Abdellah Ajji

Montreal Polytechnic, Montréal, Quebec, Canada

Are you Abdellah Ajji?

Claim your profile

Publications (136)208.19 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: In this work, plasticized chitosan-based materials were produced through a molten process. A thermo-mechanical treatment was used to achieve chitosan plasticization in the presence of water, acetic acid, and glycerol. Water and glycerol acted as plasticizers, while acetic acid was used as a solvent and plasticizer for chitosan. The influence of acetic acid total content, chitosan/acetic acid solution ratio, and chitosan/glycerol ratio were examined in this study. The various plasticized compounds were blended with a metallocene polyethylene (mPE) and the morphology, rheological, and antibacterial properties of this novel blend system were examined. It was found that an increase in acetic acid content allowed better chitosan dissolution, while a higher glycerol concentration resulted in improved dispersion of the plasticized chitosan phase in the mPE. Following thermo-mechanical treatment, blends presented good antibacterial properties with a reduction of the number of bacteria (non-pathogenic Escherichia coli) by 2 log(CFU/mL) for the chitosan-containing systems with respect to neat mPE. Mechanical properties of the mPE/plasticized chitosan blends were improved by compatibilization with ethylene vinyl acetate, while antibacterial properties were not affected.
    Journal of Materials Science 08/2014; 49(15). · 2.16 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this study, the effect of uniaxial stretching on the thermal, oxygen barrier and mechanical properties of aliphatic polyamide 6 (PA6) and aromatic Poly(m-xylene adipamide) (MXD6) nylon films as well as their in-situ polymerized nanocomposites with 4 wt% clay were studied. Cast films were prepared by extrusion process and rapidly cooled using an air knife. The precursor films were uniaxially stretched at 110°C with draw ratios varying from 1.5 to 5. DSC results showed that the cold crystallization temperature (Tcc) of the uniaxially stretched MXD6 and MXD6/clay films drastically shifted to the lower temperatures when draw ratio increased. The aromatic nylon films had lower oxygen permeability than those of the aliphatic films, due to more rigidity and chain packing. However, the oxygen permeability of the stretched films increased with draw ratio (DR) up to a critical value for each sample, while further stretching resulted in a reduction in the oxygen permeation. This phenomenon was related to the changes in free volume upon uniaxial stretching. The ability of different geometrical models to describe the experimental relative permeability data was investigated. The Bharadwaj model that took into account clay orientation was the most successful one to predict the oxygen barrier characteristics of the stretched nanocomposites at high draw ratios. The Young's modulus and tensile strength of the aliphatic and aromatic nylons increased with uniaxial deformation, while the flexibility and elongation at break of the former decreased with increasing DR. A larger increase in the Young's modulus of the uniaxially stretched nanocomposite films compared with the neat samples was observed and could be related to the improvement in the clay orientation as well as a better alignment of the crystalline phase due to incorporating the clay platelets in the polymer matrix. In contrast, the flexibility of the stretched MXD6 improved remarkably (ca., 25 times) compared with the precursor film (DR = 1) when the draw ratio increased to 1.5. This could be related to the effect of hot stretching on the enhancement of polymer chains relaxation and mobility at low draw ratios. POLYM. ENG. SCI., 2014. © 2014 Society of Plastics Engineers
    Polymer Engineering and Science 07/2014; · 1.24 Impact Factor
  • Source
    Dataset: pi4761
    Ahmad Zohrevand, Abdellah Ajji, Frej Mighri
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this work, the surface morphology and properties of ternary polymer blends and the migration of minor component molecules to the top surface layer of the films were studied. We used polystyrene (PS), poly(butylene adipate-co-terephthalate), polycaprolactone, poly(methyl methacrylate), and polylactide as second minor phases in a blend of polyethylene terephthalate-poly(ethylene glycol) (PET-PEG). The morphology of the ternary systems predicted using the spreading coefficient and relative interfacial energy concepts was confirmed by scanning electron microscopy images. The surface characterization results showed a higher rate of migration of PEG to the polymer-air interface in the systems with a nonwetting morphology and the highest in the PET-PS-PEG blend. Atomic force microscopy images suggested that the high surface hydrophilicity of the PET-PS-PEG blend is due to a dendritic pattern of PEG crystals on the film surface, which were not observed for the other samples.
    The journal of physical chemistry. B. 06/2014;
  • Source
    Ahmad Zohrevand, Abdellah Ajji, Frej Mighri
    [Show abstract] [Hide abstract]
    ABSTRACT: Porous Nanocomposites films based on polypropylene (PP) and titanium dioxide (TiO2) nanoparticles were prepared by melt extrusion followed by uniaxial stretching. Effects of drawing temperature, extension rate, stretching ratio, and composition of the base films on final properties and microstructure of the stretched films were studied. Water vapor permeability results showed significant decrease in permeability of the films stretched at temperatures higher than 60 °C. Porosity, pore size, and water vapor transmission rate (WVTR) in the porous nanocomposite films had a direct relation with nanoparticle content, extension rate and stretching ratio. Study on morphology of the stretched films, using SEM, revealed that the pores form due to PP/TiO2 interfacial debonding at low stretching ratio. Higher stretching ratios causes an enlargement of the pores and formation of PP fibril structure parallel to the stretching direction. Quantification of dye adsorption revealed that the quantity of adsorbed dye increased with porosity and surface area of the pores.
    Polymer International 05/2014; · 2.13 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this study, a novel method to increase the surface roughness of polyethylene terephthalate (PET) films is proposed. The mechanism of phase coarsening at the surface in extruded thin films of PET blended with low concentrations of polystyrene (PS) was investigated. A small amount of poly(hyroxyl ether) of bisphenol A (phenoxy resin, PKHH) was found to significantly increase the surface roughness due to its effect on the PS-PET interfacial tension. X-ray photoelectron spectroscopy (XPS) results indicated that in the presence of PKHH, PS droplets migrated spontaneously towards the surface of the polymer film. An increased local concentration of PS near the surface took the form of encapsulated droplets. Above the flow temperature of the blend, the local concentration of PS eventually reached a level where a co-continuous morphology occurred, resulting in the instabilities on the surface of the film. The adhesion properties of films with various roughnesses were determined using a pull-off test and found to be significantly increased, which suggested that co-continuous morphology and the coarsening process increased the adhesive properties of the film.
    ACS Applied Materials & Interfaces 04/2014; · 5.01 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In the quest to reduce risk of thrombosis in vascular grafts, it is essential to provide a surface with morphological and mechanical properties close to those of the extracellular matrix beneath the luminal endothelium, and to favor the growth of a confluent, stable monolayer of endothelial cells. This is accomplished here by combining electrospun poly(ethylene terephthalate) (PET) mats with an amine-rich thin plasma-polymerized coating, designated “L-PPE:N.” Its deposition does not modify the open, highly porous mats and leads only to small changes in mechanical properties. L-PPE:N significantly improves the adhesion and growth of human umbilical vein endothelial cells (HUVEC) and their resistance to flow-induced shear stress. These properties favor the formation of desired confluent HUVEC monolayers on the topmost surface, unlike conventional vascular grafts (ePTFE or woven PET), where cells migrate inside the material. This combination is therefore highly advantageous for the pre-endothelialization of the luminal side of small-diameter vascular prostheses.
    Macromolecular Bioscience 04/2014; · 3.74 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cast films of aliphatic (PA6) and aromatic (MXD6) nylons and their in situ polymerized nanocomposites with 4 wt % clay were prepared by an extrusion process and rapid cooling using an air knife. The precursor films were then uniaxially stretched at 110 °C with draw ratios varying from 1.5 to 5. The changes in orientation of clay and crystal axes of all the crystalline phases and amorphous region were examined using X-ray diffraction and Trichroic Infrared analyses. The clay alignment was measured with three different techniques: FTIR peak deconvolution, FTIR interactive spectral subtraction and X-ray diffraction. It was found that the clay platelets are mainly oriented in the machine direction (MD) and their orientation improved upon uniaxial stretching. X-ray analysis showed that γ crystals (designated as γ1) of both nylons were mainly formed during rapid cooling of cast films. However, only the PA6/clay films showed an extra γ crystal population (designated as γ2). WAXD and FTIR analyses revealed that the c-axis of γ1 crystal population was oriented in the normal and transverse directions (ND and TD), while the c-axis of γ2 was aligned in the normal direction (ND), indicating that this later crystal population formed perpendicular to the (001) plane of the clay platelets. The orientation of γ1 and γ2 crystal populations increased after uniaxial deformation. The MXD6 showed very little crystallinity due to its higher stiffness and low relaxation rate of the aromatic chains. The amorphous region had a lower orientation in the nanocomposite films due to the spatial hindrance caused by the presence of clay platelets.
    Macromolecules 03/2014; 47(7):2384–2395. · 5.93 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In many industrial sectors, the surface properties of polymers are of particular importance. This applies, for instance, to painting, printing, and any coating on surface of polymeric objects. Hydrophilicity and wettability characteristics are known to be determined by the chemical makeup of the polymer surface. Blending with an additive or a polymer containing high-energy functional groups is widely recognized as a potential technique to overcome disadvantages of low surface energy of polymers due to its convenient processing. Surface migration of polyethylene glycol (PEG) in Polyethylene Terephthalate (PET) host was investigated using a low-molecular-weight PEG (8 kDa) because of its good hydrophilicity, low toxicity, biocompatibility, and chain mobility. A twin-screw extruder was used to blend the materials and prepare the polymer blend films. The results of surface characterizations showed that PEG renders the PET surface more hydrophilic, but not high enough for many applications. In a second approach, the addition of a third component, polystyrene (PS), to the blend in a small amount resulted in a remarkable surface enrichment of PEG at the polymer/air interface for the ternary polymer blend (PET-PEG-PS). Surface analysis revealed that the surface concentration of PEG in the ternary polymer blend film was significantly larger than that of the binary one. POLYM. ENG. SCI., 2014. © 2014 Society of Plastics Engineers
    Polymer Engineering and Science 02/2014; · 1.24 Impact Factor
  • Source
    Ahmad Zohrevand, Abdellah Ajji, Frej Mighri
    Rheologica Acta 01/2014; · 1.63 Impact Factor
  • Polymer. 01/2014;
  • Farhad Sadeghi, Abdellah Ajji
    [Show abstract] [Hide abstract]
    ABSTRACT: Three single site catalysts metallocene polyethylenes (mPE) different in molecular structure were selected and films from them were produced using a semi-industrial cast film extrusion line. Rheological and gel permeation chromatography tests were performed on the mPE resins to assess their molecular structure. Mechanical, physical and sealability properties of the films were evaluated as well as flexural cracking and particles encapsulation (caulkability) and the results are discussed in relation to the molecular structures of the resins. It was found that molecular weight and distribution of short chain branching (comonomer) on the backbone of the polyethylene chains are the main factors that control sealability, flexural cracking and mechanical properties. The placement of comomoner on medium length chains generated crystals with smaller size that show a lower melting peak. Sealing was controlled by crystal distribution, chain diffusion and entanglement formation at the interface. mPE with lower melting point and linear molecular structure showed greater hot tack and seal strength. Polydispersity along with molecular weight contributed to toughness and puncture resistance. Flexural cracking resistance was revealed to be related to crystallinity, tie chain density and more importantly to fraction of amorphous phase. The amorphous part could absorb flexural energy and hinders crack initiation and propagation. Seal through contamination (caulkability) was found to be related to flowability of the melt. The resin with stronger shear thinning in melt state and lower heat seal initiation temperature showed an improved caulkability.
    The Canadian Journal of Chemical Engineering 01/2014; · 1.00 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The development of inorganic nanocrystals (NCs) based bulk-heterojunction (BHJ) solar cells provides an alternative way to harvest sunlight for energy conversion. BHJ solar cells attract significant interest due to their simple fabrication, low cost and high performance. Among all the inorganic NCs, Pb and Cd chalcogenide (PbX and CdX, X=S, Se or Te) NCs as an electron acceptor materials theoretically improve the performance of BHJ solar cells due to their enhanced absorption and multiple exciton generation (MEG). However, their performance in BHJ solar cell devices still does not match with the BHJ solar cell devices made from phenyl-C61-butyric acid methyl ester (PCBM). The initial part of this review introduces the concept, materials, structure, device fabrication, working principles and characterization of BHJ solar cells. Then, the different solution processed approaches and details on reported BHJ solar cell devices based on Pb and Cd chalcogenide NCs are summarized. Finally, critical factors limiting the performance of BHJ solar cell devices are discussed and strategies for the improvement of the power conversion efficiency (PCE) are demonstrated by presenting recent examples from literature.
    Nano Energy. 01/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Semiconductor nanocomposites, which are composed of titanium dioxide (TiO2) nanorods, cadmium sulphide (CdS) nanoparticles (NPs), and Ni clusters, were synthesized. The following steps were adopted: (i) surfactant-capped TiO2 nanorods with controlled length were synthesized in autoclave using oleic acid and amino hexanoic acid as surfactants. By using a ligand-exchange procedure, in which nitrosonium tetrafluoroborate (NOBF4) was used to replace the original surfactants, hydrophilic NOBF4-TiO2 nanorods were obtained; (ii) the resulting nanorods were deposited with CdS NPs and (iii) then deposited selectively with Ni clusters (as cocatalyst) on the nanocomposite surface. Under visible-light illumination of the nanocomposite, the generated electrons from the conduction band of CdS are transferred to TiO2 via TiO2/CdS interface, then to metallic Ni cluster. As a result, the electron/hole separation was highly enhanced leading to a Ni-TiO2/CdS nanocomposite with high photocatalytic performance for the production of hydrogen (H2).
    Ind. Eng. Chem. Res. 01/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Semiconductor nanocomposites, which are composed of titanium dioxide (TiO2) nanorods, cadmium sulphide (CdS) nanoparticles (NPs), and Ni clusters, were synthesized. The following steps were adopted: (i) surfactant-capped TiO2 nanorods with controlled length were synthesized in autoclave using oleic acid and amino hexanoic acid as surfactants. By using a ligand-exchange procedure, in which nitrosonium tetrafluoroborate (NOBF4) was used to replace the original surfactants, hydrophilic NOBF4-TiO2 nanorods were obtained; (ii) the resulting nanorods were deposited with CdS NPs and (iii) then deposited selectively with Ni clusters (as cocatalyst) on the nanocomposite surface. Under visible-light illumination of the nanocomposite, the generated electrons from the conduction band of CdS are transferred to TiO2 via TiO2/CdS interface, then to metallic Ni cluster. As a result, the electron/hole separation was highly enhanced leading to a Ni-TiO2/CdS nanocomposite with high photocatalytic performance for the production of hydrogen (H2).
    Industrial & Engineering Chemistry Research 01/2014; · 2.24 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cast films based on polypropylene (PP) blended with commercial maleic anhydride or acrylic acid grafted polypropylene (PP-g-MA and PP-g-MA) at different weight ratios were prepared by melt extrusion. These films were used to produce hydrophilic microporous membranes. The membranes were prepared by annealing at elevated temperatures followed by cold and hot stretching, respectively. DSC, FTIR and SAXS analyses showed that the addition of the modifiers changed the crystalline lamellar structure and, consequently, the membrane morphology. Membrane morphology observations using SEM showed smaller pore size and lower number of pores as the modifier content increased. Porosity and pore dimensions of the microporous membranes were also measured using mercury porosimetry and their results confirmed SEM observations. Oxygen content of the precursor film surface was analyzed using XPS. Water vapor permeability was increased significantly at low concentrations of the modifiers, compared to the neat PP. This was attributed to the presence of sufficient concentration of polar groups on the surface with a minimal change in the crystalline structure. Finally, the tensile properties of the precursor films in the machine directions (MD) as well as the puncture resistance of the precursors and the membranes in the normal direction (ND) were evaluated.
    Journal of Membrane Science 01/2014; 462:50–61. · 4.09 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this study, rheological, crystal structure, barrier, and mechanical properties of polyamide 6 (PA6), poly(m-xylene adipamide) (MXD6) and their in situ polymerized nanocomposites with 4 wt % clay were studied. The extent of intercalation and exfoliation as well as type of crystals, crystallinity, and thermal transitions were investigated using X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. Dynamic rheological measurements revealed that incorporation of nanoclay significantly increases complex viscosity of MXD6 nanocomposites at low frequencies, which was related to the formation of a nanoclay network and exchange reaction between MXD6 chains. The comparative study of dynamic characteristics (G′ (ω) and G″ (ω)) for aliphatic and aromatic polyamide nanocomposites with their neat resins as well as the relaxation spectra for both polymer systems confirmed the possibility of the aforementioned phenomena. Although, the crystallinity of MXD6 films was lower as compared to PA6 films, the permeability to oxygen was more than 5 times better for the former. Incorporating 4 wt% clay enhanced the barrier property, tensile modulus, and yield stress of PA6 and MXD6 nanocomposite films in both machine and transverse directions without sacrificing much puncture and tear resistances. The PA6-based films showed higher tear and puncture strength as compared to MXD6 films. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers
    Polymer Engineering and Science 11/2013; · 1.24 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Neural stem cells (NSCs) provide promising therapeutic potential for cell replacement therapy in spinal cord injury (SCI). However, high increases of cell viability and poor control of cell differentiation remain major obstacles. In this study, we have developed a non-woven material made of co-electrospun fibers of poly l-lactic acid and gelatin with a degradation rate and mechanical properties similar to peripheral nerve tissue and investigated their effect on cell survival and differentiation into motor neuronal lineages through the controlled release of retinoic acid (RA) and purmorphamine. Engineered Neural Stem-Like Cells (NSLCs) seeded on these fibers, with and without the instructive cues, differentiated into β-III-tubulin, HB-9, Islet-1, and choactase-positive motor neurons by immunostaining, in response to the release of the biomolecules. In addition, the bioactive material not only enhanced the differentiation into motor neuronal lineages but also promoted neurite outgrowth. This study elucidated that a combination of electrospun fiber scaffolds, neural stem cells, and controlled delivery of instructive cues could lead to the development of a better strategy for peripheral nerve injury repair.
    Biomaterials 10/2013; · 8.31 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: There is currently no treatment for neurodegenerative diseases such as Parkinson's or Alzheimer's diseases. While spinal cord injury has no treatment either, nerve injuries are being treated with autologous grafts, a procedure that in turn translates into a loss of function in the donor area. The development of therapies for these pathologies has become urgent as population keeps on ageing. A promising direction of investigation is the use of regenerative techniques to re-grow healthy and functional tissue in the injured area. In this review article, various approaches currently investigated to promote neural regeneration are covered. Those include approaches based on (and many times combining) stem cell therapy, scaffolds made of hydrogel, electrospun fibers and conductive materials as well as the use of soluble or non-diffusible growth factors.
    Stem cell reviews 10/2013; · 5.08 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This study examines the effect of electrospun polyethylene terephthalate mats fiber diameter, orientation, and surface properties on the Human Aortic Endothelial Cell behavior. Mats with two different average fiber diameters (740±200 nm and 1.8±0.2 μm); orientations (low and high); NaOH-treated and untreated were prepared. NaOH treatment altered mats physical properties. AlamarBlue assay revealed that all four test mats supported cell adhesion and growth. Cell growth was observed to be faster for mat with large fiber diameter than for the small fiber diameter mat. Fluorescent staining and scanning electron microscopy showed that fiber diameter and orientation influenced cell morphology. Cells were randomly spread on the 740-nm diameter fibers whereas most of them were oriented along the fibers with 1.8 μm diameter. Mat with higher fiber alignment showed higher cell orientation. Cells penetrated into the mats having 1.8±0.2 μm fiber diameter but remained on the surface of the mat with 740±200 nm, as determined from histological analysis. These findings highly suggest that the two mats may be potential materials to construct a two layer vascular graft scaffold in which the mat with small diameter fibers forms the luminal surface and the mat with larger fiber diameter the abluminal surface.
    Journal of Biomedical Nanotechnology 07/2013; 9:1195-1209. · 7.58 Impact Factor

Publication Stats

480 Citations
208.19 Total Impact Points

Institutions

  • 2003–2014
    • Montreal Polytechnic
      • Département de génie chimique
      Montréal, Quebec, Canada
  • 1995–2011
    • National Research Council Canada
      • Industrial Materials Institute (IMI)
      Ottawa, Ontario, Canada
  • 1995–2007
    • Laval University
      • Département de Génie Chimique
      Québec, Quebec, Canada
  • 1994–1995
    • Université du Québec
      Québec, Quebec, Canada