Vulcanizate tensile properties

Among the main molecular structural variables in EPDMs that are stipulated by catalyst systems and that affect the vulcanizate tensile properties we may mention molecular weight (MW) and MWD, degree of unsaturation (LG=C 1) and its distribution in the polymer, composition (C S) and monomer sequence length distribution along molecular chains, and long-chain branching if present. Effect of... 

Comparison of vulcanizate tensile properties of the six sets of comparable samples (Figures 7A-F) gave results (Table I, last column) pointing to the ability of the systems in giving decreasing tensile strength in the following orders... 

High MW fraction in EPDM ought to contribute favorably to the vulcanizate tensile properties ( ). The following preliminary observations were gathered to examine whether difference in. tensile strength of samples prepared with various catalysts studied was due primarily to the difference in MWD of the terpolymers. ... 

Furthermore, it has to be noted that both VOCI3- and V3.-9-EPDMs have multimodal GPC profiles signifying the presence of high MW fractions, yet they have the greatest disparity in vulcanizate tensile properties, again suggesting MWD to be not a major determinant in defining the observed tensile differences. 

Wire and cable insulation based on vulcanizates of PZ has also been studied. Again, low fire risk was the target property, and this was achieved. The need to vulcanize the coating, somewhat modest tensile properties, tensile strength of 5.2 to 12.2 MPa (760 to 1770 psi), and high dielectric constant (4—5 at 10,000 Hz) limited interest in this appHcation (19). 

For both EPDM-LDH and XNBR-LDH nanocomposites, the various tensile properties are summarized in Table 13 and their typical stress-strain plots are shown in Fig. 58 [104]. In Fig. 58a, the gum vulcanizates of both rubber systems showed typical NR-like stress-strain behavior with a sharp upturn in the stress-strain plot after an apparent plateau region, indicating strain-induced crystallization. With the addition of LDH-C10 in the XNBR matrix, the stress value at all strains increased significantly, indicating that the matrix undergoes further curing (Fig. 58b). 

Overall, the plasma-treated samples show an improvement in terms of dispersion and tensile properties. Treatment with different plasma monomers show different levels of improvement in terms of dispersion and final vulcanizate properties due to the different levels of compatibilization in the polymer blend and, more specifically, with the different polymers used in this blend. The most important aspect for achieving an optimal balance between the properties of a filled polymer blend for a specific application is the selection of the proper monomer for the plasma modification of the silica surface, in relation to its required compatibility with a particular polymer in the blend. 

In the case of HTI at least 1.8 mol % of triene is necessary to obtain 80% of gelled rubber and hence good tensile properties of the vulcanizate. 

Silica reinforcement using the sol gel technique on epoxidized natural rubber 25 mol% (ENR 25) has been reported. ENR was first pre-ciued with 3-aminopropyltriethoxysilane (APS). APS was mixed into ENR and the ENR-APS mixture was cured at 180 °C to produce pre-ciued rubber sheets with tensile properties much lower than those of normally ciued rubber vulcanizates. The crosslinking of ENR utilizing the epoxy groups as crosslinking sites using amine functional groups catalysed by bisphenol A has been established. The ENR-APS network is shown in Scheme 7.2. 

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