Cyclic Peel Evaluation of Sterilized Medical Packaging
22nd Annual Meeting of the Adhesion Society, Proceedings, pp.116-118, (1999)

J.C. CONTI1,2, E.R. Strope2, R.D. Gregory3, and P.A. Mills1

1 Department of Physics, Southwest Missouri State University, Springfield, MO
2 Dynatek Dalta® Scientific Instruments, Inc., Galena, MO
3 Springfield Applied Mathematics, Springfield, MO


Introduction

Peel testing is a standard way of evaluating the fundamental adhesion properties and work of adhesion necessary to separate an adhesive joint. However, the packaging industry experiences many unpredictable seal failures before, during, and after the development and manufacturing procedures associated with new packaging, even though the aforementioned standard tests had been used to design the package seals.

Since it has been demonstrated that the magnitude of peel adhesion and the mechanism of peel failure are functions of the viscoelastic properties of the adhesive and adherends [I-5], and that the time dependent properties of these materials affect the values of peel adhesion obtained when the experiments were carried out at different rates [6-8], it has been suggested that the unpredicted failures might be the result of loading characteristics not replicated by the bench tests.

It has been demonstrated that single pull peel testing does not always predict joint failures that occur as a result of cyclic loading at subcritical loading levels [9- l0].

A set of experiments was designed to evaluate the rate of peel of an adhesive joint located in the seal of a medical package whose lid was attached via hot melt adhesive. This was a standard medical package used to house synthetic vascular grafts.

Experimental

Nine samples of Tower Dual Peel Tubing® distributed by Baxter Healthcare Corporation that had been heat sealed using the manufacturer's recommended procedures were cut into one-eighth inch wide strips perpendicular to the seal. These strips were prepared such that when mounted into the cyclic peel tester the exposed region of the joint representing the inside of the package was peeled. These samples were exposed to a single pull, 180 ° peel test at the displacement rate of 250 microns per second. These data were analyzed to determine the load at first yield. Samples were then exposed to subcritical cyclic loading between 20 and 300 millinewtons per cycle at 1,5, and 10 Hz to determine the rate of peel under the cyclic protocol.

Results

Table 1 is a compilation of the nine experiments used to determine load at first yield. As shown, the loads at first yield varied from 390 to 610 millinewtons. Since cyclically loading this adhesive joint at subcritical levels was of primary interest, 300 millinewtons was chosen as the maximum loaded level because it was below all of the load at first yield numbers that were obtained.



The cyclic experiments were designed such that the joint was loaded from a minimum of 20 up to a maximum to 300 millinewtons each cycle at 1,5, and 10 Hz. This represents a loading rate of 560, 2,800 and 5,600 millinewtons per second. Figure 1 is an example of the single pull load versus time experiment. Figure 2 demonstrates the cyclic loading experiment. The 1,5, and 10Hz cyclic loading experiments result in a displacement rate of 123, 1,400, and 2,350 microns per second, respectively.



Figure 3 is an example of the position versus time tracing of one of the full experiments, in this case, 5 Hz. As shown, there are four distinct regions in this tracing. The first is one in which the automatic feedback loop of the system was adjusting and should be ignored. The second region represents the shoulder or transition region into the more stable long term results that were obtained. Region Ill represents the section that leads up to the most stable rate of peel, and Region IV is the more stable rate of peel suggesting that the joint would continue peeling indefinitely at this rate.



Table 2 is a compilation of the rates of peel of the nine experiments. As previously described, Regions II, III, and IV are presented independently.



Discussion

The results clearly indicate that these adhesive joints, when cyclically loaded at levels below the load at first yield determined in the single pull experiments, can open up at appreciable rates. The explanation for the three different regions and varying rates of peel are unknown at this time, but might be related to the changing mechanical properties of the adherends or experimentally induced thermal effects caused by the work being put into the joints.

It would be important that packaging critical to human health be guaranteed to remain intact. Better knowledge of the "in the field" loading on this joint can be used to design a seal that can maintain its integrity.

References

1. D.H. Kaelbe, J. Adhesion 1, 102 (1969).

2. A.N. Gent and R.P. Petrich, Proc. R. Soc. London Ser. A310, 433 (1969).

3. E.H. Andrews and AJ. Kinloch, Proc. R. Soc. London Ser. A332, 385 (1973).

4. D.H. Kaelbe, J. Colloid Sci. 19, 413 (1964).

5. D.W. Aubrey, Ned Rubberind 36 (2), 1 (1975).

6. D.W. Aubrey and M. Sheriff, J. Polymer Sci., Polymer Ed. 18, 2597 (1980).

7. A. Mayer, T. Pith, G. Hu and M. Lambla, J. Polymer Sci. Part B: Polymer
    Physics, 33, 1781, (1975).

8. Ibid, 33, 1793 (1995).

9. J.C. Conti, E.R. Strope and, E. Jones, Proceedings of the 20th Annual Meeting
    of the Adhesion Society, 425-427, (1997).

10. J.C. Conti, E.R. Strope, E. Jones, and D. Rohde, Proceedings of the 21st
      Annual Meeting of the Adhesion Society, 418-419, (1998).

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