EP3767032A1 - Formgebung von delignifiziertem holz - Google Patents

Formgebung von delignifiziertem holz Download PDF

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Publication number
EP3767032A1
EP3767032A1 EP19187447.8A EP19187447A EP3767032A1 EP 3767032 A1 EP3767032 A1 EP 3767032A1 EP 19187447 A EP19187447 A EP 19187447A EP 3767032 A1 EP3767032 A1 EP 3767032A1
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EP
European Patent Office
Prior art keywords
wood
delignified
piece
mold
densified
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EP19187447.8A
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English (en)
French (fr)
Inventor
Marion Andrea FREY
Clemens Dransfeld
Meri Tuuli ZIRKELBACH
Tobias KEPLINGER
Etienne TRACHSEL
Mikael Hannus
Ingo BURGERT
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Eidgenoessische Technische Hochschule Zurich ETHZ
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Eidgenoessische Technische Hochschule Zurich ETHZ
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Priority to EP19187447.8A priority Critical patent/EP3767032A1/de
Publication of EP3767032A1 publication Critical patent/EP3767032A1/de
Pending legal-status Critical Current

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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21J—FIBREBOARD; MANUFACTURE OF ARTICLES FROM CELLULOSIC FIBROUS SUSPENSIONS OR FROM PAPIER-MACHE
    • D21J3/00—Manufacture of articles by pressing wet fibre pulp, or papier-mâché, between moulds

Definitions

  • Delignified densified wood is a new promising lightweight, high-performance and bio-based material, which potentially could substitute natural fiber reinforced composites or glass fiber reinforced composites.
  • the process is based on delignification of wood (removal of the matrix lignin), which results in a flexible cellulose scaffold followed by a subsequent densification step, leading to a material with high stiffness, strength and toughness.
  • Patent application EP17168238.8, 2017 (M.Frey et al., 2018).
  • the densification is currently conducted in closed molds by simple pressing.
  • the material cannot be processed in fully wet state, as the free water creates a counter pressure, leading to a reduced densification, distorted fiber alignment and cracks ( Figure 1 ).
  • the material has to be conditioned before densification in order to remove the free water. This, however, leads to a reduced formability of the scaffold and a longer processing time.
  • the present invention is directed towards shape forming of delignified wood, which allows for combining shaping, densification and drying in a simple and scalable approach.
  • a first aspect of the present invention relates to a method for producing densified delignified wood.
  • the method comprises the steps of
  • wet delignified wood - such as veneers, layers, strips - is draped onto a mold in a predefined lay-up.
  • Delignified wood may be obtained by standard delignification methods, wherein lignin is removed from wood. The delignified wood is densified and dried in a vacuum bag surrounding the mold. This leads to an increased fiber volume content, resulting in higher mechanical properties, and drying locks the structure in its shape. Water is either removed through pores in the mold, or through a porous layer (e.g. mesh grid, textile) placed on top or below the delignified wood ( Fig. 2 ).
  • a porous layer e.g. mesh grid, textile
  • the delignified piece of wood may be of any shape.
  • the delignified piece of wood comprises mainly parallel aligned cellulose fibers.
  • the minimal volume can be in the ⁇ m 3 range. More easily treatable units in terms of the densification treatments are characterized by a volume in the cm 3 range.
  • the maximum volume is defined by the size of the densification apparatus and the feasibility of the delignification since the delignification solution has to infiltrate the whole piece of wood in order to achieve an almost complete removal of lignin.
  • concentration dc(x,t) c, concentration; x, diffusion distance, t, time
  • the distance x is proportional to t 0.5 .
  • the delignified piece of wood is densified in the direction perpendicular to the extension of the cellulose fibers.
  • the cellulose fibers When placed in the mold, the cellulose fibers are parallel to the molding surface. If the molding surface is curved, the cellulose fibers are bent accordingly.
  • the molding surface relates to that section of the surface of the mold that forms the negative shape, which corresponds to the desired positive shape, i.e. the shape of the densified piece of wood.
  • wet delignified wood is used. Delignified wood is referred to as being "wet” if it comprises water. Water molecules might be present in form of bound water or free water. Bound water relates to water molecules, which are bound to macromolecules of the delignified wood e.g. by adsorption. Free water relates to water molecules that are present in lumina within the delignified wood structure. When stored at 65 % RH, delignified wood has a water content ⁇ 11 %. The water is mainly bound water. Usually, the fibers within the delignified wood are saturated with bound water at a water content of approx. 23 %. Thus, free water is also present if the water content is ⁇ 23 %. Small variations may occur depending on the type of wood.
  • the water content relates to the mass of water in relation to the total mass of the delignified piece of wood.
  • the water content of the delignified piece of wood is ⁇ 11 %, particularly between 11 % and 440 % (fully water-saturated state).
  • the water content of the delignified piece of wood is ⁇ 23 % (storage at 95% RH), particularly between 23 % and 440 %.
  • lignin is important for the formability of the piece of wood. Delignified wood is obtained by an almost complete removal of lignin. A suitable method for the delignification of wood is described below in more detail.
  • lignin contributes to the brown color of lignocellulosic material, i.e. the characteristic color of wood.
  • wood In a fully delignified state, wood consists mainly of cellulose fibers that are whitish. If the delignification is inhomogeneous, the delignified wood does not appear evenly whitish. Upon tensile loading such materials will crack or break in the brownish colored areas or at the interface to the whitish areas.
  • the lignin content of the delignified piece of wood is below 10 %.
  • the lignin content of the delignified piece of wood is below 3 %.
  • the lignin content of the delignified piece of wood is ⁇ 1%.
  • the delignified piece of wood is obtained from a veneer, layer or a strip of wood.
  • High densification i.e. a high number of fibers/volume
  • the cellulose fibers align parallel to the molding surface/perpendicular to the direction of the pressure applied.
  • a large number of parallel fibers in a piece of wood can be achieved if it is prepared by cutting techniques in longitudinal direction / growth direction such as rift cut, crown cut or rotary cut. In contrast to other densification methods, the orientation of the fibers is maintained.
  • the delignified piece of wood is obtained from a veneer, layer or a strip of wood obtained by a rift cut, crown cut or rotary cut.
  • the delignified piece of wood has a thickness between 0.5 mm and 10 mm.
  • the delignified piece of wood has a thickness between 1 mm and 3 mm.
  • the piece of wood for example softwood, contains fibers (precisely tracheids, in a biological context) which are approximately 3 mm long and 30 ⁇ m in diameter.
  • the cell walls of the fibers consist of cellulose microfibrils.
  • a microfibril is formed by several cellulose chains and possesses a length of approximately 15 nm length and a diameter of approximately 3 nm. Lignin and hemicellulose fill spaces between the cellulose fibrils.
  • the microfibrils in normal wood are predominately aligned in longitudinal direction (small microfibril angle). This mainly parallel alignment is maintained upon removal of lignin, in particular when the delignification method described in the following is applied.
  • the delignified piece of wood is obtained by treating a piece of wood with
  • the piece of wood is hardwood or softwood.
  • the method can be performed using any kind of hardwood or softwood.
  • the piece of wood is from Acer spp., Betula spp., Fagus sylvatica, Quercus spp. Fraxinus excelsior, Eucalyptus spp., Populus spp., Prunus avium, Tilia spp., Robinia pseudoacacia, Tectona grandis, Ulmus spp., Juglans regia, Carpinus betulus, Ochroma pyramidale, Pseudotsuga menziesii, Taxus baccata, Picea abies, Pinus sylvestris, Larix decidua, Thuja plicata, Abies alba, or Pinus strobus.
  • Lignin constitutes approximately 20 to 35 % of the dry mass of wood, for example the lignin content in conifers ranges from 27 % to 32 % and in deciduous trees (Betula, Fagus) from 19 % to 23 % ( H. G. Hirschberg: Handbuchmaschinestechnik und Anlagenbau. Springer Verlag 1999: p. 436 ).
  • lignin an additional partial removal of hemicellulose and amorphous cellulose occurs.
  • the delignification may also be performed until the respective loss of weight is reached, in particular a loss of weight is reached, which corresponds at least to the amount of lignin of the starting material.
  • delignification causes a weight loss of 20 % to 40 % of the dry mass of the piece of wood, particularly a weight loss of 28 to 40 % of the dry mass of the piece of wood (lignocellulosic material) from a conifer and a weight loss of 20 to 32 % of the dry mass of the piece of wood (lignocellulosic material) from a deciduous tree.
  • the delignification process can also be monitored by assessing the loss of color.
  • Lignin contributes to the brown color of lignocellulosic material, i.e. the characteristic color of wood.
  • wood In a fully delignified state, wood consists mainly of cellulose fibers that are whitish. Thus, depending on the thickness of the piece of wood, delignification has to be performed until the delignified wood appears white.
  • the delignified piece of wood is obtained by treating the piece of wood with at least one acid.
  • the pH is adjusted between 1 and 6, particularly 1.
  • the delignified piece of wood is obtained by treating the piece of wood at least with one inorganic or organic acid.
  • the delignified piece of wood is obtained by treating the piece of wood with acetic acid, sulfuric acid, chloric acid or peracetic acid.
  • the delignified piece of wood is obtained by treating the piece of wood with at least one oxidizing agent under alkaline or acidic conditions. Under alkaline conditions, the pH is adjusted between 8 and 14. Under acidic conditions, the pH is adjusted between 1 and 6.
  • the delignified piece of wood is obtained by treating the piece of wood with hydrogen peroxide, sodium chlorite, sodium sulfite or ozone under alkaline or acidic conditions.
  • the delignified piece of wood is obtained by treating the piece of wood with hydrogen peroxide under alkaline or acidic conditions.
  • the delignified piece of wood is obtained by treating the piece of wood with at least one oxidizing agent under acidic conditions.
  • the delignified piece of wood is obtained by treating the piece of wood with hydrogen peroxide, sodium chlorite, sodium sulfite or ozone under acidic conditions.
  • the delignified piece of wood is obtained by treating the piece of wood with hydrogen peroxide under acidic conditions. In certain embodiments, the delignified piece of wood is obtained by treating the piece of wood with acetic acid in combination with H 2 O 2 .
  • acetic acid in combination with H 2 O 2 is a less poisonous treatment, compared to other delignification treatments.
  • the delignified piece of wood is obtained by treating the piece of wood with at least one base.
  • the pH is adjusted between 8 and 14, particularly 14.
  • the delignified piece of wood is obtained by treating the piece of wood with sodium hydroxide.
  • the delignification solution has to infiltrate the piece of wood completely.
  • the delignified piece of wood is obtained by an incubation of the infiltrated piece of wood at a temperature between 20 °C and 90 °C.
  • the delignified piece of wood is obtained by an incubation of the infiltrated piece of wood at a temperature between 60 °C and 90 °C.
  • the delignified piece of wood is obtained by an incubation of the infiltrated piece of wood at a temperature between 75 °C and 85 °C.
  • the delignified piece of wood is obtained by an incubation of the infiltrated piece of wood at 80 °C.
  • the densification is performed in a mold which comprises a molding surface.
  • the molding surface forms the negative shape, which corresponds to the positive shape of the desired densified piece of wood.
  • the cellulose fibers align parallel to the molding surface/perpendicular to the direction of the pressure applied. If the molding surface is curved, the cellulose fibers are bent accordingly.
  • the densification may be performed in an open mold or in a closed mold.
  • the mold is an open mold or a closed mold.
  • the mold is an open mold.
  • closed porous molds or closed solid molds with the addition of porous/conductive layers in between the two molds (or upper and lower part of a mold) can be used.
  • the advantage of such an approach is the increased surface quality of the final composite part.
  • the mold is a closed mold.
  • the closed mold may consist of two parts, e.g an upper and a lower part.
  • the lower part may comprise a molding surface, which forms the negative shape that corresponds to one side of the positive shape of the desired densified piece of wood and the upper part may comprise a molding surface, which forms the negative shape that corresponds to the other side of the positive shape of the desired densified piece of wood.
  • the shape of the molding surface of the upper and the lower part are complementary to each other.
  • the upper and the lower part may be separable or connected, e.g. by a hinge.
  • the mold may comprise a porous section that forms the molding surface.
  • the pores of this section form a network of channels and interstices so that the water can flow out of the mold.
  • the whole mold may be made of a porous material or a part of the mold, which is connected to a drain, is made of a porous material.
  • the mold comprises a porous section, which forms the molding surface and at least one section of the outer surface of the mold or the mold comprises a porous section, which forms the molding surface and is connected to a drain.
  • the mold comprises a porous section, which forms the molding surface and at least one section of the outer surface of the mold.
  • the mold comprises a porous section, which forms the molding surface and is connected to a drain.
  • the mold is porous.
  • the open mold is porous.
  • the closed mold is porous.
  • the closed mold comprises at least two parts, in particular an upper and a lower part.
  • both the upper and the lower part are porous or one of the upper and the lower part is porous and the other part is solid.
  • the upper and the lower part are porous.
  • Suitable molds withstand the pressure that is applied to generate the pressure difference.
  • a mold has to withstand at least a pressure of 1 atm (101325 Pa) in the vacuum process.
  • suitable molds should be heat-resistant if the densification is performed at elevated temperatures such as 65 °C.
  • the pores of the mold comprise open pores which form a network of cavities, channels and/or interstices. This network allows water, which is pressed out of the delignified wood, to flow from the molding surface towards the outer surface of the mold. Finally, the water exits the mold.
  • the water may also be removed via a porous layer.
  • a porous layer may additionally be used in a porous mold as described above or in a solid mold.
  • the porous layer may consist of one layer, may comprise sublayers or may be composed of several porous layers.
  • the porous layer may comprise a flow mesh and a textile layer.
  • porous layers may be present in the mold assembly.
  • an open porous mold may be covered by a textile layer to allow a smooth surface finish of the delignified wood and below the mold may be a flow mesh connected to a vacuum tube to facilitate the removal of water.
  • the flow mesh may be placed on top of the delignified piece of wood.
  • the porous layer consists of at least one layer.
  • the porous layer comprises one or more layers.
  • the porous layer comprises one or more layers made of different materials.
  • the porous layer is placed below and/or above the delignified piece of wood.
  • the porous layer may be placed below or above the delignified piece of wood.
  • one or more porous layers may be used.
  • one or more, particularly two, porous layers are present in the mold.
  • one or more, particularly two, porous layers are present in the closed mold.
  • the closed solid mold comprises at least two parts, in particular an upper and a lower part.
  • the upper and the lower part each comprise a molding surface which comprises a negative shape, which corresponds to the upper and the lower side of the desired densified piece of wood (positive), respectively.
  • the porous layer is placed on the molding surface of the lower part and the delignified piece of wood is placed on the (lower) porous layer.
  • a further (upper) porous layer is placed on the piece of wood before the upper part is placed on the delignified piece of wood/the upper porous layer.
  • the size and shape of the porous layer matches the size and shape of the molding surface. Furthermore, the porous layer either contacts a drainage system within the mold and/or the porous layer extends to the outer surface of the mold so that the water can flow out.
  • Suitable porous layers withstand the pressure that is applied to generate the pressure difference, i.e. the pores are still water-permeable when pressure is applied. For example, a porous layer has to withstand at least a pressure of 1 atm (101325 Pa) in the vacuum process.
  • suitable porous layers should be heat-resistant if the densification is performed at elevated temperatures such as 65 °C.
  • the porous layer is a continuous-fiber fabric, a polymer mesh or a flow grid.
  • the porous layer is placed on top and/or below the delignified piece of wood.
  • the porous layer is placed on top and below the delignified piece of wood.
  • the porous layer is placed on top or below the delignified piece of wood.
  • the pores of the mold and the porous layer are too big, the negative of the porous structure may be visible on the densified piece of wood.
  • the size of the pores should be small to obtain a smooth surface of the densified piece of wood.
  • the pores have to be big enough to provide sufficient water flow.
  • the size of the pores of the mold and/or the porous layer is between 0.1 mm and 2 mm, particularly between 0.3 mm and 0.5 mm.
  • the size of the pores of the mold is between 0.1 mm and 2 mm, particularly between 0.3 mm and 0.5 mm.
  • the size of the pores of the porous layer is between 0.1 mm and 2 mm, particularly between 0.3 mm and 0.5 mm.
  • the size of the pores of the mold and/or the porous layer is between 0.1 mm and 2 mm, particularly between 0.3 mm and 0.5 mm, at the molding surface.
  • the mold or the porous layer is made of a material with a high number of pores per volume.
  • suitable materials are clay or wood.
  • 3D printed porous molds or porous layers made of ABS (acrylonitrile butadiene styrene), PVA (polyvinyl alcohol) or PLA (polylactic acid) may be used.
  • the pores of the mold may vary in diameter and form a gradient, for example from the molding surface towards the outer surface of the mold.
  • the pore size increases from the molding surface towards the outer surface.
  • the same may apply to the porous layer.
  • the pore structure may result in an uneven surface of the densified piece of wood if the pores are too big.
  • smaller pore size towards the surface leads to a smoother surface finish.
  • the drying speed can be increased by using a mold or a porous layer with increasing pore size towards the outer surface.
  • the porosity of the mold and/or the porous layer is homogeneous or gradual.
  • the porosity of the mold is homogeneous or gradual.
  • the porosity of the mold is homogeneous.
  • the porosity of the mold is gradual.
  • the porosity of the porous layer is homogeneous or gradual.
  • the porosity of the porous layer is gradual.
  • the porosity of the porous layer is homogeneous.
  • the molding surface may be covered by a (porous) textile layer.
  • the molding surface is covered by a textile layer.
  • wet delignified wood allows various shape forming.
  • densified wood with a flat or a curved surface may be obtained.
  • the molding surface is characterized by one or more radii of curvatures between 200 ⁇ m to infinite (flat).
  • the molding surface is flat.
  • the inventive method provides particularly densified pieces of wood having at least one section with a curved surface.
  • the surface might be curved everywhere or the surface may comprise curved and flat sections.
  • the molding surface is characterized by at least one curvature having a radius of curvature ⁇ 200 ⁇ m.
  • the molding surface is characterized by at least one curvature having a radius of curvature ⁇ 1 mm, particularly ⁇ 1 cm.
  • the molding surface is characterized by at least one radius of curvature between 200 ⁇ m and 10 m, particularly 200 ⁇ m and 1 m.
  • the molding surface is characterized by at least one radius of curvature between 1 mm and 10 m, particularly 1mm and 1 m.
  • Curved surfaces may be required for example in the automotive industry or in the field of aviation.
  • Formed parts such as door panels, covers or door handles comprise curved surfaces having curvatures in the cm to m range.
  • the molding surface is characterized by at least one curvature having a radius of curvature ⁇ 1 cm.
  • the molding surface is characterized by at least one radius of curvature between 1 cm and 100 m, particularly between 1 cm and 10 m.
  • a pressure difference is applied.
  • the pressure difference may be generated by using a positive pressure, e.g. pressing the upper part of the mold in the direction of the lower part of the mold in combination with vacuum or by using a negative pressure only (vacuum).
  • negative pressure may be applied by using a vacuum bag.
  • Vacuum may be applied from above the densified piece of wood or from below the mold.
  • a combination of using a positive pressure and negative pressure is possible.
  • pressing the upper part of the mold on the lower part of the mold may be further supported by applying a vacuum.
  • Intracellular water is removed during densification. Hereby, water molecules cross the cell walls which comprise mainly cellulose fibrils after delignification.
  • a vacuum or vacuum in combination with a positive pressure the integrity and orientation of the cellulose fibrils is maintained.
  • the maximum pressure applied depends on the materials and devices used. For example, autoclave processing allows applying an external pressure of up to 10 bar.
  • a negative pressure or a negative pressure in combination with a positive pressure is applied, wherein the pressure difference to atmospheric pressure is ⁇ 1 bar, particularly ⁇ 2 bar, when a positive pressure is applied, or the pressure difference is ⁇ 0.9 bar, particularly ⁇ 0.99 bar, when a negative pressure is applied.
  • a negative pressure vacuum
  • only a negative pressure may be applied.
  • a negative pressure is applied.
  • the pressure difference is ⁇ 1 bar, particularly ⁇ 2 bar, when a positive pressure is applied, or the pressure difference is ⁇ 0.9 bar, particularly ⁇ 0.99 bar, when a negative pressure is applied.
  • the pressure difference is ⁇ 1 bar, particularly ⁇ 2 bar, when a positive pressure is applied.
  • the pressure difference relates to the pressure applied and the atmospheric pressure (approx. 1 bar). For instance, if a pressure of 3 bar is applied, the pressure difference to the atmospheric pressure is 2 bar.
  • the pressure difference is ⁇ 0.9 bar, particularly ⁇ 0.99 bar, when a negative pressure is applied.
  • the pressure difference relates to the negative pressure applied and the atmospheric pressure (approx. 1 bar). If a negative pressure of 10 -2 bar is applied, the difference to the atmospheric pressure is 0.99 bar.
  • the fiber alignment of shaped densified parts is retained by drying. To prevent deformations of the shaped densified piece of wood, the densification is performed until at least the free water is completely removed.
  • the delignified piece of wood is simultaneously densified and dried.
  • the densification may be performed at ambient temperature or elevated temperature. At higher temperatures, the drying/densification time can be reduced.
  • the densification is performed at a temperature between 18°C and 180 °C.
  • the densification is performed at a temperature between 18°C and 30 °C.
  • the densification is performed at a temperature between 30°C and 180 °C.
  • the densification is performed at a temperature between 30°C and 70 °C.
  • the densification is performed at a temperature between 40°C and 65 °C.
  • the densification is performed at 65 °C.
  • the piece of wood may be further processed by applying an additional positive pressure and/or an additional drying step.
  • the additional positive pressure may be applied in the same set up used for simultaneous shaping, densification and removal of at least the free water or in another device. Further densification is achieved by applying an additional positive pressure.
  • the additional drying step may be performed in the set up used in the steps before or in another device or drying chamber.
  • the delignified piece of wood may be processed in one process or machine at one station or in several processes/machines at several stations.
  • shaping may be finished by dye-cutting the edges of the densified piece of wood.
  • the densified piece of wood is further dried in an additional drying step.
  • the densified piece of wood is further shaped by cutting the edges, in particular by dye-cutting the edges.
  • the cellulose fibers of the delignified wood are interconnected. In wood as naturally grown, the fibers are oriented in growth direction. To further enhance the tensile strength of the densified wood, several pieces of densified wood may be combined upon densification.
  • one or more delignified pieces of wood form one or more layers.
  • the cellulose fibers of one or more delignified pieces of wood are oriented in the same direction within one layer.
  • the cellulose fibers of one layer are oriented in a different direction with regard to the direction of the cellulose fibers of an adjacent layer.
  • the cellulose fibers in one layer extend perpendicular to the fibers in an adjacent layer (0°/90°). Also quasi-isotropic arrangements are possible.
  • adhesives may be applied.
  • the fiber volume content is controlled by the fiber:matrix ratio and not by densification through the applied vacuum.
  • an adhesive is applied between the layers or infiltrated into the delignified piece of wood before the pressure difference is generated.
  • the adhesive is selected from natural glues and/or synthetic adhesives.
  • the natural glue is selected from starch, tannins, microfibrillated cellulose (MFC), nanocrystalline cellulose (NCC), methylcellulose and the synthetic adhesive is selected from thermoplastic polymers, in particular polyethylene polymers (PE), polypropylen polymers (PP), polymethylmethacrylat polymers (PMMA), polylactic acid polymers (PLA), or duroplastic polymers, in particular epoxy polymers, melamine urea formaldehyde polymers (MUF), urea formaldehyde polymers (UF).
  • PE polyethylene polymers
  • PP polypropylen polymers
  • PMMA polymethylmethacrylat polymers
  • PMMA polylactic acid polymers
  • duroplastic polymers in particular epoxy polymers, melamine urea formaldehyde polymers (MUF), urea formaldehyde polymers (UF).
  • a second aspect of the invention relates to a densified wood comprising one or more layers of delignified wood, wherein the cellulose fibers within one layer are oriented in the same direction and/or wherein the cellulose fibers of one layer are oriented in a different direction with regard to the direction of the cellulose fibers of an adjacent layer, characterized in that fiber density is between 0.3 gcm -3 and 1.5 gcm -3 in particular between 1 gcm -3 and 1.5 gcm -3 .
  • the densified wood comprises one layer of delignified wood, wherein the cellulose fibers within the layer are oriented in the same direction, characterized in that fiber density is between 0.3 gcm -3 and 1.5 gcm -3 in particular between 1 gcm -3 and 1.5 gcm -3 .
  • the densified wood comprises two or more layers of delignified wood, wherein the cellulose fibers within one layer are oriented in the same direction and wherein the cellulose fibers of one layer are oriented in a different direction with regard to the direction of the cellulose fibers of an adjacent layer, characterized in that fiber density is between 0.3 gcm -3 and 1.5 gcm -3 in particular between 1 gcm -3 and 1.5 gcm -3 .
  • the densified wood is obtained by the method according to the first aspect of the invention.
  • the densified wood is characterized by one or more radii of curvatures between 200 ⁇ m to infinite (flat).
  • the term "delignification” relates to the removal of lignin from lignocellulosic materials such as wood.
  • Lignin is a branched polymer located between the cellulose microfibrils in the cell walls of lignified parts of a plant, in particular wood.
  • the lignin polymer contains several functional groups such as ether linkages, phenolic hydroxyl groups, aliphatic hydroxyl groups, unsubstituted or methyl-substituted C2, C3, C5 or C6 moieties, unsaturated moieties and ester groups that may react during delignification.
  • ethers may be cleaved by nucleophilic attacks, carbonyl and aldehyde groups react with nucleophiles, hydroxyl groups may be ionized or -O-methyl groups demethylated to allow a nucleophilic attack of the oxygen ion.
  • conjugate addition, formaldehyde addition, epoxide addition and aldol condensation reactions might contribute to the depolymerisation of lignin. These chemical reactions result in the depolymerization of the lignin polymer into smaller moieties that diffuse from the lignocellulosic material into the surrounding solution and/or that are removed by several washing steps.
  • the term "delignified piece of wood” relates to a piece of wood that is obtained by delignification of said piece of wood.
  • Naturally grown wood comprises cellulose, which forms fibers that extend in growth direction.
  • the delignified wood also comprises cellulose, wherein the cellulose forms fibers that are arranged in a mainly parallel orientation. Thus, the structural integrity of the fibers is maintained.
  • structural integrity relates to the spatial arrangement of fibers in wood, delignified wood and densified wood in longitudinal direction, i.e. in growth direction. Fibers in wood are arranged in a mainly parallel orientation. This parallel alignment is maintained during delignification and densification. If a mold having a curved molding surface is used during densification, the fibers are bent according to the curvature of the molding surface.
  • the term "densification” relates to the compression of delignified wood.
  • the volume is reduced.
  • the volume may be reduced by the loss of water without further compression of the cellulose fibers.
  • Further compression relates to the reduction of the distance between the cellulose fibers. A pressure is particularly applied until a predefined thickness of the delignified wood or the maximum compression is achieved.
  • the term "densified piece of wood” relates to a wood that is obtained by densification of delignified wood.
  • the densified wood comprises cellulose, wherein the cellulose forms fibers that are arranged in a mainly parallel orientation. If a mold having a curved molding surface is used during densification, the fibers are bent according to the curvature of the molding surface.
  • the density of densified wood ranges from more than 100 kg/m 3 to 1500 kg/m 3 .
  • the term "hardwood” relates to wood of deciduous trees.
  • the deciduous trees may be non-modified or genetically modified.
  • Non-limiting examples for deciduous trees are Acer spp., Betula spp., Fagus sylvatica, Quercus spp. Fraxinus excelsior, Populus spp., Prunus avium, Tilia spp., Robinia pseudoacacia, Tectona grandis, Ulmus spp., Juglans regia, Carpinus betulus, Eucalyptus spp., Ochroma pyramidale.
  • the term "softwood” relates to wood of conifers.
  • the conifers may be non-modified or genetically modified.
  • Non-limiting examples for conifers are Pseudotsuga menziesii, Taxus baccata, Picea abies, Pinus sylvestris, Larix decidua, Thuja plicata, Abies alba, Pinus strobus.
  • oxidizing agent relates to agents that oxidize lignin.
  • Such oxidizing treatments are achieved by treatments comprising enzymes such as laccase, fungi or chemical substances such as Cl 2 in water, HCIO, peracetic acid (PAA), NaOH, NaClO 2 , Na 2 S 2 O 4 , ClO 2 , HAc/H 2 O 2 or O 3 , ionic liquids or treatments which use catalysts, e.g. manganese salts.
  • radial direction relates to a direction that is perpendicular to the longitudinal direction of the cellulose fibers and crosses the annual rings of a piece of wood.
  • tangential direction relates to a direction that is perpendicular to the longitudinal direction of the cellulose fibers and aligns to a tangent of an annual ring of a piece of wood.
  • the term "elastic modulus” relates to the slope of a stress-strain curve in the elastic deformation region and is a measure of the elastic deformation of the material. Stress is the force per cross section in a tensile test that can cause deformation of a material and strain is the elongation of the material related to its original length.
  • the SI unit for the elastic modulus is pascal (Pa) or N/m 2 , the practical unit is gigapascal (GPa).
  • Pa pascal
  • GPa gigapascal
  • the loading direction was in the longitudinal direction, which means in the direction of the cellulosic fibers.
  • tensile strength relates to the maximum tensile stress the cellulosic material can withstand.
  • the loading direction was in the longitudinal direction, which means in the direction of the cellulosic fibers.
  • the SI unit for tensile strength is pascal (Pa) or N/m 2
  • the practical unit is megapascal (MPa) or N/mm 2 .
  • the term "mold” relates to at least one block of material having a molding surface.
  • the molding surface relates to that section of the surface of the mold that forms the negative shape, which corresponds to the desired positive shape, i.e. the shape of the densified piece of wood.
  • the mold can be made of a solid or porous material or a mix thereof.
  • the mold may consist of two parts, e.g. an upper and a lower part, wherein the delignified piece of wood may be placed between the upper and the lower part and subsequently densified by pressing the upper and the lower part together in combination with vacuum. If the mold is porous, the pores may be of irregular shape, i.e. variations in length, diameter and degree of branching occur.
  • the mold comprises pores of the same shape, for example open-ended through-pores (channels) having the same diameter.
  • the mold can also be a grid if the grid possesses mechanical stability when shaped and the pore/opening range is in the proper range, i.e. the pores/openings should be small enough that the surface of the delignified piece of wood remains smooth upon densification and the pores/openings should be bid enough that water can flow through.
  • pore or "porous” is understood according to the IUPAC definition ( Pure & Appl. Chem. 1994, Vol. 66, No. 8, pp. 1739-1758 , particularly the paragraph “Porous solid” on page 1742 and the section “Qualitative description of a porous solid” on pages 1742 to 1743).
  • a pore is a cavity, channel or interstice of a solid.
  • the cavity, channel or interstice is deeper than wide.
  • a rough surface is not porous unless it has irregularities that are deeper than they are wide.
  • Pores may be classified according to their availability to an external fluid. Pores that are totally isolated from their neighbors are related to as closed pores. They influence such macroscopic properties as bulk density, mechanical strength and thermal conductivity, but are inactive in such processes as fluid flow and adsorption of gases. Closed pores may occur in porous molds or porous layers according to the invention. However, as they lack any continuous channel to the external surface, they do not contribute to draining off water.
  • Pores which have a continuous channel of communication with the external surface of the body are related to as open pores. Some may be open only at one end; they are then described as blind (i.e. dead-end, or saccate) pores. Others may be open at two ends (through pores). Pores can also form a branched network of cavities, channels and/or interstices.
  • the porous mold or porous layer according to the invention comprises open pores, which allow draining off the water during densification.
  • Rotary cut spruce veneers were cut to the dimensions 150 x 30 x 3 mm 3 (longitudinal x tangential x radial) and were then delignified in a 1:1 H 2 O 2 and HAc solution followed by heating-up to 80°C. Delignification times were set to 80, 160, 240 and 360 minutes. After delignification, samples were washed with water until a pH value of minimum 4.5 was reached.
  • Example 3 Multiple layers - lay-up
  • the delignified wood veneers are draped to the mold in the desired layup (unidirectional (UD), 0°/90°, quasi-isotropic%) to optimize for loading-conditions in in the final composite.
  • the layers are glued by using natural glues (starch, tannins, MFC, NCC, methylcellulose%) or synthetic glues (thermoplastic or duroplastic polymers).
  • the inventive process will lead to eased and fast production of large-scale densified cellulose fiber composites, e.g in the automotive industry (door panels, floor, dashboard ...), where the material could replace metals or fiber reinforced composites in order to reduce the weight for better fuel efficiency and to improve recyclability ( Fig. 10 ).

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical And Physical Treatments For Wood And The Like (AREA)
EP19187447.8A 2019-07-19 2019-07-19 Formgebung von delignifiziertem holz Pending EP3767032A1 (de)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2024077344A1 (en) * 2022-10-10 2024-04-18 Varden Process Pty Ltd A process for forming a moulded pulp fibre product

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2413301A (en) * 2004-04-20 2005-10-26 Glory Team Ind Ltd A method of producing pulp-moulded products, a mould for use in such a method and an apparatus for incorporating such a method
US20080263890A1 (en) * 2005-04-04 2008-10-30 Edmond-Pierre Picard Wood Heat Treating Method, a Plant for Carrying Out Said Method and Heat Treated Wood
EP3396063A1 (de) * 2017-04-26 2018-10-31 ETH Zurich Verfahren zur herstellung eines verdichteten celluloseverbundstoffmaterials

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2413301A (en) * 2004-04-20 2005-10-26 Glory Team Ind Ltd A method of producing pulp-moulded products, a mould for use in such a method and an apparatus for incorporating such a method
US20080263890A1 (en) * 2005-04-04 2008-10-30 Edmond-Pierre Picard Wood Heat Treating Method, a Plant for Carrying Out Said Method and Heat Treated Wood
EP3396063A1 (de) * 2017-04-26 2018-10-31 ETH Zurich Verfahren zur herstellung eines verdichteten celluloseverbundstoffmaterials

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Title
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PURE & APPL. CHEM., vol. 66, no. 8, 1994, pages 1739 - 1758

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2024077344A1 (en) * 2022-10-10 2024-04-18 Varden Process Pty Ltd A process for forming a moulded pulp fibre product

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