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Review
. 2022 Apr 18;14(8):1626.
doi: 10.3390/polym14081626.

Tailoring the Barrier Properties of PLA: A State-of-the-Art Review for Food Packaging Applications

Stefania Marano  1 , Emiliano Laudadio  1 , Cristina Minnelli  2 , Pierluigi Stipa  1
Affiliations
Review

Tailoring the Barrier Properties of PLA: A State-of-the-Art Review for Food Packaging Applications

Stefania Marano et al. Polymers (Basel). .

Abstract

It is now well recognized that the production of petroleum-based packaging materials has created serious ecological problems for the environment due to their resistance to biodegradation. In this context, substantial research efforts have been made to promote the use of biodegradable films as sustainable alternatives to conventionally used packaging materials. Among several biopolymers, poly(lactide) (PLA) has found early application in the food industry thanks to its promising properties and is currently one of the most industrially produced bioplastics. However, more efforts are needed to enhance its performance and expand its applicability in this field, as packaging materials need to meet precise functional requirements such as suitable thermal, mechanical, and gas barrier properties. In particular, improving the mass transfer properties of materials to water vapor, oxygen, and/or carbon dioxide plays a very important role in maintaining food quality and safety, as the rate of typical food degradation reactions (i.e., oxidation, microbial development, and physical reactions) can be greatly reduced. Since most reviews dealing with the properties of PLA have mainly focused on strategies to improve its thermal and mechanical properties, this work aims to review relevant strategies to tailor the barrier properties of PLA-based materials, with the ultimate goal of providing a general guide for the design of PLA-based packaging materials with the desired mass transfer properties.

Keywords: PLA; barrier properties; biocomposites; clay nanoparticles; copolymers; food packaging; molecular dynamics; nanoconfinement.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic representation of the general mechanism of the permeation of small molecules through semicrystalline polymers.
Figure 2
Figure 2
(A) Water vapor permeation estimated fraction of the α form in PLLA films; (B) optical micrographs of compression molded PLLA films after cold crystallization; (C) water vapor permeability of PLLA films crystallized as a function of degree of crystallinity. Adapted from [83] with permission from Elsevier. Copyright © 2011.
Figure 3
Figure 3
Schematic representation of the arrangement of crystalline, rigid amorphous and mobile amorphous fractions.
Figure 4
Figure 4
WAXD patterns of drawn and thermally crystallized PLA films. Adapted from [62] with permission from American Chemical Society. Copyright © 2012.
Figure 5
Figure 5
(A) SC crystalline lattice; adapted from [115] with permission from Elsevier. Copyright© 2016. (B) Optical microscopy micrographs of different PLLA/PDLA films with PLLA content of 75% (a,d), 50% (b,e), and 25% (c,f), crystallized at 200 °C; reproduced from [116] with permission from American Chemical Society. Copyright © 2010.
Figure 6
Figure 6
(A,B) POM and cross-sectional micrograph of crystal morphology for PLA with a nucleating agent showing an epitaxial growth lamellae and interlocked structure, respectively; (C) Oxygen permeability coefficient (p) values for all PLA samples as a function of nucleating agent content. Adapted from [125] with permission from American Chemical Society. Copyright © 2014.
Figure 7
Figure 7
Example of typical AFM phase images of multilayered film cross-section with on-edge and in-plane orientations. Adapted from [133] with permission from John Wiley and Sons. Copyright © 2011.
Figure 8
Figure 8
(A) AFM images of the multilayer film with PLA in light and PBSA in dark; (B) gas permeability and solubility coefficients for the monolayer films of PLA and PBSA and the multilayer film of PLA/PBSA. Adapted from [137] with permission from American Chemical Society. Copyright © 2017.
Figure 9
Figure 9
Types of morphology in immiscible polymer blends.
Figure 10
Figure 10
SEM images of (A) PLA/TPS sheets with CA (including WVP values), adapted from [191] and (B) fracture surface of neat PHBV, neat PLA, and their blends (including WVP and oxygen permeability values), adapted from [193] with permission from Elsevier. Copyright © 2013.
Figure 11
Figure 11
Simplified drawing of the “tortuous path” produced by the incorporation of exfoliated clay nanoparticles into a polymer matrix. (A) Neat polymer (diffusing gas molecules follow a pathway perpendicular to the film orientation); (B) non-interacting nanocomposite (impermeable platelets hinders direct diffusion); (C) interacting nanocomposite (the polymer strands are “immobilized” at the polymer–nanofiller interface and the overall free volume available is reduced.
Figure 12
Figure 12
Example of the typical structure of the 2:1 layered silicates. Redrawn from [212] with permission of Elsevier. Copyright © 2015.
Figure 13
Figure 13
From left to right: (A) TEM image of PLA based nanocomposite films containing 6 wt% CH 30B along with oxygen and WVP values of untreated nanocomposites and annealed at 130 °C for 10 min as a function of nanoclay content. Adapted from [231] with permission of Wiley Periodicals. Copyright © 2016. (B) TEM and SEM images of PLA-CH 30B nanocomposites along with the relative oxygen permeability of nanocomposites with different volume fraction of clays (CNa:CH Na+, CRDP:Fyrolflex, and C30B:CH 30B). Adapted from [234] with permission from Elsevier. Copyright © 2016.
Figure 14
Figure 14
TEM image of (A) neat PLA and (B) the PLA–NCFHL biocomposite (with lignin) in which fibrils were well embedded within the PLA matrix (indicated by arrows); (C) confocal laser microscope image showing well dispersed lignin fibrils on the PLA surface; (D) Water vapor transmission rate of the neat PLA and PLA/lignin biocomposite. Adapted from [248] with permission from American Chemical Society. Copyright © 2018.
Figure 15
Figure 15
(A) TEM images of surface coated PLA nanocomposites filled with 1 and 3 wt% of ZnO nanoparticles (even dispersion), adapted from [262] with permission from Elsevier. Copyright© 2013. (B) SEM images of PLA nanocomposites containing 1–1.5 wt% of ZnO without any surface treatment (particle agglomeration indicated by red arrows), adapted from [158] with permission of Elsevier. Copyright © 2018.
Figure 16
Figure 16
(A) Schematic synthesis of semicrystalline or amorphous poly(isobutylene)-graft-acetylated poly(lactide) (PIB-g-(P(L)LA−Ac)). (B) Comparison of oxygen permeability values between the newly synthesized polymers and common ones. Adapted from [274] with permission from American Chemical Society. Copyright © 2020.
Figure 17
Figure 17
Representations of PLA nanoparticles using (A) full atoms (FA), (B) united atoms (UA), and (C) course grained (CG) methods.
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