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. 2024 Oct;18(4):1048-1061.
doi: 10.1055/s-0044-1779427. Epub 2024 May 14.

Effect of Vinyl Acetate, Glass Fibers Contents, and Buffer Space on EVA's Mechanical Property and Shock Absorption Ability

Shinji Togo  1 , Takahiro Sakaue  1 , Arata Tsutsui  1 , Yoshiaki Matsuda  1 , Kazunori Nakajima  1 , Tomotaka Takeda  1 , Kenichi Fukuda  2 , Pekka Vallittu  3 , Lippo Lassila  3
Affiliations

Effect of Vinyl Acetate, Glass Fibers Contents, and Buffer Space on EVA's Mechanical Property and Shock Absorption Ability

Shinji Togo et al. Eur J Dent. 2024 Oct.

Abstract

Objectives: The aim of the study was to evaluate the mechanical properties and impact absorption capacity of prototype materials comprising ethylene vinyl acetate (EVA) of different hardness reinforced using different amounts of glass fibers (GFs), considering a buffer space.

Materials and methods: Six prototype materials were made by adding E-GFs (5 and 10 wt%) to EVA with vinyl acetate (VA) contents of 9.4 wt% ("hard" or HA) and 27.5 wt% ("soft" or SO). Durometer hardness and tensile strength tests were performed to evaluate the mechanical properties of the materials. Moreover, an impact test was conducted using a customized pendulum impact tester to assess the impact absorption capacity (with or without a buffer space) of the specimens.

Results: The mechanical properties of the prototypes, namely, durometer hardness, Young's modulus, and tensile strength, were significantly higher in the HA group than in the SO group, regardless of the presence or added amount of GFs. The addition of GFs, particularly in a large amount (10 wt%), significantly increased these values. In terms of the impact absorption capacity, the original hardness of the EVA material, that is, its VA content, had a more substantial effect than the presence or absence of GFs and the added amount of GFs. Interestingly, the HA specimens with the buffer space exhibited significantly higher impact absorption capacities than the SO specimens. Meanwhile, the SO specimens without the buffer space exhibited significantly higher impact absorption capacities than the HA specimens. Moreover, regardless of the sample material and impact distance, the buffer space significantly improved impact absorption. In particular, with the buffer space, the impact absorption capacity increased with the added amount of GFs.

Conclusion: The basic mechanical properties, including durometer hardness, Young's modulus, and tensile strength, of the EVA prototype were significantly increased by reducing the amount of VA regardless of the presence or added amount of GFs. Adding GFs, particularly in large amounts, significantly increased the values of aforementioned mechanical properties. Impact absorption was significantly affected by the hardness of the original EVA material and enhanced by the addition of the buffer space. The HA specimen had a high shock absorption capacity with the buffer space, and the SO specimen had a high shock absorption capacity without the buffer space. With the buffer space, impact absorption improved with the amount of added GFs.

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Conflict of interest statement

None declared.

Figures

Fig. 1
Fig. 1
Scanning electron microscopy (SEM) images of specimens. Hard specimens (HA) without glass fibres (GF) ( A ). Soft specimens (SO) without GF ( D ). In the HA and SO, the GF are shorter or slightly longer than the original average length ( B, C, E, F ) ,and the fibers are randomly oriented in the matrices ( E,F ). The polymer matrices seemed to be properly impregnated with the fibers ( B, C, E, F ).
Fig. 2
Fig. 2
( A–C ) Customized pendulum impact testing machine and impact testing conditions.
Fig. 3
Fig. 3
Durometer hardness. The hard (HA) group shows significantly higher values than the soft (SO) group. Regarding the effect of the presence or added amount of glass fibers (GFs), in the HA group, HA10 and HA5 are significantly harder than HA0. In the SO group, SO10 is significantly harder than SO0 and SO5 (** p  < 0.01).
Fig. 4
Fig. 4
Young's modulus. In the hard (HA) group, HA10 and HA5 show significantly higher values than HA0. In the soft (SO) group, SO10 shows a significantly higher value than SO0 and SO5, and SO5 shows a significantly higher value than SO0.
Fig. 5
Fig. 5
Tensile strength. In the hard (HA) group, HA10 and HA5 show significantly higher values than HA0. In the soft (SO) group, SO10 shows a significantly higher value than SO0 and SO5, and SO5 shows a significantly higher value than SO0. The number of fractured samples also decreases with the added amount of glass fibers (GFs) in the HA group.
Fig. 6
Fig. 6
Impact absorption (15-cm impact distance without buffer space). Regarding the effect of the ethylene vinyl acetate (EVA) material hardness, the impact absorption rates of the soft (SO) group are significantly higher than those of the hard (HA) group, regardless of the presence or added amount of glass fibers (GFs). Regarding the effect of fiber addition and content, in the HA group, no significant effect is observed. In the SO group, SO10 shows significantly lower values than SO0 and SO5.
Fig. 7
Fig. 7
Impact absorption test results (15-cm impact distance with buffer space). Regarding the effect of ethylene vinyl acetate (EVA) material hardness, the impact absorption rates of the hard (HA) group are significantly higher than those of the soft (SO) group, regardless of the presence or added amount of glass fibers (GFs). Regarding the effect of fiber addition and content, no significant effect is observed in the HA group. In the SO group, SO5 and SO10 show significantly higher values than SO0.
Fig. 8
Fig. 8
Impact absorption (30-cm impact distance without buffer space). Regarding the effect of ethylene vinyl acetate (EVA) material hardness, the impact absorption rates of the soft (SO) group are significantly higher than those of the hard (HA) group, regardless of the presence or added amount of glass fibers (GFs). Regarding the effect of fiber addition and content, in the HA group, HA10 shows significantly lower values than HA0. In the SO group, SO10 shows a significantly lower value than SO0 and SO5.
Fig. 9
Fig. 9
Impact absorption (30-cm impact distance with buffer space). Regarding the effect of fiber addition and content, in the hard (HA) group, HA10 shows a significantly higher value than HA0 and HA5. In the soft (SO) group, SO10 and SO5 show significantly higher values than SO0, and SO10 shows a significantly higher value than SO5.
Fig. 10
Fig. 10
Regarding the presence or absence of buffer space, the impact absorption rate increases significantly with the addition of buffer space in all prototype materials under two test impact distance conditions.
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