Band 35, Heft 1

Hydroxyalkyl derivatives containing oxamidoester and oxamide fragments have been separately obtained using oxamic acid, oxamide and alkylene carbonates. It has been proven that the presence of oxamidoester and oxamide structural fragments in oligomer structures is responsible for the thermal stability of these products. Rigid, thermally stable polyurethane foams were obtained with the use of oligomers with oxamidoestercarbamidoimide, carbamide, oxamidoester and oxamide groups as polyols components. The properties of these foamed materials were compared with each other and with the properties of reference foams. It was found that the polyurethane foams characterized by the best properties were obtained from hydroxypropyl derivatives of oxamide.

Based on experimental viscosity data collected from single material and binary system mixtures, a group contribution method was introduced to estimate viscosities of a range of polyol oligomers and urethane polymers at temperatures from 25 to 150°C. Use of mixture rules then extends the estimation method to multi-component reacting systems. Mixture viscosity data were used to determine the Gibbs free energy (G) in the Grundberg-Nissan equation which can be used to estimate mixture viscosities with correction for some non-idealities. The resulting model is able to accurately predict mixture viscosities based on binary interaction. The goal of this work is to estimate the viscosities of urethane-forming reactions; accurate viscosity information is critical as an intermediate step to predict how successful a foam formulation would be and to ultimately estimate the final physical properties of the foam.

Four types of peroxides in combination with two types of co-agents were used as cross-linking agents for the preparation of rubber compounds based on natural rubber. The effects of Type I and Type II co-agents on cross-linking and physical-mechanical properties of vulcanizates were investigated. The correlation between mechanisms of the interaction of co-agents with the rubber matrix in relation to the characteristics of tested systems was discussed. The results showed that the Type I co-agent influenced the rate and the state of cure. Physical-mechanical properties were improved by addition of the Type I co-agent. By contrast, the Type II co-agent had no contribution to the rate and state of cure. Moreover, physical-mechanical properties of vulcanizates deteriorated in the presence of this type of co-agent.

Polycarbonate (PC) is mainly used as plastic glass in the industrial field. PC has many advantages such as light weight and high impact strength as compared to inorganic glass. However, the long-term stability of PC through the service life has not been fully examined. The authors analyzed the degradation behavior of PC glass through long-term artificial weathering conditions. The PC glass became yellowish through artificial weathering; however, the mechanical strength, for example, the flexural strength and the impact strength, were sufficient for its use as actual window glass of the public transportation. Moreover, improved PC is expected to have a longer service life as compared to ordinary PC. In addition, the evaluation of the degradation of PC-based plastic glass was studied with use of color measurement.

Different generations of dendritic architecture with piperazine in core moiety and hydroxyl groups on the periphery were designed by divergent method. 1,4-biz(4,6-trichloro-1,3,5-triazin-2-yl)piperazine was synthesized as a core for dendrimer synthesis. Dendrimer was then grown to G3 from core compound using diethanolamine and cyanuric chloride as branching units. Dendrimer generations were characterized by infrared (IR) spectroscopy [Fourier transform IR (FTIR)], 1 H-nuclear magnetic resonance (NMR), 13 C-NMR, electrospray ionization-mass spectrometry (ESI-MS), and elemental analysis. The thermal behavior of both full- and half-generation dendrimers was investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The TGA study revealed that dendrimer generations had a moderate thermal stability. Chlorine-terminated half-generation dendrimers were thermally more stable than hydroxyl-terminated full-generation dendrimers. The DSC technique was employed to determine the glass transition temperatures (Tg) of dendrimer generations. It was observed that the glass transition temperatures of synthesized dendrimer generations were of low value, which is similar to the values reported for the polyamidoamine (PAMAM) dendrimer of the same generation. It was also observed that, with the increase in the molecular weight or generation number of dendrimer, the glass transition temperature was also increased.

The method of manufacturing nanofibers using the electrospinning technique from trans-polyisoprene (TPI) is presented in this study, possibly for the first time. The process parameters such as solution concentration, applied voltage, distance and feeding rate for electrospinning were investigated and optimized with respect to fiber morphology, as observed from scanning electron microscopy (SEM) photomicrographs. Smooth and uniform nanofibers were found to generate at the optimum conditions with 1% melt concentration, 15 kV of voltage, tip-to-collector distance (TCD) of 15 cm and injection rate 4 ml/h. The physicochemical properties of pure TPI and electrospun TPI fibers were characterized by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) analysis. Both DSC and FTIR characterization results show predominant transformation of TPI crystalline structure from the β form to the α form upon electrospinning.

The concept of a gas-assisted melt differential electrospinning device with hollow disc electrode is presented. As the electric field force is the only drawing force stretching polymer melt jet to fibers, it is necessary to study the distribution and electric field intensity of the electric field created in the spinning region caused by the hollow disc electrode. A series of electric field simulations, including the distribution of the electric field and the relationship between electric field intensity and various parameters were carried out by the finite element method. In addition, experiments of melt electrospinning were conducted, mainly focusing on several electrical parameters affecting the fiber diameter. The results of simulations were compared with those of experiments, proving experimental phenomena and conjectures. The results of simulations and experiments were mutually corroborated and consistent with each other. All results provided significant support and basis for future exploration and development of melt electrospinning.

Poly(piperazine-amide) thin film composite (TFC) nanofiltration (NF) membranes were prepared via interfacial polymerization (IP) of trimesoyl chloride (TMC) in cyclohexane and piperazine (PIP) in water. The effect of polymerization time on the physicochemical characteristics of poly(piperazine-amide) layers and the final membrane performance was studied in detail. The morphological structures of prepared membranes were investigated using atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), by contrast, was used to determine the chemical characteristics of the membranes. It is evident that the surface roughness increased with increasing polymerization time due to the formation of a supergranule-like structure over the interfacially synthesized poly(piperazine-amide) layer. Moreover, increasing the polymerization time led to a dramatic reduction of water permeability due to the significant increase of crosslinking poly(piperazine-amide) barrier layers. Experimentally determined data showed that the TFC NF membrane prepared at 10 s of polymerization time experienced 51.2 l/m 2 .h of water permeability with 97.02% of Na 2 SO 4 salt rejection at an operating pressure of 0.6 MPa.

Biodegradable blended films from methylcellulose (MC) and potato starch (PST) have been developed by the casting process. In the present work the influences of concentrations of MC and PST on rheological properties, swelling, mechanical properties such as tensile strength, percentage elongation at break and water vapor transmission rate (WVTR) of the prepared blended films have been studied. Fourier transform infrared (FTIR) analysis of pure MC, PST, their mixture and the mixture with glutaraldehyde and urea was performed to investigate the interactions in blended films. The blended films of MC and PST showed an increase in tensile strength due to the cross linking reactions of the amylopectin molecule of PST in the physical gel state. The change of percentage elongation at break increased with MC concentration and the opposite trend was found in the case of the WVTR due to the network structure of the blended films. The blended films showed a large improvement in the abovementioned properties compared with each single component, due to the interaction formed between hydroxyl groups of PST and the methoxy groups of MC. Experiments were also conducted to investigate the controlled urea release through blended films and the kinetics of the process. Interesting results were found with the prepared MC and PST blended films.

The behavior of gelatin/sodium carboxymethylcellulose (NaCMC) mixtures in an aqueous medium was investigated as a function of the pH, the protein to polysaccharide weight ratio and the total biopolymer concentration. The polydispersity of these solutions was investigated by measuring the UV-vis absorbance of the mixture at 650 nm. The change in the absorbance at 650 nm for all gelatin/NaCMC/water dispersions showed that the most significant interaction by this technique was at a pH of 4.2. Increasing the total concentration of biopolymers greatly increased the interaction between gelatin and NaCMC. It was also found that at this value of pH, and at a remarkable value of the protein to polysaccharide weight ratio of 1:1, the electrostatic interactions between gelatin and NaCMC were maximum. It was demonstrated that the addition of an anionic polysaccharide such as NaCMC can affect the behavior of gelatin in solution. In addition to the pH of the solution, other factors such as the presence of NaCl, CaCl 2 and glucose may affect the rate of helicity and the scattering power of the gelatin. This has been confirmed by infrared spectroscopy as well as polarimetry.