Hydrogels Derived from Lignin with pH Responsive and Magnetic Properties

Abstract

Smart lignin hydrogels with pH responsive and magnetic properties was prepared by free radical polymerization from lignin and acrylamide. In order to improve its swelling properties, calcium carbonate as pore- foaming agent was introduced to the polymer formulation, then magnetic particles (Fe3O4) was formed in the polymer by in situ reaction and co- precipitation. The results showed that degree of swelling of pH responsive hydrogels (PLH) containing the pore-foaming agent increased 47% compared to the original hydrogels (OLH) without pore-foaming agent, and the swelling rate of PLH reached 100% within 13.5 min under optimum pH conditions (pH = 6.8) which is a shorter amount of time, 1.5 times, compared to the OLH. The swelling-deswelling experiments showed that the hydrogels retained good reversibility and stability. Fourier transform infrared (FTIR) spectra indicated that the molecular chain of the PAM matrix hydrogels was successfully grafted on the lignin and the magnetic particles (Fe3O4) precipitated in the hydrogel. The X-ray diffraction (XRD) results showed that the magnetic particles in the hydrogels were composed of magnetite. The presence of a mesoporous structure was observed in scanning electron microscopy (SEM) images. The composition of hydrogels was analyzed by energy dispersive spectroscopy (EDS). The vibrating sample magnetometer (VSM) measurements also showed good magnetic properties.