Insight into industrial PLA aging process by complementary use of rheology, HPLC, and MALDI

Abstract

Nowadays, there is a growing availability of biodegradable industrial materials intended to food contact applications whose service life behavior needs to be further investigated. This article is focused on the degradation of two materials based on polylactic acid. The correlation between the rate of degradation and the amount of trapped degradation products was investigated applying three characterization techniques in parallel, namely rheology, high‐performance liquid chromatography (HPLC), and matrix‐assisted laser desorption/ionization (MALDI). The rate of degradation was studied through the evaluation of their rheological properties and calculation of the number of average molecular weights, and weight‐average molecular weights. Water‐soluble oligomers and lactic acid were quantified by HPLC‐ultraviolet. Changes in cyclic and linear oligomers were monitored by MALDI‐time‐of‐flight mass spectrometry. Specimens of 4‐mm thickness of each biopolymer were subjected to hydrolysis in deionized water up to 6 months at two temperatures, simulating service conditions of food packaging. The diminution in viscosity and consequently in molecular weight distribution (20–60%) showed the degradation of the molecular structure of both polylactic acids. The chain scission was followed through the increasing values of lactic acid and hydrolyzed oligomers (twofold to eightfold), and the predominant signal of the linear oligomers over the cyclic ones with aging. Rheology, HPLC, and MALDI showed to be complementary tools to better understand the changes in the molecular structure. The obtained results showed the necessity of adding suitable stabilizers for each particular food packaging application. Copyright © 2013 John Wiley & Sons, Ltd.

Mechanical recycling of polylactide, upgrading trends and combination of valorization techniques

“…Mass Spectrometry (MALDI-TOF-MS) [28]- [30], Nuclear Magnetic Resonance (NMR) [31], or Raman and Fourier-Transfrom InfraRed Spectrometry (FT-IR) are used [32]. The determination of the molar-mass distribution and the chemical nature of the polymer chains and/or their chemical groups along the recycling procedure permits monitoring the structural changes.…”

“…Different extraction techniques coupled with chromatographic and spectrometric techniques are widely used at lab-scale [28], [43].…”

Identification and quantification of oligomers as potential migrants in plastics food contact materials with a focus in polycondensates – A review

“…Food packaging applications include yoghurt cups and water, milk and juice bottles. Oligomers present in PLA extracts can be cyclic or linear (Dopico-Garcia et al, 2013). Polyamides, more precisely nylon, are frequently used for cooking utensils.…”

Reactive Desorption Electrospray Ionization Mass Spectrometry To Determine Intrinsic Degradability of Poly(lactic-co-glycolic acid) Chains

“…30 Because of the high background noise induced by matrix-related ions in the low m/z range, use of MALDI has been barely employed. 31 Instead, use of laser-based techniques with no matrix assistance has been reported, such as laser desorption/ionization (LDI) for GAbased triblock copolymers 32 or desorption/ionization on silicon (DIOS) 33 for LA-based diblock copolymers. 34 Secondary-ion MS (SIMS) 35 has also been implemented for the analysis of hydrolyzed PLA, PGA, and PLAGA.…”

“…In this context, ESI is best suited for soft ionization of polar compounds expected after the degradation of PLA and PLAGA, as reported in studies that performed MS, − high-performance liquid chromatography–MS (HPLC–MS), , or MS/MS . Because of the high background noise induced by matrix-related ions in the low m / z range, use of MALDI has been barely employed . Instead, use of laser-based techniques with no matrix assistance has been reported, such as laser desorption/ionization (LDI) for GA-based triblock copolymers or desorption/ionization on silicon (DIOS) for LA-based diblock copolymers .…”