Lignopolymers as viscosity-reducing additives in magnesium oxide suspensions

Abstract

Lignopolymers are a new class of polymer additives with the capability to be used as dispersants in cementitious pastes. Made with kraft lignin cores and grafted polymer side-chains, the custom-synthesized lignopolymers were examined in terms of the molecular architecture for viscosity reducing potential in inert model suspensions. Lignin-poly(acrylic acid) (LPAA) and lignin-polyacrylamide (LPAm) have been found to vary the rheology of magnesium oxide (MgO) suspensions based on differences in chain architecture and particle-polymer interactions. A commercial comb-polymer polycarboxylate ester was compared to LPAA and LPAm at 2.7 mg/mL, a typical dosage for cement admixtures, as well as 0.25mg/mL. It was found that LPAm was a more effective viscosity reducer than both LPAA and the commercial additive at low concentrations, which was attributed to greater adsorption on the MgO particle surface and increased steric dispersion from PAm side-chain extension. The influence of chain adsorption and grafted side-chain molecular weight on rheology was also tested.

Influence of adsorbed and nonadsorbed polymer additives on the viscosity of magnesium oxide suspensions

“…Additionally, the total organic carbon results from a previous study of stabilized cementitious suspensions are consistent with the zeta potential measurements. PAA‐PEO had 91.9% adsorption to MgO particles when added at a concentration of 2.7 mg/mL with higher concentrations having more adsorption than lower concentrations …”

Lignin‐based polymers via graft copolymerization

“…Then the vinyl monomers are polymerized from this RAFT agent moiety on a lignin. The grafted polymers on lignin include acrylamide [Scheme (a,b)] and soybean oil derived monomers [Scheme (c)] . Azobisisobutyronitrile is commonly used to initiate the polymerization and DMF is a popular solvent for the polymerization.…”

Molecular Engineering of Superplasticizers for Metakaolin‐Portland Cement Blends with Hierarchical Machine Learning

“…The same conditions were used to determine the electrosteric effects of polymer and MK by adding 0.5 wt% polymer in a 50 wt% MK suspension. Following a previously published method, [30] the height of the supernatant was measured after 24 h and 120 h. Electrosteric parameters are expressed in percent change in supernatant height relative to suspensions in pure water. Positive numbers imply lower dispersion, resulting in a more-compact sediment and more supernatant, and negative numbers imply good dispersion relative to suspensions in pure water.…”