Ethylene Vinyl Acetate Foam Research Articles

Heat and Moisture Transfer Depending on 3D-Printed Thermoplastic Polyurethane and Ethylene-Vinyl Acetate Foam and the Presence of Holes for 3D Printing Clothing Development.

Recently, clothing development 3D printing and the evaluation of its physical characteristics have been explored. However, few studies have tackled thermal comfort, which is a major contributor to the wearers' comfort. Therefore, this study was designed to suggest effective materials and hole sizes for clothing obtained by 3D printing to maintain a comfortable clothing environment. In particular, two main variables, namely five different materials and three-hole sizes, were analyzed. All samples were placed on a hot plate (36 °C), and their surface temperature and humidity were measured for 10 min. The samples with only thermoplastic polyurethane (TPU) achieved the largest temperature change of 3.2~4.8 °C, whereas those with ethylene-vinyl acetate (EVA) foam exhibited the lowest temperature change of -0.1~2.0 °C. Similarly, the samples with only TPU showed the greatest humidity change of -0.7~-5.5%RH. Moreover, the hole size had a larger effect on humidity change than material type. The samples with large holes achieved the largest humidity change of -4.4%RH, whereas the samples without holes had the smallest humidity change of -1.5%RH after 10 min (p < 0.001). Based on these results, various combinations of materials and hole sizes should be considered to fit the purpose of 3D printing clothing.

Novel Design of a Bandwidth Enhanced and Frequency Reconfigurable, Wearable Antenna for Body Centric Communication

This paper proposes a novel design for a frequency reconfigurable and bandwidth-enhanced antenna for use in biomedical telemetry applications. Data pertaining to a patient’s body parameters, such as blood pressure, pulse, and temperature, are gathered using sensors and then transmitted to a remote place for monitoring. The proposed antenna is connected to a wearable transmitter, which transfers the body parameter data to a centrally located nearby control unit. The antenna operates in the 5.8 GHz band in single-band mode and in the 4.27 GHz (C band) and 5.8 GHz industrial, scientific, and medical (ISM) bands in dual-band mode. The use of ethylene-vinyl acetate foam as a substrate makes the structure waterproof and ultraviolet resistant. The basic antenna structure equipped with proximity coupling offers a front-to-back ratio (FBR) of 17.62 dB and a bandwidth of 122 MHz. With an additional upper patch and resonant slots, bandwidth enhancement of 82.85% and 11.57% improvement in the FBR are achieved, respectively. Overall, a maximum FBR of 19.66 dB and gain of 5.0 dBi are attained over the resonant frequency. The specific absorption rate is found to be 0.145 W/kg for 10 gram of tissue.

Analyzing the Thermal Characteristics of Three Lining Materials for Plantar Orthotics.

The choice of materials for covering plantar orthoses or wearable insoles is often based on their hardness, breathability, and moisture absorption capacity, although more due to professional preference than clear scientific criteria. An analysis of the thermal response to the use of these materials would provide information about their behavior; hence, the objective of this study was to assess the temperature of three lining materials with different characteristics. The temperature of three materials for covering plantar orthoses was analyzed in a sample of 36 subjects (15 men and 21 women, aged 24.6 ± 8.2 years, mass 67.1 ± 13.6 kg, and height 1.7 ± 0.09 m). Temperature was measured before and after 3 h of use in clinical activities, using a polyethylene foam copolymer (PE), ethylene vinyl acetate (EVA), and PE-EVA copolymer foam insole with the use of a FLIR E60BX thermal camera. In the PE copolymer (material 1), temperature increases between 1.07 and 1.85 °C were found after activity, with these differences being statistically significant in all regions of interest (p < 0.001), except for the first toe (0.36 °C, p = 0.170). In the EVA foam (material 2) and the expansive foam of the PE-EVA copolymer (material 3), the temperatures were also significantly higher in all analyzed areas (p < 0.001), ranging between 1.49 and 2.73 °C for EVA and 0.58 and 2.16 °C for PE-EVA. The PE copolymer experienced lower overall overheating, and the area of the fifth metatarsal head underwent the greatest temperature increase, regardless of the material analyzed. PE foam lining materials, with lower density or an open-cell structure, would be preferred for controlling temperature rise in the lining/footbed interface and providing better thermal comfort for users. The area of the first toe was found to be the least overheated, while the fifth metatarsal head increased the most in temperature. This should be considered in the design of new wearables to avoid excessive temperatures due to the lining materials.

Solar-Driven Multistage Device Integrating Dropwise Condensation and Guided Water Transport for Efficient Freshwater and Salt Collection.

Interfacial solar vapor generation (ISVG) is an emerging technology to alleviate the global freshwater crisis. However, high-cost, low freshwater collection rate, and salt-blockage issues significantly hinder the practical application of solar-driven desalination devices based on ISVG. Herein, with a low-cost copper plate (CP), nonwoven fabric (NWF), and insulating ethylene-vinyl acetate foam (EVA foam), a multistage device is elaborately fabricated for highly efficient simultaneous freshwater and salt collection. In the designed solar-driven device, a superhydrophobic copper plate (SH-CP) serves as the condensation layer, facilitating rapid mass and heat transfer through dropwise condensation. Moreover, the hydrophilic NWF is designed with rational hydrophobic zones and specific high-salinity solution outlets (Design-NWF) to act as the water evaporation layer and facilitate directional salt collection. As a result, the multistage evaporator with eight stages exhibits a high water collection rate of 2.25 kg m-2 h-1 under 1 sun irradiation. In addition, the desalination device based on the eight-stage evaporator obtains a water collection rate of 13.44 kg m-2 and a salt collection rate of 1.77 kg m-2 per day under natural irradiation. More importantly, it can maintain a steady production for 15 days without obvious performance decay. This bifunctional multistage device provides a feasible and efficient approach for simultaneous desalination and solute collection.

Effect of ethylene vinyl acetate foam-graphene composite material on the mechanical properties of sports footwear

Ethylene vinyl acetate (EVA) foam is widely used as midsole material in athletic footwear due to its lightweight and cushioning properties. However, EVA foam suffers from low mechanical strength, abrasion resistance, and fatigue resistance. Reinforcing EVA foam with graphene nanoplatelets is a promising approach to improving its mechanical performance for footwear applications. This study investigated the effect of 0.1–1 wt% graphene nanoplatelets on the properties of EVA foam composites relevant to midsole performance. The results showed that 0.1–0.2 wt% graphene provided optimal reinforcement, exhibiting 33–40% higher impact energy absorption, 50–60% lower compressive stiffness, 30% higher flexural stiffness, and up to 40% lower abrasion volume loss. Under simulated use conditions, the composites demonstrated higher energy return and fatigue resistance. The graphene nanoplatelets acted as effective reinforcements within the EVA foam by improving stress transfer, inhibiting crack propagation, and shielding the foam surface. The findings indicate that reinforcing EVA foam with small amounts of graphene nanoplatelets can develop midsole materials with enhanced mechanical performance for athletic footwear.

Injection moulding process parameter and strain rate dependence mechanical properties measurement and theoretical estimation of EVA polymer foam

Abstract In this study, the combined experimental and theoretical estimation on elastic characteristics of EVA (ethylene-vinyl acetate) copolymer material is demonstrated. Strain rate dependence stress–strain behavior of EVA in raw and foam material form are measured by the quasi static and dynamic compression test. Simultaneously, the influence of different mould temperature and injection pressure on mechanical properties of EVA foam are investigated. According to the usage scenario of EVA foam in sport footwear application, the EVA foam is generally deformed under higher strain rate as compared with the quasi-static compression condition. For this reason, the stress–strain behavior of EVA foam under high strain rates of 2.66 × 10−3 and 2.66 × 10−2 s−1 are estimated. The analytic results revealed that the strain rate slightly enhanced the modulus of EVA foam, and the foregoing strain rate effect is substituting into the classic Young's modulus estimation equation of closed cell cellular solid. Accordingly, the strain rate dependence Young's modulus of EVA foam is successfully estimated by both experiment and theoretical estimation.

Preparation and Characterization of Carrot Nanocellulose and Ethylene/Vinyl Acetate Copolymer-Based Green Composites

This study aims to investigate the effect of nanocellulose on the properties and physical foaming of ethylene/vinyl acetate (EVA) copolymer. The nanocellulose is prepared from waste carrot residue using the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation method (CT) and is further modified through suspension polymerization of methyl methacrylate (MMA) monomer (CM). The obtained nanocellulose samples (CT or CM) are added to EVA to create a series of nanocomposites. Moreover, the EVA and CM/EVA composite were further foamed using supercritical carbon dioxide physical foaming. TEM results show that the average diameters of CT and CM are 24.35 ± 3.15 nm and 30.45 ± 1.86 nm, respectively. The analysis of mechanical properties demonstrated that the tensile strength of pure EVA increased from 10.02 MPa to 13.01 MPa with the addition of only 0.2 wt% of CM. Furthermore, the addition of CM to EVA enhanced the melt strength of the polymer, leading to improvements in the physical foaming properties of the material. The results demonstrate that the pore size of the CM/EVA foam material is smaller than that of pure EVA foam. Additionally, the cell density of the CM/EVA foam material can reach 3.23 × 1011 cells/cm3.

Mechanical Behavior of Closed-Cell Ethylene-Vinyl Acetate Foam under Compression.

The static and dynamic compressions of closed-cell ethylene-vinyl acetate (EVA) foams with different densities were conducted under various strain rates. The stress-strain curves were processed to determine the corresponding curves of energy absorption per unit volume and energy absorption efficiency, and energy absorption diagrams were produced. The influences of density and strain rate on the elastic modulus, yield strength, energy absorption per unit volume, optimal strain, densification strain, and energy absorption diagrams were analyzed and discussed. The whole stress-strain curve can be fitted with the Rusch formula. The strain rate does not change the shape of stress-strain curve, and has little influence on the elastic modulus. There exists the optimal density of EVA foam corresponding to its maximum energy absorption efficiency. Under a fixed strain rate, the optical energy absorption per unit volume is proportional to the optical stress on the envelope line in the energy absorption diagrams of EVA foams with different densities. The change in strain rate leads to the envelope line in the energy absorption diagrams of EVA foams with a given density having the larger slope and a negative intercept where the optical energy absorption per unit volume relies linearly on the optical stress. The empirical formulas of elastic modulus, yield strength, optimal strain, and envelope lines and their slopes are derived from the tested results.

Enhancing dynamic impact performance and cushioning of EVA copolymer foams with thermoplastic elastomers

This study examines the effect of thermoplastic elastomers (TPE) on the physical, mechanical, and dynamic impact properties of ethylene-vinyl acetate (EVA) copolymer foam using traditional chemical blowing process. The blending of EVA with TPE aims to improve both physical and dynamic impact cushioning to achieve optimal energyreturn EVA foam. Comparative analysis reveals that adding a 10–20 wt% fraction of propylene elastomer (POE) to EVA significantly reduces foam density while maintaining dynamic energy absorption and energy return. However, high POE content (30 wt%) leads to inferior mechanical and dynamic impact properties due to excessive softness. Blending EVA with terpolymer elastomer (PTW) enhances compression strength (∼16%), hardness (∼27%), and dynamic energy return (∼9%). EVA/POE/PTW hybrid blend foams display intermediate properties. The impact behaviors of foams vary between high and low dynamic impact loading rates. The presence of TPE enhances cushioning by absorbing impact forces through deformation, with EVA/PTW exhibiting remarkably improved rebound properties. Impact peak force decreases linearly with increasing PTW content. Foam morphology, including phase compatibility, cell size and density, plays a role in determining dynamic impact properties. Hard segmented TPE store more energy and quickly recover, resulting in a higher rebound effect as compared to soft segmented TPE. Incorporating TPE provides the ability to control the EVA foam's dynamic rebound, and impact cushioning, expanding its potential in sports-related applications.

A One-Dimensional Dynamic Constitutive Modeling of Ethylene Vinyl Acetate (EVA) Foam.

Ethylene vinyl acetate copolymer (EVA) is good for impact protection and energy absorption, and belongs to rate sensitive-dependent materials. This study aimed to investigate the influence of increased strain rate and the presence of entrapped air on the enhancement of foam material strength. The compression deformation behavior of EVA foams containing a microporous structure was extensively investigated over different strain rates of 0.0017/s, 0.033/s, and 0.17/s, where each test was conducted at a constant compression velocity. A one-dimensional dynamic constitutive model was established to describe the large deformation response of EVA to different strain rates. The model included two components, the material action part and the air pressure part. Quasi-static and dynamic compression tests were used to determine the constitutive relations of three parameters, a1, a2, and the leaking rate δ·. The samples with EVA foams at different strain rates were fitted using ORIGIN software, and the constitutive model parameters were obtained. It was found that the ratio of the air leaking rate to the strain rate gradually decreases, causing air within the EVA to be trapped in the cells rather than escaping in a timely manner with increasing strain rates.

Processing plastic waste via pyrolysis-thermolysis into hydrogen and solid carbon additive to ethylene-vinyl acetate foam for cushioning applications

A strategy for enhancing value creation from pyrolysis gas and oil, derived from plastic waste, through the generation of two additional outputs of solid carbon and hydrogen was investigated. Three types of hard-to-recycle plastic waste (marine plastic litter, household mixed plastics and cosmetic products packaging) were thermally treated in two stages: (i) decomposition of feedstock into gas and oil via pyrolysis at 600 °C; and (ii) thermolytic conversion of the pyrolysis gas and a fraction of oil into hydrogen and solid carbon at 1300 °C separately. The thermolysis of both pyrolysis gas and oil fractions predominantly resulted in the production of solid carbon (39–70 wt% per plastic feedstock and carbon content of 91.3–98.6 wt%) and H2-rich gas (H2 yield of 5.9–10.8 wt% per plastic waste feedstock and H2 content of 71.4–97.2 vol% per gas volume). The incorporation of pyrolysis oil into the thermolysis process could enhance the outputs of solid carbon and hydrogen. Characterizations of solid carbon and hydrogen obtained from pyrolysis gas and oil fractions were further conducted. The observed similar properties of H2 and solid carbon from pyrolysis gas and oil supported the feasibility of introducing all the pyrolytic products together into the thermolysis process without condensation of oil. To enhance the value of these solid carbon derived from plastics for practical usage, we utilized the obtained solid carbon as a reinforcing agent for polymer composite foam development. The solid carbon reinforced composite foam displayed great abrasion resistance (wear loss: 240 mg), compression strength (0.347 MPa), and dynamic impact properties (energy returned: 124 J/m and energy absorbed: 57.3 J/m), emphasizing the viability of solid carbon as a nucleating agent and reinforcing filler in polymer foam for cushioning applications. Overall, the strategy of pyrolysis-thermolysis, which harnesses both pyrolysis gas and oil, unlocks additional value creation by producing two new outputs from plastic waste. Depending on the market prices for solid carbon and hydrogen, this can substantially change the economics of plastic waste management and create new revenue streams, incentivizing plastic waste collection and processing.

Calculation of the depth of rope-tightening soft material and analysis of its relationship with the tightening force

To analyze the relationship between the tension force of a rope and the bundled material's indentation, a model of tightening by rope for soft material was designed for testing. By calculating the indentation depth of soft materials from rope stretching displacement, the variation law of the indentation depth of tightening soft materials with different mechanical properties of ropes was analyzed. As the stretching progresses, the more the rope winding turns, and the shallower the indentation depth. The friction coefficient between the soft material and the rope does not significantly affect the theoretical indentation depth. The theoretical indentation depth of high-strength ropes shows a linear variation pattern. The theoretical indentation depth of high-extension ropes is negative. With the theoretical indentation depth of the ordinary rope increasing first and then decreasing, its indentation depth curve shows a parabolic shape. Aromatic polyester rope, cotton chainette thread, and polypropylene rope were used to tighten ethylene-vinyl acetate (EVA) foam and test the indentation depth. The results show that the deformation of the rope is much lower than that of the EVA foam, and the depth of the strangulation is closely related to the tensile displacement and tightening tension. The measured value of the indentation depth is lower than the calculated value, and the greater the stiffness of the rope, the smaller the difference between the measured and calculated indentation depth. The indentation depth method was used to calculate the tightening effect of ropes with high rigidity and has excellent results.

Micromechanical properties of shear stiffening gel reinforced ethylene–vinyl acetate foam

In previous study, a novel composite foam that possesses cushioning properties is developed by incorporating shear stiffening gel (SSG) into Ethylene-vinyl (EVA) foam. In this work, uniaxial compression is used to obtain the mechanical properties of the proposed material under static loading. The test results demonstrate the additive SSG could effectively enhance the energy absorption capacity. With the aid of in-situ Scanning Electron Microscope (SEM), two characteristics, the homogeneous microstructural morphology and phase separation between SSG and EVA, are found that played dominant roles in the improvement of cushioning properties.

Impact of hollow glass microsphere addition to poly(ethylene vinyl) acetate foam on mechanical properties of sports footwear

AbstractSamples of ethylene vinyl acetate (EVA) co‐polymer foams in form of plates and industrial outsoles of prototyped sport shoes containing 0% (reference), 2.5%, and 5.0 weight % (wt%) of hollow glass microspheres (HGM) were made. The goal was to study the influence of HGM on properties of EVA foam in laboratory conditions followed by the industrial trial, where the most promising laboratory result was applied. The physical properties of samples and behavior of material under dynamic load were examined. EVA foams with HGM filler demonstrated that they have better ability to reduce impact peak force and increase absorb impact impulse compared to the reference foam without HGM. Addition of 5.0 wt% of HGM in laboratory foam increased its absorbed impact pulse by two‐fold. Meanwhile for industrial prototype outsoles, the impact peak force was reduced by 5%–7% in walking simulated conditions and by 11% in case of simulated running. It is also observed that, addition of 5.0 wt% of HGM in EVA foam increased its abrasion resistance by three times, which generally helps to increase the lifetime of sport footwear. Under dynamic load, samples with the addition of HGM behave interestingly and result shows a small decrease in energy return (7%) which is logical, because this composite tends to absorb energy and not return it. Samples with 2.5 wt% HGM are stiffer than reference until 40% compression deformation, but beyond that point it becomes softer, and better absorbs impact energy than reference. Outsole with 2.5% of HGM in EVA outsole increased resistance of shoe at lateral bending of 50% and 20% rise of resistance was found at medial twist. Impact absorption and flexibility resistance are useful for protection against impact which are also helpful to prevent sport injuries. The obtained results show the addition of HGMs which are cheap by‐products in several technologies brings improvement to properties of EVA foams which is the most common materials for the sport footwear industry.

Effect of shear thickening gel on microstructure and impact resistance of ethylene–vinyl acetate foam

To satisfy the ever-increasing demand for better anti-impact performance of personal protective equipment, a composite foam by incorporating shear thickening gel (STG) with ethylene–vinyl acetate (EVA) was developed. The superiorities of EVA foam in softness, lightness and flexibility were maintained in the novel material. The microstructure of STG/EVA composite foam was characterized using Scanning Electron Microscope. A series of experimental approaches including Dynamic Mechanical Analysis test, compression test, Split Hopkinson Pressure Bar test and drop hammer test were applied to study the material properties at different strain rates. Attributed to the shear thickening property of STG, STG/EVA exhibited significant strain rate sensitivity. The results showed that STG/EVA foam possessed better mechanical performance than plain EVA foam. In the ballistic test, the body armor consisting of the STG/EVA buffer layer possessed better protective performance than the regular one. The improvement mechanism was interpreted with micromorphological changes before and after tests. The introduced STG reinforced the integrity and continuity of microstructure to enhance the capability of the composite material in absorbing and dissipating impact energy. Therefore, the application prospect of the developed STG/EVA foam in personal protective equipment is promising.

Design and performance evaluation of multifunctional midsole using functionally gradient wave springs produced using multijet fusion additive manufacturing process

Additive manufacturing (AM) is getting more attention and is considered a better choice of fabrication in almost every industry due to its unlimited design freedom, optimization, light-weight and customization. Currently, manufacturing constraints, limited design freedom and customization issues restrict manufacturers from designing specific shoes for each particular application e.g., walking, running, hiking, sports, etc. However, AM can design and fabricate a multifunctional, usable single shoe-midsole for all aforementioned applications. This study aims to design a multifunctional shoe midsole incorporated with functionally gradient wave springs (FGWS) at the critical areas of foot pressure (heel, forefoot and toe) measured using the F-scan system (insole plantar pressure measurement system). The non-critical areas were designed by a gradient cellular structure with graded unit cells as per load requirement. The designed midsole with FGWS was printed by an HP MultiJet Fusion printer using PA 12 (polyamide). A LISA printer (selective laser sintering) using TPU (thermoplastic polyurethane) material was also used to check its manufacturability. Compression testing, each spring up to 80% of its compressible distance studied the load-bearing capacity, energy absorption, stiffness and cushioning properties. The load-bearing capacity of FGWS was decreased and energy absorption was enhanced by compressing each spring with EVA (Ethylene-vinyl acetate) foam while traditionally manufactured non-contact metal wave springs showed a lower load-bearing capacity than AM (contact) wave springs. Moreover, the fatigue properties of both were compared after 100 cycles of compression, which found a good response of AM wave springs. Experimental compression results revealed a gradual smooth response of load against compression, i.e., cushioning and more energy absorption, validated by finite element analysis (FEA) with very little deviation.

Exploration of double-dart injection technique as a supplemental application for remote drug delivery system for zoo and wild animals.

Background and Aim:Remote drug delivery has become an essential tool for safely delivering medication and vaccines to free-ranging, non-domestic, or dangerous animals. All dart guns currently use a single dart per injection, and it might occasionally be not practical with large animals. Shooting the dart more than once on an animal may cause flight, injury, stress, and ultimately unsuccessful delivery. Furthermore, purchasing many dart guns and hiring and training more staff may be unfeasible in developing countries. Therefore, employing the double-dart injection technique may help reduce the cost of operation, save time for capturing animals, minimize stress and injury, and improve animal welfare. The objectives of this study were to test the possibility of using the double-dart injection technique and optimizing the guidelines for this procedure.Materials and Methods:A standard brand-calibrated darting rifle was used to deliver the darts to the target board constructed from paper, polypropylene, and ethylene-vinyl acetate foam. The shot stage and shooter were fixed, and the shooting range was 5-20 m. The pressure of the gun was varied according to a company’s recommendation. The single dart (control dart) was first shot to the target point, and then the double darts were shot 3 times for each condition. The experiment was done in the field with no wind. The inclusion criteria were that two darts must hit the target and not penetrate the target board deeply. The distances between the control dart and double darts (first and second darts) and between each dart of the double darts were measured, and the standard curve graphs and formulas were created.Results:The results showed that the distance between the control dart and the double darts was shortened as the pressure was increased. All double-dart injections hit the target below the control dart. We were able to create many formulas to predict the optimal gun pressure and aim point for double-dart injection in each shot range. It usually requires more pressure settings than a single-dart injection, particularly the long shot range. It also needs to aim the target point above the original point.Conclusion:Double-dart injection technique can be used efficiently in 5-20 m distance, and it usually requires increasing the pressure from the company’s recommendation and adjusting the injecting point.

The Effectiveness of Dental Protection and the Material Arrangement in Custom-Made Mouthguards

Experimental research studies have shown that wearing a mouthguard (MG) is an effective way to prevent tooth or maxillofacial trauma. However, there is a lack of scientific information regarding how the material arrangement within the mouthguard can modify its mechanical response during an impact. Hence, this study aimed to evaluate the influence of material arrangement within custom-made mouthguards on stress transmitted to anterior teeth, bone, and soft tissue after impact. Four 3D finite element models of a human maxilla were reconstructed based on the CBCT of a young patient and analyzed according to the presence or absence of a mouthguard and the type of material arrangement within those with a mouthguard: model NMG with no mouthguard; model CMG representing the conventional arrangement with a single 4 mm-thick ethylene-vinyl acetate (EVA) foil; model FMG presenting layer arrangement with two 1 mm-thick foils of EVA in the outer shell and one 2 mm-thick foil of EVA foam in the core; model HMG presenting a 1 mm-thick compact inner and outer shell of EVA and a 2 mm wide air-filled zone in the core. Linear quasi-static analysis and frontal load were used to simulate an impact with an energy of 4.4 J. Isotropic linear elastic properties were assumed for the bone and teeth but not for the mouthguard protection and oral soft tissues. The results were evaluated and compared in terms of displacement, stretches, and stresses. All the mouthguards analyzed reduced the risk of injury to teeth and bone, reducing the displacement and stress of these structures. However, the implementation of a honeycomb structured layer allowed more significant displacement and deformation of the mouthguard’s external layer, thus promoting higher protection of the anatomic structures, namely the root dentin and the bone tissue. Nevertheless, the results also indicate that improving the mouthguard flexibility might increase the soft tissue injuries.

Impact response of different materials for sports mouthguards

Up to this moment, there is no guideline regarding the materials to produce mouthguards. The most used is Ethylene-Vinyl Acetate (EVA). Studies indicate that laminating EVA sheets with rigid components could increase the protection capacities of the mouthguards whereas other studies suggest that only replacement of the material within it structure can increase energy absorption. The aim of this work is to evaluate the impact response of four different foils when compared to a 4 mm thickness EVA sheet. Five groups of different materials were subjected to impact tests with energies of 1.72 J, 2.85 J and 4.40 J. In this context was considered the following materials: EVA foils (G1), EVA foils with an EVA foam core (G2), EVA foils with an acetate core (G3), Foils of Erkoloc-pro (G4) and Foils of Ortho IBT resin (G5). Comparisons between the materials were made by qualitative analysis of the average energy-time and load-displacement curves, as well as by comparison of the peak load, maximum displacement, contact time and absorbed energy using the Kruskal-Wallis test. It was possible to conclude that statistically significant differences were found in the energy absorbed (p=0.001). Laminated foils with a soft core (G2) are a good option to produce mouthguards, while EVA foils with an acetate core (G3) and foils of Ortho IBT resin (G5) were declared unsuitable.

Designing flocked energy-absorbing material layers into sport and military helmet pads

A systematic study is reported on applying flocked energy-absorbing materials (FEAM) to designing sport and military helmet pad structures. An executed parametric study shows that the impact force absorbing (IFA) properties of FEAM elements are optimized when using (a) higher denier flock fiber (60 to 100 denier) and (b) longer flock fibers (3 to 4 mm length) at higher flock densities. Continuing work focuses on the importance of IFA/areal density ratios in helmet pad functional design. It is found that foam materials like vinyl-nitrile and ethylene vinyl acetate (EVA) inherently exhibit higher IFA/areal density (IFA/AD) ratios than FEAM material structures. With this finding, a new strategy for developing sport and military helmet pads was devised involving the combination of foam and FEAM layer elements. Here, the meritorious properties of foam materials (light weight and excellent IFA properties) and the excellent IFA and breathability (wearer comfort, sweat and heat management) properties of FEAM could be favorably encompassed. A plan was conceived and implemented whereby combination foam/FEAM test pads having high amounts of the high IFA/AD ratio VN-600 or EVA foam layer component were impact tested. By gradually introducing the more comfortable, breathable, body-heat managing FEAM layers into the helmet pad structure, some “trade-off” helmet pad configurations were designed and evaluated. Experiments showed that helmet pad designs having not more than 40% to 50% FEAM content should produce adequate IFA/AD ratio “trade-off” property helmet pad configurations.