Polybutadiene urethane elastomer

Figure 4.1.5. Volume of the increased swelling of crosslinked polybutadiene urethane elastomer, Xh b-85. Labels of points ...

Typical OH-terminated polybutadiene urethane elastomer formulations are usually prepared using an NCO/OH ratio of 105. All ingredients, other than the diisocyanate, are normally blended by mechanical stirring and then degassing for 30 min at 80°C after which the diisocyanate is added. Test sheets are usually cured for 24 h at 23°C and post-cured for 24 h at 80°C. Pot life can be varied by adjusting the catalyst concentration. 

Figure 4.1.5. Volume of the increased swelling of cross-linked polybutadiene urethane elastomer, Xh s o 83 -Labels of points 1 - outside volume, points with coordinates corresponding to solvents 2 - inside volume, points with coordinates corresponding to solvents 3 -the points with coordinates corresponding to polymer. This is the center of the volume. 4 - points placed on a...

Elastomeric materials find use as vial closures, as syringe plungers, and as liquid delivery components. Elastomers, called sometimes simply rubber, are also polymeric materials, and are known by their common names, halobutyl, silicone, urethane, neoprene, polybutadiene, etc. Elastomers themselves... 

The obtained theoretical predictions have been verified in experiments on real elastomers. The elastomers tested in our experiments were amorphous polybutadiene urethanes (PBU) wifli polymer network of different density 0.3 kmol/m (PBU-1), 0.05 kmol/m (PBU-2), 0.2 kmol/m (PBU-3), 0.1 kmol/m (PBU-4). Oligooxypropylene triol - Laprol 373 was used as a crosslinking agent at the curing of prepolymer of oligobutadiene diol. The elastomer specimens were manufactured in the form of disks, 35 mm in diameter and 2 mm thick. The kinetics of specimen swelling was determined in low-molecular liquids toluene, dibutyl sebacate (DBS), dioctyl sebacate (DOS). 

When the properties of H12MDI elastomers are compared with those of the analogous MDI series it is found that elastomers based on the aliphatic isocyanate generally had superior mechanical properties. This pattern of behaviour applies to both polyester, polyether, polycaprolactone and polybutadiene polyol-based urethane elastomers. 

Polymer-based rocket propellants are generally referred to as composite propellants, and often identified by the elastomer used, eg, urethane propellants or carboxy- (CTPB) or hydroxy- (HTPB) terrninated polybutadiene propellants. The cross-linked polymers act as a viscoelastic matrix to provide mechanical strength, and as a fuel to react with the oxidizers present. Ammonium perchlorate and ammonium nitrate are the most common oxidizers used nitramines such as HMX or RDX may be added to react with the fuels and increase the impulse produced. Many other substances may be added including metallic fuels, plasticizers, stabilizers, catalysts, ballistic modifiers, and bonding agents. Typical components are Hsted in Table 1. 

Three urethane-crosslinked polybutadiene elastomers (TB-1, TB-2, and TB-3) of varying crosslinking levels, along with a similarly crosslinked styrene-butadiene copolymer (HTSBR) and two polybutadiene polymers randomly crosslinked with dicumyl peroxide (PB-1 and PB-2), have been investigated to determine their viscoelastic behavior. Elsewhere, TB-1, TB-2, and TB-3 have been designated as HTPB-1, HTPB-2, and HTPB-3, respectively. 

Torsional creep measurements were made on the urethane-crosslinked polybutadiene elastomers at temperatures between —68 C and 25 C. The average molecular weight of a networks chain. Me, is 3400, 5200, and 8300 for TB-1, TB-2, and TB-3, respectively. The reduced shear creep compliance Jpit/ax) curves obtained for the three samples are shown in Figure 5.13. The reference temperatures are chosen to be 7.4°C, 0.0 C, and 17.0°C for TB-1, TB-2, and TB-3, respectively, so that superposition is achieved at shorter times... 

FIGURE 5.13 The logarithm of the reduced shear creep compliance curves, Jp t) (in Pa ), for the three urethane-end Unked polybutadiene elastomers displayed as a function of the logarithm of the reduced time t/ap (in seconds). The reference temperatures of reduction are chosen so that superposition is achieved at short times in the primary softening dispersion, (o) TB-1, 74 C, ( ) TB-2, 0°C, (e) TB-3, 17°C. 

Figure 5.1.2. Dependence of equilibrium swelling of crosslinked elastomer of polyester urethane (1) and polybutadiene nitrile mbber (2) on the volume fraction of acetone in the toluene-acetone mixture. [Adapted, by permission, from V.V. Tereshatov, V.Yu. Senichev,...

Torsional creep measurements were made on the urethane-crosslinked polybutadiene elastomers at temperatures between -68 and 25°C.The average molecular weight of a networks chain. Me, is 3400, 5200, and 8300 for TB-1, TB-2, and TB-3 respectively. The reduced shear creep compliance Jp(t/ar) curves obtained for the three samples are shown in Fig. 18. The reference temperatures are chosen to be 7.4,0.0, and 17.0°C for TB-1, TB-2, and TB-3 respectively so that superposition is achieved at shorter times in the primary softening dispersion. The most loosely urethane-crosslinked TB-3 has the largest 7e = 2.5 x lO Pa There is a plateau intermediate between the glassy compliance 7g (not reached in these measurements) and /e, and its level is about 2.0 X 10 Pa in all three samples. The network chain density does not affect the form of the time-dependent response up to and including the intermediate plateau in the Jp(t) curves. Only the terminal dispersion, i.e., the approach to /e, is influenced. The shift factors, Uj, that were used to obtain the... 

FIGURE 19 The logarithm of the reduced retardation spectrum, Lp, shown as function of the logarithm of the reduced retardation time, 2/at, for the three urethane-end linked polybutadiene elastomers. (O) TB-1, ( ) TB-2, (0) TB-3. The response has been reduced to corresponding state temperatures of 74°C, 0°C, and 17°C, respectively for the primary softening transition. 

The logarithm of the reduced shear creep compliance Jp t/aj) of several elastomers are compared at 0°C in Rg. 20 as a function of the logarithm reduced time-scale log(i/flr)- The elastomers include (1) the urethane-crosslinked polybutadiene elastomer, TB-2, described in Subsection B (2)... 

---