Fibreglass items would be interesting to have lying around, but unfeasible for player-made crafting, because:
Unlike glass fibers used for insulation, for the final structure to be strong, the fiber's surfaces [b]must be almost entirely free of defects[/b], as this permits the fibers to reach gigapascal tensile strengths. If a bulk piece of glass were to be defect free, then it would be equally as strong as glass fibers; however, it is generally impractical to produce bulk material in a defect-free state outside of laboratory conditions.
The manufacturing process for glass fibers suitable for reinforcement uses large furnaces to gradually melt the silica sand, limestone, kaolin clay, fluorspar, colemanite, dolomite and other minerals to liquid form. Then it is extruded through bushings, which are bundles of very small orifices (typically 5–25 micrometres in diameter for E-Glass, 9 micrometres for S-Glass). These filaments are then sized (coated) with a chemical solution. The individual filaments are now bundled together in large numbers to provide a roving. The diameter of the filaments, as well as the number of filaments in the roving determine its weight. This is typically expressed in yield-yards per pound (how many yards of fiber in one pound of material, thus a smaller number means a heavier roving, example of standard yields are 225yield, 450yield, 675yield) or in tex-grams per km (how many grams 1 km of roving weighs, this is inverted from yield, thus a smaller number means a lighter roving, examples of standard tex are 750tex, 1100tex, 2200tex).
These rovings are then either used directly in a composite application such as pultrusion, filament winding (pipe), gun roving (automated gun chops the glass into short lengths and drops it into a jet of resin, projected onto the surface of a mold), or used in an intermediary step, to manufacture fabrics such as chopped strand mat (CSM) (made of randomly oriented small cut lengths of fiber all bonded together), woven fabrics, knit fabrics or uni-directional fabrics.
A sort of coating, or primer, is used which both helps protect the glass filaments for processing/manipulation as well as ensure proper bonding to the resin matrix, thus allowing for transfer of shear loads from the glass fibers to the thermoset plastic. Without this bonding, the fibers can ‘slip’ in the matrix and localised failure would ensue.
Emphasis mine; there’s a lot of things here that are pretty much impossible in the post-apocalyptic condition.
-Free of Defects: That level of precision is impossible, in something you’re just scraping together; you need a well-oiled industrial process.
-Large Furnaces: These aren’t the puny stoves you use for cooking and forging; we’re talking like a house-sized industrial furnace, which you probably cannot power.
-Micrometer Orifices: Micrometers are small. You can’t produce things with such tiny, precise openings without very high-end equipment, which is bulky and difficult to run.
-Hundreds of Yards of Material per Pound: That’s some really fine weaving. Given the precision needed (read: free of defects), you absolutely need a huge machine to do this for you.
Now, if/when we get to a level of re-powering old factories, these projects stop looking completely impossible. But until then, you’re not going to do much fibreglass crafting short of maybe using a patch kit to repair a fibreglass item.
