BE1031480B1 - RECYCLED POLYETHYLENE COMPOSITIONS WITH IMPROVED PROPERTIES AND A PROCESS FOR PREPARING THEM - Google Patents

Abstract

The invention relates to a material composition with improved mechanical properties, characterized in that it consists of: (a) a quantity >50% of recycled polyethylene chosen from recycled HDPE, recycled LLDPE and their mixtures and (b) a quantity <50% of PLA chosen from virgin PLA, mechanically recycled PLA and their mixtures without there being an addition in any form whatsoever of a virgin polyethylene resin.

Description

COMPOSITIONS OF RECYCLED POLYETHYLENE WITH PROPERTIES

IMPROVED AND A PROCESS FOR PREPARING THEM

FIELD OF THE INVENTION

For several years, there has been a growing interest in addressing environmental issues and, as a result, there has been a focus on using polymers from renewable resources, such as polylactide acid (PLA), rather than polymers from petroleum.

There is also a definite interest in the use of recycled polymer.

But it is also well known that the mechanical properties of PLA are poor and their improvement is achieved in particular by mixing them with polyolefins such as polyethylene or polypropylene.

Given the increasing use of recycled polymers, the present invention relates firstly to the preparation of materials consisting of mixtures containing

PLA and recycled polyolefins

In particular, the present invention relates more particularly to materials consisting of mixtures comprising recycled polyethylenes with PLA, recycled or not.

It is understood that the invention also relates to the process for preparing these mixtures as well as the processes for molding objects with these mixtures, in particular by extrusion, blowing, thermoforming, injection or by rotational molding.

In the context of the present invention, it should be recalled that it is also well known that some mechanical properties of PLA are weaker than those of virgin or recycled polyethylene, while on the other hand PLA is more rigid, has excellent dimensional stability and low shrinkage, while having a glossy surface. It can even be said that by mixing them, they can improve each other and become complementary.

Given the current situation, it can easily be said that there is a need to use new materials containing PLA and recycled polyethylene resins in order to obtain objects benefiting from the properties of both types of resins.

In order to overcome the shortcomings of using polyethylene or PLA when used alone, the present invention relates to the preparation of materials composed mainly of

Recycled HDPE and LLDPE and a minority of PLA, the properties of the new material are improved.

> BE2023/0092

PRIOR STATE OF THE FIELD OF THE INVENTION

Mixtures of PLA with polyolefins in the presence of a compatibilizer are already known as described in patent EP 1777263 or in patent

US 2005/0192405, but in these documents only virgin resins are used.

It is known that there are similar blends prepared from virgin polyethylene and PLA polymers, but the present invention aims to obtain with recycled polymers mechanical and physical properties at least equivalent if not improved compared to those obtained with virgin resins.

There was also an article mentioning 90-10 blends by weight of PLA with

Recycled HDPE but without this bringing an improvement in the properties, on the contrary a drastic reduction in the mechanical properties of the order of 50% is mentioned.

There is therefore a need to develop materials made from polyethylene resins, particularly high, medium and low density and recycled, and PLA.

An object of the present invention is to prepare mixtures containing a minor amount of

PLA and mainly recycled polyethylene chosen from recycled HDPE and recycled LLDPE, without any loss of mechanical properties compared to those of blends made with virgin PE resins.

Another object of the invention consists of a material containing recycled polyethylene and

Recycled PLA or not, in which no virgin polyethylene resin is added.

Another object of the invention is to use as recycled polyethylene resin a mixture of

HDPE and LLDPE.

Another object of the invention is to develop a process for obtaining these materials.

Yet another object of the present invention is to use these materials to mold objects, in particular tanks, either by injection or by rotational molding.

The Applicant has now found that the above-mentioned drawbacks can be overcome by preparing a material consisting of: (a) a quantity >50% by weight of a mixture of recycled HDPF polyethylene and recycled LLDPE polyethylene and (b) a quantity <50% by weight of recycled or non-recycled PLA. The recycled type polyethylene is preferably in the form of a mixture of recycled HDPE having an MI2 of between 4 and 12g/10° and a density > or = 0.955 with recycled LLDPE having an M2 < or = 2.5 g/10° and preferably < or = 1g/10° and a density of between 0.915 and 0.935 g/cc in a weight ratio varying between 70/30 and 30/70 and preferably between 60/40 and 40/60.

Recycled HDPE and LLDPE and their blends can be monomodal or bimodal.

PLA, recycled or not, has more than 96% of the -L- isomer and less than 4% of the -D- isomer and an MFI between 4 and 30g/10”.

The material of the invention may be added during its preparation with a compatibilizing agent at a rate of 0.2 to 5% by weight, preferably 0.5 to 2% by weight based on the weight of the material.

Such a material can be prepared by extruding, at a temperature between 150°C and 260°C, a mixture of recycled polyethylene, preferably bimodal, and recycled or non-recycled PLA. The amount of recycled polyethylene represents an amount of more than 50% by weight of the material and is constituted by recycled HDPE and recycled LLDPE with an amount of less than 50% by weight of PLA, preferably between 0.1 and 45%, more preferably between 3 and 40% and even more preferably between 5 and 30% of PLA, the latter having at least 96% of -L- isomer and an MFI between 4 and 30g/10°

The Applicant has also found that during extrusion it is possible to add from 0.2 to 5% of a compatibilizing agent well known to those skilled in the art.

According to the method of preparation of the material of the invention, there is no addition of virgin polyethylene resin, in any form whatsoever.

For the purposes of the present invention, the term "recycled polymer" means post-consumer or post-industrial polymer waste and not a product resulting from a depolymerization of these polymers to recover the basic monomers.

DESCRIPTION

The first element of the material of the invention consists of recycled high-density HDPE, originating from production waste such as injection-molded objects or HDPE originating from post-consumer waste. 5 This recycled HDPE, called HDPE(1), has an MI2 of between 2 and 14 g/10°, preferably between 4 and 12 g/10° and a density > 0.953 g/cc and preferably greater than 0.955 g/cc

This mixture may also include a second recycled polyethylene of the LLDPE type originating from production or post-industrial waste such as film and called LLDPE(2), the latter having an MI2 < or = 2.5 g/10 “, preferably < or = 1.0 g/10° and a density of between 0.910 and 0.940 g/cc and preferably between 0.915 and 0.935 g/cc

According to the present invention, HDPE(1) is most often selected from the group comprising injection-molded object production waste or post-consumer HDPE and the like. On the other hand, as regards LLDPE(2), it is most often selected from the group comprising film production waste or post-consumer HDPE and the like.

These two grades of polyethylene, respectively recycled HDPE (1) and recycled LLDPE (2), are obtained by polymerization processes well known in the state of the art while using catalysts chosen indifferently between chromium, Ziegler-Natta or metallocene.

The weight ratio between HDPE (1) and LLDPE (2) is generally between 70/30 and 30/70, preferably between 60/40 and 40/60. The material of the invention also contains less than 50% and preferably between 0.1 and 45%, more preferably between 3 and 40% and even more preferably between 5 and 30% by weight, based on the total weight of the material, of a PLA having at least 96% of the -L- isomer and an MFI of between 4 and 30g/10”

When preparing the final mixture, 0.2 to 5%, preferably 0.5 to 2%, of a compatibilizing agent well known to those skilled in the art can be added during extrusion.

The recycled polyethylene, both HDPE(1) and LLDPE(2), used in the compositions of the invention is obtained by polymerization of ethylene optionally with a co-monomer chosen from alpha-olefins having from 3 to 10 carbon atoms. The HDPE(1) polyethylene has a density > 0.953 and preferably > 0.955 g/cc

The polymerization is carried out according to one or other well-known standard process, in the presence of a catalyst which can be chromium, a Ziegler Natta catalyst or a catalyst

° BE2023/0092 metallocene. The recycled polymer of the invention comes either from production waste during the production of the polymer or in particular from the production of injection-molded or extruded objects in the form of film or from post-consumption.

The recycled LLDPE(2) polyethylene forming part of the composition of the invention has a density of between 0.915 and 0.935 g/cc if it is prepared with a Ziegler-Natta or metallocene catalyst.

To prepare the material of the present invention, a weight mixture of between 70/30 and 30/70 and, preferably, between 60/40 and 40/60 of recycled HDPE/recycled LLDPE is used.

In the material of the invention, the amount of recycled polyethylene is greater than 50% and preferably between 70 and 95% by weight.

Although monomodal recycled polyethylene can be used in the compositions of the invention, it is preferred to use bimodal recycled polyethylene.

PLA is a polymer of lactic acid, this monomer coming from a renewable natural source. This polymer can be obtained by processes well known to those skilled in the art as notably described in US patent 7488783 comprising an oligomerization of lactic acid and then its conversion into lactide which is finally polymerized into polylactide or PLA.

Virgin or recycled PLA during its production, or its use during its transformation into objects prepared from PLA or even coming from the post-consumption of PLA is formed of more than 96% of the -L- isomer and has an MFI between 4 and 30g/10°.

In the material of the invention, the quantity of virgin or recycled PLA present is less than 50% by weight, preferably between 3 and 40% by weight and more preferably between 5 and 30% by weight.

In the context of the preparation of the material of the invention, it is perfectly known that recycled or non-recycled polyethylene resins are difficult to mix with recycled or non-recycled PLA resins.

For this purpose, it is well known to add compatibilizing agents during the preparation of the material, such as block or graft co- or terpolymers.

Examples of such agents include ethylene-acrylic acid copolymers, ethylene/glycidyl methacrylate copolymers, ethylene methacrylate/glycidyl methacrylate terpolymers, elastomeric polyolefins grafted with glycidyl methacrylate, ethylene/vinyl acetate copolymers or polyethylene grafted with maleic acid.

7 BE2023/0092

These compatibilizers are added during the extrusion of recycled polyethylene and

PLA, recycled or not, at a rate of 0.2 to 5%, and preferably 0.5 to 2% by weight relative to the weight of the material.

The preparation of the material of the invention consists of extruding together, in the proportions defined above, the recycled polyethylene, the recycled PLA or not, as well as the compatibilizing agent.

Extrusion to obtain the unprocessed material is carried out at a temperature between 150°C and 230°C., .

The material thus extruded is then transformed into granules or powder depending on its future use.

When this material is used to obtain objects by molding, the operating conditions are adapted

Thus, in the case of preparation of objects by injection molding, the material granules are introduced into the feed hopper located upstream of the injection unit where the granules are heated to reach the molten state. The molten polymer is then injected into a mold at a temperature between 200 and 240°C and under high pressure of the order of 1000 bar.

After the mold has cooled, the finished object is recovered.

To use the material to prepare an object by rotational molding, the material granules are first transformed into powder; the grains of this powder generally have a dimension between 100 and 600um.

The powder is then placed in a rotating mold which is itself introduced into a heated oven; the oven temperature is then raised to a value between 150°C and 260° for a period of 15 to 25 minutes.

After keeping the oven at its maximum temperature for about 5 minutes, it is then cooled to a temperature between 80 and 25°C.

The rotomolded object is then recovered.

The composition of the invention and its uses are also described by means of the examples below which in no way constitute a limitation thereof.

Example 1

A material according to the present invention was prepared by extruding a mixture consisting of recycled HDPE granules having an MI2 = 4 g/10° and a density of 0.960 g/cc from the recycling of non-carbonated natural water and fruit juice bottle caps with recycled LLDPE granules from the recycling of film and having an MI2 = 1 g/10° and a density of 0.960 g/cc.

, BE2023/0092 density of 0.935 g/cc. The HDPE/LLDPE weight ratio is 70/30. During the extrusion of this blend, 10% by weight of PLA granules were added, previously dried at a temperature of about 45°C for a few hours in order to reduce the residual water concentration, having an MI = 4 g/10° and an L-isomer content >96% as well as 1.5% by weight of the compatibilizer Lotader AX 8840. The extrusion was carried out on a co-rotating twin-screw extruder with an L/D ratio of 44 and a diameter of 26 mm. The recycled polyethylenes, PLA and

Lotader AX 8840 pre-mixed are fed into the hopper of the twin-screw extruder rotating at a rotation speed of 200 rpm. The mixture is heated and melted at a temperature of 190°C to 220°C along the extrusion screw. The mixture thus extruded was transformed into pellets for further use.

Example 2

The granules of the material obtained in Example 1 were used and introduced into the feed hopper upstream of an injection unit. The granules are distributed by the screw into the heating zone, transported rapidly to the front of the screw and melted.

The molten polymer mixture was finally injected into the injection mould at a temperature of between 200 and 240°C along the screw under a pressure of 1000 bar, the temperature and rotation speed being controlled. It was then allowed to cool for a period during which the material crystallised, causing it to shrink.

Samples of the injection-moulded object were then taken and its resistance to slow crack growth (ESCR) by strain hardening was estimated according to ISO 18488 using a tensile test at a temperature of 80°C. The value found by this method is twice as high as for the same object obtained from a material not containing PLA.

For comparison, a composition similar to that described in Example 1 was prepared but using virgin HDPE and LLDPE resins. These had a density of 0.960 g/cc and an MI2 of 4 g/10' for HDPE and a density of 0.935 g/cc and an MI2 of 1 g/10° for LLDPE, respectively. A 70/30 weight blend of these resins was thus prepared and extruded with the same compatibilizing agent. The granules obtained were subjected to injection molding as described above. The ESCR properties of the injected object are equivalent to those obtained with recycled resins.

Example 3

A material according to the present invention was prepared by extruding a mixture consisting of

3 BE2023/0092 50% by weight of recycled HDPE from recycled PE bins and whose characteristics are as follows: an MI2 = 9 g/10° and a density of 0.960 g/cc with 50% by weight of a grade

Recycled LLDPE from film recycling and having an MI2 = 0.6 8/10’ and a density of 0.925 g/cc.

During the extrusion of this recycled PE blend, 20% by weight of PLA with an MI2 of 10 g/10° and a D-isomer content of < 1% and 1% by weight of the compatibilizer Lotader were added.

AX 8900.

The mixture thus extruded was first transformed into granules and these are then micronized to obtain a powder whose grains have a diameter of between 200 and 600 um.

PLA granules can be pre-dried as in the example.

Example 4

The powder obtained in Example 3 was used and placed in an aluminum mold intended for rotational molding which is rotating around two axes, and which is introduced, while maintaining rotation, into an oven gradually heated to a temperature between 150 and 260°C for 20°. The maximum temperature is then maintained for 6 minutes and the mold is then cooled in air to a temperature between 80 and 25°C in 20 minutes and finally the rotationally molded object is removed from the mold.

It was noted that the rotomolded object did not exhibit any deformation or porosity.

A sample of the rotomolded object was taken and the ESCR was estimated using the method described in Example 2.

The measurement showed that the ESCR value had tripled compared to that measured on an object obtained from a similar material but not containing PLA.

This example was repeated using virgin polyethylene resins and the ESCR results obtained with the rotomolded object are similar to those obtained with recycled resins.

Claims (10)

CLAIMS BE2023/0092 1. Composition of material with improved mechanical properties characterized in that it consists of: (a) a quantity >50% by weight of recycled polyethylene chosen from recycled HDPE, recycled LLDPE and their mixtures and (b) a quantity <50% by weight of PLA chosen from virgin PLA, mechanically recycled PLA and their mixtures. 2. Composition according to claim 1, characterized in that the quantity of recycled polyethylene in the composition of the material is preferably between 70 and 95% by weight, and that of the PLA is between 0.1 and 45% by weight, preferably between 3 and 40% by weight and more preferably between 5 and 30% by weight. 3. Composition according to claims 1 and 2, characterized in that the recycled type polyethylene is in the form of a mixture of recycled HDPE and recycled LLDPE having respectively an MI2 of between 4 and 12g/10° and a density > or = 0.953 and preferably > or = 0.955 for HDPE and an MI2 < or = 2.5 g/10° and preferably < or = 1g/10° and a density of between 0.910 and 0.940 g/cc and preferably between 0.915 and 0.935 g/cc for LLDPE. 4. Composition according to claims 1 and 3, characterized in that the recycled type polyethylene is in the form of a mixture whose weight ratio varies between 70/30 and 30/70 respectively of HDPE and LLDPE and preferably in the form of a mixture varying between 60/40 and 40/60 by weight respectively of recycled HDPE and recycled LLDPE. 5. Composition according to any one of claims 1 to 4, characterized in that the PLA, recycled or not, has a quantity greater than or equal to 96% of -L- isomer as well as a quantity of less than 4% of -D- isomer and an MFI of between 4 and 30g/10°.-. 6. Composition according to any one of claims 1 to 5, characterized in that it also comprises a compatibilizing agent between the polyethylene and PLA resins at a rate of 0.2 to 5% by weight and preferably 0.5 to 2% by weight based on the weight of the composition. 7. Composition according to claim 6, characterized in that the compatibilizing agent is chosen from: ethylene-acrylic acid copolymers, ethylene/glycidyl methacrylate copolymers, ethylene methacrylate/glycidyl methacrylate terpolymers, elastomeric olefins grafted with glycidyl methacrylate, ethylene/vinyl acetate copolymers or polyethylene grafted with maleic acid. 8. Process for the preparation of the composition claimed in any one of claims 1 to 7, characterized in that the material is extruded on an extruder with a temperature profile of between 170 and 260°C and preferably between 190 and 220°C. 9. Method according to claim 8, characterized in that during the extrusion a compatibilizing resin as described in claim 7 is added at a rate of 0.5 to 2% by weight based on the quantity of material to be extruded. 10. Object obtained by molding, either by extrusion, or by injection, or by rotational molding, or by thermoforming from the material described in any one of claims 1 to 0.