Wall Moisture Content Research Articles

Water sorption in wood cell walls–data exploration of the influential physicochemical characteristics

The material properties of wood are intimately tied to the amount of moisture contained in the wood cell walls. The moisture content depends on the environmental conditions, i.e. temperature and relative humidity, but also on material characteristics of the wood itself. The exact mechanisms governing moisture equilibrium between wood cell walls and environmental conditions remain obscure, likely because multiple material characteristics have been proposed to be involved. In this study, we used a data exploration approach to illuminate the important wood characteristics determining the cell wall moisture content in the full moisture range. Specimens of nine different wood species (two softwoods and seven hardwoods) were examined in terms of their material characteristics at multiple scales and their cell wall moisture content was measured in equilibrium with both hygroscopic conditions and at water-saturation. By statistical analysis, the chemical composition was found to be the most important predictor of the cell wall moisture content in the full moisture range. For the other wood characteristics the importance differed between the low moisture range and the humid and saturated conditions. In the low moisture range, the cellulose crystallinity and hydroxyl accessibility were found to be important predictors, while at high moisture contents the microfibril orientation in the S1 and S3 layers of the cell walls was important. Overall, the results highlighted that no single wood characteristic were decisive for the cell wall moisture content, and each of the predictors identified by the analysis had only a small effect in themselves on the cell wall moisture content. Wood characteristics with a major effect on the cell wall moisture content were, therefore, not identified..

Water in Wood: A Review of Current Understanding and Knowledge Gaps

Wood-water interactions are central to the utilization of wood in our society since water affects many important characteristics of wood. This topic has been investigated for more than a century, but new knowledge continues to be generated as a result of improved experimental and computational methods. This review summarizes our current understanding of the fundamentals of water in wood and highlights significant knowledge gaps. Thus, the focus is not only on what is currently known but equally important, what is yet unknown. The review covers locations of water in wood; phase changes and equilibrium states of water in wood; thermodynamics of sorption; terminology including cell wall water (bound water), capillary water (free water), fiber saturation point, and maximum cell wall moisture content; shrinkage and swelling; sorption hysteresis; transport of water in wood; and kinetics of water vapor sorption in the cell wall.

How much water can wood cell walls hold? A triangulation approach to determine the maximum cell wall moisture content.

Wood is a porous, hygroscopic material with engineering properties that depend significantly on the amount of water (moisture) in the material. Water in wood can be present in both cell walls and the porous void-structure of the material, but it is only water in cell walls that affects the engineering properties. An important characteristic of wood is therefore the capacity for water of its solid cell walls, i.e. the maximum cell wall moisture content. However, this quantity is not straight-forward to determine experimentally, and the measured value may depend on the experimental technique used. In this study, we used a triangulation approach to determine the maximum cell wall moisture content by using three experimental techniques based on different measurement principles: low-field nuclear magnetic resonance (LFNMR) relaxometry, differential scanning calorimetry (DSC), and the solute exclusion technique (SET). The LFNMR data were furthermore analysed by two varieties of exponential decay analysis. These techniques were used to determine the maximum cell wall moisture contents of nine different wood species, covering a wide range of densities. The results from statistical analysis showed that LFNMR yielded lower cell wall moisture contents than DSC and SET, which were fairly similar. Both of the latter methods include factors that could either under-estimate or over-estimate the measured cell wall moisture content. Because of this and the fact that the DSC and SET methods are based on different measurement principles, it is likely that they provide realistic values of the cell wall moisture content in the water-saturated state.

Innovation in Wood Preservation.

The wood preservation industry has depended on toxicity as a mechanism of effectiveness against decay fungi to extend the life of wood used in adverse conditions. An alternative to toxicity, however, is to study and understand the mechanism of fungal attack and stop it before it can start. Knowing that fungi need moisture for colonization, a new approach to wood preservation is to lower the cell wall moisture content below that needed for fungal attack. Acetylation chemistry is known to reduce the moisture content in the cell wall, and it was used to study moisture levels in the bulk cell wall and in the isolated cell wall polymers. Resistance to brown-rot was determined using a 12-week soil block test with Gloeophyllum trabeum. Weight loss was measured and an analysis of what was lost was determined.

Effects of Changes in Biopolymer Composition on Moisture in Acetylated Wood

To investigate the effects of changes in biopolymer composition on moisture in acetylated poplar wood (Populus euramericana Cv.), the acetylation of control wood was compared to the acetylation of wood with reduced hemicellulose or lignin content (about 9% reduction of total specimen dry weight in both cases). Time-domain nuclear magnetic resonance relaxometry of water-saturated wood gave spin–spin relaxation times (T2) of water populations, while deuteration in a sorption balance was used to characterize the hydroxyl accessibility of the wood cell walls. As expected, the acetylation of pyridine-swelled wood reduced hydroxyl accessibility and made the cell wall less accessible to water, resulting in a reduction of cell wall moisture content by about 24% compared with control wood. Hemicellulose loss per se increased the spin–spin relaxation time of cell wall water, while delignification had the opposite effect. The combined effect of hemicellulose removal and acetylation caused more than a 30% decrease of cell wall moisture content when compared with control wood. The acetylated and partially delignified wood cell walls contained higher cell wall moisture content than acetylated wood. An approximate theoretical calculation of hydroxyl accessibility for acetylated wood was in the low range, but it agreed rather well with the measured accessibility, while acetylated and partially hemicellulose-depleted and partially delignified wood for unknown reasons resulted in substantially lower hydroxyl accessibilities than the theoretical estimate.

Leachability and Decay Resistance of Wood Polyesterified with Sorbitol and Citric Acid

Research Highlights: Polyesterification of wood with sorbitol and citric acid (SCA) increases decay resistance against brown-rot and white-rot fungi without reducing cell wall moisture content but the SCA polymer is susceptible to hydrolysis. Background and Objectives: SCA polyesterification is a low-cost, bio-based chemical wood modification system with potential for commercialisation. Materials and Methods: This study investigates moisture-related properties and decay resistance in SCA-modified wood. Scots pine sapwood was polyesterified at 140 °C with various SCA solution concentrations ranging from 14–56% w/w. Dimensional stability was assessed and leachates were analysed with high-performance liquid chromatography (HPLC). Chemical changes were characterized with attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) and spectra were quantitatively compared with peak ratios. Low-field nuclear magnetic resonance (LFNMR) relaxometry was used to assess water saturated samples and decay resistance was determined with a modified EN113 test. Results: Anti-swelling efficiency (ASE) ranged from 23–43% and decreased at higher weight percentage gains (WPG). Reduced ASE at higher WPG resulted from increased water saturated volumes for higher treatment levels. HPLC analysis of leachates showed detectable citric acid levels even after an EN84 leaching procedure. ATR-FTIR analysis indicated increased ester content in the SCA-modified samples and decreased hydroxyl content compared to controls. Cell wall water assessed by non-freezing moisture content determined with LFNMR was found to increase because of the modification. SCA-modified samples resisted brown-rot and white-rot decay, with a potential decay threshold of 50% WPG. Sterile reference samples incubated without fungi revealed substantial mass loss due to leaching of the samples in a high humidity environment. The susceptibility of the SCA polymer to hydrolysis was confirmed by analysing the sorption behaviour of the pure polymer in a dynamic vapour sorption apparatus. Conclusions: SCA wood modification is an effective means for imparting decay resistance but, using the curing parameters in the current study, prolonged low-level leaching due to hydrolysis of the SCA polymer remains a problem.

IMPROVING WATERPROOFING PROPERTIES IN THE WALL BASEMENT AREA BY INJECTION METHOD

The article is focused on the natural experimental research of injection waterproofing impact on basement areas of existingbuildings brick walls. Two types of experimental installations for waterproofing material injection have been developed. Thesecond type turned out to be more efficient due to the fact that it could cover larger waterproofing wall area. It can possiblyspeed up the process of walls waterproofing and major repairs of buildings in general. According to the experimental data, after the injection waterproofing placement, the wall moisture content decreased by half due to the high quality waterproofingmaterial and performed installation work.

Moisture in modified wood and its relevance for fungal decay

Water plays an essential role in fungal decay of wood, and limiting the cell wall moisture content by chemical modification can effectively improve the durability of the material. Investigating the wood-water relations of modified material under climatic conditions relevant for fungal decay are, however, experimentally challenging. Most studies in literature therefore focus on moisture sorption under conditions outside those of importance for fungal decay. This review discusses the validity of such data for characterising the wood-water relations at very humid climatic conditions, relevant for fungal decay. Moreover, the review attempts to cover the basics of fungal decay, the important role of water, and how controlling water content by modification can improve durability.

Measured moisture in buildings and adverse health effects: A review.

It has not yet been possible to quantify dose-related health risks attributable to indoor dampness or mold (D/M), to support setting specific health-related limits for D/M. An overlooked target for assessing D/M is moisture in building materials, the critical factor allowing microbial growth. A search for studies of quantified building moisture and occupant health effects identified 3 eligible studies. Two studies assessed associations between measured wall moisture content and respiratory health in the UK. Both reported dose-related increases in asthma exacerbation with higher measured moisture, with 1 study reporting an adjusted odds ratio of 7.0 for night-time asthma symptoms with higher bedroom moisture. The third study assessed relationships between infrared camera-determined wall moisture and atopic dermatitis in South Korea, reporting an adjusted odds ratio of 14.5 for water-damaged homes and moderate or severe atopic dermatitis. Measuring building moisture has, despite extremely limited available findings, potential promise for detecting unhealthy D/M in homes and merits more research attention. Further research to validate these findings should include measured "water activity," which directly assesses moisture availability for microbial growth. Ultimately, evidence-based, health-related thresholds for building moisture, across specific materials and measurement devices, could better guide assessment and remediation of D/M in buildings.

The states of water in Norway spruce (Picea abies (L.) Karst.) studied by low-field nuclear magnetic resonance (LFNMR) relaxometry: assignment of free-water populations based on quantitative wood anatomy

Abstract Low-field nuclear magnetic resonance (LFNMR) relaxometry was applied to determine the spin-spin relaxation time (T 2) of water-saturated Norway spruce (Picea abies (L.) Karst.) specimens cut from mature sapwood (sW) and mature and juvenile heartwood (hW), where earlywood (EW) and latewood (LW) were separated. In combination with quantitative wood anatomy data focusing on the void volumes in various morphological regions, the NMR data served for a more reliable assignment of free-water populations found in water-saturated solid wood. Two free-water populations were identified within most sample types. One was assigned to water in the tracheid lumen and the other to water inside bordered pits. Whether water in the ray cell lumina was included in one or the other of these two populations depends on the curve-fit method applied (continuous or discrete). In addition, T 2 differences between the different tissue types were studied and, for comparison, sorption isotherms were measured by means of a sorption balance. There was a significant difference between EW and LW as well as between juvenile wood and mature wood in terms of T 2 related to the cell wall water. However, no differences were seen between the sorption isotherms, which indicates that the observed T 2 differences were not due to differences in cell wall moisture content (MC).

Coating Acetylated Wood

Wood exposed to the outdoor environment is susceptible to weathering due to a series of chemical, biological and physical processes. Acetylation of wood is known to reduce cell wall moisture content, improve dimensional stability and durability against fungal decay. As a result of these improvements, less stress is created between the coating and the wood surface improving the performance of the coating and increasing its useful lifetime. This paper is a review of research done on the chemistry of the acetylation process, the coating performance of acetylated wood and concentrates on the factors influencing coating performance.

Measurement of moisture content in solid brick walls using timber dowel

Moisture within walls can have a serious detrimental impact on buildings and undermine their long-term durability and integrity. This paper investigates the accuracy of the timber dowel method for measuring wall moisture content in a solid brick wall. The timber dowel is inserted in the wall and removed at intervals and moisture readings obtained using a resistance-based, moisture-meter. The moisture content of timber dowels and the surrounding brick and mortar in a laboratory wall is measured and compared to the moisture content in the timber dowel, brick and mortar in different relative humidity environments (saturated salt solutions). The paper finds that a linear relationship of increasing moisture content in the dowel and laboratory wall is observed. At medium dowel moisture content (dowel moisture content >15 %), the moisture content in the dowel, brick and mortar is similar in both the laboratory wall and the RH environments. At higher moisture content there is a divergence whereby at the same dowel moisture content, the laboratory brick and mortar show higher moisture contents than those achieved in the RH environments. It appears that liquid water present in the wall has difficulty transferring to the dowel and consequently the dowel underestimates at high moisture contents. It is concluded that the dowel gives a good indication of the moisture content in the wall when the dowel readings are not higher than 15 % and indicates changes in relative wetness above this. In-situ monitoring of the moisture content of a nineteenth century brick wall following the application of lime plaster showed expected changes in moisture content. An increase in wall moisture content following the application of the plaster and the wall returned to its original moisture state by 9 months.

Analysis of Starch Bubble Breakage during Extrusion Expansion by Finite Elements Method

Major factors that influenced the breakage of starch bubbles during extrusion expansion such as the initial bubble radium, the initial cell wall thickness, the initial cell wall temperature, the initial cell wall moisture content, the stress strength constant of starch and the changes of failure stress of bubble wall, stress of bubble wall, bubble radium, cell wall thickness, pressure different with time were investigated and the critical breaking points for each operation parameters under certain conditions were determined. The results showed that the smaller the initial bubble radium, the higher the initial cell wall thickness, and within certain range, the lower the initial temperature, the lower the initial moisture content, and the higher the stress strength constant of starch, the lower the tendency the bubble broke.

Effect of mechanically induced ventilation on the indoor air quality of building envelopes

Experiments were conducted to study the effect of mechanically induced fresh-air ventilation on the indoor air quality (IAQ) of the Tuskegee Healthy House (THH), selecting the outdoor weather conditions almost identical during the “fan OFF” and “fan ON” periods. Measurements of outdoor and indoor temperature and relative humidity (RH), in addition to the indoor dust particle concentration levels and interior wall moisture content, were systematically carried out during the summer month of August 2008. Results show that the effect of mechanically induced ventilation (“fan ON” period) is to raise the indoor RH, interior wall moisture content, and indoor dust particle concentration values significantly above those measured during the “fan OFF” period. The indoor temperature increases only slightly during the “fan ON” period.

Assessing the effects of soil grading on the moisture content-dependent thermal conductivity of stabilised rammed earth materials

New data for both the dry-state and the moisture content-dependent thermal conductivity of cement-stabilised rammed earth (SRE) materials is presented. For highly compacted SRE materials, no correlation was found between thermal conductivity and dry density or void ratio. The thermal conductivity of SRE materials increases linearly with the saturation ratio, S r of the material and can be expressed as λ ∗, the moisture content-dependent thermal conductivity. The sensitivity of λ ∗ to an increase in the saturation ratio of SRE materials varies according to soil grading. The influence of grading parameters on λ ∗ can cause material variations of approximately 0.8 m 2 K/W. The experimental data has been applied to standard SRE wall design configurations and the effect of wall moisture content on the total thermal resistance has been shown. The R-value of an SRE wall irrespective of cavity insulation can vary by as much as 0.13 m 2 K/W.

HygroScope: A Moisture Transfer Simulator for Buildings

Moisture transfer is one of the most important factors related to the energy performance, indoor quality, and maintenance of buildings. HygroScope is a simulator that takes into account the moisture transfer mechanisms, the wall configuration, the construction materials properties, and seasonal meteorological data for the region and calculates the seasonal wall moisture content along with the corresponded equilibrium moisture height. HygroScope is an application developed under Visual Studio 2005 using the C# programming language and consists of three units: the database, the mathematical model library, and the graphical user interface.

A powerful simulator for moisture transfer in buildings

The seasonal moisture transfer to and from the walls of a building is the most important factor concerning the deteriorating effect of moisture in buildings envelopes. The presented simulator takes into account the (a) moisture transfer mechanisms to and from the building (capillary rise, drying, etc.), (b) wall configuration (materials and size), (c) construction materials properties, (d) seasonal region meteorological data (air temperature, humidity and velocity) and calculates the (a) seasonal wall moisture content along with the corresponding equilibrium moisture height, (b) capillary rising water flow rate, (c) wall drying flow rate, etc. The simulator has been developed in an Excel platform in a user-friendly environment and consists of four units: (a) process model, (b) problem solution algorithms, (c) database and (d) graphics interface. The proposed simulator is a powerful tool in decision-making concerning the building deteriorating evolution and the selection of appropriate protecting strategy, e.g., the plaster selection (material, size, replacing time), contributing to the sustainability of masonries.

Investigation into the Variations of Moisture Content of Two Buildings Constructed with Light Earth Walls

This paper briefly describes the background to light earth buildings and details a series of moisture measurements undertaken upon the clay and straw (light earth) constructed walls of two U.K.-based buildings. The methodology of measurement that was based upon previous studies undertaken on walls made from straw bales is described. A novel “in-wall” wet heating system used in one of the two buildings allows the investigation of the effects of direct wall heating upon the distribution of moisture in the walls. The influence of exterior and interior temperature and humidity are described as are the variations in moisture migration introduced by the in-wall heating system. It was concluded that both buildings have exterior wall moisture content readings that indicate little risk of degradation due to interior wall moisture levels (although the Studio walls do exhibit higher and if suffered over long time periods, dangerous moisture readings for part of the measurement period).

Impregnation of softwood cell walls with melamine-formaldehyde resin.

Melamine-formaldehyde (MF) resin impregnation has shown considerable potential to improve a number of wood properties, such as surface hardness and weathering resistance. In this study, selected factors influencing the uptake of MF resin into the cell wall of softwood were studied. Using UV-microspectroscopy, it could be shown that water soluble MF diffused well into the secondary cell wall and the middle lamella. Concentrations as high as 24% (v/v) were achieved after an impregnation of 20 h. High cell wall moisture content, high water content of the resin used for impregnation, and low extractive content are factors which are favourable for MF resin uptake into the cell wall. For dry cell walls, solvent exchange drying improved resin uptake to a similar extent, as was the case when cell walls were soaked in water.