Entropy-Driven Ultratough Blends from Brittle Polymers

Abstract

Polymer blends with synergetic performance play an integral part in modern society. The discovery of compatible polymer systems often relies on strong chemical interactions. By contrast, the role of entropy in polymers is often neglected. In this work, we show that entropy effect could control the phase structure and mechanical behaviors of polymer blends. For weakly interacting polymer pairs, the seemingly small mixing entropy favors the formation of nanoscale cocontinuous structures. The abundant nanointerfaces could initiate large plastic deformations by crazing or shear, thus, transforming brittle polymers (elongation < 9%) into superductile materials (elongation ∼ 146%). The resultant polymer blends display high transparency, strength (∼70 MPa), and toughness (∼60 MJ/m 3 ) beyond most engineering plastics. The principle of entropy-driven blends may also be applied in other polymer systems, offering a strategy to develop mechanically robust bulk polymeric materials for emerging applications such as biomedicine and electronics.

Strong Interface via Weak Interactions: Ultratough and Malleable Polylactic acid/Polyhydroxybutyrate Biocomposites

“…This may arise from a thicker PMMA interfacial layer that is more susceptible to internal crack formation as PMMA is inherently brittle. Compared with binary blends developed previously, [23] the ternary biocomposites require much less non-biodegradable PMMA to achieve optimum performance, thus maximizing the biodegradability (Figure S4, Supporting Information). The ternary biocomposites exhibit a combination of high strength and tensile toughness that exceeds commercial polymer blends and advanced biocomposites (Figure 3b).…”

“…[29] PMMA is also a brit-tle plastic with 𝜖 = 7%. [23] Surprisingly, adding 2.5% of PMMA into PLLA/PHB blends leads to significant increase of 𝜖 from 3% to 112%, a 38-fold increase compared to matrix PLLA, and the ultimate toughness (UT) from 1 to 30 MJ m −3 . More notably, M5 exhibits stable plastic deformation at ≈118%, while M7.5 exhibit a maximum 𝜖 ≈ 165%, up to 55-fold compared to neat PLLA, while the strength is maintained at ≈50 MPa (Figure 3a).…”

“…Weak interaction between PMMA and PLLA facilitate the migration of PMMA to the interface, while entropy effects of PMMA-PLLA and PMMA-PHB drives agile chain motion and entanglements. [23]…”

Correlating thermodynamics, morphology, mechanics and thermal transport in PMMA-PLA blends

“…These systems consist of, but are not limited to, linear polymers, copolymers, polymers with different architectures and/or polymer blends. In this context, the latter is of particular interest because a polymer blend provides an additional flexibility to design functional materials with tunable properties [8,10,13]. Here, however, the microscopic phase behavior is important for the usefulness of these materials for their desired applications [14,15].…”

“…Therefore, it is important to achieve a compatible chemical composition that is not only simple from the processing point of view, but also provides a reasonably stable homogeneous blend. Here, the standard commodity polymers, such as poly(methyl methacrylate) (PMMA), poly(N −acryloyl piperidine) (PAP), poly(lactic acid) (PLA), poly(acrylic acid) (PAA), and poly(acrylamide) (PAM), have been shown to provide extraordinary phase, mechanical, and thermal behavior [8][9][10][13][14][15][16][17][18]. * debashish.mukherji@ubc.ca…”