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Advanced Polymer Science and Engineering

Polymer science has long been a research strength in the Department of Materials Engineering, ranging from thermoplastics to copolymers, thermosets to interpenetrating polymer networks, specialty polymers to composites and nanocomposites. Another strength has been the wide and varied range of characterisation techniques used – mechanical, thermal and spectroscopic. Combined with the processing capabilities that exist on both a large and small-scale in the department, materials can be produced, manipulated and characterized to achieve improved relevant properties such as increases in toughness, conductivity, barrier properties, flame retardance, optical and magnetic functionality, and so on. Work ranges from the fundamental to commercial with research well supported both by national competitive grants, as well as industrial funding. In particular, the Polymer Group has played both a formative, and ongoing role, in the Cooperative Research Center for Polymers (CRC-P) which is now in its third manifestation, having been in existance for around 15 years.

Much research has been focussed into new polymeric nanocomposites. These are mixtures of materials and particles of another phase, where at least one dimension is in the order of nanometers. This is perhaps one of the first areas where nanotechnology will really take off commercially, and some products are on the market already. In the department, we are looking at the mixing of materials such as conductive nanotubes, fullerenes, graphite and carbon blacks with commodity and specialty polymers for a range of purposes, from conductive materials for shielding and electrical discharge applications, to their use in high value areas such as displays and for electron emission (such as for lighting). Mechanical, thermal, tribological, flame retardance and other properties are candidates for property improvement, and we have the capability to look at all of these.  A common thread of this work is the need to be able to manipulate the properties of materials, most often by their surface treatment and particulate dimension. In the case of carbon nanotubes, for example, a range of chemical modification techniques are being used. Such functionality allows further reaction of functional groups onto the surface and ensures good dispersion in a monomer or matrix, but also allows higher loadings of these materials as required.

Nanocomposites with platelet-like nanoclays (layered silicates such as montmorillonite or bentonite) have been extensively studied over many years, in a range of matrices from nylon, to polyolefins to epoxy resins. Work in the latter class has involved including them in high functionality, aerospace-type epoxy matrices for improved toughness and modulus (found to simultaneously occur – unusual and advantageous), as well as other properties such as improving their flammability and barrier properties (such as water uptake). The clay is also found to influence the reactivity of the epoxy, and indeed can help to accelerate the reaction. A more recent focus has been the investigation of ternary systems (polymer + clay + another phase), the latter often being a rubber, in order to see whether optimal properties of modulus, strength and toughness can be produced in such a system. As for nanotubes, surface treatment is found to be key to intercalation and exfoliation, and the properties that result from such a morphology. Much of the above nanocomposite work has been done by the Simon group (often in collaboration with others such as CSIRO), but other polymer researchers at Monash such as Graham Edward and Wayne Cook have been looking at the effect of using nanoparticles on fatigue in various matrices and weldlines (Edward), or as additives in reactive thermoset - thermoplastic composite systems (Cook). 

The Simon group has also been involved with a range of other specialty polymers. In particular, much work has been done on globular, nanoscopic molecules called dendrimers and hyperbranched polymers. These materials are globular in shape (highly branched, like a tree) and have unique properties due to this quasi-spherical nature, with a very high level of surface functionality. This gives them interesting glass transition, solubility and rheological properties. A number of these types of material have been studied as a function of structure, and also blended into other materials where they can be used to reduce viscosity and toughen the material. Work has also been done where the end groups are functionalised with reactive groups, and they can become covalently incorporated into the matrix. Recently work has extended to looking at thermoplastically-processable starches, relevant to a local start-up company, Plantic, and undertaken as part of the CRC for Polymers. Other specialty polymers, such as those with improved optical properties, are being examined by the group of Forsythe. This work is in collaboration with a consortium of microelectronic manufacturing companies including Intel, IBM, Texas Instruments and Hewlett-Packard and is targeted at synthesizing new high refractive index polymers to allow for smaller features sizes on computer chips.  The project involves synthesizing and characterising new generation polyphosphazene resists with tunable refractive indices. Forsythe also uses biodegradable polymers and copolymers to make three dimensional nano- and micro-porous scaffolds for seeding with cells, for tissue engineering purposes, in particular regenerating materials such as bones and neural pathways in the brain (More information can be found in the Biomaterials and Tissue Engineering section. One way in which this is done is by electrospinning the polymers. This is a technique where high voltages and electric charge build up is used to produce fibres of nanometer size scale in either non-woven mats or in aligned geometries, and this has been recently commissioned in the department. Forsythe and Simon are also exploring electrospinning of neat polymers, and of nanocomposites (such as with nanotubes), to produce new types of nano-fibrous and non-woven matting for a range of biomaterial, conductive and mechanical property applications.

The research of Edward concerns the effects of processing on the properties of injection molded products. Injection molding of semicrystalline polymers results in multiple layered structures where the interplay between the internally stressed layers has profound effects on the properties of the final product. The structure of the layers can be affected by molding conditions, and by additives such as colorants. This project is systematically investigating the morphology and properties of moldings, using ultra fine synchrotron X-ray beams to differentiate between the thin layers. Typically the layers near the surface are highly oriented, with so-called shish kebab crystalline structures lined up along the flow direction, whereas the central layers display a non oriented spherical (spherulitic) crystalline arrangement. The results have commercial significance in the development of simulation and predictive design software, and have also resulted in a number of prestigious publications.

Cook's research interests deal with the relationships between polymer structure, reaction kinetics and mechanical, thermal, electrical, photochemical and rheological properties. This work involves two aspects: firstly, the investigation of well defined (and stable) materials to provide structure-property fundamentals and secondly, the extrapolation (and extension) of this knowledge to the structure as it changes due to chemical, thermal, photochemical, temporal or stress induced change. Four specific polymer areas are currently being targeted. The first area is that of polymer networks in which three dimensional structures are formed by crosslinking reactions. In most of these studies, the photocuring technique is used as a convenient way of controlling the polymerization process. The influence of gelation and vitrification on the reaction kinetics and the final structure and morphology are being examined by thermal, microscopy and spectroscopic techniques and are related to the materials properties and applications.  Together with Forsythe, work has also progressed in the area of studying kinetics of cure within thick polymer-fibre composites eg. an aircraft wing, since this influences the final properties of the specimen.  Uneven cure may lead to stresses and therefore warpage or diminished mechanical properties.  Research carried out involves the use of optical fibres interfaced with near infrared spectroscopy to monitor in real time the cure of thick composite sections with respect to time, depth and temperature of cure.

The second area of Cooks research deals with the mechanisms of yielding and toughening of polymers and methods to improve these properties. These include studies of phase-precipitation, core-shell and particulate toughening; yielding mechanisms and viscoelastic processes; and ageing phenomena. The third area is that of polymer blends. This work is studying the effect of the polymer-polymer interaction and processing conditions on the final morphology and hence physical properties of the blend. Work on polymer blends also includes blends of crosslinked polymers (IPNs) and of blends of crosslinked polymers and thermoplastics. These blended polymer systems allow optimisation and in some cases startling improvement of properties of polymer processibility.  The last targeted area deals with nano-structures in crosslinked polymers produced either by inclusion of nano-fillers into the polymer matrix or by the creation of nano-structures in the matrix by controlled polymerisation techniques.

Active researchers in this field: