Preparation and characterization of hybrid conducting foams based on cellulose nanofibers and carbon particles

Preparation and characterization of hybrid conducting foams based on cellulose nanofibers and carbon particles

• Autor
• Gabriele Polezi
• Co-autores
• Diego Magalhães do Nascimento , Juliana da Silva Bernardes
• Resumo

• Cellulose is a biopolymer of glucose united by ß-1,4 glycosidic bonds. Each glucose monomer has three reactive ?OH groups, allowing facile functionalization. This abundant polymer can be extracted from lignocellulosic biomasses, such as sugarcane bagasse (SB), and mechanically processed to isolate nanofibers (CNF), which present outstanding properties. 

  CNF foams have shown potential as renewable functional porous materials. However, for their practical applications, low electrical conductivity and weak mechanical properties compared to petroleum-based polymer foams still need to be improved. In this study, to overcome their poor mechanical performance and confer electrical properties to CNFs, SB-derived cellulosic foams containing carbon black (CB) were prepared by a directionally freeze-drying process. 

  First, sugarcane bagasse fibers were subjected to organosolv and bleaching pulping to remove non-cellulosic components, followed by a mechanical treatment to reduce their size. Then, the cellulosic fibers were chemically modified by sodium hypochlorite (NaClO) and glycidyl trimethylammonium chloride (GTMAC) reagents to synthesize oxidized (TCNF) and cationic (CCNF) nanofibers, respectively. To analyze the dispersibility of CB in water with CNFs, carbon nanoparticles were added to nanofibers' aqueous suspensions (0.3 wt%) and then centrifuged. Foams were prepared by unidirectional ice-templating followed by lyophilization of CNF/CB suspensions (mass ratios of 1:0.1, 1:0.5, 1:1, and 1:2). Morphology and electrical conductivity of foams surface were analyzed by scanning electron microscopy (SEM) and two-probe measurements. 

  Particle aggregation and sedimentation were only observed for dispersions prepared with oxidized cellulose nanofibers. The better dispersibility of cationic CNFs may result from the electrostatic interaction between trimethyl ammonium groups with polarizable pi electrons of aromatic rings from CB. Therefore, conductive foams were prepared with positively charged nanofibers. 

  SEM images indicate that foams exhibit three-dimensional pore structures with pore sizes of hundreds of micrometers. Control foam (without CB particles) presented smooth pore wall surfaces. In contrast, the foams composed of CCNF/CB have a certain roughness due to the deposition of carbon particles on the cellulose fibers. The adsorption promotes the formation of an interconnected conductive network that increases the conductivity of the materials. On the other hand, higher CB concentrations make the foam brittle. 

  In the non-compressed state, CCNF/CB 1:0.1 foam does not conduct electrical current, while CCNF/CB 1:0.5, 1:1, and 1:2 present average conductivity of 540, 5479, and 15097 ?S/cm, respectively. When the foams are compressed (90% of compression), the electrical conductivity increases for all samples, reaching average conductivity of 58259, 479140, and 3616658 ?S/cm for CCNF/CB 1:0.5, 1:1, and 1:2, respectively. With compression, the CB particles are closer to each other, decreasing the current flow resistance and improving the electrical conductivity through the material. 

  Conclusions drawn from this study suggest that CCNF can be combined with CB to prepare well-dispersed CCNFs/CB suspensions. Taking advantage of the CCNF-CB interaction, we could create foams with high electrical conductivity, structural anisotropy, and good mechanical properties, enabling new high-value applications for sugarcane bagasse, for instance, as packaging for sensitive electronic devices.

• Palavras-chave
• Sugarcane bagasse, cationic cellulose nanofibers, carbon black, foams.
• Modalidade
• Pôster
• Área Temática
• Nanociências & Nanotecnologia