Recovery of reinforcing fibers from fiber-reinforced composites
Processing fiber-reinforced composite to recover reinforcing fibers includes first treating the composite with a normally-liquid first solvent for material of the matrix followed by second treating of solid residue including reinforcing fibers from the first treating with a normally-gaseous material contacted with the solid residue under conditions of temperature and pressure at which the normally-gaseous material is in a liquid or supercritical fluid form. Treating a crude product including released reinforcing fibers and residual material of the matrix and/or fiber sizing includes first converting a normally-gaseous substance from a fluid form to a solid form and thereafter second converting the solid form to a gaseous form, to assist dislodgment of such residual material.
1. A method for processing a crude product containing reinforcing fibers recovered from a composite including the reinforcing fibers held in a matrix of a plastic material or a precursor for plastic material, wherein the crude product comprises some residual material of one or both of the matrix and fiber sizing on the reinforcing fibers, the method comprising:
with the crude product in the presence of the normally-gaseous substance, converting the normally-gaseous substance from a fluid form to a solid form in contact with the crude product, the first converting comprising reducing the temperature of the normally-gaseous substance; and
after the first converting, second converting the normally-gaseous substance in the solid form from the solid form into a gaseous form, to assist dislodgment of at least a portion of the residual material from the reinforcing fibers.
2. The method according to claim 1 , wherein the first converting comprises reducing temperature of the at least a portion of the normally-gaseous substance from a first temperature of at least 0° C. to the reduced temperature, wherein the reduced temperature is lower than −50° C.
3. The method according to claim 1 , wherein the second converting comprises converting the normally-gaseous substance of the solid form from the solid form to the gaseous form in a time period of no greater than 60 seconds.
4. The method according to claim 1 , wherein the second converting comprises contacting the crude product with a heat transfer fluid at a temperature that is at least 50° C. greater than a temperature of the solid form of the normally-gaseous substance.
5. The method according to claim 4 , wherein the heat transfer fluid comprises a member selected from the group consisting of liquid water, liquid oil, air, steam and combinations thereof.
6. The method according to claim 1 , wherein the normally-gaseous substance is carbon dioxide.
7. The method according to claim 1 , wherein the normally-gaseous substance comprises a member selected from the group consisting of tetrachloroethylene, 1,1,1,2-tetrafluoroethane, difluoromethane, pentafluoroethane, and combinations thereof.
8. The method according to claim 1 , wherein the second converting comprises rapid sublimation of the normally-gaseous substance.
9. The method according to claim 1 , wherein the normally-gaseous substance is a solvent from prior processing of the composite to prepare the crude product.
10. The method according to claim 1 , wherein the first converting comprises:
reducing pressure of the normally-gaseous substance from an elevated pressure; and
gas expansion cooling of the normally-gaseous substance during the reducing pressure.
11. The method according to claim 10 , wherein the elevated pressure is at least 2 MPa.
12. The method according to claim 11 , wherein the reducing pressure comprises reducing pressure of the normally-gaseous material from the elevated pressure to a lower pressure of 0.518 MPa or lower.
13. The method according to claim 3 , wherein the second converting comprises contacting the crude product with a heat transfer fluid at a temperature that is at least 50° C. greater than a temperature of the solid form of the normally-gaseous substance.
14. The method according to claim 13 , wherein the normally-gaseous substance is carbon dioxide.
15. The method according to claim 14 , wherein the second converting comprises rapid sublimation of the normally-gaseous substance.
16. The method according to claim 15 , wherein the first converting comprises:
reducing pressure of the normally-gaseous substance from an elevated pressure of at least 2 MPa to a lower pressure of 0.518 MPa or lower; and
gas expansion cooling of the normally-gaseous substance during the reducing pressure.