Development of a photocuring system for cationic epoxy formulations using side emitting optical fibres.
PhD thesis, University of Nottingham.
Photocuring of polymers and polymer composites, from epoxy resin based formulations, has been of growing interest over the past two decades. The photocuring occurs when an epoxy formulation is exposed to electromagnetic radiation, usually ultraviolet (UV) radiation. This process has been explored widely and it can be described as an open mould process by which the epoxy formulation is exposed directly to the radiation. However, for a closed mould process, thermal curing, rather than radiation curing, typically is employed. The potential of using photocuring for a closed mould process has not yet been investigated in detail. The challenge in photocuring of polymers and polymer composites in a closed mould is directing the radiation into the mould to activate the photocuring process, which is not possible using the conventional methods. Hence, for this reason the present work is focused on the development of a closed mould photocuring system using side emitting optical fibres.
This photocuring system using side emitting optical fibres relies upon the optimisation of epoxy based resins. As a result, an extensive characterisation of different types of UV curable cationic epoxy resins is carried out using two pre-formulated commercial resins, formulations from bisphenol A/F, and formulations from cycloaliphatic epoxy. The formulations showed different reactivity and hardness. An important result is that the cycloaliphatic epoxy resin formulations cured much faster than the other bisphenol A/F formulations, having a more uniform hardness distribution and UV radiation transparency during the curing.
Side emitting optical fibres are adopted to photocure epoxy in a closed mould. Different types of side emitting optical fibres are characterised to determine irradiation efficiency. The optical fibres had either a silica core or a PMMA core. The silica core fibres have a silicone cladding containing radiation scattering particles (either ZnO or Al2O3) and diffuser (either PA6 or ETFE). The PMMA core polymer optical fibres (PMMA POFs) have a PVDF cladding with micro-perforations as a side emission mechanism. Silica core fibres with the Al2O3 scattering particles and the PMMA core fibre are more suitable for the closed mould application as they transmitted efficiently in the UV radiation band. The high side emission characteristics of the PMMA POF compared to the silica core fibre showed higher potential for use in the closed mould photocuring process.
As the polymerisation speed is influenced by the amount of flux density of the radiation source, a high flux lamp (Hg lamp, 40 W/cm2) is coupled to the side emitting optical fibres. This lamp caused thermal degradation to the PMMA POF at the launch point when in use. A cooling device is made to minimise the thermal degradation generated by radiation absorption. After improving the optical transmission stability of the PMMA POF, its side emission is enhanced by various treatments, such as permanent modification of the fibre geometry with adjusted bend radii as well as by mechanically embedding silica scattering particles into the fibre and applying micro-cuts.
The developed, closed mould photocuring system consists of: enhanced side emitting PMMA POF, a cooling device, high emission Hg lamp, and a closed mould setup. 1.5 mm and 5 mm thick components, made from an optimised epoxy formulation (based on cycloaliphatic epoxy), are cured using the photocuring system. The 1.5 mm thick component (20 mm wide and 245 mm long) is cured in 45 minutes using a single PMMA POF treated with silica particles (side emission of ~81 % of the total launched emission). The 5 mm thick component (75 mm wide and 170 mm long) partly cured in 45 minutes by simultaneously using three PMMA POFs treated with silica particles and geometric modification (side emission of ~96 % of the total launched emission). This sample eventually cured with time (up to 36 hours) due to dark reaction. The efficiency of the developed closed mould photocuring system is validated by curing a 1.5 mm thick component made from a pre-formulated polyester resin formulation. This component cured in 7 minutes (30 mm wide and 245 mm long) using a single PMMA POF treated with silica particles.
Thesis (University of Nottingham only)
||Closed mould photocuring system, Epoxy resin based formulations, Optical fibre characterisation, Photocuring of polymers
||T Technology > TP Chemical technology
||UK Campuses > Faculty of Engineering > Department of Mechanical, Materials and Manufacturing Engineering
||12 Mar 2010 15:38
||16 Sep 2016 09:12
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