Microcellular Foaming Behavior of Chain‐Extended Polyethylene Naphthalate

ABSTRACT In this paper, polyethylene naphthalate (PEN) microcellular foam is successfully prepared via chain extension and in situ fibrillation. The introduction of triglycidyl isocyanurate (TGIC) into PEN improves its melt strength and further improves its foamability. The foam containing 0.6 phr of TGIC exhibits a complete cell structure with an average cell size of 17.96 μm. The chain‐extended PEN (CEPEN) is blended with poly(tetrafluoroethylene) (PTFE) to generate in situ PTFE fibers. PTFE functions as a melt strength promoter, crystallization nucleating agent, and bubble nucleating agent during foaming, and it improves the melt strength and crystallization ability of CEPEN. The heterogeneous nucleation effect of PTFE increases the nucleation rate during foaming, which is crucial for preparing microcellular foam. When the PTFE content is 0.9 phr, microcellular foam with the smallest cell diameter (reduced from 12.78 to 2.38 μm) and the highest foam density is obtained. In addition, a high PTFE content considerably increases the compressive strength of PEN foam. The compressive strength of PEN foam containing 0.3 phr of PTFE is 0.45 MPa, whereas that containing 0.9 phr of PTFE is 1.11 MPa, indicating a 147% increase.