Ruihua Lv

Efficient and rapid transformation of high silica CHA zeolite from FAU zeolite in the absence of water

High silica CHA zeolite plays an important role in selective catalytic reduction of NOx with NH3 (NH3-SCR), but its synthesis is not highly efficient due to the use of a relatively high-cost structural directing agent (SDA) N,N,N-trimethyl-adamantammonium hydroxide (TMAdaOH) and relatively long crystallization time under hydrothermal conditions. Herein, we report an efficient and rapid synthesis of a high silica CHA zeolite possessing good crystallinity and uniform crystals (CHA-ST). The method includes interzeolite transformation of high silica FAU zeolite in the absence of water but the presence of zeolite seeds and a bromide form of the SDA. The absence of water in the synthesis significantly improves the zeolite yield by avoiding dissolution of aluminosilicate species in aqueous media, while the addition of zeolite seeds remarkably enhances the crystallization rate under solvent-free conditions. In addition, this route allows the use of a low-cost bromide form of the SDA. Catalytic tests in the NH3-SCR show that copper-exchanged CHA-ST (Cu-CHA-ST) exhibits comparable catalytic properties to those of Cu-SSZ-13 obtained from the conventional hydrothermal route.

Unexpected Reorganization Effects of Cold-Crystallized Polylactide Stereocomplex

Cold crystallization of poly (l-lactide)/poly (d-lactide) blends at low temperatures results in the formation of a stereocomplex with loose intermolecular packing. Upon heating, it undergoes significant reorganization into a compact one with an extremely high melting point via a solid–solid transition. In contrast, the stereocomplex crystallized at high temperatures exhibits little reorganization and thus a relatively low melting point.

Insight into the Role of Filler Network in the Viscoelasticity of a Carbon Black Filled Thermoplastic Elastomer: A Strain Dependent Electrical Conductivity Study

In conventional rheological and mechanical tests, particle‐particle interactions in the filler network are always entangled with polymer‐particle ones, and thus knowledge of their relative role in the viscoelasticity of filled elastomer is still lacking. In this study, a strain‐dependent, electrical conductivity measurement during cyclic deformation was adopted for the first time to elucidate the role of the filler network in the viscoelasticity of filled elastomers, since electrical conductivity only depends on the particle‐particle interactions in the filler network. The results indicate that a percolating carbon black (CB) network is broken down under large strain and can be partly reformed again with the release of the strain. Further, the weakening of particle‐particle interactions dependent on the percolation of the CB network can find its origin in the hystersis and stress softening effects in the mechanical measurements. It is concluded that the mechanical viscoelasticity of filled elastomer is to a large extent related to the filler network rather than to the polymer‐particle interactions.

Stretch-Induced Shish-Kebabs in Rubbery Poly(L-Lactide)

The oriented crystallization in stretched rubbery poly(L-lactide) has been studied with the aid of in-situ rheo-Fourier transform infrared spectroscopy (FTIR) measurements and morphological observations. The oriented segments that survived after stretching are first transformed into shish structure composed of helical sequences via intra-chain conformational ordering and propagation, followed by the transverse growth of kebabs from the coiled chains in the surrounding matrix. Moreover, the formation of shish structure and kebabs shows different dependences on the stretching temperature as a result of different controlling molecular processes.

Formation of highly porous structure in the electrospun polylactide fibers by swelling-crystallization in poor solvents

The electrospun fibers made of polylactide (PLA) have been attracting much attention in many applications because of biodegradability and biocompatibility. Introducing porous structure into electrospun PLA fibers is helpful to enhance surface area and thus to extend their applications. Here we report a novel and facile route to produce highly porous structure in the electrospun PLA fibers by simple immersion in poor solvents. It arises from swelling and subsequent solvent-induced crystallization in the electrospun PLA fibers, depending on solvent polarity, immersion temperature and PLA molecular weight. The highly porous PLA fibers have a very large surface area of 137.7 m2 g−1, which is almost unapproachable by other routes.

Composition dependent phase transformation of poly(vinylidene fluoride) in its miscible blends upon stretching

This study reports the phase transformation of poly(vinylidene fluoride) (PVDF) in its miscible blends with poly (3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) upon stretching. The original α-form of the PVDF component in the blends is converted into the β-form by stretching, which is decreased with the increasing P34HB content. Moreover, α → β transformation of the PVDF component in the blends exhibits a sharp transition at the P34HB content of about 15 wt%. It is correlated with composition dependent dissolution and crystallization of the P34HB component in the amorphous phase of the PVDF component.

Nanocellulose-mediated hybrid polyaniline electrodes for high performance flexible supercapacitors

Cellulose, abundant in nature, is very attractive for application in energy storage devices. Herein, cellulose nanofibers (CNF), detached from natural cellulose, are employed to fabricate flexible electrodes with polyaniline (PANI) as the active material for high performance supercapacitors. The presence of CNF in conductive composite substrates can tailor the morphology and doping of grown PANI worm-like nanorods during in situ polymerization, resulting in the improvement of specific capacitance. A maximum specific capacitance of 421.5 F g−1 is achieved for hybrid PANI electrodes based on composite substrates with 20 wt% CNF loading at a current density of 1 A g−1. Moreover, good rate capability and energy/power density balance are exhibited by the hybrid PANI electrodes. All-solid-state supercapacitors assembled from the hybrid PANI electrodes show excellent electrochemical performance and capacitance retention under repeated bending over 1000 cycles due to the mechanical flexibility of composite substrates with CNF as binders. This research provides a facile route to fabricate high performance flexible supercapacitors from bio-sourced CNF and low-cost PANI.

Robust polylactide nanofibrous membranes by gelation/crystallization from solution

Most porous membranes are fabricated from petroleum-based polymers without biodegradation, which could pose environmental problems in the disposal stage after use. In this case biodegradable polylactide (PLA) is adopted to produce porous membranes by gelation/crystallization from solution. Abundant nanofibers prevail in the resulting porous membranes, which becomes remarkable with the decrease in the gelation/crystallization temperatures and PLA concentration in solutions. The nanofibers in the porous membranes are well interconnected with each other which is responsible for superior mechanical properties. Notably, very high rejection towards bovine serum albumin is realized by the nanofibrous membranes.

Embrittlement of poly (L-lactide)/poly (ε-caprolactone) blends upon physical aging

Toughening of poly (L-lactide) (PLLA) by flexible poly (ε-caprolactone) (PCL) is very attractive for biomedical applications. However, PLLA/PCL blends usually behave brittle fracture, which is ascribed to the immiscibility between two components. This study demonstrates that without physical aging dispersed PCL particles can induce significant ductile deformation of PLLA matrix, accompanied by remarkable decreasing of yield strength, opposite to what is observed in the aged blends. It is deduced that segmental mobility of PLLA matrix and crystalline order of PCL domains, rather than immiscibility, play vital role in determining the ductility of PLLA/PCL blends.

Formation of Ring-Banded Spherulites of Poly (L-lactide) in its Miscible Mixture with an Ionic Liquid

ABSTRACT Incorporation of an ionic liquid, nonvolatile and thermally stable, promoted formation of ring-banded spherulites in poly (l-lactide) (PLLA) during its sol–gel transition. Their formation is correlated with low viscosity and insignificant chain entanglements in the mixtures induced by the ionic liquid. In addition to a driving force for lamellar twisting that depended on the crystallization temperatures, it is believed that reduced lamellar twisting resistance caused by the ionic liquid plays a vital role in the formation of the ring-banded spherulites of PLLA from the mixtures. This study gives further insights into the structural formation of PLLA during a sol–gel transition, which could open new opportunities to tailor the properties of ion gels based on PLLA.