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Polylactide with natural antioxidants: Active packaging films and stability effects on the polymer
KTH, School of Chemical Science and Engineering (CHE).
2014 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Polylaktid med naturliga växtantioxidanter: Aktiva förpackningsfilmer och stabiliseringseffekter på polymeren (Swedish)
Abstract [en]

Polylactic acid (PLA) is a bio-based and biodegradable polymer that has gained a lot more interest in the packaging industry because of environmental concerns and decreasing prices. However, PLA as a food packaging material has some problems like the high oxygen permeability as oxygen causes lipid oxidation of the food product. Preventing this process is usually done by adding synthetic antioxidants (AOs) to the food but these AOs are toxic and could even be carcinogenic. Natural AOs present in plants are therefore a good alternative. By mixing plants with the PLA, an active packaging material could be obtained and less amounts of AOs need to be added to the food.   

Active packaging films were prepared by adding 3 wt% of dry or lyophilized (lyo) plants of white tea, borage, thyme and rosemary to PLA. Also, model antioxidant films (butylated hydroxytoluene, caffeic acid, epigallocatechin gallate and rosmarinic acid) with 1.5 wt% were solution casted.

The films were migration tested at 37°C for 10 days in the food simulants water and 95% ethanol. LDI-MS of the food simulants were conducted at 18h, 68h and 240h. LDI-MS of the original plants showed that the lyo extracts mostly contained low molecular weight compounds whereas the whole dry plants had substantial amount of compounds in higher m/z regions. Because of the solubility and rapid loss of cyclic lactide oligomers in ethanol, a larger mass loss was seen during migration testing in this food simulant compared to the migration to water (confirmed with LDI-MS).

A large water uptake was seen for the plant films (11.7-29.4%) and large holes on the surface were observed with SEM after water migration tests (however, not for borage). These large holes could result in a high hydrolysis rate in the long run. The plant films after ethanol migration did not display the same features as plant films after water migration: the holes were small and the ethanol uptake lower. The solubility of the plants and model AOs in the food simulants are important for extending the induction period (the time which the food has unnoticeable rancidity and remained sensory properties). The induction period was extended fivefold for the best film (containing lyo rosemary) compared to the pure PLA film. The induction period increased to 20 days instead of four.

Migration tests in the food simulants water and ethanol showed differences between the plant films and the model AO films: the plant material contained a larger fraction of water-soluble compounds compared to the model AOs (which are all quite insoluble in water).

The TGA showed a large improvement of the onset of degradation temperature for most of the films with plants and model AOs, some up to around 20°C higher. For example THY lyo had an onset of degradation temperature 334°C. Borage showed however a lower thermo-oxidative stability than pure PLA that had an onset of degradation temperature at 313°C. The plant material can therefore be used as additive in PLA to stabilize the polymer e.g. when high-temperature processing is required.

Place, publisher, year, edition, pages
2014.
Keyword [en]
polylactide, natural antioxidants, active packaging, lipid oxidation, polyphenols
National Category
Polymer Technologies
Identifiers
URN: urn:nbn:se:kth:diva-159174OAI: oai:DiVA.org:kth-159174DiVA: diva2:782788
Available from: 2015-01-22 Created: 2015-01-22 Last updated: 2017-08-31Bibliographically approved

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