Iranian Polymer Journal
Year:2013 | Volume:22 | Issue:3|Papers Count:8

Mulberry silk fibroin is being used as biomaterial for tissue engineering applications. In the present work, comparisons are made between mulberry and eri silk fibroin scaffolds prepared by electrospinning method. The scaffolds are treated with ethanol to improve their dimensional stability, and the physical and chemical properties of the scaffolds are assessed using thermogravimetric analyzer (TGA), differential scanning calorimetry, Fourier transform infrared spectroscopy and X-ray diffractometry. The FTIR spectra confirm the structural change of silk fibroin from α-helical to b-sheet structure when mulberry and eri silk scaffolds are treated with ethanol. The thermal stability of the eri silk scaffold is found to be better than that of mulberry silk. Ethanol-treated eri silk displays higher tensile stress than the ethanol-treated mulberry silk. The hemolysis percentages of eri silk and mulberry silk scaffolds are found to be 1 and 3 %, respectively. While the platelet adhesion on eri silk fibroin scaffold is found to be lower than that of mulberry silk fibroin scaffold, the cell attachment, binding and spreading of L6 fibroblast cells on the eri silk scaffold are better than those on the mulberry silk fibroin, and the cell viability is found to be better on eri silk fibroin scaffold.

To examine the effect of mobil composition of matter 41 (MCM-41) nanoparticles on the kinetics of free radical and 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT)-mediated reversible addition fragmentation chain transfer (RAFT) polymerization, the polymerization reaction using various amounts of as-synthesized MCM-41 were performed. To study the reaction kinetics, conversion, molecular weight and polydispersity index (PDI) were obtained during the polymerization. Also, differential scanning calorimetry (DSC) was used to determine the glass transition temperature (T g) values of samples. According to the results, in free radical polymerization, conversion was increased by adding nanoparticles but the reverse trend was observed in RAFT polymerization. The same results were obtained for molecular weight values. In free radical polymerization, increasing the MCM-41 content led to higher PDI value, while in RAFT polymerization it did not appreciably affect the PDI value. In RAFT polymerization, no induction time was observed which indicates that DDMAT is an appropriate RAFT agent for styrene polymerization. Also in free radical polymerization, the addition of MCM-41 particles reduced T g values in comparison to neat PS. On the other hand, there was an increase in T g value up to 5 wt% of MCM-41 loading and a drastic reduction was observed in 7 wt% MCM-41 loading in the RAFT polymerization. Finally, the T g values of nanocomposites produced by RAFT method were higher than those in the nanocomposites synthesized using the free radical method.

It is very helpful to guide design production and processing conditions for polymer-based inorganic or organic nano-composites by investigating their rheology. In this study, an intercalated nano-composite of montmorillonite (MMT)-dioctadecyl dimethyl ammonium bromide (DOAB) was added and reacted with vinyl acetate (VAc) to form the exfoliated nano-composite of polyvinyl acetate (PVAc)-MMT-DOAB through five different synthesis processes. The MMT-DOAB was exfoliated into nano-particles of layers or sheets and dispersed randomly in PVAc matrix. The different synthesis processes affected the dispersion and apparent viscosity of PVAc and PVAc-MMT-DOAB. With the polymerization time shortening and the water decreasing, the dispersion got bad and the apparent viscosity increased. PVAc and PVAc-MMT-DOAB were pseudo-plastic non-Newtonian fluids and both possessed the normal stress effect (Weissenberg effect) that is also called the pole-climbing phenomenon. By the help of the apparent viscosity analyzed using the power-law function equation, Newtonian fluid flow equation and Cross-Williamson model viscous equation, the different synthesis processes and MMT–DOAB had a certain effect on the rheology of PVAc and PVAc-MMT-DOAB. With the change of different synthesis processes and the increase of MMT-DOAB content in the synthesis system, the estimated molecular weight of PVAc–MMT–DOAB was also increased accordingly.

A new interesting class of linear Schiff-base poly (sulfone-ester) s has been synthesized by polycondensation of (E)-1-(4, 4′-(4-hydroxy-3-chlorobenzylidene) thiocarbamoylaminophenyl-sulfonylphenyl) -3-(4-hydroxy-3-chlorobenzylidene)thiourea with 2,6-pyridinedicarbonyl chloride/thiophene-2,5-dicarbonyl dichloride. The enhancement of physical properties (thermal stability, glass transition temperature, mechanical strength, molar mass, electrical conductivity, etc.) of polymeric materials while maintaining their processability was the foremost aspiration of this research work. The pyridine or thiophene-based heteroaromatic poly (sulfone-ester) s (PSEs) showed ample solubility in amide solvents and good yield. PSEs possessed high inherent viscosity of 1.79-1.93 dL/g and molar mass 125 × 103-145 × 103 g mol-1. The polymers were thermally stable with 10 % weight loss in the range 538–547oC and glass transition temperature between 293 and 296oC. Further aim was to obtain novel miscible nano-blends exhibiting good electrical conductivity and heat stability. For this purpose, PAN doped with dodecylbenzenesulfonic acid (PAN/DBSA) was prepared by in situ doping polymerization, and then blended in solution/melt with PSEs. The resulting high performance materials potentially combined the fine thermal properties and processability of poly (sulfone-ester) s with electrical characteristics of polyaniline. FESEM of melt-blended PSEs/PAN/DBSA showed nano-level homogeneity of the microstructure liable for better electrical conductivity (2.7–3.2 S cm-1). The azomethine and pyridine moieties introduced in the backbone render these polymers thermally and mechanically stable as well as electrically conducting. The miscible blends, exhibited good heat stability (T 10 520–527oC, T g 281-285 oC) and mechanical strength (55.20-57.18 MPa) compared with reported azomethine/polyaniline-based structures. New processable and high-performance engineering plastics, attractive for aerospace applications, can be fabricated using novel blends.

Our study is focused on the investigation of polyamide 12 (PA 12) grade behavior in rotational molding process. Hence, some rotational molding tests of polyamide 12 were conducted on a STP LAB 40 machine. To simulate the cooling stage within the rotational molding, the crystallization behavior of polyamide 12 was studied using differential scanning calorimetry technique and the obtained results for non-isothermal crystallization were fitted with Ozawa model. Furthermore, morphology survey has been carried out by a hot stage method using a microscope to investigate the spherulites evolution which depends on the temperature. The micro-tensile properties have been studied using micro-tensile bench (MVTV2) to explain the mechanical behavior of polyamide 12 during crystallization. As a result, the rotational molding of PA 12 was successfully carried out. The simulation of the melting and crystallization stages, by application of Ozawa model coupled with enthalpy method gave a good representation of experimental data on one hand. On the other hand, all characterization revealed useful information to understand the different phenomena that govern the rotational molding process.

In this study, 3-(2-Aminoethyl thiophene) (2AET) monomer was electropolymerized on glassy carbon electrode (GCE) using various electrolytes (lithium perchlorate (LiClO4), sodium perchlorate (NaClO4), tetrabutyl ammonium tetra fluoroborate (TBABF4) and tetraethyl ammonium tetra fluoroborate (TEABF4) in acetonitrile (CH3CN) as solvent. Poly (3-(2-aminoethyl thiophene) (P(2AET))/GCE was characterized by cyclic voltammetry (CV), Fourier transform infrared reflectance spectrophotometry (FTIR-ATR), scanning electron microscopy, energy dispersive X-ray analysis (EDX), and electrochemical impedance spectroscopy (EIS) techniques. The electrochemical impedance spectroscopic results were given by Nyquist, Bode-magnitude, Bode-phase, capacitance and admittance plots. The highest low frequency capacitance (C LF) value obtained was 0.65 mF cm-2 in 0.1 M LiClO4/CH3CN for the initial monomer concentration of 1.5 mM. The highest double layer capacitance (C dl = ~0.63 mF cm-2) was obtained in 0.1 M LiClO4/ACN for [2AET] 0 = 0.5, 1.0 and 1.5 mM. The maximum phase angles (q= 76.1o at 26.57 Hz) and conductivity (Y” = 3.5 mS) were obtained in TEABF4/ACN for [2AET] 0 = 0.5 and 1.0 mM, respectively. An equivalent circuit model of R (Q (R (Q (R (CR))))) was simulated for different electrolytes (LiClO4, NaClO4, TBABF4 and TEABF4)/P(2AET)/GCE system. A good fitting was obtained for the calculated experimental and theoretical EIS measurement results. The electroactivity of P (2AET)/GCE opens the possibility of using modified coated electrodes for electrochemical micro-capacitor electrodes and biosensor applications.

Nitroxide-mediated free radical polymerization (LREP) was employed for the first time to prepare graft copolymer by having arylated polypropylene (Cl-PP) as a backbone and polystyrene (PS) as branches. The graft copolymerization of styrene was initiated by arylated PP carrying 2, 2, 6, 6-tetramethyl-1-piperidinyloxy (TEMPO) groups as a macroinitiator. Thus, maleic anhydride was grafted onto polypropylene by peroxide-catalyzed swell grafting method (PP-MAH). Next, PP-MAH reacted with ethanolamine to produce a hydroxyl group containing polypropylene (PP-OH) and the obtained PP-OH was treated with α-phenyl chloroacetyl chloride and converted to a chloroacetyl group containing polypropylene (PP-Cl). Finally, 1-hydroxyl-2, 2, 6, 6-tetramethylpiperidine (TEMPO-OH) was synthesized by reducing TEMPO with sodium ascorbate and this functional nitroxyl compound was coupled with a-phenyl chloroacetylated polypropylene. The resulting macroinitiator (PP-TEMPO) for free radical polymerization was then heated in the presence of styrene for the formation of the graft copolymer. The prepared graft copolymer was characterized by Fourier transform infrared spectroscopy and 1H NMR techniques. Glass transition temperature of grafted copolymer was investigated using thermogravimetric analysis and differential scanning calorimetric techniques. This approach using nitroxide-mediated macroinitiators is an effective method for the preparation of new materials.

Polypyrrole is prepared with different molar ratios of dodecylbenzene sulfonic acid (DBSA) (0.1, 0.2, 0.3 and 0.4) by in situ chemical polymerization method. The reaction temperature was 0-5 oC for 24 h. The FTIR spectrum confirmed the attachment of sulfonyl group in the pyrrole structure. The intensity of polypyrrole increased with increase in sulfur content. SEM graphs revealed the granular morphology of the doped polymer surface. DBSA has had strong effect on morphology with formation of aggregated particles at higher concentrations. Higher concentration of DBSA-doped PPy shows higher thermal stability. The promotion of electron from ground state to excited state of polypyrrole is confirmed by UV spectroscopic studies. Various sizes in particle distribution of DBSA-doped PPy were analyzed by a particle size analyzer. Solubility of polypyrrole was determined at room temperature. The solubility and quantity of polypyrrole increased with higher dopant concentration. Current–voltage (I-V) characteristics were carried out over the temperature range 313-343 K, which was found to be linear. The conductivity of doped-PPy showed high conductivity at low concentration of dopant while, conductivity decreased with increasing concentration of DBSA. The higher doping level of DBSA was confirmed by elemental analysis.