This study compares the damping behavior of boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs) as reinforcement in PLC, a biodegradable copolymer. The damping behavior of PLC composites reinforced with 2 wt % or 5 wt % nanotube filler is evaluated by nanodynamic mechanical analysis (NanoDMA). The addition of 2 wt % CNT leads to the greatest enhancement in damping (tan δ) behavior. This is attributed to pullout in CNTs because of lower interfacial shear strength with the polymer matrix and a more effective sword-in-sheath mechanism as opposed to BNNTs which have bamboo-like nodes. BNNTs however have a superior distribution in the PLC polymer matrix enabling higher contents of BNNT to further enhance the damping behavior. This is in contrast with CNTs which agglomerate at higher concentrations, thus preventing further improvement at higher concentrations. It is observed that for different compositions, tan δ values show no significant changes over varying dynamic loads or prolonged cycles. This shows the ability of nanotube mechanisms to function at varying strain rates and to survive long cycles.
Morphological and chemical transformations in boron nitride nanotubes under high temperature atmospheric conditions is probed in this study. We report atmospheric oxygen induced cleavage of boron nitride nanotubes at temperatures exceeding 750 °C for the first time. Unzipping is then followed by coalescence of these densely clustered multiple uncurled ribbons to form stacks of 2D sheets. FTIR and EDS analysis suggest these 2D platelets to be Boron Nitride Oxide platelets, with analogous structure to Graphene Oxide, and therefore we term them as “White Graphene Oxide” (WGO). However, not all BNNTs deteriorate even at temperatures as high as 1000 °C. This leads to the formation of a hybrid nanomaterial system comprising of 1D BN nanotubes and 2D BN oxide platelets, potentially having advanced high temperature sensing, radiation shielding, mechanical strengthening, electron emission and thermal management applications due to synergistic improvement of multi-plane transport and mechanical properties. This is the first report on transformation of BNNT bundles to a continuous array of White Graphene Oxide nanoplatelet stacks.
The
growing demand for a sustainable leather industry with a low
environmental impact has prompted the development of alternative vegetable-based
materials. In this study, a biodegradable mushroom-based leather derived
from the fruiting body of Phellinus ellipsoideus is investigated. The biodegradable leather proves to be thermally
stable up to 250 °C. The mechanically robust macrostructure combines
a tensile strength of 1.2 MPa and ductility (101% strain at break)
attributed to the natural balance of chitin (0.3) and proteins (0.7)
constituting the mycelium fibers. The chitin–protein system
results in an intrinsic scratch-resistant structure with exciting
damping properties in a low frequency range. Enhanced damping capabilities
within 5–20 Hz (tan δ: 0.1–0.20) are attributed
to the macrostuctural alignment of the mycelium under cyclic tension.
Whereas, increasing frequencies >20 Hz induce micromolecular interactions
between chitin and proteins within the fibers. Exposure of the bioleather
to acidic (pH 4, 5) and basic (pH 8, 9) media demonstrated the selective
dissolution of proteins (basic) and chitin (acid) components within
the mycelium, opening an opportunity for tunable mechanical response.
Reducing the protein content induced an increase in stiffness and
strength (pH 8 and 9), while reducing its chitin component showed
variable ductility (pH 4 and 5). Owing to the entirely natural composition
of the mushroom leather, intrinsic antifungal and antibacterial properties
found in the mycelium resist fungal invasion and bacterial growth.
Thus, this study displays the unique morphology–property relationship
of a biodegradable mushroom leather, proving its potential as a fully
sustainable and environmentally friendly alternative.
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