Ali Akbar Yousefi

A novel, industry‐oriented strategy was developed to enhance flame retardancy in polyester fibers through a zinc phosphinate‐based masterbatch. The masterbatch was prepared via twin‐screw extrusion using 20 wt% Exolit OP950 and high‐viscosity bottle‐grade PET granules, selected to mitigate molecular degradation and preserve rheological integrity during melt‐spinning. It was subsequently incorporated into virgin fiber‐grade PET at 3%, 5%, and 7 wt% concentrations to produce flame‐retardant fibers. Rheological evaluations revealed pronounced shear‐thinning behavior and increased elasticity with higher flame retardant (FR) loading, indicating improved melt strength and viscoelastic stability. Thermal analyses demonstrated enhanced char formation and reduced heat release, with residual carbon content rising from 5.7% in neat PET to 10.7% in the 7% FR sample. The limiting oxygen index (LOI) increased from 20.5% to 24.5%, and vertical burning tests confirmed a UL‐94 V‐2 rating with significantly reduced melt dripping. Mechanical testing showed that fibers maintained appropriate tenacity (2.98 g/den), although accompanied by reduced elongation at break, highlighting the trade‐off between strength and ductility. SEM/EDX analysis confirmed uniform dispersion of FR particles and the presence of phosphorus and zinc. This approach provides a scalable solution for producing flame‐retardant PET fibers without compromising industrial processability, while balancing mechanical performance and fire safety.

This study examines the development of flame‐retardant and spinnable composites using multiply recycled‐recycled polyethylene terephthalate (rrPET), modified with zinc phosphinate (ZPi) and Cloisite 30B C30B (C30B). To address the deteriorated spinnability of rrPET, 0.4 wt% of an epoxy‐based chain extender (CE) was incorporated, significantly improving melt strength and viscoelastic properties. Ten formulations were prepared based on Taguchi experimental design. The optimal composition (containing 4.5 wt% ZPi and 1 wt% C30B) achieved a limiting oxygen index (LOI) of 28.03%, indicating notable flame retardancy. Structural and rheological analyses showed effective nanoparticle dispersion and interaction, resulting in improved chain entanglement and processability. The intrinsic viscosity (IV) increased from 0.376 to 0.596 dL/g, confirming substantial recovery in molecular weight. Thermogravimetric analysis revealed an increase in char residue from 0.73% to 8.02%, while crystallinity remained relatively unchanged. Mechanical tests indicated that CE‐modified rrPET fibers reached a tenacity of 0.276 N/tex and elongation at break of 38.56%. Although tensile strength slightly decreased (0.169 N/tex), C30B inclusion enhanced ductility, raising elongation at break to 42.43% due to improved flexibility and interfacial bonding. Overall, the synergistic use of CE, ZPi, and C30B led to a structurally optimized rrPET composite with enhanced thermal stability, flame resistance, and spinnability.

Polymer composite are very interesting materials in automotive industry. Nanocomposites play a crucial role in the automotive parts and cars weight reduction fields. Hybridization of polymer nanocomposites is appeared as a process of choice in obtaining the required property/weight ration. Simple and hybrid nanocomposites of polypropylene (PP) blend with carbon nanotubes (CNTs) having different aspect ratios and nanosilica at different nanosilica contents were prepared in molten state in an internal mixer. Scanning electron microscopic images along with rheological and tensile properties revealed that only 0.2 wt% CNT is high enough to finely disperse nanosilica particles in PP matrix in the absence of any chemical compatibilizer. Differential scanning calorimetric thermograms showed that none of nanoparticles has any effect on crystallinity of PP. Mechanical characterizations showed that hybrid composites are superior to PP‐S3 composite. Due to its more intensive hydrodynamic motions it was also observed that the longer CNT showed a higher ability to disintegrate nanosilica particles aggregates. Transmission electron microscopic images well portrayed the nanosilica particles in the vicinity of CNTs' surfaces which accounts for electrostatic adsorption of fine nanosilica particles. At such a low CNT content (say 0.2 wt%) in the absence of any chemical compatibilizer, elongation at break of the tensiled nanocomposites raised from 13.23% to 35.41% and fracture energy was mounted from 1253 to 2750 J. This divulges the effectiveness of CNTs to disperse nanosilica in PP matrix but a poor adhesion between the particles and PP matrix is an overwhelming drawback yet. Under these conditions a maleic anhydride grafted PP (PP‐g‐MA) was added to the composite in molten state. The tensile strength of these chemically compatibilized nanocomposites increased with respect of that of their counterpart physically mixed nanocomposites. For example, in the presence of this chemical compatibilizer, the tensile strength of PP‐S3 nanocomposite raised from 21 to 28 MPa.

In this study, a mathematical model for the time evolution of molecular weight distribution (MWD) was developed. This temporal model is based on the well-known Ziegler–Natta polymerization mechanism and reaction kinetics by the parametric solving of related differential equations. However, due to the generality of the reactions involved, the model can be extended to the other type of catalysts, such as metallocenes, Phillips, etc. The superiority of this model lies in providing the possibility of a more precise prediction over the active sites and kinetic parameters using a simple mathematical equation, which leads to improved reactor design in large-scale production. The model uses a function to develop a methodology for MWD calculations. In this way, the transient response is limited to the first few minutes of the reaction; however, it is important as it demonstrates the establishment of the final MWD. According to the results, almost for practical conditions with negligible transfer resistances, the time dependency of the MWD has a transient interval, depending on the kinetic constants of polymerization reactions. Increasing the time to infinity results in an increase in MW and a widening in MWD, which confirms the experimental plots well. In short, the main advantage of our proposed model over the previous ones is its ability to predict the MWD even before the completion of the polymerization reaction. The results of the present model match well with those of the well-known Schulz–Flory distribution, which only predicts the final molecular weight distribution, thus confirming that the model is reliable and generalizable.

In this research, piezoelectric polymer nanocomposite films were produced through solution mixing of laser-synthesized Au nanoparticles in poly (vinylidene fluoride) (PVDF) matrix. Synthetization of Au nanoparticles was carried out by laser ablation in N-methyle-2-pyrrolidene (NMP), and then it was added to PVDF: NMP solution with three different concentrations. Fourier transformed infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were carried out in order to study the crystalline structure of the nanocomposite films. Results revealed that a remakable change in crystalline polymorph of PVDF has occurred by embedding Au nanoparticles into the polymer matrix. The polar phase fraction was greatly improved by increasing the loading content of Au nanoparticle. Thermogravimetric analysis (TGA) showed that the nanocomposite films are more resistant to high temperature and thermal degradation. An increment in dielectric constant was noticed by increasing the concentration of Au nanoparticles through capacitance, inductance, and resistance (LCR) measurement. Moreover, the mechanical properties of nanocomposites were numerically anticipated by a finite element based micromechanical model. The results reveal an enhancement in both tensile and shear moduli.

In this study, it was aimed to increase the piezoelectric and pyroelectric properties of electrospun polyvinylidene fluoride (PVDF) nanofibers simultaneously by using specific nanofillers. Graphene oxide (GO), graphene, and halloysite nanotubes with different concentrations (0, 0.05, 0.4, and 1.6% wt/wt) were combined with PVDF solution and were fabricated in the form of nanofibers through electrospinning. Pyroelectric properties of samples were measured by submerging sealed samples in hot water (360°K) and ice (270°K). The piezoelectric properties of the samples were evaluated through bending tests. The microstructural, mechanical, and thermal properties of the electrospun PVDF nanocomposite were investigated using scanning electron microscope, Instron instrument, and thermogravimetric analysis, respectively. To further support the experimental observations for generating electric voltage in the bended nanogenerator, the PVDF nanogenerator (PNG) was also modeled by a finite element analysis based on the theory of linear piezoelectricity using COMSOL Multiphysics simulation software. Experimental results showed that adding nanofillers could improve the piezoelectric and pyroelectric properties of all samples, associated with the increment of β‐phase in the nanofibers. It was concluded that adding nanofillers could increase pyroelectricity about 50% more than piezoelectricity in pristine PVDF nanofiber web. The PNG containing 1.6 wt% GO showed the highest efficiency in terms of piezoelectricity and pyroelectricity. In addition, the results showed that the ratio of piezoelectric to pyroelectric coefficients was constant (~1.5) and it was independent of the nanofiller type and content. The effect of external force and vibration frequency on the output voltage was also investigated. Increasing the compressive force and vibration frequency caused a greater output voltage. Finally, the fabricated nanogenerator was integrated on insole and elbow to investigate its energy harvesting capabilities from body movement.