FR2776663A1 - Method for recycling polymers based on vinyl chloride - Google Patents

Abstract

Method for recycling article based on at least a vinyl chloride polymer comprises tearing article into pieces measuring 1-50 cm; contacting pieces with anhydrous solvent in azeoptropic form to dissolve them; precipitating polymer by addition of water vapor; and recovering polymer.

Description

Sheet recycling process based on vinyl chloride polymers

  The present invention relates to a process for recycling sheets

  composites based on vinyl chloride polymers.

  Polymers of vinyl chloride, and in particular polyvinyl chloride (PVC), are abundantly used, in particular, for the manufacture of composite sheets - reinforced with reinforcing fibers - intended for example for the covering of vehicles, for the concealment of buildings under construction, the production of decorations for shows or for advertising purposes. These composite sheets generally have a large surface. In addition, in many applications, especially in advertising or stage decoration applications, which are currently in full expansion, their service life is short, typically a few weeks or months. For these reasons, large quantities of such sheets are discarded each year. Their

  recycling therefore constitutes an important ecological and economic problem.

  The same applies to other articles comprising sheets based on vinyl chloride polymer (s) reinforced with reinforcing fibers, for example with regard to conveyor belts or

  elements for the interior trim of vehicles.

  Thorough grinding of these sheets would lead to a mixture of fine particles of variable composition, the purification and reuse of which would be difficult. In addition, in such cases, the fibers often form a kind of cotton wool.

  which greatly complicates the reuse of shredded material.

  Various methods based on dissolution using organic solvents have already been proposed; however, they often pose safety and pollution concerns. In addition, they do not always make it possible to collect plastics of sufficient purity to allow them to be economically advantageous for reuse. Another disadvantage of these methods is that they generally cause an extraction of the additives (eg plasticizers) contained in the vinyl chloride polymers, which is opposed to a

direct reuse of these.

  Therefore, the present invention aims to provide a process for recycling reinforced sheets that is simple, economical, safe, low pollution, and which allows to collect plastics of high purity, avoiding -2-

  substantially extract any additives therefrom.

  More specifically, the present invention relates to a process for recycling a sheet based on at least one vinyl chloride polymer reinforced with reinforcing fibers, according to which: (a) the sheet is shredded into fragments of one dimension average from 1 cm to cm; (b) the leaf fragments thus obtained, dry, are brought into contact with a solvent capable of dissolving the vinyl chloride polymer, substantially anhydrous, and in which the fibers are substantially insoluble; (c) separating the fibers from the solvent containing the dissolved polymer; (d) the polymer dissolved in the solvent is precipitated by adding water; (e) the solvent-water mixture is heated so as to cause the solvent to evaporate, and to leave a mixture essentially consisting of water and solid polymer particles,

  (f) collecting the polymer particles.

  The term “sheet based on at least one vinyl chloride polymer” is intended to denote any composite sheet or plate, monolayer or multilayer, reinforced with reinforcing fibers, in which these fibers are embedded in a matrix of plastic material comprising at least one polymer of vinyl chloride (VC) and optionally one or more additives such as for example plasticizers, stabilizers, antioxidants, flame retardants, pigments, fillers, etc. The term “VC polymer” is intended to denote any homo- or copolymer containing at least 50% by weight of VC. Polyvinyl chloride (PVC) is generally used, that is to say a homopolymer. These sheets have any thickness, generally less than 10 mm; their thickness is most often between 0.1 and 5 mm. The process is particularly advantageous for the recycling of tarpaulins, intended in particular for tarpaulin vehicles, for the concealment of buildings under construction, for the production of decorations for shows

or for advertising purposes.

  The fibers can be of any kind, natural or synthetic; it is possible in particular to use glass, cellulose or plastic fibers. They are often plastic fibers, and in particular polyester fibers. Polyethylene terephthalate (PET) gives good results in this application. Their diameter is usually of the order of 10 to 100 lim. These are generally continuous fibers, the length of which can reach several meters. However, it can also be shorter fibers, a few millimeters to a few centimeters in length, forming a nonwoven or a felt. By way of illustration, the fibers can represent from 20 to 40% of the weight of a reinforced sheet. The sheets may have been made by any technique; they are often made by coating a weft of fibers with a plastisol

and heating.

  The first step of the process according to the invention consists in shredding the

  leaves so as to reduce them into small fragments, easy to handle.

  The average size of these fragments is preferably at least 1 cm. Through

  elsewhere, it is advantageously at most 30 cm.

  Shredding using conventional devices such as slow two-shaft shredders with no grate or fast knife shredders (speed greater than about 400 rpm) generally does not give excellent results, since these devices often transform fibers reinforcement in a kind of cotton wool, difficult to re-use and / or disrupting the functioning of the

shredding device.

  Consequently, in the context of the present invention, a slow grinder with a grid is used, capable of shredding reinforced sheets as described above without causing excessive heating, and which, as regards the reinforcing fibers, prevents the formation of cotton wool by ensuring their fragmentation, so that the average length of the pieces of fiber is however at least

minus 5 mm.

  It has proved advantageous to use a shredding device comprising two rotary shafts provided with knives, partially nested, rotating above and at a short distance from a grid (the central part of which is approximately in the form of a double sector of cylinder) provided with perforations of an average dimension of the order of 1 to 10 cm (for example of round shape). These so-called main shafts rotate in opposite directions, preferably at a speed not exceeding 100 rpm. Each of these two main shafts is associated with an auxiliary shaft, also rotary, carrying knives partially nested relative to the knives of the corresponding main shaft. Each auxiliary shaft preferably rotates in a direction opposite to that of the corresponding main shaft, at a speed not exceeding rpm. These auxiliary shafts are intended to prevent fragments of leaves from being trapped between the main knives. Grinders of this type

  are notably marketed by the company Untha.

  The leaf fragments thus obtained are then subjected to the action of a solvent having several specific characteristics. This operation can be carried out in any suitable device, taking particular account of safety and environmental requirements, for example in a closed reactor having

  sufficient chemical resistance. The reaction medium is preferably stirred.

  In order to prevent the fibers from catching on the stirring means and disturbing their operation, an advantageous variant consists in carrying out the dissolution in a container in which is arranged a perforated rotary drum, rotating at a moderate speed ( preferably less than 100 rpm). The axis of the drum is preferably approximately horizontal. An additional advantage of such a device is that after having extracted the majority of the solvent from this container, the drum can be rotated at high speed, so as to

  "spin" the fibers it contains.

  The solvent used is a substance - or a mixture of substances capable of dissolving the vinyl chloride polymer (s) that the treated sheet comprises. The solvent must not, however, cause the reinforcement fibers to dissolve. Surprisingly, it has been found that it is extremely important that the solvent used is substantially anhydrous, that is to say that it contains less than 2% (by weight) of water, otherwise the power Solvent dissolution can be unacceptably reduced. The same naturally applies to the leaf fragments to be treated, which, before being subjected to the action of the solvent, must also be dry, that is to say contain less than 5% water. To this end, a drying step can advantageously be provided before and / or

after shredding.

  It is also necessary, in the context of the process according to the invention, that the solvent used is miscible with water. Preferably, the solvent

forms an azeotrope with water.

  Given all these conditions, the solvent is advantageously chosen from methyl ethyl ketone (MEK), methyl isobutyl ketone and tetrahydrofuran. It is preferred to use MEK, which forms with water an azeotrope comprising (at atmospheric pressure) 11% water and 89% MEK (by weight). The dissolution (b) takes place at any temperature, at which it is however evident that the solvent must be liquid. It is preferred to operate at a temperature between 20 and 100 ° C., preferably from 50 to 80 ° C. When the solvent is MEK, good results have been obtained by carrying out the dissolution.

  at a temperature of 75 C (+ 4 C).

  The dissolution can be carried out under any pressure. It is preferred to carry it out at atmospheric pressure. The quantity of solvent to be used must be chosen so as to prevent the increase in viscosity caused by the dissolution of the polymer from disturbing the smooth running of the process (filtration, etc.). It is preferred that, during the dissolution step (b), the quantity of sheet does not exceed 200 g per liter of solvent, and in

particular 100 g / l.

  With a view to a new use of the vinyl chloride polymer thus collected, an advantageous variant of the process according to the invention consists in incorporating into the solvent, before or during the step of dissolving the polymer, one or more additives ( stabilizers, plasticizers, etc.), the types and quantities of which are adapted to the properties which it is desired to impart to the recycled polymer. It is desirable, in this case, that the additive (s) thus incorporated are soluble in the solvent used. Possible insoluble additives

  can however be finely dispersed in the solvent.

  At the end of the dissolution step (b), there is a mixture comprising on the one hand a liquid phase consisting of the solvent in which the polymer is dissolved, and on the other hand the fibers (not dissolved) . These are separated from the liquid phase (step c), for example by filtration using a fabric or sieve whose openings have dimensions of the order of 1 to 10 mm. It is found that the fibers thus recovered are of high purity. In order to increase this purity, the fibers can optionally be subjected to a subsequent centrifugation and / or washing step, for example using the same solvent, in order to remove any residual traces of polymer. The solvent which has been used for rinsing can advantageously be mixed with the fresh solvent used for the dissolution step; the fact that it contains traces of dissolved polymer is not detrimental to the effectiveness of the dissolution. The fibers can be reused directly for the manufacture of reinforced articles based

of plastic.

  In addition to the fibers, this separation step (c) also makes it possible to collect any "accessories" such as metal eyelets, labels, etc. attached to the sheet and which would not have been removed before it was subjected to the process according to the invention. If necessary, the solvent containing the dissolved polymer can be filtered more finely in order to remove any dust, for example by using a fabric or sieve whose openings have dimensions of the order

from 25 to 250 jim.

  To the solvent containing the dissolved polymer, a quantity of water is then added sufficient to cause precipitation of the dissolved polymer (step d). In particular, when the solvent forms an azeotrope with water, a large excess of water is added relative to the azeotropic composition. For example, in the case of MEK, generally 1 to 3 kg of water are added per kg of MEK. This addition causes the precipitation of the vinyl chloride polymer in the form of solid particles. Surprisingly, it has been found that these polymer particles had an extremely satisfactory morphology, and in particular a very dispersed particle size. The water added for this purpose is preferably at a temperature close to (less than 10 ° C.) than that which the solvent exhibits during the dissolution step. However, precipitation takes place at a temperature below the evaporation temperature of the mixture.

  (if necessary of the azeotrope) solvent-water.

  A particular advantage of solvents such as MEK is that when they are used, the polymer particles collected still contain a large fraction of the additives which the polymer initially contained (at least those of these additives which are soluble in the solvent; this generally does not concern any fillers, for example). This situation is particularly advantageous since these additives are often of high cost, and furthermore said particles can thus be reused directly in a process for manufacturing articles based on this polymer. This reuse is facilitated by the fact that the particles thus recovered are pregelified, which simplifies the implementation by comparison with the implementation of a heterogeneous mixture of polymer granules and

additives added separately.

  The solvent is then heated (step e), so as to cause the complete evaporation of the solvent (if necessary of the azeotropic fraction), which can be collected and condensed (for example, the evaporation temperature MEK-water azeotrope is about 73.5 C at atmospheric pressure). The remaining mixture (which has not been evaporated) consists essentially of water and solid polymer particles. It is advantageous to carry out this evaporation under reduced pressure, preferably under less than 0.05 MPa, which

  allows operation at a temperature below 73.5 C.

  -7- Having thus isolated the mixture of water and polymer particles, it is advantageous for this mixture to be heated, preferably to about 95 ° C. (5 ° C.), in order to reduce the traces of solvent which would be still permeated the

  polymer, before collecting the latter (f).

  The polymer particles can then be easily collected (step f), for example by filtration of the water-particle mixture, and optionally dried

  before being stored or reused.

  The above steps a-b-c-d-e-f are normally performed in this order. However, as a variant, the polymer particles can be collected (f) before the step of heating the solvent-water mixture (e); however, this variant causes the loss of a higher fraction of the initial additives of the polymer and generally leads to a high solvent content in the

polymer particles.

  Given the cost of the solvent and the disadvantages that its release into the environment could present, it is desirable to treat the fraction (if necessary azeotropic) evaporated in order to recover the solvent. This can be done

  in different ways, for example by extraction and distillation.

  According to a preferred variant, the solvent forms an azeotrope with water, and the azeotropic fraction collected during the evaporation step (e) is treated by adding to it a separation agent causing its decantation into an aqueous phase and a phase. essentially made up of solvent. (It goes without saying that the azeotropic fraction must be in the liquid state before being subjected to this decantation. A condensation step can be provided for this purpose.) The separating agent is preferably soluble in water. The separating agent is advantageously a salt insoluble in the solvent. Sodium chloride (NaCl) or calcium chloride (CaCl2) can in particular be used, the latter being preferred. This choice gives in particular good results when the solvent is MEK. The separation agent can be used in the solid state or in aqueous solution. This latter possibility is particularly advantageous insofar as, following this separation, the aqueous phase contains this dissolved agent; it can thus be directly reused (after possible reconcentration, for example by evaporation of water) as a separation agent, in

closed loop.

  High amounts of separating agent are recommended in order to reduce as much as possible the amount of residual water present as a mixture in the solvent thus collected (as explained above, the solvent used during the dissolving step must be substantially anhydrous). For example, in the case of the separation of an azeotropic MEK-water mixture using CaCl 2, amounts of more than 20 g of CaCl 2 per 100 g of water have proved necessary to reduce to less than 10% (in by weight) the residual azeotrope content in the MEK fraction separated after one hour of decantation (at a temperature of 20 to 60 ° C.). This reduction is significant with a view to reusing the solvent in the process according to the invention, since the

  solvent used for the dissolution of the polymer must be substantially anhydrous.

  When the solvent is MEK, 1-propanol can also be used as another separating agent. If this variant is chosen, the preferred procedure consists in injecting the solvent containing the polymer dissolved in the propanol, preferably hot, in causing the evaporation of the solvent, with entrainment of a large part of the 1 - propanol, and in then filter and dry the polymer particles formed. Propanol can be separated from the solvent by

  example by distillation, and reused.

  The process according to the invention can be carried out continuously or

  discontinuous (batch), the latter variant being preferred.

  An important advantage of the said process is that it can operate in a closed loop, without generating polluting discharges, since both the solvent and the optional agent for separating the solvent-water mixture can be recycled and

reused in the process.

DESCRIPTION OF THE FIGURE

  The appended figure schematically illustrates, without limitation, the progress of a particular variant of the method according to the invention, applied to

  recycling of PVC tarpaulins reinforced with polyester fibers.

  The symbols used have the following meanings P solid polymer F: fibers S: solvent (p): dissolved polymer

W: water K: separation agent.

  The tarpaulins are first shredded (DECH) (step a), then the polymer which they comprise is dissolved (DISS) (step b) under the effect of the solvent S, in which some additives may have been dissolved. one wishes to incorporate into the polymer. The mixture thus obtained is then filtered (FILT1) (step c), which makes it possible to separate the fibers F from a solution of the polymer in the solvent (S + (p)). The fibers are rinsed (RIN) using solvent S, and can

  then be wrung, dried and stored or reused (steps not shown).

  -9- After a reconcentration (CONC1) of the solution S + (p), the polymer is precipitated (PREC) (step d) by adding water (W) to this solution. After removal of the solvent-water azeotrope by evaporation (EVAP) (step e), the solid particles of polymer P are separated by filtration (FILT2) (step f) of water W which can be reused in PREC, then dried (SECH). The azeotrope W + S, after having been condensed (step not shown), is separated by decantation (DECA) under the effect of a separating agent K in solution in water, which provides a firstly a fraction of solvent S, which can be reused, and secondly an aqueous phase containing the settling agent (W + K), which can also be reused, optionally after reconcentration (CONC2). The water collected during this reconcentration can be eliminated, or

  reused for example for the precipitation of the polymer (PREC).

  The solvent collected during the possible reconcentration of the solution (CONC 1) as well as that collected by separation of the azeotrope (DECA) can be reused in the step of dissolution of the polymer (DISS), either directly or (as illustrated ) indirectly, after having served to rinse (RIN) the F fibers.

- 10 -

Claims (8)

  1 - Process for recycling a sheet based on at least one vinyl chloride polymer reinforced with reinforcing fibers, according to which: (a) the sheet is shredded into fragments with an average size of 1 cm to 50 cm ; (b) the leaf fragments thus obtained, dry, are brought into contact with a solvent capable of dissolving the vinyl chloride polymer, substantially anhydrous, and in which the fibers are substantially insoluble; (c) separating the fibers from the solvent containing the dissolved polymer; (d) the polymer dissolved in the solvent is precipitated by adding water; (e) the solvent-water mixture is heated so as to cause the solvent to evaporate, and to leave a mixture essentially consisting of water and solid polymer particles,   (f) collecting the polymer particles.   2 - Method according to claim 1, wherein the dissolution step (b)   is carried out in a container in which is disposed a perforated rotary drum.   3 - Method according to one of the preceding claims, wherein the   solvent forms an azeotrope with water.   4 - Method according to one of the preceding claims, wherein the   solvent is chosen from methyl ethyl ketone (MEK), methyl isobutyl ketone and tetrahydrofuran.   - Method according to one of the preceding claims, wherein, during   the dissolution step (b), the quantity of sheet does not exceed 200 g per liter of solvent.   6 - Method according to one of the preceding claims, wherein the   mixture of water and polymer particles collected after the evaporation step (e) is heated in order to reduce the traces of solvent which would still be impregnated   polymer, before collecting the latter (f).   7 - Method according to one of the preceding claims, wherein the   -11- solvent forms an azeotrope with water, and in which the azeotropic fraction collected during the evaporation step is treated (e) by adding a separation agent causing it to decant into an aqueous phase and a phase   essentially made up of solvent.   8 - Method according to the preceding claim, wherein the agent   separation is a salt insoluble in the solvent.   9 - Method according to the preceding claim, wherein the agent   separation is calcium chloride.