Volume 36, Issue 7

Protein immobilization studies with high protein binding sensitivity are of primary concern for any bio-sensing applications. In the present study, glutaraldehyde (GA) was utilized to chemically cross-link with the cellulose compound in mixed cellulose (MC) membrane and the protein molecules. Optimal cross-linking process on membrane was determined statistically and corresponded responses of protein immobilization were described through a quadratic empirical model. Field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) micrographs and thermogravimetric analysis (TGA) have demonstrated the successful deposition of GA on membranes. The optimum GA integration process condition was found at 3 wt% of GA on a single layer and 30 min of integration time, with protein binding predicted at 896.6 μg/cm 3 . The experimental validation was conducted at this optimum condition, and the result was found at 911.9 μg/cm 3 , with standard deviation of 1.6%. This small error confirms the adequacy of the empirical model and its ability to predict the GA-protein immobilization performances.

As south India is abundant with agricultural residues such as coir pith, rice husk and groundnut shell, this investigation is focused on using these residues as particle reinforcement for epoxy composites. The properties of coir pith, rice husk and groundnut shell particles were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). Moreover, particle sizes of residues were confirmed with a particle size analyzer. The particles were hybridized with different combinations and reinforced in epoxy matrix by means of the compression molding technique. The weight fraction of hybrid particles in the composites was varied in different proportions (7.5 wt%, 15 wt%, 22.5 wt% and 30 wt%) and their effects on mechanical, wear and water absorption properties were studied. The fracture mechanisms of the composites were studied using scanning electron microscopy (SEM). The result showed that the addition of rice husk with coir pith and groundnut particles improved the mechanical and water retention properties of the composites, whereas addition of groundnut particles with coir pith improved the wear behavior of the composites.

The effects of poly( d -lactide) (PDLA), nanoclay, talc, and stereocomplex formation were investigated in blends where these materials were added as a minor phase in a major phase of poly( l -lactide) (PLLA). Blends containing 2% PDLA, nanoclay, or talc as nucleants were prepared via melt blending and showed a strong increase in the crystallization rate as revealed by isothermal and nonisothermal crystallization measurements. The blending of 2% PDLA with PLLA led to the highest crystallization rate. Moreover, a stereocomplex formation was observed in a PLLA/PDLA blend (50:50). Wide-angle X-ray diffraction and differential scanning calorimetry verified that complete stereocomplex crystallites that do not form homocrystallites can be achieved. Compared with pure PLLA, the stereocomplex had a higher melting temperature and a higher crystallization temperature, by more than 50°C and 25°C, respectively.

Polymer/mineral filler nanocomposites are more and more used for diverse applications. As mineral fillers, layered double hydroxides (LDHs) present a great advantage as flame retardants from an environmental point a view (reduction of smoke and toxic gases). This article deals with the use of LDH as flame retardants as compared to montmorillonite (MMT). In situ bulk polymerization of styrene was carried out in the presence of MgAl LDH modified with dodecyl sulfate (DDS) and dodecylbenzene sulfonate (DBS) surfactants. LDH concentrations used were lower than 10 wt.%. X-ray diffraction analysis of the LDH-styrene suspensions revealed the monomer intercalation into the DDS-LDH galleries and a slight decrease in the DBS-LDH basal spacing. Transmission electron microscopy analysis showed that the polymerization occurred outside the DBS-LDH galleries, leading to exfoliation of the layers on the outer surface of LDH platelets. DDS-LDH particles were trapped in the PS polymer. The thermal stability effect was observed for all LDH nanocomposites by thermogravimetric analysis. Cone calorimetry measurements revealed that only the DBS-LDH nanofiller resulted in a reduction of the peak heat released rate (PHHR) and a decrease of smoke released. DBS-LDH/PS exhibited fire properties close to those of clay-PS nanocomposite at 7 wt.% montmorillonite. The PHRR reduction remained small and the total heat release rate constant at 7 wt.% DBS-LDH loading.

The fracture behavior and deformation mechanism of polypropylene (PP)/ethylene-propylene-diene rubber (EPDM) were studied by scanning electron microscopy and transmission electron microscopy analyses. The deformation mechanism was investigated under different conditions. Voids were seen under all the conditions because of matrix shear yielding, indicating that rubber particle cavitation took place during the blend fracture process; moreover, the void size and density increased as the fracture surface was approached. However, the void density and extent of elongation of the rubber particles in the deformation zone decreased with increasing test speed rate. Many voids were positioned in the rubber particles, confirming that matrix shear yielding initiated by rubber particle cavitation was the main deformation mechanism during ductile fracture in the matrix.

The extensive research on polymer composites is motivated by the fact that it can result in obtaining new materials with enhanced properties. This research primarily focuses on investigating basic mechanical properties which determine the use of a particular composite material. This paper presents the results of tests investigating the mechanical properties, i.e. tensile strength, hardness and impact strength, of hybrid injection mouldings produced at constant processing parameters. We used five metal powder fillers: aluminium, zinc, tin, iron and copper powders, with their contents ranging from 2.5 wt% to 15 wt% relative to a polypropylene matrix composite material. The relationships were determined between different contents of the aforementioned metal powder fillers and Young’s modulus, maximum tensile stress, tensile stress at break, strains, Shore hardness and Charpy impact strength. The research also involved investigating mould shrinkage. Relevant conclusions were drawn.

Carbon fibers (CFs) are incorporated into ethylene propylene diene monomer (EPDM) rubber to fabricate charring elastomeric ablative composites for ultrahigh temperature applications. Ablation characteristics of the ablative composites were evaluated using ASTM E285-08. Variant content incorporation of short CFs in the basic composite formulation reduced the backface temperature acclivity and the ablation rate rose up to 48% and 78%, correspondingly. Thermal stability and endothermic capability were improved with increasing short fiber contents in the rubber matrix. Experimental thermal conductivity measurement results elucidate that thermal conductivity reduces 60% at 473 K with 6 wt% addition of the fibers. A remarkable improvement was scrutinized in the tensile strength and rubber hardness with increasing fiber to matrix ratio. Scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS) analysis of the composite specimens revealed the uniform dispersion of CFs within the host matrix, formation of voids during ablation, char-reinforcement interaction and composition of the charred ablators and the impregnated fibers.

The tribological properties of polystyrene (PS) samples with different mechanical strengths were systematically investigated. The friction of the PS samples tested against a 6 mm steel ball significantly increased with increased working temperature from room temperature (RT) to glass transition temperature (T g )+20°C, while their wear apparently decreased. The harder PS samples exhibited lower friction and wear for all working temperatures. Lubricating the PS samples with wax lubricant at RT resulted in much lower friction and wear compared to those of the ones tested dry, because the wax lubricant effectively lubricated the rubbing surfaces. Addition of soda lime glass microspheres into the wax lubricant slightly lowered the friction of the PS samples with lower hardness compared to that of the same ones lubricated without the microspheres, due to the reduced direct contact between two rubbing surfaces and the free-rolling effect of the microspheres.

Plastic pipes, tubes or catheters are extruded by pressure-driven flows through annular dies. Whereas die lands are straight, the section connecting the die land to the extruder either converges or diverges, converging when the product is smaller than the extruder barrel, and diverging when larger. In this paper, we carefully consider the converging or diverging connecting flows, in spherical coordinates, for the most common configuration: the Newtonian pressure-driven flow through the annulus between two coapical coaxial cones. We derive the exact analytical solution for the velocity profile, and then use this to arrive at the exact analytical solution for the temperature rise caused by viscous heating. We care about this rise because it often governs maximum throughput, since pipe makers must protect the melt from thermal degradation. We find that both the velocity profile, and the temperature profile, peak over the same conical surface and this surface is nearer the inner die wall. We also provide analytical expressions for the nonlinear pressure profile and the die cooling requirement. We find that this cooling requirement is always higher on the inner cone.

The main goal in the design of spiral mandrel dies for blown film extrusion is to achieve a homogeneous velocity distribution of the plastics melt at the die outlet. However, thermal inhomogeneities in the die can lead to an uneven flow distribution despite a rheologically optimized design of the die. The thermal inhomogeneities are especially dominant in the predistributor of spiral mandrel dies. Against this background, the temperature influence on the melt distribution in the predistributor is investigated for different polyolefins with the help of flow simulations in Polyflow (Ansys). The simulation models the whole predistributor and takes both the heat transfer in the predistributor and the shear heating in the melt into account. Afterwards, simulations are conducted in which the thermal design measures for the homogenization of the flow in the die are applied. With the combination of heating cartridges, brass inserts, and isolating gaps in the die, a significant homogenization of the predistribution can be achieved. Finally, the simulation results are validated in practical tests, whereby a good agreement between simulation and measurement can be observed.