Phenolic composites, interlaminar shear

Figure 35. Mechanical properties of carbon-carbon epoxy-resin hybrid composites, compared with the properties of the composite skeletons before resin impregnation (61,62). The composite skeletons were prepared from Sigrafil HM 3 PAN based fiber, rigidized with a phenolic resin, and densified by four cycles with coal-tar pitch plus sulfur the carbonization temperature was 1000 C. (b) Flexural strength. (c) Interlaminar shear stress, measured with two sample thicknesses.

Including 4-bromophenol in the phenol-formaldehyde resol system impacts the cross-link density of the cured product. In a systematic study of this copolymer, a comparison was made among the polymers obtained using phenol only, a 9 1 mole ratio of phenol to 4-bromophenol and a 1 1 mole ratio of phenol to 4-bromophenol. Comparisons included measurement of interlaminar shear strength and cone calorimetry tests of composites prepared using these phenolic resins and S2-glass fiber plain weave. 

Table 1 Interlaminar shear strength properties of phenolic composites...

Donnet and coworkers [89-91] have studied adhesion between epoxy resins and carbon acid. The number of add groups on the fiber surface was used to neutralize strong addic groups such as carbo l and phenol. Sodium ethoxide was used to neutralize weaker addic groups such as hydro l and carbonyl. A direct correlation was found between the number of carboxylic add groups and the interlaminar shear strength of the composite (Figure 13). 

These results suggest that for the initial design stages, similar levels of properties can be assumed for the main thermosetting laminating resins. However the interlaminar shear strength of phenolic composite can be appreciably less than polyester or epoxy ones and so the level of shear stresses may need to be checked. 

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