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Lignin from steam-exploded wood as binder in wood composites/Ligninas is garo sprogdinimo budu apdirbtos medienos kaip risamoji medziaga medienos kompozituose/[TEXT NOT REPRODUCIBLE IN ASCII].

1. Introduction

Natural wood is a complex and multifunctional composite material composite material or composite, any material made from at least two discrete substances, such as concrete. Many materials are produced as composites, such as the fiberglass-reinforced plastics used for automobile bodies and boat hulls, but the  used by humans for a vast variety of their needs from the source of energy to the stuff for arts competing successfully with other substances and modern synthetics. During millennia humans have learned to improve and modify the natural properties of wood for special needs by special treatment and selection (Nagyvari et al. 2006). Plywood and a variety of pressed boards are well-known composite materials widely used in building constructions and furniture. Developed technologies allow to utilize low-quality wood and waste from forest and wood industries, particularly sawmills, to make value-added products complying with demands of zero-waste principles (Gravitis 2007). Indeed, by reducing pollution and utilizing waste the zero emissions and zero-waste technologies efficiently promote protection of the environment (Vaboliene and Matuzevicius 2005; Kvasauskas and Baltrenas 2008; Baltrenas and Zagorskis 2008). The general Zero Emissions concept emphasizes the shift from traditional linear industrial models in which wastes are considered the norm, to systems of integrated technologies where everything is used. It advocates an industrial transformation whereby businesses emulate sustainable cycles found in nature and where society minimizes the stress it imposes on the natural resource base and learns to do more with what the earth produces. In this way, industries are reorganized into clusters such that each industry's wastes/by-products satisfy the input requirements of another industry, and the integrated whole produces no waste of any kind (Gravitis 1999, 2006a, 2008; Gravitis and Della Senta 2001; Gravitis et al. 2001).

Some adhesive substance is the usual other component used to make composite boards the main ingredient of which is wood or other kind of biomass. Presently phenols are the main source of industrially used adhesives. About 95 percent of phenol phenol (fē`nōl), C6H5OH, a colorless, crystalline solid that melts at about 41°C;, boils at 182°C;, and is soluble in ethanol and ether and somewhat soluble in water.  produced in North America North America, third largest continent (1990 est. pop. 365,000,000), c.9,400,000 sq mi (24,346,000 sq km), the northern of the two continents of the Western Hemisphere.  is derived from cumene Cu´mene   

n. 1. (Chem.) A colorless oily hydrocarbon, C6H5.C3H7, obtained by the distillation of cuminic acid; - called also cumol ltname>.
 oxidation. Cumene is made from petrochemicals--benzene and propylene propylene /pro·pyl·ene/ (pro´pi-len) a gaseous hydrocarbon, CH3CHdbondCH2.

propylene glycol  a colorless viscous liquid used as a humectant and solvent in pharmaceutical preparations.
 for which reason the costs of these chemicals are driven by the price of oil. As the oil prices increase dramatically, the costs of wood composites (plywood, oriented strand board Oriented strand board, or OSB, or waferboard, or Sterling board (UK), is an engineered wood product formed by layering strands (flakes) of wood in specific orientations.  (OSB OSB
abbr.
Order of Saint Benedict
), medium density fibre (MDF (1) (Main Distribution Frame) A wiring rack that connects outside lines with internal lines. It is used to connect public or private lines coming into the building to internal networks. ) board, etc.) rise dramatically too--the prices of phenol-based adhesive resins show a direct correlation Noun 1. direct correlation - a correlation in which large values of one variable are associated with large values of the other and small with small; the correlation coefficient is between 0 and +1
positive correlation
 with the oil market prices. The other major adhesive component is formaldehyde produced from natural gas. However, in 2004 the International Agency for Research on Cancer The International Agency for Research on Cancer (IARC, or CIRC in its French acronym) is an intergovernmental agency forming part of the World Health Organisation of the United Nations.

Its main offices are in Lyon, France.
 has classified formaldehyde as human carcinogen carcinogen: see cancer.
carcinogen

Agent that can cause cancer. Exposure to one or more carcinogens, including certain chemicals, radiation, and certain viruses, can initiate cancer under conditions not completely understood.
. Along with economic considerations suggesting reducing the costs of wood adhesives by using aromatics from renewables at stable pricing of feedstock carbon, lately there is a growing interest in cheap self-binding (self-adhesive) wood composites.

The present study some results of which have been reported at meetings in Vilnius (Abolins et al. 2008) and Riga (Gravitis et al. 2008) and has been taken on as an attempt to use lignin lignin (lĭg`nĭn), a highly polymerized and complex chemical compound especially common in woody plants. The cellulose walls of the wood become impregnated with lignin, a process called lignification, which greatly increases the strength and  extracted from wood processed by steam explosion auto-hydrolysis as the adhesive in hot-pressed fibre boards and plywood. The present report comprises a wider field of SE applications and new experimental results of other samples.

2. Experimental

2.1. Steam Explosion

Steam explosion (SE) is principally a rather simple process but complicated in technical details ([TEXT NOT REPRODUCIBLE IN ASCII ASCII or American Standard Code for Information Interchange, a set of codes used to represent letters, numbers, a few symbols, and control characters. Originally designed for teletype operations, it has found wide application in computers. ] 1987). The biomass is treated with saturated steam steam at the temperature of the boiling point which corresponds to its pressure; - sometimes also applied to wet steam.

See also: Steam
, usually at pressures up to 4 MPa. The treatment time varies from some seconds to some minutes. After the treatment, within a split second, the biomass is decompressed (exploded) to the pressure of ambient atmosphere. The diagram of the SE process is shown in Fig. 1. The steam is generated by heating water in the boiler. Upon reaching the necessary steam parameters the sample is filled into the reactor and treated by steam at temperature of 235[degrees]C and pressure of 3.2 MPa. After having been subject to treatment for a chosen duration the sample is forced out into receiver wherefrom where·from  
conj.
From which.
 it further proceeds to the separation column (Fig. 1). The steam-exploded material was used as a composite for self-binding fibre boards (see also Fig. 7).

[FIGURE 1 OMITTED]

Empirically, conditions of the steam explosion can be characterised by a single treatment severity index comprising temperature and time (Overend and Chornet 1987). During SE the decomposed wood components, particularly lignin, act as self-supplying adhesives. SE wood fibres are a modified hierarchical assembly of thermodynamically ther·mo·dy·nam·ic  
adj.
1. Characteristic of or resulting from the conversion of heat into other forms of energy.

2. Of or relating to thermodynamics.
 incompatible components. Modified tailored fibres, particularly nano-particles, have been generated under certain SE conditions (Kallavus and Gravitis 1995; Gravitis 2006b).

The biomass after steam explosion auto-hydrolysis represents a mixture of its main ingredients--cellulose, soluble sugars, and lignin. The soluble parts are removed by adding water. Lignin is extracted from the residual by solving it in 0.4% solution of NaOH wherefrom it is precipitated by adding hydrochloric acid hydrochloric acid: see hydrogen chloride.
hydrochloric acid
 or muriatic acid

Solution in water of hydrogen chloride (HCl), a gaseous inorganic compound.
 to neutralise the solution. Precipitated mass is rinsed in water to remove the remnant of sodium chloride sodium chloride, NaCl, common salt. Properties


Sodium chloride is readily soluble in water and insoluble or only slightly soluble in most other liquids. It forms small, transparent, colorless to white cubic crystals.
 before filtration. After drying in air the filtrate filtrate /fil·trate/ (fil´trat) a liquid or gas that has passed through a filter.

fil·trate
v.
To put or go through a filter.

n.
 turns into powder presented as steam-exploded lignin used as the binder in the hot-pressed sample boards or plywood adhesive supplement in the tested plywood samples. The block diagram A chart that contains squares and rectangles connected with arrows to depict hardware and software interconnections. For program flow charts, information system flow charts, circuit diagrams and communications networks, more elaborate graphical representations are usually used.  of fractionation fractionation /frac·tion·a·tion/ (frak?shun-a´shun)
1. in radiology, division of the total dose of radiation into small doses administered at intervals.

2.
 of SE wood is shown in Fig. 2.

[FIGURE 2 OMITTED]

2.2. Instrumental methods

The raw material for hot-pressed board samples was studied by an L&W Fibre Tester analyser to determine such fibre parameters as length, width, shape factor (the ratio of projected to actual length), coarseness (mass per unit length), and ratio of fines (fibers less than 0,2 mm), of the steam-exploded wood biomass and extracted cellulose.

A Mettler Toledo Mettler-Toledo is a manufacturer of scales and analytical instruments. It is the combination of two companies: Mettler, based in Switzerland, and Toledo Scale, based in Columbus, Ohio, USA.  TGA/SDTA851 thermal gravimeter gra·vim·e·ter
n.
1. See hydrometer.

2. An instrument used to measure variations in a gravitational field.



gra·vim
 and a Mettler Toledo DSC (1) (Digital Signal Controller) A microcontroller and DSP combined on the same chip. It adds the interrupt-driven capabilities normally associated with a microcontroller to a DSP, which typically functions as a continuous process. See microcontroller and DSP. 822 differential scanning calorimeter calorimeter: see calorimetry.
calorimeter

Device for measuring heat produced during a mechanical, electrical, or chemical reaction and for calculating the heat capacity of materials.
 were used to detect thermal effects and anomalies (loss of mass and glass transition temperature The glass transition temperature is the temperature below which the physical properties of amorphous materials vary in a manner similar to those of a solid phase (glassy state), and above which amorphous materials behave like liquids (rubbery state).  [T.sub.g]) in samples of the extracted lignin.

The concentration of lignin in hot-pressed board samples was evaluated from infrared spectra recorded by a Perkin Elmer "Spectrum One" Furrier fur·ri·er  
n.
1. One that deals in furs.

2. One whose occupation is the dressing, designing, cleaning, or repairing of furs.
 transform spectrometer. The 32 repeated infrared absorption spectrum absorption spectrum: see spectrum.  scans at the rate of 0.2 [cm.sup.-1]/s at resolution of 4 [cm.sup.-1] of each of the three samples prepared for the purpose covered the range from 450 to 2000 [cm.sup.-1]. The Spectrum 5.0.1 (Perkin Elmer Instruments LLC (Logical Link Control) See "LANs" under data link protocol.

LLC - Logical Link Control
) software was used for correction of the base line and normalisation 1. (data processing) normalisation - A transformation applied uniformly to each element in a set of data so that the set has some specific statistical property. For example, monthly measurements of the rainfall in London might be normalised by dividing each one by the total  of the spectra.

Mechanical properties (modulus of elasticity modulus of elasticity

The ratio of the stress applied to a body to the strain that results in the body in response to it. The modulus of elasticity of a material is a measure of its stiffness and for most materials remains constant over a range of stress.
 and bending strength (EN 310:1993)) of hot-pressed board samples were tested by a universal machine for testing material resistance ZWICK/Z100 at the LSIWC. The same kind of testing machine testing machine

Machine used in materials science to determine the properties of a material. Machines have been devised to measure tensile strength, strength in compression, shear, and bending (see strength of materials), ductility, hardness, impact strength (
 was used to examine the properties of plywood samples at the Joint Stock Company "Latvijas Finieris".

The testing results of the board and plywood samples were compared with European standards (EN 312: 2003, EN 622-2:2004, EN 314-2:1993).

2.3. Sampling

Lignin used in the experiments was extracted from long-term sample growths of grey alder (Alnus incana L.) Moench) wood after being processed for 2 min by saturated steam at 235[degrees]C under pressure of 3.2 MPa. The same kind of raw material was used to make the experimental hot-pressed fibre board samples.

Five kinds of board samples of the size 10 x 10 cm hot-pressed in a single stage at 8 MPa during 10 min were prepared for tests:

B1--binderless boards of shredded alder chips sifted through a 2 mm mesh sieve;

B2--self-binding boards of shredded alder chips mixed with lignin extracted from the steam-exploded mass at the proportion 4:1 by weight of absolutely dry mass;

B3--self-binding boards of ground SE cellulose residue of the steam-exploded pulp after extraction by water and 0.4% solution of NaOH;

B4--self-binding boards of ground SE cellulose mixed with SE lignin at the proportion 4:1;

B5--self-binding boards of non-fractioned air-dried steam-exploded pulp.

The hot-pressed boards were left in the press for two hours to cool down while the pressure decreased. Conditions under which the board samples have been pressed are specified in Table 1.

The weight of all samples was calculated to contain 100 g of absolutely dry mass. The dry mass of a B2 sample contains 80 g of shredded chips and 20 g of lignin powder. The moisture content and mass of samples are given in Table 2. The wood component for a board sample first is mixed with the lignin binder on a sheet of paper, then discharged into a flask and shaken until reaching a uniform colour. Ingredients for B1 and B2 samples were prepared to make three sample boards, the masses for B4 and B5--for two, and mass for B3--for one sample board.

Mechanical properties of the boards were tested on 30 x 95 mm specimens cut from the hot-pressed samples. After mechanical tests the same test pieces were used to evaluate the effect of moisture on form stability (swelling) for which purpose the fractured side of one of the broken halves was cut off to 30*30 mm specimens to obtain a smooth surface.

The plywood samples were prepared in the laboratory of Joint Stock Company "Latvijas Finieris" from three birch veneer sheets of the size 600 x 900 x 1.5 mm bonded by 5 different kinds of adhesives (Table 3) spread uniformly over the surface of a veneer sheet prior to covering it with the next sheet to be glued to at right angle between the direction of fibres of adjacent sheets. Commercial phenol formaldehyde resin The earliest commercial synthetic resin is based on a Phenol formaldehyde resin (PF) with the commercial name Bakelite, and is formed from an elimination reaction of phenol with formaldehyde.  adhesive ([PF.sub.com]) was taken for two samples (P1). Adhesive for other two samples (P2) was made of mixture of the commercial phenol formaldehyde resin with steam-exploded lignin (L) in the proportion of 9:1 of absolutely dry masses of the components. Adhesive of the group of 4 plywood samples (P3) was the commercial phenol formaldehyde resin mixed with glue used by the factory to bond plywood sheets.

The same adhesive mixed with the steam-exploded lignin in the proportion of 9:1 of absolutely dry mass was used to make one plywood sample (P4). Adhesive for one more sample (P5) was made mixing commercial phenol formaldehyde resin with steam-exploded lignin solution in 0.4% NaOH (25% lignin and 75% NaOH) in the dry substance weight proportion of 9:1.

Amount of adhesive consumed was within the range of 165-195 g/[[m.sup.2].sup.] The packets of veneer sheets were put under pressure of about 0.1 MPa for 15-30 min to flatten the layers before binding under higher pressure (1.8 MPa) at 127[degrees]C temperature.

The binder adhesion was evaluated on test pieces of the size 25 x 150 mm cut from the plywood sheet samples. From both sides of each sample about 2.5 mm wide cuts were made through the surface layer at the distance of 25 mm (EN 314-1:2004).

2.4. Testing of board and plywood samples

Density determined as mass per unit volume (in g [cm.sup.-3]) of the hot-pressed board samples calculated as the ratio of sample mass m divided by the product of length a, width b, and thickness t of the sample:

[rho] = m / a x b x t. (1)

Density was calculated for each of the three specimens of the size 95 x 30 mm cut from each of the hot-pressed sample boards.

[FIGURE 3 OMITTED]

The modulus of elasticity is calculated from data of bending test (Fig. 3) in the course of which the ends of a specimen are rested on two supports while the central part is bent by loading at the rate of 1mm per minute until the specimen breaks (EN 310:1993):

[E.sub.m] = [l.sup.3.sub.1] x ([F.sub.2] - [F.sub.1]), 4 x b x [t.sup.3] x ([a.sub.2] - [a.sub.1]) (2)

where [l.sub.1] is the distance between supports, in mm; b-width of the specimen, in mm; t-thickness of the specimen, in mm; ([F.sub.1] - [F.sub.2])--increase of the load over the linear part of the bending curve, ([a.sub.2] - [a.sub.1])--increase of deformation with respect to ([F.sub.1] - [F.sub.2]) in the middle of the test piece.

The bending strength [f.sub.m] is calculated from the maximum force of load [F.sub.max] in N [mm.sup.-2] (EN 310:1993):

[f.sub.m] = 3 x [F.sub.max] x [l.sub.1]/2 x b x [t.sup.3]. (3)

All the board samples were tested for swelling after soaking for 24 hours Adv. 1. for 24 hours - without stopping; "she worked around the clock"
around the clock, round the clock
 in deionised water, the thickness being measured before and after the treatment. The swelling [G.sub.t] is calculated as the ratio (EN 317:1993):

[G.sub.t] = [t.sub.2] - [t.sub.1]/[t.sub.1] x 100, (4)

where [t.sub.1] is thickness before soaking, in mm; [t.sub.2]--thickness after soaking in water for 24 hours, in mm.

After that the board samples were dried in air for about two weeks until reaching constant weight to calculate residual swell:

[G'.sub.t] = [t'.sub.2] - [t.sub.1]/[t.sub.1] x 100, (5)

where [t.sub.1] is thickness of the sample before the swelling test, in mm; [t'.sub.2]--thickness of the sample dried for 2 weeks after the swelling test, in mm.

Shear strength characterising the plywood binder quality is calculated (in N [mm.sup.-2]) from the failing force of the test piece from equation 6 (EN 314-1:2004). The load applied at a constant rate of motion so that rupture occurred within 30[+ or -]10 s.

[f.sub.v] = F/h x b, (6)

where F is the failing force of the test piece, in N; h-length of the shear area, in mm; b-width of the shear area, in mm.

Before The shear strength test, the length and width of the shear area of the plywood specimens were measured to the accuracy of 0.1 mm and recorded. After that the specimens were pre-treated as required for non-covered exterior plywood (EN 314-2:1993)--for 4 h in boiling water, then dried in the ventilated drying oven for 16 h to 20 h at 60[+ or -]3[degrees]C, then immersed in boiling water for 4 h, followed by cooling in water at 20[+ or -]3[degrees]C for at least 1 h.

3. Results and discussion

3.1. Lignin structure

Absolutely dry (a) and air-dry (b) samples of lignin extracted from alder chips processed by SE for 1, 2, and 3 minutes, respectively, were prepared (Table 4).

The glass transition temperature [T.sub.g] of the alder-wood SE lignin determined by calorimetric cal·o·rim·e·ter  
n.
1. An apparatus for measuring the heat generated by a chemical reaction, change of state, or formation of a solution.

2.
 test of the samples was found to be in the range of 137-157[degrees]C (Fig. 4). As seen from Fig. 4, the glass transition temperature of air-dry SE lignin (L2b) is higher than that of absolutely dry lignin sample (L2a). The thermo-gravimetric (TG) curves of air-dry lignin samples extracted from steam-exploded masses processed under pressure and high temperature during 1 min (L1b) and 2 min (L2b) are shown in Fig. 5. In case of L1b lignin the loss of mass occurred earlier compared with the L2b lignin suggesting that glass transition temperature of the L2b lignin sample is lower than glass transition temperature of the L1b lignin.

Infrared spectra of lignin, extracted from the steam-exploded mass, and the boards are shown in Figs. 6a, b, c. Intensity of the IR carbonyl carbonyl /car·bon·yl/ (kahr´bah-nil) the bivalent organic radical, C:O, characteristic of aldehydes, ketones, carboxylic acid, and esters.

car·bon·yl
n.
The bivalent radical CO.
 band at 1702 [cm.sup.-1] is growing in spectra of the SE lignin samples with the increase of duration of SE treatment of the mass from which lignin is extracted (Fig. 6c).

Vibration bands of the aromatic ring aromatic ring,
n closed ring structure formed by six carbon atoms, with a single hydrogen atom attached to each one. Also called a
phenyl ring or a
benzene ring.
 of lignin at 1600 [cm.sup.-1], 1510 [cm.sup.-1], and 1420-1450 [cm.sup.-1] are more expressed (Sarkanen, Ludwig 1975) in board samples of material containing admixture of lignin (compare curves 2 and 1 in Figs. 6a and 6b). They are more distinct in spectra of chip boards (Fig. 6a) compared with boards pressed of the cellulose residue (Fig. 6b) after extraction of lignin.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

3.2. SE fibre parameters

Particle size statistics was studied with fibres of air-dried steam exploded mass (F1), residue of the steam exploded mass after extraction of the components soluble in water and 0.4% solution of NaOH (F2), and ground residue (F3). The obtained results are summarised in Table 5. As seen in the table, the average length and width of the fibres decreases, but the amount of smaller particles increases after farther treatment--rinsing with water and solution of NaOH, grinding (Abolins et al. 2008).

Since the average ratio of length to width of undamaged fibres in the natural aspen and birch wood are equal to 1.2/0.033 and 1.2/0.024, respectively (MepcoB 1989), the length of fibres after SE is smaller the width being the same as of natural fibres.

[FIGURE 6 OMITTED]

Compared with dimensions of industrial fibres (MepcoB 1989) the dominating fibre length is 1 mm in both cases the length of industrial fibres reaching 12.8 mm while the length of SE fibres does not exceed 7.5 mm.

3.3. Properties of hot-pressed boards

An illustration of the sequence of procedures used to obtain the board samples is demonstrated in Fig. 7. All the board samples were 7-8 mm in thick.

Density, bending strength ([F.sub.m]), modulus of elasticity ([E.sub.m]), and the instant ([G.sub.t]) and residual swell ([G'.sub.t]) of thickness of the hot-pressed board samples are presented in Table 6.

[FIGURE 7 OMITTED]

Comparing density of the tested samples it obviously increases with the content of lignin in samples B1-B2 and B3-B4.

The highest density, however, is reached in samples (B4) pressed of the steam-exploded cellulose residue with admixture of lignin (20% by mass) extracted from the steam-exploded mass of wood, which is less than the content of lignin in natural wood samples (B1) or in the steam-exploded mass (B5).

The rather considerable difference between the density of samples B1 and B4 may be assigned to the much smaller size of fibrous particles of the steam-exploded cellulose mass compared to the size of shredded wood chips.

[FIGURE 8 OMITTED]

Enhanced resistance to moisture is another obvious effect of lignin content in the hot-pressed boards. As seen from Table 6, swelling of the board samples in water decreases in the same order as increases the density, the board containing 20% of additional lignin (B2) compared with natural wood (B1) or mixture of cellulose with 20% of the extracted lignin (B4) and pulp (B5) being most resistant. As might be expected, there is a strong correlation between the instant and residual swell (Fig. 8).

Correlation of mechanical properties with the content of lignin is not as unambiguous as in case of density or resistance to moisture. Nevertheless, the board of hot-pressed cellulose residue (B3) has the lowest value of the modulus of elasticity (Table 6). The samples of the mixture of 80% cellulose and 20% lignin (by mass) showed the highest values of the modulus of elasticity (Table 6).

The results partly compare to requirements of the European Standard for commercial boards. The hot-pressed boards of raw alder chips (B1) meet the requirements for general purpose particleboard types P1 and P2 for use in dry conditions (type P1) and for interior fitments including furniture under dry conditions (type P2) (EN 312:2003). Admixture of SE lignin to alder chips improves the hot-pressed board (B2) form stability to resist moisture while reducing mechanical strength (Table 6). The properties of B2 samples are close to non load-bearing boards for use under humid conditions (EN 312:2003). Admixture of lignin binder to the cellulose residue improved the quality of hot-pressed boards B4 compared to B3 (Table 6). The properties of board samples B3 do not meet the minimum requirements for any board type of the EU Standard 6222:2004. The form stability of hot-pressed boards B4 complies with type HB (hard board) of the Standard for use under dry conditions while bending strength is below the required minimum. The board samples of SE wood (B5 in Table 6) show best results of the tested properties complying with requirements for load-bearing boards for use in dry conditions (EN 622-2:2004). The form stability properties of these samples meet the requirements for use in humid conditions while mechanical properties fail to meet the requirements.

Test results of board samples B5 obtained from hot-pressed air-dry steam-exploded wood suggest that mechanical strength may depend on the temperature at which the boards are pressed. More studies are necessary to obtain the evidence and data revealing the effect of hot-pressing temperature on the board properties.

The board samples of dried SE mass show the best results of all the obtained samples and compete with commercial wood fibreboards. However, if samples are removed from the press unit before having cooled below 60[degrees]C, cavities are formed in the bulk material.

3.4. Plywood properties

Results of plywood sample tests are presented in Table 7. As seen from the results of testing shear strength, admixture of SE lignin to commercial phenol-formaldehyde resin up to 10% does not affect the quality of adhesion. Using the sodium hydroxide sodium hydroxide, chemical compound, NaOH, a white crystalline substance that readily absorbs carbon dioxide and moisture from the air. It is very soluble in water, alcohol, and glycerin. It is a caustic and a strong base (see acids and bases).  solvent for better mixing of lignin into the resin has not improved cohesion, as one may see comparing shear strength of samples P1 and P5 (Table 7). Shear strength of all the samples exceeds the value of 1 N [mm.sup.-2] and satisfies the mean apparent cohesive failure (Fig. 9, EN 314-2:1993). As seen from Table 7, adhesion in all the samples comply with the requirements for products of the Joint Stock Company "Latvijas Finieris". More studies are necessary to find conditions for rational use of SE lignin as substitute for PF resins in plywood production.

[FIGURE 9 OMITTED]

4. Conclusions

1. Lignin extracted from steam-exploded alder wood (Alnus incana (L.) Moench) acts as binder in wood particle and fibre boards improving form stability.

2. The hot-pressed boards of raw alder chips (B1) meet the requirements for general purpose particleboard types P1 and P2 for use in dry conditions (type P1) and for interior fitments including furniture under dry conditions (type P2) (EN 312:2003). (EN 312).

3. The properties of hot-pressed board samples (B2) of mixture of raw alder chips and SE lignin are close to non load-bearing boards for use under humid conditions (EN 312:2003).

4. The properties of hot-pressed board samples (B3 and B4) of SE cellulose and a mixture of SE cellulose with SE lignin do not meet the minimum requirements for any board type of the EU Standard 622-2:2004.

5. Self-binding board samples hot-pressed from SE grey alder fibres (B5) comply with requirements for application in loaded construction in dry environment (EN 622-2:2004).

6. Results obtained with admixture of lignin extracted from steam-exploded wood to plywood binder are promising for more laboratory tests applying higher lignin concentrations in the adhesives and varying the binding regimes.

7. Properties of the obtained hot-pressed board samples and adhesives demonstrate the feasibility of using waste to make value-added products representing an efficient way of protection of the environment.

doi: 10.3846/jeelm.2010.09

Acknowledgements

The study has been supported by the National Research Program for rational use of hardwood resources. The authors are grateful to the staff of the Joint Stock Co. "Latvijas Finieris" for courtesy and assistance preparing and testing the plywood samples.

Submitted 07 Sep. 2009; accepted 22 Nov. 2009

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Gravitis, J. 2007. Zero techniques and systems--ZETS strength and weakness. Review, J. of Cleaner Production, 1190-1197. doi:10.1016/j.jclepro.2006.07.038

Gravitis, J. 2008. Biorefinery: biomaterials and bioenergy from photosynthesis, within zero emissions framework, in Barbir, F.; Ulgiati, S. (Eds.). Sustainable Energy Production and Consumption. Benifits, Strategies and Environmental Costing. NATO Science for Peace The NATO Science Committee and the Committee on the Challenges of Modern Society (CCMS) were restructured in 2006 to create “Science for Peace and Security” (SPS). The programme resulted from the emergence of common priorities for the NATO Programme for Security through  and Security. Springer, 327-337.

Gravitis, J.; Abolins, J.; Veveris, A.; Tupciauskas, R.; Alksnis, B. 2008. Self-binding wood composites by steam explosion processing, in Energy Evaluation of Steam Explosion. Book of abstracts of the XV International Conference on Mechanics of Composite Materials, Riga, Latvia, 97-98.

Gravitis, J.; Della Senta, T. 2001. Global prospects of substituting oil by biomass, in Palo, M.; Uusivuori, J.; Mery, G. (Eds.). World Forests, Markets and Policies. Kluwer Academic Publ., Dordrect, London, Boston, III, 23-39.

Gravitis, J.; Vedernikov, N.; Zandersons, J.; Kokorevics, A. 2001. Furfural furfural (fûr`fərəl) or furfuraldehyde (fûr'fərăl`dəhīd) [Lat.,=bran], C4H3  and levoglucosan production from deciduous deciduous /de·cid·u·ous/ (de-sid´u-us) falling off or shed at maturity, as the teeth of the first dentition.

de·cid·u·ous
adj.
1.
 wood and agricultural wastes, in Bozell, J. J. (Ed.). Chemicals and Materials from Renewable Resources. American Chemical Society 784: 110-122.

Kallavus, U.; Gravitis, J. 1995. A Comparative investigation of the ultrastructure ultrastructure /ul·tra·struc·ture/ (-struk?chur) the structure beyond the resolution power of the light microscope, i.e., visible only under the ultramicroscope and electron microscope.  of steam exploded wood with light, scanning and transmission electron microscopy, Holzforchung 49(2): 182-188. doi:10.1515/hfsg.1995.49.2.182

Kvasauskas, M.; Baltrenas, P. 2008. Anaerobic anaerobic /an·aer·o·bic/ (an?ah-ro´bik)
1. lacking molecular oxygen.

2. growing, living, or occurring in the absence of molecular oxygen; pertaining to an anaerobe.
 recycling of organic waste and recovery of biogas bi·o·gas  
n.
A mixture of methane and carbon dioxide produced by bacterial degradation of organic matter and used as a fuel.


biogas
Noun

gaseous fuel produced by the fermentation of organic waste
, Ekologija 54(1): 57-63. doi:10.2478/V10055-008-0011-3

Nagyvary, J.; DiVerdi, A.; Owen, N. L.; Tolley, H. D. 2006. Wood used by Stradivari and Guarneri, Nature 444: 565. doi:10.1038/444565a

Overend, R. P.; Chornet, E. 1987. Fractionation of lignocellulosics by steam-aqueous pretreatments, Phil. Trans. R. Soc. A. 321: 523-536. doi:10.1098/rsta.1987.0029

Sarkanen, K. V.; Ludwig, C. H. (Ed.). (Russian translate 1975). Lignins. Occurrence, Formation, Structure and Reactions. Wiley Interscience.

Vaboliene, G.; Matuzevicius, A. B. 2005. Investigation into biological nutrient removal from wastewater, Journal of Environmental Engineering and Landscape Management 13(4): 177-181.

[TEXT NOT REPRODUCIBLE IN ASCII]. [Gravitis, J. A. Theoretical and applied aspects of the steam explosion plant biomass autohydrolysis method], [TEXT NOT REPRODUCIBLE IN ASCII] 5: 3-21.

MepcoB, E. [TEXT NOT REPRODUCIBLE IN ASCII]. [Mersov, E. D. Fiber board industry]. Mockba: [TEXT NOT REPRODUCIBLE IN ASCII]. 232 c.

Janis Gravitis (1), Janis Abolins (2), Ramunas Tupciauskas (3) and Andris Veveris (4)

(1,3,4) Laboratory of Biomass Eco-Efficient Conversion, Latvian State Institute of Wood Chemistry, 27 Dzerbenes Str, LV-1006 Riga, Latvia

(2) Institute of Atomic Physics and Spectroscopy, University of Latvia University of Latvia (LU) (Latvian: Latvijas Universitāte) is the oldest university in Latvia located in Riga, Latvia. History
LU was established in 1919.
, 4 Skunu Str, LV-1586 Riga, Latvia E-mails: (1) jgravit@edi.lv; (2) jclover@latnet.lv; (3) rtupciauskas@hotmail.com; (4) a.veveris@inbox.lv

Janis GRAVITIS. Dr Habil. Chem.; Professor, Head of laboratory of the Biomass Eco-Efficient conversion. Employment: Professor (1993); Head of Department (1992); Head of Laboratory (1988); senior researcher and head of research group (1979); Visiting Professor, University of Tokyo “Todai” redirects here. For the restaurant called Todai, see Todai (restaurant).

The University of Tokyo (東京大学
 (1998-2000). Visiting Professor and Lecturer for Ph.D. students (1996-2000), United Nations University, Institute of Advanced Studies, Tokyo, Japan. 12 Keynote lectures at the International Conferences and Symposiums. Publications: author/co-author of more than 300 publications, 10 reviews, chapters of 5 books. Honorary awards and membership: Corresponding Member of the Latvian Academy of Sciences (2006); The Latvian Academy of Sciences Presidium pre·sid·i·um  
n. pl. pre·sid·i·a or pre·sid·i·ums
1. Any of various permanent executive committees in Communist countries having power to act for a larger governing body.

2.
 First Award (1979, 1984); The Latvian Academy of Sciences Presidium First Award for Young Scientists (1982); Member, Habilitation and Promotion Council, Latvian State Institute of Wood Chemistry (1992); Member of the American Chemical Society, (1993); The International Lignin Institute, Switzerland (1993); Fellow of the International Academy of Wood Sciences (1994); Japan Wood Research Society; Foreign member of the International Research Centre for Sustainable Materials (Tokyo). Invited lectures: Los Alamos National Laboratory Los Alamos National Laboratory (LANL) (previously known at various times as Site Y, Los Alamos Laboratory, and Los Alamos Scientific Laboratory) is a United States Department of Energy (DOE) national laboratory, managed and operated by Los Alamos National  (U.S.), the Science Council of Japan. Research interests: formation and structure of the wood cell wall lignin-carbohydrate matrix; Zero-Emissions concept and environment protection; Bio-refinery approach for bio-fuels and chemicals; Biomass-Based Production Systems (BPS (Bits Per Second) The measurement of the speed of data transfer in a communications system.

1. BPS - Basic Programming Support
2. bps - bits per second
); Eco-technologies, identification and operation of new sustainable and integrated clusters for forest, agricultural and plantation biomass--based industries in framework of the UNU UNU United Nations University
UNU Université des Nations Unies (French: United Nations University) 
 ZERI (Zero Emissions Research Initiative) Program.

Janis ABOLINS. Dr Sc. Phys., senior research fellow of the Institute of Atomic Physics and Spectroscopy of the University of Latvia. Employment: Teaching Assistant (1962), Senior Lecturer (1964), Docent (1984) of the University of Latvia. Publications: Textbook (structure of molecules and quantum chemistry), papers on spectroscopy of complex crystals, energy consumption, sustainable development, and biomass conversion. Research interests: renewable sources of energy, technological sustainability.

Ramunas TUPCIAUSKAS. PhD student, Dept of Wood Processing, Latvia University of Agriculture (LLU LLU Loma Linda University
LLU Local Loop Unbundling
LLU Lending Library Unit
LLU Layered Language Understander
LLU Local Logic Unit
). Master of Engineering Science (Wooden Materials and Technologies), Latvia University of Agriculture, 2008. Bachelor of Industrial Engineering (Wood Products Design and Technology), Kaunas University of Technology Kaunas University of Technology (Lithuanian: Kauno Technologijos Universitetas (KTU)) is the largest technical university in the Baltic States and the second largest university in Lithuania.  (Lithuania), 2006. Employment: engineer (2006), Latvian State Institute of Wood Chemistry (LSIWC). Publications: co-author of 4 research papers. Research interests: engineering of wood composite materials, self-binding and binder-less materials.

Andris VEVERIS. Assistant, laboratory of Biomass Eco-Efficient Conversion, Latvian State Institute of Wood Chemistry (LSIWC). University Diploma (Organic Chemistry), Latvian University, 1979. Publications: co-author of about 20 research papers. Research interests: chemical and physical wood structure and steam explosion.
Table 1. Processing regimes of hot-pressed board sample.
In all cases the pressing pressure was 8 MPa and the
duration 10 min

Sample   Temperature,    Components
         [degrees]C

B1       225             Alder chips (2 mm mesh)
         221
         227
B2       196             Alder chips : Lignin = 4 : 1
         192
B3       225             SE cellulose residue
B4       186             SE cellulose : Lignin = 4 : 1
         196

Table 2. Moisture and outweigh mass of
components of the board samples

Sample                        B1     B2     B3     B4    B5

Moisture,   Main component   7.91   7.91   5.94   5.94   4.8
%           Lignin (L2)       --    5.90    --    5.90   --

Mass, g     Main component   109     87    106    85.1   105
            Lignin (L2)       --    21.2    --    21.2   --
            Sample           109    108    106    106    105

Table 3. Adhesives and bonding regime of plywood samples

Sample           Adhesive             Temp.      Press   Time
                                    [degrees]C    MPa    min

P1       [PF.sub.com]
P2       [PF.sub.com]:L = 9:1
P3       [PF.sub.com] + hardener
P4       ([PF.sub.com] + harden.)      127        1.8     4
P5       :L 9:1
         [PF.sub.com].: (0.25 L
         + 0.75 NaOH) = 9:1

Table 4. Moisture content of SE lignin samples, % of mass:
a) absolutely dry samples--air-dry samples after being dried
in oven at 105[degrees]C and stored in desiccator over phosphorus
pentoxide; b) air-dry samples--samples held in air at room
temperature to reach equilibrium moistures

Samples            L1        L2       L3

Absolutely dry a   0         0        0
Air-dry        b   5.95      5.90     6.17

Table 5. Determined fibre parameters. Shape - the ratio of the
perceptible to the actual fibre length. Fines - fibers less
than 0,2 mm. Aspect ratio - AS = average length/average width

Sample                      F1      F2      F3

Number of fibres           14502   20042   20014
Temperature at testing,
  [degrees]C               40.5     40     39.3
Average length, [micro]m    855     799     637
Average width, [micro]m    30.9    26.4    29.6
Shape, %                   84.8    85.9    86.3
Fines, %                   10.2    11.6    29.9
Coarseness, [micro]g/m      339     172     225
Aspect ratio               27.7    30.3    21.5

Table 6. Properties of hot-pressed sample boards.
[+ or -]--standard deviation

Sample                Pressing T,        Density, g
                       [degrees]C        [cm.sup.-3]

B1       Chips,           221         1.18 [+ or -] 0.04
         2 mm mesh        227         1.17 [+ or -] 0.04

B2       Chips:           196         1.24 [+ or -] 0.01
         L 4:1            192         1.27 [+ or -] 0.02

B3       SE               225         1.12 [+ or -] 0.02
         cellulose

B4       SE cell:         187         1.29 [+ or -] 0.04
         L 4:1            196         1.33 [+ or -] 0.04

B5       Dried            170         1.34 [+ or -] 0.04
         SE mass          190         1.24 [+ or -] 0.06

Sample                 [f.sub.m]          [E.sub.m]
                      N [mm.sup.2]      N [mm.sup.-2]

B1       Chips,      21 [+ or -] 3    3570 [+ or -] 600
         2 mm mesh   20 [+ or -] 5    3650 [+ or -] 820

B2       Chips:      15 [+ or -] 6    3330 [+ or -] 430
         L 4:1       14 [+ or -] 5    3420 [+ or -] 410

B3       SE          13 [+ or -] 2    2400 [+ or -] 250
         cellulose

B4       SE cell:    22 [+ or -] 4    5080 [+ or -] 485
         L 4:1       17 [+ or -] 2    4230 [+ or -] 375


B5       Dried       30 [+ or -] 5    4700 [+ or -] 1250
         SE mass     15 [+ or -] 4    3000 [+ or -] 750

Sample                 [G.sub.t]          [G.sub.t]
                           %                  %

B1       Chips,      35 [+ or -] 5      16 [+ or -] 3
         2 mm mesh   43 [+ or -] 9      23 [+ or -] 4

B2       Chips:      18 [+ or -] 11     10 [+ or -] 7
         L 4:1       12 [+ or -] 11      6 [+ or -] 8

B3       SE          39 [+ or -] 3      18 [+ or -] 2
         cellulose

B4       SE cell:    25 [+ or -] 8      12 [+ or -] 5
         L 4:1       19 [+ or -] 5       9 [+ or -] 3

B5       Dried        9 [+ or -] 1       3 [+ or -] 1
         SE mass     11 [+ or -] 2       3 [+ or -] 1

Table 7. Shear strength and elasticity of plywood samples.
* Requirements of Joint Stock Company "Latvijas Finieris"

                                     Shear
                                  strength, N
Sample   Adhesive                 [mm.sup.-2]

*        [PF.sub.comm]           [greater than
                                 or equal to] 1

P1       [PF.sub.comm]         1.83 [+ or -] 0.34

P2       [PF.sub.comm] +       1.86 [+ or -] 0.30
         SE lignin

P3       [PF.sub.comm] +       1.66 [+ or -] 0.22
         hardener

P4       [PF.sub.comm] +       1.52 [+ or -] 0.44
         hardener +
         SE lignin

P5       [PF.sub.comm] +       1.33 [+ or -] 0.22
         SE lignin:NaOH

                   Bending strength,
                    N [mm.sup.-2]

               along                 across
Sample         fibres                fibres

*                23                    75

P1         30 [+ or -] 2         163 [+ or -] 7

P2         32 [+ or -] 2        133 [+ or -] 23

P3         28 [+ or -] 5         132 [+ or -] 6

P4         28 [+ or -] 1         148 [+ or -] 7

P5         31 [+ or -] 2        153 [+ or -] 14

                  Modulus of elasticity,
                     N [mm.sup.-2]

               along                 across
Sample         fibres                fibres

*               500                  10 000

P1       1 284 [+ or -] 86    17 940 [+ or -] 840

P2       1 200 [+ or -] 70    16 370 [+ or -] 1340

P3       1 290 [+ or -] 440    14240 [+ or -] 990

P4       1 170 [+ or -] 70    17 700 [+ or -] 1220

P5       1 275 [+ or -] 110   18 200 [+ or -] 1020
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Author:Gravitis, Janis; Abolins, Janis; Tupciauskas, Ramunas; Veveris, Andris
Publication:Journal of Environmental Engineering and Landscape Management
Article Type:Report
Geographic Code:4EXLA
Date:Jun 1, 2010
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