Phenol formaldehydes, fracture

Proppants are solid particles used to hold open the fracture after conclusion of the well treatment. Criteria to choose the economically most effective proppant for a given set of formation conditions have been discussed (7 6). While sand is the most commonly used proppant because of its low cost, resin-coated sand, sintered bauxite, and A O particles have also been used because of their greater compressive strength and resistance to dissolution at high temperature and pH (55). While epoxy resins are most commonly used, the use of other resins such as phenol-formaldehyde has been described. 

Although epoxies dominate the thermoset fracture literature, work has been reported on other systems, e.g., polyester resins, phenol-formaldehyde compounds, peroxide cured polystyrene, and highly crosslinked polyurethanes. In general, these materials exhibit fracture behaviors similar to epoxies, and suggest that thermosets, as a class of materials, display characteristic crack growth properties. 

Figure 2. Fracture surface of a phenol-formaldehyde pol3nner (X2). Reproduced with permission from Ref. 11 Copyright 1971, John Wiley Sons, Inc.

Figure 7 Fracture surface of a phenol-formaldehyde adhesive showing striations (arrow) indicative of plastic deformation, yielding, and toughness. 

Figure 9 Overview of fracture surface of phenol-formaldehyde bonded joint showing exposed adhesive layer (A) without preexisting cure-shrinkage cracks and surface of lower adherend (B). The sloped test fracture surfaces (arrow) characteristic of phenol-formaldehyde and toughened urea-formaldehyde adhesive layers show where the crack jumped from one interphase to the opposite as the crack traveled in the fiber direction.

Figure 11 Fracture surface of Southern pine flakeboard showing unfractured fillet of phenol-formaldehyde adhesive (A) original surface of wood flake (B) adhesive fillet (C) fragment of SI layer of secondary wall from second wood flake.

Ku H, Rogers D, Davey R, Cardona F and Trada M (2008), Fracture toughness of phenol formaldehyde composites pilot study , J Mater Eng Perform, 17, 85-90. 

Bakelite, made by the reaction of phenol with formaldehyde, was one of the first plastics to be commercially manufactured. The product was a very dark hard brittle material that in its initial state had been capable of being shaped under pressure in a mould. Once heated to complete the reaction it hardened into its final form after which it could not be re-softened by heat. Since articles were usually made in highly polished metal moulds the surface of the plastic is itself very smooth and shiny but when broken the interior reveals a rough jagged fracture surface. 

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