Esterification of Luffa with Acetic Anhydride under Microwave Radiation determined by FTIR

Luffa, mainly made up of cellulose, hemicellulose, and lignin, is fruit of the sponge gourd. It has a special porous physical structure, which leads to a high adsorption property. In this study, luffa was pretreated in alkali/ethanol/water solution. XRD of luffa showed that after pretreatment, the cellulose structure in luffa changed from cellulose I to II, which implied that the crystal structure was destroyed to some extent and the accessibility to reaction was increased. The analysis by FT-IR indicated that the alkali treatment had little significant effect on luffa's chemical structure but can remove the lignin. The pretreated luffa was then esterified with acetic anhydride under microwave radiation, and the relative esterification degree was quantified by FT-IR using an improved internal standard method. The results showed that microwave radiation could rapidly increase the esterification degree in the reaction process. The esterification degree of luffa esterified 20 min under microwave radiation was nearly 25 times that esterified 90 min under oil heat. The esterification degree initially increased quickly with radiation time and trended to become constant after 15 min radiation.