Study On The Construction And Performance Of Graphene/Waterborne Polyurethane Functionalized Synthetic Leather Coatings

Synthetic leather with textile fabrics as base and polyurethane?PU?as coating has a history of more than 80 years and is widely used in every aspect of our daily life.Prepared with solvent PU as raw materials,the traditional PU synthetic leather can't solve the problems about organic solvent volatilization and pollution.Therefore,preparing high-performance and multifunctional coating using eco-friendly and functional materials are extensively studied as a new and high-technology in synthetic leather industry.Waterborne polyurethane?WPU?,using water as medium,is non-toxic and eco-friendly.However,it has some drawbacks,such as poor mechanical properties,low abrasive resistance and hydrolysis resistance.With excellent mechanical properties and electrical properties,graphene?G?can be applied to improve the mechanical properties,heat stability and conductivity of PU base.Therefore,graphene modified WPU has become research focus and is in great demand for the sustainable development of the national industry.Based on the idea of being eco-friendly and enhancing product-addition value,this study aims to prepare eco-functional fabric coating through graphane,graphane oxide?GO?functional modification WPU and modified WPU.As a result,a set of production technology systems of eco-functional coating materials for replacing solvent PU are developed.The research involve the fields of WPU preparation,GO preparation and its functional modification,graphene/WPU composites,WPU dry film form and wet solidification film mechanism,mainly focusing on the following five aspects:?1?A stable graphene aqueous solution was prepared by using PVP as a dispersing agent,and G/WPU3751,G/WPU6156 composite materials were prepared by solution blending method,and the films were formed by drying film formation and wet solidification formation,respectively.The relationship between the structure and properties of composite films was studied and the mechanism of dry and wet solidification formation were clarified.The results are shown as below:When G additive amount was 1.0%of WPU3751 mass,graphene dispersed uniformly into WPU.The film presented better performance:its tensile strength increased by 43.9%than that of blank film;the elongation at break reached 388%;the surface resistivity reached 5.05×10⁶?,reducing by 5orders of magnitude than that of blank film.The water absorption of formed film decreased and the abrasive resistance increased obviously.When G additive amount was 0.8%of WPU6156 mass,wet solidification time was 6⁷ min,the formed film foam became uniform.The wet film formation is generally lower in mechanical strength but the tensile strength is 97.8%higher than that of the blank film.The tensile strength of formed film incresaed by 84.5%,and the surface resistivity decreased by 4 orders of magnitude.The composite membrane has good air permeability and water vapor permeability,and has a good foam structure and hand feeling.It was found that graphene addition has a significant impact on the microstructure and performance of formed film.Moderate graphene addition can improve WPU mechanical properties and electrical properties,increasing coating abrasive resistance significantly.?2?GO/HWPU was synthesized by acetone method with IPDI,polyether glycol,GO and HPAE as basic materials,DMPA as hydrophilic chain extender,and the influence of GO additive amount on formed film properties were studied.The research results indicate the following:GO with interlayer space?0.83 nm?and lamella thickness?1² nm?was prepared by modified Hummers method.And GO microstructure was analyzed by XPS,XRD,TEM and AFM.FT-IR shows that GO was successfully grafted into HWPU molecule.When the added amount of GO was 0.6%,the thermal properties of GO/HWPU complex film were improved,increasing by 48.67?than the thermal decomposition temperature of pure HWPU;its tensile strength and elongation at break increased by 79.3%,28.7%respectively;Composites volume resistivity was 7.76×10⁹?·cm.Above results indicate that GO has better mechanical enhancing properties.However,because of the existence of oxygen-containing groups?-O-?-COOH and-OH?on the GO surface,the conjugated structure was destroyed,leading to the poor conductivity of GO.Although the WPU electrical insulating property can be reduced by in-situ,however,only anti-static electricity effect GO/HWPU was improved.?3?Sulfonated modified graphene?SGO?was prepared using 2-chloroethyl sulfonate to modify GO,and the hydrophilic sulfonic acid group was introduced on GO with good dispersibility;SGO is a hydrophilic chain extender in-situ method to prepare SGO/WPU composites and study film-forming properties.FT-IR and XPS show that–SO₃^-groups were introduced to GO surface by covalence modification.SEM,TEM and AFM show that nanoscale lamellar structure was obtained.FT-IR analysis indicates that SGO was chemically grafted into PU macromolecule.TEM verifies that SGO dispersed uniformly in the WPU and were in nanoscale lamellar morphology.XRD shows that the influence of SGO addition on PU degree of crystallinity is not obvious.When the added amount of SGO was 0.8%,SGO/WPU complex film tensile strength was enhanced by 46.5%than that of blank film.What's more,SGO dispersed uniformly into WPU and was linked by covalent bond and hydrogen bond with PU molecules,improving the abrasive resistance of the complex film significantly.SGO is added to the WPU and the sulfonic acid group is introduced so that the SGO/WPU has a good self-foaming effect and can be used as a synthetic leather foaming layer resin.?4?GO was modified by epichlorohydrin?ECH?to obtain epoxidation modified graphene oxide?EPGO?.Using WPU as basic resin,EPGO as nanofiller mixed with WPU,EPGO/WPU complex film was prepared.The effects of EPGO dosage on formed film enhancing abrasion resistance were studied.The results are as follows:more epoxy groups were introduced on the surface of GO by ECH reacting with GO carboxyl.TEM experiment verifies that prepared EPGO has nanoscale lamellar structure while its thickness increased compared with that of GO.In the process of dry method formed film,epoxy group of EPGO first reacted with carboxyl of WPU molecules,then crosslinked between WPUs.XRD shows that EPGO and PU bonded fully in two phase interface to make modified graphene materials crystal arrangement more complete.Formed film microstructure was observed by hyperfocal distance microscope.It was further confirmed that EPGO dispersed uniformly into WPU.With its big area dimension and epoxy group and PU molecules crosslinking together,three-dimensional network structure appeared between molecules.So it can be concluded that coating abrasive resistance increased obviously with the increase of EPGO dosage.?5?Diethylenetriamine?DETA?was first used to modify GO.Then IPDI,PTMEG2000 were used as raw materials,DMPA and NGs as chain extender to synthesize NGs/WPU by in-situ polymerization and dewatering antistatic coating was prepared.The effects of NGs addition on formed film properties were studied.The results are as follows:FT-IR and XPS show that active amino groups were introduced to GO surface by amino group modification.TEM shows that NGs from the lab has nanoscale lamellar structure.But its thickness increased than that of GO.By hyperfocal distance microscope,it can be seen that NGs dispersed uniformly to WPU.With its big area dimension and amino group and PU molecules link together,presenting three-dimensional network structure between molecules.When NGs addition was 0.9%,the complex film volume resistivity turned to 7.41×10⁷?.cm,reducing by 5 order of magnitudes than that of blank film.Its static contact angle from 61.4°increased to 138.8°,indicating that the coating has good dewatering effect.NGs addition can significantly increase coating hydrophobicity and hydrolysis resistance,making their respective merits complementary to each other.Thanks to the above merits,the coating materials exhibited unique functionality such as dewatering,anti-static electricity,etc.Ultimately,the fabric coating and synthetic leather are fully upgraded.This paper focuses on the systematical study of the following aspects:1)graphene/GO functional modification,2)preparation of functional graphene/WPU and functional coating design,3)WPU dry method and wet method forming film mechanism.The results are helpful to the research of the preparations of graphene functional modification and WPU/graphene composites.It also plays an important role in promoting the development of ecological functional synthetic leather processing and manufacturing technology.