Lignopolymer Superplasticizers for Low-CO₂ Cements

Abstract

Grafting hydrophilic polyacrylamide from a kraft lignin core results in a lignopolymer that effectively plasticizes portland cement paste. Here, the potential of this sustainably sourced lignopolymer is examined for improving the workability of portland cement blended with two natural, finely divided mineral materials (kaolin clay and clinoptilolite zeolite), which can be potentially used in combination with portland cement as a means to reduce the cement clinker content and the concomitant embodied energy and greenhouse gas emissions in concrete. Both mineral materials are known to affect cement hydration reactions but can significantly reduce workability when blended with portland cement, presenting a challenge for their practical large scale use. , The plastic behavior of mineral-cement combinations dosed with polyacrylamide-grafted kraft lignin was compared to the behavior of those with a lignosulfonate developed for plasticizing portland cement and a commercial polycarboxylate ether (PCE). Compared to the other admixtures, the lignopolymer was found to adsorb strongly to both kaolin and clinoptilolite and resulted in the lowest yield stresses in pastes containing 25% mineral material and 75% Type I/II portland cement at both high (5 mg/mL, 0.25 wt %) and low (0.5 mg/mL, 0.025 wt %) admixture content, but no significant retardation was observed in calorimetry measurements of hydration kinetics. In contrast, the PCE had a low affinity for both mineral admixtures at higher concentrations compared to that of both lignin superplasticizers, and the resulting tests of slump spread and viscosity were similar for these two minerals. Lignosulfonates had affinity for the mineral phases similar to that of the other superplasticizers but were ineffective at improving workability, pointing to the need for steric interactions in plasticizing mineral materials used in combination with cement. These results indicate that lignopolymers could be an effective superplasticizer for a broad range of high surface area minerals to be used in combination with portland cement.

Carbon nanotube reinforced poly(trimethylene terephthalate) nanocomposites: Viscoelastic properties and chain confinement

“…The Takayanagi model is so close to the experimental values by considering E 0 = 2.5 GPa and E 1 = 1,054 GPa. The modulus values shown by composites are greater than the theoretical values because of higher reinforcement effect of MWCNT [38]. This is more visible in composite with 2 wt% MWCNT.…”

Tuning Lignin Characteristics by Fractionation: A Versatile Approach Based on Solvent Extraction and Membrane-Assisted Ultrafiltration

“…Lignin represents, however, a highly abundant natural aromatic feedstock with potentially very interesting applications in a sustainable economy scenario, especially considering the high primary production volumes and the inherently renewable nature of this resource [ 12 ]. Several studies are actually under way for the development of valuable lignin derivatives, such as raw chemicals [ 6 ], polymers [ 13 , 14 , 15 , 16 , 17 , 18 ], high-performance concrete admixtures [ 19 , 20 ], and hydrogels [ 21 ].…”

Effect of Polyacrylic Acid on Rheology of Cement Paste Plasticized by Polycarboxylate Superplasticizer

“…It has been revealed that adsorption of PCE onto the surface of cement particles is the precondition for exerting high dispersion efficiency of PCE [ 3 , 20 ]. Carboxyl groups exist in the side chain of PAA, and these active groups can adsorb on the surface of cement particles by means of chemical combination and electrostatic force [ 21 , 22 , 23 ]. In this case, mutual influence on adsorption of PAA and PCE, namely competitive adsorption, may take place.…”