Development of self-assembled bacterial cellulose–starch nanocomposites

A bioinspired bottom-up process was developed to produce self-assembled nanocomposites of cellulose synthesized by Acetobacter bacteria and native starch. This process takes advantage of the way some bacteria extrude cellulose nanofibres and of the transport process that occurs during the gelatinization of starch.Potato and corn starch were added into the culture medium and partially gelatinized in order to allow the cellulose nanofibrils to grow in the presence of a starch phase. The bacterial cellulose (BC)–starch gels were hot pressed into sheets that had a BC volume fraction higher than 90%. During this step starch was forced to further penetrate the BC network. The self-assembled BC–starch nanocomposites showed a coherent morphology that was assessed by Atomic Force Microscopy (AFM) and Environmental Scanning Electron Microscopy (ESEM). The nanocomposites structure was studied using X-ray diffraction and ATR-FTIR spectroscopy. The degree of crystallinity of the final nanocomposites was used to estimate the volume fraction of BC. The aim of this paper is to explore a new methodology that could be used to produce nanomaterials by introducing a different phase into a cellulose nanofibre network during its assembly.     

Preparation and characterization of melt-extruded thermoplastic starch/clay nanocomposites

A series of gelatinized starch–clay nanocomposites which exhibit intercalated and exfoliated structures have been developed. Various nanoclay dispersions were prepared (either by standard mixing or through the use of ultrasonics) prior to their combination with a high amylose content starch using high-speed mixing and extrusion technology. Intercalated and exfoliated type structures were observed in the sheet extruded nanocomposites using X-ray diffraction and transmission electron microscopy (TEM). Due to the hydrophilic nature of the gelatinized starch nanocomposite a novel preparatory technique was developed to produce nano scale sections for TEM. A range of plasticiser levels were used in conjunction with different unmodified nanoclays (sodium montmorillonite (Na-MMT) and fluorohectorite (Na-FHT)) having different cationic exchange capacities. It was shown that an optimum level of both plasticiser and nanoclay existed to produce a gelatinized starch film with the highest levels of exfoliation, resulting in superior properties. The use of ultrasonics was only advantageous in terms of clay dispersions at medium clay concentrations in the Na-MMT nanocomposites and higher clay concentrations in the Na-FHT, most probably due to the difference in cationic exchange capacity; however when the level of clay, water and starch was optimised an exfoliated structure was produced via standard mixing which exhibited comparable improvements in mechanical properties to ultrasonically treated samples.     

Morphological and thermomechanical characterization of thermoplastic starch/montmorillonite nanocomposites

A combination of starch and clay for the preparation of nanocomposite materials is proposed. In this work, starch was plasticized by pequi (Caryocar brasiliense) oil, and thermoplastic starch (TPS)/montmorillonite (MMT) nanocomposites were analyzed by X-ray diffraction (XRD), thermogravimetry (TG), thermomechanical analyses (TMA) and scanning electron microscopy (SEM). Exfoliated and intercalated nanocomposites were found to be dependent on MMT content. Exfoliation is the predominant mechanism of clay dispersion for low filler loading. Increase of the clay loading (>5 wt.%) causes intercalation. The introduction of low content (?5 wt.%) of MMT improves the thermal stability and the stiffness of the materials. There is a limit content of clay that can be added to improve the thermal and thermomechanical properties of the composites. Beyond that value the composite presents properties below the original polymer.     

Reduced water vapour sorption in cellulose nanocomposites with starch matrix

The effects of microfibrillated cellulose nanofibers from wood on the moisture sorption kinetics (30% RH) of glycerol plasticized and pure high-amylopectin starch films were studied. The presence of a nanofiber network (70 wt% cellulose nanofibers) reduced the moisture uptake to half the value of the pure plasticized starch film. The swelling yielded a moisture concentration-dependent diffusivity. Quite surprisingly, the moisture diffusivity decreased rapidly with increasing nanofiber content and the diffusivity of the neat cellulose network was, in relative terms, very low. It was possible to describe the strong decrease in zero-concentration diffusivity with increasing cellulose nanofiber/matrix ratio, simply by assuming only geometrical blocking using the model due to Aris. The adjusted model parameters suggested a “simplified” composite structure with dense nanofiber layers oriented in the plane of the film. Still, also constraining effects on swelling from the high modulus/hydrogen bonding cellulose network and reduced amylopectin molecular mobility due to strong starch–cellulose molecular interactions were suggested to contribute to the reductions in moisture diffusivity.     

Recent advances and perspectives on starch nanocomposites for packaging applications

Starch nanocomposites are popular and abundant materials in packaging sectors. The aim of this work is to review some of the most popular starch nanocomposite systems that have been used nowadays. Due to a wide range of applicable reinforcements, nanocomposite systems are investigated based on nanofiller type such as nanoclays, polysaccharides and carbonaceous nanofillers. Furthermore, the structures of starch and material preparation methods for their nanocomposites are also mentioned in this review. It is clearly presented that mechanical, thermal and barrier properties of plasticised starch can be improved with well-dispersed nanofillers in starch nanocomposites.     

High-performance nanocomposites based on polyetherketones

Polyetherketones, PEKs, are an important family of high-performance thermoplastic materials that display a unique combination of toughness, stiffness, thermooxidative stability, chemical and solvent resistance, flame retardancy, and retention of physical properties at high temperatures. A relevant step forward in the development of these materials has been the recent incorporation of nanofillers to extend their utility in advanced technological applications. This review provides an extensive overview of the research on PEK-based nanocomposites with a special emphasis on both carbon-based nanofillers, such as nanotubes or nanofibers, and inorganic nanoparticles. Nanocomposites can be fabricated by simple, low-cost conventional techniques such as extrusion and compression molding, generally combined with pre-processing stages involving mechanochemical treatments in organic solvents. Different strategies employed to efficiently incorporate carbon nanofillers into these matrices, including polymer functionalization, covalent grafting and nanofiller wrapping in compatibilizing systems are described. The analysis of the influence of the preparation and processing conditions as well as the nanofiller type, attributes and loading on the structure and properties of the resulting materials is also considered. Composites incorporating carbon nanofillers display remarkably improved thermal stability, electrical and thermal conductivity as well as mechanical property enhancements compared to the neat polymers. On the other hand, the incorporation of inorganic nanoparticles such as WS₂, SiO₂ or Al₂O₃ significantly enhances the tribological properties of the matrix, mainly the coefficient of friction and wear resistance. Finally, current and potential applications of these multifunctional nanocomposite materials in fields such as medicine, telecommunications, electronics, aerospace, automobile and chemical industries are described.     

Characterization and thermophysical properties of unsaturated polyester-layered silicate nanocomposites

The thermophysical properties of unsaturated polyester (UPE) nanocomposites reinforced by organo-montmorillonite clay nanoplatelets are reported. The organo-clay nanoplatelets were sonicated in acetone for 2 hours to be dispersed in the UPE matrix. Vacuum extraction removed not only the acetone but also the styrene present in the UPE solution. The same mechanical and thermophysical properties of UPE were regained after adding the lost amount of styrene to the UPE solution. Both delaminated and intercalated clay morphologies were observed by transmission electron microscopy. It was found that the sonication process was effective to delaminate clay nanoplatelets for more homogeneous dispersion, dependent on organic chemical modifications for clay nanoplatelets. A higher storage modulus enhancement was obtained when the organo-clay nanoplatelets were delaminated and more homogeneously dispersed. The reinforcing effect of both delaminated and intercalated clay nanoplatelets was theoretically evaluated with the Halpin-Tsai equations. It was evaluated that the aspect ratio of delaminated clay nanoplatelets was approximately 150. The increase of the storage modulus below and above the glass transition temperature was achieved without reducing glass transition temperature and Izod impact strength with increasing clay content.     

聚合物基纳米复合材料的研究进展

本文综述了近年来聚合物基纳米复合材料的研究进展情况 ,对聚合物基纳米复合材料的各种制备方和已研究的体系及其特点进行了归纳和分析 ,并对聚合物基纳米复合材料的应用前景进行了展望     

Electrochemiluminescence immunosensor based on CdSe nanocomposites

A novel strategy for the enhancement of electrochemiluminescence (ECL) was developed by combining CdSe nanocrystals (NCs), carbon nanotube-chitosan (CNT-CHIT), and 3-aminopropyl-triethoxysilane (APS). A label-free ECL immunosensor for the sensitive detection of human IgG (HIgG) was fabricated. The colloidal solution containing CdSe NCs/CNT-CHIT composite was first covered on the Au electrode surface to form a robust film, which showed high ECL intensity and good biocompatibility. After APS as a cross-linker was covalently conjugated to the CdSe NCs/CNT-CHIT film, the ECL intensity was greatly enhanced. And, an intensity about 20-fold higher than that of the CdSe NCs/CNT-CHIT film was observed. After antibody was bound to the functionalized film via glutaric dialdehyde (GLD), the modified electrode could be used as an ECL immunosensor for the detection of HIgG. The specific immunoreaction between HIgG and antibody resulted in the decrease in ECL intensity. The ECL intensity decreased linearly with HIgG concentration in the range of 0.02-200 ng mL(-1), and the detection limit was 0.001 ng mL(-1). The immunosensor has the advantages of high sensitivity, speed, specificity, and stability and could become a promising technique for protein detection.     

聚苯硫醚结构功能一体化纳米复合材料的研制

探索性的运用机械共混法制备了兼具较好力学性能和吸波功能的聚苯硫醚(PPS)基纳米复合材料.掺加刚性纳米粒子后,PPS的韧性明显改善,稀土/PPS试样在悬臂粱无缺口冲击试验中出现冲不断现象.稀土C/铁氧体M/PPS纳米复合材料在14.5～15GHz之间有最大吸收峰为-2.25dB,在13.6～15.7GHz之间的反射率低于-2.0dB.     

Characterization of IrO2/CNT nanocomposites

IrO₂ nanocrystals (NCs) were grown on vertically aligned carbon nanotube (CNT) templates, forming IrO₂/CNT nanocomposites, by metal organic chemical vapour deposition using (C₆H₇)(C₈H₁₂)Ir as a source reagent. The surface morphology, structural and spectroscopic properties of the nanocomposites were characterized using field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman scattering. IrO₂ varied from particle- to tube-like NCs as the deposition time increased from 5 to 60 min. The particle-like IrO₂ NCs may be used as a protective layer on CNTs, providing stable and uniform field emission application. The tube-like structure may increase the surface-to-volume ratio which makes the IrO₂/CNT nanocomposites as an attractive candidate for the supercapacitor application.     

Characterization and finite element modeling of montmorillonite/polypropylene nanocomposites

Finite element modeling can be a useful tool for predicting the behavior of composite materials and arriving at desirable filler contents for maximizing mechanical performance. In the present study, to corroborate finite element analysis results, quantitative information on the effect of reinforcing polypropylene (PP) with various proportions of nanoclay (in the range of 3–9% by weight) is obtained through experiments; in particular, attention is paid to the Young’s modulus, tensile strength and failure strain. Micromechanical finite element analysis combined with Monte Carlo simulation have been carried out to establish the validity of the modeling procedure and accuracy of prediction by comparing against experimentally determined stiffness moduli of nanocomposites. In the same context, predictions of Young’s modulus yielded by theoretical micromechanics-based models are compared with experimental results. Macromechanical modeling was done to capture the non-linear stress–strain behavior including failure observed in experiments as this is deemed to be a more viable tool for analyzing products made of nanocomposites including applications of dynamics.     

Characterization of PAN/ATO nanocomposites prepared by solution blending

Conducting nanocomposites of polyacrylonitrile (PAN) and antimony-doped tin oxide (ATO) were prepared by solution blending. Electrical properties of the nanocomposites were characterized by means of electrical conductivity measurements and the phase structures were investigated via scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analyses (TGA) and dynamical mechanical analysis (DMA). This study unveiled a remarkable, interpenetrating network of chainlike nano-ATO within the PAN matrix, consistent with the existence of connected conducting paths at content as low as 4 wt% of the nano-ATO. The storage modulus of the nanocomposites increased with increasing content of ATO, due to formation of immobilized layer between polymer and filler. The interactions between ATO and PAN molecules resulted in high tan δ for the PAN/ATO nanocomposites. Thermal stability of the nanocomposites was found remarkably enhanced by the incorporation of nano-ATO.     

聚吡咯/蒙脱土纳米复合材料的表征与复合机理

以水为介质，用化学氧化就地吸附聚合法(in：situpolymerization)制备了聚吡咯(PPy)／蒙脱土(MMT)纳米复合导电材料。利用红外光措(FT-IR)、热失重(TGA)、X射线衍射(XRD)和四探针技术表征了材料的组成、结构和性能。结果表明PPy键已进入MMT内层空间，二者达到了纳米级复合。纳米复合材料的电导率已达50S／cm。     

Natural rubber latex/potato starch nanocrystal nanocomposites: Correlation morphology/electrical properties

This paper discusses the preparation and characterization of nanocomposites obtained with potato starch nanocrystals, and their use as fillers in order to realize nanocomposites with a natural rubber latex matrix. The preparation of potato starch nanocrystals was done by hydrolysis of potato starch powder using sulfuric acid. The synthesized potato starch nanocrystal suspensions were mixed with natural rubber latex by latex stage mixing process using a magnetic stirrer. In this way, composites containing up to 20% w/w of fillers have been obtained. Morphological studies indicated a relatively uniform dispersion of starch nanocrystals in the nanocomposites until 15% w/w filler loading. Dielectric measurements confirm the existence of a threshold at a composition close to 15% w/w of filler at which the fillers become agglomerated.     

Improving the mechanical properties of thermoplastic starch/poly(vinyl alcohol)/clay nanocomposites

Thermoplastic starch/poly(vinyl alcohol) (PVOH)/clay nanocomposites, exhibiting the intercalated and exfoliated structures, were prepared via melt extrusion method. The effects of clay cation, water, PVOH and clay contents on clay intercalation and mechanical properties of nanocomposites were investigated. The experiments were carried out according to the Taguchi experimental design method. Montmorillonite (MMT) with three types of cation or modifier (Na⁺, alkyl ammonium ion, and citric acid) was examined. The prepared nanocomposites with modified montmorillonite indicated a mechanical improvement in the properties in comparison with pristine MMT. It was also observed that increases in tensile strength and modulus would be attained for nanocomposite samples with 10%, 5% and 4% (by weight) of water, PVOH and clay loading, respectively. The clay intercalation was examined by X-ray diffraction (XRD) patterns. The chemical structure and morphology of the optimum sample was also probed by FTIR spectroscopy and transmission electron microscopy (TEM).     

Characterization of magnetization-induced second harmonic generation in iron oxide polymer nanocomposites

We have measured the magnetization-induced second harmonic generation (MSHG) of a nanocomposite consisting of iron oxide nanoparticles in a polymer film. The existing theoretical framework is extended to include DC magnetic fields in order to characterize the MSHG signal and analyze the measurements. Additionally, magnetic hysteresis loops are measured for four principal polarizer-analyzer configurations, revealing the P(IN)-P(OUT) and S(IN)-P(OUT) polarizer-analyzer configurations to be sensitive to the transverse magnetic field. These results demonstrate the use of MSHG and the applied formalism as a tool to study magnetic nanoparticles and their magnetic properties.     

High strain rate compression of epoxy based nanocomposites

This work aimed to investigate the strain-rate effect (0.001–3000 s⁻¹) on compressive properties of the highly cross-linked epoxy and the epoxy sample filled with 10 wt% sol-gel-formed silica nanoparticles. As the strain rate increased, the compressive modulus and transition strength of both samples went up distinctly, the strain at break and ultimate strength decreased more or less, while the strain energy at fracture nearly did not change. Adding the sol-gel-formed silica nanoparticles can improve effectively the compressive modulus, transition strength as well as strain energy at fracture of the epoxy polymer owing to their homogeneous dispersion in epoxy matrix.     

Characterization of hot extruded Mg/SiC nanocomposites fabricated by casting

Mg–1%SiC nanocomposites were fabricated using an ultrasonic cavitation based casting method, resulting in the dispersion of the reinforcing SiC nanoparticles to form Mg–metal matrix nanocomposite (Mg–MMNC) billets. The MMNC billets were then processed using hot extrusion at 350 °C. Micrographic observations illustrate a significant grain size reduction and the presence of microbands that align the SiC nanoparticles parallel to the direction of extrusion for Mg–MMNCs. Observations from the cross-section at 90° of the extrusion direction show uniform nanoparticles dispersion. Results from the extruded Mg–MMNCs tensile testing at different temperatures (25, 125 and 177 °C) reveal an increase of the yield strength, ultimate tensile strength, and ductility values as compared to the un-reinforced and extruded Mg-alloy; such increase was also observed from the microhardness testing results where an increase from 19 to 34% was measured.