Flexible ceramic fibers and polymer composite and method of making the same

Abstract

The present application discloses and claims a method to make a flexible ceramic fibers (Flexiramics™) and polymer composites. The resulting composite has an improved mechanical strength (tensile) when compared with the Flexiramics™ alone. Several different polymers can be used, both thermosets and thermoplastics. Flexiramics™ has unique physical characteristics and the composite materials can be used for numerous industrial and laboratory applications.

What I claim is: 
     
         1 . A process to make a flexible composite material comprising a flexible ceramic filler (Flexiramics™) and a polymer, the process comprising the steps of:
 a. Preparing a ceramic fibers' precursor solution, the precursor solution comprising (i) a dissolved metal's precursor for ceramic selected from the group consisting of metallic ions and metal containing polymer, where the metals are selected from the group consisting of Si + , Zr 4+ , Ti 4+ , Al 3+ , Zn 2+ , Mg 2+ , Pb 4+ , Ni 2+ , Sr 2+ , Ca 2+ , La 3+ ; (ii) a polymer to increase the precursor solution's viscosity, with the solid content of the precursor solution (polymer plus precursor) being above 15% by weight in order to obtain the required deposition, and (iii) a solvent capable of providing the precursor solution with a sufficiently high evaporation rate; 
 b. Allowing the dissolved metal precursors for ceramic to form a final metal oxide otherwise known as ceramic; 
 c. Maintaining the precursor solution's viscocity between 0.01 and 1000 Pascal-second (Pa·s) at a shear rate of 0.1 s −1  in order to spin usable fibers; 
 d. Spinning the precursor solution by using a spinning process selected from the group consisting of forcespinning, electrospinning and blowspinning wherein the spinning parameters are tunable so that the spinning step can result in a continuous film or polymeric fiber and with the spinning parameters being adaptable to each precursor solution; 
 e. Annealing the polymeric fibers obtained from the spinning process, which polymeric fibers comprise metals precursor for ceramic, until all the organic content is burned out and the metallic ion oxidizes to form a ceramic; 
 f. Tunning and calibrating annealing parameters, the annealing parameters comprising heating and cooling rates, annealing temperature and dwell time consistent with the thermal profile shown in  FIG. 3  so a crystallinity comprising a crystal size of 1-100 nm and a smoothness of 0.05-5 nm of Rq of the resulting 20-10000 nm thick fibers is obtained, the annealing parameters being distinct and specific with respect to each material composition; 
 g. Setting the annealing temperature above the ceramic fiber's crystallization point resulting in the formation of ceramic material; and 
 h. Setting a dwell time from 0 to 5 hours. 
 
     
     
         2 . The process to make a flexible composite material of  claim 1  wherein the composition of the flexible ceramic fiber is selected from the group consisting of 3% yttria-stabilized zirconia, zirconia, titania, alumina, zinc oxide and pervoskites such as lead zirconium titanate. 
     
     
         3 . The process to make a flexible composite material of  claim 1  wherein the metal oxide is magnesium oxide. 
     
     
         4 . The process to make a flexible composite material of  claim 1  wherein the polymer is selected from the group consisting of polydimethylsiloxane (PDMS), polyimide, polypropylene (PP), polyethylene (PE), polyether ether ketone (PEEK), polyethylenimine (PEI), polyurethanes (PUR), cyanate esters, epoxy resins, polyesters, vinyl esters, urea-formaldehyde, allylics, polyphthalamide (PPA) and polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE) and where the ceramic content are between 0.1 to 99.9% of ceramic/total weight resulting in a composite that retains a flexibility of nearly 0 bending radius. 
     
     
         5 . The process to make a flexible composite material of  claim 1  wherein the resulting flexible ceramic filler comprises a fiber diameter that ranges between 20 and 10000 nanometers thus allowing bendability, a fiber length being measurable up to 4 centimeters, a crystal size ranging from 1 to 100 nanometers, a fiber smoothness ranging from 0.05 and 5 namometers Root Mean Square Roughness and the fibers bing disposed in a non-woven mat form in which the fibers are not physically attached to each other thus allowing the fibers to freely move and be extremely bendable at a macroscopic scale. 
     
     
         6 . A process to make a flexible composite material comprising a flexible ceramic and a polymer of  claim 1  further comprising the steps of:
 a. Impregnating a Flexiramics sample by applying a polymer solution over the top of a Flexiramic sample that has been previously extended on a flat and rigid surface; 
 b. Allowing the ceramic nanofiber sample to be completely impregnated with the polymer solution via capillarity and gravity; 
 c. Thermally curing the polymer solution spread over the ceramic nanofiber by placing the sample into an oven at temperatures ranging between 60° C. and 300° C., noting that the curing step can be achieved at temperatures as low as 20° C. with the only effect being longer curing times; 
 d. The resulting cured sample being able to maintain a desired fibrous structure by applying the polymer as a thin coating on every individual ceramic nanofiber with the coating being the in the preferred range of a few tenths to a few hundred nanometers; 
 e. Achieving desired polymer/ceramic nanofiber ratios by embedding the ceramic nanofiber in polymer precursor solutions ranging in viscosity from 1500 to 15000 milliPa·s; 
 f. Casting the non-diluted solutions on flat and rigid surfaces with preferred thickness between 0.1 to 5.0 millimeters; 
 g. Depositing the ceramic nanofiber on top of the casted solution thus allowing the solution to permeate through the entire sample via capillarity forces; and 
 h. Thermally curing the resulting solution permeated sample by placing the sample into an oven at temperatures between 60° C. and 300° C. over a pre-determined curing time, the curing time being directly proportional to the thickness of the sample, and the cured sample comprising a polymer layer on one side between 0.1 and 5.0 millimeters and a thin polymer layer on the other side typically from 1 to 50 micrometers. 
 
     
     
         7 . A process to make a flexible composite material of  claim 6  wherein the resulting composite fiber material comprises a high cermamic content of over 90% which is achieved by impregnating the ceramic fibers with a polymeric solutions of low viscosity of between 80 and 200 mPa·s so that individual fibers are coated between a few tenths to few hundreds of nanometers with the coating step being achieved by using the steps selected from the group consisting of casting a polymeric solution on top of Flexiramics, allowing impregnation by gravity and capillarity and using a spray gun to impregnate the Flexiramics. 
     
     
         8 . A process to make a flexible composite material of  claim 6  wherein the resulting composite material comprises a medium to low ceramic content of 10 to 90% which is achieved by embedding the Flexiramics with polymeric solution of high viscosity, of between 1500 to 15000 mPa·s with the coating step selected from the group consisting of casting a polymeric solution over a flat substrate and depositing Flexiramic over the polymeric solution by allowing impregnation by capillarity so that the composite comprises a thick coating of between 1 micrometer to 5 millimeters on both sides. 
     
     
         9 . A process to make a flexible composite material of  claim 6  wherein the resulting composite material comprises a medium to low ceramic content of between 10 and 90% which is achieved by casting a polymeric solution through a commercially available casting device selected from the group consisting of a pistol equipped with a slot die head, a casting knife and a doctor blade on top of the Flexiramic thus allowing impregnation by capillarity. 
     
     
         10 . A process to make a flexible composite material of  claim 6  wherein the resulting composite material comprises a medium to low ceramic content ranging between 10% and 90%, which is achieved by pressing and heating the solid polymer and the Flexiramic with typical pressures ranging between 1 and 10 kiloNewtons in a hot press melt. 
     
     
         11 . A process to make a flexible composite material of  claim 6  wherein the resulting composite material comprises a medium to low ceramic content ranging between 10 and 90% which is achieved by using thermosets requiring curing temperatures ranging from 20 to 300° C. and thermoplastics requiring melting temperatures up to 400° C. 
     
     
         12 . A process to make a flexible composite material of  claim 6  wherein the resulting composite material can be used to replace the currently used flexible printed circuit boards substrates which are usually made using Polylmide or Polylmide with low ceramic fillers. 
     
     
         13 . A process to make a flexible composite material of  claim 6  wherein the resulting composite material can be used to replace polymeric protective layers used for cable insulation such as polyethylene.