Studies have show that certain adhesive joints exhibit a dramatic loss of strength when exposed to humidities above a certain critical value. Although much is know about this effect, questions still exist. This study combines neutron reflectivity experiments that determine the distribution of water in the bonded specimen with fracture testing to measure the joint strength. For a model system, the water concentration in the polymer near the interface was found to be higher than that away from the interface. At a critical humidity, the total amount of water near the interface increased significantly and the adhesive strength of the interface dropped. It is proposed that the excess water near the interface not only weakens the bonding but may also generate swelling stresses that facilitate interfacial crack growth. Experiments on a polymer with similar chemistry but much lower modulus showed no critical humidity, perhaps because the lower modulus resulted in smaller swelling stresses.
Proceedings Title: 10th International Conference on the Science and Technlogy of Adhesion and Adhesives
Conference Dates: September 3-5, 2008
Conference Location: Oxford, UK
Conference Title: same
Pub Type: Conferences
adhesion, durability, moisture, humidity, fracture