Molecular orientation in crystalline miscible blends

• Published in: Polymer (Guilford) 1999, Vol.40 (1), p.243-251
• Main Authors: Keroack, Daniel, Zhao, Yue, Prud'homme, Robert E.
• Format: Article
• Language: English
• Subjects: Applied sciences; Crystalline miscible blends; Exact sciences and technology; Infrared dichroism; Organic polymers; Orientation; Physicochemistry of polymers; Properties and characterization; Structure, morphology and analysis
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/S0032-3861(98)00187-6

The orientation induced by stretching uniaxially in the solid state two semi-crystalline miscible blends of poly(ε-caprolactone) (PCL) with poly(vinyl chloride) (PVC) and poly(styrene- co-acrylonitrile) (SAN) was investigated by infrared dichroism. In both cases, the deformation of the solution-cast films, having a high PCL crystallinity degree of about 50% and containing up to about 40 wt% of PVC or SAN, leads rapidly to a very high segmental orientation for the crystalline PCL as a result of a structural transformation from lamellae to microfibrils. Meanwhile, the amorphous components, being miscible and located in the interlamellar regions inside the spherulites, show a much lower orientation as compared with the crystalline PCL regardless of the blend composition. SAN is found to orient to the same degree as the amorphous PCL in the PCL/SAN blends, while the orientation of PVC is higher than that of the amorphous PCL in the PCL/PVC blends. Furthermore, the slow crystallization of PCL in blends containing around 40% of PVC made it possible to follow the orientation behaviour as a function of the crystallization time by stretching a series of films before and after the crystallization of PCL started. It was found that, even with as little crystalline PCL as 5% of the total blend weight, the stretching-induced crystalline orientation is almost as high as for the samples with high degrees of crystallinity. A stretching-induced crystallization forming microfibril-like crystallites of PCL is suggested to be at the origin of the high crystalline orientation for those blends, which have a dominant proportion of amorphous components during the stretching, instead of the transformation of existing lamellae to the microfibrillar structure for stretched highly crystalline blends.