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Research subject: In recent years, several studies have been performed for improving the adhesion properties of polyurethane and acrylic pressure-sensitive adhesives (PSAs). Generally, polyurethane PSAs are of higher shear strength, while acrylic PSAs have higher tack. This research is a feasibility study of exploiting the properties of both of these adhesives through a simple blending method, and the adhesion properties were evaluated.
Research approach: First, acrylic copolymer (Ac) consisting of 82 vol. % butyl acrylate and 18 vol. % methyl methacrylate was solution polymerized. On the other hand, a thermoplastic polyurethane (TPU) containing 17.5 wt. % hard segment was prepared by bulk polymerization. Blending of these two polymers was performed by solution mixing. Solutions of the pure polymers and their blends at different contents were cast on polyethylene terephthalate backing and dried at room temperature. Fourier transform infrared spectroscopy, gel permeation chromatography, and differential scanning calorimetry were used to identify TPU and Ac. Loop tack, static shear strength, dynamic mechanical behavior, contact angle of sessile drop, morphology, and haze of the PSAs were evaluated.
Main results: Tack of the acrylic PSA was higher than TPU PSA. Tack of the blend PSAs containing 20, 40, and 60 wt. % TPU was higher than the pure components and that of the blend containing 40 wt. % TPU was maximum. This blend demonstrated the lowest water contact angle compared to the other blends and the shortest relaxation time compared to the pure polymers, which resulted in better wetting and higher tack. The shear strength of the PSAs increased with increase in the content of TPU to higher than 40 wt. % in the blends compared to the acrylic PSA; so that the pure TPU showed the highest modulus at various frequencies and hence exhibited high-shear PSA characteristics in the Chang’s viscoelastic window and the highest adhesion strength. The immiscibility of the blends was confirmed by measuring the haze and calculating the Hansen solubility parameter.

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This note presents a theoretical analysis and numerical simulation of hydraulic transients in pressurized pipeline system made of a local polyethylene pipe-wall located at a steel pipeline system. The continuity and momentum equations are solved by the method of characteristic (MOC) taking into account the viscoelastic effect of the pipe-wall for polyethylene pipe. The polyethylene pipe length and location at the pipeline and the discharge flow rate are changed and their influence on transient flow is investigated. By comparing this pipeline system with one that is made of polyethylene pipe totally, the possibility of using local polyethylene pipe due to its effect on the pressure wave is investigated.

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In recent years, significant efforts have been focused on advancements of novel biomaterials based on natural polymers and utilization of efficient methods such as skin tissue engineering for wound treatment. In this study, a 3D printed polycaprolactone (PCL) scaffold coated via immersion in a 1:4 blend of 40% silk fibroin from Bombyx mori cocoons and TEMPO-oxidized was developed. The pore size and the porosity were 180 µm and 85%, respectively. The results demonstrated an enhancement in exudate absorption (swelling and water uptake of 1342% and 80%, respectively), improvement in storage modulus (G’) from 500 to 4000 Pa, as well as viscoelasticity up to 60%, which all are favorable for wound dressing applications. Moreover, the wettability and biodegradability studies revealed an overall increase in contact angle and degradation rate of 19.9°±3, and 95%, respectively. Cell viability and migration studies on fibroblastic cells (L929) using MTT assay, DAPI/ Phalloidin staining, and scratch test showed over 90% viability up to 7 days and complete scratch repair within 24 hours. These findings show that 3D printed PCL scaffolds coated with silk fibroin and oxidized nanocellulose are promising for wound healing applications and might pave the way to natural polymer-based wound dressings.
 

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Fractional calculus is a branch of mathematics which in recent decades has been of great interest to scientists in various disciplines, including engineering. One of the applications of this branch in engineering, is in modeling the viscoelastic materials using fractional differentiation. In this article, by inserting fractional calculus as a viscoelastic material compatibility equations in nonlocal beam theory, a viscoelastic Euler-Bernoulli nano-beam with different boundary conditions at two ends, has been modeled. Material properties of a carbon nanotube is considered and two methods, pure numerical and numerical-analytical have been used for solving obtained equations in time domain. Main method is completely numerical and operator matrices used in it to discrete equations in time and spatial domain. Second method is introduced for validation of pervious method’s answers. In this method equation of system reduced to an ordinary differential equation using Galerkin and obtained equation solved using a numerical direct integrator method. Finally, in a case study, the effects of fractional order, viscoelasticity coefficient and nanlocal theory coefficient on the time response of the viscoelastic Euler-Bernoulli nano-beam with different boundary conditions have been studied.

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The mechanical properties of fruit are one of the most important determinants of standards for designing, transforming, processing, and packaging systems. One of the methods for changesdemonstraction in the internal structure of fruits during storage is to perform stress relaxation tests in different predetermined strains. Therefore, the purpose of this study was to investigate the orange compression behavior in quasi-static mechanical loadings by performing stress-relaxation tests of samples at predetermined levels of strain and modeling the Maxwell and Peleg method and comparing it with image processing method. In addition, in this study, cross-sectional area changes were measured during loading by image processing. The modulus of elasticity in the image processing method, the Maxwell model and the Peleg model on days 0 to 9 increased from 3.91 to 4.5, 3.6 to 4.53 and 2.7 to 3.45, respectively. which in spite of increasing trend there was no significant difference between them Since, no significant difference in the output of these two models (Maxwell and Peleg) was observed Peleg with the less number of elements (only two constants) was preferred compared to Maxwell method

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Stem cells due to their ability of self-renewing and the potential of differentiating to different cell lineages are the ideal choices in regenerative tissue engineering. Under cyclic loading, these cells could differentiate to those kind of cells that experience similar conditions inside the body, like osteocytes and chondrocytes. In this research, the purpose is to investigate the effect of the 10 percent cyclic strain with the frequency of 1 Hertz on the mechanical response of a single mesenchymal stem cell cultured in a fibrin hydrogel block, using the finite element method and considering the role of integrins and implementing the Simo’s hyper-viscoelastic model for the cytoskeleton as long as the uniaxial loading leads the cell to differentiate toward Fibrochondrocyte. The results of presented model show that the averages of the circumferential, radial and shear stresses are 240, 260 and 140 Pascal, respectively and corresponding forces are 24, 45 and 15 Pico-Newton. The results imply that stresses and forces generated inside the cytoskeleton are large enough to elicit a different response from the cell. This research results can be very effective for better designing of biological experiments.

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In this paper the nonlinear dynamic of an electrostatically actuated microbeam with viscoelastic-anelastic behavior considering size effect is studied. The micro-beam is deflected using a bias DC voltage and then driven to vibrate around its deflected position by a harmonic AC load. Regarding the stress-strain behavior of anelastic materials, the constitutive equation of microbeams is derived based on the modified couple stress theory (MCST). Assuming electrostatic and mid-plane stretching forces as the main sources of the nonlinearity and taking advantage of the Galerkin projection method, the partial differential equation is transformed to a set of nonlinear ordinary differential equation (ODE). Multiple scales method is used to obtain an approximate analytical solution for nonlinear resonant curves. The effect of different mechanical behaviors of materials including elasticity, viscoelasticity and anelasticity, length scale parameter, anelastic relaxation time and relaxation intensity on the nonlinear vibration analysis are studied. The results demonstrate that there is very large dependence of resonance curves on the different mechanical behavior of materials. It is seen that there are special conditions which the elastic and anelastic models predict similar results while the predicted results from anelastic and viscoelastic models are different from each other. It is found that the relaxation intensity and anelastic relxation time can change the resonant curves significantly.

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Linear viscoelastic constitutive laws, such as hyperelasticity with the Prony series, are commonly used in commercial software to simulate polymer materials. However, these models are not accurate regarding large strain problems despite performing well for small strain problems. To gather experimental data for soft adhesives, various shear modes were employed, including monotonic, creep, and low-cycle tests using single-lap shear specimens. These tests were conducted on optically clear adhesives (OCAs). Initially, the validity range for linear viscoelasticity was established, revealing the inability to predict large strains accurately using this approach. Subsequently, the three-network viscoplastic (TNV) model parameters were calibrated experimentally under large strains. The calibration procedures took advantage of variations in loading modes, enhancing the precision and improving the accuracy of the constitutive models. For calibration purposes, it is recommended to utilize the low-cycle loading-unloading test as it offers a suitable and cost-effective means of precision. This approach provides a cost-effective way to accurately predict material behavior, owing to the variations in loading modes. Finally, the characteristic model was used to evaluate the results through the finite element method. The results showed that the proposed model accurately predicts stress values, energy dissipation, and energy loss due to softening