Morphological structures of poly(vinylidene fluoride)/montmorillonite nanocomposites

Poly(vinylidene fluoride) (PVDF)/montmorillonite (MMT) nanocomposites were prepared by melt blen- ding a kind of organically modified montmorillonite with PVDF. The morphological structures of the nanocomposites were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC). The re- sults indicate that organically modified montmorillonites are in the form of intercalation, exfoliation, and fragments in the PVDF matrix. For the composites, the (001) peak position of MMT was found to shift to a lower angle in XRD patterns, and some MMT fragments could be observed under TEM. MMT loading was favorable to producing the piezoelectric β phase in the PVDF matrix and caused internal stress in α crystals. At the same time, the crystallinity and spherulite size of PVDF decreased with the MMT content. MMT induced β phase is stable even at high temperatures (160℃). For these changes in morphological structures, some possible explanations were proposed based on the experimental re- sults.     

Thermoreversible Gelation of Poly(vinylidene fluoride) – Camphor System

Poly (vinylidene fluoride) (PVF₂) produces thermoreversible gel in camphor when quenched to 25°C from the melt under sealed condition. The SEM micrograph of dried PVF₂/camphor gel (Wequation/tex2gif-inf-3.gif= 0.25) indicates presence of fibrillar network structure and the gels at different composition shows reversible first order phase transition. The phase diagram of the gel suggest the formation of a polymer- solvent complex. The melting enthalpy gives a stoichiometric composition of the complex at Wequation/tex2gif-inf-5.gif= 0.25. This corresponds to a molar ratio of PVF₂ monomer/camphor ≈ 4/5. Temperature-dependent synchroton experiments further support the conclusions derived from the phase diagram.     

Crystallization of Poly(ethylene adipate) within γ-Phase Poly(vinylidene fluoride) Matrix

The effects of PEA on the γ-phase PVDF crystal structure and the crystallization of PEA within the pre-existing γ-phase PVDF spherulites have been investigated by optical microscopy(OM), infrared spectroscopy(IR) and scanning electron microscopy(SEM). The results demonstrate that the γ-phase PVDF spherulites consist of the lamellae exhibiting a highly curved scroll-like morphology and develop preferentially in PEA-rich blend. With increasing PEA concentration, the scroll diameter increases and the scrolls are better separated from each other. PEA crystallizes first in the interspherulitic region and transcrystalline layer develops. Subsequently, the transcrystalline layer of PEA continues to grow within the γ-phase PVDF spherulites, e.g., in the region between the scrolls, until impinging on other PEA transcrystalline layers or spherulites. The crystallization kinetics results indicate that the growth rate of PEA crystals in the intraspherulitic region of γ-phase PVDF shows a positive correlation with content of PEA, but a negative one with the crystallization temperature of γ-phase PVDF.     

Enhanced αγ′ Transition of Poly(vinylidene fluoride) by Step Crystallization and Subsequent Annealing

Poly(vinylidene fluoride)(PVDF) exhibits pronounced polymorphs. Its γ phase is attractive due to the electroactive properties. The γ-PVDF is however difficult to obtain under normal crystallization condition. In a previous work, we reported a simple melt-recrystallization approach for producing γ-phase rich PVDF thin films through selective melting and subsequent recrystallization. We reported here another approach for promoting the αγ′ phase transition to prepare γ-phase rich PVDF thin films. To this end, a stepwise crystallization and subsequent annealing process was used. The idea is based on a quick generation of a large amount of α-PVDF crystals with some of their γ-PVDF counterparts at suitable crystallization temperature and then annealing at a temperature above the crystallization temperature for enhancing the molecular chain mobility to overcome the energy barrier of phase transition. It was found that crystallizing the PVDF melt first at 152 °C for 4 h, then quenching to room temperature and finally annealing the sample at 160 °C for 100 h was the most efficient to produce γ-PVDF rich films. This is related to the melting and recrystallization of the α-PVDF crystals produced during quenching in the annealing process at 160 °C, which favors the formation of γ-PVDF crystals for triggering the αγ′ phase transition.     

Enhancement of β-Phase Crystal Content of Poly(vinylidene fluoride)Nanofiber Web by Graphene and Electrospinning Parameters

Electrospun poly(vinylidene fluoride)(PVDF) nanofiber web has been widely utilized as a functional material in various flexible sensors and generators due to its high piezoelectricity, ease processability, and low cost. Among all the crystalline phases of PVDF, β-phase is a key property for PVDF nanofiber web, because the content of β-phase is directly proportional to piezoelectric performance of PVDF nanofiber web.Herein, the impact of graphene content(GC), tip-to-collector distance(TCD), and rotational speed of collector(RSC), as well as their interactions on the β-phase formation of PVDF nanofiber web is systematically investigated via design of experimental method. The fraction of each crystalline phase of PVDF nanofiber web is calculated by FTIR spectra, and the crystallinity is determined by XRD patterns. The influences of GC,TCD, and RSC on both β-phase fraction and crystallinity of PVDF nanofiber are analyzed using Minitab program. The results show that GC, TCD,and RSC all have significant effect on the β-phase content of PVDF nanofiber web, and GC is the most significant one. In addition, an optimal electrospinning condition(GC = 1 wt%, TCD = 4 cm, and RSC = 2000 r·min–1) to fabricate high β-phase crystallinity of PVDF nanofiber web is drawn, under which the crystallinity can reach 41.7%. The contributions in this study could provide guidance for future research on fabricating high performance PVDF nanofiber web based sensors or generators.     

Largely Improved Stretch Ductility and β-Form Room-temperature Durability of Poly(vinylidene fluoride) by Incorporating Aliphatic Polyketone

In this study, we attempt to prepare a new blending system of poly(vinylidene fluoride) (PVDF) and aliphatic polyketone (POK) by melt compounding. The latter is a promising engineering plastic with comprehensive mechanical performances. When POK acted as minor phase to homogeneously disperse in and intimately contact with PVDF matrix, the brittle tensile behavior of neat PVDF transferred into a remarkably flexible manner (the elongation at break increased for 20 times), and more interestingly, the roomtemperature durability of β-form PVDF in the uniaxially drawn blend film was obviously better than that in the neat PVDF film. Fourier transform infrared spectroscopy revealed that specific dipole interaction existed between CF_2 group of PVDF and C=O group of POK.The intermolecular dipolar interaction induced good compatibility in the PVDF/POK blends, as evidently proved by fine two-phase morphology and decreased melting points of POK crystals. Therefore, the good compatibility and interfacial enhancement are responsible for the improvement of the stretch ductility and β-form room-temperature durability of the PVDF/POK blends.     

Poly(ε-caprolactone) (PCL)/cellulose nano-crystal (CNC) nanocomposites and foams

Poly(ε-caprolactone) (PCL)/cellulose nanocrystal (CNC) nanocomposites were produced via twin-screw extrusion. Microcellular nanocomposite samples were produced with microcellular injection molding using carbon dioxide (CO₂) as physical blowing agent. The foaming behavior, physical properties, thermal properties, crystallization behavior, and biocompatibility were investigated. It was found that the CNCs interacted with the PCL matrix which led to a strong interface. The CNCs effectively acted as nucleation agents in microcellular injection molding. Both solid and foamed samples with higher levels of CNC content showed higher tensile moduli, complex viscosities, and storage moduli due to the reinforcement effects of CNCs. Furthermore, improvement in the foamed samples was more significant due to their fine cell structure. The addition of CNCs caused a reduction of the decomposition temperature and an increase in the glass transition temperature, crystallization temperature, and crystallinity of PCL. Moreover, the biocompatibility of the foamed nanocomposites with low CNC content was verified by 3T3 fibroblast cell culture.     

Shape-memory poly(p-dioxanone)–poly(ε-caprolactone)/sepiolite nanocomposites with enhanced recovery stress

Shape-memory poly(p-dioxanone)–poly(e-caprolactone)/sepiolite(PPDO–PCL/OSEP) nanocomposites with different OSEP nanofiber loading were fabricated by chain-extending the PPDO-diol and PCL/OSEP precursors. The precursors and the composites were characterized by1 H NMR, FT-IR, GPC, SEM and TEM.The results demonstrate that a part of PCL segments grafted on the surface of OSEP and composites display a fine dispersion of OSEP fiber in nanoscale with low OSEP content. The shape memory effect(SME) was evaluated by DMA, the results reveal that the PPDO–PCL/OSEP nanocomposites exhibit desirable shape-memory performance. The reinforcement of composites by incorporation of trace OSEP nanofiber evokes an effective improvement in shape-memory recovery stress.     

Crystalline Morphology and Crystallization Kinetics of Melt-miscible Crystalline/Crystalline Polymer Blends of Poly（vinylidene fluoride） and Poly（butylene succinate-co-24mol% hexamethylene succinate）

Poly（vinylidene fluoride） （PVDF） and poly（butylene succinate-co-24 mol% hexamethylene succinate） （PBHS）, both crystalline polymers, formed melt-miscible crystalline/crystalline polymer blends. Both the characteristic diffraction peaks and nonisothermal melt crystallization peak of each component were found in the blends, indicating that PVDF and PBHS crystallized separately. The crystalline morphology and crystallization kinetics of each component were studied under different crystallization conditions for the PVDF/PBHS blends. Both the spherulitic growth rates and overall isothermal melt crystallization rates of blended PVDF decreased with increasing the PBHS composition and were lower than those of neat PVDF, when the crystallization temperature was above the melting point of PBHS component. The crystallization mechanism of neat and blended PVDF remained unchanged, despite changes of blend composition and crystallization temperature. The crystallization kinetics and crystalline morphology of neat and blended PBHS were further studied, when the crystallization temperature was below the melting point of PBHS component. Relative to neat PBHS, the overall crystallization rates of the blended PBHS first increased and then decreased with increasing the PVDF content in the blends, indicating that the preexisting PVDF crystals may show different effects on the nucleation and crystal growth of PBHS component in the crystalline/crystalline polymer blends.     

Synthesis of carbon nanotube—nanodiamond hierarchical nanostructures and their polyurea nanocomposites

Hierarchical carbon nanostructures (HCNs) comprising functionalized nanodiamond particles (ND) covalently bonded to carbon nanotubes (CNTs) through urea or ethylene diamine linkers were synthesized using wet chemistry technique. Atomic force microscopy, transmission electron spectroscopy, and scanning electron spectroscopy reveal the pearl-necklace-like morphology of new HCNs with up to 50% of the CNT surface decorated by ND particles. Nanocomposites fabricated using polyuria/polyurethane hybrid polymer matrix and 0.2 wt.% of HCNs as a reinforcing filler show a 64% increase in tensile and elongation strength at break relatively to neat polymer.     

Synthesis and properties of novel aliphatic polycarbonate from carbon dioxide with 1,2-butylene oxide and ε-caprolactone

A new degradable aliphatic poly(butylene-co-e-caprolactone carbonate) (PBCL) was synthesized through the terpolymerization of carbon dioxide, 1,2-butylene oxide (BO) and e-caprolactone (CL), a polymer supported bimetallic complex (PBM) was used as a catalyst. The terpolymers prepared were characterized by FT-IR,1H NMR, 13C NMR, WXRD and DSC. The hydrolysis tests were carried out to appraise the degradability of the copolymers.     

Thermal Analysis of Poly(AN—co—St) and Poly(AN—St—MMA)

Poly(AN—co—St) (PAS) and poly(AN—St—MMA)(PASM) were synthetized by emulsion polymerisation. The glass transition temperatures (T_g) of the copolymers and the relationship between T_g and the components of the copolymers were investigated by differential scanning calorimetry. The results show that T_g for the AN—St bipolymers has apeak value in the range 115–118°C at a content of 50 mass% St. When methyl methacrylate was added, the T_g of the terpolymer was decreased by about 2–6°C.The thermostability and the activation energy E of degradation were determined by thermogravimetric analysis.This revised version was published online in November 2005 with corrections to the Cover Date.     

The effect of crystallization behavior on high conductivity,enhanced mechanism and thermal stability of poly(ε-caprolactone)/multi-walled carbon nanotube composites

Poly(ε-caprolactone) (PCL) composites filled by multi-walled carbon nanotubes (MWCNTs) which was non-covalently modified by the combined surfactants of poly(sodium 4-styrenesulfonate) and cetyltrimethyl-ammonium bromide (PSS-CTAB) were fabricated via simple solution precipitation method. PCL/MWCNTs composites provided with the low procolation threshold (0.4?wt%) and high electrical conductivity due to good dispersion of MWCNTs. And the excellent mechanical properties and enhanced thermal stability were also obtained with the addition of modified MWCNTs. In addition, all PCL composites showed significantly enhanced crystallization with increasing the MWCNTs contents, which demonstrated that the MWCNT-induced crystallization of PCL could effectively regulate the properties of composites. In a word, introducing non-covalent functionalized MWCNTs in the polymer system was a promising way for developing excellent conductive composites.     

Synthesis and characterization of silver—poly(methylmethacrylate) nanocomposites

The optical properties of silver nanoparticles embedded in poly(methylmethacrylate) (PMMA) was investigated as well as the influence of silver nanoparticles on the thermal properties of polymer matrix. The average size and particle size distribution of silver nanoparticles was determined using transmission electron microscopy. The obtained transparent nanocomposite films were optically characterized using UV-Vis and FTIR spectroscopy. Thermal stability of polymer matrix was improved upon incorporation of small amount of silver nanoparticles. Also, silver nanoparticles have pronounced effect on thermo-oxidative stability of PMMA matrix. The glass transition temperatures of nanocomposites are lower compared to the pure polymer.     

Synthesis and Application of Polyethylene Oxide Macromers (Ⅰ——Synthesis and Characterization of Poly(Ethylene Oxide)Macromers with Allyl-End Group

Polyethylene oxide(PEO) macromers with allyl-end group were synthesized by two different methods(initiating and deactivating).The products obtained were characterized accurately by means,of several techniques including H NMR,IR,VPO,GPC and the double-bond titration,and the results show that such kinds of product possess expected structure.The macromers were copolymerized with small molecular acrylamide,and a series of copolymers with different composition,were obtained by adjusting copolymerization conditions.Moreover,some evidence concerning allyl-group rearrangement in synthesis of the macromers was observed and suitable condition for laboratorial preparation of the macromers is proposed.     

Thermal properties and flammability performance of poly (vinyl alcohol)/α-zirconium phosphate nanocomposites

Nanocomposites of poly (vinyl alcohol) with ethylamine modified zirconium phosphate (ZrP-EA) were prepared by solution blending. Their morphologies were elucidated with X-ray diffraction and transmission electron microscopy, while the thermal stability and flammability performance were characterized by thermogravimetric analysis, Fourier transform infrared spectra and microscale combustion calorimetry. It was established that the morphology of the nanocomposites evolved as ZrP-EA content increased. In the nanocomposites, catalytic degradation of the acetate groups remaining in poly (vinyl alcohol) occurred and catalytic carbonization was observed. Microscale combustion calorimetry revealed that the flammability performance of poly (vinyl alcohol) was improved by the introduction of zirconium phosphate nanoplatelets.     

Polylactones. 13. Transesterification of Poly(L-Lactide) with Poly(Glycoude), Poly(β-Propio-Lactone), and Poly[ε -Caprolactone)

Homogeneous blends of poly(L-lactide) (M _n = 30 000 to 40 000) and poly(β-propiolactone) or poly(ε-caprolactone) were prepared in solution. The solvent-free blends were subjected to transesterification catalyzed by means of methyl triflate, triflic acid, boron trifluoride, or tributyltin methoxide at 100 or 150°C. At 100°C, transesterification was barely detectable even after 96 h. When poly(β-propiolactone) was used as the reactant at 150°C, degradation was faster than transesterification regardless of the catalyst. The same negative result was obtained for heterogeneous blends of poly(L-lactide) and poly(glycolide). In the case of poly(ε-caprolactone), copolyesters with slightly blocky sequences were obtained with tributyltin methoxide as catalyst, whereas the acidic catalysts caused rapid degradation. The copolyesters were characterized by means of ¹H-NMR spectroscopy with regard to their molar composition, by means of ¹³C-NMR spectroscopy with regard to their sequences, and by means of differential scanning calorimetry with regard to crystallinity.