Glass transition temperatures curing conditions, effect

Effect of curing conditions on the glass-transition temperature 68... 

Effect of Curing Conditions on the Glass-Transition Temperature... 

The curing and dynamic properties of precipitated nano-silica on NR without and with the sulfur addition (NR with S), synthetic polyisoprene (IR), polybutadiene (BR) and SBR was investigated. Silica was treated with bis(3-triethoxysilylpropyl)tetrasulfane (TESPT) to form bonds at interfaces. Cure, Mooney viscosity, glass transition temperature, bound rubber, crosslink density and DMA were measured. The properties of silica-filled SBR and BR correlated with highest rolling resistance and SBR-silica correlated with best skid resistance. A Payne effect was observed in the loss modulus under some experimental conditions. In addition to possible filler de-agglomeration and network disruption, the nanoscale of the filler may have further contributed to the non-linear response typified by the Payne effect. ... 

Perhaps, the earlier materials found to have a useful capacity for adhesive bonding underwater depended upon the use of a stoichiometric excess of water-scavenging polyamide hardener in an epoxide-based adhesive. This approach can lead to the production of effective joints in the short term, but formulations of this type, which are hydrophilic in the uncured state, are also likely to absorb significant amounts of water in the cured condition. It is a widely accepted view that the extent of joint weakening in susceptible joints, quite apart from the consequences of plasticization, is a function of the water-uptake characteristics of the adhesive (see Glass transition temperature). The consequence is therefore likely to be that such joints will show poor durability in the presence of water, when rapid uptake of water may lead to equally rapid degradation of both cohesive and interfacial properties (see Durability fundamentals). 

Post-Treatment. A post-bake (post-curing) can have a beneficial effect on the thermal stability and dimensional stability of phenolic molded parts. Early work showed that the glass transition temperature Tg) increases with cure in phenolics.More recently it has become apparent that the Tg of an as-molded phenolic novolak part strongly influences the post-bake conditions to be used. If parts are molded above the Tg, an unacceptable expansion can occur 102,103 continues to increase during... 

Above the glass transition, the material starts to undergo post-cure reactions, so that the linear thermal expansion is attenuated by the contemporaneous chemical shrinkage effect until the post-cure reaction is completed. At the end of the post-cure reaction, the now fully-cured system expands, only because of temperature changes. Penetration of the probe into the top of the resin specimens cannot be excluded. This further condition will be limiting for any further possible analysis of the curves at T > Tg. 

---