The role of lignin in polypropylene composites with semi-bleached cellulose fibers: Mechanical properties and its activity as antioxidant

• Published in: Polymer degradation and stability Vol. 108; pp. 23 - 34
• Main Authors: Gadioli, Renan, Morais, Jaqueline A., Waldman, Walter R., De Paoli, Marco-A.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-10-2014; Elsevier
• Subjects: Applied sciences; Cellulose fiber composites; Composites; Exact sciences and technology; Forms of application and semi-finished materials; Lignin; Mechanical properties and stabilization; Polymer industry, paints, wood; Polypropylene; Semi-bleached cellulose; Technology of polymers; Mechanical properties and stabilization; Lignin; Semi-bleached cellulose; Polypropylene; Cellulose fiber composites; Strengthening; Fiber reinforced material; Paper pulp; Composite material; Thermal stability; Eucalyptus; Additive; Dicotyledones; Angiospermae; Myrtaceae; Weathering; Olefin polymer; Photochemical degradation; Propylene polymer; Mechanical properties; Lignocellulosics; Tensile property; Antioxidant; Experimental study; Thermal properties; Bending strength; Ultraviolet radiation; Stabilizer agent; Bleaching; Concentration effect; Injection molding; Photochemical stability; Artificial ageing; Spermatophyta; Kinetics
• ISSN: 0141-3910; 1873-2321
• DOI: 10.1016/j.polymdegradstab.2014.06.005

Reports on the use of bleached Eucalyptus cellulose as a reinforcing agent for polypropylene and on the use of lignin, from Eucalyptus and other vegetal species, as a stabilizer for different polymers can be found in the scientific literature. This work focuses on polypropylene composites using cellulose fibers with different bleaching levels, i.e. containing controlled lignin contents. We compared the properties and stability of composites with bleached and with semi-bleached fibers. These were prepared by twin-screw extrusion and injection molding and characterized by their tensile and flexural mechanical properties, thermogravimetry, oxidation induction time, reflectance infrared spectrophotometry and scanning electron microscopy. The kinetic evaluation of the accelerated and environmental aging of the injection molded test samples was followed by mechanical properties variation and reflectance infrared spectrophotometry. An increase in the reinforcing effect of the fibers and on the stability of the composites was observed for composites containing semi-bleached Eucalyptus fibers, with different lignin contents, compared to composites with the bleached cellulose fibers. The lignin present in these semi-bleached fibers positively affected the mechanical properties of the composites and the hindered phenols in the lignin structure acted as a primary anti-oxidant, indicating their advantageous use in comparison to the bleached fibers. Scanning electron micrographs showed that the excellent bulk fiber/matrix adhesion was not affected by accelerated or environmental aging.