Lignopolymers as viscosity-reducing additives in magnesium oxide suspensions

Area of Science:

• Materials Science
• Polymer Chemistry
• Colloid Science

Background:

• Lignopolymers, derived from kraft lignin cores with grafted polymer side-chains, are emerging as novel polymer additives.
• These additives demonstrate potential as dispersants in cementitious pastes.
• Understanding their molecular architecture is key to optimizing their performance.

Purpose of the Study:

• To investigate the viscosity-reducing capabilities of custom-synthesized lignopolymers in inert model suspensions.
• To compare the rheological performance of lignin-poly(acrylic acid) (LPAA) and lignin-polyacrylamide (LPAm) against a commercial polycarboxylate ester.
• To analyze the impact of molecular architecture, particle-polymer interactions, and side-chain characteristics on rheological behavior.

Main Methods:

• Synthesis of custom lignopolymers: LPAA and LPAm.
• Rheological testing of magnesium oxide (MgO) suspensions with varying lignopolymer additives.
• Comparison of performance at typical cement admixture dosages (2.7 mg/mL) and lower concentrations (0.25 mg/mL).
• Analysis of particle-polymer interactions and chain adsorption.

Main Results:

• LPAm demonstrated superior viscosity reduction compared to LPAA and the commercial additive, particularly at low concentrations.
• The enhanced performance of LPAm was attributed to increased adsorption onto the MgO particle surface and greater steric dispersion from polyacrylamide (PAm) side-chain extension.
• Differences in chain architecture and particle-polymer interactions significantly influenced the rheology of MgO suspensions.

Conclusions:

• Custom-synthesized lignopolymers, especially LPAm, are effective viscosity reducers for cementitious applications.
• LPAm's effectiveness is linked to its molecular structure, promoting strong adsorption and steric stabilization.
• Further research can explore the influence of side-chain molecular weight and adsorption on rheological properties for tailored dispersant design.