Structural Design And Properties Of Functional Composites Based On Bacterial Cellulose

The new generation of bio-based functional composites has the advantages of light weight,high strength,high stability and abundant functional active sites,so as to meet the application requirements of high-performance enrichment identification or wearable functional devices.In order to achieve a balance between mechanical properties and functional characteristics of materials,it is necessary for the substrate materials to have both ordered microscale structure and good composite interface effect.Bacterial Cellulose（Bacterial Cellulose,BC）secreted by microorganisms is known as one of the new generation structural base material of biomimetic functional composites due to its low density,high tensile strength and elastic modulus,high specific surface area and high biocompatibility.Nowadays,there are few reports on the structural regulation and modification methods of BC,mainly focusing on the fields of biomedical materials.However,the research shows that BC fiber is particularly fit for the composite construction of multilevel ordered structure due to its high fiber aspect ratio and abundant three-dimensional（3D）network structure,which further expands its application in the field of flexible biomimetic functional materials.In this paper,BC was used to prepare several typical flexible biomimetic functional composites,to verify the common ideas and application propects in this field.The details are as follows:（1）Inspired by the active interface strengthening mechanism of mussel adhesion protein,the polymerization of polydopamine（PDA）in the template of BC hydrogel was studied firstly,and a BC/PDA secondary raction platform with large specific surface area and high reactivity was created.On this basis,the anatase type titanium dioxide particles（Ti O₂）were coated along the radial direction of the nanofibers uniformly.The obtained BC/PDA/Ti O₂gel with a 3D hierarchical ordered structure performed synergistic effect of high adsorption capacity,high photocatalytic degradation performance and and long-term structural stability for typical dye molecules in water.（2）Inspired by the specific recognition performance of biosensors for enzymes,proteins and other macromolecules,a sol-gel method was carried out to onstruct the molecularly imprinted functional layer in the framework structure of BC/PDA/Ti O₂ gel.BC/PDA guidance molecularly imprinted polymers（MIPs）along the fiber radial uniform coating,and Ti O₂ particles provides high specific surface area for MIPs hard imprinting basement.As a result,the obtained molecularly imprinted membrane provided great specificity adsorption capacity(up to 45.6 mg g^-1)and high separation factor（up to 6.8）towards the cresol isomers（including o-cresol,m-cresol and cresol）.This strategy provides a novel approach for the expansion of surface molecularly imprinting method from two-dimensional（2D）monolayer structure to 3D network structure and verifies the excellent design potential of BC/PDA secondary reaction platform.（3）The bacterial cellulose nanofibers（BCNF）with ultrahigh aspect ratio and rich interfiber structure were prepared by TEMPO oxidation and high-pressure homogenization under optimized reaction conditions.The structural differences between BCNF and traditional nanofiber materials（plant cellulose nanofibers,BC flocs,cellulose nanocrystals,etc.）were systematically studied.Inspired by the“brick and mortar”layered structure and strengthening mechanism of nacre,the BCNF was used as an efficient reinforcing locking unit to composite with MXene nanosheets.The obtained MXene/BCNF material performed outstanding tensile strength（252.2 MPa）,fold resistance（3000 times）as well as excellent electromagnetic shielding efficiency(up to 19652 d B cm² g^-1),promising candidate for wearable devices and human electronic equipment.（4）Nonmetallic conductive fibers have wide applications prospect in flexible biomimetic functional materials.Based on the unique fiber structure,an optimized interface polymerization method was carried out to create a“core-shell”polypyrrole（PPy）layer onto the BCNF.Furthermore,the PPy/BCNF were used as mechanical enhancements and conductive fillers for the natural rubber（NR）matrix,to prepare the elastic conductive polymer composites（ECPC）.As a result,the PPy/BCNF@NR elastomer has high tensile sensitivity（GF value up to 353.3）and large range of tensile strain（389.0%）,which can be widely used in the design of portable and wearable electronic sensor.（5）Conductive hydrogels with self-healing properties have excellent development prospects in the field of flexible biomimetic functional materials.Considering the unique three-dimensional structural enhancement mechanism of BCNF,an enhanced polyvinyl alcohol-borax（PVA-B）based composite hydrogel was fabricated by introduce BCNF physical crosslinked network into it.Besides,the MXene nanosheets were used as the conductive unit through the guidance of nanofiber at low contents to form the high conductive path in the hydrogel.The obtained composite hydrogel has good sensing sensitivity（GF value up to 46.6）and rapid self-healing performance at a large tensile range,which can meet the application requirement of wearable sensor that is worn close to the body.