Treatments of jute fibers aiming at improvement of fiber-phenolic matrix adhesion

Abstract

Abstract:Composites based on a thermoset phenolic matrix and jute fibers were prepared and characterized. The fibers were alternatively treated with ionized air or aqueous alkaline solution (mercerization) with the aim of introducing changes in the morphology, dispersive component of surface free energy, g S D (estimated by Inverse Gas Chromatography, IGC) and the acid/base character of their surfaces, shown by their AN s /DN s ratio (estimated by IGC), and their degree of crystallinity. The final objective was to investigate the influence of these modifications on the adhesion at the jute fiber/phenolic matrix interface in the composites. The untreated jute fiber showed 50% crystallinity, g S D =18 mJ m -2 and AN s /DN s = 0.9 (amphoteric surface), tensile strength = 460 MPa and maximum elongation = 0.7%, while the respective composite had an impact strength of 72.6 J m -1 . The treatments positively modified the fibers and the adhesion at the interface was better in the composites reinforced with treated fibers than with untreated fibers. The best set of results was exhibited by the fiber treated with 10% NaOH [46% crystallinity, , AN s /DN s = 2.1 (acidic surface)] for further use as reinforcement of a phenolic matrix, but their partial degradation during the treatment decreased their tensile properties (395 MPa and 0.5% for tensile strength and maximum elongation, respectively) and their action as reinforcement (impact strength of the respective composite approximately 73 J m -1 ).

Thermal treatment of açaí (Euterpe oleracea) fiber for composite reinforcement

“…Alkaline treatment causes a decrease of the lignin and hemicellulose contents and increases the fiber surface roughness, improving tensile strength and Young's modulus [17][18][19] .…”

Gamma radiation effect on sisal / polyurethane composites without coupling agents

“…Such result could be attributed to the fact that the fibers extremities act as stress risers and crack initiation sites, decreasing the material flexural strength [6] . In this case, the higher fiber-to-matrix volume ratio contributed to this decrease in flexural strength, since there are more stress risers points [34,35] . It was also observed that the incidence of gamma radiation decreased the mechanical strength of the materials, because of the degradation on fibers caused by radiation [7] , which was evidenced by the surface fractures observation.…”

Síntese de termorrígidos fenólicos simultaneamente à formação de compósitos: fibras e mantas como reforço vegetal

“…A utilização de resinas lignina-aldeído ou lignina-fenol-aldeído como substituintes da resina fenólica convencional podem ser utilizadas tanto na preparação de compósitos de matriz termorrígida usando fibras lignocelulósicas como bagaço de cana de açúcar (PAIVA; FROLLINI, 2001), fibra de juta RAZERA et al, 2014), fibra de curauá (TRINDADE et al, 2008), fibra de sisal (RAMIRES et al, 2010;DE OLIVEIRA et al, 2017) como reforço estrutural, quanto na preparação de painéis de madeira: MDF, madeira compensada, painéis de partículas orientadas, painéis de palha, dentre outros (YANG et al, 2015;GHORBANI et al, 2017).…”

“…A MFS utilizada no presente estudo como agente de reforço de matriz termorrígida fenol-formaldeído foi caracterizada em termos de sua composição química após processo de extração ciclohexano: etanol (1:1) (Tabela 13). , 2006;HASSAN et al, 2010;RAZERA et al, 2014;DE OLIVEIRA et al, 2015).…”

“…Portanto, o fato da fibra rayon ser constituída por celulose pode ter levado a maior interação entre os grupos hidroxilas presentes nesta macromolécula e os grupos hidroxilas (polares) presentes na matriz (Figura 45) (RAZERA et al, 2014;DE OLIVEIRA et al, 2017) e, consequentemente, pode levar a um aumento na adesão interfacial entre ambas e impregnação da resina pela manta de rayon (PRASHANTH et al, 2019). Outro fato importante, é que fibras mais flexíveis possuem maior capacidade de absorção de energia comparativamente às fibras mais rígidas e frágeis (BUNEA et al, 2019).…”