Extension of the use of cellulose nanowhiskers in composite materials

This thesis explores the use of cotton derived cellulose nanowhiskers (CNWs) in composite materials in the form of nanocomposite films, surface modified polymer fibres and also in self-reinforced (SR) composites. Cellulose nanowhiskers (CNWs) were produced from cotton via sulphuric acid hydrolysis process and blended with polylactic acid (PLA) to produce CNW-PLA and was added to hydroxyethyl cellulose (HEC) to manufacture CNW-HEC nanocomposite films. The aggregated morphology and hydrophilicity of CNWs, hydrophobicity of PLA and the solvent used (Chloroform) played a major role in creation of voids within the CNW-PLA nanocomposites. In addition, the aggregated morphology of the CNWs also influenced the surface roughness and light transparency properties of the CNW-HEC films. Improvement in the mechanical, thermal and thermomechanical properties for both types of nanocomposites was achieved due to the reinforcing effect of the rod-like nanowhiskers. An increase in the crystallinity of the nanocomposites indicated that the CNWs induced crystallisation in the matrices. Incorporation of CNWs also had a significant influence on accelerating the degradation profile of the CNW-PLA nanocomposites and reducing the swelling capacity and initial swelling rate for the CNW-HEC films. PLA fibres were also produced with varying diameters (11 µm to 38 µm) via a melt drawing process employing increasing take-up velocities. A higher degree of chain orientation as well as an increase in crystallinity for the thinner fibres was achieved due to strain-induced crystallisation. The variation in PLA fibre diameter also revealed a noticeable influence in their mechanical and moisture absorption properties at various humidity levels. Further, the hydrophobic and smooth surface of the PLA fibres was coated with various blends of CNWs (65 to 95 wt%) and polyvinyl acetate (PVAc) to impart roughness, where PVAc acted as a binder. An increase in tensile modulus and moisture absorption properties were achieved for the CNW/PVAc coated PLA fibres. These surface modified PLA fibres were aligned to produce unidirectional (UD) fibre mats prior to hot compaction (at 95oC) to manufacture SR PLA composites. Incorporation of CNW/PVAc within the SR PLA composites revealed an increase in their flexural and ductile properties compared to the control composite

Extension of the use of cellulose nanowhiskers in composite materials

This thesis explores the use of cotton derived cellulose nanowhiskers (CNWs) in composite materials in the form of nanocomposite films, surface modified polymer fibres and also in self-reinforced (SR) composites. Cellulose nanowhiskers (CNWs) were produced from cotton via sulphuric acid hydrolysis process and blended with polylactic acid (PLA) to produce CNW-PLA and was added to hydroxyethyl cellulose (HEC) to manufacture CNW-HEC nanocomposite films. The aggregated morphology and hydrophilicity of CNWs, hydrophobicity of PLA and the solvent used (Chloroform) played a major role in creation of voids within the CNW-PLA nanocomposites. In addition, the aggregated morphology of the CNWs also influenced the surface roughness and light transparency properties of the CNW-HEC films. Improvement in the mechanical, thermal and thermomechanical properties for both types of nanocomposites was achieved due to the reinforcing effect of the rod-like nanowhiskers. An increase in the crystallinity of the nanocomposites indicated that the CNWs induced crystallisation in the matrices. Incorporation of CNWs also had a significant influence on accelerating the degradation profile of the CNW-PLA nanocomposites and reducing the swelling capacity and initial swelling rate for the CNW-HEC films. PLA fibres were also produced with varying diameters (11 µm to 38 µm) via a melt drawing process employing increasing take-up velocities. A higher degree of chain orientation as well as an increase in crystallinity for the thinner fibres was achieved due to strain-induced crystallisation. The variation in PLA fibre diameter also revealed a noticeable influence in their mechanical and moisture absorption properties at various humidity levels. Further, the hydrophobic and smooth surface of the PLA fibres was coated with various blends of CNWs (65 to 95 wt%) and polyvinyl acetate (PVAc) to impart roughness, where PVAc acted as a binder. An increase in tensile modulus and moisture absorption properties were achieved for the CNW/PVAc coated PLA fibres. These surface modified PLA fibres were aligned to produce unidirectional (UD) fibre mats prior to hot compaction (at 95oC) to manufacture SR PLA composites. Incorporation of CNW/PVAc within the SR PLA composites revealed an increase in their flexural and ductile properties compared to the control composite

Structural, mechanical and swelling characteristics of 3D scaffolds from chitosan-agarose blends

This study aimed to explore the correlation between mechanical and structural properties of chitosan-agarose blend (Ch-Agrs) scaffolds. Porosity of Ch-Agrs scaffolds was constant at 93%, whilst pore sizes varied between 150 and 550 μm. Pore sizes of the blend scaffolds (150 - 300 μm) were significantly smaller than for either agarose or chitosan scaffolds alone (ca. 500 μm). Ch50-Agrs50 blend scaffold showed the highest compressive modulus and strength values (4.5 ± 0.4 and 0.35 ± 0.03 MPa) due to reduction in the pore size. The presence of agarose improved the stability of the blends in aqueous media. The increase in compressive properties and residual weight after the TGA test, combined with the reduction in the swelling percentage of the blend scaffolds suggested an interaction between chitosan and agarose via hydrogen bonding which was confirmed using FTIR analysis. All wet blend scaffolds exhibited instant recovery after full compression. This study shows the potential of Ch-Agrs scaffolds for repairing soft tissue

Phosphate glass fibres and their composites

An overview of the research conducted utilising phosphate glass fibres (PGFs), their manufacturing processes and utilisation potential for biomedical applications is presented in this chapter. Phosphate glasses of varying compositions in the form of fibrous structures alone and as fibrous reinforcements within composites are discussed. This chapter also highlights the methodologies used for the manufacture of these resorbable glass fibres and their composites. The advantages of using bioresorbable fibres in terms of their mechanical, dissolution, ion release, and in vitro and in vivo biocompatibility properties for the replacement, augmentation, guidance and growth of both hard and soft tissue in repair applications are also presented

Effect of varying the Mg with Ca content in highly porous phosphate-based glass microspheres

Natural ventilation is a low energy strategy used in many building types. Design approaches are mature but are dependent on variables with high uncertainty, such as the aerodynamic behaviour of purpose provided openings (PPOs), which need improved characterisation. An analytical framework is used to define different types of flow through openings based on the balance of environmental forces that drive flow, and the different flow structures they create. This allows a comprehensive literature review to be made, where different studies and descriptive equations can be compared on a like-for-like basis, and from which clear gaps in knowledge, technical standards, and design data are identified. Phenomena whose understanding could be improved by analysis of existing data are identified and explored. A Statistical Effective Area Model (SEAM) is developed from academic data to estimate the performance of butt hinged openings during the design stage, that accounts for the impact of aspect ratio and opening angle. Its predictions are compared against available empirical data and are found to have a standard error of 1.2%, which is substantially lower than the 15–25% prediction errors of free area models commonly used in practice. An analytical model is made based on entrainment theory to explain the increase in flow rate that occurs through two aligned openings. This model defines characteristic design parameters and predicts a detrimental impact on the ventilation of the wider space. Finally, an analytical model is created to explain the reduction in discharge coefficient that occurs when a large temperature difference exists across an opening. This model defines novel dimensionless parameters that characterise the flow, and predicts empirical data well, suggesting that it should be integrated into design equations

Stable cellulose nanofibril microcapsules from Pickering emulsion templates

[Image: see text] Electrostatic attractions are essential in any complex formation between the nanofibrils of the opposite charge for a specific application, such as microcapsule production. Here, we used cationized cellulose nanofibril (CCNF)-stabilized Pickering emulsions (PEs) as templates, and the electrostatic interactions were induced by adding oxidized cellulose nanofibrils (OCNFs) at the oil–water interface to form microcapsules (MCs). The oppositely charged cellulose nanofibrils enhanced the solidity of interfaces, allowing the encapsulation of Nile red (NR) in sunflower oil droplets. Microcapsules exhibited a low and controlled release of NR at room temperature. Furthermore, membrane emulsification was employed to scale up the preparation of microcapsules with sunflower oil (SFO) encapsulated by CCNF/OCNF complex networks

The effect of MgO/TiO2 on structural and crystallization behavior of near invert phosphate-based glasses

Varying formulations in the glass system of 40P2O5─(24 − x)MgO─(16 + x)CaO─(20 − y)Na2O─yTiO2 (where 0 ≤ x ≤ 22 and y = 0 or 1) were prepared via melt-quenching. The structure of the glasses was confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), micro Raman and solid-state nuclear magnetic resonance (NMR) spectroscopies. The thermal properties and the activation energy of crystallization (Ec) were measured using thermal analysis and the Kissinger equation, respectively. The glass forming ability of the formulations investigated was seen to decrease with reducing MgO content down to 8 mol% and the glass stability region also decreased from 106 to 90°C with decreasing MgO content. The activation energy of crystallization (Ec) values also decreased from 248 (for 24 mol% MgO glass) to 229 kJ/mol (for the 8 mol% MgO content) with the replacement of MgO by CaO for glasses with no TiO2. The formulations containing less than 8 mol% MgO without TiO2 showed a strong tendency toward crystallization. However, the addition of 1 mol% TiO2 in place of Na2O for these glasses with less than 8 mol% MgO content, inhibited their crystallization tendency. Glasses containing 8 mol% MgO with 1 mol% TiO2 revealed a 12°C higher glass transition temperature, a 14°C increase in glass stability against crystallization and a 38 kJ/mol increase in Ec in comparison to their non TiO2 containing counterpart. NMR spectroscopy revealed that all of the formulations contained almost equal percentages of Q1 and Q2 species. However, FTIR and Raman spectroscopies showed that the local structure of the glasses had been altered with addition of 1 mol% TiO2, which acted as a network modifier, impeding crystallization by increasing the cross-linking between phosphate chains and consequently leading to increased Ec as well as their glass forming ability

Long-Term Culture of Stem Cells on Phosphate-Based Glass Microspheres: Synergistic Role of Chemical Formulation and 3D Architecture

Phosphate-based glasses (PBGs) are biomaterials that degrade under physiological conditions and can be modified to release various ions depending on end applications. This study utilized slow-degrading (P45:45P2O5-16CaO-24MgO-11Na2O10 4Fe2O3, mol %) and comparatively faster degrading (P40:40P2O5-16CaO-24MgO-20Na2O, mol %) PBG microspheres with or without porosity, to evaluate the combined effect of chemical formulation and geometry on human mesenchymal stem cells (MSCs), a clinically relevant cell source for orthopedic applications. Scanning electron microscopy showed 2, 46, and 29% of P45 bulk (P45-B), P40 bulk (P40-B), and P40 porous (P40-P) microspheres, respectively, that had cracks or peeling off surfaces after 42 days of incubation in culture medium. Cytotoxicity assessment showed that glass debris released into the culture medium may interact with cells and affect their survival. Direct-contact cell experiments up to 42 days showed that P45-B microspheres did not sustain viable long-term cell cultures and did not facilitate extracellular matrix formation. On the other hand, P40-B microspheres enhanced alkaline phosphatase activity, calcium deposition, and collagen and osteocalcin production in MSCs. Introduction of porosity in P40 glass further enhanced these parameters and proliferation at later time points. The small pore windows

Role of geometrical cues in bone marrow-derived mesenchymal stem cell survival, growth and osteogenic differentiation

Mesenchymal stem cells play a vital role in bone formation process by differentiating into osteoblasts, in a tissue that offers not a flat but a discontinuous three-dimensional (3D) topography in vivo. In order to understand how geometry may be affecting mesenchymal stem cells, this study explored the influence of 3D geometry on mesenchymal stem cell-fate by comparing cell growth, viability and osteogenic potential using monolayer (two-dimensional, 2D) with microsphere (3D) culture systems normalised to surface area. The results suggested lower cell viability and reduced cell growth in 3D. Alkaline phosphatase activity was higher in 3D; however, both collagen and mineral deposition appeared significantly lower in 3D, even after osteogenic supplementation. Also, there were signs of patchy mineralisation in 3D with or without osteogenic supplementation as early as day 7. These results suggest that the convex surfaces on microspheres and inter-particulate porosity may have led to variable cell morphology and fate within the 3D culture. This study provides deeper insights into geometrical regulation of mesenchymal stem cell responses applicable for bone tissue engineering

Flexible and transparent films produced from cellulose nanowhisker reinforced agarose

Transparent and flexible nanocomposite films with a range of Agarose to Cellulose Nano-Whisker (CNW) ratios were produced using never-dried CNWs. The incorporation of never-dried CNWs within Agarose played an important role in the surface roughness (Ra 7–15 nm) and light transparency of the films (from 84 to 90%). Surface induced crystallisation of Agarose by CNWs was also found with increasing percentage of crystallinity (up to 79%) for the nanocomposite films, where CNW acted as nucleating sites. The enhanced tensile strength (ca. 30% increase) and modulus (ca. 90% increase) properties of the nanocomposite films compared to the control Agarose film indicated the effectiveness of the nanowhiskers incorporation. The storage modulus of the nanocomposite films increased also to be tripled Agarose alone as the CNWs content reached 43%. The swelling kinetics of the nanocomposites revealed that addition of CNWs reduced the long-term swelling capacity and swelling rate of the nanocomposite