Preparation And Application Research Of Nanocellulose Reinforced Poly(Vinyl Imidazole) Cryogels

Microfibrillated cellulose(MFC),also called cellulose nanofibrils(CNFs)or nanofibrillated cellulose,is a kind of nanocellulose and derived from natural plant cellulose that is abundant and low cost.As an emerging nanomaterial,MFC has been widely used to reinforce the mechanical strength of polymer composites due to its high aspect ratio and fiber entanglements.Cryogel is a three-dimensional peculiar type of gelation,which is fabricated by cryogenic treatment of the precursor solution and using solvent crystals as the porogen.The cryogel is s a potential adsorbent for removing metal ions with macroporous structure.However,traditional cryogel has the disadvantages of fragile,unstable,poor preparation process reproducibility,the ice crystal growth is difficult to control and the application is not ideal.The chemical composition and technological process of the traditional cryogel were researched,we found that monomer concentration,temperature,crosslinking agent ratio,ice crystal size,initiator and hydroxyethyl methacrylate(HEMA)all have great influence on the structure and properties of cryogel.In this paper,we improved the strategy of traditional vinyl imidazole(VIM)cryogel preparation,adding the pre freezing step and using MFC as the reinforcing agent.We successfully fabricated poly(VIM-HEMA)cryogel,poly(VIM)cryogel and poly(VIM)/MFC cryogel with excellent comprehensive performance.Cryogels can treat flowing metal ion solution under gravity with stable structure and pore size of 10-150 ?m.The adsorption capacities of traditional poly(VIM-HEAM)cryogel for multiple metal ions were less than 10 mg/g.However,the adsorption capacities of poly(VIM)cryogel and poly(VIM)/MFC cryogel to Cu(II)in this paper were 58 times and 34 times higher than that of traditional cryogel.The adsorption isotherms and kinetic models were fitted to the adsorption data,indicating a monolayer adsorption on a homogenous surface and chemical adsorption.The adsorption mechanism was the combination of imidazole group and metal ions.The adsorption capacity depended on the density of imidazole group.To simulate the environmental contaminants cleanup,the dynamic Cu(II)adsorption of the cryogels was quantitatively evaluated by continuously monitoring the Cu(II)concentration of the solution flowing through the cryogels.The experimental results show that 99.99% removal efficiency and the concentration of Cu(II)was lower than the US EPA(1.3 mg/L)and EU DWD(2.0mg/L)standards after adsorption.The metal-ion adsorbent needs excellent underwater mechanical properties.The underwater cyclic compressive stress-strain curves of cryogels were tested.The results show that poly(VIM)/MFC cryogel has the best underwater fatigue-resistance performance,which can be compressed 200 times without any damage.An excellent metal-ion adsorbent needs underwater fatigue-resistance performance,large processing fux,can treat flowing waste water,easy operation and high removal efficiency.As a three-dimensional porous material,most researchers focused cryogel on biomedical field,and the potential of metal ion adsorption is seriously underestimated.We improved the traditional strategy,adding pre-freezing steps and use MFC as a reinforcement.In this paper,pure poly(VIM)cryogel was first fabricated and used for highly effective adsorption of metal ions.MFC was first used as reinforcement in cryogels.This work provides a new idea and technical basis for the construction of the robust cryogels.