Polyethylene terephthalate/clay nanocomposites with polyhedral oligomeric silsesquioxane as dispersant

Polyethylene terephthalate (PET)/clay nanocomposite is an attractive high performance material that can be used for demanding applications due to its potential to exhibit superior properties at low clay loadings. However, organoclays do not have the adequate thermal stability to withstand the high temperatures required for processing PET and this limits the complete exfoliation of the organoclays and ultimately the properties and applications of the resultant nanocomposites. In order to overcome the degradation issues of the organic surfactants, the thesis focuses on two approaches, i.e. (1) to incorporate thermal stable polyhedral oligomeric silsesquioxane (POSS) into the PET/clay system to replace conventional organic surfactants, and (2) to completely do away with organic surfactant and prepare PET/clay nanocomposites with surfactant-free clay. In this work, the preparation of PET/clay nanocomposites using POSS compounds either as a surfactant (POSS-imidazolium salt) or a spacer (trisilanolphenyl POSS, Tsp-POSS) was investigated. In particular, the resultant structures and properties of the nanocomposites were evaluated in the areas of the extent of clay dispersion, thermo-mechanical properties and thermo-oxidative properties.DOCTOR OF PHILOSOPHY (MSE

Synthesis and structures of hydrogen-bonded liquid crystalline polymers

222 p.Hydrogen-bonded liquid crystalline polymers have unique properties that combine many attractive features that are characteristic of conventional polymers and liquid crystals. Additionally, they have the ability to respond to external stimuli due to the reversibility of the hydrogen bond. The diverse properties of these materials have therefore opened up a multitude of promising applications and disciplines. Consequently, in order to attain a deeper understanding and aid the exploration of potential technological advancements in such materials, new hydrogen-bonded main chain liquid crystalline polymers were prepared. The structure-property relationships were reviewed and their thermal and liquid crystalline properties were examined.Master of Engineering (MSE

Temperature and pH dual-responsive behavior of dendritic poly(N-isopropylacrylamide) with a polyoligomeric silsesquioxane core and poly(2-hydroxyethyl methacrylate) shell

Novel temperature and pH dual-responsive dendritic polyoligomeric silsesquioxane (POSS)–poly(N-isopropylacrylamide) (PNIPAm)–poly(2-hydroxyethyl methacrylate) (PHEMA) copolymers are prepared via atom transfer radical polymerization and click reactions. The cloud points (Tc) decrease with decreasing pH from 10.0 to 5.0 due to the weakened inter-molecular interactions and enhanced intra-molecular hydrogen bonding, whereas the Tc exhibits a small increase from pH 5.0 to 4.0 because of the better solvation of PHEMA at highly acidic conditions. The above findings are corroborated by the different sizes of aggregates observed by dynamic light scattering. The encapsulation of a fluorescent dye and stimulated release by temperature and pH changes are also demonstrated

Poly(ethylene terephthalate)/clay nanocomposites with trisilanolphenyl polyhedral oligomeric silsesquioxane as dispersant : simultaneously enhanced reinforcing and stabilizing effects

This paper presents a new approach for the preparation of poly(ethylene terephthalate) (PET)/clay nanocomposites using surfactant-free clay (sodium montmorillonite, Na-MMT) with trisilanolphenyl polyhedral oligomeric silsesquioxane (Tsp-POSS) as dispersant. The dispersion of clay in the PET/Na-MMT/Tsp-POSS nanocomposites is enhanced over that in PET/Na-MMT by using a very small amount of Tsp-POSS, which acts as functional spacer to keep clay platelets apart and pull monomers in, and, at the same time, acts as a PET chain extender. As a result, thermomechanical properties and thermo-oxidative stability of PET/Na-MMT/Tsp-POSS are improved simultaneously compared with those of PET/organoclay nanocomposites.ASTAR (Agency for Sci., Tech. and Research, S’pore

Reinforcing nylon 6 via surface-initiated anionic ring-opening polymerization from stacked-cup carbon nanofibers

This article reports the preparation of nylon 6/stacked-cup carbon nanofiber (CNF) nanocomposites via in situ anionic ring-opening polymerization partially initiated from caprolactam-functionalized CNFs. As a result of the successful functionalization of CNF surface, good dispersion of the CNFs was observed by transmission electron microscopy (TEM). Moreover, with the addition of a very small amount of CNFs, significant enhancements in tensile modulus and yield strength were achieved together with slightly improved impact resistance. The enhanced stiffness may be attributed to effective filler–matrix stress transfer induced by interfacial covalent bonds. On the other hand, SEM micrographs provided evidence for the possible unraveling of the stacked-cup CNF, which may allow the CNFs to bridge the matrix during crack propagation, hence resulting in the toughening of the nanocomposites.ASTAR (Agency for Sci., Tech. and Research, S’pore

Highly conductive graphene by low-temperature thermal reduction and in situ preparation of conductive polymer nanocomposites

Polydopamine-coated graphene oxide (DGO) films exhibit electrical conductivities of 11 000 S m−1 and 30 000 S m−1 upon vacuum annealing at 130 °C and 180 °C, respectively. Conductive poly(vinyl alcohol)/graphene and epoxy/graphene nanocomposites show low percolation thresholds due to the excellent dispersibility of the DGO sheets and their effective in situ reduction

Reinforcement of polyether polyurethane with dopamine-modified clay : the role of interfacial hydrogen bonding

Dopamine-modified clay (D-clay) was successfully dispersed into polyether polyurethane (PU) by solvent blending. It is found that the incorporation of D-clay into PU gives rise to significant improvements in mechanical properties, including initial modulus, tensile strength, and ultimate elongation, at a very low clay loading. The large reinforcement could be attributed to the hydrogen bonds between the hard segments of PU and stiff D-clay layers that lead to more effective interfacial stress transfer between the polymer and D-clay. Besides, the interactions between D-clay and PU are also stronger than those between Cloisite 30B organoclay and the PU chains. Consequently, at a similar clay loading, the PU/D-clay nanocomposite has much higher storage modulus than the PU/organoclay nanocomposite at elevated temperatures

Simultaneous Enhancements of UV Resistance and Mechanical Properties of Polypropylene by Incorporation of Dopamine-Modified Clay

Inspired by the radical scavenging function of melanin-like materials and versatile adhesive ability of mussel-adhesion proteins, dopamine-modified clay (D-clay) was successfully incorporated into polypropylene (PP) using an amine-terminated PP oligomer as the compatibilizer. Although the PP/D-clay nanocomposites exhibit intercalated morphology, the incorporation of D-clay greatly improves the thermo-oxidative stability and UV resistance of PP owing to the strong radical scavenging ability of polydopamine (PDA) and large contact area between PP and the PDA coating on clay mineral. Moreover, the reinforcement effect brought by D-clay is fairly significant at very low clay loadings probably owing to the strong interfacial interactions between the layered silicates and the compatibilizer as well as that between the compatibilizer and the PP matrix. The work demonstrates that D-clay is a type of promising nanofiller for thermoplastics used for outdoor applications since it stabilizes and reinforces the polymers simultaneously

Reinforcement of Polyether Polyurethane with Dopamine-Modified Clay: The Role of Interfacial Hydrogen Bonding

Dopamine-modified clay (D-clay) was successfully dispersed into polyether polyurethane (PU) by solvent blending. It is found that the incorporation of D-clay into PU gives rise to significant improvements in mechanical properties, including initial modulus, tensile strength, and ultimate elongation, at a very low clay loading. The large reinforcement could be attributed to the hydrogen bonds between the hard segments of PU and stiff D-clay layers that lead to more effective interfacial stress transfer between the polymer and D-clay. Besides, the interactions between D-clay and PU are also stronger than those between Cloisite 30B organoclay and the PU chains. Consequently, at a similar clay loading, the PU/D-clay nanocomposite has much higher storage modulus than the PU/organoclay nanocomposite at elevated temperatures