Crystallites In Poly Research Articles

A Facile Strategy to Enhance the Formation of Stereocomplex Crystallites in Poly(L-lactic acid)/Poly(D-lactic acid) Blend with High Molecular Weights

A Facile Strategy to Enhance the Formation of Stereocomplex Crystallites in Poly(L-lactic acid)/Poly(D-lactic acid) Blend with High Molecular Weights

Enhanced formation of stereocomplex crystallites in Poly(l-lactic acid)/Poly(d-lactic acid) blends by silk fibroin nanodisc

Blending of poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) is known to form stereocomplex crystallites (SC). In this research, the impact of a biobased filler, silk fibroin nanodisc (SFN), on the crystallizability of the PLLA/PDLA (50/50) blend was examined by differential scanning calorimetry (DSC), polarizing optical microscope (POM), and time-resolved small- and wide-angle X-ray scattering (SWAXS) measurements. The crystallization temperature (Tc), measured by non-isothermal DSC cooling scan, was increased by the addition of 1% SFN in the PLLA/PDLA (50/50) blend. The inclusion of SFN enhanced the formation of SC, as indicated by increasing the melting enthalpy of SC. Isothermal crystallization study at 110 °C by DSC and WAXS suggested that the SFN enhanced the SC crystallization while it suppressed the homocrystal (HC) crystallization, as indicated by crystallization half-time (t0.5) values. It was found that SFN not only enhances the SC crystallizability but also increases the fraction of SC crystals in the PLLA/PDLA blend. The long period of HC and SC lamellar stack was reduced by the addition of SFN, as indicated by the SAXS results. The POM results suggested that SFN significantly enhanced the number of SC nuclei for the isothermal crystallization at 170 °C from the melt.

Tailor-Made Dispersion and Distribution of Stereocomplex Crystallites in Poly(l-lactide)/Elastomer Blends toward Largely Enhanced Crystallization Rate and Impact Toughness.

Stereocomplex (SC) crystallites, formed between poly(l-lactide) (PLLA) and poly(d-lactide), exhibit great potential to substantially enhance crystallization rate of PLLA-based materials as an eco-friendly nucleating agent. However, the nucleation efficiency of the SC crystallites is still far below an expected level, mostly on account of their strong aggregation tendency in PLLA/PDLA melts. Herein, taking PLLA/poly(ethylene-methyl acrylate-glycidyl methacrylate) (E-MA-GMA) blends as an example, we report a unique and facile strategy to control the dispersion and distribution of SC crystallites within the PLLA matrix by using elastomeric E-MA-GMA as carrier for the incorporation of PDLA. To do this, PDLA was first blended with E-MA-GMA or chemically grafted onto the E-MA-GMA. During subsequent melt-blending of PLLA and the E-MA-GMA/PDLA master batch, the PDLA chain clusters predispersed in the E-MA-GMA phase can gradually migrate into PLLA matrix and then collaborate with the matrix chains to form large amounts of tiny and well-dispersed SC crystallites. Compared with the SC-crystallite agglomerates formed by the direct melt-blending of PLLA and PDLA components, such tiny SC crystallites are much more effective in accelerating PLLA matrix crystallization. More interestingly, when PDLA chains are grafted onto the EMA-GMA, the formed SC crystallites tend to preferentially distribute at the blend interface and thus induce not only optimal nucleation efficiency but also superior impact toughness because these interface-localized SC crystallites can also serve as bridges to enhance interface adhesion. This work could open a new avenue in designing heat-resistant and supertough PLLA blends via controllable construction of SC crystallites.

Influence of high pressure on higher-order structures of poly(oxyethylene) in its blend with poly(d,l-lactide)

The effect of high pressure on the higher-order structures of poly(oxyethylene) (PEG) crystallites in poly(d,l-lactide)/poly(oxyethylene) (PDLLA/PEG) blends during melting and recrystallization was investigated by in situ small-angle X-ray scattering (SAXS) measurements. It was found that melting temperature (T m) increases at 50 MPa in accordance with the prediction by the Clausius–Clapeyron equation. However, T m at slightly pressurized state (5 MPa) surprisingly decreased, suggesting that the effect of pressure is not so straightforward. It may be due to an increase of the miscibility under higher pressure, causing the melting point depression. Meanwhile, an advantage of analyses of SAXS data enabled us to determine directly discrete distribution of lamellar thickness as a function of temperature under pressure. As a result, lamellar thickening was observed at 5 and 50 MPa as temperature approaches closer to the melting point, but the tendency of thickening was lesser as compared to that observed at ambient pressure.

Formation of piezoelectric β-phase crystallites in poly(vinylidene fluoride)-graphene oxide nanocomposites under uniaxial tensions

A combination of chemical addition and mechanical deformation is employed to develop a nearly pure β crystalline phase in poly(vinylidene fluoride) (PVDF). The mechanical strains for the formation of pure β phase in PVDF-graphene oxide (PVDF-GO) nanocomposites are found to be only half of that for PVDF deformed at the same temperature. Based on the creep experiments, piezoelectric force microscopy and mechanical anelastic relaxation, it is shown that the attachments of PVDF molecule chains to the GO sheets caused by the interaction between the –CF2 or –CH2 groups of PVDF and the functional groups of GOs could facilitate the formation of piezoelectric β-phase crystallites in the stretched nanocomposites. A model is proposed to elucidate the easy formation of the piezoelectric β phase in the PVDF-GO nanocomposites under uniaxial tensions.

Poor solvent and thermal annealing induced ordered crystallites in poly(3-dodecylthiophene) films

The influence of poor solvent and thermal annealing, with their specific roles, in the crystalline ordering of P3DDT films, which is important to their performance as semiconducting materials, were investigated using complementary techniques.

Dynamics in Crystallites of Poly(ε-caprolactone) As Investigated by Solid-State NMR

We investigate the molecular dynamics within the crystallites of poly(e-caprolactone), PCL, crystallized from the melt by means of high-field 13C and low-field 1H NMR spectroscopy, addressing the question of whether it can be classified as a “crystal-fixed” polymer without chain motion through the crystallites. We address fast, slow, and intermediate-regime (microseconds to milliseconds time scale) motions by means of high-resolution of 13C DIPSHIFT and CODEX MAS experiments as well as low-resolution static 1H FID and MSE measurements over a range of temperatures. The DIPSHIFT data provide information on motionally averaged 13C–1H dipole–dipole couplings and indicate the presence of fast (≤1 μs) methylene group librational motions within the crystalline phase, where the amplitudes increase with increasing distance from the rather rigid ester groups. The CODEX experiments, addressing slow (≥ms) local rotations of the chemical-shift anisotropy tensors, suggest the absence of slow intracrystallite chain dyna...

The deformation of the chain molecules and crystallites in poly([ R]-3-hydroxybutyrate) and poly(4-hydroxybutyrate) under tensile stress

The uniaxial stretching behaviour of poly([ R]-3-hydroxybutyrate) (P(3HB)) and poly(4-hydroxybutyrate) (P(4HB)) molecules were characterized using molecular simulation techniques. The stretching deformation mechanism of P(3HB) molecule made progress in the two-step feature and P(4HB) in the one-step mechanism. The first step mechanism of P(3HB) (from α-form to β-form) was to disentangle the helical structure of the molecule and the second was to elongate the molecule like a spring. The uniaxial stretching deformation mechanism of P(4HB) molecule was the same as the latter case of P(3HB). The modulus in the stretching deformation of β-form P(3HB) asymmetric unit was 44.26 kJ mol −1 nm −2 and that of P(4HB) was 34.00 kJ mol −1 nm −2. The elastic properties of the crystallites were also examined. The P(3HB) crystallite was not stretched elastically in the first step deformation. The elastic constant in the second step stretching of P(3HB) unit cell was 0.58 GPa. That of P(4HB) unit cell was 0.74 GPa.

Lamellar morphology of random metallocene propylene copolymers studied by atomic force microscopy

Four sets of propylene based random copolymers with co-units of ethylene, 1-butene, 1-hexene and 1-octene, and a total defect content up to ∼9 mol% (including co-unit and other defects), were studied after rapid and isothermal crystallization. Etched film surfaces and ultramicrotomed plaques were imaged so as to enhance contrast and minimize catalyst and co-catalyst residues. While increasing concentration of structural irregularities breaks down spherulitic habits, the formation of the gamma polymorph has a profound effect on the lamellar morphology. Lamellae grown in the radial axis of the spherulite and branches hereon are replaced in γ-rich copolymers with a dense array of short lamellae transverse or tilted to the main structural growth axis. This is the expected orientation for γ iPP branching from α seeds. Spherulites are formed in copolymers with non-crystallizable units (1-hexene and 1-octene) up to ∼3 mol% total defect content and were observed up to ∼6 mol% in those with partially crystallizable comonomers (ethylene and 1-butene). However, lamellae were observed in all the copolymers analyzed, even in the most defective ones, highlighting the important role of the gamma polymorph in propagating lamellar crystallites in poly(propylenes) with a high concentration of defects. Long periods measured from AFM and SAXS are comparatively analyzed.

The existence of a stable β form in oriented poly(butylene terephthalate)

The existence of stable β form crystallites in poly(butylene terephthalate) has been investigated. Wide angle X-ray measurements suggest that such crystallites are only stable provided that they are of comparatively small dimensions and that they are then poorly connected to the bulk polymer. A simple theoretical model is presented to explain the stability of the crystals in terms of the contributions to the free energy from both the crystallites and the surrounding amorphous material.

Formation of .BETA.-sheet crystallite in poly(.GAMMA.-methyl L-glutamate) by immersing into formic acid and drawing.

The processes of the formation of β-sheet crystallites in poly (γ-methyl L-glutamate) were investigated by infrared spectroscopy and X-ray diffraction. By immersion into a formic acid-water (50/50v/v) mixture, the β-sheet crystallites did not form at room temperature, while the size of α-helix crystallites increased and the α-helices became to be packed more tightly each other in the crystallites. At higher temperatures, the β-sheet crystallites grew from the random-coil conformation even immediately after the immersion. At the same time, the α-helices existing at the surface of the α-helix crystallites were transformed to the random-coil conformation and then turned to the β-sheet crystallites. By drawing of untreated specimen, the β-sheet crystallites grew slightly from the random-coil conformation. When the specimen was drawn after immersing into a formic acid-water mixture for 2h at 70°C and 80°C, the β-sheet crystallites grew from the remaining random-coil conformation and the α-helices existing at the surface of α-helix crystallites were transformed to the random-coil conformation and then the β-sheet crystallites formed from the random-coil conformation.

Glass transition, melting and crystallization of poly (chlorotrifluoroethylene) at high pressures

Glass-transition temperature, melting point, energetic parameters of nucleation, and morphology of crystallites in poly(chlorotrifluoroethylene) have been investigated in dependence on hydrostatic pressure applied during crystallization from the melt; high-pressure dilatometry, optical and electron microscopy, and electron diffraction have been used. An usually rapid increase (in comparison with otther flexible-chain polymers) of glass-transition and melting temperatures with pressure has been observed, accompanied at pressures higher than 28 MPa by a stepwise change in surface free energy at the frontal faces crystallization nuclei, brought about by a transition of macromolecules from a folded to a more extended conformation in the crystal.

Terpolymers. III. Isochronal viscoelastic parameters for terpolymers of vinyl stearate, vinyl acetate, and vinyl chloride

AbstractIsochronal viscoelastic parameters were collected for many of the copolymers, terpolymers, and diluent mixtures whose mechanical properties at ambient temperatures were reported in the preceding paper. In the polymeric systems, vinyl stearate, acting as the primary internal plasticizer, was introduced into terpolymers by displacing vinyl acetate from base copolymers of vinyl acetate and vinyl chloride, across the range of composition. In the diluent mixtures, poly(vinyl chloride) was plasticized by di‐2‐ethylhexyl phthalate across the range of compositions. For direct comparison with the mixtures, vinyl chloride was plasticized by copolymerization with vinyl stearate across the same range of compositions. Moduli for the co‐ and terpolymers reached the low values characteristic of soft materials at room temperature only through a short range of vinyl stearate composition. At higher internal plasticizer compositions, side‐chain crystallization stiffened the samples and raised their moduli. In contrast, moduli for the mixtures decreased steadily with increase in diluent at ambient temperature. The effective use temperature ranges were narrow for the co‐ and terpolymers but broad for the mixtures. Curve broadening was similar for both types of systems, but reached a maximum at about 40 weight‐% plasticizer for the diluent mixtures. The slopes of the glassy modulus with decreasing temperature at 50°C below Tg for the vinyl stearate copolymers were relatively large. However, moduli close to that of poly(vinyl chloride) were reached only near the temperature range associated with the γ‐transition. Consequently, this behavior was attributed to motions of the side chains in the glassy matrix. Room temperature moduli, which could be obtained before the onset of melting, were correlated with the fractional side‐chain crystallinity for polymers having a high vinyl stearate content. From this relation, the modulus for the hexagonal crystal form of the side‐chain crystallites of poly(vinyl stearate) was estimated to be 1.2×1010 dynes/cm2. Moduli for the glassy amorphous phase of this same polymer appeared to have one sixth of this value at 40°C below the glass transition. The glass transition temperature occurred about 10° below the inflection temperature at 109 dynes/cm2, as an average for all of the systems studied.