All issues / Volume 1 (2007) / Issue 6 (June)
Different kinetic models like the Avrami, Tobin and Urbanovici-Segal models have been applied for determining the isothermal crystallization kinetics of virgin poly(ethylene terephthalate) (PET) and PET/poly(methyl methacrylate) (PMMA) blends. The different compositions investigated were PET90/PMMA10, PET75/PMMA25 and PET50/PMMA50 [wt/wt%]. The experimental data was fitted using Solver, a non-linear multi-variable regression program and linearization method. The effect of composition variation of PET/PMMA on parameters like crystallization rate constant and crystallization exponent were investigated. Urbanovici-Segal and Avrami models gave the best fit to the experimental data. Tobin model does not seem to fit the experimental data for the systems under investigation. Experimental results indicated that the crystallization rate constant values increased with decreasing temperatures.
In this study, the surface characteristics of blends and composites of epoxy resin were investigated. Poly(styrene-co-acylonitrile) (SAN) was used to modify diglycedyl ether of bisphenol-A (DGEBA) type epoxy resin cured with diamino diphenyl sulfone (DDS) and the modified epoxy resin was used as the matrix for fibre reinforced composites (FRP’s). E-glass fibre was used as the fibre reinforcement. The scanning electron micrographs of the fractured surfaces of the blends and composites were analyzed. Morphological analysis revealed different morphologies such as dispersed, cocontinuous and phase-inverted structures for the blends. Contact angle studies were carried out using water and methylene iodide at room temperature. The solid surface energy was calculated using harmonic mean equations. Blending of epoxy resin increases its contact angle. The surface free energy, work of adhesion, interfacial free energy, spreading coefficient and Girifalco-Good’s interaction parameter were changed significantly in the case of blends and composites. The incorporation of thermoplastic and glass fibre reduces the wetting and hydrophilicity of epoxy resin.
In this study, novel amphiphilic fluorescent copolymers poly(N-vinylpyrrolidone)-b-poly(N-methacryloyl-N'-(α-naphthyl)thiourea) (PVP-b-PNT) were synthesized via ATRP with poly(N-vinylpyrrolidone)-Cl as macroinitiator and N-methacryloyl-N'-α-naphthylthiourea (NT) as hydrophobic segment. PVP-b-PNT copolymers were characterized by 1H NMR, GPC-MALLS and fluorescence measurements. The aggregation behavior of PVP-b-PNT in water was investigated by transmission electron microscope (TEM) and dynamic light scattering (DLS) measurement. The photophysics behavior of PVP-b-PNT showed that block copolymer formed strong excimer. The interaction of DNA with the block copolymer made the excimer of block copolymer quench. The cytotoxicity result of PVP-b-PNT in cell culture in vitro indicated that this copolymer PVP-b-PNT had good biocompatibility.
Nanocomposite materials consisting of polymeric matrix materials and natural or synthetic layered minerals like clay are currently an expanding field of study because these new materials often exhibit a wide range of improved properties over their unmodified starting polymers. Epoxy/organoclay nanocomposites have been prepared by intercalating epoxy into the organoclay via direct mixing process. The clay exfoliation was monitored by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Water diffusion and sulfuric acid corrosion resistance of epoxy-based nanocomposites were evaluated. Diffusion was studied through epoxy samples containing up to 6 phr (parts per hundred resin) of an organically treated montmorillonite. The diffusion of the environmental solution was measured by noting the increase in weight of the samples as a function of immersion time in these solutions at 80°C. The effect of the degree of exfoliation of the organoclay on water barrier and corrosion resistance was specifically studied. The data have been compared to those obtained from the neat epoxy resin to evaluate the diffusion properties of the nanocomposites. The flexural strength of the epoxy/organoclay nanocomposites samples made was examined to compare their mechanical performance under corrosive conditions as a function of immersion time and temperature. It was found, that the organoclay was mainly intercalated with some exfoliation and that addition of the organoclay yields better flexural strength retention under immersion into sulfuric acid.
Blends of styrene-acrylonitrile (SAN) with ethylene-propylene-diene (EPDM) with and without high impact polystyrene (HIPS) as a compatibilizer were studied. One series of blends was prepared in composition 95/5, 90/10, 85/15, 80/20 and 60/40; and the second series of blends was prepared with addition of 5 wt % of HIPS. Their morphology and thermal behaviour were inspected by scanning electronic microscopy (SEM) and dynamic mechanic analysis (DMA), respectively. Further on, blends were separated to their components by Soxlet extraction in selective solvent and characterized by Fourier Transform Infrared Spectroscopy (FTIR) and gel permeation chromatography (GPC), respectively. The results of morphological observations revealed that the addition of a small percentage of compatibilizer decreases the domain size of the dispersed phase and the compatibility of the blends was enhanced. The shifts of values of glass temperatures (Tg) in the examined blends also indicate that with addition of compatibilizer HIPS miscibility between SAN and EPDM is improved.
In this study, thermal, mechanical and fire retardant properties of silane-crosslinked low-density polyethylene (XLPE) containing ethylene-vinylacetate (EVA) copolymer, alumina trihydrate (ATH) and antimony trioxide (Sb2O3) have been studied. Samples were prepared in a single-screw extruder and the silane type was vinyltrimethoxy silane (VTMOS). Incorporation of ATH and Sb2O3 into polyethylene at sufficiently high loading introduces good fire retardancy expressed by limiting oxygen index (LOI). However, some tensile properties decreased. These limitations could be overcome by silane crosslinking. By incorporation of EVA into XLPE gel content increased and curing time decreased. Differential scanning calorimetric (DSC) analysis indicated the existence of two distinct melting endothermic peaks corresponding to two different crystalline phases. Results from mechanical properties showed that mechanical properties of XLPE/EVA blends improve by increasing EVA content up to 15 wt%.
Polyanilines are reported to exhibit stabilizing effects in rubber mixtures submitted to gamma-irradiation and thermo-oxidative treatment. Such abilities may be explained by their action as radical scavengers. Since radical formation followed by main chain scission is a widely accepted mechanism for radiolytic degradation of PMMA, polyaniline is a promising additive for commercial plastics submitted to radiosterilization processing. In this work, we investigated the ability of polyaniline emeraldine salt nanofibers (PANF-HCl) in preventing radiation damage on PMMA matrix. Effects of gamma-irradiation on PMMA/PANF-HCl composites films were assessed by comparison of the variation of viscosity-average molar mass (Mv) of PMMA at 25 kGy dose when compared to commercial PMMA films. Samples containing 0.15% PANF-HCl (wt/wt) retained 92% of the initial Mv after irradiation while control sample presented 42% of Mv retention. When exposed to 60-200 kGy doses, PANF-HCl embedded into PMMA matrix preserved their oxidation state but started to exhibit mild deprotonation. PANF-HCl nanofibers were characterized by Diffuse Reflection Infrared Fourier Transform Spectroscopy (DRIFTS) and Scanning Electronic Microscopy (SEM). PMMA/PANF-HCl composites films were characterized by SEM and UV-VIS spectroscopy.
Copolymerization of N-cyclohexylacrylamide (NCHA) and n-butyl acrylate (BA) was carried out in dimethylformamide at 55±1°C using azobisisobutyronitrile as a free radical initiator. The copolymers were characterized by 1H-NMR spectroscopy and the copolymer compositions were determined by 1H-NMR analysis. The reactivity ratios of the monomers were determined by both linear and non-linear methods. The reactivity ratios of monomers determined using linear methods like Fineman-Ross (r1 = 0.37 and r2 = 1.77 ), Kelen-Tudos (r1 = 0.38 and r2 = 1.77), ext. Kelen-Tudos (r1 = 0.37 and r2 = 1.75) Yezrieler-Brokhina-Roskin (r1 = 0.37 and r2 = 1.77) and non-linear methods like Tidwell-Mortimer (r1 = 0.37 and r2 = 1.76), ProCop (r1 = 0.36 and r2 = 1.82). The Q and e values for NCHA are 0.67 and 0.68 respectively. Mean sequence lengths of copolymers are estimated from r1 and r2 values. It shows that the BA units increases in a linear fashion in the polymer chain as the concentration of BA increases in the monomer feed.
A new liquid formulation of commercial bismaleimide and n-acryloylmorpholine was prepared that could be UV cured as an alternative to traditional thermal cure methods presently used for BMI in the industry. UV curing was shown to be an efficient method which promoted the reaction rate significantly and was able to achieve this at low temperatures (30–50°C). A free radical polymerization approach has been used to explain the cure mechanism and cure kinetics, using data elucidated from the DPC and FTIR. The cured thin film was shown to achieve very high thermal stability (~400°C), with the BMI shown to retard the thermal degradation temperature and rate.