聚偏氟乙烯/有机累托土纳米复合超滤膜的制备及应用

利用溶液插层法制备了聚偏氟乙烯/有机累托土纳米复合超滤膜,研究了纳米掺杂含量对纳米片层分散状态的影响,测定了膜的各项性能,并将膜用于3种水样的处理。结果表明:纳米粘土的加入对复合膜的性能有很大影响;少量粘土的加入,能同时提高膜水通量和截留性能,在纯水通量性能测试时,其阻力增大系数由4.79下降到2.16;在对3种水样进行处理时,粘土的加入不仅能大大地提高膜在实际水处理中的抗污染能力,显著提高膜的反冲洗通量恢复率,还能获得比初始膜更好的出水水质。     

Preparation and characterization of melt processed poly(l-lactide)/layered double hydroxide nonocomposites

This work reports the fabrication and physical properties of biodegradable poly(l-lactide) (PLLA) composites containing a fraction of unmodified layered double hydroxides (LDH–NO₃) and γ-polyglutamate-modified layered double hydroxides (γ-LDH) by melt blending process. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) experimental results showed that the original LDH–NO₃ with the certain amount of aggregates was unevenly dispersed throughout the PLLA matrix. Conversely, γ-LDH allows the formation of an intercalated nanocomposite. Although the water vapor permeability of the PLLA/LDH systems was decreased with increasing the loading of LDH, the barrier property of PLLA reinforced with γ-LDH is superior to that of PLLA-L composites. The effects of both LDHs on mechanical and thermal properties of PLLA were also investigated.     

Crystallization behavior of poly (vinylidene fluoride)/multi-walled carbon nanotubes nanocomposites

The non-isothermal and isothermal crystallization of poly (vinylidene fluoride) (PVDF)/multiple-walled carbon nanotubes (MWNTs) composites containing pristine (MWNT1) and carboxyl group (–COOH) functionalized MWNT (MWNT2) were investigated. The effects of MWNT on the crystallization behavior of PVDF were dependent on the dispersion state of MWNT. Pristine MWNT could increase the nucleation due to better dispersion, and thus, PVDF/MWNT1 composites exhibited higher crystallization peak temperatures (T _cps) and crystallinities (X _cs) compared with PVDF/MWNT2 composites. Meanwhile, the formation of MWNT network confined the growth of crystals. For the isothermal crystallization, MWNT acted as nucleating agents, and the crystallization rate constant k was increased with the addition of MWNT. Besides, the half crystallization time, t _0.5, was remarkably shortened with the increase of MWNT content, especially for the pristine MWNT.     

Large dielectric constant and high thermal conductivity in poly(vinylidene fluoride)/barium titanate/silicon carbide three-phase nanocomposites

Dielectric polymer composites with high dielectric constants and high thermal conductivity have many potential applications in modern electronic and electrical industry. In this study, three-phase composites comprising poly(vinylidene fluoride) (PVDF), barium titanate (BT) nanoparticles, and β-silicon carbide (β-SiC) whiskers were prepared. The superiority of this method is that, when compared with the two-phase PVDF/BT composites, three-phase composites not only show significantly increased dielectric constants but also have higher thermal conductivity. Our results show that the addition of 17.5 vol % β-SiC whiskers increases the dielectric constants of PVDF/BT nanocomposites from 39 to 325 at 1000 Hz, while the addition of 20.0 vol % β-SiC whiskers increases the thermal conductivity of PVDF/BT nanocomposites from 1.05 to 1.68 W m(-1) K(-1) at 25 °C. PVDF/β-SiC composites were also prepared for comparative research. It was found that PVDF/BT/β-SiC composites show much higher dielectric constants in comparison with the PVDF/β-SiC composites within 17.5 vol % β-SiC. The PVDF/β-SiC composites show dielectric constants comparable to those of the three-phase composites only when the β-SiC volume fraction is 20.0%, whereas the dielectric loss of the PVDF/β-SiC composites was much higher than that of the three-phase composites. The frequency dependence of the dielectric property for the composites was investigated by using broad-band (10(-2)-10(6) Hz) dielectric spectroscopy.     

Segregated poly(vinylidene fluoride)/MWCNTs composites for high-performance electromagnetic interference shielding

Conductive polymer composites (CPCs) that contain a segregated structure have attracted significant attentions because of their promising for fulfilling low filler contents with high electromagnetic interference (EMI) properties. In the present study, segregated poly(vinylidene fluoride) (PVDF)/multi-walled carbon nanotubes (MWCNTs) composites were successfully prepared by mechanical mixing and hot compaction. The PVDF/MWCNTs samples with 7 wt% filler content possess high electrical conductivities and high EMI shielding effectiveness (SE), reaching 0.06 S cm⁻¹ and 30.89 dB (in the X-band frequency region), much higher than lots of reported results for CNT-based composites. And the EMI SE greatly increased across the frequency range as the sample thickness was improved from 0.6 to 3.0 mm. The EMI shielding mechanisms were also investigated and the results demonstrated absorption dominating shielding mechanism in this segregated material. This effective preparation method is simple, low-cost, and environmentally-friendly and has potential industrial applications in the future.     

Synthesis and characterization of biodegradable poly(l-lactide)/layered double hydroxide nanocomposites

This study reports the preparation and physical properties of biodegradable nanocomposites fabricated using poly(l-lactide) (PLLA) and magnesium/aluminum layered double hydroxide (MgAl-LDH). The MgAl-LDH with molar ratio of Mg/Al = 2 were synthesized by the co-precipitation method. In order to improve the chemical compatibility between PLLA and LDH, the surface of LDH was organically-modified by polylactide with carboxyl end group (PLA–COOH) using ion-exchange process. Then, the PLLA/LDH nanocomposites were prepared by solution intercalation of PLLA into the galleries of PLA–COOH modified LDH (P-LDH) in tetrahydrofuran solution. Both X-ray diffraction data and Transmission electron microscopy images of PLLA/P-LDH nanocomposites indicate that the P-LDHs are randomly dispersed and exfoliated into the PLLA matrix. Mechanical properties of the fabricated 1.2 wt.% PLLA/P-LDH nanocomposites show significant enhancements in the storage modulus when compared to that of neat PLLA. Adding more P-LDH into PLLA matrix induced a decrease in the storage modulus of PLLA/P-LDH nanocomposites, probably due to the excessive content of PLA–COOH moleculars with low mechanical properties. The thermal stability and degradation activation energies of the PLLA and PLLA/P-LDH nanocomposites can also be discussed.     

Piezoelectric formation mechanisms and phase transformation of poly(vinylidene fluoride)/graphite nanosheets nanocomposites

The β-phase of poly(vinylidene fluoride) (PVDF) is of great technical importance because of its high dielectric constant and piezoelectric effect. In this work, we exfoliated and dispersed natural graphite to prepare 2D-graphite nanosheets (GNS) and prepared PVDF/GNS nanocomposites with different GNS volumes from 1 to 7 ml as film via solution casting method. The concentration of the supernatant was about 0.3 mg/mL. The effect of GNS on the β-phase formation and mechanisms of piezoelectric formation in the PVDF/GNS nanocomposites were investigated. The results showed that with the varying amounts of GNS, the crystalline structure, the morphology, and the dielectric and piezoelectric properties of PVDF/GNS nanocomposites changed. GNS acts as an effective nucleation agent with the orientation almost parallel to the surface of the film meanwhile increasing the amount of beta phase in the PVDF matrix with increasing amount of GNS, also the relative dielectric constant and dielectric loss of the nanocomposites increased with increasing amount of GNS. The value d₃₃ also increased with increasing amount of GNS, and reached a maximum (6.7 pC/N) with 6 ml GNS. The mechanism of piezoelectric formation was proposed based on experiment results of PVDF/GNS nanocomposites.     

Intermediate temperature proton electrolytes based on cesium dihydrogen phosphate and poly(vinylidene fluoride-co-hexafluoropropylene)

Proton conductivity, morphology, phase composition and mechanical properties of (1-x)CsH₂PO₄-xp(VDF/HFP) (x?=?0.05–0.25, weight ratio) polymer electrolytes were investigated for the first time. The chemical interaction of the organic matrix and acid salt was not observed and crystal structure of CsH₂PO₄ was preserved. A method for the synthesis of thin membranes with uniform distribution of the components was proposed. Thin flexible membranes with uniform distribution of sub-micrometer CsH₂PO₄ particles in the polymer membranes and improved hydrolytic stability were obtained firstly by using a bead mill. The mechanical strength of the hybrid polymer compounds was determined using the Vickers microhardness measurements. Proton conductivity in the (1-x)CsH₂PO₄-xp(VDF/HFP) electrolytes decreases monotonically with x increase due to the «conductor–insulator» percolation. Nevertheless, the values of proton conductivity remain sufficiently high, and along with small thickness, flexibility, improved mechanical and hydrophobic properties, it makes polymer electrolytes based on CsH₂PO₄ promising for membranes of medium-temperature fuel cells.

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DSC and conductivity studies on PVA based proton conducting gel electrolytes

An attempt has been made in the present work to prepare polyvinyl alcohol (PVA) based proton conducting gel electrolytes in ammonium thiocyanate (NH₄SCN) solution and characterize them. DSC studies affirm the formation of gels along with the presence of partial complexes. The cole-cole plots exhibit maximum ionic conductivity (2.58 × 10⁻³ S cm⁻¹) for gel samples containing 6 wt% of PVA. The conductivity of gel electrolytes exhibit liquid like nature at low polymer concentrations while the behaviour is seen to be affected by the formation of PVA-NH₄SCN complexes upon increase in polymer content beyond 5 wt%. Temperature dependence of ionic conductivity exhibits VTF behaviour.     

Nanostructure and morphology of poly(vinylidene fluoride)/polymethyl (methacrylate)/clay nanocomposites: correlation to micromechanical properties

Nanocomposites based on poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) with untreated clay were prepared in one step by reactive melt extrusion. Chemical reactions took place between the polymer matrices, the inorganic clay particles, and three reactive agents, leading to the PVDF/PMMA/clay nanocomposites. The microstructure characterizations were carried out by differential scanning calorimetry and wide-angle X-ray scattering (WAXS). The mechanical behavior was investigated by tensile experiments, impact tests, and microhardness measurements. The morphological characterization was carried out by optical and atomic force microscopy (AFM). The decrease of the melting and crystallization temperatures of the PVDF with the increasing PMMA content is attributed to the interactions between the oxygen of the PMMA carbonyl group and the PVDF’s hydrogen atom. WAXS analysis shows that there is neither an intercalation step nor total exfoliation in any composition. As the PMMA content increases, WAXS diagrams show either the PVDF α-crystallographic form, both, α- and β-forms, or only the β-form. For PMMA contents higher than 40 wt%, the materials became amorphous. The microhardness of the samples decrease for a PMMA content up to 20 wt%. The study by optical microscopy and AFM illustrates the significant effect in the presence of clay on the film’s surface morphology.     

Preparation and mechanical properties of exfoliated CoAl layered double hydroxide (LDH)/polyamide 6 nanocomposites by in situ polymerization

Novel exfoliated nanocomposites based on polyamide 6 (PA6)/CoAl layered double hydroxide (CoAl-LDH) have been successfully prepared via in situ polymerization. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results indicated that the inorganic nanoplatelets of CoAl-LDH were homogeneously dispersed in the PA6 matrix. Mechanical testing (by tensile tests and nanoindentation measurements) shows that, compared with neat PA6, the tensile modulus, the yield strength, and the hardness of the nanocomposites are substantially improved by about 100%, 75%, and 25%, respectively, with incorporating only 1 wt% CoAl-LDH. In addition, tensile fracture morphologies of neat PA6 and its nanocomposites are also compared and discussed.     

The creep behaviour of poly(vinylidene fluoride)/“bud-branched” nanotubes nanocomposites

The creep behaviour of poly(vinylidene fluoride) (PVDF)/multiwall carbon nanotubes nanocomposites has been studied at different stress levels and temperatures. To fine-tune the ability to transfer stress from matrix to carbon nanotubes, bud-branched nanotubes, were fabricated. The PVDF showed improved creep resistance with the addition of carbon nanotubes. However, bud-branched nanotubes showed a modified stress–temperature-dependent creep resistance compared with carbon nanotubes. At low stress levels and low temperatures, bud-branched nanotubes showed better improvement of the creep resistance than that of virgin carbon nanotubes, while at high stress levels and high temperatures, the virgin carbon nanotubes presented better creep resistance than that of bud-branched nanotubes. DSC, WAXD, and FTIR were employed to characterise the crystalline structures and dynamic mechanical properties were characterised by DMA testing. The Burgers’ model and the Findley power law were employed to model the creep behaviour, and both were found well describe the creep behaviour of PVDF and its nanocomposites. The relationship between the structures and properties was analysed based on the parameters of the modelling. The improved creep resistance for PVDF by the addition of nanotubes would benefit its application in thermoset composite welding technology.     

Etching and morphology of poly(vinylidene fluoride)

The lamellar structures within spherulites of melt-crystallized poly(vinylidene fluoride) have been examined following the development of an etching technique which allows the study of representative morphologies in this polymer. The banded -spherulites, which predominate at crystallization temperatures below 165°C, are found to be made up of densely packed lamellae with an intrinsically planar habit, whilst the -spherulites which develop preferentially at higher temperatures, have a curious architecture in which the lamellae adopt a highly curved scroll-like morphology. These observations are discussed in terms of existing models for spherulite banding and non-planar lamellar habits.     

氧化石墨烯-氨基酰化酶/聚偏氟乙烯复合膜的制备及特性

通过静电吸附法成功制备了氧化石墨烯-氨基酰化酶（GO-acylase）颗粒。将GO和GO-acylase颗粒分别添加到聚偏氟乙烯（PVDF）铸膜液中,通过相转化法制备了GO/PVDF和GO-acylase/PVDF复合膜。结果显示,GO-acylase/PVDF复合膜的粗糙度最低（R_a=8.21 nm）,表面最平滑。GO/PVDF和GO-acylase/PVDF复合膜的接触角较小（73.72°和71.31°）,说明复合膜的亲水性优于纯PVDF膜。由于GO的添加会增强溶质和非溶质之间的转化过程,从而导致GO/PVDF复合膜的纯水通量最大（69.0 L/（m2 h））。经过测定,GO-acylase/PVDF复合膜的生物活性在4℃下可以持续4周左右。研究结果表明,GO-acylase/PVDF复合膜的成功制备为抗生物污染膜的研发提供了新思路。      

温敏聚偏氟乙烯中空纤维膜的制备和结构表征

制备了聚偏氟乙烯(PVDF)接枝N-异丙基丙烯酰胺(NIPAAm)共聚物(PVDF-g-PNIPAAm),进而采用干-湿法纺丝工艺,首次纺制出温敏PVDF-g-PNIPAAm中空纤维膜.通过红外光谱(FT-IR)、X射线衍射(XRD)、差示扫描量热仪(DSC)、扫描电镜(SEM)等对中空纤维膜的结构和形态进行了表征与研...