Flame Retardancy Enhancement of Jute Fabric Using Chemical Treatment Izboljšanje ognjevarnosti jutne tkanine s kemično obdelavo

This work aims to improve the flame retardancy of jute fabric. Raw and bleached plain weave jute fabric was used in this work. Flame retardants borax, diammonium phosphate and thiourea were applied in different concentrations in a raw and bleached jute fabric with the padding method. The influences of flame retardant finishing on the vertical flammability behaviour and tensile properties as well as wash resistance were investigated. Flame spread time was found to significantly increase when these simple flame retardant finishing agents were used. It was found that the borax-treated raw and bleached specimens exhibited higher flame spread time among all. The assessment of physical properties such as weight gain percentage and breaking load along warp and weft direction of the control and treated fabrics revealed that the increase of flame retardant finishing weight gain caused a decrease in breaking load. Furthermore, the specimens treated with borax and diammonium phosphate flame retardant showed better results than thiourea for flame retardancy and wash durability. These flame retardant jute fabrics have industrial protective textile applications as brattice cloth in mines and many other potential fields of application, e.g. flame retardant kitchen apron, furnishings for public hall, theatre and hospital, etc.


Introduction
Jute is a lignocellulosic fibre with a different percentage of hemicellulose (22-24%), α-cellulose (58-60%) and lignin (12-14%) as the key constituents with other elements as well [1]. Despite jute being one of the most important biodegradable, eco-friendly, anti-statistic and annually renewable agro products, it is nowadays facing tough competition with synthetic fibres both home and abroad. Therefore, for the competitiveness of this environment friendly fibre, it is necessary to diversify its uses and develop new products for domestic and industrial purposes that can at least partially overcome the present unfavourable situation of jute [2][3][4][5]. In South Asia, jute is the most versatile natural fibre gifted to man by nature. At present, jute can be defined as an eco-friendly natural fibre with multipurpose application prospects ranging from low value geotextiles to high value products, e.g. fancy bags, carpets, home furnishings, composites, papers, particle boards, car components, fashion accessories and gift articles [6]. Apart from its conventional use as packaging material, jute fabrics are now extensively used in furnishing clothes and home textiles as this fibre has good spinnability [7][8][9][10]. Due to its versatility, jute is the second most important bast fibre after cotton. However, it ignites easily and is frequently involved in fire. Jute cellulose undergoes decomposition upon ignition, forming highly explosive volatile compounds, mainly laevoglucose with the spread of fire causing injuries and fatalities a) b) c) d)

Figure 1: Jute: a) plant, b) fibre, c) yarn and d) fabric
Flame Retardancy Enhancement of Jute Fabric Using Chemical Treatment in fire accidents [11,12]. Since consumers are now increasingly becoming aware of a safe lifestyle, expectations and demand for diversified value-added flame retardant jute products are steadily increasing. The flame retardant jute product demand is also on an increase due to its prolonged life cycle and boosted application for home textile and furnishing purposes [13]. Different chemical formulations have been reported for preparing flame retardant jute fabrics. It has been found that different inorganic salts, borax-boric acid composition, hydrated metal oxide like sodium silicate, different phosphorous and nitrogenous compounds and their combinations have been mostly used to make fire-retardant jute [12][13][14][15][16]. Studies also have been reported on the application of nitrogen and sulphur based thiourea on jute fabric, and their flame retardancy properties have been evaluated [17,18]. This study reports on the application of borax, diammonium phosphate and thiourea for developing flame retardant functionality on a jute fabric (cf. Figure 1). The thermal behaviour in terms of vertical flammability was investigated, and the weight gain and breaking load changes of the jute fabric were reported.

Materials
A raw and bleached plain weave jute fabric commonly known as a hessian cloth with mass per unit area of 241 g/m 2 was fabricated for this research. The fabric construction is shown in Table 1 and its breaking load is stated in Table 2. After the bleaching, fabric mass per unit area became 232 g/m 2 .

Bleaching process
The bleaching was conducted according to the exhaust method using an infrared lab dyeing machine (Xiamen Rapid, China) at 85 °C for 60 min. Then, the bleaching bath was cooled to 40 °C. Samples were washed at room temperature and neutralised with 0.5 g/L acetic acid for 10 min. The specimens were air-dried in a flat dryer machine (Mesdan, Italy). For both the bleaching and neutralising, the material to liquor ratio was 1 : 40. The recipe for bleaching the jute fabric is tabulated in Table 3.
where W 1 and W 2 indicate the oven-dry weight of the untreated and treated fabric samples, respectively.

Tensile strength
Warp and weft breaking strength of untreated and treated jute fabric samples was determined according to the EN ISO 13934-2 standard test method [19] by using a universal strength tester (Titan 3, James Heal, England). The sample size was 20 cm × 10 cm for the breaking strength measurement.

Vertical flammability test
Raw and chemical-treated bleached jute fabric samples with 30.48 cm × 7.62 cm (12 inch × 3 inch) in size were prepared and placed in a specimen holder for the measurement. Afterwards, the specimens were exposed to a standard flame at 90° angle for 12 s ± 0.2 s and left for burning. The flame spread time after the burning was measured in line with the ASTM D6413 standard test method [20].

Wash durability of fabrics
The wash durability of the chemical-treated samples (sample size 30.48 cm × 7.62 cm) was tested by washing the samples in a bowl taking 500 ml of water. Each wash cycle was performed for 30 min at 45 °C followed by drying at 80 °C for 10 min to simulate the Samsung auto (WF8500NHS) laundering machine. The flame spread time of fabrics was repeatedly measured after different wash cycles and the average value was reported.

Sampling
The samples are identified as stated in Table 3.     Figure 2). Regarding the bleached jute fabrics, the weight gain of samples followed in the order BB1 < BB2 < BB3 < BB4 after being treated with borax in a different amount of chemical loading, BD1 < BD2 < BD3 < BD4 for the samples treated with DAP and BU1 < BU2 < BU3 < BU4 for the samples treated with thiourea (cf. Figure 3). Due to the 2%, 6%, 8% and 12% borax concentration treatment of bleached jute fabric, the weight gain was by 1.45%, 1.63%, 4.03% and 6.08% higher for the samples BB1, BB2, BB3 and BB4. The weight gain was by 2.50%, 4.67%, 6.13% and 7.60% higher for the samples BD1, BD2, BD3 and BD4 compared to the bleached jute fabric. The weight gain showed a 0.80, 1.25%, 3.51% and 4.02% increase for the samples BU1, BU2, BU3 and BU4 compared to the bleached jute fabric (cf. Figure 3). The same results were observed for RB1 and BU1 at 2% chemical concentration, RB1 being the sample of raw jute fabric treated with borax and BU1 the sample of bleached jute fabric treated with thiourea (cf. Figures 2 and 3). At 2% chemical concentration, the weight gain was by 0.08%, 3.14% and 1.20% higher for the samples RB1, RD1 and RU1 compared to the raw jute fabric,  Figures 2 and 3). Finally, it was concluded that the weight gain percentage of raw and bleached jute fabrics increased together with increased chemical concentration. The highest value was observed at DAP treated samples.

Flammability properties
The provides a barrier between the material and the heat source. In the case of thiourea-treated jute fabric, at high temperatures, it enables the formation of stable molecular compounds that stop the decomposition process (pyrolysis) and prevent the release of flammable gases. It also releases inert nitrogen gases that inhibit the chain reaction leading to combustion. Regarding raw jute fabrics, the sample order was RB4 > RB3 > RB2 > RB1 after the treatment with borax in a different amount of chemical loading, RD4 > RD3 > RD2 > RD1 for the samples treated with DAP and RU4 > RU3 > RU2 > RU1 for the samples treated with thiourea (cf. Figure 4) Figure 4). Regarding bleached jute fabrics, the sample order was BB1 < BB2 < BB3 < BB4 after the treatment with borax in a different amount of chemical loading, BD1 < BD2 < BD3 < BD4 for the samples treated with DAP and BU1 < BU2 < BU3 < BU4 for the samples treated with thiourea (cf. Figure 5) Figures 4 and 5).
The flame retardancy of the jute fabric improved after the flame retardant finishing agent was applied. The concentrations of chemicals also had a beneficial effect on flame retardancy. The raw and bleached jute fabrics were shown to improve their flame retardant behaviour.

Breaking load
Raw and bleached jute fabrics were subjected to a treatment with three different flame retardant formulations under specific treatment conditions, and the changes of the breaking load of the treated samples were evaluated. The results of breaking load both in warp and weft direction are reported in Figures 6  and 7. Figures 6 and 7 show that both warp and weft direction breaking load values gradually decreased with the increase of loading percentage of chemicals in all formulations. It may be presumed that due to a mild acidic hydrolysis of jute cellulose, the breaking load falls. Regarding raw jute fabrics, the sample order of breaking load was RB1 > RB2 > RB3 > RB4 after being treated with borax in a different amount of chemical loading, RD1 > RD2 > RD3 > RD4 for the samples treated with DAP and RU1 > RU2 > RU3 > RU4 for the samples treated with thiourea in warp direction. A similar scenario was observed in weft direction (cf. Figure 6). After the raw jute fabric being treated with 2%, 6%, 8% and 12% borax , the breaking load was by 3.12%, 6 Figure 6). Regarding bleached jute fabrics, the sample order of breaking load was RB1 > RB2 = RB3 > RB4 after being treated with borax in a different amount of chemical loading, RD1 = RD2 > RD3 > RD4 for the samples treated with DAP and RU1 > RU2 = RU3 > RU4 for the samples treated with thiourea in warp direction. A regular decreasing scenario was observed in weft direction for all samples (cf. Figure 7). The breaking load was by 1.120%, 4.0%, 4.0% and 12.0% lower for the samples BB1, BB2, BB3 and BB4 in warp direction, and by 1.19%, 3.34%, 13.04% and 13.04% lower in weft direction after treating the bleached jute fabric with 2%, 6%, 8% and 12% concentration borax (cf. Figure  7).  Figure  7). Under the same amount of breaking load, there was a 4.0% decrease recorded for BB2, BB3, BD1 and BD2, and an 8.0% decrease for BU2 and BU3 in warp direction, and a 13.04% decrease for BB3, BB4, BD2, BD3, BU3 and BU4 in weft direction (cf. Figure 7). At 2% concentration of chemicals, the breaking load showed a 3.12%, 1.56% and 0.92% fall for the samples RB1, RD1 and RU1 in warp direction, and a 3.33%, 0.56% and 3.33 fall for the same samples in weft direction when compared to the raw jute fabric, and a 1.12%, 4.0% and 2.0% fall for the samples BB1, BD1 and BU1 in warp direction, and a 1.19%, 4.34% and 2.17% fall for the same samples in weft direction in comparison with the bleached jute fabric (cf. Figures  6 and 7). At 6% chemical concentration, the breaking load showed a 6.25%, 6 Figures  6 and 7). A lower breaking load in weft direction is responsible for a lower density of picks compared to the density of ends.

Wash durability
The washability of the chemical-treated samples after several wash cycles (1-5) was evaluated and the results are shown in Figure 8. After wash cycle 1, the treated samples experienced a slight decrease in flame spread time compared to the unwashed samples. This was probably due to the removal of unfixed chemical substances from the fabric surface after the washing. Furthermore, increasing the number of wash cycles to 3 and 5 resulted in a decrease of flame spread time. The latter can be attributed to the surface damage of coated layers caused by rigorous stirring during the washing [1]. Nevertheless, a moderate decrease in the flame spread time pattern was observed after the wash cycle 5, which is comparable to the raw and chemical-bleached unwashed jute samples, suggesting that the chemical-treated jute samples have moderate wash durability.

Conclusion
This study describes the added value of a jute fabric by imparting flame retardancy by using borax, diammonium phosphate and thiourea. It was found that the flame spread time of a jute fabric significantly improved through the application of these simple flame retardant agents. The weight gain percentage increased with the increase of concentration of chemicals whereas the breaking load decreased. It was also established that the specimens treated with borax and diammonium phosphate flame retardant showed better results than those treated with thiourea. Since borax, diammonium phosphate and thiourea are abundantly available and the application process is simple, the scope of applying these flame retardant finishes to impart flame retardancy in jute fabrics is appealing, better wash durability further reinforcing the use in wearable textile applications.