Design,Construction And Application Of Highly Mechanical Cellulose-based Conductive Materials

Flexible electronic devices have great application values in artificial skin,strain sensors,wearable devices and so on.For the development of flexible electronic devices,it is more necessary to improve the mechanical properties of substrates.Noticeably,flexible substrates,such as hydrogels and flexible films,based on natural polymers have received immense considerations in the field of electronics,due to their excellent properties such as safety and inexhaustibility.Cellulose with non-toxic,biodegradable and renewable properties,is abundant natural polymer,and is a strong candidate for the fabrication of environmentally friendly and biocompatible products.At present,many studies focus on improving the functional performance of cellulose,while using cellulose to prepare flexible substrates with high mechanical performance remains a challenge.Aiming at improving mechanical performance of cellulose-based flexible substrates,this thesis develops ionic conductive cellulose-based hydrogels with high mechanical performance,and transparent cellulose films with high mechanical properties and weak hydrophilicity are prepared based on cellulose hydrogels.In addition,this thesis also explores their applications in flexible electronic devices.Allyl cellulose is prepared by functionalized modification of cellulose,for preparation of novel fiber products.Allyl cellulose is prepared by homogeneous reaction of cellulose in sodium hydroxide/urea solution,in which allyl glycidyl ether is used as modifier.When the molar ratios of allyl glycidyl ether to anhydroglucose unit of cellulose are 5,6,7,8 and 9,the substitution degrees are 0.75,1.05,1.52,1.79 and 2.23,respectively.With the increase of the allyl glycidyl ether amount,the intensity and width of the O-H band on the modified cellulose gradually decrease.The crystal structures of allyl cellulose with different degrees of substitution are almost the same.Cellulose ionic hydrogels with high stretchability(tensile strain ?126%)and compressibility(compressive strain ?80%)among pure natural polymer-based hydrogels including cellulose,chitosan and chitin,are prepared by free radical polymerization of allyl cellulose.Cellulose ionic hydrogels also have excellent transparency(transmittance ?89% at 550 nm)and ionic conductivity(?0.16 m S /cm),and can be worked at-20 °C without freezing and visual loss of transparency.In addition,cellulose ionic hydrogels coated with commercial tape can be used as reliable and stable strain sensors,and have been successfully used to detect human activities.Significantly,the various properties of cellulose ionic hydrogels can be controlled through rationally adjusting the chemically crosslinked density.The double-cross-linked cellulose ionic hydrogels are prepared by ammonium persulfate initiating chemical crosslinking of free radical polymerization of allyl cellulose,and by sodium chloride inducing physical cross-linking.The acquired double-cross-linked cellulose ionic hydrogels display ultrastretchability(?236% of tensile strain)and high compressibility(?82% of compression strain)among pure polysaccharide-based hydrogels including cellulose,chitosan,and chitin,at room temperature.The soaking strategy in saturated sodium chloride solution also endows the double-cross-linked cellulose ionic hydrogel with good antifreeze property.The double crosslinked cellulose ionic hydrogel has good stretchability(strain up to 100%)at-24 ? and high transparency at-30 ? to-16 ?.In addition,the double-cross-linked cellulose ionic hydrogels as strain sensors have the advantages of high reliability,fast response speed and wide range strain sensor,which is demonstrated by investigating the output electrical signals,showing its potential application in flexible electronic devices under wide range temperature.Cellulose-based hydrogels with high stretchability,strain sensitivity and ionic conductivity are prepared by random copolymerization of allyl cellulose and acrylic acid.Cellulose-based hydrogels exhibit high stretchable properties(tensile strain ?142%)and transparency(transparency ?86% at 550 nm).In a wide tensile strain range(0-100%),the resistance change ratio of cellulose-based hydrogels varies with tensile strain,showing high linear relationship and the gauge factor.In addition,cellulose-based hydrogels as strain sensors exhibit good repeatable and stable signals,even after 1000 cycles.Wearable sensors based on the hydrogels are successfully constructed and used to monitor human movements.Transparent cellulose films with high mechanical properties and weak hydrophilicity are prepared based on cellulose hydrogels.Cellulose films not only exhibit high tensile strain(34%)and good mechanical stability,but also have high transparency(over 90%)over a wide wavelength range(520 nm to 800 nm).In addition,replacing the hydrophilic hydroxyl group on the cellulose chain by allyl glycidyl ether endows the cellulose with the double bond,and also reduces the hydrophilicity of the cellulose films.The initial water contact angle of cellulose film is ?79°,and the tensile stress is still 3.5 MPa after soaking for 2 days in deionized water.The cellulose film prepared by chemical reaction is degradable.The degradation half-life of cellulose film in natural farmland soil is 20 days,at 30 ?.Cellulose film also has good thermal stability(starting thermal decomposition temperature ?200 ?).Noticeably,transparent cellulose films with high mechanical properties and weak hydrophilicity can be successfully used to construct flexible electroluminescent devices.