Abstract:
Composite materials containing non-plasticized, non-gelatinized starch, a compatibilizer and a synthetic resin, such as polyethylene and/or polypropylene, may be used to make wood replacement products for use as construction materials.

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. application Ser. No. 60/646,931, filed Jan. 25, 2005, which is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention pertains to the field of composite materials and, more particularly, to composites containing fillers mixed with a plastic resin or the like. The composites may be shaped into products for use in the construction industry, such as artificial boards or panels that may optionally be embossed to provide a wood grain texture. 
     2. Description of the Related Art 
     Wood-plastic composites are widely used in residential and commercial structures for decking board, fencing, railing and so forth. In the manufacture of these products, wood flour or wood fiber is mixed with a resin and the composite is extruded. Warm extruded profiles may be embossed to create a real wood or wood grain appearance. Adding wood flour or wood fiber helps reduce cost, improve flex modulus and add wood appearance. 
     Initially, these products represented a marked cost savings over actual wood when used for the same purposes. Over time, however, the cost of wood flour and wood fiber has increased dramatically. A decade ago, wood flour and wood fiber were little-used by-products of the paper and lumber industries. Today, the opposite is true; trees are grown for the specific purpose of direct conversion into wood flour or wood fiber for use in wood-plastic composites. 
     In addition to their increasing cost, wood-plastic composites have several drawbacks. The use of wood as a reinforcing filler in composites creates a strong wood color that is very difficult to change in the presence of a plastic resin. For example, significant amounts of titanium dioxide are needed in formulations where a light color is desired. Titanium dioxide is an expensive additive, and its use in large quantities creates an unnatural look with a lackluster appearance. Further, abundant quantities of lubricant are needed to allow the composite to be extruded into a board, and the resulting board is not completely hydrophobic. Wood flour and wood fiber can both adsorb a large amount of water. Wood-plastic composite profiles also have a stronger than normal wood smell due to high process temperatures used in the production process. This makes wood-plastics composites unattractive for many in-house applications. 
     In an attempt to replace wood flour and wood fiber in composites, various agricultural materials have been used. For example, pure cellulose fibers have been used to impart a light color on composite profiles. However, pure cellulose fibers are very costly and difficult to process at high fiber content. Composite profiles with high cellulose fiber content are thus not commercially viable as replacement construction materials. 
     SUMMARY 
     The present instrumentalities advance the art and overcome the problems that are outlined above. 
     In one aspect, a manufactured product for use as a wood substitute, includes from 20-80% by weight starch; from 0.5-4% by weight of a compatibilizer; from 20-78% by weight of a synthetic resin; and from 0-15% by weight fibers. 
     In one aspect, a method of making a substitute wood product includes the steps of combining ingredients including from 20-80% by weight starch, from 0.5-4% by weight of a compatibilizer, from 20-78% by weight of a synthetic resin, and from 0-15% by weight fibers; processing the ingredients to achieve a melt temperature of the synthetic resin; and extrusion shaping the substitute wood product. 
     In another aspect, a manufactured product for use as a wood substitute, includes from 20-80% by weight granular starch; from 20-78% by weight of a synthetic resin; from 0.5-4% by weight of a compatibilizer; from 0-15% by weight of a fiber; from 0.5-4% by weight of a lubricant, said lubricant containing no metal ions; from 0-2% by weight of a foaming agent; from 0-1% by weight of a colorant; from 0-5% by weight talc; from 0-2% by weight of an antimicrobial agent; and from 0-0.3% by weight of a UV stabilizer. 
     In another aspect, a method of making a substitute wood product includes the steps of combining ingredients including from 20-80% by weight predried starch, from 20-78% by weight of a synthetic resin, from 0.5-4% by weight of a compatibilizer, said compatibilizer having a melt index of 2-150, from 0-15% by weight fiber, from 0.5-4% by weight of a lubricant, said lubricant containing no metal ions, from 0-2% by weight of a foaming agent, from 0-1% by weight of a colorant, from 0-5% by weight talc, from 0-2% by weight of an antimicrobial agent, and from 0-0.3% by weight of a UV stabilizer; processing the ingredients to achieve a melt temperature of 260-400° F.; and extrusion shaping the substitute wood product. 
     In yet another aspect, a manufactured product for use as a wood substitute includes from 20-80% by weight granular starch; from 20-78% by weight of a synthetic resin; from 0.5-4% by weight of a compatibilizer; and from 0-15% by weight of a fiber. 
     In yet another aspect, a method of making a substitute wood product includes the steps of combining ingredients including from 20-80% by weight predried starch, from 20-78% by weight of a synthetic resin, from 0.5-4% by weight of a compatibilizer, said compatibilizer having a melt index of 2-150, and from 0-15% by weight of a fiber; processing the ingredients to achieve a melt temperature of 260-400° F.; and extrusion shaping the substitute wood product. 
    
    
     DETAILED DESCRIPTION 
     The present formulations utilize starch as a filler, where the starch is neither gelatinized by moisture nor plasticized by a plasticizing agent, such as glycerine or propylene glycol. The use of starch as a filler is economical and gives a very light color to composites, such that the composites can be easily made white with the addition of a minimal amount of titanium dioxide. Further, the use of starch as a filler improves modulus and dimensional stability of composite boards; the result is improved nailing and sawing qualities. 
     Suitable starches for use in the disclosed formulations include those that are cost effective as fillers, for example, wheat, corn, rice, tapioca, and potato. Additionally, starches that are chemically, physically and/or genetically modified may be used. 
     Starch as a filler does not have as good a reinforcing effect as fibers for flex modulus. Thus, adding a small amount of fiber helps overcome this problem in some embodiments. The disclosed formulations may, for example, include fibers selected from the group consisting of glass fibers, cotton, hardwood fibers, softwood fibers, flax, abaca, sisal, ramie, hemp, bagasse, recycled paper fibers, cellulose fibers, polymer fibers, and mixtures thereof. 
     Resins for use in the disclosed formulations include those selected from the group consisting of polyolefines, polyethylene, polypropylene, polyurethane, polystyrene, polyamides, polyesters, and combinations thereof. It will be appreciated that combinations of polymers may include both physical mixtures and chemical combinations, e.g., block-copolymers. 
     Compatibilizers are generally polymers that are functionalized with grafting compounds. For example, maleic anhydride is a grafting compound that may be reacted with polyethylene or polypropylene to create the compatibilizers maleated polyethylene or maleated polypropylene. The grafting compound facilitates binding of the starch to the compatibilizer, while the polymer portion of the compatibilizer interacts with the resin component of the composite. 
     Although reference has been made to maleic anhydride as a grafting compound and to polyethylene and polypropylene as suitable compatibilizer polymers, one skilled in the art will appreciate that numerous other grafting compounds and polymers may be used to create suitable compatibilizers. 
     Generally speaking, composite resins described herein have bulk densities in the range of 25-45 lbs/ft 3 . The density of an extrusion profile made from one of these resins may be controlled to fall within a range of 0.7-1.1 g/cm 3 . 
     The following examples teach by way of illustration, and not by limitation, to illustrate preferred embodiments of what is claimed. 
     Example 1 
     Starch-polyethylene Composite Resin and Profile Extrusion 
     Formulation for Composite Resins: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Native corn starch* 
                 45%  
               
               
                   
                 TC2500 (cellulose fiber) 
                 15%  
               
               
                   
                 High density polyethylene (4 melt) 
                 33%  
               
               
                   
                 Polybond ® 3109** (compatibilizer) 
                 3% 
               
               
                   
                 Talc 
                 2% 
               
               
                   
                 Titanium Dioxide 
                 1% 
               
               
                   
                 TPW 113 (lubricant) 
                 1% 
               
               
                   
                   
               
               
                   
                 *Corn starch is predried by a flash tube dryer to 3.5% moisture. 
               
               
                   
                 **Polybond ® 3109 is a maleic anhydride grafted linear low density polyethylene (1.0 wt. % MA). 
               
             
          
         
       
     
     Polyethylene, Polybond® 3109, titanium dioxide, talc, and TPW 113 were fed to the main feeding hopper of a ZE75A-UT twin screw extruder. The plastic pellets were melted in the plasticating zone and mixed with other ingredients. The barrel temperature at the die end was set at 270° F. Predried corn starch and cellulose were fed by a side feeder. Venting ports were provided for moisture and air escape. A vacuum stuffer was used near the barrel end to pull moisture. The melt was pelletized by an underwater pelletizing system. The pellets coming out of the spin dryer of the underwater system were sent to a belt dryer for further drying. The belt dryer was kept at about 230° F. Final moisture in the pellets was controlled to less than 1.0%. 
     The above described resin was used for making profile extruded fencing boards with a die dimension of ⅝″×5⅜″ on a single screw extruder (3.5″ Prodex) using the following formulation: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Pellets (as above) 
                 97.5% 
               
               
                   
                 TWP 113 (lubricant) 
                 2.5% 
               
               
                   
                   
               
             
          
         
       
     
     The barrel temperature was set at 265° F. The melt profile passed through a water spray chamber, which provided slow surface cooling, and then through a heated embossing roll, which imparted wood grain texture or another surface pattern. Following the embossing, the board was cut with a flying saw. The final profile extruded fencing board had an excellent white color. 
     Example 2 
     Starch-polyethylene Direct Profile Extrusion 
     Formulation for Composite Resins: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Native corn starch* 
                 55%  
               
               
                   
                 TC2500 (cellulose fiber) 
                 5% 
               
               
                   
                 High density polyethylene (0.5 melt) 
                 30.5%   
               
               
                   
                 Polybond ® 3109 (compatibilizer) 
                 3% 
               
               
                   
                 Talc 
                 2% 
               
               
                   
                 Titanium Dioxide 
                 1% 
               
               
                   
                 TPW 113 (lubricant) 
                 3.5%   
               
               
                   
                   
               
               
                   
                 *Corn starch is predried by a flash tube dryer to 3.5% moisture. 
               
               
                   
                 **Polybond ® 3109 is a maleic anhydride grafted linear low density polyethylene (1.0 wt. % MA). 
               
             
          
         
       
     
     Polyethylene, Polybond® 3109, titanium dioxide, talc, and TPW 113 were fed to the main feeding hopper of a ZE75A-UT twin screw extruder. The plastic pellets were melted in the plasticating zone and mixed with other ingredients. The barrel temperature at the die end was set at 280° F. Predried corn starch and cellulose were fed by a side feeder. Venting ports were provided for moisture and air escape. A vacuum stuffer was used near the barrel end to pull moisture. 
     The melt passed through a profile shape for standard decking board that lead to a water spray chamber, which provided slow surface cooling. The decking board was then passed through a heated embossing roll, which imparted wood grain texture or another surface pattern. Following the embossing, the board was cut with a flying saw. The final profile extruded decking board had an excellent white color. 
     Example 3 
     Starch-polypropylene Composite Resin and Profile Extrusion 
     Formulation for Composite Resins: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Native corn starch* 
                 50%  
               
               
                   
                 TC2500 (cellulose fiber) 
                 10%  
               
               
                   
                 Homo-polypropylene (2 melt) 
                 33%  
               
               
                   
                 Polybond ® 3200** (compatibilizer) 
                 3% 
               
               
                   
                 Talc 
                 2% 
               
               
                   
                 Titanium Dioxide 
                 1% 
               
               
                   
                 TPW 113 (lubricant) 
                 1% 
               
               
                   
                   
               
               
                   
                 *Corn starch is predried by a flash tube dryer to 3.5% moisture. 
               
               
                   
                 **Polybond ® 3200 is a maleic anhydride grafted polypropylene (1.0 wt. % MA). 
               
             
          
         
       
     
     Polypropylene, Polybond® 3200, titanium dioxide, talc, and TPW 113 were fed to the main feeding hopper of a ZE75A-UT twin screw extruder. The plastic pellets were melted in the plasticating zone and mixed with other ingredients. The barrel temperature at the die end was set at 330° F. Predried corn starch and cellulose were fed by a side feeder. Venting ports were provided for moisture and air escape. A vacuum stuffer was used near the barrel end to pull moisture. The melt was pelletized by an underwater pelletizing system. The pellets coming out of the spin dryer of the underwater system were sent to a belt dryer for further drying. The belt dryer is kept at about 230° F. Final moisture in the pellets was controlled to less than 1.0%. 
     The above described resin was used for making profile extruded foamed fencing boards with a die dimension of ⅝″×5⅜″ on a single screw extruder (3.5″ Prodex) using following formulation: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Pellets (as above) 
                 96.1% 
               
               
                   
                 GMA411 (foaming agent) 
                 1.0% 
               
               
                   
                 TWP 113 (lubricant) 
                 2.5% 
               
               
                   
                 Hostanox ® O16 (phenolic antioxidant) 
                 0.1% 
               
               
                   
                 Everlight 91 (UV stabilizer) 
                 0.3% 
               
               
                   
                   
               
             
          
         
       
     
     The barrel temperature was set at 330° F. The foamed melt profile passed through a water spray chamber, which provided slow surface cooling, and then through a heated embossing roll, which imparted wood grain texture or another surface pattern. Following the embossing, the board was cut with a flying saw. The density of the board was 0.91 g/cm 3  and the final profiled extruded fencing board had an excellent white color. 
     Example 4 
     Formulations for Starch-polyethylene Composites 
     Composite resins for direct profile extrusion: 
     20-80% native starch, 
     20-78% polyethylene such as high density polyethylene, low density polyethylene with a melt index of 0.25-15, 
     0-15% fibers such as chopped glass fibers or cellulose fibers, 
     0.5-4% maleated polyethylene with a melt index of 2-150, 
     0.5-4% lubricant/lubricants that contains/contain no metal ions, 
     0-1% titanium dioxide or other colorants/pigments, 
     0-2% foaming agents, 
     0-5% talc, 
     0-2% antimicrobial agents, i.e., zinc borate, 
     0-0.3% UV stabilizers and antioxidants. 
     Profile extrusion using compound resins: 
     90-100% composite resin, 
     0-4% lubricants, 
     0-15% fibers, 
     0-2% foaming agents, 
     0-1% pigments, 
     0-5% talc, 
     0-2% antimicrobial agents, i.e., zinc borate. 
     Example 5 
     Processing of Starch-resin Composites 
     Composite resins for direct profile extrusion: 
     20-80% native starch, 
     20-78% polypropylene with a melt index of 0.25-10, 
     0-15% fibers such as chopped glass fibers or cellulose fibers, 
     0.5-4% maleated polypropylene with a melt index of 2-150, 
     0.5-4% lubricant/lubricants that contains/contain no metal ions, 
     0-2% foaming agents, 
     0-1% titanium dioxide or other colorants/pigments, 
     0-5% talc, 
     0-2% antimicrobial agents, i.e., zinc borate, 
     0-0.3% UV stabilizers and antioxidants. 
     Profile extrusion using compound resins: 
     90-100% composite resin 
     0-4% lubricants 
     0-15% fibers 
     0-1% pigments 
     0-2% foaming agents 
     0-5% talc, 
     0-2% antimicrobial agents, i.e., zinc borate. 
     Example 6 
     Processing of Composites 
     Commercially available starch may be pre-dried in a flash tube dryer or tornesh dryer to a moisture content of 1-5%. Resins, together with some additives, are fed into the main extrusion hopper and melted in the plasticating zone. The filler, together with some additives, is fed with a side feeder after the resins have melted. The screws mix the filler, plastics and other minor ingredients. Venting ports are provided to release air and moisture in the melt. A down-stream venting port is provided with a vacuum stuffer. 
     For composite pellets, one may use die face pelleting, an underwater pelleting system, or a melt sheet dicer system depending on the formulation. The pellets may be dried or cooled to a moisture content of less than 1% before final packaging. 
     For profiles, melt flows out of a shaping die. The processing temperature for the melt is controlled from 260-380° F. for the polyethylene composite system and from 320-420° F. for the polypropylene composite system. The melt profile is cooled with calibration for shape size control. The hot profiles are further cooled with water cooling tanks or with water spray. After proper cooling, the profiles can be embossed with embossing rolls. After cutting with a synchronized sawing table, the profiles are cooled further on a cooling tower or table for final dimensional stability control. 
     Twin-screw compounders are used for making composite pellets. Twin-screw extruders are also used for direct profile extrusion, without an intermediate step of forming composite pellets. Both twin-screw and single-screw extruders are used for making profiles. Single-screw extruders are often used when composite pellets are the main feed. 
     Changes may be made in the above systems and methods without departing from the subject matter described in the Summary and defined by the following claims. It should thus be noted that the matter contained in the above description should be interpreted as illustrative and not limiting. 
     All references cited are incorporated by reference herein.