WO2025083226A1

WO2025083226A1 - Method for adding additives to a polyolefin melt or a polyolefin solution

Info

Publication number: WO2025083226A1
Application number: PCT/EP2024/079532
Authority: WO
Inventors: Andreas Albrecht; Joel FAWAZ; Alexandra Romina ALBUNIA; Noureddine AJELLAL; Lukas SOBCZAK; Henry Sleijster; Pablo AGUAYO; Mubashar SATTAR; Novdeep Singh DHILLON
Original assignee: Borealis GmbH
Current assignee: Borealis GmbH
Priority date: 2023-10-20
Filing date: 2024-10-18
Publication date: 2025-04-24
Anticipated expiration: 2026-04-20

Abstract

The present invention is concerned with a method for adding additives to a polyolefin melt or to a polyolefin solution by means of a solution or dispersion of additives in n-alkane. In particular, the present invention relates to such a method that ensures a homogeneous distribution of the additive in the polyolefin melt or the polyolefin solution and cost savings. Furthermore, the present invention is concerned with a solvent based polyolefin recycling process comprising said method for adding additives in n-alkane. Furthermore, the present invention concerns with a process for producing polyolefin pellets comprising carrying out said method for adding additives in a melt extruded polyolefin.

Description

Method for adding additives to a polyolefin melt or a polyolefin solution.

The present invention is concerned with a method for adding additives to a polyolefin melt or to a polyolefin solution by means of a solution or dispersion, such as a suspension, of additives in n-alkane. In particular, the present invention relates to such a method that ensures a homogeneous distribution of the additive in the polyolefin melt or in the polyolefin solution, and allows cost savings. Furthermore, the present invention is concerned with a solvent based polyolefin recycling process comprising said method for adding additives in n-alkane. Furthermore, the present invention concerns with a process for producing polyolefin pellets comprising carrying out said method for adding additives in a melt extruded polyolefin.

Background

Additives, such as stabilizers, antioxidants, but also nucleating agents and pigments, are usually fed to polyolefin streams such as polyolefin melts or polyolefin solutions.

For example, it is common to add ultraviolet inhibitors or light stabilizers to polyolefins. The addition of stabilizers or antioxidants may be particularly relevant for high temperature process steps like solvent removal by degassing for polyolefin sensible to high temperatures. For example, when processing polyolefin dissolved in alkanes, e.g., in a polypropylene (PP) solvent-based recycling process or in polyethylene (PE) solution polymerization processes such as in the Borceed™ technology, feeding of stabilizers or antioxidants might be required.

Additives are usually added in rather low concentrations of several hundred parts per million (ppm) based on weight of the polymer to which it is added. Additives may be further insoluble in polymers. For taking full effect all over the bulk of the polymer, homogeneous distribution of the additives is required. The quality, the function, the aesthetic of the polymer is often altered by the uniformity of the dispersion of the additive in the polymer. If the additive is not homogeneously distributed, the intended effect of the additive may vary within the polymer. Depending on the nature of the additives, including its aggregation state (solid or liquid/melted form), and the viscosity of the polyolefin melt or solution a homogeneous distribution can be quite challenging to achieve.

Typical compounding operations, usually other homogenization tasks, e.g., for blending polymers with modifiers and/or fillers, require intensive mixing. This entails a significant specific energy input (SEI) into the melt. Particularly in larger scale operations it is attempted to keep SEI as low as possible. When the process task is not actual compounding but just homogeneous distribution of additives in a polyolefin, a procedure allowing homogeneous distribution of the additive at minimum energy input is particularly valuable. A simplified way of additive feeding would also reduce the Capital Expenditure (CAPEX) for plants. Furthermore, improved quality of mixing allows to reduce additive contents while maintaining the desired effect, thereby generating savings.

WO 2015/000681 relates to a solvent-based plastics-recycling method which comprises a) mixing the polymer-containing waste with an organic solvent containing at least one thermal stabilizer for polymers, at least one polymer being dissolved in the organic solvent and an insoluble portion of the waste remaining; b) at least partially separating the solution containing at least one polymer and at least one thermal stabilizer from the insoluble part of the waste; c) at least partially separating the organic solvent from the at least one polymer.

Therefore there is the need for a method for adding additives to a polyolefin melt or a polyolefin solution that ensures at the same time a homogeneous distribution of the additive(s) and cost savings, e.g. savings on energy and additives costs (via lower concentration of additive), respectively.

Summary of the invention

It has now surprisingly been found that the above mentioned objective can be achieved by adding, and thereafter mixing, an additive in a n-alkane solution or in a n- alkane dispersion, such as a n-alkane suspension, to a polyolefin melt or to a polyolefin solution comprising a hydrocarbon solvent.

Thus, in a first aspect the invention relates to a method for adding an additive to a polyolefin, the method comprising the steps of a) providing a solution or a dispersion of the additive in a n-alkane, b) adding the solution or the dispersion of step a) to a polyolefin being in melted form (i.e. a polyolefin melt) or being dissolved in a hydrocarbon solvent (i.e. a polyolefin solution), thereby providing a product comprising the additive and the polyolefin ; and c) mixing the additive and the polyolefin comprised in the product obtained in step b) to obtain a mixed product.

It has surprisingly been found that n-alkanes show excellent miscibility with polyolefin melt as well as with polyolefin solution. Therefore, the addition of additives in a n-alkane solution or in a n-alkane dispersion, such as a n-alkane suspension, is a simple way to obtain a very efficient mixing and to provide an homogeneous distribution of the additive in the polyolefin melt or polyolefin solution. At the same time, cost saving is achieved. In particular, energy saving is obtained due to the reduced energy input required for mixing and yet obtaining a homogeneous dispersion. Saving on additives costs are obtained due to the better mixing quality that allows reducing the concentration of the additive to achieve the desired effect.

In addition, since the additives solution or dispersion in n-alkane is directly added to the polyolefin melt, the preparation of an additive melt in a separate extruder is avoided, thereby resulting in a simplified process and further cost savings.

In a further aspect, the present invention is directed to a solvent based polyolefin recycling process comprising the method for adding additives of the above disclosed aspect. Preferably, the solvent based polyolefin recycling process comprises one or more polyolefin/solvent separation steps of a polyolefin/solvent stream wherein the solution or the dispersion comprising an additive is added to the polyolefin/solvent stream before at least one of the one or more separation steps.

One of the last steps of the solvent based polyolefin recycling process is the solvent removal. However, this step may require high temperatures that cause thermal degradation of the polyolefin, which can for example be polypropylene. The thermal degradation may be further enhanced by the fact that in solvent based polyolefin recycling process additives such as stabilizers are removed from the polyolefin along with the undesired impurities upstream of the solvent removal step.

It has been discovered that when additives such as antioxidants are added to the polyolefin/solvent stream before a separation step according to the method of the invention, thermal stabilization of the polyolefin is achieved.

In a still further aspect, the present invention is directed to a process for producing polyolefin pellets comprising carrying out the method for adding additives according to the above aspect on a melt extruded polyolefin. The process comprises the step of pelletizing the product obtained after mixing the additive with the polyolefin melt. The pelletization is preferably carried out after removing the volatiles (and therefore the n-alkane) from the melt by degassing. However, no pelletizing problem has been observed when, for example, up to 3 wt% of heptane was retained in the melt. It was expected that the n- alkane in the melt would have caused melt foaming and pelletizer plugging by evaporating upon pressure release at the pelletizer die plate. By contrast, it has been found that up to 3 wt% n-alkane retained in the melt does not affect the pelletizing process. This further shows that the n-alkane, and therefore the additive is uniformly distributed in the melt. Definitions

The expression ‘volatiles’ or ‘volatile compounds’ as used herein has to be understood as compounds having significantly lower molecular weight in comparison to the polyolefin separated in the process of the invention. Such compounds typically are present in the gaseous form when being exposed to a flash separator. Commonly, the volatile compounds are a mixture of volatile hydrocarbons and include the n-alkane of the method of the invention.

‘Flash separators’ have been known in the prior art for decades (also as low- pressure separators). As it is well known in the art, a liquid feed is passed to a flash vessel operated at a reduced pressure. Thereby a part of the liquid phase vaporizes and can be withdrawn as an overhead stream (or a vapor stream) from the low pressure separator. The part remaining in liquid phase is then withdrawn as a condensed stream from the flash vessel. Operating the low pressure separator under conditions such that both vapor and liquid phases are present in the flash vessel describes this situation.

‘Gravity separators’ or ‘liquid-liquid separators’ as used herein comprise a vessel in which a two-phase (i.e. liquid/liquid) system can be separated. The liquid phase with the lower relative density (polyolefin-lean phase) is withdrawn from the upper end of the vessel whereas the liquid phase with the higher relative density (in the present case the polyolefin-rich phase) is withdrawn from the bottom end of the vessel.

The term ‘vacuum pressure conditions’ as used herein denotes vacuum pressures between 5 mbar to 100 mbar. Pressures lower than 5 mbar are disadvantageous in view of energy consumption and resulting costs. Pressures higher as 100 mbar result in too high amounts of volatiles in the final polymer.

The term “ primary antioxidants" denotes compounds that react with chain-propagating radicals such as peroxy, alkoxy, and hydroxy radicals in a chain terminating reaction. These antioxidants donate hydrogen to the alkoxy and hydroxy radicals which convert them into inert alcohols and water, respectively. "Primary antioxidants" are also known as “free radicals scavengers”.

Typical commercial primary antioxidants are sterically hindered phenols and secondary aromatic amines. These compounds come in a wide range of molecular weights, structures, and functionalities. “Sterically hindered phenols" are a known class of primary antioxidants. These compounds act as a primary antioxidants by converting peroxyl radicals to hydroperoxides. Thus, they inhibit auto-oxidation of organic polymers by reducing the amount of peroxyl radicals.

The term “secondary antioxidant" denotes compounds that decompose hydroperoxides (ROOH) into nonreactive products before they decompose into alkoxy and hydroxy radicals. They are also known as "peroxide scavengers".

Examples of secondary antioxidants are trivalent phosphorus compounds (phosphites). They reduce hydroperoxides to the corresponding alcohols and are themselves transformed into phosphates. Another class of secondary antioxidants are thioethers or organic sulfides. They decompose two molecules of hydroperoxide into the corresponding alcohols and are transformed to sulfoxides and sulfones.

With the term "polyolefin melt” is meant one or more polyolefins in the molten state.

Description of the drawings

Figure 1 shows a schematic set up of inventive examples IE1 to IE6 and comparative examples CE1 to CE2.

Figures 2a, 2b, and 2c show the melt flow rate (MFR2) (Figure 2a), the oxidation induction time (OIT) (Figure 2b), the yellowness index (Yl) (Figure 2c) measured as a function of the antioxidant concentration and processing step (samples 1 and 3) of comparative example CE1 and inventive examples IE1 to IE6.

Figure 3 shows a schematic set up of comparative example CE3.

Detailed description of the invention

In the following, the invention is described in detail.

In the most general embodiment of the invention, the method for adding an additive to a polyolefin comprises the steps of a) providing a solution or a dispersion (e.g. a suspension) of the additive in a n-alkane; b) adding the solution or the dispersion of step a) to a polyolefin being in melted form (referred herein to as polyolefin melt) or being dissolved in a hydrocarbon solvent (referred herein to as polyolefin solution), thereby providing a product comprising the additive and the polyolefin; c) mixing the additive and the polyolefin comprised in the product obtained in step b) to obtain a mixed product.

It is understood that according to the invention one or more additives can be added to a polyolefin. Therefore, the term “an additive” is not necessarily limited to a single (one) additive.

It is understood that according to the invention one or more n-alkanes can be added to a polyolefin. Therefore, the term “a n-alkane” is not necessarily limited to a single (one) n- alkane.

A dispersion of the additive in a n-alkane may be in the form of an emulsion of the additive in a n-alkane or a suspension of the additive in a n-alkane depending on whether the additive is in liquid or solid form.

Therefore, the present invention is directed to a method for adding an additive to a polyolefin melt wherein the method comprises the steps of a) providing a solution or a dispersion of the additive in a n-alkane; b) adding the solution or dispersion of step a) to the polyolefin in melted form (polyolefin melt) thereby providing a product comprising the additive and the polyolefin; c) mixing the additive and the polyolefin comprised in the product obtained in step b) to obtain a mixed product.

Therefore, the present invention is directed to a method for adding an additive to a polyolefin solution wherein the method comprises the steps of a) providing a solution or a dispersion of the additive in a n-alkane; b) adding the solution or dispersion of step a) to the polyolefin dissolved in a hydrocarbon solvent (polyolefin solution) thereby providing a product comprising the additive and the polyolefin; c) mixing the additive and the polyolefin comprised in the product obtained in step b) to obtain a mixed product.

Preferably, the polyolefin is selected from the group consisting of polyethylene, polypropylene, and any mixture thereof. Therefore, the polyolefin comprises or consists of polypropylene homopolymer(s), polypropylene copolymer(s), polyethylene homopolymer(s), polyethylene copolymer(s) or any mixture thereof. The polyolefin can be for example a polymer selected from the list consisting of polyethylene (PE), in particular high density polyethylene (HDPE), low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE), and polypropylene (PP) or any mixture thereof. Preferably, the polyolefin comprises polypropylene homopolymer(s) or polypropylene copolymer(s) or any mixture thereof.

The expression “propylene homopolymer” denotes a propylene polymer that consists of at least 99.0 wt.-%, preferably at least 99.5 wt.-%, more preferably at least 99.8 wt.-% of propylene monomer units, based on the total weight of the propylene polymer, determined by quantitative ¹³C{¹H} nuclear magnetic resonance (NMR) spectroscopy. In one embodiment, only propylene monomer units are detectable in the propylene homopolymer.

The expression “propylene copolymer” denotes a propylene polymer that generally comprises propylene monomer units and other comonomer units, preferably, ethylene comonomer units and/or one or more alpha-olefin(s) comonomer units having from 4 to 10 carbon atoms, most preferably ethylene comonomer units. Preferably, the content of the propylene monomer units in the propylene copolymer is at least 70 wt.-%, based on the total weight of the propylene copolymer, determined by quantitative ¹³C{¹H}-NMR spectroscopy, or alternatively 70 mol-%, based on the total molar content of the propylene copolymer, determined by quantitative ¹³C{¹ H}-NMR spectroscopy.

The solvent of the polyolefin solution before the addition of the solution or dispersion prepared in step (a) preferably comprises or consists of a hydrocarbon solvent. Preferably the hydrocarbon solvent comprises or consists of an alkane, such as one or more cycloalkanes and/or one or more n-alkanes. Examples of suitable cycloalkanes are cyclopropane, cyclobutane, cyclopentane and cyclohexane or any mixture thereof. More preferably, the hydrocarbon solvent comprises or consists of a n- alkane, wherein the n-alkane is preferably a C4 (n-butane), C5 (n-pentane), C6 (n- hexane), C7 (n-heptane), C8 (n-octane), C9 (n-nonane) or C10 (n-decane) n-alkane or any mixture thereof. Preferably the n-alkane is a C4, C5, C6, C7 or C8 n-alkane or any mixture thereof, more preferably, the n-alkane is a C6, C7 or C8 n-alkane or any mixture thereof. This means that the n-alkane is selected from n-hexane, n-heptane, n- octane or any mixture thereof.

The polyolefin melt, before the addition of the additive solution or dispersion in n-alkane may as well comprise a small amount of solvent. The solvent is preferably a hydrocarbon solvent. Preferably the hydrocarbon solvent comprises or consists of an alkane, such as one or more cycloalkanes and/or one or more n-alkanes. Examples of suitable cycloalkanes are cyclopropane, cyclobutane, cyclopentane and cyclohexane or any mixture thereof. More preferably, the hydrocarbon solvent comprises or consists of a n- alkane, wherein the n-alkane is preferably a C4 (n-butane), C5 (n-pentane), C6 (n- hexane), C7 (n-heptane), C8 (n-octane), C9 (n-nonane) or C10 (n-decane) n-alkane or any mixture thereof. Preferably the n-alkane is a C4, C5, C6, C7 or C8 n-alkane or any mixture thereof, more preferably, the n-alkane is a C6, C7, C8 n-alkane or any mixture thereof. This means that the n-alkane is selected from n-hexane, n-heptane, n- octane or any mixture thereof.

In an embodiment of the method, the method comprises the steps of: a) providing a solution of an additive (such as an antioxidant) in a n-alkane, particularly a C6, C7, or C8 n-alkane or any mixture thereof; b) adding the solution of step a) to a polyolefin melt (such as a polypropylene melt) thereby providing a product comprising the additive and the polyolefin; c) mixing the additive and the polyolefin comprised in the product obtained in step b) to obtain a mixed product.

Particularly, in step b) the addition to the polyolefin melt is carried out at a temperature of the melt in the range of from 100°C to 300°C.

Step a)

A solution or a dispersion, such as a suspension, of additive(s) in n-alkane as referred to in step a) may be provided by any method of preparing a solution or a dispersion of additives in n-alkane, including optionally heating the n-alkane prior to, during and/or after addition of the additive(s).

The solvent of the additive solution or dispersion comprises or consists in a n-alkane. The n-alkane is preferably a C4 (n-butane), C5 (n-pentane), C6 (n-hexane), C7 (n-heptane), C8 (n-octane), C9 (n-nonane) or C10 (n-decane) n-alkane or any mixture thereof. More preferably the n-alkane is a C4, C5, C6, C7, C8 n-alkane or any mixture thereof, more preferably, the n-alkane is a C6, C7 or C8 n-alkane or any mixture thereof. This means that the n-alkane is selected from n-hexane, n-heptane, n-octane or any mixture thereof.

Therefore, preferably, the method for adding an additive to a polyolefin melt or polyolefin solution comprises the steps of a) providing a solution or a dispersion of the additive in a C4, C5, C6, C7 or C8 n-alkane or any mixture thereof, preferably in a C6, C7 or C8 n-alkane or any mixture thereof; b) adding the solution or dispersion of step a) to the polyolefin melt or to the polyolefin solution, wherein the polyolefin of the polyolefin solution is dissolved in a hydrocarbon solvent, thereby providing a product comprising the additive and the polyolefin; c) mixing the additive and the polyolefin comprised in the product obtained in step b) to obtain a mixed product.

Therefore, preferably, the present invention is directed to a method for adding an additive to a polyolefin melt wherein the method comprises the steps of a) providing a solution or a dispersion of the additive in a C4, C5, C6, C7,C8 n-alkane or any mixture thereof, preferably in a C6, C7, C8 n-alkane or any mixture thereof; b) adding the solution or dispersion of step a) to the polyolefin melt thereby providing a product comprising the additive and the polyolefin; c) mixing the additive and the polyolefin comprised in the product obtained in step b) to obtain a mixed product.

Therefore, preferably, the present invention is directed to a method for adding an additive to a polyolefin solution wherein the polyolefin is dissolved in a hydrocarbon solvent wherein the method comprises the steps of a) providing a solution or a dispersion of the additive in a C4, C5, C6, C7 or C8 n-alkane or any mixture thereof, preferably in a C6, C7 or C8 n-alkane or any mixture thereof; b) adding the solution or dispersion of step a) to the polyolefin solution thereby providing a product comprising the additive and the polyolefin; and c) mixing the additive and the polyolefin comprised in the product obtained in step b) to obtain a mixed product.

With regard to the additives, there is no particular limitation as far as they form a solution or dispersion in the n-alkane. Additives according to the invention are, for example, antioxidants, stabilizers, nucleating agents, pigments or combinations thereof.

With regard to the antioxidants, they preferably comprise or consist of primary antioxidants and secondary antioxidants or combinations thereof. According to the present invention, primary antioxidants alone or in combination with secondary antioxidants are preferred. Preferably the primary antioxidant comprises or consists of a sterically hindered phenol.

Examples of primary antioxidants are disclosed in the below Table 1 : Table 1

Preferably the primary antioxidant is selected from octadecyl 3-(3’,5’-di-tert. butyl-4- hydroxyphenyl)propionate, 2,2’-thiodiethylenebis-(3,5-di-tert. butyl-4-hydroxyphenyl)- propionate, 2,5,7,8-Tetramethyl-2(4’,8’,12’-trimethyltridecyl)chroman-6-ol or any mixture thereof.

Examples of secondary antioxidants according to the invention are reported in the below table 2. Table 2

Preferably the secondary antioxidant is selected from tris (2,4-di-f-butylphenyl) phosphite, di-lauryl-thio-di-propionate, di-octadecyl-disulphide or any mixture thereof.

With regard to the stabilizers, any suitable stabilizer is contemplated according to the method of the invention provided that it forms a solution or a dispersion in n- alkane. Suitable stabilizers are for example UV stabilizers and light stabilizers

Examples of UV absorbers and hindered amine light stabilizer (HALS) are reported in the below table 3.

Table 3

With regard to the nucleating agent, any suitable nucleating agent is contemplated according to the method of the invention provided that it forms a solution or dispersion in n-alkane.

Suitable types of [3-nucleating agents are

• dicarboxylic acid derivative type diamide compounds from Cs-Cs-cycloalkyl monoamines or C6-C12 -aromatic monoamines and Cs-Cs-aliphatic, Cs-Cs-cycloaliphatic or C6-C12 - aromatic dicarboxylic acids, e.g

• N, N'-di- C5-C8-cycloalkyl-2,6-naphthalene dicarboxamide compounds such as N, N'- dicyclohexyl-2,6-naphthalene dicarboxamide and N,N'-dicyclooctyl-2,6- naphthalene dicarboxamide,

• N, N'-di- Cs-C8-cycloalkyl-4,4-biphenyldicarboxamide compounds such as N, N'- dicyclohexyl-4,4-biphenyldicarboxamide and N,N'-dicyclopentyl-4,4- biphenyldicarboxamide, • N.N'-di-Cs-Cs-cycloalkyl-terephthalarnide compounds such as N. N'- dicyclohexylterephthalamide and N,N'-dicyclopentylterephthalamide, •

N, N'-di- Cs-Cs-cycloalkyl-l ,4-cyclohexanedicarboxamide compounds such as N, N'- dicyclo-hexyl-1 ,4-cyclohexanedicarboxamide and N,N'-dicyclohexyl-1 ,4- cyclopentanedicarboxamide,

• diamine derivative type diamide compounds from Cs-Cs-cycloalkyl monocarboxylic acids or Ce-Ci2-aromatic monocarboxylic acids and Cs-Cs-cycloaliphatic or C56-C12- aromatic diamines, e.g.

• N.N'- C6-C12 arylene-bis-benzamide compounds such as N,N'-p-phenylene-bis- benzamide and N,N'-1 ,5-naphthalene-bis-benzamide,

• N.N'- Cs-Cs-cycloalkyl-bis-benzamide compounds such as N,N'-1 ,4-cyclopentane- bis- benzamide and N,N'-1 ,4-cyclohexane-bis-benzamide, • N.N'-p- C6-C12 -arylene- bis- Cs-Cs-cycloalkylcarboxamide compounds such as N,N'-1 ,5- naphthalene-bis- cyclohexanecarboxamide and N,N'-1 ,4-phenylene-bis- cyclohexanecarboxamide, and

• N.N'- Cs-Cs-cycloalkyl-bis-cyclohexanecarboxamide compounds such as N,N'-1 ,4- cyclopentane-bis-cyclohexanecarboxamide and N,N'-1 ,4-cyclohexane-bis- cyclohexanecarboxam ide,

• amino acid derivative type diamide compounds from amidation reaction of Cs-Cs-alkyl, Cs-Cs-cycloalkyl- or C6-Ci2-arylamino acids, Cs-Cs-alkyl-, Cs-Cs-cycloalkyl- or C6-C12- aromatic monocarboxylic acid chlorides and Cs-Cs-alkyl-, Cs-Cs-cycloalkyl- or C6-C12- aromatic mono-amines, e.g.

• N-phenyl-5-(N-benzoylamino)pentaneamide and N-cyclohexyl-4-(N-cyclohexyl- carbonylam ino)benzam ide.

Further suitable [3-nucleating agents are

• quinacridone type compounds, e.g. quinacridone, dimethylquinacridone and dimethoxyquinacridone,

• quinacridonequinone type compounds, e.g. quinacridonequinone, a mixed crystal of 5, 12-dihydro(2,3b)acridine-7, 14-dione with quino(2,3b)acridine-6,7, 13,14- (5H,12H)-tetrone and dimethoxyquinacridonequinone and

• dihydroquinacridone type compounds, e.g. dihydroquinacridone, dimethoxydihydroquinacridone and dibenzodihydroquinacridone.

Still further suitable [3-nucleating agents are

• salts of dicarboxylic acids with metals of group II of the periodic table, particularly salts of dicarboxylic acids with at least 7 carbon atoms with metals from group II of the periodic table, e.g. pimelic acid calcium salt and suberic acid calcium salt; and

• mixtures of dicarboxylic acids and salts of metals from group Ha of periodic system.

Still further suitable [3-nucleating agents are

• salts of metals from group Ila of periodic system and imido acids of the formula

wherein x = 1 to 4; R = H, -COOH, C1-C12 -alkyl, Cs-Cs -cycloalkyl or Ce-Ci2-aryl, and Y = C1-C12 -alkyl, Cs-Cs-cycloalkyl or Ce-Ci2-aryl - substituted bivalent C6-C12 - aromatic residues, e.g. calcium salts of phthaloylglycine, hexahydrophthaloylglycine, N-phthaloylalanine and/or N-4-methylphthaloylglycine.

With regard to the pigments, any suitable pigment is contemplated according to the method of the invention provided that it forms a solution or dispersion in n-alkane.

With regard to the amount of the additive(s) and of the n-alkane, the solution or dispersion are prepared so that the amount of the n-alkane to be removed from the polyolefin melt or polyolefin solution is as low as possible. Accordingly, the amount of the additive in the solution is as high as permitted by solubility, or the amount of the additive in the dispersion is as high as the stability of a dispersion allows. In the step of providing a solution of the additive(s) in the n-alkane, the n-alkane may be optionally heated prior to, during and/or after addition of the additive(s) to facilitate dissolution of the additive(s) in the n-alkane whereas the solubility of the additive(s) may be higher at higher temperature.

With regard to the antioxidant, the antioxidant is present in the dispersion or solution in an amount ranging from 100 ppm to 4000 ppm based on the polyolefin weight, more preferably in an amount ranging from 200 to 3000 ppm based on the polyolefin weight, more preferably in an amount ranging from 300 to 2500 ppm based on the polyolefin weight, more preferably in an amount ranging from 400 to 2000 ppm based on the polyolefin weight. Preferably, the solution or dispersion of any embodiments of the invention comprises the primary antioxidant in an amount ranging from 50 ppm to 2500 ppm based on the polyolefin weight, more preferably in an amount ranging from 200 to 1800 ppm based on the polyolefin weight, more preferably in an amount ranging from 300 to 1200 ppm based on the polyolefin weight. Preferably, the primary antioxidant and the secondary antioxidant (together) are present in the solution or dispersion in an amount from 100 ppm to 4000 ppm based on the polyolefin weight, more preferably in an amount ranging from 200 to 3000 ppm based on the polyolefin weight, more preferably in an amount ranging from 300 to 2500 ppm based on the polyolefin weight, more preferably in an amount ranging from 400 to 2000 ppm based on the polyolefin weight. The solution or dispersion of any embodiments of the invention may comprise the secondary antioxidant preferably in an amount ranging from 50 to 1500 ppm based on the polyolefin weight.

With regard to the stabilizer, preferably, the stabilizer in the solution or in the dispersion is in the range of from 200 ppm to 2500 ppm based on the polyolefin weight, preferably in the range of 400 to 2000 ppm based on the polyolefin weight, more preferably in the range of 600 to 1800 ppm based on the polyolefin weight.

With regard to the nucleating agent, preferably nucleating agent in the solution or in the dispersion is in the range of from 50 to 200 ppm based on the polyolefin weight.

With regard to the pigments, preferably, the pigment in the solution or in the dispersion is in the range of from 200 ppm to 2500 ppm based on the polyolefin weight, preferably in the range of 400 to 2000 ppm based on the polyolefin weight, more preferably in the range of 600 to 1800 ppm based on the polyolefin weight.

Step b) In step b), the solution or dispersion of step a) is added to a polyolefin melt or to a polyolefin solution, wherein the polyolefin is dissolved in a hydrocarbon solvent. Thereby a product is obtained. The product is the polyolefin solution further comprising the additive and the n-alkane of step a) or the product is the polyolefin melt further comprising the additive and the n-alkane of step a).

The polyolefin melt or the polyolefin solution before the addition may be provided as a stream or may be comprised in a pot. The polyolefin melt may be contained in an extruder.

Any method for adding the solution or dispersion of step a) to the polyolefin melt or the polyolefin solution is suitable. For example, the solution or dispersion of step a) can be injected in the polyolefin melt or the polyolefin solution. The solution or dispersion of step a) may be heated prior to being injected in the polyolefin melt or the polyolefin solution.

The polyolefin melt is a polyolefin melt provided from any suitable process. For example, the polyolefin melt can be provided from a process for separating a polyolefin solution from a volatile wherein the polyolefin is separated as a melt and the volatile component is released as gaseous phase. As another example, the polyolefin melt can be provided from a polymerization process. Here, the polymerization process might provide the polyolefin either as a melt, or in solid form that is molten in any suitable device, e.g. in an extruder.

The polyolefin melt can be a melt-extruded polyolefin.

As to the temperature, the addition of the additive solution or dispersion in n-alkane to the polyolefin melt is carried out at any temperature at which the polyolefin is in a melted state. Preferably the addition is carried out at a temperature of the melt in the range of from 100°C to 300°C, more preferably in the range of 120 - 250°C for polyethylenes and 200 - 280°C for polypropylenes. The solution or dispersion of step a) may, when added to the polyolefin melt, have the same or similar temperature as the polyolefin melt. For example, the solution or dispersion of step a) may, when added to the polyolefin melt, have a temperature of in the range of from 100°C to 300°C or from 120 to 250°C or from 200 to 280°C (depending on the polyolefin).

As to the pressure, the addition to the polyolefin melt is carried out at any suitable pressure provided that the polyolefin is melt. Preferably, the addition is carried out at a pressure in the range of from 1 to 200 barg, more preferably at a pressure in the range of from 5 to 100 barg.

The polyolefin solution is a polyolefin solution provided from any suitable process. For example, a process wherein the polyolefin is dissolved in a hydrocarbon e.g. a solution polymerization (such as the Borceed™ process) or a solvent based recycling process. As to the temperature, the addition to the polyolefin solution is carried out at any temperature at which the polyolefin is in solution. Preferably the addition is carried out at a temperature of the polyolefin solution in the range of from 100°C to 300°C, more preferably in the range of from 150 - 280°C. The solution or dispersion of step a) may, when added to the polyolefin solution, have the same or similar temperature as the polyolefin solution. For example, the solution or dispersion of step a) may, when added to the polyolefin solution, have a temperature of in the range of from 100°C to 300°C, such as within the range of from 150°C to 280°C.

As to the pressure, the addition to the polyolefin solution is carried out at any suitable pressure provided that the polyolefin is in solution. Preferably, the addition is carried out at a pressure in the range of from 1 to 200 barg, more preferably at a pressure in the range of from 5 to 100 barg.

The solvent of the polyolefin solution before the addition of the solution or dispersion prepared in step a) comprises or consists of a hydrocarbon solvent. Preferably, the hydrocarbon solvent comprises or consists of a n-alkane, wherein the n-alkane is preferably a C4 (n-butane), C5 (n-pentane), C6 (n-hexane), C7 (n-heptane), C8 (n-octane), C9 (n-nonane) or C10 (n-decane) n-alkane or any mixture thereof. More preferably the n- alkane is a C4, C5, C6, C7, C8 n-alkane or any mixture thereof, more preferably, the n- alkane is a C6, C7, C8 n-alkane or any mixture thereof. This means that the n-alkane is selected from n-hexane, n-heptane, n-octane or any mixture thereof.

The amount of solution or dispersion of step a) added to the polyolefin solution is preferably up to 10 weight % of the total weight, wherein the total weight is the sum of the weight of the solution or dispersion of step a) and of the weight of the polyolefin solution. The amount of solution or dispersion of step a) added to the polyolefin solution is more preferably up to 5 weight % of the total weight. The amount of solution or dispersion of step a) added to the polyolefin solution is most preferably up to the 1 weight % of the total weight.

The polyolefin melt, before the addition of the additive solution or dispersion in n-alkane may as well comprise a small amount of solvent. The solvent is preferably a hydrocarbon solvent. Preferably, the hydrocarbon solvent comprises or consists of a n-alkane, wherein the n-alkane is preferably a C4 (n-butane), C5 (n-pentane), C6 (n-hexane), C7 (n- heptane), C8 (n-octane), C9 (n-nonane) or C10 (n-decane) n-alkane or any mixture thereof. More preferably the n-alkane is a C4, C5, C6, C7, C8 n-alkane or any mixture thereof, more preferably, the n-alkane is a C6, C7, C8 n-alkane or any mixture thereof. This means that the n-alkane is selected from n-hexane, n-heptane, n-octane or any mixture thereof. The amount of solution or dispersion of step a) added to the polyolefin melt is preferably up to the 10 weight % of the total weight, wherein the total weight is the sum of the weight of the solution or dispersion of step a) and of the weight of the polyolefin melt. The amount of solution or dispersion of step a) added to the polyolefin melt is more preferably up to the 7 weight % of the total weight. The amount of solution or dispersion of step a) added to the polyolefin melt is most preferably up to the 5 weight % of the total weight.

Preferably the solvent of the polyolefin solution or of the polyolefin melt (if present), before the addition of the additive solution or dispersion in n-alkane, is the same n-alkane of the additive solution or dispersion in n-alkane of step a).

Therefore, preferably, the method for adding an additive to a polyolefin melt or polyolefin solution comprises the steps of a) providing a solution or a dispersion of the additive in a C4, C5, C6, C7 or C8 n-alkane or any mixture thereof, preferably in a C6, C7 or C8 n-alkane or any mixture thereof; b) adding the solution or dispersion of step a) to the polyolefin melt or polyolefin solution wherein the polyolefin is dissolved in a C4, C5, C6, C7 or C8 n-alkane or any mixture thereof, preferably in a C6, C7 or C8 n-alkane or any mixture thereof, thereby providing a product comprising the additive and the polyolefin; c) mixing the additive and the polyolefin comprised in the product obtained in step b) to obtain a mixed product.

Therefore, preferably, the present invention is directed to a method for adding an additive to a polyolefin melt wherein the method comprises the steps of a) providing a solution or a dispersion of the additive in a C4, C5, C6, C7 or C8 n-alkane or any mixture thereof, preferably in a C6, C7 or C8 n-alkane or any mixture thereof; b) adding the solution or dispersion of step a) to the polyolefin melt thereby providing a product comprising the additive and the polyolefin; c) mixing the additive and the polyolefin comprised in the product obtained in step b) to obtain a mixed product, wherein the polyolefin melt, before the addition of the solution or dispersion of step a) optionally comprises a C4, C5, C6, C7 or C8 n-alkane or any mixture thereof, preferably comprises a C6, C7 or C8 n-alkane or any mixture thereof, wherein preferably, the n- alkane of the polyolefin melt before the addition of the solution or the dispersion of step a) and the n-alkane of the solution or the dispersion of step a) are the same n-alkane. Therefore, preferably, the present invention is directed to a method for adding an additive to a polyolefin solution wherein the solvent of the polyolefin solution is a C4, C5, C6, C7 or C8 n-alkane or any mixture thereof, preferably a C6, C7 or C8 n-alkane or any mixture thereof, wherein the method comprises the steps of a) providing a solution or a dispersion of the additive in a C4, C5, C6, C7 or C8 n-alkane or any mixture thereof, preferably in a C6, C7 or C8 n-alkane or any mixture thereof; b) adding the solution or dispersion of step a) to the polyolefin solution thereby providing a product comprising the additive and the polyolefin ; and c) mixing the additive and the polyolefin comprised in the product obtained in step b) to obtain a mixed product, wherein preferably, the n-alkane of the polyolefin solution before the addition of the solution or the dispersion of step a) and the n-alkane of the solution or the dispersion of step a) are the same n-alkane.

Step c)

Any method for mixing the solution or dispersion of step a) with the polyolefin melt or the polyolefin solution is suitable according to the present invention.

With regard to the polymer melt is it preferred that the mixing is carried out by melt mixing with an extruder, e.g. a multi-screw, a twin screw or a single screw extruder, or any other type of dynamic melt mixing system, or with a static mixer.

With regard to the polymer solution it is preferred that the mixing is carried out with any suitable dynamic or static mixer, or simply by turbulent flow occurring naturally in the process or being induced in the process by suitable design.

It has been found that, due to the excellent miscibility of n-alkane with polyolefin melts or polyolefin solutions, the addition of the solution or dispersion of step a) wherein the additive is dissolved or suspended in a n-alkane is easier, more cost-effective and produces a more homogenous mixture as compared for example to customary addition of additives as solid.

Step d)

The method of the invention may further comprise, after step c), removing the n-alkane, preferably by degassing, to obtain a devolatilized product.

In step d), the solvent of the polyolefin melt (if present) and of the polyolefin solution is preferably also removed. When the solvent of the polyolefin melt or of the polyolefin solution before the addition of the solution or dispersion of step a) is an alkane, preferably the same n-alkane of the additive solution or dispersion, the n-alkane is removed.

Methods for removal of solvents from a polyolefin melt or solution are known in the art.

Suitable methods for removing a solvent from the polyolefin melt are for example degassing in an extruder or any other type of dynamic degassing equipment. These methods are also suitable to carry out step d) of the method of the invention.

Suitable methods for removing a solvent from the polyolefin solution are for example flash devolatilization, thin film evaporation or degassing in an extruder or any other type of dynamic degassing equipment. These methods are also suitable to carry out step d) of the method of the invention.

Generally the removal of the solvent from a polyolefin solution or melt may require high temperature up to 300 °C. At such high temperatures a polyolefin, such as polypropylene, may undergo thermal degradation. It has been surprisingly found that the addition of an antioxidant according to the method of the invention to a polyolefin solution or polyolefin melt prevents or reduces the thermal degradation of the polyolefin e.g. vis a vis, a polyolefin solution or melt without antioxidant.

Preferably, the antioxidant is a primary antioxidant wherein preferably the primary antioxidant is a sterically hindered phenol. Preferably, the primary antioxidant, preferably the sterically hindered phenol is added together with a secondary antioxidant, preferably a phosphite such as a Tris(2,4-di-tert-butylphenyl)phosphite (Irgafos 168).

Preferably, along with the n-alkane, the other volatiles, if present in the product of step c), are removed in step d). In a further aspect, the present invention is directed to a solvent based polyolefin recycling process comprising the method for adding additives according to the present invention as disclosed herein above. In the solvent based polyolefin recycling process, a purification step is carried out wherein impurities are removed from a polyolefin/solvent solution, for example, via settling, filtration and/or absorption column(s). Also useful additives, such as antioxidants or UV stabilizers may be removed in this purification step. Therefore, the polyolefin is unprotected e.g., towards the thermal degradation caused by e.g. a subsequent devolatilization or removal of the solvent at high temperatures. Advantageously, the addition of antioxidants as disclosed above e.g. to a polyolefin/solvent stream that has undergone the purification step prevents or reduces the thermal degradation of the polyolefin. Preferably, according to the invention, the solvent based polyolefin recycling process comprises one or more polyolefin/solvent separation steps of a polymer/solvent stream wherein the solution or the dispersion comprising an additive, preferably an antioxidant, in the n-alkane is added to the polyolefin/solvent streams before at least one of the one or more separation steps.

Any suitable separation step of the polyolefin from the n-alkane and the solvent is suitable according to the invention. It is preferred that together with the n-alkane and the solvent, any other potentially present volatiles are removed from the polyolefin.

The separation step can be carried out as a vapor-liquid separation step or as a liquidliquid separation step. Preferably, the separation step is carried out as a vapor-liquid separation step, most preferably as a flash separation step. Preferably, a stream comprising the polyolefin, the additive and the n-alkane is separated in a polyolefin rich stream and a polyolefin-lean stream, wherein the polyolefin lean stream is rich in the n- alkane. When part of a solvent based polyolefin recycling process, the polyolefin-lean stream may be returned to the polymer recycling process upon adjusting pressure and temperature to the requirements of the recycling process with or without any further purification.

If the separation step is a vapor-liquid separation step, more preferably a flash separation step, it is preferably carried out at a temperature of 150 to 300°C, more preferably 175 to 275 °C, and most preferably 200 to 250 °C. Moreover, in such case, the separation is preferably carried out at a pressure of 1 to 15 bar, more preferably 2 to 12 bar, and most preferably 2.5 to 10 bar. Most preferably, in such case, the separation is carried out at a temperature of 200 to 250 °C and at a pressure of 2.5 to 10 bar.

If the separation step is carried out as a liquid-liquid separation step, the separation temperature is preferably 100 to 400 °C, more preferably 1 10 to 380 °C and most preferably 120 to 370 °C. Moreover, in such case, separation step is preferably carried out at a pressure of 10 to 70 barg, more preferably a 15 to 65 barg, and most preferably at 20 to 60 barg. Most preferably, in such case, separation step is preferably carried out at a temperature of 120 to 370 °C and at a pressure of 20 to 60 barg.

In a solvent based polyolefin recycling process, following the above (first) separation step), a second separation may be carried out as a vapor-liquid separation step or as a liquid-liquid separation step. Preferably, the second separation step is carried out as a vapor-liquid separation step, most preferably as a flash separation step. Preferably, the stream is separated into a first condensed polyolefin rich stream and first polyolefin-lean vapor stream, wherein first polyolefin-lean vapor stream is rich in the n-alkane. When part of a solvent based polyolefin recycling process, the first polyolefin-lean vapor stream may be returned to the polymer recycling process upon adjusting pressure and temperature to the requirements of the recycling process. The first polyolefin-lean vapor stream may then be returned to the recycling process after further purification and condensation.

Preferably, the second separation step is carried out as a flash separation step. In such case, preferably, the above (first) separation step is carried out at a temperature of 150 to 300 °C, more preferably 175 to 275 °C, and most preferably 200 to 250 °C. Moreover, in such case, the second separation step is preferably carried out at a pressure of 1 to 15 bar, more preferably 2 to 12 bar, and most preferably 2.5 to 10 bar. If flash separation steps are carried out several times in a row, the pressure is lowered step after step and the temperature of the polyolefin is usually increased step after step. Thus, the pressure in the second separation step has to be lower than in above (first) separation step, if the above (first) separation step is carried out as a flash separation step. Furthermore, the temperature in the second separation step has to be higher than in the above (first) separation step if the above (first) separation step is carried out as a flash separation step. Most preferably, in such case, the second separation step is carried out at a temperature of 200 to 250 °C and at a pressure of 2.5 to 10 barg.

The addition of the additive solution or dispersion is added to the suitable streams

-either before the first separation step or the second separation step or,

-before the first separation step and then before the second separation step.

It is preferred that the addition of the additive solution or dispersion is carried out after the purification step.

In a further aspect, the present invention is directed to a process for producing polyolefin pellets comprising carrying out the method of adding an additive according to the invention to a melt extruded polyolefin, the process further comprising a step e) pelletizing the mixed product of step c) or the devolatilized product of step d), preferably pelletizing the devolatilized product of step d).

A suitable pelletizer is for example a strand pelletiser, an underwater pelletizer, a waterring pelletiser, or any other type of pelletiser suitable for polyolefins. Test Methods a) Volatile content & n-alkane content

The volatile content of the polyolefin is determined by using static head space analysis similar to VDA 277:1995 using a gas chromatograph equipped with a flame ionization detector. Headspace extraction is performed on pellets (about 2 g in 20 ml headspace vial) using 120 °C (PP) and 100 °C (PE) incubation for 5 hours prior to the GC measurement. The gas chromatographic separation is performed with a WCOT-capillary column (wax type) or a PLOT column, respectively. The total emission is measured on the basis of the sum of all values provided by the emitted substances after gas chromatography analysis and flame ionization detection with acetone as the calibration standard. The total emission value is reported in the unit of microgram carbon per gram of sample and refers to the carbon content in the acetone standard.

The amount of the added C4, 05, 06, C7 or C8 n-alkane is also determined similar to VDA 277:1995 but using the single component approach. Therefore, the emission is determined on the basis of the corresponding n-alkane calibration. In case a calibration standard is not available, the semi-quantitation of the individual n-alkane is done by using the response factor of n-hexane. b) The melt flow rate (MFR)

The melt flow rate (MFR) was determined according to ISO 1133 and is indicated in g/10 min. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR2 is determined at 230 °C and at a loadings of 2.16 kg. c) The Yellowness index

The yellowness index, was calculated according to ASTM E313 employing a spectrophotometer. The yellowness index is an indicator of the whiteness or yellowness of an analyzed material. d) Oxidation Induction Time (OIT) method

The OIT test was performed according to ASTM-D3895, ISO/CD 11357 and EN 728 using a Differential Scanning Calorimeter (DSC). A circular sample with a diameter of 5 mm and a weight of 5-6 mg of the material (i.e. the crosslinked polymer composition of the present invention) to be tested is introduced into the DSC at room temperature, and the sample is heated to 200 °C (20°C/min) in nitrogen atmosphere. After 5 min stabilization isothermally at 200°C, the gas is changed from nitrogen to oxygen. The flow rate of oxygen is the same as nitrogen, 50 ml/min. Under these conditions the stabilizer is consumed over time until it is totally depleted. At this point the polymer sample degrades or oxidizes liberating additional heat (exothermal reaction).

The Oxidation Induction Time (OIT) is defined as the time measured from the oxygen switch on to the onset inflection point for the exothermal reaction occurring when the stabilizer is depleted. Thus, OIT is a measure of the thermal stability of the material. Parallel measurements are performed for each condition and mean value is calculated. e) Determination of antioxidants by High performance liquid chromatography (HPLC)

Antioxidant (chemicals like Irganox® 1010 and Irgfos® 168, i.e. , Pentaerythrityl-tetrakis(3- (3’,5’-di-tert. butyl-4-hydroxyphenyl)-propionate) and Tris (2,4-di-t-butylphenyl) phosphite) content was determined via high performance liquid chromatography (HPLC) after extraction with ethyl acetate. Therefore, about 10 g of the sample were cryo-milled with the aid of liquid nitrogen. After that, a portion of approximately 0.5 g of the milled sample was extracted using ethyl acetate as a solvent. Extraction was performed at 95 °C for 90 min under constant stirring. After letting the mixture cool down to room temperature again it was filtered and put to the HPLC test for the quantification of antioxidants. The HPLC system was equipped with a C18 column for the separation and a diode array detector (DAD) for detection.

Examples

Reference Example

In an initial experiment, up to 3 weight% n-heptane was injected into a polypropylene (PP) melt in a pilot scale twin screw extruder. The polypropylene was a homopolymer with a weight average molecular weight (M_w) of 440 kg/mol. It has been observed that the n- heptane does not affect subsequent pelletizing of that melt with an underwater pelletizer. This is despite no degassing was used, thus keeping the alkane in the melt. It had been expected that n-heptane (boiling temperature = 97°C) evaporating upon pressure release at the pelletizer die plate would lead to melt foaming and pelletizer plugging. Instead, no melt foaming and pelletizing plugging was observed. This shows that n-heptane and therefore the additive potentially contained is mixed very well with the PP melt without any pelletizing problems. The extrusion conditions were constant at 400 rpm screw speed and 5 kg/h throughput. The set temperature profile was 195°C, and the melt temperature was about 200°C.

Inventive examples IE1 to IE6 and Comparative example (CE1)

A first solution comprising 10 weight% of the primary antioxidant Irganox 1076 in n- heptane was prepared. The solubility of Irganox 1076 in n-heptane at room temperature is > 10 weight%.

A second solution comprising both the primary antioxidant Irganox 1076 (2.5 weight%) and the secondary antioxidant Irgafos 168 (5 weight%) in n-heptane was prepared. The solubility at room temperature for the latter it is only ~ 5 weight%. The solutions were injected into a melt of non-stabilized (with no antioxidant) PP homopolymer powder in a lab scale twin screw extruder. The polypropylene was a homopolymer with a weight average molecular weight (M_w) of 440 kg/mol. The respective formulations and antioxidant (AO) target concentrations are given in Table 4. Antioxidant (AO) target concentrations in Table 4 are given in weight ppm based on the total weight of the composition of PP, n- heptaneand antioxidant(s).

For comparative example CE1 , this same procedure was done without adding any stabilisers to the PP.

Table 4: Target concentrations of the AOs in PP

The antioxidant solution injection set up and the sampling scheme is reported in Figure 1 .

The extrusion conditions were always kept constant at 400 rpm screw speed and 5 kg/h throughput. The set temperature profile was 195°C, and the melt temperature was about 200°C for all runs. The first compounding step providing sample 1 was followed by two further re-compounding passages providing sample 2 and sample 3 under the same conditions to simulate the thermo-mechanical stress of subsequent process steps (e.g. conversion operations).

The MFR2 was measured for all samples prepared. Oxidation induction time (OIT), AO content by HPLC, and Yellowness index (Yl) were measured additionally for samples 1 and 3. The results are shown in Figures 2a (MFR2), 2b (OIT) and 2c (Yl), respectively.

Without stabilizer (CE1 ), the MFR2 of the homo PP reaches ~13 dg/min after the first processing, and it increases to over 40 dg/min after two further extruder passages (Figure 2a).

With the maximum stabilization package (IE6) used, i.e. 1000 ppm Irganox 1076 and 2000 ppm Irgafos 168, a MFR of ~2 dg/min was reached, which increased only slightly over the two following extruder passages.

The results show that the present method of adding an antioxidant in a solution of n- heptane provides satisfactory stabilization of the polyolefin with reduced mixing energy input compared to when the antioxidants are added as solids to the extruder main hopper.

Inventive example IE5’, comparative examples CET, CE2 and CE3

Examples IE5’ and CET were carried out according to the procedure disclosed above. CE2 was carried out according to the procedure disclosed above with the exception that a solution comprising both the primary antioxidant Irganox 1076 (2.5 weight%) and the secondary antioxidant Irgafos 168 (5 weight%) in petroleum benzine (PB) as the solvent was used. Example CE3 was carried out according to the procedure disclosed above with the following exception: for the dry feeding, the same target concentrations of the stabilisers were achieved by feeding them to the extruder main hopper in dry, particulate form together with the PP powder (figure 3). This is the conventional approach that is e.g. typically used in PP compounding. The respective formulations of IE5’, CET, CE2 and CE3 and antioxidant (AO) target concentrations are given in Table 5.

Table 5: Target concentrations of the AOs in PP

The MFR2 and the VOC were measured for all samples prepared. The results are shown in Table 6.

Table 6

Without stabilizer (CET), the MFR2 of the homo PP reaches 16,91 dg/min after the first processing, and it climbs to over 40 dg/min after two further extruder passages. With the addition of stabilizers the degradation of the PP is reduced. However, the best stabilization, looking at the MFR increase over the three processing steps, is achieved when using n- heptane. Specific energy input (SEI) in the compounding step is highest for CE3 with the stabilisers fed in dry form. It is 6 - 10 % lower for feeding the stabilisers as solutions in n- heptane and PB, respectively.

It has also been observed that the oxidation of the Irgafos 168 in the first compounding step is higher when using a dry feeding of the stabilizers.

The results show that the present method of adding an antioxidant in a solution of n- heptane provides satisfactory stabilization of the polyolefin with reduced mixing energy input compared to when the antioxidants are added as solids to the extruder main hopper or as a solution of a solvent different from n-alkane.

Claims

1 . A method for adding an additive to a polyolefin, the method comprising the steps of a) providing a solution or a dispersion of the additive in a n-alkane; b) adding the solution or dispersion of step a) to a polyolefin being in melted form or being dissolved in a hydrocarbon solvent, thereby providing a product comprising the additive and the polyolefin; c) mixing the additive and the polyolefin comprised in the product obtained in step b) to obtain a mixed product.

2. The method of claim 1 , wherein the polyolefin is selected from the group consisting of a polyethylene, a polypropylene and any mixture thereof.

3. The method of claim 1 or 2, wherein the n-alkane is a C4, C5, C6, C7, C8, C9 or C10 n-alkane or any mixtures thereof, preferably a C4, C5, C6, C7 or C8 n- alkane or any mixture thereof, more preferably a C6, C7 or C8 n-alkane or any mixture thereof.

4. The method of any one of claims 1 to 3, wherein the hydrocarbon solvent used in step b) is a n-alkane, preferably a C4, C5, C6, C7, C8, C9 or C10 n-alkane or any mixture thereof, more preferably C6, C7 or C8 n-alkane or any mixture thereof.

5. The method of any one of claims 1 to 4, wherein the hydrocarbon solvent used in step b) and the n-alkane used in step a) are the same n-alkane.

6. The method of any one of claims 1 to 5, wherein the additive comprises, or consists of, one or more antioxidants, a UV stabilizer, a nucleating agent or any combinations thereof.

7. The method of claim 6, wherein the additive comprises one or more antioxidants selected from one or more primary antioxidants, preferably comprising or consisting of a sterically hindered phenol, and one or more secondary antioxidants, preferably comprising or consisting of one or more phosphites and/or one or more phosphonites.

8. The method of claim 6 or 7, wherein the additive comprises one or more UV stabilizers selected from UV absorbers and a hindered amine light stabilizers (HALS).

9. The method of any one of claims 6 to 8, wherein the additive comprises a nucleating agent which preferably is selected from quinacridone

10. The method of any one of claims 6 to 9, wherein the nucleating agent in the solution or dispersion is in the range of from 50 to 100 ppm based on the weight of the polyolefin.

11 . The method of any one of claims 1 to 10, wherein

-in step b) the polyolefin, in melted form or dissolved in a hydrocarbon solvent, has a temperature in the range of from 100°C to 300°C.

12. The method of any one of claims 1 to 11 , wherein, in step a) the amount of the additive in the solution is as high as permitted by solubility, or the amount of the additive in the dispersion is as high as the stability of the dispersion allows.

13. The method of any one of claims 1 to 12, wherein after step c) the method comprises d) removing the n-alkane, preferably by degassing, to obtain a devolatilized product.

14. A solvent based polyolefin recycling process comprising the method of any one of claims 1 to 13, wherein preferably the process comprises one or more polyolefin/solvent separation steps of a polyolefin/solvent stream wherein the solution or the dispersion comprising an additive is added to the polyolefin/solvent stream before at least one of the one or more separation steps.

15. A process for producing polyolefin pellets comprising carrying out the method of claims 1 to 13 on a melt extruded polyolefin, the process further comprising the step of e) pelletizing the mixed product of step c) or the devolatilized product of step d), preferably pelletizing the devolatilized product of step d).