Improvement of bonding properties of polypropylene by low-pressure plasma treatment

Bonding of rapidly expanded polypropylene (PP) remains poor unless a specia l pretreatment of the PP substrate is performed. In the past mainly chemica l primers were used. A replacement of this type of pretreatment by plasma p retreatment offers advantages from an environmental viewpoint. From the pre sent investigations, where the plasma parameters were systematically varied , it can be concluded that a very short exposure to the plasma and new curi ng conditions led to the best results. The lap shear (bond) strength after plasma pretreatment became even higher than after a primer pretreatment. ESCA analyses and ultrasonic C-scan analyses of the fracture areas were per formed. It was found that a long exposure to the plasma weakened the bounda ry layer. The C-scan analyses showed that the failure of the plasma pretrea ted bonds appears different from that at the primer pretreated specimens. A nother important finding - especially from a practical viewpoint - was that the beneficial effect of the plasma pretreatment before bonding lasted in a laboratory environment much longer than after a primer pretreatment. (C) 1999 Elsevier Science S.A. All rights reserved.