Study On Preparation And Characterization Of Waterborne Cellulose Acetate Emulsion

Solvent-based coatings pose a serious hazard to the environment and human health.Therefore,research and development of water-based coatings with water as the medium,low price,and green environmentally friendly volatile organic compounds are the main development directions of polymer materials.Cellulose acetate(CA)is a biodegradable natural polymer material with excellent stability,acid resistance and easy film formation.It is used in coatings,adhesives,textiles and other fields.However,cellulose acetate is insoluble in water and only dissolves in some organic solvents.During the process of use,a large amount of volatile organic compounds are generated,which is extremely harmful to the environment.In this paper,CA is used as a substrate to form a-NCO-terminated hydrophilic prepolymer by polymerizing an isocyanate group(-NCO)on a bridging agent with a hydroxyl group(-OH)on a hydrophilic monomer,and then on the prepolymer.-NCO reacts with-OH on the CA molecular chain,introduces the hydrophilic prepolymer into the CA molecular chain to make it hydrophilic,and can disperse itself in water to prepare an aqueous cellulose acetate emulsion.The emulsion is expected to be used in the waterborne coatings industry to develop new products for waterborne coatings.The main research contents of this thesis include the following parts.(1)Preparation and Properties of Aqueous cellulose acetate(WCA)Emulsion with HDI(hexamethylene diisocyanate)as Bridging AgentA WCA emulsion was prepared by grafting DMBA(dimethylol butyric acid)and HDI copolymerized product onto CA molecular chain.The effects of DMBA and HDI content on WCA emulsion and film properties were investigated by single factor experiment.The results show that the n(HDI):n(CA)=1.0?1,n(HDI):n(DMBA)=2?1.4,the prepared WCA emulsion has smaller particle size and is stable.Good to store,can be stored for 86 days at room temperature,average particle size and dispersion coefficient(PDI)are 80 nm and 0.075,respectively,water absorption of film is 1.95%,water contactangle is 107.5 °,compared with CA,WCA coating surface more flat.The thermal stability of the film has also been significantly improved.(2)Preparation and Properties of aqueous cellulose acetate(HIWCA)Emulsion with HDI and IPDI(Isophorone Diisocyanate)as Bridging Agent.The HIWCA aqueous cellulose acetate emulsion was prepared via the method self-emulsification.With CA as film-forming,HDI and IPDI as the bridging agent,and DMBA as the hydrophilic monomer.The results show that when n(HDI):n(IPDI)=7:1,the emulsion and coating film have the good performance.Infrared spectroscopy(FT-IR)showed that the-NCO in IPDI and HDI had been completely reacted,and the hydrophilic group was successfully introduced into the CA molecular chain.The nanoparticle size analyzer showed that the average particle size and PDI of the HIWCA emulsion were 68 nm and0.06,respectively.Transmission electron microscopy(TEM)showed that the microstructure of the HIWCA emulsion particles was a core-shell structure.We tested the film properties by scanning electron microscopy(SEM)and atomic force microscopy(AFM)to show that the surface roughness of the HIWCA film was lower than that of the CA film;The contact angle of the HIWCA film was114.5°,which was 46.2° higher than that of the CA film;the thermogravimetric analyzer(TGA)showed that the prepared HIWCA had better thermal stability than the CA film.The above analysis showed that the obtained aqueous HIWCA emulsion was stable and the coating film performance was good.(3)Preparation and properties of polyvinyl alcohol/aqueous acetate fiber composite emulsionOn the basis of the preparation of HIWCA emulsion,in order to further improve emulsion stability and film properties,polyvinyl alcohol modified aqueous cellulose acetate fiber was prepared by adding physical solution to polyvinyl alcohol(PVA)solution with good stability and membrane properties.It was confirmed by FT-IR and TEM that the target product had physical blending characteristics.The effects of PVA amount ranged from 4 to 20wt% on the properties of the composite emulsion and film were investigated.The results show that the particle size of the emulsion gradually decreases with the increase of the PVA mass fraction.When w%(PVA)=12%,the emulsion has an average particle diameter of 58.6 nm,a dispersion coefficient of 0.033,good stability,and can be stored at room temperature for 98 days,and the film contact angle is108.7°.The tensile strength was 14 MPa and the elongation at break was329.9%.In addition,the PVA/HIWCA film was found to have good thermal stability by thermogravimetric analyzer(TGA)testing.