Amorphous Fraction Research Articles

Time and Temperature Evolution of the Rigid Amorphous Fraction and Differently Constrained Amorphous Fractions in PLLA

In semi‐crystalline polymers, amorphous segments located in different regions and distance from the crystalline domains can exhibit different dynamics. In poly(l‐lactic acid) (PLLA), the existence of (i) two distinct mobile amorphous fractions (a completely mobile amorphous fraction and a slightly constrained mobile amorphous fraction), which vitrify/devitrify in the Tg region, and (ii) a rigid amorphous fraction, which vitrifies/devitrifies at temperatures higher than Tg, has been reported in the literature. The percentage of the three different amorphous fractions, characterized by different segmental mobility, is generally calculated at Tg. In the present study, for the first time, the time and temperature evolution of all the amorphous fractions of PLLA are measured in parallel with the crystalline phase (i) during crystallization at two different temperatures, and (ii) upon the successive cooling step down to room temperature. The kinetics of vitrification/devitrification of the different amorphous fractions in diverse conditions of crystallization and solidification has been determined during the entire thermal history of the material. Rigid amorphous fraction is found to develop not only during crystallization but also upon cooling, after completion of crystallization. image

Rigid amorphous fraction and segmental dynamics in nanocomposites based on poly(l–lactic acid) and nano-inclusions of 1–3D geometry studied by thermal and dielectric techniques

Polymer nanocomposites (PNCs) based on poly(l-lactic acid) (PLLA) and four fillers differing in shape geometry: silica and Ag spherical nanoparticles (3D), multi-wall carbon nanotubes (CNTs) (2D), and graphene oxide (GO) nanosheets (1D), were prepared and investigated. Low filler contents were used, 0.5–2.5wt%, where nanoparticles act as nucleating agents, being partly embedded in the crystals, and maximize degree of crystallinity (CF). Differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS), supplemented by scanning electron microscopy (SEM) and wide angle X-ray scattering (WAXS) for morphology, were employed to study effects of filler on glass transition and segmental dynamics and on the amount of CF and of the rigid amorphous fraction (RAF). CF and RAF for different thermal protocols, normalized to 1wt% filler content, increase in general on addition of filler in the order silica<Ag<GO<CNT, which correlates with that of increasing aspect ratio of the fillers. The results suggest that RAF should be correlated with polymer crystals rather than NPs (RAF=RAFcryst) and it is determined by crystal size (polymer chain diffusion) and semicrystalline morphology, next to nucleation. Analysis of the DSC and DRS results of isothermal cold crystallization at 75°C shows that for both neat PLLA and the NCs time scale (logfmax,α) and strength (Δεα) of the segmental α relaxation decrease faster with time than the amorphous fraction (1−CF), and Δεα decreases faster than logfmax,α for all the samples studied. Results for the time scale of the segmental α relaxation and the glass transition temperature Tg suggest that constraints imposed to polymer molecular mobility by attractive interaction with the filler dominate for silica, whereas loosen molecular packing of the chains resulting in increase of free volume prevails for the other fillers. Measurements at higher silica contents, where the nucleating activity of the filler is expected to saturate and additional filler NPs not to be embedded in polymer crystals, indicate immobilization of a polymer fraction around the silica NPs, next to the fraction immobilized around the polymer crystals.

Physico-chemical Characterization and In Vitro Evaluation of Biopharmaceutics Classification System Class II Drug Febuxostat

Aim: Febuxostat (FBX) is a non-purine selective inhibitor of xanthine oxidase/xanthine reductase. It belongs to Biopharmaceutics Classification System Class II with low solubility and high permeability. Because of low solubility, the bioavailability of the drug is hampered, food also interferes with the absorption of the drug and decreases the Cmax by 38-49%. The bioavailability of a drug is a function of dissolution rate of the drug which is controlled by the surface area of the drug. In the category of poorly soluble drugs, the change in surface area of the drug will show considerable changes in the solubility and dissolution of the drug. Materials and Methods: In the present study, the attempts were made to improve the bioavailability of FBX by solid dispersions technique by employing poly vinyl pyrrolidone K30 (PVP K30) and hydroxy propyl methyl cellulose E15 (HPMC E15) as carrier molecules. Different ratios on weight basis were prepared, viz., 1:1,1:2,1:3,2:1 with PVP and 1:1, 1:2, 1:3,1:4 with HPMC were prepared. Results and Discussion: These preparations were characterized in liquid state by phase solubility studies and in solid state by differential scanning calorimetry, Fourier transform infrared spectroscopy, Powdered X-ray diffraction studies, and scanning electron microscopy. The aqueous solubility of FBX is favored by the presence of both the carriers. Solid state characterization indicated that FBX was present as fine amorphous form in the carrier polymeric molecules. Conclusion: In contrast to the solution rate of pure FBX, the dissolution of drug in carriers considerably improved the dissolution rate, this can be attributed to the increased wettability and dispersibility as well as decreased crystallinity and increased amorphous fraction of the drug

Development the technology of obtaining microcrystalline cellulose from the hemp fibers

A new, environmentally cleaner, technology of obtaining microcrystalline cellulose of fibers of hemp was proposed. The various stages of obtaining microcrystalline cellulose were studied and the optimum values of technological parameters of alkali extraction of hemp fibers, organosolv pulping, chelation and hydrolysis of cellulose were defined. It was determined that the consistent treatment of fibers of hemp by extraction of 5 % KOH solution during 210 minutes at the temperature of 95 °С, performic cooking in a mixture of 85 % formic acid and 30 % of hydrogen peroxide in the ratio of 60:40 of volume % at 100 °C during 210 min, chelation by the solution of trilon B of the concentration of 10 g/l during 30 min at 50 °C and hydrolysis by a mixture of 98 % acetic acid and 30 % of hydrogen peroxide solution in the ratio of 70:30 of volume %, allows obtaining microcrystalline cellulose in the form of white powder with a degree of polymerization 80 and the content of sulfate ash of 0.10 %. Using the methods of scanning electronic microscopy, thermogravimentric analysis and X­ray diffraction confirmed that the consistent multistage chemical treatment increases the content of crystalline part of cellulose by the removal of extractive and mineral substances, hemicelllulose and amorphous fraction of cellulose of the fibers of hemp. Application of the proposed technology of obtaining microcrystalline cellulose from the fibers of hemp is environmentally more friendly and enables to reduce significantly the cost of finished products by using national, annually renewable plant raw materials compared to imported cotton or pine cellulose.

From a Three-Phase Model to a Continuous Description of Molecular Mobility in Semicrystalline Poly(hydroxybutyrate-co-hydroxyvalerate)

In most cases, a three-phase model consisting of crystalline domains surrounded by rigid amorphous areas dispersed in the mobile amorphous phase is required and eventually sufficient to accurately describe the microstructure of semicrystalline polymers. This work shows that the microstructure developed by poly(hydroxybutyrate-co-hydroxyvalerate) by cold crystallization is better described by a complex two-phase model in which the boundaries of the crystalline domains and the surrounding amorphous environment form a “continuum of mobility”. This concept can be extended to a wide range of semicrystalline polymers. When the crystalline and the amorphous phases are strongly coupled, the rigid and mobile amorphous fractions are hardly fractionated, and the whole noncrystalline phase should be rather depicted as continuum with a broad distribution of the relaxation times associated with the glass transition. Such a depiction of the amorphous phase allows taking into account any modification of the mobility land...

Comparative Dynamic Characteristics of Electrospun Ultrathin Fibers and Films Based on Poly(3-hydroxybutyrate)

The dynamic of polymer chains for electrospun poly(3-hydroxybutyrate) (PHB) fibers and the PHB films was studied with spin probe characteristics obtained by ESR technique. The ESR data combined with DSC analysis reveal the presence of two TEMPO probe populations with different correlation times indicating the heterogeneous structure of intercrystalline areas in the films, fibers and the cold rolled fiber mats. The ESR data are in agreement with the 2-mode model of amorphous state in semicrystalline polymers. The difference in peak intensities shows that effective correlation time in the electrospun fibers exceeds the same characteristic in the film, that also indicates the slower molecular mobility in the low-dense amorphous fraction of PHB fibers as compared to the film. The impact of potential aggressive factors such as water, temperature and ozone upon probe mobility allows suggesting that both the fiber electrospinning and the cold-rolling procedure lead to rearrangement in the intercrystalline fields of PHB that contribute to the progress in the fiber stabilization against the aggressive factors.

Rigid amorphous fraction and multiple melting behavior in poly(butylene terephthalate) and isotactic polystyrene

The multiple melting behavior of many semicrystalline polymers is generally attributed to fusion of original crystals reorganized/recrystallized upon heating at conventional scanning rates. In the present study, the triple and double melting behavior of poly(butylene terephthalate) (PBT) and isotactic polystyrene (iPS), which is observed after isothermal crystallization at low and high T c s, respectively, is put into relation with the presence and absence of rigid amorphous/crystal interphase around the original primary crystals. Such constrained amorphous interphase has been recognized as decisive for the definition of the mechanical, thermal, and barrier properties of semicrystalline polymers. The method for the approximate determination of the limit temperature for the presence of this rigid amorphous fraction (RAF), already applied to poly[(R)-3-hydroxybutyrate] (PHB) and poly(ethylene terephthalate) (PET), is here utilized for PBT and iPS. The complex melting behavior displayed by all these polymers is explained by assuming that two distinct morphologies of primary crystals develop during crystallization at temperatures lower than the RAF limit temperature, in a percentage that is a function of the crystallization temperature. Simultaneously with the RAF devitrification, these distinct morphologies differently reorganize/recrystallize upon heating at low scanning rate, originating the triple melting behavior. On the contrary, after crystallization at high T c s, a single reorganization route is followed by all the primary crystalline structures, characterized by the same morphology made of tightly chain-folded lamellae and absence of vitrified RAF at the amorphous/crystal interphase.

Anisotropic mechanical properties of zircon and the effect of radiation damage

This study provides new insights into the relationship between radiation-dose-dependent structural damage due to natural U and Th impurities and the anisotropic mechanical properties (Poisson’s ratio, elastic modulus and hardness) of zircon. Natural zircon samples from Sri Lanka (see Muarakami et al. in Am Mineral 76:1510–1532, 1991) and synthetic samples, covering a dose range of zero up to 6.8 × 1018 α-decays/g, have been studied by nanoindentation. Measurements along the [100] crystallographic direction and calculations, based on elastic stiffness constants determined by Ozkan (J Appl Phys 47:4772–4779, 1976), revealed a general radiation-induced decrease in stiffness (~54 %) and hardness (~48 %) and an increase in the Poisson’s ratio (~54 %) with increasing dose. Additional indentations on selected samples along the [001] allowed one to follow the amorphization process to the point that the mechanical properties are isotropic. This work shows that the radiation-dose-dependent changes of the mechanical properties of zircon can be directly correlated with the amorphous fraction as determined by previous investigations with local and global probes (Rios et al. in J Phys Condens Matter 12:2401–2412, 2000a; Farnan and Salje in J Appl Phys 89:2084–2090, 2001; Zhang and Salje in J Phys Condens Matter 13:3057–3071, 2001). The excellent agreement, revealed by the different methods, indicates a large influence of structural and even local phenomena on the macroscopic mechanical properties. Therefore, this study indicates the importance of acquiring better knowledge about the mechanical long-term stability of radiation-damaged materials.

Mobile amorphous, rigid amorphous and crystalline fractions in isotactic polypropylene during fast cooling

Crystallization of isotactic polypropylene was analyzed by fast scanning calorimetry (Flash DSC) at cooling rates between 1 and 4000 K s−1. By quantitative analysis of the glass transition intensity and the specific transformation enthalpy, the amount of mobile amorphous (MAF), rigid amorphous (RAF) and crystalline fractions (CFs) and its dependency on the cooling rate were determined. During cooling, two different crystalline phases are formed. At slow cooling rates (below 90 K s−1), the α-phase is crystallized. At faster cooling rates mesophase aggregates are formed. The crystalline phase reduces the relaxation time in the MAF independently from the kind of the crystalline phase. The RAF is formed during the crystallization process. In the case of mesophase crystallization, the ratio between CF and RAF is independent of the crystallinity. For α-phase crystals, this ratio depends on the crystallinity. A model for the CF-RAF structure is derived from the reported results.

Synthesis of branched poly(butylene succinate): Structure properties relationship

A series of branched poly(butylene succinate) (PBS) were synthesized with several branching agents namely trimethylol propane (TMP), malic acid, trimesic acid, citric acid and glycerol propoxylate. The structure of the branched polymers was analyzed by SEC and 1H-NMR. The effect of branching agent structure on crystallization was also investigated and played a significant role. Isothermal studies showed that glycerol propoxylate could act as a nucleating agent. By contrast high content of TMP disturbed the regularity of the chain and hindered the crystallization of PBS. From the non-isothermal kinetic study, it was found that glycerol propoxylate increased noticeably the crystallization rate due to the flexible structure of the branching agent. A secondary nucleation was observed with glycerol propoxylate attributed to the crystallization of amorphous fraction included between crystallites formed at the primary crystallization. Chain topology was obtained through rheological investigations and the synthesized polymers showed a typical behavior of a mixture of linear and randomly branched PBS. The incorporation of branches improved the processability of PBS for film blowing application and the modulus and the stress at break of the resulting film were significantly increased.

The distribution and elevated solubility of lead, arsenic and cesium in contaminated paddy soil enhanced with the electrokinetic field

The objectives of this study were to investigate fractionation, solubility and potential bioavailability of Pb, As and Cs in Mississippi River Delta paddy soil under an electrokinetic field (EKF). Effects of EKF on soil pH changes and solid-phase distributions of metal(loid)s were examined. Results showed that fractionation of Pb, As and Cs was largely determined by the nature of elements, loading levels and EKF treatment. Native Pb in the soil was mostly in the amorphous iron oxide, organic matter and residual fractions, native As in the amorphous iron oxide, easily reducible oxide and residue fractions while native Cs in the residue fraction. Added Pb, As and Cs showed distinguished solid-phase distributions: Pb dominantly in the organic matter fraction; As in the amorphous iron oxide fraction, and Cs in the residue with a significant water-soluble plus exchangeable fraction. EKF treatment is effective on lowering soil pH to 1.5 near the anode due to water electrolysis releasing proton which is beneficial for dissolution of metal(loid)s, increasing their overall solubility. The acidification in the anode soil efficiently increased the water-soluble Pb and the exchangeable Cs, implying enhanced solubility and elevated their overall potential bioavailability in the anode region while lower solubility in the cathode area. The building up of water-soluble As in the anode region may be from electromigration of As anion from the cathode. This study shows significant enhancement of redistribution, elevated solubility and overall bioavailability of Pb, As and Cs in Mississippi Delta paddy soil under the EKF.

Effective Method of Purification of Betulin from Birch Bark: The Importance of Its Purity for Scientific and Medicinal Use.

A new and relatively simple method for purification of betulin from birch bark extract was developed in this study. Its five purification steps are based on the differential solubility of extract components in various solvents and their crystallization and/or precipitation, on their affinity for Ca(OH)2 in ethanol, and on the affinity of some impurities for silica gel in chloroform. In addition, all used solvents can be simply recycled. Betulin of more than 99% purity can be prepared by this method with minimal costs. Various observations including crystallization of betulin, changes in crystals during heating, and attempt of localization of betulin in outer birch bark are also described in this work. The original extract, fraction without betulinic acid and lupeol, amorphous fraction of pure betulin, final crystalline fraction of pure betulin and commercial betulin as a standard were employed to determine the antiproliferative/cytotoxic effect. We used WST-1 tetrazolium-based assays with triple negative breast cancer cell line BT-549. The decrease in cell survival showed clear relationship with the purity of the samples, being most pronounced using our final product of pure crystalline betulin. WST-1 proliferation/cytotoxicity test using triple negative breast cancer cell line BT-549 clearly showed the importance of purity of betulin for biological experiments and, apparently, for its medicinal use.

Crystalline-amorphous silicon nano-composites: Nano-pores and nano-inclusions impact on the thermal conductivity

The thermal conductivities of nanoporous and nanocomposite silicon with incorporated amorphous phases have been computed by molecular dynamics simulations. A systematic investigation of the porosity and the width of the amorphous shell contouring a spherical pore has been made. The impact of amorphous phase nanoinclusions in a crystalline matrix has also been studied with the same amorphous fraction as the porosity of nanoporous silicon to achieve comparison. The key parameter for all configurations with or without the amorphous phase is proved to be the interface (between the crystalline and amorphous phases or crystalline and void) to volume ratio. We obtain the sub-amorphous thermal conductivity for several configurations by combining pores, amorphous shell, and crystalline phase. These configurations are promising candidates for low cost and not toxic thermoelectric devices based on abundant semiconductors.

Pressure‐Dependent Polymorphism and Band‐Gap Tuning of Methylammonium Lead Iodide Perovskite

AbstractWe report the pressure‐induced crystallographic transitions and optical behavior of MAPbI3 (MA=methylammonium) using in situ synchrotron X‐ray diffraction and laser‐excited photoluminescence spectroscopy, supported by density functional theory (DFT) calculations using the hybrid functional B3PW91 with spin‐orbit coupling. The tetragonal polymorph determined at ambient pressure transforms to a ReO3‐type cubic phase at 0.3 GPa. Upon continuous compression to 2.7 GPa this cubic polymorph converts into a putative orthorhombic structure. Beyond 4.7 GPa it separates into crystalline and amorphous fractions. During decompression, this phase‐mixed material undergoes distinct restoration pathways depending on the peak pressure. In situ pressure photoluminescence investigation suggests a reduction in band gap with increasing pressure up to ≈0.3 GPa and then an increase in band gap up to a pressure of 2.7 GPa, in excellent agreement with our DFT calculation prediction.

The interfacial restructuring to amorphous: A new adhesion mechanism of cold-sprayed coatings

A new plausible adhesion mechanism of cold-sprayed coatings on hard, non-deformable substrates was proposed. Interface analysis of both the heavy (Cu) and light (Al) metal coatings on the ceramic substrates such as AlN and ZrO2 showed that the amorphous cascade volume fractions were created on impact. Furthermore, these amorphous volume fractions provided the channels for quick and effective atomic level intermixing to yield high bond strength in the cold spray process. The important parameters to determine the total amorphous cascade volume were relative hardness, mechanical deformability and density of colliding particles. Therefore, the final bonding strength would be predicted based on the fit between these parameters for coating and substrate materials.

Probing the chain segment mobility at the interface of semi-crystalline polylactide/clay nanocomposites

The concept of Cooperative Rearranging Region (CRR), an efficient probe of the interaction level in nanocomposites, has been used in Poly(lactic acid) (PLA)-based composites with phyllosilicates prepared in the melt with organomontmorillonite (O-MMT) and using poly(butylene adipate-co-terephthalate) (PBAT) as coupling agent. The samples were crystallized from various thermal treatments in order to obtain a wide range of morphologies and microstructures and accurately characterized by XRD, TEM, standard DSC and MT-DSC with the aim to highlight the effect of lamellae dispersion and distribution at nanoscale onto the thermal features of resulting nanocomposites. The presence of different interaction levels at the interface PLA/O-MMT, even tuned by the presence of PBAT, affects both the crystalline phase structure (by differently promoting crystallization of α and α′ forms) and the distribution between the amorphous fractions (rigid and mobile). The variations of molecular dynamics are classified in two categories depending on the composite microstructure. Only in amorphous materials the cooperativity is driven by the filler/matrix interactions. In semi-crystalline materials, the morphological features linked to the presence of O-MMT and PBAT are overwhelmed by the confinement of the amorphous phase. Comparison between the two crystallization modes evidences a stronger change in the glass transition dynamics for systems exhibiting preponderant nucleation and high percentage of rigid amorphous fraction.

Thermal pretreatment of a high lignin SSF digester residue to increase its softening point

Residues high in lignin and ash generated from the simultaneous saccharification and fermentation of corn stover were thermally pretreated in an inert (N2) atmosphere to study the effect of time and temperature on their softening points. These residues are difficult to feed into gasifiers due to premature thermal degradation and formation of reactive liquids in the feed lines, leading to plugging. The untreated and treated residues were characterized by proximate and ultimate analysis, and then analyzed via TGA, DSC, 13C NMR, Py-GC–MS, CHNO/S, and TMA. Interpretation of the compositional analysis indicates that the weight loss observed during pretreatment is mainly due to the thermal decomposition and volatilization of the hemicelluloses and amorphous cellulose fractions. Fixed carbon increases in the pretreated material, mostly due to a concentration effect rather than the formation of new extra poly-aromatic material. The optimal processing time and temperature to minimize the production of carbonyl groups in the pretreated samples was 300 °C at a time of 30 min. Results showed that the softening point of the material could be increased from 187 °C to 250 °C, and that under the experimental conditions studied, pretreatment temperature plays a more important role than time. The increase in softening point was mainly due to the formation of covalent bonds in the lignin structures and the removal of low molecular weight volatile intermediates.

Amorphous Phase Formation Analysis of Rapidly Solidified CoCr Droplets

This paper investigates amorphous phase formation and rapid solidification characteristics of a CoCr alloy. High cooling rate and high undercooling-induced rapid solidification of the alloy was achieved by impulse atomization in helium atmosphere. Two atomization experiments were carried out to generate powders of a wide size range from liquid CoCr at two different temperatures. Amorphous fraction and kinetic crystallization properties of impulse atomized powders were systematically quantified by means of differential scanning calorimetry. In addition, different but complementary characterization tools were used to analyze the powders microstructures. The fraction of amorphous phase within the investigated powders is found to be promoted by high cooling rate or smaller powder size. The critical cooling rate for amorphous phase formation, which is influenced by the oxygen content in the melt, is found to be ~3 × 104 K s−1 and corresponds to a 160-µm-diameter powder atomized in helium. Hardness of the powders is found to follow a trend that is described by the Hall–Petch relation when a relatively high fraction of crystalline structures is present and decreases with the fraction of amorphous phase.

Fluoropolymer microstructure and dynamics: Influence of molecular orientation induced by uniaxial drawing

Fluorinated semi-crystalline polymers are attractive for dielectric film applications due to their chemical inertness and high thermal stability. In the present investigation we explore the influence of orientation induced by uniaxial drawing on the crystalline microstructure and relaxation processes of poly(ethylene-tetrafluoroethylene) (ETFE), in order to ascertain how morphological control can benefit polymer dielectric design. When drawn below or near the Tg, the crystallinity of the drawn films is unchanged, and oriented amorphous structures and crystalline microfibrils form at high draw ratios. This orientation slows segmental relaxation, reflected by an increase in the dynamic Tg. When drawing above Tg, the films undergo strain-induced crystallization at high draw ratios. For these films, an increase in dynamic Tg is also observed, in addition to a second segmental relaxation process, appearing as a shoulder on the primary process. We propose that this represents a contribution from a rigid amorphous fraction, having slowed chain dynamics.

Highly Enhanced Mesophase Formation in Glassy Poly(l-lactide) at Low Temperatures by Low-Pressure CO2 That Provides Moderately Increased Molecular Mobility

The mesophase structuring in melt-quenched poly(l-lactide) (PLLA) treated in low-pressure CO2 at 2 MPa and 0–35 °C was investigated by using infrared spectroscopy, differential scanning calorimetry (DSC), temperature-modulated DSC, and atomic force microscopy (AFM). It was found that the mesophase formation in glassy PLLA was significantly enhanced, in particular at lower temperature (0 °C), which promoted a distinctly faster formation rate. AFM results revealed that the CO2-enhanced mesophase exhibited nodular morphology with dramatically increased nucleation density. A framework of multistage model in combination with the moderately improved molecular mobility exerted by CO2 was proposed to explain the main findings. Because of the moderate molecular mobility, a tremendous number of metastable mesomorphic layers were formed and stabilized by the accompanying development of the rigid amorphous fraction (RAF), leading to the immobilization of the remaining mobile amorphous fraction (MAF). The mesomorphic ...