Compatibility and epitaxial crystallization between Poly(ethylene) and Poly(ethylene)-like polyesters

- Blends of PPDL and HDPE are phase separated but show epitaxial growth of PPDL from the HDPE substrate.
- Films of blends of PPDL and LDPE are highly transparent and have good optical properties.
- PPDL rich films show a shish-kebab type of crystal morphology, in which PPDL kebabs are grown from LDPE shishes.

This work describes the phase behavior of blends of 'polyethylene-like' polypentadecalactone (PPDL) and polyethylene. Blends of high-density polyethylene (HDPE) and PPDL were shown to be immiscible at the onset of crystallization of polyethylene, resulting in phase-separated morphologies. However, epitaxial crystallization of PPDL onto the HDPE crystals was observed by transmission electron microscopy (TEM), resulting in lamellae penetrating through the interface of the two polymers. Furthermore, PPDL/low-density polyethylene (LDPE) blends were produced and used for film extrusion, yielding clear films with good optical properties, despite the presence of fully phase-separated morphology. For PPDL-rich blends, TEM analysis revealed the formation of highly elongated crystalline domains of LDPE, from which the PPDL domains were epitaxially crystallized yielding a shish-kebab type of morphology. In these structures, the extended LDPE domains formed shishes with LDPE micro-kebabs, onto which PPDL macro-kebabs crystallized. The shish-kebab morphology was furthermore confirmed using x-ray analysis. The high aspect ratio of the LDPE domains is caused by the long relaxation times of LDPE in combination with the low interfacial tension between LDPE and PPDL. As a consequence of the lower relaxation time of PPDL (due to the linear chain architecture), the PPDL domains in the LDPE-rich blends have a lower aspect ratio. The strong epitaxial crystallization in combination with anisotropy in the morphology has a positive effect on the optical properties of the films.

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