Volume 32, Issue 8-9

Sensitivity analysis of free-volume theory para­meters have been done in ternary polymer-solvent-solvent systems. Two ternary polymer-solvent-solvent systems have been studied: poly(styrene)-tetrahydrofuran- p -xylene and poly(methyl methacrylate)-ethylbenzene-tetrahydrofuran systems. Simulation analysis has been done to see the effect of all parameters involved in predicting the self-diffusion coefficient in polymer-solvent systems. Sensitivity analysis showed that the predictions are highly sensitive to ξ 13 and ξ 23 and, therefore, they need to be predicted with good accuracy and these two are not pure component properties.

Melt mixed metallocene-catalyzed ­polyethylene elastomer (mPE)/clay nanocomposites, using a functionalized polyolefin elastomer (mPE-g-silane) as a compatibilizer, with the addition of the commercial clay with different intercalant types (Cloisite 20A and 30B) were prepared to investigate the importance of interfacial interaction. Cloisite 30B gave a relatively higher polarity than Cloisite 20A, but smaller original d-spacing. According to X-ray diffraction (XRD) and transmission electron microscopy (TEM) results, Cloisite 20A-filled nanocomposites depicted fairly well-dispersed clay within the mPE matrix, except with higher clay content. By contrast, the clay agglomerates were evident for Cloisite 30B-filled cases. A continuous increase of gel content for Cloisite 20A-filled systems was observed, but only a limited variation for Cloisite 30B-filled systems was found. The roles of the polarity degree of the organically modified clay, original d-spacing, and the compatibilizer, were quite essential. Young’s modulus of Cloisite 20A-filled samples increased with increasing clay content, from 23.8±1.3 MPa [0 parts per hundred resins (phr)] to 34.1±2.0 MPa (9 phr), whereas modulus of Cloisite 30B-filled samples did not show a significant variation. The tear strength of Cloisite 20A-filled nanocomposites increased up to two-fold with increasing clay content, reaching 9 phr. Only a slight increase in tear strength of Cloisite 30B-filled nanocomposites was observed. For the cutting strength, Cloisite 20A-filled cases also conferred higher values in comparison with Cloisite 30B-filled cases.

The ternary blends of three versatile polymers of polyamide 1010 (PA1010), polypropylene (PP), and ABS resin (ABS) were studied. As a compatibilizer, PP was multimonomer melt grafted in the presence of maleic anhydride (MAH), styrene (St), and dicumyl peroxide. The effects of multimonomers melt grafting blends of MAH and St on the crystallization behavior, morphology, and mechanical properties of PA1010/ABS/PP blends were investigated. The results showed that the graft copolymer generated in situ by the anhydride groups of grafted PP (g-PP) and the amino end of PA1010 has reduced the interfacial tension of blends efficiently. The interaction of St groups of the graft copolymer with ABS was helpful to improve the compatibility of the three components during melt blending process. The size of dispersed phases in the blends was reduced remarkably and the mechanical pro­perties were greatly improved when the content of g-PP in PA1010/ABS/PP blends is increased to 10%. The tensile strength of the compatibilized PA1010/ABS/PP blends was improved by a factor of 11.7, whereas the impact strength and elongation at break were increased by 4 and 4.9 times, respectively. The introduction of multimonomer melt g-PP is shown to be an effective approach to modifying immiscible multipolymer blends, which have many potential applications.

Na + montmorillonite (MMT) was modified with benzyldimethyltetradecylammonium chloride (B13) and further with (3-mercaptopropyl)triethoxysilane and vinyltrimethoxysilane to prepare B13-MMT, mercaptomethylorthosilicate modified MMT (MTMO), and vinyltrimethoxysilane modified MMT (VTMO), respectively. The pristine and modified clays were compounded with an HTV-type silicone rubber (GP-30 ® ), and the physical properties and morphology of the resulting rubber composites were examined. Both HTV/MTMO and HTV/VTMO exhibited an intercalated/exfoliated coexisting morphology, but the degree of exfoliation of the former composite was higher than that of the latter. Moreover, the thermal stability, as assessed by the onset temperature of thermal degradation, as well as the tensile stress, elongation at the break, and tear strength of HTV/MTMO was higher than those of HTV/B13-MMT and HTV/VTMO. However, the cross-linking density of HTV/MTMO was the lowest among the composites examined because the thiol groups of MTMO extinguished and abstracted the radicals formed by the curing agent. Accordingly, the improved mechanical and thermal properties of HTV/MTMO were attributed to the enhanced interactions between HTV and MTMO due to the chemical reaction between the thiol groups of MTMO and the vinyl groups of HTV.

Four different surface treatments were performed on aluminum sheets that were then bonded with an epoxy-based film adhesive in an autoclave to achieve good adhesion. Specimens were examined to determine the microstructure of the porous oxide layer on the aluminum sheet surface and its effects on the bonding performance. Based on the failure modes of the bonded surfaces, the peeling strength, and an analysis of the microstructure of the porous oxide layer, this study showed that chromic anodizing the aluminum sheet had the best bonding performance, whereas sulfuric and hard anodizing exhibited the worst bonding performance. Hot etching exhibited a bonding performance somewhere between that of chromic anodizing and that of sulfuric anodizing. The chromic anodizing surface treatment can produce more pores on the oxide layer of aluminum sheet surface, which can enlarge the bonding areas and consequently enhance its bonding performance.

The thermooxidative degradation of natural rubber (NR) coagulated by microwave radiation (NR-m) was investigated by thermogravimetry (TG) analysis, and compared with NR coagulated by acid (NR-a). It was found that the degradation process is not a one-step reaction, the main degradation process occurs at 300–400ºC, and the equilibrium degradation temperatures of NR-m are higher than those of NR-a. Different methods were used to find the most probable kinetic model and the Arrhenius para­meters (activation energy E and preexponential factor A ) for the main stage of thermooxidative degradation of NR-m. The results show that the values of E and A , obtained from the Coats-Redfern method, are highly variable with the kinetic model chosen and the heating rate ( β ), and the apparent activation energy ( E 0 ) when β approaches zero for the D n type kinetic model is in the range of 96.7–106.4 kJ ∙ mol-1. The mean values of E , calculated by the Friedman and Flynn-Wall-Ozawa (FWO) methods, are 113.8 and 83.3 kJ ∙ mol-1, respectively, suggesting E in the range of 83.3–113.8 kJ ∙ mol-1. Comparison of these two ranges indicates the most probable kinetic model to be D n type kinetic models, corresponding to a diffusion-controlled mechanism.

Applicability and subsequent modification of various composite models for the prediction of the relative tensile modulus of polyolefin nanocomposites has been studied. A number of models, such as the modified Halpin-Tsai, Guth, Mori-Tanaka, Hui and Shia and Takayanagi models, as well as factorial and mixture designs, were considered. Various assumptions in the models, such as uniform shape and size of filler (i.e., complete exfoliation), alignment, as well as interfacial bonding between the components, restrict their application for the prediction of the nanocomposite modulus. The modified Guth model and Halpin-Tsai model, with the ∅ m concept, were developed further to incorporate the modulus reduction factors for polyolefin nanocomposites. This allowed the generation of master curves of the modulus reduction factor as a function of the aspect ratio of the filler in the composite. It was observed that the Mori Tanaka model, modified by constructing models of various representative volume elements (RVEs) of the underlying structure of the nanoclay filled polymers, matched the experimental values of the tensile modulus of polyolefin nanocomposites. The modified Hui and Shia model, incorporating the non-bonding interfacial effects, as well as the three component modified Takayanagi model, were also able to predict the tensile modulus of polyolefin nanocomposites efficiently. Factorial and mixture designs did not require the conventionally used assumptions and satisfactorily reflected the material behavior, and were specific to the particular components used to generate nanocomposites. These models were also helpful in predicting the aspect ratio of the filler in the composites, when synergistically combined with other modified models.

Some properties of canna ( Canna indica L.) and bore ( Alocasia macrorrhiza ) starches were evaluated and compared using cassava starch ( Manihot esculenta Crantz ) as a reference. Proximate analysis, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and viscosity measurements were performed. Canna and bore starches showed a similar degree of purity as that of the cassava starch. Canna starch exhibited higher thermal stability and viscosity of solution values than those of bore and cassava starches. XRD spectra showed that canna starch crystallizes as a B-type structure; however, bore and cassava starches crystallize as an A-type structure. Results proved that canna and bore starches are promising bio(materials), obtained from unconventional sources, to be used for industrial applications, as their physicochemical properties are similar to those of cassava starch, which it is known has potential applications in this area.

A variant process incorporating the method of bag compression into resin transfer molding (RTM), called vacuum assisted compression RTM (VACRTM), has been developed to reduce the cycling period and improve the quality of the part. The process utilizes a flexible bag placed between the upper mold and the preform compared with RTM. By controlling the stretchable bag, the resin is easily introduced into the cavity filled with a loose preform. Then, ambient pressure is applied on the bag that compacts the preform and drives the resin through the remaining dry preform. The objective of this research is to explore the simplified VACRTM feasibility and investigate the effects of process variables, including resin temperature, resin infusion pressure, mold cavity height and cure temperature, on the mechanical strength of the part, by applying Taguchi’s method. The results show that VACRTM has advantages in terms of its being an easy and good seal among mold parts and the the lack of a need to clean the upper mold. The resin infusion pressure is a significant variable for improvement of the mechanical strength of the part. Optimal VACRTM reduces the filling time by 58% and increases the flexural strength by 10%, as compared with typical vacuum assisted RTM (VARTM).

Different stacking sequences of woven basalt and jute fiber hybrid composites were prepared using compression molding techniques. The static mechanical properties such as tensile, flexural, and impact behaviors were studied. A constant pressure was applied to all the fabricated composites, and fibers were arranged in different layering patterns. It was found that from the different layering patterns, the tensile and flexural properties slightly increased for hybrid composites having alternate layers of basalt and jute fiber. To study the fracture surface morphology of the hybrid composites, scanning electron microscopy was also performed.

The present investigation addresses the influence of process variables on the mechanical properties of montmorillonite (MMT) nanoclay with unsaturated polyester, using the mechanical shear mixing process. The rotational speed, mixing time, rotor blade design and clay content were chosen as process variables. The influence of these process variables on mechanical properties were studied with the help of grey relational analysis. Organically modified MMT nanoclay was used as the reinforcing filler, in order to increase the swelling of the clay with the polyester resin. Nanocomposites were fabricated based on the experimental design using the L 9 orthogonal array. Among the parameters studied, blade design was identified as the parameter with the most influence, due to the presence of a varying shear force, which peeled off the clay platelets from the stacked arrangement of clay tactoids. Grey relational analysis was used to obtain the optimum process parameters for multiple quality characteristics such as tensile, flexural and impact strength. It was observed that the Shore D hardness values for all nine experiments possess higher values than virgin polyester. Morphological studies have been carried out for the specimen with optimum process parameters using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile, flexural and impact fractured specimens were studied using scanning electron microscopy (SEM) for optimum conditions.

Maleic anhydride (MAH) grafting onto isotactic polybutene-1 (iPB-1) was prepared using di-tert-butyl peroxide (DTBP) as the initiator in the internal mixer. The influence of the reaction temperature, rotor rate, initiator content, monomer and co-monomer content, on grafting ratio (G/%) and melt flow rate (MFR), was investigated. The results showed that the temperature and rotor rate had little effect on the grafting ratio and MFR when the temperature was 160°C–200°C, and the rotor rate was 50 rpm–90 rpm. Besides, as the initiator content increased, the grafting ratio increased, but excessive initiator content led to degradation of macromolecules and a significant increase in MFR. The grafting ratio reached a peak value with an MAH content of 4.5 phr and a fixed initiator content of 0.3 phr. As a co-monomer, styrene (St) can enhance the G/% and decrease the MFR. The crystallization properties of iPB-1 were also studied. The grafting of MAH onto iPB-1 remarkably accelerated the crystal form II to I transformation of iPB-1 and the transformation rate increased with an increase in the G/% of iPB-1.

Nowadays, several procedures are used for manufacturing wind tunnel models. These methods include machining, casting, molding and rapid prototyping. Raw materials such as metals, ceramics, composites and plastics are used in making these models. Dimension accuracy, surface roughness and material strength are significant parameters which are effective in wind tunnel manufacturing and testing. Wind tunnel testing may need several models. Traditional methods for constructing these models are both costly and time consuming. In this research, a study has been undertaken to determine the suitability of models constructed using rapid manufacturing (RM) methods for use in wind tunnel testing. The aim of this research is to improve the surface roughness, dimensional accuracy and material strength of rapid manufacturing models for testing in wind tunnels. Consequently, the aerodynamic characteristics of three models were investigated and compared. The first model is made of steel, the second model from FDM-M30, and the third model is a hybrid model. Results show that metal models can be replaced by hybrid models in order to measure aerodynamic characteristics, reduce model fabrication time, save fabrication cost and also to verify the accuracy of aerodynamic data obtained in aerospace industry.

Waste polymer reconditioning was examined by a method of dissolution/reprecipitation on low- and high-density polyethylene (PE) and polypropylene (PP). Toluene and petroleum ether, in different proportions, were used as solvents, and n-hexane was used as a non-solvent. Commercial polymer products used on an everyday basis were used with a virgin polymer, to optimize the qualities of the final product, and 98% polymer was recovered in each case. Fourier transform infrared spectroscopy (FTIR) images and tensile mechanical properties of the samples, before and after recycling, were analyzed. The potential recycling-based degradation of the polymer was further investigated by measuring the thermal properties (melting point and crystallinity) before and after recycling, using differential scanning calorimetry (DSC). High reconditioning was observed in most recycled samples, with no significant difference from the virgin materials. The studied technique seems to be viable for waste polyolefin polymer recycling.