The present invention refers to a recycling proces of waste carpets, i.e. post consumer carpets, wherein main components of the waste carpets are separated and recovered for further use thereof.

The mayority of carpets are composed of a face fiber material such as nylon 6, nylon 66, polyester, polypropylene or other fibers embedded or tufted in a primary backing that contains polypropylene fabric as the backing material. After the face fiber is tufted through the primary backing, an adhesive coating is applied to the back side of the carpet for further holding the face fiber in place. The adhesive coating is typically composed of a latex, such as a styrene-butadiene rubber (SBR), ethylene vinyl acetate (EVA), etc. and includes inorganic materials as fillers, such as calcium carbonate, fly ash, clay or hydrated alumina. Before the adhesive coating is cured, a second fabric, commonly referred to as a secondary backing, is attached to the back of the carpet. The secondary backing is typically made of polypropylene fabric.

Typically the face fiber material represents 10-50 wt. % of the carpet, the balance being backing material and adhesive coating, i.e. latex and fillers, wherein the amount of the backing material is up to 20 wt. % of the carpet and the amount of the adhesive coating is between 40 to 50 wt. % of the carpet. Typically the adhesive coating is composed of 20 wt. % of latex and 80 wt. % of filler, preferably calcium carbonate, calculated to the amount of the adhesive coating.

Today only 1-3 % of all the post consumer carpets in Europe are recycled, the majority of the waste carpets are sent to the landfill site or are incinerated. Since incineration is harmful for the environment and for the people there are incentives in some countries to legally prohibit the disposal of carpets in landfills and incineration thereof. Thus it will be even more desirable to develop practical and economical methods to recover the materials of carpet waste, especially the polymeric face fiber, which may be than depolymerized to yield a desired monomer, i.e. in the case of nylon 6 face fibers, a desired monomer to be recovered is ε-caprolactam. Several recycling procesess of waste carpets are proposed but they all have drawbacks.

One approach to recovery of materials, predominantly nylon from waste carpet involves depolymerization of essentially a whole carpet. This process is not suitable for all depolymerization processes as the primary and secondary backing fiber materials may interfere substantially with the depolymerization process, and thereby render the process uneconomical and impractical.

Other approaches involve an initial separation process wherein face fiber is at least partially separated from the backing material, and the separated face fiber material is then depolymerized to recover the desired monomer. One example of such a separation process involves mechanical shearing of carpet to remove a portion of the face fiber from the backing. Unfortunately, since a great deal of the face fiber is below the surface of the primary backing, much of the face fiber is not recovered by the shearing process. Also, mechanical shearing of face fiber from post-consumer carpet presents problems. The carpet must be fed to the shearing device flat and neatly spread out.

In US patent No. 5230473 a method for reclaiming carpet is disclosed through a process which softens the latex adhesives with steam or water, then tears the face fiber out of the backings using a series of brushes and serrated rolls. This process suffers from deficiencies similar to the aforementioned shearing device.

In US patent No. 5722603 a process for separating and recovering waste carpet material components, especially face fiber material, includes removing adhesive material from the waste carpet material feedstock to obtain a mixture containing face fiber material which is passed with a liquid medium to a hydrocyclone, where the solids in the mixture are separated on the basis of specific gravity, and recovered. The recovered components can then be processed into desired products. The proposed process requires multiple hydrocyclones in a cascade for adequate separation of main components.

So there was a need to develop a recycling process and a device for separation and recovery of waste carpets which is efficient with very low material loss and wherein all main components are separated with very high yield. In the proposed process according to the invention practically all of the filler, i.e. calcium carbonate, is removed prior to fine grinding and passing the mixture to a high speed centrifuge for separation of the face fiber material from the backing material, thus there is no need for multiple centrifuge steps in a cascade for adequate separation of main components. In the proposed process the fine grinding of the material to be recycled is done only once right before passing the mixture to the centrifuge by which the loss of the fiber material is highly reduced before its separation into nylon and polypropylene and also the life time of the fine grinder and the centrifuge is prolonged. The material which passes to the centrifuge contains in this step only minimal amounts of the filler. Inorganic filler is hard and abrasive and can, if present in higher amounts, cause faster wear of the fine granulator and the centrifuge. The use of only one centrifuge makes the proposed process also cost effective.

The proposed process will be illustrated hereinafter by way of drawings, in which:

Figure 1 represents a schematic diagram of the process of the invention

Figure 2 represents a dry centrifugal separation machine.

For the purpose of this application the term backing material is to be understood to include ^' primary backing material and secondary backing material. For the purpose of this application the term adhesive coating is to be understood to include latex, typically SBR and filler, typically calcium carbonate.

The process according to the invention includes the following steps:

A: shredding of waste carpets in a shredding machine wherein the size of the carpet is reduced to pieces with an average size of 5 to 10 cm. The size reduction serves to reduce the size of the waste carpet into sizes that are more easily managed in the later steps of the process and to initiate separation of the face fibre material and backing material from the adhesive coating. In this step any conventional, commercially available, size reduction equipment such as guillotines, rotary cutters, shear shredders, open rotor granulators, closed rotor grinders, and rotor shredding machines can be used so long as the size reduction operation does not produce a substantial amount of fine face fiber particles that can be lost in later operations to thus preclude their recovery. Preferably a single shaft shredder is used which provides less than 2 wt. % of fine face fiber particles loss because of the coarse 5-10 cm shredding.

B: sieving of the material obtained in step A through at least one screen that has a mesh size between 1-5 mm and is designed to retain face fiber material and backing material while passing through the smaller particles of the adhesive coating, i.e. predominantly filler (calcium carbonate). In this step the majority of the material which represents the face fiber and the backing material remains on the mesh and is led further to step C. The residue which is predominantly filler, i.e. calcium carbonate, is removed so that up to 10 wt. % of the filler calculated to the weight of the carpet is removed from the material.

C: prewashing of the material obtained in step B in a pre-washer with a washing agent and wherein the material is wetted to reduce its volume. The pre-washer is preferably a low friction machine, a washing agent is preferably water. The weight ratio of water to material is between 30:1 and 10:1, preferably 10:1. In this step no size reduction takes place but due to the action of the internal parts of the pre-washer, the amount of the filler, i.e. calcium carbonate, is further reduced by maximum of additional 5wt. % calculated to the weight of the carpet. Water which contains the filler is led to a single cone centrifugal separation wherein the filler is removed from water and water is recycled to the beggining of the washing process.

D: washing of the material obtained in step C is done in a high friction washer, wherein due to the action of high friction forces predominantly the filler is removed from the material. In this step no size reduction takes place and thus the loss of the fiber material is minimized. The amount of the filler in the material which passes to the next step is reduced to less than 3 wt. % calculated to the weight of the carpet. The washing agent is preferably water. In the high friction washer high friction between rotating drum which contains exchangable pins and the cylinder with exchangeble friction plates to control the friction occurs. With such a design of the high friction washer no size reduction of the material takes place only the filler, which is still present in the material, is loosened and is removed from the material due to the action of high friction forces and water. In this step the rest of the filler, i.e. calcium carbonate, which is abrasive and have negative impact on further process steps, is removed from the material and thus possible negative impact is reduced. Water from the high friction washer which contains the filler is led to a single cone centrifugal separation wherein the filler is removed from water and water is recycled to the beggining of the washing process.

E: dewatering of the material obtained in step D is carried out in a centrifuge dryer wherein the excess water is removed from the material. After dewatering the water content in the material is up to 55 wt. %, the rest, up to 45 wt. % are predominantly fibers of the face fiber material and the backing material, i.e. nylon and polypropylene fibers. Excess water which contain some filler is led to a single cone centrifugal separation wherein the filler is removed from water and water is recycled to the beggining of the washing process. Drying is preferably done in a centrifuge dryer or with screw press - dewatering.

F: fine wet grinding of the material obtained in step E in a wet granulator wherein the size reduction of the fibers takes place and wherein the size of the fibers is reduced to an average size of 10 mm. The reduction in fiber size is needed for effective separation of nylon fibers from polypropylene fibers in a further step. The fibers which come from step E are long because no size reduction was performed during prior steps of the process. Thus the fibers of face fiber material which are predominantly of nylon and the fibers of backing material which are predominantly of polypropylene are mixed and tangled and the complete and effective separation in a later step without prior fine grinding would be incomplete and with very poor yield.

G: fluid separation of the material obtained in step F in a centrifuge, preferably double cone centrifuge, with water wherein with the forces in the centrifuge which reach several 1000 g, up to 3000g, instant separation of nylon and polypropylene fibers takes place. The fluid separation of fibers based on different specific weight of nylon and polypropylene fibers in relation to water with the use of high g forces is known from the prior art. With this separation two phases are obtained, a heavy phase which contains pure nylon fibers with yield up to 95 % and a lighter phase which contains pure polypropylene fibers with yield up to 97 % .

H: recovery of separated nylon and polypropylene fibers for further processing, for example depolymerization of nylon fibers to caprolactam.

Optionally instead of step B and C, i.e. the use of a sieve and a prewasher, the material obtained in step A is led to step B', to a dry centrifugal separation in a dry centrifugal separation machine. Instead of a two step process only one step is used for removal of the filler to reach 15 wt. % of filler in the carpet. In this step no size reduction of the material takes place. Dry centrifugal separation machine is in a form of a drum 1 mounted on a rotating shaft 4 equipped with holders 5 onto which paddles 6 are adjustably attached. The paddles 6 are adjustably attached on the holders 5 that are fixed to the shaft 4 perpendicularly to the shaft axis x. The distance between the holders 5 should be at least such as to enable the rotation of the paddles 6, preferably the holders 5 are fixed to the shaft 4 at regular intervals. The paddles 6 are adjustably fixed to the holder 5 in such a way that the smooth air flow facilitates the flow of the material through the machine. The paddles 6 are rotatable along both axes a, b, i.e. along the axis b which is perpendicular to the shaft axis x and along the axis which is parallel to the shaft axis x, at a certain angle, preferably at an angle between 0 - 45°. The shaft 4 with paddles 6 rotates with a speed up to 3000 RPM. The material obtained from step A, which is rich with the filler, enters the machine at an inlet 2 and travels along the shaft axis. The paddles 6 hit the material with a high speed and thus the removal of predominantly filler from the material is achieved. The bottom part 7 of the drum 1 is perforated to form a kind of a sieve with the mesh with the size between 1 - 5 mm. The material which is poor with the filler exits the machine through an outlet 3 and is led directly to step D. The paddles 6 are exchangeable due to the wear which appears because of friction caused by carpet fillers. The machine is thus designed to retain face fiber and backing material while passing through the smaller particles of the adhesive coating, i.e. predominantly calcium carbonate. In this step the majority of the material which represents the face fiber and the backing material remains on the mesh and is led further to step D. The residue which is predominantly calcium carbonate is removed so that up to 15 wt. % of the calcium carbonate calculated to the weight of the carpet still remains in the material. With such a design of the dry centrifugal separation machine no size reduction of the material takes place. Only the filler is loosened and is removed from the material and thus less than 2 wt. % of fine face fiber particles loss is achieved.

In table 1 the yields of the recovery of waste carpet components after step G are presented and which confirm that pratically all the filler was sucessfully removed prior to step F and G.

CaC0 ₃ content PA6 content Residue content

(of dry sample) [%] (of dry sample) [%] (of dry sample) [%]

PA6 2,8 95,0 2,2

PP 2,2 0,8 97,1

PA6 2,4 94,9 2,7

PP 1,8 1,5 96,7

Table 1