Patent Application
20080061468
Disclosed herein are polymeric compositions comprising a high ethylene random copolymer and a nucleator. These compositions may be used in the production of fibers. The fibers may be produced by any methodology known to one of ordinary skill in the art; alternatively the fibers are produced through the methodologies disclosed herein. In an embodiment, polymeric compositions comprising a high ethylene random copolymer (HERCP) and a nucleator may be more readily processed into a fiber than an otherwise identical composition lacking a nucleator.
In an embodiment, the polymeric composition comprises a HERCP. The HERCP may be, for example a copolymer comprising a high ethylene content along with one or more alpha olefin monomers such as propylene, butene, hexene, etc. In an embodiment, the HERCP is a random ethylene-propylene (C2/C3) copolymer. Herein the HERCP may comprise greater than 3 weight percent (wt. %) ethylene, alternatively greater than 4 wt. % ethylene, alternatively greater than 5 wt. % ethylene, alternatively greater than 6 wt. % ethylene.
The HERCP may be further characterized by a high xylene solubles content (XS %). In an embodiment, the HERCP may comprise greater than 5 wt. % xylene solubles, alternatively greater than 6 wt. % xylene solubles, alternatively greater than 7 wt. % xylene solubles. Methods for determination of the XS % are known in the art, for example the XS % may be determined in accordance with ASTM D 5492-98. Typically, the XS % in the polymer is indicative of the extent of crystalline polymer formed. In determining the xylene soluble fraction (XS %), the polymer is dissolved in boiling xylene and then the solution cooled to 0° C. which results in the precipitation of the isotactic or crystalline portion of the polymer. The XS % is that portion of the original amount that remained soluble in the cold xylene. The total amount of polymer (100%) is the sum of the xylene soluble fraction and the xylene insoluble fraction.
The HERCP melt flow rate (MFR) may vary over a range of values. In an embodiment, the HERCP has a melt flow rate ranging iteratively from 1 g/10 min. to 1000 g/10 min., alternatively from 5 g/10 min. to 100 g/10 min., alternatively from 10 g/10 min. to 50 g/10 min., alternatively from 10 g/10 min. to 35 g/10 min. As defined herein, the MFR refers to the quantity of a melted polymer resin that will flow through an orifice at a specified temperature and under a specified load. The MFR may be determined using a dead-weight piston Plastometer that extrudes a polymer through an orifice of specified dimensions at a temperature of 230° C., and a load of 2.16 kg in accordance with ASTM D-1238. Without intending to be limited by theory, HERCPs of this disclosure having the indicated MFR will facilitate fiber spinning.
In some embodiments, the HERCP MFR may optionally be adjusted by various techniques such as visbreaking. Herein visbreaking refers to a chemical reaction that lowers the viscosity of the polymer melt through the controlled scission of polymer chains. Specifically, visbreakers are compounds which may be incorporated in the polymeric composition in order to modify the MFR. Such compounds are well known to one of ordinary skill in the art and may include for example and without limitation peroxides and hydroxylamine esters. Visbreakers AND methods of increasing the MFR by visbreaking are described in U.S. Pat. Nos. 6,503,990 and 7,030,196 each of which is incorporated by reference in its entirety.
In an embodiment, the HERCP contains peroxide as a visbreaking agent. In such embodiments, a peroxide used for visbreaking may be present in an amount ranging iteratively from 50 ppm to 1000 ppm, alternatively from 100 ppm to 500 ppm, alternatively from 200 ppm to 300 ppm.
In an embodiment, the HERCP may have a melting point of less than or equal to 140° C.; alternatively less than or equal to 135° C., alternatively less than or equal to 126° C. As used herein, melting point is measured by differential scanning calorimetry using a modified version of ASTM D 3418-99. Specifically, for a sample weighing between 5 mg and 10 mg, the following standard test conditions involved heating the sample from 50° C. to 210° C. to erase the thermal history of the sample, followed by holding the sample at 210° C. for 5 minutes. The sample is then cooled to 50° C. to induce recrystallization and subsequently subjected to a second melt in the temperature range 50° C. to 190° C. For each of these temperature changes, the temperature is increased at a rate of 10° C./min.
Without limitation, examples of a suitable HERCP are Z9450 and Z9470 which are ethylene-propylene random copolymers available from Total Petrochemicals USA, Inc. In an embodiment, the high ethylene random copolymer (e.g., Z9450) has generally the physical properties set forth in Table I.
(1)MP determined with a DSC-2 Differential Scanning Calorimeter.
(2)CRed is Controlled Rheology and refers to polymer that has been vis-broken or undergone chemically-induced chain scission.
A HERCP may be formed by the catalyzed polymerization of a mixture of C2 and C3 olefin monomers using any means known to one of ordinary skill in the art. For example, a HERCP may be prepared through the use of conventional Ziegler-Natta catalysts, such as described in U.S. Pat. Nos. 4,298,718 and 4,544,717, each of which is incorporated herein by reference. A HERCP may also be prepared through the use of metallocene catalysts of the type disclosed and described in further detail in U.S. Pat. Nos. 5,158,920, 5,416,228, 5,789,502, 5,807,800, 5,968,864, 6,225,251, and 6,432,860, each of which is incorporated herein by reference.
Standard equipment and procedures for polymerizing the propylene and ethylene into a random copolymer are known to one skilled in the art. The olefin polymerization may be carried out using solution phase, gas phase, slurry phase, bulk phase, high pressure processes or combinations thereof, for example. See, U.S. Pat. Nos. 5,525,678, 6,420,580, 6,380,328, 6,359,072, 6,346,586, 6,340,730, 6,339,134, 6,300,436, 6,274,684, 6,271,323, 6,248,845, 6,245,868, 6,245,705, 6,242,545, 6,211,105, 6,207,606, 6,180,735 and 6,147,173, which are incorporated by reference herein. Alternatively, other types of polymerization processes may be used, such as stirred reactors in series, parallel or combinations thereof, for example. Upon removal from the reactor, the polymer may be passed to a polymer recovery system for further processing, such as addition of additives and/or extrusion, for example.
In an embodiment, a high ethylene polymeric composition (HEPC) and the fiber produced therefrom comprises a nucleator. Any nucleator chemically compatible with the HERCP and that is able to improve the mechanical properties thereof may be included in the composition. Such mechanical properties are known to one of ordinary skill in the art and may include for example the fiber tenacity and fiber stiffness. Herein nucleators or nucleating agents refer to compounds that increase the rate of crystallization of the polymer. Without wishing to be limited by theory, a nucleator may provide a heterogeneous surface that acts as a crystallization site and increases the rate of polymer crystallization. In the presence of a nucleator, crystals may form at higher temperatures and the higher rate of crystal formation induces formation of smaller crystals such as spherulites.
Without intending to be limited by theory, a nucleator suitable for use in this disclosure is one capable of promoting rapid nucleation following a fiber spinning process such that the newly formed fiber develops mechanical strength, tenacity, and stiffness sufficient to withstand subsequent processing steps.
Nucleators may be added in any amount sufficient to impart improved mechanical properties in a HEPC. In an embodiment, the nucleator is a norbornane carboxylic acid salt, such as [2,2,1]heptane-bicyclodicarboxylic acid present in amounts in a HEPC ranging iteratively from 50 ppm to 1000 ppm, alternatively from 100 ppm to 800 ppm, alternatively from 150 ppm to 600 ppm, alternatively from 250 ppm to 500 ppm. An example of a norbornane carboxylic acid salt is HYPERFORM HPN-68, available from Milliken Chemical of Spartanburg, S.C. Alternatively, the nucleator may be a metal benzoate, sodium benzoate, a sorbitol, an organophosphate, a talc, or combinations thereof. In such embodiments, the nucleator may be present in the HEPC in amounts ranging iteratively from 50 ppm to 3000 ppm, alternatively from 100 ppm to 2000 ppm, alternatively from 150 ppm to 1000 ppm, alternatively from 250 ppm to 800 ppm.
An HEPC is formed upon nucleation of a HERCP. In an embodiment, a HERCP may be nucleated by adding the nucleating agent in the form of a powder or a fluff after the polymerization process but before the polymer is melted and formed into pellets. Alternatively, a HERCP may be nucleated after the polymer has been formed into pellets upon remelting immediately prior to extrusion. Various techniques for blending polymeric components may be used to produce a HEPC and are known to one skilled in the art. Examples of suitable blending techniques include without limitation solution blending, solid state physical admixture, molten state admixture, extrusion admixture, roll milling, screw extrusion, and the like.
In an embodiment, the HEPC may optionally contain modifiers or additives as necessary to impart desired physical properties. Examples of modifiers include without limitation stabilizers, clarifiers, ultra-violet screening agents, oxidants, acid neutralization agents, anti-oxidants, anti-static agents, ultraviolet light absorbents, fire retardants, processing oils, mold release agents, coloring agents, pigments/dyes, fillers, and/or the like with other components. The modifiers may be added in amounts effective to suit the particular needs or desires of a user or maker, and various combinations of the additives may be used. For example, stabilizers or stabilization agents may be employed to help protect the polymer resin from degradation due to exposure to excessive temperatures and/or ultraviolet light. The aforementioned modifiers may be used either singularly or in combination to form various formulations of the polymer. These modifiers may be included in amounts effective to impart the desired properties. Effective modifier amounts and processes for inclusion of these additives to a HEPC are known to one skilled in the art.
In an embodiment, a HERCP may be nucleated, forming a HEPC, and further processed into a fiber. The processing steps may be carried out in any order capable of producing a fiber using any device capable of carrying out the disclosed steps as would be known to one skilled in the arts. As illustrated in
The improved fiber processing disclosed herein may also be applicable to aspirators in a typical spun bonded fiber extrusion line, such as known to one skilled in the art. In such an embodiment, the filaments extruded from the spinneret are initially quenched in air and then pass to an air Venturi aspirator where they are exposed to high-velocity stream of heated air that stretches and orient the filaments. Draw down takes place at very high speeds up to 5000 meters per minute. At the outlet of the aspirator, the fibers are randomly blown onto an endless mesh belt, where, with suction assistance, they form a mat or web. The web is subsequently stabilized by a variety of means including for example hot air bonding, adhesive bonding, stitching or needle punching. The web may be calendered to provide a smooth or textured surface and may also be oriented by tentering.
A HEPC and fibers manufactured there from may display an improved tensile strength as determined by an increase in the tensile modulus. In an embodiment, the HEPC has a tensile modulus ranging iteratively from 60,000 psi to 90,000 psi, alternatively from 65,000 psi to 90,000 psi, alternatively from 70,000 psi to 90,000 psi as determined in accordance with ASTM D-638. The tensile modulus may be measured by determining the force required to stretch a specimen to the breaking point and the amount the specimen elongates when stretched to that point. Test specimens are often in the shape of bars but other shapes can be used as appropriate for the material being tested. The test procedure is typically performed by an automated apparatus specially designed for performing tensile tests. Two gripping devices within the apparatus are clamped to the specimen at a specified distance from each other. The apparatus moves the gripping devices away from each other so that they pull the specimen apart and stretch it until it breaks. Automated data acquisition modules within the test apparatus measure and record the tensile modulus.
The HEPC and fibers manufactured there from may display an improved stiffness as determined by an increase in the flexural modulus. In an embodiment, the HEPC have a flexural modulus ranging iteratively from 60,000 psi to 90,000 psi, alternatively from 65,000 psi to 90,000 psi, alternatively from 70,000 psi to 90,000 psi as determined in accordance with ASTM D-790. Flexural modulus is an indicator of material stiffness and specifically is a measure of the resistance to breaking or snapping when a material is bent or flexed. The flexural modulus may be tested by measuring the force required to bend a sample material beam. Test specimens are typically 2.5 inch by 0.5 inch by 0.125-inch bars, but other sizes and shapes could be used. A test specimen is typically placed across a span and a load is applied to the center of the specimen. The load is increased until a specified deflection occurs. The length of the span, the load, and the amount of deflection determines the flexural force.
In an embodiment, the fiber produced by the method disclosed above may have an improved strength and/or toughness. For instance, the fiber product may exhibit a tenacity greater than or equal to 1.0 grams per denier, alternatively greater than or equal to 2.0 grams per denier, alternatively greater than or equal to 3.0 grams per denier as determined in accordance with ASTM D-3822.
In an embodiment, the fiber is capable of being drawn at a draw ratio of 2.0:1 to 5.0:1. Alternatively, the fiber may exhibit a draw ratio of 3.0:1 to 5.0:1. Moreover, the fiber produced by the method disclosed above may have an improved secant modulus. The fiber may comprise a measured 5% secant modulus ranging iteratively from 2.0 grams per denier to 20 grams per denier, alternatively from 7.0 grams per denier to 15 grams per denier, as measured by ASTM D-882. The secant modulus is a measure of the stress to strain response of a material or the ability to withstand deformation under an applied force. The 5% secant modulus for each HEPC may be determined in accordance with ASTM D-882.
In an embodiment, the fiber has a denier per filament of from 1.0 grams per 9000 meters to 20.0 grams per 9000 meters, alternatively from 1.0 grams per 9000 meters to 15 grams per 9000 meters, alternatively from 1.0 gram per 9000 meters to 10 grams per 9000 meters, as measured in accordance with ASTM D1907-01. Denier per filament (dpf) is the weight in grams of 9,000 meters of the individual filament. It can be calculated by taking the yarn denier and dividing it by the number of filaments in the yarn bundle.
Examples of end use articles into which the fiber made from the HEPC may be formed include individual and woven fibers such as yarns and fabrics. In an embodiment, the end-use articles are individual fibers for use in concrete reinforcement and fibers suitable for use as binding fibers in multi-fiber woven fabrics. Additional end use articles would be apparent to those skilled in the art.
The disclosure having been generally described, the following examples are given as particular embodiments of the disclosure and to demonstrate the practice and advantages thereof. It is understood that the examples are given by way of illustration and are not intended to limit the specification of the claims in any manner. Unless otherwise indicated, physical properties were determined in accordance with the test methods previously identified in the detailed description.
The effect of nucleators on the processability of high ethylene random copolymers was investigated. A polymeric composition, Sample 2, was visbroken from 5 MFR to 18 MFR using LUPERSOL 101, a peroxide visbreaker available from Arkema Inc. In order to improve the fiber processing characteristics, 250 ppm HYPERFORM HPN-68, a nucleator, was also added to Sample 2. A control run, Sample 1, without the addition of the nucleator was also performed. Table II shows the resin properties of the control sample, Sample 1, compared to the resin properties of the sample containing nucleator, Sample 2.
(1)Differential Scanning Calorimeter.
(2)Yes means the strands can be aspirated continuously with aspirator wand.
During experimentation, it was observed that Sample 1 could not be aspirated with the aspirator wand under the cooling chimney of a Fourne fiber line. Without wishing to be limited by theory, this may be due to the high xylene solubles content of the polymer resin. As a result, even fully oriented yarns could not easily be made at relatively low spinning rates. However, an improvement in aspiration was noticed with the addition of 250 ppm HPN-68 in Sample 2. Without intending to be limited by theory, the improvement in aspiration is hypothesized to be due to the increased degree of crystallinity and chain orientation of the strands in the presence of the nucleating agent as the strands reach the aspirator below the cooling chimney, although the apparent stick points are not improved. Even though Sample 2 containing HPN-68 cannot be run under partially oriented yarn protocol at high take-up speed, fully oriented yarns can easily be produced as the first pair of uptake rollers, also known as the godet duo, is run at lower speeds. This is to say that HPN-68 effectively accelerates the re-crystallization rate during fiber spinning of high ethylene polymeric compositions even for finer denier yarns. The physical properties of the fibers produced with Sample 2 are shown in Table III.
The results demonstrate that the addition of 250 ppm HPN-68 noticeably improves the fiber processing, including aspiration, of a high ethylene and xylene level random copolymer. As a result, the sample containing the nucleator, Sample 2, could easily produce fully oriented yarns with a maximum draw ratio of 5:1.
The effect of visbreaking and different nucleators on the processability of high ethylene random copolymers was investigated and the results are shown in Table IV. Sample 3 is a reactor grade 5 MFR non-nucleated resin, and Sample 4 is also non-nucleated but visbroken from 5 MFR to 18 MFR resin. Samples 5 through 9 are visbroken 18 MFR materials nucleated with NaBz, NA-11, NA-21, Millad 3988, HPN-68L, respectively. In this example, Sample 3 could not be aspirated. However, visbreaking helped improve the fiber processing as demonstrated by the result that Sample 4 could be easily aspirated. Various nucleating agents may have also helped fiber processing of the visbroken materials, but the improvement could not be identified due to the excellent aspiration of the visbroken base resin.
The tensile properties and shrinkages of the fully oriented yarns (FOY) made at 3:1 draw ratio are shown in Table IV. For the two non-nucleated compounds, it is expected that visbreaking cuts short the molecular weight and results in less chain orientation and hence low yarn tenacity. However, with the same melt flow rate, i.e. 18 MFR, yarn tenacities of the nucleated compounds can be almost 50% higher than the non-nucleated yarns made at the same draw ratio. Without intending to be limited by theory, the improvement in aspiration is hypothesized to be due to the improved total chain orientation. The FOY protocol is actually composed of two drawing stages, i.e. spin draw (partially oriented) and cold draw (mechanical draw). Even though the second stage cold draw ratio is the same, without being bound to any one theory, the nucleators apparently accelerated the crystallization of the skins of the spin line, resulting in higher degree of orientation during the melt spin draw stage. As a result, the final yarns of nucleated resins possess a higher tenacity than non-nucleated yarns.
While embodiments of the disclosure have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the disclosure. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications disclosed herein are possible and are within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from 1 to 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). Use of the term “optionally” with respect to any element of a claim is intended to mean that the subject element is required, or alternatively, is not required. Both alternatives are intended to be within the scope of the claim. Use of broader terms such as comprises, includes, having, etc. should be understood to provide support for narrower terms such as consisting of, consisting essentially of, comprised substantially of, etc.
Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present disclosure. Thus, the claims are a further description and are an addition to the disclosed embodiments of the present disclosure. The discussion of a reference herein is not an admission that it is prior art to the present disclosure, especially any reference that may have a publication date after the priority date of this application. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference, to the extent that they provide exemplary, procedural or other details supplementary to those set forth herein.
