Nanostructured materials isolated from bio-residues, and their characterization

Sammanfattning: The use of natural components in nanocomposites has continuously increased, due to environmental problems that are growing day by day. The use of bio-residues from forest industries to develop new materials will not only alleviate ecological problems but also affect the economy of forest industries positively.The aim of this work was to characterize cellulose nanowhiskers isolated from two different industrial bio-residues, one from bioethanol production and another from specialty cellulose production. Furthermore, the structure and permeability of thin films made of these nanowhiskers were studied. In the first study, the characteristics of nanowhiskers isolated from bioethanol residue were compared with nanowhiskers from microcrystalline cellulose (MCC). The nanowhiskers from ethanol residue had lower surface charge compared with whiskers obtained from MCC when analyzed by conductometric titration. The AFM microscopy showed that both cellulose nanowhisker suspensions presented individualized whiskers with diameters less than 10 nm. Nanowhiskers from ethanol residue showed higher relative crystallinity than the nanowhiskers from MCC, and the films made from both whiskers showed transparency in visual light. In addition, the nanowhiskers extracted from bio-residue were more thermally stable than the whiskers extracted from MCC, having a higher degradation onset temperature and maximum degradation temperature.In the second study, nanowhiskers isolated from two different bioresidues were compared. It was seen that both nanowhiskers suspensions (reject cellulose and ethanol residue) exhibited flow birefringence. Transmission electron microscopy study showed that the nanowhiskers extracted from the reject cellulose were slightly longer (377 nm) than the ones extracted from the ethanol residue (301 nm). The casted films of nanowhiskers from reject cellulose showed a stronger interference in the UV and visible region, compared with the other films. The comparative crystallinity was higher for reject cellulose nanowhiskers than for ethanol residue whiskers. Moreover, the thermal stability was slightly higher for the ethanol residue whiskers than for the reject cellulose whiskers. In the last study, cellulose nanowhiskers were isolated from the reject cellulose using hydrochloric and sulphuric acid hydrolysis processes with a aim to obtain different surface characteristics. Sulfuric acid whiskers had higher surface charge than the hydrochloric acid whiskers. Thin spin-coated films with two different configurations were prepared; one with alternate layers of poly(allylamine hydrochloride) (PAHCl) and cellulose nanowhiskers, and the second one with a single layer of PAHCl coated with 25 layers of whiskers. In addition, the film roughness, and surface charge of the whiskers was shown to increase the hydrophilic behavior of the films, being highest for a single layer of PAHCl coated with cellulose nanowhiskers. The gas permeability was measured and the coefficient was highest for hydrogen (H2) followed by helium (He), oxygen, (O2) and carbon dioxide (CO2) and nitrogen (N2). It was observed that the surface charge did not affect the gas permeability of the films and did not display selective gas barrier. The results showed that CNW can be extracted from ethanol residue and reject cellulose, and that these whiskers had similar characteristics as nanowhiskers obtained from other non-residual sources. This work has demonstrated that bio-residues can potentially be used as a source of new nanosize materials, thereby increasing the value of the forest resources.