A layered wood product

Abstract

Disclosed is a layered wood product. The layered wood product comprises at least two veneers that are glued together with an adhesive forming a glue line. The adhesive is formed of a lignin-based binder composition combined with a calcium-containing hardener, and the adhesive comprises calcium in a total amount of 0.01 – 20 weight-% based on the total wet weight of the adhesive. The glue line comprises calcium and sulphur, wherein the ratio of sulphur to calcium in the glue line is 0.05 – 1.5.

Description

[0001] A LAYERED WOOD PRODUCT

[0002] FIELD OF THE DISCLOSURE

[0003] The present disclosure relates to a layered wood product comprising at least two veneers that are glued together with an adhesive forming a glue line .

[0004] BACKGROUND

[0005] Layered wood products , such as plywood, are often formed of veneers glued together by using an adhesive . Known is that di f ferent adhesives work in di fferent manners . There i s a need for adhesives speci f ically suitable for producing layered wood products such as plywood or laminated veneer lumber .

[0006] SUMMARY

[0007] Disclosed is a layered wood product , wherein the layered wood product comprises at least two veneers that are glued together with an adhesive forming a glue line , and wherein :

[0008] - the adhesive is formed of a lignin-based binder composition combined with a calcium-containing hardener, and wherein the adhesive comprises calcium in a total amount of 0 . 01 - 20 weight-% based on the total wet weight of the adhesive ; and

[0009] - the glue line comprises sulphur and calcium, wherein the ratio of sulphur to calcium in the glue line is 0 . 05 - 1 . 5 .

[0010] DETAILED DESCRIPTION

[0011] Disclosed is a layered wood product , wherein the layered wood product comprises at least two veneers that are glued together with an adhesive forming a glue line , and wherein : - the adhesive is formed of a lignin-based binder composition combined with a calcium-containing hardener, and wherein the adhesive comprises calcium in a total amount of 0 . 01 - 20 weight-% based on the total wet weight of the adhesive ; and

[0012] - the glue line comprises sulphur and calcium, wherein the ratio of sulphur to calcium in the glue line is 0 . 05 - 1 . 5 .

[0013] The inventors surprisingly found out that an adhesive having a lignin-based binder composition and a hardener that contains calcium, i . e . a calcium-containing hardener, as its components is superior for producing layered wood products , such as plywood or laminated veneer lumber of high quality . The inventors surprisingly found out that the speci fic ratio of lignin, that is present in the binder compos ition, and calcium in the adhesive may beneficially af fect the viscosity level of the adhes ive and thus the bonding strength of the layered wood product .

[0014] The inventors surprisingly found out that the presence of both sulphur and calcium in the glue line of the layered wood product , may enhance the mechanical properties of the resulting product . Such an improvement may primarily be due to the role of the sul fur as a cross-linking agent ( such as a vulcani zation reaction) , where the sulfur atoms may form cross-links between the lignin-polymer chains in the adhesive . When then calcium ions are introduced into the adhesive , they may facilitate the cross-linking process by coordinating with the sul fur atoms , thus creating stronger chemical bonds . The cross-linking of polymer chains may then increase the cohesion and adhesion of the adhesive , leading to better bonding between wood veneers . This , in turn, has the added utility of resulting in enhanced structural integrity and mechanical properties of the layered wood product , such as plywood . The presence of sul fur and calcium has the added utility of preventing the adhesive to become brittle , thereby improving its flexibility and impact resistance .

[0015] The calcium-containing hardener is a hardener that contains calcium . The calcium-containing hardener may be chalk, calcium carbonate , precipitated calcium carbonate , ground calcium carbonate , or any mixture or combination of at least two o f these . The calcium-containing hardener may thus also be a mixture of any of the above with for example starch or an additive .

[0016] When used in the adhesive the hardener may act as an extender or a rheological modi fier forming a matrix in the adhesive . When the adhesive is used to prepare a layered wood product , the calcium-containing hardener has the added utility of providing strength and bulk to the glue line by binding water and preventing too fast absorption o f the adhesive into the wood . The calcium-containing hardener may further assist in applying or spreading the adhesive onto the veneers .

[0017] The layered wood product may comprise at least two veneers that are glued together with the adhesive and thus a glue line is formed between the veneers . The inventors surprisingly found out that the speci fic ratio of sulphur to calcium in the glue line has the added utility of af fecting the bonding strength of the layered wood product in a desired manner . As the used binder composition is a lignin-based binder composition the glue line will comprise sulphur that originates from the lignin component of the binder composition .

[0018] In one embodiment , the glue line comprises sulphur in an amount of 1 - 20 weight-% , or 3 - 18 weight- % , or 5 - 16 weight-% . In one embodiment , the glue line comprises calcium in an amount of 1 - 75 weight-% , or 5 - 60 weight-% , or 7 . 5 - 55 weight-% .

[0019] The amount of sulphur and calcium in the glue line may be determined by cutting the layered wood product , e . g . the plywood, and the scratching the glue line from the surface and then analyz ing the glue l ine with energy-dispersive X-ray spectroscopy (EDS, EDX, EDXS or XEDS) . Energy-dispersive X-ray spectroscopy, which is sometimes also called energy dispersive X-ray analysis (EDXA or EDAX) or energy dispersive X-ray microanalysis (EDXMA) , is an analytical technique used for the elemental analysis or chemical characterization of a sample. It relies on an interaction of some source of X- ray excitation and a sample. Its characterization capabilities are due in large part to the fundamental principle that each element has a unique atomic structure allowing a unique set of peaks on its electromagnetic emission spectrum (which is the main principle of spectroscopy) . The peak positions are predicted by the Moseley's law with accuracy much better than experimental resolution of a typical EDX instrument.

[0020] In one embodiment, the ratio of sulphur to calcium in the glue line is 0.05 - 1 or 0.06 - 1.3, or 0.075 - 1.5 or 0.10 - 1. The inventors surprisingly found out that the specific ratio of sulphur to calcium has the added utility of making the glue line between the veneers strong. Thus, taking the other way around, the ratio of sulphur to calcium in the glue line may be taken as an indicator the bonding strength of the layered wood product.

[0021] In one embodiment, the adhesive comprises cal- cium-containing hardener in a total amount of 0.01 - 50 weight-%, or 0.5 - 45 weight-%, or 1 - 40 weight-%, or 3 - 35 weight-%, or 5 - 30 weight-% based on the total wet weight of the adhesive. By using an adhesive comprising a calcium-containing hardener one is able to provide calcium to the glue line.

[0022] By the term "total wet weight" is to be understood in this specification unless otherwise stated the total weight of components forming the adhesive including water. In one embodiment, the calcium-containing hardener comprises 10 - 50 weight-%, or 12 - 45 weight- %, or 14 - 40 weight-%, of calcium.

[0023] In one embodiment, the adhesive comprises calcium in a total amount of 0.03 - 18 weight-%, or 0.05 - 15 weight-%, or 0.1 - 10 weight-%, or 0.15 - 7 weight- % , based on the total wet weight of the adhesive.

[0024] In one embodiment, the adhesive comprises lignin-based binder composition in a total amount of 50 - 99.99 weight-%, or 55 - 99.5 weight-%, or 60 - 99 weight- %, or 65 - 97 weight-%, based on the total wet weight of the adhesive. In one embodiment, the adhesive comprises lignin in a total amount of 5 - 25 weight-%, or 7 - 22 weight-%, or 10 - 20 weight-%, based on the total wet weight of the adhesive. Using a lignin-based binder composition in the adhesive has the added utility of the glue line containing sulphur that originates from the lignin used in the lignin-based binder composition.

[0025] The lignin-based binder composition can be formed by different manners. The lignin-based binder composition can be formed by simply mixing lignin with a previously produced composition comprising crosslinking agent polymerized with e.g. synthetic polymerizable substance. Alternatively, the lignin-based binder composition can be formed by forming an aqueous composition comprising lignin and other reactant components, and by allowing polymerization reactions to take place between these reactant components under the influence of heating the composition. In one embodiment, an aqueous composition comprising polymerizable substance, such as lignin, and crosslinking agent, is formed and heated in order to polymerize the polymerizable substance and the crosslinking agent. The aqueous composition may be heated at a temperature of 30 - 150 °C for allowing polymerization reactions to take place. In one embodiment, the aqueous composition comprising polymerizable substance, such as lignin, and crosslinking agent, is heated at a temperature of 65 - 140 °C, or at a temperature of 70 - 100, or at a temperature of 75 - 85 °C or at a temperature of about 80 °C. The heating may be carried out for polymerizing the different reactant components such that the viscosity of the formed lignin-based binder composition is increased.

[0026] The heating can be continued until a predetermined viscosity value is formed. The predetermined viscosity value of the final lignin-based binder composition may vary. The polymerization reactions may be allowed to continue until a lignin-based binder composition with a viscosity value of 80 - 1200 cp is formed. The viscosity is measured at 25 °C using a rotary viscometer (Brookfield viscometer, plate spindle RV2, speed 50 rpm) . In one embodiment, the polymerization reactions are allowed to continue for 0.5 - 6 hours, or 1.0 - 5 hours, or 2 - 4 hours, or 1.5 - 3.0 hours.

[0027] In one embodiment, the lignin-based binder composition is prepared by polymerizing at least polymerizable substance and crosslinking agent, wherein 50 - 100 weight-%, 60 - 99 weight-%, or 70 - 97 weight-%, or 80 - 95 weight-%, or 85 - 93 weight-%, or 87 - 91 weight- % , of the polymerizable substance originates from lignin. The polymerizable substance may comprise or consist of lignin and at least one compound selected from the class of phenols. In one embodiment, the polymerizable substance comprises or consists of lignin and at least one of phenol, cresol, and resorcinol. In one embodiment, the polymerizable substance comprises or consists of lignin and phenol. In one embodiment, the polymerizable substance consists of lignin.

[0028] The crosslinking agent may be an aldehyde, such as formaldehyde or paraformaldehyde. In one embodiment, the aldehyde is prepared from bio-methanol. The aldehyde may thus be of biobased origin. The aldehyde may alternatively be of fossil origin. I.e. produced from a fossil material. In one embodiment, the aldehyde is prepared from methanol.

[0029] At least one catalyst may be used for the production of the lignin-based binder composition. The catalyst may be a base. In one embodiment, the catalyst comprises a salt or a hydroxide of an alkali metal or alkali earth metal. In one embodiment, the catalyst is selected from a group consisting of sodium hydroxide, potassium hydroxide, barium hydroxide, and their combinations. In one embodiment, the catalyst is sodium hydroxide. In one embodiment, the catalyst is an organic amine .

[0030] The components and their precise amounts used for producing the lignin-based binder composition may vary and the choice of the different components and their amounts is within the knowledge of the skilled person based on this specification. The temperature and any other values can be controlled and adjusted if needed during the production process.

[0031] In the context of this specification, the term "lignin" may refer to lignin originating from any suitable lignin source. In one embodiment, the lignin is essentially pure lignin. By the expression "essentially pure lignin" should be understood as at least 70 % pure lignin, or at least 90 % pure lignin, or at least 95 % pure lignin, or at least 98 % pure lignin. The essentially pure lignin may comprise at most 30 %, or at most 10 %, or at most 5 %, or at most 2 %, of other components and / or impurities. Extractives and carbohydrates such as hemicelluloses can be mentioned as examples of such other components. The lignin may contain less than 30 weight-%, or less than 10 weight-%, or less than 5 weight-%, or less than 3 weight-%, or less than 2.5 weight-%, or less than 2 weight-% of carbohydrates. The tannin may contain less than 20 weight-%, or less than 15 weight-%, or less than 10 weight-% of carbohydrates. The amount of carbohydrates present in lignin or tannin can be measured by high performance anion exchange chromatography with pulsed amperometric detector (HPAE- PAD) in accordance with standard SCAN-CM 71.

[0032] The ash percentage of lignin may be less than 7.5 weight-%, or less than 5 weight-%, or less than 3 weight-%, or less than 1.5 weight-%. The ash percentage of tannin may be less than 10 weight-%, or less than 5 weight-%, or less than 3 weight-%. The ash content can be determined in the following manner: Dry solid content of the sample is determined first in an oven at 105°C for 3h. Ceramic crucibles are pre-heated to 700 °C for 1 hour and weight after cooling. A sample (1.5 g - 2.5 g) is weighted into a ceramic crucible. The crucible with a lip is put into a cold oven. Temperature of the oven is raised: 20-200 °C, 30 min => 200-600 °C, 60 min => 600-700 °C, 60 min. Burning is continued without the lid at 700 °C for 60 min. The crucible is let to cool in desiccator and few drops of hydrogen peroxide (H2O2, 30 %) is added to the sample followed by burning in the oven at 700 °C for 30 minutes. If there are still dark spots in the ash, the hydrogen peroxide treatment and burning is repeated. The crucible is cooled down and weighted. All weigh-in is done with a precision of 0.1 mg and after cooling in a desiccator.

[0033] Calculation of the results

[0034] (b x c) a = weight of the ash, g b = weight of the sample, g c = dry solids of the sample, %

[0035] Ash content of a sample refers to the mass that remains of the sample after burning and annealing, and it is presented as percentage of the sample's dry content. In one embodiment, the lignin is technical lignin. In the context of this specification, the term "technical lignin" may refer to lignin that is derived from lignin in any biomass by any technical process. In one embodiment, technical lignin is lignin received from an industrial process.

[0036] The lignin used for preparing the binder composition may be selected from a group consisting of kraft lignin, steam explosion lignin, biorefinery lignin, supercritical separation lignin, hydrolysis lignin, flash precipitated lignin, biomass originating lignin, lignin from alkaline pulping process, lignin from soda process, lignin from organosolv pulping, lignin from alkali process, lignin from enzymatic hydrolysis process, and any combination thereof. In one embodiment, the lignin is wood based lignin. The lignin can originate from softwood, hardwood, annual plants or from any combination thereof.

[0037] By "kraft lignin" is to be understood in this specification, unless otherwise stated, lignin that originates from kraft black liquor. Black liquor is an alkaline aqueous solution of lignin residues, hemicellulose, and inorganic chemicals used in a kraft pulping process. The black liquor from the pulping process comprises components originating from different softwood and hardwood species in various proportions. Lignin can be separated from the black liquor by different, techniques including e.g. precipitation and filtration. Lignin usually begins precipitating at pH values below 11 - 12. Different pH values can be used in order to precipitate lignin fractions with different properties. These lignin fractions differ from each other by molecular weight distribution, e.g. Mw and Mn, polydispersity, hemicellulose and extractive contents. The molar mass of lignin precipitated at a higher pH value is higher than the molar mass of lignin precipitated at a lower pH value. Further, the molecular weight distribution of lignin fraction precipitated at a lower pH value i s wider than of l ignin fraction precipitated at a higher pH value . The precipitated lignin can be puri fied from inorganic impurities , hemicellulose and wood extractives using acidic washing steps . Further puri fication can be achieved by filtration .

[0038] The term " flash precipitated lignin" should be understood in this speci fication as lignin that has been precipitated from black liquor in a continuous process by decreasing the pH of a black liquor flow, under the influence of an over pressure of 200 - 1000 kPa, down to the precipitation level of lignin using a carbon dioxide based acidi fying agent , preferably carbon dioxide , and by suddenly releasing the pressure for precipitating lignin . The method for producing flash precipitated lignin is disclosed in patent application FI 20106073 . The residence time in the above method is under 300 s . The flash precipitated lignin particles , having a particle diameter of les s than 2 pm, form agglomerates , which can be separated from black liquor using e . g. filtration . The advantage of the flash precipitated lignin is its higher reactivity compared to normal kraft lignin . The flash precipitated lignin can be puri fied and / or activated i f needed for the further processing .

[0039] The l ignin may be derived from an alkal i process . The alkali process can begin with liquidi zing biomass with strong alkali followed by a neutrali zation process . After the alkali treatment , the l ignin can be precipitated in a similar manner as presented above .

[0040] The lignin may be derived from steam explosion . Steam explosion is a pulping and extraction technique that can be applied to wood and other fibrous organic material .

[0041] By "biorefinery lignin" is to be understood in this speci fication, unless otherwise stated, lignin that can be recovered from a refining facility or process where biomass is converted into fuel , chemicals and other materials .

[0042] By " supercritical separation lignin" is to be understood in this speci fication, unless otherwise stated, lignin that can be recovered from biomass using supercritical fluid separation or extraction technique . Supercritical conditions correspond to the temperature and pressure above the critical point for a given substance . In supercritical conditions , distinct liquid and gas phases do not exi st . Supercritical water or liquid extraction is a method of decomposing and converting biomass into cellulosic sugar by employing water or liquid under supercritical conditions . The water or liquid, acting as a solvent , extracts sugars from cellulose plant matter and lignin remains as a solid particle .

[0043] The lignin may be derived from a hydrolysis process . The lignin derived from the hydrolysis proces s can be recovered from paper-pulp or wood-chemical processes .

[0044] The lignin may originate from an organosolv process . Organosolv is a pulping technique that uses an organic solvent to solubili ze lignin and hemicellulose .

[0045] In one embodiment , the lignin consists of softwood Kraft lignin . In one embodiment , the lignin is softwood Kraft lignin . In one embodiment , the lignin is a combination of softwood lignin and hardwood lignin . In one embodiment , at most 30 weight-% , or at most 25 weight-% , or at most 10 weight-% , or at most 5 weight- % of the lignin originates from hardwood .

[0046] The lignin may also be lignin from an enzymatic hydrolysis process . Enzymatic hydrolysis is a process , wherein enzymes assist in cleaving bonds in molecules with the addition of elements of water . In one embodiment , the enzymatic hydrolysis comprises enzymatic hydrolysis of cellulose .

[0047] In one embodiment , the adhesive is an aqueous adhesive . The adhesive may be formed of a lignin-based binder composition combined with a calcium-containing hardener and water.

[0048] In addition to the lignin-based binder composition and the calcium-containing hardener, the adhesive may comprise further components. The adhesive may comprise water, extenders, additives, and / or catalysts. The adhesive may be prepared by combining and / or mixing the used components. Having combined the components the adhesive may be let to swell and stabilize before being used, while preventing that phase separation takes place. The temperature of the adhesive may be 10 - 40 °C, or 20 - 25 °C, when being applied on the veneers.

[0049] The viscosity of the adhesive may vary depending e.g. on the origin of the veneer or amount of lignin used for preparing the lignin-based binder composition. The viscosity of the adhesive may vary between 20 - 250 s when measured with a Ford cup 6 mm. In one embodiment, the viscosity of the adhesive may be 30 - 40 s when measured with a Ford cup 6 mm, when applies onto the veneers. In one embodiment, the viscosity of the adhesive may be 180 - 220 s when measured with a Ford cup 6 mm, when applies onto the veneers.

[0050] In one embodiment, the layered wood product fulfills the Exterior Weather resistant gluing requirements according to SFS EN 314-1 Plywood - Bonding class 3-non-covered exterior (2004) . This means that when a layered wood product fulfills this standard it is applicable for exterior use.

[0051] In one embodiment, the layered wood product is a plywood or a laminated veneer lumber (LVL) product.

[0052] Plywood is wood product that can be used for e.g. furniture and building material. LVL is suitable for use e.g. as beams, trusses, planks, and rafters. When cross-bonded for increased stiffness LVL can be used to form wall and floor panels with load-bearing capacity . The layered wood product may be formed of thin wood sheets, also called veneers, on to which the adhesive is applied on or spread. The thickness of the veneer can be varied. Typically, the thickness of wood veneer is below 3 mm. The veneers may then be subjected to e.g. cold pressing and / or hot pressing at a temperature of 120 - 170 °C to join the veneers together by the adhesive that is thus cured for forming the layered wood product.

[0053] The material of the veneer may vary. The veneer may be made of softwood and / or hardwood. The veneer may be selected from a group consisting of pine veneer, poplar veneer, beech veneer, spruce veneer, and birch veneer. In one embodiment, the veneer is spruce veneer or pine veneer. In one embodiment, the veneer is birch veneer. Thus, the veneer may be a wood veneer.

[0054] The layered wood product as disclosed in the current specification has the added utility of exhibiting a strong glue line as a result of the specific sulphur to calcium ratio provided thereto. The fact that the glue line comprises both sulphur and calcium in a specific ratio enables the production of layered wood product for different applications.

[0055] The layered wood product as disclosed in the current specification has the added utility of having an increased resistance to ignition and flame spread. This may be considered as a result of the combination of sulphur and calcium acting as a fire retardant in the glue line. Thus, the layered wood product has the added utility of being safer to use in e.g. construction applications, where safety is of high importance.

[0056] The synergistic effect of sulfur and calcium in adhesive has the added utility of enhancing mechanical properties by promoting cross-linking between the lignin-polymer chains and thus increasing the bonding strength of the adhesive.

[0057] The layered wood product as disclosed in the current specification has the further added utility of being a product with a lowered carbon footprint and thus being a more sustainable product than corresponding traditional layered wood products . The use an adhesive that is based on a lignin-based binder composition beneficially af fects these properties .

[0058] The use of non-mineral components during the production of the layered wood product has the added utility of helping in maintaining the circular saw blades used in the wood proces sing industry in a good shape .

[0059] EXAMPLES

[0060] Reference will now be made in detail to the described embodiments , examples of which are illustrated in the accompanying drawings .

[0061] The description below discloses some embodiments in such a detail that a person skilled in the art is able to utili ze the method based on the disclosure . Not all steps of the embodiments are discussed in detail , as many of the steps will be obvious for the person skilled in the art based on this speci fication .

[0062] EXAMPLE 1 - Producing layered wood products with di fferent adhesives

[0063] In this example di f ferent adhesives were prepared and used for producing plywood . Also two reference adhesives were prepared by using a phenol- formaldehyde binder composition that did not contain any sulphur .

[0064] The lignin-based binder compositions used in this example were prepared with varying the amount of lignin used . The lignin used was Kraft lignin . The lignin-based binder compositions were prepared by allowing the reactant components to polymeri ze . In addition to lignin, phenol was used as polymeri zable agent and formaldehyde as the crosslinking agent . Firstly, the lignin was dispersed in alkaline water . Thereafter phenol ( i f used) and formaldehyde were added . These were allowed to react and polymeri ze to form the lignin-based binder composition . The preparation of a lignin-based binder composition as such is known to the person skilled in the art .

[0065] The adhesives were prepared by mixing the used components together . The prepared lignin-based binder composition was put into a mixing j ar whereto the calcium-containing hardener was added followed by addition of water . These were then mixed for 10 - 20 minutes with a Diaf mixer device to ensure proper mixing . After the mixing, the adhesive was allowed to stand for 2 - 4 hours to obtain a desired viscosity . The prepared adhesives had a viscosity of 30 - 40 s measured with a Ford cup 6 mm . The exception was the adhes ive ( adhesive 4 ) , where no phenol was used, the viscosity of which was 200 s with Ford cup 6 mm .

[0066] The calcium-containing hardener used in these tests was a combination of calcium carbonate and wheat .

[0067] The reference adhesives were prepared following the above description .

[0068] The following adhesives were prepared and tested :

[0069] Composition of adhesive 1 (used for gluing birch veneers ) :

[0070] Lignin-based binder composition : 74 %

[0071] - lignin-phenol- formaldehyde ( 50 weight-% of the polymeri zable substance originated from lignin)

[0072] - the amount of lignin in binder composition : 13 %

[0073] Calcium-containing hardener : 13 %

[0074] Water : 14 % Properties of adhesive 1: amount of calcium-containing hardener 12 % amount of lignin 9.6 % amount of Ca 2 % amount of sulphur 0.17 % ratio of sulphur to calcium 0.10

[0075] Composition of adhesive 2 (used for gluing birch veneers) :

[0076] Lignin-based binder composition: 74 %

[0077] - lignin-phenol-formaldehyde (65 weight-% of the polymerizable substance originated from lignin)

[0078] - the amount of lignin in binder composition : 17 %

[0079] Calcium-containing hardener: 15 %

[0080] Water: 11 %

[0081] Properties of adhesive 2: amount of calcium-containing hardener 14 % amount of lignin 12.6 % amount of Ca 2 % amount of sulphur 0.22 % ratio of sulphur to calcium 0.11

[0082] Composition of adhesive 3 (used for gluing birch veneers) :

[0083] Lignin-based binder composition: 85 %

[0084] - lignin-phenol-formaldehyde (80 weight-% of the polymerizable substance originated from lignin)

[0085] - the amount of lignin in binder composition: 20.6 %

[0086] Calcium-containing hardener: 7 %

[0087] Water : 8 % Properties of adhesive 3: amount of calcium-containing hardener 7 % amount of lignin 17.6 % amount of Ca 1 % amount of sulphur 0.30 % ratio of sulphur to calcium 0.33

[0088] Composition of adhesive 4 (used for gluing birch veneers) :

[0089] Lignin-based binder composition: 91 % lignin-formaldehyde (100 weight-% of the polymerizable substance originated from lignin)

[0090] - the amount of lignin in binder composition: 21 %

[0091] Calcium-containing hardener: 3.8 %

[0092] Water : 5.6 %

[0093] Properties of adhesive 4: amount of calcium-containing hardener 1 % amount of lignin 19 % amount of Ca 0.15 % amount of sulphur 0.33 % ratio of sulphur to calcium 2.18

[0094] Composition of adhesive 5 (used for gluing spruce veneers) :

[0095] Lignin-based binder composition: 79 %

[0096] - lignin-phenol-formaldehyde (50 weight-% of the polymerizable substance originated from lignin)

[0097] - the amount of lignin in binder composition: 14 %

[0098] Calcium-containing hardener: 13 % Water : 8

[0099] Properties of adhesive 5: amount of calcium-containing hardener 12 % amount of lignin 11% amount of Ca 3 % amount of sulphur 0.19 % ratio of sulphur to calcium 0.07

[0100] Composition of adhesive 6 (used for gluing spruce veneers) :

[0101] Lignin-based binder composition: 78 %

[0102] - lignin-phenol-formaldehyde (65 weight-% of the polymerizable substance originated from lignin)

[0103] - the amount of lignin in binder composition: 18.6 %

[0104] Calcium-containing hardener: 14 %

[0105] Water: 8 %

[0106] Properties of adhesive 6: amount of calcium-containing hardener 14 % amount of lignin 14.5 % amount of Ca 3 % amount of sulphur 0.25 % ratio of sulphur to calcium 0.08

[0107] Composition of adhesive 7 :

[0108] Lignin-based binder composition: 70 %

[0109] - lignin-phenol-formaldehyde (50 weight-% of the polymerizable substance originated from lignin)

[0110] - the amount of lignin in binder composition: 13 %

[0111] Calcium-containing hardener: 25 % Water :

[0112] Properties of adhesive 7 : amount of calcium-containing hardener 18 % amount of lignin 9 % amount of Ca 7 % amount of sulphur 0.16 % ratio of sulphur to calcium 0.021

[0113] Composition of adhesive 8:

[0114] Lignin-based binder composition: 83 %

[0115] - lignin-phenol-formaldehyde (50 weight-% of the polymerizable substance originated from lignin)

[0116] - the amount of lignin in binder composition: 13 %

[0117] Calcium-containing hardener: 13 %

[0118] Water: 4 %

[0119] Properties of adhesive 8: amount of calcium-containing hardener 13 % amount of lignin 11 % amount of Ca 3 % amount of sulphur 0.19 % ratio of sulphur to calcium 0.07

[0120] Composition of adhesive 9:

[0121] Lignin-based binder composition: 84 %

[0122] - lignin-phenol-formaldehyde (65 weight-% of the polymerizable substance originated from lignin)

[0123] - the amount of lignin in binder composition: 17 %

[0124] Calcium-containing hardener: 13 %

[0125] Water : 3 % Properties of adhesive 9 : amount of calcium-containing hardener 13 % amount of lignin 14 % amount of Ca 3 % amount of sulphur 0 . 25 % ratio of sulphur to calcium 0 . 09

[0126] Composition of reference adhesive 1 (used for gluing birch veneers ) :

[0127] Phenol- formaldehyde binder composition : 65 %

[0128] Calcium-containing hardener : 15 %

[0129] Water : 20 %

[0130] Properties of reference adhesive 1 : amount of calcium-containing hardener 15 % amount of lignin 0 % amount of Ca 2 % amount of sulphur 0 % ratio of sulphur to calcium 0

[0131] Composition of reference adhesive 2 (used for gluing spruce veneers ) : Phenol- formaldehyde binder composition : 70 %

[0132] Calcium-containing hardener : 15 %

[0133] Water : 15 % Properties of reference adhesive 2 : amount of calcium-containing hardener 14 % amount of lignin 0 % amount of Ca 2 % amount of sulphur 0 % ratio of sulphur to calcium 0 The above prepared adhesives 1 - 6 and reference adhesives 1 and 2 were used to form plywood by spreading the adhesive on veneers , which were then subj ected to hot pressing at a temperature of about 130 - 150 °C, depending on the veneer type , to j oin the veneers together by the adhesive that is thus cured for forming the plywood . The veneers used were made of either birch or spruce .

[0134] The properties of formed plywood were then analyzed and especially the sulphur and calcium content of their glue lines were analyzed by as disclosed in the current speci fication . Five samples were prepared for each adhesive and the average result was calculated . The results are presented in the below table 1 :

[0135] Table 1 : Amount of sulphur and calcium in glue line

[0136] From table 1 on can see that with the applied adhesives 1 - 6 one was able to form layered wood products , the glue lines of which contained the ratio of sulphur to calcium, and that therefore have properties making the layered wood products usable in further applications . EXAMPLE 2 - Ef fect of ratio of sulphur to calcium in the glue line on the bonding strength of the glue line

[0137] In this example it was tested whether plywood panels prepared with the above adhesives ful filled the standard "The Exterior Weather resistant gluing requirements according to SFS EN 314- 1 Plywood - Bonding class 3-non-covered exterior ( 2004 ) " . The plywood were prepared of either birch veneers or spruce veneers .

[0138] The formed plywood were tested according to above standard SFS EN 314- 1 , with soaking taking place for 24 h in water at 2013 ° C, followed by immersion for 4 h in boiling water, then drying in a ventilated drying oven for 16-20 h at 6013 ° C, followed by immersion in boiling water for 4 h, fol lowed by cool ing in water at 2013 ° C for at least 1 h .

[0139] The results are presented in table 2 and table 3 below .

[0140] Table 2 . Results from testing in accordance with stand- ard SFS EN 314 -1 for birch plywood

[0141] Table 3 . Results from testing in accordance with stand- ard EN 314 -1 for spruce plywood

[0142] From the results it could be concluded the tested plywood exhibited as good values as the references both in shear strength (N / mm2) values and wood failure ( % ) . This means that when a layered wood product ful fills this standard it is applicable for exterior use .

[0143] It is obvious to a person skil led in the art that with the advancement of technology, the basic idea may be implemented in various ways . The embodiments are thus not limited to the examples described above ; in- stead they may vary within the scope of the claims .

[0144] The embodiments described hereinbefore may be used in any combination with each other . Several of the embodiments may be combined together to form a further embodiment . A layered wood product as disclosed herein, may comprise at least one of the embodiments described hereinbefore. It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The em- bodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item refers to one or more of those items. The term "compris- ing" is used in this specification to mean including the feature (s) or act(s) followed thereafter, without excluding the presence of one or more additional features or acts.

Claims

CLAIMS1. A layered wood product, wherein the layered wood product comprises at least two veneers that are glued together with an adhesive forming a glue line, and wherein :- the adhesive is formed of a lignin-based binder composition combined with a calcium-containing hardener, and wherein the adhesive comprises calcium in a total amount of 0.01 - 20 weight-% based on the total wet weight of the adhesive; and- the glue line comprises calcium and sulphur, wherein the ratio of sulphur to calcium in the glue line is 0.05 - 1.5.

2. The layered wood product of claim 1, wherein the glue line comprises calcium in an amount of 1 - 75 weight-%, or 5 - 60 weight-%, or 7.5 - 55 weight-%.

3. The layered wood product of any one of the preceding claims, wherein the glue line comprises sulphur in an amount of 1 - 20 weight-%, or 3 - 18 weight- % , or 5 - 16 weight-%.

4. The layered wood product of any one of the preceding claims, wherein the ratio of sulphur to calcium in the glue line is 0.05 - 1 or 0.06 - 1.3, or 0.075 - 1.5 or 0.10 - 1.

5. The layered wood product of any one of the preceding claims, wherein the adhesive comprises calcium in a total amount of 0.03 - 18 weight-%, or 0.05 - 15 weight-%, or 0.1 - 10 weight-%, or 0.15 - 7 weight-%, based on the total wet weight of the adhesive.

6. The layered wood product of any one of the preceding claims, wherein the adhesive comprises ligninbased binder composition in a total amount of 50 - 99.99 weight-%, or 55 - 99.5 weight-%, or 60 - 99 weight-%, or 65 - 97 weight-%, based on the total wet weight of the adhesive.

7. The layered wood product of any one of the preceding claims, wherein the adhesive comprisescalcium-containing hardener in a total amount of 0.01 - 50 weight-%, or 0.5 - 45 weight-%, or 1 - 40 weight-%, or 3 - 35 weight-%, or 5 - 30 weight-%, based on the total wet weight of the adhesive.

8. The layered wood product of any one of the preceding claims, wherein the adhesive is an aqueous adhesive .

9. The layered wood product of any one of the preceding claims, wherein the lignin-based binder composition is prepared by polymerizing at least polymerizable substance and crosslinking agent, wherein 50 - 100 weight-%, 60 - 99 weight-%, or 70 - 97 weight-%, or 80 - 95 weight-%, or 85 - 93 weight-%, or 87 - 91 weight- % , of the polymerizable substance originates from lignin .

10. The layered wood product of any one of the preceding claims, wherein the layered wood product fulfills the Exterior Weather resistant gluing requirements according to SFS EN 314-1 Plywood - Bonding class 3- non-covered exterior (2004) .

11. The layered wood product of any one of the preceding claims, wherein the layered wood product is a plywood or a laminated veneer lumber product.

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