Study of the use of lignins as coupling agent in composites reinforced with celulose from sugarcane bagasse and straw

Author(s)

Patrícia Câmara Mileo

• Document type: Doctoral Thesis
• Press: Lorena.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de Lorena (EEL/ASDI)
• Defense date: 2015-04-28

Examining board members

Adilson Roberto Gonçalves; Larissa Canilha; Priscila Maziero; Pedro Carlos de Oliveira; Mary Mitsue Yokosawa

• Advisor: Adilson Roberto Gonçalves

Abstract

The need of developing new materials that attend economic and environmental aspects leads to the search of using natural resources for various technological applications. Thus, the development of polymeric composite materials using natural fibers as reinforcement is growing, and occupying new market segments, due to the low cost of fibers, biodegradability, low density and good mechanical properties. This work aimed to separate the main components of sugarcane straw and bagasse for obtaining chemical products with higher economic value, it proposes the obtaining and characterization of cellulose, which will be used as a reinforcement, and of the lignin that will act as coupling agent in polymeric composites. To achieve these objectives, it was carried out a dilute acid pretreatment of straw and bagasse of sugar cane, followed by a step of delignification with NaOH. The pulps of bagasse and straw were submitted to a pre-bleaching with xylanase and a bleaching step, composed by an alkaline extraction, EDTA chelation and a treatment with hydrogen peroxide. The black liquor was acidified for the precipitation of the lignins. After washing, drying and milling, the lignins obtained were subjected or not to an oxidation reaction in acid medium with hydrogen peroxide. In addition to the chemical characterization of the fractions at each stage of processing, the Kappa number and viscosity were determined, and it was also made measures of DRX and MEV for bagasse and straw. The confirmation of the oxidation reaction of the lignins was analysed by NMR, FTIR, MEV and TGA/DSC. The composites were obtained by mixing in thermokinetic mixer and once injected, they were characterized by mechanical tests, thermal analysis, microscopy, FTIR, contact angle and surface energies, water absorption and dynamic vapor sorption. The results obtained by the chemical characterization, Kappa number and viscosity indicated a great solubilization of hemicelluloses and lignin during all stages of production of bleached cellulose, both from bagasse and straw, but it was also observed an expressive cellulose loss. The results of DRX showed a great decrease of cellulose crystallinity, for both biomasses, demonstrating that the removal of hemicellulose and lignin affected the structure of cellulose. The FTIR and NMR results confirmed the change in structure of the lignins after oxidation. The mixing time of composites varied with the composition and the presence or absence of lignin/oxidized lignin. From TGA analyses it was observed that the composites PP/cellulose without the addition of oxidized lignin/lignin showed an initial degradation temperature lower than the composites in which lignin was used as an additive. The DSC curves of composites presents profile and temperature peaks and enthalpies of fusion similar to pure PP. Lignin has no remarkable effect on the mechanical properties of the composites, and the improvement in these properties is mainly due to the incorporation of the cellulosic fibers. MEV pictures of lignins showed that the oxidation had a great effect on the surface of this material. From the analysis of the static contact angle for lignins, it was observed that the oxidation produced a more hydrophobic material. The energies of surface showed that the composites have a more hydrophobic surface than the pure PP. FTIR curves of materials were quite similar, however the greatest differences were in the intensity of the bands corresponding to the hydroxyl groups present in the fibers and the aromatic rings of lignin structure. DVS results showed that the moisture absorption of composites is very low, and corroborates the results of water absorption. (AU)

• FAPESP's process: 10/20414-6 - Study of lignins utilization as coupling agent in polypropylene composites reinforced with cellulose from sugarcane bagasse and straw
• Grantee: Patrícia Câmara Miléo
• Support Opportunities: Scholarships in Brazil - Doctorate