| Polyester/cotton blend fabric, due to its high performance and durability, becomes one of the most widely used textile products. When used in protective clothing and interior decoration, the polyester/cotton fabrics are required to have satisfied fire-retardant properties. Great efforts in researches have done to produce flame retardant polyester/cotton fabrics, but it remained a difficult and unsolved problem. In the later 20 th century, the essence of inherent flame-retardant fibers such as aramid 1313(Nomex) and aramid 1414(Kelvar) unveiled major breakthrough in textile flame retardant, aramid products are widely used in aerospace, defense, personal protection and sports and other fields. However, the high equipment investment and production costs make aramid fibers and textiles very pricy. In this paper, the thermal performance analysis of nylon/cotton and Nomex/cotton blend fabrics were investigated and flame retardant cotton blends were produced and tried to achieve low-cost textiles but with effective protection in special circumstances, also the addition of celluloses can make fabrics more comfortable and breathable. Up to now, the research on the combustion and flame retardant nylon/cotton and Nomex/cotton blends is inadequate; the lack of relevant literature highlights the importance of this study.In this paper, the combustion and pyrolysis process of three cotton blends(nylon/cotton, polyester/cotton and Nomex/cotton blended fabrics) were firstly studied and compared. Then the mutual interactions of two kinds of fibers in the three cotton blended fabrics in the combustion process were analyzed. Heat release rate(HRR) is the most important indicator to measure the fire hazard ofthe materials, the HRR values of textiles can be effective and quantitative characterization to represent the fabric flammability and fire-retardant properties. At present, the traditional methods of thermal analysis such as differential scanning calorimeter(DSC) or thermal analysis(TG) were unable to obtain HRR values of materials during combustion process. While the cone calorimeter can measure HRR but have certain requirements for size, shape, and thickness of the samples, which limits its application in textiles industry. In addition, cone calorimeter test require large quantity of samples and the results are highly dependent on the ignition source, sample thickness, sample orientation, ventilation and edge conditions.As a new thermal analysis instruments, micro-calorimeter(micro-scale combustion calorimeter, MCC) is currently the only one machine on millig level, which can measure the heat release rate of materials while guaranteeing stability and reliability of the results. In this study, the heat release rate and other thermalparameters of the polyester/cotton, nylon/cotton and Nomex/cotton blended fabrics were measured by MCC, andthus their combustion properties were compared. The result discovered that nylon/cotton and Nomex/cotton blendsdoes not have the similar “scaffolding effect” as polyester/cotton fabrics. Unlike polyester/cotton blend fabrics with the flammability increased compared to its single cotton or polyester fabrics, when nylon and cotton blended together, the interactions between two fibers allowed theblend flammability decreased. The flammability of Nomex/cotton did not change compared with its individual fabrics, and the two fibers(cotton and Nomex) nearly have no interaction in the combustion process. In addition, the char yield of the nylon/cotton blend during combustion decreased with the increase of nylon component, while the polyester/cotton followed the opposite trend.We then applied an organphosphorus oligomer(HFPO) to impart the flame retardancy to these different kinds of cotton blends to explore the effects on the flame retardant fabrics by the interaction between their individual fibers in the blends. Also, a crosslinkable binder is needed for binding HFPO onto the cotton blends, and thus improving the fabric flame retardancy. And different measurements were used in this study to evaluate the flame retardant performance of the cotton blend fabrics treated with the organphosphorus flame retardant system.(1) The interaction between two fiber components of the 50/50 nylon/cotton blend fabric reduces the flammability of blended fabrics with HFPO finishing. The presence of the phosphorus-based HFPO/DMDHEU reduced the PHRR, TPHRR, and the heat absorption for decomposition, and increased char formation for nylon, cotton and the 50/50 nylon/blend fabrics. Moreover, the presence of the flame retardant system caused higher reduction in PHRR and heat absorption for decomposition and higher char formation of the nylon and cotton in the blend than those of nylon and cotton as single fibers. Thus, the data indicated that the nylon and cotton fibers in the blend interacted with each other during the decomposition of the nylon/cotton blend treated with the HFPO/DMDHEU system. Consequently the treated nylon/cotton blend fabric had lower flammability than the treated nylon and cotton as fabrics of single fibers as shown by lower char length.(2) HFPO was bound onto the nylon/cotton blend fabrics via the bridge and crosslinking network with dimethylol-dihydroxy ethylene urea(DMDHEU). We then studied the bonding mechanism of the HFPO/DMDHEU system on the nylon/cotton blend fabrics and evaluated the performance of the nylon/cotton blend fabrics treated with the HFPO/DMDHEU system. We found that cotton and nylon interact with each other during the degradation process of the treated nylon/cotton blend fabric and such interactionreduces the flammability of the blend fabric.The research results indicated that HFPO was bound to the nylon/cotton blend fabrics by forming a HFPO/DMDHEU crosslinked polymeric network on both nylon and cotton and bridging of DMDHEU between cellulose and HFPO on cotton. The data demonstrated that the relative quantity of HFPO/DMDHEU crosslinked network and that of DMDHEU-bridging form on the nylon/cotton blend was decidedly influenced by HFPO-to-DMDHEU ratio. The data also showed that HFPO/DMDHEU was a highly durable flame retardant system for the nylon/cotton military blend fabrics. The treated fabrics demonstrate high levels of hydrolysis resistance by passing the vertical fabric burning test after 40-50 home laundering cycles. We also found that a nylon/cotton blend fabric with higher cotton-to-nylon ratio could have more HFPO bound to the blend and higher hydrolysis resistance. The changes in the mechanical strength and stiffness of the treated blend fabrics were also discussed.(3) We then applied HFPO/DMDHEU finishing system to the polyester/cotton fabrics. The flame retardant performance and laundering durability was investigated by limited oxygen index(LOI), vertical burning test and micro-scale combustion calorimeter(MCC). We found that the HFPO/DMDHEU system is much more effective on cellulose than polyester in the blends. The treated fabrics showed a decrease in the total heat release and increase in the char production. And the 50/50 polyester/cotton fabrics treated with 36%HFPO/10%DMDHEU can resist 20 home laundering cycles.(4) Heat release property and flammability of the 65/35 Nomex/cotton blend fabric treated with a nonformaldehyde organphosphorus flame retardant system HFPO / 1,2,3,4-butanetetracarboxylic acid(BTCA) / triethanolamine(TEA) system was applied and impart the flame retardancy onto the 65/35 Nomex/cotton blends by using the traditional pad-dry-cure finishing process. After treated with HFPO/BTCA, the total heat release(THR) of the 65/35 Nomex/cotton blends decreased while its char yiled increased. TEA can react with BTCA to inhibit the calcium deposited onto the blends and thus increasing the durability of fabric flame retardancy. We also found that the addition of TEA in the flame retardant finishingsystem improves the hydrolysis resistance of the HFPO bound to the Nomex/cotton blend and enhances the flame retardant performance of HFPO by meansof phosphorus–nitrogen synergism. After 25 home laundering cycles, the 65/35 Nomex/cotton fabrics treated with 8%HFPO/3%BTCA/2%TEA passed the vertical burning teat with a char length at 66 m and the LOI is 27.0%. |
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