Wide-angle X-ray Diffraction Curves Research Articles

Polymorphic structure in ultrasonic microinjection-molded poly(butylene-2,6-naphthalate)

The formation and distribution of different crystal forms in ultrasonic microinjection-molded poly(butylene 2,6-naphthalate) (PBN) samples prepared using different mold temperatures were investigated by microfocus wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and polarized-light optical microscopy (POM). The relative fractions of liquid-crystalline (LC) mesophase, α-phase and β′-phase along the thickness direction of microinjection-molded samples were obtained via a decomposition of the WAXD curves. The results indicate that the mold temperature affects the formation of the LC mesophase and α-crystals, but not the formation of β′-crystals. Moreover, the LC mesophase and α-phase were detected in both skin and core regions of the microinjection-molded PBN samples, while the β′-crystals were only observed in the skin layer. In the heating process, the crystals in the core region and skin layer began to melt at temperatures of about 240 and 250 °C, respectively, which is consistent with the different thermal stabilities of the α- and β′-phases. It is inferred that the β′-phase is able to form under a certain high shear flow, implying that the polymorphic structure of injection-molded parts of PBN can be tailored by variation of the molding conditions. • PBN tensile bars were prepared using an ultrasonic microinjection-molding machine. • The LC mesophase and α-phase were detected in both skin and core regions. • The β′-crystals were only observed in the skin layer. • Formation of β′-phase is influenced more by the shear flow than by the cooling rate. • Polymorphic structure of PBN can be tailored by variation of the molding conditions.

The role of an objective function in the mathematical modelling of wide-angle X-ray diffraction curves of semi-crystalline polymers.

To decompose a wide-angle X-ray diffraction (WAXD) curve of a semi-crystalline polymer into crystalline peaks and amorphous halos, a theoretical best-fitted curve, i.e. a mathematical model, is constructed. In fitting the theoretical curve to the experimental one, various functions can be used to quantify and minimize the deviations between the curves. The analyses and calculations performed in this work have proved that the quality of the model, its parameters and consequently the information on the structure of the investigated polymer are considerably dependent on the shape of an objective function. It is shown that the best models are obtained employing the least-squares method in which the sum of squared absolute errors is minimized. On the other hand, the methods in which the objective functions are based on the relative errors do not give a good fit and should not be used. The comparison and evaluation were performed using WAXD curves of seven polymers: isotactic polypropylene, polyvinylidene fluoride, cellulose I, cellulose II, polyethylene, polyethylene terephthalate and polyamide 6. The methods were compared and evaluated using statistical tests and measures of the quality of fitting.

Application of the particle swarm optimization method for the analysis of wide-angle X-ray diffraction curves of semicrystalline polymers

The analysis of wide-angle X-ray diffraction curves of semicrystalline polymers is connected with a thorough decomposition of these curves into crystalline peaks and amorphous components. A reliable and unambiguous decomposition is the most important step in calculation of the crystallinity of polymers. This work presents a new algorithm dedicated to this aim, which is based on the particle swarm optimization (PSO) method. The PSO method is one of the most effective optimization techniques that employs a random choice as a tool for going through the solution space and searching for the global solution. The action of the PSO algorithm imitates the behaviour of a bird flock or a fish school. In the system elaborated in this work the original PSO algorithm has been equipped with several heuristics. The role of heuristics is performed by procedures which orient the search of the solution space using additional information. In this paper it is shown that this algorithm is faster to converge and more efficiently performs a multi-criterial optimization compared with other algorithms used for this purpose to date.

Effects of Fabric Structures on the Mechanical and Structural Properties of Poly(ϵ-Caprolactone)/Silk Fabric Biocomposites

To develop novel biocomposites, three different types of silk fibroin (SF) fabrics were, respectively, blended with poly(ϵ-caprolactone) (PCL) by a solution blending method. The effects of fabric structures on the mechanical and structural properties of PCL/SF biocomposites were investigated. Scanning electron microscopy photographs showed that SF were linked with PCL matrix. Wide-angle X-ray diffraction curves showed that PCL/SF biocomposites had higher crystallinity than pure PCL. Differential scanning calorimetry results indicated that the addition of three different types of silk fabrics changed the values of relevant thermodynamic parameter of PCL/SF biocomposites.

A hybrid immune–evolutionary strategy algorithm for the analysis of the wide-angle X-ray diffraction curves of semicrystalline polymers

Decomposition of wide-angle X-ray diffraction curves into crystalline peaks and amorphous components is one of the most difficult nonlinear optimization problems. For this reason, the elaboration of a reliable method that provides fast unambiguous solutions remains an important and topical task. This work presents a hybrid system dedicated to this aim, combining two methods of artificial intelligence – evolution strategies and an immune algorithm – with the classical method of Rosenbrock. A combination of the mechanisms of these three methods has given a very effective and convergent algorithm that performs very well a multicriterial optimization. Tests have shown that it is faster to converge and less ambiguous than the genetic algorithm.

Effects of ultrasonic wave pretreatment on the fibrillation of cellulose fiber

Pinus massoniana Lamb. was used as the raw cellulose fiber material to investigate effects of ultrasonic wave pretreatment and PFI pretreatment on fiber bonding and absorbability. Influences of ultrasonic wave pretreatment on fiber crystalline structure and hydrogen bonds were also analyzed by wide-angle X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy. The absorption and internal bond strength of fiber pretreated by ultrasonic waves increased by 23.49% and 4.07%, respectively, in comparison with those of virgin fiber, which would result in the improvement of weak bonding and absorbability. Instead, when fiber was pretreated by PFI, absorption decreased in comparison with virgin fiber and internal bond strength increased as much as 1.33 times than that of virgin fiber. The analysis of wide-angle X-ray diffraction curves and FTIR spectroscopy curves revealed that the crystallinity of fiber decreased by 20.59% in comparison with that of virgin fiber when treated by ultrasonic waves. Moreover, the effect of ultrasonic wave pretreatment on intramolecular hydrogen bonds was rather stronger than that of intermolecular hydrogen bonds. Therefore, the optimal swelling ability of fiber would be obtained.

Toward environment‐friendly composites of poly(ε‐caprolactone) reinforced with stereocomplex‐type poly(l‐lactide)/poly(d‐lactide)

AbstractIn this work, stereocomplex‐poly(l‐ and d‐lactide) (sc‐PLA) was incorporated into poly(ε‐caprolactone) (PCL) to fabricate a novel biodegradable polymer composite. PCL/sc‐PLA composites were prepared by solution casting at sc‐PLA loadings of 5–30 wt %. Differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD) demonstrated the formation of the stereocomplex in the blends. DSC and WAXD curves also indicated that the addition of sc‐PLA did not alter the crystal structure of PCL. Rheology and mechanical properties of neat PCL and the PCL/sc‐PLA composites were investigated in detail. Rheological measurements indicated that the composites exhibited evident solid‐like response in the low frequency region as the sc‐PLA loadings reached up to 20 wt %. Moreover, the long‐range motion of PCL chains was highly restrained. Dynamic mechanical analysis showed that the storage modulus (E′) of PCL in the composites was improved and the glass transition temperature values were hardly changed after the addition of sc‐PLA. Tensile tests showed that the Young's modulus, and yield strength of the composites were enhanced by the addition of sc‐PLA while the tensile strength and elongation at break were reduced. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40208.

Application of immune and genetic algorithms to the identification of a polymer based on its X-ray diffraction curve

This paper describes how a combination of two methods of artificial intelligence, an immune algorithm and a genetic algorithm, can be used to recognize a polymer by the shape of its X-ray diffraction curve. To this end, the hybrid algorithm uses a database which contains theoretical functions describing wide-angle X-ray diffraction curves of different polymers. These curves are compared by the algorithm with the experimental diffraction curve and the most similar are chosen. Such theoretical curves are kept in the immunological memory, and their parameters can be set as the starting ones in the optimization methods used for decomposition of the experimental curve into crystalline peaks and amorphous component. Using this algorithm, the preparation of the starting parameters is much easier and faster. Decomposition is the most important step in polymer crystallinity determination.

CRYSTALLIZATION BEHAVIOR OF CHAIN-DISENTANGLED POLY(ETHYLENE TEREPHTHALATE)

The chain-disentangled poly ( ethylene terephthalate) ( PET) samples were prepared by freeze-extracting PET solutions (with concentrations ranged from 0. 1 ～ 10 g /dL,in three types of solvent) and were characterized by Fourier transform infrared spectroscopy ( FTIR),wide-angle X-ray diffraction ( WAXD) and differential scanning calorimetry (DSC). WAXD curves showed that,compared with the chain interpenetrated and entangled PET sample quenched from the melt,chain-disentangled PET samples crystallized more easily. By FTIR spectra,it was found that the level of chain disentanglement and crystallinity increased with decreasing solution concentration. But at high dilution,distances between chains became too great to crystallize during the extracting process. For a solution concentration near the overlap concentration c* ,it's advantageous not only to chain disentanglement,but also to the formation of ordered structure and crystallization. Moreover crystallization behavior of PET was affected by solvent used to prepare samples due to the influences of solvent power on the interactions between coils and then the level of chain disentanglement of these samples. When the concentrations of the solutions are lower than the overlap concentration c* ,the PET samples prepared from the good solvent have more orderly structure due to much fewer interchain entanglements. While the concentrations of the solutions are higher than c* ,samples prepared from the bad solvents have more orderly structure. Furthermore,The DSC and WAXD analysis results indicated the samples prepared by freeze-extracting PET solutions were partially crystallized. It's not full disorder in amorphous regions and was a metastable state between order and diorder. After the same annealling,chain-disentangled PET samples were prone to form ordered structure and had a higher crystallinity compared with the chain-entangled PET samples.

Preferential formation of electroactive crystalline phases in poly(vinylidene fluoride)/organically modified silicate nanocomposites

AbstractThe role of organically modified silicate (OMS), Lucentite STN on the formation of β‐crystalline phase of poly(vinylidene fluoride) (PVDF) is investigated in the present study. The OMS was solution blended with PVDF and cast on glass slide to form PVDF‐OMS nanocomposites. Solution cast samples were subjected to various thermal treatments including annealing (AC‐AN), melt‐quenching followed by annealing (MQ‐AN), and melt‐slow cooling (MSC). Fourier‐transform infrared spectroscopy (FT‐IR), wide angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC) were used to investigate the crystalline structure of thermally treated samples. As a special effort, the combination of in situ thermal FT‐IR, WAXD, and DSC studies was utilized to clearly assess the thermal properties. FT‐IR and WAXD results of MQ‐AN samples revealed the presence of β‐phase of PVDF. Ion‐dipole interaction between the exfoliated clay nanolayers and PVDF was considered as a main factor for the formation of β‐phase. Melt‐crystallization temperature and subsequent melting point were enhanced by the addition of OMS. Solid β‐ to γ‐crystal phase transition was observed from in situ FT‐IR and WAXD curves when the representative MQ‐AN sample was subjected to thermal scanning. Upon heating, β‐phase was found to disappear through transformation to the thermodynamically stable γ‐phase rather than melting directly. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2173–2187, 2008

Blends of thermoplastic polyurethane and polypropylene. I. Mechanical and phase behavior

AbstractPure thermoplastic polyurethane (TPU), polypropylene (PP), and TPU/PP blends with different weight ratios prepared in a twin‐screw extruder were investigated by dynamic mechanical analysis (DMA), the universal tester for mechanical investigation, and by wide‐angle X‐ray diffraction (WAXD). The addition of PP above 20 wt % to the TPU stepwise changed the ductility and Young's modulus, i.e., apparently a kind of ductile → brittle transition occurred between TPU/PP 80/20 and TPU/PP 60/40 blends. This fact and the result of analysis of WAXD curves indicated matrix → dispersed phase inversion in this concentration region. TPU melt enabled easier migration of the PP chains and prolonged crystallization of PP matrix during solidification process affecting thus crystallite size, orientation, and crystallinity. In accordance to this fact, DMA results indicated partial miscibility of PP with polyurethane in the TPU/PP blends due to the lack of interfacial interaction and adhesion between the nonpolar crystalline PP and polar TPU phases. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104, 3980–3985, 2007

A quantitative analysis of small- and wide-angle X-ray diffraction curves of homogeneous ethylene-1-octene copolymers

This paper presents a comparison of the results obtained with two methods employed in the analysis of small-angle X-ray scattering (SAXS) curves of isothermally crystallized homogeneous ethylene-1-octene copolymers: a method based on the calculation of the one-dimensional correlation function and a method based on model calculations and curve fitting. Data obtained from time-resolved SAXS investigations are supported by the results of simultaneous wide-angle X-ray diffraction (WAXD) measurements of crystallinity development during isothermal crystallization.

Poly(caprolactone triol) as plasticizer agent for cellulose acetate films: influence of the preparation procedure and plasticizer content on the physico‐chemical properties

AbstractThe influence of the plasticizer content and film preparation procedure on the morphology, density, thermal and mechanical properties of cellulose acetate (CA) films plasticized with poly‐(caprolactone triol) (PCL‐T), were studied. Differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), scanning electron microscopy (SEM), wide‐angle X‐ray diffraction (WAXD) and infrared spectroscopy (FT‐IR) techniques were used. The films were prepared by dry‐casting CA and CA/PCL‐T in acetone or acetone/water solutions, which produced transparent and opaque films, respectively. In contrast to the transparent films, which were dense, the opaque films presented a porous morphology. However, the presence of PCL‐T reduced the opaque film porosity, increasing, in consequence, its bulk density. The TMA results revealed that PCL‐T reduced the glass transition temperature more significantly in the transparent than in opaque films. Only the transparent CA/PCL‐T films presented a melting temperature, that reduced with higher concentrations of PCL‐T, suggesting a higher ordering (crystallinity) when the films were prepared in the absence of water, as observed from WAXD curves. The mechanical properties also showed that the transparent films were more soft and tough than the opaque films. In summary, PCL‐T was a good plasticizer agent for CA films due to the presence of hydrogen bonds between the components (FT‐IR spectra). The presence of water in the dry casting process has a significant effect mainly on film morphology and mechanical properties. Copyright © 2004 John Wiley & Sons, Ltd.

Effect of glycerin on structure transition of PVA/SF blends

AbstractBlend films of silk fibrion (SF) and poly(vinyl alcohol) (PVA), with glycerin as an additive, were made, and the structure and properties of the blends were investigated by scanning electron microscopy (SEM), Fourier transform infrared (FT‐IR) spectroscopy, differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction (WAXD) and with an Instron Material Tester. The results showed that SF and PVA are principally incompatible and the blends made by the two polymers were phase‐separated. The results, however, also demonstrated that the blend structure could be changed to some extent by addition of 3–8% glycerin. The boundary of the PVA and SF phases became indistinct, as reported by SEM, a new peak appeared in the WAXD curves, the width of the OH absorption peak in the FT‐IR spectra increased, and the melting points changed in the DSC curves. In particular, the mechanical properties obviously increased, from 350 kg/cm2 and 10% of PVA/SF (80/20) film to 832 kg/cm2 and 39% of PVA/SF (80/20) film because of the increase in glycerin. It was suggested that glycerin plays a role in building the relationship between PVA and SF, strengthening the interaction between them and improving their compatibility. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2342–2347, 2002

On the analysis of wide-angle X-ray diffraction curves of poly(vinyl chloride) samples

The calculation of crystallinity values based on wide-angle X-ray diffraction (WAXD) curves of poly(vinyl chloride) (PVC) is subject to three conditions, which are not always explicitly stated. First, the sample should have no orientation or else an averaging factor must be applied to the intensity data. Secondly, on subtracting the non-crystalline component from the WAXD profile the resulting crystalline curve must conform to some identifiable unit cell. Thirdly, the potential presence of a mesomorphous phase implies that there may be no unique non-crystalline profile applicable to all PVC WAXD curves. This last condition is highlighted through the use of a Fourier-transform filtering function, which can be applied to separate the amorphous contribution from the overall WAXD profile. While this technique has been found to be applicable to a wide variety of semicrystalline polymer WAXD profiles, it consistently fails in the case of commercial PVC WAXD curves. The presence of a variable mesomorphous phase can alter the expected intensity relation between the 200 and 110 reflections, thus interfering in any straightforward crystallinity calculation based on WAXD profiles.