Enzymatic Synthesis of Lignin-Based Concrete Dispersing Agents.

Lignin is the most abundant aromatic biopolymer, functioning as an integral component of woody materials. In its unmodified form it shows limited water solubility and is relatively unreactive, so biotechnological lignin valorisation for high-performance applications is greatly underexploited. Lignin can be obtained from the pulp and paper industry as a by-product. To expand its application, a new synthesis route to new dispersing agents for use as concrete additives was developed. The route is based on lignin functionalisation by enzymatic transformation. Screening of lignin-modifying systems resulted in functionalised lignin polymers with improved solubility in aqueous systems. Through grafting of sulfanilic acid or p-aminobenzoic acid by fungal laccases, lignin became soluble in water at pH≤4 or pH≤7, respectively. Products were analysed and evaluated in miniaturised application tests in cement paste and mortar. Their dispersing properties match the performance criteria of commercially available lignosulfonates. The study provides examples of new perspectives for the use of lignin.

Conformation of adsorbed comb copolymer dispersants.

Comb copolymers with an adsorbing backbone and nonadsorbing side chains can be very effective dispersants, particularly when a high ionic strength strongly penalizes electrostatic stabilization. For this reason, they have become essential components of concrete over the past decade. This article examines the steric hindrance characteristics of such polymers through the use of atomic force microscopy (AFM) on calcium silicate hydrate, the main hydration product of Portland cement. It is found that solution and surface properties (hydrodynamic radius, radius of gyration, surface coverage, steric layer thickness) and force-distance curves obtained during AFM measurements can be well described by a scaling approach derived in this paper. This represents the first real quantitative step in relating these properties directly to the molecular structure of such comb copolymer dispersants.