Preparation And Applications Of Organohydrogels Via The CAA-HRP-H₂O₂-initiated Polymerization Of CAA-stabilized Emulsion Templates

Recently,with the increasing conflict between the energy consumption and environmental protection,the green,efficient and controllable preparation methods and energy-efficient and adaptable functional materials have attracted much attention.Cellulose is an abundant and environmental-friendly natural polymer material,which can be chemically modified into the reactive cellulose acetoacetate（CAA）.CAA containing acetoacetyl group can work with HRP and H₂O₂ to form a mild and efficient CAA-HRP-H₂O₂ ternary enzyme initiation system for radical polymerization.Due to the amphiphilicity of the molecular structure,CAA can act as the polymer emulsifier to form the oil-in-water（O/W）emulsion that could encapsulate and release hydrophobic substances,which effectively improves the functionality and applicability of the system.Hydrogels with a great deal of water in the three-dimensional hydrophilic network have been widely used in wound dressings,drug delivery,flexible electronic devices because of its high water content,biocompatibility,stimulus responsiveness and so on.In this paper,we propose a biphasic organohydrogel with excellent performance and wide applications,which was synthesized by the CAA-HRP-H₂O₂ enzyme-initiated in situ polymerization of the O/W emulsion template.The primary research contents and results are as follows:Firstly,the cellulose acetoacetate（CAA）was prepared by the transesterification reaction of the wood pulp cellulose and tert-butyl acetoacetate.The CAA-HRP-H₂O₂ enzymatic system was used to initiate the polymerization and crosslinking of zwitterionic monomers to obtain the hydrogel,which verifies the reactivity of CAA and the feasibility of CAA-HRP-H₂O₂enzymatic polymerization.Then,CAA acting as the emulsifier formed a stable thyme oil-in-water emulsion template by virtue of ultrasonication.The morphology and stability of the emulsion were observed.The CAA-HRP-H₂O₂ enzymatic system initiated the aqueous phase to polymerize and crosslink to obtain the organohydrogel.The microscopic morphology and mechanical properties of organohydrogels were characterized.The antibacterial performance was tested.The experimental results demonstrate that CAA-stabilized emulsion has uniform distribution and stability,organohydrogels possess good mechanical properties and significant antibacterial effect on the Escherichia coli and Staphylococcus aureus.The organohydrogel encapsulating thyme oil could be applied as antibacterial wound dressings as well as the drugs encapsulation and release carriers.In order to further investigate the universality of the CAA-HRP-H₂O₂ enzyme-mediated polymerization of emulsion templates to prepare organohydrogels and expand the properties and applications of organohydrogels,the hydrophilic and hydrophobic components of the eicosane-in-water emulsion stabilized by CAA were simultaneously in situ polymerized by the CAA-HRP-H₂O₂enzyme initiation system to obtain the biphasic organohydrogel.The phase-transition polylauryl methacrylate micro-inclusions containing eicosane were encapsulated in the continuous polyacrylamide hydrogel network.The microstructure,mechanical properties and thermal stability of the phase-transition organohydrogel were characterized,as well as the shape memory effect and the cooling performance in buildings were further investigated.The experimental results show that organohydrogels exhibit excellent thermomechanical performances and shape memory properties,which attributed to the synergistic effect of the wrapped phase-transition micro-inclusions and the continuous hydrogel network.The thermal decomposition temperature of eicosane was delayed by101℃,indicating organohydrogels possess the great thermal stability.The cooling effectiveness of the organohydrogel was demonstrated by decreasing the interior surface temperature of the wood model house roof by 13℃in comparison to the roof without gel under solar radiation（1000 W/m²）,which ascribed to the endothermic characteristic of the water evaporation and eicosane melting.These results indicate that the biphasic phase-transition organohydrogel is expected to be an efficient and reliable thermal management material in building thermoregulations.