Tensile synergism

Blends of EMA copolymer and EPDM containing vinyl norborene as a third monomer were also investigated. Blending was carried out at 180°C at a rotor speed of 100 rpm. After the reaction, the blends were quenched on the cold rolls and were sheeted out. They were examined by IR spectra. The reduction of peak area related to unsaturation indicated a progressive loss of EPDM due to reaction with EMA. The extent of reaction depended on the utilization of unsaturation which is estimated to be 14% for EMA/EPDM at a 70 30 ratio and 53% at a 50 50 blend ratio. The tensile properties exhibit synergism as the EMA proportions change from 0% to 50%. 

A very intriguing possibility, although less frequently observed, is when blends of polymer A and B show synergism with respect to some property. Here, we refer to the situation where some property, such as tensile strength, for the blend is larger than that for either pure A or pure B. Clearly, such a maxima in the plot of property vs. composition is not predicted by any additivity relationship. A few examples of this kind of behavior are known and offer unique possibilities when they exist Two examples of synergism of tensile strength will be mentioned later. 

Morphology of Low Density Polyethylene/ EPDM Blends Having Tensile Strength Synergism... 

We have begun to study the morphology of these blends in an attempt to learn what causes the tensile strength synergism. This chapter gives our initial results and interpretations. 

In contrast to polyamides in polystyrene phenolic antioxidants are not able to reduce the decrease in tensile strength during UV irradiation [141]. UVAs as well as HALS stabilizers are effective in polystyrene (PS). The best protection can be reached by using combinations of a UVA and a HALS. According to Gugumus [133,134] the synergism between UVA and HALS is distinct when the time until a AYI = 5 is taken as failure criterion (see Table 17.12). However, when as criterion the yellowness index after 1600 h in a Weather-Ometer is taken, the synergism between a UVA and a HALS is much smaller (see Fig. 17.14). 

A blend of low-density polyethylene (LDPE) polyethylene (LDPE) with the terpolymer ethylene-propylene-diene monomer rubber (EPDM) exhibits a synergistic effect on tensile strength if EPDM is partially crystalline, but a nonsynergistic effect if the EPDM is amorphous [65]. This example shows the dramatic effect that morphology can have on properties of polymer blends. The synergism apparently arises from a tendency for crystallites in the LDPE to nucleate crystalli2ation of ethylene segments in the EPDM. 

While the water absorbtion of PPO -PA blend is a straight function of the polyamide content (fig.10), the net effect on the mechanical properties shows major synergism as Indicated in the tensile stress-strain diagram (fig. 11) where the dry as molded and 50 % relative humidity conditioned PP0 /PA blends maintains very close properties. A major drop In tensile strength is observed for Its parent polyamide 66. 

This block copolymer melt flow was improved by adding ethylene ionomer [79]. vs blend ratio was S-shaped, indicating a two-phase system and tensile modulus and yield showed evidence of synergism [206]. 

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