Films of PLLA/PHBV: Thermal, morphological, and mechanical characterization

Abstract

Blends of poly(l-lactic acid)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PLLA/PHBV), both semicrystalline polymers, were prepared in different compositions (100/0, 80/20, 60/40, 50/50, 40/60, 20/80, and 0/100) and characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), polarized light microscopy (PLM), and tensile tests. Although PLLA/PHBV blends do not present clear phase separation by SEM, the analyses by TGA, DSC, and DMA showed that the PLLA/PHBV blends are immiscible. The cross sections observed by SEM showed that the morphology of the blends changes from porous to dense, due to the composition. DSC and DMA data showed two distinct glass transition and melting temperatures. However, the DMA analysis related to frequency variation showed partial molecular interactions between PHBV and PLLA.

Combined compatibilization and plasticization effect of low molecular weight poly(lactic acid) in poly(lactic acid)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) blends

“…This gradual decrease of the T g of PLA phase can be understood as an increase of compatibility of PLA/PHBV blends due to the presence of the oLA, miscible with both PLA and PHBV. The cold crystallization temperature of PLA is decreased from 119 to 105°C with the addition of PHBV, as already observed by previous authors [15,16,45], and is not influenced by oLA addition. The PLA degree of crystallinity also remains extremely low in every case (<5%).…”

“…Zhang et al [21] found that melt blended samples exhibited greater compatibility than those prepared by solvent casting at room temperature, possibly due to a transesterification reaction between PHB and PLA occurring at high temperature. This transesterification, or more generally the presence of specific interactions between the two polymers, has been evidenced by many other authors [14,15,[22][23][24], especially for blends containing a low amount of PHB(V). For such PLA/PHBV blends (typically weight fractions of 90%/10%), Gerard and Budtova [22] observed a peculiar morphology, with very small PHBV nodules (about 400 nm) well dispersed in PLA matrix, with increased adhesion at the interface, presumably explaining the increase of ductility (elongation at break of 200% when tested immediately after sample preparation) measured for this composition by the authors.…”

“…Among polyhydroxyalcanoates (PHAs), which are aliphatic polyesters obtained by microbial fermentation, poly(3-hydroxybutyrate) (PHB) and its copolymers (poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly , poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx)…) have been largely used for PLA-based blends [9]. Some of the resulting blends exhibit improved properties compared to neat PLA: higher toughness and increased elongation at break [10][11][12][13][14][15][16], improved gas barrier properties [17,18], increased thermal stability [16], enhanced biodegradability [14].…”

Polylactide/poly(hydroxybutyrate-co-hydroxyvalerate) blends: Morphology and mechanical properties

“…Its properties are known to depend on hydroxyvalerate (HV) content [10]. At very low HV content, PHBV is similar to conventional petrochemical thermoplastics, such as polypropylene, in terms of melting temperature, crystallinity, and tensile strength [11][12][13][14][15]. Most of literature agrees on immiscibility of PLA and PHBV [16][17][18][19].…”

Effect of salt leaching on PCL and PLGA(50/50) resorbable scaffolds

“…Several factors determine the degradation rate of those polymers, including the site of the implant, the chemistry and stereoisomeric composition of the material, crystallinity, size and morphology of the scaffold, external pH medium and other parameters 7 . Thus, the in vitro and in vivo degradation studies have been proposed to establish relationships among those factors 8,9 . Within the many types of bioresorbable material applications, porous morphology is the preferred ones.…”