Linear profile made of reconstituted wood

Abstract

The invention relates to a linear profile (1) comprising a core (2) made of a composite material based on wood fibers or particles and at least one binder, said core being covered with a mechanically reinforcing sheath (3) made of braided natural textile fibers (4), said sheath (3) being bonded to said core (2). Fig. 1

Description

Title of the invention: Linear profile made of reconstituted wood technical field

[0001] The technical field of the invention is that of the design and production of linear profiles, such as in particular panels, boards or beams, made of composite materials obtained from mixtures of fibers or wood particles and binders.

[0002] Such linear profiles are conventionally used in joinery as a substitute for timber. When they possess suitable mechanical properties, they can also be used in building construction. The invention relates more specifically to linear profiles that can be used in this field. Prior art

[0003] In the prior art, there are many types of linear profiles made of composite materials obtained from mixtures of wood fibers or particles and binders. These materials are known by different names that vary according to their composition, in particular according to their proportions of wood particles or fibers.

[0004] Among the materials constituting such linear profiles, we can distinguish in particular the materials corresponding to the generic name of "agglomerated wood" and those corresponding to the generic name of "composite wood".

[0005] Among particleboard, one is particularly well-known: "particleboard," which comes in the form of panels obtained by hot-pressing mixtures of wood fibers and glue. The most frequently used glues contain formaldehyde. These are often urea-formaldehyde or phenol-formaldehyde glues. The wood fibers or particles used are generally residues or waste from the wood industry, making this material inexpensive. Wood fibers generally represent 97% to 98% of the material's weight. Particleboard panels are industrially produced and benefit from consistent quality, good mechanical strength, and are available in various thicknesses, widths, and lengths. Depending on the project, it is possible to obtain large panels with excellent dimensional stability.Unlike solid wood, these panels do not change dimensions in response to temperature variations. However, particleboard panels have unsightly, unfinished surfaces and irregular, rough edges. They are therefore mainly used for concealed elements.

[0006] Another type of agglomerated wood is OSB (Oriented Stranded Board). This type of material comes in the form of panels obtained by hot-pressing wood particles oriented in specific directions and synthetic resins, generally formaldehyde- or isocyanate-based. The proportion of wood fibers in this type of material is typically around 95% by weight. The main advantage of OSB lies in its mechanical performance, due to its unique structure. Furthermore, although robust, OSB is lightweight, making it easy to handle, cut, and drill. It is often favored for interior design projects with a "natural" aesthetic.

[0007] Yet another type of particleboard is known as MDF (Medium Density Fiberboard). This material comes in the form of panels made from mixtures of ground wood fibers and synthetic resins. The wood fiber content of these panels is generally around 85%. This material has the advantage of an attractive appearance, making it suitable for exposed elements. Furthermore, it exhibits good mechanical strength; in particular, it is isotropic, meaning it displays the same properties in all three dimensions. It allows for clean sawing and does not splinter when drilled.

[0008] “Wood composites,” also known as WPC (Wood Plastic Composite), are materials composed of wood fibers embedded in a polymer matrix such as polypropylene, polyethylene, or polyvinyl chloride. These plastics can come from recycling streams. The proportion of wood fibers in this type of material is lower than that of particleboard and generally ranges from 50% to 70% by weight. The appearance and density of wood composites are similar to those of solid wood, particularly exotic woods. They are therefore frequently used as a replacement for solid wood, especially for exterior elements such as decking or exterior wall insulation. However, they have the disadvantages of swelling when exposed to prolonged heat and of having altered mechanical and aesthetic properties when exposed to UV radiation.

[0009] Unlike solid wood, engineered or composite wood products have few, if any (OSB), mechanical properties induced by the direction of the wood fibers. Part of the mechanical strength of these composite materials is conferred by the proportion of binder they contain. In many cases, the greater the proportion of binder in the material, the more its mechanical properties allow for the manufacture of linear profiles whose mechanical properties approach those of linear profiles of the same size made of solid wood.

[0010] However, the use of such binders in the context of composite materials based on wood fibers or particles constituting linear profiles for joinery or construction poses several problems.

[0011] First, some of these binders, such as formaldehyde-based glues, are harmful to humans or the environment. This compound, which is a component of many particleboard products, is also released into the ambient air after the installation of panels made from these materials. This molecule is classified as a carcinogen by the International Agency for Research on Cancer. Its involvement in nasopharyngeal cancers has been documented. Formaldehyde is also believed to be implicated in certain leukemias. Therefore, the use of particleboard containing formaldehyde is not recommended for interior components and has been significantly restricted since the 1980s.

[0012] In order to avoid using formaldehyde-containing binders, it is known to use thermosetting resins, particularly isocyanate-based resins, in the manufacture of particleboard. Although less toxic than formaldehyde-based adhesives, they are nevertheless relatively complex to process. Indeed, they are obtained from two distinct compounds that react with each other under specific conditions, particularly temperature.

[0013] Secondly, the presence of these binders in particleboard or wood composites excludes the waste produced by these products from conventional recycling channels. In practice, it is very difficult, and often economically unfeasible, to separate the binders they contain from the wood particles or fibers with which they are intimately bound, in order to recycle the latter. Alternatively, incinerating this waste leads to the emission of toxic fumes that must be treated, thus reducing its suitability for use in heat production facilities.

[0014] Another drawback of these binders stems from their fossil origin. This origin significantly increases the carbon footprint of the profiles in which they are used. However, the laws and regulations in force in many countries call for a drastic reduction in greenhouse gas emissions and a decrease in the carbon footprint of industrial processes. Societal changes linked to climate change are also resulting in a growing public interest in low-carbon products. Objectives of the invention

[0015] The main objective of the invention is to offer linear profiles that can be used in the field of construction and made from composite materials obtained from a mixture of wood fibers or particles but without a binder of fossil origin, or at least incorporating proportions of binder of fossil origin much lower than in the materials of the prior art, and this while offering equivalent mechanical properties for equivalent profile dimensions.

[0016] One objective of the invention is thus to describe such profiles whose material composite obtained from a mixture of wood fibers or particles, does not, in at least some embodiments, contain any glue based on formaldehyde or other chemicals, and any glue based on isocyanate-type resins or other chemicals.

[0017] Another objective of the invention is to disclose such profiles which, in at least some embodiments, do not incorporate compounds of fossil origin but essentially compounds of plant origin.

[0018] The invention therefore aims to present linear profiles obtained from wood fibers or particles and binders which have both an improved carbon balance compared to those of the prior art while showing, at equal dimensions, equivalent mechanical characteristics.

[0019] An objective of the invention is to propose such linear profiles that can be used in the field of construction and that have mechanical characteristics that are stable over time. Presentation of the invention

[0020] The invention relates to a linear profile that can be used in building construction, said profile comprising a core made of a composite material based on wood fibers or particles and at least one binder, said core being covered with a mechanical reinforcement sheath made of braided textile fibers.

[0021] According to the invention, part of the mechanical properties of the linear profile result from the presence of a mechanical reinforcing sheath surrounding the composite core. Such a mechanical reinforcing sheath enables the linear profile to have superior mechanical properties compared to the core alone. In particular, this sheath provides the profile with better flexural strength, shear strength, and compressive strength than the core alone.

[0022] Compared to linear profiles of the prior art, the mechanical properties of the profiles according to the invention are therefore less dependent on the nature and proportion of the binder used in the composition of the composite material based on wood fibers or particles and binder. Thus, it is possible to consider reducing the proportion of binder in this composite material or using other types of binders than those conventionally used in the prior art.

[0023] According to the invention, the mechanical reinforcement sheath provided around the core of composite material based on wood fibers or particles and at least one binder is made of braided textile fibers. By definition, such textile fibers can be spun and woven.

[0024] These braided textile fibers form a braid over the entire surface of the linear profile, except, where applicable, at its ends. This braid may have several shapes. It can be made from several interlaced strands to form stitches with, for example, a square, triangular, or diamond shape. This braiding can be applied to each side of the core or wrapped around it like a sock.

[0025] Although the mechanical reinforcement sheath made of braided textile fibers may simply be in contact with the core of the composite material, the sheath will preferably be bonded to it. Such bonding between the core and the sheath prevents any relative movement between the core and the sheath, thus transferring the mechanical properties provided by the sheath to each point of the linear profile. The mechanical reinforcement provided by the mechanical sheath bonded to the core thus gives the profile overall mechanical properties superior to the simple sum of the individual contributions of its components.

[0026] This bonding between the sheath and the core can be achieved simply by gluing the sheath to the core using a suitable adhesive.

[0027] However, this bonding is preferably achieved during the manufacturing of the linear profile by bringing the core and the sheath into contact while the core binder is still sufficiently adherent. This results in a linear profile in which the mechanical reinforcement sheath made of textile fibers forms a bond with the core. This technique avoids the need for a specific adhesive to bond the reinforcement sheath to the core.

[0028] According to a preferred embodiment, said wood fibers or particles entering into the composition of the core come from wood residues or wood waste.

[0029] Such wood residues come mainly from the wood industry or its processing, in particular from sawmills, joineries or furniture manufacturers, and are generally in the form of sawdust or shavings.

[0030] As for wood waste, it differs from residues in that it may contain other materials such as paints, varnishes, glues, or metal inserts, and may originate from waste disposal sites or recycling channels. To be used in the manufacture of particleboard or composite wood, it is often necessary to process this waste to remove the other materials, particularly metals, and then to shred it.

[0031] The use of such wood residues or waste makes it possible to reduce the cost of profiles while preserving the wood resource and offers a way to valorize these products.

[0032] The textile fibers used in the composition of the reinforcement sheath of the linear profiles according to the invention can be synthetic or natural fibers.

[0033] Polyamide fibers can be used as synthetic fibers, in particular. or polyester.

[0034] As natural fibers, mineral fibers or vegetable fibers can be used.

[0035] Regarding mineral fibers, these can for example be made of glass or basalt fibers.

[0036] However, preferably, said natural textile fibers are vegetable fibers.

[0037] Preferably, these fibers are chosen from the group consisting of flax fibers, jute fibers, hemp fibers, and cotton fibers. Preferably, the textile fibers are flax fibers. This plant is indeed known for its particularly strong fibers.

[0038] Regarding the binder used in the composition of the core, a hydraulic binder may be used, such as a binder based on ash, blast furnace slag or lime, or alternatively a binder consisting of a thermosetting or cold crosslinking resin (epoxy resin for example).

[0039] However, preferably, the binder used is a binder based on at least one plant-based polymer that hardens upon the addition of water and, where appropriate, in the presence of heat. This plant-based polymer may, in particular, be starch. This starch may advantageously be obtained from plant oilseed cakes such as corn, rapeseed, or sunflower.

[0040] According to a preferred embodiment, the composite material composing the core of the profile includes mechanical reinforcing fibers embedded within it. Such reinforcing fibers are preferably made of plant fibers from textile plants. According to an interesting embodiment, these fibers are fragments of flax straw recovered during the scutching of this plant.

[0041] According to another interesting embodiment of the invention, the composite material constituting the core of the linear profile includes mineral fines. The use of such mineral fines aims to reduce the void ratio of this material. It could, for example, consist of silica fines. List of figures

[0042] The invention and its various advantages will be more easily understood with the aid of the following description of embodiments thereof given by way of example with reference to the drawings in which: - Fig. 1 represents a first embodiment of a linear profile according to the invention during its manufacture; - Fig. 2 represents a second embodiment of a linear profile according to the invention during its manufacture; - Figure 3 schematically represents a testing machine used for perform bending tests on linear profiles according to the invention and linear profiles according to the prior art; - Figures [Fig.4], [Fig.5] and [Fig.6] show results in the form of force / displacement curves from bending tests carried out using the testing machine according to [Fig.3]. Description of implementation methods

[0043] A mixture having the following composition was prepared with the following weight proportions:

[0044] 65% of a mixture of wood chips and sawdust with a bulk density of 50 kg / m3;

[0045] 15% of short fibers (length less than 2.5 mm) obtained by grinding and sieving flax shives with a density of 200 kg / m3;

[0046] 10% of fine siliceous particles, with an average size of less than 80 µm, derived from residues of dust from quarry aggregate crushing;

[0047] 10% binder composed of a 60 / 40 by weight mixture of corn starch and carbohydrates.

[0048] A first mixture of dry materials, free of binder, was prepared and homogenized. This mixture was then preheated to an average constituent temperature of 80°C, and the binder was then incorporated. This final, still-warm mixture was kneaded at room temperature until a homogeneous paste with a moisture content of less than 6% was formed. This paste was then fed into an extrusion die to be hot-formed to a core temperature of 160°C into a solid parallelepiped-shaped core of composite material with a width of 45 mm and a height of 27 mm. A conventional extrusion die, of the type used for manufacturing particleboard, was used for this purpose. It should be noted that this method of manufacturing the core by extrusion is given here merely as an example and is in no way limiting.This manufacturing process can therefore be carried out using other methods such as, for example, hot pressing.

[0049] With reference to figures 1 and 2, upon exiting the extrusion die E, the core 2 was covered with a mechanical reinforcement sheath 3 to form a linear profile 1 according to the invention, in the form of a beam with a width of 45 mm and a height of 27 mm.

[0050] According to [Fig.1], this reinforcing sheath 3 is made up of textile fiber yarns 4 consisting of polyamide monofilaments interlaced together to form an extensible braided net.

[0051] According to [Fig. 2], this reinforcing sheath 3 consists of sixteen textile fiber yarns 4 made of flax fibers parallel to the axis of the core 2, equally distributed around it by means of as many reels B (only one of which is shown) and two fiber yarns textiles 4a and 4b woven around core 2 and coming respectively from two reels C and D.

[0052] Mechanical tests

[0053] A battery of tests was carried out to evaluate the flexural strength and breakage behavior of beams according to [Fig.2] on the one hand and on the other hand of beams of the same dimensions made of solid wood and reconstituted wood obtained from wood residues and formaldehyde glue following the usual prior art technique of hot pressing by jack.

[0054] These tests, known as "3-point bending tests", were carried out according to standard NF EN 408 in a temperature-controlled laboratory (20°C) and in a controlled environment (relative humidity 65%) using an MTS E45-105 tensile testing machine shown schematically in [Fig. 3]. Such a machine has two support points separated by a center distance of 460 mm on which the ends of the tested specimen rest, and a loading point on the central part of the specimen.

[0055] For each type of beam, five test specimens were tested, all having the same dimensions, namely a length of 500 mm, a height of 27 mm and a width of 45 mm.

[0056] At the loading point, symbolized by the arrow in [Fig. 3], a loading speed of 5 mm / min was used. Force measurements were taken using a force sensor with a capacity of 25 kN and a displacement sensor located below the loading point.

[0057] The corresponding force / displacement curves are shown in Figures 4 to 6:

[0058] [Fig. 4] T1 to T5 solid wood test specimens,

[0059] [Fig.5] Test specimens B1 to B5 5 made of reconstituted wood according to the prior art,

[0060] [Fig.6]: BRI to BR5 test specimens made of reconstituted wood with a textile sheath according to the invention.

[0061] These measurements made it possible to calculate the modulus of elasticity and the bending stress, reflecting the strength and stiffness of each of these specimens. For each type of beam, the average of the values ​​obtained for each of the five specimens was calculated, as well as the corresponding standard deviation. These average values ​​are presented in Table 1 (bending stress) and Table 2 (modulus of elasticity) below. [Table 1] Bending Stress (MPa) Beam type Average of 5 specimens Standard deviation Solid wood (T) 64.93 4.53 Engineered wood (BR) 1.87 0.54 According to the invention (BRL) 5.14 0.59 [Table 2] Modulus of elasticity (MPa) Beam Type Average of 5 Specimens Standard Deviation Solid Wood (T) 10578.84 935.52 Reconstituted Wood Prior Art (BR) 305.80 29.82 According to the Invention (BRL) 330.90 67.09

[0064] According to these tests, the mechanical stress and stiffness characteristics known in the literature for solid wood and engineered wood according to the prior art were achieved. Thus, for the same beam cross-section, the breaking strength and the modulus of elasticity of engineered wood are much lower than those of solid wood, by a ratio of approximately 1 / 30.

[0065] These results confirm that reconstituted wood according to the prior art does not have sufficient flexural strength to be used for making construction profiles.

[0066] These results also show that the displacements at failure of the tested solid wood and engineered wood beams are essentially constant and similar, averaging 14 mm and 12 mm respectively (see [Fig. 4] and 5), while the displacements at failure of the beams with the reinforcing sheath of the invention are much higher, averaging 32 mm, representing an increase of 260 to 280%. This demonstrates the ability of the linear profiles according to the invention to deform without breaking and therefore their suitability for use as structural profiles.

Claims

Demands

1. Linear profile (1) used in building construction or joinery, in particular a panel, a board or a beam, comprising a core (2) made of a composite material based on wood fibers or particles and at least one binder, said core being covered with a mechanical reinforcement sheath (3) made of braided natural textile fibers (4), said sheath (3) being attached to said core (2).

2. Linear profile according to claim 1 characterized in that said wood fibers or particles originate from wood residues or wood waste.

3. Linear profile according to claim 1 or 2 characterized in that said natural textile fibers are vegetable fibers.

4. Linear profile according to claim 3 characterized in that said plant fibers are chosen from the group consisting of flax fibers, jute fibers, hemp fibers, cotton fibers.

5. Linear profile according to claim 4 characterized in that said vegetable fibers are flax fibers.

6. Linear profile according to any one of claims 1 to 5 characterized in that said binder is based on a vegetable polymer.

7. Linear profile according to claim 6 characterized in that said vegetable polymer is starch.

8. Linear profile according to any one of claims 1 to 7 characterized in that said composite material includes mechanical reinforcing fibers.

9. Linear profile according to claim 8 characterized in that said mechanical reinforcing fibers are vegetable fibers from textile plants.

10. Linear profile according to claim 9 characterized in that said reinforcing fibers are derived from flax shives.

11. Linear profile according to any one of claims 1 to 10 characterized in that said composite material includes mineral fines.

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