Monitoring the evolution of PET branching through chemorheology

Abstract

There is a high interest in modifying the rheological properties of polyethylene terephthalate (PET) through structural modifications while maintaining its thermoplastic nature. This article reports real‐time spectroscopic and rheological monitoring of the effects of reactive melt modification of PET with a multi‐functional epoxide—triglycidyl isocyanurate (TGIC)—that lead to chain extension/branching and subsequently formation of gel‐like structures. An infrared spectroscopic technique to monitor the simultaneously occurring degradation and chain extension/branching reactions was evaluated. The effects of reaction temperature, shear rate, and residence time were also investigated. Frequency scans at various time intervals on the reacting samples provided information on changes in the degree of branching and melt elasticity. The effect of method of sample preparation for chemorheological testing was also evaluated in this study. A 50% excess of the stoichiometric amount of TGIC for complete reaction with terminal carboxyl groups resulted in a self‐similar polymeric structure of PET near the sol‐gel transition point or a critical gel formation whose linear viscoelastic properties obey scaling law. An estimated fractal dimension from the experimental results was used to quantify the evolution of the branched network structure during the reactive melt modification. Polym. Eng. Sci. 44:474–486, 2004. © 2004 Society of Plastics Engineers.

High‐melt‐elasticity poly(ethylene terephthalate) produced by reactive extrusion with a multi‐functional epoxide for foaming

“…19,20 Xia et al 21 investigated the batch foaming behavior of PMDA-modified PET, a broad foaming temperature window was obtained for PET modified with 0.8 wt % PMDA. The improvement of viscoelasticity caused by some epoxy-based modifiers, such as tetraglycidyl diamino diphenyl methane 22,23 and triglycidyl isocyanurater [24][25][26] had also been demonstrated. Joncryl is a multi-functional epoxy oligomer and can be used to increase the melt properties of poly(lactic acid).…”

Rheology and extrusion foaming of chain‐branched poly(lactic acid)

“…For polyesters, chain-extension consists in increasing the molecular weight by bridging the hydroxyl or carboxyl reactive-end groups using bi or poly-functional molecules. For PET, branching was obtained by reaction with pyromellitic dianhydride, [24][25][26], and with various epoxy-based chain-extenders, [27][28][29][30][31]. For PLA, various diisocyanate were investigated for this purpose [32][33][34][35][36][37][38][39].…”

Modification of poly(ethylene terephthalate) by combination of reactive extrusion and followed solid‐state polycondensation for melt foaming

“…As PMDA was not that effective for modification of r‐PET, two multifunctional epoxides, i.e., TGIC and ADR, as the chain extenders were used to investigate their modification effects on the r‐PET. Different from PMDA reacting only with one terminal hydroxyl group of PET, the epoxides can react with both the carboxyl and hydroxyl groups of PET by esterification and etherification, and the secondary hydroxyls formed from these reactions may further react with carboxyl or epoxy groups leading to branching or cross‐linking . At the extrusion conditions of main motor's rotation speed of 240 rpm, the IV of the reactive extruded r‐PET with the addition of different concentrations of TGIC or ADR is shown in Table .…”

“…showed that the IV of recycled bottle‐grade PET effectively increased from 0.69 to 0.85 dL/g with bis‐oxazolines as the chain extender. Other chain extenders such as pentaerythritol (PENTA) and triglycidyl isocyanurate (TGIC) were also used to improve the IV of PET. Adding different chain extenders together could also effectively achieve the chain extension.…”