Outer Bark Research Articles

The physicochemical properties of cellulose surfaces modified with (depolymerised) suberin and suberin fatty acid

This paper provides evidence for the adsorption of suberin onto cellulose and illustrates the effect of suberin and suberin fatty acid (SFA) treatment on the physicochemical surface properties of the modified cellulose substrate. Suberin and SFA were extracted from the outer bark of birch (Betula pendula Roth) and characterized by Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry (GC–MS). The results confirmed the extracts to comprise primarily of depolymerised suberin and SFA. The adsorption of suberin and SFA on cellulose was studied by treating the filter paper with solutions of suberin and SFA. Changes in the surface topography of the filter paper following treatment were analysed with atomic force microscopy and the effect on wettability assessed through contact angle measurement. X-ray photoelectron spectroscopy analysis showed that the cellulose substrate was evenly covered. GC–MS analysis showed which suberin monomers were preferentially adsorbed on the cellulose surfaces. Based on these results, it can be inferred that suberin and SFA have the potential for cellulose surface modification. This finding supports the view that suberin and SFA could be used to improve the interfacial properties of cellulose fibre reinforced composites. The novelty in this study is that it provides detailed information, derived though advanced experimental techniques, about the manner and mechanisms behind changes in surface physiochemical properties of cellulose obtained through suberin and SFA adsorption.

Cork from Quercus suber L.: Forest certification system for sustainable management of cork oak forests

Cork is the outer bark of the cork oak (Quercus suber L.), it is a secondary protection structure of tree, and its chemical composition is different from that of other lignocellulosic materials, as wood, agricultural, or forestry wastes. The best cork sheets are used to manufacture natural cork stoppers, vital in the aging process of “great” wines. It is a Mediterranean species covering an overall area of 2,139,942 hectares; Portugal and Spain countries where it occupies a larger area. This paper was developed to assess the possibility of implementing a system of payment for ecosystem services and/or a certification of forest management for small stands of cork oak privately owned areas of less than 25 hectares. The process is leaded by the Regional Groups of Forest Certification and Chain of Custody, main regional institutions. The system used is the Programme for the Endorsement of Forest Certification (PEFC). As specified by the multifunctional forestry applied in these ecosystems, its main use is the production of natural cork stoppers for the quality aging wines. The cork oak forests are living representatives of sustainability and a driving force of sustainable development.

Effect of Alkali Treatment on the Tensile Properties of Grape Cane Fibers by Integrating Digital Image Correlation Method

The objective of this study was to investigate tensile properties of two grape cane fibers, namely, outer bark (OB) and inner bark (IB). The cane is a necessary annual by-product from vineyards and is produced at approximately 36 million tons yearly around the world, which currently has no substantial commercial utilization. Grape cane fibers were subjected to an alkali treatment, at different concentrations, to separate the fibers from the cane. Moreover, two displacement methods such as system compliance (Cs) and digital image correlation (DIC) were performed to determine Young’s modulus of the samples, and the results were compared. The OB fibers had better overall properties than IB fibers. The effect of the treatment concentrations (1, 3, 5, and 7 wt% of sodium hydroxide) and gage lengths (10, 25, and 40 mm) on the tensile properties was not consistent for both fiber types. The DIC method consistently yielded greater tensile modulus of the samples than the Cs method for OB fibers.

Specific Gravity of Inner and Outer Larch Bark

Larch bark is an interesting resource for the production of insulation panels. As it consists of a sugar-rich inner bark and an outer bark containing more durable components, there is the requirement to separate these compartments. Additionally, bark is often mixed with wooden pieces after industrial debarking processes. In this study, the wet density, dry density, and specific gravity of wood, whole bark, and inner and outer bark are investigated using the pycnometer method, which has been proven to be adequate for the volume measurement of irregularly shaped, light objects such as bark flakes. Soaked with water, the density of the inner bark is highest, followed by wood, and the lightest is the outer bark. Because of different moisture contents, the wet density is not directly comparable. The outer bark sucked up less water than the inner bark. Focusing on the specific gravity, the wood is the heaviest, followed by the outer bark and the inner bark. The differences are significant for both methods, displaying a promising physical basis for separation methods based on density differences. These might be a means to pick out more durable and less hygroscopic outer bark particles from a bark mixture in order to produce optimized bark composites.

Chemical and structural characterization of Myracrodruon urundeuva barks aiming at their potential use and elaboration of a sustainable management plan

The objective of this work was to characterize chemically and structurally barks from Myracrodruon urundeuva Allemao in order to provide information that values its use and that is relevant to elaborating sustainable management plan. Anatomy and thickness of the periderm and secondary phloem, and also the bark histochemistry were analyzed. Ash, extractive, suberin, lignin, and polysaccharide contents were determined. The mineral composition of the ashes, the phenolic composition, and the antioxidant activity of the bark extracts were also analyzed. The M. urundeuva bark presented rhytidome frequently anastomosing periderm layers, forming a reticulate pattern. It was marked by the presence of secretory ducts and dead phloem between the periderms. Great amount of phenolic content was noted in the outer bark. The average chemical composition of the bark was 26.96% total extractives, 25.38% total lignin, 0.95% suberin, 9.24% ash, and 37.13% polysaccharides. Total phenolic content was 165.90 mg GAE g−1 of extract, flavonoids 91.36 mg catechin g−1 of extract, and tannin content 8.50 mg catechin g−1 of extract. An interesting processing route for the use of the M. urundeuva bark would be to obtain polar extractives, which presented a good antioxidant activity, and ash removal that can be used as fertilizer in forest plantations. Subsequently, use the fibrous structure of these barks as a source of lignocellulosic material for different uses.

Biological traits and life history of Pagiophloeus tsushimanus (Coleoptera: Curculionidae), a weevil pest on camphor trees in China

Cinnamomum camphora (L.) J. Presl. (Laurales: Lauraceae) is widely cultivated as an important landscape tree species in many urban areas in South China, especially in Shanghai City. Pagiophloeus tsushimanus Morimoto has become a destructive insect pest of C. camphora plantations in Shanghai, but the biological and ecological traits of this pest remain largely unknown. In this study, we investigated the damage and life history and determined the larval instar of P. tsushimanus. The results indicated that P. tsushimanus is a monophagous weevil pest, and C. camphora is the unique host tree species. C. camphora plantations in all administrative districts of Shanghai have been seriously damaged by P. tsushimanus. Adults often aggregate for feeding on the tender bark of twigs and occasionally on newly emerged buds. After experiencing damage, the twigs shrink and crack and the buds will shrink. Adults tend to repeatedly mate and oviposit, and all females lay single eggs at a time. Eggs will be covered with a mixture of secretions and wood chips by female adults. Larvae (1st–2nd instar) feed on the phloem, while 3rd–5th instar can bore into the phloem and the cambium. Massive tunnels, including three shapes (inverted “L”, inverted “T”, and inverted “Z”), were observed in the trunk of each tree, and resulted in swelling of the outer bark. P. tsushimanus has one life cycle per year in Shanghai. Both adults and larvae (3rd–5th instar) overwinter from early November to early April. Adults overwinter in grooves on the underside of branches or at branch nodes, and larvae overwinter in tunnels. Five larval instars of P. tsushimanus were determined according to Dyar's and Crosby's rules. The biological traits and life history of P. tsushimanus have been identified and can provide guidance in terms of pest control and plantation management.

Foraging Activity of Woodpeckers on Various forms of Artificially Created Deadwood

Many woodpecker species rely on different forms of deadwood for nesting and foraging. However, the knowledge of the effect of enrichment of their habitat with different types on deadwood of this species group is lacking. Complex conservation-oriented management, including deadwood enrichment, was applied in a 20 ha even-aged oak-dominated woodland in Hungary. The foraging activities of woodpecker species were documented on selected treated trees over one, two and three years since these measures were implemented. The 109 individual oak trees examined represented five deadwood types: damaged-, girdled-, felled trees, and low- and tall stumps. We analysed the relationships between three variables (depth of foraging work, type of deadwood, and year) and foraging activity. Our results illustrated the prompt responses of woodpeckers to the treated trees. The woodpeckers used the five deadwood types in very different ways, and foraging activity was found to vary greatly in terms of depth of foraging and between years. More activity was carried out on both low- and tall stumps than on any other type one year after the treatment, whilst work on girdled trees and tall stumps predominated two and three years after the treatment. The utilisation of felled- and damaged trees by woodpeckers proceeded at a markedly slower pace than that of girdled trees and stumps, but the utilisation increased gradually. Most of the foraging activity was found to be on the outer bark, however, work on the inner bark and in the sapwood increased between the three years. The measures to conserve the woodpecker species should include the permanent creation and maintenance of various forms of deadwood to provide diverse and continuous foraging sites for woodpeckers.

Influence of PVA Molecular Weight and Concentration on Electrospinnability of Birch Bark Extract-Loaded Nanofibrous Scaffolds Intended for Enhanced Wound Healing.

Triterpenes from the outer bark of birch (TE) are known for various pharmacological effects including enhanced wound healing. Apart from an already authorized oleogel, electrospun nanofiber mats containing these triterpenes in a polyvinyl alcohol (PVA) matrix appear to be an advantageous application form. The effects of PVA molecular weight and concentration on the fiber morphology have been investigated. Three different molecular weights of PVA ranging from 67 to 186 kDa were used. The concentration of PVA was varied from 5 to 20 wt%. Polymer solutions were blended with colloidal dispersions of birch bark extract at a weight ratio of 60:40 (wt.%). The estimated viscosity of polymer solutions was directly linked to their concentration and molecular weight. In addition, both pure and blended solutions showed viscoelastic properties with a dominant viscous response in the bulk. Fiber morphology was confirmed using scanning electron microscopy (SEM). Both polymer concentration and molecular weight were found to be significant factors affecting the diameter of the fibers. Fiber diameter increased with a higher molecular weight and polymer concentration as more uniform fibers were obtained using PVA of higher molecular weight (146–186 kDa). In vitro drug release and ex vivo permeation studies indicated a faster drug release of betulin from electrospun scaffolds with lower PVA molecular weight. Our research suggests that the fabricated TE-loaded PVA electrospun dressings represent potential delivery systems of TE for wound care applications.

Состояние и перспективы использования древесной коры

The tree bark has been used by mankind for centuries in various ways. The bark has special structure and chemical components, and it is used mostly among the natural raw materials. The bark has numerous functions during the lifespan of the plant, while itself is also changing due to its age. The outer bark is very diverse, depending on the species, the age and ecological factors. Between 3 and 4 hundred thousand cubic meter bark is produced yearly by forestry and woodworking industry, which is utilized in many ways, most of the bark is still burned. The article provides a literature review in the field of studies of the structure, properties, traditional and modern methods of using tree bark. After a short anatomical review, the protective role of bark for a living tree, the use of bark as an indicator of environmental pollution are discussed. Physical properties, chemical composition of the bark, debarking methods are considered. The complex chemical composition, wide variety of secondary metabolites, the physical and mechanical properties of the bark make it possible to use bark in medicine, the energy sector, agriculture and various fields of industry. The chemical exploration of the bark and producing different compounds from it, the production of particle and fiber boards based on bark, heat-insulating boards, composite materials, and water and gas clarification are increasingly comes to the front and becoming the most perspective areas of application of tree bark as a unique natural material and a renewable resource representing huge potential for use in various fields of human life.

Metabolic Effects of a Eucalyptus Bark Lipophilic Extract on Triple Negative Breast Cancer and Nontumor Breast Epithelial Cells.

In this work, untargeted metabolomics was used to unveil the impact of a Eucalyptus (Eucalyptus nitens) outer bark lipophilic extract on the metabolism of triple negative breast cancer (TNBC) and nontumor breast cells. Integrative analysis of culture medium, intracellular polar metabolites, and cellular lipids provided a comprehensive picture of cell metabolic adaptations, which enabled several hypotheses about the metabolic targets and pathways affected to be proposed. One of the most marked effects in MDA-MB-231 breast cancer cells, upon 48 h incubation with the E. nitens extract (15 μg/mL), was the enhancement of the NAD+/NADH ratio, likely reflecting a shift to mitochondrial respiration, which appeared to be fueled by amino acids and fatty acids resulting from hydrolysis of neutral lipids (triglycerides and cholesteryl esters). Contrastingly, in MCF-10A breast epithelial cells, the E. nitens extract appeared to intensify glycolysis and the tricarboxylic acid cycle (resulting in a decreased NAD+/NADH ratio), while having no effect on the cell lipid composition. This knowledge improves the current understanding of the biological activity of E. nitens bark extracts and is potentially useful to promote their development in the field of TNBC anticancer therapy.

Fate of Antioxidative Compounds within Bark during Storage: A Case of Norway Spruce Logs.

Softwood bark is an important by-product of forest industry. Currently, bark is under-utilized and mainly directed for energy production, although it can be extracted with hot water to obtain compounds for value-added use. In Norway spruce (Picea abies [L.] Karst.) bark, condensed tannins and stilbene glycosides are among the compounds that comprise majority of the antioxidative extractives. For developing feasible production chain for softwood bark extractives, knowledge on raw material quality is critical. This study examined the fate of spruce bark tannins and stilbenes during storage treatment with two seasonal replications (i.e., during winter and summer). In the experiment, mature logs were harvested and stored outside. During six-month-storage periods, samples were periodically collected for chemical analysis from both inner and outer bark layers. Additionally, bark extractives were analyzed for antioxidative activities by FRAP, ORAC, and H2O2 scavenging assays. According to the results, stilbenes rapidly degraded during storage, whereas tannins were more stable: only 5–7% of the original stilbene amount and ca. 30–50% of the original amount of condensed tannins were found after 24-week-storage. Summer conditions led to the faster modification of bark chemistry than winter conditions. Changes in antioxidative activity were less pronounced than those of analyzed chemical compounds, indicating that the derivatives of the compounds contribute to the antioxidative activity. The results of the assays showed that, on average, ca. 27% of the original antioxidative capacity remained 24 weeks after the onset of the storage treatment, while a large variation (2–95% of the original capacity remaining) was found between assays, seasons, and bark layers. Inner bark preserved its activities longer than outer bark, and intact bark attached to timber is expected to maintain its activities longer than a debarked one. Thus, to ensure prolonged quality, no debarking before storage is suggested: outer bark protects the inner bark, and debarking enhances the degradation.

Antioxidant Activity and Isoflavonoid Components in Different Sections of Pueraria lobata Root

The isoflavonoids content and antioxidant activity in different sections of Pueraria lobata roots, including the root outer bark, kudzu root and whole root were investigated in this study. Isoflavonoid concentrations in p. lobata roots were determined by high performance liquid chromatography. The antioxidant activity of P. lobata roots was assessed by total phenol content. DPPH free radical scavenging assay, ABTS free radical scavenging assay and reducing power. The root outer bark of P. lobata root possessed higher isoflavonoids content than whole root or kudzu root (p ＜ 0.05). The levels of antioxidant potential of the root outer bark assayed by total phenolic content, DPPH, ABTS and reducing power were significantly higher than those of the whole root or the kudzu root (p ＜ 0,05) , The main isoflavonoids in all sections of P. lobata roots were puerarin, daidzin, daidzein, genistin and genistein. The major isoflavonoid puerarin in root outer bark exhibited the greatest antioxidant activity in P. lobata roots.

Development and characterization of eco-sustainable banana fiber nonwoven material: surface treatment, water absorbency and mechanical properties

In this study, four types of ecofriendly non-woven materials were developed from different parts of bark and leaf of banana plant i.e. outer bark, middle bark, inner bark (IB) and mid rib (MR) by wet laid web formation. Fibers were extracted chemically by treating with NaOH from all the parts. Due to the very high absorbency of banana fiber, the prepared non-wovens were treated with water repellent (WR) chemical for improving their hydrophobicity. The effects of WR on the physical, mechanical and morphological properties of the non-wovens were also investigated. The hydrophobicities of all the nonwovens were improved remarkably with the concentration of WR. It took 1.25, 2.69, 4.20 and 4.67 h to absorb a drop of water for OB nonwovens at a concentration of 1%, 5%, 10% and 20% WR respectively where, all the untreated nonwovens took almost zero seconds. Just like OB, all other nonwovens followed exactly the same trend. OB nonwoven exhibited the highest tensile strength (TS), Elongation-at-break (EB) and young‘s modulus (YM) of 8.56 Mpa, 12.56% and 215 Mpa respectively where, IB showed the lowest TS and YM of 1.23 and 67 Mpa respectively and MR showed the lowest EB of 1.77%. Although there were no remarkable effects of WR on tensile properties nevertheless, TS and YM were increased but EB was decreased to a small extent with the concentration of WR. The chemical bonding, morphology of the fiber and nonwovens were also investigated by FTIR and SEM analysis.

Comparison of alkali treatments on selected chemical, physical and mechanical properties of grape cane fibers

Grape cane is a necessary annual by-product of a vineyard. It is available in large quantities, an estimated 9 million tons (oven-dry weight) annually, having approximately 18 million acres worldwide. There is currently no substantial commercial utilization of grape cane fiber, with the majority incinerated. The main objective of the current study is to characterize grape cane fibers extracted at different alkali treatment concentrations and to determine the optimum treatment concentrations that can produce better fiber properties. The fibers were treated at 1, 3, 5 and 7 wt% of sodium hydroxide (NaOH) at 100 °C for 2 h. The grape cane fibers can be categorized into two types, namely outer bark (OB) and inner bark (IB) fiber after the treatment process. Aspect ratio, chemical composition, crystallinity, changes in the functional groups using FTIR, and tensile properties of OB and IB fibers were investigated. The results show that these two fibers demonstrated dissimilar anatomical structures, cell types, cell dimensions, and tensile properties. Meanwhile, the chemical compositions and crystallinity are equivalent to each other. The overall properties of both fibers were found superior at the lower treatment concentrations.

An Evaluation on Acoustic Behavior of Untreated Tree Trunks Depending on Bark Physical Properties and Fiber Cell Structure

ABSTRACT In recent years, noise pollution generated by increasing global urbanization has become an important issue. This study focused on determining the sound absorption coefficients (SACs) of untreated tree trunks as natural fiber-based materials and predicting their noise reduction coefficients (NRCs). It also evaluated the effects of noise reduction using numerical data. One of the most effective acoustic characteristics is the normal incidence SAC; this was obtained for trunks belonging to species of black locust, narrow-leafed ash, stone pine, silver lime, sweet chestnut, sessile oak, maritime pine, cedar, and plane in the frequency range of 50–6000 Hz using an impedance tube based on a two-microphone transfer function method. The absorbance of sound was found to correlate with the tree species, trunk diameter, bark shape, and the bark’s fibrous structure. The results confirmed that when compared with deciduous species, the trunks of coniferous species exhibit higher NRC values which were recorded as 0.302 ± 0.005 for stone pine and 0.233 ± 0.004 for cedar. Furthermore, the surface morphology of the outer bark of different tree species obtained via scanning electron microscopy revealed that significant variations exist in the microstructure of the bark’s fiber cells.

ОСОБЛИВОСТІ РОЗПОДІЛУ 137Сs У КОМПОНЕНТАХ ЛІСОВОГО БІОГЕОЦЕНОЗУ СВІЖИХ БОРІВ УКРАЇНСЬКОГО ПОЛІССЯ

Вивчено особливості розподілу 137Cs у компонентах лісового біогеоценозу свіжих борів Українсь-кого Полісся. Щільність радіоактивного забруднення ґрунту на пробній площі становила 267±9,6 кБк/м2. Питома активність 137Cs у компонентах біогеоценозу відрізнялася на кілька поряд-ків, з мінімумом у глибинних горизонтах ґрунту (28–30 см шар – 40 Бк/кг) і максимумом у надземнійфітомасі окремих видів рослин (щитник шартрський – 85937 Бк/кг). Компоненти соснового дерево-стану можна розмістити в такий ряд за зменшенням величини питомої активності 137Cs: пагони >кора внутрішня > шпильки > кора зовнішня > гілки тонкі > гілки товсті > деревина, а для трав’яно-чагарничкового покриву характерний такий ряд: щитник шартрський > чорниця > верес звичайний> брусниця > плаун булавовидний > ортилія однобока > ожика волосиста. Моховий покрив характе-ризується вищими величинами питомої активності радіонуклідів порівняно з лишайниковим покри-вом, де епіфітні види лишайників мають менший вміст 137Cs, ніж епігейні. У сосновому біогеоценозіґрунтовий покрив утримує основну частку сумарної активності радіонуклідів (76,66 %), з них на лі-сову підстилку припадає – 14,24 %, а на мінеральні шари ґрунту – 62,42 %. На інші компоненти при-падає – 23,34 %, де сосновий деревостан та моховий покрив відповідно становлять 12,02 та11,04 %, а на підріст, лишайниковий та трав’яно-чагарничковий покрив припадає лише 0,28 %. Осно-вна частка фітомаси фітоценозу припадає на деревний ярус – 85,10 %, на моховий покрив – 14,48 %,а роль інших ярусів рослинності в цьому екотопі була незначною та становила 0,42 %. Розподіл су-марної активності 137Cs по компонентах значно відрізняється порівняно з розподілом фітомаси наодиницю площі. Так, максимальну частку валового запасу 137Cs утримує деревний ярус (51,49 %) тамоховий покрив (47,32 %). Частка решти ярусів незначна, становить 1,19 % і представлена у тако-му порядку за зменшенням утримуючої здатності радіонуклідів: трав’яно-чагарничковий покрив >лишайниковий покрив > підріст. У сосновому біогеоценозі ключовими компонентами в утримуванійздатності та інтенсивності біогеохімічного кругообігу радіонуклідів є лісовий ґрунт, деревний яруста моховий покрив.

Influence of temperature and moisture content on bark/wood shear strength of black spruce and balsam fir logs

The effects of temperature (T) and moisture content (MC) on bark/wood shear strength (BWSS) were studied. Fifteen stems of black spruce (Picea mariana (Mill.) B.S.P.) and balsam fir (Abies balsamea (L.) Mill.) logs were selected and cross-cut into three 1.25 m log sections, corresponding to bottom (1.3 m), middle (3.8 m), and top (6.3 m) positions. BWSS was measured at five temperatures, ranging from 10 to − 30 °C, and at five levels of sapwood moisture contents (SMC), obtained by air-drying, from green state to near to the fiber saturation point (FSP). Bark and sapwood properties, MC and basic density (BD) were also determined. Temperature had a significant effect on BWSS for both species. This property was similar between 10 and 0 °C, and significantly increased as temperature decreased below 0 °C. However, the influence of temperature on BWSS depended on SMC and it varied between the two species. For black spruce, for each temperature between 0 and − 20 °C, BWSS showed similar values for SMC between 157 and 62%. At − 30 °C, BWSS showed a tendency to increase with SMC. For balsam fir, the BWSS increase due to the decrease in temperature was more important as the SMC increased. BWSS increased as SMC approached the FSP of wood for both species. Among the studied covariates, inner bark MC and inner and outer bark BDs significantly affected BWSS. Inner bark MC and SMC affected BWSS similarly. Multiple regressions were developed for prediction purposes, which explained 68 and 69% of BWSS variability for black spruce and balsam fir, respectively.

Changes in Composition of Birch Outer Bark Extractives After Recrystallization with C2-C5 Alkanols

The effects on birch outer bark (BOB) ethanolic extractives’ chemical composition after recrystallization with C2–C5 alkanols were studied in this paper. Ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and 1-pentanol were used as solvents. The solubility of BOB extractives at the solvents boiling point was determined empirically. It was found that, with an increase of the boiling point of the solvents, the solubility of the extractives increased, reaching up to 486 g/L in 1pentanol at 142.2 °C. Recrystallization yields reached up to 67 wt% using 2-butanol and the purity of betulin up to 96 wt% using 2‐propanol as a solvent. Considering the yield of recrystallization, betulin content, boiling point of the solvent, solvent loss, toxicity and eco-friendliness of the solvent, ethanol was chosen to be the most suitable solvent for industrial scale purification of betulin in the BOB extractives. Using only one recrystallization step the content of betulin was increased by 20% — from 75 to 95 wt% and the yield of recrystallization was 32.1 g per liter of solvent.

Hygroscopic properties of thin dead outer bark layers strongly influence stem diameter variations on short and long time scales in Scots pine (Pinus sylvestris L.)

Time series of stem diameter variations (SDVs) recorded by dendrometers are composed of two components: (i) irreversible radial stem growth and (ii) reversible stem shrinking and swelling caused by dynamics in water storage in elastic tissues outside the cambium. However, SDVs measured over dead outer bark (periderm) could also be affected by absorption and evaporation of water from remaining dead bark layers after smoothing the stem surface to properly mount dendrometers. Therefore, the focus of this study was to determine the influence of hygroscopicity of a thin dead outer bark layer on the reversible component of dendrometer records of Scots pine (Pinus sylvestris) under field conditions. To accomplish this, SDVs deduced from dendrometers mounted over dead outer bark were compared among living and dead saplings and mature trees. Results revealed that dead trees showed high synchronicity in reversible daily SDVs compared to living trees throughout several growing seasons (mean Pearson correlation coefficient (r) = 0.844 among saplings and r = 0.902 among mature trees, respectively; P<0.001). Furthermore, diurnal and long-term SDVs closely followed changes in relative air humidity (RH) in living and dead trees. A multiple linear regression analysis of environmental influence on SDVs in dead and living trees revealed that the most important predictor of daily SDVs was RH (relative importance 64 %). Hence, results indicate that dendrometers mounted over dead outer bark with a thickness of <4 mm record hygroscopic shrinking and swelling of the bark tissue, which can amplify fluctuations in whole-tree water status. To conclude, hygroscopic processes must be taken into account when extracting intra-annual radial growth, determining environmental drivers of SDVs, and evaluating changes in tree water status from SDVs recorded by dendrometers, which were mounted over even thin dead outer bark layers.

One-step preparation of bilayered films from kraft lignin and cellulose acetate to mimic tree bark

This contribution presents the development of a dry-cast method for the one-step preparation of bio-based films from wood polymers that mimic the bilayered structure of tree bark, the natural protective layer of the tree. In a simplified view, natural bark can be considered as the superposition of an external homogeneous and non-porous layer (outer bark) and a porous substructure layer (inner bark). This work is a first step for the future development of bio-based biomimetic wood coatings. The film had a bark-like appearance and its total density, bulk density and porosity were similar to values measured in natural bark. Furthermore, the structural characteristics of the studied film, namely specific surface area (BET) and pore size distribution, as well as the performance of the water adsorption ability were investigated and discussed.