doktorska disertacija
Mirko Kariž (Author), Milan Šernek (Mentor)

Abstract

Proučevali smo vpliv temperature termične modifikacije na utrjevanje in kakovost lepilnih spojev. Uporabili smo les smreke, ki je bil termično modificiran pri temperaturah 150, 170, 190, 210 in 230 °C ter različna lepila: fenol-formaldehidno (FF) za vroče lepljenje ter tri lepila za hladno lepljenje: polivinilacetatno (PVAc), poliuretansko (PU) ter melamin-urea- formaldehidno (MUF). Utrjevanje lepil smo spremljali z merjenjem reoloških lastnosti z reometrom pri čemer smo namesto standardnih aluminijastih diskov uporabili diske iz termično modificiranega lesa z različno stopnjo modifikacije ter z različnimi vlaţnostmi. Uporabili smo oscilatorni test z "multiwave" tehniko merjenja. Ugotovili smo, da so PVAc, PU ter MUF lepila utrjevala počasneje glede na stopnjo termične modifikacije lesa, vendar so bili razlogi različni. PVAc in MUF lepili sta utrjevali počasneje zaradi slabše absorpcije vode v modificiran les, PU lepilo pa zaradi niţje vlaţnosti modificiranega lesa. Termična modifikacija lesa je vplivala tudi na striţno trdnost lepilnih spojev. Striţna trdnost FF lepilnih spojev je padala z naraščanjem temperature modifikacije lepljencev, kar je bila posledica manjše utrjenosti lepila in niţje trdnosti modificiranega lesa. Po namakanju v vodi se je striţna trdnost FF spojev prepolovila, vendar so bolj modificirani preskušanci obdrţali večji deleţ začetne trdnosti. Povprečna efektivna penetracija FF lepila je sicer nekoliko naraščala s stopnjo modifikacije, vendar razlike niso bile statistično značilne. Termična modifikacija je zmanjšala omočitev površine lesa z vodo, toda izboljšala omočitev površine lesa s FF lepilom. Pri spojih s PVAc lepilom sta striţna trdnost spojev in deleţ loma po lesu padala s stopnjo termične modifikacije tako pri suhih preskušancih kot po namakanju preskušancev v vodi. Trdnost suhih PU lepilnih spojev se je zniţala glede na stopnjo termične modifikacije lesa, vendar manj kot pri PVAc lepilu. Po namakanju preskušancev v vodi pa sta se trdnost PU spojev in deleţ loma po lesu povečevala s stopnjo modifikacije lesa. Razlog je bil verjetno v navzemu vode in nabrekanju lesa. Navzem vode med 24 urnim namakanjem lepljencev v vodi je padal s stopnjo termične modifikacije lesa. Pri MUF lepilu je striţna trdnost suhih spojev padala s stopnjo termične modifikacije nekoliko bolj kot pri PU lepilu, vendar precej manj kot pri PVAc lepilu. Po namakanju preskušancev je striţna trdnost MUF spojev padla na polovico začetne trdnosti suhih spojev ter bila neodvisna od stopnje termične modifikacije, vendar je deleţ loma po lesu ostal 100 %. Skupna ugotovitev pri vseh lepilih je bila, da višja kot je bila stopnja termične modifikacije, manjša je bila deformacija pri kateri je prišlo do loma ter bolj krhek je bil lom. Skupna delaminacija PVAc lepilnih spojev je bila precej velika in se je povečevala s stopnjo termične modifikacije lesa. Pri PU in MUF lepilnih spojih izrazite delaminacije ni bilo.

Keywords

lepljenje;termična modifikacija lesa;utrjevanje lepil;reologija;delaminacija;strižna trdnost;lepilni spoji;les;smreka;lepilo;lastnosti;

Data

Language: Slovenian
Year of publishing:
Typology: 2.08 - Doctoral Dissertation
Organization: UL BF - Biotechnical Faculty
Publisher: [M. Kariž]
UDC: 630*82:532.135(043.3)
COBISS: 753015 Link will open in a new window
Views: 395
Downloads: 65
Average score: 0 (0 votes)
Metadata: JSON JSON-RDF JSON-LD TURTLE N-TRIPLES XML RDFA MICRODATA DC-XML DC-RDF RDF

Other data

Secondary language: English
Secondary title: Influence of thermal modification of wood on curing of adhesives and bond performance
Secondary abstract: In the thesis the effect of the temperature used for the thermal modification of wood on the curing of adhesive and on bond performance was investigated. Spruce wood, heat treated at temperatures of 150, 170, 190, 210 and 230 °C, and four different types of adhesives were used: one adhesive for hot pressing, phenol-formaldehyde (PF), and three adhesives for cold setting: polyvinyl acetate (PVAc), polyurethane (PU) and melamine-urea-formaldehyde (MUF). The curing of the adhesives was monitored by measuring their rheological properties with a rheometer. Wooden discs, prepared from wood that had been subjected to different degrees of thermal modification and having different moisture contents, were used, instead of standard aluminium discs. The oscillation test with the "multiwave" measurement technique was used. It was found that the PVAc, PU and MUF adhesives cured more slowly depending on the degree of thermal modification, but the reasons for the retardation of curing were different. PVAc and MUF curing was slower because of the lower degree of adsorption of water in the modified wood, whereas the PU cured slower because of the lower moisture content of the modified wood. Thermal modification had a significant influence on the shear strength of the adhesive bonds. The shear strength of the PF adhesive bonds decreased with an increasing temperature of thermal modification, because of the lower degree of adhesive cure and the lower strength of the modified wood. After soaking in water, the shear strength of the PF joints reduced by half, but the more strongly modified specimens retained a greater proportion of the initial shear strength. The average effective penetration of the PF adhesive slightly increased with the degree of thermal modification, but these differences were not statistically significant. Thermal modification reduced surface wetting with water, but improved wetting with the PF adhesive. The shear strength and wood failure of the PVAc adhesive bond (of dry specimens and after soaking in water) decreased with a higher degree of thermal modification. The shear strength of the PU adhesive bonds decreased with degree of thermal modification of the wood, but less than in the case of the PVAc adhesive bonds. After soaking in water the shear strength and wood failure of the PU adhesive bonds increased with the degree of thermal modification. The reason was probably water intake and swelling of the wood. The water intake after 24 h of soaking decreased with the degree of thermal modification of the wood. The shear strength of the MUF adhesive bonds decreased with the degree of thermal modification slightly more than that of the PU adhesive bonds, but much less than that of the PVAc adhesive bonds. After soaking in water the shear strength of the MUF adhesive bonds dropped to half the initial dry strength, and was observed to be independent of the degree of thermal modification. The average wood failure of the wood remained at 100 %. In the case of all the adhesives bonds is was noticeable that with a higher degree of thermal modification the deformation was smaller when failure of the bond occurred, and that the failure was more brittle. The total delamination of the PVAc adhesive bonds was quite high, and increased with the degree of thermal modification of the wood. Delamination of the PU and MUF adhesive bonds was not pronounced.
Secondary keywords: bonding;heat treatment of wood;adhesive curing;rheology;delamination;shear strength;wood;spruce wood;
Type (COBISS): Dissertation
Thesis comment: Univ. Ljubljana, Biotehniška fak., Podiplomski študij bioloških in biotehniških znanosti, področje lesarstvo
Pages: XV, 137 f.
ID: 12867795