Preparation And Properties Of Cellulose Nanocrystal-based Stimuli-responsive Film

Multi-stimulus response film can selectively respond to external stimuli(humidity,pH,temperature,light and force,etc.).It has an important application in the fields of intelligent sensors,food detection,anti-counterfeiting and biomedicine.At present,many stimulus response film materials are expensiveness,environmental pollution,toxicity,slow response and other problems.Therefore,it is necessary to develop a light-weight,portable,low-cost,high-sensitivity,high-selectivity and good stability colorimetric sensors by cellulose nanocrystals.Therefore,this study takes the chiral nematic structure and enhancement of cellulose nanocrystals as the starting point.The humidity-,pH-and multi-responses of the cellulose nanocrystal stimulation films were studied.The application of cellulose nanocrystal film in the fields of humidity sensor,food preservation and food freshness detection were realized.And the application field of cellulose-based functional film materials was expanded.It is a great significance to the high-value utilization of cellulose resources.The details are as follows:A pH-sensing film consisting of HPG,CNC,Bmim Cl,and Anth was fabricated,which can be used for the visual detection of NH₃.CNC was used as a reinforcing agent.Anth extracted from blueberries was used as a pH indicator.Bmim Cl was used as a plasticizer to improve the flexibility of film,which also endowed the film with a wide range of discoloration.The structure,optical properties,and mechanical strength of the composite films were investigated.HPG/CNC/Anth/IL film showed good flexibility,high transparency,compact structure,and low cost.Compared with HPG/CNC/Anth film,the HPG/CNC/Anth/IL film exhibited a more distinguishable color change.The Most importantly,The HPG/CNC/Anth/IL film possessed remarkable performance for NH₃ detection,including high sensitivity,fast response(2?3 s),low detection limit(1?g/m L),good reversibility(>15 cycles),and good stability(>10 weeks).The HPG/CNC/Anth/IL film could achieve the real-time,visual,and contactless detection of the food freshness,especially the seafood,which showed promising applications as flexible smart labels in cold chain logistics or household use such as refrigerators.As a promising class of green chemicals,deep eutectic solvents(DESs)have gained much attention due to their low-cost,non-toxicity and biodegradability.An eco-friendly and sustainable multifunctional pH-sensing film comprised of hydroxypropyl guar(HPG),cellulose nanocrystals(CNCs),deep eutectic solvents(DESs)and anthocyanin(Anth)was fabricated.CNCs were added to decrease water and oxygen permeance while increasing mechanical reinforcement.DESs based on choline chloride and glucose,which can be used as a plasticizer to improve the flexibility of film and acted as a toner to enhance a color-change ability of anthocyanin(Anth).Anth is an edible extract from fruits,vegetables and flowers that has antioxidant,antibacterial and antimutation properties.The effects of DESs on the physicochemical properties of the pH-sensing film were investigated,and performance tests indicated that moderate amounts of DESs could endow the pH-sensing film with the following properties:high transparency(61%),compact structure,low oxygen permeability(3.01cm³/m²·day·Pa),high sensitivity(1?2 s)and dramatic distinguishable color change(?E*>5).Furthermore,the shelf life of the fruit coated with the pH-sensing film was longer than the counterpart without the treatment.The pH-sensing film could be used as both a preservative packaging film for fresh fruit,and as a flexible smart label for the detection of ammonia and organic acids generated during seafood,meat and milk storage.A CNC iridescent composite film with good mechanical properties,tunable structural color and humidity sensitivity using CNCs as the substrate and glucan as an additive was fabricated a.The effect of glucan with different molecular weights on the mechanical performance and tunable structural color of iridescent CNC composite films was investigated.The existence of glucan did not influence the self-assembly performance of CNCs but rather led to an improvement in the mechanical performance,enabling cholesteric CNC composite films with adjustable structural color.Simultaneously,the iridescent films showed a conspicuous redshift and enlarged initial pitch without obstruction of the chiral structure.In response to environmental humidity,the structural colors of the iridescent composite films can be changed by regulating their chiral nematic structure.In particular,the films demonstrate a reversible structural color change between blue and red at RH between 50%and 98%.The resulting biobased iridescent composite films have potential applications in decorative coating,optical and humidity sensing and anti-counterfeiting.A flexible and humidity-sensitive composite films employing cellulose nanocrystal(CNC)and polyols,i.e.,glycerol(G),xylitol(X)and sorbitol(S)was fabricated.The effects of polyols with different hydroxyl numbers on the structure,optical properties,mechanical strength and humidity response of the composite films were investigated.Notably,the CNC-S film exhibited obvious reversible color changes from light green to red upon a relative humidity(RH)change from 50%to 98%.Moreover,it was found that the CNC-S film had a dramatic distinguishable color change(?E*>27),high sensitivity(29 s)good reversibility(>10 cycles).Overall,the results demonstrated that the CNC-S composite film can be used as a functional material for the preparation of flexible humidity sensors for the detection of environmental humidity changes in agriculture,industry,and other fields.A facile approach to fabricate multi-stimuli responsive photonic films by the co-assembly of anthocyanin(Anth)and sorbitol(S)was demonstrate.CNCs endows the multi-responsive films with humidity sensitivity,Anth offers pH-response and the elastic sorbitol provides the flexibility and water wettability.The prepared multi-responsive films were studied in terms of optical properties,mechanical performances,and responsive behavior to humidity,solvent and pH stimuli.Notably,the photonics film showed dramatic invertible color from blue to purple and high sensitivity(30 s)at a relative humidity from 50%to 100%.Moreover,the photonics film exhibited fast response(1 min)and good reversibility under different ethanol and tetrahydrofuran concentrations.Significant color changes of the photonics film were also observed in response to pH change in the range of 2 to 12.Particularly,the humidity,solvent and pH responsiveness of the photonics film did not interfere with each other.These multiple-stimuli-responsive bio-based films may find applications in smart packaging and anti-counterfeiting materials.