In this work we report on the microstructural and the mechanical characteristics of high density polyethylene (HDPE)-clay nanocomposites, with particular attention to the creep behaviour. The samples were prepared through melt compounding, using two high-density polyethylenes with different melt flow rate (MFR), two different organo-modified clays, and changing the relative amount of a polyethylene grafted with maleic anhydride (PEgMA) compatibilizer. The intercalation process is more effective as the matrix melt viscosity decreases (higher MFR), while the clay interlamellar spacing increases as the compatibilizer amount increases. The relative stiffness of the nanocomposites increases with the addition of clay, with a limited enhancement of the relative yield stress. The better intercalation obtained by the addition of the compatibilizer is not accompanied by a concurrent improvement of the tensile mechanical properties. The creep resistance is enhanced by the introduction of clay, with an appreciable dependence on both the polyethylene and the clay type.
By using mercaptosuccinic acid-cerium(IV) sulfate and mercaptosuccinic acid-KMnO4 redox systems in acid aqueous medium, the polymerization of acrylamide monomer was performed at room temperatures. Water soluble acrylamide polymers which contain mercaptosuccinic acid end-groups were synthesized. The dependence of polymerization yield and the molecular weight of polymer on the initiator concentration(nMSA=nCe(IV)) at different acid concentrations, polymerization time, temperature, and concentration of sulfuric acid was investigated. The decrease in the initiator concentration resulted in an increase in the molecular weights but a decrease in the yield. The increase of reaction temperature from 20 to 60°C resulted in an increase in the molecular weights and slight decrease of the yield of polymer. Cerium and manganese ions are reduced to Ce(III) and Mn(II) ions respectively in polymerization reaction. The existence of Ce(III) ion bound to polymer was investigated by UV-visible spectrometry and fluorescence measurements. The amount of Mn(II) which is incorporated to the polymer was determined.
The waterborne polyurethane (WPU) dispersions from the reaction of cycloaliphatic diisocyanates [4,4’-methylenebis(cyclohexyl isocyanate) (H12MDI) and isophorone diisocyanate (IPDI)] and polyethylene glycol (PEG) with various molecular lengths were synthesized using our modified acetone process. Differetial scanning calorimeter (DSC) and Fourier transform infrared spectroscopy (FTIR) were utilized to characterize WPU films for the behavior of their crystallinity and H-bonding of WPU films. The Tg value of WPU increases with increasing the molecular length of PEG, whereas the Tm of WPU decreases with increasing PEG length. Alternating current (AC) impedance experiments were performed to determine the ionic conductivities of WPU films. The WPU gel electrolytes exhibits an ionic conductivity as high as ~ 10-5 S/cm at room temperature.
Transparent Nonlinear Optical (NLO) inorganic/organic (polyimide/silica) hybrid composites with covalent links between the inorganic and the organic networks were prepared by the sol-gel method. The silica content in the hybrid films was varied from 0 to 22.5/wt%. The prepared PI hybrids were characterized by IR, UV-Vis, Thermogravimetric analysis (TGA), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). They exhibited fair good optical transparency. The SiO2 phase was well dispersed in the polymer matrix. DSC and TGA results showed that these hybrid materials had excellent thermal stability. The polymer solutions could be spin coated on the indium-tin-oxide (ITO) glass to form optical quality thin films. The electro-optic coefficients (γ33) at the wavelength of 832 nm for polymer thin films poled were in the range of 19-27 pm/V.
The heat transfer and burning behavior of the intumescent fire-retardant polypropylene were studied by the cone calorimeter at heat flux levels of 50 kW.m-2 to establish an essential physical model for the intumescence process in fire. A mathematical model for the burning process of fire-retardant intumescent polymer was put forward based on the assumption that an intumescent front existed between the char layer and virgin layer. The model emphasizes the thermodynamic aspect of the intumescence process and a corresponding submodel is presented. Meanwhile the thicknesses and mass loss rates of the intumescent polypropylene during burning were measured for the validation of the modeling results. Thermal conductivity and heat capacity of polymer material were also measured as input parameters of the model. The validation results showed that the intumescent thicknesses and mass loss rates predicted by the model were in good agreement with the experimental results. The model was also used to predict the temperature distribution across the sample thickness during burning. The study shows that the present model can appropriately describe the intumescent behavior of the polymer and numerically predict its mass loss rates and temperature distribution in fire.
Sulfadiazine monomer (SDM) was synthesized by the reaction of sulfadiazine with acryloyl chloride. The SDM was characterized by 1H-NMR and IR spectra. A novel hydrogel with –SO2NH- group was obtained by the radical copolymerization of SDM with N-vinyl-pyrrolidone (NVP). Effects of the reaction temperature, reaction time, the monomer ratio, and the amount of the cross-linker on the pH sensitivity of the hydrogel were investigated. Results indicate that the hydrogel shows strong pH sensitivity in the pH range of 6.5 to 7.2. It also exhibits a good swelling reversibility at buffer solutions of pH 6.5 and 7.2. At last, drugs tests demonstrated the release effect of the hydrogel in pH range of 6.5 to 7.2.
Ethylene-propylene-diene-graft-polystyrene (EPDM-g-PS) copolymers were synthesized to obtain different structures of graft copolymers with different graft lengths and graft densities. The structure of synthesized EPDM-g-PS copolymers was characterized by gel permeation chromatography (GPC) and by Fourier transforms infrared spectroscopy (FTIR). These presynthesized graft copolymers were added (5 phr) to styrene-acrylonitrile (SAN) and ethylene-propylene-diene (EPDM) blends, prepared to maintain the following SAN/EPDM ratios a) 95/5 and b) 90/10. SAN/EPDM blends were characterized by the determination of mechanical properties (tensile strength, elongation at break) while their morphology was inspected by scanning electronic microscopy, SEM. The obtained results show that various structures of EPDM-g-PS copolymers influence the miscibility in SAN/EPDM blends. Optimal concentration of side branches of graft copolymers provide the finest morphology and enhance mechanical properties.
The in-plane (plane stress) fracture toughness of two polyester (PET, PETG) sheets were assessed using the essential work of fracture (EWF) method after thermal and hygrothermal aging performed just below glass temperature. This ensured that physical aging takes place. On the aged sheets the yield stress (σy), enthalpy relaxation (ΔH) and EWF parameters were determined. It was observed that the essential work of fracture component related to the specific yielding (we,y) is suitable for assessing physical aging - independently of the humidity content. A good linear correlations exists between we,y, σy and ΔH.