PROCESS FOR ENHANCING THE MELT STRENGTH OF PROPYLENE-BASED POLYMER COMPOSITIONS

Abstract

Disclosed is a process for preparation of a propylene-based polymer composition involving the steps of: (a) mixing a propylene-based polymer and a peroxydicarbonate in a mixing device, wherein the mixing takes place at a temperature of 30 C., wherein the peroxydicarbonate is introduced into the mixing process in a dry form; (b) keeping the mixed composition at a temperature of 30 C.; (c) feeding the mixed composition into a melt extruder; (d) homogenizing the mixed composition at a temperature where the propylene-based polymer is in solid state during an average residence time of 6.0 and 30.0 seconds; (e) further homogenizing the mixed composition at a temperature at which the propylene-based polymer is in the molten state; and (f) extruding the homogenized material from a die outlet of the melt extruder followed by cooling and solidification; wherein the steps (a) through (f) are conducted in that order.

Claims

1. Process for preparation of a propylene-based polymer composition comprising the steps of: (a) mixing a propylene-based polymer and a peroxydicarbonate in a mixing device, wherein the mixing takes place at a temperature of 30 C., wherein the peroxydicarbonate is introduced into the mixing process in a dry form, thereby obtaining a mixed composition; (b) keeping the mixed composition obtained in (a) at a temperature of 30 C.; (c) feeding the mixed composition obtained in (a) into a melt extruder via a feed inlet; (d) homogenizing the mixed composition fed into the melt extruder at a temperature where the propylene-based polymer is in solid state in a first section of the melt extruder during an average residence time of 6.0 and 30.0 seconds; (e) further homogenizing the mixed composition fed into the melt extruder in a subsequent second section of the melt extruder at a temperature at which the propylene-based polymer is in the molten state, thereby obtaining a homogenized material; and (f) extruding the homogenized material from a die outlet of the melt extruder followed by cooling and solidification; wherein the steps (a) through (f) are conducted in that order.

2. Process according to claim 1 wherein the propylene-based polymer is fed to the mixing device in the form of solid particles having an average particle size of 3000 m as determined as D.sub.50 according to ISO 9276-2 (2014).

3. Process according to claim 1 wherein a ratio of an average particle size of the propylene-based polymer and an average particle size of the peroxydicarbonate that are introduced in step (a) is 0.5 and 1.5, wherein the average particle size of the propylene polymer and the average particle size of the peroxydicarbonate are determined as D.sub.50 according to ISO 9276-2 (2014).

4. Process according to claim 1 wherein step (a) comprises 0.05 wt % and 3.00 wt % of the peroxydicarbonate, with regard to the weight of the propylene-based polymer.

5. Process according to claim 1 wherein the peroxydicarbonate is selected from diisopropyl peroxydicarbonate, dibutyl peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate, di(4-tert-butyl cyclohexyl) peroxydicarbonate, ditetradecyl peroxydicarbonate or dihexadecyl peroxydicarbonate.

6. Process according to claim 1 wherein the melt extruder is a twin-screw melt extruder.

7. Process according to claim 6 wherein the twin-screw melt extruder has a length: diameter ratio of 36, wherein the length is the length of the barrel of the extruder and the diameter is the outermost diameter of an individual extruder screw.

8. Process according to claim 6 wherein the melt extruder is a co-rotating twin-screw extruder.

9. Process according to claim 1 wherein the step (d) takes place at an extruder barrel temperature of 75 C.

10. Propylene-based polymer composition obtained via the process according to claim 1.

11. (canceled)

12. Foamed object produced using a propylene-based polymer composition obtained via the process according to claim 1.

Description

EXAMPLES

[0097]

TABLE-US-00001 TABLE I Materials used PP1 Propylene-based polymer of grade SABIC PP571P, obtainable from SABIC, a homo-polypropylene having a melt mass-flow rate as determined in accordance with ISO 1133-1 (2011), at a temperature of 230 C. and a load of 2.16 kg, of 5.70 g/10 min, and having an average particle size as determined as D.sub.50 according to ISO 9276-2 (2014) of 1200 m. PP2 Propylene-based polymer of grade SABIC PP527K, obtainable from SABIC, a homo-polypropylene having a melt mass-flow rate as determined in accordance with ISO 1133-1 (2011), at a temperature of 230 C. and a load of 2.16 kg, of 3.00 g/10 min, and having an average particle size as determined as D.sub.50 according to ISO 9276-2 (2014) of 1200 m. Peroxydicarbonate Dihexadecyl peroxydicarbonate of grade Perkadox 24L, obtainable from Akzo Nobel, having an average particle size of 1200 m (CAS registry nr. 26322- 14-5) Phenolic stabiliser Pentaerythritol tetrakis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate of grade Irganox 1010, obtainable from BASF (CAS registry nr 6683-19-8) Phosphite stabiliser Tris(2,4-di-tert-butylphenyl) phosphite of grade Irgafos 168, obtainable from BASF (CAS registry nr. 31570-04-4)

[0098] A. Preparation of Powder Mixture

[0099] 100 parts by weight of a propylene-based polymer of was mixed in the solid phase at room temperature (23 C.) under nitrogen atmosphere for 30 m. in a Nauta single-screw conical mixer with a quantity of peroxydicarbonate and a quantity of stabiliser to obtain a homogeneously distributed powder mixture. The material compositions used for the preparation of the powder mixtures are presented in Table II.

TABLE-US-00002 TABLE II Phenolic Phosphite Example PP1 PP2 Peroxydicarbonate stabiliser stabiliser I 100.0 2.0 0.15 0.05 II (C) 100.0 0 0.15 0.05 III (C) 100.0 0 0.15 0.05

[0100] The numbers in Table II are parts by weight. Examples II and III are presented for comparative purposes.

[0101] B. Reactive Extrusion

[0102] The obtained powder mixture of example I from step A was introduced to a co-rotating twin-screw extruder having a screw diameter of 112 mm. The extruder had a length to diameter ratio (L/D ratio) of 42. The extruder was operated using temperature profiles as listed in Table III:

TABLE-US-00003 TABLE III extruder temperature profiles Temperature Zone Zone length (L/D) Profile I Profile II 1 4 40 40 2 4 150 130 3 5 150 170 4 3 160 180 5 4 225 225 6 4 225 225 7 4 225 225 8 3 230 230 9 3 230 230 10 4 230 230 11 4 230 230

[0103] The zones as presented in the above table represent subsequent zones along the length of the extruder. The powder mixture was introduced in zone 1, and removed from the extruder via a die positioned subsequent to zone 11. The temperatures in table Ill are set zone temperatures in C.

[0104] During the reactive extrusion process in which the extruder was operated using set temperatures according to profile I, the extruder was operated with a screw speed of 130 RPM and a throughput of 650 kg/h. The melt temperature at the die was 265 C., and the melt pressure at the die was 65 bar. The temperature conditions were set in such way that the powder mixture was kept at such temperatures that the propylene-based polymer was in the solid state in the first section of the extruder. As such, this section acted as solid mixing section. The reaction between the peroxide and the propylene-based polymer takes place in this section. The average residence time in this section was 7.0 s. From the extruder, a modified polypropylene (IA) was obtained by cooling and pelletizing the extruded product.

[0105] During the reactive extrusion process in which the extruder was operated using set temperatures according to profile II, the extruder was operated with a screw speed of 120 RPM and a throughput of 575 kg/h. The melt temperature at the die was 266 C., and the melt pressure at the die was 39 bar. The residence time in the solid state was 5.0 s. From the extruder, a modified polypropylene (IB) was obtained by cooling and pelletizing the extruded product.

[0106] C. Foaming

[0107] Foam structures were made using the modified polypropylenes (IA) and (IB) of step B and the reference polypropylenes (II) and (III). The polypropylenes were fed together with 1.0 wt % with regard to the weight of the polypropylene of Schulman PHBFPE50T, a 50% wt masterbatch of talc in LDPE and 1.0 wt % of glycerol monostearate (CAS registry nr. 31566-31-1) to a co-rotating ZSK 30 twin screw melt extruder having an L/D ratio of 40, equipped with a Aixfotec melt cooler and an annular foam die. The extruder was operated at a throughput of 10 kg/h, and the die pressure was maintained at 30 bar. In the extruder, the polypropylene was heated to 260 C. at which the material was in a molten condition. A quantity of isobutane as blowing agent to produce the foam was introduced into the melt in the extruder via an inlet positioned at zone 7 of the extruder. The quantity of isobutane used was 2.3 wt % with regard to the weight of the polypropylene. By further melt mixing of the material composition comprising the molten polypropylene and the blowing agent, a molten foamed material was obtained having a uniform foam cell distribution. In the Aixfotec melt cooler, the melt was cooled to temperatures of 175 C. in the area before the die. The molten foamed material forced out of the extruder via the annular die and cooled to form a solidified foam structures. The temperature in the area of the die was reduced stepwise from 175 C. down to 160 C. in steps of 2-3 C. At each temperature, foamed material was collected from which the density and the closed cell content were measured in order to determine the foamability window.

[0108] D. Determination of Properties

[0109] Of the modified polypropylene (IA) and (IB) of step B and the reference polypropylenes (II) and (III), the melt mass-flow rate, the strain hardening and the viscosity ratio was determined. Of the foams of polypropylenes (IA), (II) and (III), the foamability window, the foam density of foams prepared at 162 C. and the quantity of closed cells of foams prepared at 162 C. was determined. The results are presented in Table IV.

TABLE-US-00004 TABLE IV Example IA IB II (C) III (C) FW 13 CC 99.7 <60 <75 FD 130 >400 >350 MFR.sub.2.16 2.00 2.50.sup.A) 6.70 3.00 SH.sub.1.0 10.2 1.0 1.0 VR.sub.0.1 0.53 0.90 0.90 VR.sub.1 0.24 0.64 0.60 VR.sub.10 0.09 0.31 0.23 VR.sub.100 0.03 0.10 0.08 .sub.0 21260 5746 .sup.A)Due to significant fluctuations in the melt mass-flow rate of the material IB, it was not possible to produce foams from this material.

[0110] In which: [0111] FW is the foamability window ( C.) as determined via the method described above; [0112] CC is fraction of closed cells as determined by the above described water absorption method of the foam as produced at 162 C. (%); [0113] FD is the density of the foam as produced at 162 C., determined as the apparent overall density according to ISO 845 (2006) (kg/m3); [0114] MFR2.16 is the melt mass-flow rate as determined in accordance with ISO 1133-1 (2011), at a temperature of 230 C. and a load of 2.16 kg (g/10 min); [0115] SH.sub.1.0 is the strain hardening coefficient as determined according to the method described above (). For determining the strain hardening coefficient, an ARES G2 rheometer equipped with an EVF (extensional viscosity fixture) was used at 170 C. [0116] VR is the ratio of the complex viscosity * at given frequency : complex viscosity at a frequency of 0.01 rad/s (.sub.0.01), wherein the complex viscosity is determined via DMS as described above (). In the table, VR.sub.0.1 is the ratio of the complex viscosity at 0.1 rad/s (*0.1) : .sub.0.01; VR.sub.1 is the ratio of *.sub.1: *.sub.0.01; VR.sub.10 is the ratio of *.sub.10: .sub.0.01; VR.sub.100 is the ratio of *.sub.100: .sub.0.01; [0117] .sub.0 is the zero shear viscosity as determined using DMS (Pa.Math.s) where viscosity data are fit using the Cross-model.

[0118] For determining the DMS spectrum, an ARES G2 rheometer was used at 200 C. measuring at frequencies of 0.01 rad/s to 100 rad/s, at a linear viscoelastic strain of 5%, using plates of 0.5 mm thickness produced according to ISO 1872-2 (2007).

[0119] The melt mass-flow rate of the peroxide-modified polypropylenes obtained from the reactive extrusion step B and the reference polypropylenes was determined according to ISO 1133-1 (2011). ISO 1133-1 (2011) relates to determination of the melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics. The melt mass-flow rate was determined at 230 C. at a load of 2.16 kg.

[0120] From these results, it can be understood that a process according to the invention leads to an improved melt strength as presented by the stain hardening coefficient, the zero shear viscosity and the ratio of complex viscosity at given frequency : complex viscosity at a low frequency of 0.01 rad/s VR.sub.0.1, VR.sub.1, VR.sub.10, and VR.sub.100.

[0121] Furthermore, a process according to the invention leads to an increased closed cell content of the foams. Also, a process according to the invention leads to an improved foamabiltiy window.