Moisture-induced changes in the mechanical behavior of 3D printed polymers

Abstract

Commonly used 3D printing polymers, such as nylon and polylactic acid (PLA), can experience significant material degradation when exposed to moisture and high temperatures for extended periods. Understanding the extent of their degradation is critical to their long term use and can also inform end-of-life strategies, such as recycling or recovery. Specimens of nylon, carbon fiber-reinforced nylon composite, and PLA, three popular 3D printing materials, were 3D printed and immersed in deionized water at 21 °C and 70 °C to evaluate the effect of moisture and temperature on their mechanical and chemical properties. Water absorption rates were much higher at elevated temperatures and, at both temperatures investigated, the nylon-based materials absorbed up to 10 times more water than PLA. A direct relationship between moisture absorption and reduction in flexural properties was observed for the nylon-based specimens, with the flexural modulus of nylon decreasing by as much as 60% after 7 days of immersion. PLA, however, displayed negligible mechanical property degradation after immersion at 21 °C, but showed substantial physical degradation after being immersed in water at 70 °C for 7 days. Analogous changes in chemical structure and crystallinity were observed via Fourier transform infrared spectroscopy and differential scanning calorimetry.