Effect of cold plasma treatment on surface roughness and bonding strength of polymeric substrates Chiara Mandolfino 1, a * , Enrico Lertora 1,b and Carla Gambaro 1,c 1 Polytechnic School of Genoa - Dept. of Mechanical Engineering Via all’Opera Pia 15 16145 – Genoa – Italy a chiara.mandolfino@unige.it, b e.lertora@unige.it, c gambaro@diptem.unige.it * Corresponding author Keywords: Cold plasma treatment, Surface roughness, Polyolefin. Abstract. For an effective application of polymers, it is essential to have good adhesion behaviour to ensure good mechanical properties and durable components. Unfortunately, in general terms, polymers are characterized by high chemical inertness, which leads to very low surface energy values and, consequently, poor adhesive properties; this is particularly true for polyolefins. In this study, the effects of low pressure plasma treatment on surface roughness of polyethylene and polypropylene samples and on shear properties of adhesive bonded joints based on these substrates have been investigated. In particular, the optimization of three plasma process parameters, exposure time, voltage and working gas, were studied performing roughness measurement, contact angle evaluation and lap-shear tests. The experimental results show that the optimized plasma process may remarkably change the surface morphology, increasing wettability properties of the surfaces and shear strength of the bonded joints. These good properties remain almost unchanged even after some days of storage in the laboratory. Introduction In recent times, considerable efforts have been made in several industrial fields for the development of lighter materials, such as polymers and composites, which are often manufactured by adhesive bonding to form structural components. Indeed, numerous studies on bonding techniques compared to welding and riveting have been conducted for a great number of materials and applications [1,2] and a good adhesive bonded joint offers several advantages compared to other conventional joining processes, namely acoustic insulation, vibration attenuation, structure lightening, reduction of corrosion problems and a more uniform stress distribution [3]. In particular, the main aspect to take into account for an efficient application of polymers is good adhesion behaviour which ensures good mechanical properties and durable components. Unluckily, in general terms, polymers are characterized by high chemical inertness, which leads to very low surface energy values and, consequently, poor adhesive properties and this is particularly true for polyolefins [4]. Therefore, the surface preparation of polymeric adherends is extremely important in the adhesive bonding process to increase the necessary surface properties of hydrophilicity and roughness. A number of surface treatments based both on chemical or physical modifications have been developed in recent years in order to improve the surface activity of polymers [5,6]. Chemical treatments modify both the morphology and chemical structure of polymers, but they present serious environmental problems of waste disposal. On the other hand, physical methods based on mechanical abrasion are used to increase surface roughness and the bonding area, but could cause an extensive degradation to the treated specimens [3-6]. Key Engineering Materials Vols. 611-612 (2014) pp 1484-1493 Online available since 2014/May/23 at www.scientific.net © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/KEM.611-612.1484 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 130.251.66.93-30/06/14,09:06:17)