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A study was carried out to determine dichlorodiphenyltrichloroethane (DDT) and its metabolites in Gangetic mystus, Mystus cavasius and spotted snakehead, Channa punctatus. DDTs was extracted by QuEChERS method, cleaned-up by H2SO4 treatment and analyzed by GC with Electron Capture Detector. The calibration curves were linear over the range of the tested concentrations as shown by the fact that the correlation coefficients (r2) for the linearity range were 0.995-0.999. The detection limit was found to be 5ppb for DDTs and the quantification limit was 6.5ppb. Recoveries were found (70-130%); this is acceptable for fish samples according to standard methodology. The DDT and its metabolites were not detected in the liver of M. cavasius and C. punctatus. In this study, M. cavasius was found to contain detectable amount of residual targeted pesticides DDTs at 64.21 ppb in digestive tract, 75.23 ppb in gill, 119.82 ppb in gonad and 45.84 ppb in muscle. The C. punctatus residual targeted DDTs were at 8.42 ppb in digestive tract, 4.04 ppb in gill, 56.44 ppb in gonad and 23.15 ppb in muscle. However, this study shows the higher DDT and its metabolites were in the gonad of M. cavasius and C. punctatus. Bangladesh J. Zool. 49 (3): 393-402, 2021

Improvement in hydrophobicity is important for polymers used in various applications such as biomedical applications, as it can delay their degradation due to long-term exposure to moisture environments. Although a number of surface modification techniques have been developed over the years to improve hydrophobicity, their specific influences on hydrophobicity enhancement as well as long-term mechanical and tribological performances are yet to be fully understood. In this study, surface textures, with variation in type and geometry, are introduced on Ultrahigh Molecular Weight Polyethylene (UHMWPE) and High Density Polyethylene (HDPE) surfaces to study the effect of surface modification on hydrophobicity and long-term mechanical and tribological performances. Based on the theoretical study using Wenzel and Cassie-Baxter models, surface textures of various types and dimension are introduced on UHMWPE and HDPE surfaces. The results show that introduction of surface textures significantly improves the hydrophobicity of polymers. Specific relationship between texture type and geometry, and improvement in hydrophobicity is explored. Based on the comparison between experimental results and theoretical models, transition state modeling seems to be more suitable in describing the change in hydrophobicity with the addition of surface texture. The study provides useful guidelines to improve hydrophobicity of polymers for biomedical applications.

Essential work of fracture method has been successfully used to characterize the fracture behavior of ductile polymeric films. The observed essential and non-essential fracture process zones are related to the toughness of the films. Three-dimensional finite element method (FEM) modeling has been carried out in this study to elucidate the film fracture process based on the essential work of fracture concept. Experimental observation on a model linear low-density polyethylene (LLDPE) blown film was used to validate the FEM model. The numerical model facilitates an in-depth understanding of the development of stress and strain fields and the fracture process zones at different loading steps. The FEM findings show that film thickness and ligament length have significant influence on the development of stress and strain fields at and around the ligament area. Furthermore, the numerical analysis reveals how various material properties, such as yield stress and strain hardening slope, can influence the development of fracture process zones. Usefulness of FEM modeling for developing tough polymeric films is discussed.

A test methodology to evaluate the adhesive strength of poly(ethylene terephthalate) (PET) multi-layer articles was developed by implementing a linearly increasing normal load scratch test (ASTM D7027-13/ISO 19252:08). The adhesive failure load between the layers and the failure modes near or at the interface were experimentally determined. The load required to induce adhesive failure and the scratch coefficient of friction were determined from the scratch test. The role of substrate deformability on adhesive failure during the scratch test was also investigated. Finite element method (FEM) modeling was carried out to investigate the corresponding stress state that causes adhesive failure to occur during scratching. FEM simulations allow for the geometric factors and material constitutive behavior to be taken into account in determining the interfacial stresses in the multi-layer system. By combining the scratch test with FEM modeling, the proposed approach can semi-quantitatively assess the delamination strength of semi-rigid multi-layer polymeric systems.

The scratch behavior of a series of model cast polyurethane elastomers (CPU) is investigated according to the ASTM D7027/ISO 19252 scratch test methodology. Four model CPU systems considered in this study were synthesized by the same hard segment, but with four different types of soft segment polyols to systematically alter their phase morphology, coefficient of friction (COF), yield stress, tensile strength and damping behavior. Attenuated total reflectance Fourier transform infrared spectroscopy, atomic force microscopy, COF measurement, uniaxial tensile and compressive true stress-strain curves generation, and dynamic mechanical analysis (DMA) were carried out to link intrinsic material properties to the observed scratch-induced deformation mechanisms of the model CPU systems. The observed scratch damage mechanisms of the model CPU systems are found to correlate well with COF, tensile strength, compressive yield stress and DMA damping behavior. The present study demonstrates that the scratch performance of polymers can be predicted by their intrinsic material properties. Implication of the present study for designing scratch resistant polyurethane elastomers is discussed. Keywords: Polyurethane, Soft segment, True stress-strain curve, Scratch behavior, Mechanical property

A three-dimensional finite element method modeling along with experimental study on multilayer acrylic coating systems on a hard and brittle substrate has been performed to understand their scratch-induced deformation and damage mechanisms. The experimental results show that, while all else kept the same, an increase in soft (i.e., low Young's modulus and low strength) base layer thickness or hard (i.e., high Young's modulus and high strength) top layer thickness improve the scratch resistance of brittle coating systems by delaying the onset of cracking. The onset of plowing is delayed with the increase in hard top layer thickness, whereas increase in soft base layer thickness results in an earlier onset of plowing. The numerical analysis of the stress and strain field explains the mechanics behind the observed scratch behavior in the multilayer coating systems. The study provides insights toward designing scratch-resistant multilayer coating systems. Keywords: Multilayer coatings, Scratch resistance, FEM

Polyetheretherketone (PEEK) polymers are increasingly used in tribological applications where fretting damage occurs. Fretting wear results from the repeated sticking and slipping of mutually loaded contacts. In this study, a custom built multi-axis tribometer is used to replicate fretting of filled and unfilled PEEK in a pin-on-flat configuration in both dry and wet conditions. The performance of the PEEK based polymers is shown to depend on the shear stresses generated when adhesive contacts are broken during slip. Unfilled PEEK experiences frictional heating that leads to softening of the wear surface. The softened material can be easily sheared from the bulk and leads to cratering and fracture of the samples. The extent of damage depended strongly on MW. The buildup of heat is prevented when water lubrication is used and wear is also reduced. Lubricating fillers such as PTFE and graphite lower the frictional forces and reduce the tractive shear stresses. Filled samples however were susceptible to softening from water that exacerbated fretting damage. The fretting performance appears strongly tied to the static friction response on the material. Static friction measurement along with FEA analysis was conducted to better understand the observed phenomena. A stop-go experiment was used to capture the friction response due to the shearing of adhesive contacts.

A new experimental approach based on essential work of fracture (EWF) method and an in-situ digital image correlation strain mapping analysis has been developed to quantify different aspects of fracture energy on model metallocene linear low-density polyethylene (m-LLDPE) blown films. Three distinctive fracture process zones have been identified from the photoelastic observation of the model m-LLDPE blown films. These three zones include the essential work ( W e ) zone due to necking and crack propagation, the non-essential plastic deformation zone ( W p ), and a newly proposed recoverable viscoelastic deformation zone ( W v ), which is found to be nontrivial. Furthermore, in contrast to the assumption involved in the EWF theory, W e is found to be proportional to the volume of the materials involved in the inner fracture process zone. The current approach allows for exact physical interpretation of the EWF parameters and their correlation to material characteristics. Usefulness of the present work for development of stronger polymeric blown films is discussed.

Effect of thermal history on scratch performance of acrylonitrile styrene acrylate (ASA) and acrylonitrile butadiene styrene (ABS) model systems was studied. ASAs with rubber particle sizes of 100 nm and 1 µm, respectively, and ABS with rubber particle size of 100 nm were investigated. Linearly increasing normal load scratch tests were performed according to the ASTM-D7027/ISO-19252 standard. An improvement in scratch resistance is observed in ASAs when annealed at 140 °C whereas a noticeable drop in scratch resistance is found in ABS under the same condition. Various microscopic analyses were conducted to determine the corresponding deformation mechanisms for the observed dependence of scratch performance on annealing. Implication of the present findings for design of scratch resistant rubber toughened polymers is discussed.

Effects of rubber particle size and type on scratch performance were investigated using two types of styrenic copolymers: acrylonitrile styrene acrylate (ASA) and acrylonitrile butadiene styrene (ABS). ASAs with rubber particle sizes of 100 nm and 1 μm, respectively, and ABS with rubber particle size of 100 nm were examined. Linearly increasing normal load scratch tests were performed according to the ASTM D7027/ISO 19252 standard. A noticeable drop in scratch resistance is found in ASA with 100 nm rubber particles when compared to ASA containing 1 μm rubber particles. ABS is observed to exhibit a higher scratch resistance when compared to ASA with comparable rubber particle size. Detailed deformation and damage mechanisms have been investigated to explain the observed differences in scratch performance of the model systems. Implication of the present findings for design of scratch resistant polymers is discussed.

In-depth understanding of how the presence of dispersed particles influences the scratch behavior of multiphase polymeric systems requires extensive knowledge of the corresponding local deformation and damage mechanisms during scratching. Effects of particle type, size, and concentration on scratch behavior of multiphase polymeric systems have been investigated based on a three-dimensional finite element method (FEM) modeling effort. Effect of particles location underneath the surface during scratch has also been studied. The results show that the presence of hard and soft particles can drastically affect the stress and strain field development during the scratching process. The FEM stress and strain field analysis explains the experimentally observed scratch-induced damages in multiphase polymeric systems reported in the literature.

In order to predict scratch performance of polymers, the present study focuses on quantitative assessment of various scratch-induced deformation mechanisms based on a set of model amorphous polymers via numerical modeling. A modification of Ree-Eyring theory is used to account for the rate dependent behavior of the model polymers at high strain rates using the experimental data obtained at low strain rates. By incorporating the rate and pressure dependent constitutive and frictional behaviors in the finite element methods (FEM) model, good agreement has been found between FEM simulation and experimental observations. The results suggest that, by including appropriate constitutive relationship and frictional model in the numerical analysis, the scratch behavior of polymers can be quantitatively predicted with reasonable success. Usefulness of the present numerical modeling for designing scratch resistant polymers is discussed.

Juniperus excelas is an important flowering medicinal plant belonging to the Cupressaceae family. Essential oil was obtained from fresh fruit of J. excelas by hydro-distillation in a Clevenger apparatus and analysed by gas chromatography–mass spectrometry (GC–MS). The chemical constituents of the essential oil were identified by their mass spectra, retention time and retention indices. The yield was 0.27%. We identified 48 chemical compounds accounting for 89.74% of the composition. The major chemical components were α-terpinene (23.85%), limonene (23.42%), fenchene (6.57%), camphene (6%), δ-3-carene (4.17%), 4-terpineol (2.93%), germacrene B (2.21%), myrcene (1.96%), α-pinene (1.77%), β-pinene (1.53%) and abietatriene (1.13%). The antimicrobial activity of the essential oil of J. excelas was determined against one Gram-positive and two Gram-negative foodborne pathogenic bacteria, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. No activity was detected.

Surface friction plays an important role in influencing the stress field development during scratch process, thus, scratch-induced deformation mechanisms. In this study, three-dimensional finite element method (FEM) parametric study was performed along with experimental validation to investigate the effect of surface friction on scratch-induced deformation and its correlation with the constitutive behavior of polymers. As scratch depth and shoulder height are the key parameters for causing scratch visibility, the focus is to investigate the effect of surface friction on these two scratch-induced deformation features and how the surface friction effect can be altered by varying the constitutive parameters. The FEM findings and experimental observations indicate that onset of groove formation during the scratch process is strongly influenced by yield stress and coefficient of surface friction. Also, the relative frictional effect on scratch-induced deformation becomes minimal if the post-yielding strain hardening slope of the polymer is high. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Numerical modeling and experimental work were performed to establish a correlation between the bulk mechanical properties and scratch-induced deformation features in polymers. Three-dimensional finite element method (FEM) parametric study was carried out to investigate the effect of asymmetric tension–compression constitutive behavior on scratch-induced deformation of polymers. The scratch depth and shoulder height of the groove formed during the scratch was analyzed by considering different hypothetical asymmetric tension–compression constitutive behaviors. Experimental work on a set of model polymers was also carried out to validate the FEM findings following the ASTM D7027-05 scratch testing protocol. The results indicate that the compressive behavior, not the tensile behavior, dominates the scratch depth and shoulder height formation. Implication of the present findings for designing scratch resistant polymers is discussed.

The physical aspect of mar behavior is studied by applying a standardized progressive sliding load methodology to smooth and textured automotive-grade thermoplastic olefins. It is shown that surface texture has a strong effect on light scattering and, hence, the propensity for mar visibility. It is also shown that digital imaging via a desktop scanner can be used to quantitatively and objectively assess mar resistance using contrast as a basis. Incorporation of slip agent definitively improves the mar resistance for both types of surfaces. Relationships between contrast, gloss and surface roughness in relation to mar visibility are discussed.

Three-dimensional finite element method (FEM) parametric study was performed by simulating linearly progressive load scratch process on a polymer substrate with a spherical-tip indenter, following the established ASTM D7027-05 and ISO 19252:08 testing protocol. The scratch depth and shoulder height of the groove formed during scratch, which has been shown to be directly related to the scratch visibility resistance of polymers, is simulated by varying a set of material constitutive parameters, namely, yield stress, strain softening slope, strain hardening slope, strain at stress recovery, and strain before hardening. The simulation results indicate that yield stress and strain at stress recovery are two most important parameters that affect scratch depth and shoulder height, thus scratch visibility resistance, of a polymer. Implication of the present findings for designing scratch resistant polymers is discussed.

Susceptibility of polymer surfaces to acute visibility upon scratching has presented a serious challenge to the polymer industry for quite some time. The ability to design polymers with good scratch visibility resistance requires extensive knowledge about scratch deformation mechanisms and their propensity for light scattering. After examining the physical nature of human vision and surface optical characteristics, a new methodology is developed to quantitatively determine the onset of scratch visibility of polymers via an inexpensive desktop scanner. Taking into account the sample background color, texture, gloss and feature size, the proposed methodology can consistently and reliably determine polymer scratch visibility resistance regardless of the sample surface characteristics. Good correlation is found between this method and actual human perception. Quantitative analysis of the scratched surface is carried out with scanning laser profiling confocal microscopy and strong correlations among scratch visibility, observation angle and various scratch damage features such as roughness and scratch grooves are established. The proposed approach will greatly assist the development of scratch-resistant polymeric materials where surface aesthetics is of primary concern.

_______________________________________ *Author for correspondence. e-mail: nilufarnahar@yahoo.com Dissipation of Cypermethrin in Bean and Cauliflower Nilufar Nahar*, Mohammad Motaher Hossain, Md. Nashir Uddin Al Mahmud, Mohammad Shoeb, Gulshan Ara Latifa and Kamal Humayun Kabir Department of Chemistry, Dhaka University, Dhaka, Bangladesh Department of Zoology, Dhaka University, Dhaka, Bangladesh Entomology Division, Bangladesh Agricultural Research Institute, Gazipur, Bangladesh

Poor compression strength and interlaminar properties, which are matrix related properties, are the limitations of fiber reinforced composites. One approach to enhance mechanical as well as multifunctional properties of fiber reinforced composites is through modifying the polymer matrix by nano-sized fillers. This paper focuses on improving the mechanical properties of the matrix by reinforcing with nanosilica, while the reinforced matrix will be later used in fiber reinforced composites. The matrix chosen was SC79 epoxy and the nanofiller chosen was Nanopox F400 supplied by Nanoresins AG, Germany. Nanocomposites were made by mixing SC79 epoxy resin, Nanopox F400, and curing agent using a mechanical stirrer, followed by curing. TEM analysis showed uniform dispersion of silica nanoparticles with the size of the majority of the nanoparticles in the range of 14 to 21 nm. Dynamic mechanical analysis and ASTM standard tension, compression, shear and plane-strain fracture toughness tests were conducted. Storage, tensile, compressive, and shear modulus as well as the fracture toughness of the nanocomposites increased monotonically with the addition of nanosilica. For 20% wt. nanosilica, the improvement in tensile, compressive and shear modulus was 20%, 20% and 17%, respectively, and fracture toughness increased by 30%. The 0.2% offset tensile and compressive strengths as well as Poisson’s ratio did not change with the addition of nanosilica. The comparison of experimental tensile and compression moduli agreed well with the predicted data from Halpin-Tsai equation and also with the literature. The results presented in this paper are encouraging to use the material in fiber reinforced composites.