METHOD TO RECYCLE A FIBROUS CARPET PRODUCT

Abstract

The present invention pertains to a method for recycling a carpet product, the carpet product comprising a fibrous sheet comprising polymer yarns, wherein at least one surface of the sheet is provided with a layer of polymer adhesive, wherein the carpet product is a substantially pure polyester carpet product, wherein the polymer yarns comprise polyester having a molecular weight above 50,000 g/mol and a melting point between 180 and 300 C., the adhesive is a polyester adhesive having a crystallinity between 5% and 35% and a viscosity of 5-55 Pa.Math.s at 150 C., the method comprising homogenising the carpet product by extrusion. The invention also pertains to recycled polymer obtainable by this method, to fibres comprising this recycled polymer material, to fibrous products comprising these fibres and to polyester adhesive.

Claims

1. Method for recycling a carpet product, the carpet product comprising a fibrous sheet comprising polymer yarns, wherein at least one surface of the sheet is provided with a layer of polymer adhesive, wherein the carpet product is a substantially pure polyester carpet product, wherein the polymer yarns comprise polyester having a molecular weight above 50,000 g/mol and a melting point between 180 and 300 C., the adhesive is a polyester adhesive having a crystallinity between 5% and 35% and a viscosity of 5-55 Pa.Math.s at 150 C., the method comprising homogenising the carpet product by extrusion.

2. Method according to claim 1, wherein the amount of polyester adhesive is between 0.5 and 25% w/w with regard to the total amount of polyester in the carpet product.

3. Method according to claim 1, wherein the amount of polyester adhesive is at least 1% w/w with regard to the total amount of polyester in the carpet product.

4. Method according to claim 1, wherein the amount of polyester adhesive is between 2% and 20% w/w, optionally between 5 and 15% w/w, with regard to the total amount of polyester in the carpet product.

5. Method according to claim 1, wherein the carpet product is mechanically cut into pieces having dimensions below 20 cm in width and length, wherein the carpet product pieces are compressed before being fed to an extruder to be homogenised.

6. Method according to claim 5, wherein the carpet product pieces are compressed to reach a bulk density of at least 0.3 g/cm.sup.3, preferably at least 0.5 g/cm.sup.3.

7. Method according to claim 5, wherein the carpet product pieces are compressed at an elevated temperature between room temperature and the melting temperature of the polyester adhesive.

8. Method according to claim 7, wherein the carpet product pieces are compressed at a temperature between 80-100 C.

9. Method according to claim 1, wherein the fibrous sheet comprises a primary backing having polyester yarns stitched therein to form a pile on a front surface of this primary backing and loops at an opposite back surface of the primary carrier, the polyester adhesive being applied to the back surface of the primary carrier.

10. Method according to claim 9, wherein the carpet product is made by contacting the back surface of the primary carrier with a surface of a hot body to at least partly melt the loops of the yarns to create a mass of molten material before the polyester adhesive is applied to this back surface.

11. A method according to claim 10, wherein the carpet product is made by providing the surface of the hot body at a relative speed with respect to back surface of the primary carrier, in particular by providing the surface of the hot body as a stationary object, the primary carrier being transported along the hot body.

12. Recycled polyester obtainable by a method according to claim 1.

13. Fibres comprising the polyester material of claim 12.

14. Fibrous products comprising the fibres according to claim 13.

15. A polyester adhesive having a crystallinity between 5% and 35% and a viscosity of 5-55 Pa.Math.s at 150 C.

Description

EXAMPLES

[0042] FIG. 1 is a schematic representation of the respective layers of a carpet product for use in the recycling method according to the invention.

[0043] FIG. 2 schematically depicts a recycle set-up for use in the method according to the invention.

[0044] Example 1 describes a method to determine the crystallinity of a low molecular weight polyester adhesive.

[0045] Example 2 describes a method to determine the viscosity in Pa.Math.s at 150 C. of a low molecular weight polyester adhesive.

[0046] Example 3 describes a method to determine melting point of a high molecular weight polyester.

[0047] Example 4 describes a test to assess the usability of a recycled polyester material.

[0048] Example 5 describes the extrusion of various types of low molecular weight polyester adhesive in combination with a high molecular weight polyester resin.

[0049] Example 6 describes the extrusion of various amounts of low molecular weight polyester adhesive in combination with a high molecular weight polyester resin.

FIG. 1

[0050] FIG. 1 is a schematic representation of the respective layers of a carpet product, in this case a carpet tile, for use in the recycling method according to the invention. The tile comprises a first sheet 2, the so called primary backing. This sheet is a dual layer polyester sheet (the separate constituting layers not being indicated in FIG. 1), of which the basic layer is a sheet made of woven polyester tape. The warp yarns of this woven sheet consist of a 1.0 mm wide polyester tape of 42 Tex, and they are woven at 112 yarns per 10 cm. The weft yarns, made of a 2.0 mm wide polyester tape of 86 Tex, are woven at 59 yarns per 10 cm. This results in a mechanically relatively strong sheet, which has a very low weight of about 100 g/m.sup.2 and is inexpensive to produce. The back surface (in FIG. 1 corresponding to the lower surface indicated with numeral 4) of this woven polyester sheet is covered with a thin felted fibrous layer. This layer is made by covering the back surface of the sheet with 5 dTex low melting polyester fibres (Tm about 230 C.) having a length of about 50 mm. The fibres are provided in an amount of about 45 g/m.sup.2. This layer is needle-felted to the woven polyester sheet, thereby forming a dual layer primary backing 2. Alternatively, a certain percentage of polyamide or other polymer fibres can be used in the felted layer next to the polyester fibres.

[0051] The primary backing is tufted with polyester (PET) yarns obtained from Shaw Industries, Dalton USA, having a melting point of 260 C. The yarns 5 extend from the first surface 3 of the sheet and are sealed to the second surface 4 of the sheet using a sealing process as known from WO 2014/198731 as described therein in conjunction with FIGS. 3, 4 and 5 therein. This is a sealing method wherein the back surface of the primary carrier after the yarns have been applied therein is contacted with a surface of a hot body to at least partly melt the loops of the yarns to create a mass of molten material before the polyester adhesive is applied to this back surface. In particular the carpet product is made by providing the surface of the hot body at a relative speed with respect to back surface of the primary carrier, in particular by providing the surface of the hot body as a stationary object, the primary carrier being transported along the hot body. The weight of the primary backing with tufted yarns is about 700 g/m.sup.2. The polyester adhesive used is a hot melt glue obtained from DSM Coating Resins, Zwolle, the Netherlands (having a crystallinity of 21% and a melt viscosity at 150 C. of about 45 Pa.Math.s), which is applied as a thin layer 11 (about 200 g/m.sup.2) to secure a resilient layer 10 to the primary backing. This layer is a knitted polyester layer (obtainable as Caliweb from TWE, Emsdetten, Germany), having a thickness of about 1 mm. The weight of this knitted polyester layer is about 300 g/m.sup.2. In order to provide sufficient mechanical stability, the carpet 1 comprises a second sheet 6, in this case a backing of a polyester needle felt backing fleece obtained as Qualitex Nadelvlies from TWE, Emsdetten, Germany. The weight of this second sheet is about 800 g/m.sup.2 as a thin layer 12. This sheet is adhered to the layer 10 using a polyester hot melt glue applied at about 300 g/m.sup.2. The total weight of the carpet tile is thus about 2.3 kg/m.sup.2.

[0052] In this embodiment the different layers are interconnected using the same polyester adhesive applied in the form of a layer having a weight of about 100-300 g/m.sup.2 (about 0.1 to 0.3 mm thick). However, different adhesives could be used for the two layers 11 and 12. It is also envisaged that before recycling de-coupling of one or more of the adhesive layers is necessary to arrive at a substantially pure polyester carpet product in view of recycling this product as a whole via extrusion. This could be the case for example when sheet 6 is made of a non-polyester polymer and thus needs to be separated before the remaining polyester carpet product. However, this could also be the case when the yarns are made of a different type of polymer (e.g. nylon), and thus the primary backing needs to be separated from the fibrous polyester sheet 10 and polyester backing 6 (in which case the sheet 10 and 6 together, with the adhesive layer in between constitute a substantially pure polyester carpet product in the sense of the present invention). In general, the adhesive may be provided as a layer having a thickness of less than 1 mm, usefully less than 0.5 mm, more usefully from 0.2 to 0.4 mm. Whereas in the prior art carpets on the market, the adhesive layer typically has a thickness well above 1 mm, applicant found that when reducing the thickness of this polyester adhesive layer to 1 mm or below an adequate adhesion can still be obtained.

FIG. 2

[0053] An extrusion recycling line that can be used for the recycling of a substantially pure polyester carpet product in line with the present invention is depicted schematically in FIG. 2. The carpet product (not indicated in FIG. 2) is firstly conveyed by conveyor belt 20 (which includes a metal detector, not shown, to make sure any metal parts are detected such that they can be removed before entering the further process) and led to a combined cutting device 21 that includes a single shaft cutter with a width of 800 mm and a temperature controlled shredder shaft (operating at a temperature of 90 C.). The material cut this way is fed into a shredder cyclone 22 which also operates at the same elevated temperature of 90 C. This cyclone is for further cutting the product and at the same time compressing the relatively fluffy carpet product into a mass having a density of between 0.4 and 0.6 g/cm.sup.3. The obtained compressed product is fed via a vacuum controlled dosing screw (not shown as such) into a high speed extruder 23 at a temperature about 20-30 C. above the melt temperature of the high molecular weight polyester with a single screw design extruder (Starlinger, Germany) rotating at 180 rpm. The extruder is provided with a degassing unit 24. At the downstream end, the extruded material passes a filter 25 with backflush (type SPB-180-H, Starlinger). After that the extruded material is led to a water ring pelletizer 26 (type WRP 120R CC, Starlinger). The resulting material is stored in silo 27 until further use. Also, a different type of pelletizer was used, namely an automatic strand pelletizer (type A-SPU PUSG 100, Starlinger) and adequate results were obtained as well.

[0054] This process has been used to recycle various polyester carpet products such as complete carpet (primary backing plus secondary backing), a primary backing sealed according to the teachings of WO 2014/198731 and provided with a polyester adhesive to its back surface, and various types of polyester secondary backings (in each case a fibrous sheet of polyester yarns) provided with a layer of polyester adhesive to at least one of their surfaces. In each case the carpet products (being either complete carpet or a part thereof obtained after separating the non-polyester layers) comprised a fibrous sheet of high molecular weight PET having a melting point of around 260 C. (being extremely high in viscosity) in combination with a polyester adhesive having a crystallinity between 5 and 35% and being very low in viscosity at 150 C. (between 5 and 55 Pa.Math.s). In each case, the extruder showed a good performance and a stable run independent of the type of carpet product. The typical throughput was 160 kg/h at a filter loss of about 3%. The intrinsic viscosity of the resulting pellets was measured and appeared to be around 0.5-0.6 dL/g for the end material as taken from the silo. By applying a common solid state post condensation technique (SSP-process; annealing the material at elevated temperatures at around 200-220 C. for 6-10 hours), the intrinsic viscosity could be increased to about 0.7 to 1.0 dL/g depending on the type of starting material and process conditions used in the SSP process.

Example 1

[0055] Example 1 describes how to determine the crystallinity of a polymer adhesive. The determination is based on ASTM standard D3418 (Standard Test Method for Transition Temperatures and Enthalpies of Fusion and Crystallization of Polymers by Differential Scanning calorimetry) using a Mettler STARe differential scanning calorimeter. For the actual measurement an adhesive sample of 10 mg is placed in a sample cup. This sample is kept in an oven for 15 minutes at 150 C. After this, the sample is cooled to 50 C. and then heated to 250 C. at a speed of 5 C./min. The sample is kept at 250 C. for 1 minute and thereafter directly cooled to 25 C. at a speed of 5 C./min. From the obtained DSC data the percentage of crystallinity in the sample polymer is calculated using the Mettler STARe SW 9.2 software.

[0056] For two polyester adhesives obtained via DSM Coating Resins, Zwolle, The Netherlands, which adhesives have excellent properties in order to obtain successful recycling in the sense of the present invention, the crystallinity was determined this way. For the first polyester adhesive (denoted A), being a low molecular weight PET (Mw=18,704 g/mol) based on diethyleneglycol, butanediol, adipic acid and terephthalic acid, the crystallinity was 11%. For the other adhesive (denoted B), also a low molecular weight adhesive (Mw=25,541 g/mol), but being based on hexanediol and butanediol, next to adipic acid and terephthalic acid, the crystallinity was 15%. In an alternative embodiment of the adhesive A, sebacic acid was used instead of adipic acid. This adhesive had a crystallinity of 14%. In another embodiment wherein as the alcohol component a mixture of ethanediol and hexanediol was reacted with terephthalic acid, the crystallinity arrived at was 26%. By varying the starting components and or relative amounts used, adequate adhesive could be obtained having a crystallinity between 5-35%, all having a low melt viscosity of about 5-55 Pa.Math.s at 150 C. (established using a method as described under example 2).

Example 2

[0057] The viscosity of a polymer adhesive is measured by using a cone and plate viscometer (Brookfield CAP 2000+, available from Brookfield Ametek, Middleboro, Mass., USA) with a 24 mm diameter spindle and a cone angle of 1.8 degrees (Brookfield Cap 2000+ spindle #4). Samples are heated to 150 C. At 150 C. the spindle is lowered on the sample. The sample is measured at 21 rpm for 30 seconds. The viscosity is determined automatically by the viscometer's default algorithm. For the two adhesives (A and B) indicated here above under Example 1, the viscosities are 6.3 Pa.Math.s and 27.1 Pa.Math.s at 150 C. respectively. For the alternative adhesives mentioned in Example 1, viz. the adhesives having a crystallinity of 26% and 14%, the viscosity established this way was 28.2 Pa.Math.s and 24 Pa.Math.s respectively.

Example 3

[0058] Example 3 describes how to determine the melting point of a high molecular weight polyester. The determination is based on ASTM standard D3418 (Standard Test Method for Transition Temperatures and Enthalpies of Fusion and Crystallization of Polymers by Differential Scanning calorimetry) using a Mettler Toledo DSC 821e differential scanning calorimeter. For the actual measurement a polyester sample of 10 mg is placed in a sample cup. After this, the sample is cooled to 50 C. and then heated to 300 C. at a speed of 5 C./min. The sample is kept at 300 C. for 1 minute and thereafter directly cooled to 25 C. at a speed of 5 C./min. From the obtained DSC plot the melting point can be read off.

Example 4

[0059] This example describes a test to assess the usability of a recycled polyester material. This test shows that a recycled polyester material obtainable with a method according to the invention has a practical use as a polymer yarn, despite the fact that the new material intrinsically differs in properties from virgin yarn-like polyester because of the mixing in of a low molecular weight polyester material. The new material is made using an extrusion process, homogenising both polyester materials and forming a new material.

[0060] Three of such new polyester materials were prepared at room temperature by mixing a standard high molecular weight virgin polyethylene terephthalate resin (D04-300 obtained from Cumapol, Netherlands, having an intrinsic viscosity iV of 0.8 dL/g, being a copolymer based on 2% isophthalic acid) with a low molecular weight polyester adhesive (Uralac CP9250 SH XP obtained from DSM, Netherlands, having a crystallinity of 21%, a viscosity of 40-45 Pa.Math.s at 150 C., and an Mw of 29,900 g/mol) in three different proportions, viz. 5% adhesive (sample BS), 10% (sample CS), and 15% (sample DS) adhesive (the other amount being polyester yarn material to arrive at 100%). The reference A and the three polyester blends BS-DS were then dried for 40 hrs. at 80 C. Then, the prepared polyester mixtures were added via a hopper equipped with a screw operating at a speed of 60 rpm to a single screw extruder (Leistritz, screw size 34 mm, screw speed 120 rpm) operating at 290 C. in all 9 zones with a total residence time of the molten material of ca. 2 minutes. The resulting polymer melt string was cooled down in a water bath (room temperature) and, subsequently, the cooled polymer string was pelletized.

[0061] The reference A and the three polyester blends BS-DS were subjected to spinning to produce partially oriented yarn consisting of 48 filaments and drawing to obtain draw textured yarn. Prior to the spinning and drawing experiments the reference A and the three polyester blends BS-DS were dried in an oven at 60 C. for 10 hrs. The reference A and the three polyester blends BS-DS were subjected to spinning to produce partially oriented yarn using an in-home spinning machine. The extruder was equipped with a spin pomp (16 rpm) operating at 260 C. to ensure continuous feed to the spinneret. At the spinneret the polymer melt was split into 48 filaments, after which the filaments were cooled down over ca. 3 m height, and bundled to form a polyester yarn. The obtained polyester yarn was wound using 3 rolls operating at different speeds. In total, for each of the reference A and the polyester blends BS-DS, 2 spools of yarn were prepared. The spools of yarn obtained were then subjected to drawing to produce draw textured yarn by using an in-home drawing machine. Drawing is carried out by stretching the polyester yarn in two steps between three sets of rollers (draw rollers) operating at different speeds. Textured yarn could be produced this way for each of the materials, including the reference material A and each of the polyester blends BS-DS.

Example 5

[0062] Example 5 describes the extrusion of various types of low molecular weight polyester adhesive in combination with a high molecular weight polyester resin.

[0063] Dry-blends of high molecular weight virgin polyethylene terephthalate resin (Invista T49H with a melting temperature of about 260 C., having an intrinsic viscosity of 0.85 dL/g) with three types of low molecular weight polyester adhesives were prepared. Type I of the low molecular weight polyester adhesive is a mixture of type Ia with a melting temperature of about 60 C., a viscosity of 1.2 Pa.Math.s and a crystallinity of 72% and type Ib with a melting temperature of 58 C., a viscosity of 2.2 Pa.Math.s and a crystallinity of 60%.

[0064] Type II of the low molecular weight polyester adhesive is a mixture of type IIa with a melting temperature of about 55 C., a viscosity of 51.4 Pa.Math.s and a crystallinity of 37% and type IIb with a melting temperature of about 55 C., a viscosity of 57 Pa.Math.s and a crystallinity of 36%.

[0065] Type III of the low molecular weight polyester adhesive has a melting temperature of about 120 C., a viscosity of about 30 Pa.Math.s and a crystallinity of about 21%. The adhesive resin materials were cryo-milled (and dried) before application in the extrusion process. All three types of adhesive were mixed in at a weight ratio of 10% (w/w).

[0066] The extrusion was performed in a 45 mm single screw extruder (Collin E45P, 31D screw length and 8-10 kg/hr throughput) operating at a temperature of 270 C. Whereas the extrusion of the composition with type Ill adhesive runs fairly continuous yielding a regular polymer strand which is stable and rarely breaks, the extrusion of the composition with type I adhesive is not continuous, showing a significant drop in die pressure and providing frequent strand breakage. Also extrusion of the composition with type II adhesive was less continuous showing a small drop in die pressure and providing more strand breakage compared to the composition with type III adhesive.

Example 6

[0067] Example 6 describes the extrusion of various amounts of low molecular weight polyester adhesive in combination with a high molecular weight polyester resin.

[0068] Dry-blends of high molecular weight virgin polyethylene terephthalate resin (Invista T49H with a melting temperature of about 260 C., having an intrinsic viscosity of 0.85 dL/g) with low molecular weight polyester adhesive were prepared. The low molecular weight polyester adhesive was mixed in at weight ratios of 1, 10, 25 and 30% (w/w) (or wt %).

[0069] The low molecular weight polyester adhesive has a melting temperature of about 120 C., a viscosity of about 30 Pa.Math.s and a crystallinity of about 21%.

[0070] The adhesive resin materials were cryo-milled (and dried) before application in the extrusion process.

[0071] The extrusion was performed in a 45 mm single screw extruder (Collin E45P, 31D screw length and 8-10 kg/hr throughput) and operated at a temperature of 270 C. Whereas it was possible to draw strands after extrusion of the compositions with 1, 10 and 25% (w/w) adhesive, the extrusion of the composition with 30% (w/w) adhesive resulted in often occurring strand breakage, thus hampering the drawing of regular strands.