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Thermoplastic elastomeric nanocomposites have a wide range of applications in the automotive, medical, electronics, and energy sectors. Good mechanical and fracture performances are typically needed to reach the desired properties for the applications. In this study, tensile and fracture properties of exfoliated graphite (EG) filled PP toughened with ethylene-vinyl acetate (EVA) are examined. Accordingly, four levels of EVA (0, 10, 20, and 30 wt.%) and EG (0, 1, 3, and 5 wt.%) are utilized. The full factorial design is employed to explain the effect of independent parameters and their interaction on responses. The essential work of fracture (EWF) methodology is also employed to investigate the fracture behavior of the blend nanocomposites. By increasing EVA, the elongation at break and non-EWF are increased by 188% and 75%, in succession. Moreover, the tensile modulus is improved up to 11% by increasing EG. The compound with 10 wt.% EVA and 1 wt.% EG has the best toughness-strength-stiffness balance based on the optimization results.

In this research, tensile and fracture behavior of polypropylene (PP) toughened with two types of thermoplastic polyolefin elastomers (TPOs) and filled with fumed silica are investigated. The TPOs are both propylene- and ethylene-based thermoplastic elastomers. Three percentages of TPO (0, 10, and 20 wt%) and four percentages of fumed silica (0, 1, 3, and 5 wt.%) are used. The addition of ethylene-based TPO to PP show higher values of modulus and tensile strength than propylene-based TPO. In contrast, propylene-based TPO show higher elongation at break which by increasing this type of TPO the elongation at break increase by 788%. The presence of fumed silica in the PP/TPOs blend improve the tensile strength and modulus but declined the elongation at break. Fracture behavior analysis of these compounds is performed by utilizing the essential work of fracture (EWF) approach. The outcomes demonstrate that both types of TPO in PP cause cavitation and fibrillar structures that increased the elastic and plastic work of fracture. Adding 10 wt.% ethylene- and propylene-based TPO to PP, the values of w e and βw p increase by 63%, 100% and 124%, 123%, respectively. Morphological observations show that fumed silica is located mainly around TPOs particles or at the PP/TPOs interfaces. The addition of fumed silica also reduce the size of the pores, which indicate a slight reduction in the amount of plastic work. However, fumed silica with low percentages increase the amount of elastic work and then reduce it. Also, the compound with 10 wt.% propylene-based thermoplastic elastomers and 1 wt.% fumed silica had the best toughness-stiffness-strength balance among the samples based on the optimization results.

Background: Management of bleeding is among the major issues in medicine, particularly during surgery. Objectives: This study investigated the effects of Pomegranate peel and flower, Myrtle, Quercus fruit, and Rhus coriaria L extracts on bleeding control in rats. Methods: In this experimental study, 32 male Wistar rats (weighing 200 - 250 g, 8-10-month-old) with free access to sufficient water and food, were randomly divided into four groups: (a) the topical application of the extracts on tail wounds (bleeding time (B.T.) measurement); (b) intraperitoneal injection of the extracts (measurement of prothrombin time (P.T.) and partial thromboplastin time (PTT) in the blood taken from the heart); (c) control group 1 (B.T. measurement on tail wounds without the topical application of the extracts); and (d) control group 2 (no intraperitoneal injection of the extracts, P.T. and PTT measurement in blood drawn from the heart). The animals in all groups received the same care and were kept under standard laboratory conditions, 12:12 h light/dark cycles, and a temperature of 23 ± 2.0°C. The data were analyzed by the one-way ANOVA and Tukey's post-hoc tests. Results: The mean of B.T. in the control group, 3.57 ± 0.20 s, was significantly higher than that in the intervention group (1.56 ± 0.13 s) (P < 0.001). The mean of P.T. in the control group was not significantly different from that in the intervention group (P = 0.499). The mean of PTT in the control group (18.2 ± 24.82 s) was significantly shorter than that in the intervention group (38.00 ± 14.49 s) (P = 0.006). Conclusions: Considering the acceptable coagulant effects of the extracts of Pomegranate peel & flower, Myrtle, Quercus fruit, and Rhus coriaria L. compared to the control group, it can be concluded that these extracts can be suitable adjuvant drugs for controlling bleeding. Although the coagulant effects of these extracts have been mentioned in many traditional medicine texts, human tests are required to reject or confirm their clinical effects.

International audience

The low deflection at break of unsaturated polyester resin-based composites is a problem in many industrial applications. In this work an attempt was made to optimize the bulk molding compound form...

Thermoplastic starch (TPS) foams was prepared by melt extrusion process and the effects of polyvinyl alcohol (PVA) and glycerol/water plasticizer contents on the physical and cellular properties of these foams were investigated. All TPS/PVA blended foams showed more uniform cellular morphology, lower density and higher cell density than the TPS foam. The density of TPS foam decreased about 70%, and cell density increased up to 60-fold by adding 20% PVA. In addition to the positive effect of the PVA on improving processability and cellular uniformity, it also acted as a polymeric plasticizer and adding it allowed to decrease another low molecular weight plasticizer content in TPS/PVA blends. As a result by statistical analysis significant improvements in expansion ratio (256%), cell density (60 times), and lower moisture absorption (60%) were achieved.

The curing and cellular structure of natural rubber (NR)/silica composite foams were investigated. The presence of an activator in the rubber formulation significantly lowered the decomposition temperature of the azodicarbonamide foaming agent, which allowed foaming before NR curing. Therefore, two foam methods were designed: foaming initially at 90°C and then curing at 140°C, and foaming and curing simultaneously at 140°C. Two-step foaming generated a lower cell density and higher cell size. Incorporation of nano silica into NR increased the foam density, but decreased the cell size. The higher foaming temperature restricted the bubble growth because of a higher curing rate and inhibited cell coalescence.

This study aims to experiment with the mechanical properties of polypropylene (PP)/thermoplastic elastomer/nano-silica/compatibilizer nanocomposite using the melt mixing method. The addition of polyolefin elastomers has proved to be an approachable solution for low impact strength of PP, while it would also reduce the Young’s modulus and tensile strength. That is why reinforcement would be applied to this combination to enhance the elastic modulus. The mechanical properties of the prepared composites were devised to train an artificial neural network to predict these properties of the system in 6256 unknown points. Therefore, the sensitivity analysis was performed and the share of each input parameter on the respective output values was calculated. Additionally, a novel parameter called nanocomposite evaluation criterion (NEC) is introduced to analyze the suitability of the nanocomposites considering the mechanical properties. Accordingly, the formulation with optimal mechanical properties of toughness, elongation at break, tensile strength, Young’s modulus, and impact strength was obtained.

In this work, the innovative bimodal insulating polypropylene (PP) foam was produced through a straightforward one-step mechanism with only one blowing agent, supercritical CO2. Based on differenti...

This study aimed to evaluate the impacts of different polypropylene (PP) chain configurations, i.e., linear and branched form, on the rheological, mechanical, and electrical properties of PP-based, graphite nanoplates (GnP)-reinforced nanocomposites. The incorporation of GnP with different particle size gave us constructive information about the influences of filler's dimension on the abovementioned properties. A solid-state shear pulverization (SSSP) technique followed by conventional melt mixing was employed to get GnP-filled samples prepared for better filler dispersion. Due to higher interfacial surface area, the obtained mechanical properties from finer GnP were more satisfying. However, the electrical and rheological percolation thresholds (the formation of conductive pathways) took place at a lower content of larger GnP, which is mainly due to its higher aspect ratio compared to GnP. Replacement of linear PP with branched one did not lead to conspicuous alterations in tensile modulus and strength. Based on rheological evaluations, however, the presence of side branches hindered the development of GnP sound network throughout PP matrix, so that in comparison to linear PP-based sample the augmentation of electrical conductivity of branched PP-based composites against filler loading demonstrated slower rates.

Thermoplastic starch (TPS) and polyvinyl alcohol (PVA) blends were prepared by extrusion method in the presence of water/glycerol and citric acid, and their phase behavior was investigated. Results of scanning electron microscopy (SEM) and X-ray diffractometry (XRD) tests demonstrated the complete plasticization of starch during the melt mixing. PVA crystal phase was not formed in blends with less than 50 wt% PVA. Fourier-transform infrared spectroscopy (FTIR) and dynamic mechanical analysis (DMA) analysis revealed high compatibility between two phases, starch and PVA. Addition of PVA to TPS resulted in the reduction of the glass transition temperature and dynamic moduli and improvement of sample flexibility. However, at 10 wt% PVA, an anti-plasticization effect caused to increase the Tg and storage modulus of the blend.

The curing behavior and microstructure of natural rubber/silica foams were studied. Error function-based and autocatalytic models were correlated with the curing characteristics data of samples. The incorporation of silica into natural rubber caused an increase in the foam density and decrease in the cell size. Moreover, by increasing the curing temperature, cell size became larger and cell size distribution became non-uniform. It was thought that the higher temperature of foaming limited the bubble growth due to faster curing reaction. Lower viscosity and lower strength of rubber at high temperature increased the cell coalescence resulting in larger cell size and non-uniform cell distribution.

The purpose of the present study was to investigate the effect of cellular structure on the impact strength of polypropylene/polyolefin elastomers blend foams produced by the continuous extrusion process. To create different cell sizes, two chemical blowing agents were employed: azodicarbonamide and sodium bicarbonate. Sodium bicarbonate created foams with bigger cell size and cell wall thickness than azodicarbonamide. The impact strength of the neat and blend foams were studied and correlated to the foam properties and structure. It was observed that the impact strength of blend foams was directly related to the concentration of polyolefin elastomers (POE). Increasing POE by up to 30 wt% increased the foam impact strength by more than 400%. On the other hand, Increasing POE content caused the cell size and cell wall thickness to be reduced. Moreover, an attempt has been made to establish a relationship between the impact strength and cellular structural parameters. It was found that in the blend foams with higher cell wall thickness the rough fracture of the cell walls was intensified and in turn, the impact strength of the foams improved further.

Ammonium polyphosphate (APP) was grafted onto the surface of exfoliated graphite nanoplatelet (GNP) to obtain a novel flame retardant, GNP-g-APP, and thereafter was incorporated into the ethylene vinyl acetate (EVA) to improve its flame retardancy. The chemical structures of the precursors and the target product were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and energy dispersive X-ray spectroscopy (EDS) techniques. FTIR spectra appeared at 1056 and 1103 cm−1 were attributed to P O C asymmetric stretching bond, that conformed formation of GNP-g-APP. Thermal stability behaviour and flame retardancy performance of the samples were evaluated by TGA, UL-94, micro-calorimetry, and cone calorimetry. TGA measurements revealed the superiority of GNP-g-APP over GNP. The micro-calorimetry analyses indicated a sharp fall in both the total heat release (THR) and the peak of heat release rate (pHRR) of EVA containing 30 wt.% GNP-g-APP, evidenced by a thick char layer formed as barrier. Cone calorimetry confirmed flame-retardant effect of GNP-g-APP featured by a reduction in pHRR (−63 %) and THR (−31.6 %) due to the formation of a cohesive char layer. Although GNP addition sharply decreased the elongation at break of 70/30 (w/w) composites from 500% for neat EVA to 71%, a very promising value of 364% for EVA/GNP-g-APP sample preserved superior flexibility.

The cellulose nano whiskers (CNWs) due to their fibrous shape and high crystalline nature seemed to be suitable as reinforcement for cementitious materials. In this research acid hydrolysis were used along with mechanical stirring and sonication to prepare cellulose nano whiskers (CNWs). Prepared nano whiskers were characterized for chemical and crystalline structure, particle size and morphology of micro/nano structure. Then, they were used as reinforcement in a fine aggregate concrete (FAC) at 0, 0.5, 1 and 1.5 vol%. Flexural behavior of the samples was evaluated by a three-point bending test. Moreover, some combinations of CNW and polyvinyl alcohol (PVA) fiber were used as reinforcement of concrete. By adding the CNW at high proportion of PVA fibers, the flexural properties of composite decreased, while, at lower contents of PVA fiber, flexural strength enhanced about 20%. Addition of CNW generally improved flexural properties of FAC, but made it more brittle. Utilizing hybrid of CNW with PVA fibers in the samples decreased the first and second cracking loads up to 40% but still retained its flexural hardening behavior such as engineered cementitious concretes.

Thermal characteristics and kinetics of the curing reaction of natural rubber latex foam (NRLF) incorporated with 0-3 phr (parts per hundred rubber) nano-alumina (NA) were comprehensively investigated. The kinetics of thermal degradation reaction of the vulcanized NRLF-NA was also modeled through a suitable kinetic mechanism, according to the Coats–Redfern (CR) model. Moreover, the foam crosslinking degree was determined via using the swelling method and the Flory–Rehner (FR) equation to create a deep insight into the impact of NA and its content on the foam network structure. The results showed that the filler of NA led to increasing the heat distribution within the compound and followed by the significant effects on the characteristics and kinetics of the vulcanization reaction, and as well as the foam crosslink density. This phenomenon caused the variation of the thermal stability, secondary crosslinking of the cured NRLF-NA and the thermal degradation mechanism. The resultant data indicated that the addition of 1 phr NA to the compound led to the highest thermal distribution which resulted in the latex foam with unfavorable thermal stability and degradation. Whereas, the NRLF-NA thermal properties were improved with increasing the loading content of NA, after 1 phr NA.

The morphology and crystallization behavior of blends of polypropylene (PP) and an ethylene-based thermoplastic elastomer (TPO) were investigated by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The SEM images showed a two-phase morphology for these blends. As TPO was partially crystalline, two distinct peaks were observed in both heating and cooling scans of DSC. The crystallization temperature of TPO in blends was higher than pure TPO. In contrast, the crystallization temperature of PP in blends was lower than pure PP. The crystallization behavior of blends was modeled by Avrami equation. It was observed that the presence of TPO accelerated the growth rate of crystals of PP in PP/TPO blends.

International audience; This work seeks to address the effect of simultaneous use of three flame retardants, having three different modes of action, (magnesium hydroxide, expanded and expandable graphite) on the thermal degradation and flame retardancy of poly(ethylene-co-vinyl acetate). Thermal conductivity of samples was measured in order to investigate the effect of the use of expanded and expandable graphite on the time-to-ignition and the peak of heat release rate in cone calorimeter test. Thermal shielding performances of chars were studied as well. It was found that there is an optimum ratio between expanded and expandable graphite in order to control thermal conductivity and therefore fire properties. Some correlations were also found between the char thickness and the first peak of heat release rate.

The Hui-Shia model, which considers the complete stress transfer between polymer matrix and particles (perfect interfacial adhesion), overpredicts the Young's modulus of clay/polymer nanocomposites (CPN). In this work, the effective aspect ratio and volume fraction of nanoclay are expressed assuming the imperfect load transfer, the minimum length of platelets required for efficient stress transfer ( L c ) and the interfacial shear strength ( τ ). Additionally, “ I ” parameter as the level of stress transfer in CPN is defined and determined using the effective parameters. The large nanoclay platelets with low “ L c ” give a high level of “ I ”. Also, high “ L c ” and slight “ τ ” observe the poor levels of effective parameters and Young's modulus of CPN. The “ I ” values are calculated for some samples which indicate the different levels of stress transfer in CPN. It is possible to analyze the levels of interfacial properties and stress transfer in CPN using the developed model.

This paper studied the effect of graphene oxide nano-platelets (GOPs) on the fracture behaviour of epoxy adhesive-bonded joints, experimentally and numerically. The double cantilever beam specimens were tested and the fracture energies and resistance curves were determined for the unreinforced and reinforced adhesives. A maximum improvement of 69% in the fracture energy was achieved with the addition of 0.3 wt% of GOPs into the adhesive layer. Moreover, the fracture surfaces were examined using the scanning electron microscopy technique to find out the toughening mechanisms involved in this improvement and mechanisms of GOP debonding and crack deflection were observed. Furthermore, a cohesive zone model was utilised to numerically study the effect of GOPs on the fracture behaviour of the adhesive. The numerical analyses showed that the damage process zone length was also influenced by GOPs. The longest damage process zone was obtained for the toughened adhesive with 0.3 wt% of GOPs.

Bubble growth during polymeric foam production by a physical nucleating agent is a result of rapid gas phase separation in a polymer/gas solution media. The dynamics of bubble growth is thought to be influenced by the material properties and processing conditions. However, the degree of effectiveness of each parameter has not been evaluated in earlier studies. In this work, a simplified single bubble growth in a polymeric media was modeled to specify the critical parameters affecting the bubble growth phenomenon. The predicted bubble growth profile was compared with some experimental data reported in the literature. The model was able to predict the observed bubble growth profile with acceptable precision. Therefore, it was applied to investigate the effect of each physical property of the polymer, i.e. viscosity, surface tension and diffusion coefficient as well as processing conditions, i.e. temperature and pressure release rate on the bubble growth profile. Furthermore, the impact of each factor was clarified.

The current work presents the preparation of polypropylene (PP) foams by the extrusion process, focusing on the influence of the foaming agent and nucleating agent on the microstructure of the foams. Sodium bicarbonate alone and also its mixture with citric acid were used as the chemical blowing agents. Expanded graphite nanoparticle and talc were also used as the nucleating agents. Great differences were found in terms of the foam structure depending on the type of nucleating and blowing agents. Using expanded graphite nucleating agent instead of talc resulted in foams with higher cell densities and more uniform cellular structures. Moreover, the foams including the mixed blowing agents exhibited higher cell densities and upper expansion ratio.

In this work, linear and branched polypropylene (PP)/ graphene nanoplatelet (GnP) composite foams were prepared using supercritical CO2. The morphology of nanocomposite foams was imaged on SEM. Branched PP foams revealed bimodal cellular morphology, while linear PP exposed nanocellular structures. The effect of cell modality and adding GnP on the mechanical and electrical properties of nanocomposite foams were investigated. Addition of GnP to linear PP decreased cell density and made cell distribution uniform due to its functionality of crystal nucleating agent While in branched PP foams, it was seen by the dynamic observation that GnP acted as bubble nucleating agent, resulting in a fine cell size and increasing the foam density. Nanocellular foams exhibited better mechanical properties than bimodal but the limited expansion ratio. However, some bimodal foams presented comparable mechanical properties to non-foamed samples, in spite of high expansion ratio. Addition of graphene nanoplatelet to some extent improved the specific tensile modulus and strength of foams. The electrical conductivity of composites was reduced by foaming. However, this reduction was very significant in the case of bimodal foams.

In this paper, the influence of the outer diameter of multi-walled carbon nanotubes (MWCNTs) on the fracture behavior of epoxy adhesives was investigated experimentally and numerically. MWCNTs with three different outer diameters of less than 8, 20-30 and 50-80 nm were used to toughen the epoxy adhesive. Double Cantilever Beam specimens were tested to determine the fracture energy. The results indicated that improvement in the adhesive fracture resistance by introducing MWCNTs was considerably dependent on the outer diameter of MWCNTs. Toughening the epoxy adhesive by incorporating MWCNTs with 8 nm diameter improved the adhesive fracture energy three times higher compared to the MWCNTs with larger diameters. The SEM fractography of the fracture surfaces was also utilized to assess the governing fracture mechanisms occurred in the toughened epoxy adhesives. Moreover, a cohesive zone model was used for numerical investigation of the effect of the MWCNT diameter on the damage behavior of epoxy adhesives.

In this research, the microstructure and mechanical properties of glass fiber reinforced unsaturated polyester (GFRP) composites modified by styrene-butadiene rubber (SBR) and fumed silica were investigated. The fumed silica particles were dispersed uniformly in the nano-scale into the unsaturated polyester resin. Then, it was mixed with SBR and chopped glass fiber by bulk molding compound (BMC) process, and molded by compression molding. A full factorial design and analysis of variance (ANOVA) were utilized to study the effect of factors and their interactions on the mechanical properties. The addition of fumed silica nano-filler improved tensile, flexural and impact strength, tensile and flexural modulus but reduced the elongation at break. On the other hand, adding SBR content decreased flexural strength and modulus and tensile modulus of composites, but, increased elongation at break, impact and tensile strength. Based on optimization results, the SBR with 10 wt% and 3 phr for fumed silica has been selected as the optimum composite formulation providing the best strength-stiffness-toughness balance among the samples.

A new processing scheme for preparing highly dispersed expanded graphite/polypropylene (PP) nanocomposites has been developed in this study. To improve the degree of dispersion of graphite throughout the PP domains, the solid-state milling has been performed followed by low-temperature melt processing in the range of melting point (Tm) and the crystallization temperature (Tc) of PP. The solid-state milling followed by low-temperature melt mixing could drastically improve the degree of graphite dispersion in the matrix. As a result, the well-dispersed graphite/PP nanocomposite supported by transmission electron microscopy (TEM) exposed a higher degree of plastic deformation and energy to break in the tensile test. The higher degree of graphite dispersion achieved in this scheme was due to the increase of local shear force near the crystalline domains formed during low-temperature melt mixing. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1834–1839, 2013