Proanthocyanidin‐Induced Horizontal Arrangement in Poly(vinyl alcohol)/Graphene Composites with Enhanced Mechanical Properties

A green approach is employed to prepare mechanically enhanced composites by adding noncovalently proanthocyanidin (PC)‐modified graphene (PC‐rGO) into poly(vinyl alcohol) (PVA). Ascorbic acid (AA) is used as the reducing agent, and PC is used as a dispersant to synthesize low‐defect and fully dispersed graphene. After static treatment, the PC‐rGO sheets in the composite form a horizontally arranged structure. Compared with neat PVA, the Young's modulus of the graphene‐modified composites is significantly enhanced by approximately 79.3% with incorporation of 0.9 wt% PC‐rGO. The composites incorporated with GO or AA‐rGO (without PC) have randomly distributed GO structures and apparent rGO agglomeration, resulting in a weaker mechanical property. The dispersibility, degree of defects, distribution state of graphene, and interactions with the polymer matrix are directly related to the final mechanical performance. This new approach to mechanically enhance graphene‐embedded PVA composites provides the possibility for large‐scale production of graphene‐reinforced composite materials.     

Preparation and Characterization of Poly (vinyl alcohol)/Antimony-Doped Tin Oxide Nanocomposites

Nanocomposites of poly (vinyl alcohol) and antimony-doped tin oxide (ATO) were prepared by solution blending. The PVA composites were characterized by FTIR, TGA, DSC, WXRD and stress-strain testing. It has been found that adding ATO to the matrix has great influence on the crystallization behavior and glass transition temperature of PVA. The mechanical properties of PVA changed with the filler content, exhibiting an initial increase in these properties due to polymer-filler interactions. After a maximum value, at about 5 wt%, the mechanical properties decreased. Thermal stability of the nanocomposites was found to be remarkably enhanced by the incorporation of ATO.     

Dramatic Improvements in Mechanical Properties of Poly(L‐lactide)/Silica Nanocomposites by Addition of Hyperbranched Poly(ester amide)

Biodegradable hyperbranched poly(ester amide) (HBP) was used as a compatibilizer to modify PLA/SiO₂ nanocomposites for the first time. The ternary composites displayed dramatically improved mechanical properties including excellent toughness and fairly high stiffness. TEM images revealed that an encapsulation structure was formed by HBP surrounding SiO₂ nanoparticles, and their surfaces became flocculent due to the migration process of silica. The linear viscoelastic behavior of the nanocomposites measured by parallel plate rheometer indicated that strong interface adhesion existed between PLA matrix and silica nanofiller after incorporating of HBP. The compatibilization effect of HBP and the enhanced mobility of nanoparticles contributed to the improved mechanical properties.

     

Preparation and characterization of graphene/poly(vinyl alcohol) nanocomposites

Graphene (GE)‐based nanocomposites are emerging as a new class of materials that hold promise for many applications. In this article, we present a general approach for the preparation of GE/poly(vinyl alcohol) (PVA) nanocomposites. The basic strategy involved the preparation of graphite oxide from graphite, complete exfoliation of graphite oxide into graphene oxide sheets, followed by reduction to GE nanosheets, and finally, the preparation of the GE/PVA nanocomposites by a simple solution‐mixing method. The synthesized products were characterized by X‐ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry, and differential scanning calorimetry analysis. The GE nanosheets were well dispersed in the PVA matrix, and the restacking of the GE sheets was effectively prevented. Because of the strong interfacial interaction between PVA and GE, which mainly resulted from the hydrogen‐bond interaction, together with the improvement in the PVA crystallinity, the mechanical properties and thermal stability of the nanocomposites were obviously improved. The tensile strength was increased from 23 MPa for PVA to 49.5 MPa for the nanocomposite with a 3.25 wt % GE loading. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermal and Morphological Properties of Poly(vinyl alcohol) and Layered Double Hydroxide (LDH) Nanocomposites

Poly(vinyl alcohol) (PVA)/layered double hydroxide (LDH) nanocomposites were synthesized with different compositions: 0, 2, 4, 6, and 8 wt% of LDH by the solution intercalation method. The effects of the layered double hydroxide platelet concentration on the properties of the PVA/LDH films were investigated by thermogravimetric analysis (TGA), optical microscopy, and Fourier transform infrared spectroscopy (FTIR). A reduction in the onset of thermal decomposition temperature was observed in PVA/LDH composites compared to neat PVA. The reduction in the onset of thermal decomposition was likely due to a nucleophilic attack mechanism. The presence of single LDH sheets in form strips in the optical micrographs shows direct evidence of exfoliation, indicating that LDH layers were well-exfoliated and dispersed in the PVA matrix in a disorderly fashion. The FTIR analysis showed good interaction between the continuous PVA matrix and the LDH nanoparticle fillers, by hydrogen bonding through hydroxyl groups. The primary focus of the present investigation was to explore the potential of LDH material as a nanofiller and to improve dispersion of LDH in polar polymers like PVA.     

Preparation and Characterization of High‐Performance Poly(trimethylene terephthalate) Nanocomposites Reinforced with Exfoliated Graphite

To improve the physical properties of poly(trimethylene terephthalate) (PTT), a series of nanocomposites based on PTT and exfoliated graphite (EG) are prepared via melt compounding and their structures, thermal stabilities, mechanical, and electrical properties are studied. XRD and SEM show that graphene nanosheets are well dispersed in the PTT matrix without forming crystalline aggregates even at high EG content. Thermal stability and dynamic mechanical moduli of the nanocomposites are substantially improved by EG addition, and a pronounced increase in electrical volume resistivity from an insulator to almost a semiconductor is observed with increasing EG content. The electrical percolation threshold of the nanocomposites is found to be formed at the EG concentration between 3.0 and 5.0 wt.‐%.

     

Preparation and characterization of poly(vinyl alcohol) nanocomposites made from cellulose nanofibers

A method using a combination of ball milling, acid hydrolysis, and ultrasound was developed to obtain a high yield of cellulose nanofibers from flax fibers and microcrystalline cellulose (MCC). Poly(vinyl alcohol) (PVA) nanocomposites were prepared with these additives by a solution‐casting technique. The cellulose nanofibers and nanocomposite films that were produced were characterized with Fourier transform infrared spectrometry, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. Nanofibers derived from MCC were on average approximately 8 nm in diameter and 111 nm in length. The diameter of the cellulose nanofibers produced from flax fibers was approximately 9 nm, and the length was 141 nm. A significant enhancement of the thermal and mechanical properties was achieved with a small addition of cellulose nanofibers to the polymer matrix. Interestingly, the flax nanofibers had the same reinforcing effects as MCC nanofibers in the matrix. Dynamic mechanical analysis results indicated that the use of cellulose nanofibers (acid hydrolysis) induced a mechanical percolation phenomenon leading to outstanding and unusual mechanical properties through the formation of a rigid filler network in the PVA matrix. X‐ray diffraction showed that there was no significant change in the crystallinity of the PVA matrix with the incorporation of cellulose nanofibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Poly(vinyl alcohol) and Polyamide‐66 Nanocomposites Prepared by Electrospinning

Summary: PVA and PA‐66 nanocomposite fibers with montmorillonite were prepared by electrospinning. Mixing of the components was conducted in two ways: polymer and montmorillonite were mixed with solvent, or monomer was polymerized in the presence of montmorillonite and was then dissolved in a solvent. Polymer/montmorillonite solutions were then electrospun on a non‐woven substrate. To the unaided eye, the coated area was either continuous coating or well‐defined spots. Characterization of the fiber structure and the particle size and distribution by SEM and elemental analysis showed the nanosized filler to be dispersed through the fiber network of the polymer/nanocomposite regardless of the preparation method. However, the clay particles within the fibers were smaller with the polymerization method than mixing in solvent. Only the PA‐66‐based nanocomposites exhibited large enough coating area on the substrate for measurements of contact angles and the time required for water penetration. Contact angles and the time required for water penetration were increased for most of the PA/nanoclay composites relative to the uncoated substrate.

SEM image of a typical fiber structure of a PVA/nanocomposite obtained by electrospinning under alkaline conditions.     

聚乙烯醇/膨润土杂化水凝胶的力学性能和溶胀行为

利用冷冻-解冻法制备了聚乙烯醇/膨润土杂化水凝胶. X射线衍射结果表明,膨润土以剥离形式分布在水凝胶基体中. 研究结果表明,与纯PVA5水凝胶相比,经过5个冷冻-解冻循环制备的含2%(w)膨润土的杂化水凝胶的拉伸模量、拉伸强度和断裂伸长率分别增加了44.0%, 74.2%和25.2%,而溶胀行为与5个循环的纯水凝胶相近. 含0.5%(w)膨润土的杂化水凝胶的拉伸模量和拉伸强度高于基体水凝胶,其在溶胀400 min时的溶胀度高于所有的样品.     

Improving the Mechanical Properties of Poly Methyl Methacrylate Nanocomposites for Dentistry Applications Reinforced with Different Nanoparticles

Properties of poly methyl methacrylate are improved using different nanoparticles for denture applications and the best combination is selected using multi-criteria decision-making methods. For these purposes, poly methyl methacrylate is melt compounded with TiO₂, SiO₂, and Al₂O₃ nanoparticles and then injection molded. The results of mechanical tests revealed that by addition of TiO₂ and SiO₂, the impact strengths of poly methyl methacrylate were increased 229 and 62%, respectively. Also, the results indicated a significant improvement in Young’s modulus and hardness. The implementation of multi-criteria decision-making methods illustrated that TiO₂ nanoparticles are the best candidate for improving the properties of poly methyl methacrylate for dental applications.     

Percolated Network Structure Formation and Rheological Properties in Nylon 6/Clay Nanocomposites

To understand the effect of the percolated clay network structure formed by the exfoliated clay layers in nanocomposites, the clay network structure in nylon‐6‐based nanocomposites is characterized using TEM and FFT analyses. A MMT volume fraction between 0.013 and 0.014 is the percolation threshold for strong network formation. The volume spanning MMT network leads to a very high flow activation energy as compared with that of neat nylon 6, resulting in the pseudo‐solid like response under molten state in N6CNs. A canonical NVT‐MD simulation was conducted in the system made up by nylon 6 molecules/Si(OH)₄ molecules. The formation of the strong interfacial interaction between nylon 6 molecules and Si(OH)₄ molecules induced by OH groups is suggested.

     

Structure and Mechanical Properties of Nanocomposites Based on an Amorphous Copolyester

Nanocomposites based on an amorphous copolyester (PCTG) were obtained by melt mixing, changing the screw speed and the nature of the surfactant, which differed in polarity and molecular volume. Using Young's modulus as a measure of the dispersion level, a less‐polar nature and a higher molecular volume of the surfactant appeared as positive structural factors for dispersion of the clay in the less‐polar PCTG. The Cloisite 20A, which led to the highest modulus (widest dispersion), was mixed at different contents with PCTG at the observed optimum screw speed (200 rpm). Intercalated structures were observed by WAXD and TEM. The dispersion was wide, as observed by TEM, and led to a large (77%) modulus increase after 7% organoclay addition and to important increases in both tensile yield stress and dimensional stability in creep.

     

Mechanical Properties and Degrading Behaviors of Aluminum Hypophosphite-Poly(Lactic Acid) (PLA) Nanocomposites

The flame retardancy of poly(lactic acid) (PLA)/aluminum hypophosphite (AHP, phosphorous content = 41.87 wt.%) nanocomposites (PLA/(AHP-x), x = 15%, 20%, 25%; and x denotes the weight percentage content of AHP) was greatly enhanced by melt blending of AHP into PLA through twin-screw extruder and injection-molding process. The UL 94 V-0 flammability rating can be reached for PLA/(AHP-20%) with the LOI value over 28.8. The well dispersion of the AHP in PLA/(AHP-x) was investigated by FT-IR spectra under the line mapping model. Based on TGA results under a non-isothermal condition, the thermal degradation kinetics of PLA/(AHP-x) composites were studied by Kissinger’s, Ozawa’s and Flynn-Wall-Ozawa’s (FWO’s) methods. And those thermal degradation dynamic analyses showed lower activation energy (E_K or E_O) (from 155 to 122 kJ·mol^–1) corresponded to higher content of AHP (from 15 to 25 wt.%) for PLA/(AHP-x) nanocomposites. Kissinger’s, FWO’s and Coast-Redfern’s methods were used to discriminate the kinetic models and kinetic parameters for the thermal degradation of PLA/(AHP-x), which suggested conversion function G (α) = [-ln(1-α)]^2/3 or G (α) = α for the investigated process. The flame retardant PLA nanocomposites obtained in this study will become safety environment-friendly potential candidates in household and automobile engineering with high performance.     

蒙脱石有机化对PVA/蒙脱石复合薄膜的性能影响

以精制钠基蒙脱石(Na-MMT)、有机化蒙脱石(OMMT)和聚乙烯醇(PVA)为原料,通过水溶液插层-流延成膜法制备纳米复合薄膜。通过X射线衍射(XRD)、扫描电子显微镜(SEM)和热重分析(TGA)对复合材料的结构和性能进行表征,重点探讨蒙脱石有机化对PVA/MMT复合薄膜性能的影响。结果表明Na-MMT和OMMT纳米颗粒在PVA基体中均得到了良好分散;有机改性剂的存在促使PVA/MMT复合薄膜的MMT片层间距扩撑更大,但由于其与PVA相容性较差,导致有效插入MMT片层间的PVA分子较少,PVA/MMT复合薄膜的热稳定性改善效果不明显。     

Chemically Functionalized Graphene Nanosheets and Their Influence on Thermal Stability,Mechanical, Morphological,and Electrical Properties of Poly(methyl methacrylate)/Poly(ethylene Oxide) Blend

Poly(methyl methacrylate)/poly(ethylene oxide) (90/10) blend containing various contents of functionalized graphene was prepared through solution technique and characterized to investigate the effects of functionalized graphene content on mechanical, thermal, and electrical properties of the nanocomposites. Infrared results revealed the interaction between matrix and functionalized graphene. Electron microscopy images of the nanocomposites exhibited a good dispersion of functionalized graphene nanosheets in the blend. The incorporation of functionalized graphene significantly increased the thermal stability and mechanical properties of poly(methyl methacrylate)/poly(ethylene oxide) blend. At electrical percolation threshold achieved at functionalized graphene loading of 4.27?wt%, the conductivity of the nanocomposites was increased by more than eight orders of magnitude.     

Revisiting the thermal relaxations of poly(vinyl alcohol)

The molecular dynamics of poly(vinyl alcohol) (PVA) were studied by dielectric spectroscopy and dynamic mechanical analysis in the 20–300°C range. The well-established plasticizing effect of water on the glass-transition temperature (T_g) of PVA was revisited. Improper water elimination analysis has led to a misinterpretation of thermal relaxations in PVA such that a depressed T_g for wet PVA films (ca. 40°C) has been assigned as a secondary β relaxation in a number of previous studies in the literature. In wet PVA samples, two different Vogel–Fulcher–Tammann behaviors separated by the moisture evaporation region (from 80 to 120°C) are observed in the low- (from 20 to 80°C) and high- (>120°C) temperature ranges. Previously, these two regions were erroneously assigned to two Arrhenius-type relaxations. However, once the moisture was properly eliminated, a single non-Arrhenius α relaxation was clearly observed. X-ray diffraction analysis revealed that the crystalline volume fraction was almost constant up to 80°C. However, the crystallinity increased approximately 11% when temperature increased to 180°C. A secondary β_c relaxation was observed at 140°C and was related to a change in the crystalline volume fraction, as previously reported. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

POSS增强PMMA热性能和力学性能研究

采用溶液共混法将笼形纳米粒子甲基丙烯酸甲酯基多面低聚倍半硅氧烷（MMA-POSS）与聚甲基丙烯酸甲酯（PMMA）共混制备无机/有机纳米复合材料。利用傅里叶红外光谱仪、核磁共振波谱仪和场发射扫描电子显微镜对材料进行了结构表征。场发射扫描电子显微镜观察复合物薄膜表面形态显示,当MMA-POSS含量较小时,薄膜表面均匀平整,MMA-POSS均匀地分散于PMMA基体中,复合材料的热稳定性和力学性能得到明显改善,其玻璃化转变温度（Tg）和热分解温度（Td）显著提高,POSS含量为1.0 %（质量分数,下同）时,Tg 和Td分别提高了16.9 ℃和21.0 ℃。     

Effect of Nanoparticles on Mechanical and Flame-retardant Properties of Polyether-Block-Polyamide Polymer Nanocomposites

In this study, polyester elastomer-based thermoplastic (TPEE) nanocomposites were fabricated for flame-retardant applications. Small amounts of graphene and nanoclay were added to the nanocomposites to investigate their effects on the mechanical and thermal properties of the nanocomposites. The addition of a phosphorous flame-retardant additive resulted in a significant improvement of the Young’s modulus and thus yield stress in the synthesized nanocomposites as compared to those made with the virgin TPEE. There was no synergistic improvement in mechanical properties with the addition of graphene and nanoclay to the nanocomposites. However, thermal properties, mainly the heat deflection temperature and fire performance (UL-94 V0), were improved significantly by the addition of graphene and nanoclay and a synergistic effect was observed. Heat distortion temperature and thermogravimetric analysis were used to analyze the thermal properties of the nanocomposites. The UL-94 testing method was used to investigate the fire performance of the nanocomposites. Scanning electron microscopy was used to observe the polymer fracture surface morphology. The dispersion of the graphene and nanoclay particles was confirmed by transmission electron microscopy analysis.     

聚环氧乙烷、聚四氢呋喃及其共聚醚力学性能的MD模拟

为寻求预示复合材料力学性能的理论方法,对优选NEPE推进剂的黏合剂预聚物提供基础信息,在COMPASS力场下,取NVT系综,对聚环氧乙烷、聚四氢呋喃和它们的无规共聚醚进行了分子动力学(MD)模拟,并计算出弹性系数、模量、泊松比和柯西压等力学参数.经比较发现,聚环氧乙烷的刚性和延展性最优,共聚醚次之,聚四氢呋喃最差.