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Technical Article


Rapid Microwave Assisted Flame Retardant Treatment for Cotton Fabric by an Industrial Byproduct – Phytic Acid

Rapid approach for preparing flame retardant (FR) cotton fabric using low-cost and renewable material has been of interest from the industrial production and sustainability perspective. Phytic acid, as the principal storage form of phosphorus in plant tissues is an abundantly available phosphorus containing compound that can react with cellulosic material. However, the utilization of phytic acid as treatment agent in large scale production of FR cotton fabric is limited by the length of treatment time and the high treatment temperature. A single-step, solvent and synthesis-free treatment method utilizing microwave-assisted technique that overcomes the limitations of conventional treatment method is reported here. The study on the effect of microwave power and irradiation time to FR characteristics of cotton has shown that the self-extinguishing cotton fabric with char length of 89 mm and no after flame could be achieved by a minimum radiation of 600 W for 4 min.

 

INTRODUCTION
Cotton fabric is one of the most widely used biopolymer textiles in the world. However, it is a quite flammable material which has even a higher fire risk when combined with other synthetic fiber forming materials where melt dripping of synthetic fibers such as polyamide and polyester due to wicking effect of the cotton fiber (Lewin, 2013). It is essential to develop a cost-effective and eco-friendly flame retardant (FR) and the corresponding FR treatment method for cotton fabric. 
Phytic acid (PA), as the major storage form of phosphorus in most phosphorus-containing plants and tissues, is one of the most abundant byproducts in food industry(Tsao et al., 1997). Due to the high reactivity and acidic nature, PA and its derivative can easily react with cellulose by pad-dry-cure technique(Nuessle et al., 1956).
It is worth mentioning that pad-dry-cure process is one of the most commonly used methods to produce flame retardant cotton fabric(Nawab, 2016). A conventional curing step in the PA treatment involves wetting of the fabric in a solution containing PA and urea at temperature greater than 150 °C for  10 to 45 minutes(Nuessle et al., 1956). Due to the long time duration of the curing step, the conventional curing method could not be applied to industrial roll-to-roll process for large scale production.
In this work, we demonstrate a rapid FR treatment of cotton fabric using microwave. Cotton fabric is directly treated by microwave irradiation after dipping in a solution containing PA and urea. The effects of microwave power and irradiation time on the weight add-on and flammability of cotton fabric are studied. 

 

RESULTS AND CONCLUSIONS
The weight add-on of cotton fabric after treated under different microwave irradiation is summarized in Figure 1. And the char length of treated cotton fabric in vertical burning test is shown in Figure 2. It is obvious that the weight add-on and char length are tuneable by the power and treatment time of microwave radiation. And a self-extinguishing cotton fabric with char length of 89 mm is achieved at the minimum microwave irradiation of 600 W for 4 min. The FR characteristic of cotton fabric prepared under these conditions are similar to that of cotton fabric prepared by conventional curing at 150 °C for 45 min


ACKNOWLEDGMENTS
The authors would like to express their gratitude towards US Army Natick Soldier RDEC (Grant number: W911QY-17-2-0004) for financial support for this project.
 

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