Propylene copolymer compositions suitable for foaming

Abstract

The disclosure relates to a method for producing a propylene copolymer, comprising extruding a molten propylene copolymer and a composition essentially comprising at least one peroxydicarbonate and at least one organic peroxide. Extruding is performed by extruding the propylene copolymer, adding the composition to the propylene copolymer, and melt extruding the propylene copolymer in the presence of the composition.

Claims

1. A method for producing a propylene copolymer, comprising extruding a molten propylene copolymer and a composition essentially comprising at least one peroxydicarbonate and at least one other organic peroxide, wherein extruding is performed by extruding the propylene copolymer, adding the composition to the propylene copolymer, and melt extruding the propylene copolymer in the presence of the composition, wherein the propylene copolymer melt extruded in the presence of the composition presents a melt flow rate (MFR) higher than the MFR presented by the propylene copolymer before the extrusion, and wherein the propylene copolymer melt extruded in the presence of the composition presents an elasticity ratio (ER) higher than the ER presented by the propylene copolymer before the extrusion.

2. The method of claim 1, wherein adding the composition to the propylene copolymer is performed after the extrusion of the propylene copolymer.

3. The method of claim 1, wherein adding the composition to the propylene copolymer is performed before or during the extrusion of the propylene copolymer.

4. The method of claim 1, wherein the at least one other organic peroxide has a half life in chlorobenzene of one hour or less at a temperature between 125 C. and 155 C.

5. The method of claim 1, wherein the at least one other organic peroxide contains at least 5% by weight of active oxygen with respect to the total weight of organic peroxide(s).

6. The method of claim 1, wherein the at least one other organic peroxide comprises at least one dialkyl peroxide.

7. The method of claim 6, wherein at least one other organic peroxide is selected from the group comprising 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, di(tert-butyl) peroxide, di(tert-amyl) peroxide; tert-butyl cumyl peroxide, di(tert-butylperoxy-isopropyl)-benzene, di cumyl peroxide, 3,6,9-tri ethyl-3,6,9-trim ethyl-1,4,7-triperoxonane, 3,6,9-trim ethyl-3,6,9-tris(ethyl and/or propyl)-1,4,7-triperoxonane, 3,3,5,7,7-pentamethyl-1,2,4-trioxepane, substituted 1,2,4-trioxacycloheptanes and combinations thereof.

8. The method of claim 7, wherein at least one other organic peroxide is selected from the group comprising 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di(tert-butyl) peroxide, 3,6,9-tri ethyl-3,6,9-trimethyl-1,4,7-triperoxonane, 3,6,9-tri methyl-3,6,9-tris(ethyl and/or propyl)-1,4,7-triperoxonane and combinations thereof.

9. The method of claim 1, wherein the at least one peroxydicarbonate has a half life in chlorobenzene of one hour or less at a temperature between 55 C. and 75 C.

10. The method of claim 1, wherein the at least one peroxydicarbonate contains up to 11% by weight of active oxygen with respect to the total weight of peroxydicarbonate(s).

11. The method of claim 1, wherein the at least one peroxydicarbonate has the formula R1-OC(O)OOC(O)OR2, wherein R1 and R2 are independently selected from the group comprising CH.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7, C.sub.4H.sub.9, C.sub.5H.sub.11, C.sub.6H.sub.13, C.sub.7H.sub.15, C.sub.8H.sub.17, C.sub.10H.sub.21, C.sub.12H.sub.25, C.sub.14H.sub.29, Cl.sub.8H.sub.37, C.sub.2H.sub.5CH(CH.sub.3), c-C.sub.6H.sub.11CH.sub.2, CH.sub.3CH(OCH.sub.3), C.sub.6H.sub.5OCH.sub.2CH.sub.2, C.sub.6H.sub.5CH.sub.2, ZC.sub.8H.sub.17CHCH(CH.sub.2).sub.8, (CH.sub.3).sub.2CHCH.sub.2CH(CH.sub.3), [C.sub.2H.sub.5OC(O)].sub.2CH(CH.sub.3), 2-oxo-1,3-dioxolan-4-CH.sub.2, i-C.sub.4H.sub.9, H.sub.2CCHC(O)OCH.sub.2CH.sub.2, C.sub.4H.sub.9CH(C.sub.2H.sub.5)CH.sub.2, H.sub.2CCHCH.sub.2, H.sub.2CC(CH.sub.3)CH.sub.2, c-C.sub.6H.sub.11, 4-[C.sub.6H.sub.5NN]C.sub.6H.sub.4CH.sub.2, C.sub.16H.sub.33, CH.sub.3OCH.sub.2CH.sub.2, H.sub.2CC(CH.sub.3), C.sub.2H.sub.5OCH.sub.2CH.sub.2, H.sub.2CCH, i-C.sub.3H.sub.7, c-C.sub.12H.sub.23, CH.sub.3OCH.sub.2CH.sub.2, C.sub.6H.sub.13CH(CH.sub.3), (CH.sub.3)C(CH.sub.3).sub.2CH.sub.2CH.sub.2, C.sub.3H.sub.7OCH.sub.2CH.sub.2, CH.sub.3OCH.sub.2CH(CH.sub.3), 2-i-C.sub.3H.sub.7-5-CH3-c-C.sub.6H.sub.9, C.sub.4H.sub.9OCH.sub.2CH.sub.2, t-C.sub.4H.sub.9, (CH.sub.3).sub.3CCH.sub.2 and combinations thereof, wherein i=iso, t=tertiary, Z=cis, and c=cyclic.

12. The method of claim 11, wherein the at least one peroxydicarbonate is selected from the group comprising dicetyl peroxydicarbonate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, dimyristyl peroxydicarbonate and combinations thereof.

13. The method of claim 12, wherein the at least one peroxydicarbonate is dicetyl peroxydicarbonate.

14. The method of claim 1, wherein the composition comprises 20% to 99% by weight of the at least one other organic peroxide and 0.1% to 80% by weight of the at least one peroxydicarbonate.

15. The method of claim 1, the method further comprising feeding the copolymer and the composition so that the amount of the at least one organic peroxide feed ranges from 50 ppm to 2000 ppm with respect to the amount of the copolymer feed.

16. The method of claim 1, the method further comprising feeding the copolymer and the composition so that the amount of the peroxydicarbonate feed ranges from 500 ppm to 50000 ppm with respect to the amount of the copolymer feed.

17. The method of claim 1, wherein extruding is performed at an extrusion temperature of from 150 C. to 300 C.

18. The method of claim 1, wherein the propylene copolymer is selected from the group comprising random propylene copolymers, impact propylene copolymers, terpolymers of propylene and combinations thereof.

19. The method of claim 18, wherein the propylene copolymer is an impact propylene copolymer.

20. A propylene copolymer composition obtained by the method of claim 1.

21. A branched propylene copolymer obtained by the method of claim 1, wherein the branched propylene copolymer has a MFR of at least 20.0 g/10 min, and an ER of at least 1.2 dyn/cm.sup.2 and a YI lower than 6.5.

22. The branched propylene copolymer of claim 21, wherein the ER is greater than 2 dyn/cm.sup.2.

Description

DESCRIPTION OF EMBODIMENTS

(1) The following examples of methods for producing a propylene copolymer are given for illustrating but not limiting purposes.

(2) The examples show the improved combination of properties of propylene copolymers produced by methods according to embodiments of the present disclosure.

(3) The examples also show the improved combination of properties of propylene copolymers produced by methods according to embodiments of the present disclosure compared to conventional methods using only organic peroxide and to conventional methods using only peroxydicarbonate. The examples show high MFR and ER and low YI in propylene copolymers produced in accordance with embodiments of the method of the present disclosure.

(4) In the following examples, compositions will be described for producing a propylene impact copolymer under extrusion conditions. However, different propylene copolymers from these exemplary copolymers may be produced by the method of the present disclosure.

(5) Also, compositions will be described comprising one organic peroxide and one peroxydicarbonate. However, a plurality of organic peroxides and/or a plurality of peroxydicarbonates may be used in accordance with one or more embodiments of the method of the present disclosure. Further, also stabilizers and/or additional additives may be used in accordance with one or more embodiments of the method of the present disclosure.

(6) Each exemplary composition at a predetermined concentration was fed with exemplary copolymer pellets through a hopper directly into an extruder comprising a vent port. However, as shown in the examples, venting is optional and is not essential to obtain the improved combination of propylene copolymers properties. Together with the composition and the propylene copolymers pellets, any stabilizers and/or additional additives may be also fed through the hopper into the extruder.

(7) The exemplary propylene copolymer and the composition were extruded in the extruder at an extrusion temperature which was varied along the length of the extruder. In particular, the extrusion temperature was adjusted to 180 C. at the extruder feed zone and increased up to 200 C. at the extruder die zone.

(8) The propylene copolymer and the composition were mixed by the screw of the extruder. During the transportation of the propylene copolymer through the extruder, propylene copolymer degradation occurred. Volatile compounds were removed during the extrusion by venting the extruder applying under-atmospheric pressure.

(9) As shown in the following, the method according to embodiments of the present disclosure resulted in final propylene copolymer pellets having high MFR and ER and low YI.

(10) The following methods were used to determine the properties reported in the examples and in any of the embodiments of the present disclosure making reference to these properties.

(11) Melt Flow Rate (MFR) is the MFR measured according to ISO 1133 with a load of 2.16 kg at 230 C.

(12) The C.sub.2 content is measured based on Fourier Transform Infrared Spectroscopy (FTIR) calibrated with 13C-NMR, using Bruker Tensor 27 instrument with Bruker OPUS software.

(13) Color formation during the production of the propylene copolymer is determined by the Yellowness Index (YI) of the propylene copolymer pellets. To determine the Yellowness Index, a color determination according to ASTM D6290 with a Group I Spectrophotometer, the LabScan XE from Hunterlab, with a D65/10 arrangement of Illuminant/Observer is performed. A sample cup is filled to the top with pellets, placed on the sensor port and covered with an opaque and light excluding cover. The measurement delivers the Tristimulus values X, Y and Z. The calculation of the Yellowness Index is done according to ASTM E313 by the following equation: YI=100 (Cx XCz Z)/Y, where the coefficients Cx and Cz are selected according to the setting of Illuminant and Observer used for the measurement of the Tristimulus values. For Illuminant D65 and Observer 10, Cx is 1.3013 and Cz is 1.1498.

(14) The Polydispersity Index (PI) and the Elasticity Ratio (ER) are determined by rheology using a dynamic oscillatory shear test, e.g. Dynamic Oscillatory Rate Sweep (DORS). A sample in the form of a compression molded disk is loaded between a parallel plate-to-plate geometry. The measurements are performed at 210 C. in a frequency range between 0.1 rad/s and 400 rad/s. The Polydispersity Index (PI), which is a measure of the molecular weight distribution, is calculated according the following equation: PI=10.sup.5 Pa/Gc, where Gc is the cross over modulus obtained from the dynamic oscillatory shear measurement (where dynamic storage modulus G=dynamic loss modulus G at the crossover frequency). The ER is defined as 1.781*10.sup.3*G (at G=500 Pa).

(15) Tensile modulus is measured according to ISO527-2 (cross head speed=50 mm/min, 23 C.) using an injection molded test specimen as described in ISO 1873-2.

(16) The melting temperature (T.sub.m) and the crystallization temperature (T.sub.c) are determined via differential scanning calorimetry (DSC): heating and cooling rate is 10 C./min, the temperature ramp from 25 C. to 200 C., 200 C. to 25 C. and 25 C. to 200 C. including 5 min isotheral annealing at 200 C. and 25 C. The thermal properties are read out from the thermogram obtained from the last temperature ramp.

(17) Charpy notched impact strength is determined according to ISO 179/1 eA at 23 C., 0 C., 20 C., 30 C. by using an injection molded test specimen as described in ISO 1873-2.

Examples 1-4

(18) Examples 1-4 show the improved combination of properties of a propylene copolymer produced by a method according to embodiments of the present disclosure compared to a corresponding propylene copolymer produced by a conventional method using no peroxides at all, a propylene copolymer produced by a conventional method using only organic peroxide and to a conventional method using only peroxydicarbonate.

(19) The polymer used in Examples 1-4 was ICP-1, a commercial heterophasic propylene copolymer produced in a Novolen plant in pellet form with a MFR of 9.2 g/10 min, containing an additive package consisting of 450 ppm tris(2,4-di-tert-butylphenyl)phosphite, 450 ppm of pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 800 ppm calcium stearate and 3500 ppm of talc.

(20) Example 1 is a control example, in which the polypropylene was not treated with any composition.

(21) The organic peroxide used in comparative Example 2 and in Example 4 was 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane. 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane contains 11.02% by weight of active oxygen with respect to the total weight of organic peroxide and has a half life in chlorobenzene of 1 hour at a temperature of 134 C. as described in the brochure of Akzo Nobel Initiators for High Polymer, 2161 BTB Communications, Issue June 2006. For the preparation of comparative Example 2 and Example 4, the commercially available 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane grade Luperox 101PP20 from Arkema, which contains 20% of the 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane on a PP carrier resin, was used.

(22) The peroxydicarbonate used in comparative Example 3 and in Example 4 was dicetyl peroxydicarbonate. Dicetyl peroxydicarbonate contains 2.80% by weight of active oxygen with respect to the total weight of peroxydicarbonate and has a half life in chlorobenzene of 1 hour at a temperature of 65 C. as described in the brochure of Akzo Nobel Initiators for High Polymer, 2161BTB Communications, Issue June 2006. For the preparation of comparative Example 3 and Example 4 the commercially available dicetyl peroxydicarbonate grade Perkadox 24L from Akzo Nobel having a purity of 91% was used.

(23) Comparative Example 2 was performed by reactive extrusion of the heterophasic propylene copolymer of Example 1 with 2000 ppm Luperox 101PP20 (containing 400 ppm pure organic peroxide Luperox 101).

(24) Comparative Example 3 was performed by reactive extrusion of the heterophasic propylene copolymer of Example 1 with 1 wt % Perkadox P24L.

(25) Example 4 according to an embodiment of the present disclosure was performed by reactive extrusion of the heterophasic propylene copolymer used in Example 1 with 2000 ppm Luperox 101PP20 (containing 400 ppm pure organic peroxide Luperox 101) and 1 wt % Perkadox P24L.

(26) All Examples 1-4 were performed under the same conditions, as detailed in the following.

(27) In all examples, the propylene copolymer pellets and a respective composition, when present, were fed in the hopper of a twin screw extruder from Brabender with an L/D (extruder Length/screw Diameter) of 20 and provided with a vent port in a decompression zone of the extruder.

(28) The feed rate of the polypropylene pellets was 3 kg/h. Volatile compounds were removed during the extrusion by applying under-atmospheric pressure (vacuum) on the vent port. The vacuum applied on the vent port was set to 400 mbar.

(29) The extrusion temperature was adjusted to 180 C. at the extruder feed zone and increased up to 200 C. at the extruder die zone.

(30) Table 1 shows detailed data of the evaluation using, as a copolymer, the above-mentioned ICP-1.

(31) TABLE-US-00001 TABLE 1 1 2 3 4 (control) (comparative) (comparative) (disclosure) Copolymer ICP-1 ICP-1 ICP-1 ICP-1 Composition 400 ppm 1 wt % P24L 400 ppm Luperox 101 Luperox 101 + 1 wt % P24L MFR 2.16 9.2 26.2 8.5 22.2 [g/10 min] C.sub.2 content 10.1 10.1 10.5 10.4 [wt %] YI [] 4.1 4.8 8.1 5.9 PI [] 2.6 2.5 3.0 2.6 ER [dyn/cm.sup.2] 1.1 0.9 2.6 2.6 Tensile Modulus 1044 1031 1075 1061 [MPa] T.sub.m [ C.] 165 164 165 164 T.sub.c [ C.] 122 122 126 125 Charpy N 23 C. 55.7 48.7 59.7 52.2 [kJ/m.sup.2] Charpy N 0 C. 9.9 9.2 14.6 11.5 [kJ/m.sup.2] Charpy N 6.7 5.9 8.6 6.8 20 C. [kJ/m.sup.2] Charpy N 5.7 5.4 7.9 6.3 30 C [kJ/m.sup.2]

(32) After reactive extrusion of the heterophasic propylene copolymer having a starting MFR value of 9.2 g/10 min, a starting Yellowness Index of 4.1 and a starting Elasticity Ratio of 1.1 dyn/cm.sup.2, by performing a method in accordance with embodiments of the present disclosure, namely by using a mixture of organic peroxide and peroxydicarbonate as in Example 4, the MFR, and thus the flowability, of the propylene copolymer increased to 22.2 g/10 min. Also, the Elasticity Ratio, and thus the melt strength, of the propylene copolymer increased to 2.6 dyn/cm.sup.2. However, color formation was much less than expected. Indeed, the value of the Yellowness Index of Example 4 indicates only a slightly increase when compared to the Yellowness Index of Example 2, while a person skilled in the art would expect that the Yellowness Index of Example 4 would be at least as high as after the reaction of the propylene copolymer used in Example 1 with the peroxydicarbonate alone, as in Example 3. This lower color formation of Example 4 shows improved performance of the method according to the present disclosure.

(33) While the method has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.