Adhesion rating criteria

This study is designed to compare the effect of ftie gel-former selected in Section 13.3.4.2 on POA wifti a size 6-0 silk suture/saline, HA, and C-TA as basic barrier and positive controls, respectively. The adhesion formation was studied using a rat sidewall model. The abdominal cavity was entered into in female Sprague-Dawley rats through a small midline incision. A 1-cm2 area of peritoneal sidewall was excised wifti a scalpel blade. The 6-0 silk was then sutured aroimd the perimeter of ftie excised area with a square knot at each corner. Aliquots of either the gel-former (100 pL) or the controls (1 mL) were injected on tiie excised site. One week postoperative, the adhesion prevention score was recorded for the different formulations on a scale of 0 to 10. A score of 10 represents maximum adhesion whereas 0 reflects the absence of any adhesions. Adhesion rating criteria were based on the work by Bums et al. ... 

When one reaches the peel rate/temperature conditions for interfacial debonding between the adhesive and the substrate, the appropriate failure criterion becomes a matter which has not been fully solved. Qualitative analysis of the curves... 

Another three-dimensional axisymmetric stress distribution for the stress around fiber breaks was obtained by Naim [93] using variational mechanics. In this study, breaks interaction was also included and it was assumed that both fiber and matrix were linearly elastic and a perfect adhesion at the fiber-matrix interface. To account for the stress singularity at the matrix crack tip of the fiber break, the matrix plastic-model was also included. Imperfect adhesion to mimic a failed fiber-matrix interface was added to this model to study the mechanism of interfacial failure, that is, the stress conditions that cause the extent of interfacial failure or its increase. It was suggested that due to the complexity of the multi-axial stress state, a simple maximum stress failure criterion was unrealistic and an energy release rate analysis was necessary to calculate the total energy release rate associated with the growth of interfacial damage. 

The assumption that the strength of the interface equals the strength of rubber is an unnecessary restriction the viscoelastic dependence of failure can be explained in simpler terms without invoking that assumption. Even when the inherent strength of adhesion is assumed to be independent of the rate of strain, it is possible to conceive the dependence of the criterion of failure on the strain rate, because the stress field which causes the failure depends upon the viscoelastic deformation of rubber. It is therefore not necessary to assume that the failure occurs within the rubber or that it is in any way related to the ultimate properties of rubber. 

Thus, to summarize, the fracture data over a wide range of rates and temperatures may all be rationalized by the concept of a critical stress acting over a critical distance. The two parameters provide a unique failure criterion for the bulk fracture of adhesives and for the fracture of joints although in the latter case it will be more complex when the development of the crack-tip deformation zone is affected by the presence of the substrates. Nevertheless, the concept of combining the critical stress and distance criterion with an analysis of the stress field in the adhesive layer as a function of joint geometry... 

Acrylic pressure-sensitive polymers consist mainly of a soft monomer with a low Tg and high Me. The three most common soft monomers are butyl acrylate, iso-octyl acrylate, and 2-ethylhexyl acrylate. All three have a Tg below —40°C and an Me above 15,000 Da see O Table 15.2. When polymerized on their own they meet the Dahlquist criterion at room temperature and well below. To increase peel, often a hard monomer is incorporated. These are high Tg monomers, and most are low Me. By moving up the Tg of the overall polymer, these hard monomers increase the viscous loss and thus the peel force, in much the same way as increasing the rate of peel. In addition, the lower Me hard monomers, such as MMA also increase the stiffness of the adhesive which further increases the peel force. Polar monomers are invariably incorporated to increase cohesive strength through intermolecular hydrogen... 

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