Abstract:
A synthetic turf surface including a synthetic grass carpet having a flexible base sheet, and a shock absorbing pad, wherein the shock absorbing pad includes a non-crosslinked polyolefin foam is shown and described. The foam may be recyclable, as it is non-crosslinked.

Description:
BACKGROUND OF INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments disclosed herein relate generally to a thermoplastic foam shock absorbing layer. In another aspect, embodiments described herein relate to a synthetic turf including a thermoplastic foam shock absorbing layer, where the foam may be recyclable. 
         [0003]    2. Background 
         [0004]    Artificial turf consists of a multitude of artificial grass tufts extending upward from a sheet substrate. The turf is usually laid upon a prepared, flat ground surface to form a game playing field intended to simulate a natural grass playing field surface. 
         [0005]    For some types of games, a resilient underpad is placed beneath the turf and upon the firm ground support surface to provide a shock absorbing effect. Also, in some instances, a layer of sand or other particulate material is placed upon the upper surface of the carpet base sheet and around the strands. An example of this type of construction is shown in U.S. Pat. No. 4,389,435 issued Jun. 21, 1983 to Frederick T. Haas, Jr. Another example is shown in U.S. Pat. No. 4,637,942 issued Jan. 20, 1987 to Seymour A. Tomarin. 
         [0006]    Further, examples of artificial turfs which are formed with the grass-like carpet placed upon a resilient underpad are disclosed in U.S. Pat. No. 3,551,263 issued Dec. 29, 1970 to Carter et al., which discloses a polyurethane foam underpad; U.S. Pat. No. 3,332,828 issued Jul. 25, 1967 to Faria et al., which discloses a PVC foam plastic or polyurethane foam plastic underpad; U.S. Pat. No. 4,637,942 issued Jan. 20, 1987 to Seymour A. Tomarin which discloses a rubber-like underpad; U.S. Pat. No. 4,882,208 issued Nov. 21, 1989 to Hans-Urich Brietschidel, which illustrates a closed cell crosslinked polyethylene foam underpad; U.S. Pat. No. 3,597,297 issued Aug. 3, 1971 to Theodore Buchholz et al., which discloses a polyurethane underpad having voids; and U.S. Pat. No. 4,505,960 issued Mar. 19, 1985 to James W. Leffingwell, which discloses shock absorbing pads made from elastomer foams of polyvinyl chloride, polyethylene, polyurethane, polypropylene, etc. 
         [0007]    Shock absorbing layers may, of course, be more broadly used in other applications, such as in energy dampening in floors, for example. What is still needed, therefore, are improved materials and methods for forming shock absorbing layers, including recyclable shock absorbing layers. 
       SUMMARY OF INVENTION 
       [0008]    In one aspect, embodiments disclosed herein relate to a synthetic turf surface comprising a synthetic grass carpet having a flexible base sheet, and a shock absorbing pad, wherein the shock absorbing pad comprises a non-crosslinked polyolefin foam. 
         [0009]    Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF FIGURES 
         [0010]      FIG. 1  illustrates instrumentation and experimentation for a shock absorption test using FIFA standards. 
           [0011]      FIGS. 2 and 2   c  compare results of the compressive stress-strain behavior analyses of foams according to embodiments disclosed herein to those of crosslinked polyethylene foams. 
           [0012]      FIGS. 3 and 3   c  compare compressive strain versus time test results for foams according to embodiments disclosed herein to those of crosslinked polyethylene foams. 
           [0013]      FIG. 4  compare compressive creep behavior test results for foams according to embodiments disclosed herein to those of crosslinked polyethylene foams. 
           [0014]      FIG. 5  illustrates synthetic turf that may be formed using embodiments of the non-crosslinked polyolefin foams described herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    General Definitions and Measurement Methods: 
         [0016]    The following terms shall have the given meaning for the purposes of this invention: 
         [0017]    “Polymer” means a substance composed of molecules with large molecular mass consisting of repeating structural units, or monomers, connected by covalent chemical bonds. The term ‘polymer’ generally includes, but is not limited to, homopolymers, copolymers such as block, graft, random and alternating copolymers, terpolymers, etc., and blends and modifications thereof. Further, unless otherwise specifically limited, the term ‘polymer’ shall include all possible geometrical configurations of the molecular structure. These configurations include isotactic, syndiotactic, random configurations, and the like. 
         [0018]    “Interpolymer” means a polymer prepared by the polymerization of at least two different types of monomers. The generic term “interpolymer” includes the term “copolymer” (which is usually employed to refer to a polymer prepared from two different monomers) as well as the term “terpolymer” (which is usually employed to refer to a polymer prepared from three different types of monomers). The class of materials known as “interpolymers” also encompasses polymers made by polymerizing four or more types of monomers. 
         [0019]    Density of resins and compositions is measured according to ASTM D792. 
         [0020]    Density of foams is measured according to ASTM D3575/W/B. 
         [0021]    “Melt Index (I2)” is determined according to ASTM D1238 using a weight of 2.16 kg at 190° C. for polymers comprising ethylene as the major component in the polymer. “Melt Flow Rate (MFR)” is determined according to ASTM D1238 using a weight of 2.16 kg at 230° C. for polymers comprising propylene as the major component in the polymer. 
         [0022]    Molecular weight distribution of the polymers is determined using gel permeation chromatography (GPC) on a Polymer Laboratories PL-GPC-220 high temperature chromatographic unit equipped with four linear mixed bed columns (Polymer Laboratories (20-micron particle size)). The oven temperature is at 160° C. with the autosampler hot zone at 160° C. and the warm zone at 145° C. The solvent is 1,2,4-trichlorobenzene containing 200 ppm 2,6-di-t-butyl-4-methylphenol. The flow rate is 1.0 milliliter/minute and the injection size is 100 microliters. About 0.2% by weight solutions of the samples are prepared for injection by dissolving the sample in nitrogen purged 1,2,4-trichlorobenzene containing 200 ppm 2,6-di-t-butyl-4-methylphenol for 2.5 hrs at 160° C. with gentle mixing. 
         [0023]    The molecular weight determination is deduced by using ten narrow molecular weight distribution polystyrene standards (from Polymer Laboratories, EasiCal PS1 ranging from 580-7,500,000 g/mole) in conjunction with their elution volumes. The equivalent polypropylene molecular weights are determined by using appropriate Mark-Houwink coefficients for polypropylene (as described by Th. G. Scholte, N. L. J. Meijerink, H. M. Schoffeleers, and A.M.G. Brands, J. Appl. Polym. Sci., 29, 3763-3782 (1984)) and polystyrene (as described by E. P. Otocka, R. J. Roe, N. Y. Hellman, P. M. Muglia, Macromolecules, 4, 507 (1971)) in the Mark-Houwink equation: 
         [0000]      {N}=KM a  where K pp =1.90E-04, a pp =0.725 and K ps =1.26E-04, a ps =0.702. 
         [0000]    “Molecular weight distribution” or MWD is measured by conventional GPC per the procedure described by Williams, T.; Ward, I. M. Journal of Polymer Science, Polymer Letters Edition (1968), 6(9), 621-624. Coefficient B is 1. Coefficient A is 0.4316. 
         [0024]    The term high pressure low density type resin is defined to mean that the polymer is partly or entirely homopolymerized or copolymerized in autoclave or tubular reactors at pressures above 14,500 psi (100 MPa) with the use of free-radical initiators, such as peroxides (see for example U.S. Pat. No. 4,599,392, herein incorporated by reference) and includes “LDPE” which may also be referred to as “high pressure ethylene polymer” or “highly branched polyethylene”. The cumulative detector fraction (CDF) of these materials is greater than about 0.02 for molecular weight greater than 1000000 g/mol as measured using light scattering. CDF may be determined as described in WO2005/023912 A2, which is herein incorporated by reference for its teachings regarding CDF. The preferred high pressure low density polyethylene material (LDPE) has a melt index MI (I2) of less than about 20, more preferably less than about 15, most preferably less than 10, and greater than about 0.1, more preferably greater than about 0.2, most preferably more than 0.3 g/10 min. The preferred LDPE will have a density between about 0.915 g/cm3 and 0.930 g/cm 3 , with less than 0.925 g/cm 3  being more preferred. 
         [0025]    “Crystallinity” means atomic dimension or structural order of a polymer composition. Crystallinity is often represented by a fraction or percentage of the volume of the material that is crystalline or as a measure of how likely atoms or molecules are to be arranged in a regular pattern, namely into a crystal. Crystallinity of polymers can be adjusted fairly precisely and over a very wide range by heat treatment. A “crystalline” “semi-crystalline” polymer possesses a first order transition or crystalline melting point (Tm) as determined by differential scanning calorimetry (DSC) or equivalent technique. The term may be used interchangeably with the term “semicrystalline”. The term “amorphous” refers to a polymer lacking a crystalline melting point as determined by differential scanning calorimetry (DSC) or equivalent technique. 
         [0026]    Differential Scanning Calorimetry (DSC) is a common technique that can be used to examine the melting and crystallization of semi-crystalline polymers. General principles of DSC measurements and applications of DSC to studying semi-crystalline polymers are described in standard texts (e.g., E. A. Turi, ed., Thermal Characterization of Polymeric Materials, Academic Press, 1981). DSC is a method suitable for determining the melting characteristics of a polymer. 
         [0027]    DSC analysis was done using a model Q1000 DSC from TA Instruments, Inc. DSC is calibrated by the following method. First, a baseline is obtained by running the DSC from −90° C. to 290° C. without any sample in the aluminum DSC pan. Then 7 milligrams of a fresh indium sample is analyzed by heating the sample to 180° C., cooling the sample to 140° C. at a cooling rate of 10° C./min followed by keeping the sample isothermally at 140° C. for 1 minute, followed by heating the sample from 140° C. to 180° C. at a heating rate of 10° C./min. The heat of fusion and the onset of melting of the indium sample are determined and checked to be within 0.5° C. to 156.6° C. for the onset of melting and within 0.5 J/g to 28.71 J/g for the heat of fusion. Then deionized water is analyzed by cooling a small drop of flesh sample in the DSC pan from 25° C. to −30° C. at a cooling rate of 10° C./min. The sample is kept isothermally at −30° C. for 2 minutes and heated to 30° C. at a heating rate of 10° C./min. The onset of melting is determined and checked to be within 0.5° C. to 0° C. 
         [0028]    Polymer samples were pressed into a thin film at an initial temperature of 190° C. (designated as the ‘initial temperature’). About 5 to 8 mg of sample is weighed out and placed in the DSC pan. The lid is crimped on the pan to ensure a closed atmosphere. The DSC pan is placed in the DSC cell and then heated at a rate of about 100° C./min to a temperature (T o ) of about 60° C. above the melt temperature of the sample. The sample is kept at this temperature for about 3 minutes. Then the sample is cooled at a rate of 10° C./min to −40° C., and kept isothermally at that temperature for 3 minutes. Consequently the sample is heated at a rate of 10° C./min until complete melting. Enthalpy curves resulting from this experiment are analyzed for peak melt temperature, onset and peak crystallization temperatures, heat of fusion and heat of crystallization, and any other DSC analyses of interest. 
         [0029]    For a polymer comprising polypropylene crystallinity is analyzed, T o  is 230° C. T o  is 190° C. when polyethylene crystallinity is present and no polypropylene crystallinity is present in the sample. 
         [0030]    Percent crystallinity by weight is calculated according to the following formula: 
         [0000]    
       
         
           
             
               Crystallinity 
                
               
                 ( 
                 
                   wt 
                   . 
                   
                       
                   
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                   % 
                 
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         [0000]    such that the heat of fusion (ΔH) is divided by the heat of fusion for the perfect polymer crystal (ΔH o ) and then multiplied by 100%. For ethylene crystallinity, ΔH o  is taken to be 290 J/g. For example, an ethylene-octene copolymer which upon melting of its polyethylene crystallinity is measured to have a heat of fusion of 29 J/g; the corresponding crystallinity is 10% by weight. For propylene crystallinity, ΔH o  is taken to be 165 J/g. For example, a propylene-ethylene copolymer which upon melting of its propylene crystallinity is measured to have a heat of fusion of 20 J/g; the corresponding crystallinity is 12.1% by weight. 
         [0031]    “Non crosslinked” As used herein, the term non-crosslinked refers to polymers that have between 0-10% gel, more preferably, 0-5%, and more preferably 0-1%. It should not be construed that absolutely zero crosslinking is present, as some crosslinking may inevitably occur during processing, but that the crosslinking should be kept to a minimum to allow for recyclability. 
       Foam Shock Absorbing Layer 
       [0032]    In one aspect, embodiments described herein relate to a thermoplastic foam shock absorbing layer. In another aspect, embodiments described herein relate to a synthetic turf including a thermoplastic foam shock absorbing layer. In selected applications, embodiments described herein relate to a thermoplastic non-crosslinked polymer foam shock absorption layer having the following characteristics: 
         [0033]    1) Foam thickness: between 8 and 30 mm; 
         [0034]    2) Foam density: between 30 and 150 kg/m3; 
         [0035]    3) Foam cell size: between 0.2 and 3 mm; and 
         [0036]    4) % Open cell volume is low, so as to avoid water uptake: typically less than 35%. 
         [0037]    Polymer 
         [0038]    The thermoplastic polymer used to form the shock absorbing layer may vary depending upon the particular application and the desired result. In one embodiment, for instance, the polymer is an olefin polymer. As used herein, an olefin polymer, in general, refers to a class of polymers fanned from hydrocarbon monomers having the general formula C n H 2n . The olefin polymer may be present as a copolymer, such as an interpolymer, a block copolymer, or a multi-block interpolymer or copolymer. 
         [0039]    In one particular embodiment, for instance, the olefin polymer may comprise an alpha-olefin interpolymer of ethylene with at least one comonomer selected from the group consisting of a C 3 -C 20  linear, branched or cyclic diene, or an ethylene vinyl compound, such as vinyl acetate, and a compound represented by the formula H 2 C═CHR wherein R is a C 1 -C 20  linear, branched or cyclic alkyl group or a C 6 -C 20  aryl group. Examples of comonomers include propylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-hexene, 1-octene, 1-decene, and 1-dodecene. 
         [0040]    In other embodiments, the polymer may be an alpha-olefin interpolymer of propylene with at least one comonomer selected from the group consisting of ethylene, a C 4 -C 20  linear, branched or cyclic diene, and a compound represented by the formula H 2 C═CHR wherein R is a C 1 -C 20  linear, branched or cyclic alkyl group or a C 6 -C 20  aryl group. Examples of comonomers include ethylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-hexene, 1-octene, 1-decene, and 1-dodecene. In some embodiments, the comonomer is present at about 5% by weight to about 25% by weight of the interpolymer. In one embodiment, a propylene-ethylene interpolymer is used. 
         [0041]    Other examples of polymers which may be used in the present disclosure include homopolymers and copolymers (including elastomers) of an olefin such as ethylene, propylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-hexene, 1-octene, 1-decene, and 1-dodecene as typically represented by polyethylene, polypropylene, poly-1-butene, poly-3-methyl-1-butene, poly-3-methyl-1-pentene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, ethylene-1-butene copolymer, and propylene-1-butene copolymer; copolymers (including elastomers) of an alpha-olefin with a conjugated or non-conjugated diene as typically represented by ethylene-butadiene copolymer and ethylene-ethylidene norbornene copolymer; and polyolefins (including elastomers) such as copolymers of two or more alpha-olefins with a conjugated or non-conjugated diene as typically represented by ethylene-propylene-butadiene copolymer, ethylene-propylene-dicyclopentadiene copolymer, ethylene-propylene-1,5-hexadiene copolymer, and ethylene-propylene-ethylidene norbornene copolymer; ethylene-vinyl compound copolymers such as ethylene-vinyl acetate copolymers with N-methylol functional comonomers, ethylene-vinyl alcohol copolymers with N-methylol functional comonomers, ethylene-vinyl chloride copolymer, ethylene acrylic acid or ethylene-(meth)acrylic acid copolymers, and ethylene-(meth)acrylate copolymer; styrenic copolymers (including elastomers) such as polystyrene, ABS, acrylonitrile-styrene copolymer, methylstyrene-styrene copolymer; and styrene block copolymers (including elastomers) such as styrene-butadiene copolymer and hydrate thereat, and styrene-isoprene-styrene triblock copolymer; polyvinyl compounds such as polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinylidene chloride copolymer, polymethyl acrylate, and polymethyl methacrylate; polyamides such as nylon 6, nylon 6,6, and nylon 12; thermoplastic polyesters such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate, polyphenylene oxide, and the like. These resins may be used either alone or in combinations of two or more. 
         [0042]    In particular embodiments, polyolefins such as polypropylene, polyethylene, and copolymers thereof and blends thereof, as well as ethylene-propylene-diene terpolymers may be used. In some embodiments, the olefinic polymers include homogeneous polymers described in U.S. Pat. No. 3,645,992 by Elston; high density polyethylene (HDPE) as described in U.S. Pat. No. 4,076,698 to Anderson; heterogeneously branched linear low density polyethylene (LLDPE); heterogeneously branched ultra low linear density (ULDPE); homogeneously branched, linear ethylene/alpha-olefin copolymers; homogeneously branched, substantially linear ethylene/alpha-olefin polymers which can be prepared, for example, by a process disclosed in U.S. Pat. Nos. 5,272,236 and 5,278,272, the disclosure of which process is incorporated herein by reference; heterogeneously branched linear ethylene/alpha olefin polymers; and high pressure, free radical polymerized ethylene polymers and copolymers such as low density polyethylene (LDPE). 
         [0043]    In another embodiment, the polymers may include an ethylene-carboxylic acid copolymer, such as, ethylene-vinyl acetate (EVA) copolymers, ethylene-acrylic acid (EAA) and ethylene-methacrylic acid copolymers such as, for example, those available under the tradenames PRIMACOR™ from the Dow Chemical Company, NUCREL™ from DuPont, and ESCOR™ from ExxonMobil, and described in U.S. Pat. Nos. 4,599,392, 4,988,781, and 59,384,373, each of which is incorporated herein by reference in its entirety. Exemplary polymers include polypropylene, (both impact modifying polypropylene, isotactic polypropylene, atactic polypropylene, and random ethylene/propylene copolymers), various types of polyethylene, including high pressure, free-radical LDPE, Ziegler Natta LLDPE, metallocene PE, including multiple reactor PE (“in reactor”) blends of Ziegler-Natta PE and metallocene PE, such as products disclosed in U.S. Pat. Nos. 6,545,088, 6,538,070, 6,566,446, 5,844,045, 5,869,575, and 6,448,341. Homogeneous polymers such as olefin plastomers and elastomers, ethylene and propylene-based copolymers (for example polymers available under the trade designation VERSIFY™ available from The Dow Chemical Company and VISTAMAXX™ available from ExxonMobil) may also be useful in some embodiments. Of course, blends of polymers may be used as well. In some embodiments, the blends include two different Ziegler-Natta polymers. In other embodiments, the blends may include blends of a Ziegler-Natta and a metallocene polymer. In still other embodiments, the thermoplastic resin used herein may be a blend of two different metallocene polymers. 
         [0044]    In one particular embodiment, the polymer may comprise an alpha-olefin interpolymer of ethylene with a comonomer comprising an alkene, such as 1-octene. The ethylene and octene copolymer may be present alone or in combination with another polymer, such as ethylene-acrylic acid copolymer. When present together, the weight ratio between the ethylene and octene copolymer and the ethylene-acrylic acid copolymer may be from about 1:10 to about 10:1, such as from about 3:2 to about 2:3. The polymer, such as the ethylene-octene copolymer, may have a crystallinity of less than about 50%, such as less than about 25%. In some embodiments, the crystallinity of the polymer may be from 5 to 35 percent. In other embodiments, the crystallinity may range from 7 to 20 percent. 
         [0045]    In one particular embodiment, the polymer may comprise at least one low density polyethylene (LDPE). The polymer may comprise LDPE made in autoclave processes or tubular processes. Suitable LDPE for this embodiment is defined elsewhere in this document. 
         [0046]    In one particular embodiment, the polymer may comprise at least two low density polyethylenes. The polymer may comprise LDPE made in autoclave processes, tubular processes, or combinations thereof. Suitable LDPEs for this embodiment are defined elsewhere in this document. 
         [0047]    In one particular embodiment, the polymer may comprise an alpha-olefin interpolymer of ethylene with a comonomer comprising an alkene, such as 1-octene. The ethylene and octene copolymer may be present alone or in combination with another polymer, such as a low density polyethylene (LDPE). When present together, the weight ratio between the ethylene and octene copolymer and the LDPE may be from about 60:40 to about 97:3, such as from about 80:20 to about 96:4. The polymer, such as the ethylene-octene copolymer, may have a crystallinity of less than about 50%, such as less than about 25%. In some embodiments, the crystallinity of the polymer may be from 5 to 35 percent. In other embodiments, the crystallinity may range from 7 to 20 percent. Suitable LDPEs for this embodiment are defined elsewhere in this document. 
         [0048]    In one particular embodiment, the polymer may comprise an alpha-olefin interpolymer of ethylene with a comonomer comprising an alkene, such as 1-octene. The ethylene and octene copolymer may be present alone or in combination with at least two other polymers from the group: low density polyethylene, medium density polyethylene, and high density polyethylene (HDPE). When present together, the weight ratio between the ethylene and octene copolymer, the LDPE, and the HDPE are such that the composition comprises one component from 3 to 97% by weight of the total composition and the remainder comprises the other two components. The polymer, such as the ethylene-octene copolymer, may have a crystallinity of less than about 50%, such as less than about 25%. In some embodiments, the crystallinity of the polymer may be from 5 to 35 percent. In other embodiments, the crystallinity may range from 7 to 20 percent. 
         [0049]    Embodiments disclosed herein may also include a polymeric component that may include at least one multi-block olefin interpolymer. Suitable multi-block olefin interpolymers may include those described in U.S. Provisional Patent Application No. 60/818,911, for example. The term “multi-block copolymer” or refers to a polymer comprising two or more chemically distinct regions or segments (referred to as “blocks”) preferably joined in a linear manner, that is, a polymer comprising chemically differentiated units which are joined end-to-end with respect to polymerized ethylenic functionality, rather than in pendent or grafted fashion. In certain embodiments, the blocks differ in the amount or type of comonomer incorporated therein, the density, the amount of crystallinity, the crystallite size attributable to a polymer of such composition, the type or degree of tacticity (isotactic or syndiotactic), regio-regularity or regio-irregularity, the amount of branching, including long chain branching or hyper-branching, the homogeneity, or any other chemical or physical property. The multi-block copolymers are characterized by unique distributions of polydispersity index (PDI or M w /M n ), block length distribution, and/or block number distribution due to the unique process making of the copolymers. More specifically, when produced in a continuous process, embodiments of the polymers may possess a PDI ranging from about 1.7 to about 8; from about 1.7 to about 3.5 in other embodiments; from about 1.7 to about 2.5 in other embodiments; and from about 1.8 to about 2.5 or from about 1.8 to about 2.1 in yet other embodiments. When produced in a batch or semi-batch process, embodiments of the polymers may possess a PDI ranging from about 1.0 to about 2.9; from about 1.3 to about 2.5 in other embodiments; from about 1.4 to about 2.0 in other embodiments; and from about 1.4 to about 1.8 in yet other embodiments. 
         [0050]    One example of the multi-block olefin interpolymer is an ethylene/α-olefin block interpolymer. Another example of the multi-block olefin interpolymer is a propylene/α-olefin interpolymer. The following description focuses on the interpolymer as having ethylene as the majority monomer, but applies in a similar fashion to propylene-based multi-block interpolymers with regard to general polymer characteristics. 
         [0051]    The ethylene/α-olefin multi-block interpolymers may comprise ethylene and one or more co-polymerizable α-olefin comonomers in polymerized form, characterized by multiple (i.e., two or more) blocks or segments of two or more polymerized monomer units differing in chemical or physical properties (block interpolymer), preferably a multi-block interpolymer. In some embodiments, the multi-block interpolymer may be represented by the following formula: 
         [0000]      (AB) n    
         [0000]    where n is at least 1, preferably an integer greater than 1, such as 2, 3, 4, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, or higher; “A” represents a hard block or segment; and “B” represents a soft block or segment. Preferably, A′ s and B′ s are linked in a linear fashion, not in a branched or a star fashion. “Hard” segments refer to blocks of polymerized units in which ethylene is present in an amount greater than 95 weight percent in some embodiments, and in other embodiments greater than 98 weight percent. In other words, the comonomer content in the hard segments is less than 5 weight percent in some embodiments, and in other embodiments, less than 2 weight percent of the total weight of the hard segments. In some embodiments, the hard segments comprise all or substantially all ethylene. “Soft” segments, on the other hand, refer to blocks of polymerized units in which the comonomer content is greater than 5 weight percent of the total weight of the soft segments in some embodiments, greater than 8 weight percent, greater than 10 weight percent, or greater than 15 weight percent in various other embodiments. In some embodiments, the comonomer content in the soft segments may be greater than 20 weight percent, greater than 25 eight percent, greater than 30 weight percent, greater than 35 weight percent, greater than 40 weight percent, greater than 45 weight percent, greater than 50 weight percent, or greater than 60 weight percent in various other embodiments. 
         [0052]    In some embodiments, A blocks and B blocks are randomly distributed along the polymer chain. In other words, the block copolymers do not have a structure like: 
         [0000]      AAA-AA-BBB-BB 
         [0053]    In other embodiments, the block copolymers do not have a third block. In still other embodiments, neither block A nor block B comprises two or more segments (or sub-blocks), such as a tip segment. 
         [0054]    The multi-block interpolymers may be characterized by an average block index, ABI, ranging from greater than zero to about 1.0 and a molecular weight distribution, M w /M n , greater than about 1.3. The average block index, ABI, is the weight average of the block index (“BI”) for each of the polymer fractions obtained in preparative TREF from 20° C. and 110° C., with an increment of 5° C.: 
         [0000]      ABI=Σ( w   i BI i ) 
         [0000]    where BI i  is the block index for the i th  fraction of the multi-block interpolymer obtained in preparative TREF, and w i  is the weight percentage of the i th  fraction. 
         [0055]    Similarly, the square root of the second moment about the mean, hereinafter referred to as the second moment weight average block index, may be defined as follows: 
         [0000]    
       
         
           
             
               
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         [0056]    For each polymer fraction, BI is defined by one of the two following equations (both of which give the same BI value): 
         [0000]    
       
         
           
             
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                       Ln 
                        
                       
                           
                       
                        
                       
                         P 
                         AB 
                       
                     
                   
                 
               
             
           
         
       
     
         [0000]    where T x  is the analytical temperature rising elution fractionation (ATREF) elution temperature for the i th  fraction (preferably expressed in Kelvin), P x  is the ethylene mole fraction for the i th  fraction, which may be measured by NMR or IR as described below. P AB  is the ethylene mole fraction of the whole ethylene/α-olefin interpolymer (before fractionation), which also may be measured by NMR or IR. T A  and P A  are the ATREF elution temperature and the ethylene mole fraction for pure “hard segments” (which refer to the crystalline segments of the interpolymer). As an approximation or for polymers where the “hard segment” composition is unknown, the T A  and P A  values are set to those for high density polyethylene homopolymer. 
         [0057]    T AB  is the ATREF elution temperature for a random copolymer of the same composition (having an ethylene mole fraction of P AB ) and molecular weight as the multi-block interpolymer. T AB  may be calculated from the mole fraction of ethylene (measured by NMR) using the following equation: 
         [0000]      Ln  P   AB   =α/T   AB +β 
         [0000]    where α and β are two constants which may be determined by a calibration using a number of well characterized preparative TREF fractions of a broad composition random copolymer and/or well characterized random ethylene copolymers with narrow composition. It should be noted that α and β may vary from instrument to instrument. Moreover, one would need to create an appropriate calibration curve with the polymer composition of interest, using appropriate molecular weight ranges and comonomer type for the preparative TREF fractions and/or random copolymers used to create the calibration. There is a slight molecular weight effect. If the calibration curve is obtained from similar molecular weight ranges, such effect would be essentially negligible. In some embodiments, random ethylene copolymers and/or preparative TREF fractions of random copolymers satisfy the following relationship: 
         [0000]      Ln  P=− 237.83 /T   ATREF +0.639 
         [0058]    The above calibration equation relates the mole fraction of ethylene, P, to the analytical TREF elution temperature, T ATREF , for narrow composition random copolymers and/or preparative TREF fractions of broad composition random copolymers. T XO  is the ATREF temperature for a random copolymer of the same composition and having an ethylene mole fraction of P x . T XO  may be calculated from Ln P X =α/T XO +β. Conversely, P XO  is the ethylene mole fraction for a random copolymer of the same composition and having an ATREF temperature of T X , which may be calculated from Ln P XO =α/T X +β 
         [0059]    Once the block index (BI) for each preparative TREF fraction is obtained, the weight average block index, ABI, for the whole polymer may be calculated. In some embodiments, ABI is greater than zero but less than about 0.4 or from about 0.1 to about 0.3. In other embodiments, ABI is greater than about 0.4 and up to about 1.0. Preferably, ABI should be in the range of from about 0.4 to about 0.7, from about 0.5 to about 0.7, or from about 0.6 to about 0.9. In some embodiments, ABI is in the range of from about 0.3 to about 0.9, from about 0.3 to about 0.8, or from about 0.3 to about 0.7, from about 0.3 to about 0.6, from about 0.3 to about 0.5, or from about 0.3 to about 0.4. In other embodiments, ABI is in the range of from about 0.4 to about 1.0, from about 0.5 to about 1.0, or from about 0.6 to about 1.0, from about 0.7 to about 1.0, from about 0.8 to about 1.0, or from about 0.9 to about 1.0. 
         [0060]    Another characteristic of the multi-block interpolymer is that the interpolymer may comprise at least one polymer fraction which may be obtained by preparative TREF, wherein the fraction has a block index greater than about 0.1 and up to about 1.0 and the polymer having a molecular weight distribution, M w /M n , greater than about 1.3. In some embodiments, the polymer fraction has a block index greater than about 0.6 and up to about 1.0, greater than about 0.7 and up to about 1.0, greater than about 0.8 and up to about 1.0, or greater than about 0.9 and up to about 1.0. In other embodiments, the polymer fraction has a block index greater than about 0.1 and up to about 1.0, greater than about 0.2 and up to about 1.0, greater than about 0.3 and up to about 1.0, greater than about 0.4 and up to about 1.0, or greater than about 0.4 and up to about 1.0. In still other embodiments, the polymer fraction has a block index greater than about 0.1 and up to about 0.5, greater than about 0.2 and up to about 0.5, greater than about 0.3 and up to about 0.5, or greater than about 0.4 and up to about 0.5. In yet other embodiments, the polymer fraction has a block index greater than about 0.2 and up to about 0.9, greater than about 0.3 and up to about 0.8, greater than about 0.4 and up to about 0.7, or greater than about 0.5 and up to about 0.6. 
         [0061]    Ethylene α-olefin multi-block interpolymers used in embodiments of the invention may be interpolymers of ethylene with at least one C 3 -C 20  α-olefin. The interpolymers may further comprise C 4 -C 18  diolefin and/or alkenylbenzene. Suitable unsaturated comonomers useful for polymerizing with ethylene include, for example, ethylenically unsaturated monomers, conjugated or non-conjugated dienes, polyenes, alkenylbenzenes, etc. Examples of such comonomers include C 3 -C 20  α-olefins such as propylene, isobutylene, 1-butene, 1-hexene, 1-pentene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, and the like. 1-Butene and 1-octene are especially preferred. Other suitable monomers include styrene, halo- or alkyl-substituted styrenes, vinylbenzocyclobutane, 1,4-hexadiene, 1,7-octadiene, and naphthenics (such as cyclopentene, cyclohexene, and cyclooctene, for example). 
         [0062]    The multi-block interpolymers disclosed herein may be differentiated from conventional, random copolymers, physical blends of polymers, and block copolymers prepared via sequential monomer addition, fluxional catalysts, and anionic or cationic living polymerization techniques. In particular, compared to a random copolymer of the same monomers and monomer content at equivalent crystallinity or modulus, the interpolymers have better (higher) heat resistance as measured by melting point, higher TMA penetration temperature, higher high-temperature tensile strength, and/or higher high-temperature torsion storage modulus as determined by dynamic mechanical analysis. Properties of infill may benefit from the use of embodiments of the multi-block interpolymers, as compared to a random copolymer containing the same monomers and monomer content, the multi-block interpolymers have lower compression set, particularly at elevated temperatures, lower stress relaxation, higher creep resistance, higher tear strength, higher blocking resistance, faster setup due to higher crystallization (solidification) temperature, higher recovery (particularly at elevated temperatures), better abrasion resistance, higher refractive force, and better oil and filler acceptance. 
         [0063]    Other olefin interpolymers include polymers comprising monovinylidene aromatic monomers including styrene, o-methyl styrene, p-methyl styrene, t-butylstyrene, and the like. In particular, interpolymers comprising ethylene and styrene may be used. In other embodiments, copolymers comprising ethylene, styrene and a C 3 -C 20  α olefin, optionally comprising a C 4 -C 20  diene, may be used. 
         [0064]    Suitable non-conjugated diene monomers may include straight chain, branched chain or cyclic hydrocarbon diene having from 6 to 15 carbon atoms. Examples of suitable non-conjugated dienes include, but are not limited to, straight chain acyclic dienes, such as 1,4-hexadiene, 1,6-octadiene, 1,7-octadiene, 1,9-decadiene, branched chain acyclic dienes, such as 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; 3,7-dimethyl-1,7-octadiene and mixed isomers of dihydromyricene and dihydroocinene, single ring alicyclic dienes, such as 1,3-cyclopentadiene; 1,4-cyclohexadiene; 1,5-cyclooctadiene and 1,5-cyclododecadiene, and multi-ring alicyclic fused and bridged ring dienes, such as tetrahydroindene, methyl tetrahydroindene, dicyclopentadiene, bicyclo-(2,2,1)-hepta-2,5-diene; alkenyl, alkylidene, cycloalkenyl and cycloalkylidene norbornenes, such as 5-methylene-2-norbornene (MNB); 5-propenyl-2-norbornene, 5-isopropylidene-2-norbornene, 5-(4-cyclopentenyl)-2-norbornene, 5-cyclohexylidene-2-norbornene, 5-vinyl-2-norbornene, and norbornadiene. Of the dienes typically used to prepare EPDMs, the particularly preferred dienes are 1,4-hexadiene (HD), 5-ethylidene-2-norbornene (ENB), 5-vinylidene-2-norbornene (VNB), 5-methylene-2-norbornene (MNB), and dicyclopentadiene (DCPD). 
         [0065]    One class of desirable polymers that may be used in accordance with embodiments disclosed herein includes elastomeric interpolymers of ethylene, a C 3 -C 20  α-olefin, especially propylene, and optionally one or more diene monomers. Preferred α-olefins for use in this embodiment are designated by the formula CH 2 ═CHR*, where R* is a linear or branched alkyl group of from 1 to 12 carbon atoms. Examples of suitable α-olefins include, but are not limited to, propylene, isobutylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene. A particularly preferred α-olefin is propylene. The propylene based polymers are generally referred to in the art as EP or EPDM polymers. Suitable dienes for use in preparing such polymers, especially multi-block EPDM type polymers include conjugated or non-conjugated, straight or branched chain-, cyclic- or polycyclic-dienes comprising from 4 to 20 carbons. Preferred dienes include 1,4-pentadiene, 1,4-hexadiene, 5-ethylidene-2-norbornene, dicyclopentadiene, cyclohexadiene, and 5-butylidene-2-norbornene. A particularly preferred diene is 5-ethylidene-2-norbornene. 
         [0066]    The polymers (homopolymers, copolymers, interpolymers and multi-block interpolymers) described herein may have a melt index, I 2 , from 0.01 to 2000 g/10 minutes in some embodiments; from 0.01 to 1000 g/10 minutes in other embodiments; from 0.01 to 500 g/10 minutes in other embodiments; and from 0.01 to 100 g/10 minutes in yet other embodiments. In certain embodiments, the polymers may have a melt index, I 2 , from 0.01 to 10 g/10 minutes, from 0.5 to 50 g/10 minutes, from 1 to 30 g/10 minutes, from 1 to 6 g/10 minutes or from 0.3 to 10 g/10 minutes. In certain embodiments, the melt index for the polymers may be approximately 1 g/10 minutes, 3 g/10 minutes or 5 g/10 minutes. In other embodiments, the polymers may have a melt index greater than 20 dg/min; greater than 40 dg/min in other embodiments; and greater than 60 dg/min in yet other embodiments. 
         [0067]    The polymers described herein may have molecular weights, M w , from 1,000 g/mole to 5,000,000 g/mole in some embodiments; from 1000 g/mole to 1,000,000 in other embodiments; from 10,000 g/mole to 500,000 g/mole in other embodiments; and from 10,000 g/mole to 300,000 g/mole in yet other embodiments. The density of the polymers described herein may be from 0.80 to 0.99 g/cm 3  in some embodiments; for ethylene containing polymers from 0.85 g/cm 3  to 0.97 g/cm 3 ; in some embodiments between 0.87 g/cm 3  and 0.94 g/cm 3 . 
         [0068]    In some embodiments, the polymers described herein may have a tensile strength above 10 MPa; a tensile strength &gt;11 MPa in other embodiments; and a tensile strength &gt;13 MPa in yet other embodiments. In some embodiments, the polymers described herein may have an elongation at break of at least 600 percent at a crosshead separation rate of 11 cm/minute; at least 700 percent in other embodiments; at least 800 percent in other embodiments; and at least 900 percent in yet other embodiments. 
         [0069]    In some embodiments, the polymers described herein may have a storage modulus ratio, G′(25° C.)/G′(100° C.), from 1 to 50; from 1 to 20 in other embodiments; and from 1 to 10 in yet other embodiments. In some embodiments, the polymers may have a 70° C. compression set of less than 80 percent; less than 70 percent in other embodiments; less than 60 percent in other embodiments; and, less than 50 percent, less than 40 percent, down to a compression set of 0 percent in yet other embodiments. 
         [0070]    In some embodiments, the ethylene/α-olefin interpolymers may have a heat of fusion of less than 85 J/g. In other embodiments, the ethylene/α-olefin interpolymer may have a pellet blocking strength of equal to or less than 100 pounds/foot 2  (4800 Pa); equal to or less than 50 lbs/ft 2  (2400 Pa) in other embodiments; equal to or less than 5 lbs/ft 2  (240 Pa), and as low as 0 lbs/ft 2  (0 Pa) in yet other embodiments. 
         [0071]    In some embodiments, block polymers made with two catalysts incorporating differing quantities of comonomer may have a weight ratio of blocks formed thereby ranging from 95:5 to 5:95. The elastomeric interpolymers, in some embodiments, have an ethylene content of from 20 to 90 percent, a diene content of from 0.1 to 10 percent, and an α-olefin content of from 10 to 80 percent, based on the total weight of the polymer. In other embodiments, the multi-block elastomeric polymers have an ethylene content of from 60 to 90 percent, a diene content of from 0.1 to 10 percent, and an α-olefin content of from 10 to 40 percent, based on the total weight of the polymer. In other embodiments, the interpolymer may have a Mooney viscosity (ML (1+4) 125° C.) ranging from 1 to 250. In other embodiments, such polymers may have an ethylene content from 65 to 75 percent, a diene content from 0 to 6 percent, and an α-olefin content from 20 to 35 percent. 
         [0072]    In certain embodiments, the polymer may be a propylene-ethylene copolymer or interpolymer having an ethylene content between 5 and 20% by weight and a melt flow rate (230° C. with 2.16 kg weight) from 0.5 to 300 g/10 min. In other embodiments, the propylene-ethylene copolymer or interpolymer may have an ethylene content between 9 and 12% by weight and a melt flow rate (230° C. with 2.16 kg weight) from 1 to 100 g/10 min. 
         [0073]    In some particular embodiments, the polymer is a propylene-based copolymer or interpolymer. In some embodiments, a propylene/ethylene copolymer or interpolymer is characterized as having substantially isotactic propylene sequences. The term “substantially isotactic propylene sequences” and similar terms mean that the sequences have an isotactic triad (mm) measured by  13 C NMR of greater than about 0.85, preferably greater than about 0.90, more preferably greater than about 0.92 and most preferably greater than about 0.93. Isotactic triads are well-known in the art and are described in, for example, U.S. Pat. No. 5,504,172 and WO 00/01745, which refer to the isotactic sequence in terms of a triad unit in the copolymer molecular chain determined by  13 C NMR spectra. In other particular embodiments, the ethylene-α olefin copolymer may be ethylene-butene, ethylene-hexene, or ethylene-octene copolymers or interpolymers. In other particular embodiments, the propylene-α olefin copolymer may be a propylene-ethylene or a propylene-ethylene-butene copolymer or interpolymer. 
         [0074]    The polymers described herein (homopolymers, copolymers, interpolymers, multi-block interpolymers) may be produced using a single site catalyst and may have a weight average molecular weight of from about 15,000 to about 5 million, such as from about 20,000 to about 1 million. The molecular weight distribution of the polymer may be from about 1.01 to about 80, such as from about 1.5 to about 40, such as from about 1.8 to about 20. 
         [0075]    In some embodiments, the polymer may have a Shore A hardness from 30 to 100. In other embodiments, the polymer may have a Shore A hardness from 40 to 90; from 30 to 80 in other embodiments; and from 40 to 75 in yet other embodiments. 
         [0076]    The olefin polymers, copolymers, interpolymers, and multi-block interpolymers may be functionalized by incorporating at least one functional group in its polymer structure. Exemplary functional groups may include, for example, ethylenically unsaturated mono- and di-functional carboxylic acids, ethylenically unsaturated mono- and di-functional carboxylic acid anhydrides, salts thereof and esters thereof. Such functional groups may be grafted to an olefin polymer, or it may be copolymerized with ethylene and an optional additional comonomer to form an interpolymer of ethylene, the functional comonomer and optionally other comonomer(s). Means for grafting functional groups onto polyethylene are described for example in U.S. Pat. Nos. 4,762,890, 4,927,888, and 4,950,541, the disclosures of which are incorporated herein by reference in their entirety. One particularly useful functional group is maleic anhydride. 
         [0077]    The amount of the functional group present in the functional polymer may vary. The functional group may be present in an amount of at least about 1.0 weight percent in some embodiments; at least about 5 weight percent in other embodiments; and at least about 7 weight percent in yet other embodiments. The functional group may be present in an amount less than about 40 weight percent in some embodiments; less than about 30 weight percent in other embodiments; and less than about 25 weight percent in yet other embodiments. 
         [0078]    The foam sheets according to embodiments disclosed herein may include a single layer or multiple layers as desired. The foam articles may be produced in any manner so as to result in at least one foam layer. The foam layers described herein may be made by a pressurized melt processing method such as an extrusion method. The extruder may be a tandem system, a single screw extruder, a twin screw extruder, etc. The extruder may be equipped with multilayer annular dies, flat film dies and feedblocks, multi-layer feedblocks such as those disclosed in U.S. Pat. No. 4,908,278 (Bland et al.), multi-vaned or multi-manifold dies such as a 3-layer vane die available from Cloeren, Orange, Tex. A foamable composition may also be made by combining a chemical blowing agent and polymer at a temperature below the decomposition temperature of the chemical blowing agent, and then later foamed. In some embodiments, the foam may be coextruded with one or more barrier layers. 
         [0079]    One method of producing the foams described herein is by using an extruder, as mentioned above. In this case, the foamable mixture (polymer+blowing agent) is extruded. As the mixture exits an extruder die and upon exposure to reduced pressure, the fugitive gas nucleates and forms cells within the polymer to create a foam article. The resulting foam article may then be deposited onto a temperature-controlled casting drum. The casting drum speed (i.e., as produced by the drum RPM) can affect the overall thickness of the foam article. As the casting roll speed increases, the overall thickness of the foam article can decrease. However, the barrier layer thickness at the die exit, which is where foaming occurs, is the diffusion length for the system. As the foam article is stretched and quenched on the casting drum, the barrier layer thickness may decrease until the foam article solidifies. In other words, it is the barrier layer diffusion length (i.e., thickness) at the die exit that is the important factor in controlling the diffusion of the fugitive gas. 
         [0080]    Blowing agents suitable for use in forming the foams described herein may be physical blowing agents, which are typically the same material as the fugitive gas, e.g., CO 2 , or a chemical blowing agent, which produces the fugitive gas. More than one physical or chemical blowing agent may be used and physical and chemical blowing agents may be used together. 
         [0081]    Physical blowing agents useful in the present invention include any naturally occurring atmospheric material which is a vapor at the temperature and pressure at which the foam exits the die. The physical blowing agent may be introduced, i.e., injected into the polymeric material as a gas, a supercritical fluid, or liquid, preferably as a supercritical fluid or liquid, most preferably as a liquid. The physical blowing agents used will depend on the properties sought in the resulting foam articles. Other factors considered in choosing a blowing agent are its toxicity, vapor pressure profile, ease of handling, and solubility with regard to the polymeric materials used. Non-flammable, non-toxic, non-ozone depleting blowing are preferred because they are easier to use, e.g., fewer environmental and safety concerns, and are generally less soluble in thermoplastic polymers. Suitable physical blowing agents include, e.g., carbon dioxide, nitrogen, SF.sub.6, nitrous oxide, perfluorinated fluids, such as C 2 F 6 , argon, helium, noble gases, such as xenon, air (nitrogen and oxygen blend), and blends of these materials. 
         [0082]    Chemical blowing agents that may be used in the present invention include, e.g., a sodium bicarbonate and citric acid blend, dinitrosopentamethylenetetramine, p-toluenesulfonyl hydrazide, 4-4 1 -oxybis(benzenesulfonyl hydrazide, azodicarbonamide (1,1′-azobisformamide), p-toluenesulfonyl semicarbazide, 5-phenyltetrazole, 5-phenyltetrazole analogues, diisopropylhydrazodicarboxylate, 5-phenyl-3,6-dihydro-1,3,4-oxadiazin-2-one, and sodium borohydride. Preferably, the blowing agents are, or produce, one or more fugitive gases having a vapor pressure of greater than 0.689 MPa at 0° C. 
         [0083]    The total amount of the blowing agent used depends on conditions such as extrusion-process conditions at mixing, the blowing agent being used, the composition of the extrudate, and the desired density of the foamed article. The extrudate is defined herein as including the blowing agent blend, a polyolefin resin(s), and any additives. For a foam having a density of from about 1 to about 15 lb/ft 3 , the extrudate typically comprises from about 18 to about 1 wt of blowing agent. In other embodiments, 1% to 10% of blowing agent may be used. 
         [0084]    The blowing agent blend used in the present invention comprises less than about 99 mol % isobutane. The blowing agent blend generally comprises from about 10 mol % to about 60 or 75 mol % isopentane. The blowing agent blend more typically comprises from about 15 mol % to about 40 mol % isopentane. More specifically, the blowing agent blend comprises from about 25 or 30 mol % to about 40 mol % isobutane. The blowing agent blend generally comprises at least about 15 or 30 mol % of co-blowing agent(s). More specifically, the blowing agent blend comprises from about 40 to about 85 or 90 mol % of co-blowing agent(s). The blowing agent blend more typically comprises from about 60 mol % to about 70 or 75 mol % of co-blowing agent(s). 
         [0085]    A nucleating agent or combination of such agents may be employed in the present invention for advantages, such as its capability for regulating cell formation and morphology. A nucleating agent, or cell size control agent, may be any conventional or useful nucleating agent(s). The amount of nucleating agent used depends upon the desired cell size, the selected blowing agent blend, and the desired foam density. The nucleating agent is generally added in amounts from about 0.02 to about 20 wt % of the polyolefin resin composition. 
         [0086]    Some contemplated nucleating agents include inorganic materials (in small particulate form), such as clay, talc, silica, and diatomaceous earth. Other contemplated nucleating agents include organic nucleating agents that decompose or react at the heating temperature within an extruder to evolve gases, such as carbon dioxide, water, and/or nitrogen. One example of an organic nucleating agent is a combination of an alkali metal salt of a polycarboxylic acid with a carbonate or bicarbonate. Some examples of alkali metal salts of a polycarboxylic acid include, but are not limited to, the monosodium salt of 2,3-dihydroxy-butanedioic acid (commonly referred to as sodium hydrogen tartrate), the monopotassium salt of butanedioic acid (commonly referred to as potassium hydrogen succinate), the trisodium and tripotassium salts of 2-hydroxy-1,2,3-propanetricarboxylic acid (commonly referred to as sodium and potassium citrate, respectively), and the disodium salt of ethanedioic acid (commonly referred to as sodium oxalate), or polycarboxylic acid such as 2-hydroxy-1,2,3-propanetricarboxylic acid. Some examples of a carbonate or a bicarbonate include, but are not limited to, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and calcium carbonate. 
         [0087]    It is contemplated that mixtures of different nucleating agents may be added in the present invention. Some more desirable nucleating agents include talc, crystalline silica, and a stoichiometric mixture of citric acid and sodium bicarbonate (the stoichiometric mixture having a 1 to 100 percent concentration where the carrier is a suitable polymer such as polyethylene). Talc may be added in a carrier or in a powder form. 
         [0088]    Gas permeation agents or stability control agents may be employed in the present invention to assist in preventing or inhibiting collapsing of the foam. The stability control agents suitable for use in the present invention may include the partial esters of long-chain fatty acids with polyols described in U.S. Pat. No. 3,644,230, saturated higher alkyl amines, saturated higher fatty acid amides, complete esters of higher fatty acids such as those described in U.S. Pat. No. 4,214,054, and combinations thereof described in U.S. Pat. No. 5,750,584. 
         [0089]    The partial esters of fatty acids that may be desired as a stability control agent include the members of the generic class known as surface active agents or surfactants. A preferred class of surfactants includes a partial ester of a fatty acid having 12 to 18 carbon atoms and a polyol having three to six hydroxyl groups. More preferably, the partial esters of a long chain fatty acid with a polyol component of the stability control agent are glycerol monostearate, glycerol distearate or mixtures thereof. It is contemplated that other gas permeation agents or stability control agents may be employed in the present invention to assist in preventing or inhibiting collapsing of the foam. 
         [0090]    Additives 
         [0091]    If desired, fillers, colorants, light and heat stabilizers, anti-oxidants, acid scavengers, flame retardants, processing aids, extrusion aids, and foaming additives may be used in making the foam. The foam of the invention may contain filler materials in amounts, depending on the application for which they are designed, ranging from about 2-100 percent (dry basis) of the weight of the polymer component. These optional ingredients may include, but are not limited to, calcium carbonate, titanium dioxide powder, polymer particles, hollow glass spheres, polymeric fibers such as polyolefin based staple monofilaments and the like. 
         [0092]    In selected embodiments, foams useful for disclosed embodiments may have thickness between 1 and 500 mm, and in some embodiments, 5 to 100 mm, and in some embodiments 8 and 30 mm. In selected embodiments foams may have a density between about 20 and 600 kg/m 3 , preferably 25 to 300 kg/m 3 , and more preferably, 30 to 150 kg/m 3 . In selected embodiments, foams may have a cell size between about 0.1 to 6 mm, preferably 0.2 to 4.5 mm, and more preferably 0.2 to 3 mm. 
         [0093]    In some embodiments, the foam layer may be perforated in order to facilitate drainage, so that in the event of rain, water may drain off of the playing surface. 
         [0094]    In some embodiments, the above described foams may be used as a shock absorbing layer in a synthetic turf. Additionally, tests may be performed to analyze temperature performance and aging, as well as the bounce and spin properties of the resulting turf. Briefly, the significant tests &amp; desired results for artificial turf performance as specified by the FIFA Quality Concept Manual (March 2006 Edition) are shown in the below table. Those having ordinary skill in the art will appreciate that this is but one use of the foams described herein, and that the artificial turf and foams described herein may be useful in a number of other applications an a number of other sports, such as rugby and field hockey, for example. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 LABORATORY TESTS - BALL/SURFACE INTERACTION 
               
             
          
           
               
                   
                 Requirements 
               
             
          
           
               
                   
                   
                   
                   
                 FIFA 
                   
               
               
                   
                 Test 
                 Test 
                 Test Conditions 
                 Recommended** 
                 FIFA 
               
             
          
           
               
                 Property 
                 Method 
                 Method 
                 Preparation 
                 Temp 
                 Condition 
                 (best ranking) 
                 Recommended* 
               
               
                   
               
               
                 Vertical ball 
                 FIFA 
                   
                 Pre- 
                 23° C. 
                 Dry 
                 0.60 m-0.85 m 
                 0.60 m-1 m   
               
               
                 rebound 
                 01/05-01 &amp; 
                   
                 conditioning 
                   
                 Wet 
                   
                 — 
               
               
                   
                 FIFA 
                   
                 Simulated 
                 23° C. 
                 Dry 
                   
                 0.60 m-1 m   
               
               
                   
                 09/05-01 
                   
                 Wear 
               
               
                 Shock 
                 FIFA 
                 Flat foot 
                 Pre- 
                 23° C. 
                 Dry 
                 60%-70% 
                 55%-70% 
               
               
                 absorption 
                 04/05-01 &amp; 
                 Mean 
                 conditioning 
                   
                 Wet 
                   
                 — 
               
               
                   
                 FIFA 
                 2 nd /3 rd   
                 Simulated 
                 23° C. 
                 Dry 
                   
                 55%-70% 
               
               
                   
                 10/05-01 
                 impact 
                 Wear 
               
               
                   
                   
                   
                 — 
                 40° C. 
                 Dry 
                   
                 — 
               
               
                   
                   
                 Flat Foot 
                 — 
                 −5° C. 
                 Frozen 
                 60%-70% 
                 — 
               
               
                   
                   
                 1 st   
               
               
                   
                   
                 impact 
               
               
                 Vertical 
                 FIFA 
                 Flat foot 
                 Pre- 
                 23° C. 
                 Dry 
                 4 mm-8 mm 
                 4 mm-9 mm 
               
               
                 deformation 
                 05/05-01 &amp; 
                 Mean 
                 conditioning 
                   
                 Wet 
                   
                 — 
               
               
                   
                 FIFA 
                 2 nd /3 rd   
                 Simulated 
                 23° C. 
                 Dry 
                   
                 4 mm-9 mm 
               
               
                   
                 10/05-01 
                 impact 
                 Wear 
               
               
                   
               
             
          
         
       
     
         [0095]    Shock Absorption 
         [0096]    Principle: A mass (20 Kgs) falls, as discussed in the FIFA Quality Concept Manual (March 2006 Edition), which is incorporated by reference in its entirety. The maximum force applied is recorded. The % reduction in this force relative to the maximum force measured on a concrete surface is reported as ‘Force Reduction’. 
         [0097]    FIFA Requirement: 
         [0098]    FIFA 2 Star: 60%-70% 
         [0099]    FIFA 1 Star: 55%-70% 
         [0100]    Vertical Deformation 
         [0101]    Principle A mass is allowed to fall onto a spring that rests and the maximum deformation of the surface is determined. 
         [0102]    FIFA Requirement: 
         [0103]    FIFA 2 Star: 4 mm-8 mm 
         [0104]    FIFA 1 Star: 4 mm-9 mm 
       EXAMPLES 
       [0105]    The usefulness of polyolefin resins having selected foam densities and thicknesses is investigated. Specifically, a number of polyethylene resins, commercially available from The Dow Chemical Company, Midland, Mich. are studied. Table 1 and Table 2 show a number of the compounds used. In Table 1, the performance of crosslinked polyethylene (comparative examples 1c-4c) versus non-crosslinked polyethylene (examples 1-4) is investigated. Specifically, with respect to Table 1, (LDPE 300E, and LDPE PG  7004 , and blends thereof, LDPE 6201, and XU 60021.24 are used to generate the data. The formulations used in creating the Table are shown below. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 Resin 
                 Foam 
                 Thick- 
                   
               
               
                   
                   
                 Density 
                 Density 
                 ness 
                 Cross- 
               
               
                 Example 
                 Resin A/B 
                 (kg/m 3 ) 
                 (kg/m 3 ) 
                 (mm) 
                 linked 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 XU 60021.24* 
                 0.922 
                 33 
                 10 
                 No 
               
               
                 2 
                 90/10 (LDPE 300E/ 
                 0.923 
                 45 
                 10 
                 No 
               
               
                   
                 LDPE PG7004) 
               
               
                 3 
                 70/30 (LDPE 300E/ 
                 0.923 
                 64 
                 10 
                 No 
               
               
                   
                 LDPE PG7004) 
               
               
                 4 
                 LDPE 620I 
                 0.923 
                 144 
                 51 
                 No 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 Resin A 
                 Resin B 
                   
               
             
          
           
               
                   
                 Density 
                   
                 Density 
                   
                   
               
               
                   
                 (g/cm 3)   
                   
                 (g/cm 3 ) 
                   
                 Foam 
               
             
          
           
               
                   
                   
                 Polymer 
                 (ASTM 
                 I 2   
                   
                 Polymer 
                 (ASTM 
                 I 2   
                 Density 
                 Thickness 
                   
               
               
                 Example 
                 (wt. %) 
                 Type 
                 D792) 
                 (g/10 min) 
                 (wt. %) 
                 Type 
                 D792) 
                 (g/10 min) 
                 (kg/m 3 ) 
                 (mm) 
                 Crosslinked 
               
               
                   
               
               
                 1 
                 100 
                 LDPE 
                 0.922 
                 3.3 
                 — 
                 — 
                 — 
                 — 
                 33 
                 10 
                 No 
               
               
                 2 
                 90 
                 LDPE 
                 0.9235 
                 0.8 
                 10 
                 LDPE 
                 0.9215 
                 4.1 
                 45 
                 10 
                 No 
               
               
                 3 
                 70 
                 LDPE 
                 0.9235 
                 0.8 
                 30 
                 LDPE 
                 0.9215 
                 4.1 
                 64 
                 10 
                 No 
               
               
                 4 
                 100 
                 LDPE 
                 0.9239 
                 1.85 
                 — 
                 — 
                 — 
                 — 
                 144 
                 51 
                 No 
               
               
                   
               
             
          
           
               
                 Comparative Examples. 
               
             
          
           
               
                   
                   
                 Foam 
                   
                   
               
               
                 Comparative 
                   
                 Density 
                 Thickness 
                 Crosslinked 
               
               
                 Example 
                 Designation 
                 (kg/m 3 ) 
                 (mm) 
                 (yes/no) 
               
               
                   
               
               
                 1c 
                 Qycell T-20* 
                 33 
                 10 
                 yes 
               
               
                 2c 
                 Qycell T-30* 
                 45 
                 10 
                 yes 
               
               
                 3c 
                 Qycell T-40* 
                 64 
                 10 
                 yes 
               
               
                 4c 
                 Qycell T-80* 
                 119 
                 11.5 
                 no 
               
               
                   
               
               
                 ‘*’ denotes foam commercially available from Qycell Corporation (Ontario, California, USA) 
               
             
          
         
       
     
         [0106]    Turning to the shock absorption, vertical deformation, and energy restitution, the performance of non-crosslinked polyethylene foams of Table 1, which are commercially available from The Dow Chemical Company, Midland, Mich. was investigated. The results of this investigation are summarized in  FIG. 1 . With respect to Table 1, the compressive stress-strain, compressive creep, and compressive stress-strain behavior is analyzed using an Instron Model 5565 Universal Testing Machine (Norwood, Mass.) fitted with compression plates and a 2 kN load cell. When the tests are performed at 65° C., an Instron environmental chamber (Model 3119-405-21) is also used. 
         [0107]    Samples 2.5 to 5 cm wide by 5 cm deep are cut from sheets of the foam. To measure compressive stress-strain behavior, the samples are inserted between the centers of the compressive plates. The thickness direction of the foam is aligned parallel to crosshead movement. A pre-load of 2.5 N was applied at 5 mm/min, and the crosshead position is re-zeroed. The sample is then compressed at 10 mm/min until the load approached the capacity of the load cell. Stress is calculated by dividing the measured compressive force by the product of the width and depth of the foam. Stress is quantified in units of megapascals (MPa). Strain in terms of percent is calculated by dividing the crosshead displacement by the starting thickness of the foam and multiplying by one hundred. Results for the compressive stress-strain behavior tests are illustrated in  FIGS. 2 and 2   c  (comparative samples). 
         [0108]    To measure the compressive hysteresis behavior, a foam sample is loaded into the Instron in the same manner as above. A pre-load of 2.5N is applied at 5 mm/min, and the crosshead position is re-zeroed. Then the sample is compressed at 10 mm/min until the stress reaches 0.38 MPA, designated as the compression step. Immediately, the crosshead is then reversed until a load of 0.0038 MPa is reached, designated as decompression. Without interruption, the sample is compressed and decompressed for 10 cycles. 
         [0109]    To measure the compressive creep behavior, a foam sample is loaded into the Instron in the same manner as above, except that the environmental chamber is in place and preheated to a temperature of 65° C. The sample is placed in between the compression plates, at 65° C. After allowing the foam sample to equilibrate inside the chamber for one hour, a pre-load of 2.5 N is applied at 5 mm/min, and the crosshead position is re-zeroed. Load is then applied at 0.16 MPa. Crosshead position is then adjusted automatically by the Instron computer, to maintain a stress of 0.16 MPa for 12 hours. Compressive strain versus time is measured, the results of which are presented in  FIGS. 3 and 3   c . After 12 hours, the crosshead returns to its starting position. After another two hours, the foam is removed and allowed to cool to ambient conditions (20° C., 50% relative humidity). The foam thickness is then remeasured. The corresponding strain is designated “strain at release, 2 hr.” The compressive creep behavior test results are presented in  FIG. 4 . 
         [0110]    To measure the energy absorption behavior of the foams FIFA quality concept methodology as described in the “March 2006 FIFA Quality Concept Requirements for Artificial Turf Surfaces,” the FIFA handbook of test methods and requirements for artificial football turf; which is fully incorporated herein by reference. These foams are tested according to this methodology and it is found that foams having a density of 144 kg/m 3 , as an example, perform acceptably. More detailed test results on shock absorption are provided below. Returning to compressive performance, the below graphs illustrate that the performance of the foam is not compromised by the elimination of crosslinking. In addition, embodiments of the present invention may be useful for any field that may use artificial turf, such as rugby and field hockey. 
         [0111]      FIGS. 3 ,  3   c , and  4  illustrate that essentially the same compressive creep performance and subsequent recovery may be achieved despite the elimination of crosslinking. 
         [0112]    Synthetic turf, using embodiments of the present invention, is shown in  FIG. 5 . Specifically, a non-crosslinked polythene foam is provided as a shock absorption layer, which may be bonded to a backing. Artificial grass is attached to the backing, and the spaces between the grass may be filled with an infill. 
         [0113]    Embodiments using non-crosslinked polyethylene may be advantageous as non-crosslinked polyethylene is recyclable, and, thus, there are no environmental issues. Embodiments of the polymer foams described herein may also be useful as heavy layers for noise and vibration dampening, among others. 
         [0114]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims. 
         [0115]    All priority documents are herein fully incorporated by reference for all jurisdictions in which such incorporation is permitted. Further, all documents cited herein, including testing procedures, are herein fully incorporated by reference for all jurisdictions in which such incorporation is permitted to the extent such disclosure is consistent with the description of the present invention.