Multilayer composites comprising heat shrinkable polymers and nanofiber sheets

1. A multilayer composite comprising:

at least one heat shrinkable polymer layer, wherein the at least one heat shrinkable polymer layer has a polymer orientation direction; and

at least one carbon nanofiber sheet layer embedded in the at least one heat shrinkable polymer layer, the at least one carbon nanofiber sheet layer comprising a plurality of carbon nanofibers aligned end to end in a nanofiber orientation direction that is parallel to a length direction of the at least one carbon nanofiber sheet layer;

wherein the multilayer composite is configured with a length and a width,

wherein the polymer orientation direction is configured along the length of the multilayer composite,

wherein the multilayer composite is configured to reduce in size by at least 10% in the polymer orientation direction in response to application of heat to the at least one heat shrinkable polymer layer,

wherein the at least one carbon nanofiber sheet layer comprises a carbon nanofiber sheet drawn directly from a carbon nanofiber forest, and densified to increase a volume density of the carbon nanofiber sheet by a factor of greater than 10 times over a volume density of an undensified carbon nanofiber sheet having a value of at least 0.002 g/cm 3 for providing a volume density of the densified carbon nanofiber sheet,

wherein the volume density of the carbon nanofiber sheet is increased while a length and a width of the carbon nanofiber sheet are reduced by less than 10% from a length and a width of the undensified carbon nanofiber sheet to provide for a length and a width of the densified carbon nanofiber sheet, and

wherein the length of the undensified carbon nanofiber sheet is greater than 1 meter, and the width of the undensified carbon nanofiber sheet is greater than 10 cm.

2. The multilayer composite of claim 1 , wherein an average nanofiber diameter of the at least one carbon nanofiber sheet layer is less than about 30 nm.

3. The multilayer composite of claim 1 , wherein the at least one carbon nanofiber sheet layer comprises a first carbon nanofiber sheet having a first nanofiber orientation direction different from an adjacent second carbon nanofiber sheet having a second nanofiber orientation direction, and

wherein one of the first nanofiber orientation direction and the second nanofiber orientation direction being parallel to the length direction of the at least one carbon nanofiber sheet layer.

4. The multilayer composite of claim 1 , wherein the at least one carbon nanofiber sheet layer further comprises at least one polymer infiltrated within the densified carbon nanofiber sheet.

5. The multilayer composite of claim 1 , further comprising a metal layer on at least one surface of the at least one carbon nanofiber sheet layer.

6. The multilayer composite of claim 1 , further comprising an additive of magnesium diboride, titanium dioxide, or lithium phosphate.

7. The multilayer composite of claim 1 , wherein the at least one carbon nanofiber sheet layer comprises at least one graphene layer on the densified carbon nanofiber sheet.

8. The multilayer composite of claim 1 , wherein the volume density of the densified carbon nanofiber sheet is greater than 10 to 1000 times greater than the volume density of the undensified carbon nanofiber sheet.

9. The multilayer composite of claim 1 ,

wherein the length and the width of the carbon nanofiber sheet, once the carbon nanofiber sheet is densified, shrinks less than 1%.

10. The multilayer composite of claim 1 , wherein end portions of the at least one carbon nanofiber sheet layer are surrounded by the at least one heat shrinkable polymer layer.

11. The multilayer composite of claim 1 ,

wherein the volume density of the carbon nanofiber sheet is increased while a thickness of the carbon nanofiber sheet is reduced by at least 200 times.

12. The multilayer composite of claim 1 , wherein the carbon nanofiber sheet has a thickness between 10 to 20 μm prior to densification and has a thickness between 10 to 50 nm after densification.

13. The multilayer composite of claim 1 , wherein the carbon nanofiber sheet has a length or a width that is more than 100 times greater than its thickness.

14. The multilayer composite of claim 1 , wherein an electrical conductivity property of the multilayer composite is maintained while volume density of the carbon nanofiber sheet is increased.