Substitution of petrochemical compounds for polyphenols of natural origin reinforced with cellulose nanofibrils to formulate adhesives for wood bonding.

Vegetable tannins are excellent options to produce adhesives for the panel industry since they have the capacity to reduce formaldehyde emissions and are derived from renewable sources. They also allow for the possibility of increasing the resistance of the glue line through the use of natural reinforcements such as cellulose nanofibrils. Condensed tannins, polyphenols isolated from tree bark, are widely studied for the production of natural adhesives as an alternative to commercial synthetic adhesives. So, the purpose of our research is to show a natural adhesive alternative for wood bonding. Therefore, the objective of the study was to evaluate the quality of tannin adhesives of different species reinforced with different nanofibrils and thus predict which adhesive is the most promising at different concentrations of reinforcement and with different types of polyphenols. To meet this objective, polyphenols were extracted from the bark, nanofibrils were obtained, and both processes followed the current standards. Then, the adhesives were produced, their properties were characterized, and they were chemically analyzed via Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). A mechanical shear analysis of the glue line was also performed. According to the results, the addition of cellulose nanofibrils affected the physical properties of the adhesives, mostly the content of solids and the gel time. In the FTIR spectra, the OH band of the 5% Pinus and 5% Eucalyptus (EUC) TEMPO in the barbatimao adhesive and the 5% EUC of the cumate red adhesive were reduced, possibly due to their higher moisture resistance. Mechanical tests of the glue line showed that barbatimao with 5% Pinus and cumate red with 5% EUC performed best in the dry and wet shear tests. The control was the best-performing sample in the test of the commercial adhesives. The cellulose nanofibrils used as reinforcement did not change the thermal resistance of the adhesives. Therefore, the addition of cellulose nanofibrils to these tannins is an interesting means of increasing the mechanical strength, as occurred in commercial adhesive with 5% EUC. Thus, the physical and mechanical properties of tannin adhesives were better with reinforcement, making it possible to expand the use of these adhesives in the panel industry. At the industrial level, it is important to replace synthetic products with natural ones. Besides environmental and health issues, there is the question of the value of petroleum-based products, which have been widely studied so that they can be replaced.

Cardanol-based adhesive with reduced formaldehyde emission to produce particleboards with waste from bean crops.

Free formaldehyde is a carcinogen whose emission reduction in particleboard has been studied recently to mitigate this environmental and human health problem. One alternative to reduce the emission of formaldehyde in particleboards is by using adhesives produced from natural sources. Cardanol-formaldehyde is an environmentally friendly adhesive made with cashew nut liquid, a byproduct from the cashew chain. This work aimed to produce particleboard using cardanol-formaldehyde in place of urea. In addition, different proportions of bean straw wastes were used to replace pine wood. The combination of eco-friendly adhesive and lignocellulosic waste particles could result in a product that meets market demands while being environmentally nonaggressive. Cardanol-formaldehyde promoted a higher modulus of elasticity (MOE) (1172 MPa) and modulus of rupture (MOR) (4.39 MPa) about panels glued with urea-formaldehyde, which presented a MOE of 764 MPa and MOR of 2.45 MPa. Furthermore, the cardanol-formaldehyde adhesive promoted a 93% reduction in formaldehyde emission, with a reduction from 16.76 to 1.09 mg/100 g oven-dry board for particleboards produced with cardanol-formaldehyde, indicating potential as an adhesive in the particleboard industry.

Effect of surface treatment on the technological properties of coconut fiber-reinforced plant polyurethane composites.

Polymeric composites reinforced with plant fibers have numerous advantages, such as low cost, high raw material availability and good physical, mechanical and thermal properties. Thus, in recent years, they have been studied as thermal insulation substitutes for synthetic polymers in buildings. The aim of this study was to evaluate the technological properties of castor oil-based polyurethane composites reinforced with coconut fibers treated with hot water, alkaline solutions of NaOH and Ca(OH)2 and corona discharge and without surface treatment as materials for the thermal insulation of buildings. The composites were produced by the hand lay-up method followed by compression; 10% by weight coconut fibers were used to replace the synthetic polymer. Specimens were produced, and physical, mechanical, thermal and microstructural tests were performed. The results showed that the polymer had a thermal conductivity of 0.016 W/(mK), while the composites produced with fibers treated with NaOH had a thermal conductivity of 0.028 W/(mK); therefore, these polymers are considered insulating materials (k = 0.01 to 1.0 W/(mK)). Thus, the composites produced with coconut fibers can be considered as lighter, less expensive and environmentally friendly alternatives to synthetic polymers.

Influence of wood species and adhesive type on the performance of multilaminated plywood.

The quality of plywood depends on factors such as the forest species and the adhesive used in their production, and understanding the interferences of these factors in the final properties of the plywood is of fundamental importance. The study aimed to develop multilayer plywood with two forest species and two types of adhesive and to evaluate the influences of these factors (forest species and adhesive) on the physical and mechanical properties of the plywood. The panels were produced with wood veneers of parica and pine with two types of adhesives, urea-formaldehyde and phenol-formaldehyde, with a weight of 150 g.m2. Then, each set was pressed for 10 min under a specific pressure of 0.98 MPa at a temperature of 150 °C. Three panels were produced for each type of veneer and adhesive, totaling four treatments. The plywood was evaluated for physical properties (moisture content, bulk density, and water absorption) and mechanical properties (parallel and perpendicular static bending strength and shear strength). The results showed that the forest species had a greater influence on physical and mechanical properties, with the best results being observed for plywood produced with pine and PF adhesive. The specific mass of the panels should be considered as it positively influenced the mechanical properties and negatively impacted water absorption. The PCA was used to reduce the dimensionality of the data from 9 dependent variables to 2 main components, explaining 76.70% of the total variance of the data. The multivariate analyzes of the differentiated independent factors showed that both the species and the adhesive affected as properties of the plywood and both independent variables must be taken into account in the production of the plywood. It is concluded that the porosity and specific mass of the paricá veneers contributed to a greater penetration of the adhesives, resulting in lower physical and mechanical properties than the pine veneers. However, in general, it is concluded that the plywoods produced can be used for internal and external applications. However, it is not indicated for structural purposes as it did not meet the requirements of the NBR 31.000.001/2:2001.

Sustainable valorization of recycled low-density polyethylene and cocoa biomass for composite production.

The development of products from wastes such as plastic and lignocellulosic materials brings great advantages from the economic and sustainable point of view. The use of waste, previously destined for disposal, enables the changes in production patterns, and prevents major environmental problems. This research investigated the inclusion of different contents of cocoa almond husk on the properties of composites with recycled low-density polyethylene (LDPE) matrix. The composites were produced by extrusion process with proportions: 0%, 10%, 20%, 30%, and 40% of cocoa waste reinforcement in the polymer matrix. The density of the composites decreased (from 0.81 to 0.61 g/cm3) with the addition of the lignocellulosic waste in the matrix. The hygroscopicity was increased, however, at considerably low levels (0.17 to 2.68 %). There was a decrease in composite strength and elongation, becoming the material more rigid. The use of the cocoa waste for composites production is feasible to use since it can be adapted to the required application and still incorporate additives requested for specific purposes. This research demonstrated that is possible the combination of recycled low-density polyethylene and lignocellulosic wastes for the production of materials with high added value.