Produção e caracterização de espumas fenólicas à base de lignina Kraft e Taninos de Stryphnodendron adstringens (Mart.) Coville

Abstract

Polymer foams are porous materials that can be produced with a wide range of properties for different applications.However, the main raw materials used to produce these foams, phenol and formaldehyde, are obtained from petrochemical sources, generating environmental and human health impacts.In recent years there has been a growing search for sustainable alternatives for the total or partial replacement of petroleum-based synthetic products with new products made from renewable resources, as is the case with polyphenol-based foams such as kraft lignin and tannins.Lignin, widely produced in the pulp and paper industries, is being the target of studies to improve its performance and develop new products with superior characteristics, increasing its added value.In addition, tannins, water-soluble phenolic compounds, also have the potential to replace phenol in the manufacture of foams.These tannins can be found in a variety of sources, such as fruit, wood, seeds, and especially tree bark.The objective of this work was to prepare and characterize different formulations of phenolic foams using the kraft lignin from Eucalyptus sp. and tannins extracted from the bark of Stryphnodendronadstringens (Mart.) Coville (Barbatimão).In addition, the effect of incorporating glycerin as an additive and cellulose nanofibrils as reinforcement in the different formulations was evaluated, analyzing the chemical, physical, mechanical properties, morphology, and fire resistance capacity.The results show that the foams produced had low densities and the SEM images show irregular cell morphology, with open and closed cells. The treatment that used lignin, tannins, glycerin, and cellulose nanofibrils in its formulation showed higher mechanical compressive strength (0.12 MPa).The water absorption was high, which can be positive for use in floral foams and as a heavy metal eliminator in polluted water.The TGA results showed that near the temperature 450/500 °C is where the carbonization point of the foams occurs, in the FTIR analysis the components that stood out were the kraft lignin and tannins, showing that the presence or absence of the other components of the formulation probably did not change the capacity/functionality of the foams.In the fire resistance analysis, the foams produced presented self-extinguishing behavior and did not propagate fire, becoming interesting alternatives as insulators.Based on the results, it is concluded that kraft lignin and tannins from the species Stryphnodendronastringens can be used as phenolic sources in the production of foams, showing promising characteristics.Furthermore, the properties of the foams can be adjusted according to the desired application, making them a natural alternative to petroleum-derived synthetic foams, since the phenolic source lignin and tannins are abundant and renewable.