Miscibility, Morphology, and Crystallization Kinetics of Biodegradable Poly(ε-caprolactone)/Ascorbic Acid Blends

Poly(ε-caprolactone) (PCL) was blended with l-ascorbic acid (AA) to achieve increased hydrophilicity and shorter degradation period as a candidate for specific biomedical applications such as bio tissue engineering scaffolds. The miscibility, morphology, and spherulite development of PCL/AA blends were investigated via several means of microscopy. Microscopic observations demonstrated that the PCL and AA form immiscible blends. At 1 and 2 wt % AA in the PCL matrix, AA was distributed in the form of small particles. For the sample with 5 wt % of AA, micrometric crystal aggregates of AA were also seen, randomly distributed. The presence of AA impacted the spherulite development of PCL upon crystallization from melt and solvent evaporation. At low percentages of AA (1 and 2 wt %), while not interacting with the lamellar growth, AA caused a minor nucleating effect on PCL, resulting in a smaller average spherulitic size. On the other hand, 5% of AA left behind micrometric crystals and the PCL spherulites tend to grow from the surface of AA microcrystals. The natural evaporation of solvent resulted in aggregates of AA; however, when given time and at elevated temperatures, AA crystals were nucleated and grown in the form of needle-like crystals at random directions. The overall isothermal crystallization of PCL/AA blends was determined by DSC. Even though AA has a small nucleating effect on PCL, the overall crystallization rate decreased with AA addition. We attribute the decrease to a reduction in spherulitic growth rate due to a possible interaction between AA and PCL, resulting in a limited diffusion and reduced mobility of PCL chains. In addition, short-term hydrolytic degradation resulted in the removal of AA particles from the surface of PCL/AA blends. As a result, a porous structure of PCL remained, which was hypothesized to have a higher rate of surface degradation.