Method for manufacturing cellulose fiber reinforced composites having reduced discoloration and improved dispersion

Abstract

The present invention provides composites prepared from melt blending compositions that generally include cellulosic pulp fibers having an alpha-cellulose purity of greater than 80% by weight, at least one water soluble binder, at least one lubricant, at least one compatibilizer, and at least one matrix polymer. The present invention further provides advantageous temperature profiles and feeding arrangements to be used in conjunction with the melt blending of such composites. The composites of the present invention exhibit reduced discoloration and improved fiber dispersion.

That which is claimed:  
     
         1 . A process for the manufacture of composites containing cellulosic pulp fibers dispersed in a matrix polymer, said process comprising: 
 (A) providing a melt blending composition including cellulosic pulp fibers having an alpha-cellulose purity of greater than 80% by weight and at least one matrix polymer exhibiting a melting point of less than about 200° C. and a melt flow index ranging from about 0.10 to 100 to a main feed throat of a compounding extruder including at least three heated regions and a heated die; and    (B) compounding said melt blending composition by transporting the melt blending composition through each of the heated regions and the die, which include 
 (i) an initial region heated to a temperature of about 10 percent below the matrix polymer melting point;  
 (ii) a first intermediate region heated to a temperature of about 15 to 20 percent below the matrix polymer melting point;  
 (iii) a second intermediate region heated to a temperature of about 15 to 20 percent above the matrix polymer melting point; and  
 (iv) a die heated to a temperature of about 35 to 40 percent above the matrix polymer melting point.  
   
     
     
         2 . A process according to  claim 1 , further comprising introducing an additional amount of said matrix polymer into a secondary feed throat positioned downstream of said main feed throat and upstream of the second intermediate region.  
     
     
         3 . A process according to  claim 2 , wherein the amount of cellulosic pulp fibers within the melt blending composition is greater than 30 weight percent, based on the weight of the melt blending composition, and the amount of matrix polymer introduced into the secondary feed throat is selected to provide a composite containing 30 weight percent cellulosic pulp fibers.  
     
     
         4 . A process according to  claim 2 , wherein the additional amount of matrix polymer exhibits a melt flow index that is substantially lower than the melt flow index of the matrix polymer introduced into the main feed throat.  
     
     
         5 . A process according to  claim 4 , wherein the additional amount of matrix polymer exhibits a melt flow index ranging from about 10 to 25 and the melt flow index of the matrix polymer introduced into the main feed throat ranges from about 30 to 90.  
     
     
         6 . A process according to  claim 4 , wherein the additional amount of matrix polymer exhibits a melt flow index ranging from about 10 to 12 and the melt flow index of the matrix polymer introduced into the main feed throat ranges from about 50 to 80.  
     
     
         7 . A process according to  claim 1 , wherein said cellulosic pulp fibers and said matrix polymer are present in said melt blending composition at fiber to matrix polymer weight ratios ranging from about 30 to 70 to about 80 to 20.  
     
     
         8 . A process according to  claim 1 , wherein said cellulosic pulp fibers and said matrix polymer are present in said melt blending composition at fiber to matrix polymer ratios ranging from about 45 to 55 to about 60 to 40.  
     
     
         9 . A process according to  claim 1 , wherein the matrix polymer is polypropylene.  
     
     
         10 . A process according to  claim 1 , wherein the matrix polymer is polypropylene and 
 (a) the initial region is heated to a temperature of about 125 to 142° C.    (b) the first intermediate region is heated to a temperature ranging from about 115° C. to 135° C.;    (c) the second intermediate region is heated to a temperature of about 160 to 190° C. and    (d) the die is heated to a temperature of about 190 to 220° C.    
     
     
         11 . A process according to  claim 1 , further comprising: 
 (a) preparing a molding composition incorporating the compounded composition; and    (b) forming the molding composition into a molded article.    
     
     
         12 . A process according to  claim 11 , wherein said forming step is selected from injection molding, compression molding, blow molding, rotational molding, extrusion and pultrusion.