WO2025061390A1

WO2025061390A1 - Polypropylene composition with improved oxidation stability and flow property

Info

Publication number: WO2025061390A1
Application number: PCT/EP2024/073172
Authority: WO
Inventors: Kankan Bhaumik; Carolus WILSENS; Kavya AT; Sadasivam GOPALAKRISHNAN
Original assignee: SABIC Global Technologies BV
Current assignee: SABIC Global Technologies BV
Priority date: 2023-09-22
Filing date: 2024-08-19
Publication date: 2025-03-27
Anticipated expiration: 2026-03-22

Abstract

The invention relates to a polypropylene composition having improved thermo-oxidation stability and flow properties, comprising: (a) > 90.0 wt.% of a propylene polymer, preferably a recycled propylene polymer; (b) ≥ 800 ppm and ≤ 5,000 ppm by weight, of an organo-phosphite additive; (c) ≥ 200 ppm and ≤ 5,000 ppm by weight, of a phenolic anti-oxidant; and (d) ≥ 700 ppm and ≤ 5,00 ppm by weight of a polyol compound. The propylene composition has high metal content for example > 100 ppm by weight. The polyol compound has a melting point of > 200 °C and ≤ 350 °C, preferably ≥ 220 °C and ≤ 300 °C. The invention further relates to process for preparing the composition and to articles prepared from such a polypropylene composition.

Description

POLYPROPYLENE COMPOSITION WITH IMPROVED OXIDATION STABILITY AND FLOW PROPERTY

[0001] The invention relates to the field of polypropylene compositions, and in particular to a composition comprising recycled polypropylene composition having improved thermo- oxidative stability and processability. The invention further relates to articles comprising such a polypropylene composition.

[0002] Thermo-oxidative stability (i.e oxidation stability under elevated temperature) is an important property requirement for a polymeric material to be used commercially for manufacturing various products. To that extent polypropylene is used extensively in the production of industrial and household articles, and improving its oxidative stability is often seen as a key consideration for plastic convertors and manufacturers.

[0003] In particular, when it comes to the use of recycled plastics, also referred to as recyclates, the issue of thermo-oxidative stability, mechanical processability, and color degradation are key consideration as recycled polymers are more prone to degradation than virgin polymers and making it a challenge to use these polymers as an alternate to virgin grade resins. The reason for this, is that in recycled polymers, degradation products present in the recyclates act as initiator points for a further oxidation. For example, during melt processing over several recycles, the recycled polypropylene may undergo structural changes due to chain scission (and occasionally branching) that results in the rapid deterioration of mechanical properties, flow properties (upswing in flow) and change in color. In particular the change in flow property over multiple cycles of extrusion affects the processability of the polymer and makes recycled polymer less reliable from a processability point of view.

[0004] In addition, recycled polypropylene have high metal loading compared to virgin polypropylene and in certain instance the presence of such metal tend to accelerate this degradation in properties. Therefore, by ensuring the desired oxidative stability allows a recycled polypropylene material to retain its mechanical and color properties despite being subjected to repeated thermal processability and physical aging over multiple life cycles. [0005] From a sustainability point of view, when recycling of plastic waste is seen as a key to reduce plastic waste, the performance and stability gap of recyclates in comparison to virgin grade resins, makes such recycled plastics to be less attractive for commercial application. For these reasons alone, mechanical recycling has not realized the full potential.

[0006] In the past, stabilizers comprising phenolic antioxidants and phosphites, have been used to protect the polypropylene composition from thermal and oxidative or photo-oxidative damage. However, the addition of certain phosphite stabilizers such as Irgafos 168 beyond a certain threshold limit may result in the increased migration of 2,4-di/c/7 butyl phenol, a NIAS regulatory substance - a degradation product of Irgafos 168 thereby limiting the use of such polypropylene material in food contact and other health sensitive application.

[0007] US20200317886A1 relates to a method for stabilizing halogen-free thermoplastic recyclates against oxidative, thermal, and/or actinic degradation. In the method described in the patent, at least one alditol or cyclitol based compounds are added to a thermoplastic recyclate as part of a stabilization package. However, alditol or cyclitol based compounds tend to char when exposed to typical polymer processing temperatures resulting in color degradation.

[0008] Therefore, it is an object of the present invention, to provide a polypropylene composition having improved thermo-oxidative stability. It is yet another objective of the invention to provide a polypropylene composition comprising a recycled polypropylene, that has improved thermo-oxidative stability over multiple extrusion cycles while retaining its flow and color property. It is yet another objective of the present invention to provide an article comprising a polypropylene composition derived from a recycled polypropylene that has improved thermo- oxidative stability over multiple extrusion cycles while retaining its flow and color property

DESCRIPTION

[0009] Accordingly, one or more objectives of the present invention is achieved by a polypropylene composition, comprising or consisting of: (a) > 90.0 wt.% of a propylene polymer with regard to the total weight of the polypropylene composition, preferably wherein the propylene polymer is present in an amount of > 98.5 wt.% and < 100 wt.%, preferably > 99.0 wt.% and < 100.0 wt.%, preferably > 99.04 wt.% and < 100.0 wt.%, preferably > 99.1 wt.% and < 100.0 wt.%, preferably > 99.2 wt.% and < 100.0 wt.%;

(b) > 800 ppm and < 5000 ppm by weight, preferably > 1000 ppm and < 2000 ppm, preferably > 1200 ppm and < 1700 ppm, of an organo-phosphite additive;

(c) > 200 ppm and < 5000 ppm by weight, preferably > 500 ppm and < 1200 ppm, preferably > 500 ppm and < 1000 ppm, preferably > 500 ppm and < 900 ppm, of a phenolic anti-oxidant; and

(d) > 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 of a polyol compound;

(e) > 100 ppm by weight of metal as determined by ISO 24047:2021 using inductively coupled plasma optical emission spectrometry (ICP-OES), wherein the polyol compound has a melting point of > 200 °C and < 350 °C, preferably > 220 °C and < 300 °C. The sum of all the components (a)-(d) is 100 wt.%

[0010] The term “ppm” as used throughout this disclosure means parts per million. Advantageously, the polypropylene composition of the present invention demonstrates improved thermo-oxidative stability enabling the polypropylene composition to retain its mechanical and flow property and resistance to color degradation even after multiple cycles of extrusion. As a further advantage, the polypropylene composition of the present invention even when derived from recycled polypropylene shows no discoloration due to charring even when processed at processing temperature while retaining the desired thermo-oxidative stability. As a further advantage, the polypropylene composition even having metal content greater than 100 ppm by weight demonstrated improved thermo-oxidative stability and minimal variation in flow and color property.

[0011] In particular, the present disclosure propylene composition comprises a recycled polypropylene, which demonstrates improved thermo-oxidative stability while retaining the desired flow property and resistance to color degradation even after multiple cycles of extrusion. The term “thermo-oxidative stability” means resistance to oxidative degradation when a sample specimen prepared from the polypropylene composition of the present invention is exposed to air at elevated temperature. A suitable indicator for measuring thermo-oxidative stability is by measuring the oxidation induction time (OIT) of the polypropylene composition in minutes. Accordingly, a higher OIT is indicative of higher thermo-oxidative stability.

[0012] In particular, the polypropylene composition of the present invention demonstrated excellent thermo-oxidative stability and minimal change of flow property even after multiple cycles of extrusion. For example, the polypropylene composition after three cycles of extrusion has at least one of:

(a) a melt flow rate (MFR) of > 50.0 and < 100.0 g/10 min, preferably > 60.0 and < 80.0 g/10 min when measured at 230°C under a load of 2.16 kg according to ASTM D1238, preferably wherein the extrusion is carried out using a twin screw extruder at a processing temperature of > 220 °C; and/or

(b) an oxidation induction time (OIT) of > 12.0 minutes and < 25.0 minutes, preferably > 14.0 and < 20.0 when determined in accordance with ISO 11357-6 (2018) and at a temperature of 220 °C in presence of air.

[0013] Preferably, the polypropylene composition after three cycles of extrusion has:

(a) a melt flow rate (MFR) of > 50.0 and < 100.0 g/10 min, preferably > 60.0 and < 80.0 g/10 min when measured at 230°C under a load of 2.16 kg according to ASTM D1238, preferably wherein the extrusion is carried out using a twin screw extruder at a processing temperature of > 220 °C, preferably at > 220 °C and < 240 °C; and

[0014] Preferably the polypropylene composition after three cycles of extrusion has a change of melt flow rate (MFR) < 0.9 %, preferably < 0.8%, preferably < 0.5 %, preferably < 0.2 %, as compared to the melt flow rate (MFR) of the polypropylene composition after first cycle of extrusion, preferably wherein the extrusion is carried out using a twin screw extruder at a processing temperature of > 220 °C; and wherein the polypropylene composition after three cycles of extrusion has an increase in oxidation induction time (OIT) of > 10.0 %, preferably > 15.0 %, preferably > 20.0% and < 30.0% as compared to the oxidation induction time (OIT) after first cycle of extrusion, preferably the oxidation induction time (OIT) is carried out at 220 °C in presence of air. Preferably, the polypropylene composition after three cycles of extrusion has a change of melt flow rate (MFR) < 0.9 % and > 0.0% as compared to the melt flow rate (MFR) of the polypropylene composition after first cycle of extrusion.

[0015] The change in melt flow rate may be measured by the formula: (MFR3 - MFR1)/MFR1, where MFR1 is the melt flow rate of the polypropylene composition after three cycles of extrusion and MFR1 is the melt flow rate of the polypropylene composition after first cycle of extrusion. It is particularly preferable to have minimal change in the melt flow rate of the polypropylene composition after three cycles of extrusion as compared to the first cycle of extrusion.

[0016] The increase in oxidation induction time (OIT) may be measured by the formula: (OIT3 - OIT1)/OIT1, where OIT3 is the oxidation induction time of the polypropylene composition after three cycles of extrusion and OIT1 is the oxidation induction time of the polypropylene composition after the first cycle of extrusion.

Propylene Polymer

[0017] The polypropylene composition comprises > 90.0 wt.%, preferably > 95.0 wt.%, preferably > 98.0 wt.% of propylene polymer, with regard to the total weight of the polypropylene composition. Preferably, the propylene polymer is present in an amount of > 98.5 wt.% and < 100 wt.%, preferably > 99.0 wt.% and < 100.0 wt.%, preferably > 99.04 wt.% and < 100.0 wt.%, preferably > 99.1 wt.% and < 100.0 wt.%, preferably > 99.2 wt.% and < 100.0 wt.%, with regard to the total weight of the polypropylene composition.

[0018] The propylene polymer may have has at least one of:

(a) a density of > 0.5 and < 0.98 g/cm³ as determined in accordance with ISO 1183-1; and/or

(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 measured at 230°C under a load of 2.16 kg according to ISO 1133. [0019] Preferably, the propylene polymer has:

(a) a density of > 0.5 and < 0.98 g/cm³ as determined in accordance with ISO 1183-1; and

(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 measured at 230°C under a load of 2.16 kg according to ISO 1133.

Recycled polypropylene

[0020] It is particularly preferred that the propylene polymer is a recycled propylene polymer. Preferably the recycled propylene polymer is a post-consumer recycled polypropylene (PCR-PP), or a mixture of post-consumer recycled polypropylene and post-industrial recycled polypropylene (PIR-PP).

[0021] It is preferred that the propylene polymer is a recycled propylene polymer with a PCR-recycled content of > 95.0 wt.%, preferably > 98.0 wt.%, preferably 100wt.% with regard to the total weight of the propylene polymer. The amount of recycled polypropylene may be determined in accordance with ISO 14021. Preferably, the recycled polypropylene is derived from a propylene polymer selected from a polypropylene homopolymer, polypropylene copolymer, heterophasic polypropylene and mixtures thereof.

[0022] The recycled propylene polymer may be derived by mechanically recycling polypropylene derived from waste plastic material. The process of mechanical recycling involves collection, sorting, washing, drying, shredding, grinding and compounding to obtain the recycled polypropylene. The mechanical recycling allows a polypropylene material once used in a product to be re-used through the process of one or more rounds of recycling - resulting in several cycles involving the steps of use, recycle and reuse. As a result, recycled polypropylene has a higher residual metal content compared to virgin or non-recycled polypropylene due to the addition of metal containing additives across several life cycles of the plastic material.

[0023] Accordingly, 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, preferably > 3,000 ppm and < 5,000 ppm by weight, with regard to the total weight of the polypropylene composition as determined by ISO 24047:2021 using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0024] In particular, when the propylene polymer is a recycled polypropylene the metal content may be > 3000 ppm by weight, with regard to the total weight of the polypropylene composition. Non-limiting examples of metal present in the polypropylene composition may include any one of titanium, calcium, iron, zinc, magnesium, silicon and combinations thereof. The metal may be present in the form of salts, oxides or in its elemental form. The metal content may be determined by using any known methods such as inductively coupled plasma optical emission spectrometry (ICP-OES) and XRF analysis.

[0025] The polymer compositions comprising recycled polypropylene, are prone to oxidative degradation due to its history of exposure to heat, light and high temperature processing across different life cycles of the polymer. However, the inventors of the present application surprisingly found that when the recycled polypropylene is stabilized using a purposeful combination of an organo-phosphite additive, a phenolic anti-oxidant and a polyol compound as described in this disclosure, the recycled propylene demonstrates improved thermo-oxidative stability even after multiple extrusion cycles while retaining suitable flow and color property.

Organo-phosphite additives

[0026] The polypropylene composition comprises > 800 ppm and < 5000 ppm by weight, preferably > 1000 ppm and < 2000 ppm, preferably > 1200 ppm and < 1700 ppm, preferably > 1200 ppm and < 1600 ppm, of an organo-phosphite additive.

[0027] The organo-phosphite additive may be selected from tris[2,4-bis(l, 1- dimethylpropyl)phenyl] phosphite, bis[2,4-bis-(l,l-dimethylpropyl)phenyl] [4-(l,l- dimethylpropyl)phenyl] phosphite, tris(2,4-ditert-butylphenyl) phosphite and any combinations thereof. Preferably, the organo-phosphite additive is tris(2,4-ditert-butylphenyl) phosphite. Preferably, the organo-phosphite additive consists of only tris(2,4-ditert-butylphenyl) phosphite. [0028] The organo-phosphite additive may be presented by the formula:

[0029] wherein each of ‘R¹’ and ‘R²’ is same or different and is individually selected from tert-butyl, 1, 1 -dimethylpropyl or hydrogen, provided at least one of ‘R¹’ and ‘R²’ is not hydrogen, Preferably each of ‘R¹’ and ‘R²’ is identical and is tert-butyl.

Polyol Compound

[0030] The polypropylene composition comprises > 700 ppm and < 5,000 ppm by weight, preferably > 700 ppm and < 1500 ppm by weight, preferably > 700 ppm and < 1200 ppm, preferably > 700 ppm and < 1100 ppm by weight, preferably > 900 ppm and < 1100 ppm by weight of a polyol compound. The term “polyol compound” as used herein means a compound having at least two hydroxyl groups. The polyol compound has a melting point of > 200 °C and < 350 °C, preferably > 220 °C and < 300 °C, preferably > 220 °C and < 280 °C. The melting point of the polyol can be measured using standard methods of determining melting point of a solid organic compound.

[0031] For example, the melting point of an organic solid compound such as a polyol may be determined by introducing an amount such as 0.5 g of the polyol compound into a capillary tube. Thereafter the tube may be attached to the stem of a thermometer centered in a heating bath and subsequently the bath may be heated. The temperatures at which melting begins and completes, may be noted to determine the melting temperature. Alternatively, in order to make the most effective use of time carry out a rapid melting point determination initially (by heating rapidly) to establish an approximate melting point and then carry out at least two further careful determinations (by heating more gently, i.e. at a rate of about 2 °C /min) until two consistent values are obtained.

[0032] It is preferred that the polyol compound is pentaerythritol (i.e 2,2- bis(hydroxymethyl)propane-l,3-diol). It is preferred that that the polyol compound is pentaerythritol (i.e 2,2-bis(hydroxymethyl)propane-l,3-diol) and is present in an amount of > 900 ppm and < 1100 ppm by weight with regard to the total weight of the polypropylene composition.

Phenolic anti-oxidant

[0033] The polypropylene composition comprises > 200 ppm and < 5000 ppm by weight, preferably > 500 ppm and < 1200 ppm, by weight, preferably > 500 ppm and < 1000 ppm, preferably > 500 ppm and < 900 ppm, with regard to the total weight of the polypropylene composition.

[0034] The phenolic anti-oxidant may be selected from l,l-dimethyl-2-(3,5-di-tertbutyl- 4-hydroxyphenyl)- 1 -nitroethane; 1 -methyl-2-(3,5-di-tertbutyl-4-hydroxyphenyl)- 1 -nitroethane, l-(3,5-di-tertbutyl-4-hydroxybenzyl)-l-nitropropane, pentaerythritol tetrakis(3-(3,5-di-tert-butyl- 4-hydroxyphenyl)propionate, and combinations thereof. Preferably, the phenolic anti-oxidant is pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate).

Processing aid

[0035] The polypropylene composition may comprise or further comprise a processing aid selected from stearic acid salt, 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 by weight, preferably > 500 ppm and < 1200 ppm, preferably > 500 ppm and < 1000 ppm, preferably > 500 ppm and < 900 ppm, with regard to the total weight of the polypropylene composition. The stearic acid salt if present, may be calcium stearate.

[0036] The polypropylene composition may further include one or more additional additives present in an amount of < 5.0 wt.%, preferably < 2.0 wt.%, preferably < 1.0 wt.% with regard to the total weight of the polypropylene composition. None limiting examples of such additional additives include UV stabilizers, anti-oxidants, color pigments, and inorganic fillers. [0037] In an aspect of the invention, (a) the propylene polymer is a post-consumer recycled polypropylene (PCR-PP) and is present in an amount of > 99.04 wt.% and < 100.0 wt.%, by weight, preferably > 99.1 wt.% and < 100.0 wt.%, preferably > 99.2 wt.% and < 100.0 wt.%;

(b) the organo-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 anti-oxidant is pentaerythritol tetrakis(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 is present in an amount of > 700 ppm and < 1200 ppm by weight, preferably > 900 ppm and < 1100 ppm by weight;

(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) a total metal content of > 3,000 ppm and < 6,500 ppm by weight, preferably > 3,000 ppm and < 5,000 ppm; with regard to the total weight of the polypropylene composition. The sum of components (a)-(f) adding up to 100 wt.%.

[0038] In an aspect of the invention, (a) the propylene polymer is a post-consumer recycled polypropylene (PCR-PP) and is present in an amount of > 99.2 wt.% and < 100.0 wt.%;

(b) the organo-phosphite additive is tris(2,4-ditert-butylphenyl) phosphite and is present in an amount of > 1,200 ppm and < 1600 ppm, by weight;

(c) the phenolic anti-oxidant is pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate) and is present in an amount of > 500 ppm and < 900 ppm, by weight;

(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;

(e) the processing aid is oleamide and is present in an amount of > 500 ppm and < 900 ppm, by weight; and

(f) a total metal content of > 3,000 ppm and < 5,000 ppm by weight; with regard to the total weight of the polypropylene composition. The sum of components (a)-(f) adding up to 100 wt.%.

Process of preparing Polypropylene Composition [0039] The polypropylene composition may be prepared by a process comprising the steps of: (a) combining a set of ingredients comprising (i) > 90.0 wt.%, preferably > 95.0 wt.%, preferably > 98.0 wt.% of the propylene polymer, > 800 ppm and < 5000 ppm by weight of the organo-phosphite additive, (ii) > 200 ppm and < 5000 ppm by weight, of the phenolic anti-oxidant, (iii) > 700 ppm and < 1500 ppm by weight of the polyol compound, and optionally the processing aid; and (b) melt extruding the set of ingredients in an extruder at an extrusion temperature ranging from > 200 °C and < 350 °C, preferably from > 220 °C and < 260 °C to obtain the polypropylene composition, wherein the polyol compound has a melting point of > 200 °C and < 350 °C, preferably > 220 °C and < 300 °C.

[0040] In an aspect of the invention, the invention is directed to an article comprising the polypropylene composition of the present invention. Preferably, the article is selected from a container, bottle, sheet, automobile component, health care pouch and film. Preferably, the article comprises > 85.0 wt.%, preferably > 90.0 wt.%, preferably > 95.0 wt.%, preferably > 98.0 wt.%, with regard to the total weight of the article, of post-consumer recycled polypropylene. Preferably, the article comprises > 85.0 wt.% and < 100 wt.%, preferably > 90.0 wt.% and 100 wt.%, preferably > 95.0 wt.% and < 100 wt.%, preferably > 98.0 wt.% and < 100 wt.%, with regard to the total weight of the article, of post-consumer recycled polypropylene.

[0041] The invention will now be illustrated by the following non-limiting examples.

EXAMPLES

[0042] Purpose: For the purposes of exemplifying the present invention, six different polypropylene compositions were prepared. The sample denoted as “IE1”, represents an inventive composition in accordance with an embodiment of the present invention while samples denoted as CE1-CE5 are comparative polypropylene compositions.

[0043] Materials: The following material were used:

Table 1

[0044] A number of polymer compositions were subjected to melt extrusion using a Werner & Pfleiderer ZSK25 twin-screw melt extruder, having a screw diameter of 25 mm, and an L/D ratio of 40. The extruder was operated at 250 rpm, using the below setpoint temperature profile for each of the zone L1-L10 of the extruder, wherein LI is the feed zone and LIO is the die zone.

Temperatures are indicated in °C. The feed rate of material to the extruder was 6.8-7.3 kg/h for recycled polypropylene and 7.3 kg/h for virgin polypropylene. All the batches processing temperature was carried out at 235 °C. All the extrusion RPM of screw were configured at 250 and drawing speed of the pelletizer was 20m/min. The Torque varied batch to batch to each extrusion cycle from 12 to max 15. The compounding of additives and resins was performed at 1 kg batch each with desired amount of additives were mixed well before put in an hopper.

Table 2

[0045] The table below provides the details of the composition for each of the samples.

Table 3

[0046] To test the stabilisation properties, each of the formulations IE1 and CE1-CE5 were subjected to extrusion according to the conditions as set out forth above for 3 cycles, to establish the stability of the formulations when exposed to multiple extrusion cycles. Thereafter, it was evaluated whether the formulations were of appropriate quality to be used in recycling applications. After each cycle, the oxidative induction time (OIT) and melt flow rate was determined. The OIT was determined in minutes after each cycle. [0047] The oxidative induction time (OIT) was measured using TA-Q2000 instrument.

The samples were first kept at equilibrium temperature of 30.00°C. Thereafter, the temperature was ramped up by 10.00°C/min to 220.00°C and thereafter kept 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. [0048] Further, the samples were visually inspected for any discoloration. The results are provided in the table below:

Table 4

[0049] From Table 4, it is clear that the polypropylene sample IE1 having recycled polypropylene polymer and stabilized using pentaerythritol demonstrated improved thermo- oxidative properties even after three cycles over that of the sample CE1 having the polyol - mannitol. The improved thermo-oxidative properties is evidenced from the higher OIT of the sample IE1 over that of the sample CE1. Further, for sample CE2 discoloration was observed after three cycles of extrusion. Such discoloration was not observed for the sample IE1. Such results were particularly notable since IE1 was prepared using post-consumer recycled polypropylene having high metal content as compared to the samples CE4 and CE5 prepared from grade virgin polypropylene. The samples CE4 and CE5 being virgin polypropylene has negligible metal content and the low variation in MFR and OIT was on expected lines.

[0050] The improved stability of IE1 as compared to the sample CE3 having minimal stabilization additive, is evident from the significantly increased OIT value for sample IE1 as compared to sample CE3. Further the extent of variation of melt flow rate (MFR) across different cycles of extrusion for sample IE1 was lower than that of sample CE3.

Claims

1. A polypropylene composition, comprising or consisting of:

(a) > 90.0 wt.% of a propylene polymer with regard to the total weight of the polypropylene composition, preferably wherein the propylene polymer is present in an amount of > 98.5 wt.% and < 100 wt.%, preferably > 99.0 wt.% and < 100.0 wt.%, preferably > 99.04 wt.% and < 100.0 wt.%, preferably > 99.1 wt.% and < 100.0 wt.%, preferably > 99.2 wt.% and < 100.0 wt.%;

(c) > 200 ppm and < 5000 ppm by weight, preferably > 500 ppm and < 1200 ppm, preferably > 500 ppm and < 1000 ppm, preferably > 500 ppm and < 900 ppm, of a phenolic anti-oxidant;

(d) > 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 of a polyol compound; and

(e) > 100 ppm by weight of metal as determined by ISO 24047:2021 using inductively coupled plasma optical emission spectrometry (ICP-OES), wherein the polyol compound has a melting point of > 200 °C and < 350 °C, preferably > 220 °C and < 300 °C.

2. The polypropylene composition of claim 1, wherein the organo-phosphite additive is selected from tris[2,4-bis(l,l-dimethylpropyl)phenyl] phosphite, bis[2,4-bis-(l , 1 - dimethylpropyl)phenyl] [4-(l,l-dimethylpropyl)phenyl] phosphite, tri s(2,4-di tertbutylphenyl) phosphite and any combinations thereof, preferably the organo-phosphite additive is tris(2,4-ditert-butylphenyl) phosphite.

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

4. The polypropylene composition as claimed in 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 stearic acid salt, oleamide, erucamide and mixtures thereof, preferably the processing aid is oleamide.

6. The polypropylene composition of 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, preferably > 500 ppm and < 900 ppm with regard 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 a 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 with a PCR-recycled content of > 95.0 wt.%, preferably > 98.0 wt.%, preferably 100 wt.% with regard to the total weight of the propylene polymer .

8. The polypropylene composition of claim 7, wherein the recycled polypropylene is derived from a propylene polymer selected from a polypropylene homopolymer, polypropylene copolymer, heterophasic polypropylene and mixtures thereof.

9. The polypropylene composition according to any one of claims 1-8, wherein the composition has 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 by weight, with regard to the total weight of the polypropylene composition as determined by ISO 24047:2021 using inductively coupled plasma optical emission spectrometry (ICP-OES).

10. The polypropylene composition according to any one of claims 1-9, wherein a. the propylene polymer is a post-consumer recycled polypropylene (PCR-PP) and is present in an amount of > 99.04 wt.% and < 100.0 wt.%, by weight, preferably > 99.1 wt.% and < 100.0 wt.%, preferably > 99.2 wt.% and < 100.0 wt.%; b. the organo-phosphite additive is tris(2,4-ditert-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 anti-oxidant is pentaerythritol tetrakis(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 is present 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. a total metal content of > 3,000 ppm and < 6,500 ppm by weight, preferably > 3,000 ppm and < 5,000 ppm; with regard to the total weight of the polypropylene composition.

11. The polypropylene composition according to any one of claims 1-10, wherein the propylene polymer has at least one of: a. a density of > 0.5 and < 0.98 g/cm³ as determined in accordance with ISO 1183-1; and/or 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 measured at 230°C under a load of 2.16 kg according to ISO 1133.

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

13. The polypropylene composition according to any one of claims 1-12, wherein the polypropylene composition after three cycles of extrusion has a change of melt flow rate (MFR) < 0.9 %, preferably < 0.8%, preferably < 0.5 %, preferably < 0.2 %, as compared to the melt flow rate (MFR) of the polypropylene composition after first cycle of extrusion, preferably wherein the extrusion is carried out using a twin screw extruder at a processing temperature of > 220 °C; and wherein the polypropylene composition after three cycles of extrusion has an increase in oxidation induction time (OIT) of > 10.0 %, preferably > 15.0 %, preferably > 20.0% and < 30.0% as compared to the oxidation induction time (OIT) after first cycle of extrusion, preferably the oxidation induction time (OIT) is carried out at 220 °C in 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 a container, bottle, sheet, automobile component, health care pouch and film.

15. The article of claim 14, wherein the article comprises > 85.0 wt.%, preferably > 90.0 wt.%, preferably > 95.0 wt.%, preferably > 98.0 wt.%, with regard to the total weight of the article, of post-consumer recycled polypropylene.