Efficient toughening

Another example of the combination of toughening and fire retardant-enhancement is the use of TPE as a carrier for master batch of FR-803 (TBS). This master batch was not only an efficient toughener for SMA but also permitted a UL-94 VO rating, unachievable for SMA/TBS alone (Fig. 6). 

The maximum particle size for efficient toughening is in the order of 5-10 /am (Kinloch, 1989 Pearson and Yee, 1991). It has been proved experimentally that larger particles are relatively inefficient (Pearson and Yee,... 

This early rubber cavitation is not necessary for an efficient toughening of amorphous PET because of its lower sensitivity to triaxial stress states (compared to semi-crystalline PET). 

For semi-crystalline PET, rubber-matrix de-cohesion does not lead an efficient toughening. 

Efficient toughening of semi-crystalline PET requires a well adhered and dispersed elastomer leading to an early cavitation (quasi-simultaneous to the overall yielding) of the nodules themselves. 

Development of efficient toughening technology (impact strength, fracture toughness and ductile/brittle transition temperature). 

Efficient toughening by the rubber modifier can be obtained, as discussed earlier, only if the RLP is capable of sufficient grafting to the epoxy matrix. Theoretically, the optimal linear rubber chain should possess two terminal reactive groups. Since this configuration could not be synthesized in dilute solution polymerization, a branched copolymer of nBA and ethylene dlacry-late (EDA), structure I, with a potentially higher functionality, was studied. Ethylene diacrylate is used primarily as a cross-... 

An efficient toughening mechanism can be set up if the crosslinking is sufficiently low. Soft or rubbery inclusions, the surface-to-surface distance of which is below a critical value, tend to induce shear deformations in the matrix and will, therefore, provide the required conditions... 

It should be emphasized that only the addition of TPE/FR-803 master batch provided an efficient combination of toughening and fire retardant enhancement. The addition of TPE alone to SMA/FR-893, although providing a certain increase of impact properties, did not enhance the fire retardant (Fig. 7, Table 8). 

The above hypothesis, that the toughening efficiency is enhanced by the formation of local agglomerations, requires intensive theoretical calculations of stress distributions as well as the preparation and characterization of morphologies with a controlled level of dispersion and local agglomeration respectively. 

According to Partridge [163], toughening is efficient when, by comparison to the neat homopolymer tested under the same conditions, the impact resistance is multiplied by a factor of 10, without losing more than 25% of stiffness. The upper temperature limit for the use of rubber-modified blends is controlled by the matrix melt temperature, Tm, their lower limit by the glass transition temperature, Tg, of the particles. As soon as the viscoelastic response of the latter is too slow to accommodate an external loading, the polymer assumes a glassy state and breaks in a brittle way. 

As PET has the ability to be obtained either in the amorphous state or not an additional scientific goal exists that is studying the interrelations between the microstructure of semicrystalline polymers and the efficiency of rubber toughening [ 1 ]. 

Conversely, nodules can significantly increase the amount of energy dissipated during deformation of notched specimens (Fig, 5., 6.). They contribute to decrease brittle to ductile transition temperature. Non-reactive nodule can toughen amorphous PET to a certain extend, being nevertheless always less efficient than reactive one. On the contrary, only the reactive nodules exhibit a certain level of efficiency in semi-crystalline PET, provided that concentration is at least 21 %. 

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