Matrix moisture sensitivity

The degradation of the matrix in a moist environment strongly dominates the material response properties under temperature, humidity, and stress fatigue tests. The intrinsic moisture sensitivity of the epoxy matrices arises directly from the resin chemical structure, such as the presence of hydrophilic polar and hydrogen grouping, as well as from microscopic defects of the network structure, such as heterogeneous crosslinking densities. 

Well-defined arene complexes of Group 4 metals in various oxidation states have been isolated. The air- and moisture-sensitive complexes Ti(r -arene)2 (56) have a sandwich structure similar to that of the related chromium compounds [176-178]. They have been used for deoxygenation of propylene oxide and coupling reaction of organic carbonyl compounds [179]. The first synthesis of 56 was cocondensation of metal vapor with arene matrix [176]. Two more convenient methods are reduction of TiCl4 with K[BEt3H] in arene solvent [180] and reaction of TiCl4(THF)2 with arene anions followed by treatment with iodine [170,176]. The latter method involves the formation of an anionic titanate complex, [Ti(ri -arene)2] (57), which can also be formed from KH and 56 [181]. 

These resins have been shown to exhibit even better properties than the first-generation phthalonitriles in terms of thermal and oxidative stability and moisture sensitivity. But, most important of all, this new reaction pathway is short and simple, and takes advantage of inexpensive starting materials. Thus, it seems to have opened up possibilities for designing polymers with a wide variety of structural variations, and for lowering the material cost to make the resins competitive with other existing composite matrix systems. 

It must be kept in mind, however, that chemical effects (strong interactions between the penetrant and the polymer), as observed, for example, in (i) the high moisture sensitivity of many polar polymers, (ii) the high solubility of some penetrants in some polymers, and (iii) the plasticization of the polymer matrix by a penetrant, can cause the behavior of a polymer-penetrant system to become quite different from what would be predicted on the basis of physical effects (such as packing efficiency) alone. 

Similar hybrid thermosets consisting of bismaleimide resins mixed with bisphenol A dicyanate ester have been commercially available (BT resin, Mitsubishi gas chemical). The presence of cross-linked triazine ether network in the matrix of bismaleimide crosslinked network is believed to improve the toughness, reduce the moisture sensitivity and improve the dielectric properties of the bismaleimide thermoset without a sacrifice in heat resistance. 

Figure 39 depicts the CPI process schematically. The matrix polymer is transported to the A extruder from the storage bunker by a gravimetric system. Material compounding of the matrix polymers and additives takes place in this extruder in a shearing and mixing process. Predrying precedes the process with moisture-sensitive matrices such as polyamides (PA) or polyethylene terephthalates. 

Despite the extreme air and moisture sensitivity of organo-lanthanoid compounds, this is a rapidly expanding research area. An exciting aspect of organolanthanoid chemistry is the number of efficient catalysts for organic transformations that have been discovered (see Box 25.5). In contrast to the extensive carbonyl chemistry of the J-block metals (see Sections 24.4 and 24.9), lanthanoid metals do not form complexes with CO under normal conditions. Unstable carbonyls such as Nd(CO)g have been prepared by matrix isolation. Since organolanthanoids are usually air- and moisture-sensitive and may be pyrophoric, handling the compounds under inert atmospheres is essential. ... 

Different compositions of wheat thermoplastic starch (TPS) and polycaprolactone (PCL) were melt blended by extrasion and injected [104]. It was noticed that the addition of PCL to the TPS matrix allowed the weakness of pure TPS to be overcome low resilience, high moisture sensitivity and high shrinkage, even at low PCL concentrations, e.g. 10 wt%. However, a fairly low compatibility between both polymeric systems was reported. For PCL-based blends, mechanical properties depend both on plasticization level and PCL content (Table 3.22). 

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