All issues / Volume 14 (2020) / Issue 7 (July)
This is an editorial article. It has no abstract.
Flame retardancy and mechanical performance of multi-layered biocomposites, consisting of polylactic acid (PLA) matrix films and plain-woven flax fabrics as reinforcement, were investigated. Full factorial design (32) was applied to evaluate the effects of the distribution of P and N containing compounds between the matrix and the fibrous carrier. Composition property correlations of the composite constituents (i.e. flax fabrics treated in aqueous solutions of diammonium phosphate and urea with differing ratio and concentrations and matrix films with 0 to 20 wt% ammonium polyphosphate based intumescent flame retardant content) were determined by thermogravimetric analyses and open flame tests. Positive interaction between the composite constituents was revealed for green composites consisting of various combinations of treated fabrics and intumescent PLA systems. The biocomposites flame retarded with a combined approach, i.e. with a balanced distribution of P containing additives between the phases, were found to gain improved mechanical performance and fire retardancy. It was confirmed by tensile testing and electron microscopy as well as by UL-94, limiting oxygen index and cone calorimeter tests. As a conclusion, interpretation is given for the optimum found.
Ionic transport studies of solid bio-polymer electrolytes based on carboxymethyl cellulose doped with ammonium acetate and its potential application as an electrical double layer capacitor
N. M. J. Rasali, M. A. Saadiah, N. K. Zainuddin, Y. Nagao, A. S. Samsudin
Vol. 14., No.7., Pages 619-637, 2020
Vol. 14., No.7., Pages 619-637, 2020
CMC-NH2CH3CO2 complexes were characterized via theoretical and experimental approaches using molecular dynamics (MD) calculation, Fourier transform infrared spectrometry (FTIR), X-ray diffraction (XRD), and electrical impedance spectroscopy (EIS) analysis. These analyses successfully disclosed the structural and ion conduction properties of the bio-polymer electrolytes (BPE) system. The FTIR analysis further revealed that an interaction exists between the carboxylate anion group (COO–) from CMC and the H+ substructure of NH4CH3CO2. The ionic conductivity value at ambient temperature was found to achieve an optimum value of 5.07×10–6 S/cm for a system containing 10 wt% NH2CH3CO2. The ionic conductivity improvement was demonstrated via the increment on the amorphous phase of the BPEs system as shown in the XRD analysis upon the inclusion of NH2CH3CO2. Based on the IR-deconvolution approach, the mobility (μ) and diffusion coefficient (D) were found to influence the ionic conductivity and aligned with the theoretical molecular dynamic (MD) calculation. To evaluate the potential application of the CMC-NH2CH3CO2, an electrical double-layer capacitor (EDLC) was fabricated from the BPE and tested using cyclic voltammetry (CV), and charge-discharge (GCD) for 300 cycles and the BPE exhibited a specific of capacitance ~2.4 F/g.
This work presents the preparation of polyurethane composite foams based on castor oil or modified canola oil as a polyol, and cellulose nanocrystals (CN) as nanofiller (0.10, 0.25, and 0.50 wt% of CN content). The bio-based composites were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and mechanical properties. The SEM images showed that composite foams had smaller cell sizes and more irregular than those observed for unloaded samples. FTIR revealed that the urethane/urea bond formation was influenced by the incorporation of CN, and was dependent on the polyol used in the formulation. The incorporation of CN did not affect the thermal stability, but the density and mechanical properties changed differently depending on the selected polyol. These results suggested that the acylglycerol structure affects the role of CN in the formulation. Also, the proliferation of MC3T3-E1 preosteoblastic cells showed that the cell viability of polyurethane bionanocomposite foams increased significantly in comparison to the unloaded material.
Small polymeric ducts incorporating a ribbon-shaped mat of densely packed magnetic nanofibers have been manufactured via electrospinning by using a cylindrical manifold, alternately under rotation or static. The magnetic nanofibers mat is located on the side of the tube and aligned to the longitudinal axis using the assistance of a magnetic field. The designed methodology ensures that the magnetic particles are completely wrapped into a protective polymer shell. Experimental results demonstrate that the innovative confinement of magnetic nanofibers, forming a longitudinal ribbon on a tube side, confers a high and reversible transverse strain under a moderate magnetic field stimulus: a magnetic field gradient ≤30 mT/mm, at a basic field intensity <0.04 T, induces a 40% decrement of the duct radius aligned with the magnetic force axis. In perspective, this is very attractive to fabricate magneto-active ducts suitable for microfluidic components, as well as biomedical devices to be applied in surgery and endoscopy.
The mechanical behavior of three crosslinked polyurea (PU) elastomers obtained by sol-gel chemistry under uniaxial monotonic and cyclic tests has been assessed. These elastic networks are composed of hard and soft domains, where the segmental molecular weight between crosslinking points differs among the samples and allow studying the effect of this parameter on the mechanical properties. In this paper, uniaxial tension tests were performed in order to capture the main characteristics of the stress-strain behavior of these PU elastomers, e.g., non-linear hyperelastic behavior, hysteresis, and softening. In addition, a constitutive model that properly represents their behavior was proposed showing that the non-linear stress-strain behavior at large strain values exhibits strong hysteresis and softening.
Blends of poly(lactic acid) (PLA) with poly(butylene succinate) (PBS) were compounded in the presence of dicumyl peroxide (DCP) to improve the compatibility and foaming capabilities. PLA/PBS blends with a weight ratio of 40/60 and DCP contents of 0, 0.1, 0.4 and 1 wt% were analyzed. Blends and neat materials were foam injection molded using azodicarbonamide as a chemical foaming agent. The thermal and rheological behaviors of materials are discussed. The morphologies and mechanical responses of the foamed samples are compared and analyzed. The best blend results were obtained with 0.1 wt% of peroxide, reaching impact strength values similar to those of neat-foamed PBS and cell population densities higher than neat PLA. Peroxide contents higher than 0.4 wt% tend to decrease the performance of the blend due to excessive crosslinking.
In this paper, a kind of lightweight poly(methyl methacrylate) (PMMA)/multi-walled carbon nanotubes (MWCNTs) composite foam with high electromagnetic interference (EMI) shielding performance was successfully fabricated by using solution coating process and supercritical fluid-assisted foaming technology. Due to the selective distribution of MWCNTs at the boundary of PMMA phases and the concentrating of MWCNTs within cell walls, the composite foam exhibits good electrical conductivity under low filler content and its percolation threshold was as low as 0.019 vol%. Moreover, trimodal microcellular structure was generated due to the gradient MWCNT concentration along the radial direction of PMMA microspheres. As a result of the segregated structure and multimodal cell structure, the PMMA/MWCNTs (5.0 wt%) foam have a good combination of low density (0.49 g/cm3), high electrical conductivity (3.19 S/m) and high shielding effectiveness (35.9 dB). Its specific shielding effectiveness is as high as 356.5 dB・cm2/g, which is superior to many reported polymer nanocomposites. The nanocomposite foams also had good mechanical properties. This work provides an optional strategy for designing multifunctional nanocomposites for efficient EMI shielding.