Pyrolysis and solvolysis recover carbon fiber, and they strip the sizing off it along with the resin. What comes out is bare filament: fluffy, hard to meter, quick to fly and bridge in equipment, and poorly bonded to whatever matrix it is compounded into. Re-sizing is the step that turns reclaimed fiber back into a product, and it is done with the same waterborne film formers used on virgin fiber lines.
What bare fiber costs you
Unsized carbon fiber resists every downstream operation: it fuzzes and clogs in chopping, bridges in hoppers, meters inconsistently through loss-in-weight feeders, and sheds abrasive filament debris into equipment. And when it does reach a matrix, the interface is weak, because nothing couples the inert carbon surface to the resin. The same fiber with a fresh film former on it chops into discrete bundles, flows, feeds, and bonds.
Choosing the re-size chemistry
The selection follows the destination matrix, exactly as it does for virgin fiber. Reclaimed fiber going back into thermoset systems takes an epoxy film former. Fiber destined for engineering thermoplastic compounds takes the chemistry matched to that melt: higher molecular weight epoxy grades for PET, PBT, and polycarbonate, and polyurethane dispersions for polyamide, including FILCO D2594 and D2596, anionic polyether-polyurethanes published for continuous and chopped carbon fiber, virgin or recycled. For melt processing at PPS and PEEK temperatures, standard epoxy sizings are not suitable, and the line carries FILCO 8902 for those conditions, a modified epoxy at 57 percent solids whose dried film loses only 5 percent of its mass at 385 degrees C, with no curing needed after drying. The carbon grade tables are on the FILCO carbon fiber film formers page and the polyurethane film formers page.
The second lever is the film former's glass transition temperature, which sets the hand of the re-sized product. Soft, low-Tg grades keep tow and chopped bundles flexible; stiffer grades give compact bundles with the bulk density and flow that automated feeding wants. The full selection logic, including the non-ionic bath requirement and particle size, is in choosing a film former for carbon fiber sizing.
Re-sizing reclaimed fiber, or fighting fuzz on a chopping line?
Tell us the fiber, the process, and where the product is headed. We will recommend a film former and support the trial.
Request a SampleChopping, converting, and blade life
Chopping unsized or badly sized tow damages fiber, generates fuzz, and clogs cutters; a well-sized tow cuts cleanly. Film-former choice influences cutting force, fuzz generation, and the abrasive debris blades see, so a converting line fighting short blade life has a real lever in the sizing, particularly in the film former's hand. Softer, more lubricious films cut differently than brittle high-Tg ones. We will not promise a blade-life number from a datasheet; the honest route is a controlled chop trial with cuts-per-blade counted, and we support those trials with samples and the manufacturer's technical team. The full logic, with the published dried-film stiffness numbers, is in sizing, chopping, and blade life in carbon fiber converting.
Oversizing: coating fiber that is already sized
Not every re-coat starts from bare fiber. Converters twisting, plying, weaving, or chopping sized fiber sometimes need more protection or different matrix compatibility than the original sizing provides. Applying an additional coat over the existing size, called oversizing, does that without stripping anything. The film former is chosen to sit compatibly on the original size and to serve the end use, and the low add-on levels involved make waterborne application straightforward.
Veils, mats, and the binder side
Wet-laid carbon veils and mats are the other place reclaimed and short-cut carbon fiber becomes product, and there the chemistry is called a binder rather than a size: it bonds the web instead of coating a tow. The spec language is the same family, waterborne dispersions and polyester powder binders, styrene-soluble grades where the veil should dissolve into a laminating resin, insoluble grades where the web has to hold its form. Polyester powder binders also serve preforms, holding chopped or directed fiber in shape into the mold. We supply all of it, from the same line, covered on the fiber sizing film formers page, with the grade tables on the chopped strand mat powder binders and continuous filament mat binders pages.
Sourcing
The FILCO film formers and binders are made by COIM in Italy on three decades of fiber sizing heritage, and we supply them to order from that plant with samples available for line trials. Recycling and converting operations rarely need full-container quantities to start, and we ship at the scale a qualification actually runs. Where reclaimed fiber needs something the catalog does not cover, development grades are a real path; tell us what the fiber has to do and we will take it to the technical team.
Frequently asked
Why does recycled carbon fiber need re-sizing?
Pyrolysis and solvolysis strip the original sizing with the resin. Bare fiber is fluffy, hard to feed, abrasive, and poorly bonded to any matrix. A fresh film former restores bundle integrity, feedability, and the fiber-matrix interface.
How is the re-sizing chemistry chosen?
By the destination matrix: epoxy film formers for thermosets, higher molecular weight epoxies for PET, PBT, and polycarbonate, polycaprolactone-based polyurethane dispersions for polyamide 6. Then Tg is set for the handling the product needs.
Does sizing affect chopping behavior and blade wear?
Sizing is what makes carbon fiber choppable: unsized tow fuzzes and clogs, sized tow cuts cleanly. Film-former choice influences cutting force, fuzz, and abrasive debris, so sizing selection is a real lever on blade life. Prove it with a controlled chop trial, which we support.
What is oversizing?
Applying an additional size coat over fiber that already carries one, to add handling protection or matrix compatibility without stripping the original. Same film formers, selected for compatibility with the existing size and the end-use resin.
Turning reclaimed fiber into product?
Send the fiber form, the process, and the destination matrix. We will recommend a film former or binder, arrange a trial quantity, and back it with technical support.
View the fiber sizing page