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Abstract The relationship between the macroscopic non-linear mechanics and the microscopic crystal structural evolution of pre-oriented high-density polyethylene (HDPE) is investigated by in situ synchrotron radiation wide-angle X-ray diffraction (WAXD) measurement over a wide temperature range from −10 to 130 °C. With the concept of stress-induced disordering of crystal, the ratio ( φ a / b ) of lattice parameters a to b is defined as a new structural variable, which can reflect the lattice distortion and then the microscopic stress state of orthorhombic crystal (O-crystal). According to the temperature-dependent non-linear variation of φ a / b with strain, the contributions of O-crystal and monoclinic crystal (M-crystal) to the macroscopic mechanics including linear elasticity, yielding, stress softening and strain hardening are clarified. It is found that M-crystal bears the main extensional stress once formed, although it survives within a limited strain window relying on temperature. By further combining the extensional phase diagram constructed in strain-temperature space, the HDPE deformation is recognized to undergo successively one-dimensional (1D) chain segments rotation of crystal, two-dimensional (2D) crystal plan shearing or slipping and three-dimensional (3D) recrystallization along with increasing strain or stress, demonstrating a multiscale structural transition and energy dissipation mechanism. Graphical abstract Image 1 Highlights • A new structural parameter is defined to characterize the lattice distortion and the microscopic stress state of crystal. • Multiscale structural evolutions of crystal are connected to the macroscopic non-linear mechanics of HDPE under deformation. • The research method can be generalized to other semicrystalline polymers to understand the structure-mechanics relationship. [ABSTRACT FROM AUTHOR]

Benefitting from the wearability, ductility and portability, flexible and stretchable strain sensors display a more extensive field of applications than traditional sensors in terms of medical diagnosis, smart home, environmental monitoring and so on. However, the critical sensing performances, such as sensitivity, sensing range, stability and detection limit of flexible strain sensors still need to be improved. Microstructural optimization has been considered as an efficient strategy for tuning the performances. In this work, a carbon nanotubes (CNTs)/carbon black (CB)/thermoplastic polyurethane (TPU) fibrous film (CCTF) is prepared through electrospinning, spraying and ultrasonic anchoring technique. Synergetic conductive layers by combining CNTs/CB and CB are constructed on both sides of CCTF. In virtue of the optimization of microstructures and the synergetic conductive network, the obtained CCTF possesses an ultrawide response range (up to 500 % strain), high sensitivity (gauge factor, GF up to 1516), short response/recovery time (80/80 ms), low detection limit (0.05 % strain), favorable sensing stability and long-term durability. CCTF with excellent strain sensing performances is assembled as a strain sensor, which accounts for full range human biological signal acquisition, including joint movements, muscle tension, and facial micro-expressions. This paper provides a certain reference significance for the preparation and fabrication of next-generation flexible strain sensors with high performances. A flexible strain sensor based on carbon nanotubes (CNTs)/carbon black (CB)/thermoplastic polyurethane (TPU) film (CCTF) is fabricated through electrospinning, spraying and ultrasonic anchoring technologies. CCTF possesses excellent sensing performance due to the optimization of the microstructure, achieving a wide sensing range (up to 500 % strain), high sensitivity (GF up to 1516), low detection limit (0.05 % strain), and short response/recovery time (80/80 ms). [Display omitted] • A fibrous strain sensor with synergetic conductive networks of CNTs/CB and CB is fabricated. • The sensor possesses both a wide sensing range (500 % strain) and high sensitivity (GF up to 1516). • Low detection limit (0.05 % strain) and short response/recovery time have also been achieved. • The sensor is demonstrated to precise full range human biological signal acquisition. [ABSTRACT FROM AUTHOR]

Nowadays, passive radiative cooling (PRC) has being attracted intensive attention because it can realize cooling effect without consuming any energy. Unfortunately, fabricating polymer film with radiative cooling effect by a facile, continuous and environmentally friendly method is still a large challenge. In this study, high density polyethylene (HDPE)/polyvinyl oxide (PEO) film were first fabricated by melt extrusion casting method, and polyethylene film composed of directional microfibrils (PFCDM) were finally obtained after selective dissolution of PEO phase in deionized water at 70 °C. The as-prepared PFCDM shows higher average solar reflectivity of 85.17% in the visible range and stronger average mid-infrared emissivity of 82.04% within the atmospheric window. It shows a sub-ambient cooling of 23.28 °C during the day and 3.1 °C at night, suggesting that it has a remarkable PRC performance. Moreover, the as-prepared PFCDM has outstanding wearability and self-cleaning property, showing promising potential of personal thermal management. This study proposes a facile but environmentally friendly method for fabricating PFCDM, paving a new way to develop wearable PRC film following the concept of thermoplastic polymers "functionalized" processing. [Display omitted] • PFCDM was efficiently prepared via melt extrusion casting and water leaching. • PFCDM shows remarkable passive radiative cooling performance. • PFCDM has higher day and night cooling power. • PFCDM has outstanding wearability and self-cleaning property. [ABSTRACT FROM AUTHOR]

Poly(lactic acid) (PLA) inherently shows the distinct brittleness at room temperature, which is a major drawback limiting its practical applications. Great efforts have been done to improve the toughness by adding high content of flexible polymers or low content of nanoparticles, which is often at the expense of tensile strength. In this work, supertoughened PLA blend with high elongation at break (247.7%) containing low content of poly(ethylene oxide) (PEO) (8%) was directly fabricated by melt extrusion method. Interestingly, its tensile strength and modulus are only slightly decreased (<25%). The reasons for the balanced mechanical property can be understood as follows: I) The increasing mobility of amorphous chains of PLA due to the plasticizing effect of PEO. II) The strengthening effect of mesophase can hinder tensile strength to be severely sacrificed. III) The rod-like PEO phase can initiate more crazes and further prevents them from developing into cracks, allowing effective energy dissipation. This study proposes a facile but efficient strategy to fabricate PLA blends containing low content of PEO with balanced mechanical property, which would provide a clue for toughening other brittle thermoplastics. [Display omitted] • PLA blend with balanced mechanical property is directly prepared by melt extrusion. • A low content of PEO can realize the supertoughness of PLA. • The tensile strength and modulus are only slightly decreased. • Mesophase and rod-like phase morphology are keys to supertoughness. [ABSTRACT FROM AUTHOR]

To get strong and anti-freezing hydrogel with multiple contact and non-contact sensing performance, a facial method is proposed in this work using multiple physical bonding crosslinking and glycerol (GL) immersing strategy. The obtained hydrogels show a tensile stress at break of 5.4 MPa, an elongation at break of 1420 %, and a compression strength of 12.2 MPa at 80 % strain. Additionally, benefiting from the GL immersing the hydrogel shows superior anti-freezing (no ice formation at −60 °C) and water retention ability (water loss less than 17 % after storing at 50 °C for 7 h). Furthermore, the volume resistance of hydrogels exhibits excellent responses against humidity, temperature, strain, and stress. The variation of the resistance against temperature can be well described by the Arrhenius equation with an activation energy of 501.3 meV, verifying a band-gap dominated diffusion hopping conductive mechanism of the hydrogel. The sufficient humidity and temperature responses make the hydrogel applicable as a non-contact sensor, and the wide temperature strain sensing (−40 to 50 °C) and stress sensing capability ensures that the hydrogel can be used as a contact sensor, ensuring that the hydrogel can be used as perfect flexible sensor for monitoring human motion and physiological signals. [Display omitted] • Strong and anti-freezing hydrogel with multiple sensing performance is obtained. • The hydrogel is prepared using multiple physical bonding crosslinking and glycerol immersing strategy. • The resistance variation against temperature is described by the Arrhenius equation with an activation energy of 501.3 meV. [ABSTRACT FROM AUTHOR]

Polyimide foams (PIFs) are usually synthesized by solution polymerization, followed by chemical foaming to prepare thermosetting foam. In this research, lightweight microcellular thermoplastic polyimide foams (TPIFs) were fabricated via a novel two-step foaming approach using supercritical carbon dioxide (scCO 2) as a blowing agent. The poly(amic acid) (PAA) and polyester ammonium salt (PEAS) precursor solutions were synthesized with pyromellitic dianhydride (PMDA) as dianhydride reagents and polyether amine Jeffamine D230 as aliphatic diamine reagent via blending and solution polymerization, respectively. The solution polymerization process demonstrated a higher molecular weight and superior formability than the blending process. The optimum thermal imidization temperature of 200 °C was optimized via the thermal and rheological property analysis. The cell morphology and mechanical properties of the TPIFs could be turned by varying the saturation time, foaming pressure, and imidization temperature. At a thermal imidization temperature of 200 °C, the TPIFs exhibited a branched structure with a small mean cell diameter (123.78 μm), and a high compressive strength (0.4 MPa) under 10 % strain at high temperature and pressure, which was more than ten times that of the TPIFs with thermal imidization temperature of 130 °C. This research provides a feasible method for producing high volume expansion ratio TPIFs with adjustable microcellular structures and outstanding mechanical properties. [Display omitted] • Poly(amic acid) and polyester ammonium salt precursor were synthesized by blending and solution polymerization, respectively. • Adding a flexible linkage provided the torsional capacity of the chain segment, and improved its flexibility. • Microcellular TPI foams were fabricated via a novel two-step foaming approach using supercritical CO 2 as a blowing agent. • The branched molecular structure was favourable for improving cell uniformity and mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract The self-assembly behavior of N,N′,N ″-tricyclohexyl-1,3,5-benzenetricarboxylamide (BTCA) and its nucleating effect on poly(lactic acid) (PLA) crystallization were studied by differential scanning calorimetry and polarized optical microscopy. The effect of melting temperatures (T f) from 190 to 240 °C, BTCA concentrations from 0 to 0.5 wt%, and cooling rates from 2.5 to 20 °C/min was investigated. It was found that, when T f was 240 °C, BTCA could dissolve completely in PLA matrix, and then self-assemble into supermolecular frameworks upon decreasing temperature. The core findings are as follows: (1) for the two-step crystallization, the half-crystallization time of PLA showed a bell shaped dependence on the pre-crystallization temperatures of BTCA, which was higher than that without pre-treatment; (2) for nonisothermal crystallization, the crystallization peak temperature of PLA presented a bell shaped dependence on the concentration of BTCA at each rate. Meanwhile, the BTCA concentration, which corresponded to the maximum crystallization rate of PLA, shifted to higher value with the increase of cooling rate. The observations were discussed in term of the effective nucleating surface area of BTCA. Graphical abstract Image 1 Highlights • We examined the nucleating effect of BTCA on PLA crystallization. • PLA crystallization presents a bell-shaped dependence on BTCA concentration. • Optimized BTCA concentration for PLA crystallization depends on cooling rate. [ABSTRACT FROM AUTHOR]

Abstract Carbon black (CB)/thermoplastic polyurethane (TPU) nanocomposites with a range of nanoparticle loadings were prepared successfully by using a joint co-coagulation technique and hot pressing. The presence of hydrogen bonding interactions between the CB particles and TPU chains was identified from the results of Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). Uniform dispersion of CB particles throughout the TPU matrix improved the overall mechanical properties of the TPU nanocomposites, as compared with the neat TPU. The thermal conductivity and thermal stability of the CB/TPU nanocomposites were also found to be enhanced with increasing the CB loading. All samples exhibited a rapid increase of erosion rate with the impact velocity between 20 and 30 m/s. The largest and smallest erosion rates (ER) were observed at 30° and 90° impact angle, respectively, for all CB/TPU nanocomposites. This shows a typical ductile erosion behavior in this material. In addition, the ER (TPU-2CB > TPU-12CB > TPU > TPU-6CB) under all test conditions showed an opposite trend to the tensile strength. These results indicate that the CB/TPU nanocomposites are suitable for protective coatings. Graphical abstract Image 1 Highlights • Thermoplastic polyurethane nanocomposites were fabricated using co-coagulation plus compression molding technique. • Uniform dispersion of CB nanoparticles effectively enhanced the tensile strength of the nanocomposites. • The solid particle erosion behavior was characterized by different impact angles, velocities and time. • The erosion rate showed an opposite trend to the tensile strength. [ABSTRACT FROM AUTHOR]

In the classical "covalent adaptive network" constructed by diglycidyl ether of bisphenol A (DGEBA) and crosslinking agent glutaric anhydride (GA), Zn-based catalyst greatly affects the curing crosslinking reaction and dynamic transesterification reaction. Herein, the crucial roles of Zn(Ac) 2 catalyst in the curing dynamics and stress relaxation were studied. The results reveal that increasing the content of Zn(Ac) 2 can significantly reduce the reaction activation energy (E α) at initial stage, thus effectively promoting the curing crosslinking reaction. The analyses of dynamic properties suggest that although stress relation time (τ) can be shortened by increasing catalyst content, the high content of catalyst would lead a fast transesterification rate at relatively low temperature, which is adverse to the mechanical stability of vitrimer resin at operating temperature. By comparison, the vitrimer resin with modest catalyst content (mole ratio of 1:0.5:0.05) shows a highest viscous flow activation energy (E τ), i.e., excellent dimensional stability and processability. Besides, the crosslinking density of resin was significantly affected by the content of catalyst. Since the competitive catalytic effects on curing cross-linking reaction and subsequent transesterification, the vitrimer resin of 1:0.5:0.05 exihits the highest crosslinking density (1855 mol/m3), so that it has highest T g (79 °C) and tensile strength (72 MPa). [Display omitted] • Increasing Zn(Ac) 2 catalyst significantly reduces E α at initial stage, thus promoting the curing crosslinking reaction. • The stress relaxation behavior relating with dynamic transesterification can be accelerated by increasing Zn(Ac) 2 catalyst. • The epoxy vitrimer with modest catalyst shows a highest E τ , thus revealing the optimal dynamic properties. • The epxoy vitrimer with modest catalyst exihits the highest crosslinking density, so that it has highest T g and tensile strength. [ABSTRACT FROM AUTHOR]

Photonic crystals structural colors have many advantages (e.g., environmentally friendly, nonfading, etc.), showing great potential application in some emerging fields of display, detection and anti-counterfeiting. Unfortunately, they are easily damaged because of the poor mechanical robustness origined from the weak interfacial adhesion between film substrate and nanoparticles. Although some photonic crystals show good mechanical robustness, they are often suffered from complex methods. Therefore, it is still a huge challenge to prepare photonic crystals with good mechanical robustness via facile methods. Herein, an efficient and facile strategy to prepare polycarbonate (PC)/silica nanoparticles (SNPs) photonic crystals film based on microgrooves is proposed. That is, with the help of micromilling and vacuum-assisted hot-pressor, microgrooves were prepared onto PC film surface, and SNPs can be spontaneously deposited into the as-prepared microgrooves via capillary force. Such PC/SNPs photonic crystals film exhibits excellent mechanical robustness, vivid structural color, and color can change with the viewing angle. Interestingly, such films with quick response (QR) code pattern can store information and can be used as anti-counterfeiting labels. This work proposes a facile strategy to prepare microgrooves based photonic crystals film with good mechanical robustness, which can further expand its applications in anti-counterfeiting. Via micromilling and vacuum-assisted hot-pressor, PC/SNPs photonic crystals film was successfully prepared. Moreover, some complex photonic crystals patterns with vivid structural colors can also be prepared by this method. More interestingly, the as-prepared PC/SNPs photonic crystals film with QR code pattern has background-dependence and can be used as anti-counterfeiting labels. [Display omitted] • Microgrooves based PC/SNPs photonic crystals film with vivid and angle-dependent structural color was prepared. • Such PC/SNPs photonic crystals film exhibits excellent mechanical robustness thanks to the microgrooves. • Various photonic crystals patterns based on microgrooves can also be prepared and the quick response (QR) code pattern can be used as anti-counterfeiting labels. [ABSTRACT FROM AUTHOR]

In many industrial processes, polymer melt undergoes complex flow-cooling environments before being solidified into the final products. Investigating polymer crystallization under processing conditions is a necessary step to predict and customize the structures and properties of semicrystalline polymers. Herein, the crystallization behavior of high-density polyethylene (HDPE) under combined melt stretching and fast cooling fields was studied through a homemade extensional rheometer. A series of HDPE samples were prepared by cooling the stretched melt at different cooling rates (0.02–220 °C/s) immediately after flow, or after waiting for different times of isothermal crystallization at 128 °C. Microstructural characterizations confirm four different structural states related to the evolution of shish-kebabs after melt stretching, namely generation of shish precursors, shish crystal growth, kebab lamellar growth, and perfection of shish-kebabs, which diversify greatly the structures and morphologies of the final solidified samples. By prolonging the isothermal crystallization time at high temperature, the fast cooling-induced lamellae keep decreasing in thickness. This supports the occurrence of molecular segregation caused by shish-kebabs growth at high temperature, which reduces the molecular weight of the remaining un-crystallized melt. In addition, quantitative analysis of crystalline orientation manifests that the lamellar growth during isothermal process takes strictly the shish as a template and adopts a high orientation, while the fast cooling-induced lamellae are only related to the chains conformation of un-crystallized melt prior to cooling. This work would be essential to advance the in-depth understanding on the actual industrial processing of semicrystalline polymeric materials. [Display omitted] • Melt crystallization of HDPE under combined stretching and fast cooling fields was studied. • Four different structural states related to the evolution of shish-kebabs after flow were identified. • Molecular segregation caused by shish-kebabs growth at high temperature was suggested. • Isothermal and non-isothermal crystallization under flow presented different lamellar growth modes. [ABSTRACT FROM AUTHOR]

Benefiting from its superior thermal and mechanical properties, the stereocomplex crystal (SC) of PLLA/PDLA is catching increasing interest. In this work, a systematic investigation was performed to reveal the effect of solid-state stretching on the formation of SC during annealing. Results show that as the stretching temperature was close to the glass transition temperature (T s = 60 °C), the polymer chains orientation was increased gradually with draw ratio (λ). As a result, the crystallization induction time (t 0) was shortened, the growth rate (G r) of SC was enlarged, and the crystallinity of SC (X SC) was elevated as a result of orientation-induced crystallization. Whereas, the saturation of t 0 , G r , and X SC appeared quickly when λ reached 2.7, although the orientation of polymer chains continued to increase. The reason is that in addition to orientation, strong phase separation between PLLA and PDLA was also triggered therein. The phase separation prohibited greatly the crystallization of SC due to a long time would be needed for PLLA or PDLA chains to diffuse to a distance close enough to activate the hydrogen-bonding interaction, which is the prerequisite of SC crystallization. When the stretching temperature was elevated to 75 °C, the phase separation became much weaker. So X SC was higher compared to that of the blend stretched at 60 °C to the same λ. Moreover, in the annealing temperature from 180 °C–190 °C, t 0 was much smaller for the blend stretched at 75 °C since the crystallization of SC in this temperature range is a diffusion-controlled process. [Display omitted] • Strong orientation of polymer chains and phase separation are induced by solid-state stretching. • Orientation of polymer chains and phase separation exhibit a competition effect on the crystallization of SC. • The more intense phase separation at lower stretching temperature gives rise to a longer crystallization. induction time [ABSTRACT FROM AUTHOR]

In this letter, both the viscoelastic and electrical properties of poly(methyl methacrylate)/carbon black (PMMA/CB) nanocomposites with different CB concentrations prior to and after annealing were investigated. The linear steady-state recoverable compliance of pure PMMA is independent of annealing as it reflects only polymer-polymer interactions. While the conductivity of PMMA/CB nanocomposites increases gradually with annealing, and the viscoelastic properties show different regions of response depending on the CB concentration. At CB contents below the percolation threshold the recoverable compliances increase after annealing, whereas the reverse trend is found at CB contents above the percolation threshold. This behavior is related to the interplay between network formation and particle-particle interactions. [ABSTRACT FROM AUTHOR]

The strain sensing behavior of multi-walled carbon nanotubes (MWCNT)/epoxy (EP) conductive composites subjected to tensile strain was studied in detail. With increasing the load to rupture, the responsivity (ΔR/R 0 , R 0 is the original resistance, ΔR is instantaneous change in resistance) increased in a linear fashion and then began to decrease at a critical strain ( ε c ), which was remarkably different from the thermoplastic conductive composites only with a monotonic increase of the responsivity. It was attributed to the decrease of the nanotube contact points, the increase in the gaps before ε c , and the reorientation and violent alignment of nanotubes in the zones of high local deformation (after ε c ). In addition, when the extension-retraction cycles were applied, the values of max ΔR/R 0 showed a distinct tendency with different strains around the ε c . These behaviors were attributed to the competition of network destruction and reconstruction during the cyclic deformation. The mechanism of this unique sensing behavior was proposed as well. [ABSTRACT FROM AUTHOR]

Isotactic polypropylene (iPP)/glass fiber (GF) composites with different specific interfacial features ( viz ., α-spherulite, α-cylindrite and β-cylindrite) were prepared via shear-induced interfacial crystallization. α-spherulite, α-cylindrite and β-cylindrite were successively encouraged at the interface between iPP matrix and GF with increasing the fiber-pulling speed. Moreover, the composite specimens containing β-cylindrite exhibited remarkably higher interfacial shear strength (IFSS) than those containing α-spherulite or α-cylindrite, as demonstrated by the single fiber fragmentation test (SFFT). More interestingly, simultaneously improved tensile strength and toughness were observed in the presence of β-cylindrite. This study offers a new insight that β-cylindrite produced by shear is an alternative approach to achieve comprehensive mechanical properties for the iPP/fiber composite systems. [ABSTRACT FROM AUTHOR]

The electrically conductive nanocomposites composing of different concentrations (0.05–1.5 wt%) of reduced graphene oxide (RGO) in the thermoplastic polyurethane/polypropylene (TPU/PP, 55/40) matrix with a fine co-continuous structure were fabricated by solution-flocculation and melt-mixing process using a micron twin-screw extruder. Both thermodynamic and kinetic theoretical analysis predicated the preferential location of RGO in the TPU rather than PP phase. Both optical microscope and field emission scanning electron microscopy (FESEM) observations verified this theoretical dispersion predication. The homogeneous dispersion of RGO in the TPU matrix is confirmed by wide-angle X-ray diffraction (WAXD) patterns and transmission electron microscope (TEM) observation. A very low percolation threshold of 0.054 wt% was achieved owing to high conductivity of RGO and favorable double percolation effect. The tensile strength and elongation at break of the composites with RGO content of only 0.5 wt% were improved by 341.9% and 354.3%, respectively. The present work provides a guideline for an efficient, facile fabrication technique of graphene based conductive polymer nanocomposites with high electrical conductivity and improved mechanical properties. [ABSTRACT FROM AUTHOR]

Isotactic polypropylene (iPP) based single-polymer composites (SPCs) were prepared by introducing iPP fibers into the molten or supercooled homogeneous iPP matrix. The influences of fiber introduction temperature ( T i ) on the resultant morphology of transcrystallinity (TC) and mechanical properties of SPCs were investigated via a polarized optical microscopy (POM) and a universal tensile test machine. The effects of interfacial crystallization on mechanical properties were also studied. The tensile strength of SPCs was observed to increase firstly and to reach a maximum value at T i = 160 °C, and then to decrease with further increasing the T i . Wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM) and POM were employed to understand the mechanical enhancement mechanism. It is found that the enhanced tensile strength of SPCs was strongly dependent on the synergistic effects of TC, high orientation degree of iPP fibers and good adhesion between the iPP fiber and the matrix. [ABSTRACT FROM AUTHOR]

This work investigated the influence of two-dimensional boron nitride (BN) on the phase transformation kinetics of isotactic polybutene-1 (iPB-1) with differential scanning calorimetry, wide angle X-ray diffraction, and small angle X-ray scattering technique. The phase transition time (t tra) from form II to I largely decreases with the increasing content of BN nanosheets. Different from that in pure iPB-1, the phase transition is accomplished without residual form II in a relatively short time. It's speculated that the addition of BN leads to the irregular lamellae packing of form II (demonstrated by the SAXS result). The irregular packing can avoid the accumulation of negative stress that is induced by the lamellae deformation of the transformed form II, which may hider the chain movement of the residual un-transformed form II. The dispersion of the negative stress obviously accelerated phase transition kinetics from form II to I in iPB-1/BN blends. In addition, it's found that the thickness of form I in iPB-1/BN blends is thicker than that in pure iPB-1. By investigation on the melting temperature of partially transformed form II/I, it showed that the thickness of form I in iPB-1/blends increased continually during the whole phase transition process, which is different from that in pure iPB-1. The continuously lamellae thickening of form I during phase transition may be due to the dispersion of negative stress which benefits the chain movement. [Display omitted] • The effect of 2D nanofillers on the phase transition from form II to I in iPB-1 is investigated. • The transformation kinetics is obviously accelerated. • Lamellar thickening of form I during phase transition is observed. [ABSTRACT FROM AUTHOR]

Herein, a porous polycarbonate blend monolith with hierarchical micro-nano structure using fluorine-free and low-cost material via a simple thermally induced phase separation is successfully prepared. The unique micro-nano structure endows the monolith with high porosity (90%) and low density (93 mg/cm3), as well as strong superhydrophobicity (water contact angle of 159°) and superoleophilicity. It shows high saturation adsorption capacity (6.25–10.58 g/g) and rapid adsorption rate (20 s reach adsorption equilibrium). Furthermore, outstanding environmental resistance in a variety of harsh conditions, such as contact angle varies slightly under various pHs (1–14) and the constant adsorption capacity at different temperatures (0–100 °C), is found. Additionally, the monolith displays good recycling performance for at least 10 cycles by simply pumping and evaporating, indicating a good application prospect in the field of practical oil-water separation. [Display omitted] • Superhydrophobic PDMS/PC monolith with hierarchical micro-nano structure is prepared. • Monolith endows the high porosity (90.8%) and low density (93 mg/cm3). • It has outstanding environmental resistance and constant adsorption capacity at 0–100 °C. [ABSTRACT FROM AUTHOR]

Shear-induced interfacial sheath structure was generated by pulling a single glass fiber (GF) in the supercooled isotactic polypropylene (iPP) melt. Its morphological evolution and microstructure were investigated by means of polarized optical microscopy (POM), ex-situ polarized Fourier transform infrared spectroscopy (FTIR), ex-situ two-dimension wide-angle X-ray diffraction (2D-WAXD) and scanning electron microscopy (SEM). The results revealed that higher fiber-pulling speed was crucial to promote the formation of sheath structure. Such sheath structure was proved to be the most thermodynamically stable α-crystal that could effectively induce the generation of β-cylindrite. Meanwhile, the thickness and orientation level of the sheath structure were increased with the increasing fiber-pulling speed. More interestingly, the sheath structure was composed of aligned shish-kebabs, and the lamellar-branched β-iPP crystals directly “rooted” in these kebabs, viz., β-iPP crystals grew at the growth front of oriented fibrillar lamellae. This study on the interfacial sheath structure provides another direct evidence for the formation mechanism of β-iPP crystals upon shear field. [ABSTRACT FROM AUTHOR]

The impacts of both shear temperature and shear rate on both the self-assembled β-nucleating agent (β-NA) in the hosting isotactic polypropylene (iPP) matrix and the subsequent crystallization of the hosting iPP matrix were investigated by polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD), and small-angle X-ray scattering (SAXS) measurements, respectively. Under static condition, β-NA could self-assemble into snowflake-like aggregate. Once shear was applied, three kinds of self-assembled aggregates could be developed prior to the crystallization of matrix depending on the applied shear temperatures, that is, snowflake-like self-assembled aggregate at 200 °C, deformed snowflake-like one with smaller branches at 180 °C, tiny and dense needle-like one if shear temperature was further decreased to 160 °C. Since β-NA with various self-assembled aggregates can act as nucleating templates for the subsequent nucleation of iPP matrix, it is conceivable that the crystallization behavior of the iPP matrix can be altered. As expected, β-phase crystallinity, long period and lamellar thickness are steadily dependent on the shear temperature and shear rate. That is, when shear was applied at 200 °C, β-phase crystallinity, long period and lamellar thickness keeps almost constant regardless of the shear rate. If melt was sheared at 180 °C, β-phase crystallinity was decreased while long period and lamellar thickness remained unchanged with elevating shear rate. At lower shear temperature (i.e., 160 °C), β-phase crystallinity, long period and lamellar thickness were further decreased with increasing the shear rate. These results are of practical significance to understand the long-term ignored issue: apart from the loading of β-NA, different self-assembled aggregates formed in flow field are another crucial factor in determining the microstructure development of matrix. [ABSTRACT FROM AUTHOR]

Abstract: Ultra-thin LLDPE parts were prepared by microinjection molding. Mechanical properties and microstructure of samples before and after annealing at different temperatures (60, 80, 100 °C) were analyzed. Tensile test indicates that toughness has been enhanced at least 7 times after being annealed in parallel with significant increase of tensile strength. Microstructure characterizations, including differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), scanning electronic microscope (SEM) and polarized Fourier transform infrared spectroscopy (FTIR) were performed to investigate the variations of microstructure and to further establish the relationship between microstructure and mechanical properties. It is suggested that the increased crystallinity and perfection of crystals upon annealing are beneficial to the reinforcement. Formation of a stronger physical cross-linking network due to the increase of connecting points is in favor of the enhanced strength as well. Moreover, the notable improvement of toughness in the annealed ultra-thin LLDPE parts is ascribed to combined effects of microvoids developed in both the annealing and deformation process. This work offers a simple approach to prepare ultra-thin LLDPE parts with excellent toughness and strength. [Copyright &y& Elsevier]

Frequent oil spills on water have always generated serious ecological disasters and environmental crises in recent years. Unfortunately, the traditional oil/water separation and collection process is in an intermittent mode and therefore suffers from expensive, time-consuming and complicated procedures. Undoubtedly, it is necessary to develop a facile method to selectively separate and collect oil from the oil/water mixture in a continuous mode. Herein, we present a low-cost, efficient and simple approach (co-extrusion molding) to continuously fabricate polymer microfibrillar tube (PMT). It shows high porosity, excellent oleophilicity and good hydrophobicity, and thereby excellent absorption and transportability is obtained. More interestingly, it is capable of continuously separating/collecting oil from flowing oil/water mixture and there is no secondary treatment (i.e., desorption) involved in such one-step process for oil/water separation and collection. This study proposes a new concept for fabricating polymer porous tube consisting of microfibril through a low-cost, efficient, simple and continuous way, showing promising potential application in continuous oil/water separation and collection. The present work represents a facile, cost-effective and environmentally friendly method to fabricate polymer microfibrillar tube (PMT). Interestingly, such PMT can one-step separate and collect oil from the oil/water mixture in a continuous way. This study proposes a new concept for fabricating polymer porous tube consisting of microfibril through a low-cost, efficient, simple and continuous way, showing promising potential application in continuous oil/water separation and collection. [Display omitted] • A low-cost, facile method through co-extrusion molding and water leaching method to fabricate PMT. • PMT exhibits excellent oleophilicity and hydrophobicity. • PMT has the ability of continuously separating/collecting oil from flowing oil/water mixture. • No secondary treatment (i.e., desorption) is involved in separation/collection process. [ABSTRACT FROM AUTHOR]

Abstract: Macroscopically aligned isotactic polypropylene (iPP) fibers with different diameters ranging from 0.7 to 13.2 μm were successfully fabricated by high-temperature solution electrospinning using an infrared (IR) heating system. Polarized optical microscope (POM), scanning electron microscope (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and polarized Fourier transform infrared (FTIR) were employed to characterize the surface morphology and microstructure of the electrospun fibers. From SEM images, three macroscopically structural models have been found: (1) cylindrical fibers, (2) twisted fibers and (3) beaded fibers. Interestingly, regardless of fiber's shape and size, they (especially for cylindrical fibers) exhibit well-defined self-similar morphology. That is, the tertiary, secondary and primary morphology are similar with each other. Thermally induced phase separation (TIPS) is the most pertinent origin to explain the formation of self-similar morphology. WAXD and DSC results show that α-form crystal prevails in the electrospun iPP fibers. For comparison, the solution-cast film was also prepared under the same conditions as those adopted in electrospinning except that the voltage was 0 kV. Compared with the solution-cast film, lower crystallinity, smaller average crystallite size and higher melting point are achieved in the electrospun iPP fibers. The results of polarized FTIR spectra demonstrate that the macroscopically aligned electrospun fibers are highly oriented along the fiber's longitudinal axis at molecular level. Furthermore, when the electrospun iPP fibers were embed in iPP matrix, surface-induced crystallization is significantly enhanced and finally develops into transcrystalline layer which can be even revived after recrystallization. As a result, it is logical that long-lived thermodynamically stable structure has been formed in the electrospun iPP fiber. Combined with FTIR result, the α-form crystal formed in the fiber is conjectured to be a kind of oriented structure with thermodynamically long-lived stability which is similar to "shish-kebab" structure. [Copyright &y& Elsevier]

Multifunctional polymer foam becomes the tendency due to the single-functional foam is difficult to adapt the various complicated environments. However, preparing multifunctional porous ultra-high molecular weight polyethylene (UHMWPE) material with high porosity is still challenge. Thus, it is desirable to develop a simple and effective method that could integrate multiple functions into polymer foam. Herein, a multifunctional UHMWPE foam was fabricated via a facile thermally induced phase separation method. The foam displays a low density of 8.23 mg cm−3, high porosity of 99.2% and robust superhydrophobicity (water contact angle of 152°), thus exhibiting excellent adsorption capacity in oil-water separation under different extreme environments. Moreover, the thermal conductivity of the foam goes down to 11.6 mWm−1K−1, which endows the foam with great thermal insulation performance under various temperature conditions. Thus, this foam can meet the demands of various practical applications. Image 1 • Multifunctional UHMPE foam was fabricated via thermally induced phase separation method. • The foam displays an ultra-light property (8.23 mg cm−3) and robust superhydrophobicity (water contact angle of 152°). • It shows excellent adsorption capacity in oil-water separation under different extreme environments. • The foam with 11.6 mWm−1K−1 thermal conductivity exhibits great thermal insulation performance. [ABSTRACT FROM AUTHOR]

Nanoscale grain refinement is a mature and powerful tool to enhance the mechanical and physical properties of metals and alloys. However, similar cases are rarely reported in the widely used semicrystalline polymers. Herein, we demonstrate a feasible strategy to fabricate the ultrafine-grained isotactic polypropylene (iPP) by rapid quenching of stretched melt. The grain refinement happens to regularly arranged nano-lamellae in both thickness and lateral directions, leading to an order of magnitude improvement in the number density of lamellae compared to normal melt crystallization. We have shown that such grain refinement greatly enhances the tensile toughness of iPP material without sacrificing the modulus and strength. Rope-like fracture morphology is observed in the toughened samples after the mechanical tests. It is indicated that the refined crystalline grains with low structural stability probably favor the formation of fibrils. This work provides a generalized approach to mechanically toughen the semicrystalline polymers by grain refinement on the nano-lamellar scale. Image 1 - Rapid quenching of stretched melt leads to a refinement of lamellar crystal in both thickness and lateral directions. - Ultrafine-grained iPP corresponds to an order of magnitude improvement in the number density of lamellae. - Grain refinement on the nano-lamellar scale greatly enhances the tensile toughness of material. [ABSTRACT FROM AUTHOR]

Cavitation is frequently encountered during the deformation of semi-crystalline polymers. Although abundant works have been performed to reveal the cavitation behavior in detail, the relationship between void formation and the plastic deformation of crystalline phase is still unclear. In this work, by in-situ synchrotron X-ray scattering, the void formation and the slip process in crystalline phase during uniaxial stretching of oriented isotactic polypropylene (iPP) were investigated. Results proved clearly that lamellae slip or/and chain slip presents a retardation effect on void formation. As the Deviation Angle (DA, defined as the angle between stretching direction and lamellae normal) was 0°, voids were initiated at a Hencky strain (ε H) of 0.04 and the longitude direction of voids was perpendicular to lamellae normal. Meanwhile, no slip process happened when voids were induced. As DA was 15°, lamellae slip took place once the stretching was started and voids were formed at ε H of 0.09. When DA was further enlarged to 30° and 45°, both lamellae slip and chain slip could be found as voids were induced. The ε H of voids formation were 0.29 and 0.31, respectively. Interestingly, it is worth noting that as DA was increased from 0° to 45°, although the orientation degree of voids was decreased, the longitude direction of voids stayed perpendicular to the normal of lamellae. When DA was enlarged further to 90°, voids were formed at ε H of 0.1 and the longitude direction of voids coincided with lamellae normal. Additionally, neither lamellae slip nor chain slip existed once voids appeared. Combining the value of micro-strain of lamellae stacks and crystal lattice, it is proposed that voids were formed either in the amorphous phase on the normal side of lamellae (0° ≤ DA ≤ 45°) or in the amorphous phase on the lateral side of lamellae (DA = 90°). Image 1 • Void formation and slip processes in oriented isotactic polypropylene (iPP) were studied by in-situ synchrotron X-ray scattering. • Lamellae slip or/and chain slip presents a retardation effect on void formation. • Combining the value of micro-strain of lamellae stacks and crystal lattice, it is proposed that voids were formed either in the amorphous phase on the normal side of lamellae or in the amorphous phase on the lateral side of lamellae. [ABSTRACT FROM AUTHOR]

Applying flow to stimulate the shish-kebab formation in semi-rigid poly(lactic acid) (PLA) is far from mature compared to that in flexible polyolefins, which waits to be solved for both academia and industry. Herein, we conduct a systematic investigation on the flow-induced crystallization of lightly crosslinked PLA melt by a combination of extensional rheology and in situ synchrotron wide and small-angle X-ray scattering. With Hencky strain above a critical value of 1.5–2.0, abundant shish-kebabs with high orientation and high regularity are identified to form, which leads to not only tremendous acceleration of PLA crystallization kinetics but also superb heat tolerance of finally solidified sample. With an affine deformation assumption, the generation of shish-kebabs is recognized to require the entanglement network deformation in crosslinked component chains reaching 67% of its maximum elongation ratio, much higher than that reported in polyethylene. In addition, we have confirmed a heterogeneous spatial distribution of crystalline polymorphs in shish-kebab body due to its morphological duality. The β-form contributes mainly to the central shish originating from strongly stretched crosslinked component chains, while the α/α′-form to the lamellar kebab from moderately orientated free chains. Then a close relationship between chains deformation, crystalline polymorphs, crystal morphology and material property is well established. This study has disclosed that imposing melt extension to lightly crosslinked PLA can result in extraordinary crystallization capacity of PLA material comparable to that of flexible polyolefins, showing potential significance for guiding the industrial processing. Image 1 • Extension with Hencky strain above 1.5–2.0 induces the massive formation of shish-kebabs. • Heterogeneous spatial distribution of crystalline polymorphs is confirmed in shish-kebab body. • Formation of shish-kebabs with high interlocking provides PLA with superb heat tolerance. • Relationship between chains deformation, crystalline polymorphs, crystal morphology and material property is elaborated. [ABSTRACT FROM AUTHOR]

In this work, a simple thermally induced phase separation method with the assistance of little water dosage to prepare thermoplastic polyurethane (TPU) microsphere for super-hydrophobic dip-coating and its oil-water separation was developed. With the increasing of water content in TPU/dioxane solution, the cloud point temperatures of the ternary system sharply rose. Meanwhile, the TPU foam evolved to smooth non-hollow microspheres and finally to nano-fibrous porous microspheres. More importantly, by controlling the water content, the microsphere surface can be controlled, forming various structures. The solution of microspheres could be used for the dip-coating of the nonwoven fabrics, and the dip-coated nonwoven fabrics shown superhydrophobicity with a water contact angle of 153°. The superhydrophobic dip-coated nonwoven fabric exhibited a good hot water, acid and alkali resistances. Additionally, it also exhibited high flux and oil-water separation efficiency. Image 1 • Water-assisted thermally induced phase separation is proposed to prepare microsphere. • Cloud point temperature of ternary system is sharply rose with water increased. • Smooth non-hollow and nano-fibrous porous microspheres are obtained. • Superhydrophobic dip-coated nonwoven fabric with water contact angle of 153° is obtained. [ABSTRACT FROM AUTHOR]

Mechanical stretching can accelerate Form II to Form I phase transitions in isotatic polybutene-1 (iPB-1). This study in-situ investigated the effect of pre-stretching on further phase transitions. Three tensile modes were considered. In mode A, the samples were stretched to their breaking point, and the phase transition was wholly completed. In mode B, the samples were pre-stretched to specific strains and annealed under quiescent conditions at room temperature. Mode C was studied under the same conditions as Mode B, but the samples were allowed free shrinkage during the phase transition. The phase transition process were investigated by mechanical testing and in situ wide-angle X-ray diffraction. The phase transition kinetics were obviously faster in the pre-stretched samples (even when stretched in the elastic zone) than in the un-stretched samples. The pre-stretching may affect the conformation or the lattice arrangement of the segments in Form II, thereby accelerating the subsequent phase transition. In the samples with pre-strain beyond the yield strain, the accelerated transition rate increased with the increased pre-strain, meanwhile, the growth dimension of Form I reduced, owing to the confinement effect of stretch-induced Form I. The residual stress in the mode-B stretched samples did not significantly affect the phase transition, because the residual stress was lower than the critical stress that triggers Form I nucleation. In summary, a small pre-strain accelerated the phase transition and affected the growth dimension of Form I. Image 1 • The phase transition from form II to form I in iPB-1 under three tensile modes was studied by wide angle X-ray diffraction technique. • The phase transition kinetics of the pre-stretched samples was obviously accelerated, even at very small strain in the elastic zone. • In samples with pre-strain beyond the yield strain, the growth dimension of Form I decreased due to the confinement effect. [ABSTRACT FROM AUTHOR]

Spontaneously phase transition from form II to I in isotactic polybutene-1 (iPB-1) products during storage at room temperature after processing limited their application. Investigations on phase transition in iPB-1 have practical importance, especially on oriented iPB-1 as oriented form II generated during processing where intense flow field is always imposed. The effects of flow on phase transition were studied with synchrotron radiation scanning X-ray microdiffraction (SR- μ SXRD) technique with beam size of 4.5 × 5.2 μm2 in the present work. Localized flow-field was imposed by pulling glass fiber through undercooled melt. Benefiting from the high resolution of SR- μ SXRD technique, the formation of fibrillar and oriented form II ( c I I f and c I I o ) were identified. The transformation from c I I f to fibrillar form I ( c I f ) completed in about 40 min, while c I I o transformed into oriented form I ( c I o ) partially in about 186 min. Quantitative analysis on SR- μ SXRD result showed that crystallographic lattice dimension of c I I f changed comparing with that of c I I o , where a and b increased while c decreased in c I I f . An obvious correlation between crystallographic lattice deformation and phase transition kinetics was is identified. Local internal stress plays an important role in promoting the phase transition kinetics, as the stress transmission efficiency in c I I f with rod-like morphology would be higher than that in c I I o with lamellar morphology. Image 1 • With in-situ SR- μ SXRD measurement, it's found that fibrillar and oriented form II were induced at high and low shear rate, respectively. • Fibrillar form II transformed into form I completely in about 40 min, which is much faster than that of oriented form II. • Deformation in lattice dimension of fibrillar form II is observed which may be due to partially conformation transition before lattice rearrangement. [ABSTRACT FROM AUTHOR]