Modification of Rice Straw for Good Thermoplasticity via Graft Copolymerization of ε-Caprolactone onto Acetylated Rice Straw Using Ultrasonic-Microwave Coassisted Technology

摘要

Developing renewable resources for industrial applications, rather than using severely depleted natural fossil, is the biggest need of recent times. In this regard, rice straw (RS) has already been considered as an alternative material. However, some structural modifications need to be performed to make RS suitable for different applications. The objective of this study was to improve thermoplasticity of RS, required for industrial purposes. Acetylated rice straw-graft-poly(ε-caprolactone) (ARS-g-PCL) copolymers were synthesized via ring-opening polymerization (ROP) of ε-CL onto ARS in the presence of stannous octoate (Sn(Oct)2), N,N-dimethylaceta-mide (DMAC), using a rapid and efficient sonochemistry-assisted microwave process. The effects of microwave power, ultrasonic power, reaction time, temperature, and amount of ε-caprolactone on grafting percentage (PG) were examined. The sonochemistry-assisted microwave process significantly increased graft efficiency. The optimized conditions for obtaining the maximum PG of 39.6% are as follows: (i) 4:1 weight ratio of ε-caprolactone to rice straw, (ii) microwave/ultrasonic power of 200 W/270 W for 40 min, (iii) reaction temperature 140 ℃. The structure and properties of ARS-g-PCL were analyzed using FT-IR, NMR, XRD, and SEM, whereas thermal performances were tested using TGA and DSC. A single glass transition at ～100 ℃ and a broad endothermic peak near 185 ℃ can be seen in the thermogram of ARS-g-PCL, indicating good thermoplasticity compared with ARS. In addition, thin films of ARS-g-PCL can be prepared without any additives. Our findings together indicate that ARS-g-PCL has potential to substitute materials derived from natural resources for different industrial applications.