Читать книгу Encyclopedia of Glass Science, Technology, History, and Culture - Группа авторов - Страница 132

First commercialized in the late 1930s [1], E‐glass fiber remains the most widely used class of fiberglass for GRP materials [3, 4]. Its composition primarily lies within the ternary CaO–Al₂O₃–SiO₂ system with B₂O₃ and F₂ contents that vary from 0 to 10 wt % and 0 to 2 wt %, respectively. For much of its history, E‐glass fiber production incorporated B₂O₃ in commercial compositions at levels of 7–8 wt %, which provided an optimal balance of melting and fiber‐forming characteristics, mechanical properties, and electrical properties. Over time, however, increasingly restrictive environmental emissions requirements for particulates have been driving costs up for emission control systems. Countries such as Canada and Norway were leaders in the push to improve environmental conditions, leading to the introduction of the first boron‐free commercial glass fibers. These glasses had in addition excellent corrosion resistance under strongly acidic conditions [7]. They have been designated as E‐corrosion resistant (E‐CR) glass fibers in the late 1970s. Over time, optimizations of minor oxide components such as TiO_2, ZnO, and MgO served to improve their cost and manufacturing efficiencies while also providing proprietary regions in the compositional space as their use was growing rapidly.

In key areas outside of the corrosion markets, however, there was resistance to move to low‐boron compositions. The electronics industry, dominated by E‐glass fabrics used in printed wiring boards (PWB), relied on the unique value set of electrical consistency, dimensional stability, processing predictability, and low cost provided by conventional E‐glass over many years and resisted any change in the E‐glass standards. The aerospace industry also resisted the change, based on a well‐defined history of performance of conventional E‐glass and a desire to minimize any risk, however small, which might be incurred by what was perceived as a significant material change.

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].