The influence of isosorbide on thermal properties of poly(L‐lactide) synthesized by different methods

Abstract

In this article, we analyzed the influence of isosorbide content on glass transition temperature and crystallinity of poly(L‐lactide). Different synthesis methods were applied to determine optimal procedure for polymerization of L‐lactide in the presence of isosorbide. Two procedures were performed with tin(II) 2‐ethylhexanoate as the catalyst: first, using the vacuum sealed vessel, and second, using microwave reactor bulk polymerizations. The solution polymerization (with trifluoromethanesulfonic acid as catalyst) was possible at the temperature of 40°C. Obtained polyesters had number average molecular weights ranging from 20,000 to 65,000 g mol–1, according to the gel permeation chromatography measurements. The polymer structure was characterized by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy. Thermal properties of the obtained polymers were analyzed using thermogravimetry (TG) and differential scanning calorimetry (DSC). According to DSC measurements, the addition of isosorbide in the polyesters influenced the increase in both glass transition temperature and degree of crystallization for all samples. The results obtained by thermogravimetric analysis confirmed the strong influence of polymerization mechanism on synthesized poly(L‐lactides) thermal properties. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

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“…Three different thermal transitions were detected on DSC thermograms: the glass‐transition, characterized by glass transition temperature ( T g ), the cold crystallization process, identified by cold crystallization temperature ( T cc ) and crystallization enthalpy ( ), and melting process characterized by melting temperature ( T m ) and melting enthalpy ( ); the values obtained for the different materials are reported in Table . The glass transition temperature of neat PLA film was detected at 42.6°C, in line with values reported in the literature , and the addition of AU extract increased polymer T g of about 3°C (+ 3.3 and + 2.9°C for PLA filled by 0.5 and 5 wt% of AU extract, respectively), thus slightly improving the thermal stability of the material.…”

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“…To initiate the reaction, 0.7 cm 3 of trifluoromethanesulfonic acid was added to the mixture, which was then stirred at room temperature for 1 h. Following this, the temperature was raised to 40 • C, and the polymerisation process was carried out for 4 h under a nitrogen atmosphere. The average molecular mass of the synthesised PDLLA was 1100 g mol −1 , with polydispersity index 1,2, which is in accordance with our previous research, which showed that this type of polymerisation yields a polymer with a narrow distribution of molecular masses [25].…”

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“…Further, crystallinity of PLA can be improved by chemical and physical modifications. Usually chemical modifications include incorporation of small molecules in PLA polymer structure (manipulation on molecular level), whereas physical modification can include addition of, for example, nanoparticles that are going to act as nucleating agents and expand crystalline regions in the polymer matrix (Pilić et al, 2015;Ristić, Radusin, Pilić, Cakić, & Budinski-Simendić, 2013). In comparison to conventional polymers, PLA cannot meet all the requirements in the field of food packaging.…”

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