Impact Value Improvement of Polycarbonate by Addition of Layered Carbon Fiber Reinforcement and Effect of Electron Beam Treatment

Polycarbonate (PC) is a highly recyclable thermoplastic with high impact strength that bodes well to re-melting extrusion and shredding for positive environmental impact. For the goal of improving impact strength further, layered carbon fiber (CF) reinforcement has been added between PC sheets by hot pressing at 6.0 MPa and 537 K for 8 min. An addition of cross-weave CF layer reinforcement to PC increased Charpy impact value, <i>a</i>_uc of the untreated [PC]₄[CF]₃ composite over that of untreated PC resin reported at all accumulative probabilities, <i>P</i>_f. At medial-<i>P</i>_f of 0.50, <i>a</i>_uc was increased 3.13 times (213%), while statistically lowest impact value <i>a</i>_s at <i>P</i>_f = 0 calculated by 3-parameter Weibull equation was boosted 2.64 times (164%). To optimize <i>a</i>_uc, effect of homogeneous electron beam irradiation (HLEBI) treatment of 43.2, 129, 216, 302, or 432 kGy at 170 kV acceleration voltage to the CF plies before assembly with PC then hot press was also investigated. The 216 kGy HLEBI dose appears to be optimum, raising <i>a</i>_s at <i>P</i>_f = 0 about 6.5% over that of untreated [PC]₄[CF]₃ and agrees with a previous study that showed 216 kGy to be optimum for static 3-point bending strength, when quality can be controlled. Electron spin resonance (ESR) data confirms 216 kGy HLEBI generates strong peaks in CF and PC indicating dangling bond (DB) generation. Bending strength increase was higher than that of impact due to lower test velocity and higher deformation area spreading along specimen length, allowing more DBs to take on the load. X-ray photoelectron spectroscopy (XPS) data of CF top ~10 nm surface layer in the sizing confirms C-O-H, C-H, and C-O peak height from 216 kGy exhibited little or no change compared with untreated. However, 432 kGy increased the peak heights indicating enhanced adhesion to PC. However, 432 kGy degraded <i>a</i>_s at <i>P</i>_f = 0 of the [PC]₄[CF]₃, and is reported to decrease impact strength of PC itself by excess dangling bond formation. Thus, the 432 kGy created increased PC/CF adhesion, but degraded the PC resin. Therefore, 216 kGy of 170 kV-HLEBI appeared to be a well-balanced condition between the PC-cohesive force and PC/CF interface adhesive force when fabricating [PC]₄[CF]₃.