Lignin nanocomposites

Lignin is a biopolymer and one of the main constituents of woody plants where it plays the role of lining agent and is comparable in this respect to cement in steel reinforced concrete. Polymer nanocomposites containing biopolymers such as cellulose, lignin, starch, proteins, etc. are the object of recent numerous studies and are known also as bio-nanocomposites. This paper deals with lignin use in various polymer nanocomposites. It presents the preparation and uses of nanolignin as a filler and lignin uses as a matrix or a matrix component in polymer nanocomposites.     

Polymer nanocomposites

Polymer nanocomposites are distinguished by the convergence of length scales corresponding to the radius of gyration of the polymer chains, a dimension of the nanoparticle and the mean distance between the nanoparticles. The consequences of this convergence on the physics of the polymer chains are considered, and some of the outstanding issues and their potential consequences on structure—property relations for polymer nanocomposites are highlighted. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3252–3256, 2007     

Clay-fulleropyrrolidine nanocomposites

In this work, we describe the insertion of a water-soluble bisadduct fulleropyrrolidine derivative into the interlayer space of three layered smectite clays. The composites were characterized by a combination of powder X-ray diffraction, transmission electron microscopy, X-ray photoemission and FTIR spectroscopies, and laser flash photolysis measurements. The experiments, complemented by computer simulations, give insight into the formation process, structural details, and properties of the fullerene/clay nanocomposites. The reported composite materials constitute a new hybrid system, where C(60) differs from its crystals or its solutions, and open new perspectives for the design and construction of novel C(60)-based organic/clay hybrid materials.     

Polyamide nanocomposites

Polyamides are thermoplastic polymers mainly used for producing synthetic fibers. Only about 10% of polyamides are used for plastics production. The market is shared roughly equally between polyamide 6 (polycaprolactam) and polyamide 66 {poly (hexamethyleneadipamide)}. More recently, the research on polyamides led to their nanocomposites. These new hybrid polyamides are reinforced with nanofillers able to increase their main properties and also bring some new interesting characteristics. This paper deals with nanocomposites made of various polyamides and nanofillers; they find application in many engineering fields.     

Silica hybrid nanocomposites

In this work we present experimental results about the formation, properties and structure of sol — gel silica based biocomposite containing Calcium alginate as an organic compound. Two different types of silicon precursors have been used in the synthesis: tetramethylortosilicate (TMOS) and ethyltrimethoxysilane (ETMS). The samples have been prepared at room temperature. The hybrids have been synthesized by replacing different quantitis of the inorganic precursor with alginate. The structure of the obtained hybrid materials has been studied by XRD, IR Spectroscopy, EDS, BET and AFM. The results proved that all samples are amorphous possessing a surface area from 70 to 290 m²/g. It has also been established by FT IR spectra that the hybrids containing TMOS display Van der Walls and Hydrogen bonding or electrostatic interactions between the organic and inorganic components. Strong chemical bonds between the inorganic and organic components in the samples with ETMS are present. A self-organized nanostructure has been observed by AFM. In the obtained hybrids the nanobuilding blocks average in size at about 8–14 nm for the particles.     

Self-reinforced cellulose nanocomposites

A self-reinforced cellulosic material was produced exclusively from regenerated cellulose microcrystals. The level of reinforcement was controlled by tailoring the crystallinity of cellulose by controlling the dissolution of microcrystalline cellulose (MCC) before its regeneration process. After the cellulose regeneration a self-reinforced material was obtained in which cellulose crystals reinforced amorphous cellulose. This structure was produced by dissolution of MCC in a non-derivatising cosolvent N,N-dimethylacetamide/LiCl followed by subsequent cellulose regeneration in distilled H₂O. The reduction of the overall crystallinity of self-reinforced regenerated cellulose was dependent on the dissolution time of the cellulose precursor. The crystallinity of regenerated cellulose was determined by wide angle X-ray diffraction. A reduction in crystal size from microcrystalline cellulose to regenerated cellulose was observed with increasing dissolution time in DMAc/LiCl cosolvent. The reduction in degree of crystallinity of regenerated cellulose led to a decrease in the tensile mechanical performance and thermal stability of the regenerated cellulose. The controlled dissolution of microcrystalline cellulose resulted in the modification of structural, physical, thermal properties and moisture uptake behaviour of regenerated cellulose.     

Silver-carboxymethyl chitin nanocomposites

Nanocomposite macromolecular systems consisting of silver nanoparticles immobilized in a carboxymethyl chitin matrix are obtained. The method of ultrasonic treatment of a heterophase system (isooctane-water) in the presence of antioxidants of plant origin is used to transfer silver nanoparticles from their micellar solution in isooctane to an aqueous polymer solution. The formation of hydrogen bonds between the functional groups of carboxymethyl chitin and hydroxyl groups of antioxidants is confirmed by Fourier transform infrared spectroscopy. This interaction can provide additional stabilization of metal nanoparticles in the macromolecular system. The transmission electron microscopy data shows that the size of silver nanoparticles increases in a series of antioxidants (gallic acid, dihydroquercetin, and syringic acid). The increase is presumably caused by significant differences in the structures of these antioxidants and their interaction with the polymer matrix.     

Superhydrophobic cellulose nanocomposites

Superhydrophobic cellulose nanocomposites were prepared using a multi-step nanoengineering process. The combination of different techniques made it possible to construct novel features at the ensuing surface, characterized by both an increase in its roughness induced by amorphous silica particles and a reduction in its energy insured by perfluoro moieties, giving rise to water contact angles approaching 150 degrees . The modification calls upon an aqueous LbL system followed by siloxane hydrolysis, both conducted at room temperature in air. Each modification was followed by scanning electron microscopy (SEM) and atomic force microscope (AFM). These original cellulose-silica-silane composite materials open the way to further valorisations of a ubiquitous renewable resource in applications such as water repellence and self-cleaning.     

Rheology of nanocomposites

In this study, a methodology is developed for the quantitative characterisation of the nanofiller network in polymer nanocomposites via dynamic rheometry. Nanoclay-reinforced poly(ε-caprolactone) (PCL) nanocomposites were prepared by melt mixing. Frequency sweep experiments in the melt state display at low frequencies a solid-like elastic response that can be attributed to the formation of a physical nanofiller network. Combining a semi empirical model and the time–temperature superposition principle permits a reliable determination of the zero shear modulus that characterises the solid-like response of nanocomposites at low frequency, and which is related to the nanofiller dispersion.     

Natural rubber nanocomposites

Natural rubber obtained from a milky colloid (latex) extras mainly from the tree Hevea Brasiliensis is approximately 95% cis-polyisopren has important physical properties. Among its shortcomings are resistance to aging and thermal stability that limits its applications. The use of fillers in rubber is almost as old as the use of rubber itself. ZnO originally used for whiteness was the first “active” filler. In 1904 carbon black was discovered and since then became the most important powder used in rubber technology. Recently various mineral and organic nanoparticles are studied as reinforcements for elastomers in view -with minimum amounts – to achieve required properties. Natural rubber nanocomposites bring together mechanical and thermal properties from the rubber matrix and special characteristics of the nanoparticles.     

Tailored interfaces in nanocomposites

Different kinds of clays based on sodium montmorillonite have been modified i) by cationic exchange of alkylammonium ions and ii) by covalent grafting of organosilane. We have prepared organophilic clays with different gallery heights (due to alkylammonium ions with alkyl chain length varying from 8 to 18 carbon atoms) and with a specific functionalisation (due to the organosilane). We have generated organoclays with different kind of organic layer properties: ionically bonded or physically adsorbed alkylammonium ions and covalently grafted organosilane. These different organoclays have shown various specific behaviours when dispersed in monomers or in a reactive mixture, proving the influence of the surfactant on the nanocomposite final properties.     

Ion transport in nanocomposites

Successive analysis of interface defect formation and its implications for the ionic conductivity was carried out for ionically conducting nanocomposites that hold much significance for technological applications. It was shown that the most efficient way to prepare such composites is through the use of nanosized particles. A review was made of the current state of research on inorganic composites and hybrid membrane materials that are already in use in alternative power engineering.     

Synthesis of silsesquioxane nanocomposites

In order to investigate the effect of presence of well defined nano-sized inorganic particles on the molecular mobility a conformation statistics of polymer chains, well defined polystyrene (PS) and poly(methyl methacrylate) (PMMA) macromolecules containing polyhedral oligomeric silsesquioxanes nanoparticles (POSS) were synthesized by copper-mediated atom transfer radical polymerization (ATRP). Two approaches were used for the synthesis — the first involves POSS as the initiator of ATRP; the second way considers an addition of POSS to the polymer (prepared by ATRP) with an appropriate functional group. Kinetics of polymerization was determined using common analytical methods and it was compared to the polymerizations initiated by low-molecular weight initiators, regarding the polymerization rate, initiation efficiency and polydispersity of the polymer. Efficiency of the initiation with POSS-containing initiators was low, causing remnants of inseparable free POSS in polymer. The second approach bypassed these disadvantages —POSS is connected to the polymer through a pending allyl group using the very efficient hydrosilylation reaction. Presented at the 1st Bratislava Young Polymer Scientists Workshop, Bratislava, 20–23 August 2007.     

PVC/MMT nanocomposites

Poly(vinyl chloride) (PVC) nanocomposites with sodium montmorillonite (Na-MMT) and organically modified MMT (O-MMT) have been prepared by melt processing using mixing and extrusion techniques. The differential scanning calorimetry (DSC) with stochastic temperature modulation (TOPEM?) results show that the glass transition temperature (T _g) of PVC is slightly higher than T _g of PVC/Na-MMT and PVC/O-MMT which would indicate that MMT plays a role of an internal plasticizer that increases the distance between the PVC macrochains. The DSC TOPEM non-reversing heat flow profiles show enthalpy relaxation effects, and the lowest value has been found for pristine PVC—the presence of MMT (both Na+ and ammonium salt modified) may generate a certain orientation level of PVC macrochains during the extrusion process. Specific heat vs temperature dependencies at different frequencies revealed that the best fit to the single profile was found for PVC/Na-MMT nanocomposite, and this observation may be related to internal stability of the composite material as confirmed by analysis of the change in the specific heat (Δc _p).     

Catalytic fire retardant nanocomposites

In this paper the chemical activity of carbon nanotubes and polyhedral oligomeric silsesquioxane during thermal degradation and combustion of polymer nanocomposites is addressed. Indeed, polymer-nanofiller systems may exhibit chemical effects capable of thermal stabilisation of polymers as well as reduction of combustion rate and heat released, owing to catalytic effects induced by the nanofillers at high temperature.Carbon nanotubes in the presence of oxygen are shown to promote oxidative dehydrogenation in polyethylene with production of a stable surface layer of carbon char that provides an effective oxygen barrier effect. A similar action is performed by metal-containing polysilsesquioxanes dispersed in polypropylene.With either carbon nanotubes or metal POSS, partial carbonisation of the polymer matrix occurs during combustion, subtracting part of the organic polymer from combustion, targeting one of the major fire retardancy aim.     

Polymetalates based organic-inorganic nanocomposites

New nanocomposites materials have been synthesized. They present electrochemical and photochromic properties. They are based on a hybrid organic-inorganic network, in which tungsten heteropolyoxometalates (PW₁₂O ₄₀ ^3– , SiW₁₂O ₄₀ ^4– , W₁₀O ₃₂ ^4– , polymeric tungstate) are entrapped. High tungsten ratios could be reached and films or bulk materials have been obtained. The structure of these materials is described on the basis of multi-spectroscopic investigations (IR, EPR, NMR). Electrochemical redox reactions have been observed in thin films. Dark blue reversible coloration of the materials is obtained under UV irradiation. The photochromic mechanism has been investigated and shows the reversible formation of carbonyl group.     

银/聚合物纳米复合材料

银/聚合物纳米复合材料是一种典型的聚合物基复合材料, 其结构和性能依赖于合成方法,因此开发材料的优异性能必须以深入研究纳米材料的先进合成技术为前提。本文综述了纳米银粒子及其与聚合物形成的纳米复合材料的最新合成进展, 重点介绍了基于液相化学还原方法合成纳米银粒子的新方法, 如溶胶-凝胶法、沉淀法、微乳液法和离子液体法, 以及纳米银粒子的分散技术和原位法合成银/聚合物纳米复合材料的新技术, 并介绍了纳米银复合材料的电绝缘性、表面增强拉曼散射性能、抗菌性及其在生物医学等领域中的应用。     

PE/Org-MMT nanocomposites

The non-isothermal crystallization kinetics of polyethylene (PE), PE/organic-montmorillonite (Org-MMT) composites were investigated by differential scanning calorimetry (DSC) with various cooling rates. The Avrami analysis modified by Jeziorny and a method developed by Mo were employed to describe the non-isothermal crystallization process of these samples very well. The difference in the exponent n between PE and PE/Org-MMT nanocomposites, indicated that non-isothermal kinetic crystallization corresponded to tridimensional growth with heterogeneous nucleation. The values of half-time, Z_c and F(T) showed that the crystallization rate increased with the increasing of cooling rates for PE and PE/Org-MMT composites, but the crystallization rate of PE/Org-MMT composite was faster than that of PE at a given cooling rate. The method developed by Ozawa did not describe the non-isothermal crystallization process of PE very well. Moreover, the method proposed by Kissinger was used to evaluate the activation energy of the mentioned samples. The results showed that the activation energy of PE/Org-MMT was greatly larger than that of PE. This revised version was published online in July 2006 with corrections to the Cover Date.     

Metal nanoparticle-conjugated polymer nanocomposites

Recent literature describing nanocomposites of metal nanoparticles and conjugated polymers and oligomers are reviewed. Preparation of these nanocomposites by chemical and electrochemical methods are described, and the electronic and optical properties of these materials are discussed. Some initial applications that have been investigated for such nanocomposites are covered.