TENDÊNCIAS TECNOLÓGICAS DOS COMPÓSITOS CONTENDO NANOCELULOSE

A associação entre tecnologias avançadas, como a nanotecnologia, e rejeitos industriais ou da agricultura é de interesse crescente por parte das universidades e empresas. A diversidade das fontes de biomassa, bem como seu potencial energético, contribui para o vasto campo de aplicação e estimula a pesquisa com esses materiais. Apesar de ser um dos constituintes das fibras vegetais estruturalmente bem conhecido e com uma gama de aplicações industriais, a celulose tem ganhado mais espaço na área de nanocompósitos apenas em anos mais recentes. O presente trabalho objetiva prospectar as patentes de nanocompósitos de celulose, na base mundial e nacional, e dentro dos resultados obtidos verifica qual a tendência dos compósitos de nanocelulose utilizados como reforço de matrizes poliméricas

Thermodynamic and Kinetic Study of Diels–Alder Reaction between Furfuryl Alcohol and N-Hydroxymaleimides—An Assessment for Materials Application

International audienceThe study of Diels–Alder reactions in materials science is of increasing interest. The main reason for that is the potential thermoreversibility of the reaction. Aiming to predict the behavior of a material modified with maleimido and furyl moieties, 1H NMR and UV-Vis solution studies of the Diels–Alder reaction between furfuryl alcohol and two N-hydroxymaleimides are explored in the present study. Rate constants, activation energy, entropy, and enthalpy of formation were determined from each technique for both reacting systems. Endo and exo isomers were distinguished in 1H NMR, and the transition from a kinetic, controlled Diels–Alder reaction to a thermodynamic one could be observed in the temperature range studied. A discussion on the effect of that on the application in a material was performed. The approach selected considers a simplified equilibrium of the Diels–Alder reaction as the kinetic model, allowing materials scientists to evaluate the suitability of using the reacting molecules for the creation of thermoresponsive materials. The proposed approach determines the kinetic constants without the direct influence of the equilibrium constant value, thereby allowing a more objective data analysis. The effects of the selection of kinetic model, analytical method, and data treatment are discusse

Grafting Diels-Alder moieties on cellulose nanocrystals through carbamation

International audienceThe Diels-Alder reaction is a promising click chemistry for the design of advanced materials from cellulose nanocrystals (CNCs). Transferring such chemistry to cellulose nanocrystals requires the precise grafting of reactive Diels-Alder moeities under heterogeneous conditions without compromising the nanocrystals morphology. In this study toluene diisocyanate is used as a spacer to graft Diels-Alder moieties viz the furyl and protected maleimido moieties onto cellulose nanocrystals. A factorial experimental design reveals that reaction time and reactant molar ratio positively affect the grafting efficiency, as evidenced by FTIR and CHNS elemental analysis. The surface degree of substitution was analyzed via CHNS elemental analysis and XPS and found to range between 0.05 to 0.30, with a good agreement between the two techniques. 13C CP/MAS NMR confirmed that the grafted moieties and CNCs are intact after reaction. Side reactions were also observed and their impact on performing controllable click chemistry between cellulose nanocrystals is discussed