FR2746078A1 - PROCESS AND MACHINE FOR THE MANUFACTURE OF BIODEGRADABLE SUBSTITUTES FOR PARTS IN PARTICULAR FOR PACKAGING AND PRODUCTS THUS OBTAINED - Google Patents

Abstract

A method for making a biodegradable substitute for materials such as polystyrene or polyethylene or polyurethane foam with a view to producing industrial parts that are particularly suitable for packaging, is disclosed. The method comprises the steps of (a) grinding and sizing cereal straw according to the desired final density of the substitute, (b) optionally but advantageously mixing the straw with bran produced by cereal processing and having a predetermined size, and moistening the straw/bran, (c) adding an adhesive and mixing, (d) compressing the resulting mixture to form an agglomerate with an isotropic structure, and (e) through-drying the mixture using means enabling water to be drawn from the inside to the outside of the agglomerate, optionally in combination with external drying. A machine for carrying out the method, and a product produced by means of said machine, are also disclosed.

Description

PROCESS AND MACHINE FOR THE MANUFACTURE OF SUBSTITUTES
BIODEGRADABLE PARTS PARTICULARLY INTENDED FOR PACKAGING
AND PRODUCTS THUS OBTAINED
The present invention relates to a process for manufacturing biodegradable parts rather intended for professional use such as, for example, prismatic tubes, molds of concrete parts for the building industry, hearts of electrical coils, and ..., and more particularly in the field of packaging, or even in obtaining wedging elements; the biodegradable parts thus obtained from cereal straws mixed with milling outlets with starchy binders, advantageously supplemented with natural biodegradable glues, constitute remarkable substitutes for plastic materials, polystyrene and other rigid or flexible foams made of polyethylene or polyurethane, systematically used in the manufacture of many industrial products.

 The invention also relates to a machine implementing such a method of manufacturing biodegradable parts, and also relates to particular products produced by said machine.

 Everyone today knows the problems relating to the preservation of the environment, linked to the use of a large number of components with a low or even zero coefficient of biodegradability. Faced with the almost insurmountable problems of recycling such components, many countries today prohibit their use, whether they are used in the manufacture of the products themselves or in their packaging, such as, for example, the wedging elements commonly produced. made of polystyrene or expanded foam.

 For a long time now, it has been thought to use, to replace these biologically non-degradable components, plants which are moreover produced in a quantity largely sufficient to enter into an industrial manufacturing process. Essentially, these are cereal straws, such as wheat, flax, etc., which are produced, for example, on 5 million hectares in France at the rate of 1.5 tonnes per hectare.

 We also know that the issues of milling, that is to say the big and small bran, which come from the transformation of cereals into flour and which can occur in different particle sizes, constitute a very interesting raw material in biodegradable plant substitutes. For this purpose, it is interesting to observe that the bran, by its highly variable size, provides in mixture with the cereal straws, a density regulator of the substitute products; moreover, everyone knows that the composition of the bran is particularly remarkable in that it can provide up to 20% starch, and we now know that the addition of bran in cereal straw mixtures contributes to a clear improvement of the surface condition by filling the interstices of the mass, while contributing to an obvious improvement in the bonding of the assembly, thanks to its high starch content.

A number of substitute products are already known which have already been the subject of prior patents; these patents can be grouped into two main categories
a) - Manufacture by molding a moistened paste based on cellulose-rich and starchy materials, followed by baking between 70 and 2500C carried out if necessary under pressure. An example of this first category is described in patent DE-4009408 in the name of
KIENLE.

 b) - Manufacture by extrusion of a paste similar to the previous category containing, where appropriate, additional additives. A typical manufacturing example is described in international application WO93 / 03976 in the name of SCHAAF TECHNOLOGY.

These two main production lines for biologically degradable products have major drawbacks, in that it is first of all difficult to control the consistency of said products, and in particular their mechanical characteristics, such as resistance to pressure, homogeneity. structure, the ability of the products to withstand pressure, bending, or even shock stresses, the surface condition which is often difficult to control; however, the major drawback of the two techniques known in the art
Prior to this, the energy consumption necessary for cooking the products is particularly high, and it should be noted that, in addition, the previous processes require large quantities of glue and water to achieve only satisfactory mechanical results.

 The main object of the present invention is therefore to propose a process for manufacturing plant substitutes according to a third sector, excluding, a priori, cooking and extrusion techniques, which consume too much energy, glue and water.

 In this regard, there is proposed according to the invention a process for obtaining a biodegradable substitute for materials such as polystyrene or polyethylene or polyurethane foam for the manufacture of industrial parts in particular intended for the packaging field, characterized by the succession of the following stages - a) grinding and sizing the cereal straw as a function of the final density of the desired substitute, - b) advantageous mixing, although not compulsory, with bran from the transformation of cereals according to a determined particle size, and humidification of the straw / bran mixture, - c) addition of glue and mixing, - d) compression of the preceding mixture to form an agglomerate with an isotropic structure, - e) drying to the core by means allowing the water to be extracted from the interior towards the outside of the agglomeration, advantageously combined with external drying.

 Of course, one of the particularly advantageous techniques for implementing step e of the method according to the invention consists in subjecting the straw / bran / glue mixture to high frequency radiation, with the advantage of extracting the internal humidity in the straw fibers from the core of the fiber to the outside thereof, insofar as it is well known that the penetration of such radiations creates in the heart of the fiber a progressive vaporization of the molecules 'water which therefore naturally tend to escape from the fiber up to its periphery.

 It is then remarkable to observe that the water vapor thus extracted from the core of the fibers of the plant mixture, advantageously wets the glue grains which, according to one of the variants of the invention detailed below, have been previously mixed. to plants in the form of a powder, the granulometric fineness of which will allow a very good distribution all around the fibers and, of course, in contact with the fibers together; the mechanism for fixing these fibers together is then well understood by bonding resulting from the advantageous combination of uniformly distributed glue grains, and from the supply of water in the form of vapor extracted from the direct action of high frequency radiation. .

 It is obvious that the quantities of residual water as well as the drying can be advantageously obtained by subjecting the agglomerate to a current of hot air at a temperature compatible with the components of the mixture.

 According to additional characteristics of the invention, provision is made to select the nature and the size of the components entering into the plant mixture if it is known that the mechanical characteristics of the agglomerate obtained by any sector, are linked to the granulation of the straw, on the one hand to the granulation of the bran on the other hand, it is however always forgotten the granulation of the binder; this is apparent from the fact that usually the binders come from liquid glue such as phenolic glues, or starchy glues or urea formaldehyde, or glue in powder form previously wetted before incorporation into the mixture of straws.

 As has been said above, the fact of introducing, according to a particularly preferred variant of the invention, a powdered glue, allows the grains of powder to be distributed fairly finely around the fibers making up the straw / milling mixture. Of course, the finer the granulation of the binder, the greater the distribution, and the more effective the inter-fiber bonding proves to be.

 It will now be understood that the process according to the invention makes it possible to obtain substitutes for a large number of industrial products formed from polystyrene, polyethylene or polyurethane foam, having at least equivalent mechanical characteristics and costs. manufacturing significantly lower than previously known sectors.

 The invention will be better understood and above all many other advantages will emerge from the description which will be given of several variants of the process for the production of biodegradable substitutes as well as a machine implementing said process and the product finally obtained, given as of nonlimiting examples with reference to the appended drawing in which the single figure schematically represents the succession of the functional steps of the method as they are implemented in the machine according to the invention.

 With reference to the single figure of the drawing, a description will now be given of a machine making it possible, for example, to continuously manufacture profiles 1 of semi-circular cross section according to steps a, b, c, d, e of the conforming process. to the invention; these sections 1, hereinafter called the half-moon, are advantageously used as industrial products for wedging volumes with straight sides to be placed inside a package of the round tube type; these half moon wedges have long been made of polystyrene or polyurethane foam and one of the aims of the invention is to replace these non-recyclable materials with plant substitutes based on cereal straws and bran.

 In accordance with the first step of the process, cereal straws 2 are mixed, for example wheat straws, previously calibrated, so as to keep only the fiber lengths equal to or less than 20 mm; without this being compulsory, a mixture with milling outlets, for example bran 3 coming from the processing of cereals, is entirely advantageous insofar as the bran brings to the mixture a significant proportion of starch (about 20% ) who will later participate in the cohesion of the final product.

Furthermore, the density of the same product may largely depend on the size of the sound that we have chosen, which can vary widely for this purpose.

 Advantageously, and according to the invention, it is chosen to add to the mixture of straws 2 and large bran 3 previously moistened with a first mixer 4, glue powder 5 whose particle size is such that, mixed in a second paddle mixer 6, the fibers of straw 2 and bran 3 are largely covered with glue at least at their contact points; it will be noted here that the mixture obtained is in the form of a sticky powder. One of the advantages which emerges from such a mixture is an obvious saving of water which conversely requires mixtures with liquid adhesives nevertheless and according to a less advantageous variant, it would always be possible to produce such a mixture with liquid adhesives, without departing from the essential characteristics of the process according to the invention.

 It will be noted by way of example that, in order to obtain profiles 1 in a half-moon having a remarkable density close to 180 kg / m3, and having a compressive strength of at least 3 kg / cm2, wheat straws were mixed , crushed and calibrated to 20 mm with large bran comprising approximately 20% starch, the mixture being previously moistened with a supply of water due to 28 to 45% by weight of the straw / bran mixture, this wet mixture being -even with powdered glue, the particle size of which is chosen to be fine enough so that when mixing straws and bran, the fibers are covered with glue at least at their contact points in proportions by weight varying from 60 to 80% for straws, 15 to 30% for bran and 8 to 20% for powdered glue.

 The agglomerate 7 thus obtained is withdrawn by gravity into a shaper 8 in which the agglomerate 7 is compressed transversely between a drive belt 9 and a shape guide 10 facing it; the guide 10 longitudinally the hollow shape of the profile 1 in a half-moon which is all the closer to the surface of the mat that it is desired to increase the transverse compression of the agglomerate 7; of course such an assembly is only a preferred example of the machine and one could quite imagine putting opposite each other two conveyor belts or a guide whose shape would be very different to obtain other types of profiles intended for wedging or parts of the same type.

 In the example, the surface of the mat 9 gives the half-moon profile 1 its flat lower part, the shape guide 10 of course giving it its semi-cylindrical shape.

 According to a more complete variant of the invention, provision could be made for the longitudinal compression of the agglomerate 7 to be obtained by hook systems 11 brought by the carpet itself and which come at a speed that the man of the Business will easily determine, pushing the agglomerate 7 in the direction of advancement, which for the same outlet section, will have the effect of overcompression providing the final product, better longitudinal mechanical strength, even if this translates into an increase. the density of said product.

 The mat 9 of the shaper 8 is arranged in such a way that it routes the preformed agglomerate 7 inside a tunnel 12 producing HF radiation whose frequency is between 10 and 3000 MHz.

 We know that subject to HF radiation of this magnitude, the drying of the fibers 2,3 of the agglomerate 7 takes place at the core, that is to say that its action is of a nature to vaporize the water at the very core of the fiber which will therefore be naturally evacuated towards the surface of the fibers, creating at this level an additional wet area which will participate in the wetting of the grains of powder, that is to say in the areas of inter-fiber contact, with ultra-rapid bonding between the same fibers. It is well understood that this extraction technique constitutes a decisive advantage not only for the quality of the bonding between the fibers, but also for the economy which the process makes it possible to produce in water for bonding and in energy for its evacuation.

 It is quite obvious that this step of drying to the core, by HF radiation, constitutes the essential characteristic of the process according to the invention that the previously known processes were totally unaware of.

 Of course, the agglomerate 7 dried to the core in the tunnel 12 will finally be subjected to a current of pulsed hot air advantageously passing through the tunnel 12, both to obtain drying on the surface of the hardened profile 1 and to extract the residual water from high frequency vaporization. This flow of forced air is maintained at around 1200C; it will be observed that in order to obtain profiles 1 having the abovementioned characteristics, it was necessary to provide a length of tunnel 12 of approximately two meters, the speed of travel of the agglomerate 7 being such that it remains subject to radiation, at least a minute and a half.

 When this drying step is completed at the outlet of the tunnel 12, the sections 1 thus obtained are then cut off 13 making it possible to form half-moon blocks directly usable as a replacement for the industrial products previously made of polystyrene.

 Incidentally and according to a particular variant of the process according to the invention, it is possible to implement the step d of compression of the mixture to form an agglomerate 7 with an isotropic structure, no longer obtained by means of a shaper 8 allowing the production in continuous profiles, but by a mold, for example in two parts, which after correct filling of agglomerate 7 may be subjected to HF radiation whose frequency may vary from 10 to 3000 MHz and at a temperature of at least 1200C; it is in fact a question of creating particular parts which will allow for example the molding and the packaging of specific products such as for example window sills in reinforced concrete.

 The mold used is obviously made of plastic and it is provided with filtering vents, so that the agglomerate 7 obtained at the end of step c of mixing can be sent inside the mold by air. under controlled pressure to obtain a complete and homogeneous filling.

 Still in accordance with an important variant of the process of the invention, it is quite possible to add to the mixture resulting from step c, up to 10% by weight of long fibers, for example flax fibers or the like in the form of 'tow, in order to increase the final resistance of the products; it is indeed possible to thus increase the flexural strength of the profiles 1 from a continuous manufacturing, through a shaper 8 as described above, and this, in order to ensure their mechanical resistance to during the cutting operation and more generally during subsequent manipulations.

 Finally, and according to an accessory variant of the methods in accordance with the invention, it is provided that additional agents are added to the mixture resulting from step c for a treatment of the final product against bacteria or also to obtain a particular coloration , or even fireproofing, etc ...; those skilled in the art can then perfectly dose the contribution of these supplements which are also quite known, in order to obtain the desired effect in the final product.

 Of course, the straws that are introduced in step a of the process can be usefully replaced by many other categories of plants depending on local production such as millet, savannah grass or mousaka from Madagascar. ...

 Likewise, It is quite obvious that all the examples which have been described and commented on above represent the preferred variants of implementation of the process for the preparation of biodegradable substitutes and any non-substantial modifications of one or the other of the stages. constituting the process or the construction of the machine, or even its use would not depart from the scope of the invention.

Claims (14)

 1 - Process for obtaining a biodegradable substitute for materials such as polystyrene or polyurethane foam for the manufacture of industrial parts in particular intended for the packaging field, characterized by the succession of the following steps - a) grinding and calibration of the cereal straw as a function of the final density of the desired substitute, - b) advantageous mixture, although not compulsory, with bran resulting from the transformation of cereals according to a determined particle size, and humidification of the straw / bran mixture, - c) addition of glue and mixing, - d) compression of the previous mixture to form an agglomerate with an isotropic structure, - e) drying to the core by means making it possible to extract the water from the inside to the outside of the agglomeration, advantageously combined with drying external.  2 - Method according to the preceding claim, characterized in that one mixes by weight - 60 to 80% of cereal straw, - 15 to 30% of bran, - 8 to 20% of glue.  3 - Method according to any one of claims 1 or 2, characterized in that the glue is of the powder glue type requiring, before step c, humidification of the mixture of step b, by adding water, at a rate of 28 to 45% by weight of said mixture.  4 - Method according to claim 3, characterized in that the particle size of the powdered adhesive is such that during mixing the fibers of the straws and bran are covered with adhesive at least at their contact points.  5 - Method according to any one of claims 1 or 2, characterized in that the adhesive is of the liquid adhesive type.  6 - Method according to any one of the preceding claims, characterized in that the drying at the heart of step e is obtained by subjecting the agglomerate to high frequency HF radiation.  7 - Method according to the preceding claim, characterized in that the external drying is obtained by pulsed hot air.  8 - Method according to any one of the preceding claims, characterized in that step d of shaping the agglomerate is carried out continuously to give a profile.  9 - Method according to claim 8, characterized in that added to the mixture obtained in step c, up to 10% by weight of long fibers, for example flax fibers in tow form, in order to increase the flexural strength of the profiles with a view to cutting or handling them.  10 - Process according to any one of the preceding claims, characterized in that additional agents are added to the mixture, in step c, for the treatment of the substitute against bacteria or to obtain a coloration, a fireproofing, etc. ..  11 - Method according to any one of claims 1 to 7, characterized in that in step d the shaping of the agglomerate is obtained in molds in two parts supporting high frequency radiation and a temperature of 1200C at less.  12 - Process according to claim 11, characterized in that the molds being pierced with filter vents, the mixture obtained at the end of step c is sent into the mold by air under controlled pressure to obtain filling complete and consistent.  13 - Machine for the continuous production of a biodegradable substitute of predetermined density and resistance to pressure implementing the method according to any one of claims 8, 9 or 10, characterized in that it comprises - a mixer (6) on pallets or the like supplied with the required quantity of cereal straws (2), bran (3), water and glue (5) in order to obtain a homogeneous mixture, sticky powder, optionally supplemented with agents according to claim 10, - a shaper (8) receiving, for example by gravity, the preceding mixture, for compressing it transversely between a drive belt (9) and a shape guide (10) facing it, the belt (9) being moreover provided with pressure means (11) in the longitudinal direction of advance of the mixture which has become agglomerate (7), - a tunnel (12), arranged around the shaping device (8) and equipped with HF radiation means for drying the core agglomerate, - a hot air producing device pulsed through the tunnel (12) for the evacuation of residual water on the surface of the agglomerate (7) which becomes a profile (1), - a profile receiving station (1) at the outlet tunnel (12) for mechanical treatment, such as cutting and conditioning.  14 - Biodegradable substitute for materials such as polystyrene or polyethylene or polyurethane foam for the manufacture of industrial parts, in particular intended for the packaging field with a density close to 180 kg / m3 having a compressive strength of 3 kg / cm2 obtained by the machine according to claim 13, characterized in that it comprises cereal straws (2), for example wheat or flax of length calibrated between 0 and 20 mm, preferably 20 mm, mixed with bran (3) comprising around 20% starch, according to a weight distribution varying from 60 to 80% straws (2), 15 to 30% bran (3), and 8 to 20% powder glue ( 5), the straw / bran mixture being previously moistened by adding water at a rate of 28 to 45% by weight of said straw / bran mixture, and in that the mixture is subjected, by means of a shaper ( 8) with strips, the molding pressures of which are adjusted, to the effe ts of an HF radiation tunnel whose frequency is adjusted between 10 and 3000 MHz for a residence time of one minute and a half, for the drying at the core, said tunnel channeling an air flow at 120 C for drying at the surface and the extraction of residual water.