Toughness and Fracture Properties in Nacre‐Mimetic Clay/Polymer Nanocomposites

Abstract

Nacre inspires researchers by combining stiffness with toughness by its unique microstructure of aligned aragonite platelets. This brick‐and‐mortar structure of reinforcing platelets separated with thin organic matrix has been replicated in numerous mimics that can be divided into two categories: microcomposites with aligned metal oxide microplatelets in polymer matrix, and nanocomposites with self‐assembled nanoplatelets—usually clay or graphene oxide—and polymer. While microcomposites have shown exceptional fracture toughness, current fabrication methods have limited nacre‐mimetic nanocomposites to thin films where fracture properties remained unexplored. Yet, fracture resistance is the defining property of nacre, therefore centrally important in any mimic. Furthermore, to make use of these properties in applications, bulk materials are required. Here, up to centimeter‐thick nacre‐mimetic clay/polymer nanocomposites are produced by the lamination of self‐assembled films. The aligned clay nanoplatelets are separated by poly(vinyl alcohol) matrix, with 106–107 nanoplatelets on top of each other in the bulk plates. Fracture testing shows crack deflection and a fracture toughness of 3.4 MPa m1/2, not far from nacre. Flexural tests show high stiffness (25 GPa) and strength (220 MPa) that, despite the hydrophilic constituents, are not substantially affected by exposure to humidity.

Filter‐Through Method of Making Highly Efficient Polymer‐Clay Nanocomposite Membranes

“…To the best of our knowledge, we show a novel aspect of particulate filtration through electrospun thermoplastic porous membranes for the first time in making flexible, strong polymer membranes with enhanced gas‐barrier properties. The novelty is based on the high‐aspect ratio delaminated melt synthesized layered silicate (clay) that is self‐assembled in a polymer matrix as a barrier‐layer between two electrospun membranes by filtration (filter‐through method) and subsequently hot‐pressed which leads to enhanced gas‐barrier properties.…”

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membranes for the first time in making flexible, strong polymer membranes with enhanced gas-barrier properties. The novelty is based on the high-aspect ratio delaminated melt synthesized layered silicate (clay) [4] that is self-assembled in a polymer matrix as a barrier-layer between two electrospun membranes by filtration (filter-through method) and subsequently hot-pressed [5] which leads to enhanced gas-barrier properties.Nanosheets of layered materials like clay (e.g., Na-hectorite [Hec]), [6][7][8][9] or graphene oxide (GO) [10,11] are the most promising fillers for the fabrication of polymer nanocomposite barrier coatings. [12][13][14][15][16] Barrier is of prime importance in applications spanning from automotive, furniture, construction, food, or optoelectronic packaging.

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Mechanical enhancement of amine‐functionalized TiO2 reinforced polyimine composites

“…Over recent decades, polymeric nanocomposites have demonstrated superior performance ranging from mechanical properties to electrical conductivity, combining the advantages of polymer and nanoparticle fillers . Therefore, polymeric composites fabricated by introducing inorganic fillers into the polymer matrix have become the focus of tremendous research in recent years to meet various application requirements . To this end, a variety of inorganic particles have been introduced into the polymer matrices as enhancing phases, such as ZrO 2 , carbon nanotube, reduced graphene oxide, clay, silica platelets, Al 2 O 3 platelets, and so on .…”

“…Therefore, polymeric composites fabricated by introducing inorganic fillers into the polymer matrix have become the focus of tremendous research in recent years to meet various application requirements . To this end, a variety of inorganic particles have been introduced into the polymer matrices as enhancing phases, such as ZrO 2 , carbon nanotube, reduced graphene oxide, clay, silica platelets, Al 2 O 3 platelets, and so on . Titania (TiO 2 ) is one of the most attractive inorganic additives owing to its unique properties and many promising applications in environmental energy areas and industrial applications ranging from photocatalysis to reinforcing polymers .…”

Nacre‐Inspired Structural Composites: Performance‐Enhancement Strategy and Perspective

“…[16] Recently, a much thicker clay-PVA composite (up to several millimeters) could be achieved by compressing and heating thin-layered films synthesized by evaporation. [22] Another typical method to produce bulk composites with layer structure is freeze-casting. [23][24][25][26] For instance, a lamellar Al 2 O 3 /poly(methyl methacrylate) (PMMA) composite with a size of dozens of centimeters showed a high combination of strength (flexural strength of 210 MPa) and toughness (32 MPa m 0.5 ), further surpassing the traditional structural materials.…”