US20060073319A1

US20060073319A1 - Method and apparatus for making products from polymer wood fiber composite

Info

Publication number: US20060073319A1
Application number: US10/958,755
Authority: US
Inventors: Philip Roberson; Larry Weber; Carl Hagberg
Original assignee: NFM Welding Engineers Inc
Current assignee: NFM Welding Engineers Inc
Priority date: 2004-10-05
Filing date: 2004-10-05
Publication date: 2006-04-06

Abstract

A method and apparatus for making products from polymer wood fiber composite is described. The method includes the steps of providing a extruder having two counter-rotating non-intermeshing screws, supplying to the extruder fiber material and polymer material, mixing and heating the fiber material and polymer material in the extruder for form a mixture, removing the mixture from the extruder and placing the mixture in a press, and compression molding the mixture in the press to form the product.

Description

FIELD OF INVENTION

The present invention relates to a method and apparatus for the continuous manufacture of products from a mixture of a fiber material, particularly wood fiber, and a polymer binder, and more particularly to a method and apparatus that allows large sized wood fiber particles to be used.

BACKGROUND OF THE INVENTION

A large number of processes have been proposed for combining wood fiber with a polymer resin binder to produce materials for making various types of finished products. The advantages of such materials include their cost and appearance, and its ability to be used as substitutes for lumber. Extensive applications have been made of these materials in making extruded components for the manufacture of windows and doors.
In many prior art processes, the wood has been supplied only in the form of a wood flour having a small particle size and specific moisture properties. The small size, limited size range and limited moisture content have been necessary in order to provide controlled mixing of the wood (in the form of flour) with the polymer resin. After the material is mixed together, it has often been processed into pellets which are subsequently used in other manufacturing processes.
It has generally been believed that the wood particle size and moisture content had to be carefully controlled so that products could be made with uniform desired properties. If the wood particle sizes were too large or if the particle sizes varied too greatly or if the moisture content of the wood particles was too great, the resulting mixture with the polymer resin would be inconsistent, and the quality of the resulting product would suffer. As a result, the wood used in many prior art processes had to be carefully selected and processed prior to its use. This increased the cost of wood material used, and thus increased the overall cost of the finished product.
Furthermore, it has been difficult to obtain desired physical properties in the finished products. In order to make a product that can be used as a substitute for a finished wood product made of lumber, the product must have a relatively high tensile strength. Lumber has a high tensile strength along the grain of the wood because of the orientation of the wood fibers. However, in manufacturing wood/polymer composite replacement products, the size of the wood particles has been very limited, so that the products made of these replacement materials have not been able to achieve comparable tensile strength. As a result many of these products have been relatively brittle and inferior to those made of actual lumber. In addition, these products have a lower flex modulus than comparable products made of actual lumber.
Another problem with prior art processes is that most of them are not continuous. Making material in batches or providing an intermediate step of forming pellets does not provide a continuous process and can result in inconsistencies in product properties and inefficiencies resulting from starting and stopping the process. Discontinuous processes are also energy inefficient, since the material must be heated and cooled more than once. Furthermore, the processing of the wood fiber polymer mixture into pellets or other intermediate products can result in degradation of the fiber size in the mixture, which can adversely affect the desired physical properties of the finished products.

SUMMARY OF INVENTION

The present invention overcomes these problems, and provides a unique and advantageous method and apparatus for making products from a composite of wood fiber particles and polymer resin.
In contrast to the non-continuous processes of the prior art, products can be made efficiently in a continuous process using the method and apparatus of the present invention, without the necessity of pre-forming pellets or other intermediate products, and without any batch mixing. The present invention avoids the necessity of batch mixing as is prevalent in the prior art. The present invention also avoids any intermediately step, such as the making of pellets which are subsequently used in another process.
The method and apparatus of the present invention utilizes the advantageous properties of a twin counter-rotating and non-intermeshing screw extruder which provides for thorough mixing of the material while minimizing detrimental destruction of the wood fibers. This extruder provides for distributive mixing, without substantial dispersive mixing, so that the wood fibers and the polymer are thoroughly mixed together, while the size of the wood fibers is not significantly affected by the mixing process, and the excess heat that is generated by dispersive mixing is minimized. The extruder is thus able to pass and process larger fiber particles while most other extruders are incapable of doing so. The method and apparatus can handle considerably larger sized wood fiber particles than have been accommodated by prior art processes. Since fibers are not destroyed and long fibers that can be used in the present invention are retained and present in the finished product, the present invention provides improved tensile strength and flex modulus to the finished product. A mixture of different sized wood fiber particles can also be used, and it is generally not necessary to segregate or screen for particles within a predetermined size range. Using prior art processes, a mixture of particles having a wide range of sizes tended to cause the particles to aggregate or glop together; this is not a significant problem with the method and apparatus of the present invention.
Most wood fiber material may be used in the present invention without pre-drying the material prior to introducing the material into the extruder. There is usually no need for a separate dryer to reduce the moisture content of the wood prior to processing it. The extruder heats the wood fiber material to a temperature sufficient to extract significant residual moisture from the wood fiber, and vents are provided along the length of the extruder. Furthermore, because the wood typically is not pre-dried, the impregnation of the polymer into the wood fiber during the mixing and heating process is reduced, resulting in lighter, less dense finished products. Some residual moisture can also be left in the product to act as a natural blowing agent. Since the use of additional foaming or blowing agents may be avoided, the additional expense of such agents can be saved, and the problems caused by controlling the foaming action can be avoided. The present invention thus provides for the manufacture of lighter wood fiber polymer products with enhanced physical properties.
The wood fiber material and the raw polymer resin may also be loaded into the same feed hopper of the extruder; there is no need for separate introduction of wood fiber and polymer resin into different entry points in the extruder stream. It is also not necessary to pre-mix the wood fiber with the polymer resin material; all necessary mixing is performed within the extruder.
Products made using the method and apparatus of the present invention are stronger than composite wood fiber and polymer products made by most prior art processes. The present invention uses a unique combination of extrusion and compression molding to allow large wood fibers to be used and to cause the fibers to be randomly oriented within the finished product for maximum strength. While the fibers are aligned along the axis of extrusion during the extrusion process, the fibers lose their original orientation during the compression molding process.
Because the fibers are randomly oriented in the finished product, the product made using the present invention has a higher strength in multiple directions than is typically achieved using extrusion alone. Using an extrusion process alone, wood fiber polymer composite products often exhibit brittleness transverse to the direction of extrusion, because the wood fibers in the material become axially oriented in the extrusion process along the axis of extrusion. While this orientation of fibers may result in acceptable axial tensile strength, it can result in brittleness and a limited flex modulus. Using the method and apparatus of the present invention, the compression molding re-orients the wood fibers randomly to all directions regardless of the direction of extrusion, so that the fibers are no longer principally aligned along the extrusion axis. The resulting products are much stronger than products made by extrusion alone.
The resulting fiber strength is also achieved by using a separate dollop of material from the extruder in each mold. If two or more dollops were used to make a single molded product, the fibers from each dollop would tend not to intermesh with each other, causing a structural weakness along the join line where the material from the two dollops meet.
The present invention is especially useful in providing products from a composite of wood fiber and polymer, but it may also be advantageously used in making composites from other fibers, both natural and man-made. Natural fibers that can be used in composites according to the present invention include flax, straw, bamboo and rice hulls. Man-made fibers that can be used include glass, nylon and other polymer fibers.
These and other advantages are provided by the present invention of a method and apparatus for making products from polymer wood fiber composite. The method comprises the steps of providing a extruder have two counter-rotating non-intermeshing screws; supplying to the extruder fiber material and polymer material; mixing and heating the fiber material and polymer material in the extruder to form a mixture; removing the mixture from the extruder and placing the mixture in a press; and compression molding the mixture in the press to form the product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a typical example of the apparatus of the present invention used for practicing the method of the present invention.
FIG. 2 is a side elevational view of the apparatus of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring more particularly to the drawings, and initially to FIGS. 1 and 2, there is shown a system 10 according the present invention for making products from a composite of wood fiber and polymer resin. The system 10 comprises an extruder 11, which receives the wood fiber material and the raw polymer resin, mixes and heats these materials, and extrudes the mixture onto a lower mold half carried in a tray 12 which moves on a material handling system 13. The material handling system 13 provides a means for moving the mold half in the tray 12 from the extruder 11 to any one of four compression molding machines 14 where the material on the mold half is molded into the finished product. If so desired, the lower mold half and the tray 12 may be provided as an integral unit.
The extruder 11 is preferably a twin-screw counter-rotating non-intermeshing extruder. A suitable extruder may be obtained from NFM Welding Engineers of Massillon, Ohio. These extruders are well known, and representative samples of this design of an extruder can be seen in U.S. Pat. Nos. 3,802,816 and 4,465,451. The extruder 11 has two parallel screws that rotate in opposite directions and do not intermesh, providing thorough mixing of the material in the extruder. While it is preferred that the twin screws do not intermesh, it is also possible to use a twin screw extruder with screws that intermesh slightly, so long as the screws are not self-wiping. One of the twin screws extends to the material exit, while the other screw extends to a point short of the exit. Extruders of this type are often used with a gear pump at the extruder exit to pump the material exiting from the extruder. However, in the present invention, such a gear pump cannot be used, since it could not accommodate the larger sized wood fiber pieces present in the material mixture. A die may be placed at the extruder exit to control the material flow from the extruder, but the shape of the die is otherwise not important to the operation of the process.
The counter rotating and non-intermeshing screws of the extruder 11 provide for optimum mixing of the material while reducing detrimental destruction of the wood fibers. The extruder 11 is operated at one or more screw speeds in a screw speed range of between about 20 revolutions per minute (rpm) and about 1,000 rpm, preferably between about 50 rpm and about 500 rpm. If necessary, a second extruder can be added to the system 10 parallel to the extruder 11 to produce additional pre-molded material mixture for placement on mold halves and feeding the compression molding machines. The use of a twin screw extruder with counter-rotating non-self-wiping screws is important to the method of the present invention, because such extruders are able to pass and process long fibers, which other extruders are incapable of doing effectively.
The material handling system 13 comprises a series of conveying lines formed of a plurality of rollers which support the trays 12 and allow the trays to be moved between several stations. The system 13 may include, for example, a loading station 15 where the mold half on each tray 12 may receive the material mixture output from the extruder 11, a first main conveyor line 16, a plurality of transfer stations 17, a plurality of processing conveyer lines 18, a plurality of processing stations 19, a second main conveyer line 20, an unloading station 21, and a return conveyer line 22. One of the compression molding machines 14 is provided at each of the processing stations 19. The layout of the material handling system 13 shown in the drawings and described here is one of many possible layouts, and the particular layout of the system 13 is not important to the operation of the system 10 of the present invention but is only offered as an example of a suitable layout.
The compression molding machine 14 is preferably a hydraulically driven bottom or top activated multiple post press, allowing for compression of 0 to 2,000 psi (14 MPa) on the molding surface area. Suitable compression molding machines may be obtained from Lawton Plastic Machinery Division of The C.A. Lawton Company of De Pere, Wis.; The French Oil Mill Machinery Co. of Piqua, Ohio; and Wabash MPI of Wabash, Ind. The compression molding machine is fitted with suitable molds which are intended to shape the material into the desired product.
In operation, one of the mold halves is placed on one of the trays 12, which is placed at the loading station 15. The wood fiber material and the raw polymer resin material are loaded into the input hopper of the extruder 11 where they fall into the extruder and are heated and mixed by the twin screws of the extruder. The wood fiber material may be hardwood or softwood, of varying particle size, containing moisture content up to 11%. If the moisture content is above 11%, it may be necessary to perform some pre-drying of the material. The material may be obtained as waste material from landscaping or lumber mills. The polymer resin material may be polyethylene, polypropylene styrenics, vinyl, nylon, or polyesters. Other polymer materials may be used, including thermosets. The wood fiber material and the polymer resin are introduced into the hopper in a predetermined ratio, depending upon the desired properties of the finished product. For example, the amount of wood fiber material may range from about 20% to about 80% by weight, and the amount of polymer resin material may range from about 80% to about 20% by weight. Both materials can be put into the same feed hopper together; there is no need for separate introduction of wood fiber and polymer resin into different entry points in the extruder stream. It is usually not necessary to pre-treat the wood fiber in any way, and, in particular, no pre-drying of the wood fiber is typically necessary. It is also not necessary to pre-mix the wood fiber with the polymer resin material; all necessary mixing is performed within the extruder.
In addition to the wood fiber material and the polymer resin, other additives may be included in the mixture fed into the extruder. For example, suitable lubricants, coupling agents, flame retardants, impact modifiers, colorants, stabilizers, UV protectants, non-fibrous fillers can be added, as is well known in the art.
The maximum size of the wood particles that can be used is limited only by the size that will pass through the extruder, and since a twin counter-rotating non-intermeshing screw extruder is used, it is possible to pass relatively large fibers through the extruder. The actual size of the wood fiber pieces than can be accommodated to produce acceptable products depends upon the size of the extruder. For example, for an extruder having a screw diameter of 6 inches (152 mm), the wood particles may be any size up to 6 inches (152 mm) in length and 1 inch (25 mm) wide. It is noted that this is considerably larger than the size of wood fiber material that has been accommodated by prior art processes. Larger particles can be used in the process, although the quality of the finished product may be affected. It is likely that larger particles would be broken down and reduced in size during the mixing and heating process. The ratio of screw size to preferred maximum particle size will be similar for other sized extruders. Thus, the fiber material may contain particles as large in length as the diameter of the screws of the extruder 11 for extruders in a range of sizes of most typical twin counter rotating screw extruders of the type used with this invention. A mixture of different sized wood fiber particles can be used, and it is not necessary to segregate or screen for particles within a predetermined size range. Using prior art processes, a mixture of particles having a wide range of sizes tended to cause the particles to aggregate or glop together; this is not a problem with the method and apparatus of the present invention.
The wood fiber and polymer are mixed together by the twin counter-rotating non-intermeshing screws of the extruder 11. At the same time, heat is applied to material mixture as it flows through the extruder. The length of the extruder should be long enough to provide adequate mixing and apply sufficient heat to the mixture, so that the material exiting from the extruder has the desired properties. The material should be heated to a temperature high enough to extract residual moisture from the wood fiber, and adequate venting should be supplied along the length of the extruder in accordance with known techniques. Because the extruder extracts the moisture from the wood fiber during the mixing and heating process, it is usually not necessary to pre-dry the wood fiber material prior to introducing it into the extruder. Furthermore, if the wood is not pre-dried, impregnation of the polymer into the wood fiber during the mixing and heating process is reduced, resulting in lighter finished products, since the residual moisture left in the wood acts as a natural blowing agent. It is thus possible using the present invention to achieve products having a specific gravity of close to 1. Such relatively light products have only been possible heretofore if a blowing agent were added to the mixture, resulting in additional expense and requiring controlling the action of the blowing agent. Since a blowing agent is often unnecessary using the present invention, lighter wood fiber polymer products with enhanced physical properties can be manufactured more easily and with less expense.
The material emerges from the output nozzle 23 of the extruder 11, where a predetermined amount of the material is placed on the mold half on the tray 12 in a large mass or dollop or “tear drop” shaped mound. These dollops or masses contain a large amount of material, enough material to make a single molded product in the compression molding machine. For example, dollops as large as 150 lb (68 kg) can be formed on the mold half. The material exits from the extruder at a temperature in the approximate range of 300° F. to 400° F. (150° C. to 200° C.). No attempt is made to pre-form the material on the mold half, since all forming of the product is accomplished in the compression molding machine.
The tray 12 carrying the mold half is then moved using the material handling system 13 to one of the compression molding machines 14 located at one of the processing stations 19. Each tray moves along the main conveying line 16 to one of the transfer stations 17, where the tray is transferred to one of the processing lines 18 that feed into one of the compression molding machines 14. The mold half with the large dollop of material is placed in the center of the compression molding machine. The material should be placed in the compression molding machine while it is still warm from the extrusion process, so that the molding process is accomplished essentially immediately after the extrusion process. Thus, the mixture is not allowed to cool excessively from the extrusion heating prior to molding. For example, if the mixture comes out of the extruder at a temperature of about 300° F. to 400° F. (150° C. to 200° C.), the compression molding should occur while the material still has a core temperature of about 275° F. to 400° F. (135° C. to 200° C.). In other words, the material should not cool by more than about 25° F. to 50° F. (15° C. to 30° C.).
The hydraulic press or other actuating mechanism of the compression molding machine 14 at the processing station 19 is then used to mold the dollop of material into the desired shape. As the compression molding takes place, the force of the press causes the wood fibers in the mixture, which were originally oriented axially along the direction of the extrusion to flow radially outwardly from the center of the mold to all corners of the molded product. This flow of material causes the wood fibers to lose their original axial orientation and to be re-oriented in various directions. The resulting orientation of fibers is random, and not primarily influenced by the initial alignment of the fibers from the extruding process. Because the fibers are randomly oriented in the finished product, the product has a higher strength in multiple directions than would be achieved using extrusion alone. Using an extrusion process alone, wood fiber polymer composite products often exhibit brittleness transverse to the direction of extrusion, because the wood fibers in the material become axially oriented in the extrusion process along the axis of extrusion. While this orientation of fibers may result in acceptable axial tensile strength, it can result in brittleness and a limited flex modulus. Using the method and apparatus of the present invention, the compression molding re-orients the wood fibers randomly to all direction regardless of the direction of extrusion, so that the fibers are no longer aligned along the extrusion axis. The resulting products are much stronger than products made by extrusion alone.
A random intermeshing orientation of fibers is achieved by making each product from a separate dollop of material from the extruder. It is preferred that each product be made from only one mass or dollop of material, which is in turn situated approximately in the center of the mold. If two or more dollops were used to make a single molded product, the fibers from each dollop would tend not to intermesh with each other, causing a structural weakness along the join line where the material from the two dollops meet. This problem is avoided by making the entire product from a single dollop. Although this structural weakness may be overcome by using a larger tonnage press, the press may have to produce a clamping force of about four times the clamping force required according to the present invention, and the use of a larger press to achieve this clamping force increases the equipment costs for the process. These increased equipment costs can be avoided by using a separate dollop of material in each mold in accordance with the present invention.
After the product has been molded in the compression molding machine 14, the tray 12 containing lower mold half with the molded product moves along the system 13 to the unloading station 15, where it is manually removed from the mold half. If desired, an automated product processing system can be connected at this point to the material handling system 13 to permit further processing of the molded products in an automated continuous operation. After the products are removed from the mold halves, the trays carrying the mold halves are returned to the loading station along the return line 22.
Using the method and apparatus of the present invention, products can be made efficiently in a continuous process, without the necessity of pre-forming pellets or other intermediate products, and without any batch mixing. This also permits the use of the heat generated by the extrusion process to be retained by the mixture when it is placed into the compression molding machine. In contrast, most prior art methods have not been continuous. In most prior art processes, material quantities were made in batches, such as by mixing of materials in a conventional Banbury mixer, or by providing an intermediate step of making pellets which were subsequently used in another process. When making products in a non-continuous process, the properties of each batch may vary, and, as a result, each batch may not be the same, and the quality of the finished products may also vary. The use of a continuous process avoids these problems. In addition, a continuous process is more efficient because, once the process is running, products can be made in a fast and efficient manner. Using the method and apparatus of the present invention, the extruder is continuously running, providing a steady stream of mixed material for further molding. The continuity of the system and continuous quality of the mixed material is assured. The provision of a continuous process is an important aspect of the present invention.
The method and apparatus of the present invention is particularly suitable for processing polymer and wood composite materials over a wide range of properties. In particular, a wide range of physical properties of the resulting molded products can be achieved using the present invention. Products having specific gravities of 0.85 to 1.05, tensile strengths of 1017 to 1709 psi (7.0 to 11.8 MPa), sheer strengths of 1300 to 1900 psi (9.0 to 13.1 MPa) are typical of those produced by the present invention.
While the present invention has been described with particular application to the use of wood fibers in polymer resin, the invention is not so limited, and the method and apparatus of the present invention may also be used to form products from fiber materials other than wood, including both natural and man-made fibers. For example, the process may be used for glass fibers mixed with polymers to form products of fiberglass. The process may also be used with shells, corn stock, rice hulls, flax, nylon fibers, polyester fibers, rubber and other materials. However, the present invention has been shown to have particular value in making products using wood polymer composite. Since wood fiber waste material is in relatively plentiful supply and provides a finished product having a pleasing appearance, the wood/polymer composite products are particularly desirable.
In particular, wood fiber polymer composite products can be used to substitute for products made of traditional lumber. The products can be made with a wood appearance, and they can be handled in a manner similar to products made from lumber. The products can be sawed like traditional lumber products, and they are otherwise handled in a similar manner. However, they are less prone to weathering and deterioration due to the presence of the polymer material, and they can be made to be stronger than comparable lumber products.
Wood fiber polymer composite products made by the method of the present invention are stronger than wood fiber polymer composite products made by simple extrusion techniques. Using an extrusion process alone, wood fiber polymer composite products often exhibit brittleness transverse to the direction of extrusion, because the wood fibers in the material become axially oriented in the extrusion process along the axis of extrusion. While this orientation of fibers may result in acceptable axial tensile strength, it can result in brittleness and a limited flex modulus. However, using the method and apparatus of the present invention, the compression molding re-orients the wood fibers randomly to all direction regardless of the direction of extrusion, so that the fibers are no longer aligned along the extrusion axis. The resulting products are much stronger than products made by extrusion alone.
The present invention utilizes the advantages provided by the devolatizing of materials in a twin screw extruder having vents located along the length of the extruder. In this way, moisture and volatiles from the wood fiber is removed during the mixing and heating process. Therefore, it is usually not necessary to start with wood fibers that have been pre-dried or that have a moisture content below a relatively low level. The provision of a material dryer to pre-dry the wood fiber is usually not necessary. Using the method of the present invention, it is possible to start with wood fibers having an initial moisture content of 10% to 12%. This is a far higher moisture content than is possible in most other prior art processes.
Besides conveying material toward the extruder exit, the extruder screws are depended upon to perform mixing of the feed material. Very generally, mixing can be defined as a process to reduce the non-uniformity of a composition. The basic mechanism involved is to induce relative physical motion in the ingredients. The two types of mixing that are important in screw extruder operation are distribution and dispersion. Distributive mixing is used for the purpose of increasing the randomness of the spatial distribution of the particles without reducing the size of these particles. Dispersive mixing refers to processes that reduce the size of cohesive particles as well as randomizing their positions. In dispersive mixing, solid components, such as agglomerates, or high viscosity droplets are exposed to stresses in excess of their yield strength, and they are thus broken down into smaller particles. In certain other applications of extruder operation, dispersive mixing is important, such as in the manufacture of a color concentrate where the breakdown of pigment agglomerates below a certain critical size is crucial. However, in the present invention, distributive mixing, without dispersive mixing, is desired, so that the wood fibers and the polymer are thoroughly mixed together, while the size of the wood fibers is not significantly affected by the mixing process, and without the excess heat that is generated by dispersive mixing.
The counter-rotating non-intermeshing twin screw extruder has unique distributive mixing capabilities that make it highly desirable for this application. The counter-rotating screws that are non-intermeshing (or at least non-self wiping) reduce destruction to the fibers. This provides an advantage of the present invention, since fiber length is maintained, and long fibers that can be used in the present invention are retained to improve the quality of the finished product. This provides increased tensile strength and flex modulus to the finished product. Other processes in which fibers are destroyed result in shortened fiber lengths and associated decreases in tensile and shear strengths and flex modulus.
The method of the present invention has shown to be particularly useful in the manufacture of pallet skids, and replaces the manufacture of pallets made by nailing up pieces of lumber. However, the method can also be used to make any items that can be molded, and it is particularly useful in making decking, panels, privacy fences, boat docks, playground equipment, trailer inner walls, and railroad ties. Products made using the method of the present invention are especially useful as structural components, since the resulting products have a high tensile strength.

EXAMPLE 1

An example of a simple product made from the method of the present invention is a plank, with dimension of approximately 4 inches (100 mm) wide and ¾ inches (20 mm) thick with a sample length of 3 feet (1 m). A product have similar dimensions would be used in a variety of applications, such as marine docks, wood walkways or pallet slats. The molding process is performed using a mold that allows for multiple planks or boards to be formed in a single mold and compression cycle, with a single panel molded and finish cut after processing to desired final dimensions. The material used is a 50% mixture of HDPE and wood fiber. The wood fiber material was waste hardwood material with particles having typical lengths up to 2 inches (100 mm), widths up to 0.5 inches (12 mm) and thickness up to 0.05 inches (1 mm). The material is processed in an extruder having a 2-inch (50-mm) diameter twin non-intermeshing screws, with a throughput of 500 lb (227 kg) and an exit temperature of 340° F. to 380° F. (170° C. to 200° C.). The size of each dollop is approximately 3.3 lb (1.5 kg). A dollop is loaded into the mold from the extruder, and held in the compression press at a clamping pressure of 200 psi (1.4 MPa) for 2 minutes total clamp time, between cooling platens and cooled mold half. The core temperature of the molded product is about 140° F. after molding, and cooling is accomplished by natural ambient conditions. The product may be required to be held in stable form as the cooling is completed after it leaves the press.

The finished product meets or exceeds the following ASTM standards: meets or exceeds the following ASTM standards:



Property	Standard	Results

Yield strength	ASTM D638	>35 MPa
Elongation at yield	ASTM D638	>2%
Flexural modulus	ASTM D790	>2480 MPa
Instrumented Dart Impact	ASTM D3763	>50 J
Strength @ 22° C.
Instrument Dart Impact	ASTM D3783	>33 J
Strength @ −25° C.
Melt Flow Rate @	ASTM D1238	>2 g/10 min and
200° C./21.6 kg		<12 g/10 min

EXAMPLE 2

A sample nestable pallet skid was molded using the method of the present invention. The extruded mixture was made using a counter-rotating twin screw extruder having 2-inch diameter non-intermeshing screws, a 42-to-1 ratio, operating at 300 rpm, with two vents, one atmosphere vent and one vacuum vent. The material supplied to the extruder was a mixture of approximately 47½% by weight wood fiber material and approximately 47½% by weight high density polyethylene, with approximately 5% by weight additives, such as wax and compatabilizer. The wood fiber material was waste hardwood material with particles having typical lengths up to 2 inches (100 mm), widths up to 0.5 inches (12 mm) and thickness up to 0.05 inches (1 mm). The extruder provided a throughput of 390 lb/hr (180 kg/hr). Extruded material was produced in dollops or masses of approximately 58 lb (26 kg) each and transferred to a compression molding machine comprising a 1200-ton press. The mixture was held in the mold in the press for approximately 3 minutes.
The resulting molded pallet measured 40 inches (1.02 m) by 40 inches (1.02 m) by 5.5 inches (0.14 m). The thickness of the top deck was ¼ inches (6 mm) minimum, 2.0 inches (50 mm) maximum. The pallet consisted of nine tapered posts each having a cross-sectional dimension measuring 5½ inch (140 mm) by 51/2 inch, tapering to 4½ inch (114 mm) by 4½ inch (114 mm), and having a height of 4 inches (100 mm). The minimum clearance below deck measured 4.0 inches (100 mm). The average pallet weight was 58 lb (26 kg).

Using ISO and ASTM pallet testing protocol, an example of the tested properties of the pallet was as follows:



	Static Strength
	Rigid load at +40° C.: 18,100 lbs
	Rigid load at −25° C.: 31,900 lbs
	Flexible load at +40° C.: 4,000 lbs
	Dynamic Strength
	Forktines through pallet 40-inch ends:
	Rigid load at +40° C.: >11.500 lbs
	Flexible load at +40° C.: 2,625 lbs
	Forktines through 48-inch sides:
	Rigid load at +40° C.: >11,500 lbs
	Flexible load at +40° C.: 700 lbs
	Corner Drop Test
	Deformation after 6 drops at ambient temperature: 0.362 inches
	Leadedge Impact Resistance:
	40-inch ends at +40° C.: 10,333 KN
	40-inch ends at −25° C.: 8,467 KN
	48-inch sides at +40° C.: 9,027 KN
	48-inch sides at −25° C.: 6,853 KN
	Post Impact Resistance:
	40-inch ends at +40° C.: No failure
	40-inch ends at −25° C.: No failure
	48-inch ends at +40° C.: 8,552 KN
	48-inch ends at −25° C.: 8,112 KN

These are only examples of testing outcomes by continuous mix and molding process. Additional enhancements are available when customized material recipe is considered for final product properties.
It should be realized that the embodiment described herein is only representative of the invention and is not intended to limit the invention to one particular embodiment as the invention includes all embodiments falling within the scope of the appended claims. Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and illustrative examples shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims

1. A method of manufacturing a fiber polymer composite product in a continuous process, comprising the steps of:

providing a extruder have two counter-rotating non-self-wiping screws;

supplying to the extruder fiber material and polymer material;

mixing and heating the fiber material and polymer material in the extruder to form a mixture;

removing the mixture from the extruder and placing the mixture in a press; and

compression molding the mixture in the press to form the product.

2. The method of claim 1, comprising the additional step of removing moisture from the fiber material in the extruder while mixing and heating the mixture.

3. The method of claim 1, wherein the fiber material and the polymer material are separately supplied to the extruder.

4. The method of claim 3, wherein the fiber material and the polymer material are supplied to the extruder through the same feed.

5. The method of claim 1, wherein the step of providing an extruder having two counter-rotating non-self-wiping screws comprises providing an extruder having screws of a certain diameter, and wherein the fiber material contains particles as large in length as the diameter of the screws.

6. The method of claim 1, wherein the fiber material is wood fiber material.

7. The method of claim 1, wherein the fiber material and polymer material mixture is heated in the extruder to a temperature of between about 300° F. and about 400° F.

8. The method of claim 1, wherein the fiber material and polymer material mixture is removed from the extruder and placed in the compression molding machine before it has had cooled more than about 50° F.

9. A method of manufacturing a fiber composite product in a continuous process, comprising the steps of:

providing an extruder having two counter-rotating non-self-wiping screws each having a certain diameter;

supplying to the extruder fiber material having fibers of a length as large as the diameter of the screws;

mixing and heating the fiber material in the extruder to form a mixture; and

removing the mixture from the extruder.

10. A product according to claim 9, wherein the fiber material is wood.

11. A product made by a process of mixing and heating a mixture of polymer and fiber material in an extruder followed by compressing molding the mixture, the product having a specific gravity of between 0.85 and 1.05, a tensile strength between 1015 psi and 1710 psi.

12. A product according to claim 11, wherein the fiber material is wood.

13. Apparatus for the manufacture of polymer fiber composite products, comprising:

an extruder having twin counter-rotating non-self-wiping screws;

a receptacle for receiving a quantity of heated mixture from the extruder; and

a compression molding machine for applying pressure to a quantity of material to mold the mixture into a finished product.

14. Apparatus for the manufacture of polymer fiber composite products according to claim 13, comprising in addition a material handling system for moving the receptacle from the extruder to the compression molding machine and from the compression molding machine.

15. Apparatus for the manufacture of polymer fiber composite products according to claim 13, wherein the extruder includes vents for removing moisture from mixture therein.