2D Wide-angle X-ray Diffraction Research Articles

In Situ Synthesized Self-Reinforced HDPE/UHMWPE Composites with High Content of Less Entangled UHMWPE and High Gradient-Distributed Oriented Structures

In this study, tailored polyethylene reactor blends with the in situ embedding of a weakly entangled ultra-high-molecular-weight polyethylene (UHMWPE) were synthesized by the polyhedral oligomeric silsesquioxane modified Ziegler–Natta (ZN) catalysts using a two-stage cascade polymerization technique. Holistic improvement of strength/stiffness/toughness was realized by the common injection modeling owing to the enhanced formation of an orientated structure which was verified by the patterns of two-dimensional (2D) small-angle X-ray scattering and 2D wide-angle X-ray diffraction, as well as the fracture morphology. 30 wt % of the less entangled UHMWPE was successfully incorporated into the high-density polyethylene (HDPE) matrix to achieve a synchronously increased tensile strength (52.4 MPa, +97.7%), Young’s modulus (604.2 MPa, +43.6%), and impact resistance (74.4 kJ/m2, +675%), compared with those of the benchmarked HDPE. However, dissipation of a shish-kebab structure was pronounced in the depth direction of the HDPE spline reinforced with the disentangled UHMWPE. This dissipation was proved to partially sacrifice the strength and stiffness. Importantly, the impact strength is greatly enhanced (+140%) due to the cocrystallization effect of the disentangled linear UHMWPE chains with the HDPE matrix. The HDPE matrix reinforced with the weakly entangled UHMWPE presents wider gradient distribution and orientation degree distribution of oriented structures (including shish-kebab and stacked lamella) along the depth direction. Thus, the balance of strength/stiffness/toughness was synergistically improved with the wider gradient distribution of oriented structures. This in situ polymerization method with the weakly entangled UHMWPE offers a promising routine for achieving the high-performance polyethylene commodity.

Helical carbon nanotubes filled phase change composites with reversible plasticity shape memory and photo-thermal conversion functions towards wide-temperature-range battery thermal management

The rigidity of battery thermal management systems (BTMS) and harsh environments are the obstacles to the development of fast charging/discharging of lithium-ion batteries. Herein, a straightforward path is provided to solve the above dilemma by synthesizing styrene-b-(ethylene-co-butylene)-b-styrene/paraffin wax/helical carbon nanotubes (SEBS/PW/HCNTs). 2D wide-angle X-ray diffraction demonstrated that the PW solid skeleton of SEBS/PW composites oriented along the stretching direction under the tensile stress resisted the elastic potential energy of SEBS to achieve room-temperature shape fixation. Furthermore, HCNTs as a three-dimensional and photo-thermal conversion filler were incorporated into SEBS/PW to impart the composites with rapid light-actuated shape memory and light-thermal conversion/storage capacities. Finally, a BTMS with high phase change efficiency (95.3%), reversible plasticity shape memory (RPSM), photo-thermal conversion and wide-temperature thermal management range from −60 to 50 °C was manufactured by combining the heating and cooling subsystems, which exhibited vast prospects in battery thermal management fields.

Insights into strain-induced solid mesophases in melt-spun polymer fibers

This article provides an overview of strain-induced solid mesophases in polymer fibers, melt-spun from amorphous (polycarbonate, cyclo-olefin polymer, copolyamide, polyethylene terephthalate glycol) and semi-crystalline materials (polyethylene terephthalate, poly-3-hydroxybutyrate). The discussed mesophases are made of stretched, conformationally disordered macromolecules that are highly oriented along the fiber axis, and that reveal variations in their lateral spacing. Fitting algorithms for respective wide-angle x-ray diffraction (WAXD) patterns are put forward, and are directly tested on fibers melt-drawn from amorphous as well as semi-crystalline polymers. Equatorial, meridional, off-axis and azimuthal profiles are extracted from WAXD patterns and are simultaneously fitted. Best fit parameters contain detailed structural information, and lead to simulated 2D WAXD patterns, which in turn can be used to quantify the phases that are present in the fibers. We postulate that mesophases, which lead to broad equatorial reflections in WAXD patterns, can be found in all types of drawn melt-spun polymer fibers.

One-Pot Synthesis of Supertough, Sustainable Polyester Thermoplastic Elastomers Using Block-Like, Gradient Copolymer as Soft Midblock

It remains challenging to synthesize supertough thermoplastic elastomers (TPEs) since the stretchability and tensile strength are mutually exclusive. Here, we report a one-pot strategy for the prep...

Microstructural Evolution of Poly(ε-Caprolactone), Its Immiscible Blend, and In Situ Generated Nanocomposites.

Polymer–polymer systems with special phase morphology were prepared, leading to an exceptional combination of strength, modulus, and ductility. Two immiscible polymers: poly(ε-caprolactone) (PCL) and polyhydroxyalkanoate (PHA) were used as components for manufacturing a nanoblend and a nanocomposite characterized by nanodroplet-matrix and nanofibril-matrix morphologies, respectively. Nanofibrils were formed by high shear of nanodroplets at sufficiently low temperature to stabilize their fibrillar shape by shear-induced crystallization. The effects of nanodroplet vs. nanofiber morphology on the tensile mechanical behavior of the nanocomposites were elucidated with the help of in situ 2D small-angle X-ray scattering, microcalorimetry and 2D wide-angle X-ray diffraction. For neat PCL and a PCL/PHA blend, the evolution of the structure under uniaxial tension was accompanied by extensive fragmentation of crystalline lamellae with the onset at strain e = 0.1. Limited lamellae fragmentation in the PCL/PHA composite occurred continuously over a wide range of deformations (e = 0.1–1.1) and facilitated plastic flow of the composite and was associated with the presence of a PHA nanofiber network that transferred local stress to the PCL lamellae, enforcing their local deformation. The PHA nanofibers acted as crystallization nuclei for PCL during their strain-induced melting–recrystallization.

Properties, X-ray data and 2D WAXD fitting procedures of melt-spun poly(ɛ-caprolactone).

Rheological and thermal properties of the poly(ɛ-caprolactone) (PCL) polymer are presented in Section 1.1. Section 1.2 summarizes results of melt-spun PCL filaments. Specifically, we show the necking point stabilization during high-speed online drawing in Section 1.2.1, filament morphology in Section 1.2.2, wide-angle X-ray diffraction (WAXD) fitting results in Section 1.2.3, WAXD patterns of aged fibers in Section 1.2.4, crystallinity analysis in Section 1.2.5 and small-angle X-ray scattering (SAXS) analysis results in Section 1.2.6. Details about the materials, experimental and analytical methods are given in Section 2. Of particular interest may be the simulation and fitting procedures of 2D WAXD patterns, which are summarized in Section 2.7.2. For more information see the publication by Selli et al. 'Mesophase in melt-spun poly(ɛ-caprolactone) filaments: structure–mechanical property relationship' [1].

Mesophase in melt-spun poly(ϵ-caprolactone) filaments: Structure–mechanical property relationship

Fine poly(ϵ-caprolactone) (PCL) filaments (diameter: 59–92 μm) were successfully melt-spun with modified drawing setups to prevent draw instabilities. Depending on the production parameters, different mechanical properties were obtained (tensile strength: 302–456 MPa, elongation at break: 69–88%). These variations are related to subtle structural differences, which we have analyzed with wide-angle x-ray diffraction (WAXD) and small-angle x-ray scattering (SAXS). SAXS was used to determine crystal widths and the spacing between crystals along the filament axis. Additionally, 2D WAXD patterns were simulated and WAXD profiles were fitted. The detailed 2D WAXD analysis revealed that a highly-oriented non-crystalline mesophase is present in drawn PCL filaments, which is most-likely situated in-between PCL crystals. A large amount of this mesophase (>16%), combined with high crystalline orientation and perfect crystals, led to higher tensile strength values. We also confirmed that PCL chains pack with non-planar chain conformations in the unit cell.

Radiation assisted pre-oxidation of polyacrylonitrile fiber: Graphite formation and lower crystal size revealed by 2D WAXD at a synchrotron facility

To accurately understand how irradiation treatment influences the crystal structure variation of polyacrylonitrile (PAN) fibers during the pre-oxidation process, the crystal structure evolution of the irradiated PAN fibers after pre-oxidation was investigated by synchrotron wide-angle X-ray diffraction (WAXD) at beamline BL16B1 in transmission geometry, using a three-slit system at the Shanghai Synchrotron Radiation Facility. By employing highly sensitive 2D WAXD analysis, we observed the deformation of the orientation structure in the irradiated PAN fibers. It was found that irradiation treatment can reduce the quasicrystal structure formed in the early stage of the pre-oxidation process (200–220 °C). Irradiation further enhanced the decrease in crystal size, crystallinity, and preferred orientation during the pre-oxidation. The diffraction peaks for PAN fibers at q = 12 nm−1 and 20.7 nm−1 almost disappeared at 260 °C; meanwhile, a new peak appeared for the irradiated samples at q = 18.2 nm−1, indicating the formation of a graphite structure, which confirmed by Raman spectra. The results showed that irradiation treatment can accelerate the pre-oxidation reaction of PAN fiber, reduce the time required for pre-oxidation, and improve the properties of carbon fiber by reducing the crystal size and crystallinity.

An Azoester-containing Photoresponsive Linear Liquid Crystal Polymer with Good Mesophase Stability

Photoresponsive linear liquid crystal polymers (LLCPs) are attractive because of the excellent stimuli-responsibility and the good processability. In this study, a new photoresponsive LLCP containing azoester (PC11AE6) with good mesophase stability was synthesized by ring-opening metathesis polymerization. By introducing photoresponsive azoester mesogenic unit, which has high rigidity and a large length-diameter ratio, the resultant polymer possesses a broad mesophase temperature interval (isotropic temperature = 180 °C). A study on mesophase by 2D-wide angle X-ray diffraction indicated that the mesogens were orientated spontaneously into smectic A phase after annealing. The orientated films and fibres exhibited macroscopic, rapid and reversible deformations under light irradiation as a result of the photoisomerization of azoester as confirmed by UV-Vis absorption spectrophotometry. We anticipate that this work provides a strategy for preparing LLCP with a broad mesophase temperature range, which is positive for potential applications.

Melt-spun industrial super-strong polycaprolactam fiber: Effects of tie-molecules and crystal transformation

Effective improvement molecular orientation in the amorphous region and regulating crystallization transformation behavior is of great significance for the industrial production of ultra-strength polycaprolactam (HSPA6) fiber. In this work, the effects of adding a small quantity of high molecular weight polycaprolactam (HmwPA) on the crystal transformation, melt viscoelasticity, molecular orientation and mechanical properties of HSPA6 fibers were systematically investigated. The results indicated that HmwPA increased the elastic modulus and loss modulus of HSPA6 melt and suppressed molecular relaxation during drawing to form a crystal structure dominated by α-form. As such, the tensile strength and elongation at break of HSPA6 fiber reached 10.32 cN/dtex and 18.7%, respectively. 1D and 2D wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and birefringence observations demonstrated that the HmwPA not only inhibited the destruction of the crystal structure during fiber drawing but also increased the molecular orientation in the amorphous region from 63.1% to 70.1%, while maintaining the crystal orientation to about 95%.

Diversified α-phase nanostructure of isotactic polypropylene under cylindrical confinement via cross diffraction analysis

Understanding polymer nanostructures is a prerequisite to manipulate their physical properties. Molecular self-assembly under confinement effectively generates novel polymer nanostructures. However, in one confined system, diffraction signals of different nanostructures are merged in a typical two-dimensional (2D) wide-angle X-ray diffraction (WAXD) measurement. For comparison, selected-area electron diffraction (SAED) of transmission electron microscopy can precisely capture the “local” diffraction signal of an individual nanoscale entity. Here, using isotactic polypropylene (i-PP) as a model polymer, we have demonstrated a cross-analysis of global X-ray and local electron diffraction results to fully reveal the structural details of i-PP nanorods. For the first time, we have decomposed completely the “mixed” 2D WAXD patterns of i-PP nanorods into five types of α-phase nanostructures: (a). Left-tilted daughter crystals; (b) Right-tilted daughter crystals; (c) Double-tilted daughter crystals; (d) a*-axis oriented crystals; (e) b-axis oriented crystals.

Effect of Wet Spinning and Stretching to Enhance Mechanical Properties of Cellulose Nanofiber Filament

Long filament made with nanocellulose has been researched due to its eminent mechanical and physical properties for next generation of natural fiber reinforced polymer composites. Wet spinning process for long filament fabrication in conjunction with stretching method has advantages of high efficiency and low-cost. To fabricate homogeneous and strong cellulose nanofiber filament, this paper experimentally investigates the process parameters, including spinning speed, pre-dry temperature and inner diameter of needle. In addition to the spinning process, a mechanical stretching process is taken into account to further improve the mechanical properties of the cellulose nanofiber filament. The effects of wet spinning and stretching are evaluated by using scanning electron microscope, tensile test and 2D wide angle X-ray diffraction. As a result, the stretched cellulose nanofiber filament exhibits its Young’s modulus of 37.5 GPa and tensile strength of 543.1 MPa, which are significantly improved from the previous reports. All about the fabrication process, characterization and evaluation of the cellulose nanofiber filaments are illustrated.

Revisiting the Thermal Transition of β-Form Polyamide-6: Evolution of Structure and Morphology in Uniaxially Stretched Films

Structure and morphology evolution of the uniaxially stretched polyamide-6 (PA6) film with the β-form upon heating were investigated mainly by synchrotron two-dimensional (2D) wide-angle X-ray diffraction and small-angle X-ray scattering. For comparison, thermal transitions of the oriented PA6 samples with the α- and γ-form were also monitored, which undergo “incomplete Brill transition” and direct melting, respectively. Using the results of oriented α- and γ-PA6 as the references, we confirm that the stretched β-PA6 is mesomorphic, which can be viewed as a solid mesophase with smectic B-like structure. We identify that upon heating the stretched β-PA6 reorganizes dominantly into γ-form crystal with the chain orientation unchanged, accompanied by the formation of a little amount of α-PA6 crystallites. Further heating to above the melting temperature of γ-PA6, the α-PA6 crystals grow through a recrystallization process. The lamellae resulting from reorganization exhibit a distribution of orientations, and the α-PA6 lamellae formed at high temperatures have the lamellar basal surface normal parallel to the stretched direction. We consider that the abundant hydrogen bonds in the stretched β-PA6 film construct a network, providing the confinement effect to reduce the chain mobility and thus favor the formation of γ-form. The lamellae with the basal surface normal tilted relative to the stretched direction can also be attributed to the hydrogen-bonded network of oriented chains.

Synthesis of poly(benzobisoxazole-co-imide) and fabrication of high-performance fibers

A novel heterocyclic and plank-shape diamine monomer, 2,6-(4,4′-diaminodiphenyl) benzo[1,2-d:5,4-d'] bisoxazole (PBOA), was successfully synthesized from readily available compounds of 4,6-diaminoresorcinol dihydrochloride (DAR) and p-aminobenzoic acid (PABA). A series of poly(benzobisoxazole-co-imide) (PBOI) fibers based on 3,3′,4,4′-biphenyltetracarboxylic anhydride (BPDA), 4,4′-diaminodiphenyl ether (ODA) and PBOA were fabricated via a two-step wet-spinning method. PBOA was characterized in detail, and the effect of the monomer in the polymer backbones on the fibers' microstructure and properties were described. 2D wide-angle X-ray diffraction indicated that the incorporated PBOA in the BPDA-ODA polyimide backbone is beneficial for forming well-defined crystalline regions in the resulted fibers during the thermal stretching process and significantly improving the crystallinity and crystal orientation of the drawn PBOI fibers. Small-angle X-ray scattering patterns of the drawn PBOI fibers suggested the presence of typical periodic lamellar crystal in the fibers. It is shown that increasing PBOA contents will result in higher values of the long period (L) and the lamellar thickness (lC). Maximum improvements of 153% in tensile strength and 282% in modulus were achieved when increasing the molar content of PBOA in the mixed diamine from 10 mol% to 50 mol%. Correspondingly, the temperature at the maximum degradation rate (Td-max) and glass transition temperature (Tg) of resulted PBOI fibers in nitrogen increased by 28 and 30 °C, respectively, making these novel polymeric fibers as good reinforcements in fabricating advanced composites.

Deformation X-ray study of propylene-based elastomers with controlled sequence distributions

Three iso-specific organometallic catalysts for ethylene and propylene copolymerization with varying products of ethylene and propylene reactivity ratios were utilized to synthesize equal-molecular-weight propylene-based elastomers (PBEs) of alternating (aPBE), random (rPBE), and blocky (bPBE) backbone sequences. To compensate for the variations in catalyst iso-specificity, the ethylene content of PBEs was varied between 11 wt % and 16 wt % in order to maintain constant amount of 50% isotactic propylene trimer concentration. Their microstructural evolutions during the initial extension-retraction cycle at a low strain ranging from 0% to 100% were investigated using 2D Wide-Angle X-ray Diffraction (WAXD) and Small-Angle X-ray Scattering (SAXS) techniques. WAXD results revealed that the crystallinity values of these PBEs changed little during the extension-retraction cycle. However, SAXS results indicated that bPBE formed distinctly ordered stacked lamellae morphologies, whereas the crystalline-amorphous repeat units in aPBE and rPBE were more disordered. In addition, the long period of the bPBE lamellar structure exhibited elastic affine deformation. The analysis suggested that initially randomly arranged crystalline lamellae in PBE become partially oriented, but not destroyed, with increasing strain, where over half of the lamellar structures were orientated parallel to the stretching direction when the strain reached 100%. Upon cessation of stress, these orientated crystalline structures could recover back to their isotropic state.

Pyrene-Based Asymmetric Supramolecule: Kinetically Controlled Polymorphic Superstructures by Molecular Self-Assembly

To understand the kinetically controlled polymorphic superstructures of asymmetric supramolecules, a pyrene-based asymmetric supramolecule (abbreviated as Py3M) was newly synthesized by connecting two pyrene headgroups (Py) to a biphenyl-based dendritic tail (3M) with an isophthalamide connector. On the basis of thermal, microscopic, spectroscopic, and scattering results, it was realized that Py3M exhibited the monotropic phase transition between a stable crystalline phase (K1) and a metastable crystalline phase (K2). This monotropic phase transition behavior was mainly originated from the competitions of intra- and intermolecular interactions (π–π interactions and hydrogen bonds) as well as from the nanophase separations. From the two-dimensional (2D) wide-angle X-ray diffraction patterns and transmission electron microscopy images of the self-assembled Py3M superstructures, it was found that Py3M formed two synclinically tilted crystalline superstructures: the 6.75 and 4.4 nm periodicities of layered st...

Isotropically small crystalline lamellae induced by high biaxial-stretching rate as a key microstructure for super-tough polylactide film

At present, polylactide (PLA) film with high toughness is on expectation, but in general, it is brittle with 45 MPa tensile strength and only 3% elongation at break. The present work clarifies that isotropically small crystalline lamellae is the key microstructure to obtain super-tough PLA (180 MPa tensile strength and 80% elongation at break). The systematic study on two parameters of biaxial-stretching technique, i.e., stretching rate and draw ratio, allows us understanding the development of microstructure, especially the crystalline phase, the regular chain packing in the crystal lattice, and the evolution of the higher-order structure. The integrated structural analyses based on Fourier transform infrared spectroscopy (FTIR), 2D-wide angle X-ray diffraction (2D-WAXD) and 2D-small angle X-ray scattering (2D-SAXS) declare that the structurally-irregular amorphous PLA starts to develop the mesophase and δ-crystal (including α-crystal) with the crystallite size of several tens of nanometers by slow biaxial-stretching (3 mm/s). At this stage, the biaxially oriented PLA (BOPLA) still shows relatively poor mechanical properties. When the stretching rate and the draw ratio increased above a certain level, i.e., 75 mm/s and 5 × 5, respectively, the small δ-crystallites of about 10 nm size with isotropic orientation are mainly formed. This structural evolution has been found to result in the drastic increase of the toughness of BOPLA film, which is about 4 times higher than the PLA film produced by conventional stretching. In this way, the present work shows for the first time that the simple way to toughen the PLA film is to induce a well-dispersed higher-order structure consisting of many but small δ-crystallites as seen in the model case of BOPLA.

Morphology and mechanical behavior of isotactic polypropylene with different stereo-defect distribution in injection molding

Large amount of work has been published on the isotacticity–properties relationship of isotactic polypropylene (iPP). However, the stereo-defect distribution dependence of morphology and mechanical properties of iPP injection molding samples is still not clear. In this study, two different isotactic polypropylene (iPP) resins (PP-A and PP-B) with similar average isotacticity but different stereo-defect distribution were selected to investigate the morphology evolution and mechanical properties (tensile and notching) of their injection molding samples using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), 2D wide angle X-ray diffraction (2D-WAXD), and scanning electron microscope (SEM). The results of DMA showed that the molecular movement ability of PP-A (with less uniform distribution of stereo-defect) was stronger than that of PP-B, meanwhile the analysis of DSC and SEM suggested that after injection molding, smaller spherullites, and crystals with higher perfection had formed in the specimens of PP-A. The resulting of tensile properties of PP-A were found to be better than that of PP-B. The results of morphology evolution by SEM observation and 2D-WAXD showed that PP-A is more likely to occur interspherulite deformation and can disperse the tensile stress more efficiently, and therefore, its crystal structure can withstand a greater force when tensile stress is applied. On the other hand, PP-B has larger spherulites and boundaries, and low perfection of lamellaes, and the intraspherulte deformation tend to take place. It is easier for the crystal of PP-B to be broken up and reoriented along the tensile direction. Copyright © 2014 John Wiley & Sons, Ltd.

Influence of the spacer and molecular weight on the phase behavior of side-chain liquid crystalline polymers containing triphenylene discotic mesogen units as side groups

Two series of side chain liquid crystalline polymers (SCLCPs), poly{[3,6,7,10,11-pentakis(hexyloxy)-2-oxytriphenylene]methacrylate} (PMTS with no flexible spacer) and poly{6-[3,6,7,10,11-pentakis(hexyloxy)-2-oxytriphenylene]hexyl methacrylate} (PMT6S with 6 methylene units as a flexible spacer), with different molecular weights (Mn) and low molecular weight distributions have been successfully synthesized via atom transfer radical polymerization (ATRP). The phase behavior of the polymers has been investigated by a combination of techniques, including differential scanning calorimetry (DSC), polarized optical microscopy (POM), and 1D and 2D wide-angle X-ray diffraction (1D and 2D WXRD). The experimental results revealed that the LC phase structures of PMTS were found to be strongly Mn dependent. The PMTS polymers were amorphous when the Mn was lower than a critical Mn of approximately 2.03 × 104 g mol−1. When the Mn was higher than this critical value, the PMTS polymers displayed a rectangular (ΦR) columnar phase. On the contrary, the PMT6S polymers displayed a higher symmetry hexagonal (ΦH) columnar phase, which was independent of Mn. A comparison between PMTS and PMT6S suggested that the spacer plays an important role in the construction of liquid crystalline (LC) ordered structures. For the former, PMTS polymers without the spacer formed rectangular ΦR phases caused by the Tp moieties and the main chain as a whole, due to the strong coupling effect between the Tp moieties and the main chain. For the latter, PMT6S polymers with 6 methylene units as a flexible spacer gave a higher symmetry ΦH phase owing to the decoupling and self-organization of the Tp moieties.

Understanding in the morphology and tensile behavior of isotactic polypropylene cast films with different stereo-defect distribution

In this study, two iPP resins with similar molecular weight and average isotacticity but different uniformities of stereo-defect distribution were used in the production of cast films. The crystalline morphology and orientation, and tensile behavior during room temperature stretching of the cast films were investigated by scanning electronic microscopy (SEM), 2D-wide angle X-ray diffraction (2D-WAXD) and 2D-small-angle X-ray scattering (2D-SAXS). It was found that under fixed processing condition, iPP with more uniform stereo-defect distribution (PP2) favors the formation of row nucleated lamellar structure during cast film production, and therefore exhibiting hard-elastic deformation behavior during stretching; meanwhile, the sample with less uniform stereo-defect distribution (PP1) shows un-oriented spherulitical morphology in the cast film, and typical plastic deformation behavior during stretching. The crystallization and rheological analysis on the iPP raw materials revealed that, the uniformity of stereo-defect distribution determines the ability of nucleation and crystallization, and further influences the response of the crystalline morphology to the elongation effect of cast film production process, which is of great importance in the structure–property design in the production of iPP membranes.