Optimizing chemical and mechanical stability of catalytic nanofiber web for development of efficient detoxification cloths against CWAs
Graphical abstract
Nanofiber mat having large amount of N–Cl functional groups for catalytic applications can be prepared via electrospinning of azide TPU, click reaction and N–Cl treatment. Surface localized hydantoin N–Cl functional groups can be prepared by surface click reaction on azide TPU nanofibers. These surface localized N–Cl groups not only show high enough catalytic efficiency for simulant of chemical warfare agent, but also have enhanced long-term stability compared to bulk N–Cl groups.
Introduction
Fibrous materials with catalytic effect against harmful chemicals or biomaterials have been of special interests in recent years because these functional building-blocks can expand their application fields of textile units such as cloths or masks into high valued products [[1], [2], [3], [4]]. For examples, textiles composed of cytotoxic functional moiety can be used as anti-microbial or biofouling applications [[5], [6], [7], [8]]. Especially, polymeric materials containing detoxification properties against certain toxins, such as chemical warfare agents or pesticides can be utilized to produce smart uniforms or field cloths [[9], [10], [11], [12]]. Among the various catalytic moieties, N–Cl groups have attained a great attention due to their excellent efficiency in detoxification of several warfare agents (i.e Mustard gas) and harmful chemicals (or microbial) [[13], [14], [15], [16]]. Although effect of N–Cl moiety is known to be quite promising, the stability of N–Cl groups under ambient condition, which will be directly related to their ‘shelter life’, are quite controversial in each previous report [[17], [18], [19], [20]]. In order to increase their stability, diverse functional groups have been suggested so far [[21], [22], [23], [24]], and the hydantoin moiety is considered as one of most promising candidate [[25], [26], [27], [28], [29]].
Previously, we have synthesized functionalizable thermoplastic polyurethane (TPU), and developed TPU containing large amount of hydantoin N–Cl groups by ‘click’ functionalization [30]. Based on high and controllable functionalization yield of click reaction, we have introduced large amount of N–Cl groups into side chain of TPU. The nonwoven nanofiber webs and porous membranes composed of these TPU show outstanding catalytic activity for detoxification of 2-chloroethyl ethyl sulfide (2-CEES), that is simulant for Mustard gas, but they are still suffered from storage stability under ambient atmosphere. We have also carried out multi-functionalization onto clickable TPU to introduce different functional groups for enhancement of N–Cl stability, previously [31].
Considering our series of experiments in terms of N–Cl stability [30,31], we have noticed that amount of N–Cl groups in products should be well-optimized; high enough concentration for catalytic activity is required, but too much high concentration will lead poor stability. Therefore, here, we want to suggest surface-localized N–Cl moieties in order to solve above dilemmatic task. Because the catalytic action is surface driven reaction, surface localized N–Cl moiety will be helpful to obtain optimized concentration of catalytic platform. Although it is quite challenging to introduce high amount of surface functional groups in general, click reaction between azide and alkyne group is well-known for surface chemistry with high yield [[32], [33], [34]]. In addition, because overall N–Cl concentration will be maintained in relatively low, the stability can be enhanced compared to that of bulk N–Cl.
Herein, we report on development of catalytic nonwoven nanofibers-mats with abundant N–Cl functional groups via surface click reaction on electrospun azido-TPU (ATPU). Nonwoven nanofiber mat is produced via electrospinning using synthesized ATPU having abundant N3 groups on side chain. Hydantoin functionalized with CC groups has been introduced onto fiber mat via surface click reaction after electrospinning process. Detoxification efficiency against simulant of chemical warfare agent and N–Cl stability has been addressed out after N-chlorination. Surface clicked N–Cl moiety shows high enough decomposition efficiency compared to that of bulk N–Cl group (hydantoin moiety was introduced before electrospinning via solution click reaction), whereas the storage stability of surface clicked N–Cl is much higher than that of bulk clicked TPU nanofiber. Substitution ratio, which will be critical to mechanical and chemical stability of final products, have been controlled via adjustment of electrospinning solution with addition of desired amount of normal TPU (nTPU) to form blended nanofibers of ATPU and TPU. It turns out that the surface dominant N–Cl functional groups show obviously enhanced stability with maintaining catalytic efficiency, which can be utilized in practical applications.
Section snippets
Materials
Epichlorohydrin (ECH) (≥99), boron trifluoride THF complex (>99.5%), dibutyltin dilaurate (95%), 4,4′-methylenebis(phenylisocyanate) (MDI) (98%), propargyl bromide solution (80% in toluene), copper (II) sulfate pentahydrate (CuSO4·5H2O) (99.0%), (þ)-sodium l-ascorbate and 2-CEES (97%) were obtained from Sigma-Aldrich Chemical Co. Methylene chloride (MC) (99.5%), tetrahydrofuran (THF) (99.5%), N, Nʹ-dimethylformamide (DMF) (99%), sodium hypochlorite solution (8.0%) and sodium azide (99%) were
Results and discussion
Chemical structures of polymers and overall preparation procedure for surface-clicked non-woven electrospun fiber mat with hydantoin functional groups are schematically illustrated in Fig. 1. Initially ATPU non-woven fiber mat have been prepared via electrospinning, which is the perfect method to prepare highly porous fibrous structures. These ATPUs that have been synthesized by the method reported previously [36], not only provide abundant azide groups in pendant chain which can be decorated
Conclusions
In conclusion, nanofiber mat containing hydantoin N–Cl functional groups is successfully prepared for detoxification of CWA simulant with high yield and enhanced N–Cl stability. Surface localized N–Cl hydantoin moiety can be achieved via surface click reaction on ATPU nanofiber mat. Surface dominant N–Cl groups is beneficial for increment of N–Cl stability without dominant decrement of catalytic activity. Mechanical properties can be adjusted by blending nTPU with ATPU during electrospinning
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work was supported by the National Research Foundation of Korea Grant funded by the Korean Government (MSIP) (Sub No. 2017R1A4A1015360 and 2019M3E6A1064139). This work was also supported by Agency for Defense Development (912751201 UD200013GD).
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