A. Grigoriou

Characterization and utilisation of vine prunings as a wood substitute for particleboard production

Abstract The vine has been a traditional cultivation in Greece for many years. Every February after pruning, large quantities of vine prunings remain as byproducts in the field, non-utilized properly. The average amount of prunings per year reaches ≈5 t/ha, which is higher than the average yield of forests in temperate zones. The aim of the present work was to investigate the suitability of vine prunings as a raw material for particleboards. After pruning, prunings from several varieties were chipped with an automobile chipper and re-chipped in a hammermill. Vine pruning particles and industrial wood particles in various proportions were used as the raw material for one-layer and for the core and surface layer of three-layer particleboards. In addition, material from vine prunings stored for 6 months in outdoor conditions was tested for its quality for particleboard production. A commercial urea–formaldehyde (UF)-resin was used as binder. Vine pruning particles were characterized by higher bulk density and lower slenderness ratio than industrial wood particles. The evaluation of the mechanical and hygroscopic properties of experimental panels showed the following results: partial substitution of wood by vine prunings negatively affects all board properties. However, the mechanical properties of three-layer boards, even those containing up to 100% vine pruning particles in the core, exceed the minimum requirements of the relevant European Standards (EN 312, Part 3, 1996) set for interior boards in dry conditions. The same happened with the hygroscopic properties. With the exception of the screw holding strength and formaldehyde release, the properties of boards made of vine prunings did not change substantially in comparison to those made of vine prunings stored for 6 months in outdoor conditions.

The potential use of Ricinus communis L. (Castor) stalks as a lignocellulosic resource for particleboards

Abstract Castor (Ricinus communis L.) stalks, which are a readily available by-product of this plant mainly cultivated for seed production, derived from experimental plantations grown in Northern Greece during the period April–October 1996 were assessed for their suitability as feed stocks for direct substitution of wood in particleboard. The average stalk yield of castor reached about 10 dry t/ha, which is higher than the average yield of forest in temperate zones. After harvesting, castor stalks were dried in a greenhouse to about 12% moisture content, and chipped by an automobile chipper and re-chipped in a hammermill. Castor particles and industrial wood particles mixed in various proportions were used as raw material for one-layer and for the middle layer of three-layer particleboards. A commercial E2 grade UF-resin was used as binder. Castor particles were characterized by a lower slenderness ratio and lower bulk density than industrial wood particles. The evaluation of the mechanical and hygroscopic properties of panels showed the following results: Partial substitution of wood by castor stalks resulted in the deterioration of all board properties. The presence of the unlignified pith and the configuration of castor particles seem to be responsible for the deleterious effect of castor stalks on board properties. However, comparing the properties of the boards produced in this study to relevant European and American Standards, it was found that, with the exception of screwholding strength for three-layer boards, the experimental one layer-, and three-layer boards containing up to 25% and 75% castor particles respectively meet or exceed the Standards requirements for interior boards.

Experimental particleboards from Kenaf plantations grown in Greece

Hibiscus cannabinus L.) plantation grown in N.Greece during the period June–October 1996 provided the raw material for experimental particleboards. After harvesting, the kenaf stems were storaged under shelter for a week, the core of each stem was separated from bark and both were dried at about 20% and 10% moisture content, respectively, and chipped by a hammermill. Kenaf core, bast fibers and industrial wood chips were mixed in various proportions in order to produce three-layer E2 grade UF bonded particleboards. Kenaf core chips were characterized by a lower slenderness ratio than wood chips of the middle layer. Bulk density of both core chips and fibers was lower than that of wood chips. Substitution of wood chips with kenaf core chips in the middle layer up to 75% slightly affects static bending and internal bond of the boards, but reduces screw holding strength and increases water absorption and thickness swelling; a 100% substitution deteriorates all properties except static bending. In boards with surface layers from kenaf bast fibers or from fibers:wood chips (50:50), static bending and surface roughness are improved, while the other properties tested are deteriorated. Substitution of kenaf core chips in the middle layer with fibers in proportion 50% negatively affects the board properties except static bending. It can be concluded that core chips and bast fibers from kenaf stems may substitute industrial wood chips in the middle and surface layers of the boards, respectively, up to 50%.Hibiscus cannabinus L.) in N. Griechenland. Nach der Ernte wurden die Kenafstengel für eine Woche unter Dach gelagert, dann wurde das Holzgewebe im Stengelinneren von der Rindenschicht getrennt, anschliessend auf ca. 20% bzw. 10% Feuchtigkeit getrocknet und beides in einer Hammermühle zerkleinert. Die Herstellung dreischichtiger harnstoffharzverleimter (E2 Typ) Spanplatten erfolgte unter Verwendung verschiedener Beimischungen aus Kenafholzspänen, Kenaffasern und Industrieholzspänen. Kenafholzspäne und Kenaffasern zeichnen sich durch eine niedrigere Streudichte als Industrieholzspäne aus; darüberhinaus weisen Kenafholzspäne einen niedrigeren Schlankheitsgrad auf im Vergleich zu den Mittelschichtspänen der Industrie. Der Ersatz von Industrieholzspänen durch Kenafholzspäne in der Plattenmittelschicht bis zu einem Anteil von 75% beeinflusst unwesentlich die Biege-, und Querzugfestigkeit der Platten, hat aber eine negative Auswirkung auf das Schraubenhaltevermögen, die Dickenquellung und die Wasseraufnahme; ein Zusatz von 100% Kenafholzspänen zur Mittelschicht bewirkt eine Verschlechterung aller Spanplatteneigenschaften mit Ausnahme der Biegefestigkeit. Spanplatten, deren Deckschichten aus reinen Kenaffasern oder aus einer Beimischung von Kenaffasern und Industrieholzspänen in einem Verhältnis von 50:50 bestehen, weisen höhere Qualität bezüglich Biegefestigkeit und Oberflächenrauhigkeit auf, aber niedrigere hinsichtlich der übrigen Eigenschaften. Der Ersatz von Kenafholzspänen durch Kenaffasern in der Plattenmittelschicht hat, abgesehen von der Biegefestigkeit, einen negativen Einfluss auf alle Platteneigenschaften. In ihrer Gesamtheit führte die Untersuchung zu dem Resultat, dass der Zusatz von Kenafholzspänen und Kenaffasern in der Mittelschicht bzw. der Deckschicht von Spanplatten bis zu einem Anteil von 50% möglich ist.

Utilisation of wood biomass residues from fruit tree branches, evergreen hardwood shrubs and Greek fir wood as raw materials for particleboard production. Part A. Mechanical properties

Abstract This paper investigates the potential of utilising wood biomass from fruit tree branches and evergreen hardwood shrubs as raw materials in the production of particleboards when mixed with Greek fir wood particles. The main mechanical properties of the boards made therefrom were determined and compared with those made of typical industrial wood (IW) particles. The highest modulus of rupture and elasticity (30.0 N/mm2 and 4330 N/mm2, respectively) in bending and screw withdrawal (SW) resistance (127.8 N/mm) were reported for boards made of Greek fir and were downgraded when the fruit tree branches or evergreen hardwood shrub particles also participated. The participation of fruit tree branch particles in proportions higher than 50% improved the internal bond (IB) of fir produced boards, while the highest IB strength (0.95 N/mm2) was reported for boards made of fruit tree branches. Particleboards made of evergreen hardwood shrubs showed inferior mechanical properties compared with those made of IW particles. The latter also showed superior bending strength but inferior SW resistance compared with boards made of fruit tree branches. Hygroscopic and other properties are under determination and will be presented and discussed in the second part of the work.

Quality characteristics of hydrothermally recycled particleboards using various wood recovery parameters

Abstract The aim of the present paper was to study the effect of some particle recovery parameters on the quality of hydrothermally recycled particleboards. The research was carried out in two phases: rough evaluation of various recovery parameters and determination of the recycled particleboard properties. It was concluded that the optimum group of hydrothermal recovery parameters (among those tested in this investigation) were 45% water retention/150°C temperature/10 min duration. This conclusion relies on the below-mentioned facts: the conditions of recovery parameters 45%/150°C/10 min resulted in the lowest agglomeration ratio in the recovered material in relation to the other recovery parameters examined in the first and second phases. Concerning the properties of the recycled particleboards, it was observed that the boards that were produced utilising the above-mentioned recovery parameters showed the best internal bond, surface soundness, modulus of elasticity in bending, hygroscopic properties and free formaldehyde content values.

Technical properties of branch-wood of apple, peach, pear, apricot and cherry fruit trees

3 and that of other species varied from 0.71 to 0.75 g/cm3. For the species examined, the mean cell dimensions ranged between 0.606–0.911 mm for fiber length, 0.250–0.404 mm for vessel length and between 0.033–0.046 mm for vessel width. The greater cell dimensions correspond to apple and the shorter to apricot trees. The dichloromethane soluble extractives were found to range between 2.02–3.71%, the hot water extractives between 12.10–15.99% and the total extractives between 13.08–16.67% (higher in cherry and lower in pear). Mean values of pH were found to vary from 4.73 to 5.68, acid equivalent from 0.0057 to 0.0084 ml/ml and alkaline equivalent from 0.0046 to 0.0081 ml/ml. The lower values of pH and the higher of acid equivalent correspond to cherry, while the higher acidity and alkaline equivalent correspond to pear.3 während die der übrigen Obstbäume zwischen 0,71 und 0,75 g/cm3 schwankte. Die Mittelwerte der Zelldimensionen der untersuchten Obstbäume variierten folgendermaßen. Fasernlänge 0,606–0,911 mm, Länge der Gefäßglieder 0,250–0,404 mm und Gefäßbreite 0,033–0,046 mm. Die grösseren Zelldimensionen wurden bei Apfelbaum-, und die kleineren bei Aprikosenbaum-Astholz gefunden. Die Dichlormethan-Extraktmengen des Astholzes bewegten sich je nach Obstbaumart im Bereich von 2,02 bis 3,71% und die Heißwasserextrakte zwischen 12,10 und 15,99%. Die Gesamtmenge der Extrakte schwankte von 13,08 bis 16,67%, wobei die höhere Menge in Kirschbaum und die niedrigere in Birnbaum beobachtet wurde. Die pH-Werte variierten von 4,73 bis 5,68, der Säure-Äquivalenzbetrag von 0,0057 bis 0,0084 ml/ml und der Base-Äquivalenzbetrag von 0,0046 bis 0,0081 ml/ml. Das Astholz des Kirschbaumes zeigte den niedrigeren pH-Wert und den höheren Säure-Äquivalenzbetrag, dagegen hatte das Astholz von Birnbaum den höheren pH-Wert und den höheren Base-Äquivalenzbetrag.

Verwendung von Astholz der Obstbaumplantagen für die Herstellung von Spanplatten

ZusammenfassungAuf griechischen Obstbaum-Plantagen (Pfirsichbaum, Apfelbaum, Birnbaum, Kirschbaum, und Aprikosenbaum) fallen durch die jährlichen Winterästungen bedeutende Mengen Astholzes an, die großeteils keine rationelle Verwertung findet. Zweck dieser Arbeit war es, die Eignung dieses Astholzes als Rohstoff für Spanplatten zu untersuchen. In der Untersuchung wurden einschichtige und dreischichtige Laborspanplatten unter Verwendung verschiedener Mischungsverhältnisse zwischen Astholzspänen und Industrieholzspänen (100∶0, 75∶25, 50∶50, 25∶75, 0∶100) hergestellt und ihre mechanischen und hygroskopischen Eigenschaften bestimmt. Es zeigte sich, daß das Zusetzen von Astholzspänen in der Mittelschicht der dreischichtigen Platten bis zu einem Anteil von 50% durchaus möglich ist, weil es keine nennenswerte negative Auswirkung auf die Spanplattenqualität hat; dagegen verursachen höhere Zusatz-mengen eine Verminderung der Biege-und Querzugfestigkeit der Platten, so daß zur Erreichung einer ausreichenden Qualität die Plattenrohdichte angemessen angehoben werden müßte.AbstractIn greece, from certain fruit-tree plantations (i.e. apple, peach, pear, apricot and cherry) large quantities of branch wood remain in the fields after pruning during the winter period and they are not utilized properly. The aim of the present work was to investigate the suitability of such branch wood from fruit-tree plantations as raw material for particleboard production. For this purpose, experimental one-layer and three-layer particleboards were produced by mixing chips from branches with chips from wood used in industry in various proportions (100∶0, 75∶25, 50∶50, 25∶75, 0∶100) and their mechanical and hygroscopic properties were determined. The results showed that the addition of chips from branches in the core of three-layer particleboards up to 50% of the total amount can be considered successful since no appreciable effects on the properties of particleboards were observed. However, chips of branches added in higher amunts were found to reduce the bending strength and the internal bond of the boards. In this case, an increase of density of particleboards produced is sugested in overcome the adverse effects on the quality of the boards.

Utilization of wood biomass residues from fruit tree branches, evergreen hardwood shrubs, and Greek fir wood as raw materials for particleboard production. Part B. Hygroscopic properties and formaldehyde content

Abstract This paper investigates the basic hygroscopic properties and formaldehyde content (FC) of particleboards produced with wood biomass from fruit tree branches and evergreen hardwood shrubs as substitute raw materials for fir particles. One-layer laboratory particleboards with two distinct target densities (0.63 g/cm3 and 0.69 g/cm3) were produced using various mixtures of the above materials. Industrially produced wood particles were also used for comparison purposes. The results showed that the replacement of fir wood (FW) by evergreen hardwood material significantly upgraded boards quality in terms of thickness swelling (TS) and water absorption (WA) (except boards with density of 0.63 g/cm3) after immersion in water for 24 h and residual swelling (RS) after reconditioning. The contribution of branch-wood (BW) particles in the production of FW boards with density of 0.63 g/cm3 induced increase of TS, WA, and RS while for boards with density of 0.69 g/cm3 did not result to significant changes except for RS. In terms of FC, boards made of BW and evergreen hardwood showed significantly lower FC compared to those produced by FW and industrial particles.