Preparation and Application of Modified Sodium Lignosulfonate Hydrogel

Lignosulfonate have a tri-dimensional network like structure containing hydroxyl,carboxyl and sulphonyl groups in their molecules, these structural features therotically ensured them to be a good raw material for preparing the hydrogel.

This paper focuses on the development and utilization of lignosulfonate. Firstly, we studied the preparation of lignosulfonate hydrogel, made an investigation into the removal of reducing sugar in lignosulfonate and preparation of modified lignosulfonate hydrogel.

Through this study, we found an effective method to reduce the reducing sugar in lignosulfonate and successfully prepared a type of modified lignosulfonate hydrogel with good water swollen capacity under conditions of no addition ofcross-linking agent. Furthermore, the corresponding studies on the application of this modified lignosulfonate hydrogel in preparation of nano-material and drug deliverywere also conducted.The research results indicate that the reducing sugar in commercially available lignosulfonate can be effectively reduced through acid-aided hydrolysis-salting outmethod. The optimal operating conditions are addition of 2wt% of sodium lignosulphate and 11.78 wt% of sulphonic acid chloride of total solution weight,4h of hydrolysis time at 80 oC and addition of 20wt% of sodium of total weight duringsalting out process. The modified sodium lignosulfonate is prepared by using sodium lignosulfonate after removal of reducing sugar as starting material through oxidationand sulphuration modification procedures. The content of phenol group, carboxylgroup and sulphonyl group in modified sodium lignosulphate is promoted by 29%,3.4% and 9.7%, respectively. The modified sodium lignosulfonate was thermally treated under acidic conditions followed by treatment in sodium hydroxide solution;the collected solid by filtration under reduced pressure is modified lignosulfonate hydrogel.

The single factor experiment was conducted by varying the level of the major impact fators that affecting the water swollen capacity and yield of modified sodium lignosulfonate, and the optimal preparation route was determined, that is:8g of purified sodium lignosulphate by hydrolysis-salting out method,200mL ofdeionized water and 6mL of 30% H2O2 was mixed, the mixture was heated to 50 oC,then 2.5g of sodium sulfite was added to the mixture and the solution was sulphonated for 80min. The solution after sulphonation was dried at 135 oC for 90 min, and then the solid was hydrolyzed in 0.3M sodium hydroxide for 40 min at roomtemperature, the yield is about 10% based on sodium lignosulfonate.

The obtained modified sodium lignosulfonate has a water swollen capacity of 30.2 g/g xerogel.A serial of experiments around the obtained wet hydrogel includes ultrasonic dispersion, scan electron microscope observation; water solubility of dried solid after ultrasonic dispersion and dynamic light scattering, the experiment results demonstrated that the obtained modified sodium lignosulfonate hydrogel is formed byphysical cross-linking. Microgel comprises of particles of micrometer size, it is an excellent template or micro-reactor for the synthesis of inorganic nano-materials.

We prepared modified sodium lignosulfonate microgel by ultrasonic dispersion, and then prepared nano silver particles with avarage particle size of 9.6 nm by reduction in-situbased on the confinement effect of microgel network structure. The dryness of themicrogel-nano silver dispersion leads to nano silver/modified sodium lignosulfonat ecomposite microgel.

This composite material is expected to be applied in the fields of medicine and catalysis. Sodium lignosulfonate is non-toxic and biocompatible, andthe modified sodium lignosulfonate prepared from it has better water swollen capacity,this feature endowed it potential as drug delivery material. The experiment confirmed that modified sodium lignosulfonate has sustained release property to piperazine ferulate. Since the water swollen capacity of this hydrogel can undergo a sharp declining under acidic environment, it can be used as sustained release carrier of drugs that has stimulation on stomach. In general, modified sodium lignosulfonate hydrogel is a novel type of natural polymeric hydrogel without any addition of cross –linking agent and formed by physical cross-linking of microgel particles. It can be dispersed into microgel by ultrasonic dispersion. Because of its unique properties, this hydrogel is expected to be applied in the fields of nano-material preparation, drugdelivery, and heavy metal ion adsorption and biochemical separation.

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