Studies on Hydrotalcite‐Catalyzed Synthesis of Poly(ethylene terephthalate)

Abstract

Summary: The hydrotalcite‐catalyzed synthesis of PET was studied to clarify the effect of hydrotalcite properties on its catalytic activity. Hydrotalcite was modified by various treatments to tune its activity as a polycondensation catalyst. Hydrotalcite activity was found to decrease upon calcination. However, rehydration of the calcinated hydrotalcite resumed the catalytic activity. The hydrotalcite activity depends on the ratio of magnesium to aluminum cations in its composition, and highest activity occurs at a molar ratio of 2:1. Replacement of the carbonate anions of hydrotalcite by more nucleophilic ones like hydroxide and alkoxide groups resulted in improved catalytic activity. Hydrotalcite has two assembly orders: primary lamination of sheets into plates and secondary agglomeration of plates into particles. Hydrotalcite with larger sheet size showed lower activity. On the other hand, milling of hydrotalcite particles did not affect its activity as it probably enters the reaction on a plate level, which is not affected by milling. Polycondensation resulted in expansion of the hydrotalcite sheets under the effect of formed polymer. Reuse of hydrotalcite after polycondensation followed by depolycondensation resulted in a large activity enhancement.High‐resolution SEM micrograph of calcinated HT after rehydration.magnified imageHigh‐resolution SEM micrograph of calcinated HT after rehydration.

Ionic Liquid as Surfactant Agent of Hydrotalcite: Influence on the Final Properties of Polycaprolactone Matrix

“…LDHs have high level of purity and can be produced using simple procedures. They have been used as active filler for polymers and biopolymers for their capability of hosting active molecules [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ], as catalysts for reactions [ 8 , 9 ], for the synthesis of polymers [ 10 ] and as surfactant adsorbents [ 11 ]. The exchange of the counter ions between the layers is not easy, therefore the modification of carbonated LDHs is generally carried out by calcination followed by immersion in a medium containing anions to be intercalated [ 12 , 13 ].…”

An advanced preparation and characterization of the PET/MgAl-LDH nanocomposites

“…Previously El-Toufaili et al reported that LDH activity depends on the presence of hydroxides or interlayer anions and all of these active sites are easily accessible. 14 For the BHET polycondensation-modied MgAl LDH as a catalyst, in this paper, we proposed the following routes for BHET polycondensation shown in Fig. 11.…”

Kinetics and Mechanistic Investigation of Hydrotalcite‐Catalyzed Melt Synthesis of Poly(ethylene terephthalate)

“…Hydrotalcite was shown to be more active than antimony in polycondensation of BHET. [4][5][6][8][9][10] In a previous paper, [11] the effects of HT properties on its activity as a BHET polycondensation catalyst were studied. It was found that the hydroxide groups of HT are necessary for its catalytic activity.…”

“…[11] The catalytic activity was also dependent on the nucleophilicity of the interlayer anions. As was shown by IR and X-ray, the carbonate anions do not exist during polycondensation as they most probably react at the beginning of the reaction with alcoholic groups present in the reaction medium and this leads to the formation of alkoxides.…”