Controlling the properties of lignin-polysaccharide macroporous materials with precursors viscoelasticity

Abstract

Lignin is a byproduct in pulp and paper industries with a high potential for different applications, such as biomedical and environmental. Based on the previous applications, different lignins (sodium lignosulfonate and calcium lignosulfonate) were embedded in some polysaccharides (gellan gum or κ-carrageenan), forming a hydrogel network by taking advantage of their reversible thermal transitions. After that, hydrogels were freeze-dried to obtain a macroporous material. Rheology, FESEM, BET, FTIR, TGA, swelling and biocompatibility characterised hydrogels and the respective dried composites. Oscillatory analysis indicated that the highest storage moduli were found for the systems gellan gum-calcium lignosulfonate and κ-carrageenan-sodium lignosulfonate since the interactions between these compounds were increased depending on the different lignin cations. The respective infrared spectra confirmed the existence of electrostatic interactions (no new bonds were formed). Textural analysis showed that the composites had a macroporous structure (porosity higher than 95 %) with different pore size distributions (pores ranging from 1 to 1000 μm with a specific surface area lower than 5 m² g⁻¹). Hydrogels with a higher storage modulus promoted the formation of composites with a smaller pore size. In contrast, adding lignin reduced the swelling capacity of these composites (from 400 % to 1500 %) due to its hydrophobic character (although some composites showed a fast erosion). Finally, in vitro, results confirmed the biocompatibility of the most suitable composites for biomedicine. Therefore, this work demonstrated that properties (swelling and textural) of the lignin-polysaccharides composites can be tuned by controlling the viscoelastic properties of the precursor hydrogels.