FR3162449A1 - Manufacturing process for a thermal and/or acoustic insulating material - Google Patents

Abstract

The invention relates to a method for manufacturing a thermal and/or acoustic insulating material containing essentially banana fibers, consisting of: (a) collecting banana fibers containing a water content greater than 30% by weight, (b) subjecting the fibers to a first mechanical pressing carried out in such a way as to reduce the water content of the fibers to between 15% and 30% by weight, (c) shaping the fibers obtained in step (b) into a sheet or panel by subjecting them to a second mechanical pressing, said pressing being carried out under a pressure of between 1000 kg/cm² and 6000 kg/cm², for a duration of between 2 minutes and 30 minutes, at a temperature of between 150°C and 200°C.

Description

Method for manufacturing a thermal and/or acoustic insulating material Technical field.

The invention relates to a method for manufacturing a thermally and/or acoustically insulating material containing essentially banana fibers.

The technical field of the invention is that of the manufacture of building materials based on plant fibers, in particular materials used as thermal and/or acoustic insulation for the construction of dwellings and industrial premises, for the automotive industry, industrial vehicles, aeronautics and/or space or the containment of equipment or enclosures subjected to high or low temperatures, as well as other applications requiring lightweight, ecological materials with good insulating properties.

State of the art.

We know of insulating building materials made from plant fibers such as hemp or cotton fibers, as well as coconut, palm, or abaca (Manila hemp) fibers. Hemp fibers are good thermal and acoustic insulators, entirely natural, and therefore easily recyclable. However, their production requires significant resources; indeed, hemp must be cultivated, harvested, and the fibers extracted before being processed.

Cotton wools have the advantage of being able to be produced from recycled cotton fibers obtained, for example, by shredding old fabrics, cleaning, and compacting the fibers. However, these cotton wools are expensive and have very low mechanical strength.

Finally, insulation made from coconut, palm or Abaca fibers is very expensive and requires very heavy resources to extract and process the fibers.

We also know in the prior art of insulating materials based on plant fibers from banana trees such as patent documents FR2846685, WO2005/092985, or WO2011/141644.

The variability in the properties of banana fibers can lead to inconsistent and/or non-homogeneous performance of insulating materials obtained using prior art processes. Furthermore, these known processes can be lengthy and complex to implement.

The invention aims to remedy this situation. In particular, one objective of the invention is to provide a manufacturing process for obtaining an insulating material with uniform and repeatable properties, regardless of the origin of the banana fibers. Another objective of the invention is to provide a manufacturing process that is simple and quick to implement. Yet another objective of the invention is to provide a manufacturing process for obtaining an insulating material with improved insulating and mechanical properties compared to those of the prior art.

Presentation of the invention.

After multiple trials and attempts, the applicant developed a manufacturing process enabling him to achieve the aforementioned objectives.

Thus, the invention relates to a process for manufacturing a thermal and/or acoustic insulating material containing essentially banana fibers, consisting of: (a) collecting banana fibers containing a water content greater than 30% by weight; (b) subjecting the fibers to a first mechanical pressing carried out in such a way as to reduce the water content of the fibers to between 15% and 30% by weight; (c) shaping the fibers obtained in step (b) into a plate or panel by subjecting them to a second mechanical pressing, said pressing being carried out under a pressure of between 1000 Kg/cm² and 6000 Kg/cm², for a duration of between 2 minutes and 30 minutes, at a temperature of between 150°C and 200°C.

This simple and quick process yields insulating boards or panels with a thermal conductivity coefficient (λ) of approximately 0.04 W/(m.K), a value that varies by less than 3% regardless of the origin of the banana fibers. The resulting insulating boards or panels also exhibit excellent resistance to combustion (flame propagation and contribution to fire) and mechanical properties.

Other advantageous features of the invention are listed below. Each of these features may be considered alone or in combination with the notable features defined above. Each of these features contributes, where applicable, to the resolution of specific technical problems defined further in the description and in which the other features defined above do not necessarily participate. The following features may therefore be the subject, where appropriate, of one or more divisional patent applications:

According to one embodiment, the second mechanical pressing is carried out under a pressure of between 2000 Kg/cm2 and 3000 Kg/cm², for a duration of between 4 minutes and 6 minutes, at a temperature of between 165°C and 180°C.

According to one embodiment, the first mechanical pressing is carried out in such a way as to reduce the water content of the fibers to 20% by weight.

According to one embodiment, step (a) consists of collecting banana fibers having an average length of between 10 mm and 20 mm.

According to one embodiment, the second mechanical pressing is followed by a controlled cooling step of the plate or panel.

According to one embodiment, before step (c), the fibers obtained in step (b) are mixed with a polymer, the polymer content of said mixture being less than 30% by weight.

According to one embodiment, the process further includes a step consisting of associating the plate or panel obtained in step (c), of a thickness between 10 mm and 30 mm, with a prefabricated plaster panel.

Another aspect of the invention relates to the use of the material obtained according to the process conforming to one of the aforementioned characteristics, as a fire-retardant material.

Description of the implementation methods.

The material obtained according to the process of the invention essentially consists of banana fibers. "Essentially" means that the material comprises at least 50% by weight of banana fibers, advantageously at least 80% by weight, preferably at least 90% by weight, and optionally 100% by weight. Such a proportion gives the material very low environmental toxicity and very good recyclability, even when the fibers are mixed with a binder. Furthermore, this significantly reduces raw material costs and therefore the production costs of the material.

This material can be used in numerous fields, particularly as thermal insulation, acoustic insulation, fire retardant, and as a heat-insulating material for heating or cooling distribution networks. The resulting sheets or panels are primarily used in residential and commercial building construction, but other applications may be suitable for professionals, such as structural components in vehicles. By way of example, but not limited to, the sheets or panels are used to contain boiler or chimney flues, hot water tanks for residential or commercial use, in the aerospace and automotive industries for containing internal combustion engines, exhaust ducts, and other components, for insulating refrigeration equipment such as cold rooms, refrigerators, and refrigerated vehicles and trucks, as ceiling tiles for acoustic insulation in rooms, as cladding or facing for fire-resistant doors and partitions, or for insulating vehicle interiors.

According to a preferred embodiment, the board or panel obtained by the process according to the invention, with a thickness between 10 mm and 30 mm, is combined with a prefabricated plasterboard panel (type BA10, BA13) to obtain a composite insulating panel that eliminates the need for the traditional use of rock wool to insulate a dwelling. Unlike rock wool, which requires additional space (generally between 80 mm and 400 mm) for installation and integration into wall or floor structures, this composite panel (with a thickness between 25 mm and 50 mm) significantly reduces the overall wall thickness. This results in a significant gain in living space in homes or buildings, while ensuring high-performance and durable insulation.

The process includes a step of collecting banana fibers. In one embodiment, these fibers are obtained by grinding and/or shredding pseudostems and flowering stems of banana plants (fruit-bearing or non-fruit-bearing). The fibers obtained generally contain a water content exceeding 30% by weight.

The best results in terms of insulating and mechanical properties are obtained when the collected fibers have an average length between 10 mm and 20 mm. By "average length" we mean that at least 50% of the fibers, preferably at least 70%, preferably at least 80%, have a length between 10 mm and 20 mm.

Fibers in this length range allow for uniform dispersion and efficient interconnection between fibers during the second mechanical pressing mentioned earlier in the description. This leads to a denser, more homogeneous structure in the formed sheets or panels, improving their air-trapping capacity and, consequently, their thermal and acoustic insulation properties. Furthermore, this fiber length contributes to strengthening the material's mechanical properties by increasing tensile and flexural strength, while maintaining a degree of flexibility.

Some of the results of thermal conductivity and acoustic absorption tests are shown in Table 1 below. Table 1 Properties 15 mm fibers 1 mm fibers 40 mm fibers Thermal conductivity (W/(m·K)) 0.041 0.048 0.052 Sound absorption coefficient (αw) 0.8 0.7 0.6

Materials made with fibers of average length 15 mm exhibit lower thermal conductivity than materials made with fibers of average length 1 mm and fibers of average length 40 mm, and therefore better thermal insulation performance. Similarly, materials made with fibers of average length 15 mm have a higher sound absorption coefficient than materials made with fibers of average length 1 mm and fibers of average length 40 mm, and therefore better sound insulation performance.

After harvesting the banana fibers, they undergo an initial mechanical pressing to reduce their water content to between 15% and 30% by weight. This pressing can be done simply by placing the fibers in a mechanical press and passing them through a rolling mill.

This reduction in initial moisture content prepares the fibers for subsequent process steps and contributes to improved adhesion and the cohesion of the final material, resulting in a more homogeneous density. The applicant observed that excessive moisture reduction, for example, through drying, can make the fibers brittle and fragile. By maintaining a moisture content between 15% and 30%, the fibers retain a degree of flexibility. Furthermore, residual moisture helps maintain fiber cohesion during the final pressing, facilitating the formation of strong inter-fiber bonds. This is particularly important for ensuring a homogeneous and dense structure in the panels or sheets. In addition, it was found that this residual moisture content ensures a uniform distribution of pressure and temperature during the second pressing. The best results are obtained when the initial mechanical pressing is performed in such a way as to reduce the fiber moisture content to 20% by weight.

The fibers obtained after the first mechanical pressing are then formed into a sheet or panel by subjecting them to a second mechanical pressing. This second pressing is carried out under a pressure between 1000 kg/cm² and 6000 kg/cm², for a duration of between 2 and 30 minutes, and at a temperature between 150°C and 200°C. Under these specific conditions, a relatively rigid sheet or panel (Shore A hardness between 80 and 90) is obtained, exhibiting excellent mechanical properties. In particular, the resulting sheet or panel does not crumble and offers very good mechanical strength, making it particularly suitable for applications in construction and insulation. The optimized conditions of pressure, temperature, and heating time promote internal cohesion and the natural adhesion of the banana fibers to each other, without the need for added binders.

The second mechanical pressing can be carried out using mechanical or hydraulic presses that allow for the uniform and constant application of high pressure to the fibers. In one embodiment, the fibers are placed in a flat mold (to obtain flat sheets or panels) or a profiled mold (to obtain sheets or panels with particular profiles, for example corrugated, curved, etc.).

In one embodiment, the mold is shaped so that the plate or panel has one or more recesses or cavities for the passage of a reinforcing post or stake (for example, a metal one) and/or one or more grooves for the passage of reinforcing metal reinforcement. In another embodiment, one or more reinforcing plastic or metal posts or stakes and/or reinforcing metal reinforcement are installed in the mold so that the fibers are pressed and heated around these elements to form a monolithic assembly. Such a reinforced plate or panel can then serve as a load-bearing or structural element in the construction industry.

Under the specific conditions of the second mechanical pressing, the thermal conductivity of the plate or panel varies between 0.041 W/m·K and 0.045 W/m·K (according to ISO 8301) and the sound absorption coefficient αw varies between 0.75 and 0.8 (according to ISO 11654). The best results in terms of thermal conductivity (λ ≈ 0.041 W/m·K) and sound absorption (αw ≈ 0.8) are obtained when the second mechanical pressing is carried out under a pressure between 2000 kg/cm² and 3000 kg/cm², for a duration of between 4 and 6 minutes, at a temperature between 165°C and 180°C.

The insulating boards or panels obtained under the specific conditions of the second mechanical pressing also exhibit very good results in terms of resistance to combustion (flame propagation and contribution to fire) and mechanical properties. The following tests were carried out on samples containing 100% banana fibers by weight:
- a vertical flammability test (IEC 60695-11-10), consisting of evaluating the burning time and the droplet of flaming particles for vertically oriented samples. The following levels are used: V-0 (flame extinguishing < 10s without flaming droplets), V-1 (flame extinguishing < 30s without flaming droplets), V-2 (flame extinguishing < 60s with a few flaming droplets).
- Flame spread test (EN 13501-1), which measures the flame spread rate and smoke density for construction materials. The following levels are used: Class A (Flame spread: 0-25), Class B (Flame spread: 26-50), Class C (Flame spread: 51-75).

The results show that the insulating boards or panels achieve level V-0 in the flammability test and level Class A in the flame propagation test. It follows that the material obtained according to the process of the invention can be produced as a fire-retardant material.

After the second mechanical pressing, the slab or panel is then removed from the mold and can be kept and stored as is for future use, or cut into specific formats, for example into standard-sized slabs or panels. They can also, if necessary, undergo post-treatment or be coated to improve their appearance.

In one embodiment, the second mechanical pressing is followed by a controlled cooling step of the slab or panel. This controlled cooling can be achieved by placing the slab or panel in a climate chamber or by subjecting it to a controlled airflow. The best results are obtained when the cooling rate is between 5°C and 10°C per hour, until ambient temperature is reached. The applicant has observed that this controlled cooling promotes better cohesion between the fibers, further consolidating the structure of the slab or panel and enhancing its mechanical stability and resistance to tensile, compressive, and flexural forces.

In one embodiment, the fibers obtained after the first mechanical pressing are mixed with a polymer before undergoing a second mechanical pressing. Thus, it is the banana fiber + polymer mixture that undergoes the second mechanical pressing. The resulting composite material is then more rigid, with higher mechanical strength.

The polymer used is preferably chosen from the following family: nitrile, PVC (polyvinyl chloride), FKM (fluoroelastomers), EPDM (ethylene propylene diene monomer), natural rubber, silicone, and PPD-T (poly(p-phenylene terephthalamide)). Nitrile, PVC, and FKM provide the material with increased protection against water absorption, mold, and weathering, thus extending its lifespan. EPDM, natural rubber, and silicone provide increased elasticity, allowing the material to better absorb shocks and vibrations. PPD-T enhances the mechanical properties of the resulting material, particularly its rigidity, as well as its thermal insulation properties.

The arrangement of the various elements and/or means and/or steps of the invention, in the embodiments described above, should not be understood as requiring such an arrangement in all implementations. Various variants may be envisaged.

Furthermore, one or more features and/or steps described only in one embodiment can be generalized to other embodiments. Similarly, one or more features and/or steps described only in one embodiment can be combined with one or more other features and/or steps described only in another embodiment.

The use of the verb "comporter", "comprendre" or "include" and its conjugated forms does not exclude the presence of other elements or steps than those stated in a claim.

Claims (8)

A process for manufacturing a thermal and/or acoustic insulating material containing essentially banana fibers, consisting of:
(a) collect banana fibers containing a water content exceeding 30% by weight,
(b) subject the fibres to a first mechanical pressing carried out in such a way as to reduce the water content of the fibres to between 15% and 30% by weight,
(c) conform the fibers obtained in step (b) into the form of a plate or panel by subjecting them to a second mechanical pressing, said pressing being carried out under a pressure of between 1000 Kg/cm² and 6000 Kg/cm², for a period of between 2 minutes and 30 minutes, at a temperature of between 150°C and 200°C. A method according to claim 1, wherein the second mechanical pressing is carried out under a pressure of between 2000 Kg/cm2 and 3000 Kg/cm², for a period of between 4 minutes and 6 minutes, at a temperature of between 165°C and 180°C. A method according to any one of the preceding claims, wherein the first mechanical pressing is carried out in such a way as to reduce the water content of the fibers to 20% by weight. A method according to any one of the preceding claims, wherein step (a) consists of collecting banana fibers having an average length of between 10 mm and 20 mm. A method according to any one of the preceding claims, wherein the second mechanical pressing is followed by a controlled cooling step of the plate or panel. A process according to any one of the preceding claims, wherein prior to step (c), the fibers obtained in step (b) are mixed with a polymer, the polymer content of said mixture being less than 30% by weight. A method according to any one of the preceding claims, comprising a step of associating the plate or panel obtained in step (c), of a thickness between 10 mm and 30 mm, with a prefabricated plaster panel. Use of the material obtained according to the process according to claim 1, as a flame-retardant material.