Abstract: The properties of polymeric materials have been enhanced by developing nanocomposites in several projects at the Technical Research Centre of Finland VTT. The improvement of conductivity, dielectric, mechanical properties and the thermal stability of polymer materials opens new application potential in electronic industry. In this paper the results of several projects are presented. By applying nano-POSS particles in polypropylene and epoxy the break down voltage was increased by 10 - 20%. The use of carbon nanotubes in polyaniline enhanced the conductivity by two decades compared to the commercially available polymers.
Abstract: Polymer materials are utilized in an increasing number of categories of products, such as components for cars, boats, airplanes, within the electronics industry and other advanced industry as well as in paints and other coatings, for special packaging etc. The uses of polymer materials in new categories of products are only limited by the product properties. It is thus a continuous need for developing polymer products with improved properties like increased scratch resistance, improved weather resistance, increased UV resistance, chemical resistance and antioxidation.
In addition to pure polymer materials, new products based on hybrid organic inorganic materials involving macromolecules with inorganic core and organic branches have been developed.
In this paper, organic inorganic hybrid polymers (HP) are prepared based on a new technology and applied as additives for polymer products like thermoset plastics and in lacquers and other types of coatings for surface protection. Used in appropriate amounts and with suitable particle size, such hybrid polymers contribute to a significant improvement of the properties of the plastic material or the lacquer, hereunder an increased wear resistance/scratch resistance and/or weather resistance.
It is shown that HP additives are suitable for a number of applications within organic chemistry and in particular within polymer chemistry and can be used as a stabilizer for thermoplastics with a broader range of utility than known mono-functional stabilizers.
Abstract: The aim of the study was to synthesize and characterize silsesquioxane-based hybrid nanocomposites with self-assembling properties to be used in monumental stone conservation. Through radical polymerization of 3-(trimethoxysilyl)propyl methacrylate, a monomer that contains both methacrylate and silica phases, in the presence of a primary amine surfactant, at different silica precursor:ethanol molar ratios, new types of hybrid nanocomposites, in which silica was dispersed as domains with typical sizes in the nanometer range, were obtained. The self-assembling properties of the synthesized composites have been ascribed to the supramolecular assembling abilities of the surfactants, as well as to the combination of linear, ladder, and cagelike fragments of silsesquioxane type. The incorporation of surfactant within the sol-gel derived matrix may also lead to the obtaining of compounds that avoid cracking of the hybrid gel while drying inside the stone.
Abstract: Polymer swelling by scCO2 was mainly studied to understand many industrial processes, especially in the field of pharmacy for drug delivery (impregnation) and also polymer processing by CO2-assisted extrusion. We have studied here another application of polymer swelling by scCO2 for the synthesis of nanocomposites. The selected model system was the direct synthesis of copper nanoparticles in a poly(ethylene glycol) matrix (PEG). The study of the formation of nanostructures in polymer matrix is constituted of three main steps: i) thermodynamical behaviour of the polymer/CO2 system, ii) viscosity of the polymer/CO2 system and iii) nucleation and growth of copper nanoparticles.
First, the thermodynamical behaviour of the PEG/CO2 system was studied by in situ IR spectroscopy. This method gives accurate values of the polymer swelling by scCO2 but also of the CO2 sorption in the polymer. For example, at 40°C-15MPa, the swelling of PEG is equal to 35% for a CO2 solubility of 23 wt%. Secondly, we have developed an original falling ball viscometer for the determination of PEG viscosity as a function of CO2 density. A good knowledge of the polymer/CO2 system is finally used for the control of formation of copper nanoparticles. This formation was followed by in situ UV - visible spectroscopy and characterized by transmission electron microscopy.
Abstract: Nanocomposite films containing up to 50 wt. % laponite have been prepared from emulsion polymerized polystyrene (PS)/laponite latexes with the laponite attached to the PS particle surfaces. Below Tg, the observed stiffness increases are accounted for by classical models for mechanical reinforcement, but these severely underestimate the stiffness above Tg. An alternative model has therefore been proposed, in which the laponite and PS with reduced mobility form a cellular network, consistent with TEM observations. This cellular network is also argued to play an important role in the decrease in fracture resistance at high laponite contents, through decreases in matrix ductility and breakdown of the laponite stacks.
Abstract: The development of polymer-layered silicate nanocomposites (PNCs) includes a long list of different possible components such as polymers, nano-additives, and co-additives, together with surface chemistry and various processing conditions. This involves the investigation of a large number of parameters that influence PNC performance. Consequently, fairly extensive research and development work is necessary, and this constitutes an obstacle in the commercialization of nanotechnology. This paper, which is based on experience from research and development for an industrial application, presents a procedure composed of high throughput (HT) screening methods for speeding up the development of PNCs.
Abstract: Blends of polypropylene with multi-walled carbon nanotubes (CNT) have been prepared and melt spun to fibre filaments. The resulted filaments have been characterised regarding conductivity, thermal properties, and morphology. DSC suggests that carbon nanotubes act as nucleating sites in polypropylene and the TGA shows a high increase in thermal stability. Conductivity around 0.001 S/cm are achieved for both as-spun fibre and drawn fibre. A higher load of CNT up to 15 wt % increases the conductivity to 2.8 S/cm in as-spun fibre, but due to a high fibre diameter variation during spinning resulting in fibre breakage, melt spinning is very difficult. This is due to a non-uniform stress distribution during the drawing steps which can be a result of a non-homogeneous PP-CNT blend and the spinning machine process limitations. Differences in conductivities for extruded rods, as-spun fibre and drawn fibre which are made from the same blends, suggests that the crystallinity can affect the conductivity of the PP/CNT fibre.
Abstract: Given their unique set of properties, carbon nanotubes are rapidly gaining importance as stress/damage sensors in addition to as mere reinforcing elements in polymer composites. In this work, single-walled carbon nanotubes (SWCNT) are used to monitor internal stresses developing during the curing process of thermoset materials. SWCNT-epoxy composites with high dispersion quality were obtained via calandering. In situ Raman spectroscopy was used to identify chemical and thermal induced stresses by following the changes in the G’-band versus time and temperature. Thermal shrinkage prompts a pronounced effect on the spectral shifts of the composite, pointing at its dominant role (over chemical shrinkage) on the development of the internal stress field. Above Tg, Raman shifts due to temperature increase are found to be negligible, confirming the existence of a stress releasing mechanism. Shift rate of the composites cooling from their processing temperatures depended on the combination of matrix/SWCNT type, pointing at the role of interfacial strength on the load transfer efficiency.
Abstract: A detailed understanding of charge density and its origins during the electrospinning process is desirable for developing new electrospinnable polymer-solvent systems and ensuring mathematical models of the process are accurate. In this work, two different approaches were taken to alter the charge density in order to measure its effect on the Taylor cone, mass deposition rate and initial jet diameter. It was found that an increase in charge density results in a decrease in the mass deposition rate and initial jet diameter. A theory is proposed for this behaviour in that an increase in charge density leads to the tip of the Taylor cone forming a smaller radius of curvature resulting in the concentration of electric stresses at the tip. This leads to the electrostatic forces drawing the initial jet from a smaller effective area or “virtual orifice”.