Ethylene Vinyl Acetate Foam Research Articles

Physical Properties of Polyethylene and Ethylene Vinyl Acetate Foam Mixtures

Previous studies on the physical properties of each Polyethylene (PE) or Ethylene Vinyl Acetate (EVA) foam have been widely reported. The current challenge is how to understand the combination of PE and EVA foam in order to obtain appropriate properties in various applications. Therefore, an experimental breakthrough in order to understand the physical mechanism on the PE:EVA mixed foam in order to maintain many appropriate properties due to their applications was studied. The physical properties of a combination of PE and EVA foam with Azodicarbonamide (ADC) as blowing agent and the addition of Zinc Oxide (ZnO) as accelerated agent in foaming process have been investigated in this study. The foams were prepared via two steps. Firstly, the various content of PE and EVA resins with combination of various content of ZnO and the addition of ADC, stearic acids and antioxidants were mixed by a single screw extrusion as the results of pellets. Furthermore, this intermediate product was pressed by compression moulding at the temperature of 175 °C and pressure of 30 bar for 5 minutes, then the pressure was released for the foaming process. The effect of the addition of ZnO were observed on the density and the mechanical properties of the foams. The density decreased with increasing of ZnO content up to 4 per hundred resin (phr) on the foam with PE content maximum of 20 phr. Interestingly the density of the foam increased with the addition of 6 phr of ZnO. Due to the increasing number of ZnO, we found the formation of foams completely. We observed the approval of the hardness, tensile and compression properties of each formulation, respectively. Furthermore, the morphology observation of the foams was conducted by scanning electron microscopy (SEM) to measure the size and homogeneous of the cells. We observed large size of cells at low density of foams, meanwhile uniform of cell was obtained at the high density of foams. Finally, the Fourier transform infrared (FTIR) spectroscopy confirmed that in general the intensity of the absorption peak at around 2216 cm-1 - 2223 cm-1 of each formulation decreased with the addition of ZnO up to 4 phr of ZnO and increased again at 6 phr of ZnO.

Advanced design and manufacturing of custom orthotics insoles based on hybrid Taguchi-response surface method

Herein, a machining strategy to fabricate custom orthotic insoles with high surface finish and wide fit tolerance is presented. CNC milling was used to machine ethylene-vinyl acetate (EVA) foam for insoles with various surface hardness, and the Taguchi-response surface method (TM-RSM) was adopted to optimize the parameters of the CNC milling process (cutting speed, feed rate, tool path strategy, and step over). EVA foam with varying surface hardness and the tolerance of the wide fit insoles corresponding to the surface roughness were analyzed. Subsequently, a mathematical model was established to determine the optimal CNC milling parameters for a standard milling cutter under dry coolants. The results of the six parameters corresponding to the mean values of surface roughness were initially examined using the signal-to-noise ratio of the Taguchi method (TM). The surface roughness obtained with the TM-RSM was up to 4.13% higher than that obtained with the TM. The EVA foam insole with a surface hardness of 50–60 HRC and a wide fit tolerance of 0.75 mm provided the ideal level of comfort and support for patients with diabetes. The results of this study demonstrated that CNC milling provided a better surface finish of orthotic shoe insoles than other methods, which can serve as guidance in the development of machining strategies for insoles made from EVA foam.

Evaluation of different mechanical recycling methods of EVA foam waste

In the present work, a proposal for the recycling of ethylene vinyl acetate (EVA) foam waste from the footwear industry using twin-screw extruder was evaluated. Parameters such as antioxidant addition, number of reprocessing, temperature, rotation speed were evaluated. The recycled material was evaluated by means of gel content, scanning electron microscopy (SEM), thermogravimetry (TG) and parallel plate rheometry. From this, the 4 samples were chosen, from the 16 extruded, with a higher probability of forming homogeneous foams to be used in the manufacture of new EVA foams. The foams were evaluated using scanning electron microscopy (SEM), dynamic mechanical analysis (DMA) and physical tests of density, abrasion and permanent compression deformation (PCD). The results showed a decrease in the content of crosslinked gel by up to 13 percentage points for the recycled material with antioxidant. However, there was a possible residual crosslinking, as the crosslinking of all recycled foams was greater than reference (foam). The greatest recycled material homogeneity, observed in the SEM, occurred in the samples processed for five repetitions without antioxidant. Some foams manufactured with recycled waste presented very similar morphological aspects to the reference foam. Foam manufactures with G1 recycled waste (extruded once, at 180°C, 450 rpm, without antioxidant), presented the most uniform and spherical cells. This foam also presented the best responses for the physical tests of PCD and abrasion, even compared to foam without recycle. As well as the lower viscosities for these same samples compared to the previous processing. It was understood that the viscosity of the recycled waste directly interferes with the formation of new EVA foam. Rheometry made it possible to identify the recycling process that resulted in an ideal viscosity material for incorporation in the manufacture of new EVA foams.

Effects of Porosity and SEBS Fraction on Dry Sliding Friction of EVA Foams for Sports Shoe Sole Applications

Ethylene vinyl acetate (EVA) foam is sometimes used in the outer soles of sport shoes. To improve the slip resistance of EVA foam, this study investigated the effects of porosity and the fraction of styrene–ethylene–butadiene–styrene (SEBS) on the dry sliding friction behavior of EVA foams. Sliding friction tests were performed against a pin specimen with a semicylindrical tip, which was covered with (rough surface) or without abrasive paper (smooth surface). The results revealed that the friction coefficient of the EVA foam increased with porosity when slid against a smooth surface, whereas its friction coefficient increased with porosity and SEBS fraction when slid against a rough surface. The results of this investigation provide insight into how to increase the dry sliding friction of resin foam against smooth and rough surfaces, which will also contribute to improving the slip resistance of shoe soles made from resin foam.

Effect of the Porosity Distribution on Dry Sliding Friction and Wear of Cross-Linked Ethylene Vinyl Acetate Foams With a Skin Layer

Shoes are an essential item in daily life to prevent slip-and-fall accidents and to improve performance in human activities such as walking, running, and jumping. These effects are supported by the friction between the outer shoe soles and the floor. In designing the friction of the outer sole, the wear resistance must be also considered to maintain slip resistance and provide a longer shoe lifetime. Rubber is the most popular material for the outer sole in shoe design, but it is also common to use a cross-linked resin foam on the outer sole to reduce the weight and improve the slip resistance. Ethylene vinyl acetate (EVA) is a popular material for the shoe foam material. In general, cross-linked EVA foam has a non-uniform porosity distribution, and especially near the surface in the low-porosity region called the skin layer. Here, it is considered that the friction and wear behaviors of cross-linked EVA foams can be changed via the skin layer, but the influence of the porosity distribution on the friction and wear behaviors has not been clarified. Using cross-linked EVA foams with a skin layer, this study focused on the foam friction and wear behaviors on a rough surface as a function of the porosity distribution. The friction and wear behaviors were found to depend on the wear surface porosity, which increased with wear progress. In addition, the friction coefficient exhibited a positive and negative correlation with the porosity of the wear surface and the normal force, respectively, while the specific wear rate increased with both parameters. These results are particularly meaningful for designing shoe materials.

Supportless Lattice Structures for Energy Absorption Fabricated by Fused Deposition Modeling.

Additively manufactured cellular structures represent a promising engineering design concept for making customized products where user-specific mechanical properties are required. One of the major challenges in the additive manufacturing (AM) process is removal of unwanted support structures from the lattice. The support structure consumes extra material, printing time, and energy for manufacturing. Postprinting, it needs extensive postprocessing work to remove it from the lattice structure chemically or mechanically. In the case of flexible materials such as thermoplastic polyurethane (TPU), removing the support structure from the lattice is very difficult with the material extrusion process. In this article, a new type of a shell-shaped lattice structure inspired by sea urchin (SU) morphology is designed. This lattice can be additively manufactured by material extrusion processes such as fused deposition modeling (FDM) without requiring any support structures. The mechanical properties of the proposed structure, such as stiffness and energy absorption during loading and unloading, have been evaluated as they are important for cushioning. The compressive results indicate that the stiffness property is almost twice as high compared with the benchmarked, bending-dominated, body-centered cubic (BCC) lattice structure of the same relative density and ethylene vinyl acetate (EVA) foam. Energy absorption is almost equal to the BCC lattice and 20% better than EVA foam. Last, a predictive model on stiffness behavior and energy return was developed to facilitate a systematic way to select optimal densities of the SU lattice structure for energy-absorbing applications. Visual inspection has also revealed that there is no sagging or failure of the lattice, which reduced the manufacturing time and postprocessing time, saving a significant amount of material without compromising on quality. Supportless lattice printing was also validated by printing the specimen with a different FDM printer and TPU filament. A possible application for supportless lattice structures can be for AM of customized shoe midsoles at low cost, ski boots, tires, automotive crush boxes, or any other energy-absorbing structures.

Surface cover method to reduce evaporation rate of crude oil

One of the problems that commonly found in petroleum industry is related to the evaporation of crude oil during storage. Hence the purpose of this study is to find lower-cost method to reduce crude oil evaporation. The method has the same principle as floating roof tank, but instead of surface covered by metal, low-density chemical substances, i.e., polyurethane foam and ethylene vinyl acetate foam (EVA mat), was used to cover the surface of crude oil. In comparison with EVA mat, polyurethane foam gave lower percentage of reduced crude oil evaporation. Increasing the thickness of the additive to 3 cm was found to be the best parameter to reduce the evaporation of crude oil. At temperatures of 40, 45, and 50°C, 3 cm thickness of polyurethane foam was able to reduce the evaporation of crude oil by 81.6 - 91.7%, 75.9 - 87.3%, and 74.2% - 86.6%, respectively. At temperatures of 40, 45, and 50°C, 3 cm thickness of EVA mat can reduce the evaporation of crude oil by 68.6 - 78.1%, 56.8 - 60.9%, and 42.4 - 49.6%, respectively.

Midsole Properties Affect the Amplitude of Soft Tissue Vibrations in Heel-Toe Runners.

Soft tissue vibrations can generate discomfort and may necessitate a greater energy demand to preserve an efficient motion in running. Vibration damping is thus of interest from a comfort and performance standpoint. Our purpose was to assess whether changes in midsole material affect the properties of (a) soft tissue vibrations and (b) myoelectric activity. Two midsole conditions were compared. The control condition corresponded to a full ethylene-vinyl acetate foam midsole. The experimental condition was a bimaterial midsole with a material combination of viscous and viscoelastic materials. Twelve participants ran on an indoor track in both conditions while recording the longitudinal acceleration and the EMG activity of vastus medialis (VM) and gastrocnemius medialis (GM). Wavelet transforms were performed for EMG and acceleration signals to assess the intensity of the muscle activity at low and high frequencies (37-128 and 170-395 Hz, respectively) and to calculate the damping coefficient (D) for soft tissue vibrations. The soft tissue vibrations were also characterized by the peak of acceleration (apeak), the frequency of the power peak (fpeak), and the power of the soft tissue vibrations (PSD[8-55]). The variables apeak and PSD[8-55] decreased for VM and GM in the viscous condition. Before heel strike, low-frequency EMG activity decreased for VM, and high-frequency EMG activity tended to decrease for GM in the viscous condition. The damping D was reduced only for VM, and fpeak was unchanged. A more viscous midsole substantially reduced the amplitude of soft tissue vibrations, but not their frequency. Looking at individual results, it was noted that muscle activity was tuned in response to the acceleration input, and that the damping of soft tissue vibrations was affected by the intensity of muscle activity.

Fabrication of medical footwear for suitable distribution of stress and strain and reduction of plantar pressure by numerical and experimental approaches.

Medical insoles and orthopedic shoes are responsible for reducing the force exerted by the ground to the plantar region of the feet. This combination is designed to develop a suitable distribution of stress and strain in the plantar region. In the present study, attempts have been made to design a prototype of medical footwear which can provide a proper stress and strain distribution in the plantar region while reducing pressure in comparison with current orthopedic footwear. For this purpose, the hyper-elastic behavior materials, including styrene-butadiene rubber, silicon, Plastazote foam, polyfoam, ethylene-vinyl acetate foam, polyurethane foam, and polyurethane, have been investigated, with different degree of hardness as well as one layer of composite with Kevlar fiber, whose effect is reducing the pressure exerted to the feet. A combination of materials was used to construct an insole sample, and uniaxial pressure tests were performed for testing its mechanical properties. Then, these properties were used in finite element analysis, whereby the best type of insole for the footwear was chosen and fabricated. The results of finite element analysis were validated using Pedar system and after performing the experimental tests both statically and dynamically. Experimental and numerical investigations suggested that the sole material of orthopedic shoe should be selected as styrene-butadiene rubber. The internal layers of styrene-butadiene rubber frame from top to bottom should be comprised of Plastazote-polyurethane with Kevlar fiber-silicon shore A6, which can be a suitable orthopedic boot in terms of proper stress and strain distribution. Generally, it could reduce the pressure exerted to the sole by 79% compared with barefoot.

Study of the Sound Absorption Performance of Ethylene-Vinyl Acetate Foam Materials

Ethylene-Vinyl Acetate (EVA) polymer foam was prepared using a mold for this investigation. The effect of the cell structure parameters and pore filling gas type on the sound absorption performance of the EVA foam materials were analyzed in terms of their sound absorption capability. The results show that the cell size, cell wall thickness and pore filling gas type have significant influence on the sound absorption performance. When the cell size is 71.3 μm, at low frequency (1000 Hz) the absorption coefficient was the largest at 0.487 and the absorption effect was good. With the increase of the cell wall thickness, the peak value of the sound absorption coefficient first increased and then decreased, and gradually transferred to the low frequency area. When the cell wall thicknesses were 14.3 μm, the foam material had optimal sound absorption properties. The cell filling gas was hydrogen, the EVA foam material had optimal sound absorption effect, and the sound absorption peak value was 0.553 at 800 Hz in the low frequency range (Ⅰ), the sound absorption performance of the foamed materials was ideal.

Energy Absorption and Low Velocity Impact Response of Open-Cell Polyurea Foams

The energy absorption and impact attenuation of low density polyurea (PU) foams (140–220 kg/m3) is presented. The stress–strain behavior, energy absorption, cushioning efficiency, and energy return (resilience) are measured at a quasi-static strain rate using an Instron load frame. In addition, the low velocity impact attenuation of the polyurea foams at 5 J and 7 J impact energies were investigated according to the American Society for Testing and Materials (ASTM) test methods F1976. The polyurea foams were then compared with widely used ethylene vinyl acetate (EVA) and thermoplastic polyurethane (TPU) foam technologies at similar densities. The PU foams displayed a 5% increase in cushioning efficiency and 30% greater energy absorption over TPU and EVA foams under quasi-static compression. Under impact testing, PU foams resulted in a reduction of up to 28.6% and 36.9% in peak transmitted impact forces when compared to EVA and TPU foams of the same thickness (20 mm) at 5 J and 7 J, respectively. These properties should allow these materials to have a wide range of cushioning/impact applications, especially as midsoles in athletic footwear.

Comparison of the Impact of an Optimized Ice Cooling Vest and a Paraffin Cooling Vest on Physiological and Perceptual Strain.

BackgroundIce cooling vests can cause tissue damage and have no flexibility. Therefore, these two undesirable properties of ice cooling vest were optimized, and the present study was aimed to compare the impact of the optimized ice cooling vest and a commercial paraffin cooling vest on physiological and perceptual strain under controlled conditions.MethodsFor optimizing, hydrogel was used to increase the flexibility and a layer of the ethylene vinyl acetate foam was placed into the inside layer of packs to prevent tissue damage. Then, 15 men with an optimized ice cooling vest, with a commercial paraffin cooling vest, and without a cooling vest performed tests including exercise on a treadmill (speed of 2.8 km/hr and slope of %0) under hot (40°C) and dry (40 %) condition for 60 min. The physiological strain index and skin temperature were measured every 5 and 15 minutes, respectively. The heat strain score index and perceptual strain index were also assessed every 15 minutes.ResultsThe mean values of the physiological and perceptual indices differed significantly between exercise with and without cooling vests (P < 0.05). However, the difference of the mean values of the indices except the value of the skin temperature during the exercises with the commercial paraffin cooling vest and the optimized ice cooling vest was not significant (P > 0.05).ConclusionsThe optimized ice cooling vest was as effective as the commercial paraffin cooling vest to control the thermal strain. However, ice has a greater latent heat and less production cost.

Low-Velocity Impacts on a Polymeric Foam for the Passive Safety Improvement of Sports Fields: Meshless Approach and Experimental Validation

Over the past few years, foam materials have been increasingly used in the passive safety of sport fields, to mitigate the risk of crash injury. Currently, the passive safety certification process of these materials represents an expensive and time-consuming task, since a considerable number of impact tests on material samples have to be carried out by an ad hoc testing apparatus. To overcome this difficulty and speed up the design process of new protective devices, a virtual model for the low-velocity impact behaviour of foam protective mats is needed. In this study a modelling approach based on the mesh-free Element Galerkin method was developed to investigate the impact behaviour of ethylene-vinyl acetate (EVA) foam protective mats. The main advantage of this novel technique is that the difficulties related to the computational mesh distortion and caused by the large deformation of the foam material are avoided and a good accuracy is achieved at a relatively low computational cost. The numerical model was validated statistically by comparing numerical and experimental acceleration data acquired during a series of impact events on EVA foam mats of various thicknesses. The findings of this study are useful for the design and improvement of foam protective devices and allow for optimizing sports fields’ facilities by reducing head injury risk by a reliable computational method.

Performance of ethylene-vinyl acetate foam as cushioning material for rigid debris-resisting barriers

This paper reports an investigation on the performance of ethylene-vinyl acetate (EVA) foam when used as a cushion layer for rigid barriers used to resist debris flow. Large-scale pendulum impact tests were conducted to study the effects of layer thickness on cushion performance under six successive impacts. Results show that for the first impact at 70 kJ, the peak contact force with the EVA foam thickness of 500 mm is about twice larger compared to that of 1000 mm. Results also reveal that the cushion mechanism of elastic collapse of cell walls in the EVA foam results in peak contact forces and maximum transmitted loads that are up to 30 and 50% lower compared to gabions for the first impact at 70 kJ, respectively. The elastic behavior of EVA foam provides consistent cushioning efficiency. Furthermore, EVA foam is found to be susceptible to degradation by ultraviolet light so that a suitable coating layer is required for outdoor use. Polyurea was identified as a suitable coating material and a small-scale coating trial was performed to confirm this. Findings presented in this paper will have direct implications on the future design of cushion layers for rigid barriers used to intercept debris flows.

Effect of Porosity and Normal Load on Dry Sliding Friction of Polymer Foam Blocks

In this study, the effect of porosity on the dry sliding fiction of ethylene-vinyl acetate (EVA) foams was investigated under different normal load conditions. EVA foam blocks with varying porosities were slid against a smooth stainless steel plate under dry conditions. The friction coefficient increased with increasing porosity under all of the normal load conditions. In addition, the contact area was estimated using a contact model considering elastic buckling of the cell walls (elastic collapse). The elastic collapse area in the anterior portion of the EVA foam block increased with increasing normal load and porosity, which resulted in an increased contact area. Furthermore, the friction coefficient was positively correlated with the estimated contact area divided by the normal load, indicating that adhesion friction increases with increasing porosity of polymer foams. These results may contribute to the design of high-friction, lightweight shoe sole tread blocks prepared using polymer foam blocks.

Comfort Fitting Using Shape Memory Polymeric Foam

Abstract Nowadays, more and more people are keen on investing in their own personal fitness. In this paper, a series of experiments were conducted to investigate the feasibility of using ethylene-vinyl acetate (EVA) foam for comfort fitting, with a special reference to shoes applications. Based on the experimental results obtained, it was concluded that the EVA foam examined in this study could satisfy most of the requirements for comfort fitting shoes in terms of shape fixity, shape recovery, and elasticity. The two problems spotted in this study may be easily solved by reducing the porosity ratio of the EVA foam and slightly decreasing the glass transition temperature of the foam.

Processing and properties of an ethylene–vinyl acetate blend foam incorporating ethylene–vinyl acetate and polyurethane waste foams

ABSTRACTWaste polyurethane foam (w‐PU) and waste ethylene–vinyl acetate foam (w‐EVA) were used as fillers for the production of an ethylene–vinyl acetate (EVA) blend foam. Two different foaming techniques (single‐stage and heat–chill processes) were used for this purpose. The waste foam concentration was varied up to 30 wt % of the original EVA. The physical, mechanical, and morphological properties of the filled foam were studied. The single‐stage process produced blend foams with a lower density and a greater cell size than the foams obtained by the heat–chill process. The density and compression strength of the blend foam increased as the percentage of w‐PU foam increased. However, for the w‐EVA/EVA blend foams, the addition of w‐EVA foam did not significantly affect the density or compression strength compared to the original EVA foams. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44708.

Shock-absorption properties of functionally graded EVA laminates for footwear design

The shock-absorbing performance of single ethylene-vinyl acetate (EVA) foams and functionally graded laminates of these foams were evaluated with simulated gait experiments. Mechanical properties such as the hardness and density were measured, along with the viscoelastic behavior. The shock-absorbing performance was found to be dependent on the cellular structure, namely the density, elastic modulus, and loss tangent of the single EVA foams. However, for the laminated samples, there were slight variations in the shock-absorption efficiency for samples with the same density. The graded materials showed higher shock-absorption efficiency compared with non-graded single materials with the same density. In addition, laminates with elastic modulus values slightly higher than those of the single EVA samples showed higher shock-absorption efficiency. Finally, since laminates with varied properties were produced, a design concept for a suitable functionally graded material is presented for footwear applications.

Biomechanical and metabolic effects of a leaf spring structured midsole in heel–toe running

Purpose: The purpose of this study was to investigate effects of a novel leaf spring midsole construction on biomechanical variables affecting running economy. The midsole construction is designed to exploit the directionality of the ground reaction force to shift the shoe anteriorly during the stance phase in running.Methods: Nine male long-distance runners ran 5 min on a treadmill (3 m s−1) with two types of shoes: a leaf spring structured midsole shoe and a standard reference shoe with a standard ethylene vinyl acetate foam midsole. Runner and shoe kinematics were analysed using a three-dimensional motion capture system, and oxygen cost was measured by an open circuit breath-by-breath spirometer. Group differences for all variables were tested using paired t-tests (p < 0.05).Results: The leaf spring structured midsole shoe significantly increased the anterior shift of the foot by 8 ± 4 mm (p = 0.001) during stance leading to an increased stride length (1%; p = 0.044), while oxygen cost (2%; p = 0.031) and stride rate (1%; p = 0.039) were significantly reduced compared to the reference shoe.Conclusion: It is concluded that the leaf spring structured midsole contributes to a more economic running style in heel–toe running at moderate running speeds.

Interaction of age and foam types used in Clinical Test for Sensory Interaction and Balance (CTSIB)

Clinical Test for Sensory Interaction and Balance (CTSIB) is a simplified method for investigating the organization of multiple sensory inputs in postural control. The accuracy of the test is based partly on the foam types. Several types of foam are available, but the validity of these foams on CTSIB and the interaction of age and foam types have not been addressed. In this study, postural sway of young (21.6±3.3 years) and older (53.2±4.9 years) participants were assessed while standing on four types of foam: NeuroCom®, sponge, Ethylene Vinyl Acetate (EVA), and memory foams. Postural sway during stance on solid floor and foams with eyes open and eyes closed were quantified by root-mean-square (RMS) of center of body mass acceleration in the mediolateral (ML) and anteroposterior (AP) directions using the acceleration-based OPAL system. Physical properties of foams including density, Young's modulus, and indentation force deflection (IFD) were determined. Results demonstrated that RMS-ML in older subjects was larger than younger subjects (p≤0.001), especially when standing on the NeuroCom® foam with eyes closed (p=0.001). There was an interaction of age and foam types as larger differences in RMS-ML were observed between young and older subjects on the NeuroCom® and EVA foams, but not the other foams. The sway characteristics were largest when standing on the NeuroCom® foam which demonstrated high density and high compliance. Our findings suggested the importance of foam selection in CTSIB on accurate postural sway analysis and balance assessment.