Mechanical and interfacial properties of phenolic composites reinforced with treated cellulose fibers

Cellulose fiber‐reinforced phenolic composites were prepared and characterized by mechanical tests and morphological analysis in this study. First, preparation of the phenolic matrix was optimized using an experimental design. The variables studied were curing temperature and time. The responses measured were strength, elongation, modulus, and strain energy density, in tensile and flexural tests. After fixing the optimal curing conditions of the matrix at 75°C and 2.75 h, the effect of a latest drying stage was studied. Strengths in tensile and flexural tests of the matrix after the incorporation of the drying stage were 156 and 189% of the strengths of the undried matrix, and elastic moduli were three‐fold. Finally, cellulose fibers were incorporated as reinforcement. Alkali treatment of the fibers (1 and 5% NaOH), employment of silanes as coupling agents [(3‐aminopropyl) trimethoxysilane (APS) and 3‐(2‐aminoethylamino) propyltrimethoxysilane (AAPS)], and combined treatments alkali‐silane were tested. The AAPS silane treated cellulose fiber‐reinforced phenolic composite was the material with the best mechanical performance and adhesion fiber–matrix. The most significant improvements obtained with the AAPS silane treatment of the fibers were 25, 52, and 110% for tensile strength, elongation, and SED, respectively, in relation to the unreinforced material properties. POLYM. ENG. SCI., 54:2228–2238, 2014. © 2013 Society of Plastics Engineers