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1. Multiwalled carbon nanotubes as hard templates to yield advanced geopolymer-based self-assembled nanostructured ceramics

   https://doi.org/10.1016/j.mechrescom.2023.104216  

   Xu, Yunzhi ; Lee, Haklae ; Buettner, Nathanial ; Akono, Ange-Therese ( December 2023 , Mechanics Research Communications)

   Novel multifunctional construction materials are needed to promote resilient infrastructure in the face of climate change and extreme weather. Nanostructured materials such as geopolymer reinforced with carbon-based nanomaterials are a promising way to reach that goal. In recent years, several studies have investigated the influence of nanomaterials on the physical properties of geopolymer composites such as compressive strength and fracture toughness. Yet, a fundamental understanding of the influence of nanomaterials on the nanoscale and micron-scale structure has been elusive so far. Our research objective is to understand how multiwalled carbon nanotubes (MWCNT) can help tailor the microstructure of geopolymers to yield architected multifunctional nanocomposites. We synthesized geopolymer nanocomposites reinforced with 50-nm thick multiwalled carbon nanotubes with mass fractions in the range of 0.1 wt%, 0.2 wt%, and 0.5 wt%. Our major finding is that MWCNTs act as hard templates that promote geopolymer formation via self-assembly. Geopolymer nanoparticle growth is observed along the walls of MWCNTs. A refinement in grain size is observed: increasing the fraction of MWCNTs by 0.5 wt% leads to a reduction in grain size by 54%. Similarly, increasing the mass fraction of MWCNTs leads to a densification of the geopolymer matrix as demonstrated by the Fourier transform infrared spectroscopy results and the statistical deconvolution analysis. Mercury intrusion porosimetry shows a nanoscale tailoring of the pore size distribution: a 26% decrease in porosity is observed as the fraction of MWCNTs is increased to 0.5 wt%. As a result of these nanoscale structural changes, a greater resistance to long-term deformation is observed for MWCNT-reinforced geopolymers, as the creep modulus increases both locally and macroscopically. At the macroscopic level, a 42% increase in the macroscopic logarithmic creep modulus is observed as the fraction of MWCNTs is increased to 0.5 wt%. These findings and the supporting methodology are important to understand how to manipulate matter below 100 nm. This research also paves the way for the design of resilient infrastructure materials with tailored microstructure and mechanical properties. 

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2. Spray‐Assisted Microwave Welding of Thermoplastics Using Carbon Nanostructures with Enabled Health Monitoring

   https://doi.org/10.1002/pen.25227  

   Kravchenko, Oleksandr G. ; Solouki Bonab, Vahab ; Manas‐Zloczower, Ica ( September 2019 , Polymer Engineering & Science)

   The present study considers the use of spray‐assisted hybrid microwave welding using suspensions with low concentration of carbon nanostructures (CNS) (0.01 wt%). The proposed method of joining allows to create micron level coverage of the CNS on the thermoplastic substrates using a spray deposition technique. Upon electromagnetic microwave exposure, the CNS coverage provided structural joining of the parts due to dielectric heating. Small clamping force was applied to introduce uniform contact between the welded substrates. The choice of CNS was based on the superior dielectric loss and storage properties when compared to conventional carbon nanotubes. Furthermore, the proposed method of bonding allowed the creation of an electrically conductive percolated network at the welded interface, which was used for structural health monitoring by detecting the changes in the electrical resistance during single lap joint mechanical testing. The proposed method was shown to provide structural levels of welds for thermoplastic with different molecular structure, namely polycarbonate, polyurethane and high‐density polyethylene. POLYM. ENG. SCI., 59:2247–2254, 2019. © 2019 Society of Plastics Engineers

    

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3. Reinforcing Microwave Absorption Multiwalled Carbon Nanotube–Epoxy Composites Using Glass Fibers for Multifunctional Applications

   https://doi.org/10.1002/adem.201900780  

   Li, Kuo ; Zhao, Rong ; Xia, Jiaxin ; Zhao, Guang-Lin ( November 2019 , Advanced Engineering Materials)

   Herein, the enhancement of the mechanical properties of microwave absorption composites, multiwalled carbon nanotubes (MWCNTs)–epoxy with various MWCNT loadings, using glass fiber (GF) reinforcement is focused upon. The tensile strength, morphologies, dielectric permittivity, and electromagnetic (EM) wave absorption properties (in a frequency range from 1 to 26 GHz) of the composites are investigated. The tensile strength of the composites is enhanced to about 400 MPa, which is comparable with that of commercial aluminum alloy 6061 (about 300 MPa), whereas the tensile strength of the pristine MWCNT–epoxy composite is around 15 MPa. The mass density of the MWCNT–epoxy–GF composites herein is found to be around 1.6 g cm⁻³, whereas aluminum alloy 6061 has a mass density of ≈2.7 g cm⁻³. In addition, the MWCNT (9 wt%)–epoxy–GF composite presents a strong EM wave absorption in a wide frequency band from 14 to 26 GHz, whereas aluminum alloys do not have much EM wave absorption. The high microwave absorption together with the enhanced mechanical strength of the composites provides a multifunctional potential for some applications.

    

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4. Electrical and mechanical tuning of 3D printed photopolymer–MWCNT nanocomposites through in situ dispersion

   https://doi.org/10.1002/app.47600  

   Chavez, Luis A. ; Regis, Jaime E. ; Delfin, Luis C. ; Garcia Rosales, Carlos A. ; Kim, Hoejin ; Love, Norman ; Liu, Yingtao ; Lin, Yirong ( February 2019 , Journal of Applied Polymer Science)

   An electric field‐assistedin situdispersion of multiwall carbon nanotubes (MWCNTs) in polymer nanocomposites, fabricated through stereolithography three‐dimensional (3D) printing technique, was demonstrated. The introduction of MWCNTs increased the elasticity modulus of the polymer resin by 77%. Furthermore, the use of an electric field forin situMWCNT dispersion helped improving the average elongation at break of the samples with MWCNTs by 32%. The electric field also increased the ultimate tensile strength of the MWCNT reinforced nanocomposites by 42%. An increase of over 20% in the ultimate tensile strength ofin situdispersed MWCNT nanocomposites over the pure polymer material was observed. Finally, it was demonstrated that the magnitude and direction of the electrical conductivity of MWCNT nanocomposites can be engineered through the application ofin situelectric fields during 3D printing. An increase of 50% in the electrical conductivity was observed when MWCNTs were introduced, while the application of the electric field further improved the electrical conductivity by 26%. The presented results demonstrated the feasibility of tuning both electrical and mechanical properties of MWCNT reinforced polymer nanocomposites usingin situelectrical field‐assisted 3D printing. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2019,136, 47600.

    

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5. Study of Agave Fiber-Reinforced Biocomposite Films

   https://doi.org/10.3390/ma12010099  

   Annandarajah, Cindu ; Li, Peng ; Michel, Mitchel ; Chen, Yuanfen ; Jamshidi, Reihaneh ; Kiziltas, Alper ; Hoch, Richard ; Grewell, David ; Montazami, Reza ( January 2019 , Materials)

   Thermoplastic resins (linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and polypropylene (PP)) reinforced by different content ratios of raw agave fibers were prepared and characterized in terms of their mechanical, thermal, and chemical properties as well as their morphology. The morphological properties of agave fibers and films were characterized by scanning electron microscopy and the variations in chemical interactions between the filler and matrix materials were studied using Fourier-transform infrared spectroscopy. No significant chemical interaction between the filler and matrix was observed. Melting point and crystallinity of the composites were evaluated for the effect of agave fiber on thermal properties of the composites, and modulus and yield strength parameters were inspected for mechanical analysis. While addition of natural fillers did not affect the overall thermal properties of the composite materials, elastic modulus and yielding stress exhibited direct correlation to the filler content and increased as the fiber content was increased. The highest elastic moduli were achieved with 20 wt % agave fiber for all the three composites. The values were increased by 319.3%, 69.2%, and 57.2%, for LLDPE, HDPE, and PP, respectively. The optimum yield stresses were achieved with 20 wt % fiber for LLDPE increasing by 84.2% and with 30 wt % for both HDPE and PP, increasing by 52% and 12.3% respectively. 

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