Preparation And Performance Of UV-induced Thermochromic Polyurethane

Intelligent color-changing textiles and electronic wearable textiles have gradually become research hotspots and become the development direction of new-generation textiles.People are not only satisfied with warm and comfortable clothing,but also pay more and more attention to textiles with additional functions.The use of thermochromic materials for textiles can realize the color change of fabrics with temperature changes,which has smart functions while having fashionable functions.Electrically induced thermochromic textiles are wearable and give the fabric extra value.However,traditional thermochromic dyes are sensitive and susceptible to environmental influences,which limits their application to textiles.The environmental influences and the application on textiles of thermochromic materials can be reduced by incorporating them into polyurethane.The raw materials of polyurethane are wide and the performance can be adjusted according to the synthesis conditions.Therefore,designing responsive monomer and incorporating into polyurethane can not only obtain thermochromic polyurethane but also it can be printed on cotton fabric to prepare the intelligent thermochromic textile.Besides,the electro-thermochromic textile can be obtained by printing the graphene paste on the back of thermochromic textile.The rhodamine B derivative RhEA which had–NH₂ was prepared with rhodamine B and ethylenediamine.Polyethylene glycol 1000,isophorone diisocyanate and 1,4-butanediol were used and RhEA was added at the end-capping stage to prepare a non-ionic rhodamine B thermochromic polyurethane.FTIR and ¹H NMR test results showed that RhEA was grafted with-NCO in polyurethane.Thermogravimetric analysis showed that the non-ionic rhodamine B thermochromic polyurethane had good thermal stability and almost did not undergo significant thermal degradation below 200?.By analyzing its UV-induced thermochromic properties,it was found that the non-ionic rhodamine B thermochromic polyurethane reached saturation at about 210 s under 254 nm UV induction,and it was red.When the temperature rose,the color of non-ionic rhodamine B thermochromic polyurethane was changed from red to colorless.Then the non-ionic rhodamine B thermochromic polyurethane was printed on cotton fabrics to obtain UV-induced thermochromic fabrics.The color of printed fabric and control cotton fabric are white.The K/S of printed fabric can reach about 3.0 at 180 s under 254nm UV induction,which was red.When the temperature increases,the corresponding maximum absorption wavelength does not change.But the K/S value gradually decreased,which showed that the color of printed fabric changed from red to white.In order to improve the water solubility of polyurethane,anionic thermochromic polyurethane was prepared by using 2,2-dimethylolpropionic acid as a chain extender.And the influence of the molecular weight of polyurethane soft segment on printing performance was investigated.The molecular weights and dispersion coefficients of anionic thermochromic polyurethanes?PU-PEG200,PU-PEG600 and PU-PEG1000?prepared using PEG200,PEG600 and PEG1000 were 3317,14273,20377 and 1.34,1.68,and 1.66,respectively.As the molecular weight of the soft segment polyethylene glycol increased,the thermal stability of the anionic thermochromic polyurethane increased.The 10%and 50%weight loss temperatures of PU-PEG200,PU-PEG600 and PU-PEG1000 were 198?,290?,298?and 327?,371?and397?,respectively.As the molecular weight increases,the phenomenon of shear thinning becomes more pronounced.In order to investigate the influence of molecular weight on UV-induced properties,the UV absorption spectrum at different UV induction was measured.In order to explore the influence of molecular weight on the UV-induced performance,the UV absorption spectrum was measured with various UV induction times.It was found that the absorbance gradually increased with the increase of UV-induced time.But when the UV-induced time was constant,PU-PEG600 had the largest absorbance,followed by PU-PEG1000,and PU-PEG200 had the lowest absorbance.After UV induction,PU-PEG200,PU-PEG600,and PU-PEG1000 all had thermochromic behaviors.Anionic thermochromic polyurethanes of different molecular weights were applied to the fabric by screen printing.It was found that the actual width of the printed lines of PU-PEG600 and PU-PEG1000 were slightly larger than the theoretical values of 0.50 mm and 1.00 mm and the permeability was small.The actual width is less than the theoretical values of 0.50 mm and 1.00 mm.And the UV-induced thermochromic performance of printed fabrics was consistent with that of anionic thermochromic polyurethane.The fabric was double-faced finished,and the thermochromic polyurethane paste was printed on the cotton fabric side by screen printing.The self-made graphene paste was printed on the other side to obtain the electro-thermochromic fabric.The temperature of electro-thermochromic fabric?169??only reached about 20?for 2 min when the voltage was 2 V,and the surface temperature increased by only 19%when the voltage was increased to 6 V.When the voltage was higher than 8 V,the surface temperature of the fabric increased significantly and the surface temperature of the fabric reached 72.5?when the applied voltage reached 16 V.And the temperature of electro-thermochromic fabric reached 34.8?,44.0? and 56.5?at 20 s,30 s,and 50 s when the operated voltages was 10 V,12 V,and 14 V, respectively.Moreover,the surface temperature of electro-thermochromic fabric was inversely proportional to the resistance of the sample at a voltage of 12 V.Electro-thermochromic fabrics had good fatigue properties at a voltage of 12 V.The temperature rose to about 42?within 45s for 5 cycles.And the electro-thermochromic fabrics were red after 254 nm UV induction.When the applied voltage reached 12 V or above,the red disappeared.And it has obvious electro-thermochromic performance,which paves the way for smart wearable textiles.