Preparation And Regulation Of Colorimetric Humidity-sensitive NCC/PAA Films

This study focuses on preparing and regulating of colorimetric humidity-sensitive nanocrystalline cellulose/poly acrylic acid?NCC/PAA?films.The effects of acid slurry ratio and acid hydrolysis temperature on the liquid crystal effect of the NCC suspension and the humidity-sensitive of the NCC iridescent films were investigated.Based on this,the colorimetric humidity-sensitive NCC/PAA iridescent films were prepared by added waterborne PAA varnish into NCC template.And the effects of the ratio of NCC to PAA on humidity-sensitive of NCC/PAA iridescent films were investigated.The regulation of colorimetric humidity-sensitive of NCC iridescent films was discussed by adding Na⁺and ultrasound treatment.The specfic works carried out in this paper are follows:?1?NCC were prepared with acid slurry ratio of 8:1,acid hydrolysis temperature of 45°C,acid slurry ratio of 8:1,acid hydrolysis temperature of 60°C,acid slurry ratio of 10:1,acidolysis temperature of 45°C,Zeta potentials were-27.5 mV,-21.4 mV,and-33.3 mV,-OSO₃^-content was 0.35%,0.49%,and 0.47%,respectively,and aspect ratios were 17.0,9.5,and 11.6,respectively.The NCC films self-assembled in a periodic spiral rotation arrangement with uniform crystal form.NCC were cellulose I type and forms liquid crystal effect.When the ratio of acid to slurry was 8:1 and the temperature was 45°C,the maximum reflection peak of visible light of NCC iridescent film red shifted from 480 nm to 520 nm,final to 543 nm,under relative humidity from 43%,75%,and 86%.When the ratio of acid to slurry was 10:1,and the temperature was 60°C,the the maximum reflection peak of visible light of NCC iridescent film red shifted from 480 nm to 520 nm,final to 543 nm,under relative humidity from 43%to 75%to86%.The maximum reflection peak wavelengths of the NCC iridescent film were finally recovered to 480 nm and 699 nm,respectively,when films were re-sequentially placed in a humidity of 75%and 43%in an 86%humidity environment.The NCC were prepared with acid slurry ratio was 10:1,the acid hydrolysis temperature was 60°C,the acid slurry ratio was 12:1,the acidolysis temperature was 45°C,the acid slurry ratio was 12:1,the acidolysis temperature was 60°C,the ratio of length to diameter was 5.8,6.1 and 2.6,respectively.NCC had both cellulose type I and type II at the same time.The crystal structure was irregular and destroyed,and the liquid crystal effect and iridescent film formation cannot be achieved.Therefore,in the preparation of humidity-sensitive NCC iridescence film by acid hydrolysis,neither the acid-slurry ratio nor the acidolysis temperature should be too large,the acid slurry ratio was 8:1or 10:1,and the acidolysis temperature was 45°C.?2?NCC as template,the colorimetric humidity-sensitive NCC/PAA iridescent films were prepared by using PAA at a ratio of 98:2,95:5,90:10,and 80:20 for NCC to PAA.With the increasing of relative content of PAA,the strongest reflection peak wavelength of visible light in iridescent film moved to long wave direction,which appeared at 430 nm,480 nm,510 nm,and559 nm,respectively.With the increasing of the environment humidity,the wavelength of the strongest reflection peak of the NCC/PAA iridescent film moved toward the long wave direction,and was 515 nm,600 nm,and 620 nm when the ambient humidity was 43%,75%,and 86%,respectively.After the NCC/PAA iridescent films with humidity of 86%were placed back into humidity of 75%and 43%,the maximum reflection peak wavelength was restored to its original position.When the ratio of NCC to PAA was 70:30,the prepared NCC/PAA composite film had no maximum reflection peak in the visible light region,and iridescent films could not be produced.?3?The colorimetric humidity-sensitive of NCC/PAA was regulated by Na⁺and ultrasound treatment.After Na⁺was added into NCC/PAA,the system changed from weakly negative electronegativity to strong positive electricity,enhanced the electrostatic repulsion of the system,and prepared a colorimetric humidity-sensitive NCC/PAA-Na iridescent film with high PAA content.In the NCC/PAA-Na iridescent film,the peak wavelength of the strongest reflection peak moved toward the long wave with the increase of the ambient humidity,and the 532 nm,601 nm,and 624 nm were observed at 43%,75%,and 86%of the ambient humidity,respectively.After the NCC/PAA iridescent film with humidity of 86%was placed back into humidity of 75%and 43%,the maximum reflection peak wavelength was restored to 532 nm.When ultrasonic treatment of NCC/PAA composite coating,the surface of NCC had more-OH,promoted the uniform dispersion of NCC and PAA,and prepared colorimetric humidity-sensitive NCC/PAA iridescent film with high PAA content.With the increasing of the ultrasound time from 10 mins to 20 mins,the wavelength of the strongest peak of visible light reflected by the iridescent film shifted from 511 nm to 633 nm.The ultrasonically treated NCC/PAA iridescent film had excellent colorimetric humidity-sensitive.With the increasing of ambient humidity,the strongest reflection peak wavelength of the NCC/PAA iridescent film moved violently toward the long wave direction,and the ambient humidity was 43%,75%and 86%,peaks were 511 nm,660 nm,and 705 nm,respectively.After the NCC/PAA iridescent films with a humidity of 86%were placed back into a humidity of 75%and 43%,the maximum reflection peak wavelength was restored to 511 nm.When the ultrasonic time was 30 min,the NCC/PAA composite film has weaker iridescent effect.The regulation of colorimetric humidity sensitivity of the NCC/PAA iridescent film by contrasting Na⁺and ultrasound treatment indicated that a highly sensitive colorimetric humidity-sensitive NCC/PAA iridescent film can be prepared by ultrasound treatment.