Iranian Polymer Journal
Year:2007 | Volume:16 | Issue:12|Papers Count:6

Bamboo natural fibres were extracted and their crystalline structure was investigated by X-ray diffraction, FTIR spectra, and 13C NMR techniques and the results were compared with common fibres, e.g., ramie, flax, and cotton fibres. The allomorph content in bamboo fibres was calculated by 13C NMR and the result shows that bamboo fibres are Ib-dominant type which has also been confirmed by FTIR analysis. The Ia phase in bamboo fibres is lower than that in ramie and flax fibres. A simple model was used to calculate crystallite size of bamboo fibres in NMR spectroscopy. The results indicate that bamboo fibres have the crystallite size similar to that of ramie, but larger than those of flax and cotton fibres. This finding is consistent with the result obtained by X-ray analysis. The crystallinity and crystallite orientation of bamboo fibres are similar to those of ramie fibres, but differ from those of flax and cotton fibres. Second derivative FTIR spectra indicate that more resolved networks of hydrogen bonds are responsible for predominant crystalline fibril in bamboo fibres. The difference of X-ray diffraction and NMR in characterization of natural cellulose is also discussed.

Effect of hard segment content was investigated on the gas permeability characteristics of polyether based urethanes. These polymers were synthesized by using 2000 molecular weight polypropylene-glycol (PPG 2000) with toluene diisocyanate (TDI). Conversion of prepolymer to a final PU was carried out by using 1,4-butane diol (BD) as a chain extender. Four different block ratios were chosen in order to prepare polyurethanes with different hard segment contents. The PPG1000 polyol based PU with the same content of hard segment was also synthesized to evaluate the effect of soft segment length on the gas separation properties of the polyurethanes. The prepared polymers were characterized and the permeability of gases was investigated. Permeation measurements of polymers have revealed that the permeabilities of gases decrease with increasing the hard segment content by which the selectivity of gases in polymers increases as well. The polymer containing 42.7 wt% hard segment has shown that its CO2 permeability coefficients and ideal separation factors relative to N2 are higher than 38.2 barrer (1 barrer =1×10-10 [cm3 (STP) cm/cm2.s.cmHg]) and 33.21, respectively. While, the polymer containing 26 wt% hard segment showed 79.5 barrer and 20.9 values, respectively. The gas permselectivities of polymers containing the same hard segment content with different soft segment lengths have shown that by increasing the soft segment length the permeability towards gases increases, meanwhile their gas selectivity decreases.

The curing reaction kinetics of an epoxy based on the diglycidyl ether of bisphenol- A (DGEBA) with an aromatic diamine, 4,4'-oxydianiline (ODA), was studied using non-isothermal DSC and FTIR isothermal curing at 120, 135, 160, and 180oC. In all cases, we have observed one exothermic peak during DSC scan up to 350oC. Kinetic parameters such as activation energy (Ea), reaction order, and rate constant were calculated from data obtained from DSC and FTIR tests. The obtained Ea values were 61 and 64 kJ/mol in the dynamic DSC measurements using Kissinger and Ozawa methods, respectively and 36.7 kJ/mol in the isothermal FTIR measurements. Thermodynamic parameters (DH¹, DS¹, and DG¹) were calculated for isothermal curing reaction. The value of DG¹ increased with increasing isothermal curing temperature. Water absorption properties of the cured samples were measured at different temperatures. The diffusion coefficient (D) was in the range of 1.6×10-12 – 7.1×10-12 m2/s from room temperature to 65oC. The diffusion activation energy was found to be 26.8 kJ/mol.

Microcellular foams are foamed plastics characterized by a cell density typically greater than 109 cells/cm3, with fully grown cells on the order of 10 mm, and a weight reduction ranging from 5 to 95%. An inert gas such as CO2 or N2 is usually used as the blowing agent. Compared to the unfoamed polymers, microcellular foams exhibit improved mechanical and physical properties, for instance, high strength-to-density, high toughness, high fatigue life, thermal properties, low dielectric constant, and reduced material weight and cost. In this paper, the influence of the saturation pressure and its drop rate on the microstructures of unfilled and glass filled ABS prepared in a batch process were investigated. Cell size distribution and cell density of foamed samples are also compared at various pressure drops and rates. The results show that although pressure drop has a significant effect on the nucleation at room temperature, its rate does not, however, affect the microstructure of the foamed samples, considerably.

Nanocomposites of PET/SiO2 (unmodified and modified by organic agents) were prepared by melt blending, to study the effect of organic modification of SiO2 on their morphology and crystallization behaviour. The crystallization behaviours of PET/SiO2 nanocomposites were investigated by differential scanning calorimetry (DSC), and the non-isothermal crystallization kinetics were analyzed by Jeziorny and Ozawa equations. The DSC cooling scanning curves showed that the crystallization peak became very narrow and Tmc shifted largely to high temperature region in presence of SiO2 which totally behaved as nucleating agent for PET. By Jeziorny equation it is shown that all the three different surface characteristics of SiO2 accelerated the crystallization rate and the values of the Avrami exponents (n) of PET/SiO2 nanocomposites remanined virtually unchanged as compared to those of the virgin PET. Ozawa equation, however, failed to reveal the non-isothermal crystallization kinetics of PET/SiO2 nanocomposites.

This research work focuses on the changes in molecular dynamics of gelatin in the early stages of gelation under temperature variations (273-330 K), pHs (3, 6.5, and 11) and concentrations (1, 3, and 5 %w/w). The early stage of gelation occurs at temperature well above the sol-gel transition point and is accompanied by increasing the viscosity of the solution. The induced variations of the local mobility of the macromolecules are detected by measurements of the spin-spin relaxation time of 1H nuclei of different amino acids. Changes in the rheological characteristics of the gelatin solutions are measured and the effects of acidity, temperature, and concentration on the early stages of the gelatin gelation process are evaluated. The experimental results were analyzed for the mobility of the individual amino acids and of the complete gel network at different temperatures and acidities. Spin-spin relaxation data indicate that the mobility of amino acids in this siane of gelation is not affected by the gelatin concentration, indicating that it is predominantly governed by intra-molecular interactions. As expected, the influence of this interaction on individual amino acids strongly depends on the polarity and their ability to form hydrogen bonds. The variation of the relaxation times reflects the specific role of each individual amino acid during the gelation process. Any deviation from the neutral pH conditions causes a strong increase in the local molecular dynamic, presumably caused by electrostatic repulsion under acidic or basic conditions. At the same time, it leads to decrease in the solution viscosity originally observed under neutral conditions.