TY - JOUR
T1 - Micro-drawing of glassy polybenzoxazole rigid rods and the molecular interactions with carbon nanotubes
AU - Lin, Chih Wei
AU - Hsu, Steve L.C.
AU - Yang, Arnold C.M.
N1 - Funding Information:
We thank the financial supports by both the National Science Council of Taiwan and the US Air Force Office of Scientific Research through the Taiwan–US Air Force Nanoscience Initiative Program ( AOARD-094024 and AOARD-104055 ).
PY - 2012/4/17
Y1 - 2012/4/17
N2 - The high-temperature (Tg > 650°) wholly aromatic polybenzoxazoles (PBO) polymer chains in thin films underwent elastic energy release via local deformation of crazing when stretched beyond a critical strain around 0.5%. The strain localization in the ultra-rigid polymer was quickly superseded by craze fibril breakdown, triggering catastrophic fracture at low extensions below ∼3%. Although the drawing stress of craze fibrillation, determined to be ∼3 GPa, was insufficient to separate chains in PBO crystallites, it forced the chains in the amorphous regions to flow into large molecular deformations (∼300% strain) at room temperature. The poor craze fibril stability of the rigid-rod chains was enhanced dramatically when surface-functionalized single-walled carbon nanotubes (SWCNTs) were dispersed into the polymer. No toughening effects were observed, however, for multi-walled carbon nanotubes (MWCNTs) although the elastic enhancement leading to increase of strain delocalization was still operative. The toughening selectivity was attributed to the PBO/CNT load transfer coupling during nanoplastic flows in which only the CNTs of compatible bending moments permitting fibril drawing were allowed to participate.
AB - The high-temperature (Tg > 650°) wholly aromatic polybenzoxazoles (PBO) polymer chains in thin films underwent elastic energy release via local deformation of crazing when stretched beyond a critical strain around 0.5%. The strain localization in the ultra-rigid polymer was quickly superseded by craze fibril breakdown, triggering catastrophic fracture at low extensions below ∼3%. Although the drawing stress of craze fibrillation, determined to be ∼3 GPa, was insufficient to separate chains in PBO crystallites, it forced the chains in the amorphous regions to flow into large molecular deformations (∼300% strain) at room temperature. The poor craze fibril stability of the rigid-rod chains was enhanced dramatically when surface-functionalized single-walled carbon nanotubes (SWCNTs) were dispersed into the polymer. No toughening effects were observed, however, for multi-walled carbon nanotubes (MWCNTs) although the elastic enhancement leading to increase of strain delocalization was still operative. The toughening selectivity was attributed to the PBO/CNT load transfer coupling during nanoplastic flows in which only the CNTs of compatible bending moments permitting fibril drawing were allowed to participate.
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U2 - 10.1016/j.polymer.2012.02.049
DO - 10.1016/j.polymer.2012.02.049
M3 - Article
AN - SCOPUS:84862793195
SN - 0032-3861
VL - 53
SP - 1951
EP - 1959
JO - polymer
JF - polymer
IS - 9
ER -