Effect of dual functional ionic liquids on the thermal degradation of poly(vinyl chloride)

Abstract

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Thermal Stability and Non-isothermal Kinetic Analysis of Suspension Poly(vinyl chloride) Films Formulated with Phosphonium-Based Ionic Liquids

“…These results indicate that the thermal degradation observed for the PVC− PhIL systems is not due to the degradation of pure compounds (PhILs or PVC) but instead due to some effects of PhILs over PVC. This behavior was also previously reported for other PVC−IL systems 7,16,25,43 and can be justified by the higher dissolution capacity of PhILs toward PVC, which facilitates the exposure of chlorine atoms, thus favoring dehydrochlorination at lower temperatures. 28,44 The higher miscibility of PhILs toward neat PVC, in comparison to DINP, can be further inferred based on solubility parameter values which are more similar for PhILs (ranging from 18.5 to 19.9 (J cm −3 ) 1/2 ) 45 and neat PVC (19.4 (J cm −3 ) 1/2 ) 8 than for DINP (15.7 (J cm −3 ) 1/2 ) 8 and neat PVC.…”

“…This observation confirms that the high thermal stability of the additives alone does not guarantee the thermal stability of the additivated polymer. Similar evidence was reported for PVC films formulated with two ILs composed of the docusate anion and two different cations (1-ethylpyridinium and tributyl­(2-hydroxyethyl)­phosphonium) . It was observed that, for both ILs, the actual thermal stability of the studied IL–PVC systems was lower than would be expected based on the intrinsic thermal stabilities of employed ILs and of PVC alone.…”

“…Moreover, the dehydrochlorination induced capacity of the studied PhILs may also result from the intrinsic high polarity of these additives (which may lead to the formation of highly polarized specimens that induce the formation of conjugated polyenes at relatively unstable PVC structural-defect sites 46 ) and also from specific favorable PhILs−PVC interactions. These interactions mostly depend on the affinity of PhILs' anions and cations for C−H and C− Cl bonds of PVC, respectively, 25,26 which ultimately depend on PhILs' Lewis basicity and hydrogen-bond-accepting capacity. 44 In fact, a clear dependency can be established between the hydrogen-bond-accepting capacity of the studied anions (quantified by the β parameter) and their PVC dehydrochlorination capacity, which follows the order 47 molecules that was incorporated, in molar terms, which may potentiate the catalytic effect of this PhIL.…”

“…Similar evidence was reported for PVC films formulated with two ILs composed of the docusate anion and two different cations (1-ethylpyridinium and tributyl(2hydroxyethyl)phosphonium). 25 It was observed that, for both ILs, the actual thermal stability of the studied IL−PVC systems was lower than would be expected based on the intrinsic thermal stabilities of employed ILs and of PVC alone. These results open the possibility of using ILs also to promote/ facilitate alternative non-metal-based PVC degradation/ recycling processes using nonharsh experimental conditions (in some cases at temperatures below 100 °C and at atmospheric pressure).…”

“…These studies showed that PhILs demonstrated the highest capacity to dissolve PVC (independently of the size of the cation), while anions, such as chlorine, acetate, triflate, trifluoroacetate, diethyl phosphate, alkyl sulfate, and sulfonate ions, presented the highest dehydrochlorination activity at the lowest temperature (>80 °C). On the contrary, ILs having the [Tf 2 N] − anion were not able to dissolve or to dehydrochlorinate PVC, while those having the dicyanamide anion ([dca] − ) were able to dissolve PVC only after exposure of the PVC–IL mixture to temperature (20 min at 150 °C). − …”