Iranian polymer journal
Volume:17 Issue: 3, 2008

The skin has an important role in human health and its defect can produce many problems in normal physiology. Because of its anatomy and physiology, most likely the skin is exposed to pathologic agents more than other organs. In this study, grafting of poly(acrylic acid) onto silicone rubber was carried out using CO2- pulsed laser as an excitation source in order to create functional groups to immobilize collagen. Collagen was immobilized onto poly(acrylic acid) grafted silicone through covalent bonding. Modified and unmodified surfaces were characterized by water contact angle; scanning electron microscopy (SEM) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Fibroblast cells (L929) were cultured onto collagen immobilized poly(acrylic acid)-grafted silicone and poly(acrylic acid)-grafted silicone films. It was observed that collagen immobilized surfaces showed significant cell adhesion and growth in comparison with poly(acrylic acid)- grafted silicone samples. It seems that collagen immobilized surfaces may have an excellent potential to be used as a derm-like matrix.

Dielectric relaxation properties of solution grown foil samples of poly(vinylidene fluoride) (PVDF) of 20 μm thickness with similar (Al-Al) electrode combination have been studied in the low frequency range of 100 Hz to 10 kHz by varying the temperature from 30ºC to 170ºC. PVDF foil samples exhibit two dielectric loss maxima, one around 130±10ºC and the other around 150±10ºC. These peaks correspond to α- and α''-relaxation processes, respectively. The variation of permittivity with temperature is attributed to the thermal expansion, orientation of dipolar molecules and the chaotic random motion of molecules in the close vicinity of α and α'' peaks, respectively. The thermally stimulated depolarization current (TSDC) spectra of PVDF foil sample are characterized by two current maximas, one at 70±10ºC (β-peak) and the other centered at 135±10ºC (α-peak). The first peak attributed to β-relaxation process was caused by local motions of side chain. However, α-relaxation peak appeared due to the formation of space charge at metal polymer interface. The peak position and activation energy do not change with the poling field (Ep), but it strongly depends upon the poling temperature (Tp). The location of the TSDC α-peak is found to be comparable with the α-peak obtained by dielectric relaxation spectroscopy.

The hybridization of two types of short fibres having different lengths and diameters offers some advantages compared to each fibre being used alone in a single polymer matrix. In this study, the polypropylene/kenaf fibre/wood flour hybrid composites were prepared in an internal mixer. The temperature was 190ºC and rotor speed was 60 rpm. The system was compatibilized by polypropylene grafted maleic anhydride. Based on dimensional aspects before and after processing, the kenaf as fibrous filler and wood flour as particulate filler were considered. The weight ratio of lignocellosic fillers was 40%. Dynamic rheological properties such as storage modulus, complex viscosity, damping factor were evaluated at 190ºC. It was observed that, the non-linearity region of hybrid composites shifted to lower strains compared to virgin polypropylene. Due to higher probability of agglomerates formation in the sample containing 40% (by wt) of wood flour, the storage modulus and complex viscosity of this sample were higher than those of the other samples. A flattened section was observed n the tan δ diagram which is attributed to different relaxation processes of composite nd neat PP. The Cole-Cole diagrams of samples showed that the relaxation times hifted to higher values with the addition of fillers and the longest relaxation times were elated to composites with pure wood flour.

The crystallization morphology of poly(phenylene sulphide) (PPS) with different molecular weights (MW), isothermally crystallized from the melt under shear condition, has been observed by polarized optical microscope (POM) equipped with a CSS450 hot-stage. The morphology of PPS is greatly influenced by shear condition, and the shish-kebab-like fibrillar crystal structure can be observed under higher shear rate and longer shear time for the higher molecular weights. Under the quiescent crystallization the growth rate was found to be essentially MW dependent i.e., the spherulite growth rate decreases with the increased MW, and a strong effect of MW on the flow induced crystallization kinetics was observed. Under shear condition the decreasing spherulite growth rate results from highly oriented chains. The molecular eight was also found to explain qualitatively the observed transition from the lowest W isotropic morphology to the higher MW shish-kebab-like fibrillar crystal structure. he melting behaviors of the three MWs performed by differential scanning calorimetry (DSC) show that multiple melting peaks can be observed after the PPS melts when subjected to shear flow. We suggest that the lower melting peak corresponds to the melt of imperfect crystal. The higher melting peak is related to the orientation of molecular chains. These orientated molecular chains form the initial lamellae, hich are thicker than the kebab-like lamellae that later develop due to chain elaxation.

Bi-supported catalyst SiO2/TiCl4/THF/MgCl2 was prepared via four steps including, (i) heat activation of silica at 600ºC, (ii) preparation of precursor composition, (iii) impregnation of catalyst components on silica, and (iv) catalyst prereduction with alkyl-aluminium. Homopolymerization was carried out at 3-15 bar pressure and 65-85ºC temperature. The GPC data was analyzed using the concept of multincentre catalysis and four types of active centres detected that differ in molecular weight. The constancy of molecular weight of each active centre with respect to monomer concentration showed that a bimolecular chain transfer mechanism exists. An increase in the ethylene concentration led to a gradual decrease of polymer fractions produced by centres I, II and III and a progressive increase in the fraction produced by centre IV. The dependency of molecular weight and activity on some other parameters such as temperature, Al/Ti ratio, polymerization time and hydrogen concentration were examined. Activity as a function of polymerization temperature showed a maximum at 70ºC. The polymerization rate was first order with respect to monomer concentration. A correlation was obtained between the average molecular weight and hydrogen concentration. The molecular weight decreased th increasing polymerization temperature, H2 concentration and Al/Ti ratio.

Soluble and photoactive novel aromatic polyesters containing acetoxynaphthalamide unit in the side chain have been synthesized with moderate molecular weights by direct polycondensation of 5-(3-acetoxynaphthoylamino)isophthalic acid with different aromatic diols using tosyl chloride (TsCl), pyridine (Py) and N,Ndimethylformamide (DMF) system as a condensing agent. The reaction was successfully applied to the preparation of thermally stable polyesters with good yields and inherent viscosities in the range of 0.28-0.62 dL/g. The resulted polymers are readily soluble in aprotic polar solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, DMF, Py and dimethyl sulphoxide. Thermogravimetric analysis data showed that these polyesters are thermally stable, with 10% weight loss being recorded above 360ºC. These macromolecules exhibited maximum UV-vis absorption at 269 and 320 nm in DMF solution. Their photoluminescence in DMF solution demonstrated fluorescence emission maxima around 360 and 428 nm for all polyesters obtained.

Synergistic effects of dope non-solvent concentration and jet draw ratio of poly(acrylonitrile) on as-spun fibre void structure and tensile properties were investigated and rationalized based on a modified designing index, namely CXη-1. The notations C, X, and η are the non-solvent diffusion coefficient normalized by the solvent diffusion coefficient through the proto-fibre, a parameter defined by solubility differences among the system components and jet elongation viscosity, respectively. An increase of dope non-solvent concentration enhanced CXη-1 leading to minute porosity decrease. On the other hand, the simultaneous dope non-solvent concentration and draw ratio increases up to 5 vol% and 4, led to reduction of CXη-1 and therefore to severe fibre porosity. The modulus-porosity relationship of the free drawn fibres were best fitted with the Wang''s second order equation E = E0e-(ap+bp) (R2 = 0.96) and hence assigned to liquid-liquid de-mixing as the governing phase separation mechanism. On the other hand, the mechanical behaviour/porosity of proto-fibre containing non-solvent in their dope and drawn with the draw ratio value of 4 was best fitted with the Eshprieg''s first order equation, E = E0e-ap (R2 = 0.97) and accordingly assigned to the solid-liquid based phase separation. Where E0 and p are modulus of the virgin sample and its porosity, respectively, while a, and b are the Eshprieg''s and Wang''s equation constants.