Aziz Hassan

Tensile, Impact and Fiber Length Properties of Injection-Molded Short and Long Glass Fiber-Reinforced Polyamide 6,6 Composites

Injection molding of fiber-reinforced polymer composites is associated with the problem of fiber breakage. If the fiber length retained in the finish product is too short, it will limit the expected improvement in the property. Extrusion and pultrusion are two methods normally employed for the melt compounding of polymer composite feedstock for the injection molding and produced short- and long-fiber composites (SFCs and LFCs), respectively. In this work, short- and long-glass fiber-reinforced polyamide 6,6 composites were injection molded at different fiber loading and tested for the tensile properties, impact properties and fiber length characteristics. It was found that both tensile strength and tensile modulus of LFCs improved compared to the SFCs counterpart despite reduction in fracture strain, while pultrusion compounded composites also showed superior fiber characteristics, in terms of fiber length distribution, Ln, Lw, etc. compared to the extrusion compounded composites counterpart. Fiber length characteristics were also in agreement with the improvement in tensile strength and tensile modulus of LFCs over the SFCs. Impact properties of LFCs also show some improvement compared to the SFCs counterpart with equivalent composition, despite longer fiber retained in composites.

Phase separation and polymer interactions in aqueous poly(vinyl alcohol)/hydroxypropyl methylcellulose blends

This paper discusses the compatibility of aqueous hydroxypropyl methylcellulose (HPMC)/poly(vinyl alcohol) (PVA) blended systems. Dynamic mechanical analysis and differential scanning calorimetry have provided clear evidence of two phases. Each phase precluded almost completely the other component. The HPMC-rich phase was amorphous with a constant Tg while the PVA-rich phase showed a limited level of crystallinity and a constant Tg for the amorphous part. Fourier-transform infra-red studies indicated hydrogen-bonding interactions involving the carbonyl and hydroxyl groups of like molecules but no detectable interactions between HPMC and PVA. A new hydrogen-bonding environment of the hydroxyls was observed in the blended system but was not capable of inducing any compatibility. The gross incompatibility was successfully predicted by the total solubility parameters of the two polymers and attributed to significant differences in the polar and hydrogen-bonding contributions. Surface energy analysis corroborated the inability of the two chains to participate in acid-base interactions between unlike molecules due to significant discrepancies in their Lewis acid-base characteristics. Finally, determination of the free energy of polymer-polymer interaction in water allowed approximate calculation of the Flory-Huggins parameters of aqueous PVA and HPMC systems.

Structural and Optical Characterization of Metal Tungstates (MWO4; M=Ni, Ba, Bi) Synthesized by a Sucrose-Templated Method

BackgroundMetal tungstates have attracted much attention due to their interesting structural and photoluminescence properties. Depending on the size of the bivalent cation present, the metal tungstates will adopt structures with different phases. In this work, three different phases of metal tungstates MWO4 (M= Ba, Ni and Bi) were synthesized via the sucrose templated method.ResultsThe powders of BaWO4 (tetragonal), NiWO4 (monoclinic) and Bi2WO6 (orthorhombic) formed after calcination temperatures of 750, 650 and 600°C for 4 h respectively are found to be crystalline and exist in their pure phase. Based on Scherrer estimation, their crystallite size are of nanosized. BET results showed NiWO4 has the highest surface area. BaWO4 exhibited less Raman vibrations than the NiWO4 because of the increased lattice symmetry but Bi2WO6 showed almost the same Raman vibrations as BaWO4. From the UV-vis spectra, the band gap transition of the metal tungstates are of the order of BaWO4 > Bi2WO6 > NiWO4. Broad blue-green emission peaks were detected in photoluminescence spectra and the results showed the great dependence on morphology, crystallinity and size of the metal tungstates.ConclusionThree different phases of metal tungstates of BaWO4 (scheelite), NiWO4 (wolframite) and Bi2WO6 (perovskite layer) in their pure phase were successfully prepared by the simple and economical sucrose-templated method. The highest surface area is exhibited by NiWO4 while largest band gap is shown by BaWO4. These materials showed promising optical properties.

pH Sensitive Hydrogels in Drug Delivery: Brief History, Properties, Swelling, and Release Mechanism, Material Selection and Applications

Improving the safety efficacy ratio of existing drugs is a current challenge to be addressed rather than the development of novel drugs which involve much expense and time. The efficacy of drugs is affected by a number of factors such as their low aqueous solubility, unequal absorption along the gastrointestinal (GI) tract, risk of degradation in the acidic milieu of the stomach, low permeation of the drugs in the upper GI tract, systematic side effects, etc. This review aims to enlighten readers on the role of pH sensitive hydrogels in drug delivery, their mechanism of action, swelling, and drug release as a function of pH change along the GI tract. The basis for the selection of materials, their structural features, physical and chemical properties, the presence of ionic pendant groups, and the influence of their pKa and pKb values on the ionization, consequent swelling, and targeted drug release are also highlighted.

Extrusion and injection-molding of glass-fiber/MAPP/polypropylene: Effect of coupling agent on DSC, DMA and mechanical properties

Glass fiber-reinforced PP composites compatibilized with maleic anhydride grafted polypropylene (MAPP) were compounded with a twin-screw extruder and injection molded. The composite specimens were subjected to DSC, DMA, tensile, and flexural property characterizations. DSC results showed that the presence of glass fiber loading and MAPP produced insignificant effect on the melting temperature of the composites. The melting enthalpy was decreased with glass fiber loadings, but no significant change was noted in the crystalline peak temperatures ( T c ). Incorporation of the compatibilizer led to a reduction in T c . Incorporation of glass fiber reduced the crystalline enthalpy of compatibilized and uncompatibilized systems. DMA results showed that composite properties were affected by the presence of the compatibilizer at low fiber loading (≤14% Vf). Tensile and flexural properties also showed sensible improvement of compatibilized against uncompatibilized composite systems.

Plasticization of aqueous poly(vinyl alcohol) and hydroxypropyl methylcellulose with polyethylene glycols and glycerol

Abstract The plasticization of aqueous hydroxypropyl methylcellulose (HPMC) and poly(vinyl alcohol) (PVA) with poly(ethylene glycols) (PEGs) with various molecular weights and with glycerol has been investigated. The plasticizing efficiency in the case of HPMC was: PEG200 > PEG400 > GLYCEROL > PEG6000 and for PVA: GLYCEROL > PEG200 > PEG400 > PEG6000. The plasticizer efficiency rating was explained with the partial solubility parameters of the polymers and the plasticizers in terms of the propensity of each polymer-plasticizer pair to set up polar and hydrogen-bonding interactions. Phase separation of the plasticizers occurred above a critical concentration which, in the case of PEGs, was inversely proportional to molecular weight. Phase separation of the plasticizer was shown to be responsible for deterioration in the plasticizing efficiency.

Polypropylene/glass fiber/nanoclay hybrid composites: morphological, thermal, dynamic mechanical and impact behaviors

Polypropylene/E-glass fiber/nanoclay were compounded with a twin-screw extruder and injection molded. Thermal, dynamic mechanical, and impact tests were carried out. Differential scanning calorimetry investigations showed that the incorporation of nanoclay into polypropylene/glass fiber composite shifted the melting temperature (Tm) to higher values. The degree of crystallinity (Xc) was strongly influenced by the presence of the glass fiber and nanoclay in the matrix. Dynamic mechanical analysis showed an increase in storage modulus (E′); indicating higher stiffness of the hybrid composites when compared to the glass fiber composites and the virgin matrix. From the tan δ curves, a strong influence of glass fiber and nanoclay content on the magnitude of tan δmax value was observed. Impact test showed a reduction in the critical strain energy release rate, Gc for hybrid composites with higher nanoclay loading. The stress intensity factor, Kc values showed insignificant effect with the presence of nanoclay and GF.

Micro-structural, thermal, and mechanical properties of injection-molded glass fiber/nanoclay/polypropylene composites

Hybrid composites of PP/NC/GF were prepared by extrusion and injection molding. Molded specimens were analyzed by XRD, SEM, and TEM, together with characterization of thermal and mechanical properties. XRD results revealed that the interaction between NC particles and the PP matrix results in intercalation of the polymer chains, which increases the clay interlayer distance. TEM results revealed NC particle intercalation. TGA results showed that the incorporation of clay into the GF composite improves the thermal stability of the material. The initial thermal decomposition temperatures also shifted to higher values. Incorporation of GF into PP lowers the tensile strength of the binary composite, indicating poor fiber–matrix interfacial adhesion; however, introducing NC increased the strength of the ternary composites. Tensile modulus was enhanced with the incorporation of GF and further increased with an introduction of NC. Flexural strength and flexural modulus are both enhanced with an increase in fiber loading. The addition of clay nanoparticles further improved these properties.

Thermal and mechanical properties of treated and untreated Red Balau (Shorea dipterocarpaceae)/LDPE composites

Red Balau saw dust was heat-treated at 180°C and 200°C for 1 h. Treated and untreated wood flour were compounded with LDPE at 9%, 20%, and 37% by weight and molded in an injection molding machine. Thermal and mechanical properties of the resultant composites were investigated as a function of filler loadings and treatment temperature. Thermogravimetric analysis revealed an increase in degradation peak temperature (Tp) of the heat-treated wood and composites. DSC revealed a decreasing trend in the degree of crystallinity (Xc) of the matrix when heat-treated wood was used as filler. On the other hand, untreated wood showed an increase in Xc with increasing wood content. Tensile modulus increased with heat treatment and filler loading. Furthermore, flexural strength and modulus were found to increase with filler loading.

Moisture Absorption Effect on Thermal, Dynamic Mechanical and Mechanical Properties of Injection-Molded Short Glass-Fiber/Polyamide 6,6 Composites

Polymer composites of polyamide 6,6 reinforced with short glass fiber were prepared by injection molding, conditioned under dry, 50 % relative humidity and wet. Investigations by DSC, DMA and tensile tests were conducted. FLD study showed that more fiber degradation occurred during processing of the composites with higher fiber loading. DSC analysis revealed that the incorporation of glass fiber and moisture into the PA 6,6 matrix resulted in a remarkable decrease in the degree of crystallinity. DMA results revealed the glass transition temperatures were sensitive to moisture absorption and their values moved to a lower temperature upon exposure to moisture. Incorporation of glass fiber into the polyamide 6,6 gave rise to a significant improvement in tensile modulus and tensile strength, while tensile strain was reduced. Exposure to different environments from dry to wet conditions resulted in a decrease in the strength and modulus, while tensile strains decreased.