Nonwoven fabric and associated composite and methods of making

Abstract

A nonwoven fabric useful for forming composite panels includes specific amounts of reinforcing fibers, a polyimide, and a block polyestercarbonate-polysiloxane. The nonwoven fabric has a density of 0.03 to 0.2 gram/centimeter3, an areal density of 100 to 400 gram/meter2, and a tensile modulus of 50 to 1000 megapascals. Also described are a method of forming the nonwoven fabric, a composite formed from the nonwoven fabric, and a method of forming the composite.

1 . A nonwoven fabric, comprising, based on the weight of the nonwoven fabric:
 25 to 55 weight percent of reinforcing fibers,   35 to 65 weight percent of a polyimide, and   5 to 20 weight percent of a block polyestercarbonate-polysiloxane;   wherein the block polyestercarbonate-polysiloxane comprises a polyester block comprising resorcinol ester units having the structure   
       
         
           
           
               
               
           
         
       
       a polycarbonate block comprising carbonate units having the structure 
       
         
           
           
               
               
           
         
       
       wherein at least 60 percent of the total number of R 1  groups are aromatic divalent groups, and a polysiloxane block comprising dimethylsiloxane units; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5 to 35 mole percent of carbonate units wherein R 1  is 1,3-phenylene, and 5 to 35 mole percent of carbonate units wherein R 1  is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units;
 wherein the nonwoven fabric has
 a density of 0.03 to 0.2 gram/centimeter 3 , and 
 an areal density of 100 to 400 gram/meter 2 ; and 
 
 wherein the nonwoven fabric has a tensile modulus of 50 to 1000 megapascals, determined according to ASTM D638-14 at a temperature of 23° C. and using a test speed of 50 millimeters/minute. 
 
     
     
         2 . The nonwoven fabric of  claim 1 ,
 wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R 1  is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R 1  is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and   wherein the nonwoven fabric further comprises 0.2 to 2 weight percent of an organophosphate ester flame retardant.   
     
     
         3 . The nonwoven fabric of  claim 2 , wherein the organophosphate ester flame retardant comprises an oligomeric phosphate ester. 
     
     
         4 . The nonwoven fabric of  claim 1 , wherein the reinforcing fibers comprise glass fibers. 
     
     
         5 . The nonwoven fabric of  claim 1 ,
 wherein the nonwoven fabric comprises, based on the weight of the nonwoven fabric,
 30 to 50 weight percent of the reinforcing fibers, 
 40 to 60 weight percent of the polyimide, and 
 5 to 15 weight percent of the block polyestercarbonate-polysiloxane; 
   wherein the nonwoven fabric further comprises, based on the weight of the nonwoven fabric, 0.3 to 3 weight percent of a flame retardant;   wherein the reinforcing fibers comprise glass fibers;   wherein the polyimide comprises a polyetherimide;   wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R 1  is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R 1  is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and   wherein the flame retardant comprises an oligomeric phosphate ester.   
     
     
         6 . A method of forming a nonwoven fabric, the method comprising:
 forming an aqueous suspension layer comprising
 water, 
 25 to 55 weight percent of reinforcing fibers, 
 35 to 65 weight percent of polyimide fibers, and 
 5 to 20 weight percent of binder fibers comprising a block polyestercarbonate-polysiloxane, 
   
       wherein weight percent values are based on the total weight of reinforcing fibers, polyimide fibers, and binder fibers;
 at least partially removing water from the aqueous suspension layer to form a fiber layer; and 
 exposing the fiber layer to a temperature of 250 to 320° C., thereby melting the binder fibers, at least partially melting the polyimide fibers, and forming a nonwoven fabric; 
 wherein the block polyestercarbonate-polysiloxane comprises a polyester block comprising resorcinol ester units having the structure 
 
       
         
           
           
               
               
           
         
       
       a polycarbonate block comprising carbonate units having the structure 
       
         
           
           
               
               
           
         
       
       wherein at least 60 percent of the total number of R 1  groups are aromatic divalent groups, and a polysiloxane block comprising dimethylsiloxane units; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5 to 35 mole percent of carbonate units wherein R 1  is 1,3-phenylene, and 5 to 35 mole percent of carbonate units wherein R 1  is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units. 
     
     
         7 . The method of  claim 6 , wherein the exposing the unconsolidated fiber layer to a temperature of 250 to 400° C. is conducted at a pressure of 40 to 400 kilopascals. 
     
     
         8 . The method of  claim 6 ,
 wherein the aqueous suspension layer and the fiber layer further comprise a viscosity modifying agent; and   wherein the method further comprises washing the fiber layer to at least partially remove the viscosity modifying agent.   
     
     
         9 . The method of  claim 6 ,
 wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R 1  is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R 1  is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units;   wherein the binder fibers further comprise an oligomeric aromatic phosphate ester; and   wherein the binder fibers comprise, based on the weight of the binder fibers,
 90 to 98 weight percent of the block polyestercarbonate-polysiloxane, and 
 2 to 10 weight percent of the oligomeric aromatic phosphate ester. 
   
     
     
         10 . The method of  claim 6 ,
 wherein the aqueous suspension layer comprises
 30 to 50 weight percent of the reinforcing fibers, 
 40 to 60 weight percent of the polyimide fibers, and 
 5 to 15 weight percent of the binder fibers; 
   wherein the aqueous suspension layer and the fiber layer further comprise a viscosity modifying agent;   wherein the method further comprises washing the fiber layer to at least partially remove the viscosity modifying agent;   wherein the reinforcing fibers comprise glass fibers;   wherein the polyimide fibers comprise a polyetherimide;   wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R 1  is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R 1  is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units;   wherein the binder fibers further comprise an oligomeric aromatic phosphate ester;   wherein the binder fibers comprise, based on the weight of the binder fibers,
 90 to 98 weight percent of the block polyestercarbonate-polysiloxane, and 
 2 to 10 weight percent of the oligomeric aromatic phosphate ester; and 
   wherein the exposing the unconsolidated fiber layer to a temperature of 250 to 400° C. is conducted at a pressure of 40 to 400 kilopascals.   
     
     
         11 . A composite, comprising, based on the weight of the composite:
 25 to 55 weight percent of reinforcing fibers,   35 to 65 weight percent of a polyimide, and   5 to 20 weight percent of a block polyestercarbonate-polysiloxane;   wherein the block polyestercarbonate-polysiloxane comprises a polyester block comprising resorcinol ester units having the structure   
       
         
           
           
               
               
           
         
       
       a polycarbonate block comprising carbonate units having the structure 
       
         
           
           
               
               
           
         
       
       wherein at least 60 percent of the total number of R 1  groups are aromatic divalent groups, and a polysiloxane block comprising dimethylsiloxane units; wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 30 to 90 mole percent of resorcinol ester, 5 to 35 mole percent of carbonate units wherein R 1  is 1,3-phenylene, and 5 to 35 mole percent of carbonate units wherein R 1  is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.2 to 4 weight percent dimethylsiloxane units; and
 wherein the composite has
 a density of 0.92 to 1.38 gram/centimeter 3 , and 
 an areal density of 100 to 3000 gram/meter 2 . 
 
 
     
     
         12 . The composite of  claim 11 ,
 wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R 1  is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R 1  is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and   wherein the composite further comprises 0.2 to 2 weight percent of an oligomeric aromatic phosphate ester flame retardant.   
     
     
         13 . The composite of  claim 11 ,
 wherein the composite comprises, based on the weight of the composite,
 30 to 50 weight percent of the reinforcing fibers, and 
 40 to 60 weight percent of the polyimide, and 
 5 to 15 weight percent of the block polyestercarbonate-polysiloxane; 
   wherein the nonwoven fabric further comprises, based on the total weight of the nonwoven fabric, 0.3 to 3 weight percent of a flame retardant;   wherein the reinforcing fibers comprise glass fibers;   wherein the polyimide comprises a polyetherimide;   wherein the block polyestercarbonate-polysiloxane comprises, based on total moles of carbonate and ester units in the block polyestercarbonate-polysiloxane, 70 to 90 mole percent of the resorcinol ester units, 5 to 15 mole percent of carbonate units wherein R 1  is 1,3-phenylene, and 5 to 15 mole percent of carbonate units wherein R 1  is 2,2-bis(1,4-phenylene)propane, and further comprises, based on the weight of the block polyestercarbonate-polysiloxane, 0.3 to 3 weight percent dimethylsiloxane units; and   wherein the flame retardant comprises an oligomeric aromatic phosphate ester.   
     
     
         14 . A method of forming a multilayer composite, the method comprising:
 exposing at least two layers of the nonwoven fabric of  claim 1  to a temperature of 250 to 400° C. and a pressure of 300 to 1,500 kilopascals for a time of 60 to 600 seconds to yield a multilayer composite.