Process and apparatus for determination of fiber length in reinforced thermoplastic composites

Abstract

The present invention comprises a method for determining the average length of a reinforcing fiber of a composite material comprising a resin and a plurality of reinforcing fibers encapsulated therein. In addition, a fiber separating apparatus for dividing a sample of reinforcing fibers into fractions defined by the relative lengths of the reinforcing fibers is also disclosed.

What is claimed is:  
     
         1 . A fiber separating mechanism comprising: 
 a top section comprising a hollow cylinder having a length sufficient to enclose therein a predetermined volume;    a screen section comprising a hollow cylinder of substantially the same diameter as the top section, the screen section having a predetermined height and a membrane of screen cloth stretched entirely across the inner diameter thereof; and    a bottom section comprising a hollow cylinder having a closed bottom end, the top section, screen section and bottom section being capable of being coupled to one another so as to form a single hollow cylinder having a closed bottom end.    
     
     
         2 . The fiber separator of  claim 1  further comprising a plurality of screen sections, the plurality of screen sections having successively finer screen cloth membranes in each successively lower screen section.  
     
     
         3 . The fiber separator of  claim 1  wherein each of the sections of the fiber separator is constructed and arranged to be threadedly connected to the other sections of the fiber separator.  
     
     
         4 . A method of determining an average length of a reinforcing fiber in a composite material comprising a resin and a plurality of reinforcing fibers, the method comprising the steps of: 
 obtaining an appropriately sized sample of the composite material;    removing the resin from the composite material by exposing the sample of composite material to an elevated temperature for a predetermined period of time;    annealing the reinforcing fibers;    weighing the resulting sample of reinforcing fibers to obtain a sample weight;    placing the sample of reinforcing fibers from the composite material in a fiber separating mechanism to divide the sample of reinforcing fiber into a plurality of fractions, each fraction comprising reinforcing fibers of substantially the same size;    weighing the plurality of fractions; and    calculating an average fiber length from the relative weights of each of the plurality of fractions and the weight of the total reinforcing fiber sample.    
     
     
         5 . A method of  claim 4  wherein the ratio of the diameter of the sample of composite material to the length of the sample of composite material is at least 1:25.  
     
     
         6 . The method of  claim 4  wherein the sample of composite material is gradually heated to remove the resin therefrom starting at a temperature of between 0° and 30° C. and rising to a temperature of approximately 350° C. at a rate of no more than 10 degrees Celsius per minute.  
     
     
         7 . The method of  claim 6  wherein the sample of composite material is subsequently exposed to a temperature of approximately 550° C. for approximately two hours.  
     
     
         8 . The method of  claim 7  wherein the sample of composite material is subsequently cooled to a final temperature of between 0° and 30° C. at a rate of no more than 20° C. per minute.  
     
     
         9 . The method of  claim 4  wherein the fiber separator comprises: 
 a top section comprising a hollow cylinder having a length sufficient to enclose therein a predetermined volume;  
 a screen section comprising a hollow cylinder of substantially the same diameter as the top section, the screen section having a predetermined height and a membrane of screen cloth stretched entirely across the inner diameter thereof; and  
 a bottom section comprising a hollow cylinder having a closed bottom end, the top section, screen section and bottom section being capable of being coupled to one another so as to form a single hollow cylinder having a closed bottom end.  
 
     
     
         10 . The method of  claim 9  wherein the fiber separator is filled with water and the sample of reinforcing fibers is placed in the water in the fiber separator.  
     
     
         11 . The method of  claim 10  wherein the water within the fiber separator is generally stirred for 10 seconds after which the water is allowed to settle for 15 seconds, this cycle being repeated a predetermined number of times.  
     
     
         12 . The method of  claim 11  wherein the stir/rest cycle is repeated at least three times.  
     
     
         13 . The method of  claim 9  wherein the bottom portion is removed from the fiber separator so as to allow the water within the fiber separator to drain out.