The use of upconversion microparticles as a novel internal radiation source for fabrication of composite materials

Upconversion (UC) microparticles were used as novel internal radiation sources for composite preparation. These particles emit Ultraviolet‐Visible radiation when exposed to Near‐infrared waves. This radiation causes uniform and deep polymerization. Two types of UC particles were prepared via a facile hydrothermal method, including NaLuF₄: Yb 20%, Tm 0.5% and NaLuF₄: Yb 40%, Tm 0.5%. The effect of three different photoinitiator systems, including titanocene, bisacylphosphine oxide, and camphorquinone, on the cure depth and the degree of conversion (DC) was investigated. Polymerization reaction rate was also studied. Moreover, the effect of weight percentage of UC particles and laser intensity on the cure depth and the DC were evaluated. Rheological behavior of the composites with different percentage of the particles (1, 3, and 5%) and the effect of temperature were studied. The results showed that the overlap of the UC particles emission spectrum with the photoinitiator absorption spectrum and the intensity of the photoinitiator absorption in the emission range of the particles are of the most important factors affecting cure depth, rate and DC. The cure depth with DC up to approximately 80% was 41 mm. Moreover, the DC was almost constant along the sample. POLYM. COMPOS., 40:884–892, 2019. © 2018 Society of Plastics Engineers