Microstructure Study and Kinetic of Conjugated Polyene Formation in Alkaline Dehydrochlorination of PVC

Polyvinyl chloride (PVC) is a widely used plastic; yet, its recycling remains challenging due to the release of hazardous chlorine compounds during conventional processing. This study investigates the alkaline dehydrochlorination of PVC using KOH and NaOH in a dimethylformamide (DMF)/ethylene glycol (EG) system at 100°C–140°C. The effects of temperature, base concentration, and base type (KOH vs. NaOH) on PVC's microstructure and dehydrochlorination kinetics were examined. Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), and ultraviolet–visible (UV–Vis) analyses, along with color changes, confirmed successful dehydrochlorination. Microstructural analysis revealed progressive decrease in meso–meso (mm, initial: 0.242) and increase in racemic–racemic (rr, initial: 0.314) triad sequences during dehydrochlorination. After 40 min, mm reached 0.163 (KOH) and 0.117 (NaOH); rr increased to 0.379 (KOH) and 0.407 (NaOH). The process occurred with a ratio ~ 9:1 via simultaneous E2 and S_N2 mechanisms. Kinetic studies using UV–Vis yielded activation energies of 21.6 and 22.03 kcal mol⁻¹ for polyene and double-bond formation, respectively, with Arrhenius constants of 2.96 × 10⁵and 2.27 × 10⁶ Alkaline dehydrochlorination was found to be faster and more direct than thermal dehydrochlorination. A reaction order of 1.0 with respect to KOH concentration supported the E2 mechanism. NaOH was more efficient than KOH in removing HCl from PVC. This work introduces a stereoselective alkaline process, achieving lower activation energies and environmental compatibility compared to thermal methods, offering a sustainable alternative for PVC recycling.