Polymers are intrinsically poor thermal conductors, which are ideal for thermoelectrics, but low electrical conductivity and thermopower have excluded them as feasible candidates as thermoelectric materials in the past. However, recent progress in polymer technology, particularly nanomaterial-polymer composites, can bring them into degenerate semiconductor or metallic regimes by incorporating a small amount of conductive filler. I demonstrate that such polymer nanocomposites can be viable for light-weight and economical thermoelectrics by using a segregated network approach for the nanocomposite synthesis. The thermoelectric properties were further improved by a change of stabilizer and drying conditions. The thermoelectric properties of the segregated network nanocomposites were measured for carbon nanotubes and the thermoelectric figure of merit, ZT, was calculated at room temperature. The influence on thermoelectric properties from filler concentration, stabilizer materials and drying condition are also discussed.

Basic physics teaches us that the frictional force (lateral force) needed to move objects on surfaces are proportional to load (normal force) – Amonton’s Laws. In tribology, this force is proportional to contact area, whereas Amonton is just a special case for contact area scaling with load. Such established laws do not seem to apply to small drops on flat, smooth surfaces in which frictional forces have an inverse relation to contact area and have time component prior to movement. Such phenomena can be explained by Shanahan-deGennes were intermolecular forces are considered for a deformed surface. Graphene is a special case where no time component is observed and frictional forces are attributed to its chemical homogeneity and stability. In the second part of this thesis, graphene is considered as nanofiller to build up polymer nanocomposites via Layer by Layer (LbL). Graphene Nanoribbons derived from multi-walled carbon nanotubes (MWCNT) offers a special case for thermoplastic polyurethane nanocomposites in that of thermally activated twisting morphology influences nanocomposite properties. Finally an electric field driven transdermal hydrogel drug delivery device has been demonstrated by just using CNTs, polyvinyl-borax gel and a CNT membrane

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Substances that consist of nano-scale fillers dispersed in a polymer matrix are known as polymer-nanocomposites (PNCs). These materials are appealing since they have high potentials for applications, due to their mechanical, electrical, and thermo electrical properties. A common problem associated with PNCs is that the nano-fillers have a tendency to aggregate into clusters and form phase separated domains, which cause the desired properties of the system to either diminish or vanish all together. Hairy nanoparticles (HNPs) can avoid the issue of agglomeration that is commonly encountered by conventional PNCs. When polymer chains are grafted to a nanoparticle, and the coverage is high, the nanoparticles have decreased inter-particle interactions which allows for enhanced dispersion and mixing into a polymer matrix. By tailoring the architecture (functionalization of polymer chains, degree of polymerization, grafting density) of HNPs, it is possible to control the final properties of the system. An in depth study was carried out to investigate the effects of hairy-nanoparticle architecture on the resulting properties of the material itself. Atom transfer radical polymerization and living anionic polymerization were used to synthesize the polymer chains, of the HNP systems, while various instrumental methods including differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were utilized to study the physical ageing affects and self-assembly of these systems. #88ABW-2015-4971

Carbon nanotubes are known as ideal fillers for polymer systems; the main advantage of carbon nanotubes over other nano-reinforcing particles is the combination of superior strength and stiffness with large aspect ratio. Carbon nanotubes may improve the mechanical, electrical and thermal properties of polymers, but to realise their potential in polymer systems uniform dispersion, strong interfacial adhesion and alignment of nanotubes within the polymer matrix are necessary. These properties are not easy to achieve and they are key challenges in producing CNT/Polymer system. This research was carried out in an attempt to understand how the properties of CNT/Polymer composite can be optimised by manipulation of additives, compounding and postcompounding conditions. Polypropylene/Multi-Walled Carbon Nanotube (PP/MCNT) composites were prepared by conventional twin screw extrusion. Dispersants and compatibilisers were used to establish good interaction between filler and polymer. Several different extruder screw configurations were designed and the properties of PP/MCNT composite prepared by each configuration investigated. The results indicated that the addition of carbon nanotubes without additives enhanced mechanical, electrical and thermal properties of polypropylene polymer. Incorporation of compatibilisers into PP/MCNT improved the stiffness but decreased the strength of the nanocomposite, whilst addition of dispersants decreased the mechanical properties of the nanocomposite. Addition of both additives at high concentration improved electrical conductivity and induced electrical percolation in the nanocomposite. Extruder screw configuration was found to have significant effect on the electrical conductivity whilst only slightly affecting mechanical properties of the nanocomposite, possibly due to the competition between dispersion and degradation of polymer chains and possible reduction of carbon nanotube length by intensive shear during compounding. The use of screw configuration with high mixing intensity promoted the dispersion of nanotubes and favoured the conduction process in the nanocomposite. Finally in an attempt to improve dispersion and alignment of carbon nanotubes, compounded PP/MCNT composite was subjected to micromoulding, fibre spinning and biaxial stretching processes and the resultant properties investigated. Application of post-compounding process was found to have significant effect on mechanical and rheological properties of the nanocomposite. Stiffness and strength of the nanocomposites treated by post-compounding processes were found to increase by up to 160% and 300%, respectively. The reinforcement effect of carbon nanotubes in the stretched nanocomposites was found to be the greatest. Rheological analysis suggested that the application of post-compounding processes enhanced dispersion of carbon nanotubes within the nanocomposite. Overall, this finding of this research has shown that carbon nanotubes can be incorporated into polypropylene using conventional equipment to provide significant improvement in properties. By careful choices of additives, compounding and postcompounding conditions, specific properties can be further enhanced.

Mechanical characterization of four polymer nanocomposite systems and two pure polymer reference systems was performed. Alumina (Al2O3) and magnetite (Fe3O4) nanoparticles were embedded in poly(methyl methacrylate) (PMMA) and polystyrene (PS) matrices. Mechanical testing techniques utilized include tensile testing, dynamic mechanical analysis (DMA), and nanoindentation. Consistent results from the three techniques proved that these nanocomposite systems exhibit worse mechanical properties than their respective pure polymer systems. The interphase, an interfacial area between the nanoparticle filler and the polymer matrix, was investigated using two approaches to explain the mechanical testing results. The first approach utilized data from thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM) to predict the structure and density of the interphase for the four nanocomposite systems. The second approach analyzed the bonding between the polymer and the nanoparticle surfaces using Fourier Transform Infrared Spectroscopy (FT-IR) to calculate the density of the interphase for the two PMMA-based nanocomposite systems. Results from the two approaches were compared to previous studies. The results indicate that Al2O3 nanoparticles are more reactive with the polymer matrix than are Fe3O4 nanoparticles, but neither have strong interaction with the polymer matrix. The poor interaction leads to low density interphase which results in the poor mechanical properties.

Cellulose nanocrystals (CNCs) are attractive nanomaterials due to their superior mechanical properties, renewability, and natural abundance. Their surface hydroxyl groups, along with surface charges induced during their production, allow CNCs to be easily dispersed in an aqueous medium, especially with sustainable water-based production methods such as emulsion polymerization. Moreover, their surface functionality makes them highly suitable for modification, thereby making them even more versatile. Emulsion polymer latexes are heterogeneous mixtures, having a continuous aqueous phase along with a dispersed organic phase. Latex polymers are used in a wide range of applications such as in coating and adhesive films. Because of the bi-phasic nature of emulsion polymerizations, the surface properties of CNCs play a crucial role in their location relative to the organic phase, and how well-dispersed they are in the cast films. In this thesis, three grades of CNCs (Celluforce Inc.) with either hydrophilic, partially-hydrophobic, or hydrophobic surface properties, were combined with conventional emulsion and miniemulsion polymer formulations to investigate their effect on the properties of pressure sensitive adhesive (PSA) films. In the first instance, hydrophilic CNCs were tested in a seeded semi-batch emulsion polymerization. Using a sequential experimental design, the effects of polar comonomer, surfactant, chain transfer agent, and CNC loading on latex stability and PSA properties were studied. By increasing polymer chain entanglements and the work of adhesion, the hydrophilic CNCs were observed to simultaneously improve the three key properties of acrylic-based PSA films, i.e., tack, peel strength and shear strength. In the second part of this project, we compared the role of hydrophilic and partially-hydrophobic CNCs in PSA property modification. Viscosity measurements and atomic force microscopy revealed differences in the degree of association between the two types of CNCs and the latex particles. Dynamic strain-sweep tests showed that hydrophilic CNC nanocomposites softened at lower strains than their partially-hydrophobic counterparts. This behaviour was confirmed via dynamic frequency tests and modelling of the nanocomposites’ storage moduli, which suggested the formation of CNC aggregates of, on average, 3.8 and 1.3 times the length of CNCs. These results confirmed that the partially-hydrophobic CNCs led to improved CNC dispersion in the PSA films and ultimately, enhanced PSA properties. In the third part of the project, mini-emulsion polymerization (MEP) was used to embed the hydrophobic CNCs within the polymer particles in contrast to the hydrophilic and partially-hydrophobic CNCs which resided mainly in the aqueous phase or near the water-particle interface. Higher CNC loadings led to increased particle size, decreased polymerization rate and number of particles, while only slightly increased the viscosity and the work of adhesion. PSA film properties decreased upon the incorporation of hydrophobic CNCs. Transmission electron microscopy showed that CNCs were expelled from the latex particles at higher loadings, suggesting the incompatibility of the acrylic polymer and the CNCs’ modifying agents. The ability to modify CNCs enables one to achieve a range of hydrophilicity/hydrophobicity. This makes them extremely versatile in a heterogeneous mixture such as in an emulsion polymerization. Because emulsion polymers are used in a wide range of applications with a broad spectrum of properties (i.e., not only as adhesives but as non-tacky coatings), our ability to control CNC location relative to the polymer particles in the latex opens the door to a world of high value-added sustainable polymer products.

Carbon nanotubes are known as ideal fillers for polymer systems; the main advantage of carbon nanotubes over other nano-reinforcing particles is the combination of superior strength and stiffness with large aspect ratio. Carbon nanotubes may improve the mechanical, electrical and thermal properties of polymers, but to realise their potential in polymer systems uniform dispersion, strong interfacial adhesion and alignment of nanotubes within the polymer matrix are necessary. These properties are not easy to achieve and they are key challenges in producing CNT/Polymer system. This research was carried out in an attempt to understand how the properties of CNT/Polymer composite can be optimised by manipulation of additives, compounding and postcompounding conditions. Polypropylene/Multi-Walled Carbon Nanotube (PP/MCNT) composites were prepared by conventional twin screw extrusion. Dispersants and compatibilisers were used to establish good interaction between filler and polymer. Several different extruder screw configurations were designed and the properties of PP/MCNT composite prepared by each configuration investigated. The results indicated that the addition of carbon nanotubes without additives enhanced mechanical, electrical and thermal properties of polypropylene polymer. Incorporation of compatibilisers into PP/MCNT improved the stiffness but decreased the strength of the nanocomposite, whilst addition of dispersants decreased the mechanical properties of the nanocomposite. Addition of both additives at high concentration improved electrical conductivity and induced electrical percolation in the nanocomposite. Extruder screw configuration was found to have significant effect on the electrical conductivity whilst only slightly affecting mechanical properties of the nanocomposite, possibly due to the competition between dispersion and degradation of polymer chains and possible reduction of carbon nanotube length by intensive shear during compounding. The use of screw configuration with high mixing intensity promoted the dispersion of nanotubes and favoured the conduction process in the nanocomposite. Finally in an attempt to improve dispersion and alignment of carbon nanotubes, compounded PP/MCNT composite was subjected to micromoulding, fibre spinning and biaxial stretching processes and the resultant properties investigated. Application of post-compounding process was found to have significant effect on mechanical and rheological properties of the nanocomposite. Stiffness and strength of the nanocomposites treated by post-compounding processes were found to increase by up to 160% and 300%, respectively. The reinforcement effect of carbon nanotubes in the stretched nanocomposites was found to be the greatest. Rheological analysis suggested that the application of post-compounding processes enhanced dispersion of carbon nanotubes within the nanocomposite. Overall, this finding of this research has shown that carbon nanotubes can be incorporated into polypropylene using conventional equipment to provide significant improvement in properties. By careful choices of additives, compounding and postcompounding conditions, specific properties can be further enhanced. / Ministry of higher education in Kurdistan region in Iraq.

Since their first observation in 1991, carbon nanotubes (CNTs) have attracted a lot of attention owing to their exceptional properties. Their excellent electrical and thermal conducting performances combined with their high toughness and transverse flexibility allow their use in a large range of varied applications. Offering at the same time a high aspect ratio (length-to-diameter) and a low density, carbon nanotubes show strong application potential in reinforced composite materials. Unfortunately, CNTs have the strong tendency to form bundles very difficult to dissociate and disperse in a majority of polymer matrices. Without efficient CNTs dispersion, nanocomposites can not present optimal mechanical, thermal and electrical properties. To overcome this drawback, one solution consists to graft polymer chains on the carbon nanotubes surface in order to disaggregate bundles and, in few cases, to improve interaction between the polymer matrix and nanotubes. The thesis work can be divided into three parts. The first is the one-step amination of multi-walled carbon nanotubes (MWNTs) via an original microwave plasma process. The MWNTs, placed in the post-discharge chamber in presence of H2, are subjected to a reactive flow of atomic nitrogen produced by the plasma. The results give evidence for efficient covalent grafting of primary amine groups along the sidewalls of MWNTs, avoiding any structural damage and alteration of properties. The so-grafted amine groups have been further consider as initiation sites for promoting the ring opening polymerization of lactone monomers yielding polyester-grafted MWNT nanohybrids. Finally, these nanohybrids have been used as highly filled masterbatches to be dispersed in the molten state within several polymer matrices, such as polycaprolactone (PCL) and high density polyethylene (HDPE), to obtain nanocomposites with largely improved properties. For instance, electrical measurements and morphological characterizations showed that the polyester surface-grafting allows for improving the dispersion state of the nanotubes in the different polymer matrices leading to enhanced electrical properties as well as thermal and mechanical performances.

In order to optimize the synthesis of metal nanoparticle-polymer systems, there are certain processes which must be understood. Perhaps the most important one is the selective interfacial interaction between the block copolymer and the growing metal nanoparticles. To investigate this interaction, four different approaches were taken. The first approach looked at the strength of interaction between the competing blocks of the copolymer and the metal nanoparticles surface. The second approach looked at the effect of polymer architecture on the metal nanoclusters. The third approach looked at the polymer composition and solvent effects on the phase behavior of the metal nanocluster-block copolymer nanocomposite. Finally, the influence of the metal precursor on the rate of the decomposition was examined. It was found that adsorbed layers of PS on the cobalt nanoparticles are completely displaced by PMMA when the solvent is a common good solvent. An adsorbed layer of only PMMA is also obtained through competitive adsorption from a common good solvent. However, in a selective solvent that is poor for PS, sequential adsorption leads to the formation of mixed layers. In homopolymer solutions, the cluster size reaches a minimum at a finite chain MW. In the case of diblock copolymers, the only parameter (for a fixed copolymer concentration) controlling the cluster size in suspensions of di-block copolymers is the molecular weight of one block, in this case PMMA, and is indifferent to other parameters including the molecular weight of the other block (PS) or the solvent quality. It was also found that the spatial distribution of the metal clusters synthesized in-situ coincided with the morphology dictated by thermodynamically-driven microdomain structure of the block copolymer. Moreover, the overall final morphology of the nanocomposite is locked into place while in solution, and fast solvent evaporation does not cause this morphology to change. Finally, results showed that the rate of nanocomposite synthesis occurred faster in the PS suspensions compared to PMMA, indicating that chemical bonds between PMMA and the cobalt nanoclusters slowed the thermal decomposition of the metal precursor. So the PMMA chains provided sites for nucleation, but did not necessarily aid particle growth.