Low formaldehyde emission,fast pressing,pine and pecan tannin adhesives for exterior particleboard

Exterior grade particleboard satisfying the requirements of the V100 test, of formaldehyde emission well within the emission standard E1 class, and of pressing times as fast as 8.5 sec/mm can be produced at higher moisture contents using fast-reacting non-modified and non-fortified procyanidin/prodelphinidin tannin extracts such as pine bark tannin extract and pecan nut pith tannin extract. Such results, under the conditions reported are not achieved with the slower reacting tannins traditionally associated with the practice of tannin adhesives. The results reported establish that the faster is the reaction of the tannin with formaldehyde, the lower is the amount of formaldehyde needed to achieve V100 standard, the lower is the formaldehyde emission, the faster is the pressing time achievable and the higher is the tolerance of the adhesive to high moisture content of the resinated wood particles.     

Effect of layers relative moisture content on the IB strength of pine tannin bonded particleboard

Relative percentage of moisture content of surface and core layers in pine tannin-bonded particleboard influences markedly the internal bond (IB) strength of the board. This is due to the differential compression exercised on the layers related to their moisture content. The moisture content differential between surface and core layers in particleboard during pressing is a determining parameter for the internal bond (IB) strength of particleboard. In the case of tannin adhesives where these differences can be more pronounced than for synthetic adhesive the effect is more easily observable.     

Starch-sugar synergy in wood adhesion science: basic studies and particleboard production

Synergic properties between starch and sugar were discovered. 100% crop-based starch and sugar formulations were studied. Classical preliminary tests such as curing temperature and gel time were measured for different starch-sucrose water suspensions. More significant information was deducted with applied tests such as plywood gluing tests and particleboard production. Wood-to-wood bonding properties were analysed applying NaOH and high temperature (180°C) as catalysts for starch gelification. Comparable strength to commercial urea-formaldehyde and polyvinyl acetate adhesives was achieved in plywood tests. Consequently, the knowledge acquired in wood bonding of flat surfaces was applied to particleboard production. These derived particleboards showed that it is possible to obtain a panel with only carbohydrates as gluing agent. Starch-sugar synergy in alkaline environment increases the internal bond (IB) of the natural panels up to 0.25 N/mm². Possible mechanisms of synergy between these saccharides were proposed. Finally, a blended formulation with Mimosa tannin allows for achieving an internal bond of 0.40 N/mm², which is the required value for interior grade particleboards (DIN EN 312). Starch-sugar-tannin adhesives are 100% environmentally-friendly formulations.     

Environmentally friendly wood adhesives based on chestnut (<Emphasis Type="Italic">Castanea sativa</Emphasis>) shell tannins

The aim of this work was the formulation of adhesives for particleboards based on tannins extracted from industrial lignocellulosic wastes, namely chestnut shell, chestnut bur and eucalyptus bark. The interest was centred on the possibility of completely removing formaldehyde from adhesive formulations. For this, hardener alternatives to formaldehyde were used: tris(hydroxymethyl)nitromethane (TRIS), glyoxal (GLY) and hexametilentetramine (HEX). The influence of the type and concentration of the hardener and pH on adhesive gel time and pot-life were studied. A comparative structural characterization of the adhesives was performed by 13C-NMR spectroscopy. Thermomechanical analyses (TMA) tests were carried out as an indication of the final strength of the adhesive systems. Particleboards type 2 of interior use (EN 312) were manufactured with adhesives based on chestnut shell tannins alone or mixed with chestnut bur/or eucalyptus bark tannins. Free-formaldehyde was determined, and boards were prepared with TRIS, GLY and HEX tannin adhesives were classified as E0.     

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.     

The effects of a two stage heat treatment process on the properties of particleboard

Steam pre-treatment can effectively improve the dimensional stability of panel products such as particleboard and fiberboard. At temperatures above 200–210 °C steam pre-treatment might result in a significant reduction of the bond strength of the panel product. The results of an effective two stage heat pre-treatment process, in which treatment temperatures below 200 °C are used, are given in this paper. The variations in process conditions which affect the particleboard properties are described in detail. A two- stage heat pre-treatment with temperatures below 200 °C appears to improve the dimensional stability of panel products. The process conditions used have an effect on thickness swelling and internal bond properties of the particleboard prepared, especially during the first process stage (hydrothermolysis). The best results were obtained with wood particles which were only thermolysed (without curing).     

Some investigations concerning density profile,internal bond and relating failure position of particleboard

Testing machines for the measurement of density profiles of wood based panels have become a wide-spread tool in production laboratories. New equipment for the in-line measurement of density profiles was presented recently. The high significance of the density profile for the properties of particleboard ticleboard is well known for some years. Maximum densities in the outer zones of the profile are closely related with MOE, bending strength, water uptake and swelling. Minimum density is closely related with shear modulus (G _(xz , (G _(yz ), shear strength and compression strength. However, results about the correlation of the minimum density with internal bond are contradictory, and statements concerning the failure positions relating to the internal bond-test are published rarely. For five different thicknesses of furniture grade particleboard the relation between internal bond, parameters derived from the density profile and the respective failure position were determined. Indeptendent of panel thickness the failure position was found to be in a range of the 25-75%-panel thickness. A correlation between the failure position and parameters derived from the density profile could not be found. There appear to be three predetermined failure lines (35, 50, 65% of panel thickness). The correlation between mean density and internal bond is high for the total sample (r=0.81). The correlation between minimum density and internal bond is lower, especially with regard to results relating to a single panel thickness.     

Steps to make the natural adhesive of Acacia mimosa tannin resistant to boiling water using Tinnevelly senna for particleboard production

Adding a small amount of Tinnevelly senna seed flour to the natural adhesive of condensed tannin from acacia mimosa type decreases the thickness swelling and water absorption in particleboards significantly. Likewise, internal bond, modulus of rupture and modulus of elasticity increase. FTIR did not show any change in the adhesive structure. DSC and TGA showed a link between the additive of Tinnevelly senna and natural adhesive of acacia mimosa tannin, which obviously brings about the resistance to boiling water in particleboard manufacturing when using this adhesive mix.     

Fast vs. slow-reacting non-modified tannin extracts for exterior particleboard adhesives

Non-fortified, non-modified tannin extracts, rather than chemically-modified tannin adhesives intermediates, can be used as effectively to produce excellent exterior grade particleoboard at fast pressing times of industrial singnificance, with considerable advantages in both handling and cost. This can be achieved by simple pH-controlled reactivity adjustments of the tannin extract in the glue mix. This new concept is shown to be applicable to all types of polyflavanoid tannin extracts: Pine, mimosa, pecan, quebracho, and gambier tannin extracts are compared as regards their performance and capabilities. The new concept applied to the faster-reacting tannins, such as pine tannin and pecan tannin extracts, is shown to produce fast hot-pressing rates and excellent high moisture content tolerances which are undreamed of for the slower-reacting tannins, modified or non-modified, which are traditionally associated with thermosetting wood adhesives. Industrially used techniques to control well viscosity and pot-life of the glue-mixes of accelerated tannin adhesives are also presented.     

Selective removal of tannins from medicinal plant extracts using a collagen fiber adsorbent

A novel adsorbent, used for the selective removal of tannins from medicinal plant extracts, was prepared from bovine skin collagen fiber. Some typical active constituents of medicinal plants were selected as probe molecules to investigate the adsorption selectivity of the collagen fiber adsorbent to tannins. In batch adsorption experiments, the extent of adsorption of condensed tannins, including larch tannin, black wattle tannin and bayberry tannin, was 100%. The extent of adsorption of tannic acid and the hydrolyzable tannins was also 100%. In contrast, for the most active constituents of medicinal plants, their amounts adsorbed by collagen fiber adsorbent were limited. For procyanidin, the common active constituents in medicinal plant extracts, its extent of adsorption was also low, although it has a similar basic structure to condensed tannins. In comparison with traditionally used polyamide adsorbent, the collagen fiber adsorbent exhibited an obvious advantage in adsorption selectivity over tannins. Therefore, this study provides a novel and effective method for selective removal of tannins from medicinal plant extracts. Copyright © 2005 Society of Chemical Industry     

Comparison of biological and chemical methods,and internal and external standards,for assaying tannins in Spanish shrub species

Tannin contents of stems, flowers and leaves of four shrub species (Erica arborea, Erica australis, Cytisus cantabricus and Genista occidentalis) were chemically assessed using two colorimetric assays (butanol–HCl and Folin–Ciocalteu) and several standards (tannic acid, purified quebracho condensed tannins (CT) and purified CT extracted from each species). A method based on the biological activity of tannins in the rumen was also used for assaying tannins. Depending on the species, the use of quebracho tannin as standard over‐ or underestimated CT contents, in comparison to the use of the respective internal standard. However, the high correlationship observed between in vitro gas production in the presence or absence of polyethylene glycol (PEG) and CT contents estimated from quebracho suggests that this standard could be used for a quicker estimate of the nutritive value of tannin‐containing plants. Tannin contents obtained by the Folin–Ciocalteu method, using tannic acid as standard, were also related to their activity on rumen fermentation. The use of the in vitro gas production technique, in the absence or presence of PEG, may provide more useful information than the chemical assays when the final aim of tannin analysis is to assess the nutritive value of feedstuffs for ruminants. Copyright © 2004 Society of Chemical Industry     

Estimation of the Mean Degree of Polymerization of Condensed Tannins from the Kernel and Shell of <Emphasis Type="Italic">Carya illinoinensis</Emphasis> by HPLC/MS and Spectrophotometric Methods

Rapid estimation of the degree of polymerization (DP) of pure tannins or mean degree of polymerization (mDP) of tannin samples is an analytical challenge and a necessity to better understand their bioactivity. In the present paper, four spectrophotometric analyses and normal phase HPLC/MS were performed to estimate mDP of tannin fractions from pecan nut (Carya illinoinesis) kernels and shells. Tannins were obtained by acetone extraction of phenolic compounds followed by size exclusion chromatography fractionation. Four final fractions were obtained, and their mDP was estimated by spectrophotometric and HPLC/MS analysis and results compared among the different methods. All assays showed good reproducibility. The combination of butanol–HCl depolymerization reaction with vanillin-acetic acid assay yielded mDP values equal to those estimated by HPLC/MS (alpha = 5%), proving this method both suitable and reliable for rapid mDP estimation of tannins in samples.     

Analysis of grape and wine tannins: Methods, applications and challenges

Tannins are polyphenolic secondary metabolites, which can be found in many higher plants and are identified by their ability to complex with and precipitate proteins. This key property is believed to be responsible for the mouth‐feel and astringency caused by wine tannins. The analysis of tannins is of interest to practitioners in a diverse range of fields, including chemistry, pharmacology, food science, animal nutrition, ecology and plant physiology. There is a desire within the Australian wine industry to exploit objective tannin measures to complement human sensory assessment for style and quality specifications. This review, therefore, concentrates on grape‐derived condensed tannins, also known as proanthocyanidins, and wine tannins formed from grape tannins. We summarise recent advances with the development of analytical methods for the quantification of tannins, review techniques for the structural characterisation of tannin molecules and emphasise the need to refine these techniques.     

Vergleichende Untersuchungen an mittelharten Faserplatten (MDF) und Spanplatten

Mechanical and physical properties of commercial medium density fiberboard (MDF) and particleboard were determined and compared. The investigation showed that bending strength and face strength for MDF were considerably higher than corresponding particleboard properties. Concerning internal bond strength and screw holding ability no remarkable differences were found between the two board types. Medium density fiberboard showed lower hygroscopicity and thickness swelling but higher linear expansion than particleboard. Both board types were found to have higher bending strength and lower linear expansion parallel rather than perpendicular to feeding direction. Furthermore MDF showed lower surface roughness than particleboard.     

Potential of tannin extracts as resorcinol replacements in cold cure thermoset adhesives

Blends of phenol resorcinol formaldehyde (PRF) resin with tannin obtained from bark offers the potential to minimise the quantity of resorcinol required in conventional two pot, cold set PRF wood adhesives. In the presence of ammonia, both quebracho and radiata pine bark extracts, resorcinolic and phloroglucinolic type tannins respectively, showed accelerated adhesive cure behaviour with formaldehyde, in a similar manner to PRF adhesive Greenweld technology for modifying glued timber processing rates. Segregation of pine bark components established that only tannin-containing fractions exhibited accelerated adhesive cure behaviour. Results from adhesive testing indicated adhesive blends of quebracho extract and PRF resin failed to attain satisfactory bond strength at full cure. Of the pine bark components, only a pure tannin fraction produced acceptable bond strength when blended with PRF (3:1). The study indicated pine bark extract can be substituted into PRF adhesives and adhesive cure rate accelerated using ammonia. However, extracts containing crude tannin or carbohydrate materials in adhesive blends led to inferior adhesives.     

The condensed tannin content of vegetative Lotus pedunculatus,its regulation by fertiliser application,and effect upon protein solubility

The condensed tannin concentration in Lotus pedunculatus (cv. Grasslands ‘Maku’) was 8–11% DM when grown in acid soils without fertiliser application and 2–3% DM when grown in high fertility soils. Application of P & S fertiliser to the acid soils increased DM yield and reduced condensed tannin content to 4–5% DM, with over 88% of the variation in condensed tannin content being explained by variation in DM yield; it also increased plant total N concentration and halved the molar ratio of condensed tannin: protein (MR). Condensed tannins quantitatively precipitated soluble protein in lotus and also effectively precipitated protein in mixtures of lotus with white clover. The minimum concentration of condensed tannin necessary to precipitate protein was 2–4% DM, corresponding to MR values of 6–13. However, protein from such mixtures could be deaminated by fermentations with rumen fluid in vitro, but potentially soluble protein in pure lotus (MR 29) was protected from deamination by condensed tannins. A portion of lotus tannin could not be bound by plant constituents in finely ground fresh herbage and was designated ‘free’ tannin. This fraction was linearly related to total plant tannin content, was predicted to be zero at 1.8% DM total tannin, and increased at 0.15 units per unit increase in total tannin content above this figure. Maximum ‘free’ tannin comprised 17% of total condensed tannin. Effects of total and ‘free’ tannin content upon the intake and digestion of lotus by sheep are discussed.     

Decrease of pressing temperature and adhesive content by metallic ion catalysis in tannin-bonded particleboard

The use of bivalent metallic ion catalysts such as zinc acetate in wattle tannin adhesives for exterior grade particleboard results in the attainment of better board properties at lower pressing temperatures without any lengthening of the pressing time of the board. Lower pressing temperatures achieved in this manner also allow a reduction in the percentage resin solids in the board. There are indications that the same effect is present when using synthetic phenol-formaldehyde resins.     

Changes in Tannin, Free Amino Acids, Reducing Sugars, and Starch During Seed Germination of Low and High Tannin Cultivars of Sorghum

Seedling growth and changes in tannin, starch, reducing sugars, and free amino acids were determined during germination of low and high tannin seeds of sorghum. The seedling growth was markedly suppressed in high tannin seeds as compared to low tannin seeds. About 73 and 20% tannins were lost during 120 hr germination in high tannin and low tannin seeds, respectively, Accumulation of reducing sugars, free amino acids, and degradation of starch were considerably low in high tannin seeds as compared to low tannin seeds. It is suggested that tannins are responsible for retarding the seedling growth by decreasing the rate of starch and protein degradation in germinating high tannin seeds.     

Tannins of Grain Sorghum: Luteoforol (Leucoluteolinidin), 3',4,4',5,7-Pentahydroxyflavan

SUMMARY– The principal tannin of sorghum is a leuco-anthocyanin yielding luteolinidin (3',4',5,7-tetrahydroxy-flavylium) when heated with mineral acid. The precursor, luteoforol, has most of the properties of 3',4,4',5,7-penta-hydroxyflavan prepared by reduction of eriodictyol. Luteoforol, when treated with concentrated mineral acid in the cold, gives a purple color with Λ_max550nm. A method for the determination of luteoforol in sorghum, based on this property, is described. The results with a number of varieties of sorghum are compared with those obtained by the AOAC Folin-Denis method. The contribution of luteoforol to the "tannin" so determined varies from 1 to < 25%. Except for one sample of Kaffir corn, which contained leucocyanidin as well as luteoforol, no other tannins were detected. The "tannin" content varied widely, (from 0.05 to 0.67% as tannic acid), a white-skinned variety having the least. The uniformity of commercial samples can be rapidly evaluated by single-grain determinations of luteoforol.     

ANTIOXIDANT ACTIVITY OF CONDENSED TANNINS OF BEACH PEA, CANOLA HULLS, EVENING PRIMROSE, AND FABA BEAN

Condensed tannins were extracted from beach pea, Cyclone canola hulls, evening primrose and faba bean using 70% aqueous acetone. The dried crude tannin extracts were purified on a Sephadex LH-20 column using first 95% ethanol as a mobile phase for elution of nontannin phenolics and then 50% aqueous acetone to elute tannins. The total content of polyphenolics in tannin extracts ranged between 10 and 405 mg catechin equivalents per 1 g extract. All tannins extracts displayed a marked antioxidant activity in a β-carotene-linoleate model system. Evening primrose and faba bean tannin extracts exhibited the best