Utilization of rice production residues as a reinforcing agent in bioadhesives based on polyphenols extracted from the bark of trees from the Brazilian Cerrado biome.

The scarcity of nonrenewable resources and the increase in environmental pollution have intensified the search for materials that exhibit specific characteristics and are nontoxic, renewable, and sustainable. Thus, the objective of this work was to produce natural polyphenol adhesives reinforced with rice husk and its ash to increase the mechanical resistance and moisture resistance of the glue line in wood bonded joints. Polyphenols were extracted from the bark of Stryphnodendron adstringens (Mart.) Coville (barbatimão). Adhesives were produced with a 50 % solid and 50 % liquid composition. Rice husk and husk ash underwent X-ray fluorescence analysis (XRF). Adhesives and reinforcement material were characterized by Fourier transform infrared (FTIR) and thermogravimetric analyses (TGA). The adhesives were glued in a mechanical press in specimens made of Pinus elliottii, which were subjected to shear testing of the wet and dry glue line. As a result, the chemical components present in rice husk and its ash positively influenced the properties of the adhesives. The mechanical glue line shear test showed that the adhesive reinforced with rice husk ash did not show a statistically significant difference. However, natural adhesives based on polyphenols from barbatimão strengthened with rice husk and ash showed improved properties, demonstrating how much it pays to use the residue of rice production to reinforce the matrix of tannin adhesives. Thus, it can be determined that reinforcement with rice husk and ash is efficient in improving some properties of natural adhesives based on polyphenols.

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.

Mandacaru cactus as a source of nanofibrillated cellulose for nanopaper production.

In this work, nanofibrillated cellulose (NFC) was extracted from cactus Cereus jamacaru DC. (mandacaru) for nanopaper production. The technique adopted includes alkaline treatment, bleaching, and grinding treatment. The NFC was characterized according to its properties and scored based on a quality index. Particle homogeneity, turbidity, and microstructure of the suspensions were evaluated. Correspondingly, the optical and physical-mechanical properties of the nanopapers were investigated. The chemical constituents of the material were analyzed. The sedimentation test and the zeta potential analyzed the stability of the NFC suspension. The morphological investigation was performed using environmental scanning electron microscopy (ESEM) and transmission electron microscopy (TEM). X-ray diffraction (XRD) analysis revealed that Mandacaru NFC has high crystallinity. Thermogravimetric analysis (TGA) and mechanical analysis were also used and revealed good thermal stability and good mechanical properties of the material. Therefore, the application of mandacaru is interesting in sectors such as packaging and electronic device development, as well as in composite materials. Given its score of 72 points on a quality index, this material was presented as an attractive, facile, and innovative source for obtaining NFC.

Influence of hemicellulose content and cellulose crystal change on cellulose nanofibers properties.

This study aimed to evaluate the properties of cellulose nanofibers (CNFs) with different hemicellulose contents and cellulose II polymorphs. A link was found between these polysaccharides and the properties of CNFs. A decrease in crystallinity (from 69 to 63%) and changes in the crystalline structure of cellulose subjected to an alkaline environment were observed, promoting the partial conversion of cellulose I to cellulose II (from 2 to 42%) and preventing CNFs production at NaOH concentrations higher than 5%. Most treatments showed pseudoplastic fluid behavior, except for the 10% NaOH treatment over 2 h, which showed Newtonian fluid behavior. The quality index of the reference CNFs (TEMPO-oxidized) was the highest (80 ± 3), followed by that of the 5% NaOH-treated (68 ± 3 and 22% energy savings compared to the untreated sample), and the untreated (63 ± 3) samples; and the 10% NaOH treatments had quality indices of 51 ± 3 and 32 ± 1, respectively.

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.