Effect of Gamma Radiation on Selective Laser Sintered Nylon-12

Injection molded (IM) and additively manufactured (AM) selective laser sintered (SLS) Nylon-12 was irradiated with gamma irradiation to determine the damage mechanism. Modulated differential scanning calorimetry was used to separate the thermodynamic (reversible) and kinetic (non-reversible) heat flows and evaluate how manufacturing method and radiation dose impacted the thermodynamics of melting, along with thermogravimetric analysis (TGA) to investigate thermal stability. Tensile testing and fractography were utilized to evaluate mechanical behavior. The bulk crystallinity of SLS Nylon-12 was not significantly affected by gamma radiation and was estimated to be 38.2 ± 2.3% averaged over all doses. Ultimately, 20 MRad of exposure to SLS Nylon-12 reduced the samples’ early-stage thermal stability by ca. 14.3 °C as measured by TGA, suggesting that the radiation may have contributed to breaking chemical bonds and/or affecting chain entanglement within the polymer structure. The ultimate tensile strength (UTS) decreased with irradiation, suggesting that radiation exposure has a weakening effect (possibly due to chain scissioning) as well as degrading particle coalescence with sintered Nylon-12. SLS Nylon-12 is more susceptible to radiation; the average UTS of Nylon-12 SLS and IM decreased by 54% and 9%, respectively. Injection molding completely transforms α -form to γ -form and results in a lower void volume than SLS.