Effect of a small amount of poly(3-hydroxybutyrate) on the crystallization behavior of poly(L-lactic acid) in their immiscible and miscible blends during physical aging

The miscibility and effect of physical aging on the crystallization behavior of poly(l-lactic acid) (PLLA)/poly(3-hydroxybutyrate) (PHB) blends with a small amount of PHB (≤10 wt%) have been investigated using differential scanning calorimetry and Fourier transform infrared spectroscopy. It is found that the miscibility of PLLA/PHB blends with a very small percentage of PHB can be modulated by varying the molecular weight of the PHB. That is, a PLLA/PHB blend with low-molecular-weight PHB is miscible, whereas that with high-molecular-weight PHB is immiscible. It is found that physical aging at temperatures far below the glass transition temperature can promote the cold crystallization kinetics of PLLA in PLLA/PHB blends with high-molecular-weight PHB rather than in those with low-molecular-weight PHB. These findings suggest that the effect of physical aging on the crystallization behavior of the main component in a crystalline/crystalline blend with a small percentage of the second component is strongly dependent on the miscibility of the blend system. Enhanced chain mobility of PLLA in the interface region of PLLA matrix and PHB micro-domains is proposed to explain the physical aging-enhanced crystallization rate in immiscible PLLA/PHB blends with high-molecular-weight PHB. © 2013 Society of Chemical Industry