Wood Content Research Articles

Plasma Treatment of Polypropylene-Based Wood-Plastic Composites (WPC): Influences of Working Gas.

In this study, a polypropylene (PP)-based wood–plastic composite with maleic anhydride-grafted polypropylene (MAPP) as a coupling agent and a wood content of 60% was extruded and specimens were injection molded. The samples were plasma treated utilizing a dielectric barrier discharge (DBD) setup with three different working gases: Ar/O2 (90%/10%), Ar/N2 (90%/10%), and synthetic air. This process aims to improve the coating and gluing properties of the otherwise challenging apolar surface of PP based wood–plastic composites (WPC). Chemical analysis with X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) showed the formation of oxygen-based functional groups on the surface, independently from the working gas used for the treatment. Laser scanning microscopy (LSM) examined the surface roughness and revealed that the two argon-containing working gases roughened the surface more than synthetic air. However, the contact angle for water was reduced significantly after treatment, revealing measurement artifacts for water and diiodomethane due to the severe changes in surface morphology. The adhesion of acrylic dispersion coating was significantly increased, resulting in a pull-off strength of approximately 4 N/mm2, and cross-cut tests assigned the best adhesion class (0), on a scale from 0 to 5, after plasma treatment with any working gas.

Hardness of chemically densified Yellow birch in relation to wood density, polymer content and polymer properties

Abstract Density of wood can be increased by filling its porous structure with polymers. Such densification processes aim to increase hardness of wood and are particularly interesting for flooring applications. This study aims to evaluate efficiency of different polymers for chemical densification based on the polymer properties. Yellow birch (Betula alleghaniensis Britt.) was chemically densified with seven monomer mixtures through acrylate monomer impregnation and electron beam in-situ polymerization. Chemical retention and polymer content of densified woods were recorded. Hardness of treated and untreated Yellow birch was measured and compared to hardness of Jatoba (Hymenaea courbaril L.). All densified woods showed higher or comparable hardness to Jatoba. Hardness of densified wood was analyzed in relation to initial density of wood and polymer content of the material using multivariable linear mixed models. Efficiency of polymers for chemical densification was evaluated through effect of polymer content on hardness with interaction coefficients. Polymer films corresponding to monomer impregnating mixtures were prepared through low energy electron beam and characterized by their glass transition temperature, micro hardness, indentation modulus and crosslinking density. Polymers showed statistically significantly different efficiencies and were separated in two main groups. Overall, polymer efficiency increased with increasing glass transition temperature of polyacrylates.

Structural Carbon Allocation and Wood Growth Reflect Climate Variation in Stands of Hybrid White Spruce in Central Interior British Columbia, Canada

Research Highlights: This research presents a novel approach for comparing structural carbon allocation to tree growth and to climate in a dendrochronological analysis. Increasing temperatures reduced the carbon proportion of wood in some cases. Background and Objectives: Our goal was to estimate the structural carbon content of wood within hybrid white spruce (Picea glauca (Moench) × engelmannii (Parry) grown in British Columbia, Canada, and compare the percent carbon content to wood properties and climate conditions of the region. Specific objectives included: (i) the determination of average incremental percent carbon, ring widths (RW), earlywood (EW) and latewood (LW) widths, cell wall thickness, and density over time; (ii) the determination of differences between percent carbon in individual forest stands and between regions; and (iii) the evaluation of the relationships between percent carbon and climate variation over time. Methods: Trees were sampled from twelve sites in northern British Columbia. Wood cores were analyzed with standard dendrochronology techniques and SilviScan analysis. Percent structural carbon was determined using acetone extraction and elemental analysis for 5 year increments. Individual chronologies of wood properties and percent carbon, and chronologies grouped by region were compared by difference of means. Temperature and precipitation values from the regions were compared to the carbon chronologies using correlation, regression, and visual interpretation. Results: Significant differences were found between the percent structural carbon of wood in individual natural and planted stands; none in regional aggregates. Some significant relationships were found between percent carbon, RW, EW, LW, and the cell wall thickness and density values. Percent carbon accumulation in planted stands and natural stands was found in some cases to correlate with increasing temperatures. Natural stand percent carbon values truncated to the last 30 years of growth was shown as more sensitive to climate variation compared to the entire time series. Conclusions: Differences between the stands in terms of structural carbon proportion vary by site-specific climate characteristics in areas of central interior British Columbia. Wood properties can be good indicators of variation in sequestered carbon in some stands. Carbon accumulation was reduced with increasing temperatures; however, warmer late-season conditions appear to enhance growth and carbon accumulation.

Effects of provenance and initial planting density on growth and wood properties in young sawtooth oak (Quercus acutissima) plantations

Provenance and stand management regimes greatly affect individual tree growth and stand productivity. The effects of provenance and initial planting density on growth and wood properties of 11-year-old sawtooth oak (Quercus acutissima Carruth.) plantations in eastern China were investigated. The average tree height growth, calorific values, and ash content of stem wood were greatly affected by provenance but not by initial planting density. The average tree diameter varied significantly among the three planting densities (5000, 2500, and 1667 trees ha−1) from tree age 6–11 years, and density-associated competition between trees mainly occurred at tree ages 6, 7, and 11 years for different provenances. The initial planting density and provenance had significant effects on the stand basal area (BA) and aboveground biomass (AGB). The annual growth in BA and AGB decreased in the eighth year after planting, especially in plots with an initial planting density of 5000 trees ha−1. The variances explained by the provenance exceeded the variance explained by the planting density for AGB at age 11 years. No significant interaction effect between initial planting density and provenance was observed for growth traits, but there was a significant effect on survival rate. Therefore, the suitable combination between provenance and planting density is crucial to increase productivity of sawtooth oak plantations. Additionally, our study confirms that, when the stands were young, initial planting density had a greater effect on productivity than provenance did, but this pattern reversed as stands aged.

Modeling the change of water content in wood at atmospheric drying

Objective: to develop a methodology for predicting changes in the water content in wood during atmospheric drying, taking into account the fast and slow stages of this process. Research methods: mathematical modeling, applied analysis of results, comparison with experimental data known from the literature, synthesis in order to better understand the regularities of drying. Results: a two-parameter model is developed, in which a phenomenological approach is used, focused on obtaining averaged estimates of wood moisture during atmospheric drying. Causal relationships are not detailed, but are taken into account in an integral form. Calculation formulas are obtained, the use of which simplifies the procedure for predicting changes in the water content in wood during atmospheric drying. The adequacy of the model and the reliability of the calculation results are confirmed by their consistency with the experimental data known in the literature. Research prospects can be focused on adapting the model to other drying methods in order to reduce the energy and time spent on a given technological process.

Evaluation of Elemental and Chemical Compositions of Some Fuelwood Species for Energy Value

Fuelwood species are a crucial part of the ecosystem; they provide energy for cooking, heating, and lightening for both domestic and industrial uses. As a result of their value, there is a need for frequent evaluation of elemental and chemical compositions for management and conservation purposes. Since fuelwood is the most common and cheapest source of energy in both rural and urban areas in northern Nigeria, the study area is facing serious challenges due to indiscriminate felling of trees for energy use, irrespective of species quality for combustion. Therefore, ten fuelwood species were selected for this study. The selected trees were harvested at Dbh level, replicated three times. Four fuel materials were obtained from each tree sample; these include wood without bark (100% wood sample), wood with 5% bark inclusion, wood with 10% bark inclusion, and whole bark samples and they were evaluated for their inherent elemental and chemical compositions by employing ASTM and TAPPI methods. The results showed that there were significant differences in the tree species and fuel material types obtained from all the ten fuelwood species used. The results of carbon content ranges from 49.54% in A. sieberiana to 50.98% in A. leiocarpus. Meanwhile, the addition of 5% and 10% bark reduces carbon content of wood by 1.25% and 2.74%, respectively. Nitrogen content ranged from 0.31% in A. leiocarpus to 1.00% in A. sieberiana. Among the fuel materials used, isolated bark contained approximately 0.45% nitrogen content compared with wood without bark. Among the tree species, hydrogen content ranged from 3.99% in P. reticulatum to 4.66% in C. arereh. The variation in sulphur contents ranged from 0.24% in C. arereh to 0.93% in A. sieberiana. Lignin content ranged from 10.68% in A. sieberiana to 25.39% in A. leiocarpu and extractive content values ranged from 7.31% in A. leiocarpus to 19.33% in P. reticulatum. Meanwhile, the fuelwood species observed in this study with higher percentage of carbon, hydrogen, and lignin and lower nitrogen and sulphur and extractive content possessed quality fuel value and thereby were encouraged to be incorporated in fuelwood plantation establishment programs (A. leiocarpus, C. molle, C. arereh, and B. aegyptiaca). Lower energy fuelwood species should be allowed for environmental amelioration and carbon sequestration. However, bark contents should be removed for better heating and low ash production during combustion.

Development and characterization of novel castor oil-based polyurethane composites containing wood sawdust and rubber tire powder

New eco-friendly composites consisting of castor oil-based polyurethane (PU) resin, wood sawdust, and rubber tire powder were produced, and the morphological, physical, and flexural properties were investigated. The composites were composed of varying the concentration of the PU matrix (30, 40, and 50 m%) and the wood-to-rubber ratio of the disperse phase (100/0, 90/10, 80/20, 70/30, 60/40, and 50/50 m%/m% wood/rubber, respectively). The morphology of the composites was studied by optical microscopy and scanning electron microscopy, and the flexural properties, water absorption (WA), and thickness swelling (TS) were also investigated. The analysis of variance was used to study the effect of each factor (PU content and wood/rubber ratio) on the characteristics of the composites. PU/wood/rubber composites were successfully molded and their characteristics are promising for commercial use. According to the results, the composites presenting higher wood content (high wood/rubber ratio) showed higher modulus of rupture and modulus of elasticity values, although the addition and the increase of rubber content decreased these properties. Moreover, increasing PU or reducing the wood/rubber ratio significantly reduced the WA and TS, improving dimensional stability.

Comparative archaeometric characterization of recent and historical oak (Quercus spp.) wood

The present paper studied the chemical composition of recent and historical oak wood comparing the extractive, holocellulose, α-cellulose, lignin, and ash contents. Comprehensive knowledge of the chemical components in recent and historical oak wood will facilitate the use of conservation agent in the restoration and conservation process of the investigated artifacts. The cyclohexane–ethanol extract of historical oak wood was significantly lower compared to recent wood, which can be explained by the leaching of extractives into the soil. No significant differences in the holocellulose and α-cellulose content of recent and historical oak wood were found. The lignin and the ash contents were significantly higher in the historical samples. The EDX analysis of the ash of historical oak wood showed remarkably higher iron content compared to the recent material. The result indicated the degradation of hemicelluloses in the historical sample. The significant difference in the amount of ash between the samples was explained by sediment materials that have been introduced into the wood from the soil. SEM imaging made these materials clearly visible as depositions in the cell lumens.

Differences in biomass production and carbon sequestration between highland and lowland stands of Picea abies (L.) H. Karst. and Fagus sylvatica L.

Despite different levels of complexity among biomass models, it is unclear how much patterns of biomass production and allocation differ between mountain and lowland forests, and how much neglecting this difference biases carbon pool estimations. To address this question, we studied chronosequences of 24 Fagus sylvatica and 24 Picea abies stands in Poland, located both in lowlands and highlands (12 stands of each species per category). We cut and weighted 192 sample trees, and we measured carbon content in wood, bark, branches and leaves. We also developed allometric tree- and stand-level models of biomass and carbon mass. Using log-transformed linear models we checked the effect sizes of elevation category (lowland and highland) on estimate output. We found small, statistically insignificant differences in biomass allocation patterns, carbon content and allometric trajectories in trees between lowland and highland stands. Tree-level allometric models without elevation category had higher accuracy than models including elevation category and explained 96.8–99.8% of biomass variability. Biomass and carbon stock of species studied was positively correlated with stand volume, age, basal area and height, and negatively with stand density. However, the differences between lowlands and highlands were low and did not exceed 38 Mg ha−1 (for P. abies foliage biomass, with model root mean squared error of 37.638 Mg ha−1). Our results revealed transferability of models developed using lowland and highland populations of the studied species. This will increase confidence in methods used to estimate carbon pools.

Perbandingan Kandungan Selulosa dan Lignin dari Kayu Acacia crassicarpa dan Acacia mangium

The development of the pulp & paper industries in Indonesia increase every year. To support the development of industries in Indonesia in order to be able to compete with similar industries from abroad, it is very important to pay attention to the quality of the paper produced. One way to determine the quality of the pulp & paper is by knowing the chemical composition and area where the wood grows. Important chemical compositions that can support the strength of wood and paper quality include cellulose and lignin. Therefore, this study was conducted to compare the levels of cellulose and lignin contained in Acacia crassicarpa wood from wetlands and Acacia mangium from dry land which is processed into pulp & paper with good quality. Determination of cellulose and lignin content in wood was carried out using the gravimetric method. Test results on Acacia crassicarpa wood species from wetlands obtained cellulose content of 55.48% and lignin 24.13%, while in Acacia mangium wood from dry land obtained cellulose content of 51.46% and lignin 27.66%. According to company standards that levels of cellulose and lignin in two different fields are obtained according to the standards set by the company. So for the results of testing Acacia crassicarpa wood from wetlands have the highest levels of cellulose with low levels of lignin

Mycelia Growth of Shiitake (Lentinula edodes) on 4-Wood Species from Leguminaceae Family

Cultivation of Shiitake mushroom (Lentinula edodes) in Indonesia has not been developed yet, due to its low productivity. It happens because of the limited information of the good ways on cultivation Shiitake in Indonesia. One of the factors that affect the growth of mushroom is the media. In Indonesia, the information about the media composition by using various species of wood have not been found yet. Therefore, this research was conducted to determine the effect of using different wood species to the growth of Shiitake. This study used four wood species from the leguminaceae family, those were: Gamal (Glicidia sepium); Johar (Samanea saman); Leucaena (Leucaena leucocephala); and Sengon (Falcataria moluccana). Those were used as the media by adding 12.5% (w/w) of rice bran and 6% (w/w) of CaCO3, and adjusting the moisture content by adding the distillate water to 65, 70, and 75%. Then, the media was put in to the petridisk (ø 90 mm) and inoculated with Shiitake mushroom. During the mycelia growth, the length of mycelia was measured every 2 days until fifty days, and then glucosamine content was analyzed. In addition, chemical analysis was also conducted to each media. The results showed that different wood species resulted different chemical content of media, except the acid soluble lignin content. The growth rate of mycelia was affected by the moisture content of media, meanwhile the glucosamin content is influenced by the moisture content and various species of wood. The best combination to cultivate the Shiitake mushroom was by using media made of gamal with 70% moisture content. There were positive correlation among the ethanol-toluen extracts content and the mycelia growth, however there was negative correlation among the hemicelullose content the mycelia growth.

ANALYSIS OF RHEOLOGICAL MODELS OF PROCESS OF SELF-FORMING OF GLUED WOODEN

The article considers a promising technology for self-shaping glued wooden elements of curved forms. This method is based on rheological processes occurring in wood, such as dehumidification and swelling of wood and its anisotropic properties.
 To predict the final curved shape of the wooden structure, the authors analyzed existing rheological models of wood and concluded that the rheological model proposed by European researchers includes the most complete list of factors that affect the process of deformation of wood: elastic and plastic deformation, drying and swelling of wood, deformation of viscous-elastic creep and mechanical sorption deformation.
 Based on the results of experimental studies and numerical modeling of the change in the curvature of glued wooden elements, which were made by European researchers, it was found that the proposed rheological model of wood needs to be clarified, namely, the correction of hygro-expansion coefficients depending on the moisture content of wood.
 A further direction of the authors’ research will be aimed at conducting model experiments to determine the hygro-expansion coefficients of different grades of wood depending on the thickness of the wooden elements and the orientation of the layers in the glued structure.

THE STATE OF SPRUCE STANDS IN THE UDMURT REPUBLIC

The article presents materials on the dynamics of spruce stands in the zone of coniferous-deciduous forests and in the south taiga zone of the European part of the Russian Federation, on the territory of the Udmurt Republic. In the process of the research, the information from the state forest register for the Udmurt Republic from 2009 to 2015 was analyzed. In order to assess the state of spruce forests, trial areas were laid in various forestry zones. It is shown that the largest reduction in the area of spruce stands is observed in the southern part of the Republic, in comparison with the Northern part, which is located in a different landscape zone. According to the data of the enumeration estimation, a high content of dry wood was noted, that exceeds the volume of raw-growing forest. As a result of research on trial areas, spruce individuals that have a good life condition along with dead trees were identified, which indicates the individual characteristics of the surviving plants. Thus, in the zone of active distribution of xylophages the surviving individuals have an increased content of tannins in the wood. The research was carried out with the financial support of RFBR No. 19-04-00353 A.

Changes in Carbon Sequestration in Wood During Decay by Brown- and White-Rot Fungi

Wood decay is a releasing process of carbon fixed in the wood. The study on carbon sequestration change caused by decay can provide a theoretical basis for wood preservation and utilization. At present, there are few reports on decay influence on wood carbon emission and no corresponding quantitative data. Therefore, one broad-leaved species, Poplar, and one coniferous species, Korean pine, were selected as the research object, and brown rot fungus (Gloeephyllum trabeum) and white rot fungus (Coriolus versicolor) were used to conduct accelerated decay test on wood samples in the laboratory. During decay, specimens were taken out in different periods to measure chemical properties, mass loss and carbon sequestration. The influence of decay time on carbon sequestration, chemical component and mass loss were then analyzed and the change rule of carbon sequestration were finally studied. The results showed that with increasing decay time, the relative carbon sequestration content of wood affected by different types rot fungi decreased, which was consistent with the change rule of mass loss, indicating that decay would lead to a loss of wood mass and affect its carbon sequestration. However, the absolute carbon sequestration (measured value of carbon sequestration) after brown rot treatment did not decrease but increased slightly, which was different from previous expectation. According to the analysis, with increasing brown rot time, the absolute content and proportion of lignin in wood samples increased slightly, while the corresponding value of holocellulose (including α-cellulose and hemicellulose) decreased significantly. The carbon content of lignin per unit mass is higher than that of holocellulose (Poplar 64.08% > 37.38%; Korean pine 66.37% > 35.94%), resulting in absolute carbon sequestration in wood increases instead of decreases. In conclusion, the change of lignin proportion during the process of brown rot is the decisive factor affecting the change of absolute carbon sequestration. This study focused on two aspects of wood decay and wood carbon sequestration, systematically analyzed the change rule and internal mechanism of wood carbon sequestration with the increase of wood decay degree, and accumulated basic data for wood carbon emission reduction and wood prevention.

Effect of repeated cycles of wetting and drying on mechanical properties of wood–polypropylene composites

Wood plastic composites (WPCs) are being used for many outdoor applications such as fencing, railing and decking. In outdoor conditions, composites are exposed to varying atmospheric conditions which may influence its mechanical properties. Among the various effects, most predominant one is the moisture absorption due to rainfall. It is necessary to evaluate the effect of moisture absorption/desorption on mechanical properties of WPC. In the present investigation, Melia dubia wood fibre-reinforced polypropylene composites were prepared with and without coupling agent at 40 and 60% fibre loading. Composites were also prepared with three different wood fibre sizes. The composites were exposed to 25 cycles of wetting and drying. During each cycle, the samples were immersed in water for a period of 100 h followed by drying in atmospheric condition for 100 h. Samples were weighed after wetting and drying in each cycle, and mechanical properties were evaluated at 0, 5, 10 and 25 cycles. The results indicated that the composites with higher wood content and fine particle size exhibited higher water absorption and increased loss in mechanical properties. Composites prepared with coupling agent exhibited relative lower moisture absorption and smaller loss in mechanical properties compared to uncoupled composites.

Debarking, pitch removal and retting: Role of microbes and their enzymes

AbstractMicrobial enzymes are green and clean alternatives for several processes in the pulp and paper industry. Enzyme treatment decreases the energy requirement and minimizes the wood losses during drum debarking. Lipophilic wood extractives are known as pitch. Pitch deposition adversely affects the pulp quality and increases equipment maintenance and operating costs during paper manufacturing. Several chemical additives have been used to remove pitch deposits. Natural seasoning of wood is used to minimize pitch content in wood, but it has some disadvantages including yield losses and decreased brightness. Controlled seasoning with white-rot fungi or albino strains of sapstain fungi is an effective tool for degradation and removal of wood extractives. Enzymes including lipase, laccase, sterol esterase, and lipooxygenase have also been used to minimize pitch-related problems. Enzymatic retting has been proved an eco-friendly and economical solution for chemical degumming and traditional retting.

Salvaged lumber for structural mass timber panels: manufacturing and testing

Portland, OR, was the first US city to implement a deconstruction ordinance in 2016. Although salvaged lumber can have a high demand, the market for small-sized lumber from deconstructed dwellings is near saturation. New applications for this material are required for market development, industry diversification, and increasing deconstruction practices. Mass timber products such as cross-laminated timber (CLT) could be a new market for this material, but presently there is minimal information qualifying the performance of mass timber panels made with salvaged lumber. Three, full-sized 3-ply experimental layups, with varying amounts of salvaged/recycled wood content, were manufactured and tested to characterize panel properties. Manufacturing processes and testing methods followed ANSI/APA PRG 320-2018; Standard for Performance Rated Cross-Laminated Timber. Each panel layup had three replicates for nine panels in total. Panels measured 1.1 m by 2.3 m by 3 plys, and test results were used to calculate the effective flatwise bending moment resistance ((FbS)eff), effective flatwise bending stiffness ((EI)eff) effective shear stiffness in flatwise bending ((GA)eff), flatwise shear resistance (Vs), percent wood failure (WF%), and percent delamination (Delamination %). Results were compared with E3 grade 3-ply CLT panels made in the United States and indicated that salvaged lumber could be used as feedstock for mass timber panels in core layers or all layers. All panel layups passed benchmarks for (FbS)eff and (EI)eff benchmarks with values greater than PRG320. Panels having salvaged lumber in core layer also met Vs benchmarks. Furthermore, all panels passed examination for WF% but struggled to meet delamination requirements. Possibilities exist for better performance if panels were made in a commercial setting. This research shows salvaged lumber has promise for manufacturing structural CLT, but more research and a larger samples size is needed to verify findings.

Terpenoids are transported in the xylem sap of Norway spruce.

Norway spruce is a conifer storing large amounts of terpenoids in resin ducts of various tissues. Parts of the terpenoids stored in needles can be emitted together with de novo synthesized terpenoids. Since previous studies provided hints on xylem transported terpenoids as a third emission source, we tested if terpenoids are transported in xylem sap of Norway spruce. We further aimed at understanding if they might contribute to terpenoid emission from needles. We determined terpenoid content and composition in xylem sap, needles, bark, wood and roots of field grown trees, as well as terpenoid emissions from needles. We found considerable amounts of terpenoids-mainly oxygenated compounds-in xylem sap. The terpenoid concentration in xylem sap was relatively low compared with the content in other tissues, where terpenoids are stored in resin ducts. Importantly, the terpenoid composition in the xylem sap greatly differed from the composition in wood, bark or roots, suggesting that an internal transport of terpenoids takes place at the sites of xylem loading. Four terpenoids were identified in xylem sap and emissions, but not within needle tissue, suggesting that these compounds are likely derived from xylem sap. Our work gives hints that plant internal transport of terpenoids exists within conifers; studies on their functions should be a focus of future research.

Simultaneous detection of density, moisture content and fiber direction of wood by THz time-domain spectroscopy

In the wood product-manufacturing process, the physical properties of wood must be monitored. The terahertz (THz) radiation has a high potential for sensing and imaging wood with a good spatial resolution. This study demonstrates the simultaneous prediction of the density, moisture content, and fiber direction of wood, which are important in determining the wood quality, using THz time-domain spectroscopy. We measured the spectra of 12 kinds of wood at various moisture contents while rotating the sample against the THz wave polarization. The fiber direction was predicted by observing the birefringence, which is the optical property of a material, in which the refractive index depends on the polarization direction. The density and the moisture content were predicted by multiple linear regression using the refractive indices and absorption coefficients obtained from the THz measurement. In a series of THz measurements, we successfully identified the wood fiber direction with an R2 of 0.90 and a root mean square error (RMSE) of 16.51° (total measured range = 0–170°), the density with an R2 of 0.97 and an RMSE of 0.022 (total measured range = 0.25–0.67 g/cm3), and the moisture content with an R2 of 0.78 and an RMSE of 4.06 (total measured range = 0.00–30.98%).

Water Absorption and Hygrothermal Aging Behavior of Wood-Polypropylene Composites.

Environmentally sound composites reinforced with natural fibers or particles interest many researchers and engineers due to their great potential to substitute the traditional composites reinforced with glass fibers. However, the sensitivity of natural fiber-reinforced composites to water has limited their applications. In this paper, wood powder-reinforced polypropylene composites (WPCs) with various wood content were prepared and subjected to water absorption tests to study the water absorption procedure and the effect of water absorbed in the specimens on the mechanical properties. Water soaking tests were carried out by immersion of composite specimens in a container of distilled water maintained at three different temperatures, 23, 60 and 80 °C. The results showed that the moisture absorption content was related to wood powder percentage and they had a positive relationship. The transfer process of water molecules in the sample was found to follow the Fickian model and the diffusion constant increased with elevated water temperature. In addition, tensile and bending tests of both dry and wet composite samples were conducted and the results indicated that water absorbed in composite specimens degraded their mechanical properties. The tensile strength and modulus of the composites reinforced with 15, 30, 45 wt % wood powder decreased by 5.79%, 17.2%, 32.06% and 25.31%, 33.6%, 47.3% respectively, compared with their corresponding dry specimens. The flexural strength and modulus of the composite samples exhibited a similar result. Furthermore, dynamic mechanical analysis (DMA) also confirmed that the detrimental effect of water molecules on the composite specimens.