Process for preparing high melt strength propylene polymer

Abstract

The invention relates to a process for preparing a high melt strength polypropylene, comprising melt-mixing a base polypropylene, a peroxide and a linear α-olefin composition comprising linear C20+ α-olefins.

Description

[0001] PROCESS FOR PREPARING HIGH MELT STRENGTH PROPYLENE POLYMER

[0002] The present invention relates to a process for preparing a high melt strength propylene polymer and articles comprising such high melt strength propylene polymer.

[0003] Polypropylene is often modified via cracking by adding a peroxide to fit certain applications where high melt flow is needed. Such polypropylene may have drawbacks such as poor melt strength and strain-hardening properties. Such polypropylene further may have difficulties in processing especially where elongational flows are essential, such as , pipe extrusion, and thermoforming.

[0004] Methods are known to prepare high melt strength polypropylene.

[0005] For example, high melt strength polypropylene can be prepared using the peroxide crosslinking method, which involves using pure polypropylene without any additives as a basic resin and reacting with grafting and crosslinking agent in situ. Crosslinking of polypropylene can be achieved via grafting reactions in a reactive extrusion.

[0006] The melt strength of PP can also be improved by adding inorganic nano-fillers, such as silica, organoclay, and carbon nanotube to the polypropylene matrix.

[0007] High melt strength polypropylene can also be achieved with irradiation by an electron beam (EB) generated from an accelerator. EB irradiation is a process that involves using high-energy electrons of high energy to treat the polymeric material.

[0008] These approaches, however, have considerable drawbacks. The crosslinking method induces severe degradation and crosslinking of PP chains apart from branching reactions through the extrusion process. Addition of inorganic nano-fillers must be chemically modified to improve dispersion into the PP matrix. The rheological properties of the resultant composites depend on the state of distribution of the fillers and the presence of chemical bonding. In the EB process, the thickness of the material limits radiation crosslinking, and the procedure requires an inert atmosphere, resulting in high costs and difficult manufacturing technologies.

[0009] W02012049690A1 discloses a process for preparing high melt strength propylene polymers having melt strength 30 % to 60% greater than that of the base propylene polymers by reactive blending of base propylene polymers, with 0.1 to 1 % w / w of poly functional acrylate monomer, in the presence of 10 to 50 ppm organic peroxide, and 0.2 to 20% w / w of at least one additive, said additive selected from the group consisting stabilizers, acid neutralizers, antioxidants and lubricants.

[0010] It is an objective of the present invention to provide a high melt strength propylene polymer in which the above-mentioned and / or other problems are solved.

[0011] Accordingly, the present invention provides a process for preparing a high melt strength polypropylene, comprising melt-mixing a base polypropylene, a peroxide and a linear a-olefin composition comprising linear C20+ a-olefins.

[0012] It was surprisingly found that the propylene polymer obtained according to the present invention has a high melt strength.

[0013] Linear C20+ a-olefins is herein meant as linear a-olefins with 20 or more carbon atoms.

[0014] The linear C20+ a-olefins used for making the high melt strength polypropylene according to the invention are generally obtained as byproducts of processes for the preparation of more commonly used lower carbon a-olefins. The linear C20+ a-olefins generally have relatively limited uses such as lubricant and waxes. The invention is highly advantageous in that new applications have been found for these byproducts.

[0015] High melt strength polypropylene

[0016] According to the invention, melt-mixing a base polypropylene with a peroxide and a linear a-olefin composition comprising linear C20+ a-olefins results in the linear C20+ a-olefins grafting onto the propylene polymer backbone, obtaining the high melt strength polypropylene.

[0017] Preferably, the process for obtaining the high melt strength polypropylene does not comprise adding inorganic nano-fillers, such as silica, organoclay and carbon nanotube, before, during and / or after the melt-mixing step.

[0018] Preferably, the process for obtaining the high melt strength polypropylene does not comprise irradiation of the polypropylene by an electron beam before, during and / or after the melt-mixing step. This advantageously avoids undesired degradation of the polypropylene.

[0019] Base polypropylene The polypropylene to be melt-mixed with the peroxide and the linear a-olefin composition to obtain the high melt strength polypropylene is referred herein as the base polypropylene.

[0020] The base polypropylene may be or comprise a propylene homopolymer, a random propylene copolymer or a heterophasic propylene copolymer or any combinations thereof. In some preferred embodiments, the base polypropylene is a propylene homopolymer. In some preferred embodiments, the base polypropylene is a random propylene copolymer.

[0021] A propylene homopolymer can be obtained by polymerizing propylene under suitable polymerization conditions. A propylene copolymer can be obtained by copolymerizing propylene and ethylene or one or more other a-olefins under suitable polymerization conditions. The preparation of propylene homopolymers and copolymers is, for example, described in Moore, E. P. (1996) Polypropylene Handbook. Polymerization, Characterization, Properties, Processing, Applications, Hanser Publishers: New York.

[0022] The random propylene copolymer may comprise as the comonomer ethylene or an a- olefin chosen from the group of a-olefins having 4 to 12 C-atoms, preferably ethylene, 1 -butene, 1 -hexene, 1 -octene or any mixtures thereof. The amount of the comonomer is preferably at most 10 wt% based on the random propylene copolymer, for example in the range from 2.0 to 7.0 wt% based on the random propylene copolymer. In particularly preferred embodiments, the random propylene copolymer is a propyleneethylene random copolymer, preferably wherein the amount of the ethylene comonomer units is 2.0 to 7.0 wt% based on the random propylene copolymer.

[0023] Heterophasic propylene copolymers are generally prepared in one or more reactors, by polymerization of propylene in the presence of a catalyst and subsequent polymerization of an ethylene-a-olefin mixture. The resulting polymeric materials are heterophasic, but the specific morphology usually depends on the preparation method and monomer ratios used.

[0024] The heterophasic propylene copolymer comprises a propylene-based matrix and a dispersed ethylene-a-olefin copolymer. The propylene-based matrix typically forms the continuous phase in the heterophasic propylene copolymer. The propylene-based matrix consists of a propylene homopolymer and / or a propylene copolymer consisting of at least 90 wt% of propylene monomer units and at most 10 wt% of ethylene and / or a-olefin monomer units, based on the total weight of the propylene-based matrix. The a-olefin in the dispersed ethylene-a-olefin copolymer is preferably chosen from the group of a-olefins having 3 to 8 carbon atoms, preferably propylene.

[0025] Preferably, the base polypropylene has a melt flow index determined according to ISO1133-1 :2022 at 230 °C and 2.16 kg of 0.1 to 10 dg / min.

[0026] Preferably, the base polypropylene has a density as determined according to ASTM D1505 of 895 to 930 kg / m3, for example 895 to 900 kg / m3or 900 to 915 kg / m3.

[0027] In some embodiments, the base polypropylene is a propylene homopolymer having a density as determined according to ASTM D1505 of 900 to 915 kg / m3.

[0028] In some embodiments, the base polypropylene is a random propylene copolymer having a density as determined according to ASTM D1505 of 895 to 900 kg / m3.

[0029] The base polypropylene may be a post consumer recycled (PCR) polypropylene.

[0030] Linear a-olefin composition

[0031] The linear a-olefin composition comprises linear a-olefins. Preferably, the amount of linear a-olefins in the linear a-olefin composition is at least 95 wt%, at least 97 wt%, at least 99 wt%, at least 99.5 wt% or 100 wt%.

[0032] Preferably, the amount of the linear C20+ a-olefins with respect to the total linear a- olefins in the linear a-olefin composition is at least 55 wt%, preferably at least 60 wt%, more preferably at least 70 wt%, more preferably at least 80 wt%, more preferably at least 90 wt%, more preferably at least 95 wt%.

[0033] The linear a-olefin composition may comprise C20-C30 linear a-olefins and C30+ linear a-olefins.

[0034] Preferably, the amount of the C20-C30 linear a-olefins with respect to the total linear a- olefins in the linear a-olefin composition is at least 55 wt%, preferably at least 60 wt%, more preferably at least 70 wt%, more preferably at least 80 wt%, for example 80 to 99 wt%, 80 to 95 wt% or 80 to 90 wt%. Preferably, the amount of the C20-C24 linear a-olefins with respect to the total linear a- olefins in the linear a-olefin composition is 50 to 90 wt% or 65 to 75 wt% and the amount of the C26-C28 linear a-olefins with respect to the total linear a-olefins in the linear a-olefin composition is 5.0 to 25 wt% or 15 to 25 wt%.

[0035] Preferably, the amount of the C30+ linear a-olefins with respect to the total linear a- olefins in the linear a-olefin composition is at most 20 wt%, for example 1 .0 to 15 wt% or 3.0 to 10 wt%.

[0036] The linear a-olefin composition may further comprise linear C4 to C19 a-olefins.

[0037] Preferably, the amount of the C4 to C19 linear a-olefins with respect to the total linear a-olefins in the linear a-olefin composition is at most 5.0 wt%, for example 0.1 to 5.0 wt% or 0.5 to 3.0 wt%.

[0038] In particularly preferred embodiments, the amount of the linear C4 to C19 a-olefins with respect to the total linear a-olefins in the linear a-olefin composition is 0.1 to 5.0 wt%, the amount of the linear C20-C24 a-olefins with respect to the total linear a-olefins in the linear a-olefin composition is 65 to 80 wt%, the amount of the linear C26-C28 a-olefins with respect to the total linear a-olefins in the linear a-olefin composition is 10 to 20 wt% and the amount of the linear C30+ a-olefins with respect to the total linear a-olefins in the linear a-olefin composition is 3.0 to 10 wt%.

[0039] Preferably, the amount of the linear a-olefin composition with respect to the base polypropylene is 0.5 to 10 wt%, more preferably 1 .0 to 5.0 wt%.

[0040] Preferably, the amount of the linear C20+ a-olefins with respect to with respect to the base polypropylene is 0.5 to 10 wt%, more preferably 1 .0 to 5.0 wt%.

[0041] Preferably, the amount of the linear C20-C30 a-olefins with respect to the base polypropylene is 0.5 to 10 wt%, more preferably 1 .0 to 5.0 wt%.

[0042] Peroxide

[0043] The peroxide may be any known peroxide used for increasing the melt flow of polypropylene. The peroxide may e.g. be selected from the group consisting of 2,5- dimethyl-2,5-bis(tert. butyl- peroxy)hexane (DHBP) (for instance sold under the tradenames Luperox 101 and Trigonox 101 ), 2,5-dimethyl-2,5-bis(tert.butyl- peroxy)hexyne-3 (DYBP) (for instance sold under the tradenames Luperox 130 and Trigonox 145), dicumyl-peroxide (DCUP) (for instance sold under the tradenames Luperox DC and Perkadox BC), di-tert.butyl-peroxide (DTBP) (for instance sold under the tradenames Trigonox B and Luperox Di), tert.butyl-cumyl-peroxide (BCUP) (for instance sold under the tradenames Trigonox T and Luperox 801 ) and 1 ,3-bis (tert.butylperoxy-isopropyl)benzene (DIPP) (for instance sold under the tradenames Perkadox 14S and Luperox DC).

[0044] Preferably, the amount of the peroxide with respect to the base polypropylene is 0.01 to 1 .00 wt%, more preferably 0.05 to 0.50 wt%.

[0045] High melt strength polypropylene composition

[0046] The present invention further provides a high melt strength polypropylene composition comprising the high melt strength polypropylene according to the invention.

[0047] The high melt strength polypropylene composition may comprise components other than the high melt strength polypropylene, such as additives and fillers. Examples of the additives include nucleating agents; stabilizers, e.g. heat stabilizers, anti-oxidants, UV stabilizers; colorants, like pigments and dyes; clarifiers; surface tension modifiers; lubricants; flame-retardants; mold-release agents; flow improving agents; plasticizers; anti-static agents; external elastomeric impact modifiers; blowing agents; and / or components that enhance interfacial bonding between polymer and filler, such as a maleated polyethylene. The amount of the additives is typically 0 to 5.0 wt%, for example 1 .0 to 3.0 wt%, with respect to the total composition.

[0048] Examples of fillers include glass fibers, talc and mica. The amount of fillers may e.g. be 0 to 40 wt%, for example 5 to 30 wt% or 10 to 25 wt%, with respect to the total polyolefin composition.

[0049] Accordingly, in some embodiments, the high melt strength polypropylene composition further comprises 0 to 5.0 wt% of additives and 0 to 40 wt% of fillers.

[0050] In some embodiments, the high melt strength polypropylene composition according to the invention has little or no fillers, i.e. the high melt strength polypropylene composition according to the invention has less than 5.0 wt%, less than 3.0 wt%, less than 1 .0 wt%, less than 0.5 wt%, less than 0.1 wt% of 0 wt% of fillers.

[0051] Preferably, the total amount of the high melt strength polypropylene, the optional additives and the optional fillers is 100 wt% with respect to the total high melt strength polypropylene composition.

[0052] The invention further provides a process for making the high melt strength polypropylene composition according to the invention, comprising melt-mixing the high melt strength polypropylene and optionally additives and / or fillers.

[0053] Pipe

[0054] The present invention further provides a pipe comprising the high melt strength polypropylene according to the invention or the high melt strength polypropylene composition according to the invention.

[0055] The term “pipe” is herein understood as a hollow elongated article. The cross section may be of various shapes e.g. be circular, elliptical, square, rectangular or triangular. The pipe according to the invention may have an outer diameter in the range of 2.5 to 255 cm and / or an inner diameter of 2 to 250 cm and / or the pipe may have one or more layers with a total layer thickness in the range of 0.3 to 100 mm.

[0056] The pipe according to the invention may be produced by any suitable process, e.g. by a pipe extrusion manufacturing process.

[0057] Preferably, the amount of the high melt strength polypropylene according to the invention with respect to the pipe is at least 90 wt%, at least 95 wt%, at least 98 wt% or at least 99 wt%.

[0058] Thermoformed article

[0059] The present invention further provides a thermoformed article comprising the high melt strength polypropylene according to the invention or the high melt strength polypropylene composition according to the invention. The thermoformed article may be prepared by providing a sheet comprising the high melt strength polypropylene according to the invention or the high melt strength polypropylene composition according to the invention and thermoforming the sheet.

[0060] The sheet can be made by an know method, such as injection molding and extrusion.

[0061] The thermoforming may be performed by known thermoforming methods, such as vacuum forming, pressure forming, solid pressure forming, solid press forming, twin sheet forming and stamping forming. Such methods generally are carried out by heating the sheets above its softening temperature in the plastic deformation range, for instance with rolls, heating plates or indirect heating means, like radiant electric heaters, and forcing the sheets to fit the shape of a mold, for instance by sucking them against the mold.

[0062] The thermoforming may be performed under pressure or under vacuum. The pressure shall be sufficient enough for the sheets to conform to the final shape. For instance, the thermoforming under pressure may e.g. be performed at a pressure of 0.1 to 10 KPa. The thermoforming under vacuum may e.g. be performed at a pressure of -1 to -100 KPa.

[0063] The thermoforming may be performed e.g. at a temperature of 100 °C to 270 °C. The suitable temperature may be selected according to the composition used for making the sheet to be subjected to thermoforming, e.g. depending on whether the composition comprises a flame retardant. If the composition comprises a flame retardant, the temperature may be selected such that decomposition of the flame retardant is prevented, e.g. at most 240 °C.

[0064] Preferably, the amount of the high melt strength polypropylene according to the invention with respect to the thermoformed article is at least 90 wt%, at least 95 wt%, at least 98 wt% or at least 99 wt%.

[0065] The invention further provides use of a linear a-olefin composition comprising linear C20+ a-olefins for increasing melt strength of polypropylene by melt-mixing the polypropylene, a peroxide and the linear a-olefin composition.

[0066] It is noted that the invention relates to the subject-matter defined in the independent claims alone or in combination with any possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims. It will therefore be appreciated that all combinations of features relating to the composition according to the invention; all combinations of features relating to the process according to the invention and all combinations of features relating to the composition according to the invention and features relating to the process according to the invention are described herein.

[0067] It is further noted that the term ‘comprising’ does not exclude the presence of other elements. However, it is also to be understood that a description on a product / composition comprising certain components also discloses a product / composition consisting of these components. The product / composition consisting of these components may be advantageous in that it offers a simpler, more economical process for the preparation of the product / composition. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps. The process consisting of these steps may be advantageous in that it offers a simpler, more economical process.

[0068] When values are mentioned for a lower limit and an upper limit for a parameter, ranges made by the combinations of the values of the lower limit and the values of the upper limit are also understood to be disclosed.

[0069] The invention is now elucidated by way of the following examples, without however being limited thereto.

[0070] Materials: hPP1 : propylene homopolymer having a melt flow index of 0.3 dg / min (ISO1133-1 : 2022, 230 °C, 2.16 kg) and a density of 905 kg / m3(SABIC® PP531 P) rPP1 : random propylene-ethylene copolymer having a melt flow index of 0.3 dg / min (ISO1133-1 : 2022, 230 °C, 2.16 kg) and a density of 898 kg / m3, ethylene content 4 wt% (SABIC® Vestolen P9421)

[0071] LAO: linear a-olefin composition having the following composition: The IR absorbance of a sample of LAO showed strong absorbance at 1642cm1attributed to unsaturated (C=C) functional group present in LAO.

[0072] Peroxide: polypropylene masterbatch comprising 40 wt% of 1 ,3-bis (tertbutylperoxyisopropyl) benzene

[0073] Materials shown in Table 1 were melt-mixed at a temperature of 200 °C for 8 minutes.

[0074] FTIR test was conducted on the obtained polypropylene to confirm that the C20+ linear a-olefins have grafted on the polypropylene. The samples made using LAO and peroxide showed peaks at 720 cm1while the samples made using peroxide without LAO did not show peaks at 720 cm1. The grafting percentage was quantified by counting the ethylene print content.

[0075] The rheological behavior of the obtained polypropylene samples was studied by ARES rheometer which uses rotational force to measure the storage and loss moduli as well as the complex viscosity of the studied samples. The temperature was fixed at 180 °C and the frequency was increased from 0.5 rad / s to 500 rad / s while measuring the complex viscosity and storage and loss moduli at each frequency. Zero Shear viscosity was extrapolated from the obtained results and shown in Table 1.

[0076] MFI of the samples was measured according to IS01133-1 (2022) at 230 °C, 2.16 kg and shown in Table 1.

[0077] Table 1

[0078] The polypropylene obtained with the addition of C20+ linear alpha-olefins according to the invention has a higher zero shear viscosity than the corresponding polypropylene obtained without the addition of C20+ linear alpha-olefins, indicating that the melt strength of the polypropylene obtained with the addition of alpha-olefin is higher.

Claims

CLAIMS1 . A process for preparing a high melt strength polypropylene, comprising melt-mixing a base polypropylene, a peroxide and a linear a-olefin composition comprising linear C20+ a-olefins.

2. The process according to claim 1 , wherein the base polypropylene comprises or is a propylene homopolymer.

3. The process according to any one of the preceding claims, wherein the base polypropylene comprises or is a random copolymer of propylene and a comonomer selected from ethylene and C4-C12 a-olefins, preferably a random propyleneethylene copolymer.

4. The process according to any one of the preceding claims, wherein the base polypropylene has a melt flow index determined according to ISO1133-1 : 2022 at 230 °C and 2.16 kg of 0.1 to 10 dg / min.

5. The process according to any one of the preceding claims, wherein the amount of the linear C20+ a-olefins with respect to the total linear a-olefins in the linear a-olefin composition is at least 55 wt%, preferably at least 60 wt%, more preferably at least 70 wt%, more preferably at least 80 wt%, more preferably at least 90 wt%, more preferably at least 95 wt%.

6. The process according to any one of the preceding claims, wherein the linear a-olefin composition further comprises linear C4 to C19 a-olefins in an amount of at most 5.0 wt%, for example 0.1 to 5.0 wt% or 0.1 to 3.0 wt%, with respect to the total linear a-olefins in the linear a-olefin composition.

7. The process according to any one of the preceding claims, wherein the linear a- olefin composition comprises C20-C24 linear a-olefins in an amount of 50 to 90 wt% or 65 to 75 wt% with respect to the total linear a-olefins in the linear a-olefin composition and C26-C28 linear a-olefins in an amount of 5.0 to 25 wt% or 15 to 25 wt% with respect to the total linear a-olefins in the linear a-olefin composition.

8. The process according to any one of the preceding claims, wherein the linear a- olefin composition comprises C30+ linear a-olefins in an amount of at most 20 wt%,for example 1 .0 to 15 wt% or 3.0 to 10 wt% with respect to the total linear a-olefins in the linear a-olefin composition.

9. The process according to any one of the preceding claims, wherein the amount of the linear C20+ a-olefins with respect to the base polypropylene is 0.5 to 10 wt%, more preferably 1 .0 to 5.0 wt%.

10. The process according to any one of the preceding claims, wherein the amount of the peroxide with respect to the base polypropylene is 0.01 to 1 .00 wt%, more preferably 0.05 to 0.50 wt%.11 . A polypropylene composition comprising the high melt strength propylene obtained by or obtainable by the process according to any one of the preceding claims and additives in an amount of 0 to 5.0 wt%.

12. A thermoformed article comprising the polypropylene composition according to claim 11 , preferably wherein the amount of the high melt strength polypropylene with respect to the thermoformed article is at least 90 wt%, at least 95 wt%, at least 98 wt% or at least 99 wt%.

13. A pipe comprising the polypropylene composition according to claim 11 , preferably wherein the amount of the high melt strength polypropylene with respect to the pipe is at least 90 wt%, at least 95 wt%, at least 98 wt% or at least 99 wt%.

14. Use of a linear a-olefin composition comprising linear C20+ a-olefins for increasing melt strength of polypropylene by melt-mixing the polypropylene, a peroxide and the linear a-olefin composition.

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