Construction of Elastomeric Nanobelts in a Glassy Polymer Matrix: Toward Supertoughened Nanoalloys with Significantly Depressed Yielding Behaviors
Rubber-toughened glassy polymers, researched as a prominent toolkit to fabricate high-performance plastics, are usually confronted with a great loss of tensile strength at the point of apparent yielding. Exploiting advanced plastic nanoalloys with high toughness and small stress difference (Δσ) between yielding and tensile platforms at high-strain levels is extremely being pursued yet challenging. Taking glassy poly(l-lactide) (PLLA) as an example, here, a viable and universal approach is discovered to elaborate supertoughened nanoalloys with significantly depressed yielding behaviors by virtue of elastomeric nanobelts to replace conventional rubber droplets in a glassy matrix by a simple reactive processing strategy. Stereocomplex crystal (SC)-immobilized EGMA, prepared by cocrystallization of enantiopure PDLA-/PLLA pairs respectively pregrafted onto EGMA chains, is used to toughen PLLA. Therefore, the structure of the elastomer, from droplets and shells to nanobelts in the PLLA matrix, can be achieved. Such controllable morphology allows for the corresponding nanoalloys with significantly enhanced notched impact strength (from 5.7 to 60.2 to 91.3 kJ/m2) and shortened Δσ (from 17.5 to 15.8 to 6.8 MPa). Furthermore, tricontinuous morphology integrates penetrative elastomeric nanobelts (EGMA), glassy polymers (PLLA), and SC phases, which are achieved by adjusting SC moieties. The authors demonstrate that the resulting nanoalloy integrates superior performance (toughness, heat resistance, and crystallization rate) and stress leveling-off without fully undergoing real yielding (Δσ = 1.4 MPa), surpassing most elastomer-toughened PLA alloys. The morphology development and underlying origin of the impact/deformation mechanism are elucidated. To our knowledge, this is the first time that the validity of such supertoughened glassy polymer alloys with significantly necking-suppressed deformation has been demonstrated. The versatile strategy can be further extended to arbitrary engineering plastics, including PET, PBT, and nylon, providing a paradigm in the development of advanced nanoalloys, which is quite challenging via existing industrial technologies.
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