Rubber bridging

Figure 13.6 Relative contributions (%) of the different toughening mechanisms in epoxy networks versus temperature ( ) rubber bridging ( ) shear yielding and (A) cavitation. (From the results of Huang et a ., 1993b.)... 

Another interaction is responsible for the recovery of the material after it is subjected to stress. " Rubber bridging the neighboring particles of filler is an example. Some particles are connected through several rubber chains which makes their association more permanent and assures filler-filler contact. These filler-filler contacts are responsible for the recovery since, unlike chain-filler contacts, they store the strain energy which is then used in the recovery process. Chain-filler contacts can easily debond or rearrange in different location and this process does not result in recovery of the initial shape. 

This is a simplification of the process occurring in a curing resin-hardener system and a detailed discussion may be found in Pascault et al (2002), Williams et al (1997) and Inoue (1995). The main parameter that it is important to control in the reactive phase separation is the diameter of the elastomer particle. This is because the toughness of the resulting network is controlled by the energy-absorbing mechanisms such as particle cavitation and rubber bridging of cracks. Also of importance is the limitation of the effect of the rubber dispersed phase on the critical properties of the cured epoxy resin such as the stiffness and Tg. This will be affected by the extent to which the rubber dissolves in the matrix-rich phase. 

At -60 °C, shear banding contributes most and rubber bridging makes the second largest contribution. 

P. B. Lindley, Design and use of Natural Rubber Bridge Bearings, NRPRA Technical Bulletin, The Natural Rubber Bureau, 1964. 

Amide derivatives as rubber bridging agents Adhesive compositions Ester derivatives as PVA extenders... 

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