Formaldehydarme Flächenverleimung mit Aminoplastharzen

Aminoplast-bonded plywood, coreboard, and venecred or faced particle board may also release formaldehyde. This report deals with the factors that have an influence on the quantity of formaldehyde released during the production of boards. The quantity of formaldehyde subsequently released by the panels is determined not only by the carrier material, but also by the working and pressing conditions in laminating and veneering. The formaldehyde content of the glue for veneering apparently also plays an important role.     

Eigenschaften formaldehydarm verleimter Sperrhölzer

Tests were carried out on both industrial plywood with low content of formaldehyde and laboratory plywood. There were eight series plywood from different industrial manufactures including blockboard and a blockboard with particleboard decks. Twelve lab-series (5×1.5 BU) were produced of different formulae by the technical department of WKI. Bending and bonding properties as well as formaldehyde emissions of plywood were determined. Creep behaviour of plywood will be described in part 2. Plywood showed good bending characteristics dependent on its structure. Bonding strength after tensile and shear tests as well as after prick test complied with IF bonding quality even after alternating climatic storages. The different series, however, differ widely with respect to IW bonding quality. The different potential of formaldehyde emissions of the series was determined according to various methods, correlations between the methods could be proved. The test, however, revealed the difficulties caused by the material to measure formaldehyde emission of plywood.     

脲醛树脂废胶液制造胶合板工艺及性能研究

研究将脲醛树脂废胶液与水混合、中和处理、异味处理、磨浆、过滤得到混合浆液,将混合浆液按一定比例添加至酚醛树脂中,用于Ⅰ类胶合板及竹木复合集装箱底板用胶合板生产。研究结果显示,混合浆液添加比例8%和15%条件下,7层胶合板和21层竹木复合集装箱底板用胶合板胶合强度、浸渍剥离性能均满足Ⅰ类胶合板指标要求;混合浆液添加比例为12%~18%的酚醛树脂可用于竹木复合集装箱底板用胶合板生产,其各项性能高于国家标准要求;同时不改变胶合板的生产工艺,减少了危险固体废物的产生,实现脲醛树脂废胶液的资源化再利用。     

Eigenschaften formaldehydarm verleimter Sperrhölzer

Tests were carried out on both industrial plywood with low content of formaldehyde and laboratory plywood. There were six series plywood from different industrial manufacturers including blockboard and a blockboard with particleboard decks. Twelve lab-series (5×1.5 BU) were produced of different formulae by the technical department of WKI. In addition to testing creep behaviour, bending and bonding properties as well as formaldehyde emissions were determined (part 1). Testing of creep behaviour was carried out in accordance with the FESYP method as is common practice when testing particleboard. Creep behaviour of plywood under permanent load in alternate climates was primarily influenced by the board structure. This can be seen in particular with regard to industrial plywood. So, for example, a blockboard with particleboard deck (vertical to block core) had a creep factor two to three times higher compared with that of a nine fold beech plywood. The influence of humidity became apparent at climatic changes. Values measured in humid climate had a factor of 0.5 higher than those measured in dry climate. Laboratory plywood of the same structure as industrial plywood had a creep factor of 2 to 3 times higher than the latter. This is mainly because of the changes in humidity of the samples experienced in alternating climates. Whereas there were hardly any differences of humidity in all plywood in the dry period with values ranging from 7.1% to 7.7%, differences became significant in the humid period, humidity of industrial plywood rose to a max. of 11.7%, laboratory plywood, however, came up to 14.3%. No connection could be detected between formaldehyde emissions and creep behaviour. Plywood with low content of formaldehyde did not show significantly higher long-term bending behaviour.     

Untersuchungen an einer aus Faserplatten- und Furnierschtichten zusammenfesetzten Schichtholzplatte (SHP)

The development of a laminated wood board of different design is, among other, a solution to the worsening situation of wood supply in production of standard veneer boards. At the same time, the supply of wood boards with speical properties may be enlarged. This was the reason to investigate a laminated wood board, composed of veneer layers and fiber boards. Analyses and comparisons showed that some mechanical and physical properties of the composite board are similar to those of plywood (C _k) (rectangular grain) and laminated board (C _x) (parallel grain).     

Characterization of a formaldehyde-free cornstarch-tannin wood adhesive for interior plywood

This study investigated the physical properties (rheological and thermogravimetric analysis) of cornstarch-tannin adhesives and the mechanical properties (dry tensile strength and 3-point bending strength) of plywood made using cornstarch-tannin adhesives. This adhesive was evaluated for its utility in interior plywood manufacture. The optimum cure temperature and cure time of cornstarch-tannin adhesives were 170°C and 4?min, respectively. Plywood bonded with formaldehyde-free cornstarch-tannin adhesive exhibited excellent mechanical properties comparable to commercially available phenol-formaldehyde plywood adhesives. It was found that cornstarch-tannin panels which do not contain formaldehyde and with an emission equal to that of heated but unbound wood can be obtained by the use of hexamethylenetetramine (hexamine) as hardener. The work has indicated that an environmentally friendly wood adhesive can be prepared from a natural renewable resource (cornstarch and wattle tannin) for bonding interior-type plywood.     

Exterior plywood resins formulated from Pinus pinaster bark extracts

Phenol-tannin-formaldehyde resins prepared by copolymerization of resoles andPinus pinaster bark tannins were used for bonding eucalyptus plywood boards. The dependence of board quality on the formaldehyde/phenol ratio F/P, the overall soda/phenol ratio S/P and the viscosity of the resol was studied using a 2×2×2 factorial design. The most critical of the variables studied was S/P, the best results being obtained with its lower value. A follow-up study using a lower S/P value confirmed this trend, better results being obtained than with commercial phenolic resins. Moreover, the pine-based resins allowed a press temperature of 160°C to be used, which further improved board quality.     

Preparation and characterization of wood-plastic plywood bonded with high density polyethylene film

This paper presents a study on the potential use of high density polyethylene (HDPE) film as wood adhesive for formaldehyde-free plywood. The physical–mechanical properties of the plywood, including thickness swelling (TS), water absorption (WA), tensile shear strength, modulus of elasticity and modulus of rupture were evaluated. Results show that HDPE film dosage positively affects the properties when ranging from 61.6 to 246 g/m². The performance of these panels was comparable to those of plywood made with commercial urea–formaldehyde (UF) resins. Comparisons of the dimensional stability between the two plywood demonstrated that 7-day TS and WA values of the panels bonded with UF resins were 5.10 and 23.5 % higher than those bonded with HDPE film, confirming the suitability of HDPE for the use as adhesive in wood-based composites intended for indoor applications subjected to high moisture. DMA tests show that HDPE bonded plywood was significantly inferior in thermal stability at 120 °C and above while it presented almost the same dynamic mechanical properties as UF plywood when the temperature was lower than 100 °C, making it suitable to be used as geothermal floor.     

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.     

Untersuchungen über den Zusammenhang zwischen dem Molverhältnis und der formaldehydabgabe bei Harnstoff-Formaldehyd-Leimharzen

The paper reports on the influence of the molar ratio of urea: form-aldehyde in UF-resins on the formaldehyde emission from resins as well as from particle boards bonded therewith. The results show that a lowering of the formaldehyde content in a UF-resin essentially decreases the formaldehyde emission from the resin as well as from particle boards. In the case of particle boards an almost linear relation between molar ratio and formaldehyde emission was found, independently from the method used for emission measurement. The influence of moisture content and density of particle boards on their form-aldehyde release is furthermore discussed.     

Utilization of bark flours as additive in plywood manufacturing

Increasing demand for wood based panel products and shortage of wood as raw material have triggered many efforts to utilize residues generated annually by the forest industries including a large portion of bark in panel production. In this study, the effects of using bark flours as additives obtained from different wood species (walnut, chestnut, fir and spruce), having much polyphenol content, on some physical and mechanical properties and formaldehyde emission of plywood panels were examined. Wheat flour, which has been used widely as additive in plywood manufacturing, served as control. Plane tree (Platanus orientalis) logs were obtained for veneer manufacturing. Urea formaldehyde (UF) resin with 55 % solids content was used as adhesive. The bonding shear strength, bending strength, modulus of elasticity (MOE), density, equilibrium moisture content and formaldehyde emission of plywood panels were determined according to related standards. It was found that the use of flours obtained from the barks of chestnut and fir trees in the glue mixture decreased the formaldehyde emission of panels. The bonding strength values of the test panels made using the glue mixture including the flour of walnut and spruce barks as additive were lower than those of the panels with adhesive containing the flour of fir and chestnut barks. The panels manufactured with adhesives including the flour of fir bark gave the highest bending strength and modulus of elasticity values.     

Influence of pulping process on the emission of formaldehyde and volatile organic acids from pulps and medium density fibreboards (MDF)

Cold water extracts from pulps produced by the chemo-thermomechanical technique (CTMP process) contain higher amounts of formate and acetate ions compared to cold water extracts from pulps produced by the thermo-mechanical process (TMP process). The CTMP shows a higher emission of acetic acid than the corresponding TMP. However, the release of formic acid is lower than that from TMP due to the higher pH-value of CTMP. Furthermore, the release of formaldehyde from CTMP is lower than that from TMP due to Cannizzaro reaction catalysed by alkali. Moreover, binderless fibreboards from CTMP are significantly lower in the formaldehyde release compared to binderless boards from TMP. The use of MUF-resin increases the formaldehyde release of the boards from TMP and CTMP. Furthermore, MUF-bonded boards from TMP and CTMP are of higher pH-value and lower emission of formic and acetic acid.     

出口胶合板甲醛释放量变化分析

应用GB／T17657——1999《人造板及饰面人造板理化性能试验方法》中的干燥器法,对胶合板样品甲醛释放量进行测定,分析总结了出口胶合板甲醛释放量变化规律。     

出口胶合板甲醛释放量变化分析

应用GB/T 17657—1999《人造板及饰面人造板理化性能试验方法》中的干燥器法,对胶合板样品甲醛释放量进行测定,分析总结了出口胶合板甲醛释放量变化规律。     

The effects of waiting time of alder (Alnus glutinosa subsp. barbata) veneers before drying on shear and bending strength of plywood

(Alnus glutinosa subsp. barbata ) veneers before drying, on some properties of plywood, were investigated. Veneers produced at laboratory conditions were divided into four groups considering their waiting time before the drying process. pH and 1% NaOH solubility of these four groups of veneers were determined. No significant differences were found in solubility and pH values obtained from test groups. In addition bending strength, shear strength and formaldehyde emission values of plywood, produced from these veneers, were investigated. While bending strength and formaldehyde emission values of the plywood showed no differences, the shear strength of the plywood produced from veneers immediately dried after production was significantly higher than the one of other groups.

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Einfluß der Dämpfung und Trocknung von Furnieren auf deren Acetylgruppengehalt und die Formaldehydabgabe von Sperrholz

In this study, the effect of log steaming and veneer drying on acetyl group content of wood and subsequent formaldehyde emission of plywood produced were investigated. This work was carried out on pine (Pinus brutia Ten.) and beech (Fagus oriantalis Lipsky) species. Changes in acetyl group contents were determined by Freudenberg, method and IR-spectra. Formaldehyde emission was determined by WKI-bottle and perferator methods. Pronounced changes were observed in acetyl group contents due to log steaming and veneer drying. Amount of formaldehyde emission occuring in pine plywood was found to be higher than that of the beech plywood. Lower formaldehyde emission was obtained in plywoods produced using veneers with rich acetyl group content.     

Formaldehyde emission from particleboards manufactured with waste materials from plywood industry

Peeling cores, dried veneer residues and plywood edge pieces containing adhesive are used for particleboard production. So, in this study, the effect of waste materials from plywood industry used for particleboard manufacturing on the formaldehyde emission of panels was investigated.     

浅析穿孔萃取法测定MDF/HDF甲醛释放量进行含水率修正的必要性

通过试验研究探讨用穿孔萃取法测定的MDF／HDF甲醛释放量值与含水率的关系，认为用穿孔萃取法检测的板材甲醛释放量值应按照含水率修正公式进行修正，以近似地反映其检测结果的一致性。     

E1级干法中密度纤维板的研究

在低物质的量比条件下,分析讨论了脲醛胶的各项力学性能和甲醛释放机理,通过研究表明:选择适合的物质的量比,改进合成工艺,可生产出综合性能较好的低毒脲醛胶,用这种脲醛胶压制的中密度纤维板,甲醛释放量达到了E1级.     

Untersuchungen zur Verleimung von Furniersperrholz mit modifizierten Diisocyanat-Klebstoffen

It was the aim of the investigations to find some modified and extended PMDI binders, suitable for bonding vencer plywood of the type AW. The bonding strength had to fullfill the requirements of DIN 68 705 part 3 resp. DIN 53 255. Pretrieatments were a cold water storage and boiling test. Three-ply boards were pressed from spruce, beech and gaboon veneers. Binders were PMDI-glues with and without emulgators and the extender tannin, Organosolv-spruce-lignin, lignosulfonic acid, casein and corn starch. The results showed the following. Veneer plywood of the type AW can be produced applying PMDI together with suitable reactive agents. The veneer wood species, the glue mixtures, the pressing conditions and the fillers have to be adjusted to the PMDI type and to the extender. Plywood made with modified, emulsified diisocyanate showed a better bonding strength and wood failure than plywood bonded with non-emulsified diisocyanate.