K.P. Pramoda

Dynamic mechanical behavior of melt-processed multi-walled carbon nanotube/poly(methyl methacrylate) composites

Multi-walled carbon nanotube/poly(methyl methacrylate) composites have been fabricated by melt blending. The nanotubes are well dispersed in the polymer matrix with no apparent damage or breakage. The dynamic mechanical behavior of the composites has been studied. The storage modulus of the polymer is significantly increased by the incorporation of nanotubes particularly at high temperatures.

Thermal degradation behavior of polyamide 6/clay nanocomposites

This paper focuses on the study of thermal degradation and evolved gas analysis using thermogravimetric analysis (TGA) coupled to Fourier transform infrared (FTIR) spectroscopy, i.e., TG–IR, to study polyamide 6 (PA6) and PA6-clay nanocomposites prepared by melt compounding. The thermal decomposition of PA6 and its clay nanocomposites takes place with the evolution of the cyclic monomer (caprolactam) first, followed by other volatile gases like CO2 and NH3, which are characterized by the presence of oligomeric products with nitrile and vinyl chain ends in the infrared (IR) spectra. The onset temperature for degradation is 12 � C higher for PA6 with 2.5 wt.% of clay loading than that for neat PA6, whereas, the onset temperature for degradation remained almost unchanged for samples with higher clay loading (i.e. 5, 7.5 and 10 wt.% clay). The above findings are related to the morphological observations that show an optimal exfoliated structure only for the nanocomposite with 2.5 wt.% clay, and distinct clay agglomeration in those with higher clay loadings. Our study suggests that only exfoliated polymer/clay nanocomposites exhibit improved thermal stability. Agglomerated clay particles do not significantly affect thermal stability of the polymer matrix. The activation energies for degradation, Ea, estimated by Kissinger method, for PA6 and PA6–2.5 wt.% clay nanocomposite were found to be 175 and 199 kJ/mol in N2, and 228 and 223 kJ/mol in air, respectively. # 2003 Elsevier Science Ltd. All rights reserved.

Poly(vinylidene fluoride)-assisted melt-blending of multi-walled carbon nanotube/poly(methyl methacrylate) composites

Multi-walled carbon nanotubes (MWNTs) were sonicated in the dimethylformamide solution of poly(vinylidene fluoride) (PVDF). The PVDF-covered MWNTs were then melt-blended with poly(methyl methacrylate) (PMMA). The dynamic mechanical behavior of various composites was studied. The presence of a small amount of PVDF leads to a significant improvement in the storage moduli of the MWNT/PMMA composites at low temperatures. The storage modulus of a PVDF/MWNT/PMMA composite containing 0.5 wt.% PVDF is almost twice as that of a MWNT/PMMA composite at 50°C. However, a further increase in the PVDF content leads to a reduction of the storage modulus. The beneficial effect of PVDF diminishes at higher temperatures.

Chemical cross-linking modification of 6FDA-2,6-DAT hollow fiber membranes for natural gas separation

Abstract A simple and practical chemical cross-linking method has been demonstrated to make 6FDA-2,6-DAT asymmetric hollow fibers more resistant to plasticization by immersing them into a p -xylenediamine or m -xylenediamine/methanol solution for a short period of time at ambient temperature. FTIR spectra confirm that chemical cross-linking reactions take place between xylenediamine and imide groups of 6FDA-2,6-DAT and form amide groups. The effects of cross-linking modifications on gas separation performance and the resistance to plasticization characteristics are examined by using both pure and CO 2 /CH 4 mixed gas tests. Permeances of all gases tested decrease with an increase in the degree of cross-linking, while CO 2 /CH 4 permselectivity varies in a narrow range. 6FDA-2,6-DAT hollow fibers show favorable resistance to plasticization once the cross-linking reaches a certain degree. XRD spectra indicate almost no changes on the average intersegmental distance of polymer chains after cross-linking modifications, strongly indicating the cross-linking modifications likely protect nodule integrity from CO 2 -induced swelling and restrict polymer chain vibration for diffusion jumps. In addition, we found that m -xylenediamine has a similar cross-linking effectiveness as p -xylenediamine on 6FDA-2,6-DAT hollow fibers, both yield hollow fiber membranes with comparable CO 2 /CH 4 selectivity and permeance.

Microstructure, crystallization and dynamic mechanical behaviour of poly(vinylidene fluoride) composites containing poly(methyl methacrylate)-grafted multiwalled carbon nanotubes

Composites of poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA)-grafted MWNTs were prepared by melt mixing. The miscibility between PVDF and PMMA helps improve the dispersion of PMMA-grafted MWNTs in the PVDF matrix and also the load transfer from the PVDF matrix to the nanotubes. MWNTs act as nucleation agents to increase the crystallization and melting temperatures of PVDF, but the nucleation effect is suppressed when PMMA is grafted onto the nanotubes. X-ray diffraction and infrared spectroscopic studies showed that MWNTs induce the formation of β-form PVDF crystallites. The storage modulus of PVDF is increased by nearly 150% at 20 °C upon the incorporation of PMMA-grafted MWNTs with MWNT content of 1.93 wt%. PMMA-grafted MWNTs are more effective than organoclay in increasing the storage modulus of PVDF.

Enhancement of stiffness, strength, ductility and toughness of poly(ethylene oxide) using phenoxy-grafted multiwalled carbon nanotubes

Phenoxy (poly(hydroxyether of bisphenol-A), also known as poly(bisphenol-A-co-epichlorohydrin)) was grafted onto multiwalled carbon nanotubes (MWNTs) by a reactive blending process. Reactions between terminal glycidyl groups of phenoxy and carboxylic acid groups of acidified MWNTs resulted in the grafting of phenoxy chains onto MWNTs. The mechanical properties of composites of poly(ethylene oxide) (PEO) and phenoxy-grafted MWNTs were studied. The miscibility between PEO and phenoxy enabled the good dispersion of nanotubes in the PEO matrix as evidenced by polarized optical microscopy and transmission electron microscopy. The spherulite size of PEO progressively decreased with increasing amount of phenoxy-grafted MWNTs added. At an optimal MWNT content of 1.5 wt%, the addition of phenoxy-grafted MWNTs led to increases of storage modulus, Youngs modulus, yield stress, tensile strength, ultimate strain, and toughness of PEO by 113, 228, 166, 442, 1240, and 4080%, respectively. Such simultaneous increases in stiffness, strength, ductility and toughness of a polymer by an additive are rather uncommon.

Dynamic mechanical behavior of in situ functionalized multi-walled carbon nanotube/phenoxy resin composite

In situ functionalized multi-walled carbon nanotube (MWNT)/Phenoxy composites were prepared by melt mixing Phenoxy with MWNT and 1-(aminopropyl)imidazole (NIm). Composites with 4.8 wt% or more of in situ functionalized MWNT show higher storage modulus than Phenoxy, provided a sufficient amount of NIm was used to aid in the dispersion of the hydrophobic MWNTs in the hydrophilic Phenoxy matrix.

Characterization and thermal degradation of polyimide and polyamide liquid crystalline polymers

Abstract The wholly aromatic thermotropic liquid crystalline polymers, polyimide [1,2,4,5-benzentetracarboxylic dianhydride (PMDA) and 1,3-bis [4-(4′-aminophenoxy) cumyl] benzene (BACB)] and polyamide [terephthaloyl chloride (TPC) and BACB] were characterized by FTIR-ATR, and DSC measurements. Three endothermic peak temperatures observed (274, 284, 307°C) for the polyamide are lower than those observed (277, 297, 337°C) for the polyimide liquid crystalline polymers. The major difference between the polyamide and polyimide is that their infrared peaks are at 1644 and 1722 cm −1 , respectively. The thermal stability, apparent activation energy and evolved gas analysis of these LCPs was done using thermo-gravimetric analysis (TGA) coupled with Fourier transform infrared (FTIR) spectroscopy. Decomposition results show that the polyamide is much less thermally stable than the polyimide. The evolved gases are found to be H 2 O, CO, CO 2 and various hydrocarbon fragments. A substantial amount of CO 2 detected during the decomposition is due to degradation of the carbonyl functional groups from the polyimide liquid crystalline polymers. Activation energies for the initial thermal degradation of this polyimide in nitrogen and air are 236 and 201 kJ/mol, and those for polyamide are 207 and 219 kJ/mol, respectively. A jump in the activation energy is observed around 40% weight loss, beyond which it decreases in the case of polyimide. However, an unusual observation was made during the degradation of polyamide. The apparent activation energy values are found to be higher under air environment than in the nitrogen environment.

Enhancement of the mechanical performance of poly(vinyl chloride) using poly(n-butyl methacrylate)-grafted multi-walled carbon nanotubes

Poly(n-butyl methacrylate) (PBMA) was grafted onto multi-walled carbon nanotubes (MWNTs) using atom transfer radical polymerization. The enhancement of the mechanical performance of poly(vinyl chloride) (PVC) using PBMA-g-MWNTs was studied. The miscibility between PVC and PBMA enabled the homogeneous dispersion of nanotubes in the PVC matrix and improved the efficiency of load transfer from the matrix to the nanotubes. At an effective MWNTs content of 0.2 wt%, the addition of PBMA-g-MWNTs resulted in increases in storage modulus (at 35 °C), Youngs modulus, yield stress, tensile strength, ultimate strain and toughness of PVC by 83, 40, 74, 84, 38 and 145%, respectively. The reinforcement values based on Youngs modulus and tensile strength are 387 GPa and 19.1 GPa, respectively. These values are significantly larger than those of 115 GPa and 2.3 GPa, respectively, for PVC reinforced by chlorinated polypropylene-grafted MWNTs reported by Blake et al (2006 J. Mater. Chem. 16 4206).

Surface study of ladderlike polyepoxysiloxanes

By using the two-liquid geometric method and the three-liquid acid-base method, we are the first to determine the surface tensions of ladderlike polyepoxysiloxanes by the measurement of contact angles on thin films. Three kinds of ladderlike polymers have been synthesized: AC (which has the alkyl group and the epoxy group graft to the ladderlike polysilsesquioxane chain), ACP (which has the alkyl group, phenyl group, and epoxy group graft to the ladderlike chain), and AP (which has the phenyl group and epoxy group in the ladderlike side chain). The results showed that when different liquids and different theories are chosen to determine the surface energies, there are some minor differences in the values but a similar trend is still exhibited. The surface energies of these three polymers are in the following order of γSAC ACP > AP, suggesting Si atoms were more likely to migrate to the polymer surface and the bulky effect of the phenyl groups could also interfere with the migration of the Si atoms. As a result, Si and O ratio at the interface determines the order of apparent surface energy for these three polymers. Experimental data also reflect that there are differences between the ladderlike polyepoxysiloxanes and the commercially available linear polysiloxanes.