Impact of Nanoconfinement on Polylactide Crystallization and Gas Barrier Properties

Abstract

The barrier properties of poly(L-lactide) (PLLA) were investigated in multinanolayer systems, probing the effect of confinement, the compatibility between the confining and the confined polymer, crystal orientation, and amorphous phase properties. The multilayer coextrusion process was used to confine PLLA between two amorphous polymers (polystyrene, PS; and polycarbonate, PC), which have different chemical affinities with PLLA. Confined PLLA layers of approximately 20 nm thickness were obtained. The multinanolayer materials were annealed at different temperatures to obtain PLLA crystallites with distinct polymorphs. PLLA annealed in PC/PLLA films at 120°C afforded a crystallinity degree up to 65%, and PLLA annealed in PC/PLLA or PS/PLLA films at 85°C had a crystallinity degree of 45%. WAXS measurements evidenced that the PLLA lamellas between PS layers had a mixed in-plane and on-edge orientation. PLLA lamellas between PC layers were uniquely oriented in-plane. DMA results evidenced a shift of the PC glass transition toward lower temperature, suggesting the possible presence of an interphase. The development of the rigid amorphous fraction (RAF) in the amorphous phase during annealing was impacted by the confiner polymer. The RAF content of semicrystalline PLLA was about 15% in PC/ PLLA, whereas it was neglectable in PS/PLLA. The oxygen barrier properties appeared to be governed by RAF content, and no impact of the PLLA polymorph or the crystalline orientation was observed. This study shows that the confinement of PLLA on itself does not impact barrier properties but that the proper choice of the confiner polymer can lead to decrease the phase coupling which creates the RAF. It is the prevention of RAF that decreases permeability.

Biodegradable PLA/PBSA Multinanolayer Nanocomposites: Effect of Nanoclays Incorporation in Multinanolayered Structure on Mechanical and Water Barrier Properties

“…In fact, in multilayered structures by nanoscale confinement, the polymer layers crystallized as single crystals in in-place orientation parallel to the layers. More recently, the confinement of PLLA by PC and PS amorphous polymer layers have been performed by means of the multilayer coextrusion process [15], and the authors have highlighted the impact on the oxygen barrier properties of the rigid amorphous fraction (RAF) generated by postannealing of the multilayer films. Annealing PLLA/PS films allowed for obtaining a high crystallinity degree without RAF and this has induced an oxygen barrier improvement by a factor of 10 with 20 nm thick PLLA layers [15].…”

“…More recently, the confinement of PLLA by PC and PS amorphous polymer layers have been performed by means of the multilayer coextrusion process [15], and the authors have highlighted the impact on the oxygen barrier properties of the rigid amorphous fraction (RAF) generated by postannealing of the multilayer films. Annealing PLLA/PS films allowed for obtaining a high crystallinity degree without RAF and this has induced an oxygen barrier improvement by a factor of 10 with 20 nm thick PLLA layers [15]. Concerning the water barrier properties for multilayer films, nowadays, only few works refer to this and the water barrier improvement was mainly obtained afterheat treatment or after a biaxial drawing [16] utilized to promote polymer crystallization.…”

Stereocomplexation Reinforced High Strength Poly(L-lactide)/Nanohydroxyapatite Composites for Potential Bone Repair Applications

“…The intermolecular interaction between PLA chains has been utilized to improve the interfacial interaction between the n-HA filler and PLA matrix; generally, PLA oligomers are grafted onto n-HA to achieve better dispersion in the PLA matrix and improve the mechanical propertie It has been reported that stereocomplex could form between enantiomeric poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) in solution, oriented drawing, interface, hot drawing, and even during 3D printing [30][31][32][33][34]; the stereocomplex produces numerous dense, micron-sized crystals that act as cross-linking points between polymer chains and connect the high-density "tie chains" between crystals, thereby significantly improving the mechanical properties [35]. The tensile strength and Young's modulus of PDLA/PLLA blend films are at least 30% higher than those of the corresponding pure PLLA films in almost any molecular weight rang The presence of stereocomplex crystals in the PLA matrix not only improves the mechanical properties but also enhances the crystallinity and thermal stability [36].…”

Structural and Barrier Properties of Compatibilized PE/PA6 Multinanolayer Films

“…For thicker layers ( 100 nm), confined spherulite morphologies that increase the tortuosity for gas diffusion have been observed for high density polyethylene (HDPE) confined against a cyclic olefin copolymer (COC) [17]. In addition to crystal orientation, other parameters may have a strong influence on the barrier properties, such as the crystal phase [18] or the amorphous phase that can be constrained [14,19,20] and/or oriented [21].…”