Vpliv instrumentalnih in vzorčnih parametrov na potek umeritvenih krivulj za določitev stopnje toplotne modifikacije hrastovega lesa

Štiftar, Nejc (author), Cerc Korošec, Romana (mentor)

Les je strateška surovina, ki jo imamo v Sloveniji na voljo v relativnem izobilju in je poleg vode naš edini naravno obnovljiv vir. Večina evropskih lesnih vrst ima neodporen les, ki se začne hitro razkrajati. Čeprav so v naravi taki procesi zaželeni, jih želimo pri lesu, katerega uporabljamo za komercialne namene, čim bolj upočasniti. V preteklosti so se za to uporabljali razni biocidni premazi, ki so danes zaradi naraščajoče okoljske ozaveščenosti Evropejcev vedno bolj nezaželeni, povečuje pa se uporaba termične modifikacije za zaščito lesa. V tem postopku les izpostavimo visokim temperaturam v anaerobnih pogojih, pri čemer v oleseneli celični steni pride do različnih kemijskih sprememb. To se odraža v nižji ravnovesni vlažnosti lesa, boljši dimenzijski stabilnosti in povečani odpornosti proti škodljivcem. Za nadzor kakovosti toplotno modificiranega lesa bi radi uvedli standardno metodo, ki bi jo lahko uporabili tudi v primeru reklamacij. Ena od možnih metod, s katero bi nadzirali stopnjo termične modifikacije določene lesne vrste, je tudi termogravimetrija. Pri tej metodi na osnovi standardnih vzorcev, ki smo jih termično modificirali pri različnih temperaturah in za katere poznamo izgubo mase med modifikacijo, konstruiramo umeritvene krivulje na podlagi TG meritev teh vzorcev. Te prikazujejo izgubo mase med TG meritvijo v odvisnosti od izgube mase med predhodno termično modifikacijo. Na potek TG krivulje pa vlivajo številni parametri, kot so masa vzorca, hitrost segrevanja, atmosfera v kateri le-ta poteka in oblika lončka, v katerem se vzorec nahaja. V okviru diplomskega dela sem se osredotočil na raziskovanje vplivov teh parametrov na potek umeritvenih krivulj, s katerimi določimo stopnjo toplotne modifikacije lesa, pri čemer sem se osredotočil na hrastov les. Najboljši parametri so tisti, pri katerih dobimo umeritveno krivuljo s čim večjim korelacijskim koeficientom R2 in smernim koeficientom k. Na osnovi te lahko določamo izgubo mase med toplotno modifikacijo neznanim vzorcev, seveda pod enakimi pogoji meritve.

• Language: Slovenian
• Keywords: toplotna modifikacija, hrast, termogravimetrija, umeritvena krivulja
• Work type: Bachelor thesis/paper
• Typology: 2.11 - Undergraduate Thesis
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2022
• PID: 20.500.12556/RUL-139461
• COBISS.SI-ID: 124729347
• Publication date in RUL: 02.09.2022

Secondary language

• Language: English
• Title: Influence of instrumental and sample parameters on the course of calibration curves for determining the degree of thermal modification of oak wood

Abstract

Wood is a strategic raw material relatively abundant in Slovenia and which, along with water, is our only naturally renewable resource. Most European wood species have a non-resistant wood that begins to rot quickly. Although such processes are desirable in nature, we want to slow them down as much as possible in wood used for commercial purposes. In the past, various biocidal coatings were used for this purpose, but these are now less and less desirable due to the growing environmental awareness of Europeans. Therefore, thermal modification is increasingly used to protect wood. In this process, the wood is exposed to high temperatures under anoxic conditions, causing various chemical changes to take place in the lignified cell wall. This is reflected in lower equilibrium moisture content, better dimensional stability and increased resistance to pests. We would like to introduce a standard method for quality control of thermally modified wood, which can also be used in case of complaints. One of the possible methods for checking the degree of thermal modification of a particular type of wood is also thermogravimetry. In this method, calibration curves based on TG measurements of standard samples that have been thermally modified at different temperatures and whose mass loss during modification is known, are established. These show the mass loss during the TG measurement as a function of the mass loss during the previous thermal modification. The shape of the TG curve is affected by many parameters, such as the mass of the sample, the heating rate, the atmosphere in which the modification takes place, and the shape of the crucible in which the sample is placed. In my diploma work, the influence of these parameters on the shape of the calibration curves used to determine the degree of thermal modification of wood was studied. We have focused on oak wood. The best parameters are those that give a calibration curve with the largest possible correlation coefficient R2 and directional coefficient k. On this basis we can determine the mass loss during thermal modification of unknown samples, of course under the same measurement conditions.

• Keywords: thermal modification, oak, thermogravimetry, calibration curve