Organophosphate-Cyclodextrin Inclusion Complex for Flame Retardancy in Doped Cellulose Acetate Butyrate Melt-Spun Fibers

Abstract

Organophosphates are widely used flame retardants (FR) in everyday applications, and their leaching over time is a gaining concern. In this research, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was chosen as a representative organophosphate FR to examine inclusion complex (IC) formation with γ-cyclodextrins (γ-CD) to enhance char formation as well as prevent the unnecessary release of toxic FR chemicals. The addition of ionic salts, sodium chloride (NaCl), and calcium chloride (CaCl2) during the formation increased the yield of IC crystals by up to 50%. However, perfect crystals were formed only when pure IC was formed, devoid of only metal crystals. Continuous melt spinning of cellulose acetate butyrate (CAB) is practically very difficult in the presence of incompatible DOPO in the system. The formed IC was compatible with biopolymer CAB due to hydroxyl groups from γ-cyclodextrin at the periphery. CAB/IC fibers were melt-spun alongside reference pure CAB and CAB/CD fibers. CAB was found to form complexation with CD in the absence of DOPO in the cavity, as corroborated by FTIR and tensile properties. Furthermore, the response to flame was noted as compared to reference pure CAB and CAB/CD fibers. CAB/IC was found to have self-extinguishing behavior via the formation of a char layer even at ∼0.8 wt % DOPO fraction in the fiber.

Computational Insights into Cyclodextrin Inclusion Complexes with the Organophosphorus Flame Retardant DOPO

“…Considering the geometry deformation, solvation, and thermodynamic effects, the resulting binding free energies indicate that γ-CD complexes were the most stable and thermodynamically favorable. This agrees with the experimental measurements performed by Park et al, whereby they obtained a greater yield of γ-CD complexes than β-CD and no yield of α-CD complexes with DOPO [32]. They also proposed a binding mode of γ-CD with DOPO, in which only the aromatic ring (ring A in Figure 1) penetrated into the γ-CD cavity (that is, forming a partial inclusion complex), based on the 1 H NMR results in a solution of DMSO.…”

“…As a result, γ-CD complexes with DOPO appeared thermodynamically favorable (negative ∆G bind , Table 5). This agrees with the experiments by Park et al, where they did not detect the yield of α-CD inclusion complexes with DOPO, and the yield of γ-CD complexes was greater than that of β-CD [32]. For the optimized structures in the gas phase, the sobEDAw analysis gave positive ∆G bind for all of the inclusion complexes, highlighting the importance of a solvation environment in the complexation of CDs with DOPO.…”

“…Organophosphate esters (OPEs) have already been detected in indoor and outdoor air and dust [16][17][18][19], wastewater [20,21], soil [22,23], fish [24,25], and so on. Recently, cyclodextrins (CDs) and their derivatives have been introduced into the formulation of OPFRs because of enhanced flame retardancy performances and their ability to reduce the release of flame retardants via forming inclusion complexes with them [26][27][28][29][30][31][32]. Cyclodextrins (CDs) are cyclic oligosaccharides obtained through the enzymatic degradation of linear starches [33], and were first discovered by Villiers in 1891 [34].…”

“…DOPO and DOPO derivatives have been widely employed as an important OPFR in epoxy resins [28,29,[42][43][44][45][46][47]; the molecular structure of DOPO is shown in Figure 1a. Very recently, Park et al [32] undertook an experimental study on the inclusion complexes of DOPO with natural CDs of α-CD, β-CD, and γ-CD, and indicated the difference in the yields of ICs. They also examined the flame retardancy of cellulose acetate butyrate fibers using γ-CD as an additive.…”

Unveiling the Intricate Supramolecular Chemistry of γ-Cyclodextrin-Epigallocatechin Gallate Inclusion Complexes

“…CDs possess a distinctive chemical architecture featuring a hydrophobic cavity capable of accommodating a diverse range of compounds, along with a substantial complement of hydroxyl (OH) groups located on the surface of their structure, facilitating their water solubility. , Consequently, CD complexation serves to augment the aqueous solubility and stability of hydrophobic pharmaceutical agents. − The cavity volumes of α-, β-, and γ-CD are 174, 262, and 427 Å 3 , respectively. − However, the natural CDs display diminished complexation efficiency due to their exclusive OH functional groups, constraining ligand interactions. As a result, chemical substitution reactions were employed to replace OH groups with various functional moieties (e.g., methyl, hydroxypropyl, and sulfobutyl ether) to maximize the interactions between host and guest in supramolecular complexes. − …”