Thermal characterization of kraft lignin (KL) prepared from mixed hardwoods was conducted to determine their thermal and thermo-oxidative stability, glass transition temperature (Tg), pyrolysis products composition, and syringyl/guaiacyl ratio. Two milled wood lignins (MWLs) from acacia (MWL-aca) and mixed hardwoods (MWL-mhw), the same hardwood species employed in the production of KL, were also characterized for comparison with KL. Thermogravimetric analysis (TGA) indicated that KL had higher thermal and thermo-oxidative stability than MWLs. Based on differential scanning calorimetry (DSC), the Tg of KL was 63.2 °C, while MWLs gave similar values near 165 °C. The syringyl (S), guaiacyl (G), p-hydroxyphenyl (H) composition of KL acquired from pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) at 675 °C was 48:44:8 (S/G ratio 1.07), while MWL-aca and MWL-mhw were 31:60:9 and 46:48:6, respectively.
This study was conducted to determine the lignin substructures, hydroxyl (phenolic + aliphatic) contents, and carboxyl contents in kraft lignin (KL) prepared from mixed hardwoods by using 2D Heteronuclear Multiple Quantum Coherence Nuclear Magnetic Resonance (HMQC NMR) and 31P NMR techniques. Based on 2D HMQC NMR analysis of KL, stilbene and vanillin substructures were present in the aromatic region, while trace amounts of β-O-4 and β-β moieties were detected in the oxygenated aliphatic region. The total hydroxyl content calculated from 31P NMR was 5.24 mmol/g KL. The aliphatic hydroxyl content was 1.04 mmol/g KL, and phenolic hydroxyl content was 4.20 mmol/g KL. Of the phenolic hydroxyl groups, the contribution of syringyl (S) and guaiacyl (G) was 1.02 and 0.97 mmol/g KL, respectively. The S/G molar ratio of KL calculated from 31P NMR was 1.05. The carboxyl content was 0.44 mmol/g KL.
A neutral extract (NE), that is soluble in cold water and has excellent antioxidant activity, from Pinus radiata pine bark was prepared by sodium bicarbonate treatment, and its chemical characteristics were investigated. NE was prepared by treating P. radiata bark with 0.8% NaHCO 3 aqueous solution with a 5 : 1 liquor-to-bark ratio at boiling temperature for 1 h, resulting in 44% yield and final pH of 6.66. The yield of NE was 11% higher than that of the hot water extract (HWE) due to the increase in the solubility of polyphenols, the main component in the bark, by NaHCO 3 treatment. NE was characterized through FT-IR, NMR, and MALDI TOF MS analyses. The results indicated that NE is mostly composed of proanthocyanidins (PAs) consisting of procyanidin (PC) units. The acetylated neutral extract (Ac-NE) had weight average molecular weight (Mw) of 5,300 Da. The Ac-NE had wide molecular weight distribution and its polydispersity (Mw/Mn) was 6 times higher than that of pure PA. The antioxidant activity of NE was determined by 2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay and showed that NE had comparable antioxidant activity with pure PA.
This study was conducted to investigate the potential of the neutral extract (NE) prepared by treating P. radiata bark with aqueous NaHCO 3 solution as a natural dyestuff. Silk and cotton fabrics were dyed at four different NE concentrations, 0.5%, 1.0%, 1.5%, and 2.0% o.w.b. (on the weight of bath). The fabric to liquid ratio of 1 : 50, dyeing temperature of 90 o C, and dyeing time of 90 min were used as the fixed condition. The appropriate NE dyeing concentration of silk and cotton fabrics was 1.5% o.w.b. Colors of the dyed silk and cotton fabrics were brown and light brown, respectively. From colorfastness assessment, both dyed silk and cotton showed good washing and rubbing fastness, but poor light fastness. NE dyed fabrics exhibited excellent ammonia deodorization property and antibacterial activity against Staphylococcus aureus and Klebsiella pneumoniae. Therefore, NE of P. radiata bark could have the potential for use as a functional brown dyestuff.
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