FR2853330A1 - METHOD AND DEVICE FOR MANUFACTURING BIODEGRADABLE THREADS OR TWINS, THREADS OR TWINS OBTAINED BY THIS METHOD AND APPLICATIONS THEREOF - Google Patents

Abstract

The invention relates to a method and a device for manufacturing a biodegradable thermoplastic polymer wire or string. The method comprises the steps of: hot extruding (1) a biodegradable thermoplastic polymeric material through a die to form a wire; cooling (2) said wire; cold drawing (3,4) said wire with a force F d 'stretching slightly less than the force F' which would cause it to break.The wires and twines obtained are biodegradable and have an almost non-existent creep. They can be used in particular in agriculture.

Description

Method and device for manufacturing biodegradable yarns or twines,

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  or strings obtained by this process and corresponding applications.

  The invention relates to the field of design and production of biodegradable yarns and twines (formed by the association of several yarns). It will be noted that, in the context of the present description, the term "strings" also includes elements which are structurally similar but which may be of different size, namely in particular cords, cords, cords, ropes, etc.

  The invention finds its application in particular, but not exclusively, in the field of agriculture.

  Many synthetic materials used in agriculture cause serious environmental problems due to their slow disappearance in the various ecological systems where their degradation does not occur until after several decades.

  Such non-biodegradable polymers consist mainly of polyethylene, polypropylene, poly (vinyl chloride), polyamide, poly (ethylene terephthalate), polycarbonate. As regards the manufacture of the strings used in the field of agriculture, it is polypropylene which is most often used.

  Operations involving recycling and incineration are already making it possible to limit the harmful effects of waste made up of synthetic plastics. The development and optimization of these operations should lead to a significant reduction in pollution.

  However, for many of these materials, the costs of sorting, cleaning and recycling are often higher than those of processing these raw materials. The revaluation is then hardly or hardly used.

  In the field of agriculture, the plastics used for crops, in particular the twine but also the mulch films, the clips, the cluster supports, must therefore be recovered from the soil after harvest, often mixed with plants. These residues can then be burned, or else be collected and stored, or even be treated in order to recycle the plastic materials that they contain, which induces a significant cost. Since July 2002, the landfill of residues is however prohibited in France (law n092-646 of 5 July 13, 1992) which obliges producers to favor such recycling or to orient themselves towards the use of biodegradable products.

  Indeed, for many years, research for the development of biodegradable materials has accelerated. Now, such products are available on the market such as polyesteramide, polycaprolactone (PCL), polylactic acid (PLA), aliphatic and / or aromatic copolyesters, polyhydroxybutyrate (PHB), polyhydroxyvalerate (PHV), poly (butylene succinate) (PBS), poly (butylene succinate / adipate) (PBSA), polyester carbonate (PEC), poly (ethylene succinate) (PES), poly (butylene adipate / terephatlate) (PBAT) , polyvinyl alcohol (PVA), cellulose acetate, into which fillers of natural origin, such as starch, can be incorporated. Such thermoplastic materials offer many applications, particularly in the field of agriculture: wide range of films intended for agriculture, packaging for food use, golf tees, caps, trash bags ...

  Thus, the users of these biodegradable materials (often called "biomaterials") have the possibility of burying the waste on site at the end of the culture, or of bringing it together for composting and reusing this compost thereafter. These last two solutions, while being ecological and preserving the environment, make it possible to best maintain the organic fertility of the soils while restoring a portion of the mineral elements consumed.

  In the field of agriculture, the use of such biodegradable materials therefore has in particular the following advantages: - gain in labor, since it is no longer necessary to rid the cultures of these materials at the end of the cycle of culture, gain in mineral fertilizing matter (regeneration by the mineralization of plants), i.e. in ions immediately assimilable by the plant (NO3_, S042, PO 43, H2 P04-, K +, Ca2e, Mg2 +, Fe3 +, Zn2 + etc.) - gain in organic fertilizing material (degradation of plant waste) 5 This organic fertilizing material represents organic molecules not yet degraded by the micro flora and fauna of the soil (that is to say not mineralized) not yet absorbable by the plant (plants are unable to absorb large organic molecules).

  However, with regard to the production of twine yarns, the use of natural biodegradable materials leads to yarns or twines having poor mechanical strength.

  In order to solve this problem of mechanical strength, various methods of manufacturing twines have been proposed which consist of including reinforcements in these twines.

  Thus, French patent FR2779157 describes a technique for producing a string where the heart of the string is an oxidizable metal wire which is covered with at least one layer of adhesive paper.

  Likewise, patent JP2000034683 describes the production of a biodegradable string from aliphatic polyester in the form of tubes in which 20 natural fibers or paper are placed, and which are then twisted.

  According to patent JP1 1032594, a biodegradable string made of biodegradable material such as paper is coated with a synthetic resin such as polyvinyl alcohol.

  Patent JP 11279962 describes the production of a string consisting in twisting bands obtained from cotton or cellulose fibers.

  However, the use of such reinforcements (metal wires, resins, etc.) complicates the manufacture of such strings and increases their manufacturing costs.

  Furthermore, the step consisting of twisting the fibers constituting the string considerably limits the profiles which such strings can have. However, there is a need for strings having profiles different from the simple twisted profile, for certain applications requiring better attachment of the elements connected by the string or supported by it.

  The objective of the present invention is to provide a simple process for manufacturing twines from biodegradable material.

  In particular, an objective of the present invention is to describe such a process which does not necessarily require the use of reinforcements but which nevertheless makes it possible to obtain threads or strings having optimal resistance to load and almost non-existent creep.

  Another objective of the present invention is to describe such a method 10 making it possible to produce strings of very varied profiles and which can in particular have projecting edges making it possible to improve some of their uses.

  Yet another objective of the present invention is to disclose such a method which leads to strings having good mechanical strength and in particular very low creep. Note that very low creep is understood to mean creep of less than about 3%.

  These objectives, as well as others which will appear subsequently, are achieved thanks to the invention which relates to a process for manufacturing a wire or a string made of biodegradable thermoplastic polymer characterized in that it comprises the steps consisting in: hot extruding a biodegradable thermoplastic polymer material through a die to form a wire; cooling said wire; cold drawing said wire with a stretching force F1 slightly lower than the force Fr which would cause it to break.

  According to the invention, the extruded and cooled wire is therefore stretched according to a drawing force which is slightly less than that which would cause it to break. This drawing operation is essential because it gives the wire the required mechanical properties of creep, tensile strength and elasticity.

  In order to determine the forces F1 and Fr, it is necessary to establish beforehand the curve d = f (F) of the displacement of the end of a wire to which a traction force is applied and this, until the breaking of that -this. This curve, which is of the type shown in FIG. 1, varies according to the nature of the material 5 constituting the wire and the dimensions of this wire. It allows to select FI at a value just below Fr. In practice, the stretching force F1 will be chosen between approximately 0.90 F. and 0.99 F. The tensile force F1 used during the stretching phase is therefore chosen as a function of the curve d = f (F). The establishment of such a curve is necessary for each thermoplastic material used and for each type of yarn desired, depending on the shape and the area of the section thereof.

  According to a preferred variant, the method comprises an additional step consisting in stretching said wire slightly hot when it leaves said die and before said step consisting in cooling it.

  There are several ways to consider cooling the wire. Alternatively, this step is performed by passing said wire through a coolant. This step will generally be carried out to bring the wire to a temperature approximately equal to room temperature.

  The wire extrusion step has the advantage of being able to obtain very varied profiles of wires, as will be described below in more detail, by adapting different dies in the extrusion means. In this regard, it will be noted that, preferably, this hot extrusion step is carried out at a temperature 30 ° C. to 70 ° C. higher than the melting temperature of said thermoplastic polymer material used.

  This biodegradable thermoplastic material may be of very varied nature and in particular be chosen from the group consisting of polyesteramide, polycaprolactone (PCL), polylactic acid (PLA), aliphatic and / or aromatic copolyesters, polyhydroxybutyrate (PHB), polyhydroxyvalerate (PHV), poly (butylene succinate) (PBS), poly (butylene succinate / adipate) (PBSA), polyester carbonate (PEC), poly (ethylene succinate) (PES), poly (butylene adipate / terephatlate) (PBAT), polyvinyl alcohol (PVA), cellulose acetate.

  It will be noted that the biodegradable thermoplastic material used may contain at least one filler of natural origin such as, for example, but not exclusively cellulose or its derivatives, native starch or its derivatives, wood, cotton, which may be directly mixed with the base material before extrusion in contents of up to 50% by mass. It is also possible to include in this material at least one dye, for example of the iron oxide or other mineral dye type, presenting no risk to the environment, at a rate of 0.1 to 1% by mass.

  Although, as indicated above, the method according to the invention makes it possible to dispense with the use of reinforcements, it will however be possible to include such reinforcements in the threads or twines produced, such as in particular, but not exclusively fibers cellulose, flax, hemp, etc. which can, for example, be covered during extrusion with the pure or additive material. Such reinforcements make it possible to obtain gains in mechanical strength of the order of 20 to 30%.

  According to a preferred variant of the invention, the thermoplastic material used will be polycaprolactone, a mixture of polycaprolactone and starch, or an aromatic aliphatic polyester. These 20 materials have indeed been tested by the Applicant and have given good results.

  The method according to the invention may comprise an additional step consisting in associating several threads together, for example by braiding, to obtain a string.

  The present invention also relates to any device for manufacturing a wire or a string made of biodegradable thermoplastic material making it possible to implement the method described above, characterized in that it comprises: - means for extruding a biodegradable thermoplastic material including heating means and at least one extrusion die allowing the formation of at least one wire; - means for cooling said wire; - means for drawing said wire.

  According to a preferred variant, said cooling means comprise at least one tank containing a cooling liquid.

  Also preferably, said stretching means comprise at least one drawing bench and braking means making it possible to optimize said stretching. This pulling bench and these braking means make it possible to implement the step of cold drawing of the wire, but also the step of hot drawing of that described.

  According to a preferred variant, the device described also comprises motorized means for winding the wire produced.

  The process according to the invention makes it possible to obtain biodegradable threads devoid of reinforcement but nevertheless having an almost non-existent creep, namely less than about 3%.

  The implementation of an extrusion step during this process makes it possible, as already indicated, to obtain biodegradable wires having very varied cross-section profiles.

  According to a particularly advantageous variant, the method according to the invention makes it possible to obtain wires showing a solid or hollow section (therefore saving material) and showing protruding edges. Such projecting edges are of great interest for many applications, in particular for market gardening applications where these wires allow good attachment of the plants.

  The method according to the invention also makes it possible to obtain wires showing a solid or hollow, round or oval section.

  Finally, according to another aspect, the yarns obtained have a solid or hollow section in the form of a dumbbell, arc ribbon, S ribbon, W ribbon. These "flat" profiles are of great interest for applications such as strings for maintaining films for tunnels used in market gardening, for 30 bales of straw, for packaging packages.

  The present invention therefore covers all the threads obtained by the process described as well as the strings resulting from the association of several of these threads, in particular, but not exclusively, by braiding.

  These yarns and twines can be used in many fields and in particular, but not exclusively in the field of agriculture. They can thus be used for example as wires or twines for staking plants or as wires or twines for the maintenance of plastic tunnels for vegetable crops, or as binder wires or twines.

  The invention, as well as the various advantages which it presents, will be more easily understood thanks to the description which follows of several embodiments given with reference to the drawings in which: FIG. 2 represents a simplified diagram of a device for manufacturing threads or twines according to the present invention; - Figure 3 shows different sections of son obtainable by the invention; - Figures 4 to 6 show graphs indicating the tensile forces leading to the breakage of wires of different diameters produced according to the invention using three different thermoplastic materials.

  With reference to FIG. 2, the device according to the invention comprises an extruder 1 of the DSK42 / 6 type manufactured by the company Brabender. This extruder is equipped with a counter-rotating twin screw showing interrupted threads and has two heating zones (zone 1 and zone 2). It is also provided with a removable extrusion die 1a and a hopper 1b for supplying biodegradable thermoplastic material.

  The extruder 1 is followed by a cooling tank 2, a drawing bench 3, brake means 4 and winding means 5.

  At its exit from the die, the extruded wire 6 has a cross-sectional diameter dl greater than the diameter d2 which it presents after its passage on the pulling bench 3 and before its passage at the level of the brake-forming means 4, diameter d2 itself greater than the diameter d3 presented by the wire after it has passed through the brake-forming means 4 when it reaches the level of the winding means. For example, a wire is extruded according to the conditions 1 10'C (zone 1), 1250C (zone 2) and 1100C (die). The die has a round profile of 4 mm (dl), the hot pre-stretching will give a diameter d2 of 3.45 mm to the wire, just before it arrives in the cooling tank and the material is frozen to this diameter. After drawing, the wire has a diameter of the order of 1.5 mm (d3).

  During the implementation of the method according to the invention, the wire is slightly drawn hot when it leaves the extruder 1 by the pulling bench 3 to start orienting the polymer chains of the material constituting it.

  This wire 6 then passes through the tank 2 containing water at room temperature (15 to 20 ° C). It is then cold drawn according to the desired tensile force F1 previously determined. During this cold drawing phase, between the winding system 5 and the braking system 4, the macromolecular chains 15 of the polymeric material constituting the wire 6 are aligned in the pulling direction.

  Several types of dies 1a can be adapted on the extruder 1, which offers the possibility of obtaining a multitude of types of wire sections 6. Non-limiting examples of wire sections which can thus be obtained are indicated in figure 3. The sections in the shape of stars, crosses, square, 20 triangular, imply salient edges interesting for certain applications, as already described.

  The method and the device according to the invention have been tested with several types of material and several types of section. The mechanical strength of the wires obtained was measured by tensile tests on an INSTRON 25 4505 apparatus at a speed of 50 mm / min.

  1st series of examples: solid rods of polycaprolactone loaded with starch For this first series of examples, a wire of 30 polycaprolactone loaded with starch was made (60% by mass of polycaprolactone for 40% by mass of starch). Such a material is marketed by Novamont under the brand MATER-BI and the reference ZF03U / A. It has a melting temperature of 620C.

  This wire was extruded in the form of a solid rod with a diameter of 3.45 mm using extrusion temperatures of 120 ° C. (zonel), 1250 ° C. (zone 2) 130 ° C. (die 1a).

  The tensile force Fr causing this wire to break was previously measured at 700% at 270 N at a tensile speed of 50 mm / min.

  The extruded rod was therefore cold drawn using a braking force 10 Fl, instilled by the braking system located upstream of the winding system, just below this breaking force Fr i.e. Fl = 260 N. Using a speed from the pulling bench at the extruder outlet of 2.4 m / min, the wire passes from a diameter of 4 mm at its exit from the extrusion die to a diameter of 3.4 mm then to a final diameter of 1 , S5mm.

  This 1.55 mm wire has an elastic modulus of 795 MPa and supports approximately 26 kg. Its elongation at break is only 0.28%.

  This thread can be knotted and used as a staking thread for plants which require such support, such as tomato, cucumber, eggplant plants, etc. It can also be used for holding plastic tunnels of vegetable crops, or as a binder thread.

  A range of solid rod wires has been produced with the same MATER-BI material having different diameters, the diameter being determined by the speed of rotation of the extruder screws and the drawing bench.

  The resistance of these wires was evaluated by measuring the tensile force necessary to break them. The results are given in table 1 below and represented in graphic form in FIG. 4.

  Initial diameter (mm) Final diameter (mm) Final section (mm2) Breaking force (N) 1.60 0.74 0.43 50 1.80 0.80 0.50 85 2.25 0.82 0, 53 90 2.35 1.00 0.79 108 2.70 0.83 0.54 164 2.85 1.10 0.95 155 2.90 1.20 1.13 190 3.00 1.30 1, 33,200 3.45 1.55 1.89 270 4.10 1.60 2.01 350 4.28 1.63 2.09 387 4.80 2.20 3.80 520 2nd series of examples: full ioncs of aromatic aliphatic polyester For this second series of examples, an aromatic aliphatic polyester yarn sold by BASF under the brand ECOFLEX and the reference FBX7011 (to which 4% by mass of the batch reference AB1 and 1% by batch mass SL1). This material has a melting temperature of 122 C.

  This wire was extruded in the form of a solid rod with a diameter of 3.60 mm using extrusion temperatures of 145 C (zonel), 155 C (zone 2) 165 C (die la) at a speed of rotation of the 23 rpm screw.

  The tensile force Fr causing this wire to break was previously measured at 800% at 250N.

  The extruded rod was therefore cold drawn using a traction force F1 instilled by the braking system just below this breaking force Fr.

  The wire thus obtained has a final diameter (d3) of 1.55 mm, an elastic modulus of 760 MPa and supports around 25 kg. Its elongation at break is only 0.15%.

  The resistance of these wires was evaluated by measuring the tensile force necessary to break them. The results are given in table 2 below and represented in graphic form in FIG. 5.

  Initial diameter (mm) Final diameter (mm) Final section (mm2) Breaking force (N) 1.3 0.60 0.28 40 1.6 0.70 0.38 55 1.6 0.75 0, 44 80 1.75 0.84 0.55 50 2.00 0.85 0.57 60 2.10 0.90 0.64 70 2.50 1.10 0.95 115 2.56 1.20 1, 13 150 2.60 1.20 1.13 165 3.60 1.55 1.89 250 3.60 1.60 2.01 280 4.10 2.00 3.14 340 4.20 2.10 3, 46,375 3rd series of examples: rods full of caprolactone For this third series of examples, a polycaprolactone wire sold by SOLVAY under the reference CAPA6800 was manufactured. It has a melting temperature of 60 C.

  This wire was extruded in the form of a solid rod with a diameter of 3.30 mm using extrusion temperatures of 115 C (zone 1), 125 C (zone 2) and 130 C (die la).

  The tensile force Fr causing this wire to break was previously measured at 700% at 250N.

  The extruded rod was therefore cold drawn using a pulling force F1 instilled by the pulling bench just below this breaking force F ,.

  The wire thus obtained has a final diameter (d3) of 1.1 mm, an elastic module of 800 MPa and supports around 25 kg. Its elongation at break is only 0.23%.

  The resistance of these wires was evaluated by measuring the tensile force necessary to break them. The results are given in table 3 below and represented in graphic form in FIG. 6.

  Initial diameter (mm) Final diameter (mm) Final section (mm2) Breaking force (N) 2.30 0.95 0.71 153 2.40 0.95 0.71 144 3.30 1.05 0, 87 250 3.80 1.60 2.01 408 4.30 1.85 2.69 537 6.00 2.50 4.91 848 4th series of examples: polveaprolactone-starch ribbons Polycaprolactone - starch ribbons ( MATER-BI ZF03U / A) are extruded at a speed of 30, 50 and 70 rpm. The properties of these ribbons are collated in Table 4 below.

10 Dimensions before Fractional force at Elongation at Dimensions after stretching rupture (N) rupture (%) stretching (mmxnmm) (mnxrnm) 0.87x 14.50 170 480 0.30x 7.60 1.10 x 7.25 108 500 0 , 45x3.90 1.10x7.10 91,490 0.44x3.78

Claims (24)

  1. A method of manufacturing a wire or a string made of biodegradable thermoplastic polymer, characterized in that it comprises the steps consisting in: hot extruding a biodegradable thermoplastic polymer material through a die to form a wire to cool said wire ; cold drawing said wire according to a drawing force F slightly less than the force F 'which would cause it to break.   2. Method according to claim 1 characterized in that it comprises an additional step consisting in stretching said wire slightly hot when it exits from said die and before said step consisting in cooling it.   3. Method according to claim 1 or 2 characterized in that said step of cooling said wire is carried out by passing said wire through a coolant.   4. Method according to any one of claims 1 to 3 characterized in that said cooling step is carried out to cool said wire to a temperature approximately equal to room temperature.   5. Method according to any one of claims 1 to 4 characterized in that said hot extrusion step is carried out at a temperature higher than 30'C to 70'C than the melting temperature of said thermoplastic polymer material.   6. Method according to any one of claims 1 to 5 characterized in that said thermoplastic material is chosen from the group consisting of polyesteramide, polycaprolactone (PCL), polylactic acid (PLA), aliphatic copolyesters and / or aromatic, polyhydroxybutyrate (PHB), polyhydroxyvalerate (PHV), poly (butylene succinate) (PBS), poly (butylene succinate / adipate) (PBSA), polyester carbonate (PEC), poly (ethylene succinate ) (PES), poly (butylene adipate / terephatlate) (PBAT), polyvinyl alcohol (PVA), cellulose acetate, and may contain a filler preferably of natural origin such as starch.   7. Method according to one of claims 1 to 7 characterized in that said biodegradable thermoplastic material used contains at least one filler of natural origin.   8. Method according to claim 7 characterized in that said filler is chosen from the group consisting of cellulose or its derivatives, native starch or its derivatives, wood, cotton.   9. Method according to any one of claims 7 or 8 characterized in that said filler is integrated into said thermoplastic material at a content of up to 50% by weight.   10. Method according to any one of claims 7 to 9 characterized in that said thermoplastic polymer is constituted by polycaprolactone, by a mixture of polycaprolactone and starch, or by an aromatic aliphatic polyester.   11. Method according to any one of claims 1 to 10 characterized in that said thermoplastic material used contains at least one dye not presenting risks for the environment at a rate of 0.1 to 1% by mass.   12. Method according to any one of claims 1 to 11 characterized in that it comprises a step of including reinforcements to said wire or to said twine, 13. Method according to any one of claims 1 to 12 characterized in that it comprises an additional step consisting of associating several son together to obtain a string.   14. Method according to claim 13 characterized in that said additional step consists in braiding several threads together.   15. Device for manufacturing a wire or a string of biodegradable thermoplastic material, characterized in that it comprises: - means for extruding a biodegradable thermoplastic material including heating means and at least one die for extrusion allowing the formation of at least one wire; - means for cooling said wire; - means for drawing said wire.   16. Device according to claim 15 characterized in that said cooling means comprise at least one tank containing a cooling liquid.   17. Device according to claims 15 or 16 characterized in that said drawing means comprise at least one pulling bench, braking means making it possible to optimize said drawing.   18. Device according to any one of claims 15 to 17 characterized in 10 that it comprises motorized means for winding the wire produced.   19. Biodegradable wire produced by implementing the method according to any one of claims 1 to 14 characterized in that it has a creep of less than 3%.   20. Biodegradable wire according to claim 19, characterized in that it has a solid or hollow section showing protruding edges.   21. Biodegradable wire according to claim 19 characterized in that it has a solid or hollow round or oval section.   22. Biodegradable wire according to claim 19, characterized in that it has a solid or hollow section in the form of a dumbbell, an arc ribbon, an S ribbon, a W ribbon. 23. Biodegradable string characterized in that it is constituted by the association of several threads according to any one of claims 19 to 22.   24. Use of a wire or a string according to any one of claims 19 to 23 as a wire or string for staking plants or as a wire or string for the maintenance of plastic tunnels for vegetable crops, or as a binder wire or twine.