From Ionic Liquid Stability to Biodegradability

3-Substituted 1-methylimidazolium, triphenylphosphonium, and most cases of pyridinium cation exemplify the problems of core stability towards biodegradation. 

Even in cases when a side chain can be metabolized, the 1 -methylimidazole [45,46] core tends to resist biodegradation [47], a problem that clearly needs to be addressed according to Anastas and Warner s 12 Principles of Green Chemistry [48], which state that new chemicals (including ILs) should be designed to biodegrade to innocuous substances (principle 10). 

A study by Romero et al. in 2008 indicated that attachment of just one octyl chain to the imidazole core had a dramatic effect on biodegradability [49]. Stolte et al. [47] 

In ILs with a high molecular weight anion, it is important to consider the relative molecular mass of both the anion and cation when assessing their respective contributions to biodegradability (Table 6.1). 

Although it is clear that the octylsulfate anion can improve overall biodegradability, the situation is complicated by the fact that in some cases the cation may actually decrease the biodegradability of the octylsulfate. In the case of [bmim][OctOS03] 

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From Ionic Liquid Stability to Biodegradability 151 Table 6.2 Ammonium ionic liquids previously used as surfactants. 

In attempts to develop new process modifiers for thermoplastics, two ionic liquids with long chain hydrophobic cations and different anions were introduced in a biodegradable polymer. Methods of incorporation included melt blending, solvent casting and microencapsulation from w/o/w systems at concentrations up to 10 wt%. The modified polymers were characterized rheologically and by TGA to determine process and thermal stability, respectively, and by DSC to determine miscibility and types of the polymer-ionic liquid interactions. Potential applications in plasticization, lubrication and emulsification are discussed for selected polymer-ionic liquid combinations. 

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