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Learning from Nature: Molecular Rearrangement in the Bismaleimide System Leading to Dramatic Increase in Impact Strength
journal contribution
posted on 2020-01-23, 15:34 authored by Mohammad
Hamza Kirmani, Prabhakar Gulgunje, Jyotsna Ramachandran, Pedro J. Arias-Monje, Po-Hsiang Wang, Satish KumarMaterials in nature
such as nacre that are made of mechanically
inferior building blocks exhibit extreme toughness at the macro scale
because of the geometry and arrangement of their constituents. Taking
a cue from these systems, we have investigated whether the molecular
rearrangement in a heterogeneous polymeric system can alter toughness
at the macro scale. To this end, a multicomponent bismaleimide system
is employed and processed by using (a) a melt and cast (termed Melt)
approach and (b) a dual asymmetric centrifuge based high-speed shear
mixing (termed HSSM) approach to enforce molecular rearrangement.
Cured HSSM BMI exhibited an extraordinary increase of 393% in impact
strength compared to the cured Melt BMI (an increase from 14 ±
6 to 69 ± 13 kJ/m2), without high shear mixing. Prior
studies in the literature have reported a maximum impact strength
of only 19 kJ/m2 for any BMI system. FTIR, Raman, and NMR
spectroscopies provide evidence of molecular rearrangement upon HSSM
processing. This molecular rearrangement also enhances the glass transition
temperature in cured HSSM BMI by 16 °C compared to the cured
Melt BMI. Small-angle X-ray scattering shows electron density heterogeneity
at the scale of ∼16 nm in cured HSSM BMI. A direct relationship
between the domain size calculated from the SAXS peak position, its
intensity, and the impact strength is observed. Fractographs of cured
HSSM BMI show unique, near-spherical micronodular features of ∼10–20
μm diameter, not observed in cured Melt BMI specimens. This
study provides a pathway for designing and manufacturing of materials
with extreme fracture toughness.
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impact strengthMelt BMIrearrangementMelt BMI specimensmacro scaleelectron density heterogeneitybuilding blocks exhibitHSSM BMIImpact Strength MaterialstoughnessFTIRCured HSSM BMIglass transition temperaturenear-spherical micronodular featuresSAXS peak positionNMRmulticomponent bismaleimide systemHSSM BMI show
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