RU2843162C2 - Polypropylene polymer compositions and articles made therefrom - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to polymer compositions for making thermoplastic polymer articles. Composition contains a polypropylene polymer and a salt of tert-butylphosphonic acid.

EFFECT: providing polymer compositions for making thermoplastic articles using a nucleating agent which provides desirable combinations of properties, for example, low turbidity and high hardness.

18 cl, 18 tbl, 6 ex

Description

Field of technology to which the present invention relates

[0001] The present application relates to polymer compositions, such as polypropylene polymer compositions, comprising a salt of a branched alkyl phosphonic acid. The salt of a branched alkyl phosphonic acid serves as a nucleating agent for the polymer.

Prior art of the present invention

[0002] Polyolefins are a group of polymer resins that are characterized by exceptional versatility. Polyolefins are semi-crystalline polymers. A polyolefin that is held for the purpose of relatively slow cooling (such as cooling that occurs during the manufacture of molded plastic articles) contains amorphous regions in which the polymer chains have a random orientation and crystalline regions in which the polymer chains have a presumably ordered configuration. Within these crystalline regions of the polyolefin, the polymer chains are oriented in domains that are commonly referred to by the term "crystalline platelets." Under normal processing conditions, the crystalline platelets grow radially in all directions as the polyolefin polymer cools from the molten state. This radial growth results in the formation of spherulites, which are spherical semi-crystalline regions that consist of numerous crystalline platelets and are interrupted by amorphous regions. The size of the spherulites is influenced by several parameters and can range from hundreds of nanometers to several millimeters in diameter. When the size of the spherulites is significantly larger than the wavelength of visible light, the spherulites will scatter the visible light passing through the polymer. This scattering of visible light results in a cloudy appearance, commonly referred to as "polymer haze" or simply "haze". Although significant levels of polymer haze may be acceptable in some applications, there are certain applications (e.g., storage containers) where relatively clear plastics are desirable to consumers and correspondingly low levels of haze are required.

[0003] Several nucleating agents for thermoplastic polymers are known in the art. Typically, said nucleating agents, by their action, form crystallization nuclei or provide centers for the formation and/or growth of crystals in a thermoplastic polymer during its solidification from a molten state. The nuclei or centers of crystallization, which are provided by the nucleating agent, allow the formation of crystals during the cooling of the polymer at a higher temperature and/or at a higher rate than in the case of the formation of crystals from an unprocessed thermoplastic polymer in which there are no crystallization nuclei. After that, said effects can allow the processing of a thermoplastic polymer composition containing crystallization nuclei in a cycle, the duration of which is less than the duration of the processing cycle of a thermoplastic polymer in which there are no crystallization nuclei.

[0004] Certain nucleating agents are capable of reducing the size of the spherulites for certain polymers (such as, for example, polypropylene) to such an extent that the polymer haze is significantly and noticeably reduced (i.e., the scattering of visible light passing through the polymer is reduced). Such nucleating agents are very advantageous because they allow the polymer to be used in applications in which reduced levels of haze are necessary or at least desirable. In addition to such improvements in optical properties, a desirable nucleating agent may improve other physical properties of the polymer, such as stiffness or impact strength. Such improvements further broaden the range of applications or end uses for which the nucleating agent-containing polymer is suitable. Furthermore, while numerous nucleating agents may provide improvements in one of the aforementioned physical properties, relatively few nucleating agents may provide improvements in two or more physical properties in a desirable combination.

[0005] Thus, in view of the above, there remains a need for thermoplastic polymers such as polypropylene for nucleating agents that provide, in a desirable combination, for example, low haze and high stiffness. The additives and polymer compositions described herein are intended to meet this need.

Brief summary of the present invention

[0006] According to a first embodiment of the present invention, a polymer composition is provided comprising: (a) a polypropylene polymer; and (b) a salt of a branched alkylphosphonic acid.

Detailed disclosure of the present invention

[0007] According to a first embodiment of the present invention, a polymer composition is provided comprising: (a) a polypropylene polymer; and (b) a salt of a branched alkylphosphonic acid.

[0008] The polymer composition may comprise any suitable polypropylene polymer. According to a preferred embodiment, the polypropylene polymer is selected from the group consisting of polypropylene homopolymers (e.g., atactic polypropylene homopolymer, isotactic polypropylene homopolymer, and syndiotactic polypropylene homopolymer), polypropylene copolymers (e.g., polypropylene random copolymers), polypropylene impact copolymers, and mixtures thereof. Suitable polypropylene copolymers include, but are not limited to, random copolymers obtained by polymerizing propylene in the presence of a comonomer selected from the group consisting of ethylene, but-1-ene (i.e., 1-butene), and hex-1-ene (i.e., 1-hexene), with ethylene being particularly preferred. In such polypropylene random copolymers, the comonomer may be present in any suitable amount, but is typically present in an amount of less than about 10 wt. % (e.g., from about 0.5 wt. % to about 10 wt. % or from about 1 wt. % to about 7 wt. %). Suitable polypropylene impact copolymers include, but are not limited to, copolymers obtained by adding a copolymer selected from the group consisting of ethylene propylene rubber (EPR), a copolymer of ethylene, propylene and a diene monomer (EPDM), polyethylene, and plastomers of a polypropylene homopolymer or a polypropylene random copolymer. In such polypropylene impact copolymers, the comonomer may be present in any suitable amount, but is typically present in an amount of from about 5 to about 25 wt. %. Suitable polypropylene impact copolymers also include, but are not limited to, copolymers obtained by polymerizing propylene and ethylene using one or more Ziegler-Natta catalysts. Typically, such polypropylene impact copolymers have a heterophase structure in which an amorphous ethylene-propylene copolymer is dispersed in a matrix consisting of a semicrystalline polypropylene homopolymer or copolymer. The polypropylene polymers described above may be branched or crosslinked, for example, as a result of branching or crosslinking that occurs as a result of the introduction of additives that increase the melt strength of the polymer.

[0009] As noted above, the polymer composition also comprises a salt of a branched alkyl phosphonic acid. As used herein, the term "branched alkyl phosphonic acid" means phosphonic acids of the following formula (C)

In formula (C), R ¹⁰¹ represents a branched alkyl group. The branched alkyl phosphonic acid salt may contain one or more suitable cations. According to a preferred embodiment, the branched alkyl phosphonic acid salt contains one or more cations selected from the group consisting of cations of Group 1 elements, cations of Group 2 elements and cations of Group 12 elements. According to a preferred embodiment, the branched alkyl phosphonic acid salt contains a cation of Group 1, preferably two sodium cations. According to a further preferred embodiment, the branched alkyl phosphonic acid salt contains a cation of Group 2. According to a particularly preferred embodiment, the branched alkyl phosphonic acid salt contains a calcium cation.

[0010] The branched alkyl phosphonic acid may comprise any suitable branched alkyl group (i.e. R ¹⁰¹ may be any suitable branched alkyl group). According to a preferred embodiment, the branched alkyl phosphonic acid comprises a branched alkyl group selected from the group consisting of isopropyl, sec-butyl, isobutyl, tert-butyl, tert-pentyl, neopentyl, isopentyl, sec-pentyl, sec-isopentyl, pentan-3-yl and 2-methylbutyl. According to a further preferred embodiment, the branched alkyl phosphonic acid comprises an alkyl group with a branch point located on an alpha carbon atom or a beta carbon atom with respect to the phosphorus atom, wherein a branch point on an alpha carbon atom is particularly preferred. According to a preferred embodiment, the branched alkyl phosphonic acid comprises a tertiary alkyl group, which is an alkyl group comprising at least one carbon atom bonded to four substituents that are not hydrogen atoms, such as three alkyl groups and a phosphorus atom. According to a preferred embodiment, the branched alkyl phosphonic acid comprises a branched alkyl group selected from the group consisting of tert-butyl, tert-pentyl, and neopentyl. According to a particularly preferred embodiment, the branched alkyl phosphonic acid comprises a tert-butyl group (i.e., R ¹⁰¹ is tert-butyl). Thus, according to a particularly preferred embodiment, the salt of the branched alkyl phosphonic acid is a calcium salt of tert-butyl phosphonic acid (i.e., calcium tert-butyl phosphonate or calcium tert-butyl phosphonate monohydrate).

[0011] The branched alkyl phosphonic acid salt may have any suitable specific surface area, which is, for example, the Brunauer-Emmett-Teller (BET) specific surface area. According to a preferred embodiment, the branched alkyl phosphonic acid salt has a BET specific surface area of about 20 m ² /g or more. According to a further preferred embodiment, the branched alkyl phosphonic acid salt has a BET specific surface area of about 30 m ² /g or more. The BET specific surface area of the branched alkyl phosphonic acid salt can be measured using any suitable technology. Preferably, the specific surface area according to the BET method for the salt of a branched alkyl phosphonic acid is measured in accordance with ISO 9277:2010, which is entitled "Determination of the specific surface area of solids by gas adsorption according to the BET method", using nitrogen as the adsorbing gas. The salts of branched alkyl phosphonic acids, which are described in this document, generally have a layered structure, which can be exfoliated using techniques known in the art. By such exfoliation of the layered structure, the specific surface area according to the BET method of the salt of the branched alkyl phosphonic acid increases, which facilitates dispersion. Physical methods for increasing the specific surface area according to the BET method of the salt of the branched alkyl phosphonic acid are air jet milling, pin milling, hammer milling, crushing and similar methods. Improved dispersion and increased specific surface area can also be achieved by using more intensive mixing and extrusion techniques, such as high intensity mixing and twin screw extrusion. Thus, those salts of branched alkyl phosphonic acids that lack the desired BET specific surface area can be exfoliated using the above and other known techniques to achieve the desired BET specific surface area.

[0012] The polymer composition may comprise any suitable amount of a salt of a branched alkyl phosphonic acid. According to a preferred embodiment, the salt of a branched alkyl phosphonic acid is present in the polymer composition in an amount of about 50 parts per million (ppm) or more, based on the total weight of the polymer composition. According to a further preferred embodiment, the salt of a branched alkyl phosphonic acid is present in the polymer composition in an amount of about 75 ppm or more, about 100 ppm or more, about 150 ppm or more, about 200 ppm or more, or about 250 ppm or more, based on the total weight of the polymer composition. The salt of the branched alkyl phosphonic acid is preferably present in the polymer composition in an amount of about 10,000 ppm or less, based on the total weight of the polymer composition. According to a preferred embodiment, the salt of the branched alkyl phosphonic acid is preferably present in the polymer composition in an amount of about 5,000 ppm or less, about 4,000 ppm or less, about 3,000 ppm or less, about 2,000 ppm or less, about 1,500 ppm or less, about 1,250 ppm or less, or about 1,000 ppm or less, based on the total weight of the polymer composition. Thus, according to successively preferred embodiments, the branched alkyl phosphonic acid salt is present in the polymer composition in an amount of from about 50 ppm to about 10,000 ppm (e.g., from about 50 ppm to about 5,000 ppm, from about 50 ppm to about 4,000 ppm, from about 50 ppm to about 3,000 ppm, from about 50 ppm to about 2,000 ppm, from about 50 ppm to about 1,500 ppm, from about 50 ppm to about 1,250 ppm, or from about 50 ppm to about 1,000 ppm), from about 75 ppm to about 10,000 ppm (e.g., from about 75 ppm to about 5,000 ppm, from about 75 ppm to about 4,000 ppm, from about 75 ppm to about 3,000 ppm, from about 75 ppm to about 2,000 ppm, from about 75 ppm to about 1,500 ppm, from about 75 ppm to about 1,250 ppm, or from about 75 ppm to about 1,000 ppm), from about 100 ppm to about 10,000 ppm (e.g., from about 100 ppm to about 5,000 ppm, from about 100 ppm to about 4,000 ppm, from about 100 ppm to about 3,000 ppm, from about 100 ppm to about 2,000 ppm, from about 100 ppm to about 1,500 ppm, from about 100 ppm to about 1,250 ppm, or from about 100 ppm to about 1,000 ppm), from about 150 ppm to about 10,000 ppm (e.g., from about 150 ppm to about 5,000 ppm, from about 150 ppm to about 4,000 ppm, from about 150 ppm to about 3,000 ppm, about 150 ppm to about 2,000 ppm, about 150 ppm to about 1,500 ppm, about 150 ppm to about 1,250 ppm, or about 150 ppm to about 1,000 ppm), about 200 ppm to about 10,000 ppm (e.g., about 200 ppm to about 5,000 ppm, about 200 ppm to about 4,000 ppm, about 200 ppm to about 3,000 ppm, about 200 ppm to about 2000 ppm, about 200 ppm to about 1500 ppm, about 200 ppm to about 1250 ppm, or about 200 ppm to about 1000 ppm), about 250 ppm to about 10,000 ppm (e.g., about 250 ppm to about 5000 ppm, about 250 ppm to about 4000 ppm, about 250 ppm to about 3000 ppm, about 250 ppm to about 2000 ppm, about 250 ppm to about 1500 ppm, from about 250 ppm to about 1250 ppm, or from about 250 ppm to about 1000 ppm), based on the total weight of the polymer composition. If the polymer composition comprises more than one salt of a branched alkyl phosphonic acid, each salt of a branched alkyl phosphonic acid may be present in the polymer composition in one of the amounts presented above, or the total amount of all salts of branched alkyl phosphonic acids that are present in the polymer composition may be within one of the ranges presented above. Preferably, when the polymer composition comprises more than one salt of a branched alkyl phosphonic acid, the total amount of all salts of branched alkyl phosphonic acids that are present in the polymer composition is within one of the ranges presented above.

[0013] Salts of branched alkyl phosphonic acids that are suitable for use in the compositions of the present invention can be prepared using any suitable process. For example, the salts can be prepared in an aqueous medium by reacting a branched alkyl phosphonic acid and a metal-containing base such as a metal hydroxide (e.g., calcium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide) or a metal oxide (e.g., calcium oxide or zinc oxide). The salts of branched alkyl phosphonic acids obtained by such a process can be hydrates (e.g., calcium t-butyl phosphonate monohydrate). Such hydrated salts can be dehydrated by heating the salts to a sufficiently high temperature, but many of such dehydrated salts (e.g., calcium t-butyl phosphonate) are sufficiently unstable that they rehydrate upon exposure to atmospheric moisture.

[0014] The polymer composition according to the present invention may also contain other polymer additives in addition to one or more of the above-mentioned salts of branched alkylphosphonic acids. Suitable additional polymeric additives include, but are not limited to, antioxidants (e.g., phenolic antioxidants, phosphite antioxidants, and combinations thereof), anti-blocking agents (e.g., amorphous silica and diatomite), pigments (e.g., organic pigments and inorganic pigments) and other colorants (e.g., dyes and polymeric colorants), fillers and reinforcements (e.g., glass, glass fibers, talc, calcium carbonate, and magnesium oxysulfate whiskers), nucleating agents, brightening agents, acidity neutralizers (e.g., metal salts of fatty acids such as metal salts of stearic acid and hydrotalcite-like materials), polymeric processing aids (e.g., polymeric processing aids for fluorinated polymers), polymeric crosslinking agents, friction reducing agents (e.g., fatty acid amide compounds obtained from the reaction between a fatty acid and ammonia or amino group-containing compound), fatty acid esters (e.g., fatty acid esters produced by the reaction of a fatty acid with a hydroxyl group-containing compound such as glycerol, diglycerol, and combinations thereof), polymeric modifiers (e.g., hydrocarbon resin modifiers such as Oppera™ modifiers sold by Exxon Mobil Corporation), and combinations of the foregoing.

[0015] According to a preferred embodiment, the polymer composition further comprises one or more acid neutralizers. As noted above, suitable acid neutralizers include metal salts of fatty acids and hydrotalcite-like materials (e.g., synthetic hydrotalcites). Suitable metal salts of fatty acids include, but are not limited to, metal salts of C ₁₂ -C ₂₂ fatty acids (e.g., C ₁₂ -C ₂₂ saturated fatty acids), such as stearic acid. According to a preferred embodiment, the acid neutralizer is selected from the group consisting of calcium, zinc, potassium, and lanthanum salts and stearic acid, with zinc stearate being particularly preferred. Hydrotalcite-like materials suitable for use as acid neutralizers include, but are not limited to, synthetic hydrotalcite materials (CAS No. 11097-59-9) under the trade names DHT-4A and DHT-4V, which are sold by Kisuma Chemicals.

[0016] One or more salts of branched alkyl phosphonic acids and the acid neutralizer may be present in the polymer composition in any suitable relative amounts. For example, one or more salts of branched alkyl phosphonic acids and the acid neutralizer may be present in the polymer composition in a ratio of one or more salts of branched alkyl phosphonic acids to the acid neutralizer that is from about 10:1 to about 1:10 based on the weight of the one or more salts of branched alkyl phosphonic acids and the acid neutralizer in the polymer composition. More preferably, one or more salts of branched alkyl phosphonic acids and an acid neutralizer are present in the polymer composition in a ratio of one or more salts of branched alkyl phosphonic acids and an acid neutralizer of from about 4:1 to about 1:4, from about 3:1 to about 1:3 (for example, from about 3:1 to about 1:1 or from about 3:1 to about 2:1), from about 1:1 to about 1:4, or from about 1:1 to about 1:3, based on the weight of the one or more salts of branched alkyl phosphonic acids and an acid neutralizer in the polymer composition. According to a particularly preferred embodiment, the one or more salts of branched alkyl phosphonic acids and the acid neutralizer are present in the polymer composition in a ratio of about 2:1 based on the weight of the one or more salts of branched alkyl phosphonic acids and the acid neutralizer in the polymer composition (e.g., about 2 parts by weight of calcium tert-butyl phosphonate monohydrate per 1 part by weight of zinc stearate). According to a further particularly preferred embodiment, the one or more salts of branched alkyl phosphonic acids and the acid neutralizer are present in the polymer composition in a ratio of about 3:1 based on the weight of the one or more salts of branched alkyl phosphonic acids and the acid neutralizer in the polymer composition (e.g., about 3 parts by weight of calcium tert-butyl phosphonate monohydrate per 1 part by weight of zinc stearate).

[0017] As noted above, the polymer composition of the present invention may contain other nucleating agents in addition to the one or more branched alkyl phosphonic acid salts described above. Suitable nucleating agents include, but are not limited to, 2,2'-methylene-bis-(4,6-di-tert-butylphenyl) phosphate salts (e.g., sodium 2,2'-methylene-bis-(4,6-di-tert-butylphenyl) phosphate or hydroxyaluminum bis(2,2'-methylene-bis-(4,6-di-tert-butylphenyl) phosphate), calcium bicyclo[2.2.1]heptane-2,3-dicarboxylate salts (e.g., disodium bicyclo[2.2.1]heptane-2,3-dicarboxylate or calcium bicyclo[2.2.1]heptane-2,3-dicarboxylate), cyclohexane-1,2-dicarboxylate salts (e.g., calcium cyclohexane-1,2-dicarboxylate, monobasic cyclohexane-1,2-dicarboxylate, dilithium cyclohexane-1,2-dicarboxylate, or strontium cyclohexane-1,2-dicarboxylate, glycerate salts (e.g., zinc glycerate), phthalate salts (e.g., calcium phthalate), phenylphosphonic acid salts (e.g., calcium phenylphosphonate), and combinations thereof. In the case of bicyclo[2.2.1]heptane-2,3-dicarboxylate salts and cyclohexane-1,2-dicarboxylate salts, the carboxylate moieties may be present in either the cis or trans configuration, with the cis configuration being preferred.

[0018] As noted above, the polymer composition of the present invention may also comprise a clarifying agent. Suitable clarifying agents include, but are not limited to, trisamides and acetal compounds, which are the condensation product of a polyhydric alcohol and an aromatic aldehyde. Suitable trisamide clarifying agents include, but are not limited to, amide derivatives of benzene-1,3,5-tricarboxylic acid, derivatives of N-(3,5-bis-formylaminophenyl)formamide (e.g., N-[3,5-bis-(2,2-dimethylpropionylamino)phenyl]-2,2-dimethylpropionamide), derivatives of 2-carbamoylmalonamide (e.g., N,N'-bis-(2-methylcyclohexyl)-2-(2-methylcyclohexylcarbamoyl)malonamide), and combinations thereof. As noted above, the clarifying agent may be an acetal compound, which is a condensation product of a polyhydric alcohol and an aromatic aldehyde. Suitable polyhydric alcohols are acyclic polyols such as xylitol and sorbitol, as well as acyclic deoxypolyols (e.g. 1,2,3-trideoxynonitol or 1,2,3-trideoxynon-1-enitol). Suitable aromatic aldehydes typically contain a single aldehyde group, while the remaining positions on the aromatic ring are unsubstituted or substituted. Accordingly, suitable aromatic aldehydes are benzaldehyde and substituted benzaldehydes (e.g. 3,4-dimethylbenzaldehyde or 4-propylbenzaldehyde). The acetal compound produced by the above reaction may be a monoacetal, diacetal, or triacetal compound (i.e., a compound containing one, two, or three acetal groups, respectively), with diacetal compounds being preferred. Suitable acetal-based brightening agents include, but are not limited to, those described in U.S. Patent Nos. 5,049,605; and 7,262,236.

[0019] The polymer composition of the present invention can be made using any suitable method or process. For example, the polymer composition can be made by simply mixing the individual components of the polymer composition, which include, for example, the polymer, one or more salts of branched alkyl phosphonic acids, and other additives, if present. The polymer composition can also be made by mixing the individual components under high shear or high intensity mixing conditions. The polymer composition of the present invention can be made in any form suitable for use in subsequent processing to make an industrial article from the thermoplastic polymer composition. For example, the thermoplastic polymer compositions can be made in a form such as a powder (e.g., a bulk powder), flakes, granules, beads, tablets, agglomerates, and the like.

[0020] The polymer composition of the first embodiment of the present invention may be in the form of a masterbatch composition for addition to or incorporation into an additive-free polymer (e.g., a nucleated polypropylene polymer). In such an embodiment, the polymer composition typically comprises a branched alkyl phosphonic acid salt in an increased amount compared to the thermoplastic polymer composition for use in making an industrial article, without further dilution or addition to the additive-free thermoplastic polymer. For example, the branched alkyl phosphonic acid salt may be present in such a polymer composition in an amount of about 0.5 wt. % or more (e.g., about 1 wt. % or more, or about 2 wt. % or more). The maximum amount of salt in the masterbatch is limited solely by manufacturing and processing considerations, although this amount is typically about 50 wt. % or less. Thus, according to successively preferred embodiments, the branched alkyl phosphonic acid salt can be present in the masterbatch in an amount of from about 0.5 wt. % to about 50 wt. % (e.g., from about 0.5 wt. % to about 40 wt. %, from about 0.5 wt. % to about 30 wt. %, from about 0.5 wt. % to about 25 wt. %, from about 0.5 wt. % to about 20 wt. %, from about 0.5 wt. % to about 15 wt. %, from about 0.5 wt. % to about 10 wt. %, from about 0.5 wt. % to about 5 wt. %, or from about 0.5 wt. % to about 4 wt. %), from about 1 wt. % to about 50 wt. % (e.g., from about 1 wt. % to about 40 wt. %, from about 1 wt. % to about 30 wt. %, from about 1 wt. % to about 25 wt. %, from about 1 wt. % to about 20 wt. %, from about 1 wt. % to about 15 wt. %, from about 1 wt. % to about 10 wt. %, from about 1 wt. % to about 5 wt. %, or from about 1 wt. % to about 4 wt. %), or from about 2 wt. % to about 50 wt. % (e.g., from about 2 wt. % to about 40 wt. %, from about 2 wt. % to about 30 wt. %, from about 2 wt. % to about 25 wt. %, from about 2 wt. % to about 20 wt. %, from about 2 wt. % to about 15 wt. %, from about 2 wt. % to about 10 wt. %, from about 2 wt. % to about 5 wt. %, or from about 2 wt. % to about 4 wt. %), based on the total weight of the polymer composition. In such a masterbatch composition, any additional additives that are contained in the composition will likewise be present in increased amounts that are intended to provide the desired concentration when the masterbatch composition is introduced into the additive-free polymer.

[0021] The polymer composition according to the present invention is considered suitable for use in the manufacture of thermoplastic polymer industrial articles. The polymer composition of the present invention can be used to produce the desired thermoplastic polymeric industrial article using any suitable technology, such as injection molding (e.g., thin-wall injection molding, overmolding, overlay molding, or two-component molding), blow molding (e.g., extrusion blow molding, injection blow molding, or injection stretch blow molding), extrusion (e.g., fiber extrusion, tape (e.g., slot tape) extrusion, sheet extrusion, film extrusion, cast film extrusion, pipe extrusion, coating extrusion, or foam extrusion), thermal molding, rotational molding, blown film molding, cast film injection molding, compression molding, extrusion compression molding, extrusion compression blow molding and similar technologies. Thermoplastic polymeric articles made using the polymeric composition of the present invention may be present in multilayer articles (such as, for example, multilayer blown or cast films or multilayer articles made by injection molding) in which one or any suitable number of a plurality of layers comprises the polymeric composition of the present invention.

[0022] The polymer composition of the present invention can be used to make any suitable industrial article. Suitable industrial articles include, but are not limited to, medical devices (e.g., pre-filled syringes for autoclave applications, intravenous containers, and blood collection devices), food packaging, liquid containers (e.g., containers for beverages, medicines, personal care products, shampoos, and the like), clothing cases, microwave-safe items, shelving, cabinet doors, mechanical parts, automotive parts, sheets, pipes, tubes, rotational molding parts, blow molding parts, films, fibers, and the like.

[0023] The above-described subject matter of the present invention is further illustrated in the following examples, but, of course, they should not be construed as limiting its scope in any way.

Example 1

[0024] This example demonstrates methods for producing polymeric compositions according to the present invention and certain physical properties of thin-walled articles produced by injection molding such polymeric compositions.

[0025] Several polymer compositions were made using various commercially available polypropylene resins. Samples labeled "1A" were made from LyondellBasell's Pro-fax 6301 polypropylene homopolymer, which has a reported melt flow rate of 12 g/10 min. Samples labeled "1B" were made from Lanzhou's HPP SF-40, which has a reported melt flow rate of 60 g/10 min. Samples labeled "1C" were made using Luoyang's HPP Q/SH3210, which has a reported melt flow rate of 80 g/10 min. Samples labeled "1D" were made from Sinopec Tianjin's PPH-M70, which has a reported melt flow rate of 70 g/10 min. All samples were stabilized by adding 500 ppm of the antioxidant Irganox® 1010 and 1000 ppm of the antioxidant Irgafos® 168, both from BASF. Some polymer compositions additionally contained calcium tert-butylphosphonate monohydrate (CaTBP), zinc stearate (ZnSt), and the acidity neutralizers calcium stearate (CaSt) and/or DHT-4V from Kisuma Chemicals. The amounts of these additional components are presented in the following tables.

[0026] Each of the polymer compositions was prepared by high-intensity mixing of the polypropylene resin and additives and then melt-blending the mixture using a Deltaplast single-screw extruder. The extruder screw speed was set at 126 rpm. The first zone of the extruder barrel was set to 200°C, the second zone of the extruder barrel was set to 215°C, and all zones from the third to the sixth extruder barrel were set to 230°C. After melt compounding, each extrudate was cut into pellets for subsequent processing.

[0027] The extruded pellets of each polymer composition were then injection molded to form 16 US fl oz (470 ml) food cups on a Husky injection molding machine with all barrels set at 220°C, an injection speed of 140 mm/sec, a back pressure of 50 psi (0.14 MPa), and a mold cooling water temperature of 45°C. The food cups had a round base that was 3.637 inches (92.38 mm) in diameter, a round opening at the top, and a rim that was 4.266 inches (108.4 mm) in diameter at the inside edge and 4.612 inches (117.1 mm) at the outside edge of the rim. The food cups had a wall thickness of 26 mils (0.66 mm).

[0028] After molding, the food cups were then tested to determine several physical properties. The compressive strength under top pressure was measured in accordance with ASTM D2659. The turbidity was measured in accordance with ASTM D1003. The crystallization properties, specifically the crystallization half-life (T _1/2 ) and the crystallization temperature (T _g ), were measured using differential scanning calorimetry. The crystallization half-life was measured at a temperature of 140 °C, and the crystallization temperature was measured at a heating rate of 20 °C/min. The results of these measurements are presented below in Tables 1-4.

[0029] As can be seen from the data presented in Tables 1-4 above, calcium tert-butylphosphonate monohydrate (CaTBP) was found to be effective for nucleation purposes for all of the polypropylene polymers. These nucleation effects are clearly demonstrated by the shorter crystallization half-lives, higher crystallization temperatures, higher top compressive strength values, and lower haze values exhibited by all of the CaTBP-containing polymer compositions compared to the corresponding control polymers, which are polypropylene resins that do not contain CaTBP. In addition, these results demonstrate that the polymer compositions containing synthetic hydrotalcite as a deacidifier (e.g., DHT-4V) exhibit somewhat improved nucleation compared to the polymer compositions containing calcium stearate as a deacidifier. And in this case, this improved nucleation is evidenced by the shorter crystallization half-lives, higher crystallization temperatures, higher compressive strength values under top pressure, and lower turbidity values exhibited by the polymer compositions containing DHT-4V, compared to the polymer compositions containing calcium stearate.

Example 2

[0030] This example demonstrates methods for producing polymeric compositions according to the present invention and certain physical properties of articles produced by thermal molding of such polymeric compositions.

[0031] Polymer compositions were made using TotalEnergies 3371 polypropylene resin, which is reported to have a melt flow rate of 2.8 g/10 min. Certain polymer compositions were nucleated using calcium tert-butyl phosphonate monohydrate (CaTBP), which was used in combination with a neutralizer such as zinc stearate (ZnSt) and calcium stearate (CaSt). The amounts of CaTBP and neutralizers used in each polymer composition are provided in the tables below. The 3371 resin and additives were subjected to high intensity mixing using a Henschel mixer prior to melt compounding, which is described below.

[0032] The polymer composition was melt compounded on a Werner & Pfleiderer zsk-40 twin-screw extruder having a screw diameter of 40 mm and a length-to-diameter (L/D) ratio of 37. The temperature of the first zone of the extruder barrel was set at 165°C, the temperature from the second to the sixth zone of the extruder barrel and the die zone were set at 175°C. The extruder speed was set at 400 rpm, and the total throughput was approximately 55 kg/hour. The polymer strands exiting the extruder head were cooled in a water bath and then cut into pellets using a pelletizer.

[0033] The granulated polymer compositions were then thermoformed into beverage cups using a Reifenhauser A-T-20-G1 sheet line coupled to an iLLig RDM 54K thermoforming machine. The sheet line extruder was set to 230°C and the die zone was set to 250°C with a die gap of 1.5 mm. The screw speed was approximately 72 rpm. The sheet exiting the die was then transferred to a set of three stacked cooling rolls set at temperatures of 65°C, 75°C and 65°C. The sheet exiting the cooling rolls had a thickness of 1.9 mm. The sheet was then passed through a heating section of a thermoforming machine, the temperature of which was set at 165°C, in order to heat the sheet to a temperature slightly below the melting point of the polymer composition. The sheet was then passed to a forming section, where it was thermoformed into beverage cups, which were then cut from the sheet and ejected from the thermoforming machine. The resulting beverage cups had a base diameter of approximately 60 mm, a top rim diameter of approximately 94 mm, and a height of approximately 140 mm.

[0034] Samples of extruded sheets and thermally formed beverage cups were collected for optical and physical properties, which are described below. Haze and clarity were measured in accordance with ASTM D1003 using a BYK Haze-gard Haze Meter. For the thermally formed beverage cups, haze measurements were made in an area 76.2 mm from the base of the cup and 25.4 mm from the top rim. Gloss (microgloss at 20°) was measured using a BYK Single Angle Gloss Meter. Measurements were made on both sides of the sample and the results were averaged to obtain an average gloss value, expressed in gloss units.

[0035] The thermal properties of the samples were measured by differential scanning calorimetry using a Mettler Toledo differential scanning calorimeter (DSC) setup (DSC 3+STAR system) and analyzed using Mettler STARe evaluation software. To measure the crystallization temperature, the samples were heated from 50°C to 220°C at a rate of 20°C/min to remove all thermal history. After holding the sample at 220°C for 2 minutes to reach equilibrium, the sample was cooled to 50°C at a rate of 20°C/min to study the crystallization behavior. The crystallization temperature ( _Tg ) is reported as the maximum value on the cooling curve. To measure the crystallization half-life, the sample was heated from 50°C to 220°C at a rate of 20°C/min to remove all thermal history, held at 220°C for 2 minutes to establish equilibrium, and then cooled to 135°C at a rate of 300°C/min and held at this temperature for 30 minutes. The crystallization half-life was calculated from the DSC curve using the software.

[0036] Flexural modulus specimens were cut from extruded sheet using a type 1 dumbbell cutting die as described in ASTM D638-10. Test specimens were taken in the machine and cross directions. The specimens were then conditioned for at least 40 hours at a temperature of approximately 23°C and a relative humidity of approximately 50%. Flexural modulus testing was then performed in accordance with ASTM D790-10 using an MTS Criterion 43 electromechanical testing system equipped with a three-point bending machine (model 642.01A). The depth of beam travel was recorded to calculate strain. The one percent secant modulus was calculated based on the stress-strain relationship when the strain reached 1%.

[0037] Cup out-of-roundness is a parameter that defines the difference in the cup diameter measured in the machine direction (parallel to the direction of exit of the sheet from the die) and the cross direction (perpendicular to the direction of exit of the sheet from the die). The thermally formed cups were conditioned for at least 24 hours before measuring (in inches) the outside diameter of the rim in the machine direction (D _MD ) and cross direction (D _TD ) using a caliper. Cup out-of-roundness, expressed in mils, was calculated using the following equation:

cup ovality = (D _MD - D _TD ) × 1000.

Shrinkage at the rim is a parameter that denotes the difference between the diameter of the rim of a thermoformed cup and the diameter of the corresponding part of the mold from which the cup was made. The diameter of the mold was 3.7427 inches. The average diameter of the cup rim (D _avg ) was measured (in inches) using a spring tension band. The shrinkage at the rim of the cup, which is expressed in mils, was calculated using the following equation:

rim shrinkage = (3.7427 - D _avg ) × 1000.

[0038] The sidewall compressive strength of a thermally formed cup was measured using a deflection-resisting force probe. The cup was positioned horizontally on its side using a cup fixture attached to the platen of an MTS Criterion Model 43 Electromechanical Testing System. The probe, moving at a constant vertical speed of 25 mm/min, was pressed perpendicularly downward against the sidewall of the cup, with a total wall deflection distance of 10 mm. After the desired total wall deflection distance was achieved, the resulting cup force was recorded as the sidewall force. The top load compressive strength of the thermally formed cup (ASTM D 2659) was measured by inverting the cup and mechanically pressing downward until the cup was observed to stop resisting due to failure. The cup was placed edge down on the fixed support platen of the MTS Criterion Model 43 Electromechanical Testing System. A ventilated support plate was used to allow air to escape from inside the cup when it was compressed. The upper compression plate, moving at a constant speed of 50 mm/min, pressed the cup until failure was detected. The maximum force recorded at failure was reported as the top compression strength.

[0039] As can be seen from the data in Tables 5-8, calcium tert-butyl phosphonate monohydrate (CaTBP) was effective in nucleating resin 3371 even at concentrations as low as 100 ppm. Although some physical properties of beverage cups (e.g., sidewall strength and top compression strength) made from the nucleating resin did not show significant improvements at all concentration levels compared to the non-nucleating resin, the crystallization temperature, crystallization half-life, flexural modulus, and optical properties were significantly improved for both sheets and cups at all CaTBP concentrations. For example, when CaTBP was added at a low concentration of 100 ppm, the haze of the extruded sheet was reduced by approximately 7 haze units, the clarity was increased from only 12.6% to over 95%, and the average gloss was increased by 13 gloss units. Additionally, in the case of thermally formed beverage cups, the addition of CaTBP reduced shrinkage (reduced rim shrinkage) compared to the unnucleated resin, and the observed shrinkage was more isotropic in nature, as evidenced by significantly reduced ovality values.

Example 3

[0040] This example demonstrates methods for producing polymeric compositions according to the present invention and certain physical properties of thermally molded articles made using such polymeric compositions.

[0041] Polymer compositions were made using TotalEnergies 3371 polypropylene resin as described in Example 2. Certain polymer compositions were nucleated using calcium tert-butylphosphonate monohydrate (CaTBP), which was used in combination with a neutralizer such as zinc stearate (ZnSt) and calcium stearate (CaSt). The amounts of CaTBP and neutralizers used in each polymer composition are listed in the tables below. The 3371 resin and additives were high intensity mixed and melt compounded in the same manner as the polymer compositions in Example 2.

[0042] The granulated polymer compositions were then thermoformed to form portion cups using equipment under the same conditions (except as noted below) as those used in Example 2. The screw speed of the sheet line extruder was set to approximately 42-45 rpm to form an extruded sheet. The sheet exiting the cooling rolls had a thickness of 1.2 mm. Another mold for making portion cups with a base diameter of 78 mm, an upper rim diameter of 94 mm, and a height of 54 mm was installed in the thermoforming machine.

[0043] Samples of the extruded sheets and thermally formed portion cups were collected for optical and physical property testing as described in Example 2. For the thermally formed portion cups, turbidity measurements were made in a region located 25.4 mm from the base of the cup and 19 mm from the top rim.

[0044] The data from Tables 9-12 further confirm that the salt of a branched alkyl phosphonic acid (in particular, calcium tert-butyl phosphonate monohydrate (CaTBP)) exhibits effectiveness in the nucleation process of resin 3371. The resin containing the nucleating substances exhibits significant improvements in optical and physical properties in both sheets and thermally formed portion cups.

Example 4

[0045] This example demonstrates methods for producing polymeric compositions according to the present invention and the improved physical properties exhibited by articles produced by injection molding using such polymeric compositions. In particular, this example demonstrates the effect of BET specific surface area on the nucleation efficiency of a branched alkyl phosphonic acid salt.

[0046] Seven polymer compositions were prepared for the injection molding experiments described herein. Sample 4A was a nucleating polypropylene homopolymer, Pro-fax 6301, from LyondellBasell. Samples 4B-4G were prepared from a mixture containing Pro-fax 6301, 1000 ppm calcium tert-butylphosphonate monohydrate (CaTBP), 500 ppm zinc stearate (ZnSt), 300 ppm Irganox® 1010 antioxidant and 600 ppm Irgafos® 168 antioxidant. The BET specific surface area for each CaTBP used in samples 4B-4G is presented below in Table 13. The BET specific surface area for the nucleating agent samples was measured according to ISO 9277:2010, entitled “Determination of the specific surface area of solids by gas adsorption - BET method”, using nitrogen as the adsorbent gas. Samples 4B-4G were separately mixed, melt compounded and granulated as described in Example 1.

[0047] A portion of each polymer composition was injection molded and formed into ASTM flexible rods in accordance with ASTM D4101-11 using a 40-ton Arburg injection molding machine. Another portion of each polymer composition was also injection molded and formed into ISO shrinkage plates in accordance with ISO 294 using a 55-ton Arburg injection molding machine. Finally, a third portion of each polymer composition was injection molded and formed into plates measuring 77 mm in length, 50 mm in width, and 1.27 mm (50 mil) in thickness using a 40-ton Arburg injection molding machine.

[0048] Heat distortion temperature (HDT) was measured in accordance with ASTM D 648-07 (using a stress of 0.4555 MPa) using the ASTM flexible injection molded bars described above. Notched Izod impact strength was measured in accordance with ASTM D 256-10 on an Instron 9050 pendulum impact tester using ASTM flexible injection molded bars that had been cut and notched in accordance with ASTM D 256-10. Thermal properties of the samples were measured by differential scanning calorimetry using a Mettler Toledo differential scanning calorimeter (DSC) setup (DSC 3+STAR system) and analyzed using Mettler STARe evaluation software as described in Example 2, except that the samples were maintained at 140°C during the test.

[0049] The flexural modulus was measured in accordance with ASTM D790-10 using an MTS Criterion 43 electromechanical testing system equipped with a three-point bending machine (model 642.01A). Prior to testing, the flexible rods were conditioned for at least 40 hours at a temperature of approximately 23°C and a relative humidity of approximately 50%. The flexural modulus in two directions, including the machine direction (MD) and the transverse direction (TD), was also measured in accordance with ASTM D790-10. The specimens used to measure the flexural modulus in two directions were prepared as described above and cut from ISO injection molded shrinkage plates. For machine direction measurements, a 9.2 mm (3.5 in) strip of material was cut along the transverse axis (leaving 50.8 mm [2 in] in the transverse direction) and the load was applied perpendicular to the flow direction. For cross direction measurements, a 9.2 mm (3.5 in) strip of material was cut along the longitudinal axis (leaving 50.8 mm [2 in] in the machine direction) and the load was applied parallel to the flow direction.

[0050] The shrinkage of injection molded ISO shrinkage plates was measured in accordance with ISO 294 on plates that had been conditioned for at least 48 hours at a temperature of approximately 23°C and a relative humidity of approximately 50% prior to testing. The shrinkage in the machine direction and transverse direction was calculated using the following equations:

MD% = (MD _mold - MD _specimen ) / MD _mold × 100%,

TD% = (TD _mold - TD _specimen ) / TD _mold × 100%.

In these equations, MD _mold is the machine direction mold size, MD _specimen is the machine direction specimen size, TD _mold is the cross direction mold size, and TD _specimen is the cross direction specimen size. The isotropy index, which is a measure of the uniformity of product shrinkage, was calculated by dividing the machine direction shrinkage by the cross direction shrinkage:

isotropy index = MD% / TD%.

[0051] The results of the measurements described above are presented below in Tables 13, 14 and 15.

[0052] The data in Tables 14 and 15 further confirm that the branched alkyl phosphonic acid salt (specifically, calcium tert-butyl phosphonate monohydrate (CaTBP)) was effective as a nucleating agent for the polypropylene polymer, specifically, resin 6301. For example, the crystallization temperature of all nucleating agent-containing samples was at least 7°C higher than that of the control sample that did not contain nucleating agents. In addition, the crystallization half-lives for all nucleating agent-containing samples were less than 11 minutes, which was significantly less than that of the resin that did not contain nucleating agents. In general, increased crystallization rates (decreased crystallization half-lives) were observed for polymer compositions containing nucleating agents (CaTBP) and having lower BET specific surface areas.

[0053] The data in Table 14 also demonstrate the significant improvement in physical properties that can be achieved by nucleation using an alkyl phosphonic acid salt, such as calcium tert-butyl phosphonate monohydrate (CaTBP). All of the nucleated samples exhibited an increase in flexural modulus above 300 MPa compared to the unnucleated polymer. In addition, the heat distortion temperatures of all of the nucleated resins were at least 17°C higher than the heat distortion temperature of the unnucleated polymer. The impact strength of the nucleated polymers was at least 16 J/m higher than the impact strength of the unnucleated polymer.

[0054] The data in Table 15 tell the same story. In fact, the increase in flexural modulus obtained with the nucleating resin composition was even more pronounced when the stiffness was measured in two directions. In these measurements, the MD and CD flexural moduli increased by approximately 400 MPa above the values obtained with the non-nucleating resin. The MD shrinkage of the nucleating resin was slightly higher than the MD shrinkage of the non-nucleating resin, and the MD shrinkage and CD shrinkage of each nucleating resin were closer to each other than the MD shrinkage and CD shrinkage of the non-nucleating resin. As a result, the resin containing nucleating agents exhibits shrinkage that is isotropic (i.e., the isotropy index approaches 1) to a significantly greater extent than the shrinkage of the resin without nucleating agents. When the isotropy index approaches 1, it can be assumed that articles made from the resin containing nucleating agents should exhibit less distortion/deformation compared to articles made from the resin without nucleating agents.

Example 5

[0055] This example demonstrates methods for producing polymeric compositions according to the present invention and certain physical properties of articles produced by injection molding using such polymeric compositions.

[0056] Two polymer compositions were made in the injection molding experiments described herein. Sample 5A is a nucleating polypropylene block copolymer, Prime Polypro J707P, from Prime Polymer. The melt flow rate of the resin was measured to be 30 g/10 min at 230°C. Polypro J707P is an antistatic impact copolymer that exhibits high impact strength and stiffness. Sample 5B was prepared from a mixture containing Polypro J707P, 1000 ppm calcium tert-butylphosphonate monohydrate (CaTBP), 500 ppm zinc stearate (ZnSt), 500 ppm Irganox® 1010 antioxidant, and 1000 ppm Irgafos® 168 antioxidant. Sample 5B was mixed, melt compounded, and granulated as described in Example 1.

[0057] Portions of specimens 5A and 5B were injection molded to produce ASTM flexible plates and ISO shrink rods as described in Example 4. The resulting rods were then used to measure thermal properties, flexural modulus, bidirectional flexural modulus, heat distortion temperature, notched Izod impact strength, shrinkage, and isotropy as described in Example 4. The results of these measurements are presented in Tables 16 and 17 below.

[0058] The data in Tables 16 and 17 demonstrate that a branched alkyl phosphonic acid salt (specifically, calcium tert-butyl phosphonate monohydrate (CaTBP)) was found to be effective in the nucleation process for a polypropylene impact copolymer such as Polypro J707P resin. These nucleation effects are evident from the increase in crystallization temperature, the significant reduction in crystallization half-life, the increase in flexural modulus, and the increase in heat distortion temperature. The increase in flexural modulus achieved with the nucleating polymer composition is again even more evident when measuring the stiffness in two directions. In these measurements, the flexural modulus increased by 300-380 MPa. In this case, the shrinkage of the resin containing nucleating substances turned out to be somewhat higher than the shrinkage of the resin not containing nucleating substances, the isotropy index approached 1, and this means that products made from resin containing nucleating substances exhibit distortion/deformation to a lesser extent compared to products made from resin containing nucleating substances.

Example 6

[0059] This example demonstrates the production of polymeric compositions according to the present invention and certain physical properties of articles produced by injection molding using such polymeric compositions.

[0060] Two polymer compositions were made in the injection molding experiments described herein. Sample 6A is SA 849S from LyondellBasell. The melt flow rate of the resin was recorded as 11 g/10 min at 230°C. SA 849S is a polypropylene random copolymer. Sample 6B was prepared from a mixture containing SA 849S, 1000 ppm calcium tert-butylphosphonate monohydrate (CaTBP), 500 ppm zinc stearate (ZnSt), 500 ppm Irganox® 1010 antioxidant, and 1000 ppm Irgafos® 168 antioxidant. Sample 6B was mixed, melt compounded, and granulated as described in Example 1.

[0061] Portions of samples 6A and 6B were injection molded into 1.27 mm (50 mil) thick plates as described in Example 4 above. The resulting plates were then used to measure flexural modulus as described in Example 4. Haze and clarity were measured for the 50 mil thick plates as described above.

[0062] The data in Table 18 demonstrate that a branched alkyl phosphonic acid salt (specifically, calcium tert-butyl phosphonate monohydrate (CaTBP)) was effective in nucleating a polypropylene random copolymer such as SA 849S resin. The turbidity of the nucleated resin was less than half that of the non-nucleated resin. The clarity of the nucleated resin was also increased compared to the non-nucleated resin. Finally, the flexural modulus of the nucleated resin was 100 MPa higher than the flexural modulus of the non-nucleated resin.

[0063] All referenced documents, including publications, patent applications, and patents, cited in this document are herein incorporated by reference to the same extent as if each referenced document were individually and specifically indicated to be incorporated by reference and were set forth in their entirety herein.

[0064] The use of the singular and similar forms in the context of describing the subject matter of the present invention (particularly in the context of the claims below) shall be construed as designating the singular and plural unless otherwise indicated herein or clearly contradicted by the context. The terms "including," "having," "comprising," and "containing" shall be construed as open-ended terms that mean "including, but not limited to," unless otherwise indicated. The recitation of ranges of values herein is intended solely as a means of briefly representing individually each individual value that falls within the range, unless otherwise indicated herein, and each individual value is included in the description of the invention to the same extent as if it were individually recited herein. All methods described herein may be performed in any suitable order, unless otherwise indicated herein or clearly contradicted by the context. The use of any and all examples or expressions indicating examples (e.g., "such as") that appear herein are intended solely for the purpose of better illustrating the subject matter of the present invention and do not establish a limitation on the scope of such subject matter unless otherwise indicated. No expression in the description of the present invention should be construed as indicating any unclaimed element as necessary for the practical implementation of the subject matter of the invention described herein.

[0065] Described herein are preferred embodiments of the subject matter of the present invention, including the best mode known to the inventors for carrying out the claimed subject matter of the present invention. Modifications to these preferred embodiments may become apparent to those of ordinary skill in the art upon review of the foregoing description. The inventors expect that those skilled in the art will be able to make such modifications as appropriate, and the inventors also contemplate that the subject matter described herein may be practiced otherwise than as specifically described herein. Accordingly, the present description includes all modifications and equivalents of the subject matter set forth in the appended claims that are permitted by applicable law. Furthermore, the present invention extends to any combination of the elements described above in all possible corresponding modifications unless otherwise indicated herein or clearly contradicted by context.

Claims (20)

1. A polymer composition for the production of thermoplastic polymer products, containing: (a) polypropylene polymer; and (b) tert-butylphosphonic acid salt. 2. The polymer composition according to claim 1, wherein the polypropylene polymer is selected from the group consisting of polypropylene homopolymers, polypropylene random copolymers, polypropylene impact copolymers and mixtures thereof. 3. The polymer composition according to claim 1 or 2, wherein the polypropylene polymer is selected from the group consisting of polypropylene homopolymers, polypropylene random copolymers and mixtures thereof. 4. A polymer composition according to any one of claims 1 to 3, wherein the salt of tert-butylphosphonic acid contains one or more cations selected from the group consisting of cations of elements of group 1, cations of elements of group 2 and cations of elements of group 12. 5. The polymer composition according to claim 4, wherein the salt of tert-butylphosphonic acid contains a cation of a group 2 element. 6. A polymer composition according to any one of claims 1 to 5, wherein the salt of tert-butylphosphonic acid is a calcium salt of tert-butylphosphonic acid. 7. A polymer composition according to any one of claims 1 to 6, wherein the salt of tert-butylphosphonic acid is calcium tert-butylphosphonate monohydrate. 8. The polymer composition according to any one of claims 1 to 7, wherein the tert-butylphosphonic acid salt has a specific surface area according to the BET method of 20 ^m2 /g or more. 9. The polymer composition of claim 8, wherein the tert-butylphosphonic acid salt has a BET specific surface area of 30 ^m2 /g or more. 10. The polymer composition of any one of claims 1 to 9, wherein the tert-butylphosphonic acid salt is present in the polymer composition in an amount of from about 50 parts per million to about 5000 parts per million, based on the total weight of the polymer composition. 11. The polymer composition of claim 10, wherein the tert-butylphosphonic acid salt is present in the polymer composition in an amount of from about 100 parts per million to about 2000 parts per million based on the total weight of the polymer composition. 12. A polymer composition according to any one of claims 1-11, wherein the composition contains an acidity neutralizer selected from the group consisting of metal salts of fatty acids, synthetic hydrotalcites and mixtures thereof. 13. The polymer composition according to claim 12, wherein the acidity neutralizer is a metal salt of a fatty acid. 14. The polymer composition according to claim 13, wherein the fatty acid is a saturated C ₁₂ -C ₂₂ fatty acid. 15. The polymer composition according to claim 14, wherein the fatty acid is stearic acid. 16. The polymer composition according to claim 15, wherein the acidity neutralizer is selected from the group consisting of calcium stearate, zinc stearate, potassium stearate, lanthanum stearate and mixtures thereof. 17. The polymer composition according to claim 16, wherein the acidity neutralizer is zinc stearate. 18. The polymer composition of any one of claims 12 to 17, wherein the tert-butylphosphonic acid salt and the acid neutralizer are present in the polymer composition in a ratio of from about 3:1 to about 1:1 based on the weight of the tert-butylphosphonic acid salt and the acid neutralizer in the polymer composition.