Ultrafast hardening of a modelling paste by UV-curing of a polyamide filled acrylic resin

A modelling paste has been hardened within seconds upon exposure to intense UV-radiation at ambient temperature. The composite formulation was made of an acrylate functionalized oligomer, a radical-type photoinitiator (0.5 wt%), and an ultrafine polyamide powder (40 wt%). The polymerization process has been quantitatively followed by near-infrared spectroscopy and shown to proceed up to conversions above 90%. A more complete curing was achieved for 1 mm thick samples than for thin films, because of the greater increase in the sample temperature caused by the heat evolved in such ultrafast exothermal polymerization. Hardening of the paste by low-intensity visible light resulted slower and less extensive photocuring. The tensile properties of the photocrosslinked polymer were evaluated from stress-strain curves, and found to reach their optimum values for a UV-dose of 5 J cm−2. The highest tensile strength (60 MPa) was obtained with a polyphenoxy-diacrylate oligomer. The addition of the polyamide filler has a negative effect on the tensile properties, depending on the granulometry of the powder. The best performing photocured composite fulfilled the specifications required for the considered moulding application, with respect to the tensile strength (40 MPa), the elongation at break (3%) and the calcination extent (100%).