Browsing by Author "Krajovic, Daniel M"

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    Data for Crystallinity-independent toughness in renewable poly(L-lactide) triblock plastics
    (2024-03-18) Krajovic, Daniel M; Haugstad, Greg; Hillmyer, Marc A; hillmyer@umn.edu; Hillmyer, Marc A; Hillmyer Research Group
    Poly(L-lactide) (PLLA)’s broad applicability is hindered by its brittleness and slow crystallization kinetics. Among the strategies for developing tough, thermally resilient PLLA-based materials, the utilization of neat PLLA block polymers has received comparatively little attention despite its attractive technological merits. In this work, we comprehensively describe the microstructural, thermal, and mechanical properties of two compositional libraries of PLLA-rich PLLA-b-poly(γ-methyl-ε-caprolactone) (PγMCL)-b-PLLA (“LML”) triblock copolymers. The rubbery PγMCL domains microphase separate from the matrix in the melt and intercalate between PLLA crystal lamellae on cooling. Despite the mobility constraints associated with mid-block tethering, the PLLA end-blocks crystallize as rapidly as a PLLA homopolymer control of similar molar mass. Independent of their degree of crystallinity, LML triblocks exhibit vastly improved tensile toughnesses (63-113 MJ m-3) over that of PLLA homopolymer (1.3-2 MJ m-3), with crystallinities of up to 55% and heat distortion temperatures (HDTs) as high as 148 °C. We investigated the microstructural origins of this appealing performance using X-ray scattering and microscopy. In the case of a largely amorphous PLLA matrix, the PγMCL domains cavitate to enable concurrent PLLA shear yielding and strain-induced crystallization. In highly crystalline PLLA matrices, PγMCL facilitates a lamellar-to-fibrillar transition during tensile deformation, the first such transition reported for PLLA drawn at room temperature. These results highlight the unique attributes of PLLA block polymers and prompt future architectural and processing optimizations to achieve ultratough, high-HDT PLLA block polymer plastics after a simple thermal history on economical timescales.
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    Supporting Information for Engineering Aliphatic Polyester Block Copolymer Blends for Hydrolytically Degradable Pressure Sensitive Adhesives
    (2025-01-06) Shuang, Liang; Krajovic, Daniel M; Hoehn, Brenden D; Ellison, Chris J; Hillmyer, Marc A; hillmyer@umn.edu; Hillmyer, Marc; Hillmyer and Ellison groups
    This work aimed to explore aliphatic polyester triblock copolymers of poly(L–lactide)–block–poly(γ–methyl–ε–caprolactone)–block–poly(L–lactide) (LML) and associated blends with renewable tackifier in pressure-sensitive adhesive (PSA) formulations and investigate effects of tackifier, composition, and processing history on microstructural, thermal, mechanical, and adhesive properties of the PSAs. After solvent casting and two–step annealing at 170 °C for 60 min and 100 °C for 5 min, LML–based PSAs showed stable and competitive adhesion properties when compared to commercial PSAs, which we attribute to both microphase separation and crystallinity in the poly(L–lactide) end blocks. Moreover, theses LML–based PSA formulations are hydrolytically degradable into water soluble or dispersible compounds at 45 ℃ under basic conditions within 30 days, offering the possibility of sustainable end–of–life scenarios for example through industrial composting.