• Effects of mould wear on hydrophobic polymer surfaces replicated using plasma treated and laser-textured stainless steel inserts

      Dimov, Stefan; Romano, J.-M.; Sarasa, J.F.; Concheso, C.; Gülçür, Mert; Dashtbozorg, B.; Garcia-Giron, A.; Penchev, P.; Dong, H.; Whiteside, Benjamin R. (2020)
      The mass production of polymeric parts with functional surfaces requires economically viable manufacturing routes. Injection moulding is a very attractive option however wear and surface damage can be detrimental to the lifespan of replication masters. In this research, the replication of superhydrophobic surfaces is investigated by employing a process chain that integrates surface hardening, laser texturing and injection moulding. Austenitic stainless steel inserts were hardened by low temperature plasma carburising and three different micro and nano scale surface textures were laser fabricated, i.e. submicron triangular LaserInduced Periodic Surface Structures (LIPSS), micro grooves and Lotus-leaf like topographies. Then, a commonly available talc-loaded polypropylene was used to produce 5000 replicas to investigate the evolution of surface textures on both inserts and replicas together with their functional response. Any wear orsurface damage progressively built up on the inserts during the injection moulding process had a clear impact on surface roughness and peak-to-peak topographies of the replicas. In general, the polymer replicas produced with the carburised inserts retained the wetting properties of their textured surfaces for longer periods compared with those produced with untreated replication masters.
    • Lotus-leaf inspired surfaces: hydrophobicity evolution of replicas due to mechanical cleaning and mold wear

      Romano, J.-M.; Garcia-Giron, A.; Penchev, P.; Gülçür, Mert; Whiteside, Benjamin R.; Dimov, S. (2020-03)
      Inspired from the low wetting properties of Lotus leaves, the fabrication of dual micro/nano-scale topographies is of interest to many applications. In this research, superhydrophobic surfaces are fabricated by a process chain combining ultrashort pulsed laser texturing of steel inserts and injection moulding to produce textured polypropylene parts. This manufacturing route is very promising and could be economically viable for mass production of polymeric parts with superhydrophobic properties. However, surface damages, such as wear and abrasion phenomena, can be detrimental to the attractive wetting properties of replicated textured surfaces. Therefore, the final product lifespan is investigated by employing mechanical cleaning of textured polypropylene surfaces with multipurpose cloths following the ASTM D3450 standard. Secondly, the surface damage of replication masters after 350 injection moulding cycles with glass-fiber reinforced polypropylene, especially to intensify mould wear, was investigated. In both cases, the degradation of the dual-scale surface textures had a clear impact on surface topography of the replicas and thus on their wetting properties, too.
    • Mechanical durability of hydrophobic surfaces fabricated by injection moulding of laser-induced textures

      Romano, J.-M.; Gülçür, Mert; Garcia-Giron, A.; Martinez-Solanas, E.; Whiteside, Benjamin R.; Dimov, S.S. (2019-05-15)
      The paper reports an investigation on the mechanical durability of textured thermoplastic surfaces together with their respective wetting properties. A range of laser-induced topographies with different aspect ratios from micro to nanoscale were fabricated on tool steel inserts using an ultrashort pulsed near infrared laser. Then, through micro-injection moulding the topographies were replicated onto polypropylene surfaces and their durability was studied systematically. In particular, the evolution of topographies on textured thermoplastic surfaces together with their wetting properties were investigated after undergoing a controlled mechanical abrasion, i.e. reciprocating dry and wet cleaning cycles. The obtained empirical data was used both to study the effects of cleaning cycles and also to identify cleaning procedures with a minimal impact on textured thermoplastic surfaces and their respective wetting properties. In addition, the use of 3D areal parameters that are standardised and could be obtained readily with any state-of-the-art surface characterisation system are discussed for monitoring the surfaces' functional response.