Long-term Water Uptake Research Articles

Changes in moisture performance of wood after weathering

After the durability of wood against wood decay fungi, its water performance is the next most important factor that influences the performance of wood in outdoor, above-ground applications. It is therefore of major importance to optimize methods that are able to predict the moisture behaviour of wood in outdoor applications. In order to elucidate these questions, samples were prepared from European oak (Quercus robur/Q. petraea), sweet chestnut (Castanea sativa), European larch (Larix decidua), Scots pine heartwood and sapwood (Pinus sylvestris), Norway spruce (Picea abies) and beech (Fagus sylvatica). The moisture performance of the samples was altered by thermal modification, wax, oil and biocide treatment. Two types of specimens were prepared; smaller specimens (1.5 × 2.5 × 5.0 cm) were exposed to natural weathering for three periods (9, 18 and 27 months) and subsequently analyzed in the laboratory with various methods (contact angle, short- and long-term water uptake and water vapor uptake). In parallel, bigger specimens (2.5 × 5.0 × 50 cm) were exposed outdoors in a monolayer exposure and equipped with moisture monitoring sensors for 18 months. Water performance of wood could change as a result of weathering, being the most evident at thermally modified wood, where the decrease of the moisture performance was the most evident. The results of the study clearly showed that the water performance of the majority of the materials decreased with natural weathering. These results indicate that in order to elucidate the moisture performance of wood fully, a variety of laboratory tests needs to be applied, relating to both liquid water performance and water vapour interactions with wood.

Influence of backbone structure, conversion and phenolic co-curing of cyanate esters on side relaxations, fracture toughness, flammability properties and water uptake and toughening with low molecular weight polyethersulphones

The effect of backbone structure and conversion of polycyanurate networks on solid state properties has been studied and compared to co-curing with bisphenol-A. Dynamic mechanical behaviour, density, flammability properties, fracture toughness and long-term water uptake were investigated. The intensity of the γ-relaxation increases, room temperature density decreases with increasing conversion, both due to increasing free volume with increasing conversion. A brittle-ductile transition was detected by precise fracture toughness measurements; above a critical conversion the fracture toughness rises suddenly from extremely low values to a plateau or maximum: Networks with higher toughness show a maximum, those with lower toughness a plateau. Bisphenol-A modification causes intrinsic toughness variations. Toughening of two different cyanate esters with polyethersulphones synthesized with various molecular weights between 3000 and 10,500 (Mn) was investigated. Significant toughening effects can be achieved already with intermediate molecular weights lower than those of commercially-available high-Tg amorphous thermoplastics. Long-term water uptake measurements at 28°C, 50°C and 70°C over two years show a non-Fickian part of the water uptake for all cyanate esters even at temperatures as low as 28°C. The effects of backbone structure, conversion and storage temperature are discussed in detail.

Influence of Artificial and Natural Weathering on the Moisture Dynamic of Wood

Wood that is used in outdoor applications is frequently exposed to weathering and is thus prone to fungal degradation. Ways to prevent fungal degradation include keeping the wood dry. The majority of hydrophobic and wood modification systems have been tested only on freshly treated wood. Little information is available on how various wood-based materials perform after a certain period of weathering. To elucidate this question, 17 wood samples were tested from the following species: oak (Quercus), sweet chestnut (Castanea sativa), European larch (Larix decidua), Scots pine heartwood and sapwood (Pinus sylvestris), Norway spruce (Picea abies), and beech (Fagus sylvatica). Moisture performance of the wood samples was improved with thermal modification, wax, oil, and biocide treatment. Specimens were exposed to various degradation-aging factors (blue stain fungi, decay fungi, artificial weathering, and natural weathering). Various moisture performance tests were applied before and after aging: short-term water uptake (tensiometer), long-term water uptake, water vapor tests, drying tests, etc. The water exclusion efficacy of wood was decreased after aging. Aging factors were found to act synergistically and to have a more prominent influence on less durable wood compared to durable or preservative-treated wood. Wax-treated wood performed best, regardless of which moisture performance test was applied.

Thermal modification of wax-impregnated wood to enhance its physical, mechanical, and biological properties

Abstract Thermal modification is the most important commercial modification procedure. Thermally modified (TM) wood has improved durability, but its performance does not meet expectations predominately under moist conditions. To reduce water uptake of TM wood, Norway spruce specimens were treated with suspensions of a natural wax by dipping impregnation (DipI) or by vacuum-pressure impregnation (VPI). Wax-treated specimens were subsequently TM at 185, 200, 215, and 230°C. Control specimens were heated up to 100°C only. Contact angle (CA), short-term and long-term water uptake, bending strength, and performance against wood decay fungi of the resulting material were determined. The results show that a combination of wax treatment and thermal modification have a synergistic effect that considerably improves hydrophobicity, reduces liquid water uptake, slows down water vapor uptake, and improves the resistance against fungal decay of the treated material.

Comparative study of long-term water uptake of Norway spruce and Douglas-fir in Moravian upland

Abstract Long-term water uptake of Douglas-fir and Norway spruce trees, growing in condition of Moravian upland, was studied with aim of comparing sap flow in small roots with flow in stems. Sap flow was measured by the heat field deformation method using multi-point sensors for stems and single-point sensors for roots. Differences between species were found in relationships between sap flow in tree stems and water uptake by roots, suggesting that Douglas-fir is able to take water from deeper soil more efficiently than spruce. This allows Douglas-fir to transpire more water especially during drought and grow faster than spruce. These biological features should be taken into account for future forest species compositions because they may have impact on both, forestry and hydrology.

Efficacy of linseed- and tung-oil-treated wood against wood-decay fungi and water uptake

Most European wood species do not have durable wood. In order to be used in outdoor conditions, non-durable material must be protected. Non-biocidal solutions for wood protection have been attracting a lot of attention, particularly in class 2 and 3 applications. One non-biocidal technique is treatment of wood with water repellents, such as wax emulsions and oils. Linseed oil and tung oil are frequently used water repellents. This research reports on the performance of linseed- and tung-oil-treated Norway spruce and beech wood against wood-decay fungi. Additionally, short-term hydrophobic properties were determined (with a tensiometer), as well as long-term hydrophobic properties (by soaking in water) in laboratory and outdoor conditions (electrical resistance measurements). Wood treated with tung oil and linseed oil is protected against brown- and white-rot fungi; however, tung oil was found more effective. Not only did the oils tested prove efficacious against wood-decay fungi, but also they worked against short-, medium-, and long-term water uptake as well. Oil treated wood takes up less water during laboratory tests, as well as during outdoor testing.

Assessment of long-term water absorption in natural fiber reinforced thermoplastic composites influenced by filler rate and compatibilizer treatment

The scope of the present article is to study the effect of reinforcing filler loading and coupling agent treatment on long-term water uptake of wood plastic composites. Polypropylene and wood flour were compounded into hake internal mixer and the test specimens were prepared by injection molding. Three different contents of wood flour as 40%, 50% and 60% were considered, and the concentration was varied from 0 to 4% for coupling agent. The long-term water absorptions of samples were evaluated by immersing them in water at room temperature for several weeks, and water diffusion coefficients were also calculated by evaluating the water absorption isotherms. The results showed that the water absorption in the samples increased with immersion time, reaching a certain value at saturation point and the composites water content remained constant. Also, the water absorption of the composites increased with increasing wood flour loading. The coupling agents had a positive effect on the water absorption of these composites. Water absorption of all formulations approached the Fickian diffusion case.

Long-term water immersion ageing characteristics of GFRP composites

This paper evaluates the water absorption characteristics of glass fibre reinforced polymers after long-term exposure to a hygrothermal environment. In particular, three types of laminates, fabricated using woven and non-crimp triaxial glass fabric with a polyester matrix, were immersed in deionised water baths for 2.5 years (30 months) at temperatures of 43, 65 and 93 °C. In order to assess the effects of through-thickness delaminations on the water absorption characteristics, a series of specimens were impacted prior water immersion with low-velocity impact using three energy levels of 2.5, 5 and 10 J. The changes in the thermo-mechanical properties of laminates after water immersion were examined using the dynamic mechanical thermal analysis (DMTA) technique. The results revealed that the long-term water uptake profiles had no similarities to the classical Fickian absorption behaviour and they were markedly different for each water immersion temperature. At higher temperatures a multi-stage diffusion was observed, which was attributed to the microporosity of the laminates as well as to the osmotically enhanced uptake through the interfaces, with the peak values showing dependency on the type of material system. The impact damage on laminates immersed in water did not cause any marked change in the maximum water absorption level or at the absorption rate compared to the undamaged specimens. DMTA have shown matrix plasticizing effects at 43 °C and some post-curing effects at 65 and 93 °C while the effect of the time of immersion at all temperatures tested resulted in a decrease of the value of storage modulus.