Reinforced-plastic glassiness

It is now well established that the thermomechanical response of glassy polymers and their composites is viscoelastic at temperatures near to, and above the glass transition temperature. Therefore, an accurate long term durability model at elevated temperatures for resins and reinforced plastics (FRP) must necessarily include viscoelastic behavior. This is especially true... 

As pointed out in Sect. 1, the role of connector molecules in reinforcing interfaces between glassy polymers is to increase the maximum stress that can be sustained by the interface before failure. If the stress becomes higher than a certain critical level (which depends on the nature of the bulk polymers on either side of the interface), mechanisms leading to plastic deformation on a scale much larger than the molecular radius of gyration will be activated and the fracture toughness of the interface will increase dramatically. The main questions are ... 

While due to their well-known plastic deformation properties glassy polymers provide excellent model systems for fracture studies, most engineering plastics are semicrystalline. Nevertheless, the molecular mechanisms of reinforcement of interfaces between semicrystalline polymers are much less well understood and the first systematic studies on the subject have only appeared recently [16, 30,96-99]. The reasons for this are mainly twofold ... 

Benkoski et al. have utilized diblock copolymers, composed of a glassy block and a semicrystalline block, to reinforce an interface [9]. Their studies indicate that the penetration of the chains from the diblock into the homopolymer allow a transfer of stress across the interface that is dependent on parameters related to the crystalline chains in the diblock. By increasing the length of the crystalline portion of the diblock, values of the fracture energy increased from 1 to 700 J mT [9]. As with the experiments of Bidaux et al, the largest values of the fracture energy were attributed to plastic deformation and cohesive failure within the semicrystalline polymer. 

When the elastic phase predominates the IPN s behave as reinforced elastomers. As the glassy component is increased the material becomes an impact resistant plastic. At midrange compositions between the two glass transition temperatures materials exhibiting leathery behavior are obtained. 

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