Introducing four different branch structures in PET by reactive processing––A rheological investigation

Abstract

Chain extension/branching by reactive processing is a well‐known method to enhance the rheological properties of polymers. In this study, pyromellitic dianhydride, poly(glycolic acid), triglycidyl isocyanurate, and bisphenol A diglycidyl ether were used as chain extender/branching agents to produce branched Polyethylene terephthalate (PETs) with four different molecular structures. According to the linear rheological characterizations, the storage modulus and complex viscosity of modified PET samples enhanced significantly after branching. The shear viscosities of modified PET show a pronounced shear‐thinning behavior and a remarkable increase at low frequencies, which can be an indication of the existence of long‐chain branches (LCBs) in the molecular structure of polymer and broadening the molecular weight distribution. Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC) analysis were used to investigate the effect of branching agents on the chemical structure and thermal properties of PET, respectively. DSC results show that higher amounts of LCBs lead to lower melting and crystallization temperatures.

Mechanical Recycling of Packaging Plastics: A Review

“…PMDA has also been used to chain extend PET, polyurethanes, PLA, and other specialty polymers. [ 104–108 ]…”

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

“…One of the most frequently investigated chain extenders for PET is pyromellitic dianhydride (PMDA), which is a tetra‐functional, low molar mass modifier. 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 .…”

“…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.…”

“…The high interest in modifying the molecular structure of polyesters by reactive processing with chain extenders has been reflected by the scientific 1–21 and patent literature 22‐25 during recent years. This is mainly due to novel commercially available chain extenders, or chain extender masterbatches, and to the rising attention to biodegradable polyesters.…”

Thermal Stabilization of Recycled PET Through Chain Extension and Blending with PBT

“…Depending on the chemical nature and number of available functional groups of CEs, linear chain extension and/or branching of PET molecules could be observed. So far, several CEs such as bis-oxazolines [24], pyromellitic dianhydride (PMDA) [22], organic phosphites [25][26][27], isocyanides [28,29] and epoxides [4,5,[29][30][31][32][33][34][35] have been proposed to extend the molecules of polyesters. Among these CEs, multifunctional epoxides better known under the trade name of Joncryl® ADR are the most commonly used CEs to enhance the melt properties of PET [36].…”