Use of chelating agents to restore the controlled degradation performance of organic peroxides and n-acyloxyamines in the presence of copper(II) ions

Abstract

A process for the thermal degradation of a polymer composition comprising polypropylene or propylene copolymers in the presence of a free radical generator and copper(II) ions, characterized in that the thermal degradation is carried out in the presence of a chelating agent selected from the group consisting of substituted triazoles, substituted salicyloyl hydrazides and substituted salicyloyl amides.

Description

[0001] USE OF CHELATING AGENTS TO RESTORE THE CONTROLLED DEGRADATION PERFORMANCE OF ORGANIC PEROXIDES AND N-ACYLOXYAMINES IN THE PRESENCE OF COP-PER(II) IONS

[0002] The present invention relates to a process for the thermal degradation of polypropylene or propylene copolymers in the presence of a free radical generator and copper(ll) ions, and further relates to a polymer composition comprising polypropylene or propylene copolymers, a free radical generator, copper(ll) ions, and a chelating agent as metal deactivator.

[0003] The controlled preparation of polyolefin grades (polymer types having different molar masses, melt viscosities, densities, molar mass distributions, etc.) by customary compounding methods, for example by extrusion or injection molding, is a routine process employed by polymer manufacturers and polymer processors / compounders. The setting of the desired parameters, for example the melt viscosity, by means of this polymer process step is critically dependent on the controlled reactivity and mode of action of the additives employed.

[0004] The use of free radical generators for modifying the melt viscosity (rheology) of polyolefins is a generally known method. Whether it results in a lowering of the molecular weight (degradation) or an increase in the molecular weight (crosslinking) depends primarily on the chemical structure of the polyolefin. The reaction of a polymer of the polypropylene type with a free-radical former during a polymer-processing process generally results in the degradation of the polymer, whereas polymers of the polyethylene type tend to crosslinking. Examples that may be mentioned here are polyethylene types, which are obtainable by means of Phillips catalysts (LDPE) or metallocene catalysts (LLDPE). Exceptions are the polyethylene types prepared by the Ziegler process, which likewise tend to undergo chain degradation when processed in the presence of free-radical formers.

[0005] In the case of copolymers and terpolymers or copolymer blends, high proportions of propylene produce polypropylene-like behavior, while high proportions of ethylene result in polyethylenelike behavior. If the above-mentioned copolymers and terpolymers or copolymer blends comprise proportions of multiply unsaturated olefins, the probability of crosslinking decreases with decreasing concentration of free double bonds. The controlled degradation of polypropylene (PP) to give a product having a lower molecular weight and a narrower molecular weight distribution is a commercially important process for producing controlled rheology polypropylene (CR-PP). While specific PP grades ("reactor grades") are obtainable by optimization of the synthesis process or the catalyst systems (metallocene catalyst, Ziegler catalyst), standard PP grades are frequently modified in process technology by means of a processing step following the synthesis. Known degradation processes proceed either thermally, in particular at temperatures above 280 °C, or in the presence of free radical generators. In process technology, the free radical-induced process is carried out in extruders or injection-molding machines at temperatures above 180 °C. Suitable free radical generators are organic peroxides which are added during the processing step in diluted form (PP Mastermix, diluted in oil, stabilized on inorganic supports) or directly as a liquid. Under the given processing conditions, the peroxide disintegrates into free radicals, which initiate the chain cleavage reactions and form polymers having the desired rheological properties (melt viscosities). The degradation of a PP to form a product having a lower molecular weight (higher melt flow rate (MFR)) is generally referred to as a viscosity-breaking or vis-breaking process.

[0006] CR-PP grades are mainly used for fiber applications and injection-molding applications in which low melt viscosities are a prerequisite for economical processing. A wide range of melt viscosities or molecular weights is nowadays required in process technology.

[0007] A further parameter that influences the processing behavior of the polymer, in addition to the molecular weight, is the molecular weight distribution (MWD). While polymer grades having broad MWDs display improved orientation behavior of the polymer chains at low pull-off speeds in a fiber spinning process, the reverse is the case for high pull-off speeds and broad MWDs. For this reason, narrow MWDs are essential at high pull-off speeds in order to achieve improved continuity in the spinning process.

[0008] In the nonwoven industry, rheology modifiers like peroxides and N-acyloxyamines are used to adjust the flow and viscosity of polymers during production. For medical nonwoven fabrics, which are often colored blue, it is critical to consider how these modifiers interact with other chemicals, especially dyes that contain metal ions such as copper ions. This interaction is important because it can potentially deactivate the effectiveness of these rheology modifiers, impacting the quality of the end product.

[0009] Rheology modifiers work by inducing controlled degradation in polymers and in particular in polypropylene. They create free radicals that initiate reactions in polymer chains, allowing better control over properties like viscosity, molecular weight, and stability during melt processing (controlling of molecular weight and melt strength) in nonwoven polyolefins. This ensures that the material remains consistent in thickness, texture, and durability during manufacturing.

[0010] However, transition metals like copper, which are often present in blue dyes, in particular in phthalocyanine-based dyes used for medical textiles, can quench or neutralize these free radicals due to their oxidizing nature. When copper(ll) ions are present, they can react with the free radicals generated by these viscosity modifier, effectively neutralizing them. This reaction disrupts and reduces the intended rheological control. For nonwoven medical textiles, this can lead to inconsistent fiber formation, potentially impacting fabric strength, uniformity, and durability.

[0011] In medical applications, textiles need to meet stringent standards for durability, consistency, and performance under various conditions. If the rheology modifier’s function is compromised by copper ions in the blue dye, the nonwoven fabric’s physical properties might be negatively affected, including:

[0012] (i) reduced fiber uniformity: This can lead to inconsistent thickness in the material, which may affect barrier properties — critical in medical applications to prevent the penetration of pathogens;

[0013] (ii) lower tensile strength: Compromised rheology modification can result in weaker bonding between fibers, making the fabric less durable under stress;

[0014] (iii) reduced color stability: If copper ions interact with the peroxides in the fabric, they may also influence dye stability and lead to color fading or uneven coloration over time, which is undesirable for medical applications where appearance is also crucial.

[0015] It is an object of the present invention to provide an improved process for the thermal degradation of a polymer composition comprising polypropylene or propylene copolymers in the presence of a free radical generator and copper(ll) ions. In particular, the thermally degraded polymer composition having a modified melt viscosity should be suitable for the manufacture of nonwoven medical textiles. It is a further object of the present invention to provide a polymer composition comprising polypropylene or propylene copolymers, a free radical generator, copper (II) ions, which is suitable for the manufacture of nonwoven medical textiles.

[0016] The object is achieved by a process for the thermal degradation of a polymer composition comprising polypropylene or propylene copolymers in the presence of a free radical generator and copper(ll) ions, characterized in that the thermal degradation is carried out in the presence of a chelating agent selected from the group consisting of substituted triazoles, substituted salicyloyl hydrazides and substituted salicyloyl amides. The further object is achieved by a polymer composition comprising polypropylene or propylene copolymers, a free radical generator, copper(ll) ions, and a chelating agent, wherein the chelating agent is selected from the group consisting of substituted triazoles, substituted salicyloyl hydrazides and substituted salicyloyl amides, and the use of the degraded polymer composition for the manufacture of nonwoven medical textiles by extrusion of the degraded polymer composition.

[0017] Suitable substituted triazoles are tolyltriazole, benzotriazole carboxylic acid, alkylbenzotriazole (e. g., methyl-, ethyl-, propyl-, butyl-, octyl-benzotriazoles) and cycloalkyl benzotriazole.

[0018] Preferred substituted aminotriazoles are the compounds of formulae (la) and (lb):

[0019]

[0020] (lb)

[0021] Suitable substituted salicyloyl hydrazides are compounds of formula (II)

[0022]

[0023] wherein Raand Rb each represent a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms or an aryl group having 6 to 18 carbon atoms, or they are connected to each other to form a ring to make a condensed ring having a total carbon atom number of 10 to 18;

[0024] R represents -NH–C(O)-(CH2)x-C(O)-NH- or -NH-(CH2)x-NH-;

[0025] n = 2;

[0026] x = 1 - 10.

[0027] A particular preferred salicyloyl hydrazide is a compound of formula (Ila)

[0028]

[0029] i.e., decamethylenedicarboxylic acid disalicyloyl hydrazide.

[0030] A particular preferred salicyloyl amide is the compound of formula (Illa)

[0031]

[0032] i.e., 3-salicylamido-1 H-1,2,4-triazole.

[0033] Suitable free radical generators are organic peroxides or substituted N-acyloxyamines.

[0034] Organic peroxides suitable as radical generators are for example:

[0035] Dicumyl Peroxide, DCP, such as Trigonox® 101;

[0036] Benzoyl Peroxide, BPO, such as Luperox® A98; 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane, such as Trigonox® 301;

[0037] 1,1-Di(tert-butylperoxy)cyclohexane, such as Trigonox® 505;

[0038] tert-Butyl peroxy-2-ethylhexyl carbonate, such as Luperox® A75.

[0039] Preferably, the free radical generator is a substituted N-acyloxyamine. Suitable substituted N-acyloxy-amines are, for example, compounds 1 to 34 as disclosed on pages 12 to 14 of W02006 / 027327.

[0040] More preferably, the free radical generator is a N-acyloxyamine of formula (IV)

[0041]

[0042] wherein

[0043] n is 1 or 2;

[0044] Rais acyl;

[0045] Ri', R2' and R3' are, independently of one another, hydrogen or methyl;

[0046] and, when n = 1 G3, represents C2-C10-alkylene, C2-hydroxyalkylene or C4-C32-acyloxy-C2-C10-alkylene, C4-C32-acyloxy-C1-C4-alkyl-C2-C10-alkylene or, when n = 2, represents the group (-CH2)2C(CH2-)2.

[0047] Still more preferably, the free radical generator is a N-acyloxyamine of formula (IVa)

[0048]

[0049] (IVa),

[0050] wherein

[0051] Rais acyl;

[0052] Ri', R2' and R3' are, independently of one another, hydrogen or methyl;

[0053] and ALK is C2-C10-alkylene or C3-C10-alkylene substituted by at least one substituent selected from the group consisting of hydroxy, C4-C32-acyloxy and C4-C32-acyloxy-C1-C4-alkyl.

[0054] Examples are compounds 24, 25, 26, 27, 28 and 30 as disclosed on pages 13 and 14 of W02006 / 027327, as follows:

[0055]

[0056] (24)

[0057]

[0058] Further suitable structures are structures 1-9 and 14-15, 17, 18 and 23 disclosed on pages 12 to 14 of W02006 / 027327, as follows: Ĩ7)

[0059]

[0060] (15)

[0061] (17)

[0062]

[0063]

[0064] (23)

[0065] Very particular preferred is the compound (30).

[0066] In general, the chelating agent is present in an amount of from 0.05 to 1.0 % by weight, preferably from 0.1 to 0.8 % by weight based on the total amount of the polymer composition.

[0067] In general, the copper(ll) ions are present in an amount of from 0.1 to 2.0 % by weight, preferably from 0.1 to 1.0 % by weight based on the total amount of the polymer composition.

[0068] The copper(ll) ions are preferably contained in the polymer composition in the form of a copper containing dye, preferably a copper phthalocyanine dye, more preferably a blue copper phthalocyanine dye.

[0069] In general, the radical generator is present in an amount of from 0.01 to 0.2 % by weight, preferably from 0.015 to 0.1 % by weight, based on the total amount of the polymer composition.

[0070] Further additives may be included. Examples are anti-agglomerants (e.g., glycerol mono stearate, calcium stearate), antiblocking agents, antifogging agents, matting agent (e.g. TiO2) and surface modifier (e.g., repellency hydrophobic agents, or hydrophilic agents). In general, the further additives are present in a total amount of from 0.1 % to 5 % by weight, preferably from 0.2 to 2 % by weight based on the total amount of the polymer composition.

[0071] The polypropylene or the propylene copolymers are processed in the presence of the additives including the radical generator, the copper(ll) ions, preferably in the form of a copper phthalocyanine dye, and the metal deactivator at an elevated temperature, in general in the range of from 160 to 280 °C. Preferred processing machines are single-screw extruders, contra-rotating and co-rotating twin-screw extruders, planetary-gear extruders, ring extruders or co-kneaders. It is also possible to use processing machines provided with at least one gas removal compartment to which a vacuum can be applied.

[0072] Suitable extruders and kneaders are described, for example, in Handbuch der Kunststoffex- tru-sion, Vol. 1 Grundlagen, Editors F. Hensen, W. Knappe, H. Potente, 1989, pp. 3-7, ISBN: 3-446-14339-4 (Vol. 2 Extrusionsanlagen 1986, ISBN 3-446-14329-7). For example, the screw length is 1 - 60 screw diameters, preferably 35-48 screw diameters. The rotational speed of the screw is preferably 10 - 600 rotations per minute (rpm), very particularly preferably 25 - 300 rpm.

[0073] The maximum throughput is dependent on the screw diameter, the rotational speed and the driving force. The process of the present invention can also be carried out at a level lower than maximum throughput by varying the parameters mentioned or employing weighing machines delivering dosage amounts.

[0074] If a plurality of components is added, these can be premixed or added individually. The polymers may need to be subjected to an elevated temperature for a sufficient period of time, so that the desired degradation occurs. The temperature is generally above the softening point of the polymers.

[0075] The process is preferably carried out by premixing the polypropylene or the propylene copolymers and the additives including the radical generator, the copper ions, preferably in the form of a copper phthalocyanine dye, and the chelating agent, or by directly introducing the additives including the radical generator, the copper(ll) ions, preferably in the form of a copper phthalocyanine dye, and the chelating agent into an extruder during processing of the polypropylene or the propylene copolymers, and melt compounding the mixture in the extruder, preferably into pellets. To facilitate the dosing of the different additives they are preferably in the form of concentrated masterbatches.

[0076] In a preferred embodiment of the process of the present invention, a temperature range from about 160 °C to 300 °C is employed. In a particularly preferred process variant, the temperature range from about 200 °C to 290 °C is employed. The period of time necessary for degradation can vary as a function of the temperature, the amount of material to be degraded and the type of, for example, extruder used. It is usually from about 10 seconds to 20 minutes, in particular from 20 seconds to 10 minutes. The invention is further illustrated by the following examples.

[0077] Examples

[0078] The following examples describe the use of different types of commercially available metal deactivators to improve the melt flow properties of polypropylene containing as radical generator an N-acyloxyamine or a peroxide for viscosity modification in the presence of radical scavenger copper(II) salt.

[0079] The following examples illustrate the significant improvement in Melt flow index and reduction in melt viscosity after reactive extrusion when the chelating compounds used according to the invention are employed.

[0080] The materials employed in these examples were as follows:

[0081] a) Polymer Component

[0082] • PP-1: The polymer used is a high molecular weight polypropylene homopolymer (PP):

[0083] HA10XT from Polychim Industriel. The polymer is in the grinded form.

[0084] b) Copper Salt

[0085] • MS-1: Copper(ll) stearate from Chemos GmbH & Co. KG, Germany.

[0086] c) Metal deactivators (chelating agents)

[0087] • MD-1: Irganox® MD1024 from BASF SE having the structure:

[0088]

[0089] • MD-2:: Hostanox® OSP 1 from Clariant having the structure: • MD-3: ADK STAB® CDA 1 from Adeka Polymer Additives Europe having the structure:

[0090]

[0091] • MD-4: ADK STAB® CDA 6 from Adeka Polymer Additives Europe having the structure:

[0092]

[0093] d) Radical generator

[0094] • RG-1: N-acyloxyamine compound (30)

[0095] • RG-2: Dicumyl peroxide, Trigonox® 101 from Nouryon HQ

[0096] The above products and PP polymers have been used in powder form and compounded before single screw extrusion. Below a description of the compounding preparation with the relative amount of the different products.

[0097] Production of the different compounding formulations: Unless stated otherwise, polypropylene, the metal salt, the metal deactivators and the radical generator were mixed using a high speed mixer (3000rpm for 30’) in the amounts as indicated in Table 1 and then melt compounded into pellets on a 25 mm co-rotating twin-screw extruder Ber-storff ZE25A x 47D, operating at 160 revolutions per minute (rpm) and at set temperatures of 200°C, in order to achieve good homogenization of the different raw materials. All formulations also contain 0.1% of Irganox® B215 and 300 ppm of Ca(stearate)2.

[0098] TABLE 1: Composition of the compounded formulations in % by weight

[0099] Ref. 1 Ref. 2 Ref. 3 Ref. 4 Ref. 5 Ref. 6 Ref. 7 Ref. 8 Ref. 9 PP-1 99.67% 99.83% 99.63% 99.83% 99.63% 99.48% 99.33% 99.48% 99.33%

[0100] Irganox 0.1% 0.1% 0.1% 0.1% 0.1% 0.1% 0.1% 0.1% 0.1% B215

[0101] Ca(ste- 0.03% 0.03% 0.03% 0.03% 0.03% 0.03% 0.03% 0.03% 0.03% arate)2

[0102] MS-1 0.2% 0.2% 0.2% 0.2% 0.2% 0.2% 0.2% RG-1 0.04% 0.04% 0.04% 0.04% 0.04% 0.04% RG-2 0.04% 0.04%

[0103] MD-1 0.15% 0.3%

[0104] MD-2 0.15% 0.3% MD-3

[0105] MD-4

[0106]

[0107] Ref. 10 Ref. 11 Ref. 12 Ref. 13 Ref. 14 Inv. 15 Inv. 16 Inv. 17 Inv. 18 PP-1 99.48% 99.33% 99.48% 99.33% 99.48% 99.33% 99.48% 99.33% 99.48% Irganox 0.1% 0.1% 0.1% 0.1% 0.1% 0.1% 0.1% 0.1% 0.1% B215

[0108] Ca(stea- 0.03% 0.03% 0.03% 0.03% 0.03% 0.03% 0.03% 0.03% 0.03% rate)2

[0109] MS-1 0.2% 0.2% 0.2% 0.2% 0.2% 0.2% 0.2% 0.2% 0.2% RG-1 0.04% 0.04% 0.04% 0.04%

[0110] RG-2 0.04% 0.04% 0.04% 0.04% 0.4% MD-1 0.15% 0.3%

[0111] MD-2 0.15% 0.3%

[0112] MD-3 0.15% 0.3% 0.15% MD-4 0.15% 0.3%

[0113]

[0114] Inv. 19 Inv. 20 Inv. 21

[0115] pp-1 99.33% 99.48% 99.33%

[0116] Irganox 0.1% 0.1% 0.1%

[0117] B215

[0118] Ca(stea- 0.03% 0.03% 0.03%

[0119] rate)2

[0120] MS-1 0.2% 0.2% 0.2%

[0121] RG-1

[0122] RG-2 0.04% 0.04% 0.04%

[0123] MD-1

[0124] MD-2

[0125] MD-3 0.3%

[0126] MD-4 0.15% 0.3%

[0127]

[0128] Performance of the formulations:

[0129] Compounded fully formulated granules were melt processed through a 1.5 mm die on a 20 mm single screw extrusion, Extrusionmeter 20D at set temperatures of 295°C for around 20 minutes and then taken for compression molding at 200°C for 3 minutes to produce A5 size 1.0 mm thick plaquette.

[0130] Melt flow index (MFI, g / 10min.) of the plaquette were measured at 230°C and 190°C according to ASTM D1238. If not stated differently a 2 mm capillary is used. The results are summarized in Table 2 below.

[0131] Formulation viscosities at 10 rad / sec, 100 rad / sec at 190°C were also measured using a rotational rheometer ARES-G2 on a 1 mm thick A5 plate after compression molding of the extruded material. The results are summarized in Table 3 below.

[0132] TABLE 2: Melt flow Index of the formulations at 230°C and 190°C

[0133] Ref.1 Ref.2 Ref.3 Ref.4 Ref.5 Ref.6 Ref.7 Ref.8 MFI 34 600* 61 65 59 58 35 99 (230°C / 2.16

[0134] Kg)

[0135]

[0136] MFI 15 307* 28 32 25 24 16 39 (190°C / 2.16

[0137] Kg)

[0138] Ref.9 Ref.1 Ref.1 Ref.1 Ref.13 lnv.14 lnv.15 lnv.16

[0139] 0 1 2

[0140] MFI 67 22 70 59 75 446* 814* 162* (230°C / 2.16

[0141] Kg)

[0142] MFI 32 12 46 24 33 181* 653* 72 (190°C / 2.16

[0143] Kg)

[0144]

[0145] lnv.17 lnv.18 lnv.19 lnv.20 lnv.21

[0146] MFI 88 529* 778* 224* 121

[0147] (230°C / 2.16

[0148] Kg)

[0149] MFI 39 268* 384* 93 50

[0150] (190°C / 2.16

[0151] Kg)

[0152]

[0153] ★Measured with 1mm capillary

[0154] TABLE 3: Viscosities of the different formulations at 10 rad / sec and 100 rad / sec measured at 190°C

[0155] Ref.1 Ref.2 Ref.3 Ref.4 Ref.5 Ref.6 Ref.7 Ref.8 10 rad / sec 460 25 268 268 329 267 400 146

[0156] 100 rad / sec 222 23 154 157 182 165 206 108

[0157]

[0158] Ref.9 Ref.1 Ref.1 Ref.1 Ref.13 lnv.14 lnv.15 lnv.16

[0159] 0 1 2

[0160] 10 rad / sec 242 487 188 246 213 28 20 76

[0161] 100 rad / sec 158 234 127 152 142 26 18 63

[0162]

[0163] Inv.17 Inv.18 lnv.19 Inv.20 Inv.21

[0164] 10 rad / sec 135 21 13 48 120

[0165] 100 rad / sec 97 20 13 42 90

[0166]

[0167] The data from T able 2 clearly show the effect of using the inventive chelating additives in restoring the MFI level in the presence of Cu2+both in case of using a well known peroxide radical generator like Trigonox 101 or in the case of the N-acyloxyamine compound (30).

[0168] From the different metal deactivator additives the ADK STAB® CDA 1 (MD-3) is the more active one (lnv.14, Inv. 15 and Inv. 18 or lnv.19). The data show even a sort of boosting effect when ADK STAB® CDA 1 is used at concentration in the range of 0.15-0.3%.

[0169] The data from Table 3 show a similar trend as the data from Table 2. Also in this case the use of the inventive metal deactivators in the presence of copper(ll) ions and radical generators is able to restore performance by enhancing the activity of the N-acyloxyamine or peroxide by producing formulations which have lower viscosities similar to if not even lower than the viscosities of the formulations of Ref. 2 and Ref. 4.

[0170] Out of the different metal deactivators the best performance are obtained with ADK STAB® CDA 1 both at 0.15 and 0.3% while also an interesting effect is observed for ADK STAB® CDA 6 but in this case especially at 0.15%. These metal complexing agents prove to be much more effective in restoring controlled radical degradation of PP with N-acyloxyamine or peroxide if compared with other state of the art metal deactivator like Irganox® MD1024 or Hostanox® OSP 1.

Claims

CLAIMS1. A process for the thermal degradation of a polymer composition comprising polypropylene or propylene copolymers in the presence of a free radical generator and copper(ll) ions, characterized in that the thermal degradation is carried out in the presence of a chelating agent selected from the group consisting of substituted triazoles, substituted salicyloyl hydrazides and substituted salicyloyl amides.

2. The process according to claim 1, wherein the free radical generator is an organic peroxide or a N-acyloxyamine.

3. The process according to claim 2, wherein the free radical generator is a N-acyloxyamine of formula (III)whereinn is 1 or 2;Rais acyl;Ri', R2' and R3' are, independently of one another, hydrogen or methyl;and, when n = 1 G3represents C2-C10-alkylene, C2-hydroxyalkylene or C4-C32-acyloxy-C2-C10-alkylene, C4-C32-acyloxy-C1-C4-alkyl-C2-C10-alkylene or, when n = 2, represents the group (-CH2)2C(CH2-)2.

4. The process according to any one of claims 1 to 3, wherein the copper(ll) ions are contained in the form of a copper containing dye, preferably a copper phthalocyanine dye, more preferably blue copper phthalocyanine dye.

5. The process according to any one of claims 1 to 4, wherein the chelating agent is selected from the group consisting of 3-salicylamido-1H-1,2,4-triazole and decamethylenedicarboxylic acid disalicyloyl hydrazide.

6. The process according to any one of claims 1 to 5, wherein the chelating agent is present in an amount of from 0.05 to 1.0 % by weight, based on the total amount of the polymer composition.

7. The process according to any one of claims 1 to 6, wherein the copper(ll) ions are present in an amount of from 0.1 to 2.0 % by weight, based on the total amount of the polymer composition.

8. The process according to any one of claims 1 to 7, wherein the radical generator is present in an amount of from 0.01 to 0.2 % by weight, based on the total amount of the polymer composition.

9. The process according to any one of claims 1 to 8, wherein the process is carried out by premixing the polypropylene or the propylene copolymers and additives including the radical generator, the copper(ll) ions and the chelating agent, or by directly introducing additives including the radical generator, the copper(ll) ions and the chelating agent into an extruder during processing of the polypropylene or the propylene copolymers, and melt compounding the mixture in the extruder.

10. A polymer composition comprising polypropylene or propylene copolymers, a free radical generator, copper(ll) ions, and a chelating agent, wherein the chelating agent is selected from the group consisting of substituted triazoles, substituted salicyloyl hydrazides and substituted salicyloyl amides.

11. The polymer composition according to claim 10, wherein the free radical generator is an organic peroxide or N-acyloxyamine.

12. The polymer composition according to any one of claims 10 or 11, wherein the free radical generator is a N-acyloxyamine of formula (IVa)(IVa)whereinRais acyl;Ri', R2' and R3' are, independently of one another, hydrogen or methyl; andALK is C2-C10-alkylene or C3-C10alkylene substituted by at least one substituent selected from the group consisting of hydroxy, C4-C32-acyloxy and C4-C32-acyloxy-C1-C4alkyl.

13. The polymer composition according to claim 11 or 12, wherein the copper(ll) ions are contained in the form of a copper containing dye, preferably a copper phthalocyanine dye, more preferably blue copper phthalocyanine dye.

14. The use of substituted triazoles, substituted salicyloyl hydrazides or substituted salicyloyl amides as chelating agent in a process for the thermal degradation of a polymer composition comprising polypropylene or propylene copolymers in the presence of a free radical generator and copper(ll) ions.

15. The use of the polymer composition of to any one of claims 10 to 13 for the manufacture of a degraded polymer composition for the manufacture of nonwoven medical textiles by extrusion of the degraded polymer composition.

Images