Iranian polymer journal
Volume:18 Issue: 6, 2009

Cure kinetics of the reaction of diglycidyl ether of a bisphenol-A based epoxy resin(DGEBA) with aromatic diamines, such as 3,6-diaminocarbazole (DAC) and N´-[7-(acetyl-4-aminoanilino)-9,9-dioctylfluoren-2-yl]-N´-4-aminophenyl acetamide (ADOAc) as curing agents have been studied by using non-isothermal differential scanningcalorimetry (DSC). DAC was prepared according to literature and ADOAc was preparedvia the reaction of 2,7-dibromo-9,9-dioctylfluorene with 4-aminoacetanilide in thepresence of 10 mol% CuI and 20 mol% N,N''-dimethylethylene diamine(DMEDA) ascatalysts and K2CO3 as a base. The parameters of non-isothermal curing kinetics, activation energy (Ea), pre-exponential factor (A) and rate constant (k) were obtainedaccording to Kissinger, Ozawa, and iso-conversion equations. The activation energy(Ea) values for DGEBA/DAC and DGEBA/ADOAc systems obtained by Kissingermethod are 88.11 and 59.50 kJ/mol, by Ozawa method are 90.75 and 64.15 kJ/mol andby iso-conversion equation are 91.45 and 65.49 kJ/mol, respectively. The values of preexponential factors (A) obtained for DGEBA/DAC and DGEBA/ADOAc systems are1.29×1010 and 9.03×105 s-1 with rate constants (K) of 0.90 and 0.12 s-1, respectively.The results show that DGEBA/ADOAc system has lower Ea and K values than theDGEBA/DAC system. The exothermic curing thermograms of DGEBA with ADOAc aremuch broader than the curing exothermic peak of DGEBA with DAC. At 300ºC bothcured systems start to lose weight and the final weight loss is higher for DGEBA/ADOAc system.

To improve the thermal property and flame retardancy of epoxy resins, a novelmodifier was synthesized through the reaction between the redistributed productof poly(2,6-dimethyl-1,4-phenylene oxide) (REPPO) and the polysiloxane havingpendant epoxy groups. Gel permeation chromatography (GPC) was used to confirmthe redistribution reaction and identify the average molecular weight of the redistributedproducts. FTIR and 1H NMR measurements were employed to characterize the structuresof the products. This REPPO-containing polysiloxane (PSREPPO) was used tomodify a bisphenol A epoxy resin at different contents where 4,4’ diaminodiphenylmethane (DDM) acting as the curing agent. The cured samples were examined by scanning electron microscope (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and limited oxygen-index (LOI) methods. The SEM results showed that the use of PSREPPO has improved the phase compatibility and increased toughness of the samples. The DSC results showed that the modifier could improve the Tgs of the epoxy resins. An epoxy/PSREPPO ratio of 100/40 gives an increase of 26.53ºC in its Tg value compared to the unmodified epoxy resin. The TGA results showed that the Td50% of the samples increased also with the increase of PSREPPO content; although it decreased when the content of PSREPPO exceeded above a certain value. Char yield at 700ºC and LOI values increased with the increase of the content of PSREPPO. In conclusion, the PSREPPO-modified samples improved the thermal properties and flame retardancy of the epoxy resins.

The aggregation of hairy-rod segments in solid films was observed using wideangle X-ray diffraction (WAXD). The films cast by evaporating the THF solventfrom MEH-PPV/THF were extremely rigid due to the strong aggregation amongthe main chains of MEH-PPV and could not be disaggregated by heat. In contrast, aggregations in the films cast by evaporating the toluene solvent from MEHPPV/toluene could be disaggregated due to the weak interactions among the side chains of MEH-PPV. Accordingly, the MEH-PPV/toluene system exhibits good thermal reversibility between aggregation while cooling and disaggregation when heated. The aggregation of the semi-rigid polymers occurs even at a concentration of well below the threshold lyotropic concentration. This process takes place in semi-rigid polymers with disk-like domains which serve as nuclei for the development of a macroscopic nematic phase as the polymer concentration increases during solvent evaporation. A film with a dominant lyotropic liquid crystalline (LC) phase was formed. As the temperature of the cast polymer film was increased, the thermotropic LC phase, rather than the lyotropic LC phase, was dominant between ca. 100ºC and 230ºC. However, both thermotropic and lyotropic LCs coexisted and associated with aggregation. The photoluminescence (PL) emission spectra and UV-vis absorption spectra of MEH-PPV in solution were obtained to elucidate the self-organized supramolecular aggregated conformation in various solvents, concentrations, and temperatures. The peaks exhibited a red shift in the PL emission spectra accompanied by a right shoulder when aggregation occurred. The shoulder grew as the concentration was increased.

One problem of polymer modified bitumens (PMBs) concerns the poor compatibilitybetween polymer and bitumens. Natural bitumen (NB) is often used for bitumen modification in order to obtain improved performance of the respective bitumen mixtures. This paper presents the results of NB modified bitumens with improved properties, prepared by incorporating styrene butadiene rubber (SBR). The effects of SBR and SBR/NB on the conventional, rheological, thermal, and morphological properties of the modified bitumens were studied. It was found that 2% content of NB shows marked improvement in high temperature properties by increasing the softening point in SBR/NB modified bitumen, while SBR of 3% content in SBR/NB modified bitumens shows significant effect on the low temperature properties and the aging resistance. The morphology in accordance with TG-DTG and DSC analysis indicated that compatibility and thermal properties were improved with a homogeneous and stable mix structure in modified bitumens. FTIR analysis shows few new weak peaks for modified bitumens indicating that physical alteration is the main changes in the modified bitumens.

Ultrahigh molecular weight polyethylene (UHMWPE)/SiO2 hybrid hollow fibremembranes were prepared by thermally induced phase separation-stretching (TIPS-S), using mineral oil as diluent and SiO2 as additive. In this study, UHMWPE/ SiO2 blends were incompatible. Therefore, an interfacial microvoid was produced in the interface between UHMWPE and SiO2 after stretching along fibre axis. Secondly, the stretching pore also appeared due to stretch. Moreover, UHMWPE/mineral oil was blended into a homogeneous phase at sufficiently high temperature and underwent phase separation when it was cooled. The TIPS pore was prepared by extracting mineral oil. Thereby, after stretching, multi-pore-structure (MPS) including interfacial microvoid, stretching pores, and pore by TIPS was built. The influential factors, including heat-treatment, draw ratio and drawing temperature were investigated. The results of this study indicated that the draw ratio had an optimum value in order to obtain the UHMWPE/SiO2 hybrid hollow fibre membranes with good permeability. The permeability of membrane showed the best performance at the 5 folds draw ratio. The effects of heat-treatment and drawing temperature on pore structure have been mainly produced from the pores contraction and defect formation. Both the pore size and the pore number of HC5 were the highest, those of C5 took second place and those of HH5 were the lowest. HC5 showed the highest pure water flux compared to HH5 and C5. The mechanical properties of membranes were the result of a set of factors including crystallinity, degree of orientation, and defects in the membrane structure.

Chemical methods are the most common routes for modification of starch. In this study, cross-linked wheat starch was produced using phosphoryl chloride as a cross-linking agent and its physico-chemical properties were studied. The crosslinked starch had a cross-linking degree of 3.86 × 10-5. In SEM micrographs, some blister- like spots were observed on the cross-linked starch granules. The results also showed that the water solubility, water absorption, and intrinsic viscosity (determined by U-tube) of the cross-linked starch were reduced compared to native starch. The crystalline pattern and the degree of crystallinity (as determined by wide angle X-ray diffractometer) of native and cross-linked starches were similar. Determination of the thermal properties of the samples using differential scanning calorimetry (DSC) revealed that the gelatinization peak temperature and the gelatinization enthalpy of the cross-linked starch increased compared to those of native starch. Determination of the pasting properties of the cross-linked starch using rapid visco-analyzer (RVA) showed that it had lower peak, breakdown, and final viscosities compared to those of native starch. Moreover, the cross-linked wheat starch showed more stable peak viscosity during heating. The results of this study suggest that the cross-linked wheat starch has the potential use in food production systems such as production of jam, baby food, soups, and salad dressing in which the increase in viscosity as a result of elevating temperature is not desirable, anymore.

Microencapsulated n-octadecane phase change materials (PCMs) with polyurethane (PU) and resorcinol-modified poly(melamine-formaldehyde) (PMF) shells were synthesized through interfacial and in-situ polycondensation, respectively, and their microstructures and phase change, thermal stabilities, and anti-osmotic properties were evaluated. FTIR were performed to verify the the quality of encapsulation of n-octadecane within two shell materials. Optical phase-contrast microscope and scanning electronic microscopy images indicate a perfect core/shell microstructure and compact polymeric shells of these microcapsules. Differential scanning calorimetry measurements demonstrate the high enthalpies for the melting and crystallization of the microencapsulated n-octadecane, while wide-angle X-ray scattering patterns have confirmed that the crystallinity of microencapsulated n-octadecane is identical with that of pure n-octadecane. Although the two microencapsulated PCMs have good phase change properties, the encapsulation ratio and efficiency of the microcapsules with PU shell are much higher than those of PMF shell. However, the microcapsules with PU shell exhibit good thermal stability but pooranti-osmotic property in comparison with those of PMF shell.