Band 33, Heft 9

Efforts were made to synthesize polystyrene (PS) using free radical solution polymerization. Four common solvents with dissimilar polarities, acetone, chloroform, benzene and toluene, with two different initiators, were selected. The homo-polymerization was conducted in an ace round-bottom pressure flask of diameter 62 mm, with a thermo well, which housed the thermometer. The reaction temperature was maintained at 120°C using a heater with a temperature controller, coupled with a magnetically driven stirrer. One hundred experimental runs of 8 different groups were carried out. Polymerization was conducted in the mass concentration of 0.1 g for each initiator [benzoyl peroxide (BPO) and its blend]. The key parameter considered is the volume ratio of monomer to solvents under different types of solvents, initiators and reaction time. Initially, there was an increase in conversion with the solvent volume and time, until a certain point where there was a gradual decline in monomer conversion. Polymerization rate and monomer conversion were observed to be higher in polar solvents (acetone). Further presented in this study is the macromolecular architecture (molecular weight) and micro-structure of some of the solution polymerized monomer. A kinetic model was also presented to predict the conversion with time profile of the polymerization process. Molecular weight determined were between acceptable ranges while the model presented though with considerable error margin but seems to respond just fairly at extremely low monomer conversion. Similar response was observed from earlier model reported in literature when tested with our experimental data.

Polyaniline (PANI) in its emeraldine salt form was synthesized by chemical method from aniline monomer in the presence of HCl mixed with LiCl and ammonium persulfate as oxidant. Then, a portion of sample was dedoped with NH 3 solution and another equal portion was separately postdoped with secondary dopants, such as H 2 SO 4 and HClO 4 , respectively. Finally, the dried samples of PANI prepared in all its three different forms (emeraldine salt form, undoped emeraldine base, and the two secondary doped forms of PANI) were characterized by UV-visible spectroscopy, cyclic voltammetry (CV) techniques, Fourier transform infrared (FT-IR) spectroscopy, and electrical conductivity measurement. The cyclic voltammograms of PANI in its emeraldine base (PANI-EB) determined the electrochemical behavior and the growth mechanisms of the polymer. The FT-IR and UV-vis spectra confirmed the expected structural modification up on doping, undoping, and postdoping processes of the polymer. Their measured electrical conductivities were from 0.02 for undoped, 156 for primary doped form, and increasing from 158 to 257 S/cm for those secondary doped PANI. The influence of secondary doping on the electrical conductivity was also investigated from their spectroscopic data which shows dramatic rise in conductivity. The result also shows that secondary doping increased the π conjugation.

Recycled polyethylene terephthalate (rPET) was used as an alternative reinforcing material for in situ microfibrillar-reinforced polyethylene (PE) based composite fibers and compared with liquid crystalline polymer (LCP). The neat PE and its composites reinforced with LCP and rPET microfibrils under the compatibilizing promotion of 5 wt% styrene-(ethylene butylene)-styrene-grafted maleic anhydride (SEBS-g-MA) compatibilizer, were prepared as fibers using a hot drawing process. Cross-ply laminates of the neat PE and the compatibilized composite fibers were then prepared using a film stacking method. The tensile, flexural and impact performances of each laminate system were examined and compared. Under tensile loading, no significant differences in the initial part of the stress-strain curves, and hence comparable tensile modulus (≈4 GPa) among all laminates, were observed. A difference was only seen in the final part of the curves. For flexural properties, the flexural moduli of the compatibilized LCP- and rPET-composite laminates were nearly the same (≈3 GPa). At high flexural strains (>1%), the different stress-strain behaviors of the laminates were clearly observed. Interestingly, the compatibilized rPET-composite laminate showed much better impact-resistance compared with PE- and compatibilized LCP-laminates. The results demonstrated a high potential for use of the rPET-composite fiber laminate in impact-resistant applications.

The effects of various ratios of virgin chloroprene rubber (vCR) and recycled chloroprene rubber (rCR) with a constant content of carbon black (CB) on the properties of natural rubber/chloroprene rubber NR/CR blends were studied. The minimum torque (M L ), maximum torque (M H ), scorch time, and cure time increased with the addition of both CRs and the effects of rCR were more pronounced than vCR on these properties. The tensile strength and fatigue life of the NR/vCR blends increased with an addition of vCR up to 25 phr and then decreased with a higher vCR. However, NR/rCR blends reflected otherwise for both properties. The elongation at break and swelling percentage of NR/CR blends decreased with the addition of both vCR and rCR.

A novel silicone-containing acrylic monomer, trimethylsiloxybutoxy dimethylsiloxybutyl acrylate (TSBA) and diethylene glycol monoallyl ether (DGME) was synthesized successfully. Then, a novel copolymeric surfactant was prepared by the free radical polymerization of TSBA and DGME in the presence of dioxane and azobisisobutyronitrile (AIBN) as a solvent and initiator, respectively. Next, a series of polyvinyl acetate (PVAc), 2-ethylhexyl acrylate (2-EHA) and polystyrene (PSt) latexes were successfully synthesized, each one throughout by the emulsion copolymerization in the presence of a copolymeric surfactant. This copolymeric surfactant exhibited excellent surface activity and the surface tension decreased with an increase in the concentration of the copolymeric surfactant.

Post-irradiation effects on nylon 6,12 crystalline fibers gamma-irradiated 6 years previously (6YI) were studied, including thermal stability and morphology; their relationship with storage time was also studied. The results of these studies were compared with those obtained for non-irradiated (NI) and namely freshly irradiated (FI) crystalline fibers. The results include analyses like thermogravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscopy (SEM) and optical images for (6YI and FI) both kinds of nylon 6,12 fibers. The results showed that the most prominent effect is related to the reaction progress. The chain scission and/or crosslinking mechanisms, as well as the free radicals, allow proceeding with the reaction, and consequently, changes on the properties of the FI samples. The melting point, degree of crystallinity, degradation temperature and morphology prove that additional chemical reactions and surface modifications keep occurring in the fibers long after the irradiation process has ended. With storage time, the surface becomes rougher, the color turns yellowish, the melting point diminishes and the degree of crystallinity increases.

Sodium alginate (SA) films were prepared by casting from methanol (MeOH) solutions and their tensile properties, like tensile strength (TS) and elongation at break (Eb %), were monitored. The resulting films of SA were photocured with vinyltriethoxysilane [H 2 C=CH–Si–(OC 2 H 5 ) 3 ] in order to improve the tensile properties. Several acrylic monomers of different functionalities as additives (2%), like ethyl acrylate (EA), 2-hydroxyethyl acrylate (2-HEA), and tripropylene glycol diacrylate (TPGDA), were incorporated with silane with the aid of UV radiation. Further analyses of the prepared films were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and a TS test. FTIR studies indicate that there are intermolecular hydrogen bonding interactions, i.e., –OH·····O=C in silane/SA blends. This blend films also exhibited the higher thermal stability and improved the tensile properties of the films. Degradation of SA by UV spectrometry induces time-dependent degradation.

Blends of nitrile butadiene rubber (NBR) and polyoxymethlene (POM) were prepared by melt mixing, with a polyether polyol (Model KGF400D) used as the compatibilizer. Scanning electron microscopy (SEM) was used to characterize the cryogenically fractured surfaces of the blends clearly, which showed that the compatibility of NBR/POM blends was significantly enhanced with the addition of KGF400D. Both differential scanning calorimetry (DSC) and rubber process analysis (RPA) results clearly indicated the mechanism of compatibility improvement. Dual functions of KGF400D within the NBR/POM blends were found: one was the lubrication effect and the other was the hydrogen bonding between the hydroxyl of KGF400D and ether oxygen group of POM or lone pair electron in the cyano group of NBR.

Ethylene-vinyl alcohol copolymers (EVOH), with appropriate barriers and processability, can be chemically modified through vinyl alcohol units. Amides and polyamides based on condensation reactions of adipoyl chloride and hexamethylenediamine were grafted onto EVOH. Grafting was characterized by contact angle measurement, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), nuclear magnetic resonance spectroscopy (NMR) and scanning electron microscopy (SEM). Amide peaks at 3302 cm -1 corresponding to –NH bond stretching and the absorption of H N-CH 2 at 7.8 ppm, were observed from ATR-FTIR and NMR, respectively, as a result of grafting. SEM showed the formation of amide structures as bundles, agglomerates and needle-like particles. Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) showed considerable changes in onset of melt temperature, crystallinity and various transitions in grafted EVOH, showing an effective alteration in the physical properties compared with the virgin resin. Nylon grafted EVOH can be considered as a potential compatibilizer in polyethylene (PE)/polyamide blends via increasing interactions at the interface.

Density, viscosity and ultrasonic velocity of polyvinyl acetate with acetic acid have been measured at a temperature of 299K for different concentrations. Density and viscosity have been measured for a binary liquid mixture with a specific gravity bottle and a viscometer. Ultrasonic velocity has been measured using a single crystal interferometer at a frequency of 2 MHz. Ultrasonic velocities for the binary mixture at 1 MHz and 2 MHz was compared by taking some values from the literature. The sound velocity ( V ), density (ρ) and viscosity (η) were used to calculate the parameters such as adiabatic compressibility (β), acoustic impedance ( Z ), intermolecular free length ( L f ), ultrasonic attenuation (α/ f 2 ) and relaxation time (τ). The variations of experimentally obtained parameters indicate the presence of molecular interaction between the molecules of the mixture. The ultrasonic velocity increased with an increase in concentration. Solute-solvent interaction is further confirmed by viscosity values, which increased with increasing concentration suggesting more association between solute and solvent molecules. The linear variations in Rao’s constant and Wada’s constant suggest the absence of complex formation.

The present investigation compares the diverse methods of cellulose extraction from rice straw. Furthermore, the purified cellulosic material was utilized for the electrospinning of cellulose nanofibers. Based on the differential scanning calorimeter and Fourier transform infrared spectroscopy analyses, the new protocol was compared to the other methods showing lower amorphous structure and also lower lignin and hemicellulose in crystalline α-cellulose structure. The protocol, which included ultrasonic mechanical treatment, showed a higher crystallinity of the corresponding cellulose giving microfibers of 2.9±0.2 μm in average diameter based on the scanning electron microscope images. Cellulose nanofiber was prepared from its solution in trifluoroacetic acid using general one-step electrospinning process. The simultaneous effects of four processing variables including solution concentration ( C ), applied voltage ( V ), spinning distance ( d ), and volume flow rate ( Q ) on mean fiber diameter (MFD) and standard deviation of fiber diameter (StdFD) were investigated quantitatively and qualitatively. A range of MFD between 96±26 nm and 292±35 nm was recorded for further analysis. The response surface methodology was employed to establish quadratic models for MFD and StdFD. was found to be 96.18% and 91.25%, respectively, for the MFD and StdFD models, showing the good prediction ability of the models. The response surface plots showed strong relationship among variables.

Rigid polyurethane foams are one of the most important cellular plastics. Castor oil was modified with glycerol to form the polyol and reacted with methyl diisocyanate and different proportions of silicon oil to achieve rigid polyurethane foam. Prepared foam was tested for its density and mechanical properties. It was found that compressive and flexural strength was improved with silicon oil content. The morphology of the resulted foams was also studied using scanning electron microscope, and it was observed that the cell size was reduced with silicon oil content, indicating a more dense and packed structure. With further increase in the silicon oil content, foam properties showed a slight decrease in value.