Effects of Resin Rheology on the Extrusion Foaming Characteristics of PET

Abstract

Extrusion foaming by injection of inert gases (carbon dioxide, nitrogen, argon) in the polymer melt is increasingly finding applications for a wide variety of resins, competing with chemical blowing agents, volatile organic compounds or microcellular foaming. The molecular weight and molecular weight distribution of the resin affect its rheological characteristics (shear and elongational viscosity, melt elasticity, melt strength), its process characteristics and control cell size and stability of the resulting foam. In the present work, a variety of PET resins (including virgin materials, recycled and post-reactor modified) having different rheological characteristics were foamed by direct carbon dioxide injection and through the use of chemical blowing agents. Formability as related to density and cell size and distribution was evaluated and correlated with rheological characteristics of the particular resin, process conditions and type of blowing agent.

Viscoelastic characteristics of chain extended/branched and linear polyethylene terephthalate resins

“…Melt flow index and die swell data, (as indicators of melt viscosity and elasticity, respectively), of the unmodified and one of the chemically modified resins were determined earlier 21,22 and are summarized in Table I along with their extrusion foaming characteristics in rod dies. A single extrusion line equipped with a rod die was used with CO 2 as the blowing agent.…”

“…A single extrusion line equipped with a rod die was used with CO 2 as the blowing agent. 21,22 Foaming of PET-ME was not attempted, because the diepoxide was only available in small quantities; for the same reasons, melt flow index (MFI) and die swell for the PET-ME resin were not measured.…”

Continuous extrusion production of microcellular rigid PVC

“…Different strategies have been proposed in the literature to increase cell wall stability, which would avoid cell coalescence [8,[11][12][13]. While processing at lower temperature could increase the viscosity of the molten polymer, it could also delay the fusion of PVC particles, thus affecting the formation of the gas/polymer solution.…”

Prediction of foamability of polyethylene terephthalate using viscous and elastic parameters

“…Polyethylene terephthalate (PET) is a semi-crystalline engineering plastic with excellent mechanical properties and high-temperature resistance. Xanthos et al [6][7][8] investigated the foaming properties of virgin PET and modified PET. The foaming extrusion with CO 2 as a blowing agent has made significant advances in recent years.…”