Preparation And Property Of Waterborne Polyurethane/Polyacrylate Clear Coatings

~Polyurethane (PU) is one of the most versatile materials in the world today,which contains a significant number of urethane groups (-HN-COO-) and ureagroups (-NH-CO-). The molecular chains can be easily to form compact networkdue to the hydrogen bonds between the urethane groups, so the PU films havebetter abrasion resistance, flexibility, low temperature and chemical resistance. Inthis study, a series of silane and acrylic monomers modified PU emulsions andfilms were prepared and their properties were discussed according to the recentstudy of the waterborne PU. The prepared PU emulsion can be used as mainbinder in clear coatings to obtain a better performance of clear coatings, and theycan be used in the surface of paper, wall and wood. The main works in this studyinclude the following parts:(1) A series of γ-Methacryloxypropyl trimethoxy silane modifiedwaterborne polyurethane(MPU) was synthesized by using isophoronediisocyanate(IPDI), polytetrahydrofuran glycol(PTMG), γ-Methacryloxypropyltrimethoxy silane(MEMO) as raw materials and aziridine was also used toimprove the property of the film. The azo initiators were used to initiate theMEMO react with the PU prepolymer. The structure was characterized byATR-FTIR. Dynamic light scattering (DLS), Multi-function mechanical testingmachine and Thermo gravimetric analysis (TGA) were used to evaluate theeffect of MEMO content on emulsion size, the mechanical properties andthermal stability of the MPU films. The X-ray photoelectron spectroscopy (XPS)was used to analysis the element of the film surface. The crystallinity and contactangle were studied. The ATR-FTIR results showed that MEMO was successfullyintroduced into the PU chains. With the increment of the MEMO content, theparticle size decreased gradually. The results also showed that when w(MEMO)=5.67%,w(COOH)=1.5%,w(AZ)=2%, the water absorption was lowto14.84%, the maximum tensile strength was17.334Mpa, the breakingelongation was232.56%. XPS result indicated that the film surface was rich insilane content. The surface energy and the crystallinity of the polyurethane filmwere decreased while the thermal stability was enhanced. The folding strengthcan be reached to90times, while the penetration time to65s. The SEM showsthat the MPU emulsion’s film formation property on the paper surface was good.(2) Polyurethane/polyacrylate (EPUA) composite emulsions weresynthesized based on the presence of preformed polyurethane chains. Glycidylmethacrylate (GMA), an acrylate monomer, was introduced into the system.Rheology measurements, Surface tension measurements, Dynamic lightscattering (DLS) and Transmission electron microscope (TEM) were used tocharacterize the property of the composite emulsions. The EPUA with acrylicmonomers displays non-Newtonian, shear-thinning behavior during shear ratesweep experiment. Surface tension measurements assured the surface activitiesof the polyurethane emulsion. Normally surface tension decreases as thesurfactant concentration increases, and comes to equilibrium above the criticalmicelle concentration (CMC). The surface tension came to equilibrium at47.98mN/m when the mass concentration is0.3%. Dynamic light scattering(DLS) result showed that the average diameters and polydispersity wereincreased with the increment of GMA content. A core-shell structure is observedby TEM. Attenuated total reflection Fourier transform infrared (ATR-FTIR) andX-ray photoelectron spectroscopy (XPS) were used to test the polymer structureand element content. The tensile test and Thermo gravimetric analysis (TGA)were used to analysis the water resistance, mechanical property and thermalstability of the films. ATR-FTIR analysis ascertains the formation of EPUA, andXPS result indicated that the upper surface was rich in PU phase. The peakdeconvolution results of XPS also confirmed the formation of EPUA. With thew(GMA) increases from0%to3%, the water absorption decrease from18%to7.8%, and the THF absorption decrease from30.1%to15.3%. Whenw(GMA)=3%，w(PA)=20%, the tensile strength was up to5.825MPa, and the gelcontent was also in a high level. TGA of the membranes showed that the thermalstability enhanced and the decomposition temperature was much higher than the pure PU membrane, due to the reaction between the carboxyl groups and theepoxide groups. Atomic force microscopy (AFM) observation performed thatwith the increment of GMA content, the quantity of hills and valleys in thesurface structure were decreased and the extremely flat surface was obtained.The waterborne coating was prepared by using the synthesized emulsion, and thetest showed that with the increment of the GMA, the pencil hardness, gloss andabrasion resistance were all increased, the impact resistance was decreased, thelight loss resistance was good, and it can be used in wall coatings.(3) Novel polyurethane/polyacrylate (PUA) composite emulsions weresynthesized by soap-free emulsion polymerization method from methylmethacrylate (MMA), butyl acrylate (BA), and2-Hydroxyethyl acrylate (HEA)in the presence of PU as seeds and a polymerizable emulsifier-Allyloxy hvdroxylpropanesulfonic salt (AHPS). Surface tension measurements, Dynamic lightscattering (DLS) and Transmission electron microscope (TEM) were used tocharacterize the property of the composite emulsions. With the increment of theAHPS content, the stability of the emulsion was good. Compared with thesurface tension of AHPS, the surface tension of all emulsions prepared by AHPSis very high (from62.5to65.6mN·m-1) and closes to that of water, it can be saidthat large part of AHPS is joined polymerization with monomer, only small partanchored on the surface of the emulsion particles. With augment of the AHPS,the conversion ratio increased sharply from89.70%to95.78%, while theaverage particle diameters of the PUAS emulsion particles, decreased from102nm to83nm as the AHPS amount increased from1to4wt%. A core-shellstructure is observed by TEM. Fourier transform infrared (ATR-FTIR) and X-rayphotoelectron spectroscopy (XPS) were used to test the polymer structure andelement content. The tensile test and Thermo gravimetric analysis (TGA) wereused to analysis the water resistance, mechanical property and thermal stabilityof the films. Fourier transform infrared spectroscopy (FT-IR) result shows thatAHPS was introduced into the PUAS chains. X-ray photoelectron spectroscopy(XPS) analysis showed that sodium was preferably enriched on the surface oflatex particles. With the increment of the AHPS content, the tensile strengthincreased, and the breaking elongation decreased. TGA of the films showed thatthe thermal stability enhanced. The DSC and DMA tests show that Tg of the films increased gradually and the compatibility between the components of thePU and PA is increased with augment of AHPS amount in polymer. Atomic forcemicroscopy (AFM) observation performed the extremely flat membrane.In this paper, we are aimed to explore PU coatings with better properties, soas to satisfy the meetings of the coatings. A series of silane, glycidylmethacrylate (GMA) and allyloxy hvdroxyl propanesulfonic salt(AHPS) wereused to modify PU emulsions and films were prepared and their properties werediscussed according to the recent study of the waterborne PU, and the modifiedPU with core-shell structure were successfully obtained. The latex formationprocess and film-forming mechanismwere also discussed.