Polypropylene composition with improved oxidative stability and flow properties

Abstract

The present invention relates to a polypropylene composition having improved thermal oxidative stability and flow properties, comprising: (a) gt; 90.0% by weight of a propylene polymer, preferably a regenerated propylene polymer; (b) > = 800 ppm and < = 5,000 ppm by weight of an organophosphite additive; (c) > = 200 ppm and < = 5,000 ppm by weight of a phenolic antioxidant; and (d) > = 700 ppm and < = 5,000 ppm by weight of a polyol compound. The propylene composition has, for example, gt by weight; and a high metal content of 100 ppm. The polyol compound has gt; 200 DEG C and < = 350 DEG C, preferably > = 220 DEG C and < = 300 DEG C. The invention further relates to a method for preparing the composition and an article prepared from such a polypropylene composition.

Description

Technical Field

[0001] This invention relates to the field of polypropylene compositions, and more particularly to compositions comprising recycled polypropylene compositions having improved thermal oxidative stability and processability. The invention also relates to articles comprising such polypropylene compositions. Background Technology

[0002] Thermal oxidative stability (i.e., oxidative stability at elevated temperatures) is an important property requirement for polymer materials intended for commercial use in the manufacture of a wide variety of products. To this extent, polypropylene is widely used in the production of industrial and household products, and improving its oxidative stability is generally considered a key consideration for plastics processors (converters) and manufacturers.

[0003] In particular, when it comes to the use of recycled plastics (also known as regenerated plastics), thermal oxidative stability, mechanical processability, and fading are key considerations, as recycled polymers are more prone to degradation than virgin polymers, making their use as replacements for virgin-grade resins challenging. This is because degradation products present in regenerated polymers act as initiators for further oxidation. For example, during several cycles of melt processing, recycled polypropylene may undergo structural changes due to chain breakage (and incidental branching), leading to a rapid deterioration in mechanical properties, flow properties (increased flowability), and color changes. Specifically, changes in flow properties over multiple extrusion cycles affect the polymer's processability, making recycled polymers less reliable from a processability standpoint.

[0004] Furthermore, recycled polypropylene has a higher metal loading than virgin polypropylene, and in some cases, the presence of such metals tends to accelerate this degradation in properties. Therefore, ensuring the desired oxidative stability allows recycled polypropylene materials to retain their mechanical and color properties despite repeated thermal processing and physical aging over multiple life cycles.

[0005] From a sustainability perspective, while recycling plastic waste is considered key to reducing plastic waste, the performance and stability gap between recycled and virgin grade resins makes such recycled plastics less attractive for commercial applications. For these reasons alone, mechanical recycling has not yet reached its full potential.

[0006] In the past, stabilizers containing phenolic antioxidants and phosphites / esters have been used to protect polypropylene compositions from heat and oxidative or photo-oxidative damage. However, the addition of certain phosphite / ester stabilizers, such as Irgafos 168, exceeding a certain threshold limit may lead to increased migration of 2,4-di-tert-butylphenol (a NIAS-regulated substance and a degradation product of Irgafos 168), thus limiting the use of such polypropylene materials in food contact and other health-sensitive applications.

[0007] US20200317886A1 relates to a method for stabilizing halogen-free thermoplastic reclaimed materials to resist oxidative, thermal, and / or photochemical degradation. In the method described in this patent, at least one sugar alcohol- or cyclic polyol-based compound is added to the thermoplastic reclaimed material as part of a stabilization package. However, sugar alcohol- or cyclic polyol-based compounds tend to char upon exposure to typical polymer processing temperatures, resulting in discoloration. Summary of the Invention

[0008] Therefore, one object of the present invention is to provide a polypropylene composition having improved thermal oxidative stability. Another object of the present invention is to provide a polypropylene composition comprising recycled polypropylene that has improved thermal oxidative stability over multiple extrusion cycles while maintaining its flowability and color properties. Yet another object of the present invention is to provide an article comprising a polypropylene composition derived from recycled polypropylene that has improved thermal oxidative stability over multiple extrusion cycles while maintaining its flowability and color properties.

[0009] Therefore, one or more objects of the present invention are achieved by a polypropylene composition comprising or consisting of the following:

[0010] (a) Relative to the total weight of the polypropylene composition, >90.0% by weight of propylene polymer, preferably wherein the propylene polymer is present in an amount of ≥98.5% by weight and <100% by weight, preferably ≥99.0% by weight and <100.0% by weight, preferably ≥99.04% by weight and <100.0% by weight, preferably ≥99.1% by weight and <100.0% by weight, preferably ≥99.2% by weight and <100.0% by weight;

[0011] (b) Organic phosphite additives with a weight of ≥800 ppm and ≤5000 ppm, preferably ≥1000 ppm and ≤2000 ppm, and more preferably ≥1200 ppm and ≤1700 ppm;

[0012] (c) A phenolic antioxidant with a concentration of ≥200 ppm and ≤5000 ppm by weight, preferably ≥500 ppm and ≤1200 ppm, preferably ≥500 ppm and ≤1000 ppm, and preferably ≥500 ppm and ≤900 ppm; and

[0013] (d) Polyol compounds with a content of ≥700 ppm and ≤5,000 ppm by weight, preferably ≥700 ppm and ≤1,500 ppm, preferably ≥700 ppm and ≤1200 ppm, preferably ≥700 ppm and ≤1100 ppm, preferably ≥900 ppm and ≤1100 ppm;

[0014] (e) Metals, such as those >100 ppm by weight, as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) according to ISO 24047:2021.

[0015] The polyol compound has a melting point of >200℃ and ≤350℃, preferably ≥220℃ and ≤300℃. The sum of all components (a)-(d) is 100% by weight.

[0016] The term "ppm" as used throughout this disclosure refers to parts per million. Advantageously, the polypropylene compositions of the present invention exhibit improved thermal oxidative stability, enabling them to maintain their mechanical and flow properties, as well as their resistance to fading, even after multiple extrusion cycles. As another advantage, the polypropylene compositions of the present invention, even when derived from recycled polypropylene, do not exhibit discoloration due to carbonization, even when processed at processing temperatures, while maintaining desired thermal oxidative stability. As yet another advantage, even polypropylene compositions with a metal content greater than 100 ppm by weight exhibit improved thermal oxidative stability and minimal change in flow and color properties.

[0017] In particular, the propylene compositions of this disclosure comprise recycled polypropylene, which exhibits improved thermal oxidative stability even after multiple extrusion cycles, while maintaining desired flow properties and resistance to fading. The term "thermal oxidative stability" refers to the resistance of a sample specimen prepared from the polypropylene compositions of this invention to oxidative degradation when exposed to air at elevated temperatures. A suitable indicator for measuring thermal oxidative stability is the oxidation induction time (OIT) of the polypropylene composition, measured in minutes. Therefore, a higher OIT indicates higher thermal oxidative stability.

[0018] In particular, even after multiple extrusion cycles, the polypropylene compositions of the present invention exhibit excellent thermal oxidative stability and minimal change in flow properties. For example, the polypropylene compositions have at least one of the following characteristics after three extrusion cycles:

[0019] (a) A melt flow rate (MFR) ≥50.0 and ≤100.0 g / 10 min, preferably ≥60.0 and ≤80.0 g / 10 min, when measured according to ASTM D1238 at 230°C and a load of 2.16 kg, preferably wherein extrusion is performed using a twin-screw extruder at a processing temperature of ≥220°C; and / or

[0020] (b) When measured according to ISO 11357-6 (2018) and at a temperature of 220°C in the presence of air, the oxidation induction time (OIT) is >12.0 min and <25.0 min, preferably ≥14.0 and ≤20.0 min.

[0021] Preferably, the polypropylene composition has the following characteristics after three extrusion cycles:

[0022] (a) A melt flow rate (MFR) ≥50.0 and ≤100.0 g / 10 min, preferably ≥60.0 and ≤80.0 g / 10 min, when measured according to ASTM D1238 at 230°C and a load of 2.16 kg, preferably wherein extrusion is performed using a twin-screw extruder at a processing temperature of ≥220°C, preferably ≥220°C and ≤240°C; and

[0023] (b) When measured according to ISO 11357-6 (2018) and at a temperature of 220°C in the presence of air, the oxidation induction time (OIT) is >12.0 min and <25.0 min, preferably ≥14.0 and ≤20.0 min.

[0024] Preferably, the polypropylene composition exhibits a change in melt flow rate (MFR) of <0.9%, preferably ≤0.8%, preferably ≤0.5%, and preferably ≤0.2% after three extrusion cycles, compared to the melt flow rate (MFR) after the first extrusion cycle, preferably wherein extrusion is performed using a twin-screw extruder at a processing temperature of ≥220°C; and wherein the polypropylene composition exhibits an increase in oxidation induction time (OIT) of ≥10.0%, preferably ≥15.0%, preferably ≥20.0%, and ≤30.0% after three extrusion cycles, compared to the oxidation induction time (OIT) after the first extrusion cycle, preferably wherein the oxidation induction time (OIT) is performed at 220°C in the presence of air. Preferably, the polypropylene composition exhibits a change in melt flow rate (MFR) of <0.9% and ≥0.0% after three extrusion cycles, compared to the melt flow rate (MFR) after the first extrusion cycle.

[0025] The change in melt flow rate can be measured by the following formula: (MFR3 - MFR1) / MFR1, where MFR3 is the melt flow rate of the polypropylene composition after three extrusion cycles, and MFR1 is the melt flow rate of the polypropylene composition after the first extrusion cycle. Particularly preferred is that the melt flow rate of the polypropylene composition exhibits minimal change after three extrusion cycles compared to the first extrusion cycle.

[0026] The increase in oxidation induction time (OIT) can be measured by the following formula: (OIT3 - OIT1) / OIT1, where OIT3 is the oxidation induction time of the polypropylene composition after three extrusion cycles, and OIT1 is the oxidation induction time of the polypropylene composition after the first extrusion cycle.

[0027] propylene polymer

[0028] The polypropylene composition comprises a propylene polymer in an amount of >90.0% by weight, preferably >95.0% by weight, and more preferably >98.0% by weight relative to the total weight of the polypropylene composition. Preferably, the propylene polymer is present in an amount of ≥98.5% by weight and <100% by weight, preferably ≥99.0% by weight and <100.0% by weight, preferably ≥99.04% by weight and <100.0% by weight, preferably ≥99.1% by weight and <100.0% by weight, and more preferably ≥99.2% by weight and <100.0% by weight relative to the total weight of the polypropylene composition.

[0029] Propylene polymers may have at least one of the following:

[0030] (a) ≥0.5 and ≤0.98 g / cm³ as determined according to ISO 1183-1 3The density; and / or

[0031] (b) A melt flow rate (MFR) of ≥50.0 g / 10 min and ≤90.0 g / 10 min, preferably ≥65.0 g / 10 min and ≤80.0 g / 10 min, as measured at 230 °C and under a load of 2.16 kg according to ISO 1133.

[0032] Preferably, the propylene polymer has:

[0033] (a) ≥0.5 and ≤0.98 g / cm³ as determined according to ISO 1183-1 3 density; and

[0034] (b) A melt flow rate (MFR) of ≥50.0 g / 10 min and ≤90.0 g / 10 min, preferably ≥65.0 g / 10 min and ≤80.0 g / 10 min, as measured at 230 °C and under a load of 2.16 kg according to ISO 1133.

[0035] Recycled polypropylene

[0036] Particularly preferred is that the propylene polymer is a recycled propylene polymer. Preferably, the recycled propylene polymer is post-consumer recycled polypropylene (PCR-PP), or a mixture of post-consumer recycled polypropylene and post-industrial recycled polypropylene (PIR-PP).

[0037] Preferably, the propylene polymer is a recycled propylene polymer having a PCR regeneration content of >95.0% by weight, preferably >98.0% by weight, and more preferably 100% by weight relative to the total weight of the propylene polymer. The amount of recycled polypropylene can be determined according to ISO 14021. Preferably, the recycled polypropylene is derived from propylene polymers selected from: polypropylene homopolymers, polypropylene copolymers, multiphase polypropylene, and mixtures thereof.

[0038] Recycled propylene polymers can be obtained by mechanically recycling polypropylene derived from waste plastic materials. The mechanical recycling process includes collection, sorting, washing, drying, shredding, grinding, and blending to obtain recycled polypropylene. Mechanical recycling allows polypropylene materials that have previously been used in products to be reused through one or more recycling processes, resulting in several cycles including use, recycling, and reuse. Therefore, recycled polypropylene has a higher residual metal content compared to virgin or non-recycled polypropylene due to the addition of metal-containing additives throughout several life cycles of the plastic material.

[0039] Therefore, as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) according to ISO 24047:2021, the composition may have a total metal content of >100 ppm, preferably >1,000 ppm, preferably >3,000 ppm, preferably ≥3,000 ppm and ≤15,000 ppm, preferably ≥3,000 ppm and ≤6,500 ppm, and preferably ≥3,000 ppm and ≤5,000 ppm, relative to the total weight of the polypropylene composition.

[0040] Specifically, when the propylene polymer is recycled polypropylene, the metal content relative to the total weight of the polypropylene composition can be >3000 ppm by weight. Non-limiting examples of metals present in the polypropylene composition may include any one of titanium, calcium, iron, zinc, magnesium, silicon, and combinations thereof. Metals may exist as salts, oxides, or in their elemental form. The metal content can be determined using any known method such as inductively coupled plasma optical emission spectrometry (ICP-OES) and XRF analysis.

[0041] Polymer compositions containing recycled polypropylene are susceptible to oxidative degradation due to their history of exposure to heat, light, and high-temperature processing throughout the polymer's various life cycles. However, the inventors of this application have surprisingly discovered that when recycled polypropylene is stabilized using a targeted combination of organophosphite additives, phenolic antioxidants, and polyol compounds as described in this disclosure, the recycled propylene exhibits improved thermal oxidative stability while maintaining suitable flowability and color properties, even after multiple extrusion cycles.

[0042] Organic phosphite additives

[0043] The polypropylene composition contains an organophosphite additive in amounts of ≥800 ppm and ≤5000 ppm by weight, preferably ≥1000 ppm and ≤2000 ppm, preferably ≥1200 ppm and ≤1700 ppm, and more preferably ≥1200 ppm and ≤1600 ppm.

[0044] The organic phosphite additive may be selected from tris[2,4-bis(1,1-dimethylpropyl)phenyl]phosphite, bis[2,4-bis-(1,1-dimethylpropyl)phenyl][4-(1,1-dimethylpropyl)phenyl]phosphite, tris(2,4-di-tert-butylphenyl)phosphite, and any combination thereof. Preferably, the organic phosphite additive is tris(2,4-di-tert-butylphenyl)phosphite. Preferably, the organic phosphite additive consists only of tris(2,4-di-tert-butylphenyl)phosphite.

[0045] Organic phosphite additives can be represented by the following formula:

[0046]

[0047] Among them, 'R 1 'and'R 2 Each of the following is identical or different, and is individually selected from tert-butyl, 1,1-dimethylpropyl, or hydrogen, provided that 'R' 1 'and'R 2 At least one of 'R' is not hydrogen, preferably 'R' 1 'and'R 2 Each of them is identical and is tert-butyl.

[0048] polyol compounds

[0049] The polypropylene composition comprises a polyol compound in an amount of ≥700 ppm and ≤5,000 ppm by weight, preferably ≥700 ppm and ≤1500 ppm by weight, preferably ≥700 ppm and ≤1200 ppm by weight, preferably ≥700 ppm and ≤1100 ppm by weight, and preferably ≥900 ppm and ≤1100 ppm by weight. As used herein, the term "polyol compound" means a compound having at least two hydroxyl groups. The polyol compound has a melting point >200°C and ≤350°C, preferably ≥220°C and ≤300°C, and preferably ≥220°C and ≤280°C. The melting point of the polyol can be measured using standard methods for determining the melting point of solid organic compounds.

[0050] For example, the melting point of an organic solid compound such as a polyol can be determined by introducing a certain amount, such as 0.5 g, of the polyol compound into a capillary. The tube can then be attached to the rod of a thermometer centered on a heating bath, which can then be heated. The temperatures at which melting begins and ends can be recorded to determine the melting temperature. Alternatively, to make the most efficient use of time, a rapid melting point determination can be performed initially (by rapid heating) to establish an approximate melting point, followed by at least two additional, more careful determinations (by gentler heating, i.e., at a rate of approximately 2 °C / min) until two consistent values ​​are obtained.

[0051] Preferably, the polyol compound is pentaerythritol (i.e., 2,2-bis(hydroxymethyl)propane-1,3-diol). Preferably, the polyol compound is pentaerythritol (i.e., 2,2-bis(hydroxymethyl)propane-1,3-diol) and is present in an amount ≥900 ppm and ≤1100 ppm by weight relative to the total weight of the polypropylene composition.

[0052] Phenolic antioxidants

[0053] The polypropylene composition contains, by weight, ≥200 ppm and ≤5000 ppm, preferably ≥500 ppm and ≤1200 ppm, more preferably ≥500 ppm and ≤1000 ppm, and more preferably ≥500 ppm and ≤900 ppm of a phenolic antioxidant relative to the total weight of the polypropylene composition.

[0054] The phenolic antioxidant can be selected from 1,1-dimethyl-2-(3,5-di-tert-butyl-4-hydroxyphenyl)-1-nitroethane; 1-methyl-2-(3,5-di-tert-butyl-4-hydroxyphenyl)-1-nitroethane; 1-(3,5-di-tert-butyl-4-hydroxybenzyl)-1-nitropropane; pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; and combinations thereof. Preferably, the phenolic antioxidant is pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

[0055] Processing aids

[0056] The polypropylene composition may contain or additionally contain processing aids selected from stearates, oleamide, erucamide, and mixtures thereof. Preferably, the processing aid is oleamide. The processing aid may be present in an amount of ≥200 ppm and ≤5000 ppm, preferably ≥500 ppm and ≤1200 ppm, preferably ≥500 ppm and ≤1000 ppm, and preferably ≥500 ppm and ≤900 ppm, relative to the total weight of the polypropylene composition. If present, the stearate may be calcium stearate.

[0057] Relative to the total weight of the polypropylene composition, the polypropylene composition may additionally contain one or more additional additives present in an amount of <5.0% by weight, preferably <2.0% by weight, and more preferably <1.0% by weight. Non-limiting examples of such additional additives include UV stabilizers, antioxidants, coloring pigments, and inorganic fillers.

[0058] In one aspect of the invention, relative to the total weight of the polypropylene composition, (a) the propylene polymer is post-consumer recycled polypropylene (PCR-PP) and is present in an amount of ≥99.04% by weight and <100.0% by weight, preferably ≥99.1% by weight and <100.0% by weight, preferably ≥99.2% by weight and <100.0% by weight;

[0059] (b) The organic phosphite additive is tris(2,4-di-tert-butylphenyl) phosphite and is present in an amount of ≥1,000 ppm and ≤1,700 ppm by weight, preferably ≥1,200 ppm and ≤1,600 ppm;

[0060] (c) The phenolic antioxidant is present in an amount of pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and by weight ≥500 ppm and ≤1000 ppm, preferably ≥500 ppm and ≤900 ppm;

[0061] (d) The polyol compound is pentaerythritol and is present in an amount of ≥700 ppm and ≤1200 ppm by weight, preferably ≥900 ppm and ≤1100 ppm by weight;

[0062] (e) The processing aid is oleamide and is present in an amount of ≥500 ppm and ≤1000 ppm by weight, preferably ≥500 ppm and ≤900 ppm; and

[0063] (f) Total metal content ≥3,000 ppm and ≤6,500 ppm by weight, preferably ≥3,000 ppm and ≤5,000 ppm. The sum of components (a)-(f) is 100% by weight.

[0064] In one aspect of the invention, relative to the total weight of the polypropylene composition, (a) the propylene polymer is post-consumer recycled polypropylene (PCR-PP) and is present in an amount of ≥99.2% by weight and <100.0% by weight;

[0065] (b) The organic phosphite additive is tris(2,4-di-tert-butylphenyl) phosphite and is present in an amount of ≥1,200 ppm and ≤1,600 ppm by weight;

[0066] (c) The phenolic antioxidant is pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and is present in an amount of ≥500 ppm and ≤900 ppm by weight;

[0067] (d) The polyol compound is pentaerythritol and is present in an amount of ≥700 ppm and ≤1200 ppm by weight, preferably ≥900 ppm and ≤1100 ppm by weight;

[0068] (e) The processing aid is oleamide and is present in amounts ≥500 ppm and ≤900 ppm by weight; and

[0069] (f) Total metal content ≥3,000 ppm and ≤5,000 ppm by weight. The sum of components (a)-(f) is 100% by weight.

[0070] Method for preparing polypropylene compositions

[0071] A polypropylene composition can be prepared by a method comprising the following steps: (a) combining a group of components comprising: (i) a propylene polymer of >90.0% by weight, preferably >95.0% by weight, preferably >98.0% by weight, an organophosphite additive of ≥800 ppm and ≤5000 ppm by weight, (ii) a phenolic antioxidant of ≥200 ppm and ≤5000 ppm by weight, (iii) a polyol compound of ≥700 ppm and ≤1500 ppm by weight, and optionally processing aids; and (b) melt-extruding the group of components in an extruder at an extrusion temperature in the range of >200°C and ≤350°C, preferably ≥220°C and ≤260°C, to obtain a polypropylene composition wherein the polyol compound has a melting point of >200°C and ≤350°C, preferably ≥220°C and ≤300°C.

[0072] In one aspect, the present invention relates to articles comprising the polypropylene composition of the present invention. Preferably, the articles are selected from containers, bottles, sheets, automotive parts, health care bags, and films. Preferably, the articles comprise post-consumer recycled polypropylene in an amount greater than 85.0% by weight, preferably greater than 90.0% by weight, preferably greater than 95.0% by weight, and preferably greater than 98.0% by weight relative to the total weight of the articles. Preferably, the articles comprise post-consumer recycled polypropylene in an amount greater than 85.0% by weight and less than 100% by weight, preferably greater than 90.0% by weight and 100% by weight, preferably greater than 95.0% by weight and less than 100% by weight, and preferably greater than 98.0% by weight and less than 100% by weight relative to the total weight of the articles.

[0073] The invention will now be illustrated by the following non-limiting embodiments.

[0074] Example

[0075] Purpose: For the purposes of illustrating the present invention, six different polypropylene compositions were prepared. The sample designated "IE1" represents the composition of the present invention according to one embodiment, while the samples designated CE1-CE5 are comparative polypropylene compositions.

[0076] Material: The following materials were used:

[0077] Table 1

[0078]

[0079] Several polymer compositions were melt-extruded using a Werner & Pfleiderer ZSK25 twin-screw melt extruder with a screw diameter of 25 mm and an L / D ratio of 40. The extruder was operated at 250 rpm, with the following setpoint temperature distribution applied to each of the extruder sections L1-L10, where L1 is the feed section and L10 is the die section. Temperatures are expressed in °C. For recycled polypropylene, the material feed rate to the extruder was 6.8–7.3 kg / h, and for virgin polypropylene, it was 7.3 kg / h. Processing temperatures for all batches were maintained at 235 °C. All extrusion RPMs of the screw were set to 250, and the granulator traction speed was 20 m / min. Torque varied with batch for each extrusion cycle, from 12 to a maximum of 15. Additive and resin compounding was performed at 1 kg per batch, where the desired amount of additive was thoroughly mixed and then fed into the hopper.

[0080] Table 2

[0081]

[0082] The table below provides details of the composition of each of the samples.

[0083] Table 3

[0084]

[0085] To test stabilization properties, each of formulations IE1 and CE1-CE5 was subjected to three cycles of extrusion under the conditions described above to determine the stability of the formulations when exposed to multiple extrusion cycles. Subsequently, the suitability of the formulations for use in regenerative applications was evaluated. Oxidation induction time (OIT) and melt flow rate were measured after each cycle. OIT was measured in minutes after each cycle.

[0086] Oxidation induction time (OIT) was measured using a TA-Q2000 instrument. The sample was initially held at an equilibrium temperature of 30.00 °C. The temperature was then increased to 220.00 °C at a rate of 10.00 °C / min and held at that temperature for 5 minutes. The melt flow rate was measured at 230 °C under a load of 2.16 kg according to ISO 1133.

[0087] Additionally, visually inspect the sample for any discoloration. The results are provided in the table below:

[0088] Table 4

[0089]

[0090] As clearly shown in Table 4, compared to sample CE1, which contains the polyol-mannitol, sample IE1, which is composed of recycled polypropylene polymer and stabilized with pentaerythritol, exhibits improved thermal oxidation properties even after three cycles. The higher OIT of sample IE1 compared to sample CE1 demonstrates these improved thermal oxidation properties. Furthermore, discoloration was observed after three extrusion cycles for sample CE2, but not for sample IE1. This result is particularly noteworthy because IE1 was prepared using post-consumer recycled polypropylene with a high metal content, compared to samples CE4 and CE5, which were prepared from virgin grade polypropylene. Samples CE4 and CE5, being virgin polypropylene, have negligible metal content, and their low changes in MFR and OIT are within expectations.

[0091] Compared to sample CE3, which has the fewest stabilizing additives, IE1 exhibits improved stability, as evidenced by the significantly increased OIT value of sample IE1 compared to sample CE3. Furthermore, the melt flow rate (MFR) of sample IE1 changed less dramatically across different extrusion cycles than that of sample CE3.

Claims

1. A polypropylene composition comprising or consisting of the following: (a) >90.0% by weight of propylene polymer relative to the total weight of the polypropylene composition, preferably wherein the propylene polymer is present in an amount of ≥98.5% by weight and <100% by weight, preferably ≥99.0% by weight and <100.0% by weight, preferably ≥99.04% by weight and <100.0% by weight, preferably ≥99.1% by weight and <100.0% by weight, preferably ≥99.2% by weight and <100.0% by weight; (b) Organic phosphite additives with a weight of ≥800 ppm and ≤5000 ppm, preferably ≥1000 ppm and ≤2000 ppm, and more preferably ≥1200 ppm and ≤1700 ppm; (c) Phenolic antioxidants with a content of ≥200 ppm and ≤5000 ppm by weight, preferably ≥500 ppm and ≤1200 ppm, preferably ≥500 ppm and ≤1000 ppm, and preferably ≥500 ppm and ≤900 ppm; (d) Polyol compounds with a concentration of ≥700 ppm and ≤5,000 ppm by weight, preferably ≥700 ppm and ≤1,500 ppm, preferably ≥700 ppm and ≤1200 ppm, preferably ≥700 ppm and ≤1100 ppm, and preferably ≥900 ppm and ≤1100 ppm; and (e) Metals >100 ppm by weight, determined by inductively coupled plasma optical emission spectrometry (ICP-OES) according to ISO 24047:2021. The polyol compound has a melting point of >200°C and ≤350°C, preferably ≥220°C and ≤300°C.

2. The polypropylene composition according to claim 1, wherein the organic phosphite additive is selected from tris[2,4-bis(1,1-dimethylpropyl)phenyl]phosphite, bis[2,4-bis-(1,1-dimethylpropyl)phenyl][4-(1,1-dimethylpropyl)phenyl]phosphite, tris(2,4-di-tert-butylphenyl)phosphite, and any combination thereof, preferably the organic phosphite additive is tris(2,4-di-tert-butylphenyl)phosphite.

3. The polypropylene composition according to any one of claims 1-2, wherein the phenolic antioxidant is selected from 1,1-dimethyl-2-(3,5-di-tert-butyl-4-hydroxyphenyl)-1-nitroethane; 1-methyl-2-(3,5-di-tert-butyl-4-hydroxyphenyl)-1-nitroethane, 1-(3,5-di-tert-butyl-4-hydroxyphenyl)-1-nitropropane, pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and combinations thereof, preferably the phenolic antioxidant being pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

4. The polypropylene composition according to any one of claims 1-3, wherein the polyol compound is pentaerythritol.

5. The polypropylene composition according to any one of claims 1-4, wherein the polypropylene composition comprises a processing aid selected from stearates, oleamide, erucamide and mixtures thereof, preferably oleamide.

6. The polypropylene composition according to claim 5, wherein the processing aid is present in an amount of ≥200 ppm and ≤5000 ppm by weight, preferably ≥500 ppm and ≤1200 ppm, preferably ≥500 ppm and ≤1000 ppm, and preferably ≥500 ppm and ≤900 ppm, relative to the total weight of the polypropylene composition.

7. The polypropylene composition according to any one of claims 1-6, wherein the propylene polymer is a recycled propylene polymer, preferably the recycled propylene polymer is post-consumer recycled polypropylene (PCR-PP), or a mixture of post-consumer recycled polypropylene and post-industrial recycled polypropylene (PIR-PP), preferably wherein the propylene polymer is a recycled propylene polymer having a PCR-recycled content of >95.0% by weight, preferably >98.0% by weight, and preferably 100% by weight relative to the total weight of the propylene polymer.

8. The polypropylene composition according to claim 7, wherein the recycled polypropylene is derived from a propylene polymer selected from: polypropylene homopolymer, polypropylene copolymer, multiphase polypropylene, and mixtures thereof.

9. The polypropylene composition according to any one of claims 1-8, wherein the composition has, relative to the total weight of the polypropylene composition, a total metal content of >100 ppm, preferably >1,000 ppm, preferably >3,000 ppm, preferably ≥3,000 ppm and ≤15,000 ppm, preferably ≥3,000 ppm and ≤6,500 ppm, preferably ≥3,000 ppm and ≤5,000 ppm, as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) according to ISO 24047:2021.

10. The polypropylene composition according to any one of claims 1-9, wherein, relative to the total weight of the polypropylene composition, a. The propylene polymer is post-consumer recycled polypropylene (PCR-PP) and is present in an amount of ≥99.04% by weight and <100.0% by weight, preferably ≥99.1% by weight and <100.0% by weight, preferably ≥99.2% by weight and <100.0% by weight; b. The organic phosphite additive is tris(2,4-di-tert-butylphenyl) phosphite and is present in an amount of ≥1,000 ppm and ≤1,700 ppm by weight, preferably ≥1,200 ppm and ≤1,600 ppm; c. The phenolic antioxidant is pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and is present in an amount of ≥500 ppm and ≤1000 ppm by weight, preferably ≥500 ppm and ≤900 ppm; d. The polyol compound is pentaerythritol and exists in an amount of ≥700 ppm and ≤1200 ppm by weight, preferably ≥900 ppm and ≤1100 ppm; e. The processing aid is oleamide and is present in an amount of ≥500 ppm and ≤1000 ppm by weight, preferably ≥500 ppm and ≤900 ppm; and f. Total metal content ≥3,000 ppm and ≤6,500 ppm by weight, preferably ≥3,000 ppm and ≤5,000 ppm.

11. The polypropylene composition according to any one of claims 1-10, wherein said propylene polymer has at least one of the following: a. a density of > 0.5 and < 0.98 g / cm3determined according to ISO 1183-1 3 ; and / or b. Melt flow rate (MFR) of ≥50.0 g / 10 min and ≤90.0 g / 10 min, preferably ≥65.0 g / 10 min and ≤80.0 g / 10 min, as measured according to ISO 1133 at 230 °C and under a load of 2.16 kg.

12. The polypropylene composition according to any one of claims 1-11, wherein the polypropylene composition has at least one of the following after three extrusion cycles: a. A melt flow rate (MFR) ≥50.0 and ≤100.0 g / 10 min, preferably ≥60.0 and ≤80.0 g / 10 min, when measured according to ASTM D1238 at 230°C and a load of 2.16 kg, preferably wherein extrusion is performed using a twin-screw extruder at a processing temperature ≥220°C; and / or b. Oxidation induction time (OIT) >12.0 min and <25.0 min when measured according to ISO 11357-6 (2018) and at a temperature of 220 °C in the presence of air.

13. The polypropylene composition according to any one of claims 1-12, wherein the polypropylene composition has a change in melt flow rate (MFR) of ≤0.9%, preferably ≤0.8%, preferably ≤0.5%, preferably ≤0.2% after three extrusion cycles compared to the melt flow rate (MFR) of the polypropylene composition after the first extrusion cycle, preferably wherein the extrusion is performed using a twin-screw extruder at a processing temperature of ≥220°C; and wherein the polypropylene composition has an increase in oxidation induction time (OIT) of ≥10.0%, preferably ≥15.0%, preferably ≥20.0% and ≤30.0% after three extrusion cycles compared to the oxidation induction time (OIT) after the first extrusion cycle, preferably wherein the oxidation induction time (OIT) is performed at 220°C in the presence of air.

14. An article comprising the polypropylene composition according to any one of claims 1-13, preferably wherein the article is selected from containers, bottles, sheets, automotive parts, health care bags, and films.

15. The article of claim 14, wherein the article comprises post-consumer recycled polypropylene in an amount of >85.0% by weight, preferably >90.0% by weight, preferably >95.0% by weight, and preferably >98.0% by weight relative to the total weight of the article.

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