Acoustic insulation characteristics of sandwich composite shell systems with double curvature: The effect of nature of viscoelastic core

A viscoelastic model is proposed in this approach to determine the sound transmission loss coefficient of a sandwich shell system with double curvature. The structure is composed of a double-walled composite shell subjected to a viscoelastic core. Investigating the efficient impresses of rotary inertia and shear deformation, vibration equations of both outer and inner shells are extracted within the framework of shear deformation shallow shell theory. Besides, the Zener mathematical model is used for viscoelastic material, which is based on a spring connected in series with a parallel mixture of spring and dashpot. This model presents the dynamic response in the whole frequency domain at which shear modulus and bulk complex modulus are frequency dependent. Since the performed studies on the sound transmission loss of this kind of structures are insignificant, the outcomes of plate models with a viscoelastic core are used to provide a reliable sound transmission loss comparison. The results show that the applied strategy can improve the acoustic characteristics of the system at high frequencies compared to that of a single-layer one with the same mass. This issue is more highlighted while the thickness of the viscoelastic layer enhances, which confirms the positive performance of the viscoelastic materials in this range of frequency, particularly in the resonant frequency. In addition to the curvature effect on acoustic features, the vibration response of the system is configured based on various frequencies and materials.

Influence of milk-clotting enzymes of animal and microbial origin on the quality and shelf life of soft cheeses

A comparative test was carried out for milk-clotting enzymes (MCE) of animal origin (Naturen® Extra), microbial origin (Marzyme®) and MCE based on recombinant camel chymosin (Chy-max® M) in the production of soft cheese “Lyubitelskiy”. By the end of the shelf life of the cheeses (12 days at a temperature of 3 ± 1 °C), differences were noted in the degree of proteolysis (DP) and the value of the complex modulus G*, which were the following ones for cheeses produced with MCE of the brands: Naturen® — DP = 17.86 ± 0.24%; G* = 4164 ± 587 Pa; Marzyme® — DP = 17.98 ± 0.49%; G* = 4581±786 Pa; Chy-max® M — DP = 9.85 ± 0.63%; G* = 7949 ± 1157 Pa. Cheeses made with Chy-max® M MCE had a denser texture than cheeses made with MCE of Naturen or Marzyme, which did not differ significantly in consistency. In the studied cheeses, the severity of the bitter taste was proportional to the content of water-soluble peptides with a mass of 0.5–3 kDa. Cheeses with Marzyme® MCE had a more intense bitterness than cheeses with Naturen® MCE. There was no bitter taste in cheeses produced with MCE of Chy-max® M. It was concluded that in the production of soft cheeses, recombinant camel chymosin can be used to increase the shelf life, and MCE of microbial origin can be recommended to replace more expensive MCE of animal origin.

Xylitol and Maltitol Improve the Rheological Property of Kappa-Carrageenan

To further extend the use of κ-carrageenan (κ-C) in real food systems (such as beverages), the understanding of gelation properties of κ-C with the presence of food ingredients is critical. The effects of xylitol and maltitol (up to 30 wt %) on the rheological and structural properties of κ-C were inspected by means of rheometer and Fourier transform infrared (FTIR). With the addition of xylitol, the gelation temperature increased from 44.1 to 57.3 °C, while the gelation temperature increased from 44.1 to 61.4 °C in maltitol systems. With the increasing concentration of both xylitol and maltitol, the values of fractal dimension df and complex modulus G* of κ-C increased, while the relaxation exponent n decreased from 0.87 to 0.39 of xylitol and 0.87 to 0.78 of maltitol, respectively. These indicated that the gel networks of aqueous κ-C were improved by the addition of xylitol and maltitol. The FTIR results showed that the interaction between κ-C and these polyols contributed to the increase of hydrogen bonds. The effects of maltitol on κ-C were stronger than those of xylitol because of more equatorial-OH bonds in maltitol. These findings contribute to a better understanding of the gelation processes of κ-C/polyols systems.

Evaluating the Rheological Properties of High-Modulus Asphalt Binders Modified with Rubber Polymer Composite Modifier

With the increasing traffic loading and changing climatic conditions, there is a need to use novel superior performing pavement materials such as high-modulus asphalt binders and asphalt mixtures to mitigate field distress such as rutting, cracking, etc. This laboratory study was thus conducted to explore and substantiate the usage of Rubber Polymer Composite Modifier (RPCM) for high-modulus asphalt binder modification. The base asphalt binder used in the study comprised A-70# Petroleum asphalt binder with RPCM dosages of 0.25%, 0.30%, 0.35%, 0.40% and 0.45%, separately. The laboratory tests conducted for characterizing the asphalt binder rheological and morphological properties included the dynamic mechanical analysis (DM), temperature-frequency sweep in the dynamic shear rheometer (DSR) device, bending beam rheometer (BBR), and florescence microscopic (FM) imaging. The corresponding test results exhibited satisfactory compatibility and potential for using RPCM as a high-modulus asphalt binder modifier to enhance the base asphalt binder’s rheological properties, both with respect to high- and low-temperature performance improvements. For the A-70# Petroleum asphalt binder that was evaluated, the optimum RPCM dosage was found to be 0.30–0.35%. In comparison to styrene–butadiene–styrene (SBS), asphalt binder modification with RPCM exhibited superior high-temperature rutting resistance properties (as measured in terms of the complex modulus and phase angle) and vice versa for the low-temperature cracking properties. Overall, the study beneficially contributes to the literature through provision of a reference datum toward the exploratory usage of RPCM for high-modulus asphalt binder modification and performance enhancements.

Comparative Study on Complex Modulus and Dynamic Modulus of High-Modulus Asphalt Mixture

In the French high-modulus asphalt mixture design system, the complex modulus of the mixture under the conditions of 15 °C and 10 Hz is taken as the design index. However, in China, the dynamic modulus under the conditions of 15 °C, 10 Hz, 20 °C, 10 Hz and 45 °C, 10 Hz was taken as the stiffness modulus index of high-modulus asphalt mixture. The difference in modulus values between the two systems caused the pavement structure layer to be thicker and the construction cost to be higher in China. In order to find out the appropriate modulus value of high-modulus asphalt mixture suitable for China’s modulus parameter conditions to better carry out the reasonable design and evaluation of high-modulus asphalt mixture in China, the modulus of four types of high-modulus asphalt mixtures under the two systems through the two-point bending complex modulus test of the CRT-2PT trapezoidal beam and the SPT uniaxial compression dynamic modulus test were analyzed in this paper. Under the premise of meeting the stiffness modulus index of the French high-modulus asphalt mixture, the relationship conversion models between the dynamic modulus and complex modulus of high-modulus asphalt mixture under different temperatures were established. According to the conversion models, the design evaluation value range of dynamic modulus suitable for China’s condition was recommended. It is recommended that the dynamic modulus of China’s high-modulus asphalt mixture at 15 °C and 10 Hz is not less than 16,000 MPa, the dynamic modulus at 20 °C and 10 Hz is not less than 14,000 MPa, and the dynamic modulus at 45 °C and 10 Hz is not less than 2500 MPa. Five kinds of high-modulus asphalt mixtures used in actual road engineering were tested to verify the reliability of the recommended dynamic modulus values based on the modulus conversion model, and the results are consistent with the recommended value range of the model.

Visualizing Impedance Spectroscopy Response for Interpretation of Collected Data

Measurements and interpretation of electrical impedance in electrochemistry and in related studies has become recently fairly commonplace as both the hardware and the interpretation software are more and more standard part of electrochemical potentiostats. With the interpretation software it is possible to model the studied system in any conceivable way, even if the physical reality may not follow the chosen model. An example is given where a circuit consisting of a capacitor with resistors in series and parallel are evaluated as if the circuit were just a pure capacitor. The method of plotting the results as complex permittivity and complex modulus is also shown.

Apparent Molecular Weight Distributions for Investigating Aging in Polymer-Modified Bitumen

The oxidative aging of bituminous binders affects the performance and durability of pavements. In the case of polymer-modified binders, aging involves both bitumen and polymers and has a strong impact on the whole architecture of the material. Rheology may help in understanding these structural changes, and interesting information may be obtained by analysing the evolution of apparent molecular weight distributions. This was demonstrated with a bituminous binder modified with a poly(styrene-butadiene) block copolymer and subjected to prolonged artificial aging. Isothermal frequency sweep tests were used to construct master curves of the phase angle and magnitude of the complex modulus. The master curves were then used to calculate relaxation spectra and apparent molecular weight distributions of the binders, as well as simulated temperature sweep tests. A comparison of the behaviour of the base and modified bitumen highlighted the role of the polymer in aging. Polymer degradation significantly damages the elastomeric network, yet the residual polymer chains still interact with the bitumen molecules and reduce their oxidative aging. The apparent molecular weight distributions were deconvoluted to create an aging index specifically developed for polymer-modified bitumen.

Novel Pastes Containing Polymeric Nanoparticles for Dentin Hypersensitivity Treatment: An In Vitro Study

Tubule occlusion and remineralization are considered the two main goals of dentin hypersensitivity treatment. The objective is to assess the ability of dentifrices containing zinc-doped polymeric nanoparticles (NPs) to enduringly occlude the dentinal tubules, reinforcing dentin’s mechanical properties. Fifteen dentin surfaces were acid-treated for dentinal tubule exposure and brushed with (1) distilled water, or with experimental pastes containing (2) 1% of zinc-doped NPs, (3) 5% of zinc-doped NPs, (4) 10% of zinc-doped NPs or (5) Sensodyne®. Topographical and nanomechanical analyses were performed on treated dentin surfaces and after a citric acid challenge. ANOVA and Student–Newman–Keuls tests were used (p < 0.05). The main results indicate that all pastes produced tubule occlusion (100%) and reinforced mechanical properties of intertubular dentin (complex modulus was above 75 GPa). After the citric acid challenge, only those pastes containing zinc-doped NPs were able to maintain tubular occlusion, as specimens treated with Sensodyne® have around 30% of tubules opened. Mechanical properties were maintained for dentin treated with Zn-doped NPs, but in the case of specimens treated with Sensodyne®, complex modulus values were reduced below 50 GPa. It may be concluded that zinc-doped NPs at the lowest tested concentration produced acid-resistant tubular occlusion and increased the mechanical properties of dentin.

Dissipative properties of composite structures. 1. Statement of problem

Object and purpose of research. The object under study is a sandwich plate with two rigid anisotropic layers and a filler of soft isotropic viscoelastic polymer. Each rigid layer is an anisotropic structure formed by a finite number of orthotropic viscoelastic composite plies of arbitrary orientation. The purpose is to develop a mathematical model of sandwich plate. Materials and methods. The mathematical model of sandwich plate decaying oscillations is based on Hamilton variational principle, Bolotin’s theory of multilayer structures, improved theory of the first order plates (Reissner-Mindlin theory), complex modulus model and principle of elastic-viscoelastic correspondence in the linear theory of viscoelasticity. In description of physical relations for rigid layers the effects of oscillation frequencies and ambient temperature are considered as negligible, while for the soft viscoelastic polymer layer the temperaturefrequency relation of elastic-dissipative characteristics are taken into account based on experimentally obtained generalized curves. Main results. Minimization of the Hamilton functional makes it possible to reduce the problem of decaying oscillations of anisotropic sandwich plate to the algebraic problem of complex eigenvalues. As a specific case of the general problem, the equations of decaying longitudinal and transversal oscillations are obtained for the globally orthotropic sandwich rod by neglecting deformations of middle surfaces of rigid layers in one of the sandwich plate rigid layer axes directions. Conclusions. The paper will be followed by description of a numerical method used to solve the problem of decaying oscillations of anisotropic sandwich plate, estimations of its convergence and reliability are given, as well as the results of numerical experiments are presented.