WO2014091309A2 - Polymeric composition with improved barrier properties - Google Patents

Abstract

A polymeric composition comprising a premium polyolefin composition comprising a mixture of a nucleating agent and a filler added for reduced permeability is disclosed. The subject composition provides improved properties as a barrier to gases, volatile organic compounds, and water vapor.

Description

POLYMERIC COMPOSITION WITH IMPROVED BARRIER PROPERTIES

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. provisional application Ser. No.

61/717,971 which was filed in the United States Patent and Trademark Office on October 24, 2012.

BACKGROUND OF THE INVENTION

[0002] Polyolefins, such as polypropylene (PP) and polyethylene (PE), are the most widely used polymers in various applications and present many advantages including flexibility, light weight, low cost, easy processing and recyclability. Polyolefins are useful for the manufacture of a variety of articles, including molded articles, films, and others structures.

However, the use of neat polyolefins is restricted because of some of its inherent properties, such as a relatively high oxygen and aroma permeability, which weakens the long shelf-life properties required for these applications. For example, PP and PE are inferior gas barriers compared to other thermoplastic materials like polyamide (PA), polyethylene terephthalate (PET), ethylene vinyl alcohol (EVOH), etc.. Thus, a need exists for PP and PE compositions with improved gas barrier properties which can supplant PA, PET and EVOH thermoplastic polymers in plastic packaging markets, which is currently not served by polyolefins.

[0003] The barrier properties are strictly correlated to the intrinsic structure of the polymer such as degree of crystallinity, crystallinity/amorphous phase ratio, nature of polymer, thermal and mechanical treatment before and after food contact, chemical groups present in the polymer (polar or not), degree of crosslinking, and glass transition temperature.

[0004] In principle, a barrier function can be improved into a polyolefm packaging material with alternative technologies, such as the surface treatment of the polymer by fluorination or sulfonation, multilayer coextrusion (the addition of a layer of barrier material), mixing the barrier materials into the base polymer or by inclusion of impermeable lamellar fillers with sufficient aspect ratio to alter the diffusion path of gas-penetrant molecules. Among the mineral fillers, the most used are those that carry a high aspect ratio, such as clay, wollastonite, mica, graphene, carbon nanotubes, talcum, etc. [0005] It is known that addition of lamellar filler to polymer may cause improvements in barrier for gases. Usually, this type of filler is impermeable to gases, and its presence creates a tortuous path to the permeant, retarding the passage through the polymer. The extent of permeation reduction depends, among others, on the filler anisotropy and dispersion in the polymer. Although mica provides improvement in barrier properties, polyolefms filled with mica have gas barrier properties below required specifications.

[0006] Mica has established its applications in a wide variety of plastic polymer compounds, namely, Polyolefm, Polyamide, Polyester, Polyurethane/Polyurea, Polypropylene (PP), Polyethylene (PE), Poly (acrylonitrile, butadiene, styrene ) (ABS) , Polycarbonate (PC), Fluoro-polymers, Poly (p-phenylene oxide) (PPO) , Polysulfone, Polyurethane (PU)

thermoplastic resins and thermosets (epoxy, phenolics, UPST (Unsaturated polyester), etc. PP is, by far, the most popular use of mica. Mica- filled PP is chiefly used for reinforcement of RRIM (Reinforced Reaction Injection Moulded) automotive parts, such as fan blades, dashboard panels, floor and grill panels, plastic seats, ignition system parts, air-conditioning heater housing including fascia and fenders fixed next to steel parts, while maintaining a similar appearance and similar coefficient of thermal expansion.

[0007] Another method that can improve barrier properties is the inclusion of nucleating agent into the polymer. In general, nucleating agents induce an increase in crystallinity in PP or PE. There is an inversely proportional relationship between the permeation and the degree of crystallinity. Apart from this, the Milliken Company supplies a commercial nucleating agent, Hyperform® HPN-20E ("HPN-20E"), which may improve barrier properties in polyethylene by the changing orientation of the crystalline lamellae of the polymer. The HPN-20E additive product contains calcium of hexahydrophthalic acid combined with an acid scavenger

compound, zinc stearate. This product is designed for addition to polymers, and for dispersion of the additive into polymer.

[0008] Nucleating agents are employed as additive in polymer resin in the manufacture of plastic articles. Such manufacture may be various methods, including by injection or extrusion molding. [0009] Nucleating agents are commonly used in polypropylene. Such agents change crystallization temperature, spherulitic size, density, clarity, impact and tensile properties of polypropylene. Similarly, nucleating agents are also used in polyethylene, particularly in linear low density polyethylene (LLDPE) to improve optical, impact, and other physical properties. However, the use of nucleating agent in high density polyethylene (HDPE) is less common because HDPE readily crystallizes without nucleating agent. In general, nucleating agents do not significantly improve the barrier properties of HDPE films.

[0010] The HPN-20E product and other nucleating agents, like glycerol alkoxide salts, are disclosed in U.S. 2008/0227900. This invention is a method for improving the barrier properties of a polyethylene film. The method comprises mixing a substantially linear HDPE with a nucleating agent and converting the mixture into a film. Large reduction in the moisture vapor transmission rate and oxygen transmission rate of the film are observed in the presence of the nucleating agent. The barrier properties of injection molded are not predictive in this invention.

[0011] U.S. 2008/0118749 relates to barrier films prepared from a blend of two high density polyethylene blend components and a high performance organic nucleating agent. The two high density polyethylene blend components have substantially different melt indices. Large reductions in the moisture vapor transmission rate of the film are observed in the presence of the nucleating agent when the melt indices of the two blend components have a ratio of greater than 10/1.

[0012] In any case, the uses of mineral fillers or nucleating agents alone do not provide improvements of polyolefm barrier properties, to reach required levels by some markets; for example, cardboard packages for milk, BOPP films, PE films for refrigerated specialty perishable products, fuel tanks and agrochemical containers. These applications require greater than 50% improved gas barrier properties compared to PP and PE base resins.

[0013] The particular combination of the mineral filler and nucleating agents can result in compositions having unexpected good oxygen barrier properties. [0014] Other additives which can be included in the compositions of the invention include, but are not necessarily limited to, pigments, stabilizers, processing aids, plasticizers, fire retardants, anti-fog, among others.

SUMMARY OF THE INVENTION

[0015] The present invention presents a polymeric composition with improved barrier to gases, volatile organic compounds and water vapor, comprising a polyolefin resin; a nucleating agent or a clarifying agent; and a filler.

[0016] The polyolefin resin may comprise polyethylene, polypropylene, or a mixture thereof. In embodiments, the polyolefin resin may be from about 99.89% to 65% by weight, or about 99.47% to 82% or about 98.95% to 88% by weight.

[0017] The polyethylene may comprise a low density polyethylene, a medium density polyethylene, a high density polyethylene, or any combination thereof.

[0018] The polypropylene may comprise a propylene homopolymer, a propylene randomized copolymer or a propylene heterophasic copolymer, or any combination thereof.

[0019] The filler may comprise lamellar filler capable of changing the crystalline structure of polyolefin resin solidified from a molten state. The filler may be organic or inorganic. Preferably, the filler may be any one component selected from a natural or synthetic filler chosen among mica, clay, graphite or graphene; more preferably, filler includes muscovite, phlogopite, vermiculite, montmorillonite, kaolinite, laponite, wollastonite, hectorite, expanded graphite, oxidized graphite or any combination thereof. In embodiments, the mineral filler can range from about 0.1 % to 30% by weight, with about 0.5%> to 15% by weight preferred and about 1%) to 10%) by weight particularly preferred.

[0020] The nucleating agent may be a one metal salt from a saturated bicyclic dicarboxylate, hexahydrophthalic acid, dibenzylidene sorbitol and dibenzylidene sorbitol derivatives, or sodium benzoate. The nucleating agent for this invention is one that is capable of changing the orientation of crystalline lamellae and/or modifies the crystal size of the polyolefin. In embodiments, the nucleating agent can range from 0.01% to 5% by weight, with about 0.03% to 3%) by weight preferred, and about 0.05%> to 2% by weight particularly preferred.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Lamellar filler is a material composed of aggregates of fine sheets of material held adjacent to one another, characterized by their flattened or squamous shape.

[0022] The inorganic substance mica is the denomination given to a lamellar filler group of hydrated silicate of potassium, which displays differences in their chemical compositions and physical properties, constituting a phyllosilicate based on potassium, sodium, aluminum, magnesium, and/or iron in its structure. Mica may be natural or synthetic.

[0023] The inorganic substance clay is the denomination of a group of lamellar filler composed of hydrated silicates of aluminum and magnesium, and may contain other elements, such as iron, sodium, potassium, lithium, etc.

[0024] As used herein, mica is construed to include hydrated silicates of potassium, which displays differences in their chemical compositions and physical properties, constituting a phyllosilicate based on potassium, sodium, aluminum, magnesium, and/or iron in its structure. Micas can have basal cleavage and are capable of peeling apart into thin platelets. Naturally occurring mica may include: Muscovite or potassium mica (H₂KAl₃(Si0₄)₃); Phlogopite or magnesium mica (H₂KMg₃Al(Si04)3); Paragonite or sodium mica (H₂NaAl₃(Si04)₃); Lepidolite or lithium mica (KLiAl(OH,F)₂Al(Si04)₃); Biotite or magnesium iron mica [(H₂K)(Mg,

Fe)₃Al(Si0₄)₃]; Zinnwaldite or lithium iron mica (Li₂K2Fe₂Al₄Si70₂₄) and others; Synthetic mica may include fluorphlogopites (Mg₃K(AlF₂0(Si0₃)₃) and may be coated, e.g. with titanium dioxide.

[0025] As used herein, clay comprises hydrated silicates of aluminum, and may contain other elements, like magnesium, iron, sodium, potassium, lithium, etc. Clay is construed to include hydrous aluminum phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations. Clays includes:

Kaolin (Al₂Si₂0₅(OH)₄), Smectite [(Ca,Na,H)(Al,Mg,Fe,Zn)₂(Si,Al)₄0io(OH)₂xH₂0)],

Illite (K,H₃O)(Al,Mg,Fe)₂(Si,Al)4O₁₀[(OH)₂,(H₂O)],

Chlorite [(Mg,Fe)₃(Si,Al)₄Oio],

Sepiolite (Mg₄Si₆Oi₅(OH)₂-6H₂0) and

Attapulgite (Mg,Al)₂Si₄Oi₀(OH) ·4(Η₂0)] .

[0026] Examples include vermiculite, montmorillonite, kaolinite, laponite, and hectorite.

[0027] The nucleating agent is a substance that modifies the crystallization of the polymer or polymeric composition. The nucleating agent may be a one metal salt from a saturated bicyclic dicarboxylate, hexahydrophthalic acid, dibenzylidene sorbitol and

dibenzylidene sorbitol derivatives, or sodium benzoate. Examples include cis-endo- bicyclo[2.2.1]heptane-2,3-dicarboxylic acid, disodium salt (Hyperform® HPN-68L),

hexahydrophthalic acid, calcium salt (Hyperform® HPN-20E), l,3:2,4-bis (3,4 dimethyl benzylidene sorbitol) (Millad® 3988 and/or Millad® 3988i), bis(4-propylbenzylidene) propyl sorbitol (Millad® NX™ 8000).

[0028] The lamellar filler disperses and/or exfoliates in the molten polymer and forms planes that may be oriented in the parallel direction to the shearing stress applied in the molten polymer during its processing, that is, in the direction of the flow of injection for injection molded items, or in the longitudinal direction for blown plastic articles. The filler acts as a physical barrier to a permeating agent (e.g., gases, volatile organic compounds, and water vapor), creating a tortuous path that delays the passage of the permeating agent. The lamellar filler is an anisotropic particle and also orientates the crystalline lamellae in the transversal direction to the shearing stress applied in the molten polymer during its processing, showing a secondary effect that may decrease the permeability of gases, volatile organic compounds, and water vapor of the polyolefin.

[0029] The nucleating agent for this invention is also capable of orienting the crystalline lamellae, change the crystallinity degree and/or modify the crystal size of the polyolefin. As described previously, the changing of crystalline orientation creates a more tortuous path for permeating agent delaying the passage of gases, volatile organic compounds, and water vapor. Besides, it is expected that reduction of crystal size improves the barrier to gases, volatile organic compounds, and water vapor by minimizing the defects in the interface between crystals.

[0030] The combination of nucleating agents with lamellar fillers presents a synergic effect, which is governed by two mechanisms: physical barrier and crystalline orientation of polymeric resin. As to various processes for producing the high barrier polymer of the present invention, the polymer may be obtained in the reactor, for different technologies, followed by dosing of additives and a nucleating agent and filler in e.g., a twin-screw extruder. The present invention may find utility in rigid and flexible packaging for drink, foods and non-foods that require a barrier to permeation of oxygen gas. As a result, the shelf life of stored food will tend to be lengthened through the use of products of the present invention.

Examples

[0031] Improved gas barrier properties are exemplified herein, using e.g. mica and talc as fillers and HPN-20E product as nucleating agent. Filler grades selected presented high or low aspect ratios, and high or low granulometry, according to Table 1.

Table 1 - Physical properties of fillers.

[0032] The fillers and the nucleating agent were incorporated into polyethylene resin in different contents via processing in molten state by twin screw extrusion. The samples were extruded at 200 °C, injection molded at 190 °C and subjected to oxygen permeation tests using Oxtran equipment, Mocon, model 2/21. Examples 1, 2, 3, 4, 5 and Comparative Examples A and B

[0033] The filler was tested for dependency upon the base resin. The tests were accomplished with two PE resin types: 1) high density polyethylene (HDPE), MFI of 20 g/10 min (190 °C; 2.16 kg, according to ASTM D1238) and 2) low density polyethylene (LDPE), MFI of 22 g/10 min (190 °C; 2.16 kg, according to ASTM D1238), both with 3 wt% of filler. The samples were injection molded into 2 mm thick specimens. The permeability results obtained with mica in different polyethylene grades, expressed as oxygen transmission rate (OTR), are displayed in Table 2. The greatest reduction in OTR was obtained with Ml 50 mica, regardless of the base resin. However, it was believed that Ml 7 mica would be more effective on the OTR reduction, even with its lower aspect ratio. The lower size of M17 mica particle tends to cause a better dispersion of filler in the resin, and consequently a higher oxygen barrier improvement. Nevertheless, based on the data presented, the aspect ratio has a greater influence in the reduction of permeability than the particle size. In embodiments, the particle size can range from about 0.01 μιη to 200 μιη, with about 0.1 μιη to 100 μιη preferred and about 0.1 μιη to 30 μιη particularly preferred.

Table 2 - HDPE and LDPE oxygen barrier properties with different types of mica.

[0034] Besides the fact that the aspect ratio is more prominent than the particle size for oxygen barrier improvement, differences between the mica performance into HDPE and LDPE resins were observed. In HDPE the gain was 27% with the Ml 50 mica, whereas in LDPE the gain was 15%. The principle of the filler is to act as a physical barrier to the oxygen, and for this reason it was expected that the percentage reduction in OTR would be indifferent to the PE resin, since the HDPE and LDPE used have similar fluidity. Nonetheless, as observed, such behavior indicates that there is a secondary effect between the mica and the polyethylene, and this effect could be related to a combination of the aspect ratio of the filler, its topography and the ability of the PE resin to crystallize.

Examples 7, 8 and Comparative Example C

[0035] In order to confirm whether the barrier property depends only on the aspect ratio of the filler, the fillers were tested for dependency upon the type (talc or mica) and aspect ratio (high or low) in HDPE resin, and results are shown in Table 3 and can be compared to Table 2. Talc T2 displays an aspect ratio of 130, higher than that of mica M150, and therefore equal or lower permeation values than the mica M150 were expected. The samples were injection molded into 0.6 mm thick plaques.

[0036] The results in Table 3 show that high aspect ratio Talc T2 did not improve the barrier property at the same level of mica Ml 50 (Table 2). In fact, the best result in barrier property was attained with the lower aspect ratio talc, but although still lower than the results with mica. For talc, results suggest that granulometry prevailed toward the aspect ratio.

Table 3 - HDPE oxygen barrier property with different types of talc.

[0037] Such behavior with talc suggests that the good results attained with mica are not due only to the aspect ratio, but probably to another morphologic, topographic or chemical aspect inherent to the mica.

[0038] It is anticipated that mica is causing changes in the crystalline structure of the polyethylene used, not in the degree of crystallinity, but in the orientation of the crystalline lamellae, in a way to leave the lateral planes of the crystalline lamellae placed in the transverse direction to the shearing stress flow of the test specimen. Examples 9, 10 and Comparative Examples A and 2

[0039] Mica was tested for dependency upon its content in HDPE. The samples were injection molded into 2 mm thick specimens and the results are shown in Table 4. A significant reduction in OTR with higher amount of mica is evidenced.

[0040] It is known that the higher amount of filler the lower oxygen permeation rate; however, presence of fillers might cause some losses in mechanical and optical properties, whiteness and specific gravity of the final product. Because of this, the plastics industry requires as little an amount of filler as possible.

Table 4 - HDPE oxygen barrier property with different amounts of mica M34.

Examples 11, 12 and Comparative Example C

[0041] An additive that operates with the same proposed mechanism for mica, that is, modifying the orientation of crystalline lamellae, is the nucleating agent HPN-20E from

Milliken. In order to evidence the effect of orientation of the crystalline lamellae in the barrier properties, 0.1 wt% and 0.5 wt% of HPN-20E product was added to HDPE and the results obtained are presented in Table 5. The samples were injection molded into 0.6 mm thick specimens.

Table 5 - HDPE oxygen barrier property with different contents of HPN-20E nucleating agent.

[0042] It is noted that the HPN-20E nucleating agent improved considerably the oxygen barrier property of polyethylene, revealing that the effect of orientation of the HDPE crystalline lamellae plays an important role in the reduction of oxygen permeability. According to the results, above 0.1 wt% of HPN-20E product did not bring about additional oxygen barrier improvement, inferring that the crystalline lamellae orientation of HDPE reached a steady state.

[0043] As the HPN-20E nucleating agent is an organic compound, it does not offer the effect of physical barrier on the permeating agent as the filler does. Additionally, it is believed that mica acts either in the physical barrier as well as in the orientation of the crystalline polyethylene lamellae. Note that the use of these two components in isolation does not result in proper barrier levels for markets like cardboard packages for milk, BOPP films, PE films for refrigerated and perishable products, fuel tanks and agrochemical containers.

Examples 13, 14, 15, 16 and Comparative Example A

[0044] According to the previous researches, a combination of mica and HPN-20E product were tested for evaluation of potential effect to improve the oxygen barrier property of HDPE. Permeability results are displayed in Table 6 and may be compared to examples shown in Tables 4 and 5. The samples were injection molded into 2 mm thick plaques.

[0045] Surprisingly, the combination of mica and HPN-20E agent results in synergic improvement in the oxygen barrier property of HDPE, which is better than their isolated performance even with considerably lower amounts of each additive. It is postulated that mica is complementing the effect of the HPN-20E product's crystalline lamellae orientation, besides its physical barrier effect. Table 6 - HDPE oxygen barrier property with different combinations of mica M34 and

HPN-20E nucleating agent.

Claims

What is claimed is:

1. A polymeric composition, comprising:

from about 99.89% to 65% by weight of a polyolefm resin;

from about 0.01% to 5% by weight a nucleating agent or a clarifying agent; and from about 0.1% to 30% by weight of a filler.

2. The composition of claim 1, wherein the polyolefm resin comprises polyethylene, polypropylene, or a mixture thereof.

3. The composition of claim 2, wherein the polyethylene comprises a low density polyethylene, a medium density polyethylene, a high density polyethylene, or any combination thereof.

4. The composition of claim 2, wherein the polypropylene comprises a polypropylene

homopolymer, randomized copolymer or heterophasic copolymer, or any combination thereof.

5. The composition of claim 1, wherein the filler comprises lamellar filler capable of changing the crystalline structure of polyolefm resin solidified from a molten state.

6. The composition of claim 1, wherein the filler comprises a filler component selected from a mica and/or a clay and/or graphite and/or graphene.

7. The composition of claim 6, wherein the filler component comprises muscovite, phlogopite, vermiculite, montmorillonite, kaolinite, laponite, wollastonite, hectorite, or any combination thereof.

8. The composition of claim 1, wherein the nucleating agent or clarifying agent comprises at least one metal salt from a saturated bicyclic dicarboxylate, hexahydrophthalic acid, dibenzylidene sorbitol and dibenzylidene sorbitol derivatives, or sodium benzoate.