| Leather finishing is praised as the crowning touch that can not only improve the appearance and style of leather,but enhance its comfort and durability,and extend its service life.Nitrocellulose,as one of the four leather finishing agents,has some shortcomings such as being difficult water-based,environment unfriendly,flammable and explosive.Cellulose acetate,which is also a cellulose derivative,has application potential in leather finishing agents due to its advantages such as non-toxicity,excellent film-forming performance,low price,and no nitrogen in the molecule.However,a similar disadvantage for cellulose acetate as cellulose is insoluble in water,limiting its application in leather finishing.Therefore,how to scientifically make cellulose acetate waterborne and further improve its comprehensive performance of the film coating would be of great significance for leather finishing.On this basis,cellulose diacetate(CDA)was used as the base material in this study.Firstly,the types of hydrophilic agents used for the preparation of CDA waterborne polymer emulsion were screened.Then,according to the structural characteristics of CDA,hexamethylene diisocyanate(HDI)was explored as the transforming agent to change the components’ control of emulsion particle sizes and coating properties by transferring reaction sites,converting reaction functional groups,adjusting the soft-hard ratio of molecular chain segments,and the modification of nano-SiO2.Carboxylate CDA waterborne polymer/SiO2 nano-composite emulsion(WCCDA/SiO2 nanocomposite emulsion),sulfonate CDA waterborne polymer/SiO2 nano-composite emulsion(WSCDA/SiO2 nanocomposite emulsion),carboxylate sulfonate CDA waterborne polymer/SiO2 nano-composite emulsion(WCSCDA/SiO2 nanocomposite emulsion)were prepared respectively.The structure characterization and properties test of these emulsions and corresponding films were performed.The finishing properties of three kinds of CDA waterborne polymer emulsion were tested by the leather finishing application experiment,and the test results were compared.The interaction mechanism of nano-SiO2 particles and the synergistic reaction of sulfonate hydrophilic agent A50 with carboxylate hydrophilic agent DMBA were analyzed and studied.The research contents of this paper include four aspects listed as follows:(1)Effect of hydrophilic agent on CDA waterborne polymer emulsion propertiesDihydroxymethylpropionic acid(DMPA),DMBA,A50,N,N-di(2-hydroxyethyl)-2-aminoethanesulfonate sodium(BES-Na),2,3-dihydroxy propyl sulfonate sodium(DHPA)and N-(2-aminoethyl)-2-aminoethanesulfonate sodium(AAS)were selected as hydrophilic agents respectively.These hydrophilic agents were introduced into CDA molecules by bridging agent IPDI to prepare CDA waterborne polymer emulsion.The results showed that the particle size and size distribution range of CDA waterborne polymer emulsion prepared by sulfonate hydrophilic agent A50 were relatively small,the solid content was high,and the storage stability of the emulsion was excellent.The coating film of CDA waterborne polymer emulsion prepared by carboxylate-type hydrophilic agent DMBA has high flexibility,strong hydrophobicity,and high elongation at break.(2)Study on WCCDA/SiO2 nanocomposite emulsionWCCDA/SiO2 nano-composite emulsion was prepared by using DMBA as a hydrophilic agent,HDI as conversion reaction sites and reactive functional groups,1,4-butanol(BDO)and polyether diol(N210)as flexible molecules to adjust the ratio of soft-hard segments of molecular chains.Nano-SiO2 was introduced into the system to improve the comprehensive performance of emulsion coating,and the interaction mechanism of nano-SiO2 was studied.The results showed that the optimal process of WCCDA/SiO2 nano-composite emulsion is as follows:1.00 wt%of nano-SiO2(8 nm),27.0 wt%of CDA,5.5 wt%of HDI,31.5wt%of IPDI,10.0 wt%of DMBA,33.0 wt%of N210,and 3.0 wt%of BDO.The average particle size of the WCCDA/SiO2 nano-composite emulsion was 178 nm with a narrow size distribution.The coating surface was compact and smooth,and the flexibility,adhesion,water resistance,yellowing degeneration resistance,mechanical properties,and thermal stability were excellent.Compared to nitrocellulose,the air permeability and water vapor permeability of leather samples coated with WCCDA/SiO2 nano-composite emulsion increased by 294%and 7.01%,and the water absorption rate decreased by 2.44%at 0.25 h and 16.54%at 24 h.When the WCCDA/SiO2 nano-composite emulsion is formed,the nano-SiO2 particles near the surface will spontaneously migrate to the surface of the coating,forming many small "mastoids" on the surface of the coating,resulting in the lotus leaf effect and improving the water resistance,medium resistance and yellowing resistance of the coating.(3)Study on WSCDA/SiO2 nano-composite emulsionWSCDA/SiO2 nano-composite emulsion was prepared by converting reaction functional groups and transferring reaction sites using A50 as a hydrophilic agent.The results showed that the average particle size of the WSCDA/SiO2 nano-composite emulsion was 109.5 nm.Compared with WCCDA/SiO2 nano-composite emulsion,the particle size was reduced by 68.5 nm,and the storage stability was improved.The adhesion,medium resistance,and yellowing resistance of the film were similar,but the water resistance,flexibility,tensile strength,and elongation at break were reduced.The air permeability and water vapor permeability of the leather after finishing were reduced by 10.78%and 1.59%,respectively.The water absorption rate increased by 1.36%at 0.25 h and 14.41%at 24 h.(4)Study on WCSCDA/SiO2 nano-composite emulsionWCSCDA/SiO2 nano-composite emulsion was prepared by converting reaction functional groups and transferring reaction sites using DMBA and A50 as the hydrophilic agent.The synergistic effect mechanism of sulfamate A50 on hydroxy-carboxylate DMBA was analyzed.The results showed that the optimal preparation technology of WCSCDA/SiO2 nano-composite emulsion is as follows:6.2 wt%of A50,5.6 wt%of DMBA,31.5 wt%of IPDI dosage.The average particle size of the WCSCDA/SiO2 nano-composite emulsion was 88.1 nm,which is smaller than both WCCDA/SiO2 nano-composite emulsion and WSCDA/SiO2 nano-composite emulsion.The flexibility,hardness,tensile strength,and elongation at the break of the film are significantly improved compared with WCCDA and SiO2 nano-composite emulsion and WSCDA and SiO2 nano-composite emulsion.Compared with the WCCDA/SiO2 nano-composite emulsion,the air permeability and water vapor permeability of the coated leather were increased by 3.59%and 1.94%,respectively.The water absorption rate decreased by 0.5%at 0.25 h and 0.82%at 24 h.The results showed that the carboxylate DMBA and sulfonate A50 were used as hydrophilic agents,and the stability of the nano-composite emulsion and the comprehensive properties of the film could be effectively improved through their synergistic action.The synergistic effect between A50 and DMBA is realized through hydrogen bonding.In conclusion,the problem of high steric hindrance and low reactivity of-OH of CDA molecules can be effectively solved by the method of transferring reaction sites and transforming reaction functional groups.The CDA waterborne polymer emulsion was prepared by using sulfonate and carboxylate as hydrophilic agents which combine the advantages of these two components,and an emulsion with better stability and comprehensive performances could be obtained.The introduction of nano-SiO2 provides CDA waterborne polymer emulsion coating with good medium resistance and yellowing resistance.This research is of great significance for the application of cellulose acetate waterborne polymer emulsion in leather finishing. |
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