Flame Retardant-Functionalized Cotton Cellulose Using Phosphonate-Based Ionic Liquids.

Karen Al Hokayem,Nicolas Le Moigne,Belkacem Otazaghine,Lenka Svecova,Roland El Hage,Rodolphe Sonnier

doi:10.3390/molecules25071629

Abstract

Cellulose from cotton fibers was functionalized through a dissolution–regeneration process with phosphonate-based ionic liquids (ILs): 1,3-dimethylimidazolium methylphosphonate [DIMIM][(MeO)(H)PO2] and 1-ethyl-3-methylimidazolium methylphoshonate [EMIM][(MeO)(H)PO2]. The chemical modification of cellulose occurred through a transesterification reaction between the methyl phosphonate function of ILs and the primary alcohol functions of cellulose. The resulting cellulose structure and the amount of grafted phosphorus were then investigated by X-ray diffraction, ICP-AES, and ¹³C and ³¹P NMR spectroscopy. Depending on the IL type and initial cotton / IL ratio in the solution, regenerated cellulose contained up to 4.5% of phosphorus. The rheological behavior of cotton cellulose/ILs solutions and the microscale fire performances of modified cellulose were studied in order to ultimately prepare flame retardant cellulosic materials. Significant improvement in the flame retardancy of regenerated cellulose was obtained with a reduction of THR values down to about 5–6 kJ/g and an increase of char up to about 35 wt%.

Highlights

Cellulose processing consists of disrupting its native hierarchical and crystalline structure by cleaving intra- and intermolecular hydrogen bonds through derivatization–dissolution or direct dissolution procedures
The objective of the present study was to investigate the functionalization of cotton cellulose through a direct dissolution–regeneration procedure using two phosphonate-based
It was shown by weighing and ICP-AES measurements that a fraction of ionic liquids remained in the regenerated cellulose

Summary

Introduction

Cellulose processing consists of disrupting its native hierarchical and crystalline structure by cleaving intra- and intermolecular hydrogen bonds through derivatization–dissolution or direct dissolution procedures. Dissolved (derivatized) cellulose is regenerated in a nonsolvent that allows preparing and shaping cellulosic products as films (nano-)fibers or porous structures (i.e., aerogels) [1]. The cellulose crystal structure generally changes from type I (in the case of native cellulose as in plant fibers, bacterial and algal cellulose) to type II after regeneration (in the case of viscose, Lyocell fibers) [2]. In order to improve the cellulose dissolution process, researchers and industrialists have investigated greener and less-destructive techniques as the direct dissolution of cellulose substrates. N-methylmorpholine N-oxide (NMMO) in its monohydrate form is efficient to dissolve a high amount of cellulose (up to 25% and typically 12–14% in technical applications) and is used at the industrial scale

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