Mangrove Tannins Research Articles

A correlation study on the phenolic profiles and corrosion inhibition properties of mangrove tannins ( Rhizophora apiculata) as affected by extraction solvents

The objective of this study was to investigate the correlation of phenolic compositions and corrosion inhibition properties of Rhizophora apiculata bark extracts as affected by nine solvent systems. Several phenolic compositions, namely, total phenolic content (TPC), total flavonoid content (TFC), condensed tannin content (CTC) were investigated. In addition, the inhibitive actions of tannin extracts on mild steel in 1 M HCl solution were studied by potentiodynamic polarization and electrochemical impedance spectroscopy. The results showed that extraction solvents had significant effects on TPC, TFC, CTC and inhibition properties of extracts. A correlation between CTC and inhibition properties of R. apiculata bark extracts was revealed.

Characterization and performance of Rhizophora apiculata mangrove polyflavonoid tannins in the adsorption of copper (II) and lead (II)

The wasted barks of Rhizophora apiculata mangrove from charcoal industry were explored as a potential source in producing tannins-based adsorbent for heavy metal ions. The polyflavonoid tannins extracted from these barks were subjected to FTIR and solid-state NMR analysis. The mangrove tannins contain high proportion of procyanidins to prodelphinidins with predominant C4–C8 interflavonoid linkages. The performance of mangrove tannins in removing copper (II) and lead (II) were evaluated. Effecting parameters like initial pH, initial concentrations of metal ions and contact time were investigated. The adsorption equilibrium data was fitted with Langmuir, Freundlich, Sips and Dubinin–Radushkevich isotherm models. Mangrove tannins-based adsorbent showed monolayer adsorption capacity of 8.78 mg/g for copper (II) and 31.32 mg/g for lead (II) in which the adsorption processes were found to follow pseudo second-order kinetic reaction. The metal ions could interact with the hydroxyl groups of mangrove tannins through an ion exchange and/or complexation process.

Inhibitive action of mangrove tannins and phosphoric acid on pre-rusted steel via electrochemical methods

The inhibitive action of mangrove tannins, extracted from mangrove barks and phosphoric acid, on pre-rusted steel in a 3.5% NaCl solution was evaluated and the inhibitive efficiency was compared with that of mimosa tannins. From the electrochemical studies, the inhibition efficiency of solutions containing 3.0 g L −1 tannins depended upon the concentration of phosphoric acid added and the pH of the solution. At pH 0.5 and pH 2.0, inhibition was greatest with mangrove and mimosa tannins alone, while at pH 5.5 the addition of phosphoric acid alone gave the highest inhibition.

Mangrove tannins in aquatic ecosystems: Their fate and possible influence on dissolved organic carbon and nitrogen cycling

We describe the fate of mangrove leaf tannins in aquatic ecosystems and their possible influence on dissolved organic nitrogen (DON) cycling. Tannins were extracted and purified from senescent yellow leaves of the red mangrove (Rhizophora mangle) and used for a series of model experiments to investigate their physical and chemical reactivity in natural environments. Physical processes investigated included aggregation, adsorption to organic matter‐rich sediments, and co‐aggregation with DON in natural waters. Chemical reactions included structural change, which was determined by excitation‐emission matrix fluorescence spectra, and the release of proteins from tannin‐protein complexes under solar‐simulated light exposure. A large portion of tannins can be physically eliminated from aquatic environments by precipitation in saline water and also by binding to sediments. A portion of DON in natural water can coprecipitate with tannins, indicating that mangrove swamps can influence DON cycling in estuarine environments. The chemical reactivity of tannins in natural waters was also very high, with a half‐life of less than 1 d. Proteins were released gradually from tannin‐protein complexes incubated under light conditions but not under dark conditions, indicating a potentially buffering role of tannin‐ protein complexes on DON recycling in mangrove estuaries. Although tannins are not detected at a significant level in natural waters, they play an important ecological role by preserving nitrogen and buffering its cycling in estuarine ecosystems through the prevention of rapid DON export/loss from mangrove fringe areas and/or from rapid microbial mineralization.

Antioxidant activities of mangrove Rhizophora apiculata bark extracts

Depolymerisation of mangrove Rhizophora apiculata bark extracts in the presence of phloroglucinol nucleophiles in ethanol was carried out. The flavan-3-ols and their phloroglucinol adducts were separated using reversed phase liquid chromatography (HPLC). The HPLC analysis of mangrove R. apiculata showed that catechin was the most common component of the flavanoid monomers. The antioxidant activities of these mangrove tannins were evaluated and compared with several commercial tannins by using reducing power, DPPH and ABTS assays with butylated hydroxytoluene, BHT and l-(+)-ascorbic acid as standards. All tannins had reducing power and percentage scavenging activities similar to the (+)-catechin and l-(+)-ascorbic acid standards. In the DPPH assay, >90% of the maximum scavenging activity was attained at 30 μg ml −1. Mangrove tannins had stronger antioxidant activity than the BHT standard in the DPPH assay. The results of the ABTS assay were correlated with the DPPH assay. Scavenging activity in the ABTS assay increased as the tannin concentration increased, up to a plateau at 50 μg ml −1.

Mangrove tannins and their flavanoid monomers as alternative steel corrosion inhibitors in acidic medium

The inhibitive behaviour on steel of flavanoid monomers that constitute mangrove tannins namely catechin, epicatechin, epigallocatechin and epicatechingallate was investigated in an aerated HCl solution via electrochemical methods. The monomers were found to be mainly cathodic inhibitors and the inhibition efficiency was dependent on concentration. To explain the adsorptive behaviour of the molecules on the steel surface, a semiempirical approach involving quantum chemical calculations using HyperChem 6.0 was undertaken. The HOMO electronic density of the molecule was used to explain the inhibiting mechanism. The most probable adsorption centers were found in the vicinity of the phenolic groups. In a second part, the use of mangrove tannin, extracted from the mangrove barks as steel corrosion inhibitors in acidic media was investigated and its inhibitive efficiency was compared with that of commercial mimosa, quebracho and chestnut tannins. The inhibitive performance of mangrove tannins was comparable to the other tannins investigated, indicating their potential in corrosion protection.

Differential scanning calorimetry of hydrolysed mangrove tannin

Mangrove-bark-tannin adhesives are potential substitutes for phenol–formaldehyde (PF) wood-bonding adhesives which are derived from petroleum, a finite natural resource. However, mangrove-bark-tannin adhesive exhibits poor adhesive properties, including brittleness, poor wet strength, and poor wood penetration. These shortcomings are due to its high reactivity and structural features. To reduce these shortcomings, the structure of the adhesive was modified by subjecting tannin to (a) caustic hydrolysis and (b) consecutive acetic anhydride and caustic hydrolysis. The effectiveness of these hydrolyses was determined by using differential scanning calorimetry (DSC) to monitor the reaction and cure characteristics of hydrolysed and unhydrolysed tannin with formaldehyde. These hydrolyses resulted in lowering both the activation energy and collision frequency of the cure reaction. Consequently, the initial reactivity of tannin towards paraformaldehyde, which was usually very high, was reduced. The resulting longer reaction time enhanced the extent of reaction, as was evident in the increase in heat of reaction of the hydrolysed tannin. © 2000 Society of Chemical Industry

Differential scanning calorimetry of hydrolysed mangrove tannin

Mangrove-bark-tannin adhesives are potential substitutes for phenol–formaldehyde (PF) wood-bonding adhesives which are derived from petroleum, a finite natural resource. However, mangrove-bark-tannin adhesive exhibits poor adhesive properties, including brittleness, poor wet strength, and poor wood penetration. These shortcomings are due to its high reactivity and structural features. To reduce these shortcomings, the structure of the adhesive was modified by subjecting tannin to (a) caustic hydrolysis and (b) consecutive acetic anhydride and caustic hydrolysis. The effectiveness of these hydrolyses was determined by using differential scanning calorimetry (DSC) to monitor the reaction and cure characteristics of hydrolysed and unhydrolysed tannin with formaldehyde. These hydrolyses resulted in lowering both the activation energy and collision frequency of the cure reaction. Consequently, the initial reactivity of tannin towards paraformaldehyde, which was usually very high, was reduced. The resulting longer reaction time enhanced the extent of reaction, as was evident in the increase in heat of reaction of the hydrolysed tannin. © 2000 Society of Chemical Industry

Fortified mangrove tannin-based plywood adhesive

Mangrove bark tannin adhesives are based on a renewable resource. They are potential substitutes or supplements for phenol–formaldehyde (PF) wood-bonding adhesives which are derived from petroleum, a finite natural resource. However, mangrove tannin adhesives exhibit poor adhesive properties including poor wet strength, brittleness, and poor wood penetration. These problems were addressed by treating tannin extract with acetic anhydride and then sodium hydroxide followed by modification with 20% resole-type PF resin. Significant structural changes occurred after the chemical treatment. Heat of reaction of tannin with formaldehyde was increased while the activation energy was drastically reduced. Premature cure was also reduced. The fortified formulations had good plywood adhesive properties. © 1996 John Wiley & Sons, Inc.

Natural adhesive-bonded particleboards

Two types of tannin-phenol formaldehyde adhesives — (i) a mixture of 70% Mangrove tannin and 30% phenol formaldehyde (PF) and (ii) a mixture of 70% Quebracho tannin and 30% PF — were used in the fabrication of two sets of particleboards. The third set of boards was prepared using 100% PF resin. The bending strength and internal bond strength of the tannin-PF bonded boards met the specifications required for commercial boards. The modulus of rupture, modulus of elasticity, internal bond and dimensional stability of the PF bonded boards were higher than those of the tannin-PF boards. Mangrove tannin-PF boards had better bending strength and dimensional stability than Quebracho tannin-PF boards.

Development of wood-products adhesives from mangrove bark

Mangrove bark was extracted using either water, ethanol, acetone, or various binary mixtures of these, as solvent. With plywood panels as substrates, joints prepared with adhesives derived from these extracts were tested for strength properties. In terms of the quantity of extracts from mangrove bark, water was the most effective solvent, followed sequentially by ethanol and acetone. However, in terms of the tannin content of these extracts, the order of extraction effectiveness of these solvents was reversed. The use of solvent mixtures in tannin extraction did not produce an observable synergistic effect. The quantity of extract and its tannin content were dictated primarily by the predominant solvent in the binary mixture. The reactivity of mangrove bark extracts is influenced significantly by formaldehyde concentration, cure temperature, type, and pH of the adhesive medium. Adhesive joints of significant bond strength were obtained from mangrove tannin adhesives. Prolonged cure periods, particularly at elevated temperatures, have deleterious effects on the strength properties of these adhesive joints.