Banded Spherulites and Lamellar Morphology on Poly(Epsilon-caprolactone)

Spherulitic morphology in melt-solidified poly(Epsilon-caprolactone), Tm=64 degrees C, has been examined by light and electron microscopy over a growth temperature (Tc) range 25 degrees C to 58 Degrees C. Lamellar morphology has also been studied in single-crystal aggregates grown from solution in 2-methoxyethanol. In neat polymer, spherulites grown at low temperature are unbanded; as Tc is increased, a relatively sharp transition to banding with a large period of 70-100um is observed at equivalent to 50 degrees C. Blending with low molecular weight polymeric diluents, e.g. poly(ethylene phthalate), lowers the Tc for onset of banding to equivalent to 27 degrees C. Banding appears insensitive to growth kinetics: it is observed in poly(Epsilon-caprolactone) at growth rates as slow as 0.2nm/s, corresponding to an accretion rate of 1 unit cell / 2 s at the preferred growth face of the b-axis oriented lamellae, while in polyethylene banded spherulites can be formed at rates at least 10 6 times faster. Our observations will be discussed in relation to mechanisms of banding.