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Vpliv velikosti delcev na določitev stopnje toplotne modifikacije hrastovega lesa
ID Hočevar, Dejan (Author), ID Cerc Korošec, Romana (Mentor) More about this mentor... This link opens in a new window

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Abstract
Zaradi želje po čim manjši uporabi biocidov v vedno večjem obsegu uporabljamo alternativne metode za zaščito lesa, med katere spada tudi toplotna modifikacija. Proizvodnja termično modificiranega lesa narašča, še vedno pa nimamo povsem razvite enotne metode za določanje stopnje modifikacije, ki bi bila potrebna zaradi nadzora kakovosti termično modificiranega lesa. Stopnja termične modifikacije lesa korelira z izgubo mase suhega lesa med tem procesom. Med segrevanjem toplotno modificiranih vzorcev v termoanalizatorju v vzorcih potekajo procesi, ki med toplotno modifikacijo pri povišani temperaturi še niso potekli. Višja kot je bila stopnja predhodne termične modifikacije, manjša bo izguba mase med termogravimetrično meritvijo v določenem temperaturnem območju, manjša pa bo tudi raven vezane vlage, saj se med modifikacijo število hidroksilnih skupin zmanjšuje in so posledično vedno manj hidrofilni. Na potek termičnega razpada vpliva več faktorjev, med katerimi je tudi velikost delcev. Manjši delci imajo večjo površino, zato je hitrost izgube mase v določenem temperaturnem območju večja v primerjavi z vzorci, pri katerih je velikost delcev večja. V okviru diplomskega sem želel preveriti, ali dve različni velikost delcev toplotno modificiranega hrasta zaznavno vplivata na izgubo mase v določenem temperaturnem območju. Najprej sem pripravil vzorce toplotno modificiranega hrasta (ti so bili toplotno obdelani v odsotnosti kisika pri temperaturah 170 °C, 180 °C, 190 °C, 200 °C, 205 °C in 210 °C). Hrastov les sem izbral zato, ker je ta lesna vrsta v Sloveniji precej razširjena in uporabna za izdelavo najrazličnejših izdelkov. Ti vzorci predstavljajo standardne vzorce, saj lahko na osnovi tehtanja vzorcev pred in po postopku termične modifikacije enostavno izračunamo izgubo mase med toplotno modifikacijo. Termično modificirane vzorce smo nato zmleli na dve različno veliki frakciji, in sicer na 0,5 mm in 1,0 mm in jih natehtali v lončke ter izpostavili vlažni atmosferi z določeno vlažnostjo. Po nasičenju smo vzorce analizirali na termoanalizatorju v pretoku inertne atmosfere in temperaturnem območju med 20 °C in 600 °C. Iz pridobljenih podatkov smo izrisali krivulje oziroma umeritvene premice, ki prikazujejo odvisnost izgube mase vzorcev med termogravimetrično analizo v odvisnosti od izgube mase med predhodno termično obdelavo. Pridobljene umeritvene premice lahko nato uporabimo za določitev izgube mase med termično modifikacijo za neznane vzorce, le-ta pa je sorazmerna s stopnjo toplotne modifikacije.

Language:Slovenian
Keywords:toplotna modifikacija, termogravimetrična analiza, hrastov les
Work type:Bachelor thesis/paper
Typology:2.11 - Undergraduate Thesis
Organization:FKKT - Faculty of Chemistry and Chemical Technology
Year:2021
PID:20.500.12556/RUL-134973 This link opens in a new window
COBISS.SI-ID:90888451  This link opens in a new window
Publication date in RUL:15.02.2022
Views:638
Downloads:52
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Secondary language

Language:English
Title:The influence of the particle size on determination of thermal modification degree of oak wood
Abstract:
Due to the desire to minimize the use of biocides, we are increasingly using alternative methods for wood preservation, including thermal modification. The production of thermally modified wood is increasing, but we still do not have a fully developed unified method for determining the degree of modification that would be required to control the quality of thermally modified wood. The degree of thermal modification of wood correlates with the loss of dry wood mass during this process. During heating of thermally modified samples in the thermoanalyzer, processes that have not yet taken place during thermal modification at elevated temperature occur in the samples. The higher the degree of previous thermal modification, the lower the mass loss during thermogravimetric measurement in a given temperature range and the lower the moisture content, because the number of hydroxyl groups decreases during modification and consequently they are less hydrophilic. The course of thermal decomposition is influenced by several factors, including particle size. Smaller particles have a larger surface area, so the rate of mass loss in a given temperature range is higher than for samples with a larger particle size. As part of my diploma work, I wanted to test whether two different particle sizes of thermally modified oak wood had a noticeable effect on the rate of weight loss in a given temperature range. Samples of thermally modified oak were prepared first. These were heat treated in the absence of oxygen at temperatures of 170°C, 180°C, 190°C, 200°C, 205°C and 210°C. We chose oak because this type of wood is quite widespread in Slovenia and can be used for the production of a wide range of products. The prepared samples are standard ones because we can easily calculate the weight loss during thermal modification by weighing the samples before and after thermal modification. The thermally modified samples were then milled into two different sized fractions, 0.5 mm and 1.0 mm, weighed into crucibles and exposed to a humid atmosphere with a certain humidity. After saturation, the samples were thermogravimetrically analyzed in an inert atmosphere and in the temperature range between 20°C and 600°C. From the data obtained, curves or calibration lines were constructed showing the dependence of the weight loss of the samples on the heat treatment. The obtained calibration lines can then be used to determine the mass loss during thermal modification for unknown samples, which is proportional to the degree of thermal modification.

Keywords:thermal modification, thermogravimetric analysis, oak wood

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