Muhammad Ilyas Sarwar

Dynamic‐mechanical thermal analysis of aramid‐silica hybrid composites prepared in a sol‐gel process

Several types of nonbonded and chemically bonded composites of silica with linear and linear-nonlinear aramid polymers were prepared using the sol-gel process. The linear polyamide chains were synthesized by the reaction of a mixture of m- and p-phenylene diamines and terephthaloyl chloride in dimethyl acetamide. The nonlinear chains were prepared using 1,3,5-benzenetricarbonylchloride along with tereph-thaloyl chloride, thereby significantly increasing the average functionality of the monomers. These increased functionality chains were then endcapped with aminophenyl-trimethoxysilane. Silica networks chemically bonded to the polyamide chains were produced by the addition of tetramethoxysilane to the aramid solution and its subsequent hydrolysis and condensation. The films cast from these solutions were yellow, and those containing up to 25 wt % silica were also transparent. Dynamic-mechanical thermal analysis was carried out to characterize interfacial bonding and interactions, in particular through the use of values of the glass transition temperatures Tg of the polymers. The presence of the silica caused increases in Tg, with the increases being largest for the composites in which there was strong interfacial bonding between the polymer chains and the ceramic silica phase.

Thermal and mechanical properties of aramid-based titania hybrid composites

The sol-gel process has been used to prepare various types of aramid-titania hybrid materials. Specifically, a mixture of m- and p-phenylenediamines was reacted with terephthaloyl chloride to produce linear polyamide chains in a dimethylacetamide solvent. Various proportions of tetrapropylorthotitanate (TPOT) were added, and its subsequent hydrolysis-condensation in the polymer solution produced a titania (TiO 2 ) network in the aramid matrix. Thin films prepared from these materials were tested for their tensile strength, which was found to decrease with increasing proportions of titania. To remedy this through chemical bonding between the matrix and the inorganic network, a slight excess of terephthaloyl chloride or 1,3,5-benzenetricarbonyl chloride was added near the end of the polymerization reaction. These aramid chains were thus end-capped with single or double carbonyl chloride groups. This allowed the chains to be further modified, with aminophenyltrimethoxysilane end caps. Chemically bonding the titania network to the aramid chains was then achieved by in situ hydrolysis-condensation of TPOT along with that of aminophenyltrimethoxysilane. In this way, thin transparent and tough films could be obtained with up to 30 wt % titania. The values of the tensile strength in the case of bonded hybrid materials increased with the addition of titania, and the polyamide system with nonlinear end groupings showed larger increases than did those with the linear chains ends. The systems with linear and nonlinear aramid chain ends were able to withstand maximum tensile stresses of the order of 193 and 246 MPa, respectively. This is presumably due to the extensive bonding between the polymeric chain ends and the inorganic phases as compared to the unbonded system. The thermal decomposition temperature of these composites was found to be in the range of 500-600°C and the overall weight loss was found to be minimized in an inert atmosphere.

Mechanical and thermal properties of nano-composites of poly(vinyl chloride) and Co-poly(vinyl chloride-vinyl alcohol-vinyl acetate) with montmorillonite

Nano-composites of poly(vinyl chloride) and co-poly(vinyl chloride-vinyl alcohol-vinyl acetate) with clay were prepared by the solution intercalation method. Montmorillonite, a three-layered clay mineral consisting of silicate sheets, was employed as reinforcing phase. Compatibilisation between the two phases was achieved by intercalation of montmorillonite with dodecylamine to increase the organophilicity of the clay. Thin films of pure polymers and their composite materials containing various proportions of clay were obtained by evaporation of the solvent. After further drying under vacuum, these films were characterised for their mechanical and thermal properties. The results have shown that the modulus and the tensile strength of the composite films increased initially compared to the pure polymers and then decreased upon further addition of the clay. The glass transition temperature of the films, measured from the maxima of the tanδ curves using dynamic mechanical thermal analysis, showed a greater shift towards higher temperatures in copolymer-clay than in PVC-clay films. This is indicative of a higher degree of interaction between the two phases of copolymer-clay composites than PVC-clay composites. The microhardness values and the decomposition temperatures also increased in both systems with the addition of an appropriate amount of the clay.

Soluble Aromatic Polyamide Bearing Sulfone Linkages: Synthesis and Characterization

New soluble and linear aromatic polyamide chains were produced by condensing 4-aminophenylsulfone with isophthaloyl chloride in dimethylacetamide as a solvent under an inert atmosphere. HCl produced as a byproduct was removed from the reaction mixture by precipitating with a stoichiometric amount of triethylamine. A clear polyamide solution was obtained after isolation of the precipitates. Thin and transparent film was cast from the solution by baking out the solvent and after drying, the film was employed for various analyses. It was found to be soluble in various organic solvents. The structure elucidation of the resulting polyamide was carried out using infrared and nuclear magnetic resonance spectroscopy. The molecular weight distribution was determined by gel permeation chromatography. These results confirmed the formation of the aromatic polyamide. Thermogravimetry, differential scanning calorimetry, water absorption and mechanical measurements were also performed to further verify the physical properties of the aromatic polyamide.

Recent Developments in Sulfur-Containing Polymers

Currently, a lot of research efforts have been directed toward exploiting the special high-performance characteristics of polymers with sulfur in the backbone. Sulfur-containing polymers fall under various classes and cover an extremely broad property range. The impetus to their development resulted from the unique properties and success in their applications, depending upon the type of linkage introduced. This review basically sets out to explain the design, synthesis, properties, and applications of various sulfur-containing polymers especially polyamides, polyimides, poly(amide-imide)s, polybenzimidazoles, polyurethanes, polyesters, etc. Outstanding performance of these polymers came up from their structures having sulfur-based groups such as thiophene, sulfide, sulfone, thiazol, and thiourea. Thus these linkages endow special features to such functional polymers. The sulfur-containing polymers are also described here with reference to their relevance as optically active, liquid crystalline, flame retardant, and fuel cell materials. Several endeavors are underway to take advantage of incorporated sulfur moiety in the polymer backbone, as a consequence to ascertain their validity on the forefront of scientific investigations.

Amidoxime porous polymers for CO2 capture

CO2 capture from fossil fuel based electricity generation remains costly since new power plants with monoethanol amine (MEA) as the scrubbing agent are under construction. Amidoximes are known to mimic MEA, and porous polymers with amidoximes could offer a sustainable solution to carbon capture. Here we report the first amidoxime porous polymers (APPs) where aromatic polyamides (aramids) having amidoxime pendant groups were synthesized through low temperature condensation of 4,4′-oxydianiline (ODA) and p-phenylene diamine (p-PDA) with a new type of nitrile-bearing aromatic diacid chloride. The nitrile pendant groups of the polyamides were converted to an amidoxime functionality by a rapid hydroxylamine addition (APP-1 and APP-2). The CO2 adsorption capacities of these polyamides were measured at low pressure (1 bar) and two different temperatures (273 and 298 K) and high pressure (up to 225 bar – the highest measuring pressure to date) at 318 K. The low pressure CO2 uptake of APP-1 was found to be 0.32 mmol g−1 compared with APP-2 (0.07 mmol g−1) at 273 K, whereas at high pressure they showed a substantial increase in CO2 adsorption capacity exhibiting 24.69 and 11.67 mmol g−1 for APP-1 and APP-2 respectively. Both aramids were found to be solution processable, enabling membrane applications.

Synthesis, morphology, and properties of self-assembled nanostructured aramid and polystyrene blends.

Aramid (Ar), produced from the reaction of aromatic diamines and diacid chloride, was reactively compatibilized with amino-functionalized polystyrene (APS) to explore blend morphology and interfacial cohesion. Two blend systems, Ar/PS and Ar/APS, were investigated over a range of pristine polystyrene (PS) or modified APS ratios. Morphology and thermal and mechanical properties were probed to evaluate the effect of amine units of APS on the compatibility with Ar. π-π stacking interactions in tandem with the random distribution of graft attachment locations and polydispersity of graft length in Ar-g-APS copolymer, aided merger of unreacted chains to drive molecular self-assembly process thus fortifying the nanostructured blends. Considerable augmentation of the blend morphology and thermal stability was achieved by incorporation of reactivity into Ar/APS system. A 20 wt % APS-containing blend was found to demonstrate optimum mechanical reinforcement, complemented by the optimal, thermal, and morphological profiles of the same blend. Future prospects are envisaged.

Synthesis and Characterization of Aromatic–Aliphatic Polyamide Nanocomposite Films Incorporating a Thermally Stable Organoclay

Nanocomposites were synthesized from reactive thermally stable montmorillonite and aromatic–aliphatic polyamide obtained from 4-aminophenyl sulfone and sebacoyl chloride. Carbonyl chloride terminal chain ends were generated using 1% extra sebacoyl chloride that could interact chemically with the organoclay. The distribution of clay in the nanocomposites was investigated by XRD, SEM, and TEM. Mechanical and thermal properties of these materials were monitored using tensile testing, TGA, and DSC. The results revealed delaminated and intercalated nanostructures leading to improved tensile strength and modulus up to 6 wt% addition of organoclay. The elongation at break and toughness of the nanocomposites decreased with increasing clay contents. The nanocomposites were thermally stable in the range 400–450 °C. The glass transition temperature increased relative to the neat polyamide due to the interfacial interactions between the two phases. Water uptake of the hybrids decreased upon the addition of organoclay depicting reduced permeability.

Probing the potential of polyester for CO2 capture

Global warming, the major environmental issue confronted by humanity today, is caused by rising level of green house gases. Carbon capture and storage technologies offer potential for tapering CO₂ emission in the atmosphere. Adsorption is believed to be a promising technology for CO₂ capture. For this purpose, a polyester was synthesized by polycondensation of 1,3,5-benzenetricarbonyl trichloride and cyanuric acid in pyridine and dichloromethane mixture. The polymer was then characterized using FT-IR, TGA, BET surface area and pore size analysis, FESEM and CO₂ adsorption measurements. The CO₂ adsorption capacities of the polyester were evaluated at a pressure of 1bar and two different temperatures (273 and 298K). The performance of these materials to adsorb CO₂ at atmospheric pressure was measured by optimum CO₂ uptake of 0.244 mmol/g at 273K. The synthesized polyester, therefore, has the potential to be exploited as CO₂ adsorbent in pre-combustion capture process.

Mesoporous template-free gyroid-like nanostructures based on La and Mn co-doped bismuth ferrites with improved photocatalytic activity

Template-free and gyroid-like mesoporous nanostructures of La and Mn co-doped bismuth ferrites were fabricated using a simple and low-cost double solvent sol–gel technique. By carefully controlling the amount of precursors and precisely optimizing the calcination process, a well-ordered and crystalline La and Mn co-doped BiFeO3 gyroid-like mesoporous nanostructures network was obtained for photo-degradation applications. The substitution of Mn ions into the Fe sites resulted in a well-ordered mesoporous nanostructure with a flexibility for optical band-gap tuning up to a large extent. Catalytic photo-degradation of Congo red under visible light irradiation occurred at a much higher rate using the mesoporous nanostructures compared to pure BiFeO3 nanoparticles. Thus, large tunability of the band gap, high activity of the mesoporous nanostructure and stability were successfully achieved. The new fabrication method presented here is the first evidence to suggest that such a well-ordered, template-free, gyroid-like mesoporous nanostructure network can be fabricated for low-cost commercial applications.