This review provides a synthesis of the last ten years of research on nanodelivery systems used for the delivery of essential oils (EOs), as well as their potential as a viable alternative to ...antibiotics in human and veterinary therapy. The use of essential oils alone in therapy is not always possible due to several limitations but nanodelivery systems seem to be able to overcome these issues. The choice of the essential oil, as well as the choice of the nanodelivery system influences the therapeutic efficacy obtained. While several studies on the characterization of EOs exist, this review assesses the characteristics of the nanomaterials used for the delivery of essential oils, as well as impact on the functionality of nanodelivered essential oils, and successful applications. Two classes of delivery systems stand out: polymeric nanoparticles (NPs) including chitosan, cellulose, zein, sodium alginate, and poly(lactic-co-glycolic) acid (PLGA), and lipidic NPs including nanostructured lipid carriers, solid lipid NPs, nanoemulsions, liposomes, and niosomes. While the advantages and disadvantages of these delivery systems and information on stability, release, and efficacy of the nanodelivered EOs are covered in the literature as presented in this review, essential information, such as the speed of emergence of a potential bacteria resistance to these new systems, or dosages for each type of infection and for each animal species or humans is still missing today. Therefore, more quantitative and in vivo studies should be conducted before the adoption of EOs loaded NPs as an alternative to antibiotics, where appropriate.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Stabilising the natural colour of wood species exposed to light in indoor conditions is a challenge that could be better addressed based on a deeper understanding of the occurring phenomena and ...influencing factors. This paper investigates comparatively the light-induced colour changes for three hardwood species, namely, European maple (Acer pseudoplatanus L.), European ash (Fraxinus excelsior L.) and European walnut (Juglans regia L.), as well as the influence of finishing with three types of clear, colourless waterborne lacquers: acrylic-polyurethane (F1), acrylic (F2) and polyurethane (F3) on their colour stability. Colour measurements in the CIELab system in conjunction with an artificial accelerated ageing test under the action of UV-VIS radiation, simulating natural light passing through window glass, and two types of test samples were employed to highlight the influence and contributions of the wood substrate and of the coating films to the global colour modifications. Coating films applied on 1 mm clear glass slides were employed as a sort of “detachable” finish for this purpose. Direct exposure to UV-VIS light caused visible colour changes for both uncoated and coated wood surfaces, the values of the calculated colour differences (ΔE) after a 72 h exposure being dependant on both the wood species and the coating material. Excepting two situations for walnut, statistically significantly higher colour differences were obtained for the uncoated samples: maple (9.36 units), ash (8.39 units), walnut (6.20 units), compared to the coated ones: maple (4.92–5.71 units), ash (2.25–3.94 units), walnut (4.74–7.70 units). The wood substrates underlying the coating films were found to bring the maximum contribution to the overall colour changes in the clear coated surfaces, while the coating films employed in this research demonstrated a fairly good colour stability to UV-VIS light exposure, with maximum colour changes (∆E) up to only 1.30 units. Overall, the wood species and the type of coating were found as influencing factors in interaction with the light-induced colour changes in wood surfaces in indoor conditions.
The acoustic features of old resonance wood in violins exhibit a superior quality when compared to those from new resonance wood. This study focuses on an assessment of the sound quality of two types ...of wood for musical instruments, spruce and maple (class A and D), before and after aging via thermal and UV exposure. The samples were characterized before and after UV aging in terms of color change (using a Chroma meter), surface morphology (using a MarSurf XT20 instrument), chemical changes (monitored by FTIR spectroscopy), and sound propagation speed (using an ultrasound device). After UV treatment, the wavier surface increased the area of exposure and degradation. Also, the color changes were found to be more accentuated in the case of spruce compared to sycamore maple. The FTIR results indicated more advanced aging processes for spruce when compared to maple under the same experimental conditions. This difference resulted mostly from the increased formation of carbonyl-containing chromophores via oxidative processes in spruce rather than in maple, which is in agreement with the color change findings. Exposure of both species to thermal and UV radiation led to an increase in sound propagation speed, both longitudinally and radially, and to a greater extent in wood quality class A when compared to quality class D.
The objective of this research was to establish comparatively some relevant features of Turkey oak and sessile oak wood, in order to better understand the drying behavior of these species. The ...analyzed samples were obtained from freshly harvested trees of the same age, originating from the Southern Sub-Carpathians. The microscopic analysis revealed that Turkey oak has larger earlywood pores than sessile oak. In heartwood, they are partly filled with tyloses for both species. The macroscopic analysis showed that Turkey oak wood has a much lower proportion of heartwood (only 50%) compared to sessile oak (90%). The comparative FTIR analysis of the two species showed similar qualitative chemical composition, but also some differences between sapwood and heartwood regarding the relative proportion of the main constituents, and very likely in the structure of lignin. High amounts of extractives were found in Turkey oak sapwood (5.34% in cold water, 7.77% in hot water, and 21.60% in NaOH 1%), close to the values obtained in sessile oak heartwood. The research also revealed that the Turkey oak sapwood and heartwood have statistically similar values of oven-dry density, shrinkage coefficient, fiber saturation point, while in sessile oak, the values are clearly higher in the heartwood.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Subfossil oak (SO) wood material, originating from three different buried trunks discovered in recent years by excavations in riverbanks on Romanian territory, was analysed in this research. Aged oak ...recovered from constructions (AO_C) and recent/new oak wood material (NO) were also investigated to provide comparative data for the SO. The oven-dry density and the basic density, the total volumetric and linear swelling and shrinkage coefficients and the compression strength parallel to the grain were the selected physical and mechanical properties considered. The experimental results showed a lower density of SO compared to NO and AO_C tested by up to about 19–20%, alongside a trend of increased dimensional instability, with variability among the tested assortments. The compression strength parallel to the grain was reduced by 19–31% compared to NO. The properties of AO-C were closer to those of NO, but differences between wood materials from different sources and of different ages were registered. A positive linear correlation was found between compression strength parallel to grain and the basic density for all types of material and assortments tested. These comparative results have to be considered by designers and engineers in the valorisation of SO in furniture design and other applications.
Color and chemical changes were investigated in beech wood (Fagus sylvatica L.) following light steaming and further heat treatment for 2.5 h at 200 °C by two techniques (industrial ThermoWood versus ...a laboratory procedure in the presence of air). Colour changes were evaluated in the CIE Lab system, while Fourier transform infrared spectroscopy with attenuated total reflection (FTIR-ATR) investigation was employed to highlight and compare the associated chemical changes. Light steaming caused only minor chemical changes (limited hydrolysis of hemicelluloses) not ready detectable by FTIR. In contrast, heat treatments caused visible changes in the FTIR spectra, especially in the region 1800 to 1500 cm-1, consisting mainly in a clear decrease of the absorption band for conjugated carbonyls at 1643 cm-1 and a slight apparent increase of the absorption bands for lignin at 1506 and 1595 cm-1. A significant variation of the ratios of relevant absorption bands indicated complex chemical changes, including hydrolytic, oxidative, and condensation reactions. FTIR ratios and the mass loss values in the two heat treatments relate, both indicating a more advanced modification in the case of the ThermoWood process.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The behavior of paulownia wood (Paulownia elongata) was investigated using three different ageing tests: simulated natural ageing under the influence of light under indoor conditions, ...temperature-induced ageing in the dark, and UV-induced ageing. Ageing effects were evaluated by color measurements in the CIE Lab system. Simulated natural ageing of wood in indoor conditions (6 months) and UV-accelerated ageing (72 h) are complex and dynamic processes, which resulted mostly in yellowing of the samples due to photo-degradation. Temperature-induced ageing (288 h at 100 C) resulted mostly in a rapid and visible darkening of the paulownia wood. Comparative in-time evolution of color changes during accelerated UV ageing testing and simulated natural ageing testing under indoor conditions allowed the estimation of an acceleration index of about 50X. Fourier transform infrared spectroscopy (FTIR) was used to examine specific chemistry changes occurring during these ageing tests. UV light from natural or artificial sources caused primarily lignin degradation followed by oxidative processes leading to carbonyl-containing chromophores. Temperature-induced partial degradation of hemicelluloses and oxidative processes resulted in the formation of chromophores containing mostly conjugated carbonyl groups. This research highlighted that paulownia wood (P. elongata) is quite sensitive to ageing under the action of light and temperature, which cause notable color and surface chemistry changes.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
This paper presents the investigations conducted on three types of fibre-reinforced epoxy-resin hybrid composites with different structures, manufactured using midrib long fibres of date palm ...(Phoenix dactylifera L.) and Calotropis procera fibres. The two types of fibres were formed into flat sheets, without adding other chemicals or resins, and employed as reinforcing layers in the structure of the multi-layered laminate composites. Three-layer and five-layer epoxy-reinforced laminates were manufactured from the sheets of date-palm fibres and Calotropis sheets bonded with laminar epoxy resin. Water resistance investigation and mechanical testing under tensile, bending and impact loads were conducted in the research in order to evaluate and compare the performance of the resulting composites. Emphasis was put on the effect of various factors, such as the type of reinforcement material and the number of plies in the laminate on the mechanical behavior of the composites. The interpretation of those results was supported by the stereo-microscopic investigation of the adhesion between the layers of the composites, and the vertical density profile (VDP), which showed the repartition of the density on the composite thickness depending on the layer material. The results of the mechanical performance of the composites showed lower values of tensile strength, tensile modulus of elasticity and impact resistance and an increase of water absorption (WA) and thickness swelling (TS) for the five-layer composites compared to the three-layer composites. Contrarily, the addition of Calotropis fibres improved the flexural strength and the flexural modulus of elasticity. The alkali treatment of the Calotropis fibres improved the mechanical performance of the composites compared to the ones made with untreated fibres, because of an apparent increase in cellulose content and free hydroxyl groups revealed by FTIR spectra.
This paper investigates the potential of clove (Eugenia caryophyllata) essential oil (C-EO) as a wood protection system for use in cultural heritage conservation. The preventive and curative ...antifungal efficacy of C-EO was compared to a boron containing wood preservative (Diffusit S) in two laboratory tests on Europe-an beech (Fagus sylvatica) and Scots pine sapwood (Pinus sylvestris) mini-blocks. Non-sterile, air-infected wood samples were employed in the first test, while wood samples with active attack, as result of inocula-tion with three fungal strains isolated from cultural heritage sites, in the second test. Untreated controls and C-EO-treated wood blocks were incubated up to 150 days to monitor and quantify fungal growth. The experimental results showed antifungal efficacy of C-EO to be higher than that of the boron wood preservative at the concentrations used. Concentrations of C-EO 5 % - 10 % in ethyl alcohol prevented mould growth for at least 150 days, while a concentration of 10 % delayed or suppressed active attack by decay fungi. This effect, determined up to 90 days of incubation, was dependant on the type of fungus
The study investigates the effect of the type of varnish and the number of layers on some acoustic properties of the resonance spruce in combination with the changes produced in some physical, ...morphological, and chemical properties of wood. In addition to color changes and surface chemistry, the surface roughness and morphology are modified by the thickness of the varnish film, 10 layers being optimal from this point of view, as well as the oil‐based finish. The sound absorption coefficient increases with the number of varnish layers and varies with the sound frequency range, varnish type, and wood quality, all contributing to the acoustic tunability. For example, for a sound frequency of 1.5 kHz, it is observed that the oil‐based varnish with 5 and 10 layers contributes to a full sound, while the alcohol varnish, due to a lower absorption coefficient for this frequency, can lead to some nasal sounds. Applying more than 10 layers of varnish does not improve the sound performance as it will soften the sound in an oil‐based finish and make the sound too sharp in the case of alcohol–varnished wood.
The novelty of the article consists of a comprehensive approach, in which the effect of the varnishing systems (varnish type, number of layers applied) on the selected acoustic parameters is analyzed in combination with the effect they produce on the physical, morphological, and the chemical properties of resonance spruce wood, all contributing to the acoustic tunability.
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