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 composite including reinforcing fibers held in a matrix of a plastic material or precursor for a plastic material for recovery of the reinforcing fibers, the method comprising:
first treating the fiber-reinforced composite with a normally-liquid first solvent for material of the matrix to prepare a first treated solid residue comprising the reinforcing fibers, the first treating comprising contacting the fiber-reinforced composite with the first solvent and first dissolving at least a majority by weight of the matrix into the first solvent; and
after the first treating, second treating at least a portion of the first treated solid residue comprising the reinforcing fibers with a second solvent of normally-gaseous material, having a different composition than the first solvent, to prepare second treated solid residue, the second treating comprising contacting the at least a portion of the first treated solid residue with the normally-gaseous material under conditions of temperature and pressure at which the normally-gaseous material is in a form of a liquid or supercritical fluid;
prior to the second treating, separating first solvent loaded with dissolved matrix material from the first treated solid residue, wherein as provided to the second treating the first treated solid residue is in the presence of a residual portion of the first solvent following the separating; and
wherein:
the normally-liquid first solvent is in the form of a liquid when at conditions of 0.1 MPa pressure and 25° C. temperature; and
the normally-gaseous material is in the form of a gas when at conditions of 0.1 MPa pressure and 25° C. temperature;
the second solvent is a solvent for the first solvent; and
the second treating comprises dissolving into the second solvent the residual portion of the first solvent associated with the first treated solid residue following the first treating.
2. The method according to claim 1 , comprising, after the second treating, third treating at least a portion of the second treated solid residue comprising the reinforcing fibers, the third treating comprising:
first converting a normally-gaseous substance in contact with the at least a portion of the second treated solid residue from a fluid form to a solid form, the first converting comprising reducing a temperature of the normally-gaseous substance; and
after the first converting, second converting the normally-gaseous substance from the solid form to a gaseous form, to assist dislodgment from the reinforcing fibers of residual material selected from the group consisting of material of the matrix, material of fiber sizing and combinations thereof.
3. The method according to claim 2 , wherein the normally-gaseous substance is carbon dioxide and the normally-gaseous substance is the normally-gaseous material of the second treating.
4. The method according to claim 1 , wherein the matrix comprises an uncured thermoset resin.
5. The method according to claim 4 , wherein the uncured thermoset resin includes a member selected from the group consisting of polyimines, unsaturated polyesters, polyurethanes, vinyl esters, epoxies, phenolics, cyanate esters, bismaleimides, polyimides, polybutadienes, benzoxazines, phthalonitriles, precursors of any of the foregoing and combinations thereof.
6. The method according to claim 1 , wherein the matrix comprises a thermoplastic composition.
7. The method according to claim 1 , wherein the reinforcing fibers comprise carbon fibers.
8. The method according to claim 1 , wherein the reinforcing fibers comprise fibers selected from the group consisting of carbon nanotube fibers, aramid fibers, glass fibers, boron fibers, basalt fibers, high-modulus polyethylene fibers, poly p-phenylene-2,6-benzobisoxazole fibers, quartz fibers, ceramic fibers, stainless steel fibers, titanium fibers, copper fibers, nickel fibers, metal coated fibers, natural fibers and combinations thereof.
9. The method according to claim 1 , wherein the first solvent comprises methylene chloride.
10. The method according to claim 1 , wherein the first solvent comprises a member selected from the group consisting of methoxy-nonafluorobutane, 2-methyltetrahydrofuran, tetrahydrofuran, tetrachloroethylene, n-propyl bromide, dimethyl sulfoxide, polyolester oil and combinations thereof.
11. The method according to claim 1 , wherein the first solvent comprises a member selected from the group consisting of, esters, ethers, acetates, acids, alkalis, amines, ketones, glycol ethers, glycol ether esters, ether esters, ester-alcohols, alcohols, halogenated hydrocarbons, paraffinic hydrocarbons, aliphatic hydrocarbons, aromatic hydrocarbons and combinations thereof.
12. The method according to claim 1 , wherein the first solvent is chemically inert with respect to the reinforcing fibers.
13. The method according to claim 12 , wherein the reinforcing fibers comprise at least 95 weight percent of the first treated solid residue.
14. The method according to claim 1 , wherein the normally-gaseous material is carbon dioxide.
15. The method according to claim 1 , wherein the normally-gaseous material comprises a member selected from a group consisting of 1,1,1,2-Tetrafluoroethane, difluoromethane, pentafluoroethane, and combinations thereof.
16. The method according to claim 14 , wherein:
the reinforcing fibers comprise carbon fibers;
the matrix comprises an uncured thermoset resin;
the first solvent is chemically inert with respect to the reinforcing fibers and is chemically nonreactive with the material of the matrix;
at least 90 weight percent of the matrix is dissolved into the first solvent during the first treating;
the pressure of the contacting of the second treating is in a range of from 2 MPa to 69 MPa; and
a temperature of the contacting of the second treating is in a range of from 0° C. to 175° C.
17. The method according to claim 1 , comprising:
recovering rich first solvent from the first treating that is rich in dissolved material of the matrix;
distilling the rich first solvent to vaporize at least a portion of the first solvent and recovering vapor of the first solvent; and
condensing and recycling as feed to the first treating at least a portion of the recovered vapor of the first solvent.
18. The method according to claim 17 , further comprising recovering precipitated solid material of the matrix formed during the distilling.