The aim of this study was to evaluate the effect of different morphologies of solvent-exchanged (NFCSE), spray-dried (NFCSD), and freeze-dried (NFCFD) nano-fibrillated cellulose on the susceptibility to surface modification with the acetic anhydride/pyridine system. The degree of substitution (DS), morphology, degree of crystallinity (Icr), hydrophobicity, and thermal stability of acetylated products were examined. Acetylated NFCSD and NFCFD had higher DS than acetylated NFCSE, suggesting that drying pre-treatment increased the susceptibility of NFC for acetylation. The morphology of acetylated NFCFD and NFCSD with higher DS was different from unmodified samples, while that of NFCSE was not affected by acetylation. Microspheres of acetylated NFCSD started to dissolve when the highest DS was reached. As opposed to unmodified NFCFD, the nanofibrillar units of acetylated NFCFD became individualised at lower DS. Acetylated samples had lower Icr than the unmodified samples. A significant increase in the contact angle was observed at higher DS of acetylated NFC samples. Acetylation markedly elevated the thermal stability of the acetylated NFC samples.
COBISS.SI-ID: 2454921
Tannin-based foams were successfully prepared, using Norway spruce and maritime pine tannins. Various parameters, including the amount of procyanidins, were varied in order to observe the effect of changes in the density of the foam, on the structure its pores, and on the homogeneity, compressive strength, and compressive modulus of the foams. It was found that an optimum amount of spruce tannin exists, which results in a foam with the lowest density whereas the amount of cross-linker affects homogeneity, and the foam morphology is defined by the surfactant. A partial replacement of pine tannin with spruce tannin decreased the foaming temperature and led to decreased compressive strength and a decreased compressive modulus of the foams. The main attribute affecting the reaction was the amount of polyphenols, or the amount of impurities (cellulosic sugars) present in the tannin extract.
COBISS.SI-ID: 1132970
There is limited information on intra-annual plasticity of secondary tissues of tree species growing under different environmental conditions. To increase the knowledge about the plasticity of secondary growth, which allows trees to adapt to specific local climatic regimes, we examined climate–radial growth relationships of Norway spruce from three contrasting locations in the temperate climatic zone by analyzing tree-ring widths for the period 1932–2010, and cell characteristics in xylem and phloem increments formed in the years 2009–2011. Variation in the structure of xylem and phloem increments in spruce clearly shows that plasticity in seasonal dynamics of cambial cell production and cell differentiation exists on xylem and phloem sides. Anatomical variables of xylem and phloem cells seem to be predominantly site-specific characteristics in spruce, because they varied among sites but were fairly uniform among years in trees from the same site. Xylem and phloem tissues formed in the first part of the growing season seemed to be more stable in structure, indicating their priority over latewood and late phloem for tree performance. Long-term climate and radial growth analyses revealed that growth was in general less dependent on precipitation than on temperature; however, growth sensitivity to local conditions differed among the sites.
COBISS.SI-ID: 4162726
We have produced hybrid liquefied wood based polyurethane (LW-PU) and LW-PU/nanosilica hybrid coatings for wood substrates. The prepared hybrid polyurethane coatings were hydrophobized by self-assembled monolayers of orthotrichlorosilane (OTS) via sol-gel dipping process. The nanosilica addition into LW-PU system enhanced the physical properties of coatings like surface hardness, and stability towards cold liquids. The OTS hydrophobized coatings were characterized by Fourier transforms infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and thermo-gravimetric analysis (TGA). The surface became hydrophobic as the contact angle (CA) for water droplet on modified hybrid coating was ~115o and very stable. The FTIR, SEM and EDS analysis confirmed the formation of OTS monolayers on hybrid coatings.
COBISS.SI-ID: 2434441
Thermal modification of wood has been commercially available for almost twenty years but the complete mechanism of improved durability is still not completely understood. It is known that the temperature and duration of the modification influences the properties of the final products. There are several potential reasons for the increased durability of the modified wood. In recent research in particular, water exclusion efficiency has been identified as one of the key mechanisms. In order to elucidate this presumption, specimens made of Norway spruce heartwood were thermally modified at 6 different temperatures (160 °C, 180 °C, 190 °C, 200 °C, 210 °C and 230 °C) for three hours according to the Silvapro procedure. Control specimens were left unmodified. Three sets of tests were performed: (a) samples were soaked in water for 4 days and then positioned on load cells and allowed to dry until a constant mass was achieved; (b) short term water uptake was determined with a tensiometer and (c) wood-water interactions were verified using constant gravimetric moisture measurement during outdoor exposure. As expected, the degree of modification was reflected in the moisture content of the wood during testing. Short and medium term water uptakes correlated quite well with the performance of wood in outdoor applications. On the other hand, long term tensiometer measurements were not in line with either short term water uptake or outdoor measurements.
COBISS.SI-ID: 2479241