Investigation on the Flammability and Washing Durability of Trevira CS and Its Blends with Cotton, Modal, and Acrylic Fabrics

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Introduction
Te majority of fame retardant treatments, formulations, and additives were discovered between 1950 and 1980 [1,2], and those of contemporary commercial interest have just lately been examined [3]. Since then, growing concerns about the toxicological and environmental consequences of using such chemical species on textile substrates with high specifc surface areas and close contact with the skin have created a barrier to new chemistry development and application. As a result, in the last 20 years or so, in response to these concerns and the perceived need for improved fame retardant performance at a reasonable cost, both research scientists and industry have considered improving the effciency of currently used retardants, replacing those where concerns exist with other existing formulations or repurposing known chemistry in novel ways [1].
Innovative fashion and technology have developed smart and integrated wearable textiles with multidimensional values in areas such as sports, fashion, defense, healthcare and safety, entertainment, and industry in the twenty-frst century. Technical advancements, on the other hand, have had a signifcant impact on the realm of wearable materials and textiles thus far. Tey are not only better than natural or synthetic fbres in terms of functionality, but they also outperform them in a variety of new and growing textile industries [4].
Smart textiles can be divided into two main groups: (i) aesthetic enhancing type: refers to the textiles that scattered and shined appearance with color changing and (ii) performance enhancing type [4]. One of the most appropriate functional aspects of smart textiles is fame retardant fnish, which delivers high-performance characteristics to textiles. As a result, new technologies, products, and materials have been developed in the feld of fame retardancy to address the difculties and needs of the contemporary period [4,5].
Textiles are common materials in our everyday lives, and they have been extensively employed in both homes and industry [6][7][8][9].
Natural polymers such as wool, silk, and cellulose, as well as synthetic polymeric units such as nylon, polyester, and polypropylene, and semi-synthetics such as rayon, have been used to produce textile substrates, which are ubiquitous in our daily lives. Tese materials are used to make high-value home appliances (apparel and typical interior products such as upholstered furniture, curtains, carpets, and bedding). Most of these items are very fammable and combustible, necessitating the desired demand for the quality and safety of textile materials, with the goal of preventing fres and loss of life. In this case, fame retardant chemicals must be utilized. Floor coverings, upholstery, drapery, home, and the aviation industry, for example, utilize fame retardant treatments to protect textile substrates against fre, which is required by fremen and emergency workers. Te most important criteria for a commercially acceptable fame retardant are little or no bad efects on the physiological and aesthetic qualities of textile materials, simplicity of application, and durability against harsh washing, cleaning, and drying cycles [4,5].
Flame retardants provide an important source of enhancing the material protection. Safety and protection of human lives and valuable are strong factors in the consumption of fame retardant (FR) and fame retardant textiles [10,11].
Textiles are now one of the most common product categories in which fame retardants are used. Garments, protective wear, children's clothing, work wear, mobile technology, and furniture are all examples of essential textile-based products. To obtain desired efectiveness in textiles and pass any standard requirement, fame retardants are necessary [10].
Due to its exceptional characteristics, cotton fabrics have been extensively applied in both military and civilian applications [12][13][14]. Te drawbacks and limits of cellulose fbers in the development of high-performance freprotective textile products include their low thermal stability, simple ignition, and rapid combustion [15].
To achieve fre resistance, textile materials are typically treated with fre-resistant resistant chemicals. Inorganic salts (e.g., aluminum or magnesium hydroxides), organohalogens (e.g., chloroparafns, bromobiphenyl ether, and bromobis-phenols), and formaldehyde-based compounds, for example, are all efcient fame retardants [4,[15][16]. Te use of halogenated and formaldehyde-based fame retardant compounds has been outlawed due to their severe toxicity. As a result, various halogen-and formaldehyde-free alternatives, such as polyphosphates, organic phosphates, and nitrogenous-based agents, have been commercialized [15][16][17]. Because of their PN synergistic impact and valued uses, nitrogen and phosphorus-based compounds are far more attractive in this aspect [18].
Compositions based on aluminum trihydrate (ATH), antimony oxides, bromine, chlorine, organophosphorus (for example, tetrakis (hydroxymethyl) phosphonium salt, and alkyl-substituted, and N-methylolphosphonopropionamide), and others are being employed as major fame retardants. Bromine-based fame retardants were largely used, although there are serious environmental issues about the chemicals emitted [10,19].
Several studies on organo phosphorus fame retardants or fame retardants (FRs) in broad, include analyses of phosphorus compounds' mechanisms [20][21][22]. Fire inhibition, heat reduction, surface change by phosphoric acidcontaining containing compounds, and char formation are all efects of phosphorus-based FRs in both the condensed phase and the fame [23][24][25]. According to the scientifc research, phosphorus is mostly retained in the char, which shields the primary material from heat and fame [26,27]. Also, it is recognized that compounds containing other fame retardant components improve the efciency of phosphorus. When phosphorus is mixed with silica gel [28] or nitrogen [29,30], the resulting combinations increase the fammability and/or thermal stability of treated fabrics, as well as diminish exothermicity.
To address the challenge and needs of ever-changing safety regulations, numerous new substituted technologies, fnishing agents, and active materials are being developed with current fame retarding materials. It is a multidisciplinary project involving a variety of scientifc and engineering instruments.
However, in this study an attempt were made to develop fame retardant fabrics and their aspects to sensitization and durability against several washing cycles. Te efects of washing cycles on the limited oxygen values were studied and discussed.
Having this in mind, this investigation presents the development and characterization of fame-retardant apparel. Te fame-retardant apparel has to provide a minimum degree of comfort to the wearer besides exhibiting essential fame-retardancy characteristics, and it is a thought of blending Trevira CS with other commodity fbres, such as cotton, modal, and acrylic. As cotton and modal fbres are well-known for their comfort and aesthetic properties and extensively used in apparel and innerwear, these are blended in certain proportions with Trevira CS fbres to produce yarns and knitted fabrics for exploring the feasibility of development of fame-retardant apparel. It is believed that when Trevira CS fbres are blended with cellulosic fbres, the former with the high heat of combustion supports the cellulosic fbres, which have a relatively lower heat of combustion and thus the pyrolysis of cellulosic fbres is enhanced.
Te characteristics of pure Trevira CS yarns, blended yarns, and of the resultant fabrics are investigated and assessed to suggest a suitable type of yarn and fabric composition for the economic production of fameretardant apparel. A study is also undertaken to improve the fame-retardant properties of fabrics produced from the blends mentioned above, through application of a durable fame-retardant fnish Pekofam DPN, popularly used for cellulosic and their blended materials. Te characteristics of the pure Trevira CS and blended fabrics are investigated and assessed to suggest the suitable type of fabric for the production of fame-retardant garments for various applications.
In this study, a product named pekofam is applied in Trevira CS and its blend with cotton, modal, and acrylic fabrics in the form of fame retardant fnish. Te fame retardant treatment carried out with a phosphorus-based compound, i.e., the Pekofam DPN. Phosphorus-based fame retardants act mainly in the solid phase of burning polymeric materials and cause the polymer to char, thus inhibiting the pyrolysis process necessary to feed the fames.
Te purpose of this research work is to explore the fame retardant action of Trevira CS and its blends. Te fame retardant characteristics of pure Trevira CS fabrics, Trevira/ cotton, Trevira/acrylic, and Trevira/modal fabric blends in specifc proportions were investigated and assessed. Te efect of consequent washing on the performance of fame retardant fabric will be studied and compared. Te suitable type of yarn and fabric composition for the economic production of fame-retardant apparel for diferent applications were suggested and revealed.

Materials.
Trevira CS fame retardant fbres are procured from Rajasthan Spinning and Weaving Mills Ltd. Also, cotton (DCH 32), modal and acrylic fbres were collected from nearby spinning mills to produce Trevira blended yarns.

Chemicals.
Te Trevira/cotton knitted fabric sample was scoured with NaOH and then bleached with H 2 O 2 . Te pure Trevira, Trevira/modal and Trevira/acrylic knitted fabric samples are given fnishing treatment with Pekofam DPN. Phosphoric acid as a catalyst was used. Detergent used to wash the sample fabrics.

Equipment/Apparatus and Machineries.
Te laboratory model G 5/1 ring-frame is used to produce ring-spun yarn. Te laboratory model fabric analysis knitter is used for knitting of the yarn samples. Apparatus required for LOI test are test chimney, test specimen holder, gas supplier, gas measurement and control devices, timing device, soot, fumes, and heat-extraction system. A padding mangle is used for uniform distribution of Pekofam DPN fnish. An oven is used for curing of the Pekofam DPN fnished sample fabrics.

Preparation of Yarn Samples.
Te yarn samples of 30 Ne are spun from pure Trevira CS fbres and from its blends with other fbres. Te 30 Ne pure Trevira yarns are spun on ring spinning systems. Te 30 Ne ring-spun yarns from blends of Trevira/cotton (80/20), Trevira/scrylic (80/20), and Trevira/modal (80/20) are produced. Te ring yarns are spun on a laboratory model G 5/1 ring-frame. Ring-spun yarns are produced to investigate the infuence of all these yarn structures on the fammability of fabrics produced from them. Te yarn spinning plan and the process parameters used are given in Table 1.

Determination of Flammability of Yarns.
Te fammability of yarn samples is determined using an in-house test method, wherein a yarn specimen of 300 mm is held vertically in a stand with suitable clamps. Te fame is applied at the bottom of the specimen for a period of 2 seconds and then withdrawn. Te length of specimen melts/burnt is recorded. At least 10 readings are taken to compute the average melt/burnt length for each sample. Te test is carried out in a controlled draught-free condition. Four samples of single jersey fabrics were produced using a 24-gauge cylinder with a positive feeder.

Determination of Flame-Resistance of Knitted Fabric
Samples. Te fame-resistant characteristics of conditioned knitted fabric samples are determined using the vertical fame test (Method A) as described in the IS: 11871-standard. Te fame-resistance of fabric samples, in an inclined confguration, is determined using the procedure described in ASTM D 1230 method. Te fammability of all the samples is also measured using a limiting oxygen index method as per the procedure described in IS: 13501 method (1992). Te details of these test methods are described as follows.

Vertical Strip Test.
A conditioned, strip of fabric sample is suspended vertically and ignited at the base by fame impinging on both sides in a standard manner. After igniting the specimen for a specifc period of time, the char length, after-fame, and afterglow characteristics are noted.

Journal of Chemistry
Te test specimen is 315 mm long × 50 mm wide. Six specimens, three in course direction and three in wales direction, are prepared.

Inclined Strip Test.
A conditioned strip of fabric sample is kept at an angle of 45°and ignited at the base by fame impinging on both sides in a standard manner. After igniting the specimen for a specifc period of time, the char length, after-fame, and after-glow characteristics are noted.
Te test specimens are about 150 mm in length × 50 mm length. Six such fabric samples, three in course direction and three in wales direction are prepared.

Limiting Oxygen Index Method.
A small test specimen is supported vertically in a mixture of oxygen and nitrogen fowing upwards through a transparent chimney. Te upper end of the specimen is ignited. Te minimum concentration of oxygen and nitrogen fowing upward in a test chimney that will just support combustion is measured under equilibrium conditions of burning. Te equilibrium is established by the relation between the heat generated from the combustion of the specimen and the heat lost to the surroundings as measured by one or the other two arbitrary criteria, namely, the period for which the burning continues, or the length of the specimen burnt. Tis point is approached from both sides of the critical oxygen concentration in order to establish the oxygen index.
A specimen of length 140 ± 5 mm × 52 ± 0.5 mm is used. It is ensured that the specimens are clean and free from faws. Te edges of the specimen are relatively smooth and free from fur or bur of material left from the machining.
Te fame is applied for up to 30 seconds, removing it for every 5 seconds for just sufcient time to observe whether or not the entire top surface of the specimen is burning. Te oxygen concentration used as the volume percent is recorded. Te limiting oxygen index (LOI) is determined by using the following equation: where O 2 � the volumetric fow of oxygen in cm 3 /sec. Te knitted sample fabrics were fnished by treatment with 400 gpl Pekofam DPN using the material-to-liquor ratio of 1 : 20. 20 gpl of phosphoric acid was used as a catalyst.
Pekofam DPN, a widely available FR agent, was utilized in this study to provide fabrics a long-lasting fame-retardant fnish. DPN Pekofam Trivera CS and its blends with cotton, modal, and acrylic are permanently fame-retardant fnished with Pekofam ® DPN, an organic phosphorus compound.
Depending on the cross linker system, it ofers great wash resistance. It has a low yellowing rate and meets Oko-tex Class IV specifcations.
A fame retardant reagent often works in one of two ways: either by reducing the amount of energy lost during burning or by raising the amount of energy required for the fber to reach the burning stage. A basic strategy for reducing the amount of energy lost during the pyrolysis process is to manage the burning process such that fewer combustible products are produced, hence reducing the amount of heat lost during the burning process [41]. Tis is also how the organic phosphorousbased freproofng material known as Pekofam DPN functions.

Washing.
Te fnished sample is given for 10, 20, and 30 consequent washes. Te amount of material used for each consequent wash is 0.5 m. Te washing method is carried out using detergent at a temperature of 40°C for 20 minutes.

Flammability of Yarns.
Te fammability values of yarns are given in Table 2  Tis shows that the Trevira yarns has fame retardancy property as compared to others. Table 3 that there is no discernible diference between the fame-resistance characteristics of fabric samples A and B as their melt-lengths values (in fabric state) are the same. Te fabric produced from T/M (80 : 20) blended yarn has fammability characteristics that are similar to those exhibited by the fabrics produced from pure Trevira-spun yarns. Te fabric C produced from T/C (80 : 20) yarns performed worst in regard to their fame-resistance as the entire test length of the fabric was burnt. (Table 4), all the fabrics, especially A, B, and D are rated as Class I as regards their fame-resistance and hence it can be concluded that these fabrics can be readily used to produce fame-retardant apparels. Furthermore, as per the test results, the fabrics C may not qualify to produce fameretardant apparel.

Characteristics of Gray, Finished and Washed Knitted
Fabric Samples. Te important constructional parameters and the LOI values of all the four types of knitted fabrics in gray, fnished, and washed states are given in Table 6. It can be observed from Table 6 that the constructional particulars of all the fabrics vary from gray through fnished to afterwashed states. Overall, there is an increase in the areal density of fabrics caused due to a general increase in the CPI and WPI in all cases caused by the chemical treatments, which clearly indicate certain shrinkage in the fabrics. Furthermore, it is clearly noticeable that there is an almost 10% increase in the areal density of gray fabrics due to application of fame-retardant fnish, Pekofam DPN.
It is clear from Table 6 and Figure 3 that in a gray state, amongst all the four fabrics (F 1 , F 6 , F 11 , and F 16 ), F 1 produced from pure Trevira-spun yarn exhibits the highest LOI of 40, followed by F 16 , F 11 , and F 6 in the decreasing order. Te fame retardancy of F 1 is considered to be very good, that of F 16 is medium, and those of F 11 and F 6 are below the minimum range (indicated by the red line in Figure 2) as required by a standard fame-retardant textile material.
Upon imparting the wash resistant, fame-retardant fnish Pekofam DPN, it is observed that the LOI of all the four treated samples (F 2 , F 7 , F 12 , and F 17 ) is signifcantly increased with the result that F 2 , F 7 , and F 12 exhibit a very high LOI in the range of 49-50, while F 17 has a value of 45. Tis clearly shows that the Pekofam DPN has a great efect in improving the fame retardancy of cellulose and its blended fabrics, and Pekofam DPN may not have a similar efect on other fbrous materials like Acrylic, which is depicted in Figure 4. Te phosphorous  Journal of Chemistry compound present in Pekofam DPN, after pyrolysis takes away the heat supplied to the fbre by external means and chars, thereby forming a barrier to the propagation of fame caused by the combustible substances. Te fame retardancy of all the four fabrics F 2 , F 7 , F 12 , and F 17 is rated to be very good.
Furthermore, Table 6 reveals that upon washing (after 10 washes), the LOI values of the fabrics F 3 , F 8 , F 13 , and F 18 , have been considerably reduced, however, no appreciable reduction in fame retardancy is noticed upon further washing of fabrics, viz. F 4 , F 9 , F 14 , and F 19 after 20 washes and F 5 , F 10 , F 15 , and F 20 after 30 washes, respectively. Tese efects can be clearly seen in Figures 5-7. Even after 30 washes the fame retardancy of fabrics F 5 , F 10 , and F 15 is very good and that of the fabric F 20 is good.
Overall, it can be stated that the pure Trevira-spun knitted fabric exhibits very good fame retardancy in gray state and hence may not require any fame-retardant fnishing treatment. Te knitted fabrics produced from   Tables 7-10, and the efect of washing cycles on fameretardancy performance were discussed. From Table 7 and Figure 8, it was observed that in the pure Trevira CS fabrics, amongst all the fve fabrics (S 1 , S 2 , S 3 , S 4, and S 5 ), S 2 produced from pure Trevira fnished exhibits the highest LOI of 50, followed by S 3 , S 4 , S 5 , and S 1 in the decreasing order. Te pure Trevira in a gray state showed very good LOI value and also when it was treated with Pekofam DPN fnishes the LOI value increased to 50. Upon     imparting washing resistant, fame-retardant fnish Pekofam DPN, it is revealed that the LOI of all the four treated samples (S 2 , S 3 , S 4 , and S 5 ) is signifcantly increased with the result that S 2 , S 3 , S 4 , and S 5 exhibit a very high LOI value. Tis clearly shows that the Pekofam DPN has a great efect in improving the fame retardancy of Trevira and its blended fabrics. Upon washing (after 10 wash), the LOI value showed a considerable reduction but still the LOI value is very good. Even after 20 wash the LOI value is similar to that of the after 10 wash. Tis indicates that after 20 wash the fame resistance of fabrics has not been changed or afected. Even upon after 30 wash the fame-resistancy of the fabric has not shown an appreciable reduction and the LOI value is still very good.
In Table 8 and Figure 9, it can be observed amongst all the fve T/C (80 : 20) fabrics (S 6, S 7, S 8, S 9 , and S 10 ) that the S 7 produced from Trevira/cotton blend (80 : 20) shows the highest LOI value of 50 followed by S 8, S 9, S 10 , and S 6 in the decreasing order. Te fame retardancy of S 7, S 8, S 9 , and S 10 is considered to be very good, while that of S 6 are below the minimum range (indicated by the red line in Figure 9) as required by a standard fame-retardant textile material.

Journal of Chemistry
Upon imparting wash resistant, fame-retardant fnish Pekofam DPN, it was observed that the LOI of all the four treated samples (S 7 , S 8 , S 9 , and S 10 ) is signifcantly increased with the result that S 7 , S 8 , S 9 , and S 10 exhibit a very high LOI in the range of 41-50. It was revealed that upon wash (after 10 wash), the LOI values of the fabric S 3 showed a signifcant reduction; however, no appreciable reduction in fame retardancy is noticed upon further washing of fabrics S 9 after 20 washes and S 10 after 30 washes, respectively.
From Table 9 and Figure         Journal of Chemistry and S 11 in the decreasing order. Te fame retardancy of S 12 , S 13 , S 14 , and S 15 is considered to be very good, while that of S 11 are below the minimum range (indicated by the red line in Figure 10) as required by a standard fame-retardant textile material. Upon imparting wash resistant, fame-retardant fnish Pekofam DPN, it was observed that the LOI of all the four treated samples (S 12 , S 13 , S 14 , and S 15 ) is signifcantly increased with the result that S 12 , S 13 , S 14 , and S 15 exhibit a very high LOI in the range of 40-49. It was revealed that upon wash (after 10 wash) the LOI values of the fabric S 13 showed a considerable reduction, however, no appreciable reduction in fame retardancy is noticed upon further washing of fabrics S 14 after 20 washes and S 15 after 30 washes, respectively.
From Table 10 and Figure 11, it was observed amongst all the fve T/A (80 : 20) fabrics (S 16, S 17, S 18, S 19 , and S 20 ) that the S 17, produced from Trevira/Acrylic (80 : 20) blend exhibited the highest LOI value of 45 followed by S 18, S 19 , S 20 , and S 16 in the decreasing order. Te fame retardancy of S 17 is considered to be very good, that of S 18, S 19 , and S 20 are good, and that of S 16 is medium.
Upon imparting wash resistant and fame-retardant fnish Pekofam DPN, it was observed that the LOI of all the four treated samples (S 12, S 13, S 14 , and S 15 ) is signifcantly increased with the result that S 12, S 13, S 14 , and S 15 exhibit a very high LOI in the range of 40-49. It was revealed that upon wash (after 10 wash) the LOI values of the fabric S 13 showed a considerable reduction, however, no appreciable reduction in fame retardancy is noticed upon further washing of fabrics S 14 after 20 washes and S 15 after 30 washes, respectively.

Conclusions
Te following conclusions are drawn from the present work: the fabric produced from 30 Ne Trevira/modal (80 : 20) ringspun yarn shows an LOI value of 26, which is above the minimum LOI value of 25 required for the production of comfortable fame-retardant apparel. Te fabrics produced from Trevira/cotton (80 : 20) yarns show very low LOI values and hence they are not suitable for production of comfortable fame-retardant apparel.
Te constructional particulars of all the knitted fabrics studied vary from gray through fnished to after-washed states. Overall, there is an increase in the areal density of fabrics caused due to a general increase in the CPI and WPI in all cases caused by the chemical treatments, which clearly indicate certain shrinkage in the fabrics. Furthermore, there is an almost 10% increase in the areal density of gray fabrics due to application of fame-retardant fnish, Pekofam DPN.
In gray state, amongst all the four fabrics (F 1 , F 6 , F 11 , and F 16 ), F 1 produced from pure Trevira-spun yarn exhibits the highest LOI of 40, followed by F 16 , F 11 , and F 6 in the

S11
S12 S13 S14 S15 Fabric Code S16 S17 S18 S19 S20 Fabric Code Trevira/Acrylic Blends decreasing order. Te fame retardancy of F 1 is considered to be very good, that of F 16 is medium, and those of F 11 and F 6 are below the minimum range required by a standard fameretardant textile material. Upon treatment with wash resistant FR fnish Pekofam DPN, the LOI of all the four samples (F 2 , F 7 , F 12 , and F 17 ) is signifcantly increased with the result that F 2 , F 7 , and F 12 exhibit a very high LOI in the range of 49-50, while F 17 has a value of 45. Te Pekofam DPN has a great efect in improving the fame retardancy of cellulose and its blended fabrics, and a slightly inferior efect on other fbrous materials like acrylic. It is found that after 10 washes, there is a considerable reduction in the LOI values of all the treated fabrics; however, no appreciable reduction in fame retardancy is noticed upon further washing of fabrics. Nevertheless, even after 30 washes the fame retardancy of fabrics F 5 , F 10 , and F 15 is very good and that of the fabric F 20 is good.
Overall, it can be stated that the pure Trevira-spun knitted fabric exhibits very good fame retardancy in gray state and hence may not require any fame-retardant fnishing treatment. Te knitted fabrics produced from T/C (80 : 20) and T/M (80 : 20) yarns are not at all suitable for fame-retardant application in gray state, however, upon application of the wash resistant, fame-retardant fnish Pekofam DPN, their LOI values exceeded beyond 40 and even after 30 washes, they show very good fame-retardancy efect. Te T/A (80 : 20) knitted fabric has medium fame retardancy in its virgin form, upon fame-retardant fnishing its LOI is increased beyond 40 and upon continuous washing it still registers a good fame-retardancy efect.
From the above-given theory, one can conclude that Trevira CS fbres can be successfully used to produce fame-retardant apparel, knitwear, sweaters, drapes, curtains, cover, and bed fabrics. Te comfort of Trevira CS products may be enhanced through blending Trevira CS with a small proportion of cotton fbres (10-20%), modal fbres (10-20%), and acrylic fbres (10-20%) without sacrifcing the fame-retardant characteristics. Tis results in economic production of fame-retardant apparel from Trevira CS and its selected blends in small proportions. Finally, the knitted fabrics from pure Trevira-spun yarns and the FR treated T/C (80 : 20), T/M (80 : 20), and T/A (80 : 20) ones qualify very well for the production of fameretardant garments for various applications in diferent forms.

Data Availability
Te data used to support the fndings of this study are available from the corresponding author upon request.

Conflicts of Interest
Te authors declare that there are no conficts of interest.