The Drying Kinetics and Equilibrium Moisture Content of MDF Fibers

An experimental device was constructed to study the drying kinetics of wood fibers under controlled conditions. The device consisted of a drying chamber in which a net basket filled with the fiber material was connected to a load cell. The drying medium was then forced through the basket at controlled levels of humidity and temperature.

Experiments were performed with spruce fibers and the drying medium at varying temperature (50–170°C) and relative humidity (1–86%). In general, the drying rate increased with increasing temperature and decreasing relative humidity. A constant drying rate period was observed in all cases. The critical moisture content was approximately 1.25. The characteristic drying curve has a slight downward concave shape. The equilibrium moisture contents obtained at ambient temperature agree well with data in the literature.     

Influence of cholesterol on the kinetics of lipid autoxidation and on the antioxidative properties of α‐tocopherol and quercetin

The autoxidation kinetics of triacylglycerols of sunflower oil (TGSO) in the presence of 10% cholesterol (Chol) at 80, 90 and 100 °C has been studied. The process was followed by monitoring the peroxide value and the formation of conjugated dienes. Cholesterol has been found to exhibit a prooxidative effect. During the oxidation of the mixture (TGSO/Chol), cholesterol peroxides were not registered. It is supposed that the initial amount of cholesterol peroxides formed decomposes to free radicals and that these radicals accelerate TGSO oxidation. A kinetic analysis of the antioxidative behavior of α‐tocopherol and quercetin (2.9 x 10^?4‐17.8 × 10^?4 M) in both TGSO and TGSO/Chol at 100 °C was performed. It was found that the effectiveness, strength, and activity of α‐tocopherol are greater in TGSO/Chol than in TGSO, while these parameters for quercetin are practically the same in both lipid systems. The differences in the mechanism of action of α‐tocopherol and quercetin are discussed.     

Inhibited Oxidation of Lipids II: Comparison of the Antioxidative Properties of Some Hydroxy Derivatives of Benzoic and Cinnamic Acids

The antioxidative properties of p-hydroxy-benzoic acid, vanillic acid, syringic acid, 3,4-dihydroxy-benzoic acid, p-coumaric acid, ferulic acid, sinapic acid and caffeic acid in lard autoxidation at 100°C are compared. The effect of phenolic acids is investigated within the concentration range 0.02 – 0.20 wt %. It is proved that the derivatives of the benzoic acid have weaker inhibiting properties than is the case of the corresponding analogues of the cinnamic acid due to the more active participation of the inhibitor in the elementary reactions of propagation and initiation of the radical chain process. The activity (a complex parameter demonstrating the efficiency and strength of the antioxidant) of the phenolic acids investigated decreases in the sequence: caffeic acid >3,4-dihydroxy-benzoic acid > sinapic acid > syringic acid>ferulic acid>p-coumaric acid>vanillic acid. The increase in concentration of the acids investigated is most advisable in the case of sinapic, syringic and ferulic acids which are not consumed in side reactions.     

Shear Adhesion Strength of Gecko-Inspired Tapes on Surfaces with Variable Roughness

With the aim to gain a wider understanding on the design rules of bioinspired adhesives for application in the medical field, the adhesion of fibrillar structures on soft and stiff polymers was determined in bench top studies on surfaces with variable roughness and in ex-vivo wet tissue tests. The adhesion strength of stiff fibrillar structures was found to be dependent on the roughness of the adherent surface. For a given fibril width and density, the optimal adhesion was seen when the length of the fibrils was of the same range as that of the roughness of the surface it was tested against. Over this limit, the adherence decreased. In the case of soft adhesive structures, the same trend was observed where an optimum adhesion was seen when the size of the pillars matched that of the adherent surface roughness. This observation was attributed to an increase in surface contact. The adhesion of fibrillar structures on tissue samples in ex-vivo tests showed a similar trend with enhanced fibrillar interpenetration favoring a larger number of contacts and a stronger capillary force expected to account for the adhesion enhancement.     

Effect of strain rate on the fracture toughness of some ductile polymers using the essential work of fracture (EWF) approach

The plane strain fracture toughness of two ductile polymers, ultra high molecular weight polyethylene (UHMWPE) and acrylonitrile‐butadiene‐styrene (ABS), was measured by using the essential work of fracture approach. Truly plane strain fracture toughness (w_Ie) was measured for ABS at quasi‐static and impact rates of loading. For UHMWPE, the measured values were only “near” plane strain values (w_Ie*). It was confirmed both w_Ie* and w_Ie were independent of specimen type but dependent on strain rate. For UHMWPE, there was a negative strain rate effect, i.e., w_Ie* decreased with increasing loading rate. At low quasi‐static loading rate (v = 10 mm/min), w_Ie* was constant at 55 kJ/m². It then decreased to 15 KJ/m² when the loading rate was increased to 100 mm/min, and remained at that value even up to impact rate of loading (v = 3.7 m/s). For ABS, a mild positive strain rate effect was observed. w_Ie increased from 13 kJ/m² at v = 10 mm/min to 17 kJ/m² at v = 3.7 m/s.     

Effect of Ionic Head Group on Admicelle Formation by Polymerizable Surfactants

One of the problems of using surfactant-modified adsorbents in a surfactant-based adsorption process is loss of surfactant because of desorption. Recently, polymerizable surfactants have been used to minimize surfactant losses by polymerization of the surfactant admicellar structure to help secure it to the solid oxide surface. In this study, adsorption of polymerizable cationic gemini surfactant was used to form polymerized bilayers on silica. UV light was used to irradiate and initiate the polymerization process. Surfactant adsorption and desorption were evaluated to compare the efficiency of polymerized and non-polymerized surfactants using gemini and conventional surfactants, respectively. Results demonstrate that the increased stability of the polymerized surfactant-modified surface can reduce the desorption of surfactant from the surface, thereby improving operating characteristics of the surfactant-modified media (e.g., maintaining adsolubilization potential, dispersion stability, etc.).     

Biaxial initial stress characterization of bilayer gold RF-switches

An analysis as been conducted to determine the biaxial initial stress state of gold bilayer switches. Results are shown that the sensitivity of the sacrificial photoresist layer to process parameters make the wafer curvature technique unreliable to determine the initial stress state of the evaporated gold seed layer. An analytical method based on the cantilever deflection method is proposed to determine the biaxial stress state on this layer. Assumptions were validated numerically using FEM and cantilevers gold bilayer of various length were elaborated and characterized.     

Influence of ultrasound on mass transport during cheese brining

 The effect of ultrasound on mass transfer during cheese brining has been investigated. The rate of water removal and NaCl gain increased when ultrasound was applied in comparison with brining performed under static or dynamic conditions, suggesting that ultrasound improves both external and internal mass transfer. A simple diffusional model was developed to simulate mass transport during acoustic brining. Model parameters were estimated using experimental data from acoustic brining experiments carried out on cheese cylinders of 1.7×10^–2m radius and 3×10^–2 m height at different temperatures (5, 15 and 20  °C). Effective water (D _W) and NaCl (D _S) diffusivities estimated using the proposed model ranged from 5.0×10^–10m²/s and 8.0×10^–10 m²/s at 5  °C to 1.3×10^–9m²/s and 1.2×10^–9 m²/s at 20  °C. Both D _W and D _S varied with temperature according to the Arrhenius equation. Through the proposed model, water losses and NaCl gains of the experiments used in the parameter identification were accurately simulated (average %var=98.2%) and also of two additional acoustic experiments carried out under different conditions of temperature (10  °C) and sample size and geometry [parallelepiped of (6×2.5×1.25)×10^–2 m] to those used in the parameter identification (average %var=98.4%). Received: 22 September 1998 / Revised version: 20 November 1998