No abstract

The bark of the tree species Myrcia eximia DC., which occurs in secondary forests in the Brazilian Amazon, is described for the first time. The aim was to provide a broad knowledge of its composition, to add value, and to direct uses to the bark of this species based on its polyphenolic content and antioxidant capacity. The bark is formed by conducting phloem, nonconducting phloem, and rhytidome. In addition, dead phloem occurs between the periderms. The average chemical composition of the bark was 45.6% total extractives, 1.4% suberin, 1.7% ash, and 21.1% lignin. The ethanol-water extract had a high content of flavonoids and condensed tannins [300.8 and 877.3 mg catechin equivalents (CE) g−1 of the extract, respectively]. High-performance liquid chromatography (HPLC) was used to quantify the presence of rutin, quercetin, and gallic, ferulic, and o-coumaric acids. The bark extract showed strong 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH) free radical scavenging activity, which was superior to that of the commercial antioxidant butylated hydroxytoluene (BHT), with an IC50 of 85.2 μg mL−1. Based on these results, it is evident that the bark of M. eximia from the Brazilian Amazon rainforest is a new and potential natural source of phenolic compounds and antioxidants, and its extracts can be used in the food and pharmaceutical industry and in various condensed tannin-based products.

No abstract

Adhesives based on vegetable tannins are already a reality in the market. However, their use is still limited due to their low mechanical resistance and weak humidity resistance. Cellulose nanofibrils (CNFs) are being used as reinforcing materials in various composites, resulting in an improvement of mechanical proprieties in general. The objective of this work was to evaluate the incorporation of CNFs in adhesives made of tannins obtained from the Angico tree (Anadenanthera peregrine). Concentrations of nanofibrils at 1, 5, and 10% were added to the adhesives on a dry basis. Tests of viscosity, pH, solids content, and gel time were performed to determine the physical proprieties of the adhesives. The Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Raman spectra measurements were also determined to understand the interaction between tannins and CNFs. Thermogravimetric analyses (TGA) were carried out to determine the thermal resistance of the composite. The FTIR and Raman characterization identified some differences in the peaks in the chemical composition of the adhesives with different percentages of CNFs. The adhesives showed no different decomposition in the thermogravimetric analyses. The shear strength in the glue line of the adhesive with 5% of CNFs in Toona ciliata woods was determined. Among all the adhesives analyzed, the one with 5% of CNFs produced an improvement in the mechanical resistance and humidity resistance on the glue line.

Tannins from Myrcia splendens from the Amazon rainforest were used for the first time in the formulation of a urea-tannin-formaldehyde (UTF) resin. The objective was to evaluate the effect of different tannin proportions on the glue line performance in Pinus sp. woods, glued with UTF adhesive. The tannins were extracted in a water bath, using 1500 mL of water and 100g of dry bark (liquor/bark 15:1), with addition of 3% Na2SO3, at a temperature of 70 °C for three hours. The adhesives formulations were based on the gradual replacement of mass of the urea-formaldehyde (UF) adhesive by tannin powder, totalizing four compositions and one control treatment. UTF adhesives were evaluated for their physicochemical properties, shear bond strength (wet and dry) and wood failure. The addition of M. splendens tannins to the urea formaldehyde adhesive promoted an increase in glue line strength. The proportion of 5.0% of tannins proved to be ideal in the formulation of the UTF adhesive, considering all the parameters evaluated. Thus, this study proves the potential use of Amazonian tannins from Myrcia splendens in the partial composition of more sustainable UTF adhesives.