Volume 38, Issue 9

Two types of random copolymer poly( d -lactide-co- ε -caprolactone) (PDLA- r -PCL) were added into poly( l -lactide) (PLLA) matrix by melt blending. The structure and property of PLLA/PDLA- r -PCL blends were investigated by thermal gravimetric analysis, differential scanning calorimetry, scanning electron microscopy, wide-angle X-ray diffraction, and mechanical measurement. The results suggested that PDLA- r -PCL had little effect on the thermal property of PLLA. PDLA- r -PCL uniformly dispersed in PLLA matrix, which contributed to the improvement of stretching properties. During stretching at 25°C, with the increased content of PDLA- r -PCL, the elongation at break of PLLA increased and the strength decreased. The degree of decrease in fracture strength was related to the molecular structure of PDLA- r -PCL. When a small amount of stereocomplex crystals (SC) were formed in PLLA/PDLA- r -PCL blends, the strength was maintained or slightly enhanced even though the elongation at break of the blends was significantly improved by soft chains of PCL. It might be caused by the synergistic effects of SC crystals and plasticization of PCL chains.

Composite materials made from high density polyethylene (HDPE) and polystyrene (PS) were successfully prepared in different HDPE/PS weight ratios, by melt mixing 3 wt% of bentonite clay organically modified with hexadecyl ammonium chloride (organo-modified bentonite, OBT). The structure and morphology of these composites were examined by X-ray diffraction and scanning electron microscopy. Morphological changes between the composite and the constituent materials were observed. The decrease in PS (or HDPE) particle size in HDPE/PS 70/30 (or 30/70) that blend after the OBT addition reflects a clear improvement in the HDPE/PS blend compatibility. The effect of OBT on the thermal and mechanical properties was investigated by differential scanning calorimetry, thermogravimetric analysis, and tensile measurements. The main results show a decrease in the HDPE crystallinity in the composite matrices, which reaches 25% for HDPE/PS/OBT 29/68/3 composite, also an improvement of the thermal stability, as evidenced by the higher T onset values, and finally a reinforcement of the tensile properties as compared to the unfilled blends. Indeed, a significant enhancement of the tensile modulus (~130%) is observed for the 68/29/3 composite matrix as compared to the 70/30 unfilled blend.

In the present study, the influence of incorporating various amounts of hyperbranched polyester (HBPE) into thermosetting resin blends composed of cyanate ester (CE) and benzoxazine (BOZ) resins was investigated for their structural, morphological, mechanical, and thermal properties. The FTIR spectra revealed that the CE/BOZ resin had reacted with the functional groups of HBPE, and the SEM test confirmed the morphological changes from a smooth surface that was observed for the virgin CE/BOZ resin to a rough surface for the maximum HBPE content. Moreover, the mechanical and thermal properties were found to be pointedly enhanced as we increased the content of HBPE. These remarkable enhancements may be due to the chemical structure of the HBPE which could form a cross-linked structure through a strong hydrogen bonding with the CE/BOZ resin. As a result, a considerable amount of applied mechanical load can be absorbed, and in parallel, the thermal stability can also be improved. We believe that the HBPE can be a good toughener for the CE/BOZ resins that could possibly expand their range of applications in various industrial sectors.

Sb-SnO 2 /potassium titanate (SSP) composites were synthesized by densely coating Sb-doped SnO 2 on the surface of fibrous-like potassium titanate. X-ray diffraction demonstrated that Sb was successfully doped into the crystal lattice of SnO 2 . To improve the dispersion of SSP composites in the acrylic resin, the as-prepared SSP was modified with sodium stearate. Fourier transform infrared spectra, thermogravimetric analysis, and transmission electron microscopy confirmed that stearate radicals existed on the surface of SSP in the form of physical adsorption. The hydrophilic degree of modified SSP was largely improved by water contact angle measurements. The properties (surface resistivity and mechanical properties) of the conductive coatings prepared by adding the obtained composites were investigated in detail. The modified SSP coatings exhibit more superior electrical conductivity due to their better dispersion in the matrix compared with SSP. Moreover, the obtained composite coatings present high pencil hardness of 4H–5H and excellent adhesion force, flexibility, and impact resistance.

Poly (vinyl alcohol) and nano-diamond, PVA/ND, hydrogels were prepared and assessed as prosthetic material suitable for replacement of the nucleus pulposus. The hydrogels were prepared by gamma irradiation at various doses (15 kGy, 25 kGy, 35 kGy, 45 kGy) and at various ND concentrations ranging from 0.25 wt.% to 3 wt.%. Extent of gelation, equilibrium water content, and viscoelastic properties of swelled hydrogels at definite water contents were measured and examined as a function of ND concentration as well as gamma dose. According to viscoelastic measurements, the strength of hydrogels increased considerably over that of pure PVA at a low concentration of ND. By increasing irradiation dose, gel percent and strength of hydrogels increased. Hydrogel water content was in a range of 80 wt.% to 90 wt.% similar to that of natural nucleus pulposus. The G ″ values of hydrogels were much smaller than G ′ values indicating elastic behavior. Also PVA/ND nanocomposite films were prepared at various ND concentrations by solution casting. The ND particles were uniformly distributed within PVA films. Tensile modulus and strength of the films increased over pure PVA.

High tensile strength ultra high molecular weight polyethylene (UHMWPE) fibers were prepared via the dry spinning method. Raw material was UHMWPE resin with 6 million viscosity-average molecular weight (Mv). Changes of morphology, mechanical properties, thermal properties and crystallization process of the fibers in the ultra-hot drawing process were studied by scanning electron microscopy (SEM), tensile tester, differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD). Results show that there was a maximum value of fracture force at a draw ratio of 40 and excessive draw ratio destroyed crystal structures in fibers and led to a decrease in the fracture force value. A shoulder peak appeared in DSC curves of ultra-drawing samples and its peak value maintained at 154°C in different samples. In addition, three peaks can be observed in all WAXD patterns of drawing samples. The mechanism of microstructural changes during the hot drawing process was elucidated.

In this study, six different types of polysulfone hollow fiber membranes were fabricated from the same polymeric dope solution by manipulating several important parameters during the spinning process, aiming to find the best membrane supports for the coating layer in the gas separation process. The experimental results showed that upon the polydimethylsiloxane (PDMS) coating process, the gas pair selectivities of all six types of membranes were significantly increased with respect to carbon dioxide (CO 2 )/methane (CH 4 ) and oxygen (O 2 )/nitrogen (N 2 ) separation. However, the membrane support spun at higher air gap and lower dope extrusion rate was found to be the best support for PDMS coating owing to its good structural integrity that led to a good balance between gas permeance and gas pair selectivity. Further investigation showed that the use of poly(ether block amide) (Pebax) as coating material did not certainly improve both gas permeance and the selectivity of hollow fiber membranes, although Pebax was previously reported to exhibit better performance than PDMS in flat sheet membranes. One of the main reasons is the difficulty of forming a defect-free Pebax coating layer on the outer surface of hollow fibers owing to the stickiness issue among fibers upon coating. More research is still needed to optimize the Pebax coating solution and its drying process in order to achieve the full potential of such coating material for hollow fiber membranes.

High-frequency electric field (HEF) was applied to prepare aligned carbon nanotube (CNT)-reinforced polypropylene (PP) matrix composites during the compression molding process in this article. The effects of the alignment of multiwalled CNTs (MWCNTs) in the PP matrix under HEF on the electrical, dielectric, and rheological properties of the resulting composites were reported. The results showed that the composites prepared in the presence of the electric field had better conductivity than those of the untreated composites. The dielectric property measurement indicates that MWCNTs aligning along the direction of the imposed electric field greatly improved the dielectric properties of composites. Rheological analysis showed that the storage modulus of the aligning direction samples is higher than the value of the untreated composites and the microstructure of the composite has been changed due to the effect of HEF.

Molecular models were established to predict the miscibility of polyimide/polythene mixing systems and the enhancing effects of compatibilizer addition of maleic anhydride grafted polythene (MAH-g-PE). Molecular dynamics simulations were applied to investigate radial distribution functions and Flory-Huggins parameters of the mixing systems. Results show that polyimide/polythene is miscible to a certain degree, and the miscibility gets better after adding MAH-g-PE. Dissipative particle dynamics (DPD) simulations display that micro-phase separation occurs in the polyimide/polythene mixing systems, however, effective interfaces appear between polyimide and polythene phases after adding MAH-g-PE. The results of molecular mechanics simulations indicate that the ability of mixing systems to resist stretch, compression and shear deformation increases after adding MAH-g-PE. This work offers a promising technique to predict miscibility properties for polyimide/polythene system prior to actual production and attempt to find a suitable compatibilizer for that system.

The aim of this work was to study the interactions between polypropylene (PP) food packaging for fatty products (margarine) and food simulant. For this purpose, a simulant (olive oil) was used in two different temperatures (20°C and 40°C). The interaction phenomena were investigated according to the rate of mass variation of PP samples with time and by using Fourier transform infrared spectroscopy, scanning electron microscopy and high-performance liquid chromatography (HPLC). The results showed the presence of two phenomena – migration of additives and sorption of the simulant, with the phenomena more pronounced at 40°C. Furthermore, the HPLC analysis identified the presence of Irganox 1010 and Irgafos 168 as antioxydants and allowed to carry out a kinetic study of Irganox 1010 migration. The concentration of Irganox 1010 decreased from 13.35 to 4.76 mg/kg at a temperature of 40°C and to 5.85 mg/kg at a temperature of 20°C after 10 days of contact with olive oil. The Irgafos 168 migration could not be evaluated because it is very sensitive to oxidation.

Polymer processing is a crucial and diverse field in the manufacturing industry. We investigated the process characteristics and effects of injection molding using ultrasonic vibration. An ultrasonic device was installed in an injection mold; polymer was directly vibrated during injection. An ultrasonic oscillation device 45 mm in diameter was placed in the cavity and used to vibrate a poly(methyl methacrylate) melt at 19 kHz. The amplitude of the acoustic unit was set at 15 μm for the measurements. Moreover, cavity pressure sensors were positioned at the front and rear sides of the vibration region to determine the melt flow behavior under ultrasonic-assisted injection molding conditions. Because of the absorption of ultrasonic energy, local heat was generated inside the resin, thus improving the flow characteristics of the melt. Moreover, the melt flow behavior around the skin layer was changed; the molecular orientation and high shear effect were reduced. Furthermore, the freezing rate of the melt was reduced; thus, the amount of melt pressure lost through the cavity was decreased and the residual stress inside the injection-molded component generated during the photoelastic stress analysis was lower.