Poly(lactic acid) Synthesis and Characterization

Abstract

Poly(lactic acid) (PLA) is a promising biodegradable polymer based on renewable resources. This paper describes scale-up studies to synthesize high molecular weight PLA (>100'000 g/mol) in five steps from commercial lactic acid. The first four steps of this process consist of synthesizing a highly pure precursor, lactide, which can be converted into a high molecular PLA by ring opening polymerization (ROP). We produced PLA with a molecular weight of 109'000 g/mol using this strategy.

Dielectric Properties of 3D Printed Polylactic Acid

“…That means "as-printed" PLA is most likely a pure glass below 331 K. The subsequent cooling from the meltdown to ambient temperatures with a cooling rate of 10 K/min confirms the result of Cao et al [21] that this rate is enough to prevent crystallization of PLA. The values for these phase transitions, especially temperatures, agree well with the results from literature [21,27,29,30]. However, the glass transition temperature in literature varies about ±5 K, which most likely originates from the different stereoisomeric composition of (d,l)-lactide in PLA.…”

“…Both effects result in a lower melting temperature. This points also towards a high molar mass of the PLA filament (>100.000 g/mol) [29]. As expected, for PLA in the purely glassy phase, which is discussed below, the entropies of the cold crystallization (16.2 J/g) and the melting (16.3 J/g) are identical within the experimental uncertainty.…”

Newly Developed Techniques on Polycondensation, Ring-Opening Polymerization and Polymer Modification: Focus on Poly(Lactic Acid)

“…This study also pointed out lower temperature (≤140 °C) could contribute to improve molecular weight by avoiding decomposition resulted from back-biting reaction [29], whereas Korhonen et al achieved better quality PLA (160,000 g·mol −1 ) at 200 °C for 1 h even without solvent as co-initiator [27]. In Korhonen’s research, the highest molecular weight was obtained at 15–20 min [27], the same trend as study result of Sanglard et al [19]. That is possibly because higher temperature (170–200 °C) aggravates both chain-growth polymerization and decomposition, but polymerization has the priority at first.…”

“…The second method was reported by researchers in Switzerland, in which a short path distillation is applied for lactic acid dehydration and reactive distillation of raw lactide, yielding 95%–97% ( w / w ), much higher than conventional condensation system [19]. However, higher amount of catalyst (3 wt %) and high temperature (250 °C) were still required.…”

“…For instance, microwave heating accelerated both PLA polycondensation and lactide synthesis [10,24]. Short path distillation and screw extruder were also suggested as effective setups to demonstrate immediate separation of product from reaction system [19,26]. …”