Flammability of carbon nanofiber–clay nanopaper based polymer composites

In this study, a hybrid nanopaper consisting of carbon nanofiber (CNF), and pristine montmorillonite clay (MMT, Cloisite Na⁺) was fabricated through a paper‐making process. The hybrid nanopaper was coated onto the surface of glass fiber (GF) reinforced polymer matrix composites through resin transfer molding process. The characterization results using scanning electron microscopy (SEM) and energy dispersion analysis of X‐ray (EDAX) show that the nanopaper had a porous structure and the polymer resin completely penetrated the hybrid nanopaper. The thermogravimetric analysis (TGA) test results revealed that the addition of MMT clay nanoparticles significantly enhanced the thermal stability of the nanopaper. The flammability of composite samples was evaluated by cone calorimeter test under a radiant heat flux of 50 kW/m². The peak heat release rate (PHRR) was dramatically reduced for the composites coated with the CNF–MMT nanopaper. For comparison, the composites coated with the CNF–organic MMT clay (OMT, Cloisite 20A) nanopaper were also evaluated with cone calorimeter test. The test results showed that the MMT clay was more effective than the OMT in the reduction of the PHRR. The combustion behavior of these samples was also examined by microscale combustion calorimetry (MCC) test. The PHRR obtained from the MCC test decreased with the MMT content in the nanopaper, which was in good agreement with cone calorimeter test results. Copyright © 2010 John Wiley & Sons, Ltd.     

Elastic properties of cellulose nanopaper

Nanopaper is a transparent film made of network-forming nanocellulose fibers. These fibers are several micrometers long with a diameter of 4–50 nm. The reported elastic modulus of nanopaper often falls short of even conservative theoretical predictions based on the modulus of crystalline cellulose, although such predictions usually perform well for other fiber composite materials. We investigate this inconsistency and suggest explanations by identifying the critical factors affecting the stiffness of nanopaper. A similar inconsistency is found when predicting the stiffness of conventional paper, and it is usually explained by the effects introduced during drying. We found that the effect of the drying cannot solely explain the relatively low elastic modulus of nanopaper. Among the factors that showed the most influence are the presence of non-crystalline regions along the length of the nanofibers, initial strains and the three-dimensional structure of individual bonds.     

Preparation and benchmarking of novel cellulose nanopaper

Cellulose - Synthetic polymers and plastics which are currently used as barrier materials in packaging applications are neither renewable nor biodegradable. Nanopaper, which is obtained by breaking...     

Hydrophobic cellulose nanopaper through a mild esterification procedure

Films of cellulose nanofibrils (CNF) (referred to as nanopaper) present a great potential in many applications due to the abundance, low environmental impact, excellent oxygen barrier properties and good mechanical performance of CNF. However, the strong hygroscopic character of the natural nanofibers limits their use in environments with high relative humidity. In this paper, we introduce a simple route for the esterification and processing of CNF with the aim of reducing their hydrophilicity, and producing hydrophobic cellulose nanopaper with reduced moisture sensitivity. The preparation steps of hydrophobic nanopapers involve vacuum filtration, solvent exchange from water to acetone, and reaction with anhydride molecules bearing different hydrophobic alkyl chains by hot pressing. Porous films having a surface area between 38 and 47 g/m² and pore sizes in the 3–200 nm range are obtained. This method preserves the crystalline structure of native cellulose, and successfully introduces hydrophobic moieties on CNF surface as confirmed by FTIR, XPS and elemental analysis. As a result, modified nanopapers have a reduced moisture uptake, both higher surface water contact angle and wet tensile properties as compared with reference non-modified nanopaper, thus illustrating the benefit of the modification for the use of cellulose nanopaper in humid environments.     

Microfibrillated cellulose and cellulose nanopaper from Miscanthus biogas production residue

The feasibility of the isolation of microfibrillated cellulose (MFC) from the fibrous residue of the production of biogas from Miscanthus straw was investigated. Studying two variants of continuous anaerobic fermentation carried out at mesophilic and thermophilic conditions, respectively, MFC was obtained after extensive extraction of non-cellulosic compounds and mechanical fibrillation. MFC crystallinity and molar mass were drastically decreased in biogas residue with increasing temperature in processing. Nonetheless, nanopaper produced from all variants showed acceptable mechanical performance considering its significantly degraded structure. High failure strain at low density is of particular interest for the thermophilic variant. Infrared spectroscopy indicates changes in surface chemistry of the thermophilic variant, which may explain its peculiar tensile properties. Production of fibrillated cellulose from biogas residue is suggested as highly interesting route for the generation of additional value from bioenergy processes.     

From paper to nanopaper: evolution of mechanical and physical properties

In the present work the evolution of physical and mechanical properties of papers and nanopapers is studied. Handsheets made of eucalyptus fibres reinforced with 0, 25, 50, 75 and 100 wt% of nanofibrillated cellulose (NFC) content were fabricated using a Rapid Köthen-like equipment. The obtained papers and nanopapers were physical- and mechanically-characterized. The results showed a significant increase in density and a reduction of porosity in the samples during their transition from paper to nanopaper; besides, nanopapers were more transparent and smoother than normal papers. These physical changes where more evident with increasing amounts of NFC. Regarding mechanical properties, nanopapers with a 100 wt% content of NFC improved their strength and rigidity in 228 and 317 %, respectively, in comparison with normal papers. The evolution of strength and rigidity from paper to nanopaper was linear in relation to the amount of NFC, which means that the ultimate tensile strength was mainly dependant on nanofibril failure.     

Toughening mechanisms in cellulose nanopaper: the contribution of amorphous regions

Cellulose nanopaper is a strong and tough fibrous network composed of hydrogen bonded cellulose nanofibres. Upon loading, cellulose nanopaper exhibits a long inelastic portion of the stress–strain curve which imparts high toughness into the material. Toughening mechanisms in cellulose nanopaper have been studied in the past but mechanisms proposed were often rather speculative. In this paper, we aim to study potential toughening mechanisms in a systematic manner at multiple hierarchical levels in cellulose nanopaper. It was proposed that the toughness of cellulose nanopaper is not, as is often assumed, entirely caused by large scale inter-fibre slippage and reorientation of cellulose nanofibres. Here it is suggested that dominant toughening mechanism in cellulose nanopaper is associated with segmental motion of molecules facilitated by the breakage of hydrogen bonds within amorphous regions .     

Polymer composites based on polyvinyl chloride

Binary and ternary polymer blends based on polyvinyl chloride with ethylene–propylene–diene rubber were studied. A comparative analysis of the effect of a low-molecular-weight plasticizer and high-molecular-weight thermoplastic additives on the deformation and strength characteristics of the composites and on the viscosity of their melt was made. The compatibilizing ability of the plasticizing additives and the possibility of the replacement of the low-molecular-weight plasticizer by the polymeric component were evaluated.     

Blends and composites based on fluoropolymers

Fluoropolymers represent a rather unique group of polymeric materials. Essentially, current most widely used commercial fluoropolymers are derivatives of ethylene and propylene, also known as fluorocarbon polymers. Other, more complex fluorinated polymers are also important technically, but these are used in considerably smaller amounts. Because of the unique chemistry and properties, fluorocarbon polymers rarely form good blends. The only exceptions are homopolymers and copolymers of vinylidene fluoride, which form blends based on thermodynamic compatibility with certain polymers, such as acrylates and methacrylates. However, most known fluoropolymers can be used to produce fiber and fabric reinforced composites as well as composite films and coatings.     

Thermal behaviour of gypsum based composites

DTA/TG and X-ray investigations were carried out on different building composites in order to examine their relative hydration processes. The presence of lime, hemihydrate gypsum, ferosilicate, and some other wastes as leaner and hydrophobic additive in different proportions into composites provokes hydration reactions, leading to calcium silicate hydrate (CSH), ettringite and an intermediate phase formation with varying chemical composition of calcium, aluminum, silicon and sulfur. DTA curves indicate several transformations taking place between composites components, related to hydration of some phases. The content of ettringite component corresponds to the properties and it is used as an indicator for the possibility of industrial application. It is found out that gypsum based cementitious binders could be used as building material in the industry. The same time it is confirmed that the selected wastes could be considered as secondary raw materials.     

Hybrid composites based on organic-inorganic sol-gel systems

Hybrid organic-inorganic composites were developed on the basis of sodium silicate modified with ɛ-caprolactam or ɛ-aminocaproic acid and isocyanate-containing oligourethane with improved physicomechanical properties and water resistance.     

Thermal analysis of aged hdpe based composites

HDPE based composites were produced with 10-20-30 and 40% composite mass of wood fiber. The coupling agents were epolene and silane. The thermal behavior of composite samples was analyzed as a function of the coupling agent content, the exposure time and the wood fibers content by means of differential scanning calorimetry. Calorimetric curves of all samples of first and second heating shows a similar behavior. Some significant relation has been observed between the exposure time and the degree of crystallinity for the same percentage of fiber samples. A linear relation between the melting enthalpy average vs. content in cellulosic fibers is detected. Nevertheless, the fibers non-pretreated with coupling agent show a lower loss of crystallinity of the HDPE matrix at low wood fiber content (10%). A slight diminution of the melting peak temperature is detected as increasing the exposure time. This revised version was published online in July 2006 with corrections to the Cover Date.     

Conducting polymeric composites based on butadiene-acrylonitrile latex

The possibility of controlling the physicochemical and electric properties of conducting latex composites based on butadiene-acrylonitrile latex and carbon fillers, using data on the content of active centers on the filler surface and their distribution with respect to donor-acceptor properties, was examined. To make the fillers compatible with the latexes and prevent their coagulation, the fillers were modified with Leukanol.     

尖晶石型含镓复合材料的研究进展

开发出环保、节能、高效的能源一直是各国的不懈追求.尖晶石型含镓复合材料化学稳定性较好,可作为催化材料和基质材料用于很多方面,这些材料由于具有很多优异的性能而备受研究者的青睐.本文作者系统总结了尖晶石型含镓复合材料的性质和用途,介绍了该材料常用的一些合成方法,并讨论了这些合成方法的优缺点及探索改善材料性能的途径.     

Conducting film-forming composites based on polyaniline-polyimide blends

A procedure is developed for preparing conducting films by their casting from polymer solutions containing polyaniline in the form of a protonated emeraldin base and polyimides in two cosolvents, N-methylpyrrolidone or m-cresol. Self-supporting films cast from composites based on polyimides and camphorsulfonic acid-protonated polyaniline combine a conductivity of 10^?1?10^?2S/cm with good mechanical properties: elastic modulus E = 2.0?2.4 GPa, breaking strength σ_b = 55?60 MPa, and elongation at break ?_b = 8?10%. It has been shown that, when m-cresol and N-methylpyrrolidone are used as cosolvents, the maximum film conductivity is achieved at polyaniline amounts in the composites of 20 and 3%, respectively. In the latter case, films with good strength parameters are formed.     

Anisotropic electroconducting polymer-silicate composites based on polyaniline

Approaches for the development of anisotropic electroconducting composite materials based on polyaniline and Na-montmorillonite prepared by the me thods of boundary and intercalation polymerization of aniline and mechanical blending are proposed. Parallel plane compression of solid and plasticized dispersions is shown to lead to the development of primarily planar ordering of anisometric clay particles with sorbed or intercalated polymer; as a result, nanocomposites with anisotropic electrical conductivity are formed. In the prepared polymer-silicate films, the parameter of anisotropy in electrical conductivity achieves 6 × 10³.     

New film composites based on alicyclic polyimide

New film composites based on alicyclic polyimide with polyethylene terephthalate and polycarbonate plasticizers were prepared. The thermodynamic parameters of mixing of film materials were determined by differential scanning calorimetry and thermogravimetry. The structure and composition of the resulting materials were studied by IR spectroscopy and X-ray diffraction analysis.     

Topochemical acetylation of cellulose nanopaper structures for biocomposites: mechanisms for reduced water vapour sorption

Moisture sorption decreases dimensional stability and mechanical properties of polymer matrix biocomposites based on plant fibers. Cellulose nanofiber reinforcement may offer advantages in this respect. Here, wood-based nanofibrillated cellulose (NFC) and bacterial cellulose (BC) nanopaper structures, with different specific surface area (SSA), ranging from 0.03 to 173.3 m²/g, were topochemically acetylated and characterized by ATR-FTIR, XRD, solid-state CP/MAS ¹³C-NMR and moisture sorption studies. Polymer matrix nanocomposites based on NFC were also prepared as demonstrators. The surface degree of substitution (surface-DS) of the acetylated cellulose nanofibers is a key parameter, which increased with increasing SSA. Successful topochemical acetylation was confirmed and significantly reduced the moisture sorption in nanopaper structures, especially at RH = 53 %. BC nanopaper sorbed less moisture than the NFC counterpart, and mechanisms are discussed. Topochemical NFC nanopaper acetylation can be used to prepare moisture-stable nanocellulose biocomposites.     

Organoinorganic composites based on tetraethoxysilane and nitrogen polybases

Hybrid organoinorganic composites insoluble in water and organic solvents were prepared by the hydrolysis of tetraethoxysilane in the presence of poly-1-vinylpyrazole, poly-1-vinylimidazole, and poly-4-vinylpyridine. The composition of the composites was determined by the nature of the polymeric nitrogen base and hydrolysis conditions. The composites synthesized showed high sorption activity in the extraction of the [PdCl₄]^2?, [PtCl₆]^2?, and [AuCl₄]^? ions from hydrochloric acid solutions.