The effects of processing parameters on the morphology of PLA/PEG melt electrospun fibers

Electrospinning of a polymer melt is an ideal technique to produce highly porous nanofibrous or microfibrous scaffolds appropriate for biomedical applications. In recent decades, melt electrospinning has been known as an eco‐friendly procedure as it eliminates the cytotoxic effects of the solvents used in solution electrospinning. In this work, the effects of spinning conditions such as temperature, applied voltage, nozzle to collector distance and collector type as well as polyethylene glycol (PEG) concentration on the diameter of melt electrospun polylactic acid (PLA)/PEG fibers were studied. The thermal stability of PLA/PEG blends was monitored through TGA and rheometry. Morphological investigations were carried out via optical and scanning electron microscopy. Based on the results, blends were almost stable over the temperature range of melt electrospinning (170 ? 230 °C) and a short spinning time of 5 min. To obtain non‐woven meshes with uniform fiber morphologies, experimental parameters were optimized using ANOVA. While increasing the temperature, applied voltage and PEG content resulted in thinner fibers, PEG concentration was the most influential factor on the fiber diameter. In addition, a nozzle to collector distance of 10 cm was found to be the most suitable for preparing uniform non‐woven PLA/PEG meshes. At higher PEG concentrations, alterations in the collector distance did not affect the uniformity of fibers, although at lower distances vigorous bending instabilities due to polarity augmentation and viscosity reduction resulted in curly fibrous meshes. Finally, the finest and submicron scale fibers were obtained through melt electrospinning of PLA/PEG (70/30) blend collected on a metallic frame. © 2017 Society of Chemical Industry     

Effect of organoclays on the rheological and morphological properties of poly(acrylonitrile‐butadiene‐styrene)/poly(methyl methacrylate)/ clay nanocomposites

Using the rheological measurements, the effect of three types of organoclays on the morphology and nanoclay dispersion in the poly(acrylonitrile‐butadiene‐styrene)/poly(methyl methacrylate) (ABS/PMMA) blends was investigated. For this purpose, polymers were melt blended with 2 and 4 wt% of organoclays in a twin‐screw extruder. Structural analysis of the blends and nanocomposites through the rheometery, theoretical approach, X‐ray diffraction, transmission electron microscopy, and scanning electron microscopy revealed that the clay content and interaction level between clays and the polymers dominated the morphology. While the morphology of the blends varied by PMMA content, smaller PMMA domains were observed for blends containing clay particles. Better‐interacted and intercalated nanoclays were mainly located within the interface at lower content. While, at higher content, they tended to migrate into the dispersed phase. Theoretical calculations of interfacial tensions and wetting coefficients confirmed this kind of migration. POLYM. COMPOS., 33:1893–1902, 2012. © 2012 Society of Plastics Engineers     

Cover Image,Volume 67, Issue 2

The cover image, by Tayebe Nazari and Hamid Garmabi, is based on the Research Article The effects of processing parameters on the morphology of PLA/PEG melt electrospun fibers, DOI: 10.1002/pi.5486 .

     

Classification of Persian carpet patterns based on quantitative aesthetic‐related features

In this work, the extraction of significant features of Persian carpet patterns was studied. Four aesthetic related features were extracted for a collection of Persian carpet images. To this purpose, a set of 134 color images of three different categories of traditional Persian designs, named “Afshan,” “Lachak Toranj,” and “Torkaman” were collected. At first, the PHOG (Pyramid of Histogram of Orientation Gradients) measure was derived for all patterns to calculate complexity, anisotropy, self‐similarity, and Birkhoff‐like features. Based on the results, anisotropy and Birkhoff‐like features significantly categorize three carpet designs. According to the results, the combination of anisotropy and Birkhoff‐like features increases the accuracy of classification of samples to 97%.     

Thermo‐rheological and interfacial properties of polylactic acid/polyethylene glycol blends toward the melt electrospinning ability

The electrospinning ability of PLA/PEG system at the melt state was investigated through the viscoelastic parameters obtained from dynamic shear and extensional rheometers. PLA and PEG were melt‐blended at various composition ratios. Effect of PEG concentration on the PLA thermal behavior was studied by the differential scanning calorimetry (DSC). According to DSC and wide‐angle X‐ray diffraction, the PLA crystallinity increased and the crystalline structure became more completed (α‐crystal form) in the presence of PEG. Viscoelastic parameters such as zero‐shear viscosity and relaxation time as an indication of elasticity were obtained. The results revealed enhanced polymer chain mobility and disentanglement ought to plasticizing effect of PEG. The critical content of PEG about 20–30 wt % at which the solid–liquid phase separation occurred was in good agreement with the viscoelastic properties. Hence, more than 20% PEG the elasticity diminished and the melt strength became zero. The interfacial tension of the PLA and PEG estimated through the rheological and morphological parameters evidenced the good miscibility of PLA/PEG system at the melt electrospinnig temperature. While the high viscose samples (η₀ > 1800 Pa/s) PLA and PLA/PEG (95/5) were not spinnable at the spinning temperature of 180 °C, blends containing 10–30% PEG were easily spun. The finest and continuous fiber mats were obtained by electrospinning of PLA/PEG (80/20) blend (d_f = 4.8 ± 0.8 μm). More than the critical concentration of PEG (Φ > 30%), lacking the elasticity suppressed the melt electro‐spinnability of PLA/PEG. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44120.     

Scanner colorimetric characterization for concentration estimation in single-component dyeing systems

Today, scanners are often promoted for color measurement applications. With a color scanner, it is possible, to some extent, to measure the color of objects if they are properly calibrated and characterized. The object of the present work is to study concentration estimation in single-component dyeing systems using a scanner. A new method is presented based on Cohen and Kappauf and single-constant Kubelka–Munk theories. The results showed a nonlinear transformation of the fundamental color stimulus that benefits from a good scalability could be applied for the aims of this study in specified illumination and viewing conditions with an adequate error range.     

A new image‐based unlevelness index

A new quantitative unlevelness index based on the Fourier transformation frequency component is introduced for evaluation of the degree of unlevelness of a set of dyed fabrics with different surface colour uniformities. A series of dyed denims with different degrees of unlevelness were prepared, and the degree of uneven appearance of fabrics was ranked by a group of observers. The surfaces of fabrics were imaged by a conventional scanner, and the Fourier transform was employed to compute the spectrum of desired images. It was found that the low‐frequency components of the computed matrix were stronger than the others, while its DC component, which related to the mean of the desired image, was too large. By this method, it was demonstrated that the fraction of the sum of the maximum of the second to sixth columns of the Fourier components of the captured image to the maximum of the first column component varied with the degree of unlevelness of the desired surfaces. The performance of the method was compared with five spectral and image based instrumental levelness–unlevelness indices, as well as those reported by visual ranking. Based on the results, the Fourier transformation method and the singular value decomposition technique show the best agreement with visual evaluation results, but the singular value decomposition method requires a longer computation time.