In the current study, polystyrene/carbon nanotubes/glass fiber (PS/CNT/GF) hybrid foam with a bimodal cellular-structure has been fabricated via microwave heating as a novel energy source. Microwave-assisted (MA) samples not only demonstrated the lowest density as compared to traditional methods but also represented superior compressive mechanical properties. Since the bimodal morphology has not been seen so far, the role of selective microwave heating has been thoroughly investigated from the microstructural point of view. Accordingly, the amount of receiving microwave radiations to heat up the system is controllable via the CNTs (as nucleating agents and absorbers) as well as radiation time. Moreover, 1-15 wt% fibers were incorporated to enhance mechanical performance, which led to turning uniform cellular structure to the bimodal pattern, and its cell morphological was studied thereafter. Electrical conductivity and dielectric permittivity properties have not been deprived of bimodality benefits which have been rigorously proven.
To prepare a fully organic polylactic acid (PLA)‐based bio‐nanocomposite, cellulose nanocrystals (CNCs) were grafted by PLA through ring‐opening polymerization (ROP) of L‐lactide monomers onto CNCs. The grafting process was evaluated by 1HNMR and FTIR spectroscopic methods. The effect of surface‐modified CNCs (M‐CNCs) was investigated on thermal, mechanical, rheological, and dynamic mechanical thermal properties of PLA. The M‐CNCs were successfully dispersed in the PLA matrix. Isothermal and non‐isothermal DSC studies revealed that M‐CNCs caused an intensive increase in crystallization kinetics and therefore nucleation density and crystallization extent. DSC, XRD, and DMTA analyses indicated the formation of different crystal structures [α, α', β] in PLA after addition of M‐CNCs. Rheological analysis was carried out for microstructural investigation of the nanocomposites. Interestingly, after the addition of M‐CNCs not only the tensile strength and modulus of the samples increased but also the toughness of PLA was considerably improved.
In this paper, carbon nanotube (CNT) fiber is chemically modified through a post-spinning process with an acid treatment and epoxy infiltration. Thermo-gravimetric analysis (TGA), FTIR, and Raman spectroscopy revealed that acid treatment reduced impurities of CNT fibers and induced the formation of carboxylic functional groups on the CNTs surface that positively affect the strength; however, some defects on the surface of the nanotubes were induced that negatively affect the elastic modulus. After the epoxy infiltration procedure, it was revealed that the pores of CNT fiber were filled with epoxy resulting in improved interfacial interaction between CNT bundles either through an interlocking of polymer chains wrapping around the tubes or even by creating covalent bonds between the carboxyl-functionalized nanotubes. Comparing the mechanical performance of epoxy/CNT fibers with and without acid treatment indicated that pre-treatment of the fibers with acid before epoxy infiltration caused a reduction in the final modulus. The modulus of epoxy/CNT fiber reaches 103 N/tex and is about 20% higher than the acid-treated counterpart. Acid treatment prior to epoxy resin infiltration generates functional groups on the CNTs surface that enhance the fiber’s strength through strong reactions between epoxy chains and CNTs. On the other hand, the structural defects on CNTs imposed by acid lead to a reduction in the elastic modulus.
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