Sustainable polymers are important alternatives to plastics and elastomers derived from petroleum resources. Poly(lactide) (PLA), a commercially available sustainable plastic, is a well-known success story. However, PLA lacks ductility and toughness, limiting the number of potential uses. In this study, small amounts of a liquid poly(ethylene oxide)-block-poly(butylene oxide) (PEO-PBO) diblock copolymer additive were blended with PLA to enhance its toughness and ductility. The incorporated PEO-PBO diblock copolymers generated a macrophase-separated morphology with particle diameters of 0.2–0.9 μm, and nearly matched refractive indices of PLA and PEO-PBO led to retention of optical transparency. Addition of just 1.8 wt % PEO-PBO into PLA led to a 20-fold increase in toughness, measured as the area under the stress–strain data in tension without affecting the bulk elastic modulus of the plastic. The micromechanical deformation process of the PEO-PBO/PLA blend was investigated via in situ small angle X-ray scattering during tensile testing. The total volume of the crazed material was proportional to the total surface area of the dispersed PEO-PBO particles, and both quantities increased with increasing PEO-PBO loading. Increasing the PEO-PBO loading also resulted in (A) an increase in particle size, causing a decrease in the craze initiation stress, and (B) an increase in fibril spacing, indicating a lower craze propagation stress. Furthermore, craze development was found to be independent of aging time. As a result, the PEO-PBO/PLA blend was able to remain ductile and tough for up to 114 days, exhibiting a 10-fold increase in elongation at break and toughness compared to neat PLA, which becomes brittle in less than 2 days. These results demonstrate that designing additives that promote deformation by crazing is an effective way to overcome the aging-induced embrittlement of glassy polymers.
Sustainable semicrystalline poly(l-lactide) (PLLA) was melt mixed with 5 wt % poly(ethylene oxide)-b-poly(butylene oxide) (PEO-PBO) diblock copolymer, resulting in blends that display an exceptional combination of properties. The blends were annealed at various temperatures, leading to different degrees of crystallinity. The addition of 5 wt % PEO-PBO produced finely dispersed liquid particles that caused a significant reduction in the time for crystallization after quenching from the melt, where T m = 166 °C. At 95 °C, the halftime for crystallization was t 1/2(95 °C) = t 1/2 o/7, while at 135 °C, t 1/2(135 °C) = t 1/2 o/5, where t 1/2 o is the time required to obtain 50% of the final extent of crystallization with pure PLLA. The block copolymer particles also enhanced the ductility of the blends by facilitating stress-induced cavitation and uniform crazing without impacting the modulus. Tensile toughness increased by 7–15 fold, scaling inversely with the degree of crystallinity. The deformation mechanism was investigated by small- and wide-angle X-ray scattering as a function of applied strain, revealing that the craze volume is dependent on crystallinity, while the crystal structure displayed minimal changes. Regardless of the extent of crystallinity, crazing was found to be the primary deformation mechanism, countering the ductile-to-brittle transition associated with the aging of PLLA. Adding 5 wt % PEO-PBO extends the strain at break from 4% for pure PLLA after 2 days to more than approximately 50% after 85 or more days of aging. These findings, along with the industrially relevant blend preparation method, reveal that PEO-PBO is a unique and potent additive that could expand the applications served by PLLA, promoting a more sustainable future.
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.
Absorber layers comprised of shear thickening fluid (STF) intercalated Kevlar ® (STF-Armor TM ) are integrated within the standard extravehicular activity (EVA) suit and tested for efficacy against both needle puncture and hypervelocity impact (HVI) tests characteristic of micrometeoroids and orbital debris (MMOD). An improvement in puncture resistance against hypodermic needle threats is achieved by substituting STF-Armor TM in place of neoprene-coated nylon as the absorber layer in the standard EVA suit. The prototype lay-ups containing STF-Armor TM have the benefit of being 17% thinner and 13% lighter than the standard EVA suit and the ballistic limit is identified in HVI testing. The results here demonstrate that EVA suit lay-ups containing STF-Armor TM as absorber layers offer meaningful resistance to MMOD threats.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.