The chemical structure and mechanical properties of phenolic resins and related polymers

Paper-based phenolic laminates are used extensively in the electrical industry. Many small components are fabricated from these materials by the process known as punching. Recently an investigation was carried out to study the effect of processing variables on the punching properties. It was concluded that further work would be justified and that this should include a critical examination of the resin properties in a more controlled and systematic manner. In this investigation an attempt has been made to assess certain features of the resin structure in terms of thermomechanical properties. The number of crosslinks in the system was controlled using resins based on phenol and para-cresol formulations. Intramolecular hydrogen bonding effects were examined using substituted resins and a synthetically derived phenol based on 1,3-di-(o-hydroxyphenyl) propane.. A resin system was developed using the Friedel Crafts reaction to examine inter-molecular hydrogen bonding at the resin-paper interface. The punching properties of certain selected resins were assessed on a qualitative basis. In addition flexural and dynamic mechanical properties were determined in a general study of the structure-property relationships of these materials. It has been shown that certain features of the resin structure significantly influenced mechanical properties. :F'urther, it was noted that there is a close relationship between punching properties, mechanical damping and flexural strain. This work includes a critical examination of the curing mechanism and views are postulated in an attempt to extend knowledge in this area of the work. Finally, it is argued that future work should be based on a synthetic approach and that dynamic mechanical testing would provide a powerful tool In developing a deeper understanding of the resin fine structure.

Degree of conversion of different composite resins photo-activated with light-emitting diode and argon ion laser

This study evaluated the degree of conversion (DC%) of one experimental and different brands of composite resins light-cured by two light sources (one LED and one argon laser). The percentage of unreacted C = C was determined from the ratio of absorbance intensities of aliphatic C = C (peak at 1637 cm−1) against internal standards before and after curing: aromatic C–C (peak at 1610 cm−1) except for P90, where %C = C bonds was given for C–O–C (883 cm−1) and C–C (1257 cm−1). ANOVA and Tukey’s test revealed no statistically significant difference among Z350 (67.17), Z250 (69.52) and experimental (66.61 ± 2.03) with LED, just among them and Evolu-X (75.51) and P90 (32.05) that showed higher and lower DC%, respectively. For the argon laser, there were no differences among Z250 (70.67), Z350 (69.60), experimental (65.66) and Evolu-X (73, 37), however a significant difference was observed for P90 (36.80), which showed lowest DC%. The light sources showed similar DC%, however the main difference was observed regarding the composite resins. The lowest DC% was observed for the argon laser. P90 showed the lowest DC% for both light-curing sources.

The synthesis and application of novel profluorescent nitroxides as probes for polymer degradation

This PhD project has expanded the knowledge in the area of profluorescent nitroxides with regard to the synthesis and characterisations of novel profluorescent nitroxide probes as well as physical characterisation of the probe molecules in various polymer/physical environments. The synthesis of the first example of an azaphenalene-based fused aromatic nitroxide TMAO, [1,1,3,3-tetramethyl-2,3-dihydro-2-azaphenalen-2-yloxyl, was described. This novel nitroxide possesses some of the structural rigidity of the isoindoline class of nitroxides, as well as some properties akin to TEMPO nitroxides. Additionally, the integral aromatic ring imparts fluorescence that is switched on by radical scavenging reactions of the nitroxide, which makes it a sensitive probe for polymer degradation. In addition to the parent TMAO, 5 other azaphenalene derivatives were successfully synthesised. This new class of nitroxide was expected to have interesting redox properties when the structure was investigated by high-level ab initio molecular orbitals theory. This was expected to have implications with biological relevance as the calculated redox potentials for the azaphenalene ring class would make them potent antioxidant compounds. The redox potentials of 25 cyclic nitroxides from four different structural classes (pyrroline, piperidine, isoindoline and azaphenalene) were determined by cyclic voltammetry in acetonitrile. It was shown that potentials related to the one electron processes of the nitroxide were influenced by the type of ring system, ring substituents or groups surrounding the moiety. Favourable comparisons were found between theoretical and experimental potentials for pyrroline, piperidine and isoindoline ring classes. Substitution of these ring classes, were correctly calculated to have a small yet predictable effect on the potentials. The redox potentials of the azaphenalene ring class were underestimated by the calculations in all cases by at least a factor of two. This is believed to be due to another process influencing the redox potentials of the azaphenalene ring class which is not taken into account by the theoretical model. It was also possible to demonstrate the use of both azaphenalene and isoindoline nitroxides as additives for monitoring radical mediated damage that occurs in polypropylene as well as in more commercially relevant polyester resins. Polymer sample doped with nitroxide were exposed to both thermo-and photo-oxidative conditions with all nitroxides showing a protective effect. It was found that isoindoline nitroxides were able to indicate radical formation in polypropylene aged at elevated temperatures via fluorescence build-up. The azaphenalene nitroxide TMAO showed no such build-up of fluorescence. This was believed to be due to the more labile bond between the nitroxide and macromolecule and the protection may occur through a classical Denisov cycle, as is expected for commercially available HAS units. Finally, A new profluorescent dinitroxide, BTMIOA (9,10-bis(1,1,3,3- tetramethylisoindolin-2-yloxyl-5-yl)anthracene), was synthesised and shown to be a powerful probe for detecting changes during the initial stages of thermo-oxidative degradation of polypropylene. This probe, which contains a 9,10-diphenylanthracene core linked to two nitroxides, possesses strongly suppressed fluorescence due to quenching by the two nitroxide groups. This molecule also showed the greatest protective effect on thermo-oxidativly aged polypropylene. Most importantly, BTMIOA was found to be a valuable tool for imaging and mapping free-radical generation in polypropylene using fluorescence microscopy.

Fumaric acid monoethyl ester-functionalized poly(D,L-Lactide)/N-vinyl-2- pyrrolidone Resins for the preparation of tissue engineering scaffolds by stereolithography

Polymer networks were prepared by photocross-linking fumaric acid monoethyl ester (FAME) functionalized, three-armed poly(D,L-lactide) oligomers using Af-vinyl-2-pyrrolidone (NVP) as diluent and comonomer. The use of NVP together with FAME-functionalized oligomers resulted in copolymerization at high rates, and networks with gel contents in excess of 90 were obtained. The hydrophilicity of the poly(D,L-lactide) networks increases with increasing amounts of NVP, networks containing 50 wt of NVP absorbed 40 of water. As the amount of NVP was increased from 30 to 50 wt , the Young's modulus after equilibration in water decreased from 0.8 to 0.2 GPa, as opposed to an increase from 1.5 to 2.1 GPa in the dry state. Mouse preosteoblasts readily adhered and spread onto all prepared networks. Using stereolithography, porous structures with a well-defined gyroid architecture were prepared from these novel materials. This allows the preparation of tissue engineering scaffolds with optimized pore architecture and tunable material properties.

Methacrylate-functionalized oligomers based on lactide, E-caprolactone and trimethylene carbonate for application in stereo-lithography

Photo-curable biodegradable macromers were prepared by ring opening polymerization of D,L-lactide (DLLA), (similar to)-caprolactone (CL) and 1,3-trimethylene carbonate (TMC) in the presence of glycerol or sorbitol as initiator and stannous octoate as catalyst, and subsequent methacrylation of the terminal hydroxyl groups. These methacrylated macromers, ranging in molecular weight from approximately 700 to 6000 g/mol, were cross-linked using ultraviolet (UV) light to form biodegradable networks. Homogeneous networks with high gel contents were prepared. One of the resins based on PTMC was used to prepare three-dimensional structures by stereo-lithography using a commercially available apparatus.

Methacrylate-functionalized oligomers based on lactide, ε- caprolactone and trimethylene carbonate for application in stereo-lithography

Photo-curable biodegradable macromers were prepared by ring opening polymerization of D,L-lactide (DLLA), ε-caprolactone (CL) and 1,3-trimethylene carbonate (TMC) in the presence of glycerol or sorbitol as initiator and stannous octoate as catalyst, and subsequent methacrylation of the terminal hydroxyl groups. These methacrylated macromers, ranging in molecular weight from approximately 700 to 6000 g/mol, were cross-linked using ultraviolet (UV) light to form biodegradable networks. Homogeneous networks with high gel contents were prepared. One of the resins based on PTMC was used to prepare three-dimensional structures by stereo-lithography using a commercially available apparatus.

Designed biodegradable hydrogel structures prepared by stereolithography using poly(ethylene glycol)/poly(D,L-lactide)-based resins

Designed three-dimensional biodegradable poly(ethylene glycol)/poly(D,L-lactide) hydrogel structures were prepared for the first time by stereolithography at high resolutions. A photopolymerisable aqueous resin comprising PDLLA-PEG-PDLLA-based macromer, visible light photo-initiator, dye and inhibitor in DMSO/water was used to build the structures. Porous and non-porous hydrogels with well-defined architectures and good mechanical properties were prepared. Porous hydrogel structures with a gyroid pore network architecture showed narrow pore size distributions, excellent pore interconnectivity and good mechanical properties. The structures showed good cell seeding characteristics, and human mesenchymal stem cells adhered and proliferated well on these materials.

Age-related trends in urinary excretion of bisphenol A in Australian children and adults : evidence from a pooled sample study using samples of convenience

Bisphenol A (BPA or 4,4’-(propane-2,2-diyl)diphenol) is a chemical intermediate in the production of polycarbonate and epoxy resins, and used in a wide range of applications. BPA has attracted significant attention in the past decade due to its frequency of detection in human populations worldwide, demonstrated animal toxicity and potential impact on human health, particularly during critical periods of development. The aim of this study was to perform a preliminary assessment of age-related trends in urinary concentration and to estimate daily excretion of BPA in Australian children (aged (>0 – <5 years) and adults (≥15 – <75 years). This was achieved using 79 samples pooled by age and gender, created from 868 individual samples of convenience collected as part of routine, community-based pathology testing. Total BPA was analyzed using online-SPE-LC-MS/MS and detected in all samples with a range of 0.65 – 265 ng/ml. No significant differences were observed between males and females. A urine flow model was constructed from published values and used to provide an estimate of daily excretion per unit bodyweight for each pooled sample. The daily excretion estimates ranged from 26.2 – 18200 ng/kg-d for children; and 20.1 – 165 ng/kg-d for adults. Urinary concentrations and estimated excretion rates were inversely associated with age, and estimated daily excretion rates in infants and young children were significantly higher than in adults (geometric mean: 107 and 47.0 ng/kg-d, respectively). Higher excretion of BPA in children may be explained by their higher food consumption relative to body weight compared to adults and adolescents, and may also reflect alternative exposure pathways and sources. Keywords: bisphenol A, biomonitoring, children, urine flow, Australia

Darling and the Great Anabranch : Talking fish - making connections with the rivers of the Murray-Darling Basin

The Lower Darling River and Great Darling Anabranch are located in south west New South Wales. Muddy waters meander over the grey soil floodplains past red dunes, spiky saltbush and gnarled red gums. These are the traditional lands of the Paakintji people. But the land and the river are no longer what the Paakintji once knew and fished...

Plasma polymer-coated on nanoparticles to improve dielectric and electrical insulation properties of nanocomposites

Polymeric nanocomposites have been shown to possess superior electrical insulation properties compared to traditional filled-resins. However, poor dispersion uniformity and insufficient filler-matrix interaction can adversely affect insulation properties of nanocomposites. In this study, the use of plasma polymerization is proposed to coat poly(ethylene oxide) polymer layers on silica nanoparticles. It is shown that better dispersion is achieved and C-O bonds are created between the surface functional groups of the nanoparticles and the host epoxy polymer. Electrical insulation tests demonstrate that the nanocomposites with plasma polymerized silica nanoparticles feature better resistance against electrical treeing, lower dielectric constant, and also mitigated space charge built-up. Therefore, plasma polymerization offers a promising fabrication technique to further improve the synthesis of nanocomposite dielectrics with superior electrical insulation properties.