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Today, heavy metal pollution is an urgent problem in the world including Vietnam. An analytical approach is very important to identify, assess and forecast environmental risks from toxic components, in which ecotoxicology is considered to be the optimal tool. We conducted a study on M. micrura in order to contribute the creation of a biological basis for the use of zooplankton as an early warning of the risk of water pollution. The results showed that M. micrura was isolated from 29/3 Park Lake, Da Nang City, central Vietnam. The acute toxicity test of potassium dichromate on M. micrura showed LC 50 at 12, 24 and 48 hr were 0.26, 0.15 and 0.08 mg.l-1 K2Cr2O7, respectively. EC 50 was 0.015 mg.l-1 K2Cr2O7 for egg parameter and 0.009 mg.l-1 K2Cr2O7for neonate parameter. The results of acute and chronic toxicity tests showed that M. micrura was more sensitive than D. magna, D. pulex and C. cornuta.

The synthesis of silver nanoparticles (Ag NPs) has been carried out using different methods, mainly by biological and chemical methods; however, comparing antibacterial activity of Ag NPs synthesized by these methods has not been conducted before. In this study, silver nanoparticles (Ag NPs) were synthesized by methods using reducing agent NaBH4/carboxymethyl cellulose (CMC) and fungal strain Trichoderma asperellum (T.asperellum). The formation of silver nanoparticles was observed visually by color change and identified by Ultraviolet-visible (UV – vis) spectroscopy. The transmission electron microscopy (TEM) image illustrated almost nanoparticles with spherical shape and average diameter of 4.1 ± 0.2 nm and 2.1 ± 0.2 nm of samples produced from chemical reduction and biosynthesis respectively. Both samples after 180 days storing have been separated lightly, but the agglomeration and absorbance peak shifting were not observed which proved the high stability of synthesized Ag NPs. Antimicrobial activity against human bacterial pathogen Escherichia coli (E. coli) showed that the inhibition zone produced by “biosynthesis” and “chemical reduction” Ag NPs were 3.17 cm and 2.42 cm respectively. With nanoparticles size smaller than 2 mm, antibacterial activity of “biosynthesis” Ag NPs against E. coli was 31 % higher than “chemical reduction” Ag NPs, although the concentration of Ag NPs produced by biosynthesis was about 10-fold less.

In this article, a new method to characterize the tear behavior of coated textiles using fracture mechanics is proposed. The energy dissipated in tearing (EDT) of as-received and thermally aged samples of polyester fabric, polyvinyl acetate rubber coating, and textile-coating composites was calculated and compared. The EDT of the coated fabric displayed a slightly smaller value than the fabric alone, whereas the EDT of the coating was found to be negligible when compared with the other two. The presence of the coating is believed to have a detrimental effect on the tearing behavior of the coated fabric as it hinders interfilament slippage. A master curve of EDT retention vs. aging time for noncoated and coated fabric samples was constructed using the time–temperature superposition principle and fitted using the Hill equation. Fourier transform infrared analyses carried out on aged fabric samples hinted at a possible chain scission process, whereas the crystallinity of fabric samples, calculated via differential scanning calorimetry, was found to decrease after thermal aging. Scanning electron microscopy images revealed an increase in surface roughness after aging that may reduce interfilament friction. These results, coupled to an increase in the adhesion strength between fabric and coating, are likely the cause of the reduction of EDT noticed in aged coated and noncoated fabrics compared with as-received ones. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

The focus of this work is the study of the hydrolytic and photochemical aging behavior of a Kevlar®-PBI blend fabric. Tensile tests carried out on yarns extracted from this fabric after either irradiation with UV light or exposure to high humidity indicated a continuous decrease of the breaking force with exposure time. ATR-FTIR analyses of photo-chemically aged samples showed evidence of a photo-oxidative reaction initiated by the cleavage of the amide bond of Kevlar. The overlapping of the breaking-force curves that was observed as the irradiance level was increased at constant temperature is believed to be caused by a “screen” effect produced by Photo-Fries products. The fact that at constant temperature the breaking force was unaffected by the variation of the relative humidity suggests that the absorption of water is not the rate-controlling step in the degradation kinetics. ATR-FTIR analyses revealed the presence of a new absorption band ascribed to carboxylic acid end groups produced during the hydrolysis of the amide linkage that occurred after humidity aging. The relative intensity of the –COOH band tended to a constant value as exposure times increased, suggesting that in addition to the hydrolysis, a competing recombination reaction takes place during degradation. A kinetic model for the hydrolytic degradation process was formulated and solved.

A previous study of the effects of thermal aging on the tensile properties of a fabric made of a 60–40 wt % blend of Kevlar and PBI fibers has shown that exposure to elevated temperatures between 190 and 320°C results in a rapid decrease in tensile breaking force retention. In this article, X-ray diffraction and Raman spectroscopy analyses were carried out to evaluate the consequences of thermal aging on the material's crystallinity. Differential thermal analyses were also undertaken to examine the evolution of the glass transition temperature of PBI following thermal exposure. X-ray diffraction profiles show a gradual increase in the crystallinity with temperature and aging time, whereas a complete disappearance of spectral lines for aged samples in Raman analysis suggests instead a decrease in crystallinity as a consequence of exposure to elevated temperatures. The seemingly contradictory outcome obtained when using the two techniques led to the proposal of a new, alternative hypothesis to explain the observed results. This hypothesis involves two simultaneous events that occur during thermal aging: the increase of crystallite size in the direction parallel to coplanar sheets, and the disruption of the crystalline lattice in the direction perpendicular to those sheets. The glass transition temperature of PBI was found to shift towards the lower temperatures after thermal aging, a phenomenon that can be associated with random polymer chain scission caused by thermal aging. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

This paper discusses the influences of plastic yielding and fracture on the entropy change in polypropylene having different morphologies, induced by different cooling rates during molding. Compressive tests were performed over various loading rates to analyze the yielding kinetics and Ree–Eyring’s model was used to analyze the entropy change in the material. The results suggest that plastic deformation implies more cooperative segmental motions for higher crystalline content, which result in higher values of the pre-exponential factor containing the entropy term. The parameters related to the secondary relaxation process did not undergo any significant change during ageing, suggesting that ageing at room temperature does not affect localized molecular motions. The transition from ductile to brittle fracture involves however the amorphous polymer that evolves with ageing. Physical ageing has thus very little influence on yielding performance, but strongly affects the fracture process of the polymer. Dielectric spectroscopy was conducted in the frequency domain using a broadband dielectric spectrometer for the lowest and highest crystalline morphologies in both aged and unaged states. The results showed significant changes in the dissipation factors of the primary relaxations of the amorphous polymer with ageing time, for both low and high crystallinity samples. On the other hand, no change in the secondary relaxation was observed in either case.

The method used in the past 30 years for describing the swelling of polymers by solvents is mainly based on the Hansen three-dimensional solubility parameters. However, the subjectivity of its implementation as well as its limited success for several polymers, and in particular elastomers, which constitute choice materials for protective gloves, has been reported by several authors. In this article, data obtained by Zellers et al. with butyl rubber and a list of 53 solvents are analyzed to identify the parameters controlling the swelling of this elastomer. The absence of a global effect of the Hansen affinity, solvent molar volume and saturation vapor pressure, and Flory–Huggins interaction parameter has been confirmed. It was also shown that one of the main factors controlling the swelling of butyl rubber appears to be the chemical class of the solvents. Within these classes, a linear relationship between butyl rubber swelling and solvent saturation vapor pressure was observed, and the correlation with molar volume is almost as good. On the other side, no correlation can be obtained with the Hansen affinity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Stress induced change in intrinsic time scale was investigated by nonlinear creep tests of polypropylene (PP) at room temperature of 27 °C. The time-dependent axial elongations of the specimen were measured at 5 different stress levels, from 10.2 to 20 MPa, and modeled according to the time-stress superposition principle. The test duration was only 1 h. The test results show that the creep compliance vs logarithm time curves at different stresses depart from each other, indicating nonlinear viscoelastic behavior, and can be horizontally shifted to overlap onto a smooth master curve up to 51.5 h at the reference stress of 10.2 MPa. It is demonstrated that the time-stress superposition principle provides an accelerated test technique to evaluate the materials’ long-term mechanical properties.

Measurements of tensile and tearing resistance have been conducted as a function of aging time and aging temperature for a polychloroprene (CR). The steady increase in stiffness indicates that crosslinking is dominant during the aging of CR. In the early stage of aging, tensile strength and tearing energy increase thanks to an optimized balance between the strength enhancement from the crosslink network and the network capability in dissipating energy. Prolonged aging after a characteristic time results in a gradual decrease in strength and tearing energy and this change is more pronounced with higher aging temperatures. The superposition principle between aging time and aging temperature was used to determine the activation energy controlling the change of tearing energy in thermal aging. This value agrees with the activation energy Ea = 91 kJ/mol reported in current literature by monitoring the oxygen consumption rates during the aging of CR, suggesting that the change in tearing energy is controlled by chemical reactions much the same as the change in oxygen consumption dissolved in the material. It was also found that the variation in the strain energy density to break is also controlled by the same activation energy.

It is generally recognized that resistance to cutting consists of two aspects, one reflecting the intrinsic strength of the material, and the other a frictional contribution. In practice, cutting usually involves a normal force and a sliding movement. This work aims to analyze the effects of friction on cutting resistance of materials in the presence of a normal force and sliding movement of a sharp object. International Standard ISO 13997 is used as a reference to evaluate the cut resistance of some selected protective materials under practical conditions in service. The resistance to cutting of a material in the presence of both a normal force and sliding movement of a sharp object is strongly controlled by friction between the blade and the cut material. An increase in the friction coefficient can enhance or reduce the cut resistance, depending on the thickness, and the microstructure of the material to be cut. Thus the total energy required to propagate a cut strongly depends on the friction coefficient and consists of two components: The lost energy dissipated by the squeezing force exerted by the cut material, due to its elasticity, on the blade sides, and the essential cutting energy at the edge of the blade. These energies have opposite effects on the cutting resistance of materials. An increase in the energy dissipated in gripping frictional force increases the cut resistance, whereas an increase in friction at the blade’s edge reduces the energy required to cut the material.

The aim of this work is to investigate the effects of two triblock copolymers, used as coupling agents, on fracture and yielding behaviors of a blend of 80 volume % of polystyrene (PS) and 20 volume % of ethylene-propylene rubber (EPR), over a large range of loading rates and temperatures. For this purpose, blends containing different concentrations of two triblock copolymers were studied at various test conditions. The focus was put on the time-temperature dependence of fracture performance of the blends. Addition of triblock copolymer makes the PS/EPR blend more ductile. The time-temperature dependence of the brittle-ductile transition in fracture performance of the blend is controlled by an energy activation process. The interfacial agent lowers the temperature at brittle-ductile transition and reduces the energy barrier controlling the fracture process. This effect, however, is much more pronounced for the lower molecular weight interfacial agent. The correlation between temperature, loading rate and yield stress of the blends seems to be controlled by a molecular relaxation process according to the Ree-Eyring theory. This model, based on the assumption of two relaxation processes (α and β) acting in parallel, allows prediction of yield stress at various loading rates and temperatures. Addition of the interfacial agents results in a reduction of the activation energy and an increase in the activation volume V * for both the α and β processes. Furthermore, the similarity of the value of the activation energy ΔH β in the β yielding process and the energy barrier ΔH controlling the brittle-ductile transition in fracture seems to suggest that a similar secondary relaxation mechanism controls the yielding and the fracture behavior of the blend.

In a previous study, two triblock copolymers of styrene/ethylene-butylene/styrene (SEBS), of different molecular weights, were used to compatibilize a blend of 80 vol% polystyrene (PS) and 20% ethylene-propylene rubber (EPR). The emulsification curve, which relates the average minor phase particle diameter to the concentration of interfacial agent added, was used to quantify the effect of the interfacial agents on the blend morphology. Links between morphology, interface, and properties were established by combining the emulsification curve with a fracture mechanics approach. The aim of this work is to foster the understanding of the effects of these two triblock copolymers on the fracture behavior of the blend over various loading rates and temperatures. The focus is on the brittle-ductile transition in fracture behavior, which is a critical condition for the application of these materials. It has been found that adding an interfacial agent lowers the temperature at brittle-ductile transition. However, this effect is much more pronounced for the copolymer with a lower molecular weight. The time-temperature dependence of fracture performance of the blend is also affected by the interface and morphology. When loading rate increases, the shift of the temperature at brittle-ductile transition is less significant for the blend with an interfacial agent having a lower molecular weight. The effect of loading rate and temperature on the brittle-ductile transition in fracture performance of the blends is controlled by an energy activation process. Adding the interfacial agents results in a plasticizing effect of the polystyrene matrix and a reduction in the energy barrier controlling the fracture process. With the addition of interfacial agent, the yield stress slightly increases at low concentration, attains a maximum value, and then decreases. The increase in yield stress confirms the coupling role of the copolymer and is in agreement with the observed emulsification curves. The reduction of yield stress and increase in ultimate strain with the copolymer concentration demonstrate the plasticizing effect of the interfacial agent. The result of stress relaxation tests also confirms the above effects of the interfacial agent.

An emulsification curve which tracks the change in dispersed phase size with interfacial modifier concentration and a fracture mechanics approach have been used to study the behavior of a variety of well-defined interfacial modifiers for a melt-processed ethylene−propylene rubber (EPR)/polystyrene (PS) blend. In this study two poly(styrene/ethylene−butylene) (SEB) diblock copolymers and a poly(styrene/ethylene−propylene) (SEP) diblock copolymer were compared. All of the above interfacial modifiers demonstrate an excellent emulsification efficacy for the EPR/PS system, and no effect was observed when changing the block structure from ethylene−butylene to ethylene−propylene. Despite the excellent capacity of all three diblock modifiers to emulsify the blend, the Charpy and notched and unnotched Izod impact testing demonstrate significantly different behaviors for the various copolymers. The higher molecular weight SEB (Mn = 187 000) and SEP (Mn = 140 000) interfacial modifiers displayed a brittle fracture b...

The in vitro binding of RS-chlorpheniramine to human proteins was studied by equilibrium dialysis. The binding to total plasma proteins and to individual albumin and alpha-glycoprotein acid is stereoselective. (+)S-chlorpheniramine is more extensively bound than its antipode to total plasma proteins (38% vs. 23%), to albumin (20% vs. 15%) and to alpha-glycoprotein acid (23% vs. 5%).

Tensile and impact properties of uncompatibilized nylon-6/ABS blends have been studied over the entire range of compositions. The blends were prepared by extrusion and, subsequently, injection molded into tensile specimens and rectangular plaques. The impact fracture performance was characterized using recently proposed models based on fracture mechanics, for various fracture behaviors. The results showed that nylon-6 breaks in a brittle manner. With the addition of ABS, the blend exhibits the same behavior with a slightly lower impact resistance up to about 60 wt %. A sudden jump in the value of impact fracture energy is observed around 70 wt % ABS with a brittle—ductile transition in the mechanism of fracture. The transition in fracture mechanisms is confirmed through observation of the fracture surfaces by scanning electron microscopy (SEM). Tensile tests showed that the elongation at break increases only slightly between 0 and 50% ABS content, but a significant jump occurs around 70% ABS, reaching a 6-fold increase in comparison to that of the pure components. SEM observation of etched samples shows that a cocontinuous morphology occurs around 70 wt % ABS. The peak observed for the elongation at break and the jump in impact performance, as well as the onset of brittle–ductile transition, are attributed to this morphological effect. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2583–2592, 1997

The objective of this work was to investigate the mechanism of brittle-ductile transition in toughened polymers. Two systems, namely, a rubber-toughened nylon 66 (Zytel ST-801) and a high impact polystyrene (HIPS), were chosen for this study. The samples were prepared by injection molding and were tested in three-point bending under various loading rates and temperatures. The brittle-ductile transition temperature (Tb–d) was determined from the observed fracture behavior as a function of temperature. Molecular relaxation temperatures of the polymers were measured by mechanical spectroscopy at various frequencies. The correlation between temperature and loading rate was estimated using the Arrhenius equation. The results show that Tb–d of Zytel ST-801 is only slightly affected by the loading rate, whereas Tb–d of HIPS strongly increases with deformation rate. It is found that for the former, within the experimental errors, an increase in Tb–d with loading rate corresponds to the shift in the secondary relaxation temperature Tb of the nylon 66 matrix. For the latter however, the increase in Tb–d is related to the glass/rubber relaxation of the polystyrene matrix. It seems that the type of molecular relaxation controlling the brittle-ductile transition corresponds to that with lower activation energy.

This paper deals with the fracture performance of injection moulded long glass fibre composites based on polybutylene terephthalate (PBT) and polypropylene (PP) matrices. The tensile behaviour of these composites is analysed using the shear lag theory taking into consideration the interfacial shear strength, fibre length distribution and fibre orientation in the mouldings. The fracture performance is investigated using the post yield fracture mechanics approach. The crack growth resistance of the PP and PBT long fibre composite was found to increase with increasing fibre volume content up to 35%. Above 35% a plateau in the fracture performance was observed. A combination of high fibre degradation and a change in the fibre orientation pattern of the moulded pieces is found to be responsible for the plateau region in the performance of the high concentration system. In fact, the dependence of the maximum crack growth resistance of the composites on fibre length and fibre orientation is also controlled by testing temperature. The competition between fibre-induced matrix deformation and the fibre pull-out determines the ability of the composites to resist crack propagation.

Effects of remolding on mechanical performance are particularly important in post-processing of thermoplastic resin composites. The effects of molding and remold ing temperatures on the Mode-I delamination toughness of APC-2 composites are in vestigated experimentally. It is found that both the initiation and the propagation energies of delamination are influenced by the remolding process, and the effect depends on the previous molding history. In particular, the extent of fiber bridging strongly depends on molding and remolding conditions. Enhanced fiber bridging results in a rising R-curve and unstable crack propagation. The observed behaviors are interpreted from the viewpoint of matrix crystalline morphology.

This paper deals with the fiber/matrix interface in carbon /PEEK compos ites. It is found that although interphase crystallinity is essential to ensure good interfacial strength in carbon /PEEK composites, it is not the primary factor responsible for the crea tion of fiber/matrix interaction in this composite. The results suggest that such interaction is a result of several complex mechanisms such as matrix adsorption on the fiber surface, fiber/matrix reaction leading to chemical bonding, and crystallization of the interphase. The concept of adsorption proposed by Brady and Porter for the carbon/polycarbonate system seems to be valid for interpreting the evolution of the short beam shear strength with residence time, as described by a Langmuir-type expression. The temperature de pendence of the formation of the fiber/matrix interaction, as measured by the short beam shear strength, is also found to follow an Arrhenius equation with an activation energy of about 324 kJ mol-1. The high value of the activation energy and the irreversibility of the interaction process suggest that chemisorption could be a dominant mechanism, since, in the range of processing temperatures for carbon / PEEK composites, there is effective modification of the matrix (chain scission and crosslinking) as well as thermal degradation leading to reactive species.

In this work, the role of the interface and matrix morphology in determining the fracture behavior of glass flake reinforced polypropylene is investigated. Differential scanning calorimetric analysis shows that silane coupling agent modifies the crystallization behavior of the polypropylene matrix. Silane treated glass flakes prepared by dry blending are found to induce nucleation and decrease the rate of development of the crystalline entities during the crystallization process. This effect is attributed to the physisorbed layer of silane on the glass flakes. The effect of matrix morphology on the fracture performance is analyzed by fracture mechanics. An increase in matrix crystallinity in pure polypropylene and in glass flake/polypropylene composites leads to a reduction in the maximum crack growth resistance. The lower ductility of a more crystalline matrix results in a reduction of the energy dissipated in the matrix stretching and, therefore, a concomitant decrease in the fracture energy. Although the effect of matrix morphology seemed to be important in the case of pure polypropylene and untreated glass flake polypropylene composites, this effect is found to be negligible for the silane treated composites. Nevertheless, microscopic observation of the fracture surfaces of silane treated composites also revealed a reduction in the ductility of the matrix in highly crystalline samples. An improvement in the matrix-filler interface seems to inhibit the effect of matrix morphology on the fracture behavior of glass flake/polypropylene composites.

This paper presents the influence of fibers on crystallization kinetics and on matrix morphology for poly(phenylene sulfide)/carbon composite. The following parameters were also considered : thermal stability, fusion/crystallization conditions and surface treatment of carbon fibers. In order to correlate these results with mechanical properties, composite samples were prepared and tested in both static and dynamic modes. The delamination resistance of the composite in shear Mode II is also discussed

Weldlines represent potentially fatal sources of weakness in injection molded thermoplastic parts. This is particularly true for filled and reinforced composi tions where usual remedies consisting in a modification of processing conditions such as increase of melt temperature, injection speed, and pressure do not always work. This paper deals with weldline strength of injection molded polypropylene containing spherical and irregularly shaped fillers (glass spheres, calcium carbonate), or reinforcements such as glass flakes and fibers, talc, and mica. Two types of weldline will be considered: weldlines formed when two melt streams meet head-on and those formed as a result of flow around an insert. It will be shown that the loss of strength is greatest in compositions reinforced with flakes and fibers. This is due to flow induced filler orientation in the weldline zone. Approaches to reduce the loss of strength which make use of known flow behavior of suspensions of fibers and flakes will be illustrated., 42nd Annual Conference of the Society of the Plastics Industry, 1987

The enantiomers of chlorpheniramine and its monodesmethyl metabolite were determined separately in urine by using a coupled achiral-chiral chromatographic system. The two enantiomers of the studied compound and the internal standard were separated from the biological matrix on a cyanopropyl column and reinjected into a chiral amylose AD column where the two enantiomers were separated and quantified by UV detection. The method was validated for chlorpheniramine and for the metabolite within the range 0-1000 ng/ml. It was also applied in a pilot pharmacokinetic study to samples from a volunteer given 8 mg of racemic chlorpheniramine by mouth.

Fillers have been widely used in commercial production of polymers to improve physical properties for specific applications. The main effects of fillers on polymers are the increase of modulus and hardness, and reduction of creep and distortion at elevated temperature [1, 2]. According to the type of reinforcement provided, fillers are often divided into three classes: one-dimensional (fibers), two-dimensional (flakes or platelets), or three-dimensional (spheres or beads).

This paper discusses the mechanisms governing the fracture toughness of polypropylene reinforced by either mica or glass flakes. The toughness of these compos ites is found to be controlled by the competition between shear yielding and voiding in the matrix. Shear yielding occurs around filler particles, because of debonding at the filler/matrix interface. The filler onentation does not affect the crack growth resistance, but there is a unique relationship between the latter and the average distance between par ticles, regardless of the nature of the filler. It has also been found that the glass-rubber relaxation of the matrix polypropylene is the governing parameter for the time dependence of the dynamic fracture toughness of these composites.

The effects of such factors as flake size, orientation, and surface treatment on the fracture mechanism of mica-reinforced polypropylene were investigated. Concepts of post-yield fracture mechanics were used to characterize the crack initiation and propagation resistances of the composite. It was found that better flake alignment slightly increases the yield strength but does not affect the crack growth resistance of the material. Flake size degradation during processing leads to an increased crack initiation resistance but reduces the tearing capacity and the maximum crack growth resistance of the composite, due to a reduction of the extent of matrix deformation. In the same manner, the use of a coupling agent diminishes the effect of matrix drawing and the total energy dissipated during the fracture process, even though the crack initiation resistance can be increased.

Reaction injection molded polyurethanes are reinforced with inorganic materials to improve stiffness and structural integrity at elevated temperatures and to reduce the coefficient of thermal expansion. This work describes the reinforcement obtained with an experimental grade of mica designed to achieve low viscosity of mica suspensions in polyol. The effect of mica on properties is essentially identical to that of glass flake (i.e., improved stiffness at the cost of reduced impact strength). Compared to hammer milled glass fiber, mica and glass flakes yield more isotropic, albeit weaker, materials. The study of unreinforced polyurethane shows that mechanical properties (tensile and impact strength, flexural modulus) are approximately proportional to the square of foam density.

The impact resistance of glass-flake reinforced polypropylene was analyzed over a wide range of loading rates and glass-flake concentrations. It was found that the dynamic fracture toughness, Kd, of the composite is strongly rate-dependent. When impact velocity is increased, Kd first decreases, attains a minimum value, and then increases with impact speed. The increase in Kd with loading rate is attributed to the blunting effect at the crack tip, induced by adiabatic heating. The addition of glass flakes substantially increases the dynamic fracture toughness of polypropylene. The increase in Kd with glass-flake content is also more pronounced when the loading rate is increased. The blunting effect was found to increase with glass-flake concentration up to 30 percent by weight, leading to a stronger increase in Kd with glass-flake content from 0 to 30 percent. Above 30 percent, the blunting effect diminishes with concentration.

Edge notched samples of polypropylene (PP) and high-density polyethylene (HDPE) containing different mica concentrations were tested in mode I tensile loading. Crack growth was approximated by a non-linear regression of exponential form using statistical software (SAS). Characterization of fatigue crack propagation (FCP) was made using the Paris-Erdogan law. The crack front in PP was preceded by a wide plastic zone in which craze developed, leading to a discontinuous crack growth. Using spline functions, a margin between maximum and minimum FCP rates, recorded during the crack progression, is presented along with the average FCP rates. It is shown that mica-reinforced PP samples exhibit higher FCP rates than unfilled PP. In HDPE, mica reduces FCP rates resulting in a higher resistance to fatigue crack propagation. Effect of test frequency is presented for unfilled polymers and 10 percent mica concentration by weight in both matrices. An increase in the test frequency has no significant effect on FCP rates for both raw and mica-reinforced PP. Unfilled and mica-filled HDPE show noticeable decrease in FCP rates with increasing frequency.

The paper is a preliminary report on glass fiber and glass flake orientation in the weldline zone of injection molded reinforced polypropylene. Two types of weldlines were studied using simple shape molds: one where two melt streams meet head-on and become immobilized, the other where the weldline formation is followed by additional flow. In the weldlines of the first type, which are characteristic of current standard molds used to test weldline strength, the anisometric particles are almost perfectly oriented perpendicular to flow. As a result, the weldlines of this type tend to be weak and brittle. In the second case when the weldline is formed by merging of melt streams separated by an insert, particle orientation in the weldline area remains different from other areas of the sample for long distances from the insert. It is shown that in molds where the weldline formation is followed by laterally expanding flow the change of particle orientation is faster than for unidirectional flow.

Concepts of post‐yield fracture mechanics were used to characterize the crack initiation and propagation resistances of mica‐reinforced polypropylene containing different mica concentrations. Although mica addition leads to an apparently brittle composite, the crack initiation resistance is slightly increased with mica concentration up to 10 percent by weight; and significant improvement in crack propagation performance was found for polypropylene reinforced by up to 20 percent of mica in comparison to that of virgin polypropylene. The debonding of the interface between mica flakes and the matrix leads to a micro‐ductility ahead of the crack tip in which the matrix is able to pull‐out from mica particles and to stretch. This micro‐ductility also prevents the brittle, unstable crack propagation, which is due to the coalescence of voids in pure polypropylene. Above 20 percent of mica, the reduction of the effective amount of the matrix material results in a substantial drop in the resistance to crack growth of mica‐reinforced polypropylene.

The method proposed by C. E. Turner and J. G. Williams for characterizing the impact resistance of polymers was reanalyzed and a new method has been developed for the study of semi‐ductile polymers. In these polymers, the fracture occurs by a set of stable and unstable crack propagation stages. The new model takes into account the first stable stage and the point of instability in order to allow the determination of two fracture energies Ḡst and Ḡinst. These fracture parameters characterize the material impact behavior. The model has been applied to polyamide 11 and 12. Molding condition and orientation effects on the impact fracture energies are presented.

For many applications with plastics the base systems are insufficient and use of reinforcing fillers is required. Glass and mica flakes are currently available for reinforcement. It has also been shown that properties of reinforced microcellular polyurethane are strongly affected by the void volume fraction. In this paper some experimental results on the applicability of far-infrared techniques to measure the state of dispersion and the concentration of mica and glass fillers in polyethylene and polyurethane are presented and discussed. It is shown that fillers can be analyzed with little perturbation from the presence of porosity, while the average orientation of the filler particles can be evaluated by varying the polarization or the angle of incidence of the far-infrared laser beam., 1986 Quebec Symposium, June 3-6, 1986, Quebec City, Canada, Series: SPIE Proceedings

The effect of silane coupling agent on the morphology and fracture performance of particulates-filled polypropylene was investigated. The onset of the crystallization at the filler-matrix interface was observed by optical microscopy. This analysis shows that the silane alters the matrix morphology by inducing nucleation at the filler-matrix interface. This effect was attributed to the physisorbed layer of silane on the filler. The fracture performance of the composites was analyzed by the post yield fracture mechanics approach. The effect of coupling agent on the fracture performance was found to occur at a very low concentration, whereas subsequent increase in silane concentration had no effect. Furthermore, the effect of coupling agent depended on concentration of filler. Silane treatment had a detrimental effect at low concentration of filler. However, at high concentration of filler, an improvement in the filler-matrix adhesion had a beneficial effect on the fracture performance. Two phenomena, the morphological effect and the competition between the contribution of the matrix-filler interface and the contribution of the matrix, were found to be possible explanations for the variation of KRmax with filler concentration and adhesion at the matrix-filler interface.