Polyester resins shear properties

P(2) Epoxy resins should be considered where higher shear strength than is available with polyester resins is required and the application requires good mechanical properties at elevated temperatures or durability. Epoxies occur in many varieties, feature high strength properties (as seen in some of the most effective engineering adhesives) and have been developed for water resistant coatings. 

Matthew JK, Virginia AD (2009) Viscoelasticity and shear stability of single-walled caibon nanotube/unsaturated polyester resin dispersions. Macromolecules 42(17) 6624—6632 Mehta H, Wangshul H, Kanagaraj S (2011) Studies on mechanical properties of carbon nanotubes/ high-density polyethylene nanocomposites by small punch technique. Int J Nanosci 10(1-2) 247-251... 

Polymers are normally classified into four main architectural types linear (which includes rigid rod, flexible coil, cyclic, and polyrotaxane structures) branched (including random, regular comb-like, and star shaped) cross-linked (which includes the interpenetrating networks (IPNs)) and fairly recently the dendritic or hyperbranched polymers. I shall cover in some detail the first three types, but as we went to press very little DM work has been performed yet on the hyperbranched ones, which show some interesting properties. (Compared to linear polymers, solutions show a much lower viscosity and appear to be Newtonian rather than shear thinning [134].) Johansson [135] compares DM properties of some hyperbranched acrylates, alkyds. and unsaturated polyesters and notes that the properties of his cured resins so far are rather similar to conventional polyester systems. 

These results suggest that for the initial design stages, similar levels of properties can be assumed for the main thermosetting laminating resins. However the interlaminar shear strength of phenolic composite can be appreciably less than polyester or epoxy ones and so the level of shear stresses may need to be checked. 

---