Study on the Interaction of Na-montmorillonite Clay with Polycarboxylates

摘要

The negative impact of sodium montmorillonite clay on dispersion effectiveness of two polycarboxylates consisting of methacrylate acid: MPEG methacrylate ester at molar ratios of 6:1 and 1.5:1 was investigated. When 1% by weight of cement (bwoc) of clay was present, cement spreads decreased by up to 60% while PCE sorption soared to ~ 400 mg/g clay (～ 100 times higher than on Portland cement). The PCEs mainly undergo chemisorption by intercalation between the alumosilicate layers via their poly(ethylene oxide) side chains. Additionally, to a minor extent (～15%), adsorption via electrostatic attraction to the positively charged clay surfaces takes place. Polyglycols can be effectively used as a sacrificial agent to protect PCEs possessing high grafting density from the negative effects of clay, while more anionic PCEs benefit, however to a certain extent only, from the addition of highly anionic polyelectrolytes such as poly(methacrylic acid).