Vpliv temperature stiskanja na kinetiko utrjevanja in dinamiko graditve trdnosti fenol-formaldehidnega lepilnega spoja : doktorska disertacija

Jošt, Matej (author), Šernek, Milan (mentor), Krajnc, Matjaž (co-mentor), Resnik, Jože (reviewer)

Proučevali smo vpliv temperature stiskanja na utrjevanje fenol-formaldehidnega (FF) lepilnega spoja. Uporabili smo FF lepilo za lepljenje vezanega lesa in bukov furnir (Fagus sylvatica L.). Za proučevanje kinetike utrjevanja FF lepila smo uporabili diferenčno dinamično kalorimetrijo (DSC), dinamično mehansko analizo (DMA) in dielektrično analizo (DEA). Dinamiko graditve strižne trdnosti (DGST) FF lepilnega spoja v lepljencu iz dveh trakov luščenega furnirja smo ugotavljali s prilagojeno metodo "Automated Bonding Evaluation System" (ABES). Z DSC smo ugotovili, da je glavnina reakcij v FF lepilu, pri katerih se sprošča energija, potekala pri temperaturah med 135 °C in 160 °C. Rezultati DMA so odražali mehanski odziv lesa in tudi odziv utrjevanja FF lepila, glede na spremembo temperature. DEA in DGST smo izvedli v majhni vroči stiskalnici pri različnih temperaturah stiskanja (140 °C, 160 °C, 180 °C in 200 °C). Pri DEA smo z LCR metrom in ploščatim IDEX senzorjem, vstavljenim v lepilni spoj, merili električno prevodnost pri treh frekvencah elektromagnetnega polja. Stopnja utrjenosti FF lepila, ki smo jo izračunali iz prevodnosti, je bila odvisna od temperature in časa stiskanja. Z naraščajočo temperaturo stiskanja se je utrjevanje FF lepila začelo prej, hitrost utrjevanja se je povečevala, zaradi česar je bila hitreje dosežena določena stopnja utrjenosti. S statistično analizo rezultatov kinetike utrjevanja smo ugotovili, da Gompertzova funkcija najbolje empirično opiše stopnjo utrjenosti FF lepila v odvisnosti od časa stiskanja. Rezultati DGST so pokazali, da sta bila strižna trdnost in delež loma po lesu FF lepilnega spoja odvisna od temperature in časa stiskanja. Pri višji temperaturi stiskalnice se je strižna trdnost formirala hitreje, kar smo matematično opisali s tri-parametrsko logistično funkcijo. Soodvisnost med rezultati DGST in DEA lahko opišemo z eksponentno zvezo, kar pa je relevantno samo za proučevano FF lepilo in pogoje stiskanja.

• Language: Slovenian
• Keywords: fenol-formaldehidno lepilo, bukov furnir, utrjevanje, temperatura, graditev strižne trdnosti, DEA, DMA, DSC
• Work type: Dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: BF - Biotechnical Faculty
• Place of publishing: Ljubljana
• Publisher: [M. Jošt]
• Year: 2009
• Number of pages: XII, 106 f.
• PID: 20.500.12556/RUL-367
• UDC: 630*824.832
• COBISS.SI-ID: 1740937
• Publication date in RUL: 11.07.2014

Secondary language

• Language: English

Abstract

In the thesis the influence of press temperature on the curing of the phenol-formaldehyde (PF) adhesive bond has been investigated. A PF adhesive for plywood and beech veneer (Fagus sylvatica L.) were used. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and dielectric analysis (DEA) were applied in order to observe the cure kinetics of the PF adhesive. The dynamics of the bond strength development (DBSD) of the PF adhesive bond on a two-ply specimen of peeled veneer were observed on a modified Automated Bonding Evaluation System (ABES). The DSC results showed that the majority of the reaction, which revealed energy, occurred between 135 °C and 160 °C. The results of DMA at increasing temperatures were dependent upon the mechanical response of wood, and also upon the curing of the PF adhesive. DEA and DBSD were performed in a miniature hot-press at different press temperatures (140 °C, 160 °C, 180 °C and 200 °C). The DEA measurements were carried out using a fringe field IDEX sensor, embedded in the PF adhesive layer, and connected to a LCR Meter, at three different frequencies. It was found that the degree of cure, calculated from the conductivity data, depends on the pressing time and the temperature. When the temperature is increased the curing of the PF adhesive begins earlier, and the speed of curing increases, so that the desired degree of cure is achieved faster. By means of a statistical analysis of the cure kinetics results it was found that the Gompertz function is best able to define empirically the degree of cure vs. time. Results of DBSD showed that shear strength and wood failure of the PF adhesive bond depend on pressing time and temperature. At higher pressing temperatures the shear strength develops faster. This was mathematically described by means of a three-parameter logistic function. The relationship between DBSD and DEA can be described by a power equation, which is, however, only relevant for the observed PF adhesive and the pressing conditions used.

• Keywords: phenol-formaldehyde adhesive, beech veneer, curing, temperature, shear strength development, DEA, DMA, DSC