Band 39, Heft 7

Natural fiber-reinforced polymer composites have been widely explored by many researchers due to their improved modulus and lightness compared to other conventional construction materials such as wood, metal, and steel. Cultivators only harvest banana and plantain fruits for food and leaves for food wrapping. The other portions of the plant are considered as wastes and a potential resource of natural fibers used as reinforcement in composites. Over the years, a plethora of research works has been done on banana and plantain fibers as fillers in plastic composites. Comprehensive catalogues of preparation techniques and mechanical properties were presented. The mechanical properties of banana fiber reinforcement in polyester and epoxy composites were compared to and contrasted with those of other natural fibers to elucidate its superiority or inferiority to those materials. This work gives an overview of the current state of knowledge of banana fiber-reinforced composites alongside the available research gaps.

Poly(methyl methacrylate) (PMMA)-based polymer electrolyte membranes are prepared through the solution cast method, with PMMA:ethylene carbonate (EC):LiCF 3 SO 3 :Al 2 O 3 weight ratio of 55.13:18.34:24.5:2. The effect of Al 2 O 3 filler grain sizes of 50 nm and 10 μm on the polymer electrolytes was studied in this work. From the Cole-Cole plot obtained through electrochemical impedance spectroscopy, the highest ionic conductivity for 50-nm Al 2 O 3 in the PMMA-LiCF 3 SO 3 -EC-Al 2 O 3 sample was measured as 1.52 × 10 −4 S/cm at room temperature. The bonding formation among the host polymer and other additives in the polymer electrolytes has been studied using Fourier transform infrared spectroscopy. A strong occurrence of CH 3 stretching mode has proven that nano size Al 2 O 3 results in a much stronger bonding effect with the host polymer. The particle sizes were calculated by applying the Debye-Scherrer equation from the X-ray diffraction results. This work considers the effect of instrument broadening to further improve the accuracy of particle broadening for particle size calculation. The average particle size of nano size Al 2 O 3 in the PMMA sample is calculated as 2.9693 nm. Moreover, a higher amorphousity level obtained from nano size filler polymer electrolyte of 98.5% computed from differential scanning calorimetry thermograms had also explained the achievement of high ionic conductivity in this work.

3-Mercaptopropyltrimethoxysilane [MPTMS, (CH 3 O) 3 SiCH 2 CH 2 CH 2 SH] can be grafted to porous silicon via a simple chemical grafting method and then sulfonated to prepare a proton exchange membrane (PEM) for application in micro direct methanol fuel cells (μDMFCs). The concentration of MPTMS and the pH of the solvent, which is varied by adding glacial acetic acid (GAA), play important roles in the chemical grafting process. In this work, PEMs based on sulfo-functionalized porous silicon were prepared at MPTMS concentrations ranging from 10 wt.% to 90 wt.% and GAA concentrations ranging from 0 wt.% to 10 wt.% to study the effects of grafting parameters on the proton transport properties of PEMs. Electrochemical impedance spectroscopy shows that the proton conductivity of the PEMs can be tuned by changing the MPTMS and GAA concentrations, and it reaches a maximum of 0.082 S/cm at an MPTMS concentration of 30 wt.% and a GAA concentration of 5 wt.%. The effects of MPTMS and GAA concentrations on the properties of PEMs are discussed in the context of two competitive reaction pathways of MPTMS molecules: dehydration condensation with silanols on the walls of porous silicon and self-polymerization.

As lead-containing products, such as lead batteries, are widely used, water pollution problems caused by Pb 2+ show a significant threat to the ecosystem and human health. To overcome this serious problem, the modified poly(methyl methacrylate) (PMMA)/chitosan (CS) composites were prepared by adding CS into the PMMA matrix as functional filler and surface modification. The structure, thermal stability, size, morphology and adsorption properties of the modified PMMA/CS composites were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and inductively coupled plasma optical atomic emission spectrometry. The results indicated that the modified PMMA/CS composites had a uniform size of about 1 μm and showed quite good thermal stability. In addition, the Pb 2+ removal of the modified PMMA/CS composite reached up to 98% when the initial Pb 2+ concentrations are under 100 mg l −1 . The results of the adsorption isotherms indicated that the Langmuir isotherm fits best to the experimental data when compared with the Freundlich isotherm and Temkin isotherm. All these results demonstrate that modified PMMA/CS has a good adsorption property and can be a promising adsorbent for chelating Pb 2+ .

Polymer-based organic solar cells are of great interest as they can be produced with low-cost techniques and also have many interesting features such as flexibility, graded transparency, easy integration, and lightness. However, conventional wide bandgap polymers used for the light-absorbing layer significantly affect the power conversion efficiency of organic solar cells because they collect sunlight in a given spectrum range and due to their limited stability. Therefore, in this study, polymers with different bandgaps were used, which could allow for the production of more stable and efficient organic solar cells: P3HT as the wide bandgap polymer, and PTB7 and PCDTBT as low bandgap polymers. These polymers with different bandgaps were combined with PCBM to obtain increased efficiency and optimum photoactive layer in the organic solar cell. The obtained devices were characterized by measuring optical, photoelectrical, and morphological properties. Solar cells using the PTB7 and PCDTBT polymers had more rough surfaces than the reference cell using P3HT. The use of low-bandgap polymers improved I sc significantly, and when combined with P3HT, a higher V oc was obtained.

The loss factor (tan δ ) and glass transition temperature ( T g ) are two important parameters for evaluating damping properties. Hydrogen bonds (H bonds) play an important role in improving damping properties. In this work, the effect of the hydrogen bond strength and number on the damping properties was studied. Four hindered phenols with different steric hindrances were used to form hydrogen bonds with different strengths to mediate tan δ and T g . Dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) showed that hindered phenol content lower than 38 wt% led to a linear increase in tan δ and T g because of the formation of H bonds. The Kwei equation was used to explain the relationship between H bonds and tan δ. When the content was higher than 38 wt%, the small molecule-hindered phenols can be divided into two categories: those that can maintain a good miscibility, thus continuously increasing the tan δ , and those that make tan δ increase slowly or decrease because of poor miscibility. These results demonstrated that tan δ is closely related to both hydrogen bond strength and number. The degree of hindrance of the hydroxyl group determines the hydrogen bond strength, whereas the miscibility determines the number.

This study investigates the correlation between the fiber orientation distribution along the thickness and mechanical anisotropy in injection-molded products using a thermoplastic resin reinforced by short fibers. To this end, polyamide-6 samples containing 15, 30, 50, and 65 wt% of short fiberglass were compounded, and flat plates with side gates were injection-molded. The fiber orientation distribution near the center of the plates was observed via X-ray computed tomography and that along the thickness was quantified via a fiber orientation tensor. Coupon test pieces were cut from the plates along the machine and transverse directions, and a three-point bending test was performed. Mechanical anisotropy was evaluated from the ratio of the flexural modulus in each direction. Evaluation results of the fiber orientation distribution and mechanical anisotropy were compared. As a result of the above investigation, a clear correlation was found between the fiber orientation distribution and mechanical anisotropy when the glass fiber content was 15–50 wt%. In the anisotropic expression under the condition of high glass fiber content (65 wt%), contributions of parameters other than the fiber orientation distribution became evident.

The objective of this study is to replace sodium alginate (bio composite polymer), urea and sodium bicarbonate (alkalinity) in the conventional reactive printing of cotton with carboxymethyl tamarind plolysaccharide (bio polymer), polyethylene glycol 400 (PEG-400) and trichloroacetic acid respectively. This study was motivated by the goal of coming up with a low-cost, eco-friendly printing process. The results were evaluated on two reactive dyes (color index numbers: Reactive Violet 01 and Reactive Blue 21) at two dose levels (2% and 4% of the printing paste weight). In the conventional recipe, sodium alginate, urea and sodium bicarbonate were added at dose levels of 2%, 15% and 2.5%, respectively; in the modified recipe, the dose levels of the substituted tamarind polysaccharide and trichloroacetic acid were 6% and 4%, respectively. The different dose levels of PEG-400 (0%, 1%, 2%, 3%) were accessed in each modified recipe. Results showed that the Sum K/S and shade strength, dye penetration, staining on white ground of the fabric, rubbing fastness (dry and wet), washing fastness, perspiration fastness (acidic and alkaline), light fastness, sharpness of the edges and fabric softness all improved in the modified recipe with 2% PEG-400. However, the increase in PEG-400 only increased the dye penetration and did not give any significant benefit with the increase in concentration.

pH-responsive polymers are attracting much interest from researchers because of their wide application potentials in areas like biosensor, bioseparator, bioreactor, biocatalysis, drug delivery, and water treatments. In this investigation a two-step process is evaluated to prepare carboxyl(–COOH) functional submicrometer-sized pH-responsive composite polymer particles. First, submicrometer-sized polystyrene (PS) particles are prepared by a modified conventional dispersion polymerization. In the second step, PS/poly(methacrylic acid-acrylamide-ethylene glycol dimethacrylate) [PS/P(MAA-AAm-EGDMA)] composite polymer particles are synthesized by seeded co-polymerization of methacrylic acid, acrylamide, and ethylene glycol dimethacrylate in the presence of PS seed particles. The size distributions and morphologies analyzed by electron micrographs suggested that seeded copolymerization smoothly occurred without formation of any secondary tiny copolymer particles. The surface composition and functionality are confirmed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance. The hydrodynamic diameter increased with the increase in pH values as part of the carboxyl groups are deprotonated, which favored the swelling of copolymer layer formed around the surface of PS particles. The adsorption of cationic and anionic surfactants at two different pH values showed that adsorption of cationic surfactant is favored at higher pH value whereas that of anionic surfactant is favored at lower pH value.

A low-cost indigenous silica powder at nano-scale was synthesized by thermal combustion and alkaline extraction technique from bamboo leaf ash. The bamboo leaf ash was prepared by heating the bamboo leaf at 750°C for 5 h. The amorphous SiO 2 nanoparticle with an average particle size of 20 nm was used for the industrial application. The synthesized nanoparticle as a filler was mixed with polydimethylsiloxane (PDMS) polymer solution to synthesize a nanocomposite membrane by a solution casting method. The morphological study was done using high-resolution scanning electron microscopy (HRSEM) with an energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and the chemical structure was studied using Fourier-transform infrared spectrometry (FTIR). Thermogravimetric analysis (TGA) analyzed the thermal stability of the membranes, and the hydrophobicity was measured using contact angle analyzer. Separation of the acetic-water mixture was carried out by nano-composite PDMS membrane to study the effect of silica loading on the PDMS membrane. It was observed that the presence of SiO 2 nanoparticles significantly improves the pervaporation flux as well as the thermal stability.