Authored By:
Adam Klett, Ph.D., Miles Kendall
L3Harris Technologies
FL, USA
Summary
Adhesively bonded joints are ubiquitous in both aerospace and medical applications given the advantages that they offer over their mechanical counterparts. Compared to fasteners, adhesives weigh less, take up less space, and can be applied much more efficiently in a large-scale manufacturing operation. There is also a wide range of properties that adhesives can offer in medical-device applications such as flexibility, biocompatibility, and sterilization compatibility. However, many substrates utilized in these high-reliability applications (e.g., PTFE and PEEK), are polymeric in nature, and do not generally form strong adhesive bonds in their native state. In this work, the effect of atmospheric plasma on seven polymeric substrates was studied.
The substrates studied were PTFE, UHMWPE, nylon 6/6, PVC, FR4, phenolic, and POM. Surface energy measurements were collected as a function of time after treatment to quantify the effects of varied processing parameters. Lap-shear coupons were also tested to assess adhesive strength. Across all substrates (except for PTFE), the plasma treatment had a measurable effect on the surface energy along with the adhesive bonding strength. In some cases, the adhesive bond became stronger than the tensile strength of the bulk material and failures within the substrate were observed. The concept of plasma susceptibility was defined to quantify the strength change as a function of plasma dose. This work demonstrates the utility of using atmospheric plasma as a surface treatment for low-surface energy polymeric substrates that will be used in high-reliability applications to ensure optimal adhesive bond strength.
Conclusions
The results from this study indicate that atmospheric plasma treatment can have a significant impact on the wettability of adhesives to polymer substrates and the resulting adhesive strength of the bond.
Surface energy measurements indicate that although a significant change is seen immediately after treatment, the full effect is only semi-permanent and to obtain the most reliable bond, adhesive bonding should occur as soon as possible after treatment, preferably within a few hours.
Since adhesive strength appears to be a function of plasma dose, a susceptibility was defined to quantify the increase in adhesive strength observed per unit dosage for each polymer and can be used to tune the treatment to maximize bond strength while minimizing other deleterious effects (e.g., degradation).
Initially Published in the SMTA Proceedings
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