Incomplete cure

Calcium hydroxide leached from incompletely cured concrete causes serious corrosion of lead (see Section 9.3). This is because carbon dioxide reacts with the lime solution to form calcium carbonate, which is practically insoluble. Carbonate ions are therefore not available to form a passive film on the surface of the lead . Typically, thick layers of PbO are formed, which may show seasonal rings of litharge (tetragonal PbO) and massicot (orthorhombic PbO) . 

The curing process renders the resin essentially inert and nontoxic. At room temperature, full curing may take several days incompletely cured resins may cause skin irritation and sensitization. Respiratory symptoms may result from inhalation of cured epoxy dusts during grinding, presumably due to release of residual curing agent. Skin irritation and sensitization have been associated with epoxy resin exposure. 

The solution to the problem is to increase the cure temperature, to let the part cure for a longer time in the mold or to change the resin formulation. It is a good idea to make a serious effort to optimize the cure cycle and resin formulation if incomplete cure should occur. 

Semi-cure - A preliminary incomplete cure applied to an article in the process of manufacture, to cause the rubber to acquire a degree of stiffness or to maintain some desired shape. 

Homogeneous nonideal, e.g. open networks, obtained from the same chemistry as the previous ones. These networks contain dangling chains as a result of incomplete cure, nonstoichiometric composition, or presence of monofunctional monomers. 

Incompletely cured networks constitute an important case of nonideal networks. They can be considered homogeneous if they result from step polycondensation. The following factors are expected to have an influence on Tg (beyond the gel point) ... 

Nonstoichiometric systems or incompletely cured stoichiometric systems behave as if they were internally plasticized systems. The modulus variation with cure conversion (x), for a typical stoichiometric epoxide-amine network, is shown in Fig. 11.8. 

High peel strength with cohesive failure is possible by increasing the 0K/NC0 ratio. At a higher ratio, slight creep is observed at room temperature in the static shear test., 0H/NC0 ratios above 2.0 for Hycar 2103 and 1.8 for Hycar 2106 result in adhesives having incomplete cures with low peel values and poor static shear strength. 

A differential scanning calorimeter (DSC 1-B, Perkin-Elmer Corporation) was used to determine the extent of cure 10-mg to 20-mg specimens were tested at a scanning rate of 10°C/min. An exothermic peak on the thermograph indicates the heat of reaction whereas an endothermic peak in the amorphous polymer indicates the presence of residual stresses or the occurrence of a transition such as the glass transition. The presence of an exothermic peak in the DSC-scan of a pre-cured sample is an indication of incomplete curing. 

Degree of cure. The titration results given in Table III reveal that from 98% to 100% of the functional groups had reacted. Similarly no evidence for incomplete cure was observed by DSC or by dynamic mechanical spectroscopy (DMS). However, it may be pointed out that 2% unreacted functional groups could result in detectable incoherence (see reference 29) in the networks prepared from high-MW epoxy prepolymers. 

Because of their carcinogenicity, amines have to be monitored. For example, primary aromatic amines (PAAs) are substances that can be transferred from food packaging materials into foodstuffs. In the production of multilayer plastic materials it is common to use reactive adhesive mixtures containing aromatic isocyanate monomers. In cases of incomplete curing, residues of the aromatic isocyanates react with water to produce PAAs. Some of these amines, including... 

Thermal Low cost. Uses existing equipment Long cycle times for most formulations. Incomplete cure may occur with fast cure, snap cure adhesives, depending on thermal mass... 

Defects such as voids, dry spots, resin-rich areas, premature failures, localized failure regions and non-uniform or incomplete cures can occur. Most aerospace components are held to within 2% weight tolerance and for strength, an excessive variation can result in uneven stress distribution, resulting in component failure. 

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