聚羧酸类超塑化剂分子结构对石膏分散性能的影响

EFFECT OF MOLECULAR STRUCTURE OF POLYCARBOXYLATE SUPERPLASTICIZERS ON GYPSUM DISPERSION

研究了甲基丙烯酸-甲氧基聚乙二醇甲基丙烯酸酯(MAA-MPEGMA)、甲基丙烯酸-烯丙基聚乙二醇醚(MAA-APEG)、丙烯酸-烯丙基聚乙二醇醚(AA-APEG)三类梳形聚羧酸类接枝共聚物以及丙烯酸均聚物(PAA)对石膏粉体分散性能和凝结时间的影响.聚合物侧链长度越短、分子量越小、电荷密度越高对石膏的分散性能越好,同时凝结时间也越长.其中电荷密度最高的PAA具有最好的分散性能和最长的凝结时间;而接枝共聚物中,侧链长度和主链长度都非常短的共聚物表现出了非常好的分散性能和较长的凝结时间.丙烯酸为锚固基团的共聚物对石膏的分散性能要好于甲基丙烯酸共聚物,而石膏的凝结时间则更长.从表面与界面化学的角度,讨论分析了聚羧酸类超塑化剂(也称为高效减水剂)分子结构对石膏性能影响的吸附分散机理.聚羧酸类超塑化剂对石膏的分散作用主要是通过影响石膏的水化反应和凝结时间来实现的;其分散作用机理与静电斥力效应密切相关而与空间位阻作用关系不大.

Effects of comb-type polycarboxylate grafted copolymers such as methacrylic acid-methoxypolyethylene 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 polyearhoxylate superplasticizer to gypsum powder is realized through affecting set time and hydration reaction of gypsum with water, and is more like the electrostatie repulsion effeet than the steric hindrance.