Method of toughening

Whisker reinforcement is a viable method of toughening composites. However, health considerations associated with the aspiration of fine, high-aspect-ratio whiskers raise serious concern about their widespread use. 

Core-shell structures (Fig. 8.7) have also been suggested as a method of toughening epoxy resin formulations. The polymeric shell, which surrounds an elastomeric core, provides good adhesion to the epoxy matrix. Hyperbranched polymers with hydroxyl... 

Over the past two decades significant advances have been made in developing epoxy based adhesives having improved performance. These improvements were made possible by (1) the discovery of unique methods of toughening adhesive and (2) the availability of new multifunctional epoxy resins. 

Both crazing and shear yielding involve the absorption of energy and most methods of toughening brittle polymers involve modifying the polymer... 

A statistical framework has been established for describing the spatial dispersion of second phase particles in a continuous matrix. Based on this scheme a computerized image analysis method has been developed for characterizing the morphology of toughened plastics. 

In the present work, a more accurate material model has been developed that consists of a collection of spheres (15). The greater accuracy of this model arises from proper consideration of material modeling, as described in the next section. The method of application of load in this model is more complex than that required for the less accurate cylindrical-material model. The importance of this new material model is demonstrated for the quantitative modeling of the toughening processes. A preliminary model of the materials toughness shows good agreement with experimental results. 

We proposed a new test method to evaluate the thermal shock resistance of epoxy resin (7). This test method uses a notched-disk specimen, and the thermal shock resistance can be evaluated analytically on the basis of linear fracture mechanics (8). In our previous studies, we reported on the use of our proposed thermal shock test and evaluation methods (8, 11) to determine the thermal shock resistance of toughened epoxy with a soft second phase (9, 10), and also with hard particulates (11). 

The recent successful synthesis in our laboratory of styrene-propylene diblock copolymer (iPS-fc-iPP), with crystalline isotactic structure in each block (20, 21), makes it possible to attempt toughening of the iPS-iPP blend by the method of block copolymer emulsification of the diblock copolymer. This... 

The oldest and most common method of POM toughening is by incorporation of TPU. Delrin POM/TPU blends were commercialized in 1960. The others followed, e.g., Celcon , Duraloy , Formaldafil , Fulton KL, Hostaform , RTP 800, TC, or Ultraform . These alloys have high impact strength and elastic recovery that depend on composition, morphology, as well as on the compounding and processing methods. Examples of these blends are listed in Table 1.66. 

Several methods of studies have been developed. Osmium-staining technique, pioneered by Kato [1967], is one of the most successful methods for observing crazing in rubber toughened plastics. It depends upon a reaction between osmium tetroxide, OsO, and double bonds in PBD and other unsaturated polymers. However, it is not suitable for saturated rubbers. 

---