Rapid synthesis of cellulose propionate and its conversion to cellulose nitrate propionate

A highly rapid synthesis of cellulose propionate (CP) with high yield from commercial cotton cellulose using FeCl₃·6H₂O and ZnCl₂ as catalysts and less amount of propionic anhydride in solvent free synthesis was investigated. It was done using different amounts of catalyst under microwave irradiation for maximum of 8 min reaction time. The degree of substitution by propionate (DS_CP) was experimentally calculated and confirmed by FTIR and ¹H-NMR. The yields of CP using ZnCl₂ and FeCl₃·6H₂O as catalysts varied from 82.20 to 98.60% with the degree of substitution (DS_CP) ranging from 2.47 to 2.96, and from 55.51 to 96.34% with DS_CP ranging from 0.38 to 2.84, respectively. The DS_CP was controlled by changing the reaction duration (2–8 min), and the amount of catalyst using fixed amount of propionic anhydride (25 mL/5.0 g cellulose). The degree of polymerization of CP is highly affected by the catalyst amount and reaction time, while the thermal stability of CP is slightly affected by the type of catalyst and reaction time. Novel cellulose nitrate-propionate mixed esters (CNP) were also synthesized by nitration of the obtained cellulose propionate with different degrees of nitration using (HNO₃ + H₂SO₄) and (HNO₃ + P₂O₅) as nitrating agents. The degree of nitration (DS_CN) ranged between 0.10 and 2.53 for the HNO₃/H₂SO₄ mixture and between 0.22 and 1.24 for the HNO₃/P₂O₅ mixture. The effect of nitrating agent and reaction time on the degree of polymerization and thermal stability of CNP were also investigated using GPC, TGA, DTA and DSC analysis.