Core Spun Yarn Comprising Short Cellulosic Staple Fibers and Polymeric Fibers and Process for Its Production

This application is related to and claims priority to European application EP24171756 filed 22 Apr. 2024 and entitled A core spun yarn comprising short cellulosic staple fibers and polymeric fibers and process for its production, the contents of which are hereby incorporated by reference as if set forth in their entirety.

The present invention relates to the field of yarn production and to fabrics in general. In greater detail, the present invention relates to a yarn using short cellulosic, e.g. cotton, staple fibers typically obtained from recycling of yarns and fabrics, wherein the yarn is suitable for workwear garments and for medical garments.

Due to the costs and to the environmental impact of natural fibers production, methods have been developed to recycle natural fibers from textile waste, in order to re-use them. A prominent example is recycling cotton from waste textiles, in particular fabrics and yarns waste, in order to obtain recycled cotton fibers.

Known recycling processes for fabrics and yarns generally include mechanically breaking down the textiles into loose fibers that can be used for spinning new yarns. In this process, machines are used that break down the fabric e.g. by means of rotating drums with metal pins. The mechanical strain on the fibers in the yarns causes the breakage of at least part of original fibres into shorter fibres.

A problem with recycled cotton fibers is that their content of short length fibers makes them unsuitable or badly suitable for yarn manufacturing, in particular in ring spinning machines, that is commonly used for denim production. Virgin cotton staple fibers have a greater amount of long fibers than recycled cotton fibers; e.g. the average length L(n) (considering all of the fibers of a yarn) of virgin cotton is usually greater than 20 mm, while recycled staple cotton fibers have an average length L(n) that is usually below 15 mm, usually between 6 and 15 mm, more commonly between 9-12 mm.

It is thus difficult to properly use the recycled (short) cotton fibers in yarn production by ring spinning.

Also, work-wear and medical garments are subject to frequent washing cycles, that usually involves temperatures and/or chemicals that are more aggressive than home washing cycles. Yarns made from recycled cotton usually are not able to withstand a high number of industrial washing cycles.

The short length of cotton fibers typically results in a yarn having a too low strength, resulting in a poor fabric, or may not even be workable into a yarn due to the breakages of the combined fibers occurring in the yarn manufacturing machines. For this reason, recycled cotton fibers have been mixed with virgin cotton fibers to impart to the final yarn acceptable mechanical properties and physical characteristics, such as the bulkiness and appearance, of yarns containing 100% virgin natural fiber, e.g. virgin cotton. The ratio of the amount of virgin cotton fibers (CO) to recycled cotton fibers (RCO) by weight in a yarn depends from the yarn production technique. Typically, open end yarns may comprise up to 100% recycled cotton, while in ring spun yarns RCO content does not exceed 40% (by weight) and generally the ratio (by weight) CO/RCO is in the range of 70/30 to 90/10.

It has also been proposed to reduce the amount of cotton in yarns with the use of polyester filaments and fibers in the yarn composition. In an embodiment polyester staple fibers are mixed with cotton fibers before being spun into a yarn; these yarns have the drawback that due to the presence of polyester they have a poor look, i.e. a non-cotton look.

US20150176160 discloses a fabric provided with core-spun yarns, having a draw textured yarn core and a cotton staple fibers sheath. JP362028426A discloses a polyolefin resin composition. EP3701840A1 discloses a method for recycling short cotton fibers residues.

Core-spun yarns having a core including polyester filaments are also known; the use of recycled cotton in core-spun yarns is usually disadvantageous as, during production, the sheath of recycled cotton tend to break and to slip with respect to the core.

There is thus the need to solve the problems of the prior art and to provide a yarn in which cotton fibers are present in good quantity, all the cotton fibers are recycled fibers, the yarn is a ring spun yarn and has a good look and good to excellent mechanical characteristics, in particular the yarn is suitable for workwear and medical garments.

An aim of the present invention is thus to provide a yarn in which all the cotton fibers are recycled, short length, cotton fibers and that has good to excellent mechanical properties and the look and aspect of a yarn obtained from virgin cotton fibers.

Another aim of the invention is to provide a yarn reaching the above mentioned scope, that is easily woven in a fabric that can withstand repeated washings in hard conditions and that is suitable for work-wear garments and for medical fabrics and medical garments.

Another aim of the invention is to provide a core spun yarn containing short length cotton fibers that is elastic and stretchable.

Said aims are reached by means of the present invention according to one or more of the enclosed claims.

In particular, the present invention relates to a yarn and a relevant production method according to the enclosed independent claims, while preferred aspects are recited in the dependent claims.

The wording “blend of fibers” in the present description is used to identify a mixture of different fibers that is suitable to be used in a ring spinning process to provide the sheath of a core spun yarn. Single fibers in the sheath of the invention yarn can be identified and physically removed from the blend forming the sheath to be tested if required.

For the present invention, the term “virgin fiber” indicates cotton staple fibers deriving from cotton that has a high average length of the fibers e.g. because it has not been recycled from yarns and fabrics.

For the present invention the term “natural cellulosic fibers” indicates fibers obtained from plants. Preferred natural cellulosic fibers are fibers as obtained or as obtainable from the recycling process of fabrics and fibers coming from plants such as cotton, hemp, linen and so on. Typically, natural cellulosic fibers used in the invention are recycled fibers, having count similar to each other.

The term “recycled cotton fibers” in the following description indicates staple fibers of cotton deriving from the mechanical treatments, e.g. opening and sorting, of yarns and fabrics; a possible way to identify these fibers is by measuring their average fiber length. In embodiments, the fiber average length L(n), as measured with DIN 53805:1980-06, is in the range of 6 to 16 mm.

The term “synthetic fiber” indicates artificial fibers, in particular fibers made from polymers synthesized from chemical compounds—see definition in ASTM D123, option (1) of “manufactured fiber”. Synthetic fibers are thus are polymeric non-cellulosic fibers. Synthetic fibers are usually produced in filament (i.e. continuous) form. Synthetic staple fibers are commercially available and can be obtained by cutting the synthetic filaments. Preferred synthetic staple fibers are selected from polyester and polyamide, preferably they are polyester fibers.

In preferred embodiments the polyester for the staple fibers is a selected from a semi-dull, dull or full-dull polyester; these polyester are known and commercially available, e.g. they contain TiOto make the filament dull. In preferred embodiments the polyester filaments for the staple fibers are not texturized.

According to the invention the yarn is a core spun yarn having a core comprising or consisting of polyester filaments. The total linear density of the polyester filaments is in the range of 20 to 300 denier. The number of filaments is in the range of 6 to 288, while the total count for the final yarn is in the range of 5/1 to 60/1 Ne.

In preferred embodiments, the ratio by weight of the polyester filaments to the total weight of the yarn is in the range of 30% to 70%, preferably 40% to 60%.

According to the invention, a yarn comprises a filament core and a staple fiber sheath. The fiber sheath is made of first and second fibers. The first fibers are natural cellulosic fibers, preferably cotton staple fibers having an average length in the range of 6 to 16 mm, even more preferably about 10 mm. These are the typical average lengths of recycled cotton fibers.

The second fibers are synthetic fibers, i.e. polymeric, non-cellulosic fibers. In preferred embodiments, the second fibers are made from polyester or polyamide.

The preferred average length for the second fibers is greater than average length of the first fibers, preferably the length is in the range between 25 mm and 40 mm, more preferably between 28 mm and 36 mm. High quality yarns have been achieved in particular with second fibers around 32 mm, such as in the range between 30 and 34 mm.

At least 95% of the fibers of the sheath are the above-mentioned first and second fibers, wherein the weight ratio of the first fiber to the second fibers is between 65/35 by weight to 35/65 by weight, preferably said ratio being in the range 40/60 by weight to 60/40 by weight.

In a preferred embodiment the first fibers are about 50% by weight of the blend and the second fibers are 50% by weight of the blend.

The blend of the fiber sheath as well as the presence of one or more polyester filaments in the core provides for the claimed fibers and filament to be workable into a yarn that is, in turn, workable into a fabric that has excellent properties on the market. In particular, the resulting yarn can be ring spun, that is a process that was previously not possible to perform in yarn having a high percentage of short fibers, such as recycled cotton fibers.

The elongation at break of the polyester filaments of the filament core is between 5% and 15%, preferably between 5% and 12%, even more preferably between 10 and 12%, when tested with DIN ISO 2062.

The claimed elongation at break is the elongation of all the filaments of the core, tested together.

In particular, it has been found that if the elongation of the core is low (i.e. less than 15% measured by DIN ISO 2062 as above discussed), the yarn production and the weaving processes are easier and much more efficient. In particular, in these embodiments the elongation of the core is usually similar to the elongation of the sheath.

In fact, if the final yarn is tensioned, a high elongation (i.e. more than 15% or more than 20%) polyester core may cause slippage of the sheath from the core and cause a breakage in the staple fiber sheath while the core filaments do not break.

The use of low elongation polyester filament(s) in the core contributes in avoiding the above-mentioned problems; indeed when a yarn according to the invention breaks, there is no or very limited slippage of the sheath with respect to the core because the core filaments also are broken. The broken yarn can thus be spliced in a conventional way.

Low elongation polyester filaments are known in the art and are commercially available. They may be obtained in different ways. A possible solution may be to provide a draft during a texturing step of POY polyester filaments. Such a draft is preferably between 1.7 and 2.5, more preferably between 1.8 and 2.1.

The polyester filaments are in fact preferably textured and, as mentioned, draft can be applied during texturing process, usually by also heating the filaments during the drafting step in the texturing process.

According to an aspect, the amount of the polyester filaments of the core is between 30% and 70% of the weight of the yarn, more preferably between 40% and 60%. The above percentage relates to the total count of polyester filaments, i.e. to the total sum of the count of the filaments.

According to an aspect, the total count of the polyester filaments is between 50 and 300 den, more preferably between 80 and 200 den, even more preferably between 100 and 150 den.

As mentioned, the second fibers of the sheath have an average length that is greater than the average length of the first fibers. Generally, the average length of the second fibers is more than 200% than the average length of the first fibers, preferably more than 250% of the length of the first fibers. In other words, the ratio of average length of the second fibers to the average length of the first fibers is preferably greater than 2.0, preferably greater than 2.5.

The fiber length can be measured via suitable machines such as Uster Afis Pro 2 or TexTechno FCS-Fibro test, with methods know in the art such as, AFIS (advanced fiber information system) according to DIN 53805:1980-06, or ASTM D1447.

In order to detect the fiber nature and measure the fiber length of the first and second fibers in the sheath of a finished yarn, the sheath should be initially separated from the core and de-structured into a plurality of fibers. This can be done e.g. via un-twisting the yarn (i.e. applying a twist opposite to the one of the yarn, such as S-twisting a Z-twisted yarn). This can be done manually or by a twisting machine. Subsequently, the fibers length can be tested e.g. via DIN 53805 or ASTM D1447, via an USTER AFIS PRO 2 or a Textechno FCS-Fibrotest. In a histogram of the fibers the amount of short fibers can be detected; similarly synthetic staple fibers generally always have substantially a same length so that they can be seen in histograms

It is also noted that, in the sheath, the first fibers can be separated from the second fibers via known chemical or biological methods. As an example, to isolate the natural cellulosic fibers, known methods can be used to dissolve the synthetic fibers, while leaving substantially intact the first fibers, in particular when the first fibers are cotton fibers and the second fibers are polyester or polyamide fibers.

Similarly, it is possible to isolate the synthetic fibers from the natural cellulosic fibers, e.g. via known enzymatic processes that degrade the cellulose, usually transforming it into glucose.

Fibers may be also manually separated to be tested.

Properties, such as the length, of the first fibers or the second fibers can thus be tested.

Preferably, in order to provide a better interaction between the first fibers and the second fibers of the sheath, the length of the second fibers is not too much greater than the length of the first fibers. A preferred ratio L(n)/L(n)between the average length L(n) of the second fibers versus the average length L(n) of the first fibers is between 1.5 and 3.8, more preferably between 2 and 3.5. The best results have been found to occur when the above discussed ratio is between 2.5 and 3.3.

The yarn according to one or more of the preceding aspects can be used to produce a fabric, in particular a woven fabric and a garment comprising such a woven fabric. It is in particular possible to produce a fabric wherein yarns according to the invention are used both in warp and weft direction.

It has been found that such a fabric, and in particular a garment made from such a fabric, can be made without using virgin (i.e. conventional) cotton, while having similar wearability properties (hand, softness, etc.) as well as optical properties (brightness, dyeability, etc.) with respect to a fabric made from conventional cotton yarns. Also, compared with fabrics made from conventional cotton yarns, the fabric according to the present invention shows similar mechanical properties, such as similar tensile strength, as well as better abrasion properties. Thus, a fabric made of yarns according to the invention can be effectively used in the production of apparels in the field of workwear and medical industry garments.