Abdellah Ajji

Laval University, Quebec City, Quebec, Canada

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Publications (155)264.36 Total impact

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    ABSTRACT: In this study, miscibility/immiscibility issues of a binary blend consisting of polypropylene (PP) and acrylic acid grafted polypropylene (PP-g-AA) were investigated using rheometry, differential scanning calorimetry (DSC), dynamic mechanical and thermal analysis (DMTA), atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Phase separation analysis of such blend systems is a challenge and complex due to chemically similar components as well as low value of acrylic acid groups in the graft copolymer. Thus, it is crucial to determine if the present blend show some degree of miscibility or develop co-continuous morphology between the components. The analysis of rheometrical, DSC and DMTA results indicated no sensitivity of those classical techniques for detecting the miscibility or immiscibility of such system. However, AFM data effectively detected dispersed-phase domains corresponding to the PP-g-AA rich phase. The results, for the first time, indicated that the start of phase separation occurred at a critical copolymer concentration, between 2 to 5 wt%. Furthermore, it was observed that as the PP-g-AA content increases, the size and continuity of the dispersed-phase increase and reach a highly continuous morphology. Additionally, ToF-SIMS chemical imaging was carried out to aid in the interpretation of the AFM data.
    No preview · Article · Jan 2016 · Polymer International
  • Ali Moayeri · Abdellah Ajji

    No preview · Conference Paper · Dec 2015
  • Ali Moayeri · Abdellah Ajji
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    ABSTRACT: Electrospinning is a simple method to produce nanofibers mats with diameters in the nanometer scale. The technique is based on the application of an electric field on a polymer solution, and it is considered one of the most efficient techniques to fabricate high performance nanofibers mats, with distinct advantages such as very high surface area to volume ratio and porosity. Polyaniline (PANi) is one of the most studied intrinsically conductive polymer, mainly due to its ease of synthesis and interesting doping mechanism. It is however daunting to process PANi compared to most other polymers. As it is common among intrinsically conductive polymers, PANi has a fairly rigid backbone because of its high aromaticity. Thus, electrospinnability of PANi is limited due its insufficient solution viscosity and rigid chemical structure. One approach to make PANi electrospinnable is by its blending with materials that may facilitate its electrospinnability such as easily electrospinnable copolymers (e.g poly(ethylene oxide) and poly(lactic acid)), as previously reported. However, the presence of an insulating copolymer decreases the fibers conductivity due to dilution of the conducting component. The coaxial electrospinning method provides an alternative and effective way of fabricating neat PANi nanofibers. Coaxial electrospinning is an innovative electrospinning method that facilitates the fabrication of unspinable polymer nanofibers with unique core−shell structures. In this technique, two dissimilar solutions are spun simultaneously through a spinneret composed of two coaxial capillaries to produce core−shell structured nanofibers with unspinable polymer at the core section. Recently, graphene, a single-atom-thick two-dimensional sheet of sp2-hybrized carbon atoms arranged in a honeycomb crystal structure, has attracted a lot of research interest and has been considered as a rising-star carbon material. Graphene has been intensively researched because of its remarkable properties such as high electrical and thermal conductivities, high mechanical strength and large surface area. Given its excellent electrical conductivity and electron mobility at room temperature, a highly conductive graphene-based polymer nanocomposite may be obtained. In this work, we report the preparation of neat polyaniline fibers filled with highly dispersed graphene sheets. The coaxial electrospinning process was used to produce core-shell structured fibers of a poly(methyl methacrylate) shell and a polyaniline core embedded with highly dispersed graphene nanosheets. The insulating shell was selectively removed by solvent etching. SEM, TEM, XPS and electrical conductivity measurements were employed to characterize these nanofibers.
    No preview · Conference Paper · Nov 2015
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    ABSTRACT: The intrinsic hydrophobic character of polypropylene limits its performance in many porous membrane applications. This can be improved by hydrophilic modification of the film surface through blending with hydrophilic polymers. For producing the precursor films and, consequently, microporous membranes with the appropriate crystalline lamellar morphology, the polypropylene chains should preserve their elongated form to serve as initial nuclei for the later development of lamellar crystals. The relaxation time of the chains is the most important factor for this stage. Commercial maleic anhydride and acrylic acid grafted polypropylenes were melt blended with a polypropylene at different weight ratios. The results showed that the modifiers lowered the crystalline orientation of the blends as compared to neat polypropylene films. The effect of the modifier on the melt relaxation spectra of the blends was investigated, and a linear relationship was found between the characteristic relaxation time of the blends and their crystalline orientation function.
    No preview · Article · Oct 2015 · Industrial & Engineering Chemistry Research
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    ABSTRACT: In this study, the seal behavior of toughened blends of poly(lactic acid) (PLA) and polycaprolactone (PCL) was investigated in details. The blended samples were prepared using melt blending in a twin-screw extruder and were processed in the form of cast films of about 30 μm in thickness. Scanning electron microscopy (SEM) study of the morphology of the blends shows that laminar morphology develops in blends of 20% and 40% dispersed phase. Analysis of the thermal behavior of the blends using DSC thermograms reveals significant effect of blending on hindering the crystallization of PCL, resulting in lower crystallinity for samples with high PLA content. Latter provide blends with more amorphous phase and chain mobility, which help lowering the Seal and Hot-tack initiation temperatures. Blending is shown to decrease Seal and Hot-tack initiation temperatures up to 30 °C compared to neat PLA. In addition, this technique is proven to be successful to increase the Hot-tack strength of the blends to a comparative level to commercially available seal grade resins at about 1100 g/25.4 mm for PCL content of 40%. The results indicate that elongation at break increases from about 4% for pure PLA to almost 150% for the blend of 40% PCL and over 400% when PCL content reaches 60%. Higher toughness is an important property for a flexible package and prevents defects caused by its handling and storage conditions.
    No preview · Article · Oct 2015 · Industrial Crops and Products
  • Ramin Yousefzadeh Tabasi · Abdellah Ajji
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    ABSTRACT: ATR-Fourier Transform infrared technique (ATR-FTIR) was used in combination with lab scale composting setup to investigate the selective composting of two-phase biodegradable blends based on Polylactic acid (PLA) or Polyhydroxybutyrate (PHB), toughened through melt blending with poly (butylene adipate-co-terephthalate) (PBAT), referred to as PLPT50 and PHPT50 respectively. All samples have been processed into films of 35 μm thickness by means of cast film process. The simulated lab scale composting setup with gas collection columns was used to measure cumulatively evolved CO2 gas as an indication of extent of biodegradation. The results from gas collection revealed a decrease in the rate of CO2 evolution as a consequence of blending. ATR-FTIR spectroscopy detected two distinctive CO ester bonds for PLPT50, PLA (1743 cm−1)/PBAT (1710 cm−1), and also PHPT50, PHB (1720 cm−1)/PBAT (1710 cm−1), indicating the phase separated morphology of blends. The absorption ratio of CO bond for PLA and PHB decreased gradually as a function of composting time leading to a decreased ratio of PLA/PBAT and PHB/PBAT ester bond absorption in the blends. SEM micrographs showed the formation of a porous three-dimensional (3D) network for both PLPT50 and PHPT50 through composting after 15 days. ATR-FTIR analysis shows that they are rich in PBAT content, thus indicating selective degradation of the PLA or PHB components in the blends. Investigation of the mechanical properties of the blends demonstrated a gradual loss of Young's modulus caused by the formation of defects through active microbial degradation and hydrolysis.
    No preview · Article · Jul 2015 · Polymer Degradation and Stability
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    ABSTRACT: In this work, the effects of annealing conditions on the microstructure of polypropylene (PP) precursor films and further on the porous structure and permeability of stretched membranes were investigated. Combinations of WAXD, FTIR, DSC and DMA results clearly showed the crystalline orientation and crystallinity of the precursor film increased with annealing temperature, while the molecular chain entanglements in the amorphous phase decreased. Changes in the deformation behavior suggested more lamellar separation occurred for the films annealed at higher temperatures. Surface morphologies of the membranes examined by SEM revealed more pore number and uniform porous structure as the annealing temperature increased. In accordance with the SEM results, the permeability of the membranes increased with annealing temperature. On the other hand, it was found that 10 min was almost enough for the annealing process to obtain the microporous membranes with an optimal permeability.
    Full-text · Article · Jul 2015 · Chinese Journal of Polymer Science
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    ABSTRACT: Thermoplastic foams have several advantages in comparison with unfoamed polymers such as lightweight, high strength to weight ratio, excellent insulation property, high thermal stability, high impact strength and toughness, as well as high fatigue life. These outstanding properties lead cellular plastics to various industrial applications in packaging, automotive parts, absorbents, and sporting equipment. Nowadays, polypropylene (PP), because of its outstanding characteristics such as low material cost, high service temperature, high melting point, high tensile modulus, low density, and excellent chemical resistance, is a major resin in the foaming industry. However, foaming of conventional PP is limited by its low melt strength leading to poor cell morphology, cell rupture/coalescence and limited density reduction. To improve PP melt strength, several strategies including particle addition as nucleating agent, introduction of long chain branching, blending with high melt strength polymers and crosslinking have been proposed. In this review, these issues are discussed and analyzed in terms of mechanical, thermal, and rheological characterizations.
    Full-text · Article · May 2015 · Cellular Polymers
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    ABSTRACT: The interfacial self-adhesion strength of polyethylene (PE) binary blends in temperatures higher than the melting point was investigated in relation to their components’ structures and elongational rheological properties. Four binary blends were prepared from the combination of a conventional polyethylene; LDPE or Ziegler-Natta LLDPE, with a metallocene catalyzed ethylene α-olefin copolymer; linear (Linear-m) or long chain branched (LCB-m). Interfacial adhesion was carried out by bringing two films into intimate contact under slight pressure and heat for 0.5 s. Adhesion strength was then measured by peeling immediately after sealing while the adherents were still in the molten state. Blending metallocene in 20, 40, and 60 wt% compositions with conventional PEs enhanced the self-adhesion. However, the adhesion strength of the blends containing 60 wt% metallocene resins was significantly lower than the adhesion strength of neat metallocene resins. This was interpreted to be due to the formation of a segregated layer of highly branched short chains of LDPE or Zn-LLDPE at the surface of films. The increase in adhesion strength of LDPE/Linear-m and Zn-LLDPE/Linear-m blends was more than LDPE/LCB-m and Zn-LLDPE/LCB-m blends. This was attributed to the faster reptation of linear chains, hence superior diffusion across the interface compared to LCB containing resin. The higher increase of adhesion strength for all compositions of LDPE blends was observed compared to their Zn-LLDPE counterparts. The temperature range in which the film showed a plateau of its highest adhesion strength was determined for all blend compositions. The results indicated that the temperature window of plateau adhesion strength for LDPE blends were broader than their Zn-LLDPE counterparts. Therefore, this work suggests that the final plateau temperature (T pf ) can be correlated with the area under stress–strain curve of the extensional rheological measurements, which is called toughness. Then, the higher melt toughness can result in a broader adhesion strength plateau.
    No preview · Article · May 2015 · Rheologica Acta
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    ABSTRACT: The present work deals with two different CdS nanostructures produced via hydrothermal and solvothermal decompositions of aminocaproic acid (ACA)-mixed Cd-thiourea complex precursor at 175 °C. Both nanostructures were extensively characterized for their structural, morphological and optical properties. The powder X-ray diffraction characterization showed that the two CdS nanostructures present a wurtzite morphology. Scanning electron microscopy and energy-dispersive X-ray characterizations revealed that the hydrothermal decomposition produced well-shaped CdS flowers composed of six dendritic petals, and the solvothermal decomposition produced CdS microspheres with close stoichiometric chemical composition. The UV-vis absorption and photoluminescence spectra of CdS dendritic flowers and microsphere nanostructures showed that both nanostructures present a broad absorption between 200 and 700 nm and exhibit strong green emissions at 576 and 520 nm upon excitations at 290 nm and 260 nm, respectively. The transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) characterizations confirmed that CdS microspheres were mesoporous and were composed of small nanocrystals. A possible growth mechanism in the formation of the CdS nanostructures was proposed based on morphology evolution as a function of the reaction time. Furthermore, the as-synthesized CdS nanostructures were found to exhibit highly efficient photocatalytic activities for the degradation of methyl orange (MeO) and rhodamine B (RhB) dyes.
    No preview · Article · Apr 2015 · Journal of Nanoscience and Nanotechnology
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    ABSTRACT: The effect of dry grinding on the morphology and structure of kaolin particles treated with potassium acetate (KAc) and dimethyl sulfoxide (DMSO) has been investigated. After treatment with KAc, the d-spacing of kaolin increased from 0.72 to 1.03, 1.30, and 1.38 nm due to the combined effects of humidity and orientation of KAc molecules. The d-spacing was increased to 1.13 nm in the case of DMSO treatment. A combination of XRD, TGA, and FT-IR showed that the crystalline structure of kaolin–DMSO and kaolin–KAc were significantly altered by grinding. The intensity of XRD diffraction peaks of ground samples was decreased due to the deterioration of the crystalline structure, and for longer grinding times those peaks almost disappeared. After grinding, the dehydroxylation temperature generally shifted to lower values and a smaller weight loss was observed. The variations of particle size and surface characteristics were also investigated.
    No preview · Article · Mar 2015 · Applied Clay Science
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    ABSTRACT: Plasticized chitosan and polyethylene blends were produced through a single-pass extrusion process. Using a twin-screw extruder, chitosan plasticization was achieved in the presence of an acetic acid solution and glycerol, and directly mixed with metallocene polyethylene, mPE, to produce a masterbatch. Different dilutions of the masterbatch (2, 5 and 10 wt% of plasticized chitosan), in the presence of ethylene vinyl acetate, EVA, were subsequently achieved in single screw film extrusion. Very small plasticized chitosan domains (number average diameter <5 μm) were visible in the polymeric matrix. The resulting films presented a brown color and increasing haze with chitosan plasticized content. Mechanical properties of the mPE films were affected by the presence of plasticized chitosan, but improvement was observed as a result of some compatibility between mPE and chitosan in the presence of EVA. Finally the incorporation of plasticized chitosan affected mPE water vapor permeability while oxygen permeability remained constant.
    No preview · Article · Mar 2015 · Carbohydrate Polymers
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    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
    Full-text · Article · Feb 2015 · Polymer Engineering and Science
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    Ali Moayeri · Abdellah Ajji
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    ABSTRACT: Conducting nanofibers of polyaniline (PANi) doped with camphor-10-sulfonic acid (HCSA), blended with poly(ethylene oxide) (PEO), and filled with 1-pyrenebutanoic acid, succinimidyl ester functionalized graphene (G-PBASE) have been fabricated using electrospinning. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transforms infrared (FT-IR) and thermal gravimetric analyzer (TGA) was utilized to characterize the PANi/PEO/G-PBASE fibers morphology and properties. The observations show that electrospun fibers are highly interconnected and possess a relatively smooth surface. The average diameter of fibers was 222 ± 60 nm. The electrical conductivity of PANi/PEO and PANi/PEO/G-PBASE at room temperature was also studied. The unique nanostructured composite of PANi/PEO/G-PBASE with small loading of G-PBASE (5 wt.% relative to PANi) showed two order of magnitude enhancement in the electrical conductivity and one order of magnitude enhancement in thermal stability in comparison to PANi/PEO nanofibers.
    Full-text · Article · Feb 2015 · Synthetic Metals
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    ABSTRACT: In this work, we present the synthesis details of uniform shape and size-controlled titanium dioxide (TiO2) nanorods followed by the deposition of cadmium sulfide (CdS) quantum dots on their surface. The achieved surfactant-capped-TiO2 nanorods as well as CdS/TiO2 nanocomposites were dispersed in nonpolar solvents, which enabled an easy solution blending with poly (2-methoxy, 5-(2-ethyl-hexy-loxy)-p-phenyl vinylene) (MEH-PPV) conjugated polymer to prepare the active layer of bulk heterojunction solar cells (BHJSCs). The properties of the synthesized capped-TiO2 nanorods, CdS/TiO2 nanocomposites, as well as those of their corresponding blends with MEH-PPV were characterized using transmission electron microscopy (TEM), thermogravimetric analysis (TGA), UV-Visible spectroscopy, and photoluminescence (PL) technique. The characterization of the effect of the surfactants (oleic acid, OA, olyamine, OM, and 6-aminohexanoic acid, 6AHA) left on TiO2 surface and CdS surface modification on BHJSC photovoltaic power conversion efficiency (PCE) showed that: i) for the same surfactants, when CdS was added on the surface of TiO2 nanorods, the PCE increased due to the higher efficiency of CdS compared to MEH-PPV; and ii) the best PEC was obtained with CdS/OA-6AHA-capped-TiO2 nanocomposite due to the shortest length of the carbon-chain of 6AHA, leading to higher charge carrier mobility.
    No preview · Article · Jan 2015 · Green Processing and Synthesis
  • Eric Audet · Frej Mighri · Denis Rodrigue · Abdellah Ajji
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    ABSTRACT: To evaluate the impact of the stretching temperature on the morphology of cellular polypropylene (PP) films, a series of PP films filled with spherical particles of calcium carbonate (CaCO3) and platy talc particles with weight concentrations varying from 15 to 35 wt% were prepared by twin-screw extrusion then biaxially stretched at three temperatures (152, 155 and 158 degrees C). Their corresponding cellular morphology was analyzed from scanning electron microscopy (SEM) micrographs. It was shown that film stretching at the lower temperature (152 degrees C) led to delamination of PP/CaCO3 or PP/talc interface, while it was not the case when these films were stretched at 158 degrees C. It was also observed that, when films were stretched at 152 degrees C, their corresponding developed cells had an average cell wall thickness t of around 3.6 mu m, an average cell height b of around 13.6 mu m, and an average cell aspect ratio a/b of around 5.6, where a (mu m) is the average cell width. These values were within the aimed cell geometrical specifications needed for cellular piezoelectric films.
    No preview · Article · Jan 2015 · Cellular Polymers
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    Ahmad Zohrevand · Abdellah Ajji · Frej Mighri
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    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.
    Full-text · Article · Dec 2014 · Polymer International
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    ABSTRACT: In this work, we describe a simple spin-coating deposition technique for lead sulphide (PbS) and cadmium sulphide (CdS) films from a methanolic metal–thiourea complex. The characterization of the films by X-ray diffraction and X-ray photoelectron spectroscopy techniques revealed that pure cubic phase PbS and CdS layers were formed via this method. As shown by atomic force microscopy and scanning electron microscopy results, both films were homogeneous and presented a smooth surface. Optical properties showed that the energy band gap of PbS and CdS films were around 1.65 and 2.5 eV, respectively. The PbS film is p-type in nature with an electrical conductivity of around 0.8 S/cm. The hole concentration and mobility were 2.35 × 1018 cm−3 and 2.16 × 10−3 cm2/V/s, respectively, as determined from Hall measurement. Both films were used to develop a thin film solar cell device of graphite/PbS/CdS/ITO/glass. Device characterization showed the power conversion efficiency of around 0.24 %. The corresponding open circuit voltage, short circuit current and fill factor were 0.570 V, 1.32 mA/cm2 and 0.32, respectively.
    Full-text · Article · Dec 2014 · Applied Physics A
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    Hanan Abdali · Abdellah Ajji
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    ABSTRACT: The use of natural antimicrobial (AM) agents in the food packaging industry has been the focus of providing a safe and effective method in protecting and delivering food to the consumer. This study investigates natural materials such as clove bud powder (Syzygium aromaticum) to determine its AM activity against Gram-negative Escherichia coli (E. coli) (DH5α) and Gram-positive Listeria innocua (L. innocua) (LSPQ3284) and Staphylococcus aureus (S. aureus) (54–73) microorganisms. The lowest concentration of clove bud powder preventing the growth of a microorganism after 24 h incubation was considered as the minimum inhibitory concentration (MIC) and the values of the minimum bactericidal concentration (MBC) was determined as well. The clove bud powder was prepared and coated onto LDPE films to evaluate its AM activity for food packaging applications. It was found that the clove bud powder inhibited the growth of the tested microorganisms. An LDPE film embedded with the clove bud powder by coating twice showed the best AM effects against E. coli bacteria.
    Preview · Article · Nov 2014 · Industrial Crops and Products
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    ABSTRACT: Hydrophilic microporous membranes were prepared based on polypropylene (PP) cast films blended with a commercial acrylic acid grafted polypropylene (PP-g-AA) via melt extrusion followed by grafting titanium dioxide (TiO2) nanoparticles on its surface, annealing and stretching. ATR-FTIR, XPS and EDS analyses showed that the hydrophilic segments of an amphiphilic modifier (PP-g-AA) acted as surface functional groups on the film surface. The results indicated that the presence of the modifier was very important for grafting TiO2 nanoparticles on the film surface. Compared to PP and PP/PP-g-AA blend films, the water contact angle decreased by a factor of 2.5 after grafting TiO2 on the surface of the films, meanwhile the water vapor permeability of the microporous membranes prepared from those films increased by a factor of 1.5. All these results indicated that the hydrophilicity of the modified PP membranes was improved.
    No preview · Article · Nov 2014 · Polymer

Publication Stats

1k Citations
264.36 Total Impact Points

Institutions

  • 2014-2015
    • Laval University
      • Department of Chemical Engineering
      Quebec City, Quebec, Canada
    • Université de Montréal
      Montréal, Quebec, Canada
    • Centre for Polymer Research
      Ciudad de México, Mexico City, Mexico
  • 2009-2015
    • Polytechnique Montréal
      • Department of Chemical Engineering
      Montréal, Quebec, Canada
  • 1996-2011
    • National Research Council Canada
      • Industrial Materials Institute (IMI)
      Ottawa, Ontario, Canada