface-active agent and from 0 to 0.1% by wt., based on the weight of the copolymer, of an ionic surface-active agent. The monomeric component (i) may be acrylonitrile or a C1-C6 alkyl acrylate and preferably forms 4 to 27% by wt. of the copolymer. The copolymer may also contain 0.5 to 5% by wt. of units derived from a mono-ethylenically unsaturated carboxylic acid or anhydride or from a partial ester of a monoethylenically unsaturated polycarboxylic acid, e.g. acrylic or methacrylic acids. The faster polymerizing monomer, e.g. acrylonitrile, may be added continuously or intermittently during polymerization. The dispersion may be formed by copolymerizing vinylidene chloride with monomeric component (i) in an aqueous medium in the presence of (a) a water-soluble salt of a peroxyacid, and (b) a water-soluble sulphur containing acid having reducing properties or alkali metal salt thereof, and either in the absence of any surface-active agent or with at most 0.1% by wt. of an ionic surface-active agent. (a) may be alkali metal and ammonium peracetates, percarbonates and persulphates, used in amount 0.2 to 1% by wt. of the monomer \sHmixture, (b) may be sulphurous acid, sodium and potassium sulphites, hydrosulphites, thiosulphites, formaldehyde sulphoxylates and metabisulphites used in amount 0.1 to 1% by wt. of the monomer mixture.ALSO:A cement composition comprises an hydraulic cement optionally aggregates, and 5-40% by weight based on the weight of the cement, of a copolymer containing at least 70% by weight of units derived from vinylidene chloride and 4-30% by weight of units derived from a monomeric component (i) comprising at least one monoethylenically unsaturated compound that is soluble in water to the extent of at least 0.5 gm. per 100 ml. of water at 50 DEG C., said copolymer being in the form of an aqueous dispersion containing no non-ionic surface-active agent and from 0 to 0.1% by weight, based on the weight of the copolymer, of an ionic surface-active agent. The monomeric component (i) may be acrylonitrile or an alkyl acrylate in which the alkyl group contains up to 6 carbon atoms and preferably forms 4 to 27% by weight of the copolymer. The copolymer may also contain 0.5 to 5% by weight of units derived from a monoethylenically unsaturated carboxylic acid or anhydride or from a partial ester of a monoethylenically unsaturated polycarboxylic acid, e.g. acrylic or methacrylic acids. The composition preferably contains no ionic surface-active agent. The cement may be Portland or plaster of Paris and the aggregate may be sand, lime or gravel.