JOURNAL OF MATERIALS SCIENCE LETTERS 13 (1994) 280-282 Environmental effects on the bondability of 02 plasma treated polyolefins G. XIAO* IPTME, Loughborough University of Technology, Leicestershire, LE11 3TU, UK B. J. HUA, J. S. YANG Beijing Research Institute of Materials and Technology, Beijing 100076, People's Republic of China J. M. WANG Department of Library Studies and Information Science, Loughborough University of Technology, Leicestershire, LE11 3TU, UK Because of the superior properties of polyolefins, such as corrosive protection, electrical insulation and easy handling, these types of materials have been widely used in many fields. However, their bondabilities are very poor, which causes problems with practical applications of these materials. To improve the bondability of polyolefins, many methods have been developed. Among them, plasma treatment has more advantages than other methods, including effective, easy operation and no pollution. Plasma treatment usually alters the poly- mer surface composition and creates some chemical groups, such as hydroxyl, carbonyl, carboxyl and other polar groups, which are capable of interacting with an adhesive [1-4]. The bondability improve- ment by plasma is thought to be mainly attributable to the introduction of these polar groups [1]. However, in industry, plasma treated surfaces are usually in contact with the environment before being used, and the effects of environment on the bond- ability and other surface properties of plasma treated materials are not very clear. Moreover, when the surfaces are contaminated, solvents are applied generally to clean them, and the effects of solvents on the bondability of plasma treated mater- ials are still unknown. In this letter some results on the effects of atmospheric exposure and solvent wiping on the bondability of oxygen plasma treated polyolefins are presented from a study in which electron spectroscopy for surface analysis (ESCA) and contact angle measuring equipment were em- ployed to correlate physical and chemical properties with bondability. Two polyolefins were investigated in this initial work: amorphous PE film, 0.14ram thick and amorphous PP film, 0.10 mm thick (both supplied by Beijing Plastic Factory). The adhesive used was epoxy adhesives (E-51 epoxy resin, 50 wt %; poly- amide, 50wt%), cured at 60 °C for 3 h. Adhesion was examined using single lap shear tests with a 25 mm x 15 mm overlap. The specimens were configured as follows: A1/adhesive/polyolefin/ adhesive/A1. The results were the average value of at least five specimens. *Author to whom all correspondence should be addressed. 280 The surface modifications were conducted by a PST-1 plasma generator (Physical Institute of Chinese Science Academy). Samples were first cleaned with acetone, air dried and then treated under different conditions according to the different requirements. The surface properties were characterized by ESCA and contact angle. An ESCA-750 spectro- meter with MgKo4,2 radiation under a pressure of 1.333 x 10 .5 Pa was employed to analyse the surface compositions, such as surface oxygen:carbon ratio. To reduce the exposure time in air, treated samples were transferred in glass bottles, since the X-ray photoelectron spectrometer was not equipped with in situ plasma treatment. The contact angle of water was taken as the standard of the wettability of polyolefins in this letter. JY-82 Contact Angle Measuring apparatus was used. A drop of water was placed on the polymer surfaces and allowed to stand for about 1 min. The contact angle was read on both sides of the drop. Measurements were made at five spots on each sample of film, and all were averaged. The study was carried out to examine the effects of atmospheric exposure and solvent wiping. Oxy- gen plasma treated polyolefins were exposed to the atmosphere for two months (temperature, 11-22 °C; relatively humidity, 49-74%). The lap shear strength, contact angle of water and surface oxygen:carbon ratio were measured once every 15 days. For solvent wiping, oxygen plasma treated poly- olefins (before and after atmospheric exposure) were wiped with acetone and air dried. The lap shear strength, contact angle of water and surface oxygen :carbon ratio were measured. The results for atmospheric exposure and solvent wiping are summarized in Tables I and III and Figs 1 and 2. Several conclusions may be drawn from these results. Firstly, atmospheric exposure does not decrease the lap shear strength of oxygen plasma treated polyolefins/adhesive joints and the failure locus. In fact, it increases the joint strength slightly for a certain exposure period, after which it remains unchanged. For PE, this period is the first 15 days, 0261-8028 © 1994 Chapman & Hall