Relative Degree Of Crystallinity Research Articles

Supramolecular structure of highly oriented wet-spun polyacrylonitrile fibers used in the preparation of high-performance carbon fibers

Highly oriented polyacrylonitrile (PAN) fibers, which are used in the preparation of high-performance carbon fibers, were prepared via a wet spinning process. The supramolecular structure—i.e., the degree of crystallinity, crystal size, and crystallite orientation—of the PAN fibers was characterized by X-ray diffraction (XRD) using fiber and powder techniques. Two equatorial diffraction peaks with 2θ ∼ 17° and 29.5° were observed in the fiber XRD patterns, which confirmed that the crystalline structure of the PAN fibers was pseudohexagonal with only two-dimensional order in the transverse direction. The powder XRD patterns were resolved into three constituent Lorentz peaks to determine the relative degree of crystallinity. In order to increase the reproducibility of the value for the crystallinity of the fibers, the Gupta–Singhal method was modified by assuming that the degree of crystallinity could be determined from the area under peak 1 (with 2θ ∼ 17°), rather than the combined area of peaks 1 and 3. The evolution of the supramolecular structure of the PAN fibers during the spinning process was also investigated. Results indicated that drying and steam stretching play important roles in the formation and growth of the crystalline structure of the PAN fibers, while the orientation of the structure was only strongly related to the degree of stretching. The effects of the supramolecular structure on the thermal properties and mechanical properties of the PAN fibers were also studied. The perfection of the supramolecular structure influenced the feasibility of cyclization reactions within the PAN fibers and the thermal decomposition of those fibers. The mechanical properties of the PAN fibers were significantly enhanced by increasing the perfection of the supramolecular structure.

Influence of NaOH treatment on the mechanical properties of particleboard

Natural fibres are widely used in a variety of industries, especially for making composites. Research on the relationship between the characteristics of natural fibres and those of composites is very important in order to produce natural fibres and composites of high quality. The aim of this study is to examine the influence of the effect of a 1% NaOH treatment on the mechanical properties of particleboard made with industrial hemp shiv treated with the 1% NaOH solution at 100°C for 0, 30, 60 and 90 minutes. The results showed that, after the 1% NaOH treatment for 0–60 minutes, microfibril angle, relative degree of crystallinity and density of hemp shiv were reduced and the middle lamellae were broken, but the mechanical properties of the resulting particleboard were improved. Thus, to improve the mechanical properties of hemp shiv particleboard, the particles can be treated by the NaOH solution.

Systematic Analysis of Pericarp Starch Accumulation and Degradation during Wheat Caryopsis Development

Although wheat (Triticum aestivum L.) pericarp starch granule (PSG) has been well-studied, our knowledge of its features and mechanism of accumulation and degradation during pericarp growth is poor. In the present study, developing wheat caryopses were collected and starch granules were extracted from their pericarp to investigate the morphological and structural characteristics of PSGs using microscopy, X-ray diffraction and Fourier transform infrared spectroscopy techniques. Relative gene expression levels of ADP-glucose pyrophosphorylase (APGase), granule-bound starch synthase II (GBSS II), and α-amylase (AMY) were quantified by quantitative real-time polymerase chain reaction. PSGs presented as single or multiple starch granules and were synthesized both in the amyloplast and chloroplast in the pericarp. PSG degradation occurred in the mesocarp, beginning at 6 days after anthesis. Amylose contents in PSGs were lower and relative degrees of crystallinity were higher at later stages of development than at earlier stages. Short-range ordered structures in the external regions of PSGs showed no differences in the developing pericarp. When hydrolyzed by α-amylase, PSGs at various developmental stages showed high degrees of enzymolysis. Expression levels of AGPase, GBSS II, and AMY were closely related to starch synthesis and degradation. These results help elucidate the mechanisms of accumulation and degradation as well as the functions of PSG during wheat caryopsis development.

Cooling rate effects on the crystallization kinetics of polypropylene/date palm fiber composite materials

AbstractNon-isothermal crystallization kinetics of polypropylene/date palm fiber (PP/DPF) composite materials were investigated in this study, using the differential scanning calorimetry (DSC) method. Different fiber contents and cooling rates, varying from 2.5°C/min to 20°C/min, were considered. The obtained results indicated that the initial crystallization temperature increases with the increase of the DPF content. This was attributed to the nucleating ability of these fibers. Several theoretical models were used to predict the non-isothermal crystallization kinetics of the materials considered in this study. Basically, it was shown that both the Avrami analysis, modified by Jeziorny, and the method developed by Mo could adequately describe such kinetics. The activation energies required during the overall crystallization process and at different amounts of the relative degree of crystallinity were also evaluated using the Kissinger method and the isoconversional analysis of calorimetric data, respectively. It was shown that the presence of the DPFs in the PP matrix decreases these energies, confirming their nucleating ability during the non-isothermal crystallization process.

Influence of Gender on the Mechanical and Physical Properties of Hemp Shiv Fiber Cell Wall in Dioecious Hemp Plant

Hemp (Cannabis sativa L.) shiv has great potential for the production of bio-composites as a reinforcement material. To gain more information about hemp shiv, this research studied the influence of gender on the physical and mechanical properties of the fiber cell wall in the shiv of three dioecious hemp plant varieties by optical microscopy, image analysis software, WXRD, and nanoindentation. The results show that a hemp plant’s gender greatly influences the properties of hemp shiv. While long and thin in female hemp shiv, the fibers are shorter with a larger diameter in male hemp shiv. In addition, the cell walls in female shiv are thinner than those in male shiv. The microfibril angle (MFA), relative degree of crystallinity, elastic modulus, and hardness values of fiber cell walls as well as the lignin content in male hemp plants are higher than those in female hemp plants. Besides, the relationship between mechanical properties and MFA do not align with those observed in previous research, which shows that the gender of an individual plant has a greater effect on the mechanical properties of the fiber cell wall than does its MFA. Thus, when the fiber from this dioecious plant is investigated or used, the sex of the plant should be known and considered.

Comparison of Endosperm Starch Granule Development and Physicochemical Properties of Starches from Waxy and Non-Waxy Wheat

Starch granule development and physicochemical properties of starches in waxy wheat and non-waxy wheat were investigated in this article. Starch granules in waxy wheat endosperm showed an early developmental process. Compared with non-waxy wheat starch granules (round-shaped), waxy wheat starch granules (ellipse-shaped) were larger and contained more B-type granules. According to the granule size, starch granules were divided into two groups in waxy wheat, but were divided into three groups in non-waxy wheat. Compared with non-waxy wheat starch, waxy wheat starch had higher swelling power, gelatinization temperatures (To, Tp, Tc), and relative degree of crystallinity. They showed similar ordered structures on external regions of starch granules. Additionally, waxy wheat starch had a higher proportion of double-helical components and a lower proportion of single-helical components than non-waxy wheat starch. Based on the previous results, it was concluded: (1) waxy wheat and non-waxy wheat not only differed in starch granule development, but also in physicochemical properties of starches; (2) waxy wheat had more potential value for producing traditional products than non-waxy wheat.

Simultaneous morphological and rheological measurements on polypropylene: Effect of crystallinity on viscoelastic parameters

A rotational rheometer equipped with an optical module is adopted to characterize the evolution of rheological parameters and at the same time the morphology development during isothermal crystallization. This allowed the determination of the effect of crystallinity on the viscoelastic functions of an isotactic polypropylene. A linear multimode Maxwell model was then applied to obtain the modulus and relaxation time of each mode as a function of the measured crystallinity degree. It was found that at low crystallinity levels, the increase of moduli with crystallinity is about the same for all the modes whereas, when crystallinity degree rises, the increase of moduli is higher for the modes characterized by higher relaxation times. Concerning the relaxation times, it was found that the increase due to crystallinity is about the same for all the modes and reaches a factor of about 10 when relative crystallinity degree is close to 10%. The effect of crystallinity on complex viscosity was also assessed by determining a shift factor due to crystallinity. It was observed that the data collected at the lowest frequencies need higher shift factors with respect to the other ones. This was ascribed to the fact that more than one shift factor is needed to describe the effect on moduli, and low frequencies stir modes with higher relaxation times, which undergo a moduli increase larger than modes with shorter relaxation times.

Specific surface, crystallinity, and dissolution of lyophilized fibrinogen. A study by combined small- and wide-angle X-ray scattering (SWAXS)

The nano-structural properties of six different batches of lyophilized fibrinogen at various contents of residual humidity (6–20%) were studied by small- and wide-angle X-ray scattering (SWAXS) and related to the dissolution properties. As structural parameters, the specific surface and relative degree of crystallinity, from SAXS and WAXS, respectively, were used, and correlated to the dissolution rates. BET surface area and electron microscopy were used as ancillary methods. The results show a complex, biphasic behavior: above 9% water content the crystallinity increased, and the specific surface decreased with increasing water contents; at the lowest water contents (6%), however, where the WAXS patterns showed amorphous structure of the fibrinogens, the specific surface and dissolution rates diverged over a wide range of values. Systematic correlations could be established between specific surface and dissolution rates for the water contents below 13%: the dissolution rates were found to decrease with increasing specific surface, most notably in the amorphous form, in contrast to expectations from classical thermodynamics. Protein conformational changes and hydrophobic surface formation upon depletion of water could be possible causes. This is supported by the protective effect of the high-HLB surfactant PS-80, which was found to enlarge the specific surface.

Nonisothermal Crystallization and Melting Behavior of EVA/OMWNTs Nanocomposites

EVA/OMWNTs nanocomposites have been successfully prepared by a simple melt compounding method. The nonisothermal crystallization behaviors of the EVA/OMWNTs nanocomposites are strongly dependent on the degree of crystallinity (Xc), peak crystallization temperature (Tp), half-time of crystallization (t1/2), and Avrami exponent (n) on the OMWNTs content and cooling rate. The dependence of the crystallization activity energy on the extent of relative crystallization for the plain EVA and the EVA/OMWNTs nanocomposites shows that ΔE increases with the increase in the relative degree of crystallinity below about 5%, and the ΔE decreased when the relative degree of crystallinity was greater than about 5%.

Heterogeneous catalytic synthesis of poly(butylene succinate) by attapulgite‐supported Sn catalyst

ABSTRACTAn attapulgite‐supported Sn catalyst (Sn‐palgorskite) was successfully prepared by ion‐exchange co‐impregnation method. The catalytic effect of Sn‐attapulgite on the melt polycondensation reaction of poly(butylene succinate) (PBS) was examined by comparing with that of anhydrous SnCl2 and a blank experiment. The structures and properties of the PBS products synthesized with the three catalytic systems were characterized by means of Fourier transform‐infrared spectra (FT‐IR), viscosity measurements, wide angle X‐ray diffraction (WARD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Meanwhile, the acidolysis degradation behaviors of the PBS samples were also studied. It was found that the intrinsic viscosities and the number‐average molecular weights of the PBS were remarkably increased under the catalysis of Sn‐attapulgite, further leading to an increase in the decomposition temperature, the crystallization temperature, and the viscous flow activation energy, while a decrease in the melting temperature, the relative degree of crystallinity, and the rate of degradation. Additionally, no significant differences were observed in the crystal structures of all the samples, regardless of the reaction system with or without catalyst. The experiment results confirmed that Sn‐attapulgite was an effective heterogeneous catalyst for the synthesis of PBS, and the recycled Sn‐attapulgite still exhibited higher activity than anhydrous SnCl2 under identical reaction conditions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41729.

Crystallization Kinetics and Mechanism of CaO–Al2O3-Based Mold Flux for Casting High-Aluminum TRIP Steels

Non-isothermal crystallization of the newly developed lime-alumina-based mold fluxes was investigated using differential scanning calorimetry. The crystallization kinetic parameters were determined by Ozawa equation, the combined Avrami–Ozawa equation, and the differential iso-conversional method of Friedman. It was found that Ozawa method failed to describe the non-isothermal crystallization behavior of the mold fluxes. The Avrami exponent determined by the combined Avrami–Ozawa equation indicates that the crystallization of cuspidine occurs through bulk nucleation and reaction-controlled three-dimensional growth, and then transforms to reaction-controlled two-dimensional growth at the crystallization later stage in lime-alumina-based mold fluxes with higher B2O3 content. For the mold fluxes with lower B2O3 content (10.8 mass pct), the crystallization of cuspidine is bulk nucleation and reaction-controlled two-dimensional growth at the crystallization primary stage followed by a diffusion-controlled two-dimensional growth process. The crystallization of CaF2 in mold flux originates from bulk nucleation and diffusion-controlled three-dimensional growth, which then transforms to two-dimensional growth. FE-SEM observations support these kinetic analysis results. The effective activation energy for cuspidine crystallization in the mold flux with higher B2O3 and Na2O contents increases as the crystallization progresses, and then decreases at the relative degree of crystallinity greater than 60 pct. The transition point of this trend approximately corresponds to the relative degree of crystallinity at which the crystallization mode of cuspidine transforms. For the mold fluxes with lower B2O3 and Na2O contents, the effective activation energy for cuspidine formation varies monotonically with the increase in the relative degree of crystallinity.

Effect of photofunctional organo anion-intercalated layered double hydroxide nanoparticles on poly(ethylene terephthalate) nonisothermal crystallization kinetics

Very recently, we report a facile preparation and strong UV-shielding function of poly(ethylene terephthalate) (PET) nanocomposites using 4,4′-diaminostilbene-2,2′-disulfonic acid anion-intercalated layered double hydroxide (LDH_DDA). Herein, the effect of the photofunctional organo anion-intercalated LDH nanoparticles on nonisothermal crystallization kinetics of PET is reported by differential scanning calorimetry technique. First, the nonisothermal crystallization behaviour is discussed by several basic parameters including crystallization peak temperature, relative degree of crystallinity with temperature or time, and half-time of crystallization. Then, Avrami and Jeziorny method, as well as Mo model were applied for the PET/LDH_DDA nanocomposites. Finally, the crystallization activation energy was investigated by Kissinger method and Flynn conversion. The results reveal that the incorporation of LDH_DDA nanoparticles acted as nucleating agent and significantly accelerated the PET nonisothermal crystallization process, whereas had little effect on the three-dimensional growth pattern of spherulites.

Structural and physicochemical characteristics of starch from sugar cane and sweet sorghum stalks

The starch present in sugar cane and sorghum juice has been considered a problem to the sugar industry. The objective of this work was to study the structural and physicochemical characteristics of the starch present in sugar cane and sweet sorghum. Sugar cane and sweet sorghum starches presented small granules (maximum 5.9 and 7.9μm), A-type diffraction pattern, high degree of relative crystallinity (44.4 and 42.0%), and low amylose content (17.5 and 16.4%), respectively. Sugar cane starch presented more uniformity in granule shape and size, more homogeneity in amylose chain length, higher number of long lateral chains of amylopectin, and higher susceptibility to enzymatic digestion. Besides being in higher amount in the juice, sweet sorghum starch presented lower values for thermal properties of gelatinization, as well as higher swelling factor, which can cause more problems during processing. Additional studies are needed to evaluate the variety and maturity influence on these properties.

Influence of some sugars on the thermal, rheological and morphological properties of “pinhão” starch

When starch is incorporated into puddings, desserts, and other foods containing sugar as the main ingredient, it will have an effect on the gelatinisation temperature and pasting properties. Many studies have been undertaken to investigate the effect of several sugars in foods and starches, as well as their physicochemical and functional properties. These studies have verified the significant influence on these properties, which are dependent on the nature of sugar and of starch. In this study, pinhao starch was extracted in the laboratory and was added, stirring for 60 min, to solutions at 1 % of each of the following sugars: fructose, glucose, sucrose, and 0.5 % fructose and 0.5 % glucose. After this time, the slurry was filtered, washed, dried at 40 °C and kept in a desiccator over anhydrous calcium chloride until constant mass. The effects of each sugar on the surface of the pinhao starch granules were observed using the non-contact method of atomic force microscopy, whereby it was possible to verify a decrease in the average diameter and an increase in the average roughness. X-ray diffractometry made it possible to evaluate the degree of relative crystallinity, which was proportional to the roughness and inversely proportional to the gelatinisation enthalpy (ΔH), which was studied by differential scanning calorimetry.

Parameters characterizing the kinetics of the non-isothermal crystallization of polyamide 5,6 determined by differential scanning calorimetry

Abstract The non-isothermal crystallization behavior of polyamide 5,6 (PA56) was investigated by differential scanning calorimeter (DSC), and the non-isothermal crystallization kinetics were analyzed using the modified Avrami equation, the Ozawa model, and the method combining the Avrami and Ozawa equations. It was found that the Avrami method modified by Jeziorny could only describe the primary stage of non-isothermal crystallization kinetics of PA56, the Ozawa model failed to describe the non-isothermal crystallization of PA56, while the combined approach could successfully describe the non-isothermal crystallization process much more effectively. Kinetic parameters, such as the Avrami exponent, kinetic crystallization rate constant, relative degree of crystallinity, the crystallization enthalpy, and activation energy, were also determined for PA56.

Physical and Mechanical Characterization of Fiber Cell Wall in Castor (Ricinus communis L.) Stalk

Castor (Ricinus communis L.) stalk is a byproduct of the production of castor oil. As a natural material, castor stalk has great potential in the production of bio-composites as reinforcement materials. To provide more information about the castor stalk for using it better, the structure, microfibril angle (MFA), relative degree of crystallinity (%), and mechanical properties of castor fiber cell walls were investigated using X-ray diffraction (XRD) and nanoindentation. The influence of chemical composition and MFA on the mechanical properties of fiber cell wall was studied as well. The cortex of castor stalks primarily contains long fibers, while the xylem of castor stalk, an excellent wood-type material, comprises most of the castor stalk (83.95% by weight); the pith of the stalk is composed of parenchyma cells. The average elastic modulus of fiber cell wall in lower, upper, and branch parts are 16.0 GPa, 18.6 GPa, and 13.2 GPa, respectively. The average hardness of fiber cell wall in lower, upper, and branch parts are 0.50 GPa, 0.54 GPa, and 0.43 GPa, respectively. As lignin content increases from 15.57% to 17.41% and MFA decreases from 21.3˚ to 15.4˚, the elastic modulus increases from 13.2 GPa to 18.6 GPa and the hardness increases from 0.43 GPa to 0.54 GPa. The mechanical properties, including the elastic modulus and the hardness of the fiber cell wall in the upper region of the castor stalk, are higher than those in the lower region, while the mechanical properties of the fiber cell wall in the branches are lower than those in either the upper or lower regions.

Effect of alkane chain segment length on the crystallization kinetics of nylon 1010, 1013 and 1014

AbstractIsothermal and non‐isothermal crystallization kinetics of long alkane chain segment nylon 1010, 1013 and 1014 were investigated by differential scanning calorimetry. The commonly used Avrami equation and that modified by Jeziorny were employed to fit the isothermal and non‐isothermal crystallizations of nylon 1010, 1013 and 1014, respectively. It was found that the crystallization rate of nylon with a longer alkane chain segment was slower than that of nylon with a shorter one at a given cooling rate. The activation energies for the isothermal and non‐isothermal crystallizations determined by the Arrhenius and the Kissinger methods, respectively, decreased with increase of the alkane chain segment length of nylon 1010, 1013 and 1014. Furthermore, the activation energy of the non‐isothermal crystallization process of these nylons, determined by the isoconversional methods of Flynn and Wall and Ozawa, was found to be a decreasing function of the relative degree of crystallinity. © 2014 Society of Chemical Industry

Measuring Order in Regioregular Poly(3-hexylthiophene) with Solid-State 13C CPMAS NMR.

We report on measurements of order in semicrystalline, high molar mass poly(3-hexylthiophene) (P3HT) by solid-state 13C cross-polarization magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) measurements. The relative degree of crystallinity was estimated for two films with different drying conditions via X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Order determined by 13C NMR does not necessarily correlate with crystallinity, indicating that local order can occur in noncrystalline regions. Slow main chain dynamics influence the 13C NMR peak widths at lower temperatures (<0 °C), with side chain motions influencing the main chain motions. At higher temperatures (>0 °C), where narrower thiophene resonances are observed, these main chain conformation rearrangements occur on fast time scales (≪3 ms). This room-temperature dynamic disorder suggests that P3HT may be classified as a conformationally disordered (CONDIS) crystal.

Kinetic Study on the Isothermal and Nonisothermal Crystallization of Monoglyceride Organogels

The isothermal and nonisothermal crystallization kinetics of monoglyceride (MAG) organogels were studied by pulsed nuclear magnetic resonance (pNMR) and differential scanning calorimetry (DSC), respectively. The Avrami equation was used to describe the isothermal crystallization kinetics and experimental data fitted the equation fairly well. Results showed that the crystal growth of MAG organogels was a rod-like growth of instantaneous nuclei at higher degrees of supercooling and a plate-like form with high nucleation rate at lower degrees of supercooling. The exothermic peak in nonisothermal DSC curves for the MAG organogels became wider and shifted to lower temperature when the cooling rate increased, and nonisothermal crystallization was analyzed by Mo equation. Results indicated that at the same crystallization time, to get a higher degree of relative crystallinity, a higher cooling rate was necessary. The activation energy of nonisothermal crystallization was calculated as 739.59 kJ/mol according to the Kissinger method. Therefore, as the results of the isothermal and nonisothermal crystallization kinetics for the MAG organogels obtained, the crystallization rate, crystal nucleation, and growth during the crystallization process could be preliminarily monitored through temperature and cooling rate regulation, which laid the foundation for the real industrial manufacture and application of the MAG organogels.

Branch chain elongation by amylosucrase: Production of waxy corn starch with a slow digestion property

Starches with high slowly digestible starch (SDS) contents were prepared by treating completely gelatinized waxy corn starch with amylosucrase. The structural properties of the prepared starches were then investigated. The content of SDS increased by up to 38.7% after amylosucrase modification, and the portion of chains with degree of polymerisation (DP) 25–36 increased, while the portion of chains with DP⩽12 decreased. Amylosucrase-modified starches showed a weak B-type crystalline structure. A slight increase in the degree of relative crystallinity was observed with increased reaction time. The thermal properties, including melting temperature and enthalpy, of the amylosucrase-modified starches were higher than for the control starch. Although the amylosucrase-modified starches showed varying structural properties according to reaction time (1–45h), their digestibilities did not change much after 6h. By controlling the reaction time of the amylosucrase treatment, a tailored starchy food containing the desired amount of SDS can be produced.