Volume 34, Issue 3

In the present investigation, a novel ladder polymer, poly(azomethine ester), was prepared via solution polycondensation polymerization between terephthalic acid and the novel monomer. Terephthalic acid was regenerated from PET waste bottles by saponification process, whereas p-phenylenediamine was obtained via Hoffmann rearrangement method. A novel monomer, namely N,N′-bis(2,5-dihydroxy benzylidene)-1,4-diaminobenzene was prepared from the reaction of 2,5-di-hydroxybenzadehyde with p-phenylenediamine in the ratio of 2:1, respectively. For the first time a solution polycondensation method has been employed for the synthesis of a ladder polymer which is otherwise prepared commonly via Diels-Alder cycloaddition reaction. The synthesized ladder polymer was characterized by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy ( 1 H NMR), carbon nuclear magnetic resonance spectroscopy ( 13 C NMR), elemental analysis (CHN), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results revealed that the ladder polymer possess highly regular ladder like framework, and that most of the ester groups have taken part in the side-by-side polymerization reaction.

This paper discusses the feasibility of the melt spinning process of polyacrylonitrile (PAN) copolymer (acrylonitrile/methylacrylate 95.6/4.4 mol% ratio) plasticized with H 2 O acetonitrile (ACN) and their mixture. The objective is to use water only as a plasticizer to melt spin PAN under specific conditions (composition, temperature etc.). The melting point and rheological measurements have been conducted by differential scanning calorimetry (DSC) and a modified capillary rheometer, respectively, for this plasticized system. The DSC results show that the melting point of the PAN copolymer can be reduced from over 300°C to below 180°C, which is the temperature for the onset of degradation (cyclization and crosslinking) of PAN. Rheological results show that the PAN copolymer can be extruded with a reasonable viscosity at 15 to 20°C above its melting point, and also the stability and viscosity are strongly dependent on temperature and the plasticizer type and content. Furthermore, the results indicate that the most appropriate condition for PAN melt spinning is for the PAN/H 2 O mixture of 70/30 wt% ratio at a temperature of 180°C for which the copolymer sample can remain stable without significant degradation for around 120 min and maintain its viscosity in the range of around 600 Pa s.

This paper suggests a methodology based on a neuroevolutionary approach to optimize the use of material in blow molding applications. This approach aims at determining the optimal thickness distribution for a certain blow molded product as a function of its geometry. Multiobjective search is performed by neuroevolution to reflect the conflicting nature of the design problem and to capture some possible trade-offs. During the search, each design alternative is evaluated through a finite element analysis. The coordinates of the mesh elements are the inputs to an artificial neural network whose output determines the thickness for the corresponding location. The proposed approach is applied to the design of an industrial bottle. The results reveal the validity and usefulness of the proposed technique, which was able to distribute the material along the most critical regions to obtain adequate mechanical properties. The approach is general and can be applied to products with different geometries.

Polycarbonate (PC)/cerium (IV) oxide (CeO 2 ) composites are prepared by a melt-compounding method using a twin-screw extruder. The effect of the CeO 2 content on the damping property of the composites was investigated using scanning electron microscopy, dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). In addition, the composites' mechanical properties were studied through tensile and impact tests. The DMA results revealed that the addition of CeO 2 (0.5 wt%) improved the damping property of the composite. TGA showed that the thermal stability was improved when the CeO 2 became 1 wt%. Mechanical tests revealed that both the tensile and impact strengths were substantially improved when 1 wt% CeO 2 was added. Finally, it can be concluded that the 0.5 wt% CeO 2 -filled PC composite can be used as a structural damping material.

The great influence of temperature on polymer's behavior is well known and a 10°C increase can lead to a 10-time reduction of the viscosity near the glass transition temperature. To manage accurate simulation of thermoforming processes, and particularly the stretch blow molding process that is managed in the vicinity of T g , it is necessary to take into account the self heating phenomena that may have impact on induced properties. In the particular case of polyethylene terephthalate (PET), injected preforms have been blown with different initial temperature and followed using a thermal camera. For an identical final volume of the blown preform, the influence of initial temperature on self-heating is discussed. Back to room temperature, induced mechanical properties are measured using digital image correlation: bottles are blown under different pressures and the strain fields are measured. Using the virtual field method on a region of interest of the bottle, these results allow the identification of the induced mechanical properties. Comparison between the self-heating and the induced modulus is managed and the effect of the self heating on the free blown shapes and induced properties is discussed.

Polypropylene (PP) is one of the fastest growing thermoplastic polymers in the world, second only to polyethylene. This is primarily due to its excellent balance of physical and chemical properties at a lower cost. PP however possesses low melt strength on account of its linear structure and hence is not easily amenable to processing techniques that involve free surface stretching deformations like thermoforming, blow molding and extrusion film casting. One way to enhance the melt strength of PP is to incorporate long chain branches in its molecular architecture. The present study focuses on the impact of rheology of linear and branched PP on their thermoforming characteristics. Two grades each of linear and long chain branched (LCB) PP homopolymer and impact copolymer (ICP) were used. It was observed that the LCB-PP homopolymer and LCB-ICP showed higher flow activation energy, reduced value of loss tangent and nearly equal frequency dependence of storage and loss moduli in shear rheology. Also, a strong strain hardening behavior was displayed in extensional rheology by the LCB grades. Plug assist thermoforming experiments were carried out to assess the effect of long chain branching on surface strain and thickness distribution for axisymmetric cups of two draw ratios. Biaxial surface strain maps of the formed cups were quantified using Grid Strain Analysis (GSA). Thermoformed cups made from LCB-PP homopolymer and LCB-impact copolymer showed lower surface strain and overall higher thickness as compared to cups made from their linear counterparts, which is in accordance with what might be expected from their rheology.

In the present study, residual stress is measured in fiber-reinforced SWCNT/epoxy at weight fractions of 0.1% and 0.5% with a cross-ply layup on a micro-scale. The mechanical properties of the SWCNT/epoxy composites were determined by tensile testing and the Young's modulus of the epoxy increased moderately with the addition of CNTs. The micro-residual stress of the cross-ply CF/epoxy and CNF-reinforced CF/epoxy laminates were measured using a new experimental approach. The micro-hole was milled by laser beam and the surface displacement was recorded by SEM after milling. In order to determine the residual stress from the recorded strain, the calibration matrix was calculated using the finite element method. The residual stress was obtained at a certain hole depth of specimens. The reliability of this approach was assessed by comparing the residual stress measurements from this method and from the standard hole-drilling method. The experimental results of the present approach confirmed that laser hole drilling SEM-DIC has excellent potential as a reliable method for measuring residual stress in polymer nanocomposites. Generally, CNT agglomerates, especially in high weight fractions, increased the micro-residual stress. An analytical method based on classical theory was used to calculate the residual stress and was compared with the experimental results. Good agreement was found between the results of the analytical methods and the experimental measurement.

The morphologies of micro-injection molded parts are influenced by the process parameters. In this paper, the influence of injection speed, mold temperature and melt temperature on the morphologies of micro-injection molded polyformaldehyde (POM) parts with different thicknesses were investigated by a single factor experimental method; the morphological structure of the parts was characterized by polarized light microscopy. The scale effect on the crystallization behavior and internal morphology of micro-injection POM parts was analyzed. The results indicated that the scale effect had a great influence on the hierarchical morphology in the thickness direction of the parts. The micro-parts with a thickness of 1.0 mm showed a skin-core structure including the skin layer, fine grain layer, oblate spherulite, and spherulite core layer, and the micro-parts with a thickness of 0.2 mm showed a skin-core structure with the skin layer, fine grain layer, and the spherulite core layer, and a larger thickness ratio of the spherulite core layer. As injection speed, mold temperature and melt temperature increase, the fine grain layer gradually disappears and the size of core spherulite tends to become larger, the thicknesses of the skin layer of all the micro-parts decrease and that of the 0.2 mm micro-parts decreases significantly.

In this work, we used a recycled low-density polyethylene (LDPE) in order to prepare flat sheet membranes with different polymer concentrations (5 and 10%). The used chemical method for the membrane's preparation is the phase inversion. After obtaining the membranes, we characterized them by atomic force microscopy (AFM) and scanning electron microscopy (SEM) to study their structure and surface characteristics. Based on the SEM images, our membranes have a dense skin layer. In addition, we observed a decrease in the porosity with the increase in the polymer concentration. When the polymer concentration increases from 5 to 10% the porosity decreases from 35.54% to 20.28%. Furthermore, we remarked significant changes in the contact angle and the surface roughness with the increase of the polymer concentration. The roughness increases from 363 to 577 nm for the same evolution of the polymer concentration. These high values of roughness imply obtaining values of contact angles greater than 90° and hydrophobic membranes, which is beneficial for the membrane distillation. Furthermore, the use of our membranes in vacuum membrane distillation (VMD) experiments showed a permeate flux up to 1.503 kg/hm 2 ; for the membrane with 35.54% of porosity and 5% of polymer concentration.