Utjecaj toplinske modifikacije na površinska svojstva i kemijski sastav bukovine (Fagus sylvatica L.)

Thermal modification leads to the degradation of the compounds in wood, thereby changing the chemical composition of wood, which can affect the further wood finishing. In order to determine the effect of thermal modification on wood finishing, it is important to know the properties of its surface. In this research, the influence of thermal modification on pH, surface free energy, contact angle of coating and chemical composition of beech wood was studied. The results of this study show that acidity and water contact angle on beech wood was higher and polar component of surface free energy was lower after thermal modification. Furthermore, contact angle of waterborne coating on beech wood was increased by increasing the modification temperature and the content of extractives soluble in hot water and in organic solvent was increased after thermal modification of beech wood.Toplinska modifikacija uzrokuje razgradnju spojeva u drvu, čime se mijenja kemijski sastav drva što može utjecati na njegovu površinsku obradu. Kako bi se utvrdio učinak toplinske modifikacije na površinsku obradu drva, važno je znati svojstva njegove površine. U ovom je radu istraživan utjecaj toplinske modifikacije na pH drva, njegovu slobodnu površinsku energiju, kvašenje premaza i na kemijski sastav bukovine. Rezultati istraživanja pokazuju da je toplinska modifikacija povećala kiselost drva i kut kvašenja vode na bukovini i smanjila polarne komponente slobodne površinske energije. Nadalje, kut kvašenja vodenog premaza na bukovini povećao se s povećanjem temperature modifikacije, a sadržaj ekstraktiva topljivih u vrućoj vodi i organskom otapalu povećao se nakon toplinske modifikacije bukovine

Odnos između hrapavosti i klizavosti površinski obrađenih drvenih podova

The present study investigates the relationship between the roughness of beech wood and oak wood surfaces treated with oil and polyurethane coating and the slip resistance in dry, water-wet and oily conditions. Pendulum tests were conducted for slip resistance assessment, and roughness measurements were performed by stylus instrument using Ra, Rt, Rp, Rz and Rsm parameters for surface roughness evaluation. Slip potential in dry conditions was low for all finished wood floors studied. Contamination of the surface with water and oil reduced the slip resistance of finished oak and beech flooring. The strong negative correlation was found between slip resistance on dry finished flooring and roughness parameters Ra, Rz, Rt and Rp, and positive correlation between slip resistance on water-wet finished flooring and roughness parameters Ra, Rz, Rt and Rp. Moreover, the correlations between roughness parameters Ra, Rt, Rp and Rz and slip resistance were very similar, and the roughness parameters correlated more strongly with the slip resistance on dry and water-wet surfaces than with the slip resistance on oil-wet surface. Comparison of the slip potential classifications of finished wood floors based on pendulum data and based on Rz surface roughness parameters showed that in some cases the Rz parameter appeared to overestimate the slip potential of the floors in wet conditions. The results confirm previous research that roughness measurements should only be used as a guide and should not be used as the only indicator of the slip potential of wood flooring materials.U radu je istraživan odnos između hrapavosti bukovine i hrastovine površinski obrađenih uljem i poliuretanskim lakom i klizavosti suhe površine te površine na koju su se prolili voda i ulje. Klizavost površine određena je klatnom, a hrapavost joj je izmjerena kontaktnim uređajem uz pomoć parametara Ra, Rt, Rp, Rz i Rsm za procjenu hrapavosti. Vjerojatnost poskliznuća u suhim uvjetima za sve je ispitivane drvene podove bila niska. Vlaženje površine vodom i uljem smanjilo je otpornost na klizanje površinski obrađenih podova od hrastovine i bukovine. Utvrđena je velika negativna korelacija između otpornosti na klizanje na suhoj površini drvenih podova i parametara hrapavosti Ra, Rz, Rt i Rp te pozitivna korelacija između otpornosti na klizanje na podovima zalivenim vodom i parametara hrapavosti Ra, Rz, Rt i Rp. Nadalje, korelacije između parametara hrapavosti Ra, Rt, Rp i Rz i otpornosti na klizanje bile su vrlo slične. Parametri hrapavosti jače su korelirali s otpornošću na klizanje na suhim površinama i površinama zalivenim vodom nego s otpornošću na klizanje na površinama zalivenim uljem. Usporedba razredbi vjerojatnosti poskliznuća na površinski obrađenim drvenim podovima dobivena klatnom i na temelju parametra hrapavosti površine Rz pokazala je da je u nekim slučajevima parametar Rz dao precijenjenu vjerojatnost poskliznuća na podovima u mokrim uvjetima. Rezultati potvrđuju prethodna istraživanja prema kojima mjerenja hrapavosti trebaju služiti samo kao vodilja i ne smiju se primjenjivati kao jedini pokazatelj klizavosti drvenih podnih materijala

Durability of polyacrylate nanocoatings on thermally modified wood

Toplinski modificirano drvo zaštićeno prozirnim premazima još je uvijek podloţno površinskoj razgradnji uslijed djelovanja vanjskih utjecaja. U ovom radu istraţena je mogućnost povećanja postojanosti prozirnih premaza na toplinski modificiranom drvu dodavanjem nanoĉesica TiO2 i ZnO u poliakrilatni vodeni premaz. Nemodificirani i toplinski modificirani uzorci bukovine površinski neobraĊeni i obraĊeni s devet sustava poliakrilatnih vodenih premaza izlagani su ubrzano i prirodno vanjskim okolišnim utjecajima. Provedena su mjerenja boje, sjaja, pojave pukotina, ljuštenja i plijesni, mehaniĉkih i toplinskih svojstva, transmitancije premaza i kemijskih promjena.Provedeno istraţivanje pokazalo je da toplinska modifikacija bukovine smanjuje gustoću, povećava kiselost, izrazito smanjuje polarnu komponentu slobodne površinske energije, povećava udio lignina, vodenog i otapalnog ekstrakta. Dodatak ZnO nanoĉestica imao je veći utjecaj na svojstva tekućeg poliakrilatnog vodenog premaza od TiO2 nanoĉestica. Dodatak ZnO nanoĉestica povećao je viskoznost premaza uz povećanje pH vrijednosti. TiO2 i ZnO nanoĉestice povećale su ĉvrstoću, modul elastiĉnosti i staklište, a smanjile istezanje poliakrilatnog vodenog premaza. Dodatkom TiO2 i ZnO nanoĉestica u pliakrilatni vodeni premaz smanjila se promjena boje sustava toplinski modificirano drvo premaz tijekom prirodnog i ubrzanog izlaganja, ali je i dalje bila vrlo izraţena i jasno vidljiva ljudskom oku. Bolji uĉinak stabilizacije promjene boje postignut je s TiO2 nanoĉesticama i povećanjem koncentracije nanoĉestica. Predobrada toplinski modificiranog drva otopinom HALS spojeva nije bila uĉinkovita u zaštiti od promjene boje tijekom prirodnog i ubrzanog izlaganja. Dodatak pigmenata u premaze s nanoĉesticama TiO2 i ZnO najviše je stabilizirao promjenu boje toplinski modificiranog drva tijekom ubrzanog izlaganja, a tijekom prirodnog izlaganja pigmenti su povećali stabilnost boje uzoraka drva obraĊenih premazima s ZnO nanoĉesticama. Dodatak TiO2 i ZnO nanoĉestica u poliakrilatni vodeni premaz nije smanjio kemijske promjene sustava toplinski modificirano drvo premaz tijekom prirodnog i ubrzanog izlaganja, dok su se kemijske promjene smanjile kombinacijom pigmenata i nanoĉestica TiO2 i ZnO. Ekstraktivne tvari pridonijele su većoj promjeni boje toplinski modificiranog drva na višoj temperaturi (212 C) tijekom ubrzanog izlaganja, što je vidljivo i na promjeni vrpce na 1595 cm-1.Thermally modified wood protected by a transparent coating is still susceptible to surface degradation due to influence of environmental factors. In this paper, the possibility of increasing the durability of transparent coating on thermally modified wood by adding TiO2 and ZnO nanoparticles in waterborne polyacrylate coating was analysed. Unmodified and thermally modified beech wood samples uncoated and coated with nine waterborne polyacrylate coatings were exposed to environmental influences. Measurements of color, gloss, cracking, peeling and mildew, mechanical and thermal properties, coatings transmittance and chemical changes were conducted.This study showed that the thermal modification beech reduced density, increased acidity, markedly reduced the polar component of surface free energy, increased the content of lignin, water and solvent extract. Addition of ZnO nanoparticles had a greater impact on the properties of waterborne polyacrylate coating than TiO2 nanoparticles. Addition of ZnO nanoparticles increased the viscosity and pH of coating. TiO2 and ZnO nanoparticles increased strength, modulus of elasticity and glass transition temperature, and reduced stretching of waterborne polyacrylate coating. Addition of TiO2 and ZnO nanoparticles in waterborne polyacrylate coating reduced colour change of thermally modified wood - coating system during natural and accelerated exposure, but it was still very pronounced and clearly visible to the naked eye. Better stabilization effect of colour change was achieved with TiO2 nanoparticles and with increasing the concentration of nanoparticles. Pretreatment of thermally modified beech wood with HALS compounds did not protect thermally modified beech wood against colour change during natural and accelerated exposure. Adding of pigments in coatings with TiO2 and ZnO nanoparticles stabilised colour of thermally modified beech wood during accelerated exposure the most and during natural exposure pigments increased colour stability of wood samples coated with coating with ZnO nanoparticles. Addition of TiO2 and ZnO nanoparticles in waterborne polyacrylate coating did not reduce chemical changes of thermally modified wood coating system during natural and accelerated exposure, while the chemical changes were reduced with combination of pigments and TiO2 and ZnO nanoparticles. Extractives contributed to the higher colour change of thermally modified wood at a higher temperature (212 C) during accelerated exposure, which was also visible in change of peak at 1595 cm-1

Durability of polyacrylate nanocoatings on thermally modified wood

Toplinski modificirano drvo zaštićeno prozirnim premazima još je uvijek podloţno površinskoj razgradnji uslijed djelovanja vanjskih utjecaja. U ovom radu istraţena je mogućnost povećanja postojanosti prozirnih premaza na toplinski modificiranom drvu dodavanjem nanoĉesica TiO2 i ZnO u poliakrilatni vodeni premaz. Nemodificirani i toplinski modificirani uzorci bukovine površinski neobraĊeni i obraĊeni s devet sustava poliakrilatnih vodenih premaza izlagani su ubrzano i prirodno vanjskim okolišnim utjecajima. Provedena su mjerenja boje, sjaja, pojave pukotina, ljuštenja i plijesni, mehaniĉkih i toplinskih svojstva, transmitancije premaza i kemijskih promjena.Provedeno istraţivanje pokazalo je da toplinska modifikacija bukovine smanjuje gustoću, povećava kiselost, izrazito smanjuje polarnu komponentu slobodne površinske energije, povećava udio lignina, vodenog i otapalnog ekstrakta. Dodatak ZnO nanoĉestica imao je veći utjecaj na svojstva tekućeg poliakrilatnog vodenog premaza od TiO2 nanoĉestica. Dodatak ZnO nanoĉestica povećao je viskoznost premaza uz povećanje pH vrijednosti. TiO2 i ZnO nanoĉestice povećale su ĉvrstoću, modul elastiĉnosti i staklište, a smanjile istezanje poliakrilatnog vodenog premaza. Dodatkom TiO2 i ZnO nanoĉestica u pliakrilatni vodeni premaz smanjila se promjena boje sustava toplinski modificirano drvo premaz tijekom prirodnog i ubrzanog izlaganja, ali je i dalje bila vrlo izraţena i jasno vidljiva ljudskom oku. Bolji uĉinak stabilizacije promjene boje postignut je s TiO2 nanoĉesticama i povećanjem koncentracije nanoĉestica. Predobrada toplinski modificiranog drva otopinom HALS spojeva nije bila uĉinkovita u zaštiti od promjene boje tijekom prirodnog i ubrzanog izlaganja. Dodatak pigmenata u premaze s nanoĉesticama TiO2 i ZnO najviše je stabilizirao promjenu boje toplinski modificiranog drva tijekom ubrzanog izlaganja, a tijekom prirodnog izlaganja pigmenti su povećali stabilnost boje uzoraka drva obraĊenih premazima s ZnO nanoĉesticama. Dodatak TiO2 i ZnO nanoĉestica u poliakrilatni vodeni premaz nije smanjio kemijske promjene sustava toplinski modificirano drvo premaz tijekom prirodnog i ubrzanog izlaganja, dok su se kemijske promjene smanjile kombinacijom pigmenata i nanoĉestica TiO2 i ZnO. Ekstraktivne tvari pridonijele su većoj promjeni boje toplinski modificiranog drva na višoj temperaturi (212 C) tijekom ubrzanog izlaganja, što je vidljivo i na promjeni vrpce na 1595 cm-1.Thermally modified wood protected by a transparent coating is still susceptible to surface degradation due to influence of environmental factors. In this paper, the possibility of increasing the durability of transparent coating on thermally modified wood by adding TiO2 and ZnO nanoparticles in waterborne polyacrylate coating was analysed. Unmodified and thermally modified beech wood samples uncoated and coated with nine waterborne polyacrylate coatings were exposed to environmental influences. Measurements of color, gloss, cracking, peeling and mildew, mechanical and thermal properties, coatings transmittance and chemical changes were conducted.This study showed that the thermal modification beech reduced density, increased acidity, markedly reduced the polar component of surface free energy, increased the content of lignin, water and solvent extract. Addition of ZnO nanoparticles had a greater impact on the properties of waterborne polyacrylate coating than TiO2 nanoparticles. Addition of ZnO nanoparticles increased the viscosity and pH of coating. TiO2 and ZnO nanoparticles increased strength, modulus of elasticity and glass transition temperature, and reduced stretching of waterborne polyacrylate coating. Addition of TiO2 and ZnO nanoparticles in waterborne polyacrylate coating reduced colour change of thermally modified wood - coating system during natural and accelerated exposure, but it was still very pronounced and clearly visible to the naked eye. Better stabilization effect of colour change was achieved with TiO2 nanoparticles and with increasing the concentration of nanoparticles. Pretreatment of thermally modified beech wood with HALS compounds did not protect thermally modified beech wood against colour change during natural and accelerated exposure. Adding of pigments in coatings with TiO2 and ZnO nanoparticles stabilised colour of thermally modified beech wood during accelerated exposure the most and during natural exposure pigments increased colour stability of wood samples coated with coating with ZnO nanoparticles. Addition of TiO2 and ZnO nanoparticles in waterborne polyacrylate coating did not reduce chemical changes of thermally modified wood coating system during natural and accelerated exposure, while the chemical changes were reduced with combination of pigments and TiO2 and ZnO nanoparticles. Extractives contributed to the higher colour change of thermally modified wood at a higher temperature (212 C) during accelerated exposure, which was also visible in change of peak at 1595 cm-1

Durability of polyacrylate nanocoatings on thermally modified wood

Toplinski modificirano drvo zaštićeno prozirnim premazima još je uvijek podloţno površinskoj razgradnji uslijed djelovanja vanjskih utjecaja. U ovom radu istraţena je mogućnost povećanja postojanosti prozirnih premaza na toplinski modificiranom drvu dodavanjem nanoĉesica TiO2 i ZnO u poliakrilatni vodeni premaz. Nemodificirani i toplinski modificirani uzorci bukovine površinski neobraĊeni i obraĊeni s devet sustava poliakrilatnih vodenih premaza izlagani su ubrzano i prirodno vanjskim okolišnim utjecajima. Provedena su mjerenja boje, sjaja, pojave pukotina, ljuštenja i plijesni, mehaniĉkih i toplinskih svojstva, transmitancije premaza i kemijskih promjena.Provedeno istraţivanje pokazalo je da toplinska modifikacija bukovine smanjuje gustoću, povećava kiselost, izrazito smanjuje polarnu komponentu slobodne površinske energije, povećava udio lignina, vodenog i otapalnog ekstrakta. Dodatak ZnO nanoĉestica imao je veći utjecaj na svojstva tekućeg poliakrilatnog vodenog premaza od TiO2 nanoĉestica. Dodatak ZnO nanoĉestica povećao je viskoznost premaza uz povećanje pH vrijednosti. TiO2 i ZnO nanoĉestice povećale su ĉvrstoću, modul elastiĉnosti i staklište, a smanjile istezanje poliakrilatnog vodenog premaza. Dodatkom TiO2 i ZnO nanoĉestica u pliakrilatni vodeni premaz smanjila se promjena boje sustava toplinski modificirano drvo premaz tijekom prirodnog i ubrzanog izlaganja, ali je i dalje bila vrlo izraţena i jasno vidljiva ljudskom oku. Bolji uĉinak stabilizacije promjene boje postignut je s TiO2 nanoĉesticama i povećanjem koncentracije nanoĉestica. Predobrada toplinski modificiranog drva otopinom HALS spojeva nije bila uĉinkovita u zaštiti od promjene boje tijekom prirodnog i ubrzanog izlaganja. Dodatak pigmenata u premaze s nanoĉesticama TiO2 i ZnO najviše je stabilizirao promjenu boje toplinski modificiranog drva tijekom ubrzanog izlaganja, a tijekom prirodnog izlaganja pigmenti su povećali stabilnost boje uzoraka drva obraĊenih premazima s ZnO nanoĉesticama. Dodatak TiO2 i ZnO nanoĉestica u poliakrilatni vodeni premaz nije smanjio kemijske promjene sustava toplinski modificirano drvo premaz tijekom prirodnog i ubrzanog izlaganja, dok su se kemijske promjene smanjile kombinacijom pigmenata i nanoĉestica TiO2 i ZnO. Ekstraktivne tvari pridonijele su većoj promjeni boje toplinski modificiranog drva na višoj temperaturi (212 C) tijekom ubrzanog izlaganja, što je vidljivo i na promjeni vrpce na 1595 cm-1.Thermally modified wood protected by a transparent coating is still susceptible to surface degradation due to influence of environmental factors. In this paper, the possibility of increasing the durability of transparent coating on thermally modified wood by adding TiO2 and ZnO nanoparticles in waterborne polyacrylate coating was analysed. Unmodified and thermally modified beech wood samples uncoated and coated with nine waterborne polyacrylate coatings were exposed to environmental influences. Measurements of color, gloss, cracking, peeling and mildew, mechanical and thermal properties, coatings transmittance and chemical changes were conducted.This study showed that the thermal modification beech reduced density, increased acidity, markedly reduced the polar component of surface free energy, increased the content of lignin, water and solvent extract. Addition of ZnO nanoparticles had a greater impact on the properties of waterborne polyacrylate coating than TiO2 nanoparticles. Addition of ZnO nanoparticles increased the viscosity and pH of coating. TiO2 and ZnO nanoparticles increased strength, modulus of elasticity and glass transition temperature, and reduced stretching of waterborne polyacrylate coating. Addition of TiO2 and ZnO nanoparticles in waterborne polyacrylate coating reduced colour change of thermally modified wood - coating system during natural and accelerated exposure, but it was still very pronounced and clearly visible to the naked eye. Better stabilization effect of colour change was achieved with TiO2 nanoparticles and with increasing the concentration of nanoparticles. Pretreatment of thermally modified beech wood with HALS compounds did not protect thermally modified beech wood against colour change during natural and accelerated exposure. Adding of pigments in coatings with TiO2 and ZnO nanoparticles stabilised colour of thermally modified beech wood during accelerated exposure the most and during natural exposure pigments increased colour stability of wood samples coated with coating with ZnO nanoparticles. Addition of TiO2 and ZnO nanoparticles in waterborne polyacrylate coating did not reduce chemical changes of thermally modified wood coating system during natural and accelerated exposure, while the chemical changes were reduced with combination of pigments and TiO2 and ZnO nanoparticles. Extractives contributed to the higher colour change of thermally modified wood at a higher temperature (212 C) during accelerated exposure, which was also visible in change of peak at 1595 cm-1

Utjecaj pripreme površine na hrapavost, kvašenje i adheziju premaza na nemodificiranome i toplinski modificiranom drvu

In this research, the influence of face milling, sanding and UV irradiation of the hornbeam and ash wood sample on the wetting and adhesion strength of solvent-based and water-borne coating was studied. The adhesion of coatings to substrates is one of the most important parameters for finishing quality and service life of wood coatings, while wetting properties are usually used to assess the quality of surfacing process and could also provide important information on the adhesion ability of coatings. Surface roughness, contact angle of coatings and water as well as adhesion strength of coatings were tested on differently prepared (face milled, sanded and UV irradiated) samples of unmodified and thermally modified ash and hornbeam wood. Surface roughness was measured with stylus-type profilometer over the traverse of 12.5 mm and with a cut-off value of 2.5. Contact angle was measured using the sessile drop method 2 s, 10 s and 30 s after the application of the liquid drop on the sample surface, and adhesion strength was measured according to ASTM D4541. Results showed that sanding of hornbeam and ash wood resulted in the least rough surface compared to the face milled and UV irradiated surface. Contact angles of the water-borne coating were on average three times higher than the contact angles of the solvent-based coating. Sanding the surface of hornbeam and ash samples increased the adhesive strength in relation to the face milled surface, while UV irradiation of the sanded surface decreased the adhesive strength of most samples coated with solvent-based coating.U radu je istraživan utjecaj čeonog blanjanja, brušenja i UV zračenja grabovine i jasenovine na kvašenje i adhezivnu čvrstoću premaza na bazi organskih otapala i vodenog premaza. Adhezija premaza jedan je od najvažnijih parametara za kvalitetu površinske obrade i trajnost premaza za drvo, dok svojstva kvašenja obično služe za ocjenu kvalitete nanošenja i adhezije premaza. Na različito pripremljenim uzorcima (obrađenim čeonim blanjanjem, brušenjem ili UV zračenjem) nemodificirane i toplinski modificirane grabovine i jasenovine ispitivana je hrapavost, kontaktni kut premaza i vode te adhezivna čvrstoća premaza. Hrapavost površine mjerena je profilometrom na duljini vrednovanja 12,5 mm, uz referentnu duljinu od 2,5 mm. Kontaktni kut mjeren je metodom s kapljicom, i to 2 s, 10 s i 30 s nakon nanošenja kapljice na površinu uzorka, a adhezivna čvrstoća određivana je prema normi ASTM D4541. Rezultati su pokazali da je brušenje grabovine i jasenovine rezultiralo najmanje hrapavom površinom u usporedbi s čeono blanjanom i UV zračenom površinom. Kontaktni kutovi vodenog premaza bili su u prosjeku tri puta veći od kontaktnih kutova premaza na bazi organskih otapala. Brušenjem površine uzoraka grabovine i jasenovine adhezivna je čvrstoća postala veća od čvrstoće čeono blanjanih površina, dok je UV zračenjem na brušenim površinama većine uzoraka smanjena adhezivna čvrstoća premaza na bazi organskih otapala

Fire retardants for wood

Drvo kao tradicionalni građevni materijal, osim brojnih prednosti, ima i neke nedostatke. Jedan od njih je zapaljivost. Uobičajeni način da se popravi vatrootpornost drva jest njegova obrada materijalima koji usporavaju gorenje i koji se mogu nanositi na površinu kao premazi, impregniranjem nanositi u drvo ili ugrađivati u kompozitne drvne proizvode. Usporivači gorenja formulirani su tako da mogu kontrolirati zapaljenje, brzinu širenja plamena površinom drva i smanjiti količinu topline oslobođene iz drva, no ne mogu učiniti drvo negorivim. Prema novomu Europskom razredbenom sustavu za građevne proizvode, drvo i drvni proizvodi prema reakciji na požar pripadaju razredu D, a ako su obrađeni usporivačima gorenja mogu, zadovoljiti zahtjeve razreda B. U radu je opisano gorenje drva, požarna svojstva drva, vrste usporivača gorenja i mehanizmi njihova djelovanja. Posebno su obrađeni prekrivni materijali (premazi) koji usporavaju gorenje drva, a posebno sustavi koji se nanose tlačnom impregnacijom.Along with many advantages, wood as traditional building material also has some disadvantages. One of them is the flammability. The most usual way to improve the fire performance of wood is by treating it with fire retardants that can be applied to wood composite products during manufacture, pressure impregnated into solid wood or wood products or added as a paint or surface coating. Fire retardants are formulated to control ignition, flame spread on the wood surface and to reduce the amount of heat released from wood. Fire retardants cannot make wood non combustible. According to the European reaction-to-fire “Euroclasses”classification system for construction products, wood treated with fire retardant can meet the requirements of Euroclass B, whereas ordinary wood products typically fall into class D. This article attempts to bring together information related to the burning of wood, fire performance of wood, types of fire retardants and mechanism of fire retardancy. Fire retardant coatings and chemical impregnation by pressure-treating are described separately

Ubrzano izlaganje vanjskim uvjetima bukovine modificirane limunskom kiselinom, neobrađene i obrađene lazurama

Chemical modification of wood can minimize wood drawbacks in exterior application, such as moisture absorption, swelling and shrinkage, susceptibility to photodegradation and microbial attack. We modified a beech wood with 7.0 % water solution of citric acid and 6.5 % sodium-hypophosphite monohydrate (SHP) as a catalyst and investigated the color stability and weathering performance of coated and uncoated wood under accelerated weathering conditions. The modified and unmodified beech wood samples were coated with transparent water-borne stain and transparent solvent-borne stain, and with reference stain. The accelerated outdoor exposure was conducted in a QUV weathering tester(Q-Panel Company) equipped with UVA-340 florescent lamps for 56 days (1344 hours). The surface of samples was examined for color and gloss changes, adhesion and appearance of flaking, cracking, blistering and chalking. The overall color change (ΔE*) of coated beech wood samples at the end of exposure was smaller in unmodified wood samples. The trend of gloss changes of modified and unmodified wood samples was very similar during the exposure. At the end of exposure unmodified beech wood samples exhibited better weathering performance than modified beech wood samples. In order to achieve the optimal protection of wood modified with citric acid the new type of finishes should be developed.Kemijskom modifi kacijom mogu se smanjiti nedostaci drva pri vanjskoj uporabi, kao što su upijanje vlage, bubrenje i utezanje, podložnost razgradnji pod utjecajem svjetlosti te pri napadu mikroorganizama. U ovom je istraživanju bukovina modificirana 7,0 %-tnom vodenom otopinom limunske kiseline uz dodatak 6,5% natrijhidrofosfita monohidrata (SHP) kao katalizatora i istraživana stabilnost boje i postojanost pri ubrzanom izlaganju vanjskim utjecajima tako modificiranoga drva, neobrađenoga i obrađenog lazurama. Uzorci su površinski obrađeni transparentnom vodenom lazurom i transparentnom otapalnom lazurom, te referentnom lazurom. Ubrzano izlaganje vanjskim uvjetima bilo je provedeno u QUV uređaju (tvrtke Q-Panel), opremljenome s UVA-340 fluorescentnim svjetiljkama, u trajanju 56 dana (1344 sati). Na površini uzoraka mjerila se promjena boje i sjaja, određivala adhezija i provjeravala pojava ljuštenja, pukotina, mjehuranja i kredanja. Ukupna promjena boje (ΔE*) obrađenih bukovih uzoraka na kraju izlaganja bila je manja od promjene na nemodificiranim uzorcima. Trend promjene sjaja modificiranih i nemodificiranih uzoraka bio je vrlo sličan tijekom izlaganja. Na kraju ubrzanog izlaganja vanjskim uvjetima nemodificirani su bukovi uzorci bili postojaniji nego modificirani. Kako bi se povećala površinska zaštita modificiranog drva, potrebno je posebno razviti novi tip premaza za drvo modificirano limunskom kiselinom