Patent Application
20240263365
The present invention relates to a heat and flame retardant fabric as well as a method of making the same. The fabric comprises a cellulose-based cotton alternative having heat and flame retardant properties.
Numerous professions require individuals to risk exposure to extreme heat and/or flames. Typical examples are industrial workers, fire fighters, police and military personnel. Such personnel are, wherever possible, provided with appropriate flame-protective garments. These garments are distinctly different from normal, every-day-use garments as they are at least partly constructed from flame retardant textiles.
Said garments must pass minimum thermal performance requirements such as flame- and/or heat-retardance, resistance to molten metal, electric arc resistance, low percentage of (estimated) body burns in thermal manikin testing, limited after-flame time and high resilience against combustion, as well as protection against radiant heat.
In addition to specialist flame-protective garments, more general workwear is often required to have elevated flame resistance, which may be certified according to one or more standards. Other important performance requirements are tensile and tear strength, elongation at break, abrasion resistance, snagging resistance and resistance to penetration by water and liquid chemicals.
In addition it is considered important that the garment provides adequate comfort, for instance by allowing vapour to be transported away from the body and ensuring that the garment is not too stiff. Also the garment must be durable in the sense that the above disclosed parameters last at least for the intended or certified lifetime of the product. This may be defined by a number of wash cycles.
Furthermore the garment must be printable or dyeable with a durable result such that, for instance, the garment can be dyed to increase visibility. An often used standard for performance requirements for heat and flame retardant clothing made from flexible materials is ISO 11612.
A known treatment for rendering cellulosic fibres or textile articles comprising cellulosic fibres flame retardant is the Proban® treatment. This treatment comprises padding a textile article with an aqueous solution comprising tetrakishydroxyalkylphosphonium (THP) salt which is pre-reacted with urea and pH adjusted to 5-8.
THP does not react substantially with the cellulosic fibre, nor does it substantially react with the textile article comprising said fibre, but instead forms an enveloping network around and/or throughout the molecular structure of the cellulosic fibre. Hence the Proban® treatment is a non-cellulose-reactive treatment which means that there is substantially no chemical reaction between the THP and the cellulosic fibre. Alternative non-cellulose-reactive treatments to Proban and THP may achieve the same effects.
An alternative flame-retardant treatment is a treatment with a N-methylol phosphonate compound, such as N-methylol dialkyl phosphonopropionamide. Commercially such treatments are offered under the brands Pyrovatex® CP and Aflammit® KWB. In this case the flame-retardant compound is grafted onto the cellulose by a reaction on the C(6) hydroxyl group of the cellulose resulting in grafted protective phosphonopropionamide molecules on the outside of the cellulose fibre. This is therefore an example of a cellulose-reactive, phosphorous-comprising compound as there is a reaction between the cellulose and the phosphorous comprising compound. The Pyrovatex treatment thus has a fundamentally different chemistry and mechanism to the Proban process.
Pyrovatex and Proban were developed to make cotton flame retardant and have many associated problems for the resulting fabric. U.S. Pat. No. 3,816,068 A1 discloses a flame retardant for cellulose fabrics and describes disadvantages of the Pyrovatex process The disadvantages of Pyrovatex treated fabric include incompatibility with many other treatments and its tendency to hydrolyse over time. Pyrovatex treated products require washing at least once a year after production (regardless of use) to prevent hydrolysis and the unpleasant smells associated therewith. Typically, the degree of fire retardancy achieved is more limited than THP treatments and the process is only compatible with a maximum of 20% synthetic fibres. EP 0709518 A1 discloses a Proban treated cotton fabric. This document is directed to solving the problems of rigidity of Proban treated cotton.
Also existing are fibres that are inherently flame retardant by their nature and do not require treatment in order to achieve this retardancy. Such fibres, including para-aramid and meta-aramid fibres, PPS, PBO and PBI may be referred to as flame resistant fibres. Other flame resistant fibres that are inherently flame retardant include fibres that are extruded from a fibre spin dope to which flame retardant additives have been added before spinning e.g as a masterbatch. The resulting fibres include FR Lyocell, Modacrylic, FR polyester and FR polyamide FR. In the following, the term flame retardant (FR) is used to refer to fibres that are treated to render them flame retardant as opposed to those with inherent flame retardant properties.
An increasing concern in the field of clothing manufacture is the choice of environmentally friendly options. Although natural fibres such as cotton may be advantageous over synthetic fibres in some respects, cotton is known to be relatively high impact in terms of the requirements for its production, in particular, water usage. It would be desirable to provide cotton alternatives to at least partially replace cotton or other natural fibres in flame retardant clothing.
One cotton alternative made from responsibly-sourced wood-chip cellulose is lyocell. This is a material similar to rayon but without the disadvantages of the viscose process. It also has a considerably lower, water footprint than cotton, using up to 95% less water. As yet however, it has not been possible to adequately substitute lyocell for cotton where flame retardancy is required in combination with durability and other workwear requirements. In particular, the tendency of lyocell to fibrillate has been seen as a major drawback.
It would be desirable to provide an alternative to conventional FR cotton having a smaller environmental footprint that nevertheless satisfies at least certain quality requirements expected of protective clothing.
According to the invention, there is provided a flame retardant (FR) treated fabric, comprising yarns formed from a mixture of natural and/or synthetic fibres, the fabric further comprising FR treated lyocell fibres, wherein the FR treatment is a non-cellulose-reactive FR treatment and the FR treated lyocell fibres are rendered low-fibrillating. In the following, the term ‘lyocell’ is used to denote artificial, cellulose-based cotton alternatives. In particular, these may denote cellulosic fibre obtained by an organic solvent spinning process although the present invention may also be applicable to some cellulosic fibres obtained by the viscose process. Although lyocell such as the Tencell® product available from Lenzing AG is well known, other similar cellulose-based cotton alternatives are available and may be equally applicable. The lyocell may be present in the form of short staple fibres, long staple fibre or as filaments or ribbons. Furthermore, in this context, reference to natural and synthetic fibres is intended to exclude the lyocell fibres i.e. these are in addition to the lyocell. Depending on the properties required, any amount of lyocell may be present. In particular, from 1-99 wt % lyocell may be present, preferably from 10-70 wt %, more preferably from 15-50 wt % lyocell or from 20 to 35 wt % lyocell.
It is well known that lyocell is prone to fibrillation. It is also understood that lyocell has reduced tensile strength when it has absorbed water i.e. in the wet fabric state. As a result of investigation in the context of the present invention, it has also been revealed that the fibrillation is further exacerbated by carrying out THP type FR treatments. In the wet state, water can penetrate into the lyocell fibrillar bundles, causing exposure of fibrils at the fibre surface. The rate of fibrillation increases with increased pH and increased temperature as experienced during conventional FR treatments. Unlike cotton, lyocell does not naturally cross-link and it is therefore desirable to provide a finish that at least partially compensates for the increased fibrillation. For lyocell-like materials, is believed that fibrils are at least partially held together by hydrogen bonding between neighbouring fibrils. A reduction in the degree of hydrogen bonding e.g. in the presence of water or as a result of certain treatments can lead to increased fibrillation.
An anti-fibrillation finish can be performed on the fabric by application of suitable additives. Preferably the additive is a substance that reacts with the hydroxyl groups of the cellulose to stabilise the fibrils. This may be either by increasing the presence of hydrogen bonding or by the formation of covalent bonds, whereby improved cross-linking of the fibrils is achieved. Additives that cross-link by formation of covalent bonds to the hydroxyl groups of the cellulose material may be referred to as reactant resins, thermosetting resins or easy-care finishes. Reactant resins include ethylene urea formaldehyde, propylene urea formaldehyde, methylated uron formaldehyde and Dimethylol dihydroxyethyleneurea (DMDHEU) modified resin. The latter is a preferred choice. The skilled person will be well aware that alternatives and equivalents to the above may also be applied. In this context, low-fibrillating may be determined qualitatively, by the presence of cross-linking to the hydroxyl groups of the lyocell. Alternatively, it may be determined experimentally e.g. by the pilling, abrasion, colour retention or other tests defined below
In one embodiment, the natural fibres comprise FR cotton. The fabric may have the general feel of a cotton fabric whereby a portion of the cotton has been replaced by the lyocell alternative. Up to around 50% of the cotton may be replaced without significantly affecting the overall performance of the fabric. Nevertheless, the softness of the fabric increases significantly and is generally experienced as very comfortable in use. In general however, where cotton is replaced by lyocell, an amount of a stronger fibre such as a synthetic fibre may be required to offset the loss in certain properties or otherwise complement the lyocell. In particular, lyocell generally has slightly lower wet strength than cotton but is significantly reduced in strength after THP processing. Therefore polyester may be added to the fibre blend to compensate. It is however not excluded that other natural fibres may be present, such as linen, or wool in greater or lesser quantities.
In an embodiment, the synthetic fibres comprise polyester. Other synthetic fibres such as polyamides or aramids may also be contemplated and it is not excluded that additional small volumes of high-performance synthetic fibres may be included. In one embodiment, the synthetic fibres comprise recycled polyester. One preferred source of recycled polyester is Repreve® from Unifi Inc, which is a mechanically recycled polyester. Chemically recycled polyester may also be used. Recycled polyester has many appealing advantages such as having energy consumption reduction by 45% in comparison to virgin polyester; water consumption reduction nearly 20% in comparison to virgin polyester; and greenhouse gas emission reduction of over 30% in comparison to virgin polyester. Recycled polyester has excellent strength properties and adds durability, although it does not respond to many FR treatments. The synthetic fibres may be present in various forms including short staple fibres, long staple fibres and filaments.
It will be understood that various possible fabrics may be envisaged, including woven and knitted fabrics. A woven fabric is preferred. The woven fabric may have any appropriate construction, being formed from warp and weft yarns in a chosen weave or pattern. The yarns in both the warp and the weft may all be the same or may be different in terms of their composition, weight etc. Each yarn may be a spun yarn. A spun yarn is understood to comprise an intimate blend of the constituent fibres. A number of ends of yarns may be twisted together to form a ply. A ply may also be formed by twisting a spun fibre with one or more filaments.
In one embodiment, the lyocell fibres may be present in the warp yarns only. This has been found most suitable for the case that the lyocell has been adequately stabilised against fibrillation by the finishing process. In that case, the lyocell may be reinforced by the presence of synthetic fibres also blended into the warp yarn. In cases where the lyocell is still subject to fibrillation, it may be preferred to include it instead only in the weft yarns in order to decrease its exposure to the exterior of the fabric, e.g. in a twill weave.
In a particular embodiment, the warp yarns comprise lyocell fibres, synthetic fibres and natural fibres. The blend may thus be of lyocell, cotton and polyester staple fibres, which together make up at least 95% of the warp. In an embodiment, as much as 50% of the warp yarn may comprise lyocell with equal amounts of cotton and polyester accounting for the remainder. In one embodiment, they may preferably be present in the warp in a wt % ratio of around 50/25/25 respectively.
It has been observed that there are certain relations between the different characteristics of the fabric that lead to an optimised result. In particular, it may be noted that an increase in usage of lyocell requires a commensurate increase in the amount of stronger synthetic fibre required for compensating for loss in strength of the lyocell (especially after being subjected to FR treatment). The synthetic fibre is then present in the yarn direction corresponding to the increased lyocell. In the case of a synthetic fibre that is neither inherently FR nor FR treatable, the total amount of the synthetic fibre that can be introduced, will depend on the degree of FR treatment of the natural fibre and the lyocell. For reasons that are explained further below, a limited degree of FR treatment may be preferred in order to avoid excess fibrillation. As such, the overall amount of non-FR synthetic fibre that can be present in the mix may be limited. For this reason, the above 50/25/25 mix in the warp has been found rather suitable and obvious variants thereof will achieve the same advantageous effect.
However, when synthetic fibres are introduced in one direction, the fabric may become destabilised with respect to e.g. shrinkage. For this reason, a limited amount of synthetic fibres may also be required in the other weave direction e.g. a 90/10 cotton/polyester blend may be appropriate. An overall blend of around 50/30/20 cotton/lyocell/polyester may ensue. It will be noted that in general, a low amount of synthetic fibre may be preferred as its primary purpose is strength compensation and it negatively influences the degree of FR of the overall fabric. Nevertheless, amounts of synthetic fibre may be achieved which exceed the amount of synthetic fibre that is achievable for Pyrovatex type treatments.
In the case of polyester, up to 50 wt % polyester may be present in the overall fabric. For other fibres such as polyamide, up to 20 wt % may be present. Alternative fibre proportions that remain below the upper limits for compatibility with THP FR treatment, may be chosen depending on the end-use and also fall within the scope of the current application. For example, to provide desired strength to softness to colour retention ratios, or to contain greater amounts of green fibres.
In an embodiment, the weft yarn may comprise a preponderance of natural fibres, preferably between 70 wt % and 95 wt % of natural fibres, in particular cotton.
Any suitable weave construction may be contemplated and the skilled person will be well aware of the respective advantages of such weaves. In an embodiment, the fabric may be woven as a twill weave, preferably a 2/1 twill. Satin weaves may also be used, where it is desired to provide a particular drape or ensure that certain yarns are exclusively provided to one face or the other. The fabric may also be a double-cloth having distinct properties of the respective front and back cloths, a two faced fabric, or a fabric with two identical faces.
According to an important aspect of the invention, the fabric comprises an anti-fibrillation finish to prevent the lyocell from fibrillating. As noted above, lyocell does not naturally cross-link and it is therefore desirable to provide a finish that at least partially compensated for the increased fibrillation. Importantly, while the use of finished lyocell fibres is well known in preventing fibrillation, it has now been found that the non-fibrillating finish is detrimental to the application of the flame retardant treatment to the lyocell fibres. By using untreated lyocell fibres i.e. lyocell fibres that have not been provided with an anti-fibrillation treatment, an improved application of the FR treatment may be achieved. This has been found especially to be the case for the Proban type (THP) treatment. Without wishing to be bound by theory, it is believed that the presence of cross-linked resins such as formaldehyde prevents operation of the THP mechanism, which requires formation of an enveloping network around and/or throughout the molecular structure of the lyocell fibre.
According to the present invention, the anti-fibrillating resin finish may be applied subsequently to the FR treatment. It has however also been found that the FR treatment may itself have a subsequent negative effect on the anti-fibrillating finishing process. This is believed to be due to steric hindrance of the hydroxyl groups as a result of the THP treatment. According to an aspect of the invention the degree of FR treatment is kept to a minimum. In this context, the amount of phosphor in the final fabric may be kept to below 2.5 wt %, preferably below 2.4 wt % or even below 2.2 wt %. Values for Nitrogen also reflect the extent of the FR treatment and these may be kept below 1.7 wt % or below 1.6 wt % or even below 1.5 wt %. These values have still been found to ensure adequate FR compliance. Nevertheless, as mentioned above, the reduced degree of FR treatment limits the overall volume of the synthetic fibres that can be present in the blend—for the case that those synthetic fibres are non-FR.
In an embodiment, the fabric further comprises a water and/or oil repellent finish. Suitable finishes include conventional PFAS (perfluorinated alkylated substances) finishes such as PTFE, Teflon® and the like. Alternatively, the fabric of the current disclosure may also be made with a PFAS-free finish, thereby being further eco-friendly.
As mentioned above, the fabric may also include other fibres or yarns for specific technical purposes. For protective workwear, antistatic fibres may be included either as fibres in the blend or as separate antistatic yarns or filaments. In an embodiment, the fabric may comprise antistatic fibres or filaments in an amount of between 0.2 wt % and 3 wt %. In the case that antistatic staple filaments are used, an amount of as much as 5 wt % may be required, depending on whether the antistatic fibres are distributed or localised.
An exemplary fabric according to the invention may comprise in the warp:
The fabric is desirably durable to laundering at least 50x according to ISO
15797 without losing its required properties. These may include one or more of:
The non-cellulose-reactive treatment may be any suitable such treatment, preferably based on a THP salt such as the Proban® treatment.
The invention also relates to a method of producing a heat and flame retardant fabric comprising a mixture of natural and/or synthetic fibres and lyocell fibres having accessible hydroxyl groups, the method comprising first subjecting the fabric to a non-cellulose-reactive FR treatment and subsequently finishing the fabric by application of a resin to stabilise fibrillation of the lyocell.
In this context, the term ‘accessible hydroxyl groups’ is intended to refer to the fact that the lyocell fibres are not treated with an anti-fibrillation additive such as a cross-linking resin. According to the present invention, it has been shown that the presence of such additives prior to the FR treatment can reduce the efficacy of the treatment. For this reason, it is desirable that the FR treatment is carried out on fabric where the lyocell fibres provided in the yarns are not yet stabilised against fibrillation by a treatment that can occupy the hydroxyl groups.
Prior to the FR treatment, the fabric may be pre-treated by one or more of processes selected from the group: desizing, scouring, bleaching, mercerising, dying, including reactive and non-reactive dyes.
The fabric may be any suitable fabric, including a woven or a knitted fabric and the method may include first constructing the fabric from the individual yarns, prior to carrying out the FR treatment. In other words, the FR treatment is carried out on the fabric rather than being applied to the yarns themselves. Constructing the fabric may comprise weaving the yarns with a warp and a weft, preferably in a twill weave. In an embodiment the lyocell is present in the yarns in the warp direction only.
Finishing the fabric by application of a resin, may comprise the use of any appropriate chemistry for preventing fibrillation. Preferably the resin is a substance that reacts with the hydroxyl groups of the cellulose to stabilise the fibrils. Such resins may be referred to as reactant resins, thermosetting resins or easy-care finishes. Reactant resins include ethylene urea formaldehyde, propylene urea formaldehyde, methylated uron formaldehyde and Dimethylol dihydroxyethyleneurea (DMDHEU) modified resin. The latter is a preferred choice although equivalents and alternatives may equally be applied. The finishing step may be completed by cross-linking of the resin, e.g. by the application of heat.
Finishing may further comprise a water and/or oil repellent treatment, preferably provided in a separate step after the application of the resin to prevent fibrillation. Both treatments may be applied together although for existing treatments, it has been found that better effectivity is achieved by first performing the anti-fibrillation finish and subsequently applying the water/oil repellent finish. Heat treatment may take place for both treatments together but preferably, the anti-fibrillation resin is cross-linked by heat treatment prior to commencing the water/oil repellent finish.
Suitable oil and/or water repellent finishes include conventional PFAS (perfluorinated alkylated substances) finishes such as PTFE, Teflon® and the like. Alternatively, the fabric of the current disclosure may also be made with a PFAS-free finish, thereby being further eco-friendly
The invention also relates to a garment manufactured by a method as described above or hereinafter.
This combination of materials results in an eco-friendly fabric that is breathable, comfortable, durable (avoids fast fibrillation) and FR. The advantageous ranges of cotton provide both sustainability and breathability to the fabric.
Several materials are particularly appealing for consideration in an eco-friendly product. Recycled materials, sustainable materials and materials have a low water scarcity have less environmental impact.
Flame retardant (FR) is hereby defined in this application to mean flame- and/or heat-retardance conferred by a treatment to the filament, fibre, yarn or fabric. This may provide a fabric with low percentage of (estimated) body burns in thermal manikin testing, limited after-flame time and highly resilient against combustion, as well as protective against radiant heat, resistances to electric arcs and molten metal. For example as meet the performance requirements for flame retardant clothing made from flexible materials of ISO 11612.
By way of a non-limiting example, the below process steps from source to product are described.
The steps of an exemplary manufacturing process are described as follows.
The staple fibres which are formed into the yarns include cotton, Lyocell and recycled polyester. Cotton is a natural fibre that provides comfort and better moisture management than synthetic fibres. Cotton is the traditionally used fibre for FR-treated fabrics.
Lyocell is a synthetic cellulosic fibre. Other alternative cellulose based cotton alternatives exist such as Livaeco™, Birla Modal™, Birla Excel™, Birla Viscose™ and Birla Spunshades™ provided by Birla Cellulose. Lyocell is an industrial and launderable fibre which loses strength in the wet state. Lyocell in fact has a strength similar to cotton in the wet state and is more sustainable than cotton. Compared to cotton, the water usage of Lyocell is 95% less than of cotton. Lyocell is more comfortable than cotton with better moisture management and is generally smoother to the skin. It is however a fibrillating fibre; for example as in the wet state water penetrates inside the fibrillar bundles causing exposure of fibrils at the fibre surface. The rate of fibrillation increases with increased pH and increased temperature.
(Recycled) polyester can be mechanically or chemically recycled. Polyester is used in the FR-treated fabric to increase durability as it a relatively stronger material, however it is also heavier than cellulose based fabrics. Polyester cannot be made flame retardant with Proban chemistry. Mechanical recycled polyester can be used to improve sustainability. Use of recycled polyester provides an energy consumption reduction by 45% in comparison to use of virgin polyester, and has a water consumption reduction of nearly 20% in comparison to virgin polyester. The greenhouse gas emissions are reduced over 30% in comparison to virgin Polyester.
For the exemplary EG 9600 fabric, yarns were spun using the following staple fibres:
An exemplary formulation of the fabric yarns is:
The EC9600 fabric is woven in a 2/1 twill weave with the above warp and weft yarns. An anti-static yarn is included at a spacing of every 1:20 in the weft direction. The overall weight percentages of the respective fibres in the final fabric are:
After a single pass THP treatment, the fabric was measured to have the following flame retardant characteristic values:
Amount of THP is measured by P, N analysis with the following results:
Fabric is after FR-treatment still vulnerable to fibrillation. Finishing the fabric after FR-treatment with a suitable resin prevents fibrillation of lyocell in the product. The resin is applied in a foulard process and the application process includes water removal by pressing and heating, followed by thermal treatment for cross linking the resin. The term non-fibrillating as used herein will be understood to mean substantially non-fibrillating, and to be exchangeable with low-fibrillating. The application of a non-fibrillation resin provides a fabric having a reduced fibrillation compared to that in its virgin state.
A second finish is required to make the fabric water- and/or oil repellent finish through fluorocarbon resin (FC) to meet ISO 13034. The resin and the FC may be combined in one bath or, to improve the fibrillation and prevent loss of colour, the resin and FC finish may be applied after each other in a 2-step process. This 2-step process reduces the fibrillation after laundering. Further improvement is to cross-link the resin first before applying the FC finish.
Laundering according to the standard ISO 15797, 750C, j requirements is possible and results in reduced and homogeneous fibrillation. The fabric remains durable even up to 50 of the rigorous launders according ISO 15797, 750C, j.
The final product has the following advantages:
Three batches of the improved FR fabric were tested and the measured properties after the final finish are shown to be repeatable and in accordance with the technical specifications with details as follows:
The technical specifications of the fabric of the invention are comparable and commensurate with the standard FR fabric and an alternative inherently flame retardant fabric known as Modal/Tencel™ in terms of properties. The improved FR fabric of the invention further has improved comfort and reduced carbon footprint. Comparison of the technical specifications is as follows:
| Number | Date | Country | Kind |
|---|---|---|---|
| 2028484 | Jun 2021 | NL | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/066529 | 6/16/2022 | WO |
