Longitudinal Swelling Research Articles

Effects of pH and aging on the texture and physicochemical properties of extruded pea protein isolate

Pea protein isolate (PPI) matrices were extruded at a water content of 50%w/w with the pH of the hydrated PPI adjusted to values between 5 and 9. The impact of the pH on the microstructure, mechanical and swelling of the extrudates was investigated by scanning electron microscopy (SEM), texture analysis and water imbibition experiments. We find that the hardness of the extruded PPI matrices as determined by texture profile analysis (TPA) decreases by ∼50% when the pH is increased from 5 to 9, while the water holding capacity (WHC) is observed to increase linearly from 126% ± 6% w/w on dry basis at pH = 5–442% ± 10% w/w on dry basis at pH = 9. The hardness of the extruded matrices at their WHC is observed to linearly decrease with the WHC. This is explained by a gradual loosening of the matrix as the balance of intermolecular forces shifts from hydrophobic to electrostatic with increasing pH. The extruded PPI matrices are swelling in an anisotropic manner when exposed to pH-adjusted water, with the longitudinal swelling strain being significantly larger than the transversal swelling strain, in particular towards lower values of the pH. Significant aging of the extruded matrices was observed for the first two days following extrusion. Owing to aging, the hardness of the matrices was observed to increase by between 18% (pH = 9) and 23% (pH = 7). Thus, the pH as well as aging are two novel parameters that can be exploited in optimizing the mechanical properties and water holding capacity of extruded PPI matrices, for instance for use in meat analogues.

Thermal Transmittance, Dimensional Stability, and Mechanical Properties of a Three-Layer Laminated Wood Made from Fir and Meranti and Its Potential Application for Wood-Frame Windows

The aim of this paper was to investigate the physical (thermal transmittance and dimensional stability) and mechanical properties of two types of three layer laminated wood made from fir and meranti; fir in surface layers and meranti in core (FMF) and vice versa (MFM) and to examine its potential application for wood-frame windows. An additional objective was to compare the properties of the laminated wood with those of solid wood, namely meranti and fir. Both types of laminated wood had by far substantial lower bending properties than solid wood. MFM laminated wood performed better than the FMF as far as the physical and mechanical properties are concerned. Water absorption and thickness swelling of MFM laminated wood were substantially lower than those of the FMF type, and all the differences were statistically significant. Longitudinal width swelling, and bending properties of MFM laminated wood were higher than those of FMF but these differences were not statistically significant. The thermal transmittance (rate of the heat transferred) of the FMF window is 13.3% better (less) compared to the MFM window. The main reason for this is believed to be the lower overall density of the FMF window, which also makes it more competitive as a result of the reduced manufacturing cost since fir is less expensive compared tomeranti. It was concluded that wood-frame windows can be successfully made from these types of laminated wood, employing therefore easily renewable materials, with low environmental impact, recyclable and manageable in the medium term.

A 3D Printed Morphing Nozzle to Control Fiber Orientation during Composite Additive Manufacturing

AbstractFiber‐filled composite materials offer a unique pathway to enable new functionalities for systems built via extrusion‐based additive manufacturing (or “3D printing”); however, challenges remain in controlling the fiber orientations that govern ultimate performance. In this work, a multi‐material, shape‐changing nozzle—constructed by means of PolyJet 3D printing—is presented that allows for the spatial distribution of short fibers embedded in polymer matrices to be modulated on demand throughout extrusion‐based deposition processes. Specifically, the nozzle comprises flexible bladders that can be inflated pneumatically to alter the geometry of the material extrusion channel from a straight to a converging–diverging configuration, and in turn, the directional orientation of fibers within printed filaments. Experimental results for printing carbon microfiber‐hydrogel composites reveal that increasing the nozzle actuation pressure from 0 to 100 kPa reduced the proportion of aligned fibers, and notably, prompted a transition from anisotropic to isotropic water‐induced swelling properties (i.e., the ratio of transverse to longitudinal swelling strain decreased from 1.73 ± 0.37 to 0.93 ± 0.39, respectively). In addition, dynamically varying the nozzle geometry during the extrusion of continuous composite filaments effects distinct swelling behaviors in adjacent regions, suggesting potential utility of the presented approach for emerging “4D printing” applications.

The post-Jaramillo persistence of Sus strozzii (Suidae, Mammalia) in Europe: New evidence from the Vallparadís Section (NE Iberian Peninsula) and other coeval sites

The Vallparadís composite section (VCS) includes the nearby paleontological sites of Cal Guardiola and Vallparadís Estació (Vallès-Penedès Basin, northeastern Iberian Peninsula). The section spans from before the Jaramillo subchron to the early Middle Pleistocene (ca. 1.2–0.6 Ma). In this study, we describe the suid record from VCS and we review those from several other European sites, in order to refine the taxonomic identity and chronostratigraphic range of Quaternary suids in Europe. The VCS sample includes a nearly complete skull, several teeth, and postcranial elements, and stands out as the richest European suid collection from the latest Early Pleistocene. Suid remains have been unearthed from both Cal Guardiola and Vallparadís Estació layers, whose age spans from the Jaramillo subchron (ca. 1.07–0.99 Ma; MIS31) to post-Jaramillo time (ca. 0.86 Ma; MIS21). Several craniomandibular and dental morphological features support an attribution to Sus strozzii. These features include a low and very deep preorbital fossa, a narrow nuchal crest, a well-developed longitudinal swelling in the middle of the mandibular corpus, the presence of styles/stylids in the upper/lower premolars, and especially the “verrucosic” morphology of the lower canine. The attribution to S. strozzii is also sustained by a cladistic analysis. These results provide interesting clues on the chronological occurrence of Quaternary suids. Sus strozzii is relatively common in Europe during the middle and early late Villafranchian (ca. 2.5–1.8 Ma), but it almost completely disappears during the latest Villafranchian (ca. 1.8–1.2 Ma). During and slightly after the Epivillafranchian (ca. 1.2–0.8 Ma), S. strozzii reappears in Europe although with relatively small samples, at VCS and several other sites including Untermassfeld (Germany; ca. 1.0 Ma), Le Vallonnet (France; ca. 1.2–1.1 Ma), Taman Peninsula (Russia; ca. 1.1–0.8 Ma), Arda River (Italy; ca. 0.99 Ma), and Slivia (Italy; ca. 0.8 Ma), among others. Consequently, in contrast to previous knowledge, we conclude that (1) S. strozzii survived in Europe (or returned there with a second dispersal event from Asia during the Epivillafranchian) at least until the end of the Early Pleistocene and (2) the arrival of Sus scrofa into that continent is not older than the Early-Middle Pleistocene boundary.

Mucoceles of the anterior ventral surface of the tongue and the glands of Blandin–Nuhn: 5 cases

IntroductionMucoceles are cystic diseases of the oral mucosa. The most common are ranula and mococeles of the lower lip. Blandin and Nuhn mucoceles, which develop at the ventral side of the tongue, are rare benign lesions. They are often misdiagnosed and sometimes confused with ranula. The recommended treatment is a complete surgical excision of the gland. Patients and methodsWe describe 5 clinical cases managed in service between 2009 and 2016. Clinical cases are presented in order to detail their clinical history, paraclinical and treatment. ResultsThe clinical appearance is a longitudinal swelling of the ventral surface of the tongue, parallel to the frenulum. The volume of the swelling is variable; it is normally around 30 × 10 mm. The paraclinical (ultrasound, CT, MRI, or ponction) could be performed. CT showed an cyst located on the ventral surface of the tongue, with liquid density. Blandin and Nunh mucocele were strictly anechogenic. MRI confirms the liquid content of this cyst (low T1signal, high T2signal and no post-contrast-enhanced). The resection of Blandin and Nuhn glands should respect the sublingual gland, the lingual nerve and the lingual veins in the mouth floor. ConclusionThis study demonstrates that Blandin and Nuhn mucoceles must be understood and recognised to propose complete excision of the Blandin and Nuhn gland and avoid recurrence.

Colorimetric Humidity Sensor Using Inverse Opal Photonic Gel in Hydrophilic Ionic Liquid.

We demonstrate a fast response colorimetric humidity sensor using a crosslinked poly(2-hydroxyethyl methacrylate) (PHEMA) in the form of inverse opal photonic gel (IOPG) soaked in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM+][BF4−]), a non-volatile hydrophilic room temperature ionic liquid (IL). An evaporative colloidal assembly enabled the fabrication of highly crystalline opal template, and a subsequent photopolymerization of PHEMA followed by solvent-etching and final soaking in IL produced a humidity-responsive IOPG showing highly reflective structural color by Bragg diffraction. Three IOPG sensors with different crosslinking density were fabricated on a single chip, where a lightly crosslinked IOPG exhibited the color change response over entire visible spectrum with respect to the humidity changes from 0 to 80% RH. As the water content increased in IL, thermodynamic interactions between PHEMA and [BMIM+][BF4−] became more favorable, to show a red-shifted structural color owing to a longitudinal swelling of IOPG. Highly porous IO structure enabled fast humidity-sensing kinetics with the response times of ~1 min for both swelling and deswelling. Temperature-dependent swelling of PHEMA in [BMIM+][BF4−] revealed that the current system follows an upper critical solution temperature (UCST) behavior with the diffraction wavelength change as small as 1% at the temperature changes from 10 °C to 30 °C.

Dimensional Changes of Tracheids during Drying of Radiata Pine (Pinus radiata D. Don) Compression Woods: A Study Using Variable-Pressure Scanning Electron Microscopy (VP-SEM).

Variable-pressure scanning electron microscopy was used to investigate the dimensional changes in longitudinal, tangential and radial directions, on wetting and drying, of tracheids of opposite wood (OW) and three grades of compression woods (CWs), including severe CW (SCW) and two grades of mild compression wood (MCW) (MCW1 and MCW2) in corewood of radiata pine (Pinus radiata) saplings. The CW was formed on the underside and OW on the upper side of slightly tilted stems. In the longitudinal direction, the shrinkage of SCW tracheids was ~300% greater than that of OW tracheids, with the shrinkage of the MCW1 and MCW2 tracheids being intermediate. Longitudinal swelling was also investigated and hysteresis was demonstrated for the tracheids of all corewood types, with the extent of hysteresis increasing with CW severity. A statistical association was found between longitudinal shrinkage and the content of lignin and galactosyl residues in the cell-wall matrix. The galactosyl residues are present mostly as (1→4)-β-galactans, which are known to have a high capacity for binding water and swell on hydration. The small proportions of (1→3)-β-glucans in the CWs have similar properties. These polysaccharides may play a functional role in the longitudinal shrinking and swelling of CW tracheids. Tangential shrinkage of tracheids was greater than radial shrinkage but both were greatest for OW and least for SCW, with the MCW1 and MCW2 being intermediate.

Creep behavior of wood under cyclic moisture changes: interaction between load effect and moisture effect

Load and moisture content (MC) changes are the essential conditions for the mechano-sorptive (MS) creep of wood. An experiment was carried out on poplar to comprehend the mechano-sorptive creep from our point view. To restore the truth of MS creep behavior especially in the first humidifying stage, three well-matched sets of specimens were loaded in third-point bending under different humidity cycles. For each set, the applied load varied from 15 to 35 % of the short-term breaking load. It was found that the wood specimens exhibited a partial recovery during all the adsorption phase and deflection increase during all the desorption phase when low load level was applied. This phenomenon was very different from that a considerable creep at first adsorption observed by large amounts of researchers, which can be ascribed to the pseudo-creep due to the difference in the normal longitudinal swelling and shrinkage of wood. The results also indicated that an amplified load effect existed within the creep under cyclic moisture changes, which usually resulted in a fast increasing rate of viscoelastic creep to veil pseudo-recovery in the first humidifying stage.

Measurement of dimensional stability of heat treated southern red oak (Quercus falcata Michx.)

The objective of this study was to investigate the effect of heat treatment on physical and mechanical properties including oven-dry density, weight loss, swelling, shrinkage, and hardness of southern red oak (Quercus falcata Michx.). The samples were treated at a temperature level of 190°C for 3h and 8h. After heat treatment of the specimens, their dimensional stability in the form of swelling and shrinkage were determined by soaking them in water for 2 and 24h. Hardness of samples as function of heat treatment was also measured using Janka hardness (ASTM D 1037–12). Tangential, radial and longitudinal swelling values of the samples exposed to 8h heat treatment and soaked in water for 2h were 0.245%, 0.236%, 0.098%, respectively. Corresponding values for the control samples were 0.504%, 0.455%, 0.135%. Overall hardness of the specimens was adversely influenced due to heat treatment. Based on the findings in this study shrinkage and swelling of the samples improved as a result of heat exposure. It appears that heat treatment would be a viable method to enhance dimensional stability of red oak for more effective utilization where enhanced hygroscopicity of such species is desired.

An anion sensing photonic gel by hydrogen bonding of anions to the N-allyl-N′-ethyl urea receptor

In this paper, a new concept for an anion sensor is demonstrated. We synthesized anion-responsive N-allyl-N′-ethylurea (AEU) that can form hydrogen-bonded complexes with various anions. An allyl functional group enables AEU to participate in copolymerization with hydroxyethyl methacrylate (HEMA) and a crosslinker to form a crosslinked gel. Photopolymerization of the mixed monomer was conducted in the presence of a polymeric opal template, and the subsequent removal of the template resulted in a blue-colored photonic gel in organic solvents owing to light reflection by an inverse opal (IO) structure. After immersing the photonic gel into an acetonitrile (MeCN) solution containing an anion sample with tetrabutylammonium counterion, the reflective color of the gel red-shifted from swelling. For anions such as acetate and dihydrogen phosphate, the photonic gel exhibited color changes within the entire visible spectrum for anion concentration ranges of 10−5 to 10−2 M. Assuming that the charge increase by anion binding is mainly responsible for the longitudinal swelling of a photonic gel sensor, we proposed a mathematical relationship between the swelling factor α and the equilibrium constant K for hydrogen bonding (H-bonding) of an anion with AEU. For five different anion samples, variations in the normalized reflectance peak were plotted as a function of anion concentration, and the equilibrium constant K was calculated by fitting the experimental data to a mathematical function. The sequence of anion sensitivity for five samples was found to be in good accordance with previous investigations on urea–anion complexation, while the lower K values obtained in our system were presumably from the weak electron donating substituent in AEU and the hindered diffusion of the analyte within the gel. However, a photonic gel anion sensor has advantages from the standpoint of simplicity. For instance, a detection apparatus is not required, and the sensor can be used multiple times. With further modification of the urea receptor, the photonic gel will find useful applicability, such as in reusable probe sensors and for the in situ monitoring of ionic species in a continuous process.

EFFECT OF HEAT TREAMENT ON THE PHYSICAL AND MECHANICAL PROPERTIES OF COMPRESSION AND OPPOSITE WOOD OF BLACK PINE

The effect of commercial heat treatment on physical and mechanical properties of compression wood (CW) and opposite wood (OW) of black pine (Pinus nigra Arnold) was investigated. Black pine logs containing CW were cut parallel to the pith and separated into CW and OW sections. A commercial heat treatment process was applied to pine lumber at 180 and 210 ºC for 3 hours. Water absorption (WA), contact angle (CA), swelling, modulus of rupture (MOR), modulus of elasticity (MOE), and impact bending strength (IBS) were measured. The results showed that heat treatment decreased water absorption and swelling of the CW and OW of black pine. Heat treatment at 210 °C temperature decreased the longitudinal swelling of CW by 51.4%. Higher immersion time lowered the effect of heat treatment on the WA values. The CA values of the CW and OW increased due to heat treatment. Heat treatment reduced the MOR, MOE, and IBS values. The results indicated that MOR, MOE, and CA values were highly affected in the CW; on the other hand, the IBS value was highly affected in the OW by heat treatment compared to control groups. The results indicate that heat-stabilized CW can be used more widely and effectively in the forest products industry.

Cellulose microfibril angles and cell-wall polymers in different wood types of Pinus radiata

Four corewood types were examined from sapling trees of two clones of Pinus radiata grown in a glasshouse. Trees were grown either straight to produce normal corewood, tilted at 45° from the vertical to produce opposite corewood and compression corewood, or rocked to produce flexure corewood. Mean cellulose microfibril angle of tracheid walls was estimated by X-ray diffraction and longitudinal swelling measured between an oven dry and moisture saturated state. Lignin and acetyl contents of the woods were measured and the monosaccharide compositions of the cell-wall polysaccharides determined. Finely milled wood was analysed using solution-state 2D NMR spectroscopy of gels from finely milled wood in DMSO-d6/pyridine-d5. Although there was no significant difference in cellulose microfibril angle among the corewood types, compression corewood had the highest longitudinal swelling. A lignin content >32 % and a galactosyl residue content >6 % clearly divided severe compression corewood from the other corewood types. Relationships could be drawn between lignin content and longitudinal swelling, and between galactosyl residue content and longitudinal swelling. The 2D NMR spectra showed that the presence of H-units in lignin was exclusive to compression corewood, which also had a higher (1 → 4)-β-d-galactan content, defining a unique composition for that corewood type.

Physical and Mechanical Properties of Laminated Veneer Lumber Manufactured by Poplar Veneer

Efficient usage of laminated veneer lumber (LVL) in the construction industry requires an understanding the effects of the heat treatment process on the physical and mechanical properties of LVL. It is well known that the heat treatment is often used to improve the dimensional stability of solid wood, but it cases to decrease mechanical properties of solid wood. However, this study aimed testing the physical and mechanical properties of LVL manufactured from heat-treated and untreated poplar veneers. The LVL samples were produced from poplar heat treated veneers (Populus nigra) in the seven ply form (3 mm each) by using urea-formaldehyde (UF) adhesive. Before manufacturing LVL, veneers were subjected to heat treatment at varying temperatures and for varying durations of heating. Significant differences were determined (P ≤ 0.05) in the physical and mechanical properties of the LVLs. The results were recorded the lowest density increment as 29%, the lowest radial swelling as 48%, the lowest tangential swelling as 45% and the lowest longitudinal swelling as 33% for LVL manufactured from heat treated veneers at 180 °C for 5 h as compared to the control sample. The highest flat-wise and edge-wise modulus of rupture (MOR) (107.67 MPa and 102.1 MPa) and modulus of elasticity (MOE) (6,190 MPa and 6,017 MPa) were obtained in the control sample manufactured from untreated veneers. It was determined that modulus of elasticity was less sensitive than modulus of rupture of composite lumber to change due to increase in temperature and heat durations. According to the statistical analyses of variance, the mechanical and physical properties of LVL were more sensitive to temperature than duration of exposure.

Generic redefinition, key and two new species of Acorystus Townes (Hymenoptera: Ichneumonidae: Cryptinae)

The taxonomic limits of Acorystus are reviewed. The genus is characterized by a body surface shiny and mostly impunctate, supra-antennal area with a conical horn, epomia and posterior transverse carina of propodeum entirely absent, ovipositor tip very slender, without nodus and with very weak teeth. Two new taxa, A. albicornis Scherrer et Santos, sp. nov., and A.circumflexus Scherrer et Santos, sp. nov., are described and illustrated. Acorystus albicornis is diagnosed mainly by the white band of the female flagellum covering only about five flagellomeres, supra-antennal area with a white central horn, with a very weak and slightly rugose longitudinal swelling, orbital band reaching supra-clypeal and supra-antennal areas, propodeum with anterior transverse carina almost straight, and pleural carina very weak, with short transverse wrinkles. It is recorded from two close localities at Espírito Santo State (19º57’55”S 40º32’25”W and 20º16’21”S 40º28’40”W), in the Atlantic Forest of Southeastern Brazil. Acorystus circumflexus is diagnosed mainly by the white band of the female flagellum covering about fifteen flagellomeres, supra-antennal area with a black central horn, with a strong and rugose longitudinal swelling, orbital band absent, propodeum with anterior transverse carina centrally arched forwards, and pleural carina entirely absent. It is recorded only from Caxiuanã (2º4’54”S 51º51’5”), Eastern Amazon Basin. A key to all three known species of the genus is provided.

Effect of steam on bonding strength and dimensional stability of laminated veneer lumbers manufactured using different adhesives

Laminated veneer lumbers (LVLs) manufactured from wood with different adhesives are being increasingly used in the construction of furniture frames and buildings. Yet there is little information available concerning the dimensional stability and shear strength of LVLs after being exposed to steam. In this study, LVLs were manufactured from poplar and beech veneers with phenol/formaldehyde (PF), poly(vinyl acetate) (PVAc), Desmodur-VTKA (D-VTKA) and urea/formaldehyde (UF) adhesives. Dimensional stability of LVLs was measured after being exposed to steam for 2, 6, 12, 24, 48 and 96 h, according to the Turkish Standard (TS) 3639, and also shear strength was measured (according to BS EN 205). The highest initial density of 0.93 g/cm3 was for beech LVL with VTKA adhesive. After exposure to steam for 96 h, the highest weight increase of 65.7% was for poplar LVL with PVAc, the highest radial swelling of 5.7% was for beech LVL with UF, the highest tangential swelling of 7.9% was for beech LVL with PF and the highest longitudinal swelling of 0.5% was for beech LVL with VTKA. The highest shear strength value of 15.8 N/mm2 among all samples without exposure to steam was obtained for beech LVL with PVAc adhesive and the lowest shear strength was obtained as 4.48 N/mm2 for poplar LVL with UF adhesive.

Comparison between HT-dried and LT-dried spruce timber in terms of shape and dimensional stability

Abstract The performance of timber studs from Norway spruce (Picea abies) in terms of shape and dimensional stability was evaluated. The shape stability studied included three modes of distortion, i.e. twist, bow and spring. The dimensional stability was assessed by measuring longitudinal shrinkage and swelling properties. The study comprised 96 studs measuring 45 mm×70 mm×2500 mm from 15 butt logs. Half the studs from each log were dried using a high-temperature method (HT) at 115°C, while the other half were dried using a conventional low-temperature method (LT) at 70°C. Distortion in the studs was measured at moisture contents of 14% and 9%. The HT-dried timber had significantly lower distortion values than the LT-dried timber. As a result, 80% of the high-temperature-dried studs were able to pass the limits for distortion, while only 60% of the low-temperature-dried studs passed the same limit. Studs cut close to the pith displayed the largest twist, independent of the drying method. A simple model for predicting twist that was used in previous studies was also valid for HT-dried timber. The most important parameters in this model for both HT- and LT-dried timber were grain angle, annual ring curvature and tangential shrinkage.

Process for production of high density/high performance binderless boards from whole coconut husk: Part 2: Coconut husk morphology, composition and properties

For production of compression moulded boards from whole coconut husk the auto-adhesive properties are derived from the intrinsic high lignin content. Since the properties of manufactured boards for a large part will depend on the input husk material these properties are studied here. Husks of different varieties and maturity have been investigated for their contents of fibre and pith. Relevant physical properties and chemical composition were determined. For accurate determination of tensile strength and stiffness of coir fibre, its density ( ρ coir = 1.2–1.3 g/cm 3) and cross-sectional area were determined. Both thickness and longitudinal swelling of the fibre were measured to assess the effects of water absorption. The constituent fibre and pith fractions of coconut husk have been chemically analysed for polysaccharide (cellulose, pectin and hemicellulose) and lignin contents. Detailed carbohydrate analysis of the fibre indicated a glucose (cellulose) content of approximately 33% in the cell wall, together with 12% xylose as the major component of the hemicellulose fraction. Coir pith only contains 16% glucose. The effects of maturing on the chemical composition of the husk is analysed and a significant increase in glucose (cellulose) is observed, while for other sugars no dramatic change in relative amounts can be measured. It was concluded that only slight differences can be observed between mature coconut husks of different origin, and all are suitable as input feedstock for boards production. More effects can be expected from the age of the nuts.

Bonding strength and dimentional stability of laminated veneer lumbers manufactured by using different adhesives after the steam test

Composite materials manufactured from woods with different adhesives are being used increasingly in the construction of furniture frames and buildings. Yet there is little information available concerning the dimensional stabilization and shear strength of laminated veneer lumbers (LVL) after being exposed to steam. In this study, LVLS were manufactured from pine ( Pinus sylvestris L) and Black sea fir ( Abies nordmanniana) veneers with Phenol-formaldehyde (PF), poly (vinyl acetate) (PVAc), Desmodur-VTKA (D-VTKA) and urea-formaldehyde (UF) adhesives. Dimensional stability of LVL were measured after being exposed to steam for 2, 6, 12, 24, 48 and 96-h-period according to the procedure of the Turkish Standards (TS) 3639, then shear strength tests were applied (based on BS EN 205). As a result, the highest density was determined for LVL with UF adhesive in both samples. The highest weight increment as 57.53% for black sea fir LVL with PF, the highest radial swelling as 9.74% for pine LVL with PF, the highest tangential swelling as 4.1% for pine LVL with VTKA and the highest longitudinal swelling as 0.44% for pine LVL with PF adhesive were determined after being exposed to 96 h steam. The highest shear strength was obtained in pine control samples with VTKA adhesive (5.36 N/mm 2) and the lowest shear strength was obtained in Black sea fir LVL with PVAc adhesive (4.48 N/mm 2).

Einfluss des Plattenaufbaus und des Pressdrucks auf die Eigenschaften dreischichtiger Massivholzplatten | Influence of layering arrangement and compression level on the characteristics of three-layered solid wood panels

The level of compression and the arrangement of layers were varied on layered solid wood panels, produced in the laboratory using technical methods and glued with polyurethane(PUR). Measurements were subsequently carried out on the Emodule,bending strength, diffusion resistance level, changes in length caused by changes ambient climate, as well as the warping in a fluctuating climate. Following results were recorded. The level of compression with the PUR glue used in the experiment had no influence on the tensile strength or the E-module. When the proportion of middle layer wood is increased in the panel, the tensile strength of the covering layer falls when stressed parallel to the direction of the fibre. It rises when the covering layer lies at a right angle to the direction of the fibre. The quality of the panel can be influenced by varying the quality of the wood used in the covering and middle layers, e.g. by sorting. Slitting the middle layer leads to a clear reduction of shearing strength (rolling shear) when the panel is stressed, and the covering layer is parallel to the longitudinal axis of the sample. On the other hand, with the longitudinal axis lies at right angles to the covering layer (stressing of the middle layer parallel to the fibre), the influence of slitting is slight because the weakening of the cross-section is considerably less. Warping in a fluctuating climate can be clearly improved with rift cut in the covering layer. Diffusion resistance only continues to increase between pressures of 1 to 2 bars,and subsequently remains constant. Differential longitudinal swelling is influenced by the arrangement in construction.

Distortion of Norway spruce timber

This paper clarifies the extent to which models based on two- and three-dimensional material descriptions can predict bow and spring deformation. Changes in longitudinal shrinkage and swelling and their variations over cross-sections of studs cause these studs to develop distortion in terms of spring and/or bow. Radial variation from pith to bark (two-dimensional) of the longitudinal shrinkage in the cross-section is often assumed to be the only physical data needed to predict spring and bow in a stud. However, using measurements from 240 studs of Norway spruce (fast-grown and one slow-grown stand), it was found that there was no correlation between shrinkage gradients measured at one longitudinal position and three-dimensional bending distortion (spring and bow). As a result, two studs, one with large spring (and no bow or twist) and one with large bow (and no spring or twist), were cut longitudinally in sections 200 mm long. From these sections, sticks were cut and the longitudinal shrinkage was measured twice on all sticks, when the climate was 90% relative humidity (RH) and 30% RH, in order to produce data which correspond to changes in moisture content in the studs, roughly between 15% and 7.5%. The difference in the longitudinal shrinkage between two faces of the studs explained spring or bow far better when the variation in shrinkage along the stud was considered. The longitudinal variation in shrinkage was very large; i.e. strains varied from 0.062% to 0.290% along one stud. Knowing the three-dimensional shrinkage variation, it appears to be possible to predict bending distortion with very good accuracy, as shown in this paper. It is clearly demonstrated that knowledge of the three-dimensional variation in longitudinal shrinkage is needed in order to predict bow and spring more accurately.