Wood-polymer-zeolite composites

Composite materials made from wood or other cellulose fibers or particles in combination with polymers such as polyethylene, polypropylene, and polyvinyl chloride have gathered increasing interest in recent years. Such “wood-polymer composites” have attracted attention due to the possibility of achieving products having the wood tone appearance of natural lumber combined with the durability of plastics. Inexpensive sources of plastics, such as from recycling operations, may provide additional advantages in terms of cost. However, one challenge is to provide composites having good physical properties relating to strength and toughness. Thus, there is commercial interest in compositions containing polymers and cellulose fibers or particles, particularly those exhibiting good physical properties.

In one aspect, the invention provides a composite material containing a consolidated mixture. The mixture includes

a) a particulate or fibrous cellulose component;

b) a zeolite; and

c) a polymer selected from the group consisting of polymers including at least 50 wt % ethylene repeat units, polymers including at least 50 wt % propylene repeat units, polymers including at least 50 wt % vinyl chloride repeat units, and mixtures thereof.

In another aspect, the invention provides a method of making a composite material containing a consolidated mixture. The method includes blending together

a) a particulate or fibrous cellulose component; b) a zeolite; and c) a polymer selected from the group consisting of polyethylene, polypropylene, and polyvinyl chloride.

Wood-Polymer-Zeolite Composites

Wood-polymer-zeolite (WPZ) composite materials according to the invention include a consolidated mixture that incorporates a) a particulate or fibrous cellulose component, b) a zeolite, and c) a polymer. By including a zeolite in the composition, the inventors have found that a composite material having excellent physical properties may be produced. In particular, proper incorporation of suitable amounts and types of zeolites may result in high tensile stress at yield, high tensile stress at break, and high flexural modulus, all of which are key engineering performance parameters for many applications, particularly those requiring structural strength. Additionally, the zeolites typically act as processing aids in the composite formulations, providing reduced usage of standardized lubricants and protecting the cellulose component during high temperature processing.

The amounts of cellulose, zeolite, and polymer in WPZ composites may be varied over a wide range, depending inter alia upon the exact identity of each ingredient, the amount and type of other ingredients (to be discussed below), and the intended use of the composite. Typically, components a), b) and c) are present within the following respective weight percent ranges:

0.5 to 90 of a); 0.1 to 80 of b); and 3.0 to 99.4 of c).

More preferably, the amounts of these components will be within the following ranges:

1 to 60 of a); 0.5 to 50 of b); and 5 to 60 of c).

Each ingredient will now be discussed in detail, followed by a description of methods of making the WPZ composites, potential applications of the composites, and Examples.

Zeolite

Zeolites suitable for use according to the invention include any known varieties, for example A, X, P, Y, and natural zeolites. As used herein, the term “zeolite” means a substantially crystalline aluminosilicate material with discrete channels and cages that allow the diffusion of small molecules into and out of their crystalline structures. The zeolite framework is made up of SiO 4 tetrahedra linked by shared oxygen atoms. Substitution of aluminum for silicon creates a charge imbalance that requires a non-framework cation to balance the charge. These cations, which are contained inside the channels and cages of these materials, may be replaced by other cations giving rise to ion-exchange properties. The water in these materials may typically be reversibly removed, leaving the host structure intact, although some framework distortion may occur.

It is desirable that at least 90% of the particles are less than 50 μm, advantageously less than 25 μm, and most suitably less than about 10 μm in size. Especially suitable are zeolites in which at least 90% of the particles are less than 4 μm in size, and in some cases 90% of the particles are less than 0.8 μm in size. In some embodiments of the invention, particularly good WPZ properties may be obtained by use of zeolite A having an mean particle size between 0.01 and 30 μm, and more particularly between 0.1 and 10 μm. Particularly suitable zeolites have a mean particle size from 0.01 to 4 μm, preferable from 0.01 to 1 μm, and more preferably from 0.01 to 0.6 μm.

Typically, suitable zeolites have a significant level of crystallinity, and in some embodiments the mean percent zeolite crystallinity is at least 50 as compared to a reference standard. In some embodiments, the zeolite has a mean micropore diameter in the range of 2.8 to 8 Å, and/or an external surface area in the range of 3 to 300 m 2 /g. Suitable exemplary zeolites are available commercially under the trade names VALFOR 100 and ADVERA 401PS, both available from PQ Corporation of Valley Forge, Pa. Also useful are zeolites in which some or all of the sodium ions have been replaced by potassium and/or calcium ions, for example zeolites 3A and 5A. Other nonlimiting examples of suitable potential ion-exchanged cations are Ag, Zn, and Cu, and replacement of sodium by these may be partial or complete.

Cellulose Component

Although the term “wood-polymer-zeolite composite” is used herein to describe the compositions of this invention, it is to be understood that the term encompasses materials in which cellulosic materials other than wood (i.e., other than wood flour, fibers, or pulp, etc.) are used, either in addition to or instead of wood-derived materials. Thus, the particulate or fibrous cellulose component may comprise cellulose in any of a number of forms, including as nonlimiting examples wood flour or fibers, wood pulp, wheat fibers, rice hulls, kenaf, flax, hemp, and mixtures of these. Typically wood fibers or flour will be used, and any commercially available variety is generally suitable for use according to the invention. In some embodiments, the wood flour is soft pine having a particle size of <40 mesh with a moisture content of <7%. However, any variety of hardwood or softwood could be used, usually dependent on the location of the manufacturer. The particle size of the cellulose component may vary over a wide range, and no particular limitations of particle size need be placed for purposes of this invention.

Polymer

Suitable polymers comprise at least 50 wt % ethylene repeat units, at least 50 wt % propylene repeat units, or at least 50 wt % vinyl chloride repeat units. In some embodiments, the polymer may comprise a low- or high-density polyethylene, polypropylene, or polyvinyl chloride homopolymer. One suitable polymer is a high-density polyethylene sold as Equistar ALATHON L 5040 by Lyondell Chemical Company of Houston, Tex. Copolymers may also be used, for example when the physical properties of the finished product need modification, such as copolymers of ethylene with hexene or heptene. Or, other copolymers such as polypropylene with approximately 3% ethylene comonomer content (as a fluxing agent) may be used when faster production rates are desired. In the case of polyvinyl chloride polymers, polyvinyl chloride homopolymer resins such as Shintech SE950EG or copolymers of vinyl chloride with 3-10% of vinyl acetate can be used. Another suitable polymer component may be a polymer made from the protein keratin (e.g., from chicken feathers), glycerol and sodium sulfite. Mixtures of any of the above-noted polymers may be used, for example mixtures of recycled polymers.

Compatibilizer

Wood-polymer-zeolite composites according to the invention may benefit from the inclusion of a compatibilizer. The choice of a suitable compatibilizer may improve the mechanical properties of the WPZ composite by increasing adhesion between the various components of the mixture. Any of a number of materials may be used, with the exact type and amount of compatibilizer depending on a number of factors well known to the person of skill in the art. The compatibilizer is typically a polymeric material that contains repeat units of some of the same monomers that constitute one or more of the component c) polymers mentioned above. It also typically contains a moiety that interacts strongly, for example by reaction, with the cellulose component a). One type of compatibilizer is a polyepoxide, for example an ethylene-glycidyl methacrylate copolymer or terpolymer. Suitable examples include LOTADER AX8840 ethylene-glycidyl methacrylate copolymer, and AX8900, 8920, and 8950 ethylene-methyl acrylate-glycidyl methacrylate terpolymers, available from Arkema of Philadelphia, Pa.

Another class of suitable compatibilizers includes polyanhydrides, for example maleic anhydride grafted polypropylenes, ethylene-propylene-maleic anhydride copolymers, and ethylene-propylene-diene-maleic anhydride copolymers. Other examples include styrene-acrylonitrile-maleic anhydride copolymers and methyl methacrylate-acrylonitrile-maleic anhydride copolymers, which may for example be suitable for use when polymer component c) includes polyvinyl chloride (or other) polymers. Other examples include styrene-maleic anhydride copolymers, such as are available commercially from NOVA Chemicals Corporation of Calgary, Alberta, Canada under the trade name DYLARK. Additional suitable polyanhydrides include ethylene-maleic anhydride copolymers, graft copolymers or terpolymers, for example ethylene-maleic anhydride-(meth)acrylic acid terpolymers or ethylene-maleic anhydride-acrylic ester terpolymers. One particularly suitable example of the latter is an ethylene-maleic anhydride-butyl acrylate terpolymer, one example of which is available commercially from Arkema under the trade name LOTADER 3210. In general, the amount of compatibilizer (if any) used in the WPZ composite may typically range between 0.01 and 5 wt %, more typically between 0.3 and 2.0 wt %, based on the total composition weight. However, any amount may be used, and the exact amount will depend upon the type and relative amount of polymer, zeolite, cellulosic component utilized.

Other Ingredients

Wood-polymer-zeolite composites may further comprise any of a number of other ingredients. Examples include stabilizers, process aids, impact modifiers (e.g., rubber-based modifiers), lubricants, plasticizers, antioxidants, UV absorbers, and pigments or other colorants. Also useful may be foaming agents, fungicides or algaecides, and/or flame retardants, all of which are known in the art. Suitable exemplary foaming agents include HYDROCEROL endothermic or exothermic compositions, available from Clariant Masterbatches of Holden, Mass., and exemplary lubricants include pentaerythritol esters such as LOXIOL G 70 S, available from Cognis North America of Cincinnati, Ohio. The WPZ composite may further comprise one or more inorganic fillers, suitable nonlimiting examples of which include talc, calcium carbonate, glass beads, and mica. Another suitable filler is bird feathers.

Preparation of Wood-Polymer-Zeolite Composites

The invention also provides methods of making WPZ composites such as described above. It has been found that processing of these compositions, for example by melt extrusion, can be performed at higher-than-expected temperatures while still avoiding excessive discoloration of the product. Higher processing throughput and/or reduced binding of composite in the extruder are frequently achieved, and are apparently related to the presence of the zeolite.

In general, methods of making WPZ composite materials comprise forming a consolidated mixture by any method known in the polymer processing art. Such forming methods include powder mixing of the components then powder pressing, powder two-roll milling and calendering or powder extruding. Injection molding of the powder blends can also be used. Suitable non-limiting examples of processing methods are extrusion and milling.

Uses of Wood-Polymer-Zeolite Composites

Wood-polymer-zeolite composites according to the invention may be used in any of a number of end-use applications, in which their superior physical performance properties may be used to advantage. One useful application is in building products, including as nonlimiting examples lumber and related structural materials. As used herein, the term “lumber” means planks, sheets, or other pieces resembling typical wood-based materials such as sawn lumber, oriented strand board, particle board, plywood, etc. Thus, WPZ composites may be used to make products such as fences, railings, decking for outdoor porches and the like, panels for floors, ceilings, wall, bath or shower stalls, cabinetry, countertops, and other structural items. They may also be used as automotive construction materials, for example in decorative interiors, door panels, headliners, seat interiors, and other uses, as well as in any of a variety of industrial products such as piers and docks, or consumer products such as furniture.

Following is an identification of various ingredients used in the Examples, and sources from which they may be obtained.

Glossary of Ingredients

Ingredient Name Description Manufacturer Location ADVASTAB TM181 methyltin mercaptide Rohm and Haas Spring House, PA ADVERA 401PS hydrated sodium zeolite A PQ Corporation Valley Forge, PA ADVERA 401F hydrated sodium zeolite A PQ Corporation Valley Forge, PA 13X Zeolite hydrated sodium zeolite 13X PQ Corporation Valley Forge, PA Zeolite P hydrated sodium zeolite P PQ Corporation Valley Forge, PA Nano-A 1 hydrated sub-micron sodium zeolite A CABSORB ZS500RW2 Chabazite GSA Resources Tucson, AZ ALATHON L5040 high density polyethylene Equistar Chemicals Cincinnati, OH GLYCOLUBE 825 glyceryl monostearate Lonza, Inc. Alendale, NJ PARALOID K120ND acrylic process aid Rohm and Haas Spring House, PA PETROTHENE polypropylene homopolymer Equistar Chemicals Cincinnati, OH PP31SF01X01L5040 EPOLENE E-43 chemically modified Eastman Kingsport, TN polypropylene SUPERPFLEX 100 calcium carbonate Specialty Minerals Bethlehem, PA Talc CT325 hydrated magnesium silicate Specialty Minerals Bethlehem, PA LOXIOL G70S high molecular weight complex Cognis Corporation Cincinnati, OH ester lubricant LOTADER 3210 Ethylene-maleic anhydride-butyl Arkema Inc. Philadelphia, PA acrylate terpolymer TYRIN 3615 chlorinated polyethylene Dow Chemical Co. Midland, MI 40 mesh wood flour soft pine wood flour American Wood Schofield, WI Fibers 1 Nano-A was prepared by the methods described in PCT International Application No. PCT/US2004/025993, filed Aug. 11, 2004, and had a mean particle size less than 1 μm and greater than 50% crystallinity. 2 CABSORB was prepared by grinding the material in a micro-mill before processing in a wood-plastic-zeolite formulation. CABSORB chabazite is a natural (mined) zeolite.

General Procedure

Unless otherwise noted, compositions in the following examples were prepared by first mixing wood flour with zeolite (and other inorganic materials, if present) in a Henschel mixer. All of the other ingredients were separately mixed by rolling, and then the two mixtures were combined in the roll mixer. All formulations are given in weight percents. In all cases, Tensile Stress was performed per ASTM D638 and Flexural Modulus was performed per ASTM D790.