POLYACRYLONITRILE RECYCLING METHOD

Generally speaking, just like other polymers, we can use mechanical and chemical recycling methods. What to consider about a PAN recycling method:

1.  PAN is not a thermoplastic polymer like PE, PP, polyester or polyamide that melt when heated. With the PAN heated at a temperature above 180ºC, the polymerization of the polymer chain begins, making it rigid and dark. This property makes PAN fiber the best known carbon fiber precursor.




2.  Virtually everything that exists in the market today containing PAN, are acrylic fibers and ABS plastic, which, being considered a thermoplastic, can be recycled in the same way as conventional plastics.




3.  Fabrics containing PAN fibers (acrylic fibers), in most cases, do not use pure acrylic fiber, but a mixture of other types of fibers such as cotton, wool, polyester or polyamide with acrylic. Mechanical recycling to separate the various fibers of a fabric is very difficult and expensive, due to the small diameter of the filaments (in the order of a few microns), small difference in density and the interweaving between them.




4.  Acrylic fibers in fabrics are almost always dyed or pigmented and that is why PAN, if recovered from such fibers by chemical method, will always have coloring or opacity, which makes this PAN unfeasible for reuse in wet and dry spinning processes, that mostly produce white fibers.




5.  As it is a very resistant and insoluble polymer, there are few solvents that can be used industrially in the chemical recycling of PAN by dissolution, followed by its precipitation by addition in water. PAN's main solvents are: DMF, DMAc, nitric acid, sodium thiocyanate, zinc chloride and ethylene carbonate. The use of solvents in PAN's chemical recycling makes the process expensive, mainly due to the need for recycling for reuse and treatment of effluents since they are toxic.




6.  Fabrics containing acrylic fibers cannot be depolymerized or cracked by thermal processes, due to the cyclization of the chain with the formation of solid waste of high carbon content in the reactor.




7.  Acrylic fiber and its fabrics cannot be used as fuel in ovens and should only be incinerated in special equipment, since they produce hydrocyanic acid (HCN) and ammonia (NH₃), which are highly toxic gases.




8.  Not even in the companies that produce acrylic fibers, their residues and production losses are recycled - despite being made up only of polyacrylonitrile -, since some characteristics of the threads such as thickness, presence of solvent, yellowing or coloring make commercialization unfeasible.




9.  A PAN recycling method must be robust enough to use all types of acrylic waste generated by the production chain, which are:

• Polymerization process, which during launch produces polymer out of specification.

• Start spinning, which produces fibers with solvents and thicker filaments.

• Loss of spinning during yarn production and dyeing.

• Losses in the fabric cutting process for clothing manufacturing.

• Discarded clothes.