Enhanced Mechanical Properties of Uniaxially Stretched Polylactide/Poly(ethylene oxide)-b-Poly(butylene oxide) Blend Films

Abstract

Chain orientation, a natural consequence of polymer film processing, often leads to enhanced mechanical properties parallel to the machine extrusion direction (MD), while leaving the properties in the transverse direction (TD) unaffected or diminished, as compared to the unoriented material. Here, we report that mixing poly(ethylene oxide)-block-poly(butylene oxide) (PEO-PBO) diblock copolymer that forms dispersed particles in an amorphous polylactide (PLA) matrix produces uniaxially stretched blend films with enhanced toughness in both the MD and TD. Small-angle X-ray scattering experiments and visual observations revealed that the dominant deformation mechanism for blend films transitions from crazing to shear yielding in the MD as the stretching ratio increases, while crazing is the primary deformation mechanism in the TD at all stretching ratios investigated. As the films age at room temperature, crazing becomes more prevalent in the MD without compromising the improved toughness. The stretched blend films were susceptible to some degree of mechanical aging in the TD but remained fivefold tougher than stretched neat PLA films for up to 150 days. This work presents a feasible route to produce uniaxially stretched PEO–PBO/PLA films that are mechanically tough, which provides a more sustainable plastic alternative.

Biaxial Toughening in Uniaxially Stretched Films of Block Polymer-Modified Semicrystalline Poly(l-lactide)

“…30,31 The impact of λ on the mechanical properties of PEO−PBO/PLLA films in the MD was nearly identical to its impact on neat PLLA, though σ Y was slightly lower in PEO−PBO/PLLA blends than in neat PLLA due to the partial miscibility of PEO−PBO in PLLA, consistent with the behavior reported previously in unstretched PEO−PBO/PLLA films. 31 It is important to point out here the synergistic influence of X c and λ in the MD. To illustrate this point, Figure S6 summarizes previously reported σ Y of unstretched amorphous PDLLA, 29 unstretched PLLA (X c = 30%), 30 PDLLA stretched to λ = 4, 31 and sample N4−5, all normalized by σ Y of unstretched PDLLA (all tested in the MD, where applicable).…”

“…It is important to point out here the synergistic influence of X c and λ in the MD. To illustrate this point, Figure S6 summarizes previously reported σ Y of unstretched amorphous PDLLA, unstretched PLLA ( X c = 30%), PDLLA stretched to λ = 4, and sample N4–5, all normalized by σ Y of unstretched PDLLA (all tested in the MD, where applicable). The addition of crystallinity in PLLA unstretched films produces a roughly 25% increase in σ Y over unstretched PDLLA.…”

Crystallinity-Independent Toughness in Renewable Poly(l-lactide) Triblock Plastics

“…Efforts to simultaneously upgrade PLLA’s thermal and mechanical properties have spawned a rich subfield. Melt-blending with rubbery polymers is the most well-explored approach, owing to the low cost of bulk rubber, translatability to existing melt-processing capabilities, and property tunability under a wide parameter space. , In blends, the most significant mechanical property enhancements most often require reactive − or nonreactive compatibilization. − In other approaches without adding rubber, polymer-grafted cellulose nanocrystals have garnered attention as crystal nucleators , and tougheners. − Amphiphilic non-PLA diblock polymers have also conferred toughness and aging resistance to atactic PLA, − as well as toughness and accelerated crystallization to semicrystalline PLLA. , Finally, thermomechanical preconditioning of PLLA − and its composites can produce highly oriented matrices with improved strength, ductility, and thermal resistance.…”

Biodegradable poly(lactic acid)/poly(propylene carbonate) blend with enhanced mechanical properties and heat resistance by uniaxial pre‐stretching

“…It is well-known that the mechanical properties of polymers can be enhanced by hot stretching. [18][19][20][21][22][23][24][25] According to Li et al, 26 uniaxial hot drawing has markedly simultaneous improved the mechanical properties of PLA, including strength and ductility, compared with the undrawn PLA, where the yield strength of 135.5 MPa and the elongation at break of 294.9% were achieved. It was discovered that gauche-gauche conformers that originated from the oriented amorphous chains were the key factor to fabricate super-toughening PLA films at low stretching stress.…”

“…It is well‐known that the mechanical properties of polymers can be enhanced by hot stretching 18–25 . According to Li et al, 26 uniaxial hot drawing has markedly simultaneous improved the mechanical properties of PLA, including strength and ductility, compared with the undrawn PLA, where the yield strength of 135.5 MPa and the elongation at break of 294.9% were achieved.…”