TY - JOUR
T1 - Importance of superior dispersion versus filler surface modification in producing robust polymer nanocomposites
T2 - The example of polypropylene/nanosilica hybrids
AU - Iyer, Krishnan A.
AU - Torkelson, John M.
N1 - Funding Information:
We thank Charlene Wilke (Biological Imaging Facility, Northwestern University) for assistance with TEM imaging. We thank Total Petrochemicals and Degussa AG for providing PP and nanosilica, respectively. We acknowledge support from the Initiative for Sustainability and Energy at Northwestern University (ISEN), Northwestern University, and a Northwestern University Terminal Year Fellowship (to K.A.I.). This study made use of Central Facilities supported by the NSF-MRSEC program (Grant DMR-1121262 ) at Northwestern University.
Publisher Copyright:
© 2015 Elsevier Ltd. All rights reserved.
PY - 2015/5/30
Y1 - 2015/5/30
N2 - With polymer nanocomposites, achieving highly effective dispersion of agglomerated nanofiller and major or optimal property enhancements remain challenges. A commonly posited solution is to improve the polymer-filler surface thermodynamic compatibility; this approach has led to significant improvements in some cases, but it has not provided a general solution. We address the question of whether achieving a metastable, well-dispersed state is better than compatibilization in attaining the goal of major property enhancements. We use solid-state shear pulverization to produce well-dispersed polypropylene (PP) nanocomposites with up to 8 or 9 wt% pristine nanosilica (p-NS) or organically modified nanosilica (m-NS). Microscopy shows that as-received, tens-of-micron-sized p-NS and m-NS agglomerates undergo very good dispersion, with ∼10-100 nm size-range nanofiller in hybrids. Rheology is consistent with very good dispersion, with only 92/8 wt% PP/p-NS indicating incipient nanofiller network formation. The PP/p-NS hybrids have superior Young's modulus and tensile strength. Relative to PP, modulus increases by 22% and 12% and tensile strength by 19% and 14% for 99/1 wt% PP/p-NS and 99/1 wt% PP/m-NS, respectively. The PP/p-NS hybrids have the largest increases in modulus (46% at 8 wt% p-NS) and tensile strength (22% at 6 wt% p-NS). Upon melting and crystallization, both PP/p-NS and PP/m-NS result in PP β-crystal formation at 1 wt% nanosilica, with p-NS having a greater effect. The PP/p-NS hybrid shows larger increases in thermal stability and nucleating efficiency for PP crystallization. Thus, with very good dispersion, unmodified nanofiller in a metastable dispersed state can result in more robust nanocomposites than when modified nanofiller is used to compatibilize the polymer-nanofiller interface.
AB - With polymer nanocomposites, achieving highly effective dispersion of agglomerated nanofiller and major or optimal property enhancements remain challenges. A commonly posited solution is to improve the polymer-filler surface thermodynamic compatibility; this approach has led to significant improvements in some cases, but it has not provided a general solution. We address the question of whether achieving a metastable, well-dispersed state is better than compatibilization in attaining the goal of major property enhancements. We use solid-state shear pulverization to produce well-dispersed polypropylene (PP) nanocomposites with up to 8 or 9 wt% pristine nanosilica (p-NS) or organically modified nanosilica (m-NS). Microscopy shows that as-received, tens-of-micron-sized p-NS and m-NS agglomerates undergo very good dispersion, with ∼10-100 nm size-range nanofiller in hybrids. Rheology is consistent with very good dispersion, with only 92/8 wt% PP/p-NS indicating incipient nanofiller network formation. The PP/p-NS hybrids have superior Young's modulus and tensile strength. Relative to PP, modulus increases by 22% and 12% and tensile strength by 19% and 14% for 99/1 wt% PP/p-NS and 99/1 wt% PP/m-NS, respectively. The PP/p-NS hybrids have the largest increases in modulus (46% at 8 wt% p-NS) and tensile strength (22% at 6 wt% p-NS). Upon melting and crystallization, both PP/p-NS and PP/m-NS result in PP β-crystal formation at 1 wt% nanosilica, with p-NS having a greater effect. The PP/p-NS hybrid shows larger increases in thermal stability and nucleating efficiency for PP crystallization. Thus, with very good dispersion, unmodified nanofiller in a metastable dispersed state can result in more robust nanocomposites than when modified nanofiller is used to compatibilize the polymer-nanofiller interface.
KW - Dispersion
KW - Nanosilica
KW - Polymer nanocomposites
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U2 - 10.1016/j.polymer.2015.05.015
DO - 10.1016/j.polymer.2015.05.015
M3 - Article
AN - SCOPUS:84930203782
VL - 68
SP - 147
EP - 157
JO - Polymer
JF - Polymer
SN - 0032-3861
ER -