مجله ایرانی پلیمر
سال:1384 | دوره: | شماره: |تعداد مقالات:9

Cross-linked poly(vinyl alcohol)/poly(vinyl pyrrolidone) (PVP/PVA) hydrogels were prepared in aqueous media using K2S2O8. The gel fraction, degree of swelling in water, and mechanical properties, such as TGA, DSC, and tensile strength were measured. It was found that the gel fraction increases with increasing potassium peroxodisulphate concentration but never reach to 100%. The swelling behaviour of the gels were specified by a relatively fast rate of swelling at the beginning of the process and measured as gram of water per minute. The amount of absorbed water as immersion water uptake of greater than 1400% is obtained. Because of the neutrality of the hydrogels, the maximum of swelling was achieved at pH=7. Maximum extents of swelling were achieved at 25°C and the swelling of hydrogels was found to decrease at higher temperatures. The hydrogel could be considered as a good barrier against common microbes including Sarcina lutea,  Escherichia Coli, and Pesudomonase aeruginosa. The thermal analysis shows that the gels are stable up to 350°C. According to the DMTA thermogram, the glass temperature of 44.8°C is observed for 50 % w/w of hydrogel sample. Tensile strength as high as 90.8-10.0 Kg/cm2 and elongation-at-break about 60% were achieved using 1.1×10-5 M concentration of KPS.

Copolymerization of acrylonitrile (AN) with acrylic acid (AA) carried out by solvent (DMF)-water suspension method, at 60 oC, using azobisisobutyronitrile (AIBN) as an initiator. The effects of mole fraction variation of acrylic acid and concentration variation of water in reaction medium, on the properties of synthesized copolymers were investigated by FTIR, viscometry, and DSC techniques. The reactivity ratios were calculated using Fineman-Ross and Kelen-Tudos methods. The results obtained show that by increasing the mole fraction of acrylic acid in the feed up to 0.0756, the conversion percentage decreases. However, the molecular weight increases in this range of feed ratio. In the samples prepared by keeping the feed ratio of comonomers constant and varying the ratio of the solvent/nonsolvent, the molecular weight increases by increasing nonsolvent amount. The reactivity ratio of AA is 6.5 times greater than that of AN. DSC Exothermic peak of homopolymer shows a single peak whereas, in copolymers it appears as doublets, due to more distinction of dehydrogenation, oxidation, and cyclization reactions.

The structures of polypropylene/nylon 6 (PP/N6) blend filaments (10, and 20 wt% N6) with and without PP-g-MAH as compatibilizer are investigated. The blend filaments produced at the take-up speeds of 300 and 800 m/min were drawn with draw ratio of 3.5 and 2, respectively. Effects of blending of N6 with PP on birefringence, crystalline, and amorphous orientation factors of the composite filaments are studied. The amorphous orientation factor, fam of PP was found to increase with the increase in the amount of N6. The blend filaments behaved like iso-strain materials and most of the force in spinning and drawing was born by the PP phase. The presence of N6 fibrils helped the PP chain molecules to orient in amorphous regions. However, the crystalline factor, fc of PP decreased with increase in the nylon fraction. This means that the presence of the crystals of N6 caused a decrease in the orientation of the PP crystals.

Six corn starch-LDPE film blends containing starch in the range 5-40% by weight, oleic acid as a Lewis catalyst with concentration of either 5% or 10%, maleic anhydride as a coupling agent with concentration of either 2% or 10% and benzoyl peroxide as free radical initiator with concentration of either 0.1% or 0.25% were prepared. Fungal growth tests (ASTM G21) using Penicillium funiculosum were carried out on the samples made according the above formulations. Tensile tests (ASTM D638) and SEM imaging were also carried out on the samples before and after incubation with Penicillium funiculosum for three weeks. The results of ASTM G21 test and SEM imaging showed that the increase in starch content from 5% to 40% in the formulations containing all three additive increases the biodegradability of the samples whereas increase in the concentration of oleic acid from 5% to 10% has an opposite effect. Formulations containing only 5% starch with a fairly high concentration of additives or 40% starch with no additives supported none or very little growth after three weeks, which indicates the importance of the concentration of starch and the presence of additives on the biodegradability of starch - LDPE film blends. Tensile test results showed that increase in starch content in the range of 2-30% leads to a decrease in the values of the tensile strength and increase in the values of the elongation-at-break whereas further increase up to 40% has the opposite effect. Tests with blends containing 40% starch and no additive or 5% starch with a fairly high concentration of additives resulted in low yield stresses and high elongation-at-break. Increase the concentration of oleic acid from 5% to 10% in the blends resulted in a decrease in both the yield stress and elongation-at-break.

A study of the phthaloylation of cellulose acetate in two reaction media consisting of acetic acid and acetone is performed respectively by using a statistical experimental design. Two kinds of cellulose acetate having degrees of acetylation of 1.62 and 1.93 are used as starting materials respectively. Two mathematical models are obtained for describing the correlation between the degree of phthaloylation of the synthesized cellulose acetate phthalates and the principal reaction parameters involved: the molar ratios of catalyst/cellulose acetate and phthaloylation agent/cellulose acetate. It is concluded that the degree of phthaloylation of the products is mainly influenced by the amount of phthaloylation agent in the case of acetic acid and by the amount of catalyst in the case of acetone used as organic solvent.

4-(4-aminophenyl)-1,2,4-triazolidine-3,5-dione (1) was reacted with one mole of acetyl chloride in dry N,N-dimethylacetamide (DMAc) at low temperature and 4-(4-acetamidophenyl)-1,2,4-triazolidine-3,5-dione [4-(4-acetanilido)-1,2,4-triazolidine-3,5-dione] APTD (3) was obtained in high yield. The compound APTD was reacted with excess acetyl chloride in DMAc solution and gave 1,2-bis-acetyl-4-(4-acetamidophenyl)-1,2,4-triazolidine-3,5-dione (4) as a model compound. Solution polycondensation reactions of monomer 3 with succinyl chloride (SucC), suberoyl chloride (SubC) and sebacoyl chloride (SebC) were performed under conventional solution polymerization techniques in the presence of different catalysts and lead to the formation of novel aliphatic polyamides. These novel polyamides have inherent viscosities in a range of 0.08-0.24 dLg-1 in N,N-dimethylformamide (DMF) at 25oC. Some structural characterization and physical properties of these novel polymers are reported.

Polyacrilonitrile (PAN) nanofibres were prepared by electrospinning of PAN/DMF solution of 12.5 wt% concentration. Fibre morphology was observed under a scanning electron microscopy. The effects of operating parameters including applied voltage, feeding rate, and tip-target distance on the morphology of electrospun PAN nanofibres were systematically evaluated. Average diameters of nanofibres decreased with increasing applied voltage from 10 to 20 kV, but broader distribution in diameters of nanofibres were obtained at 15 kV and above. Morphology of nanofibres was changed by the instability of the liquid surface from which the jet originates to beaded nanofibres. The morphological structure can be changed by changing the feeding rate of solution and tip-target distance. At lower and higher feeding rates, nanofibres with beaded were observed. At 7.5 cm tip-target distance and below, the structures of nanofibres appeared not to be stabilized completely, indicating that the spun nanofibres were mostly wet when they reached the collecting target.

An experimental study was undertaken to investigate and optimize the fabrication processing conditions of the sandwich structures designed for flexural load bearing applications. Sandwich beams, each with two glass/epoxy faces and a rigid polyurethane foam core were constructed under four different processing conditions. Wet and dry faces were applied at two temperatures to atteine these four conditions. It has been shown that in comparison with the first processing condition (wet at 25oC) the specific flexural strengths of the second one (dry at 25oC), the third one (dry at 70oC) and the fourth one (dry at 70oC with a thin layer of an adhesive) are increased by 38% and 209%, 267%, respectively. The reason behind this significant enhancement is demonstrated to be related to the debond strength of the core-face interface. It has been demonstrated that the debond strength of the core-face and core plays an important role in enhancing the flexural rigidity and controlling of the failure mechanisms. If the core material be polymeric foam, the core and debonding strengths at the core-face interface will almost entirely dictate the structural sandwich composite performance especially under flexture. Results showed that the core strength decreases, but the debonding strength of the core-face interface increases with the increment of the processing temperature during the preparation of the rigid polyurethane foam core. We also observed that by increasing the debonding strength of the core-face interface, the failure mode changes from debonding of the core-face interface to the failure of the face. Finally, the sandwich structures were obtained with the excellent performance under flexural loading.

Ten copolyesters were synthesized by high temperature polycondensation of 2-(N-ethylanilino)-4,6-bis(phenoxy-2-carbonyl chloride)-s-triazine [EAPCCT] with each of the following mixtures of diols: [Bisphenol-A(BPA)+Bisphenol-C(BPC)], [BPA+Bisphenol-S(BPS)], [BPA+Phenolphthalein(Ph)], [BPA+1,8-dihydroxyl anthraquinone(DHA-1,8)], [BPA+1,4-dihydroxy anthraquinone(DHA-1,4)], [BPA+catechol(C)], [BPA+resorcinol(R)], [BPC+Ph], [BPC+R], and [Ph+DHA-1,4]. All the copolyesters were characterized by solubility, density, and viscosity measurements, IR and NMR spectroscopy, and thermogravimetric analysis. All the copolyesters were soluble at high temperature in acetone, dimethylformamide, dimethylsulphoxide, dimethylacetamide, etc. and have reduced viscosity in the range of 0.539-0.678 dL/g in dimethylformamide at 30oC. Copolyester derived from the diol mixture [BPA+DHA-1,4] showed the greater thermal stability than the other copolyesters.