水滑石改性聚氨酯清洁粉末涂料的结构和性能

Progress in Organic Coatings 95(2016)120–126Contents lists available at ScienceDirectProgress in OrganicCoatingsj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /p o r g c o atStructure and properties of polyurethane-based powder clear coatings systems modified with hydrotalcitesBarbara Pilch-Pitera a ,∗,MichałK˛edzierski b ,Ewa Olejnik c ,Szczepan Zapotoczny daFaculty of Chemistry,Department of Polymers and Biopolymers,Rzeszów University of Technology,al.Powsta´n ców Warszawy 6,35-959Rzeszów,Poland bIndustrial Chemistry Research Institute (ICRI),ul.Rydgiera 8,01-793Warsaw,Poland cFaculty of Foundry Engineering,AGH University of Science and Technology,ul.Reymonta 23,30-059Krakow,Poland dFaculty of Chemistry,Jagiellonian University,ul.Ingardena 3,30-060Krakow,Polanda r t i c l ei n f oArticle history:Received 9October 2015Received in revised form 24February 2016Accepted 5March 2016Keywords:Polyisocyanates Polyurethanes Hydrotalcites Delamination Powder coatingsa b s t r a c tIn this study,polyurethane powder clear coating systems consisting of polyester resin,blocked polyisocyanate and hydrotalcites (HT)intercalated with carbonate,aminododecanate,and ethylenedi-aminetetraacetate were examined.The blocked polyisocyanate crosslinkers for powder coatings were synthesized using trimethyhexamethylene diisocyanate (TMDI),formic acid,␧-caprolactam,dibutyltin dilaurate and triethylamine as catalysts.The powder coatings were investigated by atomic force microscopy (AFM)and X-ray diffraction analysis (XRD).The surface structure was correlated with the chemical structure of the coatings and macroscopic surface behavior:contact angle,surface free energy,gloss,elasticity,cupping,impact and scratch resistance,hardness as well as adhesion to steel surface.©2016Elsevier B.V.All rights reserved.1.IntroductionIn recent years,the development of organic coatings frequently involves the dispersion of inorganic nanoscale materials in a poly-mer matrix to improve the mechanical,physical and thermal properties at very low filler content [1].Although cationic clays are the most often investigated layered nanofillers,their anionic analogs,namely layered double hydroxides (LDHs,hydrotalcites)are also a subject of increasing interest.LDHs are compounds with the general formula:[Me I 2+1-x Me II 3+x (OH)2][A y −x/y (n H 2O)],where Me I and Me II denote divalent and trivalent metal cations,respectively.A typical example of this class is naturally occurring magnesium-aluminium hydroxycar-bonate Mg 6Al 2(OH)16[CO 3]·4H 2O,firstly reported by Hochstetter in 1842and named as hydrotalcite (HT)due to its talc-like appearance and high water content [2].Its chemical synthesis was accom-plished a century later by coprecipitation from a mixture of Mg and Al chlorides under basic conditions [3].HT was first manufac-tured on an industrial scale in 1966by Kyowa Chemical Industry Co.,Ltd.and it found many applications as basic catalyst,adsorbent and acid scavenger (e.g.heavy metal-free PVC stabilizer)or antacid drug [4].∗Corresponding author.E-mail address:barbpi@.pl (B.Pilch-Pitera).LDH particles are composed of positively charged layers formed by edge-sharing octahedra of divalent and trivalent metal hydrox-ides.The space between the layers contains water and anionic compounds compensating the electrostatic charge (Fig.1).The lay-ered structure of LDH and possibility of making them hydrophobic by intercalation of organic anions has inspired many researchers to investigate hydrotalcite as nanofiller in polymeric matrices [5–9].It was reported that the incorporation of few percent HT additive can give an improvement in the mechanical properties,thermal stabil-ity and fire retardancy of polymers [1,10–13].Akzo Nobel company introduced into the market a range of HT modified with fatty acids (Perkalite TM )as additives for polymeric materials [14].The high surface area and anion-exchange ability of LDH make them inter-esting for corrosion protection coating applications.To this aim,various corrosion inhibiting anions were inserted into LDH inter-layer and the resulting compounds were used for modification of coatings [15].Powder coatings are high quality finishing materials,which in contrary to solvent-based paints do not emit volatile organic com-pounds during the coating process.Despite over a half century of research and development in this field,there is still need to combine the suitable processing performance (low-temperature cure,storage stability,flow and film forming properties)with good mechanical properties as well as weather and UV resistance of the final coatings.One of the methods to improve the powder coating performance is the use of nanofillers,which added even/10.1016/j.porgcoat.2016.03.0090300-9440/©2016Elsevier B.V.All rights reserved.B.Pilch-Pitera et al./Progress in Organic Coatings95(2016)120–126121in a small amount can distinctly improve the material proper-ties.Various nanosized additives have been used for this purpose, including titania and hydroxyapatite[16,17],montmorillonite clay [18]or graphene[19].There are several examples of using hydrotal-cites as nanofillers in coating materials.Epoxy coating containing HT intercalated with tungstate or(2-benzothiazolylthio)succinic acid showed improved corrosion protection for metallic substrates [20,21].In the work of Fina et al.HT intercalated with lactate, gluconate,fatty acid and rosin were used as components of nanos-tructured intumescent coatings resulting in an improved thermal shielding performance[22]Hydrotalcite-based composites applied as a primer layer provided an excellent stone chip resistance to an automotive coating system[23].Also,the thermal and mechanical properties of acrylic-urethane UV curing coatings were improved by using HT intercalated with long alkyl sulfate anions [24].Recently,it was reported that organically modified HT can be delaminated in the polyester resin used as powder coating compo-nent[25].However,there is a lack of research papers on the effect of layered double hydroxide nanofillers on the properties of powder coatings.In this work,a series of hydrotalcite-type compounds interca-lated with various organic anions was used to modify the properties of polyurethane powder coatings.The dispersion of LDH in the poly-mer matrix was investigated by X-Ray diffraction analysis(XRD). Atomic force microscopy(AFM)was employed for visualizing the surface topography,adhesion and deformation of the cured coat-ings.In order to examine the influence of LDH additive on the properties of polyurethane powder coatings,the measurements of the contact angle,surface free energy,gloss,roughness,scratch and impact resistance,hardness,elasticity,cupping and adhesion to steel were carried out.The relationship between coating properties and LDHs content and type is discussed.2.Experimental2.1.Starting materialsVestanat TMDI−a mixture of2,2,4-and2,4,4-trimethyhexamethylene diisocyanate(TMDI)was purchased from Evonik Industries A.G.(Marl,Germany).Rucote102–polyester resin based on isophthalic acid and neopentyl glycol,acid value: 11–14mg KOH/g,hydroxyl value:35–45mg KOH/g,T g:59◦C (RU),was supplied by Bayer A.G.(Leverkusen,Germany).Formic acid100%from POCH(Gliwice,Poland),␧−caprolactam(C) from Zakłady Azotowe w Tarnowie–Mo´s cicach S.A.(Tarnów, Poland)and aminolauric acid from TCI were used.WorleeAdd 902(acrylate resin),Resiflow PH-240(polyacrylic resin adsorbed on silica)and WorléeAdd ST-70(stannous octoate(II))were provided by Worlée–Chemie G.m.b.H(Lauenburg,Germany). Benzoin and magnesium-aluminium hydrotalcite in carbonate form(Mg6Al2(CO3)(OH)16·4H2O)were purchased from Aldrich (Buchs,Switzerland).Magnesium nitrate hexahydrate,aluminium nitrate nonahydrate,zinc nitrate hexahydrate and ethylene-diaminetetraacetic acid were provided by POCh S.A.(Gliwice, Poland).2.2.Preparation of hydrotalcite-type LDH compoundsOrganically modified hydrotalcite compounds were prepared using coprecipitation method.In a typical procedure0.14mol amino acid and0.14mol sodium hydroxide were dissolved in 300ml water,then solution of0.28mol aluminium nitrate(or zinc nitrate)and0.14mol magnesium nitrate in200ml water was added at1ml/min.The pH of the reaction mixture was maintained at10 by addition of1M sodium hydroxide.The process was carried out under nitrogen atmosphere to prevent the undesired reaction of mixed hydroxide with carbon dioxide.The resulting suspension of HT precipitate was then aged by heating at75◦C.2.3.Synthesis of curing agent for powder coatingsPolyisocyanate was synthesized according to the procedure described in details in earlier reports[26,27].The synthesis con-sisted of three stages:preparation of urea polyisocyanate,synthesis of biuret polyisocyanate,and blocking reaction.Urea polyiso-cyanate was obtained in the reaction of diisocyanate and formic acid at the molar ratio of4:1in the presence of dibutyltin dilau-rate and triethylamine as catalysts(both at0.1wt%with respect to diisocyanate)at60±1◦C.In order to form biuret moieties,the reaction mixture was heated up to140±1◦C,stirred and refluxed during10h.Free NCO groups were blocked by use of␧-caprolactam(C)at thefinal stage.2.4.Preparation of powder compositions and coatingsHydrotalcites were added to the polyisocyanate during thefinal stage after completion of the NCO group blocking.The amount of hydrotalcite was selected in such a way as to make sure that its content in the coating was1and3%.The mixture of HT and PIC was heating to80◦C and sonicated during30min.The hot mixture of HT and PIC was cast onto a PTFEfilm,cooled and crushed intofine pieces.The lacquer compositions consisted of:blocked polyiso-cyanates,polyester resin Rucote102(the NCO:OH molecular ratio=1:1),degassing agents WorléeAdd902(1,5%)and benzoin (1%),PU catalyst WorléeAdd ST-70(0,5%)and levelling agent Resi-flow PH-240(3%).The mixture was milled and extruded in a co-rotating twin screw miniextruder EHP2×12Sline from Zamak(Kraków,Poland) and then pulverized to the average particle size of60␮m.Tem-perature distribution in the extruder was as follows:zone I—95◦C, zone II—110◦C,zone III—120◦C,adapter—125◦C.Screw rotational speed:was250r.p.m.Thefinal powder coating was applied by electrostatic gun PEM X–1controlled by EPG Sprint X(CORONA) from Wagner(Alstatten,Switzerland)to steel panels and cured at 170◦C for30min.The obtained coatings were named according to the hydrotalcite type and content e.g.,PU/1%Mg,Al-ALA stands for polyurethane(PU)containing1wt.%hydrotalcite Mg,Al-Ala.2.5.Measurements2.5.1.Elemental analysis and BET measurements of HTElemental analysis of LDHs was performed using a Series II CHNS/O Perkin-Elmer analyser.BET surface area and average particle size were determined by nitrogen sorption experiments conducted at ambient temperature using a Micromeritics TriStar II 3020automated gas adsorption analyzer.2.5.2.X-ray diffraction(XRD)Powder X-ray diffraction(XRD)patterns of LDHs were recorded using Bruker-AXS D8Advance Series2powder diffractometer working with Co-Ka radiation(k=1.79Å).Interlayer distance was calculated from Bragg’s Law using the d003peak from the diffrac-tion pattern.XRD patterns of powder coatings were recorded on a Philips PW1040diffractometer equipped with an X-Celerator detector using Cu-K␣1/␣2radiation.Data were collected between 5.0◦and73.0◦(2␪),with a step size of0.03◦(2␪)and a counting time of300s/step.122 B.Pilch-Pitera et al./Progress in Organic Coatings95(2016)120–1262.5.3.Concentration of NCO groupsThe typical dibutylamine method was employed.Excess of unreacted dibutylamine was titrated with aqueous HCl against bro-mophenol blue[18].2.5.4.ATR FTIRAttenuated total reflection-Fourier transform infrared exper-iments were carried out with aReactIR TM15spectrometer (Mettler-Toledo)combined with DS Series 6.3mm AgX Fiber Conduit TM and a DiComp TM(diamond-composite)sensor.The IR spectra were obtained in the650-2000cm-1range with an average of256scans per sample and a spectral resolution of4cm−1.The signal data were analysed with iC IR TM software version4.3.2.5.5.Atomic force microscopy(AFM)AFM measurements of coatings surface were performed in air on ICON+instrument(Bruker)Rusing PeakForce QNM mode (Quantitative Nanomechanical Property Mapping).For all the measurements the same silicon nitride cantilever(Bruker)with nominal spring constant equal to0.56N/m was used.2.5.6Determination of surface free energy(SFE)Surface free energy(␥s),was quantified using a contact angle goniometer made by Cobrabid-Optic.Diiodomethane and water were chosen as immersion liquids.Measurements were performed at22±1◦C.Surface free energy(SFE)was determined taking into account the measured contact angles for the coatings,by means of Owens-Wendt method[28].2.5.7.GlossA micro-TRI-gloss␮tester from Byk Gardner was employed, according to PN-EN ISO2813.2.5.8.HardnessRelative hardness of the coatings was determined by means of König Pendulum manufactured by BYK,in accordance with PN-EN ISO1522.Relative hardness value was determined as the ratio of the damping time of an oscillating pendulum supported on the coat-ing surface to the damping time of the pendulum supported on a polished glass plate.2.5.9.Scratch resistanceThe measurements were performed with Clemen Tester from Elcometer in accordance with EN ISO1518.The sample was placed on the test panel with the coating upwards.A tool with no load applied,was placed on the coating,and the test panel was moved outwards,at the speed of30mm/s.If no scratch appeared on the coating,the load applied to the tool was increased by50g and sub-sequent trials were conducted until a scratch was created.Scratch resistance was defined as the lowest load applied to the tool,as a result of which a scratch appeared on the coating.2.5.10.Adhesion to steelCoatings were assessed for their surface adhesion by means of cross-cut test in accordance with PN-EN ISO2409.The coatings were incised into the substrate with a multi-cut tool equipped with six cutters with the spacing of2mm,manufactured by Byk.The surface of incision network was examined with naked eye and clas-sified on0–5six-point scale.The best surface adhesion was in the case of coatings classified with0score,whose incision edges were completely smooth,and the worst adhesion was marked with5, in this case the damaged surface of the incision network exceeded 65%.2.5.11.ElasticityThe elasticity of the cured coatings was measured using the cylindrical mandrel bend test in accordance with PN-EN ISO 1519.The coated panels were placed under the mandrel with the uncoated side in contact with mandrel and was bent180◦around it. The bent plates were examined visually for cracks or loss of adhe-sion.The test result was the smallest mandrel diameter,when the coating was not damaged.2.5.12.Impact resistanceThe measurements were performed with rapid deformation test by means of a falling weight of1kg with indenter of10mm in diam-eter in accordance with PN-EN ISO6272.The weight was fastened in a vertical tubular guide with graduation.The examined panel was placed with the painted side facing up,on a steel element with a hole of16.3mm diameter located centrally under the indenter. Subsequently,the weight was released to fall onto the indenter.The impacted spots were assessed for cracks using magnifying glass. The assumed test result was the ultimate height,expressed in cen-timeters,from which the falling weight did not damage the coating.2.5.13.CuppingThe coating cupping was investigated using the manual cupping tester according to standard PN-EN ISO1520.The cupping is the minimum depth,expressed in millimeters,at which the coating was damaged.3.Results and discussionHydrotalcite-type LDHs used for modification of powder coat-ings were prepared using coprecipitation method by mixing aqueous solutions of divalent(Mg or Zn)and trivalent(Al)metal nitrates with a solution of amino acid salt(aminolauric ALA or ethylenediaminotetraacetic EDTA).The process was carried out at pH10to ensure simultaneous precipitation of both cations in the form of layered double hydroxide.The schematic structure of magnesium-aluminium hydrotalcite intercalated with aminolau-ric acid is presented in Fig.1.The results of elemental analysis for carbon,hydrogen and nitrogen,HT interlayer distances calculated from XRD patterns and BET surface analysis data of the hydrotal-cites used in the study are presented in Table1.In the study,powder coating compositions based on the blocked polyisocyanate synthesized from trimethylhexamethylene diiso-cyanate(TMDI)were used(Fig.2).Due to its aliphatic backbone2COONH22COO2.9 nmFig.1.Schematic structure of magnesium-aluminium hydrotalcite intercalated with aminolauric acid.B.Pilch-Pitera et al./Progress in Organic Coatings 95(2016)120–126123Table 1Characteristics of HT compounds used to modify the properties of polyurethane powder coatings.Hydrotalcite typeInterlayer anionElemental compositionInterlayer distance d 003,ÅBET surface area,m 2/gAverage particle size ␮mHT Mg,Al-CO 3carbonate%C-1.997.68.110.74%H-4.00HT Mg,Al-ALAaminolaurate%C-25.5117.1,29.1 1.264.74%H-6.20%N-4.52HT Zn,Al-ALAaminolaurate%C-25.3917.2,28.79.610.62%H-5.26%N-5.55HT Zn,Al-EDTAethylenediamine-tetraacetate%C-8.0214.2,26.20.2623.2%H-2.99%N-3.72Fig.2.The chemical structure of blocked polyisocyanate TMDI/B/C.the coatings produced therefrom offer high resistance to yellowing.The isocyanate groups were blocked with the use of ␧-caprolactam (C),which is non-toxic and can be unblocked at the temperature of approx.170◦C.The synthesized polyisocyanate had solid consis-tency and was easily powdered.It may be difficult to achieve a good dispersion of LDH in solid polyurethane powder matrix.The presence of poorly dispersed filler may result in non-transparent coatings [15].Better results were obtained by dispersing HT in a liquid medium [29].In our work,HT was added to liquid PIC after blocking of the free NCO groups,then the mixture was heated to 80◦C and sonicated during 30min.The cooled and milled PIC/HT compound was than mixed with polyester resin,catalyst (WorléeAdd ST-70),levelling (Resi-flow PH-240)and degassing agents (WorleeAdd 902and benzoin).The obtained powder composition was than milled and extruded.The extrusion process allowed for further mixing of all components and dispersing LDH in the powder coating.It was reported that isocyanate groups may react with water present in the LDH structure and,at elevated temperatures,also with hydroxyl groups of LDH interlamellar surface [30].Therefore PIC in the powder coatings composition should be used in excessover the amount calculated on the basis of the hydroxyl and acid number of the polyester resin.The concentration of NCO groups was determined by dibutylamine method.The extent of the forma-tion of urethane bond during the heating of the mixture of PIC and HT at 170◦C was determined using in situ ATR FTIR spectroscopy.The increases in the intensity of the carbonyl stretching vibration band at 1700cm −1and imine group deformation vibration band at 1509cm −1were compared to those observed in the reaction of the same amount of PIC with predetermined amounts of water and octanol.It was found that under the conditions of powder coating curing process both water and hydroxyl groups present in HT react with isocyanate groups.A corresponding excess of PIC was used in the study.3.1.X-ray diffraction (XRD)XRD is a useful technique for detecting the intercalation or exfo-liation of layered clays such as LDH in a polymer matrix.Fig.3shows the XRD patterns of the PU,two kinds of HT (Mg,Al-CO 3and Zn,Al-EDTA)and the powder coatings modified with them.A typical broad peak centered at 19◦was seen for PU sample.This124B.Pilch-Pitera et al./Progress in Organic Coatings 95(2016)120–126Fig.3.X-ray diffraction patterns of PU,HT (Mg,Al-CO 3),HT (Zn,Al-EDTA)and pow-der coating modified with LDH.peak can be attributed to the amorphous conformation of the coat-ing matrix.For the pure HT strong diffraction peaks between 11.0◦and 25.0◦(2␪)were observed.On the XRD patterns of HT modified coatings,no strong peaks was observed.The disappearance of the strong diffraction peaks from HT crystalline structure indicates the complete delamination of LDH layers in PU matrix.3.2.Atomic force microscopy (AFM)Morphology of HT-modified PU coatings was studied by AFM analysis.Height and the corresponding adhesion and deformation images were obtained for 2×2␮m scan sizes and can be seen in Fig.4.In the Images 4A and 4B it is possible to observe the topog-raphy of the sample.Sample of polyurethane modified with 1%HT (Zn,Al-EDTA)reveals some higher structural entities in the topog-raphy signal in comparison with the PU sample and has a rougher surface.For the coatings containing HT,effective dispersion and evi-dence for lack of the clusters of HT particles have been observed.The sheets of the organically modified HT incorporated into the polyurethane coating were easily exfoliated and dispersed in the matrix.This process might be facilitated by the reaction between hydroxyl groups of HT with isocyanate groups of the polymer.Different morphologies can be observed in the deformation images of the investigated samples (Fig.4C and D).Sample of PU reveals a typical soft and hard phase microseparated morphology.Hard segment rich phase of PU give dark contrast and soft segment rich phase appear as bright areas.This is due to a lower penetra-tion depth of cantilever in hard phase as compared to soft phase [31].A significantly different morphology can be observed in HT-modified sample,with dark areas related to the hard delaminated sheets of HT and hard PU segments.Around the sheets of HT the soft PU phase as bright areas were observed.The HT-modified PU matrix exhibited a lower susceptibility to deformation.Adhesion was measured as a tip-sample interaction force.The variations of adhesion forces observed in Fig.4E and 4F were due by local variations in chemical composition of the surface.The hard phase of PU sample exhibits a lower adhesion,because it had more ordered structure and exhibited lower mobility of the chain [30].On the other hand,the higher chain mobility of the soft phase cor-responds to the higher adhesion.The rigid structure of HT sheets results in a low adhesion.Around the HT sheets a high-adhesion soft phase was visible.Its presence may be the result of the reaction between hydroxyl groups of HT and polyisocyanate.The remaining NCO groups can react with the resin and form a soft phase around HT.T a b l e 2S p e c i fic a t i o n s o f t h e c o a t i n g s p r o p e r t i e s .S y m b o l o f c o a t i n gP UP U /1%M g ,A l -C O 3P U /3%M g ,A l -C O 3P U /1%M g ,A l -A L AP U /3%M g ,A l -A L AP U /1%Z n ,A l -A L AP U /3%Z n ,A l -A L AP U /1%Z n ,A l -E D T AP U /3%Z n ,A l -E D T AS u r f a c e f r e e e n e r g y (S F E )m J /m 241.135.140.934.936.335.035.637.440.1G l o s s f o r t h e a n g l e o f 20◦G U 24.725.543.224.327.628.132.727.126.5G l o s s f o r t h e a n g l e o f 60◦G U 69.670.987.366.174.371.179.267.166.2H a r d n e s s –0.720.750.760.70.870.840.910.820.83S c r a t c h r e s i s t a n c e [g ]300500450250300300700300350A d h e s i o n t o t h e s t e e l s u r f a c e 0−b e s t 5-w o r s t1111E l a s t i c i t y m m 242224222I m p a c t r e s i s t a n c e c m 0-w o r s t 50-b e s t 505050505050505050C u p p i n gm m5.29.17.410.114.38.28.27.89.0B.Pilch-Pitera et al./Progress in Organic Coatings95(2016)120–126125Fig.4.AFM height(A,B)and corresponding deformation(C,D)and adhesion images(E,F)of PU powder coating(A,C,E)and PU powder coating modified with1%HT (Zn,Al-EDTA)(B,D,F).3.3.Properties of coatingsThe properties of the resulting powder coatings are presented in Table2.It was found that the modification of polyurethane coating with hydrotalcites had a significant impact on their sur-face properties.The contact angles of water and diiodomethane droplets on the coatings were measured with the use of optical goniometer.Based on contact angle data,surface free energy(SFE) and its parameters by means of Owens–Wendt method were cal-culated[4].Water(bipolar liquid)form big drops on the coating surface,while much lower wetting angle values are specific for diiodomethane(non-polar liquid).In general,SFE values for the HT-containing coatings were lower than for the unmodified coating. The lowest value of SFE was measured for the coatings modified by HT containing aminolauric acid anion with hydrophobic12-carbon atom chain.The coatings with1wt.%HT intercalated by more polar carbonate and EDTA anions also exhibited a distinct drop in SFE. This decrease in SFE is probably associated with the occurrence of metastable state in measuring drops(so-called thermodynamic hysteresis).The main cause of this hysteresis is the increase in sur-face roughness and heterogeneity of the surface[28].Increase in surface roughness with increasing of HT content was observed by means of AFM.On the other hand,SFE values increased with an increase of HT content in the coatings up to3wt.%,especially in the case of HT(Mg,Al-CO3)and HT(Zn,Al-EDTA)with more hydrophilic anions.This can be explained by more pronounced effect of HT component polarity than that of surface roughness.The samples of modified coatings exhibit higher gloss values measured at20◦and60◦in relation to those observed for unmodi-fied coatings.An increase in gloss with an increase of hydrotalcite content was noted.This may be the result of the good micro-homogeneity of the system due to the presence of hydrotalcite structures next to polyurethane chains.Relative hardness of the studied coatings measured in compari-son with that of glass plates is very good.Addition of hydrotalcites increase the coating hardness,which may be explained by the nanoreinforcement effect of LDH.Hu and al.reported a similar effect in polyurethane acrylate coatings[32].In some cases,a distinct increase in scratch resistance of HT-modified coatings was observed.It was related to hydrotalcites HT(Mg,Al-CO3)and HT(Zn,Al-ALA),which display significant higher specific surface area and lower particle size than two other LDHs. All HT-modified coatings demonstrate an increase in hardness, which may result from the presence of rigid LDH structure in polyurethane matrix.The best hardness and scratch resistance was determined for the coatings modified with Zn,Al–hydrotalcite con-taining aminolauric anion.In order to make sure that the coating provides effective pro-tection of the substrate against influence of external environment and it has good properties as decorativefinishing it is essential that its adhesion to that substrate is adequate.In the0–5(best-worst)scale the investigated coatings showed the adhesion level in the range0–1.Some HT-modified samples had lower adhesion, but remained at a good level.The adhesion of the coating corre-lated with the presence of polar groups able to interact with the substrate.Rigid structure of HT causes the chain rigidity and inter-molecular interaction of PU matrix,resulting in the decrease of polar groups contacted to the substrate and thus lower adhesion of the coatings[31].The elasticity of the coatings was at a very good level as shown in Table2.The rigid structure of HT causes the lower elasticity of the some HT-modified coatings.Also,impact resistance of the inves-tigated coatings achieved the highest rating(Table2).Addition of hydrotalcites increase the coating cupping,which indicates good interaction of HT with polyurethane matrix.In contrary to the effect of the modification of PU coatings using polysiloxane or nanopowders with polysiloxane core and。