Polypropylene copolymer films: Heat sealing and oligomer/additive migration

Abstract

Ease of heat sealing and oligomer/additive migration are two important and often interrelated phenomena that affect the engineering performance of high clarity polypropylene random copolymer (RCP) films. From a fundamental standpoint, this work investigates the non‐standard microstructural aspects that play a critical role in the heat sealing process of semicrystalline polymer films. Two different propylene–ethylene copolymers having widely different seal initiation temperatures (SITs) but similar melting points were chosen for this study. The contribution of both the amorphous phase and the crystalline phase to heat sealing was investigated utilizing dynamic mechanical analysis and thermal fractionation differential scanning calorimetry, respectively. Results indicate that the melting distribution of the thermally fractionated material plays a critical role in determining SIT while the effect of the mobility of the amorphous phase was found to be insignificant. In order to deeply understand the molecular origin of this difference in melting distribution or lamellar thickness distribution, the composition distribution of the co‐monomer was measured using Gel Permeation Chromatography‐Infra‐Red (GPC‐IR) and found to be fundamentally different. In addition, this work systematically studies the effect of oligomer/additive migration on optics, co‐efficient of friction (CoF), and most importantly heat sealing behavior. Migration is found to dramatically increase the SIT and haze while decrease the CoF of PP RCP films. POLYM. ENG. SCI., 58:1479–1484, 2018. © 2017 Society of Plastics Engineers