Fu Lefeng

EFFECT OF MOLECULAR STRUCTURE OF POLYCARBOXYLATE SUPERPLASTICIZERS ON GYPSUM DISPERSION

Effects of comb-type polycarboxylate grafted copolymers such as methacrylic acid-methoxy polyethylene glycol monomethacrylate(MAA-MPEGMA) copolymers,methacrylic acid-polyethylene glycol monoallyl ether(MAA-APEG) copolymers and acrylic acid-polyethylene glycol monoallyl ether(AA-APEG) copolymers and polyacrylic acid(PAA) homopolymer on dispersion of gypsum particles and set time of gypsum slurries were studied.Polymers with short side-chain length,low molecular weight or high density of charge have improved dispersing effects and longer set time.In all polymers studied,PAA homopolymer with highest density of charge has the best dispersing effects and longest set time.Copolymers containing very short length of both side chain and backbone have better dispersion ability and longer set time.And copolymers containing anchoring groups of acrylic acid have better dispersing ability and longer set time than that of copolymers containing anchoring groups of methacrylic acid.Effects of chemical structure on dispersion of gypsum and dispersion-adsorption mechanisms were also explained and discussed from the point of surface and interface chemistry.It shows that the dispersing mechanism of polycarboxylate superplasticizer to gypsum powder is realized through affecting set time and hydration reaction of gypsum with water,and is more like the electrostatic repulsion effect than the steric hindrance.