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Effects of the mixing ratio of poly(DL-lactide) (PDLLA) and poly (ε-caprolactone) (PCL) on the thermal and mechanical properties and morphologies of the solution-cast blends were investigated by differential scanning calorimetry (DSC), polarizing microscopy, tensile tests, and dynamic mechanical analysis. The presence of amorphous PDLLA did not disturb crystallization of PCL over the PDLLA content XPDLLA = PDLLA/(PCL + PDLLA) from 0.1 to 0.9 and allowed PCL to form spherulites over XPDLLA ranging from 0.1 to 0.6. The spherulite radius was larger for the blends than for the nonblended PCL. Phase separation occurred for the blends with XPDLLA between 0.1 and 0.9 Tm of PCL remained unchanged in the XPDLLA range up to 0.6 but decreased at XPDLLA above 0.6, whereas the crystallinity of PCL was constant around 60%, irrespective of XPDLLA. The tensile strength (σB, the yield stress (σY), the Young's modulus(E), and the storage modulus (G′) of the blends increased monotonously with XPDLLA if σB at XPDLLA = 0 and 0.6 and σY at XPDLLA = 0.6 were excluded. Elongation-at-break (εB) of PDLLA increased dramatically, while εB of PCL decreased remarkably when a small amount of the other component was added. Equations and parameters predicting σY, E, and G′ of the PCL-PDLLA blends were proposed as a function of XPDLLA. © 1996 John Wiley & Sons, Inc.
Tsuji et al. (Thu,) studied this question.