Material-jetting is a sub-field of additive manufacturing that typically produces
cross-linked products with high engineering value. Various post-treatment techniques
are often used to enhance the performance of the product. The aim of these post-treatments
is mainly to increase the cross-linking density. The use of ionising radiation can
be an excellent alternative for this purpose. In this study, gamma radiation was chosen
as the ionising radiation and its applicability as a post-treatment technique was
investigated. The printed samples were post-treated with absorbed doses between 25
and 200 kGy. Irradiation has significantly changed the mechanical properties. The
tensile modulus for the untreated sample (0 kGy) was 1.92 GPa and it increased to
2.76 GPa after irradiation with 200 kGy, while the tensile strength increased from
38.1 MPa to 64.6 MPa. The heat deflection temperature of the untreated specimen was
48 degrees C, which increased to 60 degrees C for the 200 kGy irradiated specimen.
The irradiation also had an effect on the thermal properties: the glass transition
temperature increased from 46.7 degrees C to 59.6 degrees C, which is an outstanding
result when compared to other post-treatment techniques. The changes in properties
were caused by an increase in cross-link density, as confirmed by swelling and Fourier
transform infrared spectroscopic analyses. The results presented in this study prove
that high-energy gamma irradiation is a novel and effective tool to customise the
mechanical and thermal properties of material jetting printed photopolymer parts.
Gamma irradiation has clear practical benefits in industries where it is already applied,
like medical device manufacturing, pharmaceutical or food industry, where strict sterilisation
requirements can often be fulfilled by it.
