As a consequence of these developments, commercial E‐glass fibers today fall into two major categories: low or zero B2O3 levels for general reinforcements, and higher B2O3 levels (>5%) for electronic and aerospace applications. The distinction between these categories is clearly defined in ASTM D578 [2].
2.1.3 C‐Glass
Other reinforcement fibers containing B2O3 were developed in the early 1940s as C‐glass, which has limited use as discontinuous fiber products for roofing materials. Continuous boron‐free variants of C‐glass fibers with improved chemical resistance to acids came to market in the mid‐1960s. The composition is primarily composed of Na2O, CaO, Al2O3, and SiO2. The absence of boron resulted in improved acid resistance; the mechanical performance (strength and modulus) of C‐glass fiber is inferior to those of both E‐glass and E‐CR glass, however, so that applications of this glass in the reinforcements industry have been limited to nonstructural uses such as nonwoven fabrics for corrosion liners, building insulation materials, sewage pipes, etc. For many years, C‐glass served as the primary form of glass fiber for low‐cost regions of the world in emerging markets, at present less than 10% in volume relative to E‐glass fibers produced each year in China. The balance of mineral components with no need for a boron source provided a glass fiber based on widely available raw materials that could be easily manufactured in low‐technology operations. Hence, these properties led to the broad commercialization of C‐glass as a low‐cost substitute for E‐glass fibers in regions where modern fiberglass furnace technology was not commonly available. Many early fiber producers in China used C‐glass. The trend today, however, is to move away from C‐glass fibers to the production of E‐glass and other high‐performance fibers. Little development has occurred since the mid‐1980s, and C‐glass fibers represent less than 5% of fibers used in glass fiber reinforced composites today.
Figure 1 History of commercial continuous fiberglass development (most active period in development shown and beyond 2015 most intensive research areas projected are S, R, and D glass fibers) and standard nomenclature/classification based on their key properties used in commercial applications [4].
Table 1 Composition of glass fibers found in literature and/or commercial market [2–6].
| Fiberglass | SiO2 (wt %) | Al2O3 (wt %) | MgO (wt %) | CaO (wt %) | SrO (wt %) | BaO (wt %) | B2O3 (wt %) | R2O (wt %) | F2 (wt %) | ZrO2 (wt %) |
|---|---|---|---|---|---|---|---|---|---|---|
| E including E‐CR | 52–62 | 12–16 | 0–5 | 16–25 | — | — | 0–10 | 0–2 | 0–2 | — |
| C (China)a C (Europe) | 67.0 53–65 | 6.2 3.8–16 | 4.2 2.4–3.8 | 9.5 14–16 | — | — | 0 3–6 | 127–9 | <1 0.3 | — |
| Ab | 72–72.5 | 1–1.5 | 2.5–3.8 | 9–10 | 0 | 0 | 0 | 13–14 | 0 | 0 |
| ARc | 61–71 | 0–3 | — | <5 | — | — | 0 | <18 | — | 16–22 |
| D | 72–76 | 0–1 | — | <1 | — | — | 20–25 | <4 | — | — |
| D (derivative I) | 52–60 | 10–18 | 0 | 4–8 | — | — | 20–30 | Trace | 0–2 | — |
| D (derivative II) | 50–60 | 10–18 | 1–6 | 2–5 | 1–9 | 1–5 | 14–20 | <1 | 0–2 | — |
| D (derivative III) | 60–77 | 9–15 | 5–15 | 0–11 | — | — | 5–13 | 0–4 | 0–2 | — |
| R | 58–60 | 23–26 | 5–6 | 9–11 | — | — | 0 | — | — | — |
| R (derivative) | 56–65 | 12–20 | 6–12 |
8–16
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