Rubbery plateau modulus

Crosslinking the PSA will increase the solvent resistance of the material and it will also have a significant effect on the rubbery plateau modulus of the polymer. Fig. 8 shows the effect of increasing amounts of a multifunctional az.iridine crosslinker, such as CX-100 (available from Avecia, Blackley, Manchester, UK) on the rheology of an acrylic polymer containing 10% acrylic acid. The amounts of crosslinker are based by weight on the dry weight of the PSA polymer. 

Lowering of the rubbery plateau modulus increases the compliance of the polymer making faster wet-out of a substrate possible. As a result, the PSAs show more aggressive tack properties. Provided the surface energy of the substrate allows for complete polymer wetting, a PSA with improved quick-stick and faster adhesion build will be obtained. 

Similar to the tackifiers discussed earlier, plasticizers have a very dramatic softening effect on the rubbery plateau modulus of the PSA. For this reason, high levels of plasticizers have to be avoided to maintain good cohesive strength in the adhesive, especially at elevated temperatures. Indeed, if high cohesive strength is desired, the amount of plasticizer used in a PSA is typically kept to a minimum, if used at all. 

According to a report presented by Fu et al. [180], the influence of POSS-triol on epoxy-amine reaction depends mostly on the magnitude of AT (Tg -Tc) used. Since Tg for epoxy cured with linear aliphatic diamine—2-methyl-1,5-pentadiamine (MPDA)—was higher than the Tg of the same epoxy cured with diamine-terminated polypropylene oxide (PPO), when cured at the same temperature, epoxy-cured MPDA showed a greater improvement in the value of Tg. Moreover, the addition of POSS-triol in tetraglycidyl diamino diphenyl methane (TGDDM) cured with MPDA also increased the rubbery plateau modulus (Fig. 6). 

Crystalline Systems. Lower Tqs, flatter rubbery plateau modulus, higher hard segment crystallinity, all support the view that phase separation is more complete MDI-BDO and MDI-ED0 based polyurethanes as catalyst concentration decreases. 

The entanglement strand has entanglement molar mass M = N Mq. The entanglement strand effectively replaces the network strand in the determination of the modulus for networks made from long strands, and also determines the rubbery plateau modulus of high molar mass polymer -melts ... 

Creep, Swelling, and Extraction Studies. Additional indications of component interaction were found in the results of creep experiments with the xl series shown in Tables VI and VII. Creep in the xl series is fully recoverable, i. e. there is no permanent set, consistent with a PUx continuous phase. The increase in recoverable compliance, however, indicates a reduction in apparent crosslink density with increasing delay time before irradiation. This result is reinforced by the data in Table VII Ci and Cg are the material constants in the Mooney-Rivlin equation. The rubbery plateau modulus and the crosslink density of PUx prepared in BHA, which mimics xl formation, is less than that of PU prepared neat. 

Hsieh et al. [2004] investigated the mechanical and fiow behavior of polycarbonate (PC)-based CPNC, prepared in a corotating TSE with 1.5 to 5 wt% C25A. The rubbery plateau modulus of PNC with finely dispersed intercalated clay decreased significantly. PNC with 5 wt% clay had Tg lower by about 10°C than neat PC, traced to the degradative reduction of its A/w by 43%. 

In this equation represents the glassy modulus (3 x lO dyn/cm ), T in is a characteristic relaxation time, E2 represents the rubbery plateau modulus, and E it) is the relaxation modulus as a function of time. 

This relationship implies that when polymer chains are more rigid, or the attractive interactions between chains are stronger, the rubbery plateau modulus of their bulk phase should be larger. 

Polymers are frequently plasticized to soften them. These plasticizers are usually small, relatively nonvolatile molecules that dissolve in the polymer, separating the chains from each other and hence making reptation easier. In the context of Figure 8.2, the glass transition temperature is lowered, and the rubbery plateau modulus is lowered. If the polymer is semicrystalline, the plasticizer reduces the melting temperature and/or reduces the extent of crystallinity. 

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