Structural components of cell wall and variability of chemical composition of wood

V pričujočem prispevku so klasificirane kemijske snovi v lesu in definirane strukturne komponente celične stene. Opisana je variabilnost kemijske sestave celične stene lesa iglavcev in listavcev ter pojasnjen prispevek posameznega stenskega polimera k izbranim lastnostim lesa.Chemical compounds of wood are classified and structural components of cell wall defined in this paper. Variability in chemical composition of cell wall in softwoods and hardwoods and contribution of individual wall component to selected wood properties is described

Sulfonic esters of cellulose

S spremembami v kemični zgradbi naravnih polimerov lahko bistveno vplivamo na njihove lastnosti in možnosti uporabe. Preko sulfonatov je bil pripravljen cel spekter derivatov celuloze. Predvsem tozilati so odlični intermediati pri pripravi derivatov s posebnimi lastnostmi, saj je tozilatna skupina dobro izstopajoča in jo je mogoče zamenjati s številnimi nukleofilnimi reagenti, po drugi strani pa lahko služi tudi kot zaščitna skupina pri nadaljnji funkcionalizaciji preostalih hidroksilnih skupin.Altering the molecular structure of natural polymers enables development of new materials with special properties. Cellulose sulfonates, especially tosylates, have been used as intermediates for further functionalization of cellulose. Tosylate groups can be easily replaced by various nucleophiles to yield derivatives that cannot be prepared directly. On the other hand, tosylate groups may serve as protecting groups in subsequent modifications of the remaining hydroxyl groups

Effects of UV light irradiation on colour stability of thermally modified, copper ethanolamine treated and non-modified wood

A series of experiments were carried out to investigate the colour stability of chemically treated and thermally modified wood compared to non-modified wood during long term artificial UV light irradiation. One set of wood samples was vacuum-pressure impregnated with alkaline (pH 9.8) copper (II) ethanolamine aqueous solution, while another set of samples from the same woodblock was thermally modified at 210C and -0.90 bar for 2 h. The treated and modified wood samples along with the non-modified ones were exposed to artificial UV light with the wave length in the region of UVA (315-400 nm) and UVB (280-315 nm) intermittently for 500 h. Colour measurements were carriedout throughout the irradiation period at an interval of 100 h accordingto CIEL*a*b* system, where the results are presented in terms of ?E, ?L*, ?a* and ?b* values. Better photo-stability in terms of colour changes was recorded for both treated and modified woods compared to the non-modified one. By means of EPR and DRIFT spectroscopic study it was shown that some degree of colour stability of treated and modified woods, achieved during artificial UV light irradiation, resulted from lignin modifications and monomers of phenolic compounds

Quality control of thermally modified timber using dynamic vapor sorption (DVS) analysis

The importance of thermal modification is increasing worldwide. Increased use of thermally modified timber (TMT) has resulted in a need for reliable quality control, comprising control of variation of the production within defined limits, allowing third-party control in the case of certification and the regulation of customer complaints and claims. Techniques are thus needed to characterise the modification of quality in terms of improved target properties of TMT during industrial production, and of TMT products that have been in service for an arbitrary time. In this study, we aimed to utilise dynamic vapor sorption (DVS) for this purpose. Norway spruce (Picea abies) and European beech (Fagus sylvatica) samples were thermally modified at different temperatures according to different heat treatment techniques: (1) the Silvapro process based on an initial vacuum(2) an air heat treatment, whereby samples were wrapped in aluminium foil(3) thermal modification of wood samples in the ambient atmosphere in a laboratory oven. Wood samples from closed processes were analysed for validation. TMT was characterised with respect to mass loss, colour and density. Mass loss of wood due to modification (ML$_{TM}$) was correlated with factors derived from DVS analysis. The present DVS measurements suggest that the equilibrium wood moisture content (EMC_{95%} $_{RH}$), the time to reach 10% wood moisture content (t_{10%} $_{MC}$), and the elongation factor, c, derived from a logarithmic function, can serve as alternative parameters to characterise the quality of several thermal modification processes. Further studies are recommended using other wood species, different modification processes and further parameters gained from DVS measurements to understand the robustness and the predictive power of the applied technique

Searching for optimal measurement parameters by thermogravimetry for determining the degree of modification of thermally modified wood

When wood is thermally modified, several chemical reactions take place that change the chemical and physical properties of the wood. These changes correlate with the degree of modification, which is mostly a function of the temperature and duration of modification, and consequently with the mass loss during this process. There is a lack of standardised quality control to verify the degree of heat treatment of wood and thus its quality. One of the possible methods to check the degree of thermal modification of a particular type of wood is thermogravimetry (TG). It is based on the assumption that processes that did not take place during thermal modification continue when the TG experiment is carried out. In this method, calibration curves have to be established based on TG measurements of standard samples that have been thermally modified at different temperatures and whose mass loss during modification is known. The calibration curves show the mass loss during the TG measurement as a function of the mass loss during the previous thermal modification. The course of thermal decomposition during the TG measurements is influenced by many parameters, such as the mass of the sample, the heating rate, the atmosphere in which the measurement takes place, and the shape of the crucible in which the sample is placed. In this paper, the influence of these parameters on the calibration curves was investigated. We have focused on oak wood. The best parameters result in a calibration curve with the largest correlation coefficient $R^2$ and the highest slope of the line k. On this basis, we can determine the mass loss during the thermal modification of unknown samples of the same wood species under the same measurement conditions