Cap liner comprising a sintered fluoropolymer layer

1. A cap liner, comprising:

a sintered plasma etched fluoropolymer layer having a white color; wherein the sintered plasma etched fluoropolymer layer comprises at least one of a poly(tetrafluoroethylene) or a modified poly(tetrafluoroethylene); wherein the sintered plasma etched fluoropolymer layer is free of a filler; wherein a thickness of the sintered plasma etched fluoropolymer layer is 0.02 to 0.4 millimeters; and

a backing layer in the form of a continuous layer; wherein the backing layer comprises a closed cell, compressible foam layer having a porosity of 10 to 70 volume percent based on the total volume of the backing layer; wherein the closed cell, compressible foam material comprises at least one of an elastomer or a polyolefin; wherein a thickness of the backing layer is 0.5 to 3 millimeters; and

wherein the sintered plasma etched fluoropolymer layer is in direct physical contact with the backing layer with no intervening layer located there between;

wherein the sintered plasma etched fluoropolymer layer is free of an etchant residue identifiable by Fourier transform infrared spectroscopy; and

wherein the sintered plasma etched fluoropolymer layer is a solid layer having a porosity of 0 volume percent.

2. The cap liner of claim 1 , wherein the closed cell, compressible foam layer comprises the elastomer, wherein the elastomer optionally comprises repeat units derived from at least one of ethylene, butadiene, acrylonitrile, styrene, or isobutylene.

3. The cap liner of claim 1 , wherein the backing layer further comprises a solid outer layer located on a surface of the foam layer opposite the sintered plasma etched fluoropolymer layer.

4. The cap liner of claim 1 , wherein the closed cell, compressible foam layer comprises the polyolefin; wherein the polyolefin optionally comprises a fumaric acid graft and/or repeat units derived from at least one of a 1-alkene having 4 to 8 carbon atoms, a norbornene-type monomer, maleic anhydride, ethyl acrylate, isobutyl acrylate, or vinyl acetate.

5. The cap liner of claim 1 , wherein the sintered plasma etched fluoropolymer layer forms a fluid-tight seal against a surface of a container.

6. A method of forming the cap liner of claim 1 , the method comprising:

plasma etching the sintered fluoropolymer layer to form a sintered plasma etched fluoropolymer layer; and

laminating the sintered plasma etched layer and the backing layer to form the cap liner.

7. The method of claim 6 , further comprising sintering a fluoropolymer layer to form the sintered fluoropolymer layer at a temperature of 330 to 390° C. for greater than or equal to 5 minutes.