RESUMO
Bamboo plastic composites have become a hot research topic and a key focus of research. However, many strong, polar, hydrophilic hydroxyl groups in bamboo flour (BF) results in poor interfacial compatibility between BF and hydrophobic polymers. Maleic anhydride-esterified (MAH-e-BF) and lactic acid-esterified bamboo flour (LA-e-BF) were prepared while using an in situ solid-phase esterification method with BF as the raw material and maleic anhydride or lactic acid as the esterifying agent. Fourier transform infrared spectroscopy results confirmed that BF esterification with maleic anhydride and lactic acid was successful, with the esterification degrees of MAH-e-BF and LA-e-BF at 21.04 ± 0.23% and 14.28 ± 0.17%, respectively. Esterified BF was characterized by scanning electron microscopy, contact angle testing, X-ray diffractometry, and thermogravimetric analysis. The results demonstrated that esterified BF surfaces were covered with graft polymer and the surface roughness and bonding degree of MAH-e-BF clearly larger than those of LA-e-BF. The hydrophobicity of esterified BF was significantly higher than BF and the hydrophobicity of MAH-e-BF was better than LA-e-BF. The crystalline structure of esterified BF showed some damage, while MAH-e-BF exhibited a greater decrease in crystallinity than LA-e-BF. Overall, the esterification reaction improved BF thermoplasticity, with the thermoplasticity of MAH-e-BF appearing to be better than LA-e-BF.
RESUMO
Objective: To optimize the sulfated modification conditions of Rhodiola sachalinensis polysaccharide (RSP) and improve the anti-oxidant activity of RSP. Methods: RSP were sulfated by chlorosulfonic acid-pyridine method, and the optimal conditions for the sulfated modification were determined by single factor experiments. The physical and chemical properties of RSP and sulfated RSP (S-RSP) were analyzed by infrared spectroscopy (IR) and scanning electron microscopy (SEM). The relation between substituting degree (DS) of S-RSP and anti-oxidative activity of polysaccharide was investigated by testing the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging ability of RSP and S-RSP. Results: When the volume ratio of chlorosulfonic acid to pyridine was 1∶4, the reaction time was 2 h and the reaction temperature was 60 ℃, the maximum sulfur content of S-RSP was 18.83% and the DS was the highest for 2.38. Moreover, the anti-oxidant activity of RSP was enhanced by the sulfated modification, and there was a certain positive proportional relationship between DS and DPPH free radical scavenging ability of S-RSP. Conclusion: The volume ratio of chlorosulfonic acid to pyridine affects the DS of S-RSP, and the sulfated modification can increase the anti-oxidant capacity of RSP by changing its polarity.
RESUMO
Maleoyl xanthan oligosaccharides (XGOSMAs) and phthaloyl xanthan oligosaccharides (XGOSPAs) were prepared by reacting xanthan oligosaccharides with maleic anhydride and phthalic anhydride, respectively. The substituting degrees (DSs) of XGOSMAs and XGOSPAs were determined by a neutralization reaction. XGOAMA-1 (DS=0.30), XGOSPA (DS=0.31), XGOSMA-2 (DS=0.62) and XGOSPA-2 (DS=0.60) were selected for structural characterization and antioxidant activity evaluation. Their structural changes were confirmed by Fourier transform infrared spectra (FT-IR), and their molecular weights were determined with a gel permeation chromatography method (GPC). The pyruvate acid and reducing sugar contents were determined by ultraviolet spectrophotometry and the dinitrosalicylic acid method. The antioxidant activity was evaluated by the scavenging of the superoxide anion radical (O2(-)), hydroxyl radical (OH), 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and determination of reducing power. The results indicated that XGOSPA exhibited higher antioxidant activity than XGOSMA with similar substituting degrees in all the above mentioned antioxidant evaluation systems, which may be related to the fact that phthaloyl group has a stronger electron-withdrawing effect than the maleoyl group.