Functional Materials from Paper Wastes: II–Cellulose Hydrogels with High Water Retention Capacity Obtained from Solutions of Waste Paper in DMAc/LiCl

Abstract— An efficient process for recycling paper and cardboard wastes via dissolution in N,N-dimethylacetamide/lithium chloride (DMAc/LiCl) system and regeneration from solutions to obtain hydrogels has been developed. Pretreatment of waste paper has been carried out by thermal defibrillation of waste paper in water and homogenization to obtain fibrous samples. The dissolution of fiber materials was performed in two ways by varying the process temperature and the way the reagents were added. Regeneration from solutions was carried out by spontaneous gelation without the use of antisolvents, at room temperature and atmospheric pressure. As a result, hydrogels were obtained which differed in color and transparency depending on feedstock. The physicochemical properties of the hydrogels were characterized. It was shown that they were steady in an aqueous medium, capable of retaining a significant amount of water (over 4000 wt %), and they were porous systems which was confirmed by scanning electron microscopy. According to a wide-angle X-ray scattering, the crystallographic structure of the pristine waste paper samples corresponded to a structural modification of cellulose I. Regenerated samples as freeze-dried hydrogels had the structure of cellulose II. A functional and an elemental composition studied with FTIR spectroscopy and an energy-dispersive X-ray microanalysis characterized these hydrogels as the cellulose samples containing small amount of inorganic impurities. The resulting hydrogels had a system of open pores of different sizes, and this predetermined their use as adsorbents and active matrices.