Structure and Barrier Properties of Multinanolayered Biodegradable PLA/PBSA Films: Confinement Effect via Forced Assembly Coextrusion

Abstract

Multilayer coextrusion processing was applied to produce 2049-layer film of poly(butylene succinate-co-butylene adipate) (PBSA) confined against poly(lactic acid) (PLA) using forced assembly, where the PBSA layer thickness was about 60 nm. This unique technology allowed to process semicrystalline PBSA as confined polymer and amorphous PLA as confining polymer in a continuous manner. The continuity of PBSA layers within the 80/20 wt % PLA/PBSA layered films was clearly evidenced by atomic force microscopy (AFM). Similar thermal events to the reference films were revealed by thermal studies; indicating no diffusion of polymers during the melt-processing. Mechanical properties were measured for the multilayer film and the obtained results were those expected considering the fraction of each polymer, revealing the absence of delamination in the PLA/PBSA multinanolayer film. The confinement effect induced by PLA led to a slight orientation of the crystals, an increase of the rigid amorphous fraction (RAF) in PBSA with a densification of this fraction without changing film crystallinity. These structural changes allowed to strongly improve the water vapor and gas barrier properties of the PBSA layer into the multilayer film up to two decades in the case of CO gas. By confining the PBSA structure in very thin and continuous layers, it was then possible to improve the barrier performances of a biodegradable system and the resulting barrier properties were successfully correlated to the effect of confinement on the microstructure and the chain segment mobility of the amorphous phase. Such investigation on these multinanolayers of PLA/PBSA with the aim of evidencing relationships between microstructure implying RAF and barrier performances has never been performed yet. Besides, gas and water permeation results have shown that the barrier improvement obtained from the multilayer was mainly due to the reduction of solubility linked to the reduction of the free volume while the tortuosity effect, as usually expected, was not really observed. This work brings new insights in the field of physicochemical behaviors of new multilayer films made of biodegradable polyesters but also in interfacial processes due to the confinement effect induced in these multinanolayer structures obtained by the forced assembly coextrusion. This original coextrusion process was a very advantageous technique to produce eco-friendly materials with functional properties without the help of tie layer, additives, solvents, surface treatments, or inorganic fillers.

Biodegradable PLA/PBS multinanolayer membrane with enhanced barrier performances

“…In a previous work [28], we used this nanolayer coextrusion process to elaborate a multi-nanolayer film composed of two biodegradable polymers, PLA and poly(butylene succinate-co-butylene adipate) PBSA. Despite a slight crystal orientation, the significant improvement of barrier properties was attributed to an increase of the rigid amorphous fraction, presumably densified and thus less permeable.…”

Critical Role of Interfacial Diffusion and Diffuse Interphases Formed in Multi-Micro-/Nanolayered Polymer Films Based on Poly(vinylidene fluoride) and Poly(methyl methacrylate)

“…Among the common techniques fabricating multilayer polymer films, multilayer coextrusion has been a versatile technology and attracted tremendous interest over the past two decades, mainly due to the enhanced dielectric, optical, mechanical, and gas barrier properties of the multilayered products. [1][2][3][4][5] Different from the other traditional methods based on molecular assembly concepts, such as layer-by-layer assembly, 6 multilayer coextrusion termed "forced assembly" is a top-down approach and capable of manufacturing industrially multilayer films with thousands of alternating layers at the lower environmental and pecuniary costs. 1,3 Using a layer multiplication concept, this technology controls the layer architecture/morphology and layer thickness from micro-down to nanoscale towards the target properties.…”

Polymer Nanosheet Containing Star‐Like Copolymers: A Novel Scalable Controlled Release System

“…As shown in Figure a, the multilayered nanostructure was first analyzed by utilizing phase contrast atomic force microscopy (AFM). Although the layer thickness varied ≈±18% of the nominal value due to relatively thinner polymer layers (<100 nm for PCL layer) and different elasticity of the two coextruded polymers, the polymer layers with nanoscale thickness remained intact . From the AFM images, the thicknesses of PCL layers were determined to be 85 ± 13 and 52 ± 12 nm for polyethylene oxide (PEO)/PCL‐PEI‐ b ‐PCL‐MO = 50:50 and PEO/PCL‐PEI‐ b ‐PCL‐MO = 70:30, respectively.…”

“…Although the layer thickness varied ≈±18% of the nominal value due to relatively thinner polymer layers (<100 nm for PCL layer) and different elasticity of the two coextruded polymers, the polymer layers with nanoscale thickness remained intact. [52,68,69] From the AFM images, the thicknesses of PCL layers were determined to be 85 ± 13 and 52 ± 12 nm for polyethylene oxide ( Polymer crystallization in forced assembly MPF was extensively studied by Hiltner and Baer. [49,68,70] With amorphous substrates, such as polystyrene and poly(methylmethacrylate), the crystallization behavior of crystalline polymers could be wellcontrolled in some degree.…”