Different Degrees Of Crystallinity Research Articles

Crystallization measurements via ultrasonic velocity: Study of poly(lactic acid) parts

ABSTRACTCrystallization has significant effects on the physical and mechanical properties of polymer products; therefore, crystallization measurements are important for understanding and predicting polymer products' properties. However, traditional crystallization measurement methods have disadvantages in practical applications because they can be destructive, offline, unsafe, and expensive. Recently, ultrasonic technology has shown great potential as a nondestructive, online, real‐time, and environmentally friendly measurement method for polymer characterization. In this study, a novel measurement method based on ultrasonic technology was proposed to study the crystallization characteristics of poly(lactic acid) (PLA) parts. An annealing process was employed to produce PLA parts with different degrees of crystallinity. A new ultrasonic water immersion method was used to measure the ultrasonic velocities of these annealed PLA parts. It has been found that the plot of the inverse ultrasonic velocity versus the degree of crystallinity shows good linearity over the whole crystallinity range for all three annealing temperatures. The linear relationship between the inverse of the ultrasonic velocity and the crystallinity observed in this study could provide a nondestructive method for investigating the degree of crystallinity of polymers, which can be implemented both offline and online. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 700–708

Characterization and modelling of in-situ La-based bulk metallic glass composites under static and dynamic loading

Samples of La-based bulk metallic glass composites (BMGC) were tested under both static and dynamic compression, and their deformation mechanism analysed. The strain rates imposed ranged from 6 × 10−5/s to 1.6 × 103/s. Quasi-static compression was performed using an Instron universal testing machine, while dynamic compression was applied by means of a Split-Hopkinson Pressure Bar (SHPB), which was used to study the rate sensitivity of this type of material. La-based BMGC samples with different degrees of crystallinity were also fabricated to examine the influence of crystalline volume fraction on the composite. A high speed infrared (IR) camera was employed to measure the temperature increase during deformation. This study focused on: (1) characterization of the deformation mechanism and strain rate sensitivity of BMGC; (2) the influence of crystalline volume fraction on BMGC material and (3) establishment of a large-deformation rate-independent thermomechanical constitutive model, suitable for incorporation a finite element analysis (FEA) code.

Oxidation process of dissolvable sulfide by synthesized todorokite in aqueous systems

Todorokite, formed from Mn(II) in supergene environments, can affect the transformation and migration of dissolvable sulfides in soils and water. In this work, todorokite was synthesized with different degrees of crystallinity, and the redox mechanism of dissolvable sulfide and todorokite was studied in both closed and open aqueous systems. The influences of pH, temperature, crystallinity, the amount of manganese oxides, and oxygen gas on S2− oxidation process were investigated. It is found that S2− was oxidized to S0, SO32−, S2O32− and SO42−, and about 90% of S2− was converted into S0 in closed systems. The participation of oxygen facilitated the further oxidation of S0 to S2O32−. S0 and S2O32− were formed with the conversion rates of S2− about 45.3% and 38.4% after 1h of reaction, respectively, and the conversion rate for S2O32− increased as reaction prolonged for a longer period. In addition, todorokite was reduced to Mn(OH)2 in the presence of nitrogen gas, and its chemical stability increased when oxygen gas was admitted into the reaction system during the process. The oxidation rate of dissolvable sulfide followed a pseudo-first-order kinetic law in the initial stage (within 10min), and the initial oxidation rate constant of S2− increased with elevating temperature, increasing the quantity and decreasing crystallinity of todorokite. The initial oxidation rate of dissolvable sulfide decreased with continuous feeding of O2 into the test solution, possibly due to a decrease in active Mn(III) content in todorokite. The present work demonstrates the redox behaviors and kinetics of dissolvable sulfide and todorokite in aquatic environments.

Biodegradation of starch films: The roles of molecular and crystalline structure

The influences of molecular, crystalline and granular structures on the biodegradability of compression-molded starch films were investigated. Fungal α-amylase was used as model degradation agent. The substrates comprised varied starch structures obtained by different degrees of acid hydrolysis, different granular sizes using size fractionation, and different degrees of crystallinity by aging for different times (up to 14 days). Two stages are identified for unretrograded films by fitting degradation data using first-order kinetics. Starch films containing larger molecules were degraded faster, but the rate coefficient was independent of the granule size. Retrograded films were degraded much slower than unretrograded ones, with a similar rate coefficient to that in the second stage of unretrograded films. Although initially the smaller molecules or the easily accessible starch chains on the amorphous film surface were degraded faster, the more ordered structure (resistant starch) formed from retrogradation, either before or during enzymatic degradation, strongly inhibits film biodegradation.

Study of the Thermal and Structural Properties of PVA/HPC Blends Due to Fast Neutrons Irradiation

Blends of PVA/HPC are prepared using solution casting method and are irradiated with fast neutron irradiation of fluence 1.15 x 107 n/cm2 to use as biomaterials according to their broad importance in practical and medical applications. Thermal properties and structural configuration of the blends are studied to characterize and reveal the miscibility map of such blend system. The obtained results of the thermal analyses [differential scanning calorimetry, DSC, and thermal gravimetric analysis, TGA] show variations in the first order thermodynamic transition (Tth), the melting temperature, shape and area of thermal peaks which are attributed to the different degrees of crystallinity and the existence of interactions between PVA and HPC molecules. The X-ray diffraction patterns (XRD) show broadening and sharpening of peaks at different HPC concentrations with PVA and irradiation with fast neutrons. The results obtained indicate changes in the crystallinity/amorphosity ratio, and explains the possibility of miscibility existence between the amorphous components of the two polymers PVA and HPC.

Effect of MWNTs concentration and cooling rate on the morphological, structural, and electrical properties of non‐isothermally crystallized PEN/MWNT nanocomposites

ABSTRACTThe effect of multiwall carbon nanotubes (MWNT) concentration and cooling rate on the morphological, structural and electrical properties of non‐isothermally crystallized Poly(ethylene naphthalate) nanocomposites (PEN/MWNT) was studied. PEN/MWNT nanocomposites containing 1 and 2 wt % of nanotubes were prepared by melt blending in a mini twin screw extruder. Nanocomposite samples with different degree of crystallinity (Xc) were obtained via non‐isothermally crystallization at cooling rates of 2, 10, 20, and 300°C min−1. In this study it was demonstrated that carbon nanotubes and cooling rate strongly influence morphological and structural characteristics of PEN. Calorimetric results showed that the peak crystallization temperature (Tc) of PEN nanocomposites was increased ∼9° through heterogeneous nucleation with respect to pure PEN. X‐ray diffraction revealed that carbon nanotubes modify the crystalline structure of PEN favoring the formation of β‐crystals, and this effect increases with the nanotubes content. On the basis of X‐ray scattering analysis, the variation of lamellar thickness revealed that nanotubes promote the formation of lamellar crystals with average thickness of 20 nm at different cooling rates. These structural and morphological changes play an important role on the electrical properties of nanocomposites. It was found that higher concentration of nanotubes and crystallinity promotes electrical conductivity of nanocomposites in the order of semiconductors (until 1 × 10−4 S cm−1) as well as permittivity of 20 at different tested frequencies. This may due to the interconnected networks of nanotubes throughout the crystalline structure formed in PEN nanocomposites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41765.

Impact of microcrystalline cellulose material attributes: A case study on continuous twin screw granulation

The International Conference on Harmonisation (ICH) states in its Q8 ‘Pharmaceutical Development’ guideline that the manufacturer of pharmaceuticals should have an enhanced knowledge of the product performance over a range of material attributes, manufacturing process options and process parameters. The present case study evaluates the effect of unspecified variability of raw material properties upon the quality attributes of granules; produced using a continuous from-powder-to-tablet wet granulation line (ConsiGma™ 25). The impact of different material attributes of six samples of microcrystalline cellulose (MCC) was investigated. During a blind study the different samples of MCC were used separately and the resulting granules were evaluated in order to identify the differences between the six samples. Variation in size distribution due to varying water binding capacity of the MCC samples was observed. The cause of this different water binding capacity was investigated and was caused by a different degree of crystallinity. Afterwards, an experimental design was conducted in order to evaluate the effect of both product and process variability upon the granule size distribution. This model was used in order to calculate the required process parameters to obtain a preset granule size distribution regardless of the type of MCC used. The difference in water binding capacity and its effect on granular properties was still present when combining the MCC grades with different binders.

Improvement of toughness by stereocomplex crystal formation in optically pure polylactides of high molecular weight

A solution casting method followed by thermal homogenization was performed for the preparation of 1:1 blends and non-blended films from poly(d-lactide) (PDLA) and poly(l-lactide) (PLLA) of three different molecular weights, and their thermal and mechanical properties were determined via differential scanning calorimetry (DSC) and tensile tests. According to the literature, when Mw is below 1.0×105g/mol only stereocomplex crystallization takes place, and when it is higher, both homocrystallites and stereocomplex crystallites co-exist. In order to promote crystallization as a homocrystal in neat polylactides and to promote the stereoselective crystallization as stereocomplex in the case of non-blended films, and in turn, to achieve different degrees of crystallinity, several thermal treatments of annealing were carried out in this work. Highly stereocomplexed blends were found by the stereospecific thermal treatments. As a consequence, the toughness of 1:1 blends was found significantly enhanced over those of non-blended films, irrespective of molecular weight. For instance, in B2-5050 stereocomplexed blend having poly(l-lactide) and poly(d-lactide) of Mw=1.2×105g/mol, tensile strength increased from 44.0±2.1MPa to 65.1±6.1MPa, and the elongation at break from 10.8±2.5% to 33.1±8.1% with respect to its non-blended poly(l-lactide) counterpart crystallized as homocrystal. This improvement in mechanical properties in stereocomplexed blends is not attributed to the inherent properties of the type of crystal polymorph but to the presence of a higher density of intercrystalline connections through a mobile amorphous phase, i.e. tie chains in the stereocomplexed supramolecular spherulitic entities that provide in the stereocomplexed samples enhanced strength and elongation at break at the same time.

Catalytic performance of gold nanoparticles using different crystallinity HAP as carrier materials

Gold (Au) was loaded on hydroxyapatite (HAP) supports with three different degree of crystallinity by deposition-precipitation method. Amorphous HAP and higher crystalline HAP nanoparticles were synthesized respectively by a direct precipitation process of which the aging time was 12h or hydrothermal treatment at 180°C. CO oxidation reaction was used to evaluate the behavior of catalysts. The physical properties of the catalysts were characterized by BET and TEM. The result found the catalyst with the lowest specific surface area had the highest initial activity. Patterns of XRD and XPS revealed that the HAP supports with higher crystallinity could produce more Au° over their surface which resulted in higher initial activity. This study suggested that the crystallinity of HAP supporter was another main factor to improve catalytic activity despite of specific surface area of the Au/HAP nanocatalysts.

Influence of calcination parameters on the synthesis of N-doped TiO2 by the polymeric precursors method

In this paper, the influence of calcination parameters on the synthesis of N:TiO2 catalysts obtained through the polymeric precursors method was evaluated. The powders were prepared by annealing Ti4+ precursor resins at different temperature-time conditions in air, resulting in powders with different degrees of crystallinity for N doping, which was done by adding urea to the as-prepared powders and calcining in N2 atmosphere. The N doping process resulted in band gap narrowing of TiO2 and, varying annealing temperature and time, can be an alternative method for preferential formation of substitutional N or interstitial N. It was found that the percentage of interstitial N increased with an increase in annealing temperature, resulting in the complete absence of substitutional N at 400°C. The photocatalytic performance of the powders was evaluated using Rhodamine-B and Atrazine solutions under ultraviolet and visible irradiations. The coefficients revealed that interstitial N had a positive correlation to both ultraviolet and visible photoactivity. In contrast, substitutional N showed a negative correlation. Further, the ratio of substitutional N to interstitial N indicated a strong negative correlation to ultraviolet light photoactivity and no correlation to visible light photoactivity. However, substitutional N should be controlled for better photocatalytic properties.

Synthesis of high surface area TiO2 nanoparticles by mild acid treatment with HCl or HI for photocatalytic propene oxidation

Nanostructured TiO2 photocatalysts with small crystalline sizes have been synthesized by sol–gel using the amphiphilic triblock copolymer Pluronic P123 as template. A new synthesis route, based on the treatment of TiO2 xerogels with acid–ethanol mixtures in two different steps, synthesis and extraction–crystallization, has been investigated, analyzing two acids, hydrochloric and hydriodic acid. As reference, samples have also been prepared by extraction–crystallization in ethanol, being these TiO2 materials amorphous and presenting higher porosities. The prepared materials present different degrees of crystallinity depending on the experimental conditions used. In general, these materials exhibit high surface areas, with an important contribution of microporosity and mesoporosity, and with very small size anatase crystals, ranging from 5 to 7nm.The activity of the obtained photocatalysts has been assessed in the oxidation of propene in gas phase at low concentration (100ppmv) using a UVA lamp with a wavelength of 365nm. Under the conditions studied, these photocatalysts show different activities in the oxidation of propene which do not depend on their surface areas, but on their crystallinity and band gap energies. Sample prepared with HCl both during synthesis and in extraction–crystallization steps is the most active one, with superior performance than Evonik P25.

Influence of the injection molding process on the mechanical properties of (PA6/GF/MMT) nanocomposite

This work describes the first part of a series of studies on the effect of injection molding conditions on the mechanical properties of polyamide 6/glass fiber/montmorillonite (PA6/GF/MMT) composites, wherein the effect of the injection molding mass temperature on the mechanical properties of the composite is investigated. The results demonstrate that composites processed at lower mass temperatures exhibited higher tensile strength and flexural strength. These findings are explained by the fact that the use of different mass temperatures leads to PA6 matrices with different degrees of crystallinity. In addition, changes in the mass temperature affect the fiber–matrix adhesion of the composite and the intercalation between the matrix and the various components in the nanocomposite. POLYM. COMPOS., 36:237–244, 2015. © 2014 Society of Plastics Engineers

Thermal and Structural Analyses of PMMA/TiO<sub>2</sub> Nanoparticles Composites

In the present work, composites of poly (methyl methacrylate)/titanium oxide nanoparticles (100/0, 97.5/2.5, 95/5, 92.5/7.5, 90/10 and 0/100 wt/wt%)were prepared to be used as bioequivalent materials according to their importance broad practical and medical applications. Thermal properties as well as X-ray diffraction analyses were employed to characterize the structure properties of such composite. The obtained results showed variations in the glass transition temperature (Tg), the melting temperature (Tm), shape and area of thermal peaks which were attributed to the different degrees of crystallinity and the existence of interactions between PMMA and TiO2 nanoparticle molecules. The XRD patterns showed sharpening of peaks at different concentrations of nano-TiO2 powder with PMMA. This indicated changes in the crystallinity/amorphosity ratio, and also suggested that the miscibility between the amorphous components of homo- polymers PMMA and nano-TiO2 powder is possible.The results showed that nano-TiO2 powder mix with PMMA can improve the thermal stability of the homo-polymer under investigation, lead- ing to interesting technological applications.

Analysis of the XLPE Insulation of Distribution Covered Conductors in Brazil

Cross-linked polyethylene (XLPE) has been the most common insulation applied to medium voltage covered conductors (MVCCs) in Brazil. The results of accelerated aging tests carried out at high voltage laboratory of UNIFEI (LAT-EFEI), combining the stresses of heat and voltage to ground aiming at enhancing surface corona activity assays, have identified the early failures in XLPE insulations of the Brazilian MVCCs. The observed failures indicate that complementary studies should be performed to better understand the degradation mechanisms of the MVCCs insulations manufactured in Brazil. In this paper, x-ray photoelectron spectroscopy (XPS), contact angle analysis (CA), photoacoustic spectroscopy (PAS), x-ray diffraction (XRD), and atomic force microscopy (AFM) measurements on samples of five Brazilian national/regional MVCCs are reported. XPS, CA, and PAS analysis indicated that a large variety of oxygen-containing groups associated to the oxidation of the XLPE insulations appear to be related to the manufacturing conditions. AFM analysis indicated that the average surface roughness and topography of the XLPE insulation changed significantly and depend on the selected manufacturer. XRD analysis indicates a strong heterogeneity of crystals nucleation that results into different degrees of crystallinity of the Brazilian MVCCs cables. The results of this work indicate strong evidences of manufacturing defects in the XLPE insulation of Brazilian’s MVCCs. The origin of these defects seems to be inherent to the technology used by manufacturers to the production of the MVCCs. The production-related defects are not detectable by the standard tests as partial discharges or even the standard routine—acceptance power frequency assays routinely used in dielectric compatibility tests at high voltage laboratories.

Raman Characterization of Ambient Airborne Soot and Associated Mineral Phases

Airborne particulate matter samples were collected in an urban and a rural–suburban monitoring stations of the city of Rome, Italy, and the particles were analyzed through the Raman microspectroscopy. A careful examination of the spectral bands, performed with a five-(Voigt) curve deconvolution model previously described by the literature and here adapted to the purpose, lead to the characterization of the graphitic and carbonaceous material plus the identification of the mineral particles associated with it. Statistical analysis of the full-width at half-maximum (FWHM) values of the bands, as well as of their intensity ratio, revealed the presence of two classes of soot particles that can be ascribed to a different degree of crystallinity. The population of soot collected at the urban site, where the vehicular emission component prevails, exhibits mostly crystalline characteristics (with a D1 FWHM of 150–155 cm−1), whereas the population collected at the rural–suburban site, particularly the coarse fract...

Enzymatic transesterification of soybean oil with ethanol using lipases immobilized on highly crystalline PVA microspheres

Polyvinyl alcohol (PVA) microspheres with different degree of crystallinity were used as solid supports for Rhizomucor miehei lipase immobilization, and the enzyme-PVA complexes were used as biocatalysts for the transesterification of soybean oil to fatty acid ethyl esters (FAEE). The amounts of immobilized enzyme on the polymeric supports were similar for both the amorphous microspheres (PVA4) and the high crystalline microspheres (PVA25). However, the enzymatic activity of the immobilized enzymes was depended on the crystallinity degree of the PVA microspheres: enzymes immobilized on the PVA4 microspheres have shown low enzymatic activity (6.13 U mg−1), in comparison with enzymes immobilized on the high crystalline PVA25 microspheres (149.15 U mg−1). A synergistic effect was observed for the enzyme-PVA25 complex during the transesterification reaction of soybean oil to FAEE: transesterification reactions with free enzyme with the equivalent amount of enzyme that were immobilized onto the PVA25 microspheres (5.4 U) have yielded only 20% of FAEE, reactions with the pure highly crystalline microsphere PVA25 have not yielded FAEE, however reactions with the enzyme-PVA25 complexes have yielded 66.3% of FAEE. This synergistic effect of an immobilized enzyme on a polymeric support has not been observed before for transesterification reaction of triacylglycerides into FAEE. Based on ATR-FTIR, 23Na- and 13C-NMR-MAS spectroscopic data and the interaction of the polymeric network intermolecular hydrogen bonds with the lipases residual amino acids a possible explanation for this synergistic effect is provided.

Effect of substitution group variation on the optical functions of -5-sulfono-7-(4-x phenyl azo)-8-hydroxy quinoline thin films

-5-Sulfono-7-(4-x phenyl azo)-8-hydroxy quinoline (SAHQ)-x ligands, x = NO2 or CH3 or Cl have polycrystalline structure in as synthesized condition. Thermally evaporated thin films of SAHQ-x have crystal structure depending on the substitution group; SAHQ-NO2 and SAHQ-Cl films have nano-crystalline structure with different degree of crystallinity and SAHQ-CH3 film has amorphous structure. The changes in optical functions and therefore optical constants with substitution group variation have been calculated by using spectrophotometer measurements of the transmittance and reflectance at nearly normal incidence of light in the wavelength range 200–2500 nm. Substitution group variation influences the refractive index, dispersion parameters, optical functions and bond length of SAHQ. It has no influence on mobility, relaxation time and plasma frequency of charge carriers. The obtained optical energy gaps for SAHQ-x ligands, x = NO2 or CH3 or Cl are 1.89, 2 and 2eV, respectively.

Optical, structural and electrical properties of polyaniline systems doped with C60 and small gap C60 fullerenes

In this work two systems consisting on polyaniline (Pani) doped with simple and small gap C60 fullerenes have been prepared and characterized. Composites with different doping amounts of 1,2,4 and 8 wt% have been analyzed in order to evaluate their structure together with their optical and electrical properties and the effect of fullerene type and amount on them. The shift and change of shape in Fourier transform infrared spectroscopy (FTIR) bands and solid 13C NMR spectroscopy signals showed the presence of interactions between matrix and fullerenes by electron density transfer among them. Optical properties have also been analyzed in terms of ultraviolet (UV) spectroscopy. The blue shift of several bands confirmed the charge transfer. Obtained structures have been analyzed by optical microscopy (OM) showing the different way in which both types of fullerenes have been incorporated into the polymer chains. Finally, conductivity has been measured by the four probe technique, relating obtained values with the structure of the composite and the different degree of crystallinity of simple and small gap fullerenes.

β3R3-Peptides: design and synthesis of novel peptidomimetics and their self-assembling properties at the air–water interface

In this study we present the design and synthesis of a novel class of peptidomimetics, the β(3R3)-peptides. Via alternating directions of the amide bonds along β-peptide sequences, β(3R3)-peptides can potentially extend the structural space available to β-peptidic foldamers. Detailed analysis at the air-water interface shows strand conformations and the formation of sheet assemblies with different degrees of crystallinity. Furthermore β(3R3)-peptides exhibit a high proteolytic stability thus making them an interesting new class of peptidomimetics for biomedical applications.

Materials Characterization of Potassium Sodium Niobate based Tellurite Glass-Ceramics

In this research, materials characterization of transparent glass-ceramics containing ferroelectric potassium sodium niobate (K0.5Na0.5)NbO3 (KNN) crystals in a tellurite glass system were studied. The samples were prepared via an incorporation method. Glass-ceramics containing KNN crystals were successfully fabricated by mixing KNN calcined powder with TeO2 of about 70 and 80 mol% and melting at 800°C for 15 min in a platinum crucible. The prepared glasses were then subjected to heat treatment at 350–550°C. The optical properties of the samples were characterized by UV-Vis-NIR and ellipsometer. It was found that heat treatment temperature had significantly affected the optical properties. XRD patterns of the glass-ceramics revealed an amorphous-like structure with different degrees of crystallinity. SEM results confirmed the XRD data, where the degree of crystallinity increased with increasing heat treatment temperature.