Reactive toughness

Figure 14.10 Electron micrograph of PET + 20% E-EA-GMA (reactive tough-ener - Lotader AX8900) showing the size and distribution of the rubber particles (note the 5 im scale bar). The rubber domains have been selectively etched out by solvent to provide contrast enhancement...

Figure 6.3 Creep profiles for UP-GF mat laminate (highly reactive, tough resin [P8]), test temperature 23 °C and 40 °C, respectively...

The outstanding performance characteristics of the resins are conveyed by the bisphenol A moiety (toughness, rigidity, and elevated temperature performance), the ether linkages (chemical resistance), and the hydroxyl and epoxy groups (adhesive properties and formulation latitude, or reactivity with a wide variety of chemical curing agents) (see also Phenolic resins). 

Two-package-reactive polyurethane Tough hard Good Fair Fair Good Good Some yellowing and chalking Difficult... 

Moisture-reactive polyurethane Very tough ahrasion-resistant Fair Fair Fair Good Good Fades in light yellows in shade Difficult... 

In order to increase the flexibility, and usually, in consequence, the toughness of the resins, plasticisers and flexibilisers may be added. Non-reactive plasticisers such as the conventional phthalates and phosphates have proved unsuccessful. Monofunctional materials, which in some cases also act as reactive diluents, have been used but are not of great importance. 

Fig. 11. The variation of the threshold toughness Gy with S when an end-reactive PDMS chain was coupled into a PDMS network (H.R. Brown, W. Hu, J. Koberstein, unpublished work).

In order to obtain a finely sized dispersed phase in the PET matrix, the use of reactive compatibilization has been found to be important. Small dispersed rubber particles and a small interparticle distance are necessary to induce high toughness. For effective rubber toughening of PET, it is important that the rubber domains be less than 3 im in diameter (and preferably less than 1 xm) and that the interparticle distance be between 50-300 nm. 

Figure 14.8. This reaction is critical in ensuring the reactive elastomeric tough-ener becomes grafted to the PET matrix and forms smaller, uniform domains of a rubber dispersed phase.

Pecorini and Calvert [28] attribute the role of small particles and a small interparticle distance to inducing high toughness in PET by promoting massive shear yielding in the matrix. Their study showed that the non-reactive impact modifier gives a system in which the rubber phase is not well dispersed. It was shown that this is not effective in toughening PET at levels of either 10 or 20%. The... 

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