Synthesis And Properties Of Hydrogels Based On Lignocellulosic Fiber And Its Components

As one of the most abundant natural polymers, lignocellulosic fiber has attracted much attention due to its unique advantages of biocompatibility, biodegrability and non-toxicity. The conversion of lignocellulosic fiber into a new source of raw materials for preparing degradable polymer materials is of great importance to protect the environment and save the fossil resources. In this work, hydrogels were prepared by graft copolymerization and chemical crosslinking of hydroxyethyl cellulose (HEC), respectively. pH-sensitive polyurethane- based hydrogels were synthesized from acetic acid lignin and the liquefaction products of bagasse in polyhydric alcohols,.An isocyanate-bearing unsaturated monomer (MHTI) was synthesized by the monobloking reaction of 2,4-toluene diisocyanate with 2-hydroxyethyl methacrylate. The temperature-sensitive hydrogels were prepared by the copolymerization of N-isopropylacrylamide (NIPPAm) and modified hydroxyethyl cellulose with MHTI. The results of DSC analysis revealed that the low critical solution temperature (LCST) of hydrogels was enhanced by the introduction of HEC. SEM images suggested that the cross-section of freeze-dried hydrogels was porous. The LCST of the hydrogels prepared with the mass ratio of MHEC/MNIPPAm: 1:2, 1:3, 1:4, was approximately 46℃, 40℃, 36℃respectively. The hydrogels were negatively thenmosensitive, shrank in water above the LCST and swelled in water below the LCST. The data of adsorption and release experiments for the model drug (methylene blue and methyl orange) suggest that the controlled drug release can be achieved.Hydrogels film was prepared from HEC using citric acid as a cross-linker. As the citric acid dosages increase, the swell ratio and elongation of film at break decrease, tensile strength of film increase. When the hydrogel film was prepared with the citric acid amount 20% based on HEC, the swelling ratio of film was 5.8 in pH 6.86 buffer solution and the hydrogels achieved an equilibrium swelling state within 8 h; when the swelling ratio of the film was 0.05-0.1 and 0.4-0.5, tensile strength of film was 1.74MPa and 0.13MPa, elongation of film at break was 24.12% and 66.05%, respectively.Porous hydrogels were prepared from HEC using citric acid as a cross-linker with the pores formed by a freeze-drying technique prior to the cross linking reaction. The pore size increased with the increase of the ratio of water to HEC during the preparation of the hydrogels. The data of the swelling ratio demonstrated a fast swelling property of the hydrogel. The porous structure of the hydrogels was in favor of the adsorption of protein and dye. The results of thermogravimetry demonstrated that the thermal stability of HEC was improved by crosslinking with citric acid. The data of percent weight remaining in buffer solution with different pH indicated that the hydrogels were stable in both weak acid and base media. The porous hydrogel prepared with the mass ratio of citric acid: HEC: water: 1:5:150 achieved equilibrium swelling within 8 h in pH 6.86 buffer solutions, and the equilibrium swelling ratio of the porous hydrogel was 18.5. The adsorption amount of protein and methylene blue to the porous hydrogel was 15.7mg/g and7.63mg/g respectively.Polyurethane hydrogels containing lignin were synthesized from acetic acid lignin by chemical crosslinking with isocyanate (NCO)-terminated polyurethane ionomers (IPUI). The swelling ratio of hydrogels increased with the raise of pH. The hydrogel prepared with the mass ratio of mAAL/mIPUI: 0.3:1 presented maximum swelling ratio (3.14) in pH 6.8 buffer solutions. The results of thermo gravimetric analysis demonstrated that the thermal stability of the hydrogels is improved by the introduction of lignin. The hydrogels were used as coating material for ammonium sulfate and the data of release experiments for ammonium sulfate suggest that the hydrogels can be used as coating materials in slow release fertilizer.Polyurethane hydrogels containing liquefaction products of bagasse were synthesized by emulsion polymerization of polyurethane ionomers. The polyurethane ionomer emulsion was formed by the emulsification caused by the microphase separation between hydrophilic and hydrophobic segments of the chains, and the particles in the emulsion give regular spheric, core-shell structure. The polyurethane ionomer prepared from liquefaction products of bagasse present highly microphase-separated degree owing to the hydrophoblic interaction of the lignin in liquefied bagasse. The data of the swelling ratio showed that the hydrogels were sensitive to pH and ionic strength. The results of DSC analysis revealed that the freezing water in the swollen hydrogels were all free water. The adsorption experiment of the hydrogels for Cu (II) ion suggests that the hydrogels can be used as adsorbent for removal of heavy metal ions from aqueous solutions.