Volume 32, Issue 4-5

Polyacrylamide was produced through redox polymerization in a single batch reactor. Ammonium persulfate and sodium bisulfite were applied as the redox initiators. Statistical design consisting a 2 4 full factorial design was used to determine the dependence of the factors such as temperature, concentrations of acrylamide, ammonium persulfate and sodium bisulfite, as well as their interactions in affecting the initial rate of polyacrylamide redox polymerization. All independent factors were shown to have a significant effect on the rate of polyacrylamide redox polymerization. The order of significance was: temperature>ammonium persulfate>acrylamide>sodium bisulfite. The interactive effects of the factors were also investigated. The 2 4 ull factorial design was augmented to central composite design (CCD), to optimize the rate of polyacrylamide redox polymerization. The results showed that a high rate of polyacrylamide redox polymerization occurred at a high level of the factors. A statistical design kinetics model was constructed through second-order regression to predict the rate of polyacrylamide redox polymerization and the R 2 value was 0.9888, which fitted the experimental rate of polyacrylamide redox polymerization better compared to the classical kinetics model.

Different fractions of pullulan oligosaccharide can be applied in the synthesis of pharmaceutical active compounds. Thus, the object of this study was to model the depolymerization process of pullulan polysaccharide with the change of pH, temperature and depolymerization time. The samples were analyzed by gel filtration chromatography (GFC). The chromatography separation of polymer fractions was achieved by using a Zorbax PSM-300 HP-SEC column (250×6.2 mm, 5 μm) at a temperature of 25°C. The flow rate of the mobile phase (redistilled water) was 1 cm 3 min -1 . The fractions were recorded by a refractive index detector. The obtained data were converted by thin plate spline interpolation function into matrixes. By the mathematical processing matrixes, the models of molar mass distribution in the function of pH, temperature and depolymerization time were obtained. The intervals of depolymerization parameters can be defined for obtaining the desirable pullulan oligomers, which have the efficient applications in macromolecule technology.

A newly developed initiation system, activators regenerated by electron transfer (ARGET), was employed to synthesize polystyrene-organoclay nanocomposites via atom transfer radical polymerization (ATRP). ARGET ATRP was applied since it is carried out at significantly low concentrations of the catalyst and environmentally acceptable reducing agents. Conversion and molecular weight evaluations were performed using gravimetry and size exclusion chromatography (SEC), respectively. According to the findings, addition of clay content resulted in a decrease in conversion and molecular weight of nanocomposites. However, an increase of polydispersity index is observed by increasing nanoclay loading. The living nature of the polymerization is revealed by 1 H NMR spectroscopy and extracted data from the SEC traces. X-ray diffraction (XRD) analysis shows that organoclay layers are disordered and delaminated in the polymer matrix and exfoliated morphology is obtained. Thermogravimetric analysis (TGA) shows that thermal stability of the nanocomposites is higher than the neat polystyrene. A decrease in glass transition temperature of the samples by increasing organoclay content is observed by differential scanning calorimetry (DSC). Transmission electron microscopy (TEM) reveals that clay layers are partially exfoliated in the polymer matrix containing 2 wt% of organomodified montmorillonite (PSON 2) and a dispersion of partially exfoliated clay stacks is formed.

This analysis for thermoforming cones from a viscoelastic melt gives the speed of the stresses in the deforming melt. We follow the mechanics of Kershner and Giacomin developed for thermoforming cones from a Newtonian melt, deriving an analytical solution for the corotational Maxwell (CM) model. We have distinguished what happens before and after the melt touches the conical mold (free vs. constrained forming). The CM reduces to the Newtonian solution of Kershner and Giacomin. The upper convected Maxwell (UCM) model is also investigated, but does not yield an analytical solution for conical thermoforming. Our results are confined to forming with a conical mold, the simplest relevant problem in thermoforming, using the simplest relevant constitutive equation, the CM model.

Polypropylene (PP) composites filled with hollow glass beads (HGB) were prepared by means of a twin-screw extruder. The extrudate swell ratio ( B ) of the PP/HGB composite melts was measured using a melt flow indexer under experimental conditions, with temperatures from 190°C to 230°C and loads varying from 1.20 kg to 7.50 kg, to identify the effects of the extrusion conditions and the particle size and content on the extrudate swell of composite melts. The results showed that the value of B of the composites increased nonlinearly with an increase of shear stress, while it decreased linearly with a rise of temperature. When the load and temperature were constant, the value of B increased nonlinearly with an increase of the HGB diameter, whereas it reduced nonlinearly with an increase of the HGB volume fraction. This should be attributed to the elastic deformation energy stored in the flow of the composite melts, which was decreased with an increase of the HGB number and content.

Poly(trimethylene terephthalate) (PTT) and polyamide6,10 (PA6,10) are polymers with significant bio-based content that forms an immiscible blend system of high-value engineering materials with enhanced sustainability. Knowledge of the melt viscosity of these thermoplastic materials is critical, when processing blends to achieve optimum morphologies. We measured the viscosities of five extruded blends near the phase inversion composition, over a range of shear rates using both parallel plate and capillary methods. Based on the viscosities of the end-members, Jordhamo co-continuity should be observed in the 21–44 volume percent PTT range, depending on the processing shear rate. Extruded blend viscosities were lower than the linear rule of mixtures and the phase inversion composition was identified near 55 volume percent PTT. SEM images showed clear indications of developing co-continuity in the 55 volume percent PTT. We conclude that the viscosities of immiscible polymer blends in this system do not follow the rule of mixtures, due to slip between immiscible domain interfaces, but that the viscosity and the power law index are useful in locating the phase inversion composition. The empirical Jordhamo relationship, although generally useful in immiscible polymer systems, is not as valuable in this system.

The influence of talc and poly (methyl methacrylate) (PMMA)-grafted ( g )-talc on the mechanical properties of poly (vinyl chloride) (PVC) was investigated. The graft copolymerization was carried out under nitrogen atmosphere, using the free radical initiation technique. The blend formulations were first dry blended using a mixer before being milled into sheets on a two-roll mill at 165°C, and then hot pressed into composites at 190°C. The flexural modulus of both composites increased with increasing filler content from 0 to 20 part per hundred resin (phr), however the increment of grafted (57.7%) was higher than ungrafted composites (48.5%). A similar trend has also been observed for thermal stability. The impact strength of grafted was increased by 45.82%, whereas 18.96% in reduction was observed for the ungrafted composites. The decrement of flexural strength by 16.6% and 21.1% of grafted and ungrafted, respectively, has also shown the improvement in mechanical properties of grafted composites.

A ternary composite scaffold of poly(L-lactide)/hydroxyapatite/chitosan fibers was fabricated for bone tissue engineering. Scanning electron microscopy analysis showed that hydroxyapatite particles and chitosan fibers in microscale uniformly distributing in poly(L-lactide) matrix not only increased the mechanical property but also prevented the crack and platelet formation on the pore surface of poly(L-lactide) matrix at cooling. The X-ray diffraction peak intensity of poly(L-lactide) component decrease may be due to the presence of hydroxyapatite particles and chitosan fibers as the crystal nuclei that led to the crystallinity decrease of poly(L-lactide). The in vitro degradation test showed that the degradation of poly(L-lactide) was resisted by enhancing the chitosan fiber content. The bone mesenchymal stem cell culture indicated that the composite scaffolds promoted the attachment and proliferation of cells, which would likely attach to and stretch along the chitosan fibers. Therefore, this ternary composite scaffold will be a promising matrix material for bone tissue engineering.

The objective of this work was to investigate the effect of kenaf contents on mechanical, thermal and morphological properties of recycled polyamide-6 (rPA-6)/recycled polypropylene (rPP) blends. Kenaf was used to enhance the properties of composites. Alkali treating of kenaf by sodium hydroxide (NaOH) and combination with propylene grafted maleic anhydride (PPgMA) as a compatibilizer produced good adhesion both between rPP and rPA-6, and rPA-6/rPP and kenaf. Tensile, flexural and Izod impact tests were evaluated to study the mechanical properties. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests were carried out to investigate thermal properties. Scanning electron microscopy (SEM) was performed for morphological analysis. Generally, the mechanical properties were successfully enhanced, especially Young’s modulus, flexural modulus, flexural strength and elongation at break, while there were some problems which caused the tensile strength and impact strength to be inferior. Thermal analysis showed that the crystallization of composites decreased as kenaf contents were increased. SEM showed a problem with kenaf and rPP/rPA-6 compatibility, which led to insufficient matrix at some places and agglomeration of kenaf at other places. Morphologically, there was unidirectional presence of kenaf in rPP main composites and random orientation in rPA-6 main composites.

Jute fabrics reinforced polyethylene (PE), polyvinyl chloride (PVC) and laminates of alternate PE and PVC matrices-based composites (50 wt% fiber) were prepared by compression molding. The values of tensile strength (TS), bending strength (BS), impact strength (IS), tensile modulus (TM) and bending modulus (BM) of the 60% PE+40% PVC hybrid matrices-based composites were found to be 55.2 MPa, 59.4 MPa, 24.0 kJ/m 2 , 1.59 GPa and 1.72 GPa, respectively. Gamma radiation (2–8 kGy doses) was applied on PE, PVC and jute fabrics, and then composites were fabricated. The values of TS, BS, IS, TM and BM of the irradiated (4 kGy) composites were found to improve by 15, 18, 23, 13 and 12% over non-irradiated composites. Scanning electron microscopy (SEM), water uptake and soil degradation tests of untreated and treated composites were also investigated.

The effects of single-walled carbon nanotubes (SWCNTs) on the mechanical properties of nanocomposites with epoxy matrix were studied, with the emphasis on fracture toughness under tensile loading conditions. It has been demonstrated that adding CNTs into polymer-based materials can improve the mechanical properties of this material. CNTs possess a certain potential to improve the fracture toughness of epoxy systems due to their mechanical properties and increase the fracture toughness of nanocomposites. Since the fracture toughness parameters were best manifested in the scaling properties and were the main parameters, the angles of different cracks have been simulated in a 3D finite element framework and the effects of different angles of crack, on the fracture toughness of polymers, have been modeled and investigated. The simulations are run for different bias angles. The influence of angle, the crack lengths and the variations of different lengths of nanocomposite in different volume fractions (vol%) are investigated. That is to say, at first, nanocomposites had a significantly higher fracture toughness compared to the pure epoxy. We found that nanocomposites, in the presence of SWCNTs, had a greater effect on fracture toughness of nanocomposites in a greater volume of fractions. Also, the nanocomposites exhibited a significant increase in fracture toughness, with zero angle of crack compared with greater angles. In addition, it is found that at a constant volume fracture, fracture toughness, increases by increasing crack lengths.

This work evaluates the influence of a radiopaque reinforcement, barium sulfate (BaSO 4 ), on the mechanical, rheological and thermal properties of polyoxymethylene (POM). Nanocomposites of POM containing spherical nanoparticles of BaSO 4 (0, 1, 2, 3 phr) were obtained by melt extrusion in a twin-screw equipment followed by injection molding. The mechanical, thermal and rheological properties of these nanocomposites and the dispersion state of the particles were investigated. Scanning and transmission electron microscopy revealed the morphology of the products. The main objective of this work is the production of nanocomposites with sulfate concentration enough to acquire radiopaque properties while maintaining the mechanical properties of the matrix. In this regard, mechanical and rheological properties were found similar to those of the polymer matrix, but radiopaque contrast tests revealed the influence of the nanoparticles concentration on the optical properties of the composites. The production of these nanocomposites suggests potential applications in the biomedical sector given their unique radio-opacity properties.