Plasma Penetration Depth And Mechanical Properties Of Atmospheric Plasma Treated 3D Aramid Woven Composites

Plasma treatment, as an important material modification technique, can be used to modify the chemical and physical properties of material surface without altering the bulk properties. Adhesion of fibers to matrices is critical to mechanical and physical performance of composites. However, most of the fibers used for composites do not have good adhesion with matrices. Therefore, plasma treatments have been applied to almost all kinds of reinforcing fibers. In general, the mechanical properties of the fiber reinforced composites in which the plasma-treated fibers were used as reinforcements can beimproved due to improved adhesion between the fiber and the matrix.Treating composite preforms instead of fibers or yarns can be advantageous because yarns may be stored for I ong time before bei ng woven i nto fabri cs and then impregnated in a composite. Due to aging of the plasma treatment effect, by the ti me the yarns are consol i dated i n a composite, the plasma treatment effect could be significantly weakened. Meanwhile, treating fabrics, especially net shaped preforms could minimize the application of the plasmas, saving energy and reducing cost.However, how deep the plasma can penetrate into a preform determines the effectiveness of the plasma treatment. Present researches are limited on the study of two dimension fabrics, while little has been reported on the effect of plasma treatment on the fabrics with more complicated structures such as the 3D woven fabrics for 3D composites which have been more and more frequently used because of their damage tolerance and anti-delamination properties.Three dimensional aramid woven fabrics were treated with atmospheric pressure plasma using air, on their single sides or double sides, with particular interest on the penetration depth in fabrics and the influences on final composite mechanical properties. The properties of fibers from different layers of the single side treated fabrics, including surface morphology, chemical composition, wettability and adhesion properties were investigated using scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), contact angle and micro pulling-out tests. Meanwhile, flexural properties of composites reinforced by the double sides treated fabrics were studied through bending tests. The results showed that fibersfrom the outmost surface layers of fabrics had a significant improvement in their surface roughness, chemical bonding, wettability and adhesion properties after plasma treatment, while the treatment effect became weaker for fibers in inner layers. In the third layer, the fiber properties remained approximately the same to the control. In addition 3-point bending tests indicated that 3D aramid composites had an increase of 11% in flexural strength and 12% in flexural modulus after the plasma treatment. These experimental works suggest that composite mechanical properties can be improved by the direct fabri c treatment i nstead of f i ber treatment of plasma i f the fabric is less than four I ayers thick.