Adhesion behavior of laminated thermoforming materials underwater environment

Objective: The authors have already introduced a new lamination forming technique to fabricate a custom diving mouthpiece using thermoforming materials. However, the durability performance of the custom diving mouthpiece under the sea has not tested yet. The purpose of this experimental study was to assess the adhesion behavior of the laminated thermoforming materials underwater environment. Methods: Two kinds of commercial thermoforming sheet materials with polyolefin (PO; MG21^®, CGK Co., Japan) and ethylene-vinyl acetate (EVA; Mouthguard sheet^®, ULTRADENT Co., USA) were tested in this study. Specimens were prepared by means of laminating 2 sheets of each material in an adhesive area of 7.5x4.0mm on a conventional thermoforming machine. A conventional delamination test was performed after 1-week immersion in a water bath under with and without 0.3 MPa of pressure. The delamination load and the strain at fracture of specimens among 3 conditions including a control condition (storage in the air) were statistically compared with 2-way ANOVA and Tukey's post-hoc test (p<0.05). Results: There was no significance of the delamination load of PO and EVA specimens among 3 conditions. However, the strain at fracture of PO specimens showed significantly greater than those of EVA specimens under every condition. The results are summarized in Table. Conclusion: Data showed that the adhesion behavior of laminated commercial thermoforming sheet materials maintained for 168 hours even under the environment corresponding to about 20 meters of the sea. Therefore, these results suggested that commercial thermoforming sheets with PO and EVA were available materials to fabricate the custom diving mouthpiece using the thermoforming technique.