Process for the treatment of technical textiles

Abstract

The present invention relates to a process for the treatment of technical textiles based on thermoplastic fibers and comprising a coating, such as, in particular, airbags, using the principle of centrifugal decanting to separate the fiber residues and the coating material. The invention also relates to a process for the manufacture of a thermoplastic composition, in particular for molding, obtained by use of the fiber residues as obtained and optionally of reinforcing fillers. The distinguishing feature of this invention is based on the preparation of the fabric devoid of coating, thus resulting in formulations with elevated mechanical performances.

Claims

1. A process for treating technical textiles, said technical textiles comprising thermoplastic fibers and a coating material and said process comprising the steps of: a) treating said textiles so as to obtain a mixture comprising: fibrous thermoplastic particles, and spherical or quasispherical particles of the coating material, said particles of the coating material exhibiting a mean diameter of between 15 and 750 m; b) suspending the mixture obtained in step a) with an alkaline medium which makes possible the separation of the coating material and fibrous thermoplastic particles; said medium exhibiting a density between the density of the fibrous thermoplastic particles and the density of the coating material; c) separating the coating material and the fibrous thermoplastic particles by centrifugal force; and d) drying the fibrous thermoplastic particles.

2. The process of claim 1, wherein the thermoplastic fibers are based on polyamide, polyolefin, polyester, and/or polyurethane.

3. The process of claim 1 wherein the coating is based on polyvinyl chloride, polyurethane, acrylic, elastomers, and/or silicone.

4. The process of claim 1, wherein the technical textiles are airbag residues.

5. The process of claim 1, wherein the mixture of particles of step a) is obtained by grinding the technical textiles and then micronizing the ground technical textiles.

6. The process of claim 1, wherein the separation of step c) is carried out in a horizontal-axis centrifugal decanter.

7. The process of claim 1, wherein the medium of step b) is an aqueous medium.

8. The process of claim 1, wherein the alkaline medium of step b) exhibits a pH of greater than or equal to 10.

9. A process for treating airbag textiles, said airbag textiles comprising fibrous polyamide material and a silicone coating material, to recover polyamide material, said process comprising the steps of: a) grinding and micronizing said textiles to obtain a mixture comprising polyamide particles and silicone coating particles, said silicone coating particles exhibiting a mean diameter of between 15 and 750 m; b) suspending the mixture obtained in step a) in an aqueous liquid medium having a pH of greater than or equal to 10 and a density between the density of the polyamide particles and the density of the silicone coating particles; c) separating polyamide particles from silicone coating particles by centrifugal force to recover the polyamide particles; and d) drying the recovered polyamide particles.

10. The process of claim 1, further comprising the step of treating the fibrous thermoplastic particles recovered in step c) in order to neutralise the pH.

11. The process of claim 9, further comprising the step of treating the polyamide particles recovered in step c) to neutralise the pH.

12. The process of claim 1, wherein the coating material separated is coating material particles.

Description

EXPERIMENTAL PART

(1) Manufacture of Particles According to the Invention

(2) The airbags used are industrial waste, ground into pieces, based on polyamide 66 and coated on one face with crosslinked silicone. The content of silicone polymer is 10% by weight.

(3) The airbags are cut up and then ground in a Herbold grinder comprising a row of stationary knives. Square-shaped residues of 2 cm2 cm are thus obtained. These residues are then micronized by a Herbold microniser with a row of stationary knives and a row of moving knives and a 500 m screen. Non-micronized residues will also be used by way of reference.

(4) The fibrous thermoplastic particles are then present in the form of fibers with a length of between 0.8 and 1.5 mm and the particles of the coating material are then present in the form of quasispherical particles exhibiting a mean diameter of 200 m. The size of these particles is measured by optical microscopy.

(5) The particles exhibit a median diameter D50 of 108 m.

(6) Suspending

(7) The particles are suspended in a liquid having a density of 1.1 g/cm.sup.3, either the liquid 1 comprising sodium hydroxide and exhibiting a pH of 14 or the liquid 2 comprising magnesium sulfate and exhibiting a pH of the order of 7, by way of reference. The solid/liquid ratio is adjusted to between 20% and 30%.

(8) Separation by the Centrifugal Force

(9) The suspensions are then fed to a Sorticanter from Flottweg, used for the separation of the polyamide particles and the coating particles, with the following parameters:

(10) Rotational speed of the screw: 3000 revolutions/minute

(11) Speed of the bowl of 1100 revolutions/minute

(12) Temperature: 25 C.

(13) The solid fractions present in the two exiting streams are measured and the compounds analyzed. The results are mentioned in table 1. The solid contents are determined by taking samples from the two exiting streams and drying at 80 C. in an oven at atmospheric pressure for at least one night. The solid content of each of the outlet streams is defined by weighing difference.

(14) TABLE-US-00001 TABLE 1 % solid in % solid in Residence the light the heavy Yield Material time phase phase (%) C1 Ground but non- >2 hours 69.5 73.6 56 micronized fabrics treated with an alkaline medium C2 Micronized fabrics 30 minutes 76.2 70.8* 45.3 treated with a non- alkaline medium C3 Ground but non- 1 hour 86 75* <5 micronized fabrics treated with a non- alkaline medium 1 Micronized fabrics <5 minutes 90.1 67 98.7 treated with an alkaline medium *high presence of coating particles

(15) The yield is calculated by carrying out an elemental analysis of the silicon before the treatment on ground residues and after the treatment on the fibers forming the heavy solid phase.

(16) It is thus apparent that the process according to the present invention makes possible the virtually complete removal of the silicone coating from the textile for very short residence times, with a separation medium devoid of additives, such as surfactants or alcohols, without heating said medium, and a very high yield.

(17) The fibrous particles are subsequently rinsed with water, to regain a neutral pH, in a centrifuge and subsequently dried in a tunnel dryer with hot air.

(18) Manufacture of Novel Formulations

(19) The fibrous particles obtained in the various preceding examples are subsequently used to produce filler-comprising formulations comprising 30% by weight of standard glass fibers of E type from the supplier Vetrotex. Heat-stabilizing and antioxidizing additives were also introduced into the formulations.

(20) By way of reference, in the test C4, a virgin polyamide of 66 type, Stabamid 27AE1 from Rhodia, with a VI of 138 ml/g, measured by the 3 AN 22 022 method, and with a melting point of 265 C., is used to produce a polyamide formulation comprising, as filler, 30% by weight of the same glass fibers.

(21) The experiments were carried out on a Leistritz laboratory twin-screw extruder, the main characteristics of which are as follows: screw diameter D of 34 mm, axis separation of 30 mm and length of 35 mm. The temperature of the barrel was kept constant at 285 C. over the entire length of the screw. The screw profile was designed so that venting is carried out at the extruder tail. For each of the tests, the rotational speed of the screw is 290 rpm and the throughput of the extruder is 10 kg/h. Granules are obtained and used to produce test specimens by injection molding.

(22) The mechanical performances are given in table 2 below. It is observed that, for one and the same waste in the form of a washed or unwashed powder, the mechanical performances are enhanced after washing and by the same level as for the 1.sup.st choice compound, this being by virtue of the efficiency of the separation.

(23) TABLE-US-00002 TABLE 2 Impact Tensile Tensile strength modulus strength Material (kJ/m.sup.2) (MPa) (MPa) Fibrous particles resulting 74 9900 158 from test C1 Fibrous particles resulting 62 9500 143 from test C2 Fibrous particles resulting 56 9300 125 from test C3 Reference PA66 C4 82 10 300 184 Fibrous particles resulting 81 10 600 183 from test 1 of the invention

(24) The impact strength is measured according to the standard ISO1791eU. The tensile modulus and the tensile strength are measured according to the standard ISO527/1.

(25) It is thus apparent that the treatment process according to the present invention makes it possible to prepare polyamide formulations exhibiting mechanical properties entirely comparable with the properties of a conventional formulation using a non-recycled polyamide matrix, which is not the case with the other treatments according to the prior art.