The effect of fine strands in core layer on physical and mechanical properties of oriented strand boards (OSB) made of beech (Fagus sylvatica) and poplar (Populus tremula)

This paper discusses the influence of three different content levels of fine strands in the core layers on the physical and mechanical properties of European beech and poplar oriented strand boards (OSB). The results show that increasing the fines content in the core layer from 10 to 50 %, based on total board weight has no significant effect on bending strength and modulus of elasticity (MOE). All panels exceeded the minimum requirement for bending strength and MOE set by EN standards. The highest modulus of rupture (MOR) and modulus of elasticity (MOE) was determined for panels solely made of poplar with different level of fines content. Increasing the amount of fines in the core layer raised the internal bond (IB). Panels made with 30 % fines in the core layer showed highest internal bond strength values. As the fines content increased from 10 to 50 %, thickness swelling decreased. Water absorption after 24 h showed the same declining trend as thickness swelling.     

Improving the physical and mechanical properties of particleboards made from urea–glyoxal resin by addition of pMDI

The effect of pMDI on physical and mechanical properties of the particleboards made from urea–glyoxal resin was investigated. The nontoxic and ecofriendly urea–glyoxal (UG) resin was synthesized under weak acid conditions, and its different properties were measured. Then, pMDI at various contents (4, 6 and 8% on resin solids) was added to the UG resin prepared. The thermal and physicochemical properties of the resins prepared as well as their water absorption, flexural properties (flexural modulus and strength) and internal bond (IB) strength of the particleboard panels bonded with them were measured according to standard methods. According to the physicochemical results obtained, the addition of pMDI significantly accelerated the gel time and increased the viscosity and solids content of UG resins. Differential scanning calorimetry indicated that the addition of pMDI decreases the onset and curing temperatures of the UG resin. Physical analysis results of the panels indicated that the particleboards made from UG resins with isocyanate yielded lower water absorption when compared to those bonded with the control UG resins. Based on the findings of this research work, the mechanical properties of particleboard panels bonded with UG resins could be significantly enhanced by the addition of increasing percentages of pMDI. The panels having 8 wt% pMDI exhibited the highest flexural modulus, flexural strength and IB strength value and the lowest water absorption among all the panels prepared.     

Dimensional stability of OSB made from acetylated Fir strands

Picea abies ) ring-cut strands were acetylated by reaction with acetic anhydride at 120 °C for periods of 30 and 60 minutes. The results indicated a weight gain of 11.2% and 20.4% respectively. Treated and untreated strands were used to form laboratory boards, which were tested in accordance with EN standards. Boards made from these acetylated strands exhibited significantly lower thickness swelling and water absorption when compared with the control. The internal bond strength (IBS) of test boards was significantly lowere (−19%), but still within International standards, than the control boards, and failure was due to resin bond failure. This would suggest that lower resin dosing could partially offset acetylation costs in industrially produced boards. Finally, we observed that boards made with acetylated strands were less compressible than the control boards.

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Acetylated,isocyanate-bonded flakeboards after accelerated aging

To improve flakeboard dimensional stability and mechanical properties for long-term exterior exposure, we fabricated and tested a highly durable isocyanate-bonded acetylated flakeboard. Flakeboards were tested for internal bond strength, thickness swell, modulus of elasticity, modulus of rupture, and breaking strength in bending, after two severe accelerated aging tests. Flake design, flakeboard density, resin content, and their interactions were critical to the performance of acetylated flakeboards in the aging tests. In bending tests, the longer disc-cut flakes produced much higher strength values than did the ring-cut flakes. In internal bond strength tests, the ring-cut flakes performed comparably to the disc-cut flakes. However, ring-cut flakes contributed somewhat more to reducing thickness swell than did disc-cut flakes. Acetylated flakeboards fabricated at high density were much stronger than those fabricated at low density. However, the high-density boards developed more thickness swell than did the low-density boards. The 5-% resin content contributed little to increased strength values in the bending tests, but this level of resin significantly improved flakeboard performance internal bond strength and thickness swell tests. Acetylation did not interfere to any practical degree with the isocyanate resin, and all property values were enhanced by acetylation, particularly internal bond strength and resistance to thickness swell.     

Tailor made OSB for special application

The purpose of this study was to develop speciality oriented strand board (OSB) with high stiffness for use in products such as engineered wood flooring (EWF). Three-layer oriented strand boards were manufactured from two feedstocks of strands: a mixture of 90% aspen (Populus tremuloides) and 10% of paper birch (Betula papyrifera), and 100% of small diameter ponderosa pine logs (Pinus ponderosa). The OSB panels were manufactured under a factorial design of three resin contents, two density profiles, and three weight ratios for the face and core layers. Tests to determine density, bending modulus of elasticity (MOE), internal bond (IB) and thickness swelling (TS) were performed according to ASTM standard D 1037-06a. The results showed that the higher values of bending MOE for panels made from aspen/birch mixture and ponderosa pine, 8190 and 9050?MPa, respectively, were obtained for the same combination of factors. Such high bending MOE values are very close to Baltic birch (Betula pendula) plywood, a product known for its high stiffness. The effect of resin content on IB is more pronounced for panels made from ponderosa pine than panels made from the aspen/birch mixture. Thickness swelling of panels made from ponderosa pine strands is higher than thickness swelling of panels made from a mixture of aspen and birch strands. The results indicate the potential to tailor an OSB for a specific application such as EWF.     

Oriented Strandboard (OSB) Panels Made from Kenaf Stalks and Aspen

Abstract

The specific gravity of these panels varied from 0.68 to 0.75. The amount of kenaf, resin content significantly affected the modulus of rupture and the modulus of elasticity values of aspen-kenaf boards. Boards with 25% kenaf and 75% aspen produced MOR and MOE values comparable to commercial oriented strandboard (OSB). Percentage of kenaf and resin levels were significant factors influencing the internal bond (IB) strength when compared to the commercial OSB. The 25% kenaf and 75% aspen boards produced IB values that could meet the required standard. Aspen-kenaf boards obtained lower values for linear expansion. Lower percentage of kenaf flakes and higher resin content controlled thickness swelling. However, boards with 50% kenaf and 50% aspen flakes made with 6% resin resulted in a thickness swelling of less than 10%.     

Properties of oriented strandboard made of wood species from Brazilian planted forests: Part 1: 80 mm-long strands of Pinus taeda L.

This research is part of a general study on the properties of oriented strandboard (OSB) using wood strands of species from Brazilian planted forests. The OSB industry is the latest wood related activity established in Brazil. In this particular part of the study, 80 mm long strands of Pinus taeda L. were bonded using two resin types (urea-formaldehyde and phenol-formaldehyde) at two levels of resin content (5% and 8%) to produce three-layer cross-aligned OSB to a face to core layer ratio of 1:2 and target density of 0.75 g/cm³. Physical and mechanical properties of the boards were evaluated according to ASTM standard D 1037-96a (1997) and the results compared to standards available as requirements for commercial structural panels. The results indicate that all the mechanical properties evaluated were above the requirements set forth by the Canadian standard CSA O437.0 (1993) for structural panels. The results of Janka hardness were in average 4 folds higher than the minimal requirements for Grade R-1 waferboard. Screw withdrawal values were also above the minimum required by grade M-3 of ANSI A208.1 standard (1993). Nevertheless, values of thickness swelling and water absorption were very high. The low dimensional stability may be related to the high density of the boards (“springback” effect) and also to the fact that no wax was used.     

Construction particleboards made from rapeseed straw glued with hybrid pMDI/PF resin

The paper investigates the possibility of manufacturing rapeseed particleboards (RPB) which could be used as construction material in eco buildings. Therefore, single-layer particleboards were produced from rapeseed straw particles glued with mixture of 4.4′-methylenediphenyl isocyanate (pMDI) and phenol–formaldehyde (PF) resins in the weight ratio 70:30 (hybrid pMDI/PF resin). The boards were manufactured with density of 650, 600, 550, 500 and 450 kg/m³. Next, their physico-mechanical properties were determined, i.e. modulus of rupture, modulus of elasticity, internal bond and internal bond after the boil test (V-100) and thickness swelling after 24 h soaking in water. The thermal conduction coefficient (λ) and sorption properties in changeable relative humidity conditions were also determined. Based on the obtained results, it was found that rapeseed straw may be a valuable material used in the production of construction particleboards which meet high strength requirements. Boards with density of 650 kg/m³ meet the requirements of EN 312 standard for type P7 boards. It is also possible to decrease their density to 600 kg/m³ (type P5 boards) and even 550 kg/m³ (type P3 boards). However, rapeseed particleboards are characterized by relatively high values of thickness swelling after 24 h of soaking in water. The weaker resistance to humidity has also been confirmed by tests on sorption and desorption of vapour in changeable relative humidity conditions. Nonetheless, an important advantage of these boards is the fact that they are characterized by better thermal insulation than particleboards.     

Light medium-density fibreboards (MDFs): does acetylation improve the physico-mechanical properties?

Light medium-density fibreboards (MDFs) with a target density of 580 kg m³ were produced from fibres, which were obtained by defibrillation of chips of commercially available acetylated solid wood (“Accoya^®”). The fibres were produced by thermo-mechanical pulping under industry-oriented conditions in a laboratory refiner. Infrared spectra showed that after the refiner process and board production, the material exhibited the same acetyl content as the initially acetylated solid wood. The fibres were bonded with 4 and 8% (related to the dry fibre mass) polymeric methylene diphenyl isocyanate and the properties of the obtained MDFs were compared with comparable MDFs from untreated Scots pine fibres which were produced under the same conditions. The modulus of rupture tended to be slightly lower for the acetylated boards, while the modulus of elasticity and the internal bond strength (IB) were equal for the respective resin loads. Acetylation clearly reduced the thickness swelling and the water uptake during immersion in cold and boiled water compared to the unmodified boards. IB after the boil test increased with acetylation and with the resin content. The study indicates that acetylated MDFs can be produced with maintained mechanical properties but strongly enhanced moisture-related properties by defibrillation of acetylated solid wood chips in a refiner and subsequent conventional board production.     

Particleboards production from date palm biomass

Date palm biomass is a renewable natural resource that has not widely been utilized in industry. The objective of this study was to examine some chemical properties of date palm trunk and rachis (holocellulose, cellulose, lignin and extractives) and to evaluate their suitability to produce composite panels. Particleboards were produced using trunk and rachis as an alternative raw material for forest products industry in the presence of two types of polycondensation resins (phenol–formaldehyde and melamine urea–formaldehyde) which were selected as binding agents. The panels were tested for their physical (water absorption and thickness swelling) and mechanical (modulus of rupture, modulus of elasticity and internal bond strength) properties. The internal bond strength of date palm trunk and date palm rachis based boards met the requirements of the general purpose product standards (EN 312) at 0.70 g/cm³ density. The panels made with phenol–formaldehyde resin showed better performance with respect to the panels made with melamine urea–formaldehyde. In addition, the particleboard made with date palm trunk particles had better quality compared to the particleboard made from date palm rachis particles. Based on preliminary results of this work, raw materials from date palm trunks and rachis can have a promising potential in the manufacture of particleboards and as a substitute for wood in board production.     

Characterization of properties of oriented strand boards from beech and poplar

The aim of this study was to evaluate the possibility of using European beech and poplar species to manufacture oriented strand boards (OSB). Beech and poplar strands with three different combinations of face/core ratios at densities of 650 and 720 kg/m³ were examined. Poly methylene diphenyl diisocyanate glue at 5 % was used with press conditions of 180 °C and 240 s. Findings showed that with increasing density the physical and mechanical properties of the different OSB combinations generally improved. Panels made of 60 % beech in face layers showed higher modulus of rupture and modulus of elasticity. Internal bond strength rose as the amount of beech strands in the core layer increased. Panels with 75 % beech strands in the core layer showed the maximum internal bond strength at 720 kg/m³. It was also observed that increasing the amount of beech in the core layer from 40 to 75 % decreased thickness swelling at both densities.     

Bonding behaviour of chemically modified wood particles for board production

The objective of this paper was to evaluate the bonding behaviour of chemically modified wood particles towards an isocyanate resin system, as determined from internal bond strength of the board, and to determine which resin system, isocyanate or formaldehyde is suitable for use in boards made from modified raw material. It was found that chemical modification of wood chips and strands did not significantly affect the bonding efficiency of isocyanate resin, but the bonding efficiency of formaldehyde resins was strongly influenced. This behaviour can be a consequence of the usage of a less pH dependent resin that is fully cured during hot pressing in combination with the high mobility of the resin which causes penetration to considerable depth into compressed particles repairing weak zones, which are created during the modification process as chips are exposed to elevated temperatures, by sticking them together. It is suggested therefore, that the isocyanate resin system is more suitable for use in boards made from modified raw material than the formaldehyde resin system.     

Einfluß der Lagerung von Industrierestholz der Kiefer und Fichte auf seine Eignung für die Herstellung von Spanplatten und mitteldichten Faserplatten (MDF)

Particles and fibres were prepared from saw mill wastes (chips) after different storage periods. The particles and fibres were chemically analysed regarding the change in their pH-value, buffering capacity, extractive content, release of volatile acids and formaldehyde release. Furthermore, the physical-mechanical properties of UF- and PMDI-bonded particleboards and fibreboards prepared therefrom were assessed. The results reveal:

1. Storage leads to an improvement in the properties of UF-bonded particleboards prepared from pine chips as the internal bond strength increases and the thickness swelling decreases.
2. Particleboards made from spruce prior to storage show in general better mechanical properties and lower thickness swelling compared to those prepared from pine wood. However the differences dwindle upon storage.
3. Storage seems to have almost no influence on bending properties of particles bonded with PMDI, as no significant change in the properties of the boards due to storage was detected.
4. Storage of chips from wood felled in spring has less impact on the properties of the boards than that of chips from winterfelled wood (Schäfer und Roffael, 1997).
5. The properties of MDF made from spruce using UF-resin as a binder show higher mechanical strength properties and less thickness swelling compared to those prepared from pine wood. However, after storage only subtle differences between boards made from spruce and pine were detected.
6. On using PMDI as a binder no significant changes in the properties of the MDF due to storage under the boundary conditions indicated in the work were detected.

     

Comparative properties of bagasse, canola and hemp particle boards

Residues of Bagasse (Saccharum officinarum L.), canola (Brassica napus L.) and hemp (Cannabis sativa L.) as well as industrial wood chips in various proportions from 0–100% were used as raw materials for the main component of the middle layer in urea formaldehyde bonded particle boards. The results reveal that most of the investigated mechanical-technological properties of the boards achieved the requirements of EN 312-2 (2003). Only increasing the percentage of canola chips usage in the middle layer to more than 30% negatively affect the internal bond (IB) properties. Comparing the water absorption (WA) and thickness swelling (TS) values, the boards containing up to 50% bagasse and hemp reach similar values to the ones of the reference boards, while increasing the amount of canola leads to more and more disadvantageous WA and TS. In summary, the results reveal that agri-fibers can be used for making composite panels conforming to the standards (EN 312-2 2003). One possible application for these panels could be the production of furniture.     

Zum Verhalten des Splint- und Kernholzes der Lärche (Larix decidua) bei der Herstellung von feuchtebeständigen Spanplatten unter Einsatz verschiedener Bindemittel

Chips from sap- and heartwood of 20, 40 and 102-year-old larch (Larix decidua) were prepared and chemically characterized. From the chips one-layer boards of 20 mm thickness were prepared using melamine-urea-phenol-formaldehyde resin (MUPF-resin), phenolformaldehyde resin (PF-resin), polymeric diisocyanate (PMDI), and tannin-formaldehyde resin (TF-resin). The physical and chemical properties of the boards were determined. Moreover, the influence of hot water extractives on the pH-value, viscosity and gelation time of the resins was assessed. Sap- and heartwood chips are different in their chemical properties as well as in bonding behaviour. The age of the tree has also an influence on the bonding characteristics of the chips. Thickness swelling, water absorption and equilibrium moisture content of heartwood boards were always lower than those of sapwood boards. Moreover, bending and internal bond strength of heartwood boards made from 20- and 40-year-old trees are much higher than those produced from sapwood. The strength properties of the boards deteriorate, however, with increasing age of the tree. This applies for both heartwood and sapwood boards. The water extractives of heartwood boards are of lower pH-value and higher buffering capacity than the corresponding boards from sapwood. Moreover, the emanation of acetic acid from heartwood boards is much higher than that of formic acid. In addition, boards from heartwood are in general of lower formaldehyde release compared with boards from sapwood. The addition of heartwood extractives to MUPF-resin increases the viscosity and gelation time of the resin and decreases its pH-value, whereas in case of PF-resin no such increase in the gelation time was registered. The extracts of heartwood increase the viscosity and gelation time of TF-resin.     

The manufacture of particleboards using mixture of reed (surface?layer) and commercial species (middle layer)

This research was conducted to investigate the suitability of reed (Arundo donax) as a substitute for wood in laboratory made 3-layer particleboard in order to supplement the supply of raw material for the Iranian particleboard industries. The ratio of the mixture of reed and wood particles were 20:80, 30:70, and 40:60, respectively, in the surface and middle layers. Press temperatures were chosen at two levels of 165 and 185?°C. Three levels of urea formaldehyde resin were selected for the surface layers, namely: 8, 10, and 12 percent. The experimental panels were tested for their mechanical strength including modulus of elasticity (MOE), modulus of rupture (MOR), internal bonding (IB) and physical properties (thickness swelling and water absorption) according to the procedure in DIN 68763. In general, the results show that reed has a positive effect on the mechanical and physical properties of boards. In this research, the treatment with 40% reed, 12% resin in the surface layers and a 185?°C press temperature has resulted in an optimum reed board product.     

Determination of the internal bond of particleboard and fibreboard

Tensile strength perpendicular to the surface is generally used as a measure of the internal bond of particleboard and fibreboard. This strength property cannot be used in structural strength calculations. Besides, determining the tensile strength perpendicular to the surface is troublesome. The object of this research was to find correlations between the tensile strength perpendicular to the surface and other strength properties and to detect a more easily determinable strength property for describing the internal bond of boards. The test material comprised 124 particleboards and 95 fibreboards from the standard production of Finnish factories. The following board properties were determined: density, moisture content during the tests, tensile strength perpendicular to the surface, shear strength, tension-shear strength, torsion-shear strength, torsion strength, and modulus of rigidity. The results show that torsion strength and torsion-shear strength correlate most strongly with the tensile strength perpendicular to the surface. Further investigations must thus be concentrated on developing a suitable method of determination for these strength properties.     

Untersuchung von Buchenschnittholz (Fagus sylvatica L.) hinsichtlich der Eignung für Brettschichtholz

Beech glulam for structural purposes has to be manufactured from strength graded beech lumber. At present one can assume that such material is not available on the market: There is not only a lack of practice in strength grading of beech lumber but also a lack of clearly defined raw material to be strength graded for beech glulam. This article aims to show that beech lumber graded following the Rules of the Measurement and Inspection of Hardwood and Cypress (published by the National Hardwood Lumber Association) has a potential as raw material for beech glulam. 218 beech boards approximately complying with two different grades, an upper and a common grade, were examined in regard to visual strength grading according to DIN 4074-5 (2003). The results show that 90% of the upper grade and 50% of the common grade boards fulfil the requirements for grade LS10 in DIN 4074-5 (2003). This finally enables the manufacture of beech glulam in accordance with strength class GL28. In addition, mechanical strength grading taking into account the modulus of elasticity even enables grading of 80% of the upper and 40% of the common grade boards for GL40.     

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.

     

Improvements in the production of wood fiber insulation boards using hot-air/hot-steam process

In times of climate change and shortage of non-renewable resources, building insulation becomes an important issue to save energy and resources. One option could be to use wood fiber insulation boards as a substitute for fossil fuel-based insulation materials. This document presents the manufacturing of wood fiber insulation boards by using the dry process and an innovative curing method combining hot-air and hot-steam. The aim was to reveal the positive physical effects of using hot air and steam in combination for curing of pressure-resistant insulation wood fiber boards. In addition to familiar bonding agents such as polymeric methylene diphenyl diisocyanate (pMDI), urea–formaldehyde resin (UF) and an enzymatic binder system should be partially used here for substitution. At this stage, fibers should be enzymatically pre-treated with laccase in conjunction with a suitable mediator, forming a Laccase-Mediator-System (LMS). A further goal of the paper is to investigate in which quantities LMSs can be added to the binder mixture to achieve results comparable to those of conventionally bonded fiber boards. For this purpose fiber insulating boards with a bulk density of 180 kg/m³ and a thickness of 40 mm were produced and tested in regards to physical technical properties such as internal bond strength (IB), compressive strength (CS) and water absorption (WA) over 24 h. The objective of this study was to understand whether an optimal relationship of hot-air and hot-steam exists in relation to physical technical properties. Present work has shown that the steam treatment offered enhancing effects in regards to both internal bond and water uptake after 24 h. However, the best results were achieved by using hot-air/hot-steam in combination for curing. Here the condensation heat was exploited to obtain higher temperatures for a better lignin repolymerization. In conclusion, the results show that a partial substitution of pMDI by LMS is generally possible and curing via hot-air/hot-steam is advisable; however, the maximum evaporation time should be restricted to 10 s.