Preparation And Properties Of Light-responsive Self-healing Cellulose Nanocrystals Modified Fluorinated Polyacrylate With Short Fluorocarbon Chain

In recent years,with the increase of people’s awareness of environmental protection,the water-based short fluorocarbon chain fluorinated polyacrylate has become a research hotspot.However,due to the short fluorocarbon chain,the water and oil repellency of polymers is not satisfactory,restricting their application.In addition,the polymer materials may be damaged by scratching during use,thereby shortening their service life.To solve the above problems,in this paper,the light-responsive self-healing cellulose nanocrystals modified fluorinated polyacrylate with short fluorocarbon chain emulsion was synthesized by Pickering emulsion polymerization using modified cellulose nanocrystals with light-responsive amphiphilic block polymer as stabilizer.The lightresponsive amphiphilic block polymer was synthesized by reversible additionfragmentation chain transfer(RAFT)polymerization.The Pickering emulsion polymerization can not only avoid the adverse effects of the migration of traditional small molecule emulsifiers on the properties of emulsion and film,but also combine the rough structure formed by cellulose nanocrystals with low surface energy stemmed from fluorine,improving the water and oil repellency and mechanical properties of short fluorocarbon chain fluorinated polyacrylate.In addition,introducing 7-(4-vinylbenzyl)-4-methylcoumarin(VBMC)into short fluorocarbon chain fluorinated polyacrylate endowed polymer with excellent self-healing properties by the reversible light-dimerization of coumarin groups.The specific research contents were as follows:(1)The light-responsive amphiphilic triblock copolymer,poly(2(dimethylamino)ethyl methacrylate)-b-poly(glycidyl methacrylate)-b-poly(2,2,3,4,4,4-hexafluorobutyl acrylate)-co-7-(4-vinylbenzyloxy)-4-methylcoumarin)(PDMAEMA-b-PGMA-b-P(HFBA-co-VBMC))was synthesized by RAFT polymerization.The structure and composition were determined by FT-IR and 1H-NMR.The molecular weight and molecular weight distribution index of the polymer were 1.40×103 g/mol and 1.32,respectively.In addition,the effects of different reaction conditions on RAFT polymerization of hexafluorobutyl acrylate and 7-(4-vinylbenzyl)-4-methylcoumarin were studied.The results showed that when the polymerization temperature was 70℃,the molar ratio of HFBA-co-VBMC to PDMAEMA-b-PGMA-RAFT was 75,the molar ratio of AIBN to PDMAEMA-b-PGMA-RAFT was 0.25,and the molar ratio of HFBA to VBMC was 6:4,the conversion rate of HFBA and VBMC monomers was the highest,and the linear correlation coefficient of the first-order kinetic fitting curve for the conversion rate was 0.9992,indicating high controllability of the polymerization.The PDMAEMA-b-PGMA-b-P(HFBA-co-VBMC)was grafted to the surface of CNCs to prepare poly(2-(dimethylamino)ethyl methacrylate)-gcellulose nanocrystal-g-poly(2,2,3,4,4,4-hexafluorobutyl acrylate)-co7-(4-vinylbenzyloxy)-4-methylcoumarin)(PDMAEMA-g-CNC-g-P(HFBA-coVBMC)(MCNCs)).FT-IR and XPS results showed that polymer was grafted on MCNCs surface.XRD analysis showed that polymer grafting occurred only on the surface of CNCs and did not damage CNCs crystal structure.TEM results showed that MCNCs presented a "nanorod-like" shape and were larger than CNCs.In addition,the light-responsive properties,dispersion and wettability of CNCs and MCNCs were characterized by the UV-vis,DLS,surface tension measurements and so on.Compared with the CNCs,it was found that the MCNCs had the light-responsive properties,the water contact angle of the MCNCs could reach 81.0°,and the surface tension of MCNCs aqueous could be obviously reduced with the increase of the MCNCs dosage,indicating MCNCs as Pickering stabilizers possessed the excellent emulsifying ability.(2)The oil-in-water(O/W)Pickering emulsion was prepared by using MCNCs as stabilizer,acrylate monomers as dispersed phases,and water as continuous phase.The experiment results were as follows.When the reaction temperature was 60℃,the molar ratio of hydrophobic monomer HFBA to VBMC was 6:4,the molar ratio of hydrophilic monomer DMAEMA to hydrophobic monomers(HFBA and VBMC)was 2:1,and the polymerization degree ratio of hydrophilic segment PDMAEMA to hydrophobic segment P(HFBA-co-VBMC)was 150:75,the water contact angle of MCNCs was 85.9℃,showing the excellent wettability and emulsification ability.The average size of Pickering emulsion was 5.32 μm.The correlation between the composition of hydrophilic segments and light-responsive fluorinated hydrophobic segments and the wettability and emulsifying properties of modified cellulose nanocrystals was clarified.Furthermore,when the ratio of oil to water was in the range of 1.0:2.0～1.0:4.0,Pickering emulsion was stable.With the decrease of pH value and the increase of MCNCs dosage,the volume fraction of emulsion layer of Pickering emulsion gradually increased,the size of emulsion gradually decreased,and the size distribution became more uniform.MCNCs showed good emulsification ability for petroleum ether with low polarity and benzene possessed similar composition to the MCNCs.The mechanism of MCNCs stabilized Pickering emulsion was proposed.(3)The light-responsive self-healing cellulose nanocrystals modified fluorinated polyacrylate with short fluorocarbon chain emulsion was prepared by Pickering emulsion polymerization using MCNCs as stabilizer,MMA,BA,HFBA,SMA,MTAC and VBMC as oil phase.The results showed that when the molar ratio of hydrophobic monomers HFBA to VBMC was 6:4,the molar ratio of hydrophilic monomer DMAEMA to hydrophobic monomers(HFBA and VBMC)was 2:1,and the polymerization degree of hydrophilic segment PDMAEMA and hydrophobic segment P(HFBA-co-VBMC)was 150:75,the stirring speed was 220 r/min,the dosage of AIBA was 1.0%,the pH value was 1.02,the dosage of MCNCs was 1.0%,the dosage of MTAC was 5%,the mass ratio of BA to MMA was 6:4,the dosage of HFBA was 6%,the dosage of SMA was 3%,and the dosage of VBMC was 3%,The emulsion had the larger monomer conversion and the smaller gel rate.The latex particles showed the smaller size and the narrower size distribution.TEM results showed that the composite latex particles showed a core-shell structure,in which the fluorinated polyacrylate was the core and MCNCs were the shell.The polymerization mechanism of MCNCs stabilized Pickering emulsion was proposed.(4)The water and oil repellent properties,mechanical properties,rheological properties,stress relaxation properties,thermal properties and selfhealing properties of the light-responsive self-healing cellulose nanocrystals modified fluorinated polyacrylate with short fluorocarbon chain latex film were tested and analyzed.When the stirring speed was 220 r/min,the dosage of AIBA was 1.0%,the pH value was 1.02,the dosage of MCNCs was 1.0%,the mass ratio of BA to MMA was 6:4,the dosage of MTAC was 5%,the dosage of HFBA was 10%,the dosage of SMA was 3%,and the dosage of VBMC was 3%,the maximum contact angles of the latex film to water and oil were 118.5° and 101.7°,respectively.The results of SEM and AFM studies indicated that combining the low surface energy of short fluorocarbon chain fluorinated polyacrylate with the rough structure of MCNCs endowed the latex film with excellent water and oil repellency.In addition,when the dosage of MCNCs was 1.0%,the mass ratio of BA to MMA was 6:4,the dosage of HFBA was 10%,the dosage of SMA was 3%and the dosage of VBMC was 3%,the maximum tensile strength and elongation at break of the latex film were 6.82 MPa and 556.76%,respectively.The loading-unloading cycle test results showed that when the dosage of MCNCs was 1.0%,the mass ratio of BA to MMA was 5:5,and the dosage of VBMC was 5%,the latex film presented a large dissipation energy.After standing for 5 hours,the peak stress of the latex films containing 1.0%MCNCs for loading-unloading curve could be restored about 93%of the original latex film,demonstrating excellent stress recovery ability.The results of rheological properties showed that the storage modulus(G’)and loss modulus(G")of latex film tended to increase with the increase of frequency.The complex viscosity(η)tended to linearly decrease with the increase of frequency,showing a shear thinning phenomenon,belonging to the non-Newtonian fluid behavior.And G’ was greater than G",indicating that the latex film mainly underwent elastic deformation.Meanwhile,G’ and G" could significantly increase with the increase of crosslinking sites and rigidity of the latex film.The research results of stress relaxation showed that the increase of crosslinking sites in latex films would limit the movement of polymer molecular chains,resulting in an extension of stress relaxation time.The research results of thermal performance showed that within a certain range,increasing the MCNCs dosage,HFBA dosage,VBMC dosage and mass ratio of BA to MMA were beneficial to improve the thermal stability of latex film.The research results of self-healing performance showed that when the dosage of MCNCs was 1.0%,the mass ratio of BA to MMA was 6:4,the dosage of SMA was 3%,and the dosage of VBMC was 3%,the scratches on the surface of the latex films could be completely repaired,and the latex film could achieve multiple healing.The reversible dimerization of coumarin gave the latex film excellent self-healing properties.(5)The light-responsive self-healing cellulose nanocrystals modified fluorinated polyacrylate with short fluorocarbon chain emulsion was applied to leather finishing.The water and oil repellency,abrasion resistance,self-healing properties,mechanical properties,water vapor permeability and air permeability of the coated leather were tested and analyzed.The results showed that when the pH value was 1.02,the dosage of MCNCs was 1.0%,the mass ratio of BA to MMA was 6:4,the dosage of MTAC was 5%,the dosage of HFBA was 10%,the dosage of SMA was 3%and the dosage of VBMC was 3%,the maximum contact angle of coated leather to water and oil were 119.9° and 99.6°,respectively.The abrasion resistance results showed that coated leather exhibited excellent abrasion resistance when the dosage of MCNCs was 1.0%.The abrasion resistance of coated leather was gradually increased with the increase of the MTAC dosage and VBMC dosage and the decrease of the mass ratio of BA to MMA.The self-healing performance results showed that when the dosage of MCNCs was 1.0%,the mass ratio of BA to MMA was 6:4,the dosage of SMA was 3%,and the dosage of VBMC was 3%,the coated leather had the best selfhealing properties.EDS results showed that the emulsion had good film forming properties and could form a uniform coating on the leather surface.Compared with uncoated leather,the water vapor permeability and air permeability of coated leather were reduced,but the tensile strength and elongation at break were increased.