This study reports on the effects of unmodified autohydrolyzed ethanol organosolv lignin (AH EOL) and modified autohydrolyzed ethanol organosolv lignin on the structural characteristics and antioxidant properties upon incorporation of p-hydroxyacetophenone (AHP EOL). The lignin samples isolated from black liquor of oil palm fronds (OPF) were evaluated and compared using various complementary analyses; FTIR, 1H and 13C NMR spectroscopy, 2D-NMR spectroscopy (HMBC and HSQC), CHN, GPC, HPLC and thermal analyses (TGA and DSC). Chemically modified organosolv lignin (AHP EOL) provided lignin with lower molecular weight (Mw), which has smaller fragments that leads to higher solubility rate in water in comparison to unmodified organosolv lignin, AH EOL (DAHP EOL: 19.8% > DAH EOL: 14.0%). It was evident that the antioxidant properties of modified organosolv lignin has better reducing power in comparison to the unmodified organosolv lignin. Therefore, the functionalization of lignin polymers enhanced their antioxidant properties and structural features towards a various alternative approach in lignin-based applications.
Lignin was extracted from coconut husk via alkaline pulping, either Kraft or soda. The isolated lignin samples were classified as hydroxy-benzaldehyde, vanillin, and syringaldehyde type according to Fourier-transform Infrared Spectroscopy, 1H and 13C Nuclear Magnetic Resonance (NMR) spectra. Soda lignin (SL) showed higher thermal stability and glass transition temperature (Tg) than Kraft lignin (KL) as proven by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. The soda-lignin-phenol-glyoxal (SLPG) resins with the optimum percentage of lignin substitution at 30% showed improved solid content and gel time in comparison to 30% of Kraft-lignin-phenol-glyoxal (KLPG) and phenol-glyoxal (PG) resin. The good mechanical properties in SLPG is due to the higher amount of molecular weight as well as higher phenolic and G-type unit in lignin that improve the properties of 30% SLPG adhesive. Moreover, the addition of layered double hydroxides (LDH) as reinforced filler up to 15%-30% SLPG adhesive blend shows a great performance (especially mechanical properties) as compared to 30% SLPG adhesive alone.
The most critical issues faced by the world nowadays is to provide the sustainability of consumption for energy and natural resources. Lignin is said to be one of the alternative new discoveries best-suited lignocellulosic biomass due to its low cost, sufficient availability and environmentally safe. The valuable properties exhibited by lignin can give broader applications usage such as in composite materials, wood industries, polymer composite industries, pharmaceutical and corrosion inhibitor industries. Many biomass wastes resources, isolation processes and treatments are undergoing development in order to enhance the producing new lignin-based materials on an industrial scale. Therefore, this review discussed on the current knowledge on the structure and chemistry of isolation of lignin from different sources using various common methods, its characterization, properties and its applications.
The recent study focused on lignin-phenol-glyoxal (LPG) as an alternative way to replace toxic formaldehyde used in commercially available wood adhesives. The concern of the uses of carcinogenic formaldehyde in wood adhesive industry has become major problem over human health, environmental and economy issues. In this study, lignin isolated from Kenaf (Hibiscus cannabinus) via soda and Kraft pulping were modified into SLPG (soda lignin-phenol-glyoxal) and KLPG (Kraft lignin-phenol-glyoxal) adhesives and were compared to phenol-formaldehyde (PF). Complementary analyses such as Fourier Transform Infrared (FTIR) spectroscopy, 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy, thermal stability; Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC) were utilized to characterize all isolated lignin samples. The physical properties of the resins were further characterized in term of viscosity, gel time and total solid content. It was found that soda lignin comprised higher phenolic OH content and greater molecular weight compared to Kraft lignin. Various molar ratio of adhesives were applied on plywood and were mechanically tested. The 30% (w/w) SLPG has shown to have higher tensile strength and internal bonding stress at 72.08 MPa and 53.83 N mm-2 respectively to that of PF.
Lignocellulosic materials can significantly contribute to the development of eco-friendly wood adhesives. In this work, glyoxal-phenolic resins for plywood were prepared using organosolv lignin, which was isolated from black liquor recovered from organosolv pulping of oil palm fronds (OPF) and considered to be an alternative to phenol. Glyoxal, which is a dialdehyde obtained from several natural resources, was used as substitute for formaldehyde. The structure of organosolv lignin and the resins were characterized by FTIR and NMR, and for thermal stability by TGA and DSC. The resins were further studied for their viscosity, pH, solids content and gel times. The resins performance as wood adhesive was further established from mechanical test in terms of tensile strength and modulus of elasticity (MOE) to obtain the optimum ratios of organosolv lignin, which replaces phenol in organosolv lignin phenol glyoxal (OLPG) resins. The adhesive composition having 50% (w/w) of phenol substituted by organosolv lignin, termed as 50% OLPG showed highest adhesive strength compared to phenol formaldehyde (PF) commercial adhesive.
The effects of steam explosion (SE) pretreatment on the structural properties of lignin isolated from coconut husk (CH) biomass via soda pulping were investigated in this work. The isolated SE lignin was classified as dilute acid impregnation SE lignin (ASEL), water impregnation SE lignin (WSEL), and 2-naphthol impregnation SE lignin (NSEL). The various types of functional groups isolated from SE lignin were characterized and compared using a variety of complementary analyses: FTIR spectroscopy, NMR spectroscopy, GPC chromatography, HPAEC-PAD chromatography and thermal analyses. It was revealed that ASEL has the highest solid recovery with 55.89 % yield as well as the highest sugars content compared to WSEL (45.66 % yield) and NSEL (49.37 % yield). Besides, all isolated SE lignin contain a significant quantity of non-condensed G-type and S-type units but less amount of H-type units as supported by previous research. The SE lignin produced lignin with higher molecular weight (Mw ASEL: 72725 g mol-1 > Mw WSEL: 13112 g mol-1 > Mw NSEL: 6891 g mol-1) seems to influence the success of the synthesis reaction of phenolic resins. Because of the large variances in the physicochemical properties of SE lignin polymers, their structural properties were increased toward numerous alternative techniques in lignin-based applications.
Each year, 50 to 70 million tonnes of lignin are produced worldwide as by-products from pulp industries and biorefineries through numerous processes. Nevertheless, about 98% of lignin is directly burnt to produce steam to generate energy for the pulp mills and only a handful of isolated lignin is used as a raw material for the chemical conversion and for the preparation of various substances as well as modification of lignin into nanomaterials. Thus, thanks to its complex structure, the conversion of lignin to nanolignin, attracting growing attention and generating considerable interest in the scientific community. The objective of this review is to provide a complete understanding and knowledge of the synthesis methods and functionalization of various lignin nanoparticles (LNP). The characterization of LNP such as structural, thermal, molecular weight properties together with macromolecule and quantification assessments are also reviewed. In particular, emerging applications in different areas such as UV barriers, antimicrobials, drug administration, agriculture, anticorrosives, the environment, wood protection, enzymatic immobilization and others were highlighted. In addition, future perspectives and challenges related to the development of LNP are discussed.
Rust powder collected from an archeological iron was evaluated by complementary analyses such as FTIR, XRD, XRF, and SEM/EDX. The analyses revealed that lepidocrocite (L) was the major component in the archeological iron. Coconut husk (CH) can be classified as a type of lignocellulosic biomass of renewable resources that are widely available, especially in coastal areas. In this research, the isolated lignin extracted from CH is being studied as a potential alternative for environmentally friendly applications. The isolated lignin from soda and organosolv pulping went through several analyses such as FTIR, NMR (13C and 2D-HSQC), and TGA analyses. The analyses showed that lignin isolated via soda pulping has superior antioxidant capabilities due to its greater phenolic-OH content compared to lignin isolated from organosolv pulping. The effects of lignin concentrations, pH, and reaction time were utilized in rust conversion studies of an archeological iron. 5 wt% of soda lignin (SL) was revealed as the ideal condition in this rust conversion study with a value of 84.21 %. The treated rust powder with 5 wt% of SL was then further gone through several complementary analyses, which revealed that the treated rust had nearly transformed into an amorphous state.