Functional Superhydrophobic Materials Assembled Based On Different Cellulose Nano-forms

Superhydrophobic surface is a special wetting surface constructed by abstracting and theorizing natural phenomena.Superhydrophobic materials have a wide range of applications in the fields of separation,microfluidic,self-cleaning,etc.Nanocellulose is a kind of sustainable biomass material.In recent years,the research on nanocellulose-based superhydrophobic materials has been growing vigorously.Based on different cellulose nano-forms,this thesis carries out a series of work as follows:(1)One of the prerequisites for constructing superhydrophobic materials is the construction of surface rough structure,which requires at least two or even multiple levels of roughness construction.In the work described in the second chapter,we used spray drying equipment to rebuild the aggregation structure of nanocellulose and prepared nanocellulose-based rough particles with micro-nano dual roughness(micron-scale particles and nano-scale folds)which were used as a superhydrophobic structure to design superhydrophobic coating.In this process,we expected to adjust the width and depth of the folds of nanocellulose-based micro-nano particles by adding hydrophobic lignin.But as a result,the addition of hydrophobic lignin resulted in the transformation of the particle structure from sphere to annulus.This work explored the reasons for this transformation and pointed out that the appearance of the annular structure was due to the promotion of water evaporation from hydrophobic lignin in the spray drying process.Laser confocal microscopy analysis showed that lignin was concentrated in the center of the annular particles,which was due to that the water on the surface of lignin evaporated faster than water on the surface of cellulose.Faster evaporation led to faster aggregation rate.Subsequently,we prepared a nanocellulose/lignin composite superhydrophobic coating with excellent self-cleaning ability.The maximum static contact angle was 165.2°when the amount of lignin was 10%.The smallest amount of lignin also led to a static contact angle of 158.4°.(2)On the basis of the above work,we realized that the spray drying of a multicomponent system containing hydrophilic and hydrophobic substances would not generate separated particles but composite particles,which has important value for the multifunctional configuration of particles and means that we can integrate components carrying different functional modules into a single particle through this thermal aggregation process to achieve multifunctional particles.In addition,most of the current superhydrophobic materials have satisfactory water contact angle and superhydrophobic performance but these materials still need to rely on manual tilting or shaking to remove the surface sewage,that is to say,the preparation of superhydrophobic materials that can actively and quickly remove water and pollution is still a challenge.Moreover,the application of superhydrophobic materials in cross-fields has been limited by their single function.Furthermore,poor wear resistance has always been a major problem for these fine structure-based materials,which profoundly restricts their practical application.Based on the above problems,the work in the third chapter used spray drying to integrate the basic fiber(nanocellulose)for particle structure construction,the functional fiber(carbon nanotubes)for photothermal and electrical management,and the water-based polyurethane for strengthening function into rough particles.The composite rough particles showed excellent oil-water emulsion separation ability while the granulated coating showed rapid and active water-removal ability(based on the CNT photothermal effect and the construction of thermal-conductive network),electrical conductivity(based on the construction of electrical-conductive network),antibacterial ability(based on the ability to release reactive oxygen of carbon nanotubes)and excellent wear resistance.For a superhydrophobic sample with 10% CNT addition,30 g of water can volatilize in a unit time of 10 minutes.The static contact angle of the superhydrophobic sample with 3% PU added after 300 times of rubbing was still higher than 150°.(3)The design of superhydrophobic materials based on nanocellulose in the above two chapters adopts the bottom-up principle.In the forth chapter,wood aerogel with a single cellulose component was obtained by removing lignin and hemicellulose from natural wood in an orderly manner.The alignment of nanocellulose in wood was perfectly preserved,and the wood aerogel exhibited an ordered layered structure with excellent mechanical compressibility and resilience.Then,we integrated carbon nanotubes as a photothermal management module with wood aerogels and thus assembled an aerogel device without adsorption saturation point that could rapidly and continuously separate oil and water,realizing a reasonable and efficient output path design for adsorbed objects.Especially for the processed low boiling point reagents,about 80 g can be separated within 10 min.In addition,a cycle collection platform for gaseous reagent recovery matching with the device was built.In this work,the problem of adsorption saturation point of most porous adsorbents was solved by designing the output path.Therefore the problem that most adsorbents could not continuously adsorb and purify the objects for a long time was overcome.The designed aerogel device also had excellent cyclicity(After 10 absorption/compression cycles,the adsorption capacity for olive oil only dropped from 23.1g/g to 20.3g/g.)and mechanical durability,which provided a guarantee for its use under complex and harsh conditions.The complete scheme of "adsorption-separation-recovery" proposed in this work demonstrated an efficient solution to the complex and practical oil-water separation problem.