Bearing components and processes for depositing additives, especially fluoropolymers, on cellulose
A method for applying an additive, e.g. a fluoropolymer, to cellulose. The method comprises a number of steps. First, solid cellulose, a solvent capable of dissolving cellulose, e.g. NMMO and a dispersion of the additive are brought into contact with each other. The additive is allowed to diffuse into the dissolved cellulose, which is possible as a result of the dissolution of the surface layer of the solid cellulose. The solubility of cellulose in the solvent is then reduced, whereby the additive that has diffused into the dissolved cellulose is incorporated into the resulting solid cellulose. A method for applying a fluoropolymer to cellulose as a surface coat is also described. Flexible bearing components comprising a mat of cellulose fibers and a fluoropolymer which may be made by the methods described.
1. A method of applying an additive to cellulose, said method comprising the steps of:
(a) bringing solid cellulose, a solvent capable of dissolving the solid cellulose and a dispersion of the additive into contact with each other, such that a surface layer of the solid cellulose is dissolved in the solvent;
(b) contacting the dissolved cellulose with the additive; and
(c) altering at least one of the composition, quantity or temperature of the solvent such that the solubility of cellulose in the solvent is reduced and at least a portion of the dissolved cellulose comes out of solution, whereby the additive is incorporated into, or adhered to, the cellulose.
2. The method of claim 1 , wherein said step (b) occurs prior to said step (a).
3. The method according to of claim 1 , wherein the solvent is a mixture of at least two components:
the mixture is chosen such that solubility of cellulose in the mixture is dependent on the relative amounts of the components in the mixture; and
said step (c) further comprises altering the relative amounts of the components such that the solubility of cellulose in the mixture is reduced as compared to the solubility in said step (a).
4. The method of claim 3 , wherein the mixture of the components that is initially contacted with the solid cellulose is such that it can dissolve a surface layer of the solid cellulose.
5. The method of claim 3 , wherein the proportions of components required to dissolve a surface layer of the solid cellulose are obtained by:
applying a mixture of the components to the solid cellulose; and
drying the mixture to selectively remove one component to obtain a mixture of components capable of dissolving cellulose.
6. The method of claim 3 , wherein said step of altering the relative amounts of components so that at least a portion of the cellulose comes out of solution is carried out by:
drying the mixture to selectively drive off one component and increase the concentration of the other component in the mixture.
7. The method of claim 3 , wherein the solvent comprises water and a cyclic amine oxide.
8. The method of claim 7 , wherein the cyclic amine oxide is N-methylmorpholine N-oxide (NMMO).
9. The method of claim 8 , wherein the mixture in said step (a) contains 67 to 87% N-methylmorpholine N-oxide (NMMO).
10. The method of claim 1 , further comprising the step of removing the solvent from the solid cellulose by washing following said step (c).
11. The method of claim 1 , wherein the additive is in the form of a dispersion of additive particles in a medium.
12. The method of claim 1 , wherein the additive is hydrophobic.
13. The method of claim 1 , whereby the additive is incorporated into, or adhered to, the surface layer of the cellulose, with the additive concentrated at the surface layer.
14. The method of claim 1 , wherein the solid cellulose is in the form of paper.
15. The method of claim 1 , wherein the solid cellulose is in the form of cellulose fibers or particles.
16. A product comprising solid cellulose to which an additive has beer applied by the method of claim 1 .
17. The method of claim 13 , wherein the additive is a fluoropolymer selected from the group consisting of polytetrafluoroethylene (PTFE), fluoroethylene-propylene (FEP), perfluoroalkoxy resin (PFA), perfluoromethyl vinyl ether (MFA), polyvinylidene fluoride (PVDF), ethylene tetrafluoroethylene (ETFE), ethylene chlorotrifluoroethylene (ECTFE), and tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride (THV) and a mixture thereof.
18. The method of claim 1 , wherein the additive is a fluoropolymer.
19. The method of claim 18 , wherein the fluoropolymer is polytetrafluoroethylene (PTFE).
20. The method of claim 13 , wherein the additive is incorporated into the surface layer at a depth from 0.1 to 100 μm.
21. The method of claim 20 , wherein the additive is incorporated into the surface layer at a depth from 1 to 50 μm.