Moisture Uptake Research Articles

A degradable mode I cohesive zone model developed for damage and fracture analysis of dissimilar composite/metal adhesive joints subjected to cyclic ageing conditions

Adhesive joints are frequently exposed to cyclic ageing conditions during their service life, which can have a substantial impact on the mechanical properties of both the adhesive and the substrates. The safe life philosophy, commonly employed in the design of bonded joints, underscores the importance of obtaining an accurate estimate of the adhesive's durability. Therefore, it is essential to enhance the predictive capabilities of the adhesive's mechanical behavior under cyclic ageing conditions.This research aims to expand the use of quasi-static cohesive zone modelling (CZM) for damage and fracture analysis of dissimilar adhesive joints subjected to cyclic ageing environments. The first step involved measuring the mechanical properties of the adhesive through tensile tests on unaged and cyclically aged dogbone specimens, considering their moisture content and ageing cycles. Based on the results, a degradable CZM was developed. To validate the numerical model, dissimilar double cantilever beam specimens (DCBs) of glass fibre reinforced polymer (GFRP) and aluminium were manufactured and tested before and after ageing. The load-displacement curves of the bi-materials bonded joints were successfully predicted using the developed model where the properties of the material are defined as a function of the moisture uptake and ageing cycles at each material element. The obtained results showed that after 4 ageing cycles, the maximum load of DCB specimens decrease considerably.

Thermoset-polymer matrix composite materials of jute and glass fibre reinforcements: Radiation effects determination

In this work, woven jute and glass fabrics were used as natural fiber and synthetic fiber reinforcements, respectively, and unsaturated polyester resin was used as a thermoset polymer matrix to fabricate jute/polyester and glass/polyester composites via compression molding. As expected, glass/polyester exhibited superior performance than jute/polyester composites in terms of mechanical properties and moisture uptake behavior. Further, both composite laminates were exposed to gamma (γ) irradiation at a dose of 5 kGy to enhance their performance. After γ-irradiation, it was revealed that tensile strength, bending strength, tensile modulus, bending modulus, and impact strength increased by approximately 14, 28, 20, 21, and 13%, respectively, for the case of jute/polyester composites while glass/polyester composites demonstrated 13, 27, 15, 14, and 22% increase of the values, respectively. Further characterization of the composite samples was performed via moisture uptake in water and salt solutions, Scanning Electron Microscopy (SEM), and Energy Dispersive Spectrum (EDS) analysis.

Static, fatigue and hygroscopic performance of steel-reinforced resins under various temperatures

Resins are essential structural materials predominantly used in load-bearing connections such as adhesively bonded joints and resin-injected bolted connections. In an effort to improve the latter, a new injection material, Steel Reinforced Resin (SRR), has been developed, consisting of spherical steel particles embedded in a resin. SRR's applicability has been explored in injection bolts used in composite steel-to-concrete floor systems and as an injection material in Fibre Reinforced Polymer (FRP) sandwich web-core panels of highway bridges. While the short-term and creep performance of SRR has been researched, its fatigue behaviour remains unexplored. From joint-level cyclic experiments with SRR, it was observed that joint endurance is dominated by SRR's fatigue performance. There is currently no research on the influence of temperature on SRR's mechanical properties and moisture uptake. This paper fills this gap, by investigating the static and fatigue performance of epoxy, unsaturated polyester polyurethane hybrid (UPE + PU), and vinyl ester based SRRs under ambient and elevated temperatures. Water absorption assessments were conducted on the three resins with and without steel particles to evaluate their durability and corrosion resistance. The results show that temperature significantly impacts tensile stiffness, tensile splitting strength, and fatigue life. Epoxy based SRR endured 20 times more tensile splitting stress cycles to failure compared to the UPE + PU resin based SRR at the same stress range. However, after 200 days of water exposure at maximum temperature, the epoxy resin (with and without steel shot) exhibited a weight increase of 4.0% and 0.50% respectively, suggesting that despite its superior fatigue performance, it may not be suitable for SRR applications in high moisture environments. In contrast, UPE + PU resin and its corresponding SRR displayed substantially lower water absorption.

Influence of Enzymatically Hydrophobized Hemp Protein on Morphology and Mechanical Properties of Bio-Based Polyurethane and Epoxy Foams.

Biomass fillers offer the possibility to modify the mechanical properties of foams, increasing their cost-effectiveness and reducing their carbon footprint. In this study, bio-based PU (soft, open cells for the automotive sector) and epoxy (EP, hard, closed cells for construction applications) composite foams were prepared by adding pristine and laccase-mediated lauryl gallate-hydrophobized hemp protein particles as filler (HP and HHP, respectively). The fillers were able to modify the density, the mechanical properties and the morphology of the PU and EP foams. The addition of HP filler increases the density of PU foams up to 100% and significantly increases the σ values by 40% and Emod values. On the other hand, the inclusion of the HHP as filler in PU foams mostly results in reduced density, by almost 30%, and reduced σ values in comparison with reference and HP-filled foams. Independently from filler concentration and type, the biomass increased the Emod values for all foams relative to the reference. In the case of the EP foams, the tests were only conducted for the foams filled with HHP due to the poor compatibility of HP with the EP matrix. HHP decreased the density, compressive strength and Emod values of the composites. For both foams, the fillers increased the size of the cells, while reducing the amount of open cells of PU foams and the amount of closed cells for EP foams. Finally, both types of foams filled with HHP reduced the moisture uptake by 80 and 45%, respectively, indicating the successful hydrophobization of the composites.

Moisture sources and climatic effects controlling precipitation stable isotope composition in a western Mediterranean island (Pianosa, Italy)

The Mediterranean basin is indicated as a hot spot of climate change, which is an area whose climate is especially responsive to variations. The insular environment is one of the most threatened by the current climate change, especially in terms of drought events, with serious consequences for water scarcity and water stress. This issue is even enhanced in small islands, whose ecosystems are among more sensitive to climatic changes and water availability. The stable isotope composition of hydrogen (δ2H) and oxygen (δ18O) in precipitation is globally recognized as a powerful natural tracer in the water cycle and represents the starting point to investigate hydrological processes. The understanding of the prevailing factors that drive the isotopic variability of precipitation in the Mediterranean is therefore essential to unravel the hydrological processes and to ensure proper and sustainable management of potentially vulnerable resources to climate change. Here, we discuss the results of multi-year isotopic monitoring in the period 2014–2021 of monthly precipitation collected on Pianosa Island (Italy), a small island located in the northern Tyrrhenian (western Mediterranean). The lower slope and intercept of the Local Meteoric Water Line of the island compared to the Global Meteoric Water Line indicated warmer and drier climatic conditions, suggesting the existence of sub-cloud evaporation processes of raindrops during precipitation, especially in summer. The mean δ18O of precipitation was lower with respect to other sites placed at higher elevation in this Mediterranean region, due to the lack of summer precipitation which were generally enriched in heavy isotopes. Temperature and amount effects may explain part of the δ18O variability observed at the monthly and seasonal scale. An HYSPLIT-based moisture uptake analysis indicated the area between the western Mediterranean basin, Italy, and the Adriatic Sea as the region that supplied most of the humidity associated with monthly precipitation samples on Pianosa Island. Less moisture was picked from the northwestern areas of Europe, the North Atlantic Ocean, the proximal Atlantic Ocean, the Iberian Peninsula and North Africa. Consistently with the rainout effect, the higher the moisture fraction picked from the more proximal regions, the more positive the δ18O of precipitation occurring on Pianosa Island; conversely, the higher the percentage of moisture sourced from more distal regions, the more negative the δ18O. A multiple linear model was proposed to predict the δ18O of monthly precipitation from temperature, precipitation amount and moisture origin data, which explained 45% of the δ18O variability. The deuterium excess variability on the island was partly controlled by the local climatic variables, whose effect potentially modifies the original d-excess signature imprinted at the moisture source. No relationship was found between the precipitation deuterium excess and moisture sources, suggesting that more attention should be paid when using the deuterium excess as a tracer of moisture origin, especially in the Mediterranean.

Enhancing the parboiling of pantanal rice with ultrasound-assisted hydration: Mass transfer kinetics and bioactive properties

We evaluated the effects of ultrasound-assisted hydration (UH) on process time and concentration of phenolic compounds during the parboiling of native Pantanal paddy rice (Oryza latifolia) in comparison to conventional hydration (CH). This rice variety is produced by indigenous and riverside communities in the Pantanal biome. The UH increased water absorption, with a 58% average reduction in process time. Irreversible changes in the physical structure of rice (visible to the naked eye and in electronic microscopy images) confirmed that the grains parboiled faster. The Peleg model satisfactorily predicted the moisture uptake experimental data (R2 > 0.94). The CH significantly reduced the concentration of total phenolic compounds (TPC) (16–19%), total flavonoids (TF) (30–40%), and antioxidant capacity (AA) (20–39%) of paddy rice hydrated at 65–75 °C. In turn, the UH caused minimal loss of TPC (<1%), lower reduction of TF (∼7%) and AA (4–12%). The results indicate that ultrasound enhances parboiling processes by increasing mass transfer rates during hydration, consequently shortening processing time, reducing the energy demand, and preserving the nutritional quality of rice. The preservation of phenolic compounds during parboiling via ultrasound-assisted hydration (UH) is notable because the significant loss of these compounds in conventional hydration (CH). Therefore, parboiled rice falls short of being classified as a functional food. By preserving the phytochemicals during parboiling, the proposed process here may contribute to classifying Pantanal rice as a functional food, enabling income generation for local communities through the commercialization of parboiled native rice.

Degradation ofhigh‐performancecyanate ester space composites by anodized aluminum

AbstractCyanate esters are preferred resins for space composites based on excellent mechanical, thermal and dimensional properties. Yet, they are sensitive to co‐reactions with secondary constituents making compatibility a processing challenge. Anodized aluminum mandrels are commonly used for composite manufacturing but deleterious interactions with cyanate ester is not well understood. We investigate here the interaction of anodized aluminum mandrels with surrounding environments and its impact on cure, thermal stability and mechanical properties of M55J/RS3C composites. The uptake and diffusivity of environmental moisture in mandrels was determined gravimetrically and fit to a predictive Fickian model. Cured composite properties were evaluated and correlated with glass transition temperatures (Tg) by dynamic mechanical analysis (DMA), thermal stability by thermal gravimetric analysis (TGA), mechanical properties by flatwise tensile test, and the degradation depth profile by atomic force microscopy (AFM). Parallel to previous results for RS3C but more severe, the degradation penetrated up to 500 μm with reductions of 90°C in Tg, 100°C in thermal stability and 33% mass loss. The inorganic oxide surprisingly absorbs 10× more water at 10× higher rate than composite mandrel materials. The reported results show the anodization presents a unique hydrolysis risk when manufacturing cyanate ester composites so disciplined use and environmental conditioning should be considered when developing space structures.HighlightsCyanate ester composites degraded by anodized mandrels for all conditions.Thermogram signals correlate to composite mechanical degradation.Composite degradation depth gradient determined by atomic force microscopy.

Turning waste into insulation – A new sustainable thermal insulation board based on wheat bran and banana peels

As modern buildings are getting more and more energy efficient in their operation due to improvements in the insulation envelope and building technology, the embodied emissions of the used building materials become increasingly important for the overall carbon footprint of buildings. This necessitates the creation of materials, including thermal insulation materials, with low embodied emissions, such as biomass-based materials. Here, thermal insulation boards based on wheat bran, a milling by-product, were produced using water only or a banana peel slurry as a binder. The density dependence of the thermal conductivity and compressive strength was determined and the moisture uptake, microstructure and thermal stability were evaluated. The boards showed thermo-mechanical properties comparable to other materials based on low-value or waste biomass with their thermal conductivity ranging between 50 and 66 mW/(m·K) and stress at 10% strain values between 20 and 170 kPa. Surprisingly, the properties were not significantly different when comparing those prepared with and without the banana peel binder. The wheat bran insulation boards provide a proof-of-concept for a thermal insulation board with good thermal and mechanical properties and low embodied emissions based on a low-value agricultural by-product.

Modeling and thermodynamic analysis of the hydration and germination of triticale seeds

We investigated the hydration and germination of triticale seeds to improve process efficiency and product quality. The grains were hydrated in a water bath at 20–50 °C for 15 h. Temperatures of 20 °C–30 °C and process times as of 660 min provided the best hydration rates without hindering the germination capacity of the seeds. Throughout processing, we monitored the moisture uptake and volumetric expansion of the samples by gravimetric methods. A tracer pigment added to the hydration water and the images obtained with scaning electron microscopy elucidated the mechanisms of moisture uptake throughout the grains. The water penetrated the grain primarily through the micropyle, a region of high porosity. The mass transfer (diffusion coefficient) and thermodynamic properties (enthalpy, entropy, and Gibbs free energy) indicated the process is non-spontaneous and endothermic. Such piece of information is helpful in equipment design. We also proposed mathematical models, based on Fick's Law of Diffusion, that predict the moisture content of cereal seeds hydrated at 20–50 °C for up to 15 h with great accuracy (P ≤ 3.36% and RMSE≤1.54%).

Biodegradable Composite Film of Brewers’ Spent Grain and Poly(Vinyl Alcohol)

Plastic pollution and food waste are two pressing global challenges that require immediate attention and innovative solutions. In this study, we address these challenges by upcycling brewers’ spent grain (BSG) into biodegradable composite films. BSG, a by-product of the beer brewing process, is commonly discarded in landfills or used as animal feed. By utilizing BSG as a raw material for biodegradable films, we simultaneously reduce waste and decrease plastic pollution. To create the composite films, we employed poly(vinyl alcohol) (PVA) and glycerol as binder materials, along with hexamethoxymethylmelamine (HMMM) as a water-repelling agent. By varying the ratios of these components, we investigated the effects on film properties. Our characterization included assessing moisture uptake and tensile properties. The results revealed that the practical BSG content in the films was 20–60 wt%. Films with this composition exhibited a balance between moisture absorption and mechanical strength. The addition of glycerol improved the flexibility and toughness of the films, while HMMM reduced moisture absorption, enhancing their water resistance. This study contributes to the development of sustainable materials by showcasing the potential of upcycling BSG into valuable biodegradable films. By transforming food waste into useful applications, we reduce environmental burdens and promote a circular economy. Further research is warranted to explore the potential applications and optimize the properties of BSG-based composites.

Effect of cyclic hydrothermal accelerated ageing on the mechanical behavior of components in adhesively bonded aluminum/composite joints reinforced with z-pins

This study presents an in-depth investigation into the moisture absorption and mechanical behavior of Glass Fiber Reinforced Polymer (GFRP) composites and adhesive bonded joints under hydrothermal aging conditions. The aim of this research is to assess the effects of moisture exposure and aging cycles on the performance of GFRP composites and their bonded joints. The experimental program involved preparing GFRP composite specimens and adhesive samples with specific thicknesses and subjecting them to hydrothermal aging cycles. Moisture absorption and desorption behavior of the adhesive and composite specimens were evaluated using Fick’s law, and equilibrium moisture content and diffusion coefficients were determined. Tensile tests were conducted to assess the mechanical properties of the materials, including elastic modulus, ultimate strength, and ultimate strain. The results demonstrated that both the adhesive and GFRP composite exhibited continuous moisture absorption and desorption behavior, following Fick’s law. The moisture uptake reached a saturation point, indicating equilibrium moisture content. The diffusion coefficients of the composite were found to be significantly influenced by the saturated moisture concentrations, highlighting the role of the fiber/matrix interface. Furthermore, the mechanical properties of both the adhesive and GFRP composite were evaluated under hydrothermal aging conditions. The elastic modulus of the adhesive increased after the first aging cycle, indicating the completion of the curing process. However, subsequent cycles resulted in reduced mechanical properties due to plasticization, molecular network changes, and swelling caused by moisture. The GFRP composite exhibited a reduction in ultimate strength and elastic modulus with increasing aging cycles, along with a decrease in strain. The study revealed that the moisture absorption affected the failure modes of the bonded joints, leading to a transition from fiber failure to adhesive failure. Hybrid bonded joints, incorporating pins to distribute stress, exhibited improved stability and higher ultimate loads compared to simple joints. This work contributes to the existing body of knowledge by providing a comprehensive understanding of the moisture absorption/desorption behavior and mechanical properties of GFRP composites and adhesive bonded joints under hydrothermal aging. The findings highlight the need for further investigation into the underlying mechanisms, long-term durability, and development of moisture barrier coatings to enhance the performance of GFRP composites in challenging environmental conditions.

Effect of plasma treatment of wood fiber on the wettability, dynamic mechanical and thermal properties of polypropylene composite panels

This work evaluates the effect of plasma treatment on the wettability, dynamic mechanical and thermal properties of compression-molded composite panels produced from wood fiber (WF) and polypropylene (PP). Initially, WF was treated with different plasma durations (60, 120, and 180 s radiation). Afterward, the contact angle, moisture uptake, storage modulus, loss modulus, damping loss, and weight loss of the specimens prepared from untreated and plasma-treated were evaluated. Results revealed that the plasma treatment facilitates the interactions between WF and PP, and increases the adhesion properties. Compared with the lowest contact angle of 74.8° for the untreated specimens, the highest contact angle was found in the treated specimens around 79.06°, 81.29°, and 82.7°, using 60 and 15 using 180 s plasma radiations. Furthermore, the water absorption of the specimens reduced as a result of plasma treatment. The plasma-treated specimens demonstrated better molecular restriction and larger dynamic modulus than the unmodified ones. The tan δ peak signifying the glass transition temperature of composites shifted to a higher temperature, in the presence of plasma treatment. It was noted that the thermal stability of the composite panels produced from plasma-treated wood was remarkably improved.

Surface, physicomechanical, and chemical properties of wood/polypropylene composites from various formulations after accelerated weathering

Accelerated weathering experiments were used to examine the durability and changes in various attributes of WPCs manufactured with the same wood powder size but varying polypropylene-to-wood ratios. Results from the accelerated weathering test revealed color changes, and each attribute generally declined with longer weathering times. In terms of mechanical qualities, the preservation of strength and stiffness increased with increasing plastic content. More wood flour led to higher moisture uptake in frequent humidity fluctuations and high temperatures. It also caused swelling as wells as subsequent cracks. Such surface damage could result in faster weathering and worse mechanical qualities. Additionally, the carbonyl index and the functional groups on the surface of WPCs underwent significant changes with increased weathering time.

Amikacin-Loaded Chitosan Hydrogel Film Cross-Linked with Folic Acid for Wound Healing Application.

Numerous carbohydrate polymers are frequently used in wound-dressing films because they are highly effective materials for promoting successful wound healing. In this study, we prepared amikacin (AM)-containing hydrogel films through the cross-linking of chitosan (CS) with folic acid along with methacrylic acid (MA), ammonium peroxodisulfate (APS), and methylenebisacrylamide (MBA). In the current studies, an effort has been made to look at the possibilities of these materials in developing new hydrogel film wound dressings meant for a slow release of the antibiotic AM and to enhance the potential for wound healing. Free-radical polymerization was used to generate the hydrogel film, and different concentrations of the CS polymer were used. Measurements were taken of the film thickness, weight fluctuation, folding resistance, moisture content, and moisture uptake. HPLC, FTIR, SEM, DSC, and AFM analyses were some of the different techniques used to confirm that the films were successfully developed. The AM release profile demonstrated regulated release over a period of 24 h in simulated wound media at pH 5.5 and 7.4, with a low initial burst release. The antibacterial activity against gram-negative bacterial strains exhibited substantial effectiveness, with inhibitory zones measuring approximately 20.5 ± 0.1 mm. Additionally, in vitro cytocompatibility assessments demonstrated remarkable cell viability, surpassing 80%, specifically when evaluated against human skin fibroblast (HFF-1) cells. The exciting findings of this study indicate the promising potential for further development and testing of these hydrogel films, offering effective and controlled antibiotic release to enhance the process of wound healing.

Metoclopramide loaded buccal films for potential treatment of migraine symptoms: in vitro and in vivo study

Objective Developing mucoadhesive buccal films loaded with metoclopramide for the treatment of migraine-associated vomiting. Methods Buccal films were prepared using the solvent casting method. Several tests were conducted, including measurement of film weight, thickness, drug content, moisture uptake, swelling index, and DSC analysis. The bioadhesion properties were also assessed. Furthermore, in vitro release profiles and in human bioavailability were studied. Results The developed films were transparent, homogeneous, and easy to remove. Film weight and thickness increased with higher drug content. The drug entrapment exceeded 90%. Film weight increased with moisture uptake, and DSC analysis indicated the absence of drug crystallinity. Bioadhesion properties and swelling index decreased with increasing drug content. In vitro release demonstrated that drug release depended on the drug-polymer ratio. The in vivo study showed significant improvements in Tmax (from 1.21 ± 0.33 to 0.50 ± 0.0) and Cmax (from 45.29 ± 14.66 to 63.27 ± 24.85) compared to conventional tablets. Conclusion The prepared mucoadhesive buccal films exhibited the desired characteristics and demonstrated enhanced drug absorption, evidenced by the significantly reduced Tmax and increased Cmax compared to conventional tablets. The results indicate the successful achievement of the study objectives in selecting and designing an effective pharmaceutical dosage form. as cm2

Design and Characterisation of Rosuvastatin Calcium Nanosuspension Loaded Transdermal Patch

Objective: The present investigation highlights the formulation and evaluation of nanosuspension-loaded transdermal patches of poorly soluble antilipidemic drug (rosuvastatin) Methods: Dissolution characteristics of drug was improved by preparation of nanosuspension employing precipitation–ultrasonication technique using a different blend of water-soluble film forming polymers such as hydroxyl propyl methyl cellulose (HPMC K4M), Eudragit and were further characterized by fourier transformation infrared spectroscopy (FTIR), Malvern zetasizer and SEM. Propylene glycol and tween 80 were used as stabilizers. Based on the particle size of the formulation, the best one of NS4 was selected and fabricated into the transdermal patch by solvent casting method. The prepared formulations were evaluated for various parameters like drug excipient compatibility, appearance, morphology, thickness, tensile strength, folding endurance, % elongation, % moisture content, % moisture uptake, % drug content, in-vitro drug permeation, and stability studies were performed for the optimized formula according to the ICH Q1A (R2) guideline under 4°C and 25°C RH for three months. Results: Amongst all formulation, P4 transdermal patches were considered the optimized formulation. It has the highest in-vitro drug permeation (86.01±0.05%), thickness (0.86±0.09), weight uniformity (475.0±8.60 mg), folding endurance (279.3±9.39), moisture uptake (7.06±1.75%), moisture content (6.81±2.34 %) and stable formula Conclusion: Therefore, transdermal patches were considered to be potentially suitable for the sustained release of drugs to improve patient compliance.

Box-Behnken design to optimize the cross-linked sodium alginate/mucilage/Aloe vera film: Physical and mechanical studies

The crosslinked sodium alginate/mucilage/Aloe vera/glycerin was optimized by different ratios of each factor to be an absorption wound dressing base for infected wound healing. Mucilage was extracted from seeds of Ocimum americanum. The Box-Behnken design (BBD) in response surface methodology (RSM) was used to construct an optimal wound dressing base with the target ranges of mechanical and physical properties of each formulation. The independent variables selected were sodium alginate (X1: 0.25–0.75 g), mucilage (X2: 0.00–0.30 g), Aloe vera (X3: 0.00–0.30 g), and glycerin (X4: 0.00–1.00 g). The dependent variables were tensile strength (Y1: low value), elongation at break (Y2: high value), Young's modulus (Y3: high value), swelling ratio (Y4: high value), erosion (Y5: low value), and moisture uptake (Y6: high value). The results showed that the wound dressing base with the most desirable response consists of sodium alginate (59.90 % w/w), mucilage (23.96 % w/w), and glycerin (16.14 % w/w) without Aloe vera gel powder (0.00 % w/w).

Enhancement of the hygroscopic and acoustic properties of indoor plasters with a Super Adsorbent Calcium Alginate BioPolymer

The present study introduces a novel-composition lime plaster that contains a Super Adsorbent BioPolymer (SABP) based on Calcium Alginate (CaAlg) for indoor applications, to improve hygrothermal and acoustic comfort. The sorption isotherm of the plaster, the moisture buffering value (MBV), the acoustic absorption, and the thermal conductivity have been assessed. The hygrothermal and acoustic properties of the modified plaster have been compared with those of the original composition to evaluate its performance under different concentrations of CaAlg (between 10 and 30% wt). Adding the CaAlg SABP to a conventional lime plaster consistently enhanced its hygroscopic properties. The results show a substantial increase in the equilibrium moisture uptake (between 10 and 23 fold) and MBV, from 0.9 to 9.3 g/(m2⋅%RH). The sound absorption coefficient improved by 0.1–0.2 at higher frequencies than 500 Hz. This paper provides detailed information on the characterization of the material. It includes details about using a dynamic vapor sorption (DVS) analyzer to evaluate the sorption isotherm and MBV. It also contains information on the impedance tube method used to measure the acoustic absorption of the material.

Transpiration rates decline under limited moisture supply along hillslopes in a humid karst terrain

Topographic positions can mediate subsurface water availability, but its effects on tree transpiration are controversial. In humid karst regions, climax forests are usually not limited by moisture supply, even at the summit, through absorbing water from deep layers. However, little is known on the transpiration pattern and its limiting factor on the shrubland widely distributed along the karst hillslopes. In the current study, Rhus chinensis, a widely spread constructive species in natural restoration was selected. Meteorological factors, 0–300 cm soil–epikarst moisture, sap flow, and root water uptake were studied during an entire growing season to assess how hillslope positions affected transpiration. We found the mean water content in uphill was only around 60 % of that in downhill, indicating a contrasting water supply along the slope. However, there were no significant differences in the xylem isotopic composition and lc–excess which suggested the similar water uptake strategies in both uphill and downhill. R. chinensis primarily relied on the soil water rather than epikarst water (groundwater) along the hillslope because of the MixSIAR model results and more negative lc–excess values (−13.18 ‰). R. chinensis exhibited decreases of nearly half in the transpiration rate and amount in uphill compared to those in downhill. In downhill with sufficient water availability, transpiration followed the variation in atmospheric water demand. In uphill, a poor moisture supply limited tree transpiration and its response to atmospheric water demand. Our findings revealed that the early successional species did not entirely depend on atmospheric water demand, absorbing deep epikarst water as the mature forest. The transpiration rates of those species declined by nearly half to adapt to the water–limited environment along the hillslope in the humid karst region. This study can contribute to the evaluation of eco–hydrological functions during natural restoration.

Ultra Fast Imaging NMR method for measuring fast transport processes in thin porous media

Measuring moisture distributions during fast transport processes in thin porous media is a challenging task. In this paper, Ultra Fast Imaging (UFI) NMR is proposed as a valuable measurement technique for investigating moisture uptake in porous media by achieving a temporal resolution of 10 ms and spatial resolution between 14.5 and 18 μm. This paper gives a detailed explanation about the methodology and the interpretation of the signal intensity. It is shown that there exist specific T1- and T2− relaxation time conditions for performing UFI experiments with signal-to-noise ratios that are sufficiently high. In most cases, a contrast agent is required to optimize these relaxation times and achieve the optimal measurement conditions. In the first part of this paper, both CuSO4 and Clariscan are discussed as possible contrast agents. Furthermore, it is shown that the signal intensity can be linked to the moisture content for water based liquids. The second part of this paper covers penetration experiments on porous PVDF membranes. These measurements show that the technique is able to measure moisture profiles during fast capillary penetration and allows to extract moisture front positions. Those front positions follow a linear time behavior in PVDF membranes. Lastly the NMR-measurements showed similar results when compared to scanning absorptometry (ASA).