Dielectric elastomers based on silicones filled with transitional metal complexes

New composite dielectric elastomers with improved dielectric properties were prepared on the basis of polydimethylsiloxane rubber filled with new types of metal (Mn, Fe, Cr) complexes of the bis-azomethine derived from the condensation of a siloxane diamine, 1,3-bis(aminopropyl)tetramethyldisiloxane, with 3,5-di-bromo-2-hydroxybenzaldehyde. The tetramethyldisiloxane fragment from the structure of the complexes creates the premise for a good compatibility with the silicone matrix without the need for other surface treatments while the complexed metal unit through its polar character changes the dielectric properties of the material. The resulted composites crosslinked at room temperature as dielectric elastomer films were investigated in order to establish if such materials are suitable for use in the structure of electromechanical devices. The introduction of metal complexes in the polymer matrix has led to a slight decrease of the elastic domain but increased the relative dielectric permittivity with up to 100% and the electromechanical sensitivity of the materials, with negligeable changes of the thermal behavior and overall moisture sorption capacity, thus preserving the chemical stability and hydrophobic character of siloxanes

Effects of (complementary) polyelectrolytes characteristics on composite calcium carbonate microparticles properties

This study follows the possibility to tune the thermal stability of some CaCO3/polymer composites by crystal growth from supersaturated solutions controlled by polymer structure or by using nonstoichiometric polyelectrolyte complexes (NPECs). As the ratio between the organic and inorganic parts in the composites controls the Ca2+/polymer network crosslinking density, the CaCO3/polymer weight ratio was kept constant at 50/1, varying the initial concentration of the polyanions solutions (0.05 or 0.06 wt.%), the NPECs molar ratio , n+/n- (0.2 or 0.4), or the inorganic precursors concentration (0.25 or 0.3 M). Poly(2-acrylamido-2-methylpropanesulfonic acid-co-acrylic acid) (PSA) and chondroitin-4-sulfate (CSA) were used as polyanions. Some NPEC dispersions, prepared with the same polyanions and poly(allylamine hydrochloride) (PAH), were also used for calcium carbonate crystallization. The characteristics of the prepared composites were investigated by scanning electron microscopy (SEM), flow particle image analysis (FPIA), particles charge density (CD), zeta-potential (ZP). The thermal stability of the composite particles was investigated as compared to bare CaCO3 microparticles prepared at the same initial inorganic concentrations

Interpenetrating poly(urethane-urea)–polydimethylsiloxane networks designed as active elements in electromechanical transducers

A poly(urethane-urea-siloxane) was prepared in a two-step procedure involving the synthesis of a bis-isocyanate prepolymer on the basis of 4,4′-diphenylmethane diisocyanate, a polyether glycol and dimethylol propionic acid, and its extension by reacting with 1,3-bis(3-aminopropyl)tetramethyldisiloxane. The resulted polymer was used in different percentages to prepare three series of interpenetrating networks (IPNs) with polydimethylsiloxane-α,ω-diols with molecular masses, Mn, of 70000, 230000 and 370000 g mol−1. A polydimethylsiloxane–polyethyleneoxide graft copolymer was added as a compatibilizing agent. The IPN precursors were mixed in solution and processed as films. During solvent evaporation, the chemical crosslinking of the polydimethylsiloxane-α,ω-diols occurs with tetraethyl orthosilicate in the presence of dibutyltin dilaurate, while in the case of poly(urethane-urea-siloxane) only physical crosslinking by hydrogen bonds is expected to occur. The morphology and thermal transitions of the resulted networks were examined by scanning electron microscopy, differential scanning calorimetry with dynamic mechanical analysis. The mechanical and dielectric characteristics (dielectric permittivity, loss, strength) of the aged films were studied. Their responsiveness to an external stimulus in the form of an increasing electric field was assessed by electromechanical measurements and expressed as lateral strain. The results were critically analyzed with respect to each other as a correlation with their composition and compared with those obtained for three common commercially available dielectric elastomers

Bentonite as an active natural filler for silicone leading to piezoelectric-like response material

Raw sodium bentonite (Bent) without preliminary treatments is incorporated as a filler in a silicone matrix, from 5 to 100 parts per hundred (pph), by weight, by simple mixing in solution. The mixtures are processed as films and stabilized by condensation crosslinking at room temperature. Besides being environmentally safe and non-toxic, bentonite is 30 times cheaper than polydimethylsiloxane (PDMS), so the cost price of composites can be reduced by over 40%. Studies on the effects of bentonite addition as filler on the properties of composites reveal that thermal stability is not significantly affected, while an increase in the amount of inorganic residue with an increase of Bent content is recorded. More importantly, the mechanical and dielectric properties are significantly influenced by the Bent content in the PDMS matrix. The Young's modulus increases, while the elongation decreases, indicating a stiffening of the material and a decrease in its elasticity as the Bent load increases. Most notably, the dielectric permittivity increases up to more than five times at 103 Hz by adding 100 pph Bent, while the dielectric losses remain acceptable, especially at high frequencies for all composites. Furthermore, the study of composite films through Piezoresponse Force Microscopy and piezoelectric testing system reveals an outstanding piezoelectric-like response for composites with a high Bent content. The wideangle X-ray diffraction indicates an increase of the crystalline fraction - the main factor that influences the apparent piezoelectric coefficient - with increasing the Bent loa

EFFECT OF ULTRAVIOLET LIGHT ON THE PROPERTIES OF DYED COTTON CELLULOSE

Textile dyes have been reported of causing various stages of contact dermatitis. Reactive dyes are widely applied in dyeing cellulose fiber based textiles (100% cotton), skin fibers (hemp, flax), regenerated cellulose (cellulose acetate, viscose), protein fibers (natural silk, wool). The human body comes in contact daily with such compounds. This aspect is important for elucidating their biological effects on the human body, in correlation with physico-chemical properties. Dyes are chemical compounds containing chromophore and auxochrome groups. Authors herein report results concerning the influence of UV irradiation with λ > 300 nm on the structure and properties of different colored textiles. Subjects to study were textiles painted with four azo-triazine based dyes which were exposed to 100 h UV irradiation time and irradiation dose values up to 3500 J cm-2. The five azo dyes were: reactive orange 13, reactive red 183, reactive yellow 143, reactive blue 204 and reactive red 2. Structural modifications as a result of irradiation were undertaken by UV-Vis spectroscopy. It was observed that during UV exposure there occurred partial dyes detachment from the textiles, accompanied by glucosidic units and dye photodecomposition by C–N bond scission and degradation of aromatic entities and azo based chromophores. Color modifications were also investigated. Color differences significantly increased with the irradiation dose for all the studied samples

Photochemical Stability of a Cotton Fabric Surface Dyed with a Reactive Triphenodioxazine Dye

The paper describes the photochemical stability of a commercial triphenodioxazine dye (Reactive Blue_204) linked onto a cotton fabric. Preliminary studies have shown that as a result of irradiation, the dye and its photodegradation products can pass directly onto the skin under conditions that mimic human perspiration and cause side-effects. The cotton dyed fabric was photo irradiated at different time intervals. Standard methods were employed to evaluate the color strength at various levels of pH, temperature, dyeing contact time, and salt concentration. The influence of UV radiation at different doses (λ > 300 nm) on the structural and color modifications of the dyed cotton fabrics was studied. Structural modifications before and after irradiation were compared by applying FTIR, UV–Vis, and near infrared chemical imaging (NIR–CI) techniques. Color modifications were investigated with the CIELAB system. Color differences significantly increased with the irradiation dose. High irradiation doses caused changes in the dye structure

NEW ECO-EFFICIENT PRODUCTS USED IN LEATHER INDUSTRY

In today's move to "sustainable production" the leather industry, as well as many other industries is recognized as a polluting one. Traditional chemical operations are polluting because of the levels of inorganic chemical waste. Process chemicals which are not consumed within the reactions necessary to convert collagen to leather are currently discharged to waste. These are usually applied during bulk production, such as inorganic agents from beam house and tanning processes, e.g. lime, sulphide, ammonium salts, sulphuric acid and sodium chloride, mineral tanning agents – mainly Cr(III) and the less common Al(III), Zr(III), Ti(III), Fe(III) salts -, whereas depending on the tanning process and the leather article produced organic chemical waste discharged comprises aldehydic and polyphenolic tanning products, bating enzymes, organic carboxylic acids and excess electrolyte stable synthetic fat liquors. It is rare for chemicals and water to be recovered for re-use from several of these process steps. Moreover, tanners worldwide are required to operate within strict legislative boundaries. Serious drawbacks continuously arise concerning the chrome–tanning process in leather industry and the environmental hazardous consequences of chromium containing effluents. In order to overcome this impediment, a great deal of research has been focused on developing chrome–free tanning methods in the past years, such as titanium tanning. In the present study, Ti–Al tanned bovine leather was characterized by means of SEM microscopy, EDAX elemental analysis, ATR–FTIR spectroscopy, thermogravimetry TGA, and differential scanning calorimetry DSC techniques

Effect of Hardener Type on the Photochemical and Antifungal Performance of Epoxy and Oligophosphonate S–IPNs

Due to their highly reactive character and multiple crosslinking capacity, epoxy resins are one of the worldwide market-dominating classes of thermosetting polymers and are present in a wide range of technical applications, including structural adhesives, coatings and polymer matrices for composite materials. Despite their excellent features, epoxy resins are known to be highly flammable and possess low thermal stability and a brittle character and crack easily under impact forces. An efficient approach towards eliminating such drawbacks resides in obtaining epoxy-based semi-interpenetrating polymer networks, which possess excellent control over the morphology. The article describes the comparative effect of three hardeners (aromatic, cycloaliphatic and aliphatic) in the presence of an oligophosphonate (–R–O–PO(C6H5)–O–) (2 wt.% phosphorus) on the photochemical, fire and antifungal performance of bisphenol A diglycidyl ether semi-interpenetrating polymer networks. The networks are designed as future potential outdoor protective coatings for different substrates. The fire resistance capacity of the networks was undertaken with microscale combustion calorimetry before and after photochemical aging. Structural changes during photoirradiation were monitored via color modification studies, Fourier-transform infrared spectroscopy, differential scanning calorimetry, morphological assessment through scanning electron microscopy and mass loss measurements in order to propose the action mode of the hardeners and the oligophosphonate on the material properties. Microbiological testing was also undertaken with the aid of three specific wood decaying fungi as a first substrate