Crosslinked lignin starch copolymer as a sustainable and thermally stable drilling fluid controller.

Fluid loss is a well-known challenge of drilling operations. In this work, a novel sustainable starch-lignin-based polymer was synthesized for possible use in drilling fluid applications. The X-ray photoelectron spectroscopy (XPS) analysis confirmed that kraft lignin was crosslinked with starch via ether covalent bonds. The X-ray diffraction (XRD) analysis confirmed the loss of crystallinity in starch and emerging of new amorphous structures in crosslinked starch-lignin (CSL) polymers after crosslinking with lignin. The incorporation of lignin and new covalent ether bonds improved the thermal stability of starch. The CSL had a rougher surface morphology, higher hydrophilicity, and significantly higher water absorption than starch. CSL-2, with its higher lignin content, demonstrated higher hydrophilicity, better water absorption capacity, and thermal stability than CSL-1. The rheology analysis of the CSL-2 polymer suggested that crosslinking starch with lignin would increase G' more than G" and reduce tan δ of the polymer solution, resulting in more elastic properties and more stability against the angular frequency. Due to its improved swelling, thermal, and rheological properties as compared to native starch, the produced sustainable lignin-starch copolymer could be used as a new viscosity and rheology modifier, such as a fluid loss controller for oil extraction from wells.