Analysis of high melt‐strength poly(ethylene terephthalate) produced by reactive processing by shear and elongational rheology

Abstract

Three grades of poly(ethylene terephthalate) (PET) produced by different synthesis routes and with different molar masses were reactively extruded with two tetra‐functional chain extenders, i.e., pyromellitic dianhydride (PMDA) and tetraglycidyl diamino diphenyl methane (TGDDM). The preferred reactivity of the coupling agents led to different long‐chain branched (LCB) structures, which can be related to different hydroxyl and carboxyl end group concentrations of the PET grades investigated. The complex viscosity and the transient elongational viscosity increased by up to two decades. Both the activation energy of flow and the loss angle indicate long‐chain branching. A more quantitative assessment of the extent of strain hardening was achieved by application of the molecular stress function (MSF) model. The two material parameters of the model revealed different behaviors depending on the chain extender used. The initial molar mass of PET and the concentration of end groups, i.e., hydroxyl and carboxyl, determine the structure of the polymer molecules. PMDA proved to be an excellent coupling agent for industrial processing which induces reproducibly either a star‐like, comb‐like, or randomly branched structure depending on the concentration of coupling agent added and the hydroxyl concentration of the PET employed. TGDDM led to a hyperbranched structure. POLYM. ENG. SCI., 59:396–410, 2019. © 2018 Society of Plastics Engineers

Molecular structure and rheological properties of a poly(ethylene terephthalate) modified by two different chain extenders

“…By analyzing the linear viscoelastic properties of the modified materials in shear modes, an increase of the magnitude of the complex viscosity, a change of the phase angle versus the magnitude of the complex modulus (van Gurp-Palmen plot), and a decrease of the loss factor with growing PMDA concentration were found. 3,6,7,11,14,16,18,19 Investigations under elongational deformation reveal a strain hardening behavior, which is more pronounced at higher PMDA concentrations and larger strain rates. 11,14,16,18 The changes in the rheological response can be attributed to an increase in molar mass, a broadening of molar mass distribution, and the introduction of long-chain branched structures, proven by SEC measurements.…”

Ultraviolet‐induced chain extension of poly(ethylene terephthalate) based on radical reaction with the aid of trimethylolpropane triacrylate and glycidyl methacrylate during extrusion

“…In addition, similar results were obtained with the addition of GMA‐styrene copolymer (GS) and poly(butylene terephthalate)‐GS as chain extenders, where an obvious increase in torque evolution was attributed to the chain extending, branching and crosslinking during the process . Kruse et al . utilized pyromellitic dianhydride (PMDA) and tetraglycidyl diamino diphenyl methane as chain extenders to create long‐chain branched PET.…”

“…Compared to solid‐state polymerization, reactive extrusion is a cost‐effective method that is carried out to enhance the performance of commercial PET. In the reactive extrusion process, a di‐ or multi‐functional low molecular weight compound reacts with carboxyl/hydroxyl end groups of PET to rejoin the molecular chain, resulting in increasing molar mass of the polymer and producing long‐chain branched macromolecules . Many chain extenders with different types of reactive groups have been reported to modify PET, such as oxazoline, isocyanates, organic phosphites and many kinds of epoxy‐based and anhydride‐based compounds .…”

Rheological/thermal properties of poly(ethylene terephthalate) modified by chain extenders of pyromellitic dianhydride and pentaerythritol

“…In fact, the zero shear viscosity increment in the modified samples confirmed an increase in mw and MWD in all modified samples compared to the PET sample. Concerning the samples modified with PMDA and PENTA co‐addition, as well the samples modified in the presence of a catalyst, the obvious spreading of MWD can be expressed with confidence, while for these samples, the crossover point has certainly not shown MWD alteration 2,39 …”

“…They claimed that the best PMDA amount to reach the highest viscosity value was 0.8% 25 . In addition, some studies have focused on the point that a limited number of chain extenders have the ability to be used with PMDA together 37–40 . Forsythe and coworkers used different proportions of PMDA and PENTA to modify bottle grade PET.…”