Composite Micro-Nanoarchitectonics of MMT-SiO2: Space Charge Characteristics under Tensile State

Low density polyethylene (LDPE) is a good insulating material which is widely used in cable materials due to its excellent insulation and processability. However, in the DC high voltage environment, pure polyethylene materials still face many problems, the most serious of which is space charge accumulation. The cable will inevitably be subjected to tensile stress during production, installation and operation. Therefore, it is of great significance to study the effect of stretching on the microstructure and space charge characteristics for polymers and their composites. In this paper, MMT/LDPE micro-composites, SiO2/LDPE nano-composites and MMT-SiO2/LDPE micro-nano-composites were prepared by melt blending. Mechanical stretching was carried out on pure LDPE materials and the above three kinds of composite materials. Each material was stretched according to four stretching ratios, which are 0%, 5%, 10% and 20%. The crystal morphology was observed by polarizing microscope (PLM), the crystallization perfection was tested by differential scanning calorimetry (DSC), and the space charge distribution inside each sample was measured by pulsed electro-acoustic (PEA) method. At the same time, the average charge density and apparent charge mobility for samples during depolarization were calculated and analyzed. The experimental results show that when the pure low density polyethylene sample is not stretched, its crystal structure is loose. Tensile stress can make the loose molecular chains align in LDPE and improve its crystalline structure, which is helpful to restrain the accumulation of space charge inside the sample. For MMT/LDPE, SiO2/LDPE and MMT-SiO2/LDPE composites, their internal crystal structure is compact. Stretching will destroy their original crystal structure at first, and then disorder molecular chains inside the three composite materials. With the increase of stretching ratio, the molecular chains begin to orient along the direction of force, the crystallization tends to be perfect gradually, and the space charge accumulation in samples also decreases. From the calculation results of apparent charge mobility for each sample, with the increase of stretching ratio, the trap depth and trap density inside samples firstly increased and then decreased.

A Study on the Oxygen Permeability Behavior of Nanoclay in a Polypropylene/Nanoclay Nanocomposite by Biaxial Stretching

Polypropylene (PP) has poor oxygen barrier properties, therefore it is manufactured in a multi-layer structure with other plastics and metals, and has been widely used as a packaging material in various industries from food and beverage to pharmaceuticals. However, multi-layered packaging materials are generally low in recyclability and cause serious environmental pollution, therefore we have faced the challenge of improving the oxygen barrier performance as a uni-material. In this work, PP/nanoclay nanocomposites were prepared at nanoclay contents ranging from 0.8 to 6.4 wt% by the biaxial stretching method, performed through a sequential stretching method. It was observed that, as the draw ratio increased, the behavior of the agglomerates of the nanoclay located in the PP matrix changed and the nanoclay was dispersed along the second stretching direction. Oxygen barrier properties of PP/nanoclay nanocomposites are clearly improved due to this dispersion effect. As the biaxial stretching ratio and the content of nanoclay increased, the oxygen permeability value of the PP/nanoclay nanocomposite decreased to 43.5 cc·mm/m2·day·atm, which was reduced by about 64% compared to PP. Moreover, even when the relative humidity was increased from 0% to 90%, the oxygen permeability values remained almost the same without quality deterioration. Besides these properties, we also found that the mechanical and thermal properties were also improved. The biaxially-stretched PP/nanoclay nanocomposite fabricated in this study is a potential candidate for the replacement of the multi-layered packaging material used in the packaging fields.

Microstructure and Mechanical Properties of Polyacrylonitrile Precursor Fiber with Dry and Wet Drawing Process

Polyacrylonitrile (PAN) fibers are typically used as precursor fibers for carbon fiber production, produced through wet-spinning processes. The drawing process of the spun fiber can be classified into dry and wet drawing processes. It is known that the drawing stability and stretching ratio differ depending on the drawing process; however, the elementary characteristics are approximately similar. In this study, the mechanical properties of PAN fibers have been examined based on these two drawing processes with the differences analyzed through the analysis of microstructures. Further, to examine the composition of the fiber, element analysis has been conducted, and thereafter, the microstructure of the fiber is examined through X-ray diffraction analysis. Finally, the characteristics of PAN fibers and its mechanical properties has been examined according to each drawing condition. There are differences in moisture content and microstructure according to the drawing process, and it affects the tensile behavior. The results obtained could have potential implications if the processes are combined, as it could result in a design for a stable and highly efficient drawing process.

Analyzing the impact of induced magnetic flux and Fourier’s and Fick’s theories on the Carreau-Yasuda nanofluid flow

The current study analyzes the effects of modified Fourier and Fick's theories on the Carreau-Yasuda nanofluid flow over a stretched surface accompanying activation energy with binary chemical reaction. Mechanism of heat transfer is observed in the occurrence of heat source/sink and Newtonian heating. The induced magnetic field is incorporated to boost the electric conductivity of nanofluid. The formulation of the model consists of nonlinear coupled partial differential equations that are transmuted into coupled ordinary differential equations with high nonlinearity by applying boundary layer approximation. The numerical solution of this coupled system is carried out by implementing the MATLAB solver bvp4c package. Also, to verify the accuracy of the numerical scheme grid-free analysis for the Nusselt number is presented. The influence of different parameters, for example, reciprocal magnetic Prandtl number, stretching ratio parameter, Brownian motion, thermophoresis, and Schmidt number on the physical quantities like velocity, temperature distribution, and concentration distribution are addressed with graphs. The Skin friction coefficient and local Nusselt number for different parameters are estimated through Tables. The analysis shows that the concentration of nanoparticles increases on increasing the chemical reaction with activation energy and also Brownian motion efficiency and thermophoresis parameter increases the nanoparticle concentration. Opposite behavior of velocity profile and the Skin friction coefficient is observed for increasing the stretching ratio parameter. In order to validate the present results, a comparison with previously published results is presented. Also, Factors of thermal and solutal relaxation time effectively contribute to optimizing the process of stretchable surface chilling, which is important in many industrial applications.

Crystallinity and β Phase Fraction of PVDF in Biaxially Stretched PVDF/PMMA Films

Polyvinylidene fluoride (PVDF) and poly(methyl methacrylate) (PMMA) blend films were prepared using biaxial stretching. The effects of PMMA content and stretching ratio on the crystallinity and β phase fraction of PVDF in blend films were investigated. The distributions of crystallinity and β phase fraction on variable locations were also studied. The results of FTIR and XRD showed that β phase appeared in PVDF/PMMA blends after extrusion and casting procedures. Although β phase fraction decreased after preheating, there was still an increasing trend during following biaxial stretching. More importantly, the increase in PMMA content improved β phase fraction, and the highest β phase fraction of 93% was achieved at PMMA content of 30 wt% and stretching ratio of 2×2. Besides, the reduction in PMMA content and the increase in stretching ratio improved the crystallinity of PVDF. The mechanical properties of the stretched films were significantly improved by increasing the stretching ratio as well. The uniform stress distribution on different regions of biaxial stretching films contributed to the uniform distribution of β phase fraction and crystallinity of PVDF with the aid of simulation. This work confirmed that biaxial stretching can be a candidate method to prepare PVDF/PMMA blend films with uniform distributions of comparable β phase and crystallinity of PVDF.

The Effect of Stretching on the Crystal Structure and Crystal Orientation of PA510/SiO2 Films

In order to explore the relationship between the microstructure and macroscopic properties of PA510/SiO2 films, the effect of the stretching on the crystal structure and crystal orientation of stretched PA510/SiO2 films was studied. It could be seen from the transmission electron microscopy (TEM) graphs that the layered SiO2 molecules were mainly oriented toward the machine direction (MD) and the dispersion could be improved by stretching. Through wide-angle X-ray scattering (WAXS) analysis, PA510/SiO2 stretched films only contained a γ crystal form. During uniaxial stretching, especially for 1 × 3 film, the γ1(100) crystal form was obviously oriented in the equatorial direction, and the orientation of γ2(004) and γ3(006) crystal forms could be observed in the meridian direction. According to the Herman orientation function, the orientation of the b-axis in the MD increased with the increase of the stretching ratio. It was worth noting that the orientation of the crystal region was more obvious. The addition of SiO2 and the orientation of the crystalline and amorphous regions could improve the barrier properties of the films. The changes in the optical properties of stretched films were affected by the dispersion state of SiO2 and the surface roughness.

Development of Polypropylene/Polyethylene Terephthalate Microfibrillar Composites Filament to Support Waste Management

The concept of microfibrillar composites (MFCs) is adopted to produce composites of polyethylene terephthalate (PET) fiber-reinforced polypropylene (PP) materials. The two polymers were dry mixed with PET content ranging from 22 to 45 wt%. The PET has been used as a reinforcement to improve the mechanical properties of composites. The relationship between the morphology of the MFC structure and the mechanical behavior of the MFC filament was investigated. Analysis of the structure and mechanical behavior helped to understand the influence of the stretching ratio, extruder-melt temperature, stretching-chamber temperature, and filament speed.

Ternary-hybrid nanofluids: significance of suction and dual-stretching on three-dimensional flow of water conveying nanoparticles with various shapes and densities

Increasing knowledge of hybrid nanofluid can be traced to its unique improvement of thermal performance and enhancement of heat transfer rate as applicable in the dynamics of fuel and coolant in automobiles. However, the case of water-based nanofluid conveying three kinds of nanoparticles (i.e., ternary-hybrid nanofluid) with various shapes and densities is far-fetched. The transport phenomena of water conveying smaller densities nanoparticles (i.e., copper nanotubes, graphene, and aluminum oxide) and substantial large densities of nanoparticles (i.e., copper oxide, copper, and silver) of various types through a rectangular closed domain with major emphasis on the significance of suction and dual stretching was investigated. The dimensional equation that model the aforementioned transport phenomenon, for the two cases, were non-dimenzionalized using appropriate similarity variables, parameterized, and solved numerically using shooting techniques together with fourth-order Runge-Kutta integration scheme and in-built bvp4c package of MATLAB. Enhancement in suction and stretching ratio causes the vertical velocity of the motion along x-direction and Nusselt number to be an increasing function. Due to an increase in suction and stretching ratio, fluid flow along (x, y)-directions, temperature distribution, and the local skin friction coefficients are decreasing functions. At all the levels of suction and stretching ratio, higher Nusselt numbers were found in the case of water conveying Copper oxide, Copper, and Silver nanoparticles due to their heavy densities.

Verification of Thermodynamic Theories of Strain-induced Polymer Crystallization

We studied the crystallization of nearly “homogeneous” polyethylene glycol (PEG) networks prepared by end-crosslinking of tetra-armed PEG. The influence of stretching ratio and strand length on the melting and crystallization...

Numerical and Experimental Study on Combined Seals With the Consideration of Stretching Effects

Combined seals, as a kind of reciprocating seals, are widely used in hydraulic systems. The combined seal usually contains two or more elements to achieve the sealing function. Not only the interference fit between the seal and the rod/groove should be considered, but the assembling parameters between the inner sealing elements are also essential to be investigated. Stretching ratio, as an indicator for the interference fit, usually exerts a significant influence on the sealing performance. However, in the studies of stretching effects on combined seals, the traditional axisymmetric modeling method will introduce the overstretching problems, resulting in large errors. To overcome this problem, this paper proposed a putter-movement method, where an extra putter is introduced into the model, and a mixed-lubrication theory was employed to study macro and micro characteristics among the sealing zone. As a typical kind of combined seals, the VL seal is utilized as the research object, and the material’s plastic effects are included in the reciprocating-seal modeling for the first time. The numerical results are compared with the experimental data, and good agreements are obtained. The proposed method is then employed to discuss the sealing characteristics under different interference-fit conditions systematically. The results indicate that the stretching mainly affects the contact pressure on the cavity side. Compared to the performance of the seal with the standard geometry, in the extra-stretching condition, the leakage is increased, but the friction is decreased.