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The effect of nanographene amount was evaluated relative to the physical, mechanical, thermal, and morphological features of wood-plastic composites. Composites were prepared using recycled polyethylene (high-density polyethylene), nanographene, and wood-flour. The amount of 80% of polymer matrix and 20% of wood flour, and nanographene at four weight levels of 0.5%, 1.5%, and 2.5%, were used. An internal mixture was utilized for making the samples. The results showed that with the 0.5 wt% increase of the amount of nanographene, the tensile and flexural strengths, the flexural and tensile modulus and the notched impact strength composite increased. With the addition of 2.5 wt% nanographene, these properties decreased. With the increase of the level of nanographene by 2.5 wt%, water absorption and the thickness swelling of the composite decreased. With the increase of the level of nanographene, the level of residue ash and thermal stability also increased. Scanning electron microscope images showed that the samples with 0.5 wt% nanographene had less holes and a smoother surface compared to the other samples.

The crystallization behavior of Poly(L-lactic acid) (PLLA) was studied in the presence of different nanoparticles. Two types of nanoparticles including Graphene oxide (GO) and Poly(ethylene glycol) (PEG)-grafted Graphene oxide (GO-g-PEG) were examined at various concentrations. SEM images revealed an improvement in the dispersion of nanoparticles after grafting PEG chains on the GO surface. Kinetic analysis and morphological observations indicated that GO-g-PEG has enhancing effects on the crystallization rate and nucleation ability of PLLA. This was attributed to the improved dispersion of GO-g-PEG in the PLLA matrix. The contribution of nucleation and growth steps was examined using generalized Lauritzen-Hoffman model.

Nowadays, polymer-based foams have gained much attention for absorption of electromagnetic wave due to their desirable properties such as wide absorption band, low reflection and also light weight. However, the impact of the foam morphology including shape, cell size and its structure as open and close cell, on the electromagnetic wave has been rarely investigated. In this study, the operational conditions for manufacturing various structured foams based on poly(methyl methacrylate)/graphene nanoparticle sheets have been optimized for investigating the effect of cellular structure on the characteristics of electromagnetic wave as well as electrical properties. Hence, a foaming system with great controllability and repeatability has been employed. It should be noted that this system is capable of stabilizing the cellular structure with millisecond accuracy during and after the pressure drop. The close cell structured foam showed a decrement in the electrical and electromagnetic properties with increasing the cell size and shifting from spherical to polygonal shape. Moreover, the results related to the prepared open cell structured foams with similar cell size and density to close cell ones, have demonstrated higher absorption characteristics for microcellular open cell foams while shielding was better in close cell counterparts.

The present study reports the morphological, mechanical, and sound absorption properties of polycarbonate-based nanocomposites containing nanosilica (0.3 and 0.6 wt%). To this end, the specimens we...

In this study, nanocomposite samples based on polymethylmethacrylate/poly (lactic acid)/graphene nanoplatelets (PMMA/PLA/GNP) were prepared via melt mixing method and thermal multiple shape memory was induced. Dynamic mechanical thermal analysis results showed that two polymers are miscible in the selected blend ratio (70/30, 50/50, 30/70 w/w; PLA/PMMA) and was not affected by the presence of GNP (1 and 2 phr). The dispersion and distribution status of GNP were observed by scanning electron microscopy (SEM). The co-continuous morphology was dominant in all samples due to complete miscibility of two phases. Multi-shape memory was induced using a tensile test machine equipped with the hot oven at 65 and 100 °C. The results revealed that shape recovery was affected by the presence of GNP at high temperature(for example increasing from 93.34% in neat PLA/PMMA(50/50 w/w) to 96.67% in the sample containing 1 phr of GNP) while there was no considerable effect at low temperature. At high temperature, amorphous phases of two polymers are extended and un-melted chains of PMMA can be as hard segment and leads to good recovery. Due to nucleation and reinforcement effects of GNP, the higher degree of crystallization of PLA and higher storage modulus were obtained and caused to the enhancement of the shape fixity values at the presence of GNP.

The main goal of this paper was to investigate transparency and mechano-acoustic properties of poly methyl methacrylate (PMMA)/polycarbonate (PC) based nanocomposites, reinforced with silica (SiO2), zinc dioxide (ZnO), and titanium dioxide (TiO2) nanoparticles. For this purpose, morphological, transparency, acoustical and mechanical tests were carried out on the specimens, prepared by melt-compounding method in a twin-screw extruder. The morphological test results confirmed uniform dispersion of the nanoparticles in the polymer matrix. The results also revealed that transparency of the PC and PMMA nanocomposites, characterized by the degree of light transmittance, was decreased by adding 0.3 wt% of the nanoparticles. Also, tensile modulus of the nanocomposite specimens was higher than that of neat PC and PMMA. Unlike the neat PC specimens, tensile strength showed a decrease in PMMA specimens. The presence of nanoparticles in the composites decreased mobility of polymer chains and consequently, reduced elongation at break in the specimens. After surface roughening process, noise absorption coefficient in PC/PMMA nanocomposite specimens (PCSI3-R, PMSI3-R, and PMZN3-R) showed a higher absorption coefficient than the other specimens in the dominant frequency of traffic noise (500 Hz). As conclusion, roughening the surface of materials would be one of the most important factors enhancing the absorption coefficient of some of the nanocomposites in the middle frequency. The rough surface of particles in the base matrix increases the absorption coefficient of the materials, especially in the frequency of 500 Hz, as the dominant frequency of noise traffic. The suggested materials are predestinated to be appropriate in building industry, particularly in the structure of noise barriers.

Poly(ethylene oxide) (PEO) nanocomposites containing pristine or functionalized graphene nanoplatelets (FGnP) prepared via solution blending and thermal and mechanical properties of nanocomposites were investigated. Chemical functionalization of graphene nanoplatelets was conducted through an amidation reaction between carboxylic acid groups of acidified graphene and hydroxyl groups of polyethylene glycol (PEG). An interfacial linkage and a good dispersion of FGnP was observed via scanning electron microscope (SEM). Differential scanning calorimetry (DSC) analysis revealed that the degree of crystallinity of samples decreased by addition of graphene nanoplatelets, while the size of spherulites increased as indicated by polarized optical microscope (POM). A lower degree of crystallinity and larger spherulites were detected in the case of FGnP. Filler/matrix interfacial adhesion was also remarkably influenced the mechanical properties of PEO as an effective reinforcement of matrix obtained upon the addition of FGnP nanosheets compared to untreated graphene.

In this study, a novel thermally actuated triple-shape memory polymer (triple-SMP) based on poly( l -lactide) (PLA)/poly( e -caprolactone) (PCL)/graphene nanoplatelets (GNps) nanocomposite was prepared by facile solution mixing method and the design of which was based on two well-separated melting temperatures. In order to improve the dispersion of GNps in the matrix, functionalization reactions were carried out on the GNPs surface. Functionalization was confirmed by various techniques including FTIR, Raman and TGA analysis. TEM micrographs revealed an exfoliated morphology for the functionalized GNps (FGNps) and a homogenous dispersion in the matrix. The crystallinity behaviour of nanocomposites was investigated by DSC and variable temperature XRD (VT-XRD) analysis and an increase in crystallinity was observed. Dynamic mechanical analysis (DMA) showed that the presence of FGNps improves the fixity and recovery ratios because of increase in crystallinity and thermal conductivity. The best shape memory behavior was obtained for PLA50/PCL50/FGNp 1.5 nanocomposite.

Nowadays, developing biocompatible shape memory polymers is among major expanding topics in medical applications. In this study, novel biocompatible polyurethane/graphene nanoplatelet (PU/GNp) nanocomposites were synthesized from poly(e–caprolactone)diol (PCL diol)/Castor oil and Hexamethylene diisocyanate (HDI) through in situ polymerization. Three different %wt. of GNp were incorporated into the polyol mixtures to monitor the effect of nano fillers on the shape memory behavior of PUs. The chemical structure of nanocomposites was studied by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) were used to evaluate the nanocomposites properties. GNp incorporation affected the bulk morphology as well as thermal properties and crystallinity. Dynamic mechanical thermal analysis (DMTA) revealed the higher elastic modulus values for nanocomposites compared to the pure PU. The biocompatibility of PU/GNp nanocomposites was investigated via MTT assay. Finally, based on shape memory studies, the higher crystallinity, and improved elastic modulus of the nanocomposites resulted in their excellent shape fixity (about 91-96%) and shape recovery (95-99%) behaviors. According to the results, the prepared PU/GNp nanocomposites can be considered as potential choices for applicable shape memory devices for biomedical applications. POLYM. COMPOS., 2017. © 2017 Society of Plastics Engineers

As the everyday use of petroleum-based products has raised environmental concerns, there is an urgent need to replace them with green materials. In this work, an eco-friendly, highly conductive, flexible silver nanowire/poly (lactic acid) film has been fabricated through a simple casting method by embedding the silver nanowires (AgNWs) below the surface of the poly lactic acid (PLA) matrix. The fabricated film has a high optical transparency of 89.5% with a sheet resistance of 64.8 Ω/□ and a figure of merit (FoM) of 4.92 × 10 −3 Ω −1 which is comparable to that of indium tin oxide (ITO). These films demonstrate excellent flexibility, great adhesion, smooth surface with root mean square (RMS) roughness of 11.7 nm and high mechanical properties with tensile strength and Young's modulus of 39.8 (MPa) and 1.6 (GPa). The results obtained from different testing methods show that the AgNW/PLA nanocomposites are potential candidates in flexible electronics and optoelectronics.

Rheological, dielectric and electromagnetic interference shielding (EMI) properties of multi-walled carbon nanotube (MWCNT) and graphene nano-pellets (GNP) poly(methyl methacrylate) (PMMA) composites were compared. The GNP readily formed a polymer-mediated filler network compared to MWCNT, as evidenced by rheological tests. Immobilization of the interphase region was higher under the influence of the GNP in comparison with the MWCNT. However, the MWCNT-filled samples showed superior dielectric properties in respect to the GNP-filled samples. Particle shape and polymer chain dynamics in the interphase affected the dielectric properties. It was hypothesized that intensive immobilization, resulted from the GNP network, reduced free volume for segmental chain movements and dipole orientation along the applied electric field; which caused a decrease in dielectric permittivity. The MWCNT-filled samples were more efficient in electromagnetic wave absorption and reflection in comparison with the GNP-added samples which is ascribed to the one-dimensional geometry of nanotube aggregates and better tendency to form a conductive network with direct filler–filler contacts.

The effects of the amount of nanographene on physical, mechanical, and thermal properties and morphology of the wood-plastic composites were investigated. This wood-plastic was made using recycled high density polyethylene (HDPE), nanographene, and wood flour. Four weight levels, 0, 0.5, 1.5, or 2.5 wt.% of nanographene, were combined with 70% polymeric matrix and 30% lignocellulosic material with an internal mixer. The results showed that by increasing the amount of nanographene up to 0.5% by weight, the flexural strength, flexural modulus, and notched impact strength of the composite increased. After adding 2.5 wt.% nanographene, these properties were reduced. By increasing the amount of nanographene, both the amount of residual ash and the thermal stability increased. Study of the images from scanning electron microscope (SEM) showed that the samples containing 0.5% of nanographene had less pores and were smoother than other samples.

In this study, the isothermal crystallization of poly (lactic acid) (PLA) and its graphene-based nanocomposites (containing 0.5, 1, 2, and 3 wt% of graphene nanoplatelets – GNp) was studied at 135°C under quiescent and different presheared conditions (0.1, 0.3, 0.5, 1.1, and 1.8 s for 60s). Induction time of crystallization was determined from the plot of storage modulus versus time in time sweep test. Results showed that increase in GNp content decreased the induction time significantly. The preshear flow did not significantly affect the induction time of PLA containing 0.5 wt% of GNp and neat PLA. However, an increase in the intensity of preshear for graphene-based nanocomposites containing 1, 2, and 3 wt% of GNp first decreased the induction time and then increased it. The induction time also decreased with increase in the duration of shear flow.

Wood plastic composites have received increasing attention during the last decades, because of many advantages related to their use. However the durability of Wood plastic composites after ultraviolet exposure has become a concern. In this research, hybrid nanocomposites of polyethylene and woodflour with different concentrations of nanoclay were fabricated using melt compounding followed by injection molding. Specimens were exposed for 2000 h to ultraviolet radiation and moisture cycling in a laboratory weathering device to simulate the effects of exposure to sunlight and rain. Physical and mechanical properties of the nanocomposites were evaluated, before and after weathering. The results indicated that the water absorption of wood plastic composites increased after weathering but nanoclay reduced the intensity of weathering to some extent, through decreasing of water absorption. Also results showed that weathering decreased modulus of elasticity values, however good dispersion of clay layers resulted in fewer drop of modulus of elasticity values. Fourier transform infrared spectroscopy showed that lowest carbonyl index is related to the nano wood plastic composites with 2wt% nanoclay. Also X-Ray diffraction patterns revealed that intercalation morphology has been formed for nano particles.

In this study, a temperature sensitive shape memory polymer (SMP) system based on polylactic acid (PLA) has been developed and the effect of graphene nanoplatelets (GNPs) on the shape memory properties was evaluated. Dispersion of GNPs in PLA was improved with the aid of a zwitterionic surfactant. X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that the surface modified graphene nanoplatelets (SMGNPs) were exfoliated and homogenously dispersed in the PLA matrix due to enhancement of the polymer-graphene interaction. Mechanical properties of the samples namely stiffness and elasticity were increased upon incorporation of graphene nanoplatelets accompanied by their good dispersion in the PLA matrix. Furthermore, differential scanning calorimetry (DSC) revealed that the nucleation effect of graphene promote the crystallization and noticeably enhanced the degree of crystallinity. Finally, prominent mechanical properties along with high degree of crystallization due to fine dispersion of surface modified graphenes, resulted in drastic improvement in shape memory performance.

In this study, the effect of graphene nanoplatelets (GNPs) on the shape memory properties of poly(L-lactic acid) (PLLA) was studied. In addition to thermal activation, the possibility of infrared actuating of thermo-responsive shape mem- ory PLLA/GNPs nanocomposite was investigated. The incorporated GNPs were expected to absorb infrared wave's energy and activate shape memory PLLA/GNPs. Different techniques such as differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), field emission gun scanning electron microscope (FEG-SEM) and dynamic mechanical thermal analysis (DMTA) were used to characterize samples. DSC and WAXD results indicated that GNPs augmented crystallinity due to nucleating effect of graphene particles. GNPs improved both thermal and infrared activating shape memory properties along with faster response. Pure shape memory PLLA was slightly responsive to infrared light and its infrared actuated shape recovery ratio was 86% which increased to more than 95% with loading of GNPs. Drastic improvement in the crystallinity was obtained in nanocomposites with lower GNPs contents (0.5 and 1 wt%) due to finer dispersion of graphene which resulted in more prominent mechanical and shape memory properties enhancement. Infrared activated shape memory PLLA/GNPs nanocomposites can be developed for wireless remote shape control of smart medical and bio-systems.

Developments in the dispersion of graphene nanoplatelets in polylactic acid were achieved with the aid of a zwitterionic surfactant. The graphene nanoplatelet surface modification was tracked by Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and elemental analysis. Different amounts of graphene nanoplatelets and surface-modified graphene nanoplatelets (3 and 6 phr) were used to prepare the polylactic acid nanocomposite through a solvent-mixing method. It was found that surface-modified graphene nanoplatelets were exfoliated and homogeneously dispersed in the polylactic acid matrix. Better dispersion of surface-modified graphene nanoplatelets compared with graphene nanoplatelets was due to enhancement of the polymer–graphene interaction induced by the zwitterionic surfactant. The shape memory properties of nanocomposites were evaluated using thermomechanical analysis. The obtained results revealed that the shape memory performance of nanocomposite samples wa...

We investigate the effect of graphene localization on the morphology and properties of Polyamide 6 (PA6)/Polyolefin elastomer (POE) blends. Two systems with different compositions were studied: (i) 60/40 (a composition near phase inversion) and (ii) 80/20 (a highly asymmetric composition). In this study, we demonstrate that the migration behavior of graphene is strongly dependent on its dispersion state, which is determined by mixing order. We show that the neat 60/40 (PA6/POE) blend has an unstable co-continuous morphology which breaks up over time during annealing to a droplet-matrix morphology with POE being the continuous phase. The addition of 3 wt% graphene leads to co-continuous morphologies independent of mixing order. In the case of 80/20 systems, preparation of nanocomposites with a POE master batch resulted in elongated POE dispersed domains which becomes a co-continuous morphology at higher level of graphene content (1.5 wt%). However, we observed a decrease in the continuity of the POE phase in the nanocomposite containing 3%wt of graphene due to a reduction of coalescence. Our rheological and electrical measurements revealed that the graphene formed a stronger percolated structure in 80/20 blend containing 3 wt% of graphene in comparison to 60/40/3 nanocomposites, which resulted in lower electrical resistivity. The electrical percolation threshold in this system is 0.66 wt% which demonstrates that using graphene to induce co-continuity in a highly asymmetric composition is a promising approach to design electrically conductive blends with a very low percolation threshold.

A “knotted approximation” (KA) is proposed in order to predict the Young’s modulus of blend-based polymer nanocomposites (BPNs). The BPN system is considered to have two fundamental constituents, a binary polymer blend and an effective phase (nanoparticle-containing phase). Therefore, the KA model was designed to combine the results of two different models which govern different hypothetical constituent elements of BPN systems. This was very helpful to enhance the accuracy of KA model by controlling parameters which affect each model. Furthermore, the application of different models was investigated to obtain the most efficient mathematical framework. Despite simple methodology of the KA model, the consistency of governing models on each constituent was considered as an important factor. Based on the wetting coefficient, the nanoparticles were considered to be in an individual phase of the binary polymer blend, so it could satisfy the presumptions of the effective phase. Considering the strong influences of nanoparticles on the percolation threshold of polymer phases, a general method was proposed to consider this important phenomenon. As a result, combining the fundamental concepts of KA constituent models enabled it to involve a wide range of critical parameters related to the BPN systems, e.g., morphology, random orientation of nanoparticles, nanoparticle/polymer interphase, phase inversion, polymer phase percolation threshold, etc. To evaluate the accuracy of KA model, different samples of polyamide/polyolefin elastomer/Cloisite 30B were prepared and subjected to stress–strain test in order to compare the predicted and actual values of BPNs Young’s modulus.

A correlation between molecular structure parameters and rheological behavior was determined for three different grades of high-density polyethylene (HDPE). The molecular structure parameters including number-average molecular weight (M n ), weight-average molecular weight (M w ), molecular weight distribution (MWD) and branching index were characterized by gel permeation chromatography (GPC). Moreover, a fast and easy method for investigating side chain branching using Fourier transform infrared (FTIR) spectroscopy was discussed. The rheological characterizations of both linear and non-linear viscoelastic regions were performed by a modular compact rheometer (MCR) in the dynamic mode. Zero shear viscosity (η 0), relaxation time, relaxation time distribution, stress relaxation modulus and damping function were obtained from the rheological characterization. Moreover, molecular weight distribution was calculated for each sample and compared with the GPC results. The GPC results confirmed broad molecular weight distribution for all three HDPE samples. The relationship between zero shear viscosity and molecular weight at 180 °C was found as $$\eta_{0} = 2.5 \times 10^{ - 14} M_{w}^{3.6}$$ and for zero shear viscosity and MWD at 180 °C was found as $$\eta_{0} = 1.6 \times 10^{ - 15} M_{w}^{3.6} \left( {\frac{{M_{w} }}{{M_{n} }}} \right)$$ . By choosing the mixing parameter (β) value of 0.73, the values of molecular parameters obtained from the rheology and GPC tests were significantly accommodated. Furthermore, it was found that the damping function of type C was an appropriate type for the polyethylenes of selected broad MWD.

Excessive noises frequently disturb people by fatigue, reduced working efficiency and health system disorders. An efficient method to reduce noise is to find and apply sound insulation materials. Research and development on nanocomposites as a sound insulation material are quite advanced. In this study, acrylonitrile–butadiene–styrene (ABS)/nanoclay nanocomposites were fabricated at 2, 4, 6 and 8 wt% of organically modified clay using a twin screw extruder. Sound transmission loss (STL) was determined by impedance tube device to evaluate the sound insulation properties of the samples. The results showed that ABS/clay (4 wt%) and (8 wt%) could improve the STL of virgin ABS by 6–20 and 4–5 dB at high (1600–6300 Hz) and low (700–1600 Hz) frequency ranges, respectively. In addition, the physical and mechanical characteristics of the nanocomposites were evaluated at various filler loadings to compare with sound insulation efficiency. Modulus of elasticity was improved in presence of nanoclay in accordance with increasing STL at low sound frequency. The surface density of samples varied slightly with increases in nanoclay content; therefore, it could not be a leading parameter to influence STL at all frequencies. State of dispersion in nanocomposites was investigated using X-ray diffraction and transmission electron microscopy. It was found that a sample containing 4 wt% of nanoclay showed the best dispersion accompanied by the best soundproofing efficiency.

INTRODUCTION: Hearing protection devices are one of the primary noise reduction tools in developing countries. This study is intended to produce and apply acrylonitrile butadiene styrene (ABS)/clay nanocomposites to fabricate a laboratory single cup earmuffs and then compare it with double cup and single cup pure ABS earmuffs in terms of noise attenuation performance and comfort. In addition, the noise attenuation performance of single cup pure ABS earmuffs is compared with double cup pure ABS earmuffs. METHODS: ABS/nanoclay filament was fabricated using a twin screw extruder. A three dimensional (3D) printing machine and a 3D model of earcup, designed by solid work software, were applied to print single and double cup earmuffs using ABS/nanoclay composite and pure ABS filaments. Finally, using an acoustic test fixture, objective noise attenuation test was performed on three different types of earmuffs, including with and without nano material and a secondary cup. Moreover, earmuffs weight was measured as a comfort component. RESULTS: Insertion loss and calculated noise reduction rating (NRR) of single cup ABS/nanoclay earmuffs (NRR=19.4 dB) and double cup pure ABS earmuffs (NRR=18.93 dB) were improved in comparison with single cup pure ABS earmuffs (NRR=15.7 dB). Additionally, both single cup earmuffs were significantly lighter than double cup earmuffs. Although single cup nano and double cup earmuffs had nearly the same attenuation performance, single cup nano earmuffs were 74 gr lighter than double cup earmuffs, so with reference to comfort, single cup nano earmuffs will probably be more acceptable. CONCLUSIONS: From this survey it might be concluded that, even though single cup ABS/nanoclay earmuffs was lighter than double cup pure ABS earmuffs, it had approximately more attenuation performance in comparison with double cup pure ABS earmuffs. Consequently, users are probably more prone to wear light- weight single cup ABS/nanoclay earmuffs as a result of improved comfort. In short, ABS/nanoclay composite can be considered a good choice in products with the necessity of high acoustic performance and low weight. Call Send SMS Add to Skype You'll need Skype Credit Free via Skype

In this study, the ternary blends containing microporosity based on poly(l-lactic acid) (PLLA), poly(e-caprolactone) (PCL) and polyethylene oxide (PEO) were prepared using an internal mixer via a polymer leaching technique. The particulate leaching is the most widely used technique to create porosity. To introduce macroporosity besides micropores, NaCl particulates were incorporated into the ternary blends at 40–80 wt % and macropores were formed by particulate leaching. Samples porosity were evaluated by calculating the ratio of porous scaffold density (ρ*) to the non-porous material density (ρ s). The results showed that with an increase in NaCl particulate content, the amount of porosity increased and the distribution of pore size was gradually transformed from monomodal into bimodal form. The porosity plays a key role in governing the compression properties. Mechanical properties are presented by Gibson–Ashby model. Compressive modulus decreased with an increase in NaCl particulate concentration due to the increase in porosity and thinning of pore wall that caused rupture at these weaker spots. Blending and forming of the bio-scaffold can be made using conventional polymer processing equipment. This process seems promising for a large-scale production of porous bio-scaffold of many sizes through an economic method.

Ternary blends of poly(L-lactic acid) (PLLA), poly(caprolactone) (PCL) and polyethylene oxide (PEO)were produced with different concentrations of components via melt blending. By leaching the PEO from the samples by water, porous materials were obtained with potential application for bio scaffolds. Sample porosity was evaluated by calculating the ratio of porous scaffold density(p*) to the non-porous material density(p). Highest porosity (51.42%) was related to the samples containing 50 wt%.of PEO. Scanning electron microscopy(SEM) studies showed the best porosity resulted by decreasing PLLA/PCL ratio at constant concentration of PEO. Crystallization behavior of the ternary blend samples was studied using differential scanning calorimetry(DSC). ResuIts revealed that the crystallinity of PLLA was improved by addition of PED and presented by Gibson- Ashby model.

Recently, for reasons both economical and environmental, recycling of waste tires based on (styrene butadiene rubber)/(natural rubber) (SBR/NR) has been widely considered. Response surface methodology (RSM) has been used to predict SBR/NR devulcanization behavior in a co-rotating twin screw extruder. In this study, variable parameters were barrel temperature, screw configuration, and content of devulcanization agent. A Box-Behnken design for the three variables, at three levels, was chosen. The sol fraction of devulcanized rubber, Δtorque (difference between maximum and minimum curing torque), and mechanical properties of revulcanizate samples were considered as the responses. The results indicated that an increase of devulcanization agent content at a certain temperature caused the sol fraction to increase. Samples including a higher sol fraction showed a lower cross-link density. Sol fraction for high shear rate screw configuration was lower than that for other screw configurations. Tensile strength of revulcanized rubber showed a decrease with a rise of devulcanization temperature. Moreover, a relationship connecting the residence time in the extruder with stagger angle and length of different kneading blocks were obtained. J. VINYL ADDIT. TECHNOL., 19:65–72, 2013. © 2013 Society of Plastics Engineers

Biodegradable nanofibrous mats fabricated by electrospinning are commonly used in tissue engineering, however, lack of essential mechanical properties of such nanofibers is a challenging issue. In this work, vinyltrimethoxysilane (VTMS) was grafted onto poly (lactic acid) (PLA) and the silane grafted PLA was subsequently applied in electrospinning process. Electrospun nanofibrous mats based on PLA/nanocrystalline cellulose (NCC) and PLA-g-silane/NCC nanocomposites were fabricated and immersed in hot water (70 °C) for crosslinking of silane grafted PLA. It was found that introducing NCC to the samples cause to reduction in fiber diameter and the other hand the silane crosslinking of PLA increase the mean fiber diameter. DSC thermograms also revealed that silane grafting caused a reduction in mobility of polymer segments, and consequently reduction of crystallinity. On the contrary, the NCC in the PLA-g-silane samples effectively influenced the crystal nucleation, while in the PLA nanofibers the nucleation was lower. The impact of NCC on tensile strength enhancement of samples was notable. The results suggested that the chemical crosslinking remarkably improves the mechanical properties of PLA nanofibers. Furthermore, biocompatibility of such modified nanofibers was also evaluated through cytotoxicity results, therefore the modified PLA nanocomposite can be considered as a practical candidate for hard tissue engineering applications.

Poly(l-lactic acid) (PLLA)/graphene nanoplatelets (GnP) nanocomposites were prepared through solvent casting and coagulation methods. The better dispersion of graphene was achieved by ultrasounds and its effect on crystallinity, thermomechanical and electrical properties of PLLA were studied and compared in both methods. Differential scanning calorimetry (DSC) was used to investigate the crystallinity of PLLA and its composites. Field emission gun scanning electron microscope (FEG-SEM) and wide-angle X-ray scattering (WAXS) were employed to characterize the microstructure of PLLA crystallites. Dynamic mechanical thermal analysis (DMTA) was performed to study the thermomechanical properties of the nanocomposites. FEG-SEM images illustrated finer dispersion of GnP in samples obtained by coagulation method with respect to solvent casting method. Graphene imparted higher electrical conductivity to nanocomposites obtained by solvent casting under ultrasound due to better formation of graphene network. DSC thermograms and their resulting data showed positive effects of GnP on crystallization kinetics of PLLA in both methods enhanced by the nucleating effect of graphene particles. Meanwhile, the effect of GnP, as nucleating agent, was more prominent in samples produced by coagulation method without utilization of ultrasounds. WAXS patterns represented the same characteristic peaks of PLLA in nanocomposite specimens suggesting similar crystalline structure of PLLA in presence of graphene, and the intensified peaks of nanocomposites compared to neat PLLA confirmed the DSC results regarding its improved crystallinity. Graphene increased storage modulus in rubbery region and glass transition temperature of nanocomposites in the coagulation method due to restricted mobility of PLLA chains.

NBR/phenolic interpenetrating networks (IPNs) offer a wide variety of mechanical and physical properties at moderately high temperature. This temperature stability along with oil and fuel resistance property has made IPNs appropriate candidates for various applications. In the present work, NBR compounds containing 5, 7 and 12 phr of Novolac, as a curable phenolic resin was formulated using a two-roll mill. Low and high acrylonitrile NBR; KNB 35L and Europrene N4560 were selected in the compound and the same condition of mixing was applied in the blend preparation stage. Curing test, followed by a cooling period and the stress relaxation test were carried out consecutively and automatically in a rubber process analyzer. The samples presented various relaxation times. The relaxation curves were well estimated by Maxwell model and the Prony coefficients were determined. Furthermore, compression test was performed on the samples, so that the set or permanent deformation of each sample was measured. The results of both tests have indicated that by adding phenolic resin into the NBR matrices, the viscoelastic behavior of the compounds become more elastic, to the detriment of the viscous component. This phenomenon would be due to IPN formation in the compounds. In addition, by increasing the phenolic resin content in the compounds, the difference between maximum and minimum torque (M H − M L) value became greater, which is an indicator of higher cross-link density and IPN formation. Swelling test results confirmed more extensive cross-links in the compounds by addition of more resin into the compound.

Experimental results are presented for nanocomposite foams based on unplasticized poly(vinyl chloride)/(wood flour)/(multi-wall carbon nanotubes) (PVC/WF/MWCNTs). The nanocomposite samples were prepared in an internal mixer and foamed via a batch processing method using compression molding. Nanoparticles were functionalized by sodium hypochlorite solution, and the functionalization process was monitored by Fourier-transform infrared spectroscopy. The effects of MWCNTs (both neat and functionalized) and blowing agent concentration on the morphological properties (cell size and cell density) and mechanical properties (tensile and flexural strength) of the foam samples were studied. The results revealed that foam cell sizes decreased and cell densities increased with addition of MWCNTs. The dispersion of nanoparticles in the PVC medium was increased by functionalization, and the morphological properties of the foams containing functionalized nanoparticles were improved. Density of nanocomposite foams decreased more with functionalized MWCNTs as compared to other samples. Chemical blowing agent concentration had no significant effect on sample density. Mechanical properties of the samples were improved by using functionalized MWCNTs in comparison with those of foams without this component. J. VINYL ADDIT. TECHNOL., 18:161–167, 2012. © 2012 Society of Plastics Engineers

Recently, the use of nanoparticles in Wood Plastic Composites (WPCs) has been considered by researchers. In this study, Multi-Walled Carbon Nanotubes (MWCNTs) were compounded with PVC, wood-flour, and foaming agent in an internal mixer. The wood flour amount was constant at 40 phr. For CNT and chemical foaming agent , different levels of 0, 1, 2 phr and 0, 3, 6 phr were considered respectively. The samples were foamed via batch process using a compression molding machine at 180°C. Morphology, density, water absorption, thickness swelling, and tensile properties of foamed composites were evaluated as a function of CNT and chemical foaming agent contents. The experimental results indicated that in the presence of CNT, cell density increased and cell size decreased. Density of the foamed composites was not affected by chemical foaming agent contents. Water absorption and thickness swelling of samples were decreased as compared with wood plastic composite without CNTs. Also, the maximum tensile strength and modulus were increased by up to 20% and 23% respectively.

This paper studies the morphology and tensile properties of nanocomposite foams of blends of low-density polyethylene (LDPE) and poly(ethylene-co-vinyl acetate) (EVA). Preparations of LDPE/EVA nanocomposites were conducted in an internal mixer, and then samples were foamed via a batch foaming method. Morphology of the nanocomposite blends and nanocomposite foams was studied by X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. Morphological observations showed that nanoparticle dispersion in the polymeric matrix was affected by the blend ratio in a way such that EVA-rich samples had a better dispersion of nanoclay than LDPE-rich ones. In addition, the tensile properties of the nanocomposite foams were related to different variables such as blend ratio, clay content, and foam density. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers

In this research, composites based on polypropylene (PP), beech wood flour, and organomodified montmorillonite (OMMT) were prepared and characterized for their properties. The blend nanocomposites were prepared by melt mixing of PP/WF at 50% weight ratios with various amounts of OMMT (0, 3, and 6 per hundred compounds (phc)) in a Hakee internal mixer. Then the samples were made by injection molding. The influence of organomodified montmorillonite contents on clay dispersion, physical and mechanical properties of PP/wood flour composites were investigated. Results indicated that the flexural strength and modulus, tensile strength and modulus increased by addition of 3 per hundred compounds (phc) of organomodified montmorillonite (OMMT), but decreased with 6 phc OMMT addition. However, impact strength, water absorption and thickness swelling of the composites decreased with increasing nanoclay loading. X-ray diffraction patterns (XRD) and transmission electron microscopy (TEM) revealed that the nanocomposites formed were intercalated. Also, morphological findings showed that samples containing 3 phc of OMMT had higher order of intercalation.

This article presents the correlation between rheology and morphology of nanocomposite foams of low-density polyethylene (LDPE), ethylene vinyl acetate (EVA), and their blends. LDPE/EVA nanocomposites were prepared via melt mixing and then foamed using batch foaming method. To assess the rheological behavior of polymer melts, frequency sweep and creep recovery tests were done. Morphology of the samples was also studied by scanning electron microscopy and X-ray diffraction. The results showed that with increase in clay content, storage modulus, complex and zero shear viscosities will be increased, which affect the foam morphology. In addition, elasticity plays an important role in foaming process, in a way that samples with more elasticity percentage have the highest cell density and the lowest cell size. POLYM. COMPOS., 31:1808–1816, 2010. © 2010 Society of Plastics Engineers.

High density polyethylene/tricalcium phosphate/ultra high molecular weight polyethylene (TCP/HDPE/UHMWPE) Nanocomposite as an orthopedic biomaterial (with better properties toward TCP/HDPE composite) was obtained. To evaluate the capability of this nanocomposite as a material for bone tissue replacement, mechanical and biological assessments were performed. In this study, nanosize β-TCP powders with average grain size of 100 nm were synthesized by chemical precipitation method and characterized by means of X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). To evaluate the mechanical properties of this biomaterial, tensile properties were obtained for the material. Results showed that by increasing the weight percentage of β-TCP, the elastic modulus increases, elongation at yield decreases and with no significant change in tensile strength. SEM micrographs of cryogenic fracture surface of samples indicated that distribution of nano powders in matrix is homogeneous. In vitro biological evaluations on the samples were done by performing cytotoxicity (MTT assay), alkaline phosphatase enzyme, and cell attachment tests. In all of the tests, osteoblast cells were used. Results of biological tests showed that the samples are biocompatible and they have no toxicity. Also, SEM observations demonstrated that the cells can attach to surface of nanocomposite samples, which reveals osteoconductivity of the surface. POLYM. COMPOS., 31:1745–1753, 2010. © 2010 Society of Plastics Engineers.

In this work, basic mathematical models and response surface graphs have been used to illustrate the relationship between mixing parameters in internal mixer and properties of the SBR (styrene butadiene rubber)/organoclay composites. Using a Box-Behnken statistical design experiment methodology, the effects of mixing temperature (80-140°C), mixing time (4-12 min) and nano filler amount (3-9 phr) in SBR nanocomposites on the properties (tensile properties, scorch time and Mooney viscosity) were evaluated. It was found that the mixing parameters (time and temperature) have the predomi- nant role in properties and morphology of nanocomposite. The R 2 values (the R 2 values indicate the degree of agreement between the experimental results with those predicted by model) of all responses were above 0.85. Increasing temperature and mixing time facilitated a better organoclay dispersion which resulted in a better tensile property. With increase in nan- oclay amount in composite the scorch time and Mooney viscosity decreased. The morphology of nanocomposite was stud- ied by XRD (X-ray diffraction) and TEM (Transmission electron microscope). Intercalation and exfoliation of the nanoclay were observed for samples with higher temperature and longer mixing time. Due to thermal degradation of the rubber matrix at 140°C, tensile properties of the nanocomposite were decreased.

Styrene-(maleic anhydride) copolymer (SMA) compatibilized blends of acrylonitrile-butadiene rubber (ABS) and polyamide 6 (PA6) with a variety of compositions and compatibilizer levels were prepared at various screw speeds in a corotating twin screw extruder. A Box–Behnken model for three variables, with three levels, was chosen as an experimental design, and the mechanical properties of the blends were considered as the responses. Each response was analyzed and formulated versus the considered factors by the use of response surface methodology. Impact resistance increased with increased SMA concentration and reduced screw speed. In compatibilized samples, with an increase in PA6 content, higher impact resistance was observed. Increasing PA6 content and SMA concentration, as well as decreasing screw speed, gave improvements in both tensile and flexural strengths. In each case, all of the correlations among factors were studied. Grafting of SMA was proved by detecting the graft copolymer (SMA-PA6) formed through extraction in formic acid and FTIR spectroscopy. Compared with uncompatibilized blends, compatibilized samples displayed more uniform and finer particle sizes, thereby proving the compatibilizing effect of the graft copolymer. The asymmetry trend in dispersed particle size before and after the phase inversion became more differentiated in the presence of the compatibilizer. Adding SMA lowered the phase inversion composition (based on PA6), whereas higher screw speed increased it. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers

Polypropylene/wood flour composites with different nanoclay and maleic anhydride grafted polypropylene (PP-g-MA) contents were fabricated by melt compounding and then by injection molding. The mechanical properties, such as flexural modulus, tensile modulus, elongation at break, and impact strength, were evaluated. Results indicated that the flexural modulus, tensile modulus, and elongation at break increases with increase of nanoclay up to 3 phc at the same concentration of PP-g-MA, and then decreases. However, the impact strength of the composites decreases with increased nanoclay loading. Also, the effect of compatibilzer was positive in terms of enhancing the mechanical properties of the composites. The morphology of the nanocomposites has been examined by using X-ray diffraction and transmission electron microscopy. Morphological findings revealed that intercalation form, the sample with 3 phc concentration of clay, which implies the formation of the intercalation morphology and better dispersion than 6 phc, and the d-spacing of clay layers in the composite were improved in the presence of compatibilizer.

The rheological behavior of polypropylene/wood flour (WF) composite was investigated at constant temperature over a wide range of frequencies using a mechanical compact rheometer operated in the dynamic mode. The effect of WF content, particle size, and coupling agent on melt rheological properties were investigated. The melt rheological data in terms of complex viscosity (η*), storage modulus (G′), loss modulus (G″), and loss tangent (tan δ) were studied and compared for different samples. It was found that complex viscosity increases with increasing wood content and coupling agent. Compatibilization using coupling agent increased both storage modulus and loss modulus, but the variation of storage modulus is more. By increasing wood content storage modulus increases. Complex viscosity, storage modulus, and loss modulus showed a minimum value by increasing of wood particle size. Tan δ decreases with increasing of wood content. Cole–Cole plot indicated that relaxation process changes with addition WF, coupling agent, and using different mesh size of wood. The Han plots revealed the sensitivity of rheological properties with composition at constant temperature. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

In this work, four different material models were used, namely the Mooney–Rivlin, 5-term polynomial, Ogden and Arruda-Boyce models, for various compounds and processing conditions. The applicability of these models to nanocomposites and the best fit of these mathematical models were investigated against experimentally measured data. By applying different mixing times (4, 8, 12 min) and nanoclay contents (3, 6, 9 Phr) on the SBR nanocomposites, the different morphologies were monitored by XRD. The effects of mixing time and concentration of nanofiller were studied on the morphology obtained. The stress–strain behaviours of different morphologies (intercalated and exfoliated) were determined and then compared to the predicted data from the models. It was found that the Ogden model could be used for all rubber/filler nanocomposite structures at various filler loadings and mixing times while the Arruda–Boyce equation should be used with care since it cannot predict the true behaviour of all structure...

In this study, some experimental results of the peroxide-degradation process of polypropylene (PP) in a co-rotating twin-screw extruder to produce controlled-rheology polypropylene (CRPP) are presented. The peroxide was dicumyl peroxide (DCP) and the concentration of DCP was in the range 0–0.6 wt%. It was found that the rheological properties of PP change significantly during reactive extrusion. Melt flow index (MFI) increased with DCP concentration. Complex viscosity decreases with increasing DCP concentration. Degraded resins showed more Newtonian behavior than the origin resin. Cole–Cole plots indicated that mean relaxation times of CRPP resins are shorter than for virgin PP, and the relaxation mechanism is more uniform for modified samples. From dynamic rheological data, molecular weight (MW) and molecular weight distribution (MWD) were calculated. Results indicated that MW decreases and MWD becomes narrower with increasing peroxide concentration.

Hybrid composites of wood flour/kenaf fiber and polypropylene were prepared at a fixed fiber to plastic ratio of 40 : 60 and variable ratios of the two reinforcements namely 40 : 0, 30 : 10, 20 : 20, 10 : 30, and 0 : 40 by weight. Polypropylene was used as the polymer matrix, and 40–80 mesh kenaf fiber and 60–100 mesh wood flour were used as the fiber and the particulate reinforcement, respectively. Maleic anhydride and dicumyl peroxide were also used as the coupling agent and initiator, respectively. Mixing process was carried out in an internal mixer at 180°C at 60 rpm. ASTM D 638 Type I tensile specimens of the composites were produced by injection molding. Static tensile tests were performed to study the mechanical behavior of the hybrid composites. The hybrid effect on the elastic modulus of the composites was also investigated using the rule of hybrid mixtures and Halpin–Tsai equations. The relationship between experimental and predicted values was evaluated and accuracy estimation of the models was performed. The results indicated that while nonhybrid composites of kenaf fiber and wood flour exhibited the highest and lowest modulus values respectively, the moduli of hybrid composites were closely related to the fiber to particle ratio of the reinforcements. Rule of hybrid mixtures equation was able to predict the elastic modulus of the composites better than Halpin–Tsai equation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

In this study, a new compatibilizer was synthesized to improve the compatibility of the poly(lactic acid)/thermoplastic starch blends. The compatibilizer was based on maleic anhydride grafted polyethylene glycol grafted starch (mPEG-g-St), and was characterized using Fourier transform infrared spectroscopy (FTIR), dynamic mechanical thermal analysis (DMTA) and back titration techniques. The results indicated successful accomplishment of the designed reactions and formation of a starch cored structure with many connections to m-PEG chains. To assess the performance of synthesized compatibilizer, several PLA/TPS blends were prepared using an internal mixer. Consequently, their morphology, dynamic-mechanical behavior, crystallization and mechanical properties were studied. The compatibilizer enhanced interfacial adhesion, possibly due to interaction between free end carboxylic acid groups of compatibilizer and active groups of TPS and PLA phases. In addition, biodegradability of the samples was evaluated by various methods consisting of weight loss, FTIR-ATR analysis and morphology. The results revealed no considerable effect of compatibilizer on biodegradability of samples.

Due to desirable performance/cost properties, polypropylene (PP) is a suitable alternative for acrylonitrile butadiene styrene, polyvinyl chloride and polystyrene in packaging and automotive thermoformed articles. Because of low elasticity and poor melt strength, thermoforming of PP is difficult. In this study, the effect of blending of PP with high-density polyethylene (HDPE) and ethylene propylene diene monomer (EPDM) is presented. Ternary blends of PP/HDPE/EPDM were prepared using a laboratory co-rotating twin-screw extruder. Three levels of HDPE (10, 20, 30 phr) and EPDM (5, 10, 15 phr) and 10 phr of calcium carbonate were incorporated into the PP matrix. Thermoformability of the samples was investigated by hot tensile and rheological tests. The effects of blending and processing conditions, such as sheet temperature and strain rate, were studied. The stress–strain behavior showed that the ternary blending improved thermoformability of PP. In all blends, elastic modulus, load at yield and the post yield modulus decreased in comparison with original PP. Increasing temperature and crosshead speed (strain rate) had significant effects on the hot tensile properties. Rheological properties of the blends were studied using a rheometer. It was found that blends had higher elastic share and lower tan δ , hence more elasticity relative to conventional PP. All of the results confirmed that blending with HDPE and EPDM improved the thermoformability of PP.

The effect of the delignification of hornbeam fibers on the mechanical properties of wood fiber–polypropylene (PP) composites was studied. Original fibers and delignified fibers at three levels of delignification were mixed with PP at a weight ratio of 40:60 in an internal mixer. Maleic anhydride (0.5 wt %) as the coupling agent and dicumyl peroxide (0.1 wt %) as the initiator were applied. The produced composites were then hot-pressed, and specimens for physical and mechanical testing were prepared. The results of the properties of the composite materials indicate that delignified fibers showed better performance in the enhancement of tensile strength and tensile modulus, whereas the hardness of the composites was unaffected by delignification. Delignified fibers also exhibited better water absorption resistance. Notched impact strength was higher for delignified fiber composites, but it was reduced at higher delignification levels. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4759–4763, 2006

Microcellular foam is a new class of material with superior properties due to smaller cell size and higher cell density compared to ordinary foams. In this work, microcellular foam of PP/EPDM/Organoclay with supercritical nitrogen as physical blowing agent was prepared via batch process. Experimental design was carried out according to Box-Behnken method and the effects of saturation pressure and foaming times as well as organoclay content on nucleation and final foam morphology were studied using response surface methodology (RSM). Three levels of saturation pressure, nanoclay content, and foaming time were chosen. The mathematical model and response surface graphs have been used to illustrate the relationship between considered parameters and foam properties. The results revealed that cell density and average cell diameter were affected by nanoclay content and pressure. Cell density was in the range of 109-1010 cell/cm3. Larger average cell sizes were observed as a result of increasing foaming time. Classic nucleation theory was used to study the nucleation mechanism. Nanoparticles acted as nucleating agents and changed nucleation mechanism from homogenous to heterogeneous by decreasing nucleating free energy. In order to find out nucleating energy reduction, gas-polymer-nanoparticle contact angle (Ө), was calculated by measuring surface and interfacial free energies of neat polymers and nanoparticle. In addition, nucleation efficiency of organoclay was estimated and the results showed that despite low nucleating efficiency, nucleation is dominated by presence of nanoclay.

Hybrid composites of polyethylene/wood flour/nanoclay with different concentrations of nanoclay were fabricated using melt compounding followed by injection molding. Composites were weathered in a xenon-arc type accelerated weathering apparatus for 2000 h. Physical properties of the composites were evaluated by colorimetery and water absorption before and after weathering. Changes in surface chemistry were monitored using spectroscopic techniques. The results indicated that water absorption of the composites increased after weathering, but nanoclay can reduce the intensity of weathering to some extent by decreasing water absorption. Weathering increased the degree of color change and lightness of the samples; however, the lightness of the samples containing nanoclay was less than that of neat wood-plastic composites. Fourier transform infrared spectroscopy revealed a lower carbonyl index of composites containing nanoclay. X-ray diffraction patterns revealed that the nanocomposites formed were intercalated. The order of intercalation for samples containing 2 wt% nanoclay was higher than that of 4 wt% at the same maleic anhydride grafted polyethylene content, due to some agglomeration of the nanoclay.

Localization of organoclays between two phases of polyamide 6 (PA6)/maleic anhydride grafted ethylene-butene copolymer (EB-g-MAH) blends, prepared via melt mixing, was investigated as a function of organoclay type. Cloisite 30B, Cloisite 20A and Cloisite 15A were used as different types of organoclay. The influence of different blend compositions and clay contents were also studied. Contact angle measurements have been applied to determine surface tension of components and then to calculate the wetting coefficient which is a useful parameter for prediction of the organoclay location. In general, all organoclays were found to locate in the more hydrophilic polyamide 6 phase. However, for Cloisite 20A and Cloisite 15A transmission electron microscopy (TEM) observations revealed some organoclay layers in the EB-g-MAH phase. Phase structure and nanocomposite morphology were evaluated using scanning and transmission electron microscopy and small angle X-ray scattering (SAXS). Results indicated the formation of an exfoliated or an intercalated morphology in different samples. Dynamic-mechanical thermal analysis and thermal gravimetric analysis were used as an experimental probe to confirm the location of nanoclays predicted via wetting coefficient. The shifting of glass transition temperature for PA6 phase confirmed that nanoclays are more distributed in this phase.