HYBRID RESIN PARTICLE-BOARD

TECHNICAL FIELD

The present invention relates to the field of adhesive systems comprising a hybrid resin. The present invention further relates to a particle board based on wood waste and bonded by a hybrid resin, and methods for manufacture of a particle board bonded by a hybrid resin.

TECHNICAL BACKGROUND

Efforts have been made to mix diphenylmethane-diisocyanate (PMDI) with other adhesives, such as urea formaldehyde adhesive (UF), melamine urea formaldehyde adhesive (MUF), and phenol formaldehyde adhesive (PF).

However, there is a need for cheaper and more enviromentally friendly adhesives and also it is interesting to be able to reuse waste material for the manufacture of particle boards.

SUMMARY OF THE INVENTION

An objective of the present invention is to create a hybrid adhesive for the manufacturing of particle boards (PB) as a new adhesive system which consist of both tannin formaldehyde resin (TF-resin) as a cheap natural adhesive and polymeric diphenylmethane-diisocyanate (PMDI), which is a costly fossil adhesive. Thus, the combination of TF-resin and PMDI in an adhesive would thereby help to alleviate some of the problems mentioned above.

Another objective of the present invention is to manufacture three layered particle board based on wood waste material and bonded by a combination of tannin formaldehyde resin (TF-resin) and polymeric diphenylmethane-diisocyanate (PMDI) forming a hybrid adhesive, which complies with the specifications of European standard EN 312 (2010) and fulfilled the requirement for interior fitments (including furniture) for use in dry conditions (Type P2).

In a first aspect the present invention relates to an adhesive system comprising a hybrid resin, wherein the hybrid resin comprises tannin- formaldehyde resin (TF-resin) and polymers based on diphenylmethane- diisocyanate (PMDI) in a ratio of 25%-40% TF-resin:60%-75% PMDI.

In one embodiment the present invention relates to an adhesive system, wherein the hybrid resin comprises essentially 25% or 30% or 40% tannin-formaldehyde resin and 75% or 70% or 60% polymers based on diphenylmethane-diisocyanate (PMDI).

In one embodiment the present invention relates to an adhesive system, wherein the tannin-formaldehyde resin is a water emulsion

comprising tannin and formaldehyde in 3-5 weight % of the amount of tannin.

In one embodiment the tannin-formaldehyde resin further comprises NaOFI, 2 weight % of the amount of tannin. In one embodiment the present invention relates to an adhesive system, wherein the tannin-formaldehyde resin is a water emulsion comprising 45 weight % tannin and formaldehyde, as a saturated water solution with concentration 37% by weight, 5 weight % of the amount of tannin. In one embodiment the tannin-formaldehyde resin is a water emulsion comprising 45 weight % tannin and formaldehyde 5 weight % of the amount of tannin and NaOFI, 2 weight % of the amount of tannin.

Sodium hydroxide is added because the TF-resin is an effective adhesive in the alkaline medium. Further, the concentration of the resin emulsion is optimized for the application on to wood particles as it makes spraying of the emulsion onto wood particles possible. If the resin emulsion is too

concentrated it will be a viscose solution and it is not possible to spray the resin onto wood particles. On the other hand, if the emulsion is too dilute there will be too much water added to the wood particles and thus the formation of particle board requires longer press times, which is not desirable in the manufacturing industry.

In one embodiment the present invention relates to an adhesive system, wherein the tannin-formaldehyde resin (TF-resin) comprises quebracho tannin. There are two types of tannin, hydrolysable tannin and non-hydrolysable tannin, i.e. condensable tannin. Only non-hydrolysable tannin such as quebracho tannin has the ability to interact with formaldehyde to form an adhesive while the hydrolysable tannin negatively affects the gluing process by particle board manufacturing. The present invention manages to decrease the amount of formaldehyde in an adhesive system suitable for particle boards, which is promising in view of the effect of formaldehyde on the health of the environment.

In yet another embodiment the present invention relates to an adhesive system, wherein the hybrid resin comprises 10 % - 40 % TF-resin and 60 % - 90 % PMDI, preferably 15 % - 35 % TF-resin and 65 % - 85 % PMDI, preferably 20 % - 30 % TF-resin and 70 % - 80 % PMDI, preferably 23 % - 27 % TF-resin and 73 % - 77 % PMDI.

In yet another embodiment the present invention relates to an adhesive system comprising a hybrid resin, wherein the hybrid resin comprising a combination of 25%-40% tannin-formaldehyde resin (TF-resin) and 60%-75% polymers based on diphenylmethane-diisocyanate (PMDI), wherein tannin- formaldehyde resin is a water emulsion which comprises 45 weight % tannin, preferably quebracho tannin, formaldehyde as a saturated water solution with concentration 37% by weight, 5 weight % of the amount of tannin and NaOFI 2 weight % of the amount of tannin.

In yet another embodiment the present invention relates to an adhesive system, wherein the hybrid resin comprises essentially 25 % quebracho TF- resin and 75 % PMDI, wherein quebracho tannin-formaldehyde resin is a water emulsion comprising 45 weight % quebracho tannin, formaldehyde (solution concentration 37%) 5 weight % of the amount of quebracho tannin and NaOFI 2 weight % of the amount of quebracho tannin.

In a second aspect the present invention relates to a particle board comprising wood particles and an adhesive system according to the present invention.

In one embodiment the present invention relates to a particle board comprising wood particles and an adhesive system wherein the adhesive system comprises a hybrid resin of tannin-formaldehyde resin (TF-resin) and polymers based on diphenylmethane-diisocyanate (PMDI).

In yet another embodiment the present invention relates to a particle board comprising wood particles and a hybrid resin wherein the hybrid resin comprises a combination of 25%-40% tannin-formaldehyde resin (TF-resin) and 60%-75% polymers based on diphenylmethane-diisocyanate (PMDI), wherein tannin-formaldehyde resin is an emulsion comprising 45% tannin preferably quebracho tannin, formaldehyde (solution concentration 37%) 5% of the amount of tannin and NaOFI 2% of the amount of tannin.

In yet another embodiment the present invention relates to a particle board comprising wood particles and a hybrid resin wherein the hybrid resin comprises a combination of 25%-40% quebracho tannin-formaldehyde resin (TF-resin) and 60%-75% polymers based on diphenylmethane-diisocyanate (PMDI), wherein quebracho tannin-formaldehyde resin is an emulsion comprising 45% tannin preferably quebracho tannin, formaldehyde (solution concentration 37%) 5% of the amount of tannin and NaOFI 2% of the amount of tannin.

In yet another embodiment the present invention relates to a particle board, wherein the hybrid resin comprises essentially 25 % TF-resin and 75 % PMDI.

In one embodiment the particle board according to the present invention is comprising at least one layer. In one embodiment the particle board according to the present invention is comprising one core layer and two surface layers. In one embodiment the particle board is a three-layer particle board.

In one embodiment the wood particles of the present invention have a particulate size in the range of 1.0-4.0 mm in the core layer and 0.2-1.0 mm in the surface layers.

In yet another embodiment the present invention relates to a particle board, further comprising a core layer and at least one surface layer comprising wood particles and a hybrid resin.

In yet another embodiment the present invention relates to a particle board, wherein the wood particles have a particulate size in the range of 0.2- 4.0 mm. In one embodiment the wood particles have a particulate size > 0,2 < 1 ,0 mm in the surface layers and > 1 ,0 < 4,0 mm in the core layer.

In one embodiment the present invention relates to a particle board, wherein the adhesive system comprises a hybrid resin content of 0.5-3.5 weight %, typically, 2-3 weight %, typically 3 weight % in the core layer and 1 - 5 weight %, typically 3-4 weight %, typically 4 weight % in the surface layers, relative to the wood particles, typically dry wood particles, typically oven-dried wood particles.

In one embodiment the TF-PMDI hybrid resin content in the particle board may be in the range of 0.5-4.5 weight % relative to the wood particles, typically 3-4 weight %. In one embodiment the particles are dry wood particles, typically oven-dried wood particles. In one embodiment the hybrid resin content in the core layer and the surface layers, is typically 3 weight % of said core layer and 4 weight % of said surface layers, relative to the wood particles, typically oven-dried wood particles.

In one embodiment the hybrid resin content in the particle board is in the range of 3-4 weight %, relative to oven-dried wood particles.

In yet another embodiment the present invention relates to a particle board, wherein the wood particles have a particulate size > 0,2 < 1 ,0 mm in the surface layers and > 1 ,0 < 4,0 mm in the core layer, wherein the surface layers constitute 30-50 %, typically 40 %, of the mass of the board and the core layer constitutes 50-70 %, typically 60 %, of the mass of the board.

In yet another embodiment the present invention relates to a particle board, wherein the hybrid resin content in the core layer and the surface layers is 2-3 weight %, typically 3 weight % of said core layer and 3-4 weight %, typically 4 weight % of said surface layers, relative to wood particles, typically oven-dried wood particles.

In one embodiment the hybrid resin content is 2-3 weight % of the core layer, relative to wood particles, typically oven-dried wood particles. In one further embodiment the hybrid resin content is 3 weight % of the core layer, relative to wood particles, typically oven-dried wood particles.

Further, in one embodiment the hybrid resin content is 3-4 weight % of the surface layers, relative to wood particles, typically oven-dried wood particles. In one further embodiment the hybrid resin content is 4 weight % of the surface layers, relative to wood particles, typically oven-dried wood particles.

In one embodiment the hybrid resin content in the board is based on a resin content (PMDI) of pure PMDI-bonded particle board.

In yet another embodiment the present invention relates to a particle board, wherein the particle board has an internal bond strength of 0.53 N/mm ² and/or a static bending strength of 13.6 N/mm ²

In yet another embodiment the present invention relates to a particle board, wherein the particle board has an internal bond strength of 0.53 N/mm ² .

In yet another embodiment the present invention relates to a particle board, wherein the particle board has a static bending strength of 13.6 N/mm ² .

In yet another embodiment the present invention relates to a particle board, wherein the particle board has a modulus of elasticity of 2360 N/mm ² .

In yet another embodiment the present invention relates to a particle board, wherein the particle board has a moisture content of 9.4 %.

In yet another embodiment the present invention relates to a particle board, wherein the particle board has a water absorption after 2 h and 24 h, of 9.3 % and 27.7 %, respectively.

In one embodiment the particle board has a water absorption after 2 h of 9.3 %.

Further, in another embodiment the particle board has a water absorption after 24 h of 27.7 %.

In yet another embodiment the present invention relates to a particle board, wherein the particle board has a thickness swelling after 2 h and 24 h, of 0.3 % and 6.8 %, respectively.

In one embodiment the particle board has a thickness swelling after 2 h of 0.3 %.

Further, in another embodiment the particle board has a thickness swelling after 24 h of 6.8 %. This value is better than the standard value for particle board type P4 listed in the EN312. In yet another embodiment the present invention relates to a particle board, wherein the particle board has an extractable content of formaldehyde of 1.9 mg/100 g oven-dried board.

Further, the invention also relates to a particle board, comprising physical- and mechanical properties as well as extractable formaldehyde compliant with the specifications of European standard EN 312 (2010).

In another embodiment the present invention relates to a particle board, wherein the wood particles are from massive wood, typically from untreated wood waste. In yet another embodiment the wood particles of the present invention may be from untreated wood waste (Type Al) which may be issued from clean, unpainted wood waste for example packaging and pallets made of massive wood, wherein the wood particles may be wood chips, flake, sawdust, shaving, sliver, strand, wafer. In one embodiment the wood particles may be wood chips. Since the burning of wood waste contributes to

accumulation of organic carbon and thus to mitigation of greenhouse gases, an advantage with using the wood waste for the manufacturing of particle boards instead would contribute to the decrease of the greenhouse effect.

In yet another embodiment the present invention relates to a particle board, wherein the particle board is selected from the group consisting of board, furniture, interior fitments, construction materials.

In yet another embodiment the present invention relates to a particle board, wherein the particle board fulfills the requirement for interior fitments, including furniture, for use in dry conditions, Type P2-conditions.

In a third aspect the present invention relates to a method for manufacturing of a particle board, wherein the method comprises the steps of:

A. Providing wood particles;

B. Mixing wood particles of step A with tannin-formaldehyde resin (TF-resin) and PMDI separately and consecutively, wherein the tannin-formaldehyde resin (TF-resin) is a water emulsion comprising tannin and formaldehyde 3-5 weight % of the amount of tannin; C. Pressing the mixture of step B, typically by hot pressing, wherein the press temperature is between 180-200 °C.

In one embodiment the present invention relates to a method, wherein the tannin-formaldehyde resin (TF-resin) in step B further comprises NaOH,

2 weight % of the amount of tannin.

In one embodiment the method comprises the steps of:

A. Providing oven-dried wood particles;

B. Mixing wood particles of step A with tannin-formaldehyde resin (TF-resin) and PMDI separately and consecutively, wherein the tannin-formaldehyde resin (TF-resin) is a water emulsion comprising 45 weight % tannin and formaldehyde 5 weight % of the amount of tannin and NaOFI, 2 weight % of the amount of tannin;

C. Pressing the mixture of step B, by hot pressing,

wherein the press temperature is between 180-200 °C.

In one embodiment the present invention relates to a method for manufacturing of a particle board using a hybrid resin of the present invention.

In one embodiment the present invention relates to a method, wherein the method step B, the tannin-formaldehyde resin (TF-resin) is provided first to the wood particles as an emulsion and immediately afterwards, the PMDI is provided to the particles.

In one embodiment the present invention relates to a method, wherein the tannin-formaldehyde resin (TF-resin) is provided by spraying the emulsion onto the wood particles and immediately afterwards, the PMDI is provided by spraying to the particles.

In one embodiment the present invention relates to a method, wherein the method step C is performed at a press time factor 8-10 seconds per millimeter (s/mm). Any factor which contributes to reducing press time is vitally important in particle board economics.

In a further embodiment the present invention relates to a method for manufacturing of a hybrid resin-bonded three layered particle board comprising the steps of: A. Providing wood particles;

B. Mixing wood particles of step A with a hybrid resin comprising TF-resin and PMDI;

C. Pressing the mixture of step B, typically by hot pressing.

In one embodiment the wood particles may have a moisture content of

2-5 %. In one embodiment the wood particles may be oven-dried wood particles. In one embodiment the formaldehyde resin (TF-resin) and PMDI are added separately and consecutively to the wood particles. In one embodiment the tannin-formaldehyde resin (TF-resin) is provided first to the wood particles as an emulsion and immediately afterwards, the PMDI is provided to the particles. The reason for this order of addition is that tannin-formaldehyde resin (TF-resin) and PMDI cannot blended with each other because they will react quickly and become solid, or coagulated, and block pipes and spray devices so they cannot be sprayed on the wood particle. Further, the wettability and penetrability of PMDI in the wood particle is greater than the penetrability of TF-resin. Flence, if PMDI would be provided to the wood particles first, it will penetrate the wood particles and inhibit the penetration of TF-resin. Moreover, by adding PMDI after the addition of TF-resin, preferably by spraying, also gives the best result as it loses its effectiveness quickly after the addition and will thus not provide for a sufficient adhesive system.

Another embodiment of the present invention relates to a method for manufacturing of a combination of TF-resin: PMDI-bonded three layered particle board comprising the steps of:

A. Providing oven-dried wood particles;

B. Mixing wood particles of step A with TF-resin and PMDI;

C. Pressing the mixture of step B, typically by hot pressing.

In one embodiment the present invention relates to a method for manufacturing of a combination of quebracho TF-resin: PMDI-bonded three layered particle board comprising the steps of:

A. Providing oven-dried wood particles with a moisture content of

2-5%;

B. Mixing wood particles of step A with quebracho tannin- formaldehyde resin (TF-resin) and PMDI separately and consecutively, wherein the quebracho TF-resin is fed first to the wood particles as an emulsion and immediately afterwards, the PMDI is fed to the particles;

C. Pressing the mixture of step B, by hot pressing,

wherein the press temperature is 180-200 °C and optionally the press time factor 8-10 seconds per millimeter (s/mm).

In one embodiment the invention relates to a method, wherein the wood particles are weighted to obtain a target final bulk density of 620 kg/m ³ and thickness of 19 mm.

In one embodiment the invention relates to a method, wherein the oven-dried untreated wood waste particles are weighted to obtain a target final bulk density of 620 kg/m ³ and thickness of 19 mm.

In yet another embodiment the invention relates to a method, further comprising that the TF-resin is fed to the wood particles as an emulsion.

In one embodiment the invention relates to a method, wherein the emulsion comprises TF-resin based on a tannin content of 45 weight % and small amount of formaldehyde with a concentation of 37 weight % in aqueous solution.

In one embodiment the invention relates to a method, further comprising that the TF-resin is fed to the wood particles as an emulsion and immediately afterwards, the PMDI is fed to the particles.

In one embodiment the invention relates to a method, wherein the emulsion comprises TF-resin based on a tannin content of 45 weight %, preferably quebracho tannin, and formaldehyde (solution concentration 37%) 5 weight % of the amount of tannin.

In yet another embodiment the invention relates to a method, wherein the emulsion comprises essentially tannin, formaldehyde, 5 weight % of the amount of tannin and NaOFI, 2 weight % of the amount of tannin.

In one embodiment the invention relates to a method, wherein the emulsion comprises essentially quebracho tannin, formaldehyde, 5 weight % of the amount of tannin and NaOFI, 2 weight % of the amount of tannin. In another aspect the present invention relates to an adhesive system for manufacture of a particle board based on wood particles, wherein the adhesive system is based on a hybrid resin comprising a combination of tannin-formaldehyde resin (TF-resin) and polymers based on

diphenylmethane-diisocyanate (PMDI). The wood particles may be wood waste particles, typically wood particles from untreated massive wood waste.

In yet another aspect the present invention relates to a method for manufacturing of a particle board, comprising wood particles and an adhesive system comprising a combination of tannin-formaldehyde resin (TF-resin) and polymers based on diphenylmethane-diisocyanate (PMDI), wherein the method comprises the steps of:

A. Providing oven-dried wood particles;

B. Mixing wood particles of step A with TF-resin and PMDI in

consecutive order;

C. Pressing the mixture of step B, typically by hot pressing.

In yet another aspect the present invention relates to a particle board, for use in dry conditions, typically P2-type conditions.

In one embodiment the present invention relates to a particle board, for use in interior fitments including furniture, wall, ceiling, and floor.

In another aspect the present invention relates to the use of the adhesive system according to the present invention for the manufacture of a particle board.

In one embodiment of the present invention relates to the use of the adhesive system for the manufacture of a particle board for use in dry conditions, typically P2-type conditions.

In yet another embodiment of the present invention relates to the use of the adhesive system for the manufacture of a particle board for interior fitments, such as furniture, wall, ceiling. In a further aspect of the present invention the three-layer particle board bonded by a combination of quebracho tannin-formaldehyde resin (TF- resin) and PMDI has not only comparable bonding properties to those of pure PMDI-bonded particle board and of pure TF-bonded particle board but also superior in some properties, which can be attributed to the interaction between quebracho tannin-formaldehyde resin (TF-resin) and PMDI during the hot pressing by 200 °C.

An advantage of the present invention may be that the replacement of diphenylmethane-diisocyanate (PMDI) as a costly fossil adhesive with 25%- 40% tannin-formaldehyde resin (TF-resin) as a cheap natural adhesive which is economical and environmentally friendly.

In yet another aspect of the present invention relates to a wood-based board obtainable by a method according to the present invention, comprising wood particles and an adhesive system comprising a hybrid resin wherein the hybrid resin comprises a combination of 25%-40% tannin-formaldehyde resin (TF-resin) and 60%-75% polymers based on diphenylmethane-diisocyanate (PMDI), wherein quebracho tannin-formaldehyde resin is an emulsion comprising 45% tannin, typically quebracho tannin, formaldehyde (solution concentration 37%) 5% of the amount of tannin and NaOFI 2% of the amount of tannin.

Further, the present invention relates to a particle board manufactured by a method according to the present invention, wherein the particle board has specifications that complies with the specifications of the European standard EN 312 (2010) and fulfills the requirements for interior fitments, including furniture, for use in dry conditions (Type P2).

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an environmentally friendly particle boards comprising innovative adhesive systems. Additionally, although individual features may be included in different embodiments, these may possibly be combined in other ways, and the inclusion in different embodiments does not imply that a combination of features is not feasible. In addition, singular references do not exclude a plurality.

In the context of the present invention, the terms "a", "an" does not preclude a plurality. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.

The term“particle board” or“particleboard”, as defined in“the

European Standard BS EN 309 Particle boards; Definition and classification”, is a panel material manufactured under pressure and heat from particles of wood, such as wood flakes, chips, shavings, sawdust and similar and/or other lignocellulosic material in particle form, with the addition of a polymeric adhesive. Particle board is made from wood and is traditionally known as wood chipboard.

Particle board manufactured in Europe and used in construction must be specified in accordance with BS EN 312, which contains the requirements for the following seven grades (technical classes):

• P1 : general purpose boards for use in dry conditions

• P2: boards for interior fitments (including furniture) for use in dry conditions.

• P3: non load-bearing boards for use in humid conditions

• P4: load-bearing boards for use in dry conditions

• P5: load-bearing boards for use in humid conditions

• P6: heavy duty load-bearing boards for use in dry conditions

• P7: heavy duty load-bearing boards for use in humid conditions.

Selection of a grade of panel is dependent upon the ambient climatic conditions together with the level of loading that is anticipated.

The term“dry conditions” means conditions corresponding to service class 1 of EN 1995-1 -1 :2004 which is characterised by moisture content in the material corresponding to a temperature of 20 °C and relative humidity of the surrounding air only exceeding 65% for a few weeks per year.

The term“oven-dried” (o. d.) means drying in a drying cabinet at 75 °C to reach a moisture content of the wood particles, adhesive system or the particle board of up to 5 %, typically the moisture content of the wood particles are about 2-5 %.

The term“emulsion” and“water emulssion” is herein to also include aqueous solution or mixture.

The term“untreated wood waste” or“Type Al”, is wood issued from clean, unpainted wood waste such as packaging and Pallets made of massive wood.

The term“hot pressing” means that the formed wood mat is pressed in a laboratory hot-press such as a Siempelkamp Hydr. Lab. Press A 308/1988, to the target thickness of 19 mm, preferably at press temperature 200 °C and press time factor 10 seconds/mm, wherein the press time factor is the time required for pressing the glued wood particles mat to the required thickness of the particle board and estimated per second per millimeter of the thickness.

The term“PMDI-bonded particle board” refers to particle board variant no. 1 , table 2, column 2.

The term“TF-bonded particle board” refers to particle board variant no. 2, table 2, column 3.

The term“PMDI- and TF-combination” refers to particle board variant no. 3, table 2, column 4.

Quebracho tannin is tannin that may be extracted from wood of the quebracho trees ( Schinopsis spp.), that grow in South America.

Examples

By way of examples, and not limitation, the following examples identify a variety of adhesive systems comprising hybrid resins and particle boards bonded by hybrid resins pursuant to embodiments of the present invention.

Preparation of Particles:

Wood particles produced from clean unpainted wood wastes by NSR- company were chipped by using a knife ring flaker; Moduls System ø 60 cm. The produced particles were sorted into two fractions; wood particles fraction with a particle size suitable for the core layer (CL) were separated from the wood particle fraction with a particle size suitable for the surface layers (SL) using Tumbler-sift machine; ALLGAIER. Board manufacturing:

Medium density, three-layered particle boards were produced by using different adhesives (PMDI, TF-resin, combination of TF-resin and PMDI). The information about the different adhesives used are listed in Table 1. Wood particles of SL and CL were dried at a temperature of 75 °C by using drying cabinet to reach approximately 2 % moisture content. Particles were weighted to obtain the target final bulk density of 620 kg/m ³ and thickness of 19 mm.

Tab. 1 : The information about the used adhesives: PMDI, TF-resin, TF-resin and PMDI.

The TF-resin may for example be achieved by preparing a 100 g water solution by mixing 45 g of tannin, 2.25 g formaldehyde and 0.9 g with water added up to 100 g.

For particle board production wood particles were treated with different adhesives in a laboratory scale blender, see defined production parameters in table 2. Further, the resinated material was transferred immediately into a frame with dimension 750 x 500 mm on a metal plate and pre-pressed by hands. In a next step, the frame was removed and the pre-pressed mat was hot pressed in a laboratory hot-press (Siempelkamp Hydr. Lab. Press A 308/1988). The pressed particle boards were then trimmed (700 mm x 450 mm) to avoid edge effects and sanded (grain size 60) to boards within 18 mm thickness by using a wide belt sanding machine (Felder type FW 950 C). After a conditioning phase of 4 weeks at 65±5 % relative humidity and 20 °C to reach equilibrium moisture content the boards were cut into various sizes for testing according to the used standards. For each particle board variant three boards were manufactured. Table 3 demonstrates the production parameters of the particle boards.

Tab. 2: Defined parameters of particle board manufacturing based on wood

¹ Material supplied by NSR

² Ratio PMDI: TF-resin based on SL/CL resin content of PB Variant No. 1 PMDI-bonded Particle board (PMDI-bonded PB).

³ % solid content based on oven-dried weight of the wood particles

4 % solids resin / oven-dried particles

⁵ Sasol Hydro Wax 730 batch 63845.

Determination of the physical- and mechanical properties of

manufactured variants of particle boards according to European Norms (EN: 2010).

Mechanical properties:

Static bending strength test, internal bond (IB) and modulus of elasticity (MOE) were determined according to the European standards method (EN: 2010) [Static bending strength test (EN 310) and internal bond (EN 319)].

Internal bond strength (IB):

The average values and variation coefficient of IB strength, static bending strength and MOE of the particle board variants are shown in table 3. The results in table 3 demonstrate that three-layered particle boards bonded by a TF-PMDI hybrid resin (variant no. 3) have achieved the highest internal bond strength values with 0.53 N/mm ² followed by only PMDI bonded particle boards (variant no. 1 ) with IB values of 0.49 N/mm ² . The use of TF-resin (variant no. 2) for particle board production lead to the lowest IB values with 0.27 N/mm ² . Furthermore, the table demonstrates that the particle board variants no. 1 and no. 3 do always achieve the required value of 0.35 N/mm ² for particle boards type P2 for interior fitments (including furniture) in dry conditions. However, the results of variant no. 1 and no. 3 are more than 40 % and 51 % over the requirement of the standard. As mentioned before, variant no. 2 shows the lowest strength values but in consideration of the high moisture content of 9.9 % the achieved IB strength can be evaluated as acceptable. Bending strength and Modulus of elasticity (MOE):

Table 3 presents the obtained results of static bending strength and MOE as a function of the used binder systems. Particle boards consisting of TF-resin show the lowest flexural properties with bending strength of 9.5 N/mm ² and MOE values of 1940 N/mm ² followed by TF-PMDI hybrid resin bonded particle boards (bending strength: 13.6 N/mm ² and MOE: 2360 N/mm ² ) and finally exceeded by a bending strength of 14.7 N/mm ² and MOE of 2490 N/mm ² by only PMDI bonded boards. As a function of the binder system the bending properties of the produced particle boards vary but, as a matter of fact, all three different variants fulfill the requirement for MOE and exceed the required value of 1600 N/mm ² but not all variants achieve the minimum requirement of bending strength. Flowever, variant no. 1 and no. 3 obtain 33 % or 23 % higher bending strength values than required, respectively. Furthermore, the achieved MOE values of the particle board variants are 21 % to 55 % over the minimum requirement of 1600 N/mm ² .

It can be summarized that the variants no. 1 and no. 3 do show sufficient mechanical properties and fulfill the standards of EN 310:2010 and EN 319:2010 for particle boards type P2 for interior fitments (including furniture) in dry conditions.

Tab. 3: Mean values of internal bond strength, static bending strength and modulus of elasticity of the particle board variants based on wood waste material and bonded by different adhesives.

Values are arithmetic mean values of n = 10 samples; VC = variation of coefficient; EN 312:2010 (Type P2): boards for interior fitments (including furniture) in dry conditions.

Physical properties:

Moisture content, density, water absorption and thickness swelling were determined according to European Norms (EN: 2010) [Moisture Content (EN 322), Density (EN 323), Water absorption (EN 52351 ), and Thickness swelling (EN 317)].

Mean values and variation coefficients of thickness swelling (2 h and 24 h) and water absorption (2 h and 24 h) of the different bonded particle boards are presented in table 4. According to table 4, particle boards bonded with TF-PMDI hybrid resin (variant no. 3) achieve with 0.3 % and 6.8 % the best swelling behavior followed by PMDI bonded particle boards with a measured thickness swelling of 1.6 % and 8.3 %, respectively, and exceeded by variant no. 2. Particleboard variant no. 2, TF-resin bonded particle boards show a swelling behavior of 9.5 % and 38.9 %. Table 4 shows an overview about the measured water absorption values (2 h and 24 h). The particle boards only bonded with PMDI or with a TF-PMDI hybrid resin show a water absorption of 8.8 % and 9.3 %, after 2 h of water soaking, respectively. Extended water soaking of 24 h results in respective absorption values of 29.4 % and 27.7 %. The particle boards bonded by TF-resin show with 35.7 % or 103.7 % the worst behavior, compared to these other variants. Variant no. 2 behaves poorly against water soaking. This behavior can be explained by the used TF-resin and it can be supposed that the physical properties, such as thickness swelling and water absorption can be improved by using a hydrophobic agent. There are no defined limits in the European standards of EN 310:2010 for thickness swelling (2 h and 24 h) or water absorption (2 h and 24 h) of particle boards. Tab. 4: Mean values of thickness swelling (2 h and 24 h) and water absorption (2 h and 24 h) of particle board variants based on wood waste material and bonded by different adhesives.

Values are arithmetic mean values of n= 10 samples; VC = variation of coefficient EN 312:2010 (Type P2) for interior fitments (including furniture) in dry conditions Determination of the formaldehyde:

Formaldehyde release and extractable formaldehyde of the

manufactured variants of particle boards, were determined according to European Norms (formaldehyde release according to EN 717-3 (3 h and 24 h) and extractable formaldehyde according to EN 120).

Table 5 displays mean values of extractable formaldehyde content and formaldehyde release (3 h and 24 h) of particle boards bonded by three different adhesives.

The obtained results show that particle boards consisting of PMDI resin, or a TF-PMDI hybrid resin, have the lowest extractable formaldehyde content with 0.7 mg/100 g o. d. board or 1.9 mg/100 g o. d. board,

respectively, and significantly exceeded by particle boards bonded with TF- resin with formaldehyde content of 6.7 mg/100 g o. d. board. The extractable formaldehyde values of the particle board variants comply with the

specifications EN 312 (2010) and the maximum allowed limit value of < 8.0 mg/100 g o. d. board (EPF value is 6.5 mg/100g). The results fulfill the requirement for particle boards of type P2.

The behavior of the different bonded particle boards according to formaldehyde release is similar to the observed extractable formaldehyde content. PMDI bonded boards show the lowest formaldehyde release (2.0 and 11.6 mg/1000 g o. d. board) followed by TF-PMDI hybrid resin bonded boards (4.6 and 23.4 mg/1000 g o. d. board) and exceeded by TF-resin bonded particle boards (17.9 and 100.8 mg/1000 g o. d. board). The high formaldehyde release values could be attributed to the high moisture content of formaldehyde test samples of variant no. 2 after conditioning (MC: 9.9 %).

According to EN 312 (2010) there are no defined limits for the formaldehyde release from particle boards. Tab. 5: Mean values of extractable formaldehyde content and formaldehyde release (3 h and 24 h) of particle board variants based on wood waste

*< 8.0 mg/100 g o. d. board (maximum value); **< 6.5 mg/100 g o. d. board (maximum value) as 6 month rolling average. Formaldehyde tests were carried out as double determinations. EN 312:2010 (Type P2): boards for interior fitments (including furniture) in dry conditions

Production and characterization of core and surface layer particles In a first step the shredded waste solid wood material was

mechanically crushed in the pilot plant of the Biisgen-lnstitute (University of Gottingen) to core layer particles (60% by mass) and surface layer particles (40% by mass). The particle size of the wood particles are as described by the present invention for example in tables 6 and 7.

For the production of core and surface layer particles the waste wood material was at first cut down to particles by using a knife ring flaker (Co. Modul Systeme Engineering GmbFI, Laufen/Germany). Thereafter, the particles were screened into core and surface layer particles by using a tumbler screening machine (Co. Allgaier Process Technology GmbH, Uhingen/Germany). For the PB core layer only particles between mesh >3mm x 1 mm and mesh:s; 4mm x 4mm were used. Wood material passing through mesh 3mm x 1 mm were further processed for use as particles for PB surface layers.

After screening, the amount of the core layer particles was bigger than the necessary proportion of 60% by mass. Therefore, it was decided to crush a part of the core layer particle material in a hammer mill (model F3, Co. electra, Poudenas/France) in order to get a sufficient amount of suitable material for the surface layer. For hammer milling a round-hole sieve (mesh 2mm) was used. The fine particle material gained by knife ring flaking and hammer milling respectively, was also screened into surface layer particles using the tumbler screening machine. For the PB surface layers only particles between mesh >0.4mm x 0.4mm and mesh:s; 3mm x 1 mm were used. After screening samples (500 grams) of core and surface layer particles were analysed concerning their particles size distribution by using a Retsch sieving machine (AS 400) at 250 rpm for 5 minutes. In table 6 and table 7 the results of the particles size analysis of the core and surface layer particles are compiled.

Tab. 6: Particles size distribution of the core layer particles made by knife ring iaking of the shredded waste solid wood materia .

Tab. 7: Particles size distribution of the surface layer particles made by knife ring flaking and hammer milling of the shredded waste solid wood material.

After screening, the moisture content of the core and surface layer particles was 12.0% and 12.3% respectively. For this reason the core and surface layer particles were dried in a Memmert universal drying oven at 70°C to a target moisture content of 2%. After drying the particles were packed airtight in polyethylene bags until further processing.

Production of 3 models of particle boards in laboratory scale

For preparation of laboratory PB the aforementioned dried surface and core layer particles were used. Three models of 3-layer particle boards were produced using:

1. Polymeric Diphenylmethane-diisocyanate (PMDI)

2. Tannin-Formaldehyde-resin (TF-resin)

3. A combination of TF-resin and PMDI The product l-Bond PB EM 4352 (Co. Huntsman) was used for manufacturing PMDI-bonded PB. For the production of TF-bonded particle boards a technical quebracho tannin (Colatan GT 5) (Co. Unitan/Argentina) was chosen. For the manufacturing of PMDI:TF-resin bonded PB the particles were blended first with the TF-resin; in a separate step the PMDI was sprayed on the particles. As sizing agent the product Hydrowax 730 (Co.

Sasol/Hamburg, Germany) was used for all PB models. For each PB model 3 boards were manufactured. Table 8 summarizes the conditions for preparing the laboratory PB.

After production the particle boards were stored and conditioned for 6 days in the pilot plant of the Biisgen-lnstitute under normal conditions.

Subsequently, the PB were trimmed and sanded (grain size 60) to a board thickness of 18mm by using a wide belt sanding machine (Type FW 950 C) (Co. Felder KG, Hall in Tirol/Austria). After sanding the PB were conditioned for 4 weeks at 20°C and 65 % relative humidity.

Thereafter, the boards were tested according to EN 322 for moisture content, EN 323 for density, EN 317 for thickness swelling, DIN 52351 for water absorption, EN 310 for bending strength and modulus of elasticity in bending, EN 319 for internal bond strength. The formaldehyde release of the boards was evaluated using the flask method according to EN 717-3:1996. Moreover, the extractable formaldehyde content was determined according to the perforator method (EN 120:1992).

While the invention has been described in connection with what is presently considered to be the most practical embodiments, it is to be understood that the invention is not to be limited to the disclosed

embodiments, but on the contrary, it is intended to cover various

modifications and equivalents included within the spirit and scope of the appended claims.

¹ Ratio PMDI:TF-resin based on SL/CL resin content of PB Model No. 1 (PM Dl-bonded PB)