Zeitstandversuche mit Spanplatten

Tests regarding fatigue behavior of particle boards bonded with different glue types, the characteristics of which are given, have been carried out with a loading period of 588 days. The periodically measured deflections were compared with the initial deflection and the deflection ratiof _t/f₀ was determined. After a loading period of one year the best of the tested boards had doubled their initial deflection showing no essential increase of deflection until determination of tests. The worst boards reached, already after 150 days, a deflection 5 times higher than the initial one and increased it up to more than 7 times until determination of tests. The course of the deflection ratio and the respective moisture content of the boards in dependence on the surrounding climate is demonstrated.     

Creep behaviour of commercial wood based boards under long-term loading at room conditions in Taiwan

The purpose of this study was to investigate the creep behaviour of commercial wood based boards (sanded and laminated) under long-term loading at room conditions in Taiwan. Ten types of commercial wood based boards were used to test their physical and mechanical properties in this study. Four types of these boards were used for the same test after laminating with red oak (Quercus spp.) veneer or balanced paper. The bending creep was measured at room conditions with central concentrated loading. The values for creep deflection of commercial wood based boards 18 mm thick decreased from 1.06–1.19 mm ti 1.00–1.12 mm after laminating veneer or balanced paper. The relative creep (120 days) of those specimens decreased from 1.71–3.17 to 1.43–2.04 after laminating with veneer or balanced paper in four months’ loading. The creep deflections of specimens increased with increasing loading time. The linear regression function ist/y=a+bt, wheret is time,y is deflection. When theb value is larger, the boards displayed good creep resistance. The residual bending strength of wood based boards after creep test would be retained at about 80–95%, and the residual bending strength between particleboard proved more significant than between fiberboard.     

Beitrag zur Kurzzeitfestigkeit und zum Dauerstandverhalten von MDF der ersten Generation

Characteristic features of MDF of the first generation are: manufacture of MDF from inferior wood assortments with bark, multilayer structure of the boards on fibrous materials of different fineness, gluing of the fibrous material in mixers, lower middle density. Typical properties of these MDF: density 700–730 kg/m³, internal bond 0.50–0.65 N/mm², bending strength 26–35 N/mm², modulusE _b 2700–3000 N/mm². Dealt with are results from former long-term tests in comparison with conventional particle boards for furniture (of lower bending strength). With constant load not graded according to the strength the deflection of these MDF was similar to, or higher than that of the particle boards, their creeping coefficient exceeded that of the particle boards.     

Bruchenergien,kritische Energiefreisetzungsraten und Bruchzähigkeiten von Fichte bei Zugbeanspruchung senkrecht zur Faserrichtung

It is reported on Mode I fracture energyG _f, critical strain energy release rateG _c and fracture toughnessK _c of spruce in RL-crack system. The investigations were performed with special SENB specimens acc. to a CIB W18A draft standard. For determination of size effects geometrically similar specimens of significant different sizes were tested; the cross-sectional depthd varied from 10 to 320 mm and notch length was constant 0,6d. All “tension perpendicular to grain volumes” were cut from two boards with similar mean densities of about 460 kg/m³. The paper first deals with some general aspects of related energy termsG _f resp.G _c and then gives finite element results for normalized strain energy release rates and stress intensity factors of the specific orthotropic specimen. The experimental results can be summarized as follows: Fracture energyG _f is quite independent of initial crack length and counts in mean 280 N/m; the 5th percentile value due to fitted 3parameter Weibull distribution is 180 N/m and thus about 30% lower as given implicitly in Eurocode 5 for respective density. For density dependency in the range of about 420 to 480 kg/m³ the linear relationG _f≈0,62 ρ₁₂ was found. Critical strain energy release rateG _c increases degressively with specimen depth resp. initial crack length. Compared toG _f,G _c is roughly 25% lower up to crack lengths of about 60 mm and is then of similar quantity asG _f. Fracture toughnessK _c alikeG _f, was found to be quite independent of initial crack length; for mean and characteristic values 440 resp. 280 kN/√m³ were received.     

Influence of veneer thickness on the properties of LVL from Paricá (Schizolobium amazonicum) plantation trees

The work aimed at evaluating the influence of the veneer thickness on physical and mechanical properties of laminated veneer lumber (LVL) boards made from Schizolobium amazonicum plantation trees. It is a fast growing species (20 m³/ha/year), having a straight trunk almost without any branch and producing a white-yellowish low density hardwood: usually <0.40 g/cm³. The boards were manufactured with the following thicknesses: 1.54, 2.32 and 2.71 mm. Seven LVL boards were produced for each thickness, totaling 21, all according to the following characteristics: PVAc adhesive (200 g/m²), pressed (1.0 N/mm²) at room temperature for 12 h. The following mechanical and physical properties were then evaluated: static bending modulus of elasticity (E _M ), modulus of rupture (f _M ), compression strength parallel to grain (f _c,0 ), shear strength parallel to glue-line (f _v,0 ), shear strength perpendicular to glue-line (f _v,90 ), water absorption and thickness swelling for 2 and 24 h of water immersion. The results pointed out that the utilization of thinner veneers implied improving mechanical properties, while thicker veneer reduced the water absorption. Nevertheless, in contrast, the efficiency was lower than that observed when thicker veneer was used.     

Durchbiegung und Lastannahmen im Korpusmöbelbau

Load assumptions and defined values for long-term MOE of differently coated particleboards are a precondition for calculating the deflection of loaded furniture parts. The results of some investigations are reported. In determining long-term MOE some problems result from the great scatter of values in nominally uniform boards, and from the relatively long test period of 28 days. It became evident, that after only 1 day of loading about 80%, and after 7 days about 90% of the final deflection were reached. Furthermore, loads of other objects were determined. Some of these seem to be extremely high and are not acceptable as standard loads. Therefore, the load assumptions should be investigated further. For furniture production the dimensioning of shelf-boards can be precalculated with respective data and in this way the requirements for load classes according to DIN 68 874 can be fulfilled.     

Solid–liquid expression from denaturated plant tissue: Filtration–consolidation behaviour

The objective of this study is to investigate the filtration–consolidation behaviour of biological tissue (sugar beet specimens), denaturated by pulsed electric field (PEF) and freezing–thawing pretreatments. The degree of cell membrane damage was evaluated by the tissue electrical conductivity measurement (determination of the cell disintegration index Z). The PEF-treated and freeze–thawed tissues show different structure response on the applied compressive pressure and different filtration–consolidation behaviour. The value of fracture pressure (P_f ≈ 58.5 bar) is the lowest and the value of tissue deformation under fracture (ε_f ≈ 0.46) is the highest for sugar beet tissue treated by freezing/thawing. PEF treatment leads to more rigid and more fragile tissue structure (P_f ≈ 63.8 bar, ε_f ≈ 0.28) than freeze–thawed tissue. Untreated tissue seems to be stronger and less fragile than the PEF-treated tissue (P_f ≈ 84.1 bar, ε_f ≈ 0.37). Different tissue reactions on the loading pressure evidently reflect the difference between microstructures of treated and untreated tissues. The filtration/consolidation behaviour during liquid expression from a sugar beet tissue also depends on the type and degree of structure denaturation. Tissues treated by PEF and freezing/thawing demonstrate two consolidation stages of expression (primary and secondary). However, the freeze–thawed tissue tends to modify the expression mechanism under the higher loading pressure (60 bar) with approach to the primary consolidation behaviour. The simplified semi-empirical consolidation model permits a reasonably good prediction of expression behaviour from the denaturated sugar beet tissue and estimation of consolidation coefficient b under different pressures. The extrapolation of curves b(P) shows the value of hypothetical pressure, P_max ≈ 90 bar at which the consolidation behaviour would be similar to both PEF-treated and freeze–thawed tissues.     

Material properties and nondestructive evaluation of laminated veneer lumber (LVL) made from Pinus oocarpa and P. kesiya

This study aimed at evaluating the mechanical, physical and biological properties of laminated veneer lumber (LVL) made from Pinus oocarpa Schiede ex Schltdl (PO) and Pinus kesiya Royle ex Gordon (PK) and at providing a nondestructive characterization thereof. Four PO and four PK LVL boards from 22 randomly selected 2-mm thickness veneers were produced according to the following characteristics: phenol-formaldehyde (190 g/m²), hot-pressing at 150°C for 45 min and 2.8 N/mm² of specific pressure. After board production, nondestructive evaluation was conducted, and stress wave velocity (v ₀) and dynamic modulus of elasticity (E _Md ) were determined. The following mechanical and physical properties were then evaluated: static bending modulus of elasticity (E _M ), modulus of rupture (f _M ), compression strength parallel to grain (f _c,0), shear strength parallel to glue-line (f _v,0), shear strength perpendicular to glue-line (f _v,90), thickness swelling (TS), water absorption (WA), and permanent thickness swelling (PTS) for 2, 24, and 96-hour of water immersion. Biological property was also evaluated by measuring the weight loss by Trametes versicolor (Linnaeus ex Fries) Pilát (white-rot) and Gloeophyllum trabeum (Persoon ex Fries.) Murrill (brown-rot). After hot-pressing, no bubbles, delamination nor warping were observed for both species. In general, PK boards presented higher mechanical properties: E _M , E _Md , f _M , f _c,0 whereas PO boards were dimensionally more stable, with lower values of WA, TS and PTS in the 2, 24, and 96-hour immersion periods. Board density, f _v,0, f _v,90 and rot weight loss were statistically equal for PO and PK LVL. The prediction of flexural properties of consolidated LVL by the nondestructive method used was not very efficient, and the fitted models presented lower predictability.     

Fracture in spruce: experiment and numerical analysis by linear and non linear fracture mechanics

That paper first presents a simplified Damage Mechanics (DM) model for the simulation of fracture in wood. All damage phenomena are assumed to occur on a surface (or a line in a 2D problem). Then test results of mode I fracture in spruce and fir are given. The size effect is investigated. Linear Elastic Fracture Mechanics (LEFM) and DM are compared for a simulation of three point bending tests, classically used for the determination of the fracture energy (G _f) in tension perpendicular to grain. The study of the observed size effect gives the range of applicability of LEFM. The critical energy release rate (G _c) and the fracture energy (Y _f) that are energy parameters of LEFM and DM respectively, are identified for small specimens and compared with the experimentally dissipated energy to fracture the specimen (G _f). Load-displacement curves are correctly predicted with both methods. G _f can be considered as a material parameter and it is verified that a non-linear approach is necessary for the simulation of fracture of small specimens.     

Variations of Hausdorff Dimension and Selected Textural Indices of Cheddar and Gouda Cheeses During Storage

Two imported commercial cheeses (Cheddar and Gouda) were analyzed to characterize their textural changes during a storage period from 176 to 362 days at 4°C. Fractal dimension analysis was used to examine the structure of the cheeses, and a scaling model based on stress values was used to calculate fractal dimension (D_f) by the Hausdorff dimension count method. It was found that the variation of D_f of two cheeses showed a similar trend. When two cheeses were stored from 176 to 300 days, their D_f ranged from 2.37 to 2.43 for Cheddar or from 2.06 to 2.23 for Gouda cheeses. After that, the final values of D_f increased obviously to 2.87 (Cheddar cheese) or 2.63 (Gouda cheese) at the end of the storage period. The experiments carried out showed that the variation of D_f had a poor relationship with the changes of pH 4.6 soluble nitrogen and two instrumental textural indices (hardness and springiness) of the cheeses, especially in the late storage period, but the inhomogeneous cavities existing in the cheeses could be reflected by their D_f.     

The labile pool of manganese in soil: Comparison of E and L value measurements with extraction methods

The size of the manganese labile pools of three sandy soils from south east Scotland with a history of Mn deficiency was investigated by four methods: extraction with CaCl₂; extraction with DTPA; E-value determination by exchange with ⁵⁴Mn; and L-value determination using barley as the test crop. There was little agreement between the methods. The L-values varied with the period of plant growth and with soil bulk density but greatly exceeded the E-values, which in turn were about twice the quantities obtained by prolonged extraction with CaCl₂ and an order of magnitude greater than the quantities extracted after 1 h with CaCl₂-DTPA extraction gave values three to six times those obtained with CaCl₂. Extractable Mn increased dramatically after prolonged air drying, indicating the need for standardisation of both pre-extraction conditions and extraction times when comparing the Mn availability of different soils.     

Comparison of Axial and Radial Compression Tests for Determining Elasticity Modulus of Potatoes

The effect of sample size, loading rate, and compression level on the determination of tangent modulus of elasticity of potatoes in axial (E_a) and radial (E_r) compression tests was studied. Cylindrical potato samples of 10, 15, and 20 mm diameter with length-to-diameter (L/D) ratio 1, 1.5, and 2 and loading rates of 50, 100, 200, 300, and 400 mm/min were used. A third-degree polynomial best described the force-deformation (F-D) plot of the test specimens (R²?=?0.98 to 0.99) in both tests. In view of the non-linearity of the F-D plot, E_a and E_r were calculated corresponding to 10, 20, and 30% compression. The values of E_a and E_r obtained for various combinations of sample size and compression level had coefficient of variation (CV) of about 24 and 8%, respectively, indicating relatively greater influence of experimental conditions in axial than radial compression testing. Apparently, E_a increased with an increase in compression level and loading rate whereas E_r exhibited inconsistent trend. The combined effects of sample size and compression level accounted for about 93 and 20% of the changes in E_a and E_r, respectively signifying the minimal effects of these parameters in radial compression testing. Similarly, the loading rate and compression level accounted for about 96 and 28% of the changes in E_a and E_r, respectively. The results of this article revealed that determination of modulus of elasticity of potatoes in axial compression testing was significantly influenced by testing conditions and sample size, whereas radial compression testing appeared to be independent of testing conditions and sample size.     

Untersuchungen zur Biegeprüfung dünner Holzwerkstoffe

Testing technique problems arising in the standards related bending strength determination of thin wood based boards (thicknesst< 10 mm) are described. The paper gives recommendations for a future standardization of this bending test method, based on relevant tests with thin fibre hardboard, particleboard and plywood.     

Enzyme-modified guar gum/xanthan gelation: An analysis based on cascade model

The gel properties of a mixture of enzymatically-modified guar gum (EMG) and xanthan (XG) were investigated. The guar gum sample treated with α-galactosidase to remove galactose residues had a mannose/galactose ratio of 3.02, and was capable of forming a synergistic gel with xanthan. The concentration-dependent and temperature-dependent modulus data for the EMG/XG gel were analyzed by the two-component cascade model which assumed a heterotypic association between segments of EMG and XG. The optimal functionalities (number of cross-linking sites per chain), f_EMG and f_XG, were found to be 300 and 30, respectively. The former is equal to the number of segment size with more than six unsubstituted mannose residues in a galactomannan backbone, while the latter corresponds to a cross-link density of one per 37 repeating units in a xanthan molecule. The cascade analysis of the composition dependence of critical gelling concentration was performed by introducing the effect of the homotypic association of XG or EMG, which became significant in the gel point measurement. The enthalpy change per cross-link for the heterotypic association was found to be two times higher than that for the homotypic association.     

Über die Eignung von thermo-mechanischem und chemo-thermo-mechanischem Holzstoff (TMP und CTMP) aus Buchen- und Kiefernholz für die Herstellung von mitteldichten Faserplatten (MDF)

Medium density fibreboards (MDF) were made from beech in laboratory and pilot plant scale from thermo-mechanical (TMP) and chemo-thermo-mechanical pulps (CTMP) using both melamine reinforced urea-formaldehyde resin (UF-resin) and diphenylmethane diisocyanate polymers (PMDI). The physicalmechanical and chemical properties of the boards were evaluated. From the results the following conclusions can be drawn:

1. Both TMP and CTMP led, on using UF-resin, to MDF with very high mechanical properties exceeding the required values in European standards.
2. Pulping temperature seems to have an influence on the mechanical properties of the boards, prepared from TMP and CTMP. Increasing the pulping temperature from 150°C to 170°C negatively affects the mechanical board properties, whereas the properties of MDF from CTMP (sulfonic group content between 0.2% and 0.3%) increases by elevating the maximum pulping temperature from 150°C to 170°C.
3. The pulping chemicals in the CTMP-process (Na₂SO₃ and/or NaOH) decrease the formaldehyde release from the boards, as they act as scavengers for formaldehyde.
4. Due to higher deacetylation degree during CTMP process, MDF made from CTMP release more than 4 times acetic acid than MDF from TMP. The release of formic acid is quite different, it is in MDF, made from TMP higher than in MDF from CTMP.
5. MDF with very high mechanical properties can also be made from beech pulps (TMP) using PMDI. PMDI in combination with a formaldehyde scavenger in the middle layer and UF-resin in the surface layer leads to boards with very low formaldehyde release.

     

Egg laying by unmated females of Sitotroga cerealella (Lepidoptera: Gelechiidae)

Ninety-eight out of one hundred unmated females of Sitotroga cerealella laid eggs, the total number ranging between 3 and 94. Sixteen females paired within a day of emergence laid between 91 and 177 eggs, but females not paired until 5 days after emergence laid less than half as many. No egg laid by unmated females was fertile and the fertility of eggs laid by females not paired until 5 days after emergence was also lower than that of eggs laid by females which were paired soon after emergence. Unmated females lived about 15 days; $\text{2}\text{1}\text{2}$ times as long as mated females. When mating was delayed by 5 days the longevity of these following mating, was similar to that of females paired soon after emergence.     

EXTENDED STORAGE LIFE OF LITCHI FRUIT USING CONTROLLED ATMOSPHERE AND LOW TEMPERATURE

The postharvest quality of litchi (Litchi chinensis Sonn.) cv. Bombay stored under controlled atmosphere (CA) at 3.5% O₂and 3.5% CO₂, 2C temperature and 92–95% relative humidity was studied. Fruits were also held in regular atmosphere (RA) maintained at 2C temperature and 92–95% relative humidity. Fruits kept at normal ambient conditions were used as controls. Various quality attributes measured revealed that fruits stored in CA exhibited Hunter “a” values of 11.2 after 56 days of storage, indicating the beneficial effect of CA on retaining the red color of litchi fruits. Fruits held in RA exhibited Hunter “a” values (7.9) lower than that of CA‐stored litchi, showing that browning of litchi was noticeable in RA. Loss of weight was lowest (4.9%) for the fruits stored in CA compared to those stored in RA (11.0%) and control (33.1%). Loss of acidity and ascorbic acid content of fruits stored in CA were less than that of RA. The smallest increase of litchi firmness and pericarp puncture strength of 2.2 and 3.9 times of initial level, respectively, were observed even after 56 days of storage in CA. Total soluble solid of litchi increased from 19.3° Brix at harvest to 23.0° Brix until 48 days of storage in CA after which it declined to 22.8 °Brix. The sensory evaluation of aril color and taste showed that the fruits held in CA were rated good throughout 56 days of storage.     

Mathematical modeling on the growth of Staphylococcus aureus in sandwich

The growth of Staphylococcus aureus in sandwich fillings at different incubation temperatures was tested. These growth data were fitted into the Gompertz model, Logistic model, and Baranyi model in order to compare the goodness-of-fit of the 3 primary models using several factors such as coefficient of determination (R²), the standard deviation (S_y.x), and the Akaike’s information criterion (AIC). The Gompertz model showed the best statistical fit. Hence, growth parameters such as specific growth rate (SGR) and lag time (LT) obtained from the Gompertz model were used to construct the secondary models. Further, developed models were evaluated by bias factor (B_f) and accuracy factor (A_f). For the SGR, the Bf value was 0.993 and A_f value was 1.156 which indicated conservative predictions. While for LT, a clear deviation was observed between predictions and observations (B_f=0.635 and A_f=1.592). The results, however, were also considered acceptable after comparing with previous publications.     

Untersuchungen zum Einfluss der Holzfeuchte auf ausgewählte Eigenschaften von Spanplatten und MDF

On industrially produced particle boards and MDF, the influence of wood moisture on bending MOE, bending strength and shear modulus G_zx and G_zy was determined. The equilibrium moisture content and the differential swelling of thickness proved to be smaller for MDF than for particle boards. Tensile strength and tensile MOE, shear modulus and bending strength decrease likewise with increasing wood moisture content. Furthermore the Poisson ratio μ₁₂ decreases with increasing wood moisture content.     

Indirekte Bestimmung der Scherfestigkeit des Holzes mit Hilfe der anisotropen Festigkeitstheorie

There are arising many theoretical and practical problems when determining the shearing strength. The parameters of shearing strength determined by direct methods usually depend on test conditions. The aim of this study was the elaboration of an indirect method the results of which being independent of test conditions. This independent method is based on Ashkenazi's strength hypothesis. The theoretically developed possibility to determine shearing strength had to be proved by experiments. About 1000 test specimens of spruce wood were cut in different angles to the three anatomical planes and tested for tensile and compression strength. The experimental results support the application of the indirect determination of shearting strength. It is suggested that the parameters determined by this method may be considered as real material constants. The method allows the determination of three technically most important strength vectors (t _RL, t_TL, t_RT?t_TR) without directly testing them and using only the known normal strength components (f _L, f_R, f_LR(45), f_LT(45), f_RT(45)).