Volume 35, Issue 5

Partially biodegradable polymer films from the blends of polypropylene (PP) and poly(L-lactide) (PLLA) were prepared in an internal mixer by melt blending technique, with and without compatibilizer, maleic anhydride grafted polypropylene (MAPP), followed by compression molding. With regard to tensile properties, 80/20 (PP/PLLA) and 80/20/6 (PP/PLLA/MAPP) were found as the optimum blends with best combination of the ingredients. Therefore, the blend samples, namely, PP80 (80% PP+20% PLLA) and PP80C6 (80% PP+20% PLLA+6 phr MAPP) were selected as ‘optimized’ blends and further characterized for their physical, chemical, morphological, and thermal properties. X-ray diffraction studies showed that neat PP and PP80C6 had the same crystallite size indicating compatibility between PP and PLLA due to MAPP. Fourier transform infrared spectroscopy and scanning electron microsopy investigations revealed that the two polymers were completely immiscible in absence of the compatibilizer. Bacterial biodegradation of the samples was performed by exposure to Pseudomonas stutzeri for 60 days and measured in terms of weight loss, optical density, and thermal stability of the samples before and after degradation. The results showed that 80/20 (PP/PLLA) blends undergo considerable degradation. Reduction in thermal stability of the film samples was also observed through thermogravimetric analysis, which was useful in accelerating their biodegradation.

The effects of the compositions and tensile rates on the tensile properties of the polyformaldehyde (POM)/ethylene-vinyl acetate copolymer (EVA)/high-density polyethylene (HDPE) blends and POM/EVA/HDPE composites filled with nanometer calcium carbonate were investigated by means of a tensile test machine at room temperature. The results showed that the Young’s modulus, tensile yield strength, and tensile elongation at break of the blends and the composites decreased nonlinearly with increase in the HDPE weight fraction; it should be attributed to the low stiffness and strength of the HDPE resin; the difference in the Young’s modulus and tensile yield strength between the blends and the composites was insignificant under the same experimental conditions. Both the Young’s modulus and tensile yield strength of the blends and the composites increased nonlinearly with increase in the tensile rate in the case of low tensile rate level. Moreover, the predictions of the Young’s modulus and tensile strength were roughly close to the measured data from the blends.

This paper aimed to investigate the interaction of distinct polarity polymer blends of polyethylene and polyvinyl alcohol (PVOH). Molecular mechanics and dynamics simulation were employed to determine the stability of polyethylene and PVOH complexes. It was found that the binding energies ΔE for all complexes of polyethylene and PVOH are negative values indicating that the interactions between both components are favorable to achieve a lower energy hierarchy. Such interactions are induced by the high polarity hydroxyl groups of PVOH which caused weak distortion to the dipole moment of inherently non-polar polyethylene. Furthermore, the molecular simulation results were compared with tensile strength, X-ray diffraction and morphology analyses. Tensile strength analysis revealed there was a reduction of magnitude for varying PVOH before achieving a maximum value. Adding small quantities of PVOH in polyethylene as the different polar elements would affect the ordered structure within the blends. Nevertheless, the reduction is insignificant due to the polarity of PVOH which has a slightly distorted polar network of polyethylene. The addition of PVOH (5–15 parts per hundred) into a polyethylene matrix has significantly reduced the crystallinity of the polyethylene matrix by disturbing the highly ordered arrangement structures.

This study investigates the properties of high-density polyethylene (HDPE) with different soya spent powder (SSP) blend contents upon oven aging. The aged properties of the HDPE/SSP blends were studied by using tensile test, thermogravimetric analysis, differential scanning calorimetry and Fourier transform infrared analysis. The tensile strength and elongation at break ( E b ) decreased inversely proportional to SSP content and aging period. The thermal stability of the blends was significantly reduced after 21 days of aging. After aging, the melting temperature and crystallinity of the blends decreased with increasing aging period. These results revealed that samples with higher SSP content are more brittle upon oven aging.

Different flame retardant ethylene-vinyl acetate copolymer (EVA) formulations were prepared to evaluate the synergistic effect between organo-montmorillonite (OMMT) and a Schiff-base polyphosphate ester (PAB) on the combustion behavior of EVA. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results revealed that montmorillonite platelets selectively dispersed in the PAB phase. EVA/PAB/OMMT(80/15/5) had better thermal stability and flame retardancy than EVA/PAB(80/20), as indicated by the results of thermogravimetric analysis (TGA), limited oxygen index (LOI), vertical burning test (UL-94) and microscale combustion colorimeter (MCC), showing a synergism between OMMT and PAB. For example, the onset decomposition temperature ( T 5% ) increased from 233°C to 296°C, the char residue at 600°C increased from 6.6% to 11.0%, and the peak heat release rate (PHRR) decreased from 718.1 W/g to 706.6 W/g. This is caused by the silicoaluminophosphate (SAPO) structure formed by reactions between the phosphoric acid generated from PAB and OMMT.

The effects of some important factors in the initial crystallization process of the solution casting method on the piezoelectricity of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) films were extensively explored. The experimental results revealed that there is an optimal initial crystallization temperature at around 90°C. The slow cooling speed can moderately enhance the degree of crystallinity. The most important finding was that a bilayer crystalline structure caused by an asymmetrical heating pattern can enhance the formation of packed micro-fibrillar morphologies after drawing. These three points can increase the piezoelectricity of the PVDF-HFP films, indicating the increase of the extended-chain crystals ( β -phase).

A series of mixtures of acrylic copolymer aqueous dispersions or acrylic copolymers and polyurethane water dispersions were used as environmentally friendly base coatings and an acrylic self-crosslinkable copolymer dispersion containing epoxy resin as top coating for natural leather. Samples finished with the proposed additives were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and physical-mechanical tests. FT-IR spectra show that the proposed ecofriendly dispersion used as top coating not only covers the surface of leather, but it is chemically bound with the base coat, assuring a resistant coverage. SEM images show smooth and uniform surfaces. Physical-mechanical characteristics are superior to those imposed by standards in force, demonstrating that the proposed dispersion is able to substitute successfully the top coating nitrocellulose aqueous emulsions (noted EMAL) commonly used as finishing agents, in which the nitrocellulose is dispersed as solution.

The potential of 18 wt.% polyvinylidene fluoride (PVDF) hollow fiber membrane blended with ethylene glycol (EG) for the treatment of dye solution using direct contact membrane distillation (DCMD) system was investigated. The PVDF membrane was prepared using the dry-jet wet spinning method and was characterized in terms of membrane morphology, porosity, wetting pressure, gas permeability and degree of hydrophobicity. The membrane was tested using dye solution containing 0.5 g l -1 reactive black 5 (RB5). The experimental period was prolonged to 6 h in order to analyze the fouling tendency and membrane durability during the DCMD process. The results showed that the modified PVDF membrane was able to produce consistent flux (i.e., 9.82±0.52 kg m -2 h -1 ) throughout the DCMD experiment while maintaining excellent dye rejection (i.e., 99.86±0.04%). With respect to membrane fouling, it was found that the lumen side of the membrane was significantly stained with color (compared to outer membrane surface) due to the physical-chemical interaction between reactive dye and membrane structure. Although membrane fouling was experienced in this study, its impact on MD performance in terms of flux and rejection was negligible, mainly because MD is not a pressure-driven process.

The major disadvantage of rotational molding is the cycle time, which is very long compared to other plastic processing methods. A major percentage of the cycle time besides heating and cooling results from the time necessary to remove gas inclusions from the polymer melt, which are trapped while sintering the polymer powder. In this work the formation of gas inclusions is investigated by conducting a cycle time variation on a uniaxial rotational molding machine. The influence of low pressure during melting on the formation of inclusions is investigated by examining sintering experiments with a pressure variation during the melting of the polymer. Sintering experiments are conducted with different melt residence times to investigate the mechanisms of gas inclusion removal. By comparing the time to reach a pore-free polymeric melt, the cycle time reduction potential under low-pressure application while melting the polymeric powder is estimated.

During the filling process of vacuum assisted resin transfer molding (VARTM), the infusion pressure gradient causes the resin flow and preform thickness variation. Even after the resin infusion discontinues, the resin keeps on flowing until the unnecessary resin is removed. In this study, a one-dimensional flow model coupled to the preform deformation is numerically analyzed to assess the influences of various processing scenarios on the infusion and post-infusion stages. The numerical model is implemented using a finite difference method. Results show that two strategies effectively reduce the filling process. One is to infuse less excess resin and the other is to turn the inlet into the additional vent. For a typical process using a one-sided vent, the theoretically optimum scenario is to infuse the exact required resin volume into the preform. From a practical standpoint, excess resin infusion is inevitable and a robust scenario is proposed by integrating the concept of fully filled preform and two strategies. Additional cases are performed using a vacuum assisted compression RTM (VACRTM) process for comparison purposes. Through the numerical work, a tool for optimization of the VARTM process is provided to reduce the filling process, resin waste and variability in the final composite part.

Polymers filled with conducting fibers to provide electrical conductivity performance have received great attention due to the requirements of many engineering applications. In the present article, injection molding of acrylonitrile butadiene styrene (ABS)/carbon-fiber composites using applied gas counter pressure (GCP) was conducted and the overall fiber orientation and associated through-plane electrical conductivity (TPEC) of each layer (core, shear and skin layers) and various locations (far gate, center and near gate) were characterized. Results show that GCP had significant effects on the fiber orientation and skin layer thickness, resulting in decreases in the fiber orientation level (FOL) value in all locations and TPEC increases with increasing GCP in the core region of the molded composites (improvement of 62% when 100 bar GCP was applied). However, the effect of increased skin layer thickness in reducing TPEC was stronger than the effect of decreased FOL in raising TPEC when GCP was applied. This resulted in the overall TPEC falling slightly with increasing GCP. The results also show that the electrical conductivity followed the sequence of far gate>center>near gate and the FOL followed the order of core layer<shear layer<skin layer. The results obtained in this investigation reveal the potential application of GCP technology associated with mold temperature control in injection molding to manufacture products with enhanced electrical conductivity in the future.