EP1429908A1 - Method of processing a used hdpe by means of extrusion-blow moulding - Google Patents

Abstract

The invention relates to a method of processing a used high-density polyethylene (HDPE) in particulate form by means of extrusion-blow moulding. The inventive method consists in extruding the used HDPE mixed with a polyfunctional epoxide and subsequently subjecting the extrudate to a blow moulding operation.

Description

 Process for the implementation by extrusion blow molding of a used HDPE

The present invention relates to a process for the implementation by extrusion blow molding of an HDPE (high density polyethylene) as well as fuel tanks capable of being obtained using this process. The increasing use of plastics has posed a problem for the environment for many years. For example, in the automotive industry ^{^,} laws were intended to impose a minimum weight rate of recycling of plastics used. The fuel tank, which is often produced by extrusion blow molding of high density polyethylene (HDPE), is an interesting candidate because its weight being important, it alone provides a good fraction of the weight rate to be recycled. However, to date, no project has resulted in the blowing of tanks including even a part of recycled resin. Indeed, the extrusion-blowing technique is only applicable to resins having good melt strength and being very homogeneous, which is generally not the case with resins recycled following the degradation undergone by the resin. during its lifetime and / or its recovery (reprocessing).

Generally, the resins and in particular the HDPE are stabilized so as to limit their degradation during their lifetime as a solid object, but this stabilization is not however sufficient during the use of used resins. It is therefore known to add to these resins, during their use, one or more stabilizers in order to allow this use and subsequent use without damage. Thus, in the case of HDPE, it is known that extrusion strongly degrades the polymer chains and that it is necessary to stabilize the used polymer before putting it back into use (Kartalis et al, Journal of AppHed Polymer Science, Vol. 73 , 1775-1785 (1999)). However, such a stabilization generally does not make it possible to obtain, at the outlet of the extruder, a product suitable for processing by blowing. Indeed, most of the recycled resins, even when stabilized, have in the molten state an unacceptable lengthening under their own weight, which makes manipulation of the parisons impossible during blowing.

EP 1095978 describes the extrusion of compositions comprising HDPE, at least one polyfunctional polymer or oligomer having a glass transition temperature below 10 ° C (polysiloxane) and an epoxide polyfunctional, under conditions involving a reduction in the Melt Index (MI). However, the specific use of such resins for extrusion blow molding, in particular for gasoline tanks, is not disclosed.

It has appeared that, surprisingly, the use by extrusion-blowing of a used HDPE was possible provided that it had been modified by extrusion in admixture with a polyfunctional epoxide. In addition, the resin thus modified has improved mechanical properties compared to the basic virgin resin as well as a better ability to waterproof by fluorination. The present invention therefore relates to a process for the implementation by extrusion blow molding of a used high density polyethylene (HDPE) in particulate form, according to which the used HDPE is extracted in admixture with a polyfunctional epoxide, and then the extradate to a blowing operation. The HDPE which can be used by the process according to the present invention can be a homopolymer of ethylene or a copolymer of ethylene with a monomer such as propylene, butene, hexene or octene, in particular a content generally greater than 2% or even 4% and generally not exceeding 10% or even 8%. It is preferably a copolymer of ethylene and hexene having a hexene content of between 4 and 8%. This resin can for example be obtained by using a Phillips catalyst or a Ziegler catalyst. Phillips type resins are preferred. The density of this resin is generally greater than or equal to 930, preferably greater than or equal to 940, or even 945 g / kg. Resins with an MI (measured at 190 ° C according to ISO 1133) less than or equal to 1 g / 10 min under a load of 5 kg, and greater than or equal to 1 under a load of 21.6 kg, give good results .

By used resin according to the present invention is meant a resin having already undergone at least one shaping by melting (other than a simple granulation) and having had a non-negligible lifetime in this form, during which it has undergone non-negligible degradation (and in particular, oxidation) phenomena. The present invention is particularly suitable for "aged" resins, having been polymerized and used months or even years before (20 to 25 for example) and having even been used in an aggressive chemical and / or thermal environment, such than the constituent resins of used fuel tanks. According to the present invention, the HDPE is in particulate form i.e. in the form of particles (powder, granules, fragments ...) so that it can actually be introduced into the extruder and melted.

According to the present invention, during blowing, the extradate can be used as it is or in admixture with used resin but not additive (i.e. not having been extruded in admixture with a polyfunctional epoxide) and / or with "virgin" resin. By “virgin” resin according to the present invention is meant a resin which has not undergone any shaping by melting (with the exception of any granulation) and which has not undergone significant degradation. According to the present invention, the extradate is advantageously used in admixture with used non-additive or virgin resin in weight proportions of 60:40 to 40:60. Used HDPEs of different origins can also be used as a mixture, and optionally also diluted with virgin resin, in the same proportions as those described above. The polyfunctional epoxide according to the present invention is preferably of the same type as those described in patent applications WO 94/29377, WO 97/30112, WO 00/26286 and EP 1095978. Preferably, this epoxide is combined with a phenol hindered and to a phosphite (as described in WO 94/29377), to an aromatic secondary amine (as described in WO 97/30112), or to a polyfunctional polymer or oligomer with a glass transition temperature below 10 ° C ( as described in EP 1095978). The choice as epoxide of a compound comprising at least one (preferably two) epoxy function and at least one (preferably two) alkenyl groups (as described in WO 00/26286) gives good results. The choice of a mixture based on a polyfunctional epoxide combined with a hindered phenol and / or a phosphite and / or an acid sensor gives particularly good results. Such a mixture is marketed by CUBA GEIGY under the trade name Recycloblend ® 660. In the case of the use of the Recycloblend ® 660 mixture, preferably one will be chosen. weight percentage of Recycloblend (relative to the total (Recycloblend + HDPE)) of at least 0.1%, preferably at least

0.3%, or even at least 0.4%, but not exceeding 1%, preferably 0.7% or even 0.6%. A weight content of 0.5% gives good results.

Other additives can also be incorporated into the HDPE during the implementation process according to the present invention. Thus, for example, stabilizers (such as the above-mentioned phenols and phosphites), carbon black, etc. can be introduced therein, all in usual amounts (typically from 0 to 5 g / kg). In the present invention, the extrusion mixed with the polyfunctional epoxide (or "additivation") is preferably carried out under high shear stresses making it possible to obtain a significant reduction in MI (measured at 190 ° C. according to the ISO standard). 1133 and under a suitable load to obtain a value greater than or equal to 1 g / 10 min). By "significant reduction" of the ML is generally meant a reduction of at least 5%, preferably at least 10%, or even at least 15% of the MI compared to its initial value (before extrusion).

According to the present invention, the HDPE can be extradited in a single screw or twin screw extraditor. Twin screw extraders are preferred because they induce a higher shear rate, which allows the material to melt more quickly. The profile of the screw or screws of these extradeurs will be adapted in a manner known to those skilled in the art. For example, kneading elements will be introduced as soon as possible into the screws. Preferably, these kneading elements are introduced from the first third of the screws. It is also possible, in the case of single screw extradeurs which are less kneading, to use a grooved sheath.

The polyfunctional epoxide is advantageously premixed with virgin resin in powder form ("fluff") and is then introduced with the resin to be stabilized into the extradeuse, through the main hopper.

The extrusion conditions (rotation speed, temperature profile ...) are to be optimized according to the chosen screw profile, taking into account the torque available on the chosen machine. The extradeuse is advantageously provided with a filter of suitable dimensions to effectively filter the flow of molten material, without excessively increasing the pressure.

In the process according to the present invention, the shaping by extrusion blow molding can be done in a single step, i.e. that the melted HDPE leaving the extradeuse where it was added is directly put in the form of a parison and that this is then directly blown, in line with the extraditor used for additivation. Alternatively, and preferably, the HDPE is granulated at the outlet of the extraditor where it has been additivated, and it is subsequently subjected to shaping by extrusion blow molding, optionally in admixture with used resin not additivated and or with virgin resin. The extrusion-blowing parameters (screw speed, temperature, etc.) used in this case are similar to those used for virgin resin. Preferably, the method according to the present invention is intended for the manufacture of hollow bodies intended to contain or convey fuel. According to this variant of the invention, the word "fuel" denotes both petrol and diesel or any other fuel used in internal combustion engines. Preferably, the hollow bodies are tanks or fuel pipes.

The process according to the present invention applies particularly well to HDPEs coming from used fuel tanks, and which have already been implemented by extrusion blow molding. According to this variant of the invention, it is possible to mix an HDPE coming from a petrol tank with an HDPE coming from a diesel tank.

Fuel tanks generally include metallic elements (such as the fuel filter cartridge, the ball of the non-return valve, the pump rotor, etc.) which must be separated from the HDPE before subjecting it to the method according to this variant of the invention. In addition, since the extrusion requires having the resin in a divided form, the reservoir is generally ground before subjecting its constituent resin to the process according to this variant of the invention.

It is also important to remove from the HDPE, the hydrocarbon residues which could be there before applying the method according to this variant of the present invention. To this end, it is possible, for example, to use an extraction by means of a solvent (n-hexane for example) or supercritical CO 2 (to remove heavy hydrocarbon residues), and / or stripping by means of steam. water (to remove residues of light hydrocarbons). This operation is preferably done on the ground resin, and not on the skeleton of the tank. It is important to note that when this variant of the invention applies to an industrial process for manufacturing petrol tanks, these tanks generally contain different resins, namely: virgin resin, resin from used tanks with additives, and a mixture of such resins having already been used several times. In fact, it is generally advantageous not to blow pure recycled resin, but only in a weight percentage corresponding to that imposed by environmental standards and / or the profitability of the process. In addition, only about 40% of a blown parison actually constitutes the tank, the rest being waste, which is also recycled by blowing. It has also appeared that, surprisingly, when fluorine is injected into a tank including used resin with additives according to the present invention, the F / C ratio is substantially the same at the surface and at the core in the tank. Consequently, the present invention also relates to petrol tanks capable of being obtained by the method described above and having a substantially identical F / C ratio at the surface and at the core in the tank. This F / C ratio can for example be measured by XPS (X-Ray Photoelectron Spectroscopy). In this case, a normal measurement at the surface (called measurement at 0 °) gives the F / C ratio at heart and an oblique measurement (or measurement at 60 °) gives the F / C ratio at the surface.

The present invention is illustrated in a non-restrictive manner by the following example:

Example

We made a mixture of virgin and recycled resins similar to that which would be extruded and blown in an industrial process using as primary source (so-called “fresh” product), 70% virgin resin and 30% resin from used tanks with additives. , with a recycling rate Hey at implementation of 60% (ie a use of 40% of “fresh” product and 60% of “regrind” product), by a process in several stages:

1 - Treatment of tanks:

Used fuel tanks have undergone the following stages: - shredding in a water atmosphere to avoid explosions

- demetalization where the ferromagnetic metals are removed by a permanent magnet; non-ferromagnetic metals are removed by an induced magnetic field system

- grinding and spinning to remove dust - separation by settling bath

- washing with hot hexane to remove heavy hydrocarbons

- stripping to remove light hydrocarbons

2 - Additivation:

The resin obtained in step 1 is extruded with 0.5% of Recycloblend ® 660 in a co-rotating twin-screw extender (BC 45) rotating at 111 RPM and using the following screw and temperature profile.

The MI (190 ° C, 21.6 kg) of the resin was 6.4 g / 10 min before this extrusion and 5.6 g / 10 min after, a reduction of 13%.

3 - Preparation of the fresh product:

70% virgin resin (Eltex RSB 174) was mixed with 30% recycled resin obtained in step 2.

4 - Preparation of the regrind product:

The fresh product prepared in step 3 was blown under standard conditions on a BAT 1000 type blow-molding machine. The tanks are produced in continuous extrusion under the following conditions: head: BKC 400; fiher 500mm; mold: X74. These tanks were re-shredded and re-blown 3 times.

5 - Manufacture of tanks for evaluation:

40% of the fresh product (step 3) was mixed with 60% of the regrind product (step 4). The mixture was blown under the same conditions as those of step 4. At the end of the blowing, fluorine was injected into the tank. Eltex RSB 714 supplemented with antioxidant N0060 was also extruded and blown as in step 4.

Finally, a recycled product having undergone step 1,2 and 3 but not having been re-added with Recycloblend ® 660 in step 2 but with a conventional antioxidant (Irganox ® B225) at 0.2% was also extradited and blown as in step 4.

6 - Evaluation of the results.

XPS measurements.

In order to determine the effect of fluoridation on the internal surface of the reservoirs, an XPS (X-Ray Photoelectron Spectroscopy) study was carried out. An XS AM800 (Kratos) X-ray Spectrometer was used in “Fix Analyze Transmission” mode with a passing energy of 10 eV and a non-monochromatized X MgK _α radiation (hv = 1253.7 eV). The usage parameters were 13kV and 10mA. The analyzes were carried out in a chamber maintained under ultra high vacuum (UHV) of 10 ^"7 Pa. The results were analyzed using an algorithm using least squares in a mixed Gaussian and Lorentsian mode.

The atomic F / C ratio was measured on the 3 samples. A measurement was taken perpendicular to the surface (normal: 0 °) and in obstruction relative to the surface (angle of 60 °). The normal measurement (0 °) gives an idea of the "bulk"concentration; the measurement at 60 ° is an indication of the surface concentration. The higher the F / C ratio, the more chemically carbon fluoride there is: a ratio of 2 indicates that we are in the presence of -CF ₂ - groups.

Regarding the concentration of Fluorine (bulk), the sample recycled with Recycloblend ® 660 has the highest concentration of Fluorine. In addition, this concentration seems to be constant depending on the thickness. The fluorine layer seems to be the most constant. With regard to the fluorine concentration of the virgin resin, this seems to be overall lower but slightly higher at the surface. TJ is therefore a little more fluorine on the surface but this content decreases rapidly with depth (shallower layer). Regarding the recycled resin containing only antioxidant, it has a lower concentration both in surface and in depth.

Measurement of tank properties.

Different tests have been done on the tanks. In the burst test, the pressure inside the tank is increased regularly until the tank breaks. In the drop test, a tank filled with cold ethylene glycol (-40 ° C) is released from an increasing height until the tank breaks. For permeability, the weight loss observed during 24 hours of a day / night temperature cycle (after 24 weeks).

For all tests, the recycled resin containing the Recycloblend ® is better than the virgin resin and is better than the recycled resin containing the standard antioxidant.

Measurement of rheological properties of resins.

In order to compare the rheological properties of the resins, the viscosity at 190 ° and at the stress of 1 sec ^-1 was measured on a 0.3 / 1 fiher. In this type of fihère, the flow essentially has an elongational component. The viscosities were measured on the starting resins, after the 3 blowing / grinding cycles and after mixing with the "fresh" resin.

The result of the rheological measurements is shown in FIG. 1, where the upper curve relates to resin additive with Recycloblend ® 660 and where the lower curve relates to resin additive with Ixganqx ® B225. The points of these curves relate in order to the "fresh" product, to the "fresh" product used and regrind 1, 2 and 3 times, as well as to the final mixture 40/60 ("fresh" product (Reground product). The ordinate of these curves is the viscosity measured under the conditions described above.

During the blowing and grinding cycle, it can be seen that the viscosity gradually decreases. When this product is mixed with the fresh product additivated with Recycloblend ® 660, a rise in properties is observed rheological (viscosity) and we can therefore repair the oxidation that the product undergoes. This amehoration of behavior is not observed when the additive used is a simple antioxidant.

Claims

RESELL I C A T I O N S 1 - Process for the implementation by extrusion blow molding of a used high density polyethylene (HDPE) in particulate form, according to which the used HDPE is extracted in admixture with a polyfunctional epoxide, and then the extradate is subjected to an operation blowing. 2 - Process according to claim 1, in which the extradate is diluted with used non-additive HDPE and / or virgin HDPE. 3 - Process according to claim 1 or 2, wherein the polyfunctional epoxide is combined with a hindered phenol and / or with a phosphite and / or with an acid sensor. 4 - Process according to any one of the preceding claims, in which the extrusion is carried out under high shear stresses making it possible to obtain a reduction in the Melt Index of the HDPE (measured at 190 ° C. according to standard ISO 1133 and under a load suitable for obtaining a value greater than or equal to 1 g / 10 min) of at least 5% relative to its value before extrusion. 5 - Method according to any one of the preceding claims, wherein the extrusion is done in a double screw extender equipped with kneading elements arranged from the first third of the screws. 6 - Method according to any one of the preceding claims, for the manufacture of hollow bodies intended to contain or convey fuel. 7 - Method according to the preceding claim, for the manufacture of fuel tanks and pipes. 8 - Process according to any one of the preceding claims, in which the used HDPE comes from used fuel tanks or pipes. 9 - Process according to the preceding claim, wherein the used HDPE has been extracted by means of a solvent or supercritical CO 2 and / or stripped by means of steam before extrusion. 10 - Fuel tank capable of being obtained by the process according to any one of the preceding claims, characterized in that it has a substantially identical F / C ratio at the surface and at the core.