Preparation of efficient piezoelectric PVDF–HFP/Ni composite films by high electric field poling

Poly(vinylidene fluoride) (PVDF) and its copolymers have been widely studied due to their excellent piezoelectricity and ferroelectricity. In this study, composite films are prepared by adding Ni nanoparticles (0.00–0.3 wt%) into poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) matrix by solution casting, uniaxial stretching, and high electric field poling. It is found that when the maximum electric field E max for poling is 130 MV m−1, the calibrated open circuit voltage of the pure PVDF–HFP films reaches 3.12 V, which is much higher than those poled by a lower electric field (70 MV m−1: 1.40 V; 90 MV m−1: 2.29 V). This result shows that the effect of poling on the generated output voltage is decisive. By adding 0.1 wt% Ni nanoparticles, it increases to 3.84 V, 23% higher than that of the pure PVDF–HFP films. To further understand the enhancement mechanism, the effects of Ni nanoparticles on initial crystallization, uniaxial stretching, and high electric field poling are investigated by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, and differential scanning calorimetry.

Investigation of Crystallization and Relaxation Effects in Coarse-Grained Polyethylene Systems after Uniaxial Stretching

In this study, we investigate the thermo-mechanical relaxation and crystallization behavior of polyethylene using mesoscale molecular dynamics simulations. Our models specifically mimic constraints that occur in real-life polymer processing: After strong uniaxial stretching of the melt, we quench and release the polymer chains at different loading conditions. These conditions allow for free or hindered shrinkage, respectively. We present the shrinkage and swelling behavior as well as the crystallization kinetics over up to 600 ns simulation time. We are able to precisely evaluate how the interplay of chain length, temperature, local entanglements and orientation of chain segments influences crystallization and relaxation behavior. From our models, we determine the temperature dependent crystallization rate of polyethylene, including crystallization onset temperature.

Model of deformation growth dynamics during filled polymer materials mechanical tests under cable production conditions

With the introduction into highly filled halogen-free plastics production, the mechanical strength of which in operation directly depends on the flame retardant content and application technology, it becomes important to control the cable sheath mechanical characteristics in a fireproof design. Polymeric materials and their compositions are viscoelastic materials for which the mechanical properties depend on the stress time. The results of estimating the deformation samples rate elongation from the uniaxial stretching time at different dilution rates of the clamps in the mechanical characteristics determining process for halogen-free cable plastics in regulatory tests under production conditions are presented. It is shown that the inner and outer layers of the halogen-free plastic cable sheath have significantly different values of the plasticity normative parameter: differences evidence in the polymer structure in the inner and outer layers of the sheath due to the forced deformation process during extrusion, which is forced polymer structure orientation. Elongation relative deformation experimental dependences δL(t) of the samples on the uniaxial stretching time at different clamps dilution speeds are given, which illustrate confirmed by a large data array the dependencies shape reproducibility δL(t) for different in structure similar filled halogen-free polymers. The strain rate dependence model on tensile time as the sum of instantaneous-elastic, viscoelastic and instantaneous-plastic (irreversible) is proposed: dε/dt = λпр exp ( – t/λпр) + {∫ λ1 exp(–τ/λ1).exp[–(t–τ)/λ2]dτ]}/Δt. The appropriate parameter estimates of the named samples deformation components obtained by approximating the experimental data by the proposed model are given. The proposed model, firstly, explains the presence characteristic relative deformation maximum (t = tm) as a two interdependent deformation processes superposition with different aftermath λ. Secondly, it allows to specify the requirements for testing: with increasing the clamps dilution speed, the maximum time tm decreases significantly, respectively, the higher the clamps dilution speed, the smaller interval time Δt between a successive sample control section length measurements. This conclusion was experimentally confirmed for a specific material at a speed of 250 mm/min

Effect of Uniaxial Stretching on Molecular Orientation, Crystallinity and Oxygen Permeability of Ethylene Vinyl Alcohol

This work studies the effects of uniaxial stretching on molecular orientation, crystallinity, crystallography and oxygen permeability of high barrier multilayer films based on EVOH barrier layer. Film samples were prepared using two different blow-up ratios (BUR) of 1 and 3. Uniaxial stretching was applied at 100°C using a tensile machine equipped with an environmental chamber. Fourier transform infrared (FTIR) spectroscopy was used to examine the molecular orientation in the EVOH layer before and after stretching and confirmed a considerable increase in the molecular orientation in the EVOH layer. Dynamic scanning calorimetry (DSC) and wide-angle X-ray diffraction (XRD) results point to the perfection of EVOH crystal structure by applying uniaxial stretching at high temperatures. Oxygen permeability results showed a considerable 25% decrease after stretching of the sample with lower BUR while a significant 80% reduction in oxygen permeability was observed for the sample prepared at higher BUR. The mechanism involved in increasing oxygen permeability due to the uniaxial stretching at high temperature is discussed in detail.

ОСОБЛИВОСТІ 3D МОДЕЛЮВАННЯ СТРУКТУРИ ТРИКОТАЖУ У МАКСИМАЛЬНО РОЗТЯГНУТОМУ СТАНІ

The study aims at the development mathematical basics for software for automated construction of three-dimensional geometric models of knitwear in the most stretched state due to uniaxial stretching along the wale or course direction. Methodology. The research methods of theoretical analysis, spline theory, methods of three-dimensional geometric modeling and parameterization, computer graphics tools, programming tools were used. Findings. During the research, it was assumed that in the maximally stretched state, the tangent to the centerline of the loop at the interlacing point is located at an angle of 45º to the vertical line oriented along the wale direction. Mathematical expressions are proposed for determining the co-ordinates of the characteristic points of the loop in three-dimensional space. An algorithm and its software implementation have been developed as a separate module of the Structure 3D program, designed to create models of knitwear in a stretched state. To verify the algorithm, samples of weft knitted fabrics were made with a 8th gauge flat-bed knitting machine of para-aramid and high-molecular polyethylene threads of linear density 58.8x2 tex and 44x3 tex, respectively. The parameters of the loop structure of the samples in dry-relaxed state and under maximum uniaxial stretching along the wale and the course directions. Tensile testing of specimens was performed on the machine KaoTieh KT-7010AZ. The maximum stress state of the samples was recorded using a Micro Capture Pro microscope to further determine the changes of the loop structure parameters under the action of tensile deformation. The obtained values of the the loop structure parameters of the samples were used as input data for the construction of three-dimensional models. The deviation of the value of the length of the spline representing the centerline of the thread in the loop model from the length of the thread in the loop obtained during the analysis of the samples does not exceed 5%. Scientific novelty. An algorithm for the automated construction of 3D models of knitted structures, undergoing maximum deformations coursed by uniaxial tension along the wales or course directions, has been developed. Practical value. A separate module of the 3D Structure program has been created for the automated construction of a knitted loop undergoing maximal stretching under has been developed.

The Lack of a Representative Tendinopathy Model Hampers Fundamental Mesenchymal Stem Cell Research

Overuse tendon injuries are a major cause of musculoskeletal morbidity in both human and equine athletes, due to the cumulative degenerative damage. These injuries present significant challenges as the healing process often results in the formation of inferior scar tissue. The poor success with conventional therapy supports the need to search for novel treatments to restore functionality and regenerate tissue as close to native tendon as possible. Mesenchymal stem cell (MSC)-based strategies represent promising therapeutic tools for tendon repair in both human and veterinary medicine. The translation of tissue engineering strategies from basic research findings, however, into clinical use has been hampered by the limited understanding of the multifaceted MSC mechanisms of action. In vitro models serve as important biological tools to study cell behavior, bypassing the confounding factors associated with in vivo experiments. Controllable and reproducible in vitro conditions should be provided to study the MSC healing mechanisms in tendon injuries. Unfortunately, no physiologically representative tendinopathy models exist to date. A major shortcoming of most currently available in vitro tendon models is the lack of extracellular tendon matrix and vascular supply. These models often make use of synthetic biomaterials, which do not reflect the natural tendon composition. Alternatively, decellularized tendon has been applied, but it is challenging to obtain reproducible results due to its variable composition, less efficient cell seeding approaches and lack of cell encapsulation and vascularization. The current review will overview pros and cons associated with the use of different biomaterials and technologies enabling scaffold production. In addition, the characteristics of the ideal, state-of-the-art tendinopathy model will be discussed. Briefly, a representative in vitro tendinopathy model should be vascularized and mimic the hierarchical structure of the tendon matrix with elongated cells being organized in a parallel fashion and subjected to uniaxial stretching. Incorporation of mechanical stimulation, preferably uniaxial stretching may be a key element in order to obtain appropriate matrix alignment and create a pathophysiological model. Together, a thorough discussion on the current status and future directions for tendon models will enhance fundamental MSC research, accelerating translation of MSC therapies for tendon injuries from bench to bedside.