Ahmad Asadinezhad

Polysaccharides Coatings on Medical-Grade PVC: A Probe into Surface Characteristics and the Extent of Bacterial Adhesion

Medical-grade polyvinyl chloride was coated by polysaccharides through a novel physicochemical approach. An initial surface activation was performed foremost via diffuse coplanar surface barrier discharge plasma in air at ambient temperature and pressure. Then, radical graft copolymerization of acrylic acid through grafting-from pathway was directed to render a well-defined brush of high density, and finally a chitosan monolayer and chitosan/pectin alternating multilayer were bound onto the functionalized surfaces. Surface characteristics were systematically investigated using several probe techniques. In vitro bacterial adhesion and biofilm formation assays indicated that a single chitosan layer was incapable of hindering the adhesion of a Staphylococcus aureus bacterial strain, while up to 30% reduction was achieved by the chitosan/pectin layered assembly. On the other hand, chitosan and chitosan/pectin multilayer could retard Escherichia coli adhesion by 50% and 20%, respectively. Furthermore, plasma treated and graft copolymerized samples were also found effective to diminish the degree of adherence of Escherichia coli.

Recent Progress in Surface Modification of Polyvinyl Chloride

Surface modification of polymers has become a vibrant field of research on account of a myriad of rationales which stimulated numerous efforts. The current paper serves as a condensed survey of the advances made through different approaches adopted for tuning the surface properties of polyvinyl chloride as a homopolymer extensively used on a large scale. Though it does not address all challenges involved, this paper communicates and highlights, through concise discussion, the findings of the efforts undertaken in recent decades. It is ultimately concluded with a perspective of the huge capacities and promising future directions.

Poly(ethylene succinate)/single-walled carbon nanotube composites: a study on crystallization

An investigation on the crystallization of composites based on poly(ethylene succinate) and unmodified single-walled carbon nanotube was made in this report. Both isothermal and non-isothermal modes were studied along with subsequent melting behavior using differential scanning calorimetry. Crystal morphology was then explored using X-ray scattering and infrared spectroscopy. It was observed during isothermal crystallization that carbon nanotube (CNT) could contribute to the crystallization rate through heterogeneous nucleation. Furthermore, nanotubes enhanced the crystallinity within low and high undercooling rather than medium undercooling. Similar findings were obtained in non-isothermal crystallization mode. At lower cooling rates, the crystallization rate was more strongly influenced by the nanotubes, while at higher cooling rates the crystallinity was affected to the greater extent. The onset of the cold crystallization of polymer remained unaffected in presence of the nanotube, while its extent was reduced. X-ray diffraction together with infrared spectroscopy found that the polymer crystalline morphology was of α type, and no transition from α to β occurred in presence of the CNT.

Antibacterial performance of alginic acid coating on polyethylene film.

Alginic acid coated polyethylene films were examined in terms of surface properties and bacteriostatic performance against two most representative bacterial strains, that is, Escherichia coli and Staphylococcus aureus. Microwave plasma treatment followed by brush formation in vapor state from three distinguished precursors (allylalcohol, allylamine, hydroxyethyl methacrylate) was carried out to deposit alginic acid on the substrate. Surface analyses via various techniques established that alginic acid was immobilized onto the surface where grafting (brush) chemistry influenced the amount of alginic acid coated. Moreover, alginic acid was found to be capable of bacterial growth inhibition which itself was significantly affected by the brush type. The polyanionic character of alginic acid as a carbohydrate polymer was assumed to play the pivotal role in antibacterial activity. The cell wall composition of two bacterial strains along with the substrates physicochemical properties accounted for different levels of bacteriostatic performance.

Polypropylene/Poly(trimethylene terephthalate) Blend Nanocomposite: A Thermal Properties Study

In this article, thermal properties of polypropylene/poly(trimethylene terephthalate) melt-mixed blends containing organically modified montmorillonite nanoclays and interacting compatibilizers are studied. Dynamic mechanical analysis showed an enhanced elastic modulus and reduced damping upon nanoclay fillers incorporation, also α-relaxation peak was shifted up while β-relaxation was not affected. Thermogravimetry exhibited a synergistic effect in thermal stability of the blend accompanied by a reduction in decomposition rate. This effect was more pronounced in presence of compatibilizers. The addition of nanoclay fillers generally led to an enhancement of thermal resistance; however, a dual function was evident, namely preventive and catalytic, respectively prior to and after onset of degradation.

Cyclic olefin copolymer/layered silicate nanocomposite: solid and melt viscoelastic properties and degradation behavior

Organoclay nanocomposites based on cyclic olefin copolymer (COC) with various contents of layered silicate nanoparticles were prepared via melt blending. The influence of processing conditions and nanoclay content on solid state viscoelastic and melt rheological properties as well as thermal degradation behavior was studied. The state of dispersion was investigated using X-ray diffraction technique which showed a strong dependence on composition, where an exfoliated morphology was identified in high nanoclay loading. Besides, the processing conditions, i.e., screw rotation speed and mixing time were also found to strongly influence the state of nanophase dispersion. The rheological investigations revealed a remarkable increase in storage shear modulus and complex viscosity values upon nanoclay incorporation. Furthermore, dynamic mechanical analysis gave an evidence of increasing stiffness after nanoclay was added into COC matrix; however, no detectable change in glass transition peak was brought about. The results from thermogravimetry also exhibited a rising trend in thermal stability values as nanophase organoclay was incorporated, for which the random chain scission was suggested as the prevailing mechanism based on a theoretical analysis.

Adsorption of poly(ethylene succinate) chain onto graphene nanosheets: A molecular simulation.

Understanding the interaction between single polymer chain and graphene nanosheets at local and global length scales is essential for it underlies the mesoscopic properties of polymer nanocomposites. A computational attempt was then performed using atomistic molecular dynamics simulation to gain physical insights into behavior of a model aliphatic polyester, poly(ethylene succinate), single chain near graphene nanosheets, where the effects of the polymer chain length, graphene functionalization, and temperature on conformational properties of the polymer were studied comparatively. Graphene functionalization was carried out through extending the parameters set of an all-atom force field. The results showed a significant conformational transition of the polymer chain from three-dimensional statistical coil, in initial state, to two-dimensional fold, in final state, during adsorption on graphene. The conformational order, overall shape, end-to-end separation statistics, and mobility of the polymer chain were found to be influenced by the graphene functionalization, temperature, and polymer chain length. Furthermore, the polymer chain dynamics mode during adsorption on graphene was observed to transit from normal diffusive to slow subdiffusive mode. The findings from this computational study could shed light on the physics of the early stages of aliphatic polyester chain organization induced by graphene.

Nanofilled Polypropylene/Poly(trimethylene terephthalate) Blends: A Morphological and Mechanical Properties Study

Polypropylene (PP) /poly(trimethylene terephthalate), (PTT), binary blends in the presence of two interfacial modifier as well as two organically modified nanoclay additives were studied in terms of mechanical and morphological characteristics. Scanning electron microscopy confirmed the incompatibility of the system which was solved to some extent through incorporating the nanoclay as well as functional compatibilizers. An evaluation of the specimens via static mechanical tests in tensile mode gave credence to the assumption that the higher the PTT content, the higher the mechanical performance would be. Furthermore, the compatibilizer-containing blends not only exhibited higher toughness, but also possessed enhanced stiffness when a maleated compatibilizer was added. The tensile modulus was promoted further in the presence of clay nanoparticles; however, toughness was somewhat sacrificed. The Barentsen as well as Halpin-Tsai models were found to describe the binary blends modulus. The reinforcing impact of the nanoclay was exploited to a greater degree in the presence of the compatibilizer.

Bacteriostatic activity of fluoroquinolone coatings on polyethylene films

Low-density polyethylene films were surface modified through a three-step procedure to impart antibacterial property. Plasma treatment was followed by allylamine grafting to generate active functionalities on the surface. Three potent antibiotics including norfloxacin, ciprofloxacin and ofloxacin were then separately coated onto the surfaces. Each step of surface modification was well characterized in terms of chemical composition and bioactivity. It was found that the chemical structure of the antibiotic was highly determining in extent of antibiotic immobilization as well as in final biological performance of the modified substrates. An excellent activity against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial growth was observed for norfloxacin-coated substrate which corresponded to the highest amount of the antibiotic immobilized. However, almost no activity was seen for ofloxacin-coated surface. This was attributed to the ease of the antibiotic coating on the allylamine-grafted substrate where the lowest degree of coating was found for ofloxacin due to its unfavorable chemical structure. Gram-negative bacterial strain was found more vulnerable than Gram-positive strain which was explained on the basis of their different cell wall composition. The chemical structure of the antibiotic was found to be determining in amount of the material coated and also in level of the exhibited antibacterial activity.

Dynamic and Modulated Mechanical Evaluation of Polymer Structures

Mechanical testing is foremost a means to measure material performance, however it provides a probe into the complex elastic, viscoelastic and viscoplastic behavior of polymer morphologies. The techniques in this work utilize variables of time/frequency, temperature, stress and strain with emphasis on dynamic and modulated implementation. Several instruments were used since a particular instrument does not provide all of the capabilities. The material response is complex and it has been resolved into typically instantaneous and time-dependent components. Some of the techniques are widely used and these have been extended, while other techniques introduce control over alternate variables. Polycarbonate was chosen as the main example with support from similar polymers, though the techniques are applied to many polymer types.