Crystalline Structure Of Poly Research Articles

Study of the Crystal Structure and Hydrogen Bonding during Cold Crystallization of Poly(trimethylene 2,5-furandicarboxylate).

Here, we present a detailed description of the in situ isothermal crystallization of poly(trimethylene 2,5-furandicarboxylate)(PTF) as revealed by real-time Fourier transform infrared spectroscopy (FTIR) and grazing incidence wide-angle X-ray scattering (GIWAXS). From FTIR experiments, the evolution of hydrogen bonding with crystallization time can be monitored in real time, while from GIWAXS, crystal formation can be followed. Density functional theory (DFT) calculations have been used to simulate FTIR spectra for different theoretical structures, enabling a precise band assignment. In addition, based on DFT ab initio calculations, the influence of hydrogen bonding on the evolution with crystallization time can be understood. Moreover, from DFT calculations and comparison with both FTIR and GIWAXS experiments, a crystalline structure of poly(trimethylene 2,5-furandicarboxylate) is proposed. Our results demonstrate that hydrogen bonding is present in both the crystalline and the amorphous phases and its rearrangement can be considered as a significant driving force for crystallization of poly(alkylene 2,5-furanoate)s.

Synthesis and crystalline structure of poly(p-phenylene alkylene)s and poly(p-phenylene co-alkylenes)s by Kumada coupling reaction of α,ω-dibromoalkane and p-dichlorobenzene

Synthesis and crystalline structure of poly(p-phenylene alkylene)s and poly(p-phenylene co-alkylenes)s by Kumada coupling reaction of α,ω-dibromoalkane and p-dichlorobenzene

Effects of thermal annealing and solvent-induced crystallization on the structure and properties of poly(lactic acid) microfibres produced by high-speed electrospinning

This research concentrates on the marked discrepancies in the crystalline structure of poly(lactic acid) (PLA) nano- and microfibres, achieved by different annealing strategies. PLA nonwoven mats were produced by high-speed electrospinning. The high-speed production technique allowed the manufacturing of PLA microfibres with diameters of 0.25–8.50 µm with a relatively high yield of 40 g h−1. The crystalline content of the inherently highly amorphous microfibres was increased by two methods; thermal annealing in an oven at 85 °C was compared to immersion in absolute ethanol at 40 °C. The morphology of the fibres was examined by scanning electron microscopy; crystalline forms and thermal properties were assessed using X-ray diffractometry, Raman spectrometry, differential scanning calorimetry (DSC) as well as modulated DSC. As a consequence of 45-min heat treatment, the crystalline fraction increased up to 26%, while solution treatment resulted in 33% crystallinity. It was found that only disordered α′ crystals are formed during the conventional heat treatment; however, the ethanol-induced crystallization favours the formation of the ordered α polymorph. In connection with the different crystalline structures, noticeable changes in the macroscopic properties such as heat resistance and mechanical properties were evinced by localized thermomechanical analysis and static tensile test, respectively.

Simple test method for determination of contribution level of crosslink density by crystalline structure of poly(ethylene-co-vinyl acetate) compound

Poly(ethylene-co-vinyl acetate) (EVA) has crystalline structures of ethylene sequences and the crystalline regions influence on measurement of crosslink density by swelling method. A simple test method for determination of contribution level of crosslink density by crystalline structure of EVA was developed by employing swelling step at high temperature. Besides normal swelling method at room temperature (D_RT), two novel swelling systems were employed; one is containing high temperature swelling step after drying the free organic ingredients-extracted sample (D_HT) and the other is containing high temperature swelling step without the drying step (ND_HT) in order to dissolve the crystalline regions. Crosslink densities of cured EVA samples measured by the D_RT method were much higher than those by the D_HT and ND_HT ones. The ND_HT method was found to be more efficient for dissolution of the crystalline regions than the D_HT one. Contribution level of the crosslink density by the crystalline structure was obtained by difference in the crosslink densities measured by the D_RT and ND_HT methods, and it was found that the contribution level was about 90%. Influence of co-crosslinker (triallyl isocyanurate, TAC) on the contribution level was also examined.

Correction to "Role of Ion-Dipole Interactions in Nucleation of Gamma Poly(vinylidene fluoride) in the Presence of Graphene Oxide during Melt Crystallization".

The crystallization behavior and crystalline structure of poly(vinylidene fluororide) (PVDF) in the presence of graphene oxide (GO) platelets were investigated using time-resolved Fourier transformation infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), as well as differential scanning calorimetry (DSC). It is shown that GO platelets induce the formation of γ phase when crystallizing from solution, but only α phase forms from melt crystallization. The crystallization kinetics of α phase is promoted due to heterogeneous nucleation ability of GO, which is probably originated from a weak π-dipole interaction between GO and PVDF. Intriguingly, after introduction of strong ion–dipole interactions between GO and PVDF by addition of an ionic surfactant (cetyltrimethylammonium bromide, CTAB), a significant amount of γ crystals are obtained during isothermal melt crystallization. Time-resolved FTIR results further provide a detailed evolution of the γ phase formation, and there are two distinct sta...

Evolution of Intermediate and Highly Ordered Crystalline States under Spatial Confinement in Poly(3-hydroxybutyrate) Ultrathin Films

The crystallization behavior and crystalline structures of poly(3-hydroxybutyrate) (PHB) ultrathin films (∼52 nm) under spatial confinement were investigated using infrared reflection–absorption spectroscopy (IR-RAS) and two-dimensional grazing incidence X-ray diffraction (2D-GIXD). Intermediate and highly ordered crystalline states were observed during heating and melt-cooling of these films. In the ultrathin films, the intermediate state was noticeably stable at lower temperatures, whereas the highly ordered state was more stable at higher temperatures. A transformation from the intermediate state into the highly ordered state occurred as the temperature increased, as the crystals in the intermediate state acquire sufficient thermal energy to overcome the energy barrier. 2D-GIXD results show that the intermediate state was dominant in edge-on lamellae configuration where the crystallographic b-axis is normal to the film surface. Meanwhile, the highly ordered state was predominant in flat-on lamellae con...

Relationship between crystalline structure of poly(3-hexylthiophene) blends and properties of organic thin-film transistors – a brief review

Relationship between crystalline structure of poly(3-hexylthiophene) blends and properties of organic thin-film transistors – a brief review

Dominant β-Form of Poly(l-lactic acid) Obtained Directly from Melt under Shear and Pressure Fields

Shear and pressure fields unavoidably coexist in practical polymer processing operations, but their combined influence on the crystalline structure of poly(l-lactic acid) (PLLA) has never been studied due to the limit of experiment device. In the current work, we utilized a homemade pressuring and shearing device to study the crystalline morphology and structure of PLLA under the coexistence of shear and pressure. Interestingly, we obtained almost exclusive β-form directly from PLLA melt crystallization at our experimental condition (shear 13.6 s–1, pressure 100 MPa, and crystallization temperature 160 °C). Undoubtedly, abundant β-form is helpful to tackle the major shortcoming of PLLA performance, i.e., poor toughness. This meaningful result is different from the common viewpoints that PLLA β-form can usually be obtained by hot-drawing or solid coextrusion under a high tensile ratio, suggesting that PLLA β-form can be obtained through shear-induced crystallization. In addition, the fraction of β-PLLA str...

Effects of CNT inclusions on structure and dielectric properties of PVDF/CNT nanocomposites

ABSTRACTThe effects of multiwall carbon nanotube (CNT) inclusions on the crystalline structure of poly(vinylidene fluoride) (PVDF), and on the dielectric properties of PVDF/CNT nanocomposites (NCs), prepared by melt mixing, were investigated by employing X-ray diffraction, differential scanning calorimetry, and dielectric spectroscopy techniques. Our results imply that, in the NCs, the formation of β-phase crystals depends on specific compression treatment in the melt and fast cooling. Dielectric measurements on NCs, with CNT concentrations below the electrical percolation threshold, reveal that the dielectric strength of the two relaxation processes in the amorphous phase and dielectric permittivity, ϵ′, measured within the broad temperature range from −150 °C to 60 °C, increase strongly with increasing CNT concentration. This enhancement of amorphous PVDF polarizability has been attributed to the increase of the local electric field, due to local polarization generated at the surface of conductive inclusions/CNT clusters.

Isothermal Crystallization Behavior and Kinetics of Poly (lactic acid) Filled with a Novel Nucleating Agent

The crystallization behavior and crystalline structure of poly (lactic acid) (PLA) filled with a novel nucleating agent (TMC328), which is a kind of aromatic amide derivatives, were investigated using differential scanning calorimetry (DSC) and wide angle X-ray (XRD). In isothermal crystallization from the melt, the present of TMC328 remarkably affected the isothermal crystalline behaviors of PLA. PLA/0.5% TMC328 sample exhibited very short crystallization half-times at 90-130 °C. Furthermore, the Avrami theory was used to describe the isothermal crystallization kinetics of PLA/TMC328 samples. It is confirmed that TMC328 showed a significant heterogeneous nucleation effect on the crystallization of PLA matrix. Moreover, XRD measurement indicates that TMC328 is a kind of α-form nucleating agent for PLA.

Pressure‐crystallized piezoelectric structures in binary fullerene C70/poly(vinylidene fluoride) based composites

ABSTRACTThe effective fabrication of polar crystalline structures of poly (vinylidene fluoride) (PVDF), such as beta and gamma, is crucial to the development of piezoelectric polymer devices. In this study, we report the effect of pressure on binary fullerene C70/PVDF‐based composite with an overall good C70 dispersion, which was prepared by an easy physical and mechanical route. The C70/PVDF composites were crystallized in a piston‐cylinder high‐pressure apparatus, and the polymeric crystalline structures totally with extended‐chain piezoelectric beta‐ or gamma‐form lamellae were successfully achieved in the composite samples by varying temperature, pressure, crystallization time, and composite composition. The c‐axis thickness of the extended‐chain beta‐form lamellae of PVDF in the composites increased and decreased with the increase of the applied temperature and pressure, respectively, and it increased with the increase of crystallization time. Although C70 was found to be negative for the rapid formation of beta‐form PVDF crystals, it played an important role in the growth of a beta‐form PVDF nanowire with extended‐chain crystalline substructures. The template‐free formation of such piezoelectric nanowires was attributed to a C70‐induced self‐assembly of the polymer, driven by physical interactions at high pressure. The pressure‐crystallized C70/PVDF composites, self‐reinforced with unique one‐dimensional piezoelectric structures, may diversify niche applications in advanced functional polymeric devices. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1823–1833, 2013

Crystallization behavior of poly(lactic acid)/microfibrillated cellulose composite

The effects of fillers on the crystal formation and crystalline structure of poly(lactic acid) (PLA) are unclear. In this study microfibrillated cellulose (MFC) was used as filler to compound with PLA and the crystallization behavior of PLA/MFC composites was investigated. The crystallization process of PLA/MFC composites was observed by wide angle X-ray diffraction (WAXD) and differential scanning calorimeter (DSC) synchronously to investigate the effect of MFC on the formation of crystal and evolvement of crystalline structure of PLA. Results showed that MFC enhanced the crystallization rate drastically, but had no much influence on the crystal form of PLA when isothermally crystallized at different temperature. However, different crystal forms of PLA were obtained respectively from the pure PLA and PLA/MFC composites during the same cooling process. Detailed analysis indicated that the primary cause for the phenomenon was the enhancement of the crystallization temperature of PLA due to the addition of MFC.

Crystalline structures of poly(l-lactide) formed under pressure and structure transitions with heating

The isothermally crystallized poly(L-lactide) (PLLA) samples were obtained at 135 °C under pressures (Pc) ranging from 1 bar to 2.5 kbar. The crystalline structures, the structure transition, and thermal properties of the prepared samples were investigated by wide-angle X-ray diffraction (WAXD), real time synchrotron small-angle X-ray scattering (SR-SAXS) and differential scanning calorimetry (DSC) during this process. The structural parameters, such as the size of crystallites, the inverse spacing, the long periods and lamellae thicknesses decrease with pressure increasing. Based on the peculiarities of crystalline structure and crystallization behaviors, low and high pressure regions were revealed: disordered α crystal was formed in the high pressure region (>1 kbar). A layer located intermediate between crystalline and melt-like regions was observed, which finally took on crystalline order. Reformation, disorder to order transformation, and recrystallization during heating completely changed the previous crystalline and stacking structure, a more stable crystalline structure was newly formed. The melting behaviors of samples indicate the crystalline and stacking structure formed under high pressure are more stable. Operation of lateral growth and thickness growth can explain well the influence of pressure on the structure, stability and the disorder to order transformation.

Role of Ion–Dipole Interactions in Nucleation of Gamma Poly(vinylidene fluoride) in the Presence of Graphene Oxide during Melt Crystallization

The crystallization behavior and crystalline structure of poly(vinylidene fluororide) (PVDF) in the presence of graphene oxide (GO) platelets were investigated using time-resolved Fourier transformation infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), as well as differential scanning calorimetry (DSC). It is shown that GO platelets induce the formation of γ phase when crystallizing from solution, but only α phase forms from melt crystallization. The crystallization kinetics of α phase is promoted due to heterogeneous nucleation ability of GO, which is probably originated from a weak π-dipole interaction between GO and PVDF. Intriguingly, after introduction of strong ion-dipole interactions between GO and PVDF by addition of an ionic surfactant (cetyltrimethylammonium bromide, CTAB), a significant amount of γ crystals are obtained during isothermal melt crystallization. Time-resolved FTIR results further provide a detailed evolution of the γ phase formation, and there are two distinct stages during the melt crystallization in the PVDF/GO composites in the presence of CTAB, i.e., a simultaneous growth of γ and α phases in the first stage, and a solid α to γ transition in the second stage. These results may provide a facile routine to manipulate the crystalline structure in PVDF/GO composites, and thus to gain desirable properties.

Crystalline structure and mechanical property of poly(lactic acid) nanocomposite probed by near-infrared (NIR) hyperspectral imaging

The crystalline structure of a poly(lactic acid) (PLA) nanocomposite is probed by near-infrared (NIR) hyperspectral imaging to derive penetrating insight into its improved mechanical properties by inclusion of organoclay particles. A set of PLA nanocomposite samples are prepared under varying levels of clay content. The variation of the crystalline structure of PLA and corresponding mechanical strength are examined by NIR hyperspectral imaging and thermomechanical analysis (TMA), respectively. By carrying out the detailed analysis of the NIR hyperspectral image, it effectively provided a more detailed picture of the nanocomposite system. Namely, the addition of the clay substantially increases the frequency of the spontaneous nucleation of the PLA crystals. Corresponding decrease of the amorphous portion, in turn, restricts mechanical deformation of the samples under a certain level of load. Consequently, by carrying out detailed band position shift analysis of the NIR image spectra, the chemically meaningful information concerning the nanocomposite system can be effectively extracted.

Blending Effects on Polymorphic Crystallization of Poly(l-lactide)

The effects of miscible blending on the crystallization kinetics and crystalline structure of poly(l-lactide) (PLLA) were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), Fourier transform infrared (FTIR) spectroscopy, and wide-angle X-ray diffraction (WAXD). It was confirmed that the blends of PLLA and poly(d,l-lactide) (PDLLA) are miscible at all compositions. Due to the dilution effect, the crystallization of PLLA was hindered with the presence of PDLLA. The PLLA/PDLLA blends show the irregular or ring-banded spherulites. The polymorphic behavior of PLLA is influenced by the miscible blending with PDLLA. FTIR and WAXD data indicates that the formation of the α-form crystals of PLLA is favored in the blends. With incorporation of 50 wt % PDLLA, the critical temperature for the formation of α′- and α-form crystals decreases from ∼110 (of neat PLLA) to ∼80 °C. The factors affecting the formation of the PLLA α′- and α-form crystals were discussed from the thermod...

Crystallization behavior of nano-composite based on poly(vinylidene fluoride) and organically modified layered titanate

To understand the effect of the nano-filler particles on the crystallization kinetics and crystalline structure of poly(vinylidene fluoride) (PVDF) upon nano-composite formation, we have prepared PVDF/organically modified layered titanate nano-composite via melt intercalation technique. The layer titanate (HTO) is a new nano-filler having highly surface charge density compared with conventional layered silicates. The detailed crystallization behavior and its kinetics including the conformational changes of the PVDF chain segment during crystallization of neat PVDF and HTO-based nano-composite (PVDF/HTO) have been investigated by using differential scanning calorimetric, wide-angle X-ray diffraction, light scattering, and infrared spectroscopic analyses. The neat PVDF predominantly formed α-phase in the crystallization temperature range of 110–150°C. On the other hand, PVDF/HTO exhibited mainly α-phase crystal coexisting with γ- and β-phases at low Tc range (110–135°C). A major γ-phase crystal coexists with β- and α-phases appeared at high Tc (=140–150°C), owing to the dispersed layer titanate particles as a nucleating agent. The overall crystallization rate and crystalline structure of pure PVDF were strongly influenced in the presence of layered titanate particles.

Effect of crystallization temperature on crystal modifications and crystallization kinetics of poly(L‐lactide)

AbstractThe crystalline structure of poly(L‐lactide) (PLLA) have been found to quite depend on the crystallization temperatures (Tcs), especially in the range of 100−120°C, which is usually used as the crystallization temperature for the industrial process of PLLA. The analysis of wide‐angle X‐ray diffraction and Fourier transformed infrared spectroscopy revealed that 110°C is a critical temperature for PLLA crystallization. At Tc < 110°C and Tc ≥ 110°C, the α′ and α crystals were mainly produced, respectively. Besides, the structural feature of the α′‐form was illustrated, and it was found that the α′‐form has the larger unit cell dimension than that of the α‐form. Moreover, the crystallization kinetics of the α′ and α crystals are different, resulting in the discontinuousness of the curves of spherulite radius growth rate (G) versus Tc and the half time in the melt‐crystallization (t1/2) versus Tc investigated by Polarized optical microscope and Differential scanning calorimetry, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Crystalline structure of poly(hexamethylene succinate) and single crystal degradation studies

The morphology of solution grown single crystals of poly(hexamethylene succinate) (PE 6 4) was investigated using dilute alcohol or diol solutions by isothermal crystallization. Increasing temperatures changed the morphology of truncated rhombic crystals, which became lenticular crystals. Spiral growths and multilayered crystals as well as characteristic striations which mainly form in the {110} sectors were often observed. A regular folding surface was found by using polyethylene decoration techniques. Lamellar crystals were easily degraded with different lipases. A preferential enzymatic attack was observed to occur on the crystal edges, giving rise in some cases to highly irregular borders with a fringed texture.Lamellae gave rise to well resolved electron diffraction patterns that allowed the main packing characteristics to be determined. Fiber X-ray diffraction patterns indicate a quasi planar zig-zag conformation and a large unit cell containing eight molecular segments. This cell could not be deduced from the typical hk0 electron diffraction pattern but could be assessed from the patterns of tilted specimens.Simulation of electron diffraction patterns indicates that molecular segments are arranged with setting angles close to ±46° or ±226°. In addition, neighbouring chains along both a- and b-axis have setting angles differing by 180° in order to justify the deduced cell dimensions.

Fine structure and enzymatic degradation of poly[( R)-3-hydroxybutyrate] and stereocomplexed poly(lactide) nanofibers

Fiber morphology and crystalline structure of poly[( R)-3-hydroxybutyrate] (P(3HB)) and stereocomplexed poly(lactide) (PLA) nanofibers were investigated by using scanning and transmission electron microscopies and X-ray and electron diffractions. In the P(3HB) nanofibers spun from less than 1 wt% 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) solution, planar zigzag conformation (β-form) as well as 2 1 helix conformation (α-form) structure was formed. Based on the electron diffraction measurement of single P(3HB) nanofiber, it was revealed that the molecular chains of P(3HB) align parallel to the fiber direction. From the enzymatic degradation test of P(3HB) nanofiber, it was shown that β-form molecular chains are degraded more preferentially than α-form chains. Stereocomplexed PLA nanofibers were electrospun from 1 wt% poly( l-lactide)/poly( d-lactide) (PLLA/PDLA) solution in HFIP, which contains equal amounts of PLLA and PDLA. While as-spun stereocomplexed PLA nanofiber was amorphous, PLA nanofiber annealed at 100 °C contained only racemic crystal. It was supposed that the crystallization behavior of stereocomplexed PLA in the nanofiber is affected by the electrospinning process, which forcibly exerts the strain onto the polymer chains.