EP3332072B1

EP3332072B1 - A method for producing sustainable composite materials designed for the production of elements for structural or non-structural use, and the material obtained

Info

Publication number: EP3332072B1
Application number: EP16763563.0A
Authority: EP
Inventors: Matteo BARBARI; Leonardo CONTI; Bernardo MONTI; Massimo Monti; Giuseppe Rossi; Federico Rotini; Marco TOGNI
Original assignee: Universita degli Studi di Firenze
Current assignee: Universita degli Studi di Firenze
Priority date: 2015-08-07
Filing date: 2016-07-28
Publication date: 2019-05-08
Anticipated expiration: 2036-07-28
Also published as: WO2017025786A1; CN108026726A; EP3332072A1

Description

Field of the invention

The invention relates to a new method for the production of pre-compressed elements made of composite material, such as blocks, panels, also for packaging, prefabricated walls, beams, and slabs for structural or non-structural use in the building sector, and the material thus obtained.
More in particular, the method envisages production of pre-compressed elements, such as blocks, panels, prefabricated walls, beams, and slabs, with a composite material comprising an amount of compostable dry fibrous organic material in the compressive state, contained within closed cells, the foregoing all contained within a casing. The cells and the casing are in the tensile state and made of compostable heat-meltable organic polymers, said fibrous organic material and said cells and casing being configured for maintaining a permanent state of co-action with the fibrous organic material permanently compressed and the casing made of bioplastic material permanently tensioned.
The material obtained is a composite material prevalently constituted by compostable dry fibrous organic materials, amongst which there may be listed, even though the list is not exhaustive, straw, stalks, reeds, leaves, twigs, grass, materials deriving from the processing of wood, feathers, animal bristles, or mixtures thereof, and for the remaining part by materials that possess a degree of environmental sustainability similar to that of the aforesaid fibrous organic materials, i.e., compostable organic biopolymers deriving from widely cultivated vegetal species. All the component materials are compostable in accordance with the UNI EN13432 standard.
The method according to the invention consequently envisages production of a composite material, constituted by a mixture of fibrous organic materials and solid-state bioplastic materials, and then in succession steps of compression and heating, for example with the use of generators of high-frequency electromagnetic radiation (microwaves).
The elements thus obtained present both structural load-bearing characteristics and characteristics of thermal insulation, and can be used in the building sector, as blocks, panels, prefabricated walls, beams, and slabs, to replace elements made of other materials, currently widespread in the building sector, such as thermally insulating brick blocks, expanded-clay blocks, autoclaved-aerated-concrete blocks, thermally insulated panels, prefabricated walls, prefabricated beams, prefabricated pillars, and prefabricated slabs.

Prior art

Known to the prior art are elements for structural and non-structural use made of composite material comprising straw and other fibrous materials, and binders.
An example of such elements is known from the publication "Design and performance of load-bearing shear walls made from composite rice straw blocks" filed in the name of K.R. Camann et al. (2010 Structures Congress - ASCE).
Known from the document No. CN103448107 are structural boards made of hot-pressed straw formed by a number of layers and by isocyanate resin as binding agent.
Known from the document No. CN103538138 are brick tiles made of bamboo and straw, hot-compressed and cooled.
Known from the document No. CN 103419393 are a mould and the pressing device for a process for forming a straw building block.
Known from the document No. CN102328336 is a method for producing brick tiles and prefabricated components with stalks of various species, weeds, and an adhesive with a base of polyurethane foam, which envisages cutting the weeds and stalks to a variable length, drying the material using microwaves, mixing with glue, moulding, adding polyurethane-foam adhesive, followed by a step of hot pressing.
Known from the document No. CN101736850 are wheat-straw compression-moulding blocks for walls.
Known from the document No. WO200939440 are blocks constituted by rice straw and isocyanate adhesives, for the construction of walls of buildings.
Known from the documents Nos. US20050223671 and US20030208982 are blocks, and the corresponding manufacturing method, constituted by rice-straw stalks treated with a humidity-inhibiting substance and binding material, aligned vertically parallel to one another, which are pressed laterally and held together by bands made of various materials. Made in the opposite faces of the blocks are holes for enabling passage of structural elements, mortars, and/or both.
Known from the document No. US5507988 is a machine for beating, mixing with additives, laying, and pressing fibrous materials (amongst which also straw) in order to produce building blocks. The binder used is an adhesive or alternatively a cement (mortar, etc.). The material is crushed into small pieces that are then pressed and glued. The product must be left in position for a sufficiently long time for adhesion to take place.
Known from the document No. EP345125 is a heat-shrinking system that comprises within it a layer of straw (or alternatively various polymers, such as expanded polyurethane or polystyrene, or waste products) for the production of building blocks.
Known from the document No. SE7905308 is a self-propelled machine capable of stacking and compressing the straw in all directions in space, heating it with a microwave heater, compressing it, and then cooling it to obtain a block.
From CA2229589 methods and apparatuses are disclosed by which organic fibre as wood and cereal straw are oriented into strands, packed together and tightly enclosed in strong mesh to form building blocks. The orientation of the strands and the friction between them creates a firm block structure to serve as insulating core of stressed skin sandwich walls and other building components.
Systems of a known type present, however, numerous limits, in particular in relation to the technical purpose of producing elements for structural use.
A first drawback lies in the fact that none of the systems of a known type envisages production of elements constituted exclusively by compostable materials.
A second drawback lies in the fact that the systems of a known type envisage a step of compression of fibrous materials of natural origin for the formation of elements, generally after prior wetting thereof, but do not envisage the capacity of the elements to maintain the internal state of stress, and consequently are not in a state of pre-compression in their configuration of use.
A further drawback lies in the fact that none of the systems of a known type envisages the production of elements constituted exclusively by compostable materials.
In other words, the materials of a known type are defined as "pre-compressed" simply in the sense that during packaging the product is compressed, but not that it is able to maintain its internal stresses.
In particular, in the cases where, during packaging, the fibrous organic material is wet with any liquid, it loses almost completely its own mechanical characteristics of elastic return in so far as, instead of tending to re-assume its own initial shape, it adapts "plastically" to the new shape that is imposed by the compression process.

Purpose of the invention

Consequently, a first purpose of the invention is to propose a method for producing pre-compressed elements made of composite material comprising fibrous material, for example straw, and a binding material, which, during preparation, are subjected one to compression and the other to tension, in such a way that, once the element is obtained and has acquired its final shape, it substantially preserves, for each of its own component materials, the compressive and tensile internal stresses.
In addition, a purpose of the invention is to produce elements for building purposes constituted exclusively by compostable materials.

Summary of the invention

The above purposes are achieved by a method and an apparatus according to one or more of the annexed claims.
A first advantage lies in the fact that the method enables production of prefabricated elements subject to states of internal co-action, in particular pre-compression, that are designed to improve the behaviour thereof during use. In particular, the elements produced with the present system are "pre-tested" for compression in so far as, during their production, they are subjected to stresses much higher than the ones that they will be required to withstand during use.
A further advantage of the method lies in the fact that pre-compression reduces to a significant extent the deformations of the block during use.
A further advantage of the method lies in the fact that it enables a composite material to be obtained, and hence elements produced therewith, which have a volumic mass having a value that may vary according to the uses to which they are put, i.e., whereby to a greater force of compression exerted during manufacture there corresponds a higher value of the final volumic mass, and hence a higher mechanical load-bearing capacity and a lower thermal insulation.
A further advantage lies in the fact that the elements obtained possess high characteristics of both thermal and acoustic insulation, due both to the intrinsic properties of the component materials (fibrous organic material and binding material, i.e., compostable biopolymers) and to the fact that entrapped within it are an extremely high number of air cells not communicating with one another or with the outside world.
A further advantage lies in the fact that the element obtained is not only biodegradable, but totally compostable in so far as it is made up only of materials that are compostable according to the UNI EN 13432 standard and hence possess an extremely high degree of environmental sustainability.
The above and further advantages will be better understood by any person skilled in the branch from the ensuing description and from the annexed drawings, which refer, by way of non-limiting example, to a masonry block, and in which:

Figure 1 shows an example, in cross-sectional view in any direction, of an element made of a material according to the method of the invention, highlighted in which is the arrangement within the element of the materials making up the composite material;
Figure 2 shows examples, in axonometric view, of elements obtained with the material of the invention according to Figure 1 in modular conformation;
Figure 3 shows examples, in a second axonometric view, of elements according to Figure 1 in modular conformation;
Figures 4a, 4b show examples, in two orthogonal side views, of blocks obtained with the material of the invention according to Figure 1 in modular conformation;
Figures 5-5a show by way of example, in perspective view and cross-sectional view, respectively, an arrangement of fibrous material and bioplastic material for the production of a block obtained with the material of the invention; and
Figure 6 shows a cross-sectional view of a compression machine for actuating the mould.

Detailed description

Described with reference to the attached drawings are a preferred non-limiting embodiment (referring to a masonry block) of a method according to the invention for the production of pre-compressed elements made of composite materials for structural or non-structural use in the building sector.
In the preferred embodiment described herein, the method envisages preparation of a mould 8 having a shape and dimensions corresponding to the desired final shape and dimensions of the block.
Preferably, the mould 8 is made of a material permeable to high-frequency electromagnetic radiation (microwaves). By way of non-exhaustive example, the mould may be made of aluminium, fibre-glass, wood materials, plastic materials.
The mould is formed by side walls 12, a bottom 13, and a piston/lid 9 that can slide in the mould for compressing the materials set therein.
Preferably, the mould is of a type that can be taken apart in order to facilitate extraction of the finished block.
In this description, for reasons of clarity and simplicity, it is assumed that the side walls 12 are vertical, that the bottom 13 is horizontal, and that the piston/lid 9 is horizontal and compresses the material moving from top down; however, the method may be implemented also with arrangement of the mould inclined in any way or turned over.
Once the mould has been prearranged, the method envisages formation of bundles or cylinders 4 formed by the dry fibrous organic material 7, wrapped in a sheet of bioplastic material, and laying on the bottom, on the side walls of the mould, and on top of the cylinders of sheets of bioplastic material so that they will complete the outer coating or casing 2 of the block.
In the framework of the present description, by the term "bioplastic material" is meant an organic polymer of natural origin, such as compostable bioplastic of the type used for the production of compostable bags known by the brand name Mater-bi®, manufactured by the company Novamont S.p.A starting from maize seed.
In various embodiments, the dry fibrous organic material may be constituted, by way of example by straw, stalks, reeds, leaves, twigs, grass, materials deriving from the processing of wood, feathers, animal bristles, or mixtures thereof, having a length indicatively of not less than 50 mm.
In the framework of the present description by "dry fibrous organic material" is meant a material with a very low water content, for example less than 14%, used dry in so far as it is not moistened at any point during the manufacturing process so that it will preserve its own original physical/mechanical characteristics.
Preferably, the cylinders 4 have a length approximately equal to that of the side walls 12 of the mould and have a mean diameter that can be chosen according to the physical/mechanical characteristics that it is desired to obtain for the final block made of composite material. Moreover, the cylinders 4 are in a number sufficient to fill the mould completely and are arranged vertically, i.e., according to the direction of sliding of the piston 9, so that the fibres of the fibrous organic material will be perpendicular to the piston/lid. Advantageously, with this arrangement, the fibres of the fibrous organic material completely fill the mould and are perpendicular to the piston/lid and, once compressed, assume an arrangement in all directions, and not only horizontal, so as to bestow upon the finished block 1 an adequate shear strength.
Given the same dimensions of the mould, to a smaller diameter of the cylinders there will correspond a greater number thereof, and hence a higher value of the ratio between bioplastic material and fibrous organic material. In the production of the cylinders, a pressure can be exerted having a value determined according to the desired final density, i.e., a higher value for higher densities, and a lower value when a lower density is desired. In various examples of application, blocks having a volumic mass of approximately 400 kg/m³ can be used for erecting load-bearing walls of residential buildings, for example buildings with floor slabs spanning approximately 5 m, up to ten storeys in height, whereas blocks having a volumic mass of approximately 100 kg/m³ can be used for erecting curtain walls of buildings having a frame structure.
In order to prevent the sheets of bioplastic material, by melting, from adhering to the internal surfaces of the mould it is possible to envisage laying on the bottom, on the side walls, and on the internal surface of the piston/lid a cement form-removing material, i.e., a material that facilitates detachment of the finished block 1 from the mould.
Furthermore, it is also possible to lay on the bottom, on the side walls, and on the internal surface of the piston/lid, materials that, while binding with the bioplastic that constitutes the outer casing of the block, increase adherence of mortars and glues used for production of the walls and of the building products and laying of plasters and paints. According to the use envisaged for the blocks, these materials may be: netting, or wires, or fabrics made of metal; netting, or wires, or fabrics made of fibre-glass; netting, or wires, or fabrics made of plastic; netting, or wires, or fabrics of an organic nature; granules, or sand, or powders of a non-organic nature; granules, or sand, or powders of an organic nature.
Once the materials have been introduced into the mould as described above, the mould can be installed in a pressing machine 14 equipped with a stem 10 for operating the piston/lid 9 so that the piston/lid will compress the materials inside, i.e., the cylinders 4 and the sheets of bioplastic material of the casing 2.
In various applications, the value of the pressure to be exerted varies according to the desired final dimensions and density of the block, and may be between 1.0 N/mm² and 13 N/mm², or higher.
In an example of application, to obtain a block made up of wheat straw, having dimensions of 0.4 x 0.8 m, and a final volumic mass of approximately 300 kg/m³, a pressure of approximately 4 N/mm² is required.
It is specified that, once subjected to compression testing, in the range of the values of possible variation of accidental loads during use, i.e., between 0.4 N/mm² and 0.6 N/mm², the blocks of composite material undergo a deformation indicatively in the region of 0.40 mm/m.
With the piston/lid kept in the final position reached, and hence with the fibrous material in the compressive state, the method envisages a step of heating up to approximately 80°C, preferably implemented by operating generators 11 of high-frequency electromagnetic radiation (microwaves), for the time necessary (for example, approximately 300-600 s) to obtain complete melting of the bioplastic material, and hence gluing thereof to the fibrous organic material. The generators 11 are advantageously arranged so as to obtain a uniform distribution of the electromagnetic waves in the mass of the materials contained in the mould.
According to the invention, the heating step occurs in such a way that the temperature reached is sufficient to lead to melting of the bioplastic material but not alter the physical/mechanical characteristics of the fibrous organic material.
By way of example, to produce a block made up of wheat straw, of the dimensions of 0.4 x 0.8 m, having the final volumic mass of approximately 300 kg/m³, radiation for a duration of approximately 300 s is necessary, with a power of approximately 6000 W.
At the end of the heating step, still keeping the piston in the final position reached, and hence with the fibrous material in the compressive state, a step of cooling of the materials is carried out, of a forced or spontaneous type, up to solidification of the bioplastic material and to subsequent extraction of the finished block.
With the method described a finished block 1 is obtained, comprising an amount of dry fibrous organic material 7 in the compressive state, contained within a casing 2 in the tensile state and made of a heat-meltable bioplastic compostable material.
Preferably, the fibrous organic material is, at the end of the process, constituted by stalks of fibrous material without a single preferential orientation but arranged in all directions. Advantageously, the absence of a preferential direction bestows upon the block shear strength in all directions.
With reference to Figure 1, in a preferred example of embodiment, the block 1 comprises a extensive honeycomb structure 3 within the block constituted by a tri-directional lattice of heat-meltable bioplastic compostable material, formed by a set of closed cells connected both together and to the outer casing, in which the bioplastic material constituting the outer casing and the walls of the cells adheres to the straw adjacent to the bioplastic material. Figure 1 shows, in particular, the arrangement within the block 1 of the fibrous material 7 and of the closed cells of bioplastic material 3, according to a cross-sectional view of the block taken in any direction, since the pattern of distribution of the closed cells of bioplastic material and of the straw is the same in all directions.
A material according to the invention consequently comprises an amount of dry fibrous organic material 7 in the compressive state, contained within a casing 2 in the tensile state, which is made of a heat-meltable bioplastic compostable material.
According to the invention, the fibrous organic material and the casing are configured for maintaining a permanent state of co-action, with the fibrous organic material permanently compressed and the casing made of bioplastic material permanently tensioned. Advantageously, with this solution, the block behaves like a brick tile pre-tested for compressive stresses lower than or equal to the pre-compression value.
Advantageously, the absence of a preferential direction bestows upon the block shear strength in all directions.
The material of the invention can advantageously be used, for example, for making walls. It is emphasised that this is a possible application of the material. Since the configuration of the element can change if the material is used for making beams or slabs, in this case reinforcement steel will be present.
For this purpose, it has proven useful to adopt a modular conformation, illustrated in Figures 2-4, comprising a combination of recesses 5 and protrusions 6, present for example on opposite faces of the block, configured for enabling positioning of a number of blocks 1 on top of one another and the erection of vertical walls with good strength in regard to horizontal shear stresses.
In the example described, the recesses and the protrusions 5, 6 are obtained on the horizontal faces of the block, but it is understood that, according to the use, the recesses and the protrusions may be positioned indifferently upwards and/or downwards, and/or laterally on the side faces].
Preferably, a wall according to the invention is made up of a plurality of blocks of the type described above, joined together by means of compostable adhesives, for example glue of animal origin, produced with skins and bones deriving, as waste products, from the processing of hides, or else glue of vegetable origin produced with starches of cereal origin. Furthermore, in order to increase adherence of the mortars and of the glues used for construction of the walls and of the building products and laying of plasters, the outer surfaces of the blocks are provided with materials stably adherent to the casing 2, i.e., materials that can bind with the bioplastic that constitutes the casing.
The above materials, according to the use envisaged for the blocks, may be: netting, or wires, or fabrics made of metal; netting, or wires, or fabrics made of fibre-glass; netting, or wires, or fabrics made of plastic; netting, or wires, or fabrics of an organic nature; granules, or sand, or powders of a non-organic nature; granules, or sand, or powders of an organic nature.
The present invention has been described according to preferred embodiments, but equivalent variants may be devised, without thereby departing from the sphere of protection of the invention.

Claims

A method for producing sustainable composite materials designed for the production of pre-compressed elements, such as blocks, panels, prefabricated walls, beams, and slabs for structural or non-structural use in the building sector, comprising the following steps:
providing an amount of a dry fibrous organic material (7);

providing a first outer casing made of a heat-meltable bioplastic material (2) for containing the fibrous material for formation of a composite material;

providing a plurality of inner casings containing portions of said fibrous material; and

compressing the composite material comprising the fibrous material (7) and the outer and inner casings of plastic material at a compressive stress higher than 1.0 N/mm², preferably between 1.0 N/mm² and 13.0 N/mm²;

heating the composite material in the compressive state up to melting of the outer and inner casings and gluing thereof to the fibrous organic material so as to obtain an extensive honeycomb structure (3) constituted by a tri-directional lattice of bioplastic material formed by a set of closed cells connected both together and to the outer casing and adherent to the fibrous organic material in contact therewith; and

cooling the composite material in the compressive state up to solidification of the honeycomb structure made of bioplastic material in order to maintain a state of co-action in permanent equilibrium with the fibrous organic material permanently compressed and the bioplastic material permanently tensioned.
The method according to Claim 1, wherein:
said fibrous material (7) is prearranged in the form of a plurality of bundles arranged parallel to one another and each wrapped in a sheet of heat-meltable bioplastic material to form elementary cylinders (4), which are to form closed cells for containing the fibrous material;

said cylinders (4) are arranged within a mould (8) and compressed by means of a piston (9) having a compression stroke parallel to the cylinders (4) in such a way that the fibrous material (7), as a result of compression within the mould (8), sets itself in all directions;

said heating step occurring up to melting of the casing (2) and of said sheets of the cylinders (4).
The method according to Claim 1 or Claim 2, wherein said heating step is implemented by irradiation with electromagnetic radiation at high frequency in the range of 2000 - 4000 MHz, preferably with a power of between 5000 W and 10 000 W.
The method according to either Claims 2 or Claim 3, wherein said mould is made of a material permeable to electromagnetic radiation.
The method according to any one of Claims 2-4, wherein said cylinders (4) are obtained by exerting a pressure varying according to the desired final density of the fibrous material.
The method according to any one of Claims 2-5, wherein said mould is a mould that can be taken apart.
The method according to any one of Claims 2-6, comprising a step of application of sheets of bioplastic material on the bottom and on the side walls of the mould, and between said piston and said fibrous material so as to coat the internal surfaces of the mould completely.
The method according to any one of Claims 2-7, comprising a step of application of a form-removing material in direct contact with at least part of the internal surface of the mould in order to prevent the bioplastic material, by melting, from adhering to the internal surfaces of the mould.
The method according to any one of Claims 2-8, comprising a step of application, between at least part of the internal surface of the mould and/or of the piston and the casing, of materials designed to adhere both to the bioplastic material and to the adhesive used for gluing a number of blocks, preferably materials selected from: netting, or wires, or fabrics made of metal; netting, or wires, or fabrics made of fibre-glass; netting, or wires, or fabrics made of plastic; netting, or wires, or fabrics of an organic nature; granules, or sand, or powders of a non-organic nature; and granules, or sand, or powders of an organic nature.
The method according to any one of Claims 2-9, wherein said step of irradiation with high-frequency electromagnetic radiation is implemented in a uniform way and for the time necessary to obtain complete melting of the bioplastic material, and gluing thereof to the fibrous organic material.
A material (1) for structural and non-structural use designed for the production of pre-compressed elements, such as blocks, panels, prefabricated walls, beams, and slabs for structural or non-structural use in the building sector, comprising an amount of dry fibrous organic material (7) in the compressive state, contained within closed cells made of bioplastic compostable material, the foregoing all contained in a casing (2) made of bioplastic compostable material, said cells and said casing (2) being in the tensile state, characterized in that said cells and said casing (2) are made of compostable heat-meltable organic polymers, said fibrous organic material, said cells, and said casing being configured for maintaining a permanent state of co-action with the fibrous organic material permanently compressed and the casing made of bioplastic material permanently tensioned.
The material according to Claim 11, wherein said fibrous organic material is constituted by stalks without preferential orientation so as to bestow upon the block shear strength in all directions.
The material according to either Claim 11 or Claim 12, comprising a honeycomb structure (3) constituted by a tri-directional lattice formed by a set of closed cells made of bioplastic material containing fibrous organic material and connected both together and to the outer casing.
The material according to Claim 13, obtained starting from a plurality of bundles of fibrous material (7) arranged parallel to one another and each wrapped in a sheet of heat-meltable bioplastic material to form elementary cylinders (4), the cylinders (4) being then in turn inserted in a casing (2).
The material according to any one of Claims 11 to 13, wherein one or more of the outer surfaces are provided with a layer of a material stably adherent to the casing (2), designed to enable effective adherence of plasters and paints.