Abstract
Lignosulfonates (LS) are products from the sulfite pulping process that could be applied as renewable environmentally-friendly polymeric surfactants. Being widely used as plasticizers and water-reducing admixtures in concrete formulations LS compete in the market with petroleum-based superplasticizers, such as naphthalene sulfonate formaldehyde polycondensate (NSF) and copolymer polycarboxylate ethers (PCE). In this work, different chemical modification strategies were used to improve LS performance as dispersants for concrete formulations. One strategy consisted in increasing the molecular weight of LS through different approaches, such as laccase and polyoxometalate-mediated polymerization, glyoxalation, and reversible addition-fragmentation chain transfer (RAFT) polymerization. The other strategy consisted of preparing LS-based non-ionic polymeric dispersants using two different epoxidized oligomer derivatives of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG). Modified LS were used to prepare cement pastes, which were examined for their fluidity. Results revealed that the most promising products are PPG-modified LS due to the introduction of PPG chains by reaction with phenolic moieties in LS. The enhanced dispersant efficiency of the ensuing products is probably related not only to electrostatic repulsion caused by the sulfonic ionizable groups in LS but also to steric hindrance phenomena due to the grafted bulky PPG chains.
Highlights
Lignosulfonates (LS) are sulfonated technical lignins present in spent liquor (SSL)from the sulfite pulping
Polyoxometalates (POMs) can be inorganic mediators in lignin oxidation by laccase when one-electron oxidized lignin molecules are polymerized by radical coupling and the reduced POMs, in turn, are reoxidised by laccase under aerobic conditions [31]
These results suggest that phenolic OH groups did not react or at most reacted to a small extent with poly(ethylene)glycol diglycidyl ether (PEGDE), which is in agreement with the FITR analysis (Figure 4c)
Summary
Lignosulfonates (LS) are sulfonated technical lignins present in spent liquor (SSL)from the sulfite pulping. Lignosulfonates (LS) are sulfonated technical lignins present in spent liquor (SSL). Considering the potential applications of LS, besides burning for energy recovery, it is marketed for specialty applications, such as dispersants for concrete formulations, animal feed, paint and oil industries, and agriculture, among others [2,3,5,6]. Most of these applications are due to the good water solubility of LS, which is the reason for the restriction of the world market to these technical lignins [2]. LS were first introduced as plasticizers and water-reducing admixtures to concrete in the 1930s [13]
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