Abstract
The goal of this study was to synthesize, through a facile strategy, high molecular weight poly(ethylene furanoate) (PEF), which could be applicable in food packaging applications. The efficient method to generate PEF with high molecular weight consists of carrying out a first solid-state polycondensation under vacuum for 6 h reaction time at 205 °C for the resulting polymer from two-step melt polycondensation process, which is catalyzed by tetrabutyl titanate (TBT). A remelting step was thereafter applied for 15 min at 250 °C for the obtained polyester. Thus, the PEF sample was ground into powder, and was then crystallized for 6 h at 170 °C. This polyester is then submitted to a second solid-state polycondensation (SSP) carried out at different reaction times (1, 2, 3.5, and 5 h) and temperatures 190, 200, and 205 °C, under vacuum. Ultimately, a significant increase in intrinsic viscosity is observed with only 5 h reaction time at 205 °C during the second SSP being needed to obtain very high molecular weight PEF polymer greater than 1 dL/g, which sufficient for manufacturing purposes. Intrinsic viscosity (IV), carboxyl end-group content (–COOH), and thermal properties, via differential scanning calorimetry (DSC), were measured for all resultant polyesters. Thanks to the post-polymerization process, DSC results showed that the melting temperatures of the prepared PEF samples were steadily enhanced in an obvious way as a function of reaction time and temperature increase. It was revealed, as was expected for all SSP samples, that the intrinsic viscosity and the average molecular weight of PEF polyester increased with increasing SSP time and temperature, whereas the number of carboxyl end-group concentration was decreased. A simple kinetic model was also developed and used to predict the time evolution of polyesters IV, as well as the carboxyl and hydroxyl end-groups of PEF during the SSP.
Highlights
The search for sustainable biobased alternatives for polymer production has dramatically intensified in recent years, due to an increasing awareness of finite fossil fuel resources and the Polymers 2018, 10, 471; doi:10.3390/polym10050471 www.mdpi.com/journal/polymersPolymers 2018, 10, 471 disrupting climatic effects of greenhouse gas emissions [1,2,3]
7.90 ppm were respectively assigned to the ring protons (2 H, s) of poly(ethylene furanoate) (PEF)/tetrabutyl titanate (TBT).1, PEF/TBT.2, and PEF/TBT.3
The present work is, to the best of our knowledge, the first study which investigated the feasibility of Solid-state polymerization (SSP) after remelting process to synthesize PEF polyesters
Summary
Polymers 2018, 10, 471 disrupting climatic effects of greenhouse gas emissions [1,2,3] For this reason, the interest in biomass has rapidly emerged as a renewable source of chemicals and mainly monomers for bio-based polymers production [4,5]. 2,5-Furandicarboxylic acid (FDCA) is the most promising rigid bio-based building block, which has been recognized as one of the twelve most important renewable-based monomers [8]. This furan derivative, which may provide a suitable alternative for terephthalic acid, can be prepared by catalytic oxidation of 5-hydroxymethylfurfural (HMF) derived from C6 sugars or polysaccharides [9,10]. Extensive research efforts were triggered since the last decade towards PEF, and its historical progress has been extensively described in two recent extended reports [21,22]
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