ICF100500PR Naples-Italy), has a filament diameter about 13 microns and the elastic modulus about 1 GPa. The PET filaments were treated in a cold plasma reactor using oxygen or argon gases, according to the following conditions: excitation frequency was 13,56 MHz, the power of the electrical field was 50 W, the pressure of treatment was 0,3 mbar and the treatment time varied from 5 to 100 s. For the pull-out tests in tensile mode, an INSTRON 4204 at a constant speed of 12 mm min-1 with a 10 N load cell, was used. The pull-out specimens were made according to Gao and Zeng.[6] As shown in Fig. 1, one end of a monofilament with 40cm in length was embedded in a disc of resin that rested in the metal cylindrical support which is attached to a base device; the other end is glued between two cardboard tabs and then fixed in a superior grip attached to the load cell of the equipment. The thickness of the disc which determines the immersion length (l) of the PET monofilament in the resin disc was 3 mm. The diameter of the monofilament was measured by a scanning electron microscope and the interface area was calculated. The fibre resin adhesion τ was defined according to the expression (1): Figure 1 – Pull-out specimen area interface load failure . . ≡ ≡ d l P π τ (1) The surface morphology analysis was developed using a scanning electron microscope LEICA 440S. Gold coating of the samples was carried out using EMSCOPE SC 500. RESULTS AND DISCUSSION Adhesion Table I indicates the results obtained for the pull-out tests with the treated and untreated fibres. Table1 – Tensile strength and fibre/resin adhesion values of the untreated and treated PET fibres by cold plasma, obtained with pull-out tests. Treatment Number of Sample τ(MPa) Sdt (MPa) σmin(MPa) σmax(MPa) σu (MPa) O2 100” 4 895 116 833 1083 828 O2 20” 8 862 96 650 975 816 O2 5” 4 576 87 485 650 545 Ar 100” 6 931 161 668 1167 858 Ar 20” 4 792 139 650 975 748 Ar 5” 5 859 121 730 1048 829 It is possible to observe that the plasma treatments produce a significant effect on the fibre resin adhesion strength. Table I contains the number of specimens tested in each plasma treatment condition, the fibre 3
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