Study On Properties And Applications Of Composite Films And Hydrogels Based On Cellulose Nanocrystals

Cellulose nanocrystals(CNCs)are the crystalline fiber of cellulose.It has many advantages such as high Young's modulus,high crystallinity,high strength,light weight and so on.CNCs can be used as an additive to change the mechanical strength of the polymer film and the swelling property of the hydrogel.One of the most important characteristics of CNCs is the formation of chiral nematic structure by evaporation induced self-assembly(EISA).Many new functional materials can be obtained by using the template of CNCs,and are applied in the fields of chiral catalysis,anti-counterfeit markers,humidity sensors and optical sensors.This paper focuses on the following two aspects.First,using cellulose nanocrystals(CNCs)as a template to construct flexible functional nanomaterials.Especially,the preparation of chiral optical films by evaporation self-assembly has attracted wide interest.However,the chiral optical films prepared by this method have weak mechanical properties,which limits their practical applications.In this paper,composite films(CFs)containing silicone-modified acrylic latexes(SALs)and CNCs were prepared via EISA.At mixing ratios of SALs to CNCs of 0.2–0.4,homogenous films were obtained,where the latexes cohere together to form a network that locks the chiral nematic structure.CNCs in the composite film were removed by alkali treatment and then dried after immersion in water or alcohol.The formed latex films have different structures and colors.Experiments show that the removal of CNCs leads to a smaller helical pitch in latex films and a blue-shift reflection color.In addition,the soaking solvents also affect the structural color of the latex films.Expansion and contraction induced by water adsorption and desorption make latex films generate reversible color variation.The optical latex films have good flexibility,with the maximum elongation at break reaching 34.5%,which is the maximum value obtained so far.Second,the composite hydrogels formed by CNCs and polyacrylic acid-poly acrylamide(PAA-PAM)were studied.The results showed that the hydrogel has dual responsiveness to pH and temperature,and its pH response range is 1-6,and the response range of temperature is 2-45 ?.Especially when pH is in the range of 3-4,hydrogels can undergo water absorption and swelling at high temperature and drain at low temperatures.Due to the participation of CNCs,PAA-PAM composite hydrogels exhibit better temperature and pH sensitivity.A series of characterization of the composite hydrogel structures was carried out,and the optimum compound ratio(AA+Am: CNC: KPS: BIS,2.6: 1: 0.075: 0.065,AA: Am=1: 1)was obtained.