Study On Preparation And Properties Of Polyurethane Modified Sodium Alginate Finishing Agent

In recent years,environmental pollution and energy shortage caused by the extensive use of fossil fuels have attracted widespread attention.Today,the development and improvement of sustainable natural resources has become a research hotpot of scholars all over the world in advocating sustainable development.Sodium alginate?SA?is a wide-ranging and abundant biomass poly-saccharide raw material,which not only has the advantages of biodegradability,gelation,flocculation and thickening,but also has good biocompatibility and film forming properties.It has been widely used in food packaging,heavy metal ion adsorption and biological tissue engineering.However,the application of sodium alginate material is greatly limited because of its poor water resistance and brittle film-forming.In order to overcome these shortcomings,it is necessary to modify it.In this work,epoxy terminated polyurethane?GPU?was grafted on the structure of sodium alginate,and epoxy ring opening reaction was occurred from grafting polyurethane onto the long chain of sodium alginate to improve the brittleness and hardness of the film.At the same time,because both sodium alginate and anionic polyurethane contain a lot of hydroxyl groups,calcium ion is used to cross-link the grafted product,which greatly improves the water resistance of the modified film.In this paper,polyurethane prepolymer was synthesized by isofluorone diisocyanate?IPDI?,polyether 1000?PPG1000?and 2,2-dihydroxymethyl propionic acid?DMPA?by step-by-step polymerization.Then epoxy-terminated polyurethane modifier was synthesized with 1,4-butanediol?BDO?as chain extender and propylene oxide as end-capping agent.Infrared characterization showed that epoxy-terminated polyurethane was obtained.Then the sodium alginate modified by epoxy terminated polyurethane?SA-g-GPU?was prepared by grafting reaction under alkaline conditions.The effects of reaction time,reaction temperature,pH value and the amount of modifier on the properties of modified sodium alginate emulsion and film were mainly investigated.The results showed that the modified sodium alginate emulsion had good storage stability and centrifugal stability,and the viscosity of the emulsion was 465.0mPa?s when the reaction temperature was 75?,the reaction time was 60 min,the pH was 9,and the addition amount of modifier GPU was 50%.The grafting ratio of the modified product increased first and then decreased slightly with the increase of GPU content,and the highest grafting ratio could reach 18.01%.When the amount of GPU changed from 10%to 50%,the diameter of the emulsion decreased from 300.5 nm to 127.0 nm,the tensile strength of the film decreased from 88.44 MPa to 12.51 MPa,the elongation at break increased from6.87%to 41.82%,and the water contact angle increased from 55°to 77.1°.The water vapor transmittance of the film decreased from 2450.28 g?m^-2?24h^-1 to1078.74 g?m^-2?24h^-1,and the softness increased from 5.3 to 6.2,and the film shows excellent transmittance.The above indicators can be efficiently controlled according to the amount of GPU added.The properties of GPU modified sodium alginate structure and films were characterized by nuclear magnetic resonance spectroscopy?¹H-NMR?,Fourier transform infrared spectroscopy?FT-IR?,X-ray diffraction?XRD?,gel permeation chromatography?GPC?,scanning electron microscopy?SEM?and thermogravimetric?TG?.¹H-NMR and FT-IR proved that GPU was grafted onto SA;XRD measurements showed that SA has diffuse amorphous broad peaks and low crystallization.When GPU was introduced,the crystalline structure of the modified films was changed and the crystallization was decreased;GPC analysis showed that the introduction of GPU increased the molecular weight of SA;SEM results showed that the cross-section of SA films was smooth and compact,and the cross-section of SA-g-GPU films was rough and porous.TG results showed that the introduction of GPU improves the thermal stability of SA film at low temperature?30³00??and decreases its stability at high temperature?300⁶00??.At the same time,SA-g-GPU film was crosslinked with calcium chloride to prepare cross-linked modified film?CaA-g-GPU?,which was used in leather finishing.The properties of CaA-g-GPU film and its corresponding finishing properties were investigated.It was found that the tensile strength of CaA-g-GPU films was 33.48 MPa,the elongation at break was 40.51%,the swelling degree was 16%,and the loss rate was 6.31%when the concentration of calcium chloride was 3%and the cross-linking time was 3 min.The glossiness of the coatings is 8.0 Gu,the dry rubbing grade is 4,the wet rubbing grade is 3,and the wear resistance is 2.The modified cross-linking coatings have good dry rubbing resistance and wear resistance.FT-IR measurements showed that cross-linking reaction was occurred on the calcium ion and carboxylic acid radical of sodium alginate;XRD measurements showed that the crystallization of the films decreased due to calcium cross-linking;SEM results showed that the faults of the films has more complex network structure and compact cross sections by cross-linking with calcium ions,as well as the thermal stability of the films increased,and the heat loss rate decreased from 81.52%to 77.97%.