Chao-liang Zhang

Super toughening of the poly(L-lactide)/thermoplastic polyurethane blends by carbon nanotubes

Carbon nanotubes (CNTs) were introduced into the poly(L-lactide)/thermoplastic polyurethane (PLLA/TPU) blend to prepare the ternary nanocomposites. The results showed that CNTs selectively localized in the TPU phase, leading to a morphological change from the sea-island morphology to the quasi-cocontinuous morphology. The high content of the CNTs induced the formation of the percolated network structure. Consequently, super toughened PLLA/TPU/CNTs nanocomposites were prepared successfully. More apparent cavitation of the TPU phase and the intensified local plastic deformation of the PLLA matrix under the impact load were observed on the impact-fractured surface of the ternary nanocomposites. This was believed to be the main toughening mechanisms for the ternary nanocomposites. After being annealed, besides the morphological change of the nanocomposites, PLLA matrix also exhibited a large number of crystalline structures. Furthermore, the impact toughness of the ternary nanocomposites was enhanced further.

Effect of graphene oxides on thermal degradation and crystallization behavior of poly(L-lactide)

Graphene oxides (GO) were introduced into a poly(L-lactide) (PLLA) to prepare the PLLA/GO composites with different concentrations of the GOs. The main attention of the present work was focused on the thermal degradation and crystallization behaviors of a PLLA matrix induced by GOs. The measurements based on gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) clearly proved the thermal degradation of the PLLA matrix during the melt-processing procedure. Consequently, reduced complex viscosity of the composites was achieved. The crystallization behaviors of the PLLA matrix were comparatively investigated under different crystallization conditions including melt-crystallization (nonisothermal or isothermal crystallization occurring from the melt state) and cold-crystallization (crystallization occurring from an amorphous solid state) using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide angle X-ray diffraction (WAXD). Largely enhanced crystallization ability of the PLLA matrix was achieved. The crystallization conditions and the GO content are key factors which influence the crystallization behavior of the PLLA matrix. This work proved that the stabilization of the PLLA matrix during the melt-processing procedure must be considered when designing and preparing the PLLA/GO materials.

Self-powered graphene quantum dot/poly(vinylidene fluoride) composites with remarkably enhanced mechanical-to-electrical conversion

We report a facile fabrication approach of a self-powered piezoelectric polymer matrix composite which can efficiently convert mechanical, vibrational and hydraulic energy into electricity without any treatment of electrical poling. The hybrid composite, based on poly(vinylidene fluoride) (PVDF) with a luminescent graphene quantum dot (GQD), finalized its self-polarization process by high pressure crystallization. The size-distributed GQD aggregates in situ catalyzed the self-assembly of PVDF molecules into crystalline beta form 1D nanowires and 3D micro/nanowire architectures concurrently at high pressure. Based on these, we have developed some simple piezoelectric generators. The corresponding open-circuit voltage and short-circuit current generally increased with the increase of GQD loadings. Among them, the GQD/PVDF (3/97, wt/wt) composite revealed more than four times larger electrical output if compared to the pure PVDF. Therefore, these unique self-assembled structures evidently enabled a remarkably improved electrical output during the composite deformation. Furthermore, by modulating GQD concentration together with chemical etching, controllable wettability was observed on the surfaces of the pressure-crystallized GQD/PVDF composites, due to the competition effect between enhanced surface roughening and exposed micro/nanoscale polar crystalline hierarchical structures. The study presented here may open a new avenue for the design and mass production of novel self-powered multifunctional polymer matrix composites with self-reinforcement.

Carbon nanotubes induced poly(vinylidene fluoride) crystallization from a miscible poly(vinylidene fluoride)/poly(methyl methacrylate) blend

Different contents of carbon nanotubes (CNTs) were introduced into a miscible poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend. The interfacial affinity between CNTs and components of the blend was evaluated by calculating the interfacial tension. The dispersion and microstructure of CNTs in the nanocomposites were investigated through scanning electron microscope and rheological measurement. The effect of CNTs on the crystallization of PVDF was comparatively investigated through nonisothermal and isothermal crystallization processes. The results showed that CNTs exhibited stronger interfacial affinity to PMMA. Homogeneous dispersion of CNTs in the nanocomposites was achieved. Largely enhanced crystallization temperature and increased crystallinity of PVDF were obtained by adding CNTs during the nonisothermal crystallization process. The results obtained from the isothermal crystallization process proved that CNTs induced the concentration fluctuation in the sample, which resulted in the formation of spherulites with different types, i.e., the banded spherulites and compact spherulites. Furthermore, both the crystallization temperature and the content of CNTs exhibited great influence on the crystalline morphology of PVDF.

Construction of crystalline Zn-salphen microporous polymer frameworks and their nanostructured carbons through supramolecular assembly of 1D shape-persistent polymers

Abstract

Filling the holes in piezopolymers with a solid electrolyte: a new paradigm of poling-free dynamic electrets for energy harvesting

We report the design and fabrication of a novel poling-free dynamic polymeric piezoelectret generator that has outstanding properties in kinetic energy harvesting. The piezoelectret, i.e. a solid polyelectrolyte filled cellular piezopolymer, was fabricated through solution casting of a poly(vinylidene fluoride) (PVDF)–Nafion blend followed by high pressure crystallization. The size and morphology of the Nafion-filled PVDF cells, together with their crystalline forms and substructures, were controlled at high pressure with the variation of PVDF–Nafion composition. Without any treatment of electrical poling, the open-circuit voltage output density of the PVDF–Nafion generator developed at the optimized conditions, stimulated under its dynamic deformation, reached 14.6 V cm−2, exceeding that of most of the state-of-the-art piezoelectric polymers reported in the open literature. This was attributed to a synergistic action of “intrinsic” polarity and orientation of molecular dipoles of PVDF cells, formed during pressure crystallization, with “artificial” macroscopic dipoles of Nafion fillers on a scale of several micrometers, generated by their inner ionic motions during the cell wall deformation. Moreover, the PVDF–Nafion generator showed good stability and durability, and no decay of electrical output was observed for more than 100000 continuous working cycles. Evidently, the study presented here may lead to a new paradigm of piezoelectrets, enabling the facile fabrication of a class of unique electret-transducer materials and their follow-up applications in electromechanical energy conversion.

Self-assembled porous film with interconnected 3-dimensional structure from 6sPCL-PMPC copolymer

Porous films are widely used in many fields. In this study, we reported a convenient method for the fabrication of biodegradable porous film with a fibrous frame and good interconnectivity. The porous films were formed just by evaporating the solvent of the copolymer solution, which is composed of six-armed star-shaped poly(e-caprolactone)-poly(2-methacryloyloxyethyl phosphorylcholine) (6sPCL-PMPC) in a mixed solvent of tetrahydrofuran (THF) and methanol. Since biodegradable porous films have been widely used in tissue engineering as scaffolds, this handy procedure may significantly facilitate the scaffold fabrication. Scanning electron microscopy (SEM) and 1H NMR spectra were used to investigate the formation mechanism. Factors that affect the film morphology, like temperature, water and composition of the mixed solvent, were also studied.

Greatly enhanced porosity of stretched polypropylene/graphene oxide composite membrane achieved by adding pore-forming agent

A small amount of graphene oxide (GO) was incorporated into polypropylene (PP) to prepare a composite membrane, assisted by the pore-forming agent polyoxyethyleneoctylphenyl-10 (OP-10). The composite membrane was obtained through melt-compounding and a subsequent tensile process. The dispersion of GO in the composite, the dynamic mechanical properties and the melting and crystallization behaviors of the melt-compounded samples were investigated to clearly understand the initial microstructures of the samples. Different tensile strains were applied to obtain the stretched PP composite membrane, and then the morphologies of the composite membrane and the porosity were comparatively investigated. The results showed that the dispersion of GO was apparently improved with the aid of OP-10 and many initial pores were simultaneously introduced into the PP/GO/OP-10 composite, which induced a slight decrease in the storage modulus and glass transition temperature of the PP matrix. OP-10 suppressed the crystallization of the PP matrix, while GO compensated for this effect. Both the stretched PP/OP-10 and the composite membranes exhibited larger mean pore sizes compared with the stretched pure PP membrane. Furthermore, compared with the stretched PP, PP/GO and PP/OP-10 membranes, greatly increased porosity was achieved for the stretched PP/GO/OP-10 composite membrane, especially at relatively high tensile strain. In addition, it was suggested that the initial pores, which were introduced by adding OP-10, acted as a stress concentrator, promoting the formation of more pores during the tensile process by inducing lamellar separation and breakage. This work provided a new method for the preparation of PP-based composite membranes and also endowed them with great potential in many fields.

Annealing Induced Microstructure and Mechanical Property Changes of Impact Resistant Polypropylene Copolymer

The effects of annealing on microstructure and mechanical properties of an impact resistant polypropylene copolymer (IPC) were investigated. Different annealing temperatures ranging from 80 °C to 160 °C were selected. The phase reorganization of IPC during annealing process was studied through morphological characterization technologies, including scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The crystalline structure changes in the IPC sample, including the iPP matrix and PE component, were investigated using wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). Dynamic mechanical analysis (DMA) was used to analyze the relaxation extent of IPC before and after annealing. The results showed that annealing induced phase reorganization in IPC and the degree of phase reorganization depended on annealing temperature. The annealed IPC samples exhibited largely increased crystallinity compared with the unannealed one. Intensified damping peak with increased molecular chain mobility was achieved for the annealed IPC samples. At an appropriate annealing temperature (140 °C), largely enhanced impact strength was achieved for the annealed IPC sample. The toughening mechanisms were analyzed based on the phase reorganization and relaxation behavior.

Hexagonal spiral prismatic polypyrrole nanorods prepared by chemical oxidation

Polypyrrole (abbr. PPy) with an obvious regular hexagonal section and spirally layered structure was synthesized via chemical oxidation method, in which indigo carmine (abbr. IC) and FeCl3 were used as the dopant and oxidant, respectively. The hexagonal spiral prismatic PPy nanorod should stem from the area-limited polymerization of pyrrole monomer in the hexagonal spiral prismatic micelles of IC-Fe (II) chelate which were changed from the previous formed cylindrical IC micelles through the chelated combination between the carbonyl oxygen atom of IC molecule and Fe2+ reduced from Fe3+.