No description available.

No description available.

This study is aimed at extracting cellulose and nanocelluloses (cellulose nanocrystals (CNCs) and cellulose nanofibres (CNFs)) from maize stalks and flax fibres. Both flax fibres and maize stalks are composed of cellulose, lignin, hemicellulose and extractives. The extraction of cellulose involves the removal of lignin, hemicellulose and extractives. The presence of these components in plant fibres hinders the extraction of cellulose and nanocelluloses. Prior to extraction of cellulose, the different concentrations (1 wt.%, 1.5 wt.% and 2 wt.%) of NaOH were optimised. However, chemical compositions and XRD results revealed that the treatment of flax fibres with 1.5 wt.% sodium hydroxide (NaOH) gives optimum results and this concentration was further selected for the extraction of cellulose. Cellulose was extracted by chemical treatments (sodium hydroxide (NaOH), sodium chlorite (NaClO2) and potassium hydroxide (KOH)) and a combination of chemical treatments and mechanical process (supermass colloider). The materials obtained after each treatment stage during the extraction process were characterised by different characterisation techniques such as Fourier transform infrared (FTIR) spectroscopy, environmental scanning electron microscopy (ESEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The results from the aforementioned characterisation techniques confirmed that cellulose was successfully extracted from flax fibres and maize stalks. Cellulose nanocrystals (CNCs) were extracted by sulphuric acid hydrolysis accompanied with ultra-sonication from cellulose obtained from flax fibres and maize stalks. The extracted CNCs were rod-like material with diameters and lengths in nanoscale and microscale, respectively. On the other hand, cellulose nanofibres (CNFs) were extracted by mechanical process (supermass colloider). The extracted CNFs were web-like material with diameters and lengths in nanoscale and microscale, respectively. The dimensions of nanocelluloses were measured by atomic force microscopy (AFM). Their dispersion was investigated by light polarised microscopy. The extracted nanocelluloses and cellulose were used to produce nanopapers and micropaper. Nanopapers mimic the traditional paper, the only difference of the nanopapers is that they are produced from high aspect ratio nanomaterials. Both nanopapers and micropapers were prepared by solvent evaporating method. Their thermal, optical and mechanical properties were investigated and compared. The mechanical and thermal properties of nanopapers produced from CNFs were better than those produced from CNCs and micropapers. On the other hand, nanopapers produced from CNCs were more transparent in comparison to nanopapers produced from CNFs and micropapers. Cellulosic fibres have attracted a considerable attention in composite materials due to their high tensile strength and tensile modulus. This study is focused on the development of biocomposites of polyfurfuryl alcohol (PFA) by in-situ polymerisation in the presence of acid catalyst (p-toluene sulphonic acid). Biocomposites were produced by reinforcing PFA with flax fibres (untreated and treated), nanoparticles and CNCs. The biocomposites reinforced with CNCs and flax fibres showed an improvement in mechanical, thermal and thermo-mechanical properties. On the other hand, biocomposites reinforced with nanoparticles obtained from treated maize stalks showed an improvement in mechanical and thermal properties while biocomposites reinforced with nanoparticles obtained from untreated maize stalks showed lower mechanical properties and decreased thermal stability.

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Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) were used to characterize the morphology of solvent cast hydroxypropyl cellulose (HPC) films. These techniques revealed the existence of three phases in the bulk material: 1) an amorphous phase, 2) a crystalline phase, and 3) a phase of intermediate order which arises as a consequence of liquid crystal mesophase formation during solvent evaporation. Characterization of the effect of crosslinking on the tan peak temperature led to the conclusion that these relaxations (as observed by DMTA) are similar to glass transitions (T_g's) involving large-scale cooperative motions of the main chains. This three-phase morphology presents a unique system for study with regard to the resultant morphology of binary blends with lignin. This blend system was prepared by solution blending in pyridine and dioxane, as well as melt-mixing followed by extrusion. A partially miscible system was obtained from all preparation methods; however, the injection molded and dioxane-cast materials were generally distinguished from those blends cast from pyridine solution. Their distinction is explained by an enhanced level of superstructure development in these blends as reflected by DMTA analysis and tensile properties. The dramatic improvement in modulus and tensile strength, particularly for the injection-molded samples, leads to the conclusion that lignin serves to reinforce the amorphous matrix of the resulting composite material. The modification of lignin's polyhydroxy character through ethylation, acetylation, and propoxylation, revealed that specific secondary interactions between the components play a minor role, if any, in determining the state of miscibility in this blend system. However, from the analysis of the interaction parameter, B, it is concluded that the extensive hydrogen bonding within the lignin influences the conformation and chain rigidity of this component which dramatically influences the development of supermolecular morphology, and subsequently the overall morphology of the polymeric blend. This is reflected by a substantial increase in the amorphous volume fraction as detected by both DSC and DMTA. The characterization of blends prepared from the unmodified organosolv lignin with ethyl cellulose and a cellulose acetate/butyrate ester confirms the minimal role of secondary interactions between components. However, the characteristics of the second phase suggest that the formation of liquid crystal domains in the cellulose derivatives significantly contribute to the overall morphology and properties of this blend system, as was noted for the HPC/lignin blend systems. / Ph. D.

For several years some of the graduate students, under the supervision of Dr. Scherer, have been investigating the chemical, or physical, reactions which take place in xanthation of soda cellulose. Following the previous work carried out by Scherer, Miller (1), Lin (2), and others in determining the effect of various factors (i.e. effects of temperature and aging) on rate of xanthation, the purpose of this investigation was to determine the effect of bulk number, or degree of mechanical subdivision, on rate of xanthation. In studying this it was hoped to find additional information on the relation between structure of soda cellulose and its reactions with carbon disulfide. It is possible to eliminate the factor of mechanical subdivision from consideration of the rate of reaction between CS₂ and soda cellulose. The only apparent effect is that the denser material offers greater resistance to solution and in that way very slightly modifies the degree of xanthation owing to the necessity for a somewhat longer dispersion period with the resultant possibility of decomposition. The effect of bulk number variation on either rate of reaction, or distribution of the carbon disulfide, was well within the limit of experimental error and may be disregarded. / M.S.

M.S.

Ph. D.

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No description available.