Nanotechnology has applications across most economic sectors and allows the development of new enabling science. The ability to see materials down to nanoscale dimensions and to control how materials are constructed at the nanoscale is providing the opportunity to develop new materials and products in previously unimagined ways. This review covers the academic and industrial aspects of the preparation, characterization, material properties, crystallization behavior; melt rheology, and processing of polymer/cellulose or cellulose/cellulose nanocomposites. Cellulosic materials have a great potential as nanomaterials because they are abundant, renewable, have a nanofibrillar structure, can be made multifunctional, and self-assemble into well-defined architectures. The fibrillation of pulp fiber to obtain nano-orderunit web-like network structure, called microfibrillated cellulose, is obtained through a mechanical treatment of pulp fibers, consisting of refining and high pressure homogenizing processes. Also, nano-whisker can be used as novel reinforcement in nanocomposites; it can be obtained by acid hydrolysis from various sources such as wood, tunicin, ramie, cotton, wheat straw, bacterial cellulose, and sugar beet. The properties of nanocomposite materials depend not only on the properties of their individual parents, but also on their morphology and interfacial characteristics. Compared with plant cellulose, bacterial cellulose has found many applications in the biomedical field as tissue engineering materials due to their good biocompatibility, mechanical properties similar to those of hard and soft tissue and easy fabrication into a variety of shapes with adjustable interconnected porosity. One of the drawbacks of cellulose whiskers with polar surfaces is poor dispersibility/ compatibility with nonpolar solvents or resins. Thus, their incorporation as reinforcing materials for nanocomposites has so far been largely limited to aqueous or polar systems. To overcome this problem and broaden the type of possible polymer matrices, efforts of surface modification have been made. These attempts include surfactant coating or graft copolymerization.
We exploit the force spectroscopy capabilities of the atomic force microscope in characterizing the local elasticity of rubber-like materials. Extraction of elastic properties from force curves usually relies on the linear theory pioneered by Hertz. While the Hertzian force-indentation relationships have been shown to be accurate in modeling the contact mechanics at sufficiently shallow indentation depths, the linear deformation regime of the probed material is exceeded in many practical applications of nanoindentation. In this article, a simple, nonlinear force-indentation equation based on the Mooney-Rivlin model is derived and used to fit data from the indentation of lightly crosslinked poly(vinyl alcohol) gels in equilibrium with water. The extracted values of Young's modulus show good agreement with those obtained by both macroscopic compression testing and by fitting truncated portions of the force curves with the Hertz equation.
Metal complexes were synthesized on the basis of the copolymers of radiation grafted poly-4-vinylpyridine onto polyethene and polytetrafluoroethene. The formation of the complexes was carried out in solutions of the following salts: FeCl3•6H2O, CoCl2•6H2O, VOSO4•5H2O, Na2MoO4•2H2O and Na2WO4•2H2O. The introduction of metal ions depended on the degree of grafting of 4-vinylpyridine and it was found to be from 0.03 to 14.96 and from 0.11 to 34.48 mg metal ions per g of polymer carrier for polytetrafluoroethene and polyethene, respectively. The influence of the metal ion nature on the electrochemical characteristics of nitrogen-containing copolymers was studied. The specific electric resistance of the polymer metal complexes was found to depend on the nature of the metal ion and its content in the complex. The metal complexes obtained had lower electric resistance than the initial copolymers. This can be explained with the fact that the chelate agents (salts of metals with variable valence) have free ions and electron mobility which improve the electric conductivity of the materials obtained and have a good prospect in many fields as functional polymer. The tensile characteristics of the polymer complexes of heavy metals were also affected by the nature and contents of the ions introduced.
The radical-initiated copolymerization of N-(4-bromophenyl)-2-methacrylamide (BrPMAAm) with 2-hydroxyethylmethacrylate (HEMA) was carried out in 1,4-dioxane solution at 70°C using 2,2’-azobisisobutyronitrile (AIBN) as an initiator with different monomer-to-monomer ratios in the feed. The copolymers were characterized by FTIR, 1H- and 13C-NMR spectral studies. Gel permeation chromatography was employed for estimating the weight average (Mw) and number average (Mn) molecular weights and polydispersity index (PDI) of the copolymers. The copolymer composition was evaluated by nitrogen content (N for BrPMAAm-units) in polymers, which allowed the determination of reactivity ratios. Monomer reactivity ratios for BrPMAAm (M1)-HEMA (M2) pair were determined by the application of conventional linearization methods such as Fineman-Ross (F-R), Kelen-Tüdõs (KT) and Extended Kelen-Tüdõs (EKT) and a nonlinear error invariable model method using a computer program RREVM. The characterizations were done thermogravimetric analysis (TGA). The antimicrobial effects of polymers were also tested on various bacteria, and yeast.
Triangular gold nano-plates have been synthesized by thermal decomposition of Au(I) dodecyl-mercaptide (i.e., AuSC12H25) dissolved in poly(vinyl acetate). Such special shape was achieved because of the ability of polymer side-groups (i.e., the acetate groups) to be selectively absorbed on the most acid faces of the growing gold nanocrystals, thus inhibiting crystal development along these crystallographic directions. Nano-plates had an average edge length of ca. 30nm and a thickness of a few nanometers.
In this paper, ZnO, which is processed by different surface treatment approaches, is blended together with polypropylene to produce thermal conductive polymer composites. The composites are analyzed by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) to investigate the surface modification of filler, their distribution in the matrix and the condition of two-phase interface. Optimized content of filler surface modifier is investigated as well. The results showed that using low-molecular coupling agent produces positive effect to improve the interface adhesion between filler and matrix, and the thermal conductivity of the composite as well. Macro-molecular coupling agent can strongly improve two-phase interface, but it is not beneficial at obtaining a high thermal conductivity. The blend of ZnO without modification and polypropylene has many defects in the two-phase interface, and the thermal conductivity of the composite is between those of composites produced by previous two approaches. The surface treatment of the filler also allowed producing the composites with lower coefficient of thermal expansion (CTE). As for the content of low-molecular coupling agent, it obtains the best effect at 1.5 wt%.
Replacement of conventional materials by polymeric materials (blends/composites) with improved mechanical performance is of immense importance for modern technology. Blending of fluoro polymers can contribute to such synergistic properties. PVDF, as a semi-crystalline fluoro polymer, has been blended with PVF fluoro polymer to form isomorphic polyblend specimens by altering the wt% of PVDF using a solution casting technique. Microhardness investigations have been undertaken using the Vicker’s indentation technique; measurements of Vicker’s hardness number (Hv) were carried out on virgin (untreated) and electrically stressed pure PVF and PVF/PVDF isomorphic polyblend specimens by a fixed step voltage at a fixed high temperature. The results of variation of Hv as a function of applied load are explained in terms of strain hardening phenomenon in virgin samples along with their mechanical properties. The increase of hardness produced as a result of variation of PVDF wt% within the PVF matrix has been interpreted in terms of a change in chain crosslinking. The observed higher value of hardness number in the case of electrically stressed specimens is suggested to result from modification in inter- and intramolecular interactions in such samples.
Guar gum is a natural polysaccharide that has been explored for various applications. However, there is a limited number of studies in which guar gum has been used as a filler in a polymer. The effect of guar gum and its hydroxypropyl derivatives in unsaturated polyester composites were investigated with respect to their mechanical and chemical properties. The effect of hydroxypropylation and the degree of hydroxypropylation on the properties of resultant composites were also studied. It was observed that the inclusion of guar gum and its derivatives resulted in composites with increased solvent resistance and mechanical properties. An increase in the degree of substitution resulted in increased polymer-filler interaction reflected by a positive effect on the mechanical properties of the composites. These results open an avenue for the use of polysaccharides and their derivatives as eco-friendly fillers as a replacement of mineral fillers.
An epoxy-phenolic resin suitable for use as a composite matrix was reinforced with modified nanoclay (montmorillonite type). Characterization by x-ray diffraction and transmission electron microscopy (TEM) demonstrated that intercalated nanocomposites were formed with an inter-gallery distance of approximately 10 nm. The influence of nanoparticles on tensile strength and modulus, fracture toughness, and impact toughness was measured and compared with the unreinforced polymer. The results revealed that the maximum enhancement in stiffness and toughness was achieved with 2.5 wt% filler content. The enhancement in toughness behavior was attributed to the activation of multiple energy-dissipating damage mechanisms in the nanocomposites.