Lignopolymers as viscosity-reducing additives in magnesium oxide suspensions.

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.

Rheological investigation of the shear strength, durability, and recovery of alginate rafts formed by antacid medication in varying pH environments.

The mechanical response of alginate rafts formed by mixing liquid alginate antacid medication (Gaviscon Extra Strength Liquid Antacid) with acidic solutions was investigated by deforming isolated rafts in a shear rheometer. As rafts were deformed to varying magnitudes of applied strain, rheological parameters were identified and related to the overall strength, durability, and recoverability of rafts formed at different pH (1.1-1.7) and aging conditions (0.5-4 h). Rafts formed in the lowest acidity solutions (pH 1.4, 1.7) were elastically weak ( G'0 = 60 , 42 Pa for un-aged raft) yet maintained their elasticity during applied shear deformation to large values of strain (γc∼90%, 50%, where G'≈G″), and displayed a low-to-moderate level of elastic recovery following large-strain deformation. Rafts formed in the highest acidity solution had the greatest strength ( G'0 = 500 Pa for un-aged raft and 21.5 kPa for rafts after 0.5 h of aging), reduced durability (γc∼2.5%, independent of aging), and displayed the greatest recoverability. A trade-off existed between un-aged raft strength and durability while recovery was dependent on durability, solution pH, and age. Rheometry-based evaluations of alginate rafts could be used for the informed design of future gastric retention and antacid products.