Structural Characterization Of Acetylated And Benzylated Rice Straw

In this dissertation, acetylation and benzylation reactions were applied to modify rice straw into a thermoplastic material. Acetylation of rice straw was carried out with acetic anhydride as esterifying agent with no solvent or catalyst. Benzylation was carried out with benzyl chloride as etherifying agent, NaOH as swelling agent and catalyst, cetyl trimethyl ammonium bromide as phase transfer catalyst and toluene as solvent. The microstructure of rice straw was changed greatly after modification. And modification partly eliminated the polarity of rice straw.Weight percent gained (WPG), infrared spectrum (IR spectrum), CP/MAS 13C nuclear magnetic resonance spectrum (NMR), X-ray diffraction (XRD), thermal analysis (TA) and scanning electronic microscopy (SEM) were used to investigate the changes of microstructure of acetylated and benzylated rice straw before and after modification.For acetylation of rice straw, WPG increased with reaction time. WPG got its maximum of 10.2% when reaction time was 8h. Three raw materials (rice straw, pretreated rice straw and dewaxed rice straw) were used for acetylation under the same condition. WPG of pretreated rice straw was the lowest, while WPG of dewaxed rice straw was similar to that of rice straw. WPGs were close when the solid (rice straw mass) to liquid (acetic anhydride volume) ratios (g/mL) were 1:15 and 1:20. Three characteristic absorption peaks of acetyl group in IR spectrums indicated that acetylation took place in rice straw. The relative intensities of characteristic absorption peaks were as follows:4h> 6h> 8h> 2h. The characteristic absorption signals of acetyl group in 13C-NMR proved acetylation. The thermal stability of acetylated rice straw was stronger than rice straw. The temperatures of 50% weight loss were 316.2℃and 343.0℃, respectively for rice straw and acetylated rice straw.For benzylation of rice straw, the relative intensities of characteristic absorption peaks of benzyl group in IR spectrums increased as WPG increased. The relative intensities of characteristic absorption signals of benzyl group in 13C-NMR spectrums were as follows:7h >4h. Thermal stability of benzylated rice straw decreased. The temperatures of 50% weight loss were 316.2℃and 284.4℃, respectively for rice straw and benzylated rice straw.XRD was used to observe the changes of crystalline region before and after modification. It indicated that the crystalline region become small after modification. SEM was used to observe the apparent shape of rice straw before and after modification. It was found that the surface of rice straw was smoothness, but the surface became rough after modification.