Volume 33, Issue 8

A series of polypropylenes (PPs) grafted with maleic anhydride (MA), prepared by reactive extrusion in a twin screw extruder with different contents of peroxide and MA, was characterized. For each sample, the amount of grafted MA, the molecular weight distribution, the viscoelastic properties in small amplitude oscillatory shear and the transition temperatures and enthalpies were measured. The respective influence of initial MA and peroxide concentrations on these parameters was characterized. In particular, it was shown that the rheological properties are only controlled by the molecular weight, whatever the way it has been obtained, by varying either MA content or peroxide concentration. Moreover, it is clearly shown that the presence of MA tends to enhance the PP degradation due to the peroxide.

Expanding the general knowledge of the extrusion process in a co-rotating twin-screw extruder requires several parameters to be determined, among them the residence time distribution (RTD). This contribution introduces an optical measurement setup for acquiring the residence time density and distribution function. Based on our measurement results, we derive the influence of the rotational speed of the screws, mass flow rate and of different types of screw configurations on residence time.

Conducting carbon/polypropylene (PP) and carbon/poly(butylene terephthalate) (PBT) composites containing crystalline natural graphite and carbon black (CB) were prepared by compression and injection molding. The effect of the processing technology on the electrical, mechanical, and morphological properties was investigated. Determination of the constant torque at the end of the mixing process and differential scanning calorimetric (DSC) measurements showed that graphite had better connectivity with the more polar matrix (PBT) than with the less polar one (PP). Scanning electron microscopy (SEM) studies showed that compression molding results in a homogeneous structure, while injection molding results in a skin-core structure with different orientations. Layered electrical conductivity studies showed that the electrical conductivity of the compression molded samples did not change along the thickness of the sample, while that of the injection molded samples changed throughout the material, which is due to the different structures developed with each type of processing.

Thermodynamic behavior of a ternary system with one low molecular weight component, formic acid (FA) as the solvent, water (non-solvent), and two high molecular weight polymers [polyamide-6 (PA-6) and cellulose acetate (CA)] was investigated using an extended modified Flory-Huggins model. Where, all chemicals were purchased from Leuna Werke AG (Germany). The model was solved by MATLAB SIMULINK software manufactured in the USA. The predicted results from the model explained that the miscibility of the two blend polymers, PA-6 and CA, completed over all compositions at room temperature, and the minimum point where the miscibility of the two polymers completed was in the composition of 0.2 volume fraction of PA-6 at Gibbs free energy change on mixing (Δ G m ) of -1.74015 kJ/mole. The critical temperature ( T c ) for superiority properties of the polymer blend solution are in the range between the upper critical saturation temperature (UCST) 323K and the lower critical saturation temperature (LCST) 338K. The diffusion model on the solution of the immersion precipitation process in the coagulation bath indicates that the solvent volume fractions increase with time, while the polymer solution volume fraction decreases, due to solvent removal from the polymer solution and membrane formation. According to the mathematical model, it was found that the annealing temperature can affect the densification of the membrane top layer. However, the heat treatment process leads to a decrease in thickness of the membrane bottom layer, as a result of reduced and distributed membrane pores.

A Monte Carlo (MC) model to incorporate the effect of Al 2 O 3 with different particle sizes in enhancing the ionic conductivity of composite polymer electrolytes consisting of polyethylene oxide (PEO), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), and ethylene carbonate (EC), is proposed. The simulated ionic conductivity in our MC model is validated by the results of electrochemical impedance spectroscopy, which determined the room temperature ionic conductivity of various composite electrolyte samples differing from the size of the Al 2 O 3 prepared via the solution cast method. With the simulated current density and recurrence relation, cation transference numbers, t +si of composite polymer electrolytes were derived using the steady-state current method proposed by Bruce et al. Addition of Al 2 O 3 (≤10 μm) in micron size greatly enhances the ionic conductivity to a magnitude of two orders, i.e., from 2.9025×10 -7 S/cm to 2.970×10 -5 S/cm and doubles the cation transference number from 0.230 to 0.465. However, the addition of Al 2 O 3 (<50 nm) in nano size decreases both the ionic conductivity and the cation transference number. The smaller size of Al 2 O 3 in the nano range is responsible for the congestion on the conducting pathways that traps some of the Li + in PEO electrolytes.

Magnesium hydroxide [Mg(OH) 2 ] with high flame retardant efficiency filled polypropylene (PP) composites were prepared using a twin-screw extruder. The impact fracture behavior of the composites was measured at room temperature. It was found that the toughening effect of the filler content on the PP resin was significant. The V-notched Izod impact strength of the PP/Mg(OH) 2 composites showed a nonlinear increase with increase in filler weight fraction ( ϕ f ), as ϕ f was <15%, and then it decreased slightly; When ϕ f was <15%, the V-notched Charpy impact strength of the PP/Mg(OH) 2 composite also increased nonlinearly, then it decreased slightly. The impact fracture surface was observed by means of a scanning electronic microscope, to understand the toughening mechanisms for the composite systems.

This study reports the high impact toughness of polyamide 6 (PA6)/poly (vinylidene fluoride) (PVDF) blends achieved via adding an ionic liquid. The presence of the ionic liquid in the blends promotes the transformation of sea-island structure into co-continuous morphology, which to a large extent accounts for the improvement in toughness. In addition, it is believed that the enhanced mobility of the PA6 matrix by the ionic liquid also contributes to the high impact toughness.

The study analyzed the sorption effectiveness of reactive dyes, Reactive Black 5 (RB5) and Reactive Yellow 84 (RY84), onto non-cross-linked chitosan beads (CHs) and onto CHs cross-linked with glutaraldehyde (ALD) i.e., ALD-CHs and epichlorohydrin (ECH) i.e., ECH-CHs. The study enabled determination of the optimal ratio of the cross-linking agent to chitosan and the optimal pH of the sorption process (from the range of 1:10–10:1, to 2–12, respectively). The time needed to reach the equilibrium concentration reached 504 h. Satisfactory effects of RB5 and RY84 sorption were achieved after 24 h sorption. Data were described with the heterogenous Langmuir’s model (double Langmuir’s equation). For RB5 dye, the most effective sorbent turned out to be CHs – the maximum sorption capacity reached 2025.11 (mg/g). For the other sorbents, ALD-CHs and ECH-CHs, the capacity accounted for 1797.0 mg/g and 1816.1 mg/g, respectively. In the case of RY84 dye, the most effective sorbent appeared to be ECH-CHs – 2234.3 mg/g. For CHs and ALD-CHs, the highest sorption capacities against RY84 reached 1774.2 and 2000.1 mg/g, respectively.

A UV-cured polyurethane (PU)/nano-silica composite with a flame-retarded coating system was obtained from the composition of nano-silica containing a UV-curable PU oligomer and a UV-reactive phosphonic acid [ethylene glycol methacrylate phosphate (EGMP)]. The UV-curable PU oligomer was prepared by an addition reaction of 2-hydroxyethyl methacrylate (2-HEMA) with an NCO-terminated PU pre-polymer; this was then mixed with a methanol dispersion of nano-silica. The UV-reactive phosphonic acid (EGMP) was prepared by a reaction of 2-HEMA with phosphorus pentoxide (P 2 O 5 ). The curing reaction of the PU/nano-silica composite coating system was carried out by UV irradiation with the aid of a photoinitiator (2-hydroxy-2-methylpropiophenone). The thermal properties of these PU/nano-silica composite coatings were investigated by the measurements of dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), respectively. A phosphorus (phosphonic acid) containing ingredient, EGMP in PU coating system that provides good adhesion to steel surface and flame retardation. Their physical properties (contact angle, hardness) and flame flammability [limiting oxygen index (LOI), UL-94 test] with various phosphorus contents (different dosages of EGMP) were also evaluated in this report.

Graft copolymerization of acrylonitrile and acryloyl chloride on to chitosan was prepared by γ-rays. Optimization of the grafting (%) was studied. The grafting (%) was observed to increase with increase in the irradiation dose and monomer concentration. The grafting percentages were about 52% and 36% from polyacrylonitrile and poly(acryloyl chloride), respectively. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterize the specimens. The modified chitosan was loaded with vitamin B 12 , demonstrated nearly 5.0±2.3% and 50.1±4.5% release in the media of pH 1.2 and 6.8, respectively, for amidoximated chitosan-grafted polyacrylonitrile and 3.6±1.1% and 36±2.4% in pH 1.2 and 6.8, respectively, for chitosan-grafted poly(acryloyl chloride), as determined by a traditional dissolution model. The modified chitosan specimens that uploaded with vitamin B 12 displayed a more decremental release in the acidic medium than the neutral one. However, in order to incorporate in vivo gastrointestinal conditions, such as acidic pH and high water content in the stomach, low water content, and the presence of semi-solid mass in the large intestine, a new model, called flow through diffusion cell, was also used to study the drug release. The results of the two approaches produced different release profiles at the same pH values.

In order to solve weakness, undesirable abrasion resistance, and hardness of a water-based wood coating film, modified surface nano-alumina was made in the water-based wood coating. The effect of surfactant type and amount on the performance of nano-alumina slurry was investigated. How the performance of the polyacrylate wood coating was affected by the size, amount, and mixing method of nano slurry was studied, as well as the characterization of nano-alumina slurry and modified polyacrylate wood coating. The results showed that, by compounding the non-ionic surfactant polyoxyethylene octylphenol ether (OPEO) and anionic surfactant sodium polyacrylate of surface modification of nano-alumina, the nano-alumina slurry had excellent performance and good stability when the amount of nano-alumina was 0.6 wt% and 3.2 wt%, respectively. When 1.5 wt% of nano slurry was mixed with the water-based polyacrylate emulsion to a hybrid during the pre-emulsification phase, the wood coating film had high performance, and good abrasion resistance and hardness.