Route 1—Resin Binders

Figure 3.3 shows the flowchart of the possible routes of binder composite fabrication. The technique and the problems associated with resin binders have been discussed in Sect. 3.2. Figure 3.4 shows the cmshing of the silica aerogel when used with epoxy-acetone solution. 

For rayon fiber based eomposites (Seetions 3 and 4) the fiber and powdered resins were mixed in a water slurry in approximately equal parts by mass. The isotropie piteh earbon fiber eomposites (Seetion 5) were manufaetured with less binder, typically a 4 1 mass ratio of fiber to binder being utilized. The slurry was transferred to a molding tank and the water drawn through a porous sereen under vacuum. In previous studies [2] it was established that a head of water must be maintained over the mold screen in order to prevent the formation of large voids, and thus to assure uniform properties. The fabrieation proeess allows the manufaeture of slab or tubular forms. In the latter case, the cylinders were molded over a perforated tubular mandrel covered with a fine mesh or screen. Moreover, it is possible to mold eontoured plates, and tubes, to near net shape via this synthesis route. 

The route to crosslinked phenol-formaldehyde resins via resoles corresponds to that used by Baekeland in his original commercial technique. They now tend to be used for adhesives, binders, and laminates. The resole... 

The route to crosslinked phenol-formaldehyde resins via resoles corre.sponds to that used by Baekeland in his original commercial technique, They now tend to be used for adhesives, binders, and laminates. The resole prepolymers are made typically in batch processes, using a trace of ammonia (about 2% on phenol) as the alkaline catalyst. Care has to be taken with this process since, despite the molar excess of formaldehyde, there is sufficient of each component present in the prepolymer to permit the formation of a highly crosslinked product. Indeed, such a product will form if the resole is heated excessively, but the problem can be avoided by careful attention to the conditions of reaction and by ensuring that polymerisation is not allowed to proceed for too long. 

However, there has been some interesting work in the USA on soybean, as a potential source of TS binder resins. These resins are being developed by the United Soybean Board, St Louis, Missouri, USA, under the name Proteinol. They are made from various waste cellulosic fibers tightly bound with various soy protein/phenolic binder systems. Fillers can be agricultural crop wastes such as wheat straw, corn, bagasse, kenaf, or hemp, forest waste products such as wood fibers, shavings, sawdust or chips, and shredded newsprint, de-inked office paper, and other recycled products. Extruded and compression molded shapes are being produced, which can be nailed, drilled, sawn, routed, sanded, painted and stained. 

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