The mechanism of orientation of aromatic solutes in oriented polyethylenes

Oriented linear low-density polyethylene (LLDPE) has the ability to orient many fused ring aromatic compounds. Dielectric relaxation studies of polar aromatic molecules in oriented LLDPE confirm orientability but only a fraction of the molecules are active. These immobilized molecules are located on the lateral surfaces of the polyethylene crystals through orientation mechanisms such as surface adsorption or surface crystallization. Spectroscopic and thermal analysis studies suggest specific surface adsorption on the surfaces of polyethylene crystals related to the epitaxial growth of solute microcrystals on polyethylene crystals as the major orientation mechanism. The mechanism of orientation for many of the fused ring aromatic compounds is epitaxial crystallization on the (110) and/or (100) crystal planes exposed by drawing. In order to obtain a better understanding of the fundamental interactions occurring in the systems of polyethylene and fused ring aromatic compounds, phase diagrams have been constructed using differential scanning calorimetry and X-ray diffractometry. The systems LLDPE/acridine and HDPE/phenazine exhibit formation of compound crystals.