Method for low-density cellular wood plastic composites

Abstract

A low-pressure CO 2 tank or an air compressor with a refrigerated air dryer is attached either at or after the vent zone of a standard twin-screw extruder. During or after extrusion, the gas is dissolved in the wood-plastic melt. The CO 2 expands which foams the wood-plastic material.

1 - 24 . (canceled)  
     
     
         25 . A method of manufacturing a plank comprising the steps of: a) placing a material in a hopper; b) mixing and then extruding the material from an extruder; c) injecting gas from a device located outside of the extruder, said gas being injected into the material to create foaming in the material d) shaping the extruded material with at least one die into a plank; e) tempering the plank in a controlled environment to maximize foaming; f) calibrating the shape and size of the plank through at least heating; g) cooling the plank further; and h) conveying the plank to a saw for further sizing.  
     
     
         26 . A process of making a composite comprising the steps of: a mixing finely ground wood flour with plastic in an extruder to form a plasticated mixture; introducing a blowing agent into the plasticated material outside of the extruder under low pressure; developing sufficient pressure to drive the blowing agent into the plasticated mixture to form cells within the plasticated mixture, wherein the blowing agent is incorporated under a pressure gradient in the extruder sufficient to increase the solubility of the blowing agent in the plasticated mixture and under a temperature sufficient to prevent collapse of the cells; and reducing the pressure prior to removing the plasticated mixture from the extruder.  
     
     
         27 . The process of  claim 26  wherein the wood flour is selected from the group consisting of wood flour, sawdust, pond sludge, newspapers, alfalfa, wheat pulp, wood chips, wood flakes, wood fibers, ground wood, wood veneers, wood laminates, kenaf, paper, cardboard, and straw.  
     
     
         28 . The process of  claim 26  wherein the wood flour is selected from hard and soft wood and has a particle size no greater than about 40 mesh.  
     
     
         29 . The process of  claim 26  wherein the wood flour has a particle size no greater than about 60 mesh.  
     
     
         30 . The process of  claim 26  wherein the moisture content of the wood flour is between about 1% and 9%.  
     
     
         31 . The process of  claim 26  wherein the moisture content of the wood flour is no more than about 2%.  
     
     
         32 . The process of  claim 26  wherein the thermoplastic materials are selected from the group consisting of polyethylene, polypropylene, poly-vinyl chloride, low-density polyethylene, ethyl-vinyl acetate and waste plastic sawdust.  
     
     
         33 . The process of  claim 26  wherein the thermoplastic materials are selected from the group consisting of high-density polyethylene and polypropylene.  
     
     
         34 . The process of  claim 26  wherein the ratio of wood fibers to the thermoplastic material is between approximately 3:2 and 1:4.  
     
     
         35 . The process of  claim 26  wherein the ratio of wood fibers to the thermoplastic material is approximately 2:3.  
     
     
         36 . The process of  claim 26  wherein the blowing agent is selected from the group consisting of air and carbon dioxide.  
     
     
         37 . The process of  claim 26 , wherein the pressure gradient is 5 between 1400 psi and 3800 psi.  
     
     
         38 . The process of claim  3 , where the temperature of the extrudate is controlled at a level between about 5 and 15° F. (2.7 and 8.3° C.) above the crystallization temperature of the plasticated mixture.  
     
     
         39 . A process for producing plastic/wood fiber composite foamed structures comprising the steps of: pre-drying wood fiber filler to produce dried wood fiber filler; mixing the dried wood fiber filler with plastic to produce a plastic/wood fiber mixture; feeding the plastic/wood fiber mixture into an extruder; mixing a physical blowing agent into the plastic/wood fiber mixture after the extruder to produce a plastic/wood fiber/gas mixture; subjecting the plastic/wood fiber/gas mixture to high shear forces in the presence of high pressures; and producing a plastic/wood fiber composite foamed structure.  
     
     
         40 . The process of claims  39 , further comprising the steps of: maintaining the pre-drying temperature below the degradation temperature to produce dried wood fiber filler which has a degradation temperature and an active volatization temperature; maintaining the mixing temperature below an active volatilizing temperature; maintaining the processing temperature below an active volatilizing temperature.