Patent Application
20240181119
The present invention relates to a method for recycling polyester based nonwoven comprising 5 to 50% of sheath/core or side by side or others PET and/or coPET low melt fibers into new fibers.
Polyethylene terephthalate, commonly abbreviated PET, is the most common thermoplastic polymer resin of the polyester family and is used in fibres or yarn for clothing or nonwovens, containers for liquids and foods, and thermoforming for manufacturing, and in combination with glass fibre for engineering resins.
It is known to recycle PET food containers, mainly bottles into pellets, flakes or chips to manufacture fibers for use in nonwoven materials. PET bottles being made in virtually pure PET homopolymer, the properties of the fibers obtained after recycling are only slightly modified compared to virgin PET fibers, which make them easy to use further.
This is not the case for other sources of PET. In particular, in the nonwoven industry, PET homopolymer is associated with PET copolymers (coPET), either as a mix of fibers, or even as a mix within a single fiber, in a core-sheath association. For example, thermobonded drylaid nonwovens contain 5 to 60% of low melt PET/coPET fibers as binder. A single article, for example hygiene articles, further combines several different layers of nonwovens.
The ratio between the PET/coPET being variable, the outcome of a product obtained from recycling nonwoven waste has therefore variable/unpredictable properties, and usually a lower viscosity and a lower melting temperature than virgin (not recycled) material.
Nonetheless, the applicant wishes to address the problem of recycling nonwoven waste, which can be of two types: post-industrial waste or post-consumer waste. Post-industrial waste originates mostly from the nonwoven production process or the processes to include nonwoven in further article. Post-consumer waste designates purified, cleaned or washed waste from the end-consumer. To reduce to a maximum the ecological impact of the recycling of nonwoven, it is wished to reach circularity, i.e. recycling into new fibers to make nonwovens, preferably onsite or with limited transport.
To this end, the invention concerns a method for recycling polyester based nonwovens comprising 5 to 60% of PET/CoPET low melt staple fibers comprising the steps of:
The polyester flakes can be “virgin” polyester flakes (or chips) but, preferably, the polyester flakes originate from recycled (post industrial) PET bottles.
PET/coPET preferably refers to a mixture of PET and coPET, i.e. a mixture of PET homopolymer and copolymer, either as a mix of fibers, or even as a mix within a single fiber, in a core-sheath association, as explained above.
Polyester intends to designate any kind of polyester and derivates (PBT, PTT . . . ), i.e. aliphatic homopolyesters or copolyesters as well as aromatic homopolyesters or copolyesters, or mixtures thereof, whatever the sources of polyesters, including recycled polyester and polyester from said green sources.
The polyester based nonwovens to be recycled can come in various form, depending on their origins. They can be for example pressed baled shredded nonwoven, over pressed baled nonwoven trims, non-pressed trims or off-spec rolls.
Low melt staple fibers (LMF) designate fibers having at least a sheath component melting at low temperature (i.e. melting temperature of around 180° C. or less, preferably melting temperature of around less, preferably 160° ° C. or melting temperature of around 130° C. or less and still preferably melting temperature of around 110° C. or less), and which serve as binder for other fibers having higher melting points, in the nonwoven manufacturing process. Low melt staple fibers usually have a titer of 1 dn to 30 dn but can also have a larger titer. LMF usually have a core/sheath construction, but this is not mandatory.
The polyester staple fibers (PSF) obtained by the method of the invention are regular PSF, with titers varying from 0.5 dn to 40 dn, preferably 1.5 dn to 15 dn. These PSF contain between 0.75 and 17.5% of PET and/or coPET (originating from the recycled nonwoven). Preferably, these PSF fibers have a melting point above 180° C., preferably above 200° C., still preferably above 240° C. and possibly between 245° C. and 255° C.
The polyester staple fibers obtained by the method of the invention, i.e. comprising at least 0.75% of PET and/or CoPET originating from recycled nonwovens, can be distinguished from regular polyester staple fibers by a lower intrinsic viscosity of below 0.7 dl/g, preferably between 0.6 and 0.7 dl/g, like for example between 0.65 and 0.70 dl/g for white fibers, while it could be lower for black fibers, like for example around 0.62 dl/g.
Advantageously, the polyester staple fibers (PSF) obtained by the method of the invention are further used to produce nonwovens, preferably 100% polyester-based-nonwovens, and still preferably, 100% polyester based staple fibers nonwovens. So, a further step of the method of the invention can be:
Further steps can read:
It is to be noted that staple fibers differ from filament fiber. Filaments are long continuous fibers, obtained using spinnerets, via extrusion, while staple fibers are shorter fibers, with length in the mm or cm range.
Depending on the application, the weight percentage of PSF obtained by the method of the invention in a nonwoven can vary between 5% and 100% of the nonwoven, preferably between 10% and 98%, preferably between 15% and 95%. For example, nonwoven for mattress applications typically comprises about 15% of low melt staple fibers and can comprise up to 85% of PSF, while nonwoven for hygienic applications like acquisition and distribution layers (ADL) in baby diapers typically comprise about 50% of LMF and can comprise up to around 50% of PSF.
The invention also encompasses a nonwoven material comprising 5 to 100% by weight of the PSF comprising at least 0.75% of PET and/or CoPET originating from recycled nonwovens, having an intrinsic viscosity (IV) of below 0.7 dl/g (limiting viscosity number measured as disclosed below), the nonwoven having an opacity comprised between 20% and 50% measured according to the method described below, preferably between 25% and 40%.
The invention also concerns absorbent articles incorporating nonwoven materials of the invention. The absorbent article comprises a topsheet forming a wearer-facing surface of the absorbent article, a backsheet and an absorbent core and/or an acquisition and distribution layer (ADL) interposed between the topsheet and the backsheet, wherein the absorbent article comprises a nonwoven material, said nonwoven material comprising between 5% and 100% by weight of PSF comprising at least 0.75% of PET and/or CoPET originating from recycled nonwovens, having an intrinsic viscosity (IV) of below 0.7 dl/g (limiting viscosity number measured as disclosed below).
Advantageously, the nonwoven in the absorbent article comprises at least 20% by weight core/sheath or side by side bicomponent fibers, as binder fibers. This is particularly interesting when the manufacturing process involve a heating step.
Any one or several layers of the absorbent article can be a nonwoven according to the invention. Preferably, the nonwoven is comprised at least in the ADL. The nonwoven can also be comprised in the core, as a monolayer, dual layer or triple layer within the core.
The method of the invention can include a step of mixing a coloring dye either before the repelletizing step or before the extrusion step.
The extrusion of the blend can lead to PSF having a solid cross-section or a hollow cross-section, with some void areas. They can have a cross section of any shape, like for example but not limitingly a circular cross section, a triangular cross section, a trilobal or multi-lobal cross section, . . . .
The PSF obtained preferably but not limitingly have a length of 20 mm or longer.
The invention will be better understood with the following description of several examples, referring to the accompanying drawing on which:
Referring to
Repelletising machines are well known in the art of plasturgy. The principle is that it melts the nonwoven waste to its liquid state in two phases. In a first a preconditioning phase, the polymer is demoisturized and the spinning oil is removed, then the liquid polymer is degazed and then the temperature is decreased while imparting a cylindrical or spherical shape to the polymer in order to form polyester granules or pellets 3.
The intrinsic viscosity (IV) value of the obtained granules are typically lower than normal PET flake resin, because of the presence of significant percentages of LMF.
Typical IV values found will be around 0.49 to 0.60 dl/g, while IV values of PET flakes from bottles is around 0.70 to 0.75 dl/g.
The IV required for spinning staple fibers is between 0.65 and 0.70 dl/g for white fibers, while it could be lower for black fibers, like for example around 0.62 dl/g.
A possibility to increase the IV known in the art would be to add a further SSP (solid state polymerization) step after the repelletising, but this would increase significantly the cost price of the process. The method of the invention is therefore preferably devoid a SSP step.
The melting temperature is an alternative characterizing value of the polymer. While normal PET has a melting temperature of around between 260 and 265° C., the pellets 3 have a melting temperature of several degrees lower, i.e. between 253 and 258° C., so on average 7ºC lower for the recycled material compared to the regular material.
Several repelletising machine manufacturers exist, like Erema, Starlinger, Moogetech, . . . there is no limitation here whatsoever for using a specific machinery technology.
Because the pellets 3 have an intrinsic viscosity slightly too low to be directly extruded into staple fibers, in a step B, the pellets 3 blended with polyester flakes 4, coming from recycled PET bottle. The blend comprises 15 to 35% of recycled polyester-based pellets 3 and 65 to 85% of polyester flakes 4.
The ratio of pellets 3 versus flakes 4 is preferably adjusted after measuring the IV and/or the melting temperature of the pellets 3. The higher this temperature or IV, the larger percentage of pellets can be added into the blend.
The blend is for example made in an Oerlikon Barmag mixer, or Neumag equipment, or any suitable equipment known to the person skilled in the art.
In a step C, the blend enters an extrusion unit 5 where it is extruded into polyester staple fibers (PSF). The extrusion step is classical of textile fiber production and well known to the person skilled in the art, and can be for example a two steps production method, also known as long spin method, or a single step production method, also known as short spin method.
The ratio in the blend, determined in function of the characteristics of the pellets has some impact on the characteristics of the final PSF, i.e. the tenacity, elongation, shrinkage levels, . . . of the fibers. It is important for the subsequent process of integration of the PSF into nonwoven that the PSF issued of the method of the invention fall within a PSF type 10 “virgin” (not incorporating recycled materials) Technical Datasheet.
Examples of technical characteristics obtained for virgin fibers compared to recycled fibers are given in Table 1 below.
Intrinsic Viscosity (IV) here refers to the limiting viscosity number (LVN, intrinsic viscosity, I.V., [n]) of polyesters based on polyethylene terephthalate (PET) in form of fibres, granulates, regranulates, preforms, foils, flakes, black, white and colour masterbatches (can be based on PBT), in a Viscosity meter Ubbelohde U 1a connected to an Automatic Lauda equipment to measure flow times of the sample solution and solvent, using the following procedure:
The mixture used for measurement is made of phenol (CAS: 108-95-2) and 1,1,2,2-tetrachloroethane (CAS: 79-34-5), using the weight ratio 1:3.
Phenol is distilled with an air cooler and the fraction at 182° C. is collected.
1,1,2,2-tetrachloroethane is distilled with an air cooler at ca. 140° C. Concentrated solution of soda (ca. 20 ml per 1 litre) is added to the distillation receiver in the flask. The fraction with the boiling point 144-145° C. is collected.
The polyester samples shall be completely dry. Remove any finish from the polyester fibre sample by thorough washing in distilled water and then dry it completely. Black masterbatch is milled before weighing.
Weigh out 0.2500 g of the sample, place it into the flask and add 25 ml of the solvent from the burette; let the sample dissolve in the drying oven at 105° C. (maximally 2 hours, for fiber sample 30 minutes should be enough). Agitate the flask content every 5 minutes. After visually checking that the sample has been dissolved wait 10 more minutes. After the solution cools down use a sintered glass S2 to filter it into the viscosity meter; use the first part of the filtrate to flush the viscosity meter. Suspend the viscosity meter filled with the sample solution in a thermostat bath and after 10 minutes of heating at 30° C. measure the flow time of the solution 4 times. Before measuring the sample measure the flow time of the pure solvent first (average from 3 measurements, temperation 10 minutes, 30° C.). Perform Hagenbach kinetic energy correction of the measured times for the solution and for the pure solvent:
t=tm−B/A·tm
Calculate the limiting viscosity number from the relative viscosity at the concentration
c=1 g/100 ml using the Huggins equation. The Huggins constant for PET under the given measuring conditions is k=0.25.
The limiting viscosity number (LVN) in ml·g−1 is then calculated using the following formula (which applies only to the employed experimental condition) with:
The Lauda viscosity meter with a connected computer performs all computations automatically, including measurement of the flow times and corrections. The laboratory worker only reads the LVN value.
Melt flow rate (MFR) was measured according to the ASTM D1238, ISO 1133 standard method.
The melting point was measured according by DSC, as usually done in the field, using for example a stabilization phase at 25° C. followed by a temperature ramp of 16.00° C./min up to 300° C.
The titer was measured using a VIBROSKOP instrument made by Lenzing Instruments. Individual fibres with a defined pretension are placed into the device that performs automatic measurements using the vibration principle. Twenty individual fibres are measured and the resulting value is their average.
The tensile strength (tenacity) and elongation were measured using a VIBRODYN instrument made by Lenzing Instruments. Individual fibres are fixed into tearing jaws and exposed to mechanical stress at a defined speed and clamping length. A defined force pulls the fibre until it breaks. The resulting elongation percentage at the moment it breaks is calculated as well as the total force applied to the titer ratio. Twenty individual fibres are measured and the resulting value is their average.
The shrinkage was measured in hot air at a temperature of 160° C. for 30 minutes. Shrinkage is defined as difference in length before and after fibre fixing in percents. 5 tows of 50 cm long are measured.
The nr of crimps/inch was measured using a standardized meter at a defined pretension. Individual fibres are fixed to a measuring base plate and the number of crimps is read visually. Twenty individual fibres are measured and the resulting value is their average.
The colour values was measured on a reflex spectrophotometer DT600 made by Datacolor. The measurement uses especially prepared samples and an accurately defined setup of the device at different types and wavelengths of light. The reflection principle is used to determine basic color coordinates (L, a, b). Three samples are measured and the resulting value is their average. Fibers are combed and arranged in a layer which is inserted in the spectrophotometer for read-out. The basic color coordinates (L, a, b) are extracted from the read-out.
It was generally observed that the color values of the PSF obtained by the method of the invention are slightly darker and have a stronger yellow component than “virgin” fibers.
The PSF obtained by the method of the invention can be incorporated in any kind of nonwoven, just as “virgin” fibers.
For example, a polyester based thermobonded drylaid nonwoven can be manufactured using 50% of PSF fibers obtained by the recycling method of the invention and 50% of Low Melt Fibers for incorporation as ADL (absorption and distribution layer) in a hygiene article.
For example, a polyester based thermobonded drylaid nonwoven can be manufactured using 50% of PSF fibers obtained by the recycling method of the invention, 35% of standard PSF and 15% of Low Melt Fibers for fiberfill applications.
Test 1—Thermobonded Nonwoven Material for Use in Bedding/Quilting/Furniture Applications.
A thermobonded nonwoven material according to the invention was manufactured for use in bedding 1 quilting/furniture applications.
Referring to
Carding is a mechanical process that disentangles, cleans and intermixes fibres to produce a continuous web suitable for subsequent processing. This is achieved by passing the fibers between differentially moving surfaces covered with card clothing. It breaks up locks and unorganized clumps of fibers and then aligns the individual fibers to be parallel with each other. The fibers not being straight elements, they are not strictly parallel, but globally orientated in a common general direction. The fact that the fibers are not straight elements enables some contact points between fibers, these contact points being the bonding points during the bonding step.
Depending on the thickness and/or weight expected for the nonwoven material, several layers of carded fibers, of a same or of different compositions, can be overlaid before bonding, using techniques and equipment well known to a person skilled in the art. Using several carding machines in parallel, usually up to three, allows to work at high speed. The resulting webs are then overlapped before webbonding, which can be mechanical bonding, thermobonding and/or chemical bonding. This also presents the advantage of being able to combine the different properties of several fiber blends.
In this inline configuration, the overall thickness of the nonwoven depends on the thickness of the web issued from each carding machine and of the number of carding machines operating in parallel. In general, no more than three parallel carding machines are used, limiting the weight of the resulting nonwoven to about 200 g/m2, preferably 120 g/m2, though these figures are not limiting. Moreover, the general orientation conferred to the fibers in the carding step is maintained in the bonding step, resulting in a nonwoven having a high longitudinal resistance to tear, longitudinal meaning parallel to the general orientation of the fibers, and a lower lateral resistance to tear.
However, a crosslapping step can be implemented on one or several of the carding lines after carding, leading to overlapping several layers of web of carded fibers, and additionally imprinting a deviation in the general orientation of the fibers, which is different between two consecutive overlap. The crosslapping therefore results in a much thicker nonwoven material than when using the inline process, typically over 120 g/m2. The resulting nonwoven is also more resistance to tear in all directions.
The webs obtained from the three carding machines are then combined on top of each other into a three-way oven 24 in order to form a single thermobonded nonwoven 25.
An optional step of needling can be implemented downstream of carding and overlapping, before heating the overlapped webs, resulting in entangling or mixing up the fibers in the vertical dimension. This is especially recommended when more than one carding machine are used. The vertical dimension here refers to a direction perpendicular to the longitudinal and lateral dimensions disclosed in the previous paragraphs, i.e. a direction crossing the various layers of webs. Needling enables to obtain a better adhesion of the web layers, by entangling the fibers. Hydroentanglement could also be used instead of or additionally to needling. Needling and hydroentangling are techniques well known from the person skilled in the art. Other reinforcing techniques can also be used like, for example, chemical bonding, either by extrusion of a polymer, knife over roll or any suitable coating technique, as known to the person skilled in the art.
As a final step, after bonding, the nonwoven undergoes winding and packaging.
Bonding of the fibers to finalize the nonwoven layer is here performed by thermobonding, but it can also be performed using different techniques, like mechanical or chemical bonding. In the present case, bonding preferably includes a step of thermal bonding, either alone, or in combination with another technique. Preferably, the nonwoven of the invention is a drylaid thermobonded nonwoven. A combination of mechanical, chemical and thermo-bonding is also an option.
The blend of fibers provided to the second carding machine 22 is here a blend comprising:
The blend of fibers provided to the carding machines 20 and 23 is here a blend comprising:
The carding machines 22 and 23 provide webs counting each for 30% of the final product, while carding machine 20 provides a web counting for 40% of the final nonwoven. As a result, the final nonwoven comprises 44% of recycled PSF according to the invention. The obtained nonwoven has a weight per surface area of about 150 g/m2.
Four trials were made. A sample of the nonwoven for each trial has been characterized for their opacity using the following the ASTM method, and compared to the equivalent sample made from non recycled fibers (Thermoloft 21).
Opacity is determined by the reflectance obtained from the material with a black background, as well as the reflectance obtained for the same material with a white background. The equipment used are:
The apparatus is standardized according to manufacturer's instructions, using the white, black and green tiles provided in the Colorflex EZ Standard box.
The settings are adjusted to:
125×125 mm samples of nonwovens are cut and the test can be performed according to the following procedure:
Machine direction (MD) of the sample is in line with the device and the smooth side of the sample is facing down.
The standard method to measure opacity of nonwovens is given by EDANA NWSP.060.4.R0
The opacity is measured for 5 cuts of each sample and the averages are given below:
The same four samples have been characterized for their dynamic loading measured following the pounding test according to ISO 3385. The results are gathered in following table 2.
The same four samples have been characterized for their elongation and tensile strength both in the machine direction (MD) and carding direction (CD), measured following the test according to ISO 9073-3. The results are gathered in following table 3.
The results of table 2 and 3 demonstrate the equivalence between the reference nonwoven not including recycled fibers and the nonwoven according to the invention.
In a similar manner, nonwovens having a weight per surface area of about 300 g/m2 have been manufactures and compared to the equivalent Thermoloft 21 reference.
The results are gathered in Table 4 and 5.
The fibers obtained in examples 1 to 3 are used to prepare nonwovens for hygiene, and in particular for use as ADL and/or absorbing cores to be incorporated in absorbing articles. These nonwovens are compared to the standard product DW T161 AF manufactured by TWE for ADL. The specifications of this material are given in table 2 below along with the characteristics of the nonwovens obtained in tests 2 and 3.
In test 2, a blend of fibers was prepared using 50% of the fibers of example 3 of Table 1 with 50% of melting bico-fibers.
In test 3, a blend of fibers was prepared using 50% of the fibers of examples 1 and 2 (mixed) of Table 1 with 50% of melting bico-fibers.
The nonwovens were manufactured in a standard manner (i.e. using one, two or three carding machines and thermobonding, as for example illustrated on
The Physical characteristics of the obtained nonwovens were evaluated according to the Standard Edana procedures and are given in Table 6.
The absorbing characteristics of the nonwovens of tests 2 and 3 were also measured according to the standard Edana procedures, and are given in Table 7.
The characteristics given in table 6 and 7 have been measured according to the standard method given by Edana unless otherwise stated.
As can be observed from Table 6, the nonwovens made from recycled PFS have properties falling under the specification range for the equivalent nonwoven made from virgin fibers. The opacity in the same range and the tensile strength is above the average expected value.
The Tensile Strength is the maximum tensile stress expressed in force per unit cross sectional area of the unstrained specimen e.g. Newtons per square millimeter, as measure according to Edana standard 110.4.R0 (15).
The Thickness is measured while applying various pressures on the material, according to Edana assay WSP 120.6.R0 (15).
The Elongation was measured according to Edana assay WSP 110.4.R0 (15).
The opacity is measured according to the method described above.
The Strike Through Time is the time taken for a known volume of liquid (e.g. simulated urine) applied to the surface of a test piece of nonwoven coverstock, which is in contact with an underlying standard absorbent pad, to pass through the nonwoven. It was measured using EDANA assay WSP 70.3.R1 (19). the repeated strike through time was measured according to EDANA assay WSP 70.7.R1 (19).
The Wet Back Test intends to examine the ability of a diaper coverstock to resist the transport back onto the skin of a liquid that had already penetrated the coverstock. It was measured according to EDANA assay WSP 80.10R1 (19).
The wet back after repeated strike through (ST) was measured according to Edana assay WSP 70.8. R1 (19).
The Run Off quantifies the amount of liquid which runs down a nonwoven when a specified amount is poured onto the liquid at an angle. It is measured according to Edana assay WSP 080.9.R1 (19).
As can be observed from the results of tables 6 and 7, the ADL nonwovens incorporating recycled PSF meet the specifications set for the standard product. Some specifications are even exceed the performance of the reference material. In particular, the wet back and strike through properties are far below the maximum values allowed.
These are non limiting examples of fiber ratios, manufacturing technologies and applications for the fibers of the invention.
Nonwoven manufacturing technologies in which the PSF can be used are for example, but not limited to these:
| Number | Date | Country | Kind |
|---|---|---|---|
| 21166826.4 | Apr 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/058656 | 3/31/2022 | WO |
