An official website of the United States government
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.
more »
« less
This content will become publicly available on October 1, 2026
Biaxial Stretching of PBAT/PLA Blends for Improved Mechanical Properties
Biodegradable polymers offer a promising solution to the growing issue of global microplastic pollution. To effectively replace conventional plastics, it is essential to develop strategies for tuning the properties of biodegradable polymers without relying on additives. Biaxial stretching promotes anisotropic crystallization in polymer domains, thereby altering the mechanical performance of polymer blends. In this study, we employed a design of experiment (DoE) approach to investigate the effects of biaxial stretching at three drawing temperatures (Tds) and draw ratios (λs) on a biodegradable blend of poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT), aiming to optimize both the strength and ductility. The DoE analysis revealed that the composition, the λ, the interaction between the λ and composition, and the interaction between the Td and composition significantly affect the elongation at break (εBreak). For the stress at break (σBreak), the most influential factors were the interaction between the λ and PLA concentration; a three-way interaction among the λ, PLA, and Td; the Td; the λ; and finally the PLA concentration alone. The optimal εBreak and σBreak were achieved at a λ = 5 × 5 and Td = 110 °C, with a composition of 10% PLA and 90% PBAT. The stretched samples exhibited higher crystallinity compared to the pressed samples across all compositions. This work demonstrates that in addition to the composition, the processing parameters, such as the λ and Td, critically influence the mechanical properties, enabling performance enhancements without the need for compatibilizers or toxic additives.
more »
« less
- Award ID(s):
- 2044479
- PAR ID:
- 10657680
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Polymers
- Volume:
- 17
- Issue:
- 19
- ISSN:
- 2073-4360
- Page Range / eLocation ID:
- 2651
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Semicrystalline poly(l-lactide) (PLLA) is a leading biosourced, compostable alternative to conventional plastics but lacks sufficient toughness for many applications. Chain alignment via uniaxial stretching may be used to toughen PLLA but often creates anisotropic materials that are tough in the machine direction (MD) but brittle in the transverse direction (TD). This work reports uniaxially stretched films of PLLA blended with 3 wt % poly(ethylene oxide)-block-poly(butylene oxide) (PEO-PBO), which exhibit as much as a 5-fold increase in toughness in the TD compared to similarly stretched neat PLLA films─and elucidates the impact of PEO–PBO particles on the relationship between stretching, crystallization behavior, and resultant mechanical properties. Faster stretching rates were correlated with higher yield stress and a greater degree of crystallite alignment in the PEO–PBO/PLLA blends. This trend highlights the synergistic relationship between crystallinity and chain alignment and suggests a competing mechanism of heterogeneous crystallite nucleation around PEO–PBO particles. Importantly, PEO–PBO/PLLA exhibited a TD elongation at break of 36%, five times greater than the value of similarly stretched neat PLLA and even greater than the corresponding MD value of either material. Taken together, these findings demonstrate that uniaxial stretching of PEO–PBO/PLLA blends produces biaxially tough films, with the fastest stretching conditions producing the greatest enhancement in TD toughness.more » « less
-
Abstract Poly(lactic acid) (PLA) is a commercially available bio‐based polymer that is a potential alternative to many commodity petrochemical‐based polymers. However, PLA's thermomechanical properties limit its use in many applications. Incorporating polymer‐grafted cellulose nanocrystals (CNCs) is one potential route to improving these mechanical properties. One key challenge in using these polymer‐grafted nanoparticles is to understand which variables associated with polymer grafting are most important for improving composite properties. In this work, poly(ethylene glycol)‐grafted CNCs are used to study the effects of polymer grafting density and molecular weight on the properties of PLA composites. All CNC nanofillers are found to reinforce PLA above the glass transition temperature, but non‐grafted CNCs and CNCs grafted with short PEG chains (<2 kg mol−1) are found to cause significant embrittlement, generally resulting in less than 3% elongation‐at‐break. By grafting higher molecular weight PEG (10 kg mol−1) onto the CNCs at a grafting density where the polymer chains are predicted to be in the semi‐dilute polymer brush conformation (~0.1 chains nm−2), embrittlement can be avoided.more » « less
-
Abstract 3D printing is a popular fabrication technique because of its ability to produce complex architectures. Melt‐based 3D printing is widely used for thermoplastic polymers like poly(caprolactone) (PCL), poly(lactic acid) (PLA), and poly(lactic‐co‐glycolic acid) (PLGA) because of their low processing temperatures. However, traditional melt‐based techniques require processing temperatures and pressures high enough to achieve continuous flow, limiting the type of polymer that can be printed. Solvent‐cast printing (SCP) offers an alternative approach to print a wider range of polymers. Polymers are dissolved in a volatile solvent that evaporates during deposition to produce a solid polymer filament. SCP, therefore, requires optimizing polymer concentration in the ink, print pressure, and print speed to achieve desired print fidelity. Here, capillary flow analysis shows how print pressure affects the process‐apparent viscosity of PCL, PLA, and PLGA inks. Ink viscosity is also measured using rheology, which is used to link a specific ink viscosity to a predicted set of print pressure and print speed for all three polymers. These results demonstrate how this approach can be used to accelerate optimization by significantly reducing the number of parameter combinations. This strategy can be applied to other polymers to expand the library of polymers printable with SCP.more » « less
-
Abstract Structural supercapacitors that simultaneously bear mechanical loads and store electrical energy have exciting potential for enhancing the efficiency of various mobile systems. However, a significant hurdle in developing practical structural supercapacitors is the inherent trade‐off between their mechanical properties and electrochemical capabilities, particularly within their electrolytes. This study demonstrates a tough polymer electrolyte with enhanced multifunctionality made through the controlled hydration of a solid polymer electrolyte with poly(lactic acid) (PLA) and lithium salts. Characterization via differential scanning calorimetry, X‐ray diffraction, and Fourier transform infrared spectroscopy confirms the consistent amorphous solid solution phase in varying salt concentrations, whether dried or hydrated. Electrochemical tests and tensile tests are performed to evaluate the ionic conductivity and mechanical properties of these electrolytes. The results indicate that the strategic incorporation of water in the polymer electrolyte significantly enhances the ionic conductivity while preserving its mechanical properties. A specific composition demonstrated a remarkable increase in ionic conductivity (3.11 µS cm−1) coupled with superior toughness (15.4 MJ m−3), significantly surpassing the base polymer. These findings open new horizons for integrating electrochemical functionality into structural polymers without compromising their mechanical properties. Additionally, the paper reports the successful fabrication and testing of structural supercapacitor prototypes combining carbon fibers with fabricated electrolytes, showcasing their potential for diverse applications.more » « less
