Surface cleaning technologies for the removal of crosslinked epoxide resin

This study provides details of the use of laser ablation and sodium hydride cleaning processes for the removal of crosslinked epoxide and other residues from resin transfer moulding (RTM) tool substrates, as used in the aerospace industry. The requirement for removal of such contamination is so that the mould can be re-used, following the subsequent application of an external release agent. These tools are, typically, fabricated from steel, nickel or CFRP composite materials; this paper focuses on the use of nickel substrates. The requirement to clean large surface areas quickly to satisfy commercial restraints, compromises the degree of absolute cleanliness that can be obtained. However, in applications where cleaning time is not a constraint, laser cleaning can be a very gentle and efficient process; typically Nd:YAG lasers find application in this area. In contrast, high power lasers are desirable for industrial scale applications where large areas need to be cleaned quickly. In this instance pulsed CO2 lasers can be used. The use of sodium hydride was also found to be highly successful in removing crosslinked organic contamination providing that suitable hard rinse and drying operations were also carried out

Hot and cold cleaning methods: CO2 and Nd:YAG laser ablation, sodium hydride immersion and CO2 cryoblasting

Cleaning of RTM moulds – the problem! The removal of loosely bound or weakly adsorbed contamination from surfaces can usually be achieved using conventional cleaning methods such as solvents or proprietory aqueous-based cleaning solutions. However, the removal of fully crosslinked material which might be strongly adsorbed or chemisorbed onto surfaces, such as paints or adhesives, presents a much greater challenge. Similarly, residual epoxide resins remaining on the inside surfaces of resin transfer mould (RTM) tooling post curing are strongly adhered to the mould surface and need to be removed so that the mould can be reused. The mould materials are typically steel or nickel but may be compositebased. Conventional methods cannot fully remove residual epoxide material without the use of hazardous chemicals and mechanical removal can easily result in damage to the underlying mould which may compromise its reuse. Therefore, a number of novel cleaning solutions have been investigated to address the challenging problem of how to remove fully crosslinked epoxide resins from RTM mould surfaces

A review and comparative study of release coatings for optimised abhesion in resin transfer moulding applications

In this study, a number of abhesion promoting coatings were considered in terms of their physicochemical and release properties. The techniques used to further this study include; FEGSEM, AFM, profilometry, AFM, XPS, AES, SSIMS, FTIR and contact angle analysis for coating physical and chemical characterisation along with PF-AFM and other adhesion and mechanical tests to determine surface release properties. These coatings were applied to metal substrates and were based upon silicone, fluoropolymer or metal-PTFE composite chemistry, all being potentially useful as release films for resin transfer moulding (RTM) applications. The semi-permanent Frekote B15/710 NC mould release coating system, which is based on PDMS, proved extremely effective in terms of release against a cured epoxide applied under pressure. Although fluoroalkylsilane coatings offer a number of technological advantages for release applications they generally produce very thin coatings which conform any existing surface topography and adhesion through mechanical interlocking occurs. The commercial PTFE-based coatings were found to provide poor release properties due to the presence of surface microcracks which allowed epoxide penetration when cured under elevated pressure and temperature. Electroless Ni/PTFE composite coatings comprise hard nickel-phosphorus matrix containing a very fine dispersion of PTFE particles. The matrix proved sufficiently robust for industrial applications and the low friction and surface energy provided by the embedded PTFE combined with macroscopic scale surface roughness provided efficient mould release