Calculating excess volumes of binary solutions with allowance for structural differences between mixed components

Analytical dependences of a volume’s properties on the differences between the geometric structures of initial monosystems are obtained for binary systems simulated by a grain medium. The effect of microstructural parameter k (the ratio of volumes of molecules of mixed components) on the concentration behavior of the relative excess molar volume of different types of real binary solutions is analyzed. It is established that the contribution due to differences between the volumes of molecules and coefficients of the packing density of mixed components is ~80–100% for mutual solutions of n-alkanes and ~55–80% of the experimental value of the relative excess molar volume for water solutions of n-alcohols.     

Determination of filler content for natural filler polymer composite by thermogravimetric analysis

Determination of filler content by thermogravimetric (TG) analysis is commonly utilized to investigate the effectiveness of processing methods for composite materials and to quantify the dispersion of filler within the matrix. However, the existing analysis method is not capable of accurately predicting the filler content for natural fiber composites for the case where thermal degradation of the filler and matrix occurs within similar temperature ranges. In the present study, the authors have proposed a generic equation for the determination of filler content which can be utilized for any given range of thermal degradation temperatures in natural filler polymer composites. Oil palm shell unsaturated polyester composites were selected to verify the proposed equation using the TG test with the results indicating good agreement between the estimated and experimental filler contents with a maximum error on the order of 10 %. The suggested technique provides a simple, yet generic, approach to determining the filler content of green or lignocellulose-based polymer composites by TG analysis.

     

A model of thermodynamic compatibility of the filler with the polymeric matrix in a composite

A thermodynamic approach to predicting the compatibility of the binder with the filler by calculating the nonpolar and acid-base parameters of the filler and polymeric matrix was considered. The calculated adhesion stabilities of the composite systems are consistent with the structural and functional features of their ingredients.     

Nutmeg filler as a natural compound for the production of polyurethane composite foams with antibacterial and anti-aging properties

Polyurethane (PU) composite foams were successfully reinforced with different concentrations (1 wt%, 2 wt%, 5 wt%) of nutmeg filler. The effect of nutmeg filler concentration on mechanical, thermal, antimicrobial and anti-aging properties of PU composite foams was investigated. PU foams were examined by rheological behavior, processing parameters, cellular structure (Scanning Electron Microscopy analysis), mechanical properties (compression test, impact test, three-point bending test, impact strength), thermal properties (Thermogravimetric Analysis), viscoelastic behavior (Dynamic Mechanical Analysis) as well as selected application properties (thermal conductivity, flammability, apparent density, dimensional stability, surface hydrophobicity, water absorption, color characteristic). In order to Disc Diffusion Method, all PU composites were tested against selected bacteria (Escherichia coli and Staphylococcus aureus). Based on the results, it can be concluded that the addition of 1 wt% of nutmeg filler leads to PU composite foams with improved compression strength (e.g. improvement by ~19%), higher flexural strength (e.g. increase of ~11%), improved impact strength (e.g. increase of ~32%) and comparable thermal conductivity (0.023–0.034 W m⁻¹ K⁻¹). Moreover, the incorporation of nutmeg filler has a positive effect on the fire resistance of PU materials. For example, the results from the cone calorimeter test showed that the incorporation of 5 wt% of nutmeg filler significantly reduced the peak of heat release rate (pHRR) by ca. 60% compared with that of unmodified PU foam. It has been also proved that nutmeg filler may act as a natural anti-aging compound of PU foams. The incorporation of nutmeg filler in each amount successfully improved the stabilization of PU composite foams. Based on the antibacterial results, it has been shown that the addition of nutmeg filler significantly improved the antibacterial properties of PU composite foams against both Gram-positive and Gram-negative bacteria.     

Assessing the spatial resolution of cellular rigidity sensing using a micropatterned hydrogel-photoresist composite

The biophysical machinery that permits a cell to sense substrate rigidity is poorly understood. Rigidity sensing of adherent cells likely involves traction forces applied through focal adhesions and measurement of resulting deformation. However, it is unclear if this measurement takes place underneath single focal adhesions, over local clusters of focal adhesions, or across the length of the entire cell. To address this question, we developed a composite, chip-based material containing many arrays of 6.5 μm × 6.5 μm rigid adhesive islands, with an edge-edge distance of 8 μm, grafted onto the surface of a non-adhesive polyacrylamide hydrogel. This material is thus rigid within single islands while long-range rigidity is determined by the hydrogel. On soft gels, most NIH 3T3 cells spread only across two islands in a given dimension forming small stress fibers and focal adhesions. On stiff gels, cell spreading, stress fibers, and focal adhesions were indistinguishable from those on regular culture surfaces. We conclude that rigidity sensing is dictated by material compliance across the cell length and that responses to rigidity may be inhibited at any point when large substrate strain is encountered during spreading. Our finding may serve as a guideline for the design of biomaterials for tissue engineering.     

Thermal pretreatment of silica composite filler materials

Three different silica filler materials were thermally treated in order to effect dehydration, dehydroxylation, and rehydroxylation. Samples were characterized by thermogravimetry (TG), pycnometry, elemental analysis, and scanning electron microscopy (SEM). For all fillers, our results indicate incremental removal of silanol groups at higher heating temperatures and irreversible dehydroxylation at over 673 K. To remove the organic content and maintain adequate silanol density for subsequent silanization on Stöber-type silica, we suggest heating at 673 K followed by overnight boiling in water.     

Radiation-induced modification of montmorillonite used as a filler in PP composite

In order to improve compatibility between inorganic fillers and polymeric matrix, montmorillonite (MMT) particles were modified with maleic anhydride (MA), then irradiated with electron beam, and finally were dispersed in polypropylene (PP). It was found that absorption of MA on the surface of layered clay results in the formation of salt-type bonding. Radiation treatment generates in the organic modifier stable carbon-centered radicals which, upon dispersion of activated particles in PP, induce filler-matrix linkages. Thus, such a process is another approach which has been shown to be an effective way in overcoming organophobic character of inorganic fillers in polymeric composites.     

Effect of filler networking on the response of thermosensitive composite hydrogels

Several composite hydrogels of poly(N-isopropylacrylamide) (pNIPAAm) with sodium montmorillonite (NaMM) have been synthesized using a fixed polymer/NaMM ratio (4:1 wt./wt.), but various monomer concentrations, in order to obtain hydrogels with different degrees of swelling, and thus different clay contents in the swollen state. For comparison, unfilled pNIPAAm gels have been also prepared at the same concentrations. The equilibrium swelling behaviour of the gels has been studied both in the swollen and in the shrunk state. In the swollen state, the polymer volume fraction increases with the initial monomer concentration C₀. In the shrunk state, the polymer fraction in pNIPAAm hydrogels is dependent on the specimen size and on C₀, whereas in the composite gels a constant polymer content is observed. When subjected to stepwise heating from 25 to 45 °C, unfilled gels undergo only poor deswelling. By contrast, complete deswelling takes place in composite gels. The latter show half-shrinking times varying over two orders of magnitude, depending on the monomer concentration and on the procedure followed to disperse NaMM, which determine the overall dispersion state of the filler, as evidenced by transmission electron microscopy (TEM). In particular, TEM observations show clay networking above a percolation threshold near 2.5 wt.% of NaMM. The effect of the incorporation of clay on the response to thermal stimuli is discussed in terms of the ability of NaMM to hinder the hydrophobic association of pNIPAAm segments and in terms of its dispersion state. It is suggested that, above the percolation threshold, NaMM forms a hydrophilic, physical network, through which water can flow also above the volume transition temperature, where pNIPAAm acquires a hydrophobic character.     

Preparation of epoxy composite material containing natural aluminosilicate filler

The conditions for preparing epoxy composite material in which rock containing analcime and montmorillonite serves as a filler have been investigated. The introduction of filler in amounts of up to 1 wt % has increased strength characteristics and thermal stability of the material by 20–25%.     

A novel PEO-based composite solid-state polymer electrolyte with methyl group-functionalized SBA-15 filler for rechargeable lithium batteries

Functionalized molecular sieve SBA-15 with trimethylchlorosilane was used as an inorganic filler in a poly(ethyleneoxide) (PEO) polymer matrix to synthesize a composite solid-state polymer electrolyte (CSPE) using LiClO₄ as the doping salts, which is designated to be used for rechargeable lithium batteries. The methyl group-functionalized SBA-15 (^fSBA-15) powder possesses more hydrophobic characters than SBA-15, which improves the miscibility between the ^fSBA-15 filler and the PEO matrix. The interaction between the ^fSBA-15 and PEO polymer matrix was investigated by scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry. Linear sweep voltammetry and electrochemical impedance spectroscopy were employed to study the electrochemical stability windows, ionic conductivity, and interfacial stability of the CSPE. The temperature dependence of the change of the PEO polymer matrix in the CSPE from crystallization to amorphous phase was surveyed, for the first time, at different temperature by Fourier transform infrared emission spectroscopy. It has demonstrated that the addition of the ^fSBA-15 filler has improved significantly the electrochemical compatibility of the CSPE with a lithium metal electrode and enhanced effectively the ion conductivity of the CSPE. Dedicated to Professor Oleg Petrii on the occasion of his 70th birthday on August 24th, 2007.     

Estimation of the permittivity of polymeric composite dielectrics from the surface characteristics of the filler using a thermodynamic model

A linear correlation between the permittivity of a composite dielectric based on polyvinyl alcohol cyanate and the content of active surface sites in its filler (dispersed barium titanate) was established. This correlation, in combination with a thermodynamic model of composite dielectrics, allows estimation of their permittivity from the surface characteristics of the filler.     

The superposition of small deformations on large deformations: Measurements of the incremental relaxation modulus for a polyisobutylene solution

The incremental relaxation modulus ΔG(t) for a concentrated solution of polyisobutylene has been determined from step-shear experiments in which a small deformation Δγ was superimposed on a large deformation γ₁; ΔG(t) was found to decrease with increasing γ₁ and to increase with the time t_e after the imposition of the large deformation. It was also observed that the “apparent relaxation specturm” associated with δG(t) narrows and shifts to shorter times when compared to the spectrum associated with the linear viscoelastic relaxation modulus G(t). The results are well described by the nonlinear constitutive equation of the BKZ elastic fluid theory.     

The flexural and tribological properties of UHMWPE composite filled with plasma surface‐treated wood fibers

In this paper, the wear performance of an ultra‐high molecular weight polyethylene composites filled with wood fiber were studied using a pin‐on‐disc method. The effects of surface treatment of wood fiber and sliding load and on the friction and wear of the wood fiber/UHMWPE composite are reported. The test results showed that the sliding load is an important controlling factor; its effect is diminished when the wood fiber is modified.     

New type of inorganic filler with a core-shell structure

We tried to use a new kind of filler with “core-shell” structure as a crosslinking agent for carboxylated butadiene-acrylonitrile rubber. We thought that the substance would be better dispersed in the polymer matrix than zinc oxide. Silica (ZnO/SiO₂) whose surface was modified with amorphous zinc oxide from zinc nitrate was used. Its properties were investigated using gas chromatography. Finally we obtained unconventional networks containing ionic and complex bonds (as a result of reaction of elastomers' functional groups i.e. carboxyl groups with the appropriate neutralizing agent as metal oxide). Ionic clusters were formed in vulcanizates which influenced the mechanical properties and crosslinking efficiency. We confirmed the presence of these unconventional bonds by IR spectroscopy and DMTA analyses.     

Simulation of the sorption of cations on the surface of a selective sorbent with allowance for the possibility of their desorption

The process of sorption of several kinds of cations differing in affinity to adsorption groups on a plane sorbent surface from immobile dilute liquid solutions in the kinetic regime is simulated. Formulas are derived for estimating the time dependence of the surface concentration of adsorbed cations with allowance for the processes by which free and cation-containing adsorption groups are removed from the sorbent surface. The degree of inhibition of the adsorption of a cation in the presence of other cations is determined, which can occupy vacant sites on the sorbent surface. It is shown that the calculation results are in good agreement with experimental data.