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

Particle- and medium density fibreboards (MDF) were prepared from chips of spruce and pine, a byproduct of sawing wood in a saw mill with a profiling unti. The wood residues were stored in piles of 40 m³ volume for different time periods. The physical-technological properties of the particle- and fibrebroads prepared therefrom were evalutated and the formaldehyde release of the boards was assessed. The results reveal: In general, there is a positive influence of storage on the thickness swelling and internal bond strength of UF-bonded particleboards; the bending strength of UF-bonded particleboards showed no pronounced response to storage. The prositive influence of storage onthe thickness swelling and internal bond strength was much higher in case of boards made from pine chips than in case of spruce boards. On using PMDI as a binder for particleboards no significant influence of storage on the thickness swelling, internal bond strength and bending strength was detected. The influence of storage on the thickness swelling of UF-bonded MDF from pine fibres was much less pregnant than on that of UF-bonded particleboards. On UF-bonded MDF from spruce the influence of storage, if any, was negligible. On using PMDI as a binder for MDF there was no detectable change in the thickness swelling due to storage. The internal bond strength of UF-bonded MDF experiences only subtle positive change due to storage of pine wood chips. However, no notable change was detected in case of MDF from spruce. Storage has almost no influence on the chemical properties of boards.     

Untersuchungen über das Dauerstandverhalten formaldehydarmer bzw. formaldehydfrei verleimter Industriespanplatten

13 industrial particleboards of emission class 1 were examined. Their low formaldehyde emission potential was reached by several methods, e.g. using special resins, formaldehyde scavengers as well as by subsequent treatment. 6 of these particleboards did not fulfill the requirements according to DIN 68 763 regarding the 24 h thick-ness swelling resp. the bending strength, whereas the required mini-mum value of the transversal tensile strength partially was consider-ably exceeded. As far as their density profile is concerned the parti-cleboards could be divided into 4 groups. All particleboards showed low perforator values. Some insignificant exceeding of the limit value of 10 mg/100 g dry board results from an increase in moisture due to conditioning of the samples (20/65) prior to testing. The creep be-haviour of the particleboards in alternating climate (20/85–20/30) under constant loading was assessed according to the FESYP method.     

Development of selectively densified surface laminated wood based composites

An attempt was made to develop selectively densified surface laminated wood based composites. Two types of wood composites were produced (veneer laminated Medium Density Fiberboard, MDF and wafer overlaid particleboard, PB) in this study. Veneer or wafer plasticized by NaClO₂ treatment and PF resin impregnated were laminated on both sides of the MDF or PB and compressed at ordinary pressure. The main observation was that overlaying plasticized veneer on MDF before hot pressing is a promising method for improving mechanical properties and dimensional stability of commercial MDF. The MOR and MOE of surface laminated MDF attained 177 MPa and 18 GPa, respectively. The water absorption percentage of laminated MDF decreased from 160.7 to 7.2%. Furthermore, it is interesting to note that NaClO₂ treated and resin impregnated wafer or powder laminated particleboards showed excellent performance especially in stiffness. The MOR and MOE reached 40 MPa and 7 GPa which is more than two times higher compared to untreated wafer laminated board and three times higher than particleboard. This value is comparable to commercial lauan plywood having a density of 0.78 g/cm³. The processing technique of the composite is simple and can be easily applied by the industry.     

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.

     

Prüfung und Beurteilung der Dauerhaftigkeit unterschiedlich verleimter V20-Bauspanplatten bei Belastung und Beanspruchung in definiertem Wechselklima

V20-E1/E2 particleboard specimens, manufactured with low formaldehyde content UF resin glues or with a formaldehyde catcher and/or under application of NH₃ gas, showed similar creep properties as control particleboards made with a well-established, extremely high formaldehyde content resin glue. Correlations were found to exist between creep characteristics and 24h thickness swelling of the tested low formaldehyde content particleboards. An increase in thickness swelling was seen to raise the creep factors. The lower the perforation values, the greater the thickness swelling and the creep factors appeared to be. Long term fatigue tests with different kinds of bending test specimens (FIHH-, BAM-tests) gave adequate results.     

Untersuchungen über das Dauerstandverhalten formaldehydarmer bzw. formaldehydfrei verleimter Industrieplatten

The long-term behaviour of 13 industrial particleboards of emission class 1 was examined. Their low formaldehyde emission potential was reached by several methods. Only 4 of these 13 board types showed a creep factor which was considered to be sufficient. A correlation between formaldehyde release and creep behaviour could not be assessed. Therefore, the short-term properties did not allow secure statements regarding the expected creep behaviour of a particleboard. For this purpose, a storage in alternating climate with and without loading is necessary whereas for preliminary examinations the largescale bending tests can be neglected. Based on the determined regression line it was possible to indicate maximum reduction factors which must be respected if a certain creep factor considered to be critical should not be exceeded.     

Untersuchungen über das Stehvermögen von MDF und Spanplatten

The dimensional stability of MDF and FPO-particleboards was investigated after installation into a double climate testing chamber under inside climatic conditions. Using difference climate testing with realized humidity gradient at a constant temperature of 20°C, the fundamental phase of deformation was reached after only 48 hours operating time. With the beginning of re-conditioning a prompt reverse material deformation was observed. As a result of its structure and relatively low potential of sorption the investigated MDF boards were less sensitive to the affecting climatic differences than particleboards, therefore both lower deformation and better deformation reversibility were attained. Coated wood materials were significantly less affected by humidity gradients in difference climate testing due to diffusion impediment. In temperature gradient affected deformation, a ten times lower magnitude was noted.     

Optimierung des Eigenschaftsprofils von MDF

During the last years, medium density fibreboards (MDF) became firmly established on the European wood-based material market. The production figures indicate that this tendency is still growing, although in some areas a certain saturation of the market has been reached. MDF manufactured in a dry process offering the possibility of producing such boards in comparable variety and quantity to particleboard, represent a panel product which is a serious competitor for the latter. In Germany, the MDF-production was taken over mainly by particleboard manufacturers. Thus, MDF was no more a competing product but a completion and an enlargement of the existing board range, especially in areas where the particleboard was only suitable for certain purposes. Due to its manufacturing process MDF distinctly differs from particleboard and for this reason reveils a different property profile. The user has not to deal with a substitute product offering “better properties”, therefore, he has to prepare himself for the product. The properties of MDF will be presented in detail and hints for the development of this product will be given.     

Eignung einiger Magnesiasorten zur Herstellung von Spanplatten

11 Magnesia samples and a halfburned dolomite sample were characterized chemically, by their hardening properties and by sieve analysis. Pressure strength, and their suitability for the manufacture of particleboards were investigated. Press temperature and pressing time were optimized. The effect of a partly substitution of magnesia by three kinds of latent hydraulic binders was also examined. There was no correlation between chemical composition and pressure strength or bending strength, respectively, of those samples which fulfilled the requirements of DIN 273 part 1, with regard to MgO content. However, a good correlation between the pressure strength of samples, and the bending strength of experimental particleboards was found, and also between both these values and the hydration time at 95°C. With regard to the technological properties of the magnesia-bonded particleboards, an optimum pressing temperature was found around 160°C, with clear interaction from the chemical composition of the added latent hydraulic binders. However, a specific pressing time of 0.5 min/mm was found at 110–120°C. According to theoretical considerations, the pressing time would be even shorter, if the pre-warming time could be reduced.     

Production and characterization of particleboards from cork-rich <Emphasis Type="Italic">Quercus cerris</Emphasis> bark

Single-layered particleboards were produced from granulated Quercus cerris bark containing cork and phloem granules using standard hot-press equipment and phenol–formaldehyde resin. The experimental boards were tested for thickness swelling, mechanical strength and thermal properties. Scanning electron microscopy observations were carried out to analyze the panel structure. The results showed that Q. cerris bark particleboards had low thickness swelling in water, high resistance to thermal degradation and high calorific values but their mechanical strength was below that of commercial wood particleboards. The produced Q. cerris bark particleboards were adequate for exterior applications where mechanical strength is not the key factor. Potential for process and feedstock optimization was acknowledged.     

Stand der CEN-Normung auf dem Gebiet der Span- und MDF-Platten

A breakdown of subjects related to the working programme of TC 112 “Wood based panels” and the most up-to-date status is represented in a survey table. Basic test standards have almost been completed. Standards for particleboard and OSB specifications have been drafted (prEN), while those for MDF are still under discussion. For the accepted part 1 “General Specifications” of the particleboard standardization series EN 312 two formaldehyde classes were formed. A national A-deviation was stipulated, which relates to the German “Gefahrstoff-Verordnung” (Hazardous-Material-Regulation). Over a thickness range of between 13 and 20mm a comparison is presented of property specifications for the 6 different particleboard types. This is followed by a report on the status of standardization for formaldehyde determination (assessment, measuring) methods. Mention is made of a number of issues still under discussion such as the replacement of national (DIN) by CEN standards; “Characteristic values” for structural properties of wood based boards; “Moisture resistant particleboards”; OSB and MDF standards. Further areas for which standardization work has only recently begun are wood preservation, product and production control and lastly, application-related standardization.     

Versuche zur Verringerung der Dickenquellung von Spanplatten bei der Wasserlagerung und in feuchter Luft

Investigations on the sorptional behaviour, thickness swelling, and mechanical properties of particleboards prepared from UF-resinated wood particles treated with 1% and 2% paraformaldehyde prior to pressing led to the following conclusions: Addition of paraformaldehyde decreased the hygroscopicity of particleboard only insignificantly. However, it led to a pronounced reduction in the thickness swelling of particleboards in water as well as in humid air. The reduction in thickness swelling due to treatment with paraformaldehyde was higher for particleboards prepared without paraffin as a sizing agent than for particleboards containing this additive. Moreover, the treatment with paraformaldehyde increased the transverse tensile strength of the particleboards to a high extent (35% to 50%).     

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

Medium density fibreboards (MDF) were made from thermomechanical (TMP) and chemo-thermo-mechanical pulps (CTMP) derived from pine wood. As a binder a melamine reinforced urea formaldehyde resin (UF-resin) and diisocyanate polymers (PMDI) were applied. The mechanical-technical properties of the boards as well as some of their chemical properties were evaluated. The results of the investigation led to the following conclusions: MDF from CTMP showed in general higher mechanical properties (bending strength) compared to MDF from TMP. Moreover, the formaldehyde release of the CTMP-boards was lower. This may be due to the formaldehyde scavenging properties of the used pulping chemicals during the process of CTMP. MDF from CTMP showed much higher release of acetic acid compared to MDF from TMP. This is likely to higher deacetylation of the wood substance during CTMP process compared to the TMP technique.     

Use of UF-bonded recycling particle- and fibreboards in MDF-production

The work is related to the use of thermomechanical pulps (TMP) prepared from recycling UF-bonded particle- and fibreboards as a partial substitute for TMP made directly from wood in MDF. The results reveal that TMP from recycling boards show striking differences in their morphological characteristics and chemical properties compared to TMP prepared directly from wood. TMP from recycling boards are of shorter fibre length and higher content of fine fraction. Moreover, their cold water extractives are of higher pH-value and contain appreciably higher amounts of acetate and formate ions. TMP from recycling boards releases also more formaldehyde compared to TMP made directly from wood. Moreover, the results clearly show that TMP from recycling boards can be used up to 30% as a partial substitute for TMP from wood in making UF-bonded MDF without any noteworthy deterioration of the physical-mechanical board properties. Also, the formaldehyde release of the boards made using TMP from recycling boards experiences no negative change. Only small differences were found in the content of formate and acetate ions as well as in the release of volatile acids from MDF made from recycling fibre- and particleboards on the one side and boards directly made from wood on the other side. All the results indicate that chemical interaction seems to take place between the chemically degraded resin in UF-bonded recycling boards and the new binder used in making MDF.     

Einfluß des Sorptionsverhaltens auf die Eigenschaften von Spanplatten

Commercial particleboards may differ considerably as regards hygroscopicity. This is related to a corresponding variation in sorption behavior of the boards, particularly in applications subjected to increased humidity. Following a short survey of potential factors affecting particleboard hygroscopicity, examples are given for the effects of different sorption behavior on some board properties: differences in sorption behavior under natural and defined cyclic climatic load as well as in a differentiating climate; differences under simultaneous mechanical and climatic load (creep behavior); problems in testing (V 100- tensile strength perpendicular to the surface), during further processing as well as during actual use of highly hygroscopic particleboards. Finally, consequences are discussed which follow for board production and corresponding standards for sorption behavior.     

Prozessmodellierung führt zur Online-Qualitätskontrolle und Prozessoptimierung bei der Span- und Faserplattenproduktion

The production of particleboards and fiberboards is characterized by a great number of different interrelate but independent processing steps and complex control parameters. Despite narrow limits and sophisticated process controlling, the inhomogeneous raw material properties lead to variations in the quality of produced boards. These variations are not known at the time of production and can only subsequently be determined by destructive test methods. The present paper demonstrates that by appropriate simulation of the production process and prediction of board properties reliable online quality control and model based process optimization can be developed. Using modern computer technology and statistical methods the resulting board properties (e.g. IB and MOR) can be accurately predicted based on the relevant process parameters. The promising result of online quality control of internal bond and bending strength using the process control system SPOC (Statistical Process Optimization and Control) in a MDF pilot production line are reported.     

Dimensional stability and creep behavior of heat-treated exterior medium density fiberboard

A series of commercial phenol-formaldehyde bonded MDF panels were exposed to a post-manufacture heat-treatment at various temperatures and durations using a hot press and just enough pressure to ensure firm contact between the panel and the press platens. Physical properties and static flexural strengths of the post heat-treated MDF panels were evaluated according to ASTM D 1037 (2002). The results indicated that the post-manufacture heat-treatment of the exterior MDF panels resulted in improvement of thickness swelling. Water absorption and linear expansion properties were adversely affected by the heat-treatment. Modulus of rupture and modulus of elasticity values of the heat-treated panels decreased with increasing treatment temperature. A series of three 12-week creep tests were performed in climatic chambers conditioned at 65% RH, 90% RH, and cyclic 65–90% RH, all at a steady temperature of 20 °C. The creep tests generally followed procedures as specified in ASTM D 6815-02a (2002). Creep deflections of the panels increased with increasing temperature of the post heat-treatment.     

Untersuchungen an Holzwerkstoffen für Möbel-Einlegeböden

The bending deflection of six different wood based materials used as shelves in the manufacture of furniture (unlaminated particleboard, melamine laminated particleboard, veneered particleboard, block-board, plywood and solid wood panel) of approximately equal thickness was investigated. Deflection data were obtained by applying loads to the board surfaces for a period of 28 days followed by a period of unloading of equal length. For all types of particleboards the deflections appeared to be greater than for the other wood based panels. The lowest bending deflection was found for the solid wood panel while plywood performed better than blockboard. Surface treatments improved the performance of particleboards but veneering appeared to be more advantagous than laminating with melamine. The bending deflection of the tested panels is strongly related to their bending strength and modulus of elasticity.     

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.     

Zum Sorptionsverhalten von Holzspanplatten

Investigations carried out on the influence of some typical additives (salts as hardners, sulphite liquor, and wax) on the equilibrium moisture content of particleboards led to the following results: From a certain level of relative humidity salts acting as hardners increase the equilibrium moisture content. This increase depends on the amount of salt used as well as on the nature of the salt itself. Salts having a high relative vapour pressure on their saturated aqueous solutions are less effective in increasing the moisture content of particleboards at equilibrium conditions than those with low vapour pressure on their saturated aqueous solutions. Partial substitution of urea formaldehyde resins by sulphite liquor increases the equilibrium moisture content of particleboards at high relative humidity; by contrast particleboards bonded with sulphite liquor and subjected to post thermal treatment at 180–200°C for several hours according to the Pedersen technology are by far less hygroscopic than all other known particleboards. Wax has only a slight effect on the equilibrium moisture content.