Effect of crystallization on barrier properties of formulated polylactide

Polylactide (PLA), a biodegradable polymer obtained from biomass, was formulated with a nucleating agent, talc, and a plasticizer, acetyl tributyl citrate, and cold crystallized in α and α′ form. The barrier properties of crystallized PLA were investigated as a function of the formulation and the crystalline form, thanks to three molecules with increasing polymer interactions, i.e. helium, oxygen and ethyl acetate (EA). Contrary to expectation, the oxygen diffusion coefficient in neat and formulated PLA did not decrease with crystallization. Even an increase of the diffusion coefficient was noticed for the most interacting probe, EA, in formulated PLA. Conditioning of neat and formulated PLA in an atmosphere containing EA vapour caused a modification of the material structure by plasticization and induced crystallization even at small EA activities. The plasticizing effect caused the glass transition temperature Tg to shift to below ambient temperature. In the case of neat PLA induced crystallization in solely the α form was obtained, and in the case of formulated PLA a blend of α and α′ forms was observed. Copyright © 2011 Society of Chemical Industr

Effect of crystallization on barrier properties of formulated polylactide

Polylactide (PLA), a biodegradable polymer obtained from biomass, was formulated with a nucleating agent, talc, and a plasticizer, acetyl tributyl citrate, and cold crystallized in α and α′ form. The barrier properties of crystallized PLA were investigated as a function of the formulation and the crystalline form, thanks to three molecules with increasing polymer interactions, i.e. helium, oxygen and ethyl acetate (EA). Contrary to expectation, the oxygen diffusion coefficient in neat and formulated PLA did not decrease with crystallization. Even an increase of the diffusion coefficient was noticed for the most interacting probe, EA, in formulated PLA. Conditioning of neat and formulated PLA in an atmosphere containing EA vapour caused a modification of the material structure by plasticization and induced crystallization even at small EA activities. The plasticizing effect caused the glass transition temperature Tg to shift to below ambient temperature. In the case of neat PLA induced crystallization in solely the α form was obtained, and in the case of formulated PLA a blend of α and α′ forms was observed. Copyright © 2011 Society of Chemical Industr

Analysis of the Structure-Properties Relationships of Different Multiphase Systems Based on Plasticized Poly(Lactic Acid)

Poly(lactic acid) is one of the most promising biobased and biodegradable polymers for food packaging, an application which requires good mechanical and barrier properties. In order to improve the mechanical properties, in particular the flexibility, PLA plasticization is required. However, plasticization induces generally a decrease in the barrier properties. Acetyl tributyl citrate (ATBC) and poly(ethylene glycol) 300 (PEG), highly recommended as plasticizers for PLA, were added up to 17 wt% in P(D,L)LA. In the case of PEG, a phase separation was observed for plasticizer contents higher than 5 wt%. Contrary to PEG, the Tg decrease due to ATBC addition, modelled with Fox’s law, and the absence of phase separation, up to 17 wt% of plasticizer, confirm the miscibility of PLA and ATBC. Contents equal or higher than 13 wt% of ATBC yielded a substantial improvement of the elongation at break, becoming higher than 300%. The effect of PLA plasticization on the barrier properties was assessed by different molecules, with increasing interaction with the formulated material, such as helium, an inert gas, and oxygen and water vapour. In comparison to the neat sample, barrier properties against helium were maintained when PLA was plasticized with up to 17 wt% of ATBC. The oxygen permeability coefficient and the water vapour transmission rate doubled for mixtures with 17 wt% ATBC in PLA, but increased five-fold in the PEG plasticized samples. This result is most likely caused by increased solubility of oxygen and water in the PEG phase due to their mutual miscibility. To conclude, ATBC increases efficiently the elongation at break of PLA while maintaining the permeability coefficient of helium and keeping the barrier properties against oxygen and water vapour in the same order of magnitude

Barrier properties of poly(lactic acid) and its morphological changes induced by aroma compound sorption

The barrier properties of poly(lactic acid) (PLA) play a key role in food packaging applications. For their optimization, the influence of crystallinity on the barrier properties of PLA and the interaction of PLA with the aroma compound ethyl acetate were investigated. PLA film samples with various crystallinities were fabricated by flat die extrusion and thermocompression and compared to PLA Biophan (TM). The degree of crystallinity had no effect on the oxygen permeability. However, an increase of crystallinity caused a decrease in ethyl acetate sorption. The sorption isotherm of ethyl acetate obtained using microgravimetry showed a steep increase with increasing aroma activity, a form which is consistent with a plasticization effect. This behaviour was verified using differential scanning calorimetry and dynamic mechanical analysis. Sorption caused a marked decrease in the glass transition temperature well below room temperature to approximately 0 degrees C. Furthermore, PLA underwent a solvent-induced crystallization when equilibrated in ethyl acetate atmosphere at an activity of 0.5. The results obtained show the importance of considering possible interactions between polymer and foodstuff during the optimization step of polymeric materials for food packaging applications

Characterization of PLA-limonene blends for food packaging applications

Polymers derived from renewable resources are now considered as promising alternatives to traditional petro-polymers as they mitigate current environmental concerns (raw renewable materials/biodegradability). D-limonene can be found in a variety of citrus, indeed is the main component of citrus oils and one of most important contributors to citrus flavor. The incorporation of limonene in PLA matrix was evaluated and quantified by Pyrolysis Gas Chromatography Mass Spectrometry (Py-GC/MS). Transparent films were obtained after the addition of the natural compound. Mechanical properties were evaluated by tensile tests. The effect of limonene on mechanical properties of PLA films was characterized by an increase in the elongation at break and a decrease in the elastic modulus. The fracture surface structure of films was evaluated by scanning electron microscopy (SEM), and homogeneous surfaces were observed in all cases. Barrier properties were reduced due to the increase of the chain mobility produced by the D-limonene. (C) 2013 Elsevier Ltd. All rights reserved.This research was supported by the Ministry of Science and Innovation of Spain (MAT2011-28468-C02-02). Marina P. Arrieta thanks Generalitat Valenciana (Spain) for a Santiago Grisolia Fellowship. Authors thank Professor Alfonso Jimenez from the University of Alicante, for his useful discussions.Arrieta, MP.; López Martínez, J.; Ferrándiz Bou, S.; Peltzer, MA. (2013). Characterization of PLA-limonene blends for food packaging applications. Polymer Testing. 32(4):760-768. https://doi.org/10.1016/j.polymertesting.2013.03.016S76076832

Mechanisms of gas and organic compounds tranfer into Polylactide (PLA)

La compréhension de la relation structure-propriété est un élément indispensable pour la conception et l'amélioration des matériaux, notamment ceux utilisés dans le domaine de l'emballage alimentaire. Afin de contribuer à la compréhension des phénomènes de transport dans le polylactide (PLA), les travaux de ce mémoire se sont portés sur la modulation de la microstructure du PLA en lien avec ses propriétés barrière aux gaz (oxygène, hélium) et aux composés organiques (esters éthyliques, sondes fluorescentes). La microstructure a été modulée i) par l'ajout de plastifiant (ATBC, PEG), ii) par la cristallisation selon trois procédés, le traitement thermique, la cristallisation induite par des composés organiques et le biétirage. Ces approches ont permis, respectivement, de faire varier le pourcentage de phase amorphe par rapport à la phase cristalline, la fraction de volume libre au sein de la phase amorphe, et la structure cristalline. L'augmentation de la cristallinité par recuit à partir du vitreux n'a pas conduit à une diminution systématique et importante des coefficients de transport des molécules de gaz (oxygène, hélium). Deux hypothèses principales ont ainsi été formulées pour expliquer ce comportement : la dédensification de la phase amorphe et la présence d'une phase amorphe mobile et d'une phase rigide. L'influence du biétirage sur les propriétés barrière aux gaz a été très limitée même au plus fort ratio d'étirage (4×4). Néanmoins cette technique a l'avantage de pouvoir réaliser des morphologies différentes.L'étude des coefficients de transport par plusieurs méthodes (sorption, perméation, diffusion par contact solide/solide) a mis en évidence la loi d'échelle ( ) dans le cas des molécules fluorescentes et a permis une première estimation du coefficient alpha. Une approche par Résonance Paramagnétique Electronique a permis de mettre en évidence des séparations de phase des systèmes plastifiés par ATBC et PEG. Cette méthode pourrait constituer un des moyens de sonder les hétérogénéités locales et les changements microstructuraux liés à l'interaction de molécules perméantes et de la matrice polymère, lors du transport.The understanding of the relationship between structure and properties is fundamental for materials conception and improvement, in particular for those used in food packaging industry. To contribute to the understanding of the transport phenomena in polylactide (PLA), this study was focused on the adjustment of PLA microstructure modulation related to its gas (oxygen, helium) and organic compounds (ethyl esters, fluorescent molecules) barrier properties. The microstructure was modulated i) by adding plasticizers (ATBC, PEG), ii) by crystallizing according to 3 processes, thermal treatment, organic compounds induced crystallization and biaxially orientation. These approaches, respectively enabled to vary, the ratio of amorphous phase and crystalline phase, free volume fraction into amorphous phase and the crystalline structure. The increase in crystallinity degree, by annealing from cold state, did not result in a systematic and significant decrease of the gas molecules transport coefficient (oxygen, helium). Two main hypotheses were formulated to explain this behaviour: de-densification of amorphous phase and the presence of a mobile and a rigid amorphous phase. The influence of biaxially orientation on gas barrier properties was strongly limited even at the highest stretching ratio (4×4). Nevertheless several morphologies can be formed thanks to this technique.The transport coefficient study by several methods (sorption, permeation and diffusion by solid/solid contact) highlighted a scale law with the fluorescent molecules and allowed to a first estimation of the α coefficient. Thanks to Electronic Spin Resonance approach, phase separation of plasticized systems by ATBC and PEG were highlighted. This method could be one of the means to probe the local heterogeneities and the micro-structural changes related to the interaction of permeating molecules and polymer matrix during transport

Compréhension des mécanismes de transferts de gaz et de composés organiques dans le Polylactide (PLA)

The understanding of the relationship between structure and properties is fundamental for materials conception and improvement, in particular for those used in food packaging industry. To contribute to the understanding of the transport phenomena in polylactide (PLA), this study was focused on the adjustment of PLA microstructure modulation related to its gas (oxygen, helium) and organic compounds (ethyl esters, fluorescent molecules) barrier properties. The microstructure was modulated i) by adding plasticizers (ATBC, PEG), ii) by crystallizing according to 3 processes, thermal treatment, organic compounds induced crystallization and biaxially orientation. These approaches, respectively enabled to vary, the ratio of amorphous phase and crystalline phase, free volume fraction into amorphous phase and the crystalline structure. The increase in crystallinity degree, by annealing from cold state, did not result in a systematic and significant decrease of the gas molecules transport coefficient (oxygen, helium). Two main hypotheses were formulated to explain this behaviour: de-densification of amorphous phase and the presence of a mobile and a rigid amorphous phase. The influence of biaxially orientation on gas barrier properties was strongly limited even at the highest stretching ratio (4×4). Nevertheless several morphologies can be formed thanks to this technique.The transport coefficient study by several methods (sorption, permeation and diffusion by solid/solid contact) highlighted a scale law with the fluorescent molecules and allowed to a first estimation of the α coefficient. Thanks to Electronic Spin Resonance approach, phase separation of plasticized systems by ATBC and PEG were highlighted. This method could be one of the means to probe the local heterogeneities and the micro-structural changes related to the interaction of permeating molecules and polymer matrix during transport.La compréhension de la relation structure-propriété est un élément indispensable pour la conception et l'amélioration des matériaux, notamment ceux utilisés dans le domaine de l'emballage alimentaire. Afin de contribuer à la compréhension des phénomènes de transport dans le polylactide (PLA), les travaux de ce mémoire se sont portés sur la modulation de la microstructure du PLA en lien avec ses propriétés barrière aux gaz (oxygène, hélium) et aux composés organiques (esters éthyliques, sondes fluorescentes). La microstructure a été modulée i) par l'ajout de plastifiant (ATBC, PEG), ii) par la cristallisation selon trois procédés, le traitement thermique, la cristallisation induite par des composés organiques et le biétirage. Ces approches ont permis, respectivement, de faire varier le pourcentage de phase amorphe par rapport à la phase cristalline, la fraction de volume libre au sein de la phase amorphe, et la structure cristalline. L'augmentation de la cristallinité par recuit à partir du vitreux n'a pas conduit à une diminution systématique et importante des coefficients de transport des molécules de gaz (oxygène, hélium). Deux hypothèses principales ont ainsi été formulées pour expliquer ce comportement : la dédensification de la phase amorphe et la présence d'une phase amorphe mobile et d'une phase rigide. L'influence du biétirage sur les propriétés barrière aux gaz a été très limitée même au plus fort ratio d'étirage (4×4). Néanmoins cette technique a l'avantage de pouvoir réaliser des morphologies différentes.L'étude des coefficients de transport par plusieurs méthodes (sorption, perméation, diffusion par contact solide/solide) a mis en évidence la loi d'échelle ( ) dans le cas des molécules fluorescentes et a permis une première estimation du coefficient alpha. Une approche par Résonance Paramagnétique Electronique a permis de mettre en évidence des séparations de phase des systèmes plastifiés par ATBC et PEG. Cette méthode pourrait constituer un des moyens de sonder les hétérogénéités locales et les changements microstructuraux liés à l'interaction de molécules perméantes et de la matrice polymère, lors du transport

Compréhension des mécanismes de transfert de gaz et de composés d'arôme dans des polyesters biodégradables

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Characteristics and applications of PLA

Part II : Bioplastics and BiocompositesChap. 8Poly(lactic acid) (PLA), is one of the biopolymers already available in large quantities produced by industrial fabrication in a number of different commercial grades. Its promising properties make it suitable for different types of applications in the biomedical and technical fi eld. This chapter will focus on PLA properties which are mainly used for applications in high volume markets, such as technical applications or packaging. The main focus of this chapter will be the production of lactic acid, the synthesis, the degradation and biodegradation of PLA. Knowledge of the relationship between the process and the polymer properties allows for the tailoring of the fi nal material for a given application. The main fi elds of technical applications of PLA are reviewed, and their main advantages and limitations are pointed out