In the glass fiber industry, the choice of raw materials is not only related to product quality, but also directly affects production efficiency and environmental benefits. As two common fluxes, sodium feldspar and borax have their own advantages in glass fiber production, but their action mechanisms and effects are significantly different. In recent years, with the growing demand for high-performance, low-cost fibers, sodium feldspar has gradually emerged with its unique advantages. This article will combine data analysis to deeply compare the differences between sodium feldspar and borax in glass fiber production.
Sodium Feldspar (mainly NaAlSi₃O₈) is a natural silicate mineral that provides sodium oxide (Na₂O), aluminum oxide (Al₂O₃) and silicon dioxide (SiO₂) in glass fiber production. It is an important ingredient in formulations such as E-glass by lowering the melting point and enhancing fiber strength. Borax (Na₂B₄O₇·10H₂O or its pentahydrate form) is based on boron oxide (B₂O₃), provides Na₂O and significantly reduces melt viscosity, and is widely used in borosilicate glass fibers.
The main difference between the two lies in chemical contribution and application scenarios. The multi-component characteristics of sodium feldspar make it more suitable for glass fibers that require high strength and high silicon content, while borax is often used in special fibers that are heat-resistant and chemically resistant due to its strong fluxing and low thermal expansion properties. However, the high cost and processing complexity of borax limit its widespread application in ordinary glass fibers.
Although borax performs well in specific areas, sodium feldspar shows more universal advantages in comparison with limestone, especially in terms of energy efficiency, performance and environmental protection. The following is a detailed analysis:
Lowering the melting point and improving energy efficiency
The Na₂O content of sodium feldspar is usually 10%-12%, which can effectively reduce the melting temperature of glass. According to industry tests, adding sodium feldspar can reduce the melting point from 1550°C to about 1400°C, which reduces energy consumption by 10%-15% compared to the formula using only limestone. Limestone (CaCO₃) decomposes into CaO and CO₂ at high temperatures. The decomposition process requires the absorption of about 178 kJ/mol of heat, which significantly increases energy consumption. However, sodium feldspar does not require this process and is directly integrated into the melt, which is more efficient.
Multifunctional components, simplified processes
Sodium Feldspar provides 18%-20% Al₂O₃ and 60%-65% SiO₂ at the same time, reducing the reliance on additional silica sand or clay. Taking E-glass as an example, sodium feldspar accounts for up to 15%-20%, while limestone usually accounts for only 10%-15%, providing only a single CaO (about 56% effective ingredients after decomposition). This multi-component characteristic optimizes the batching process and reduces production complexity.
Enhanced fiber performance
The Al₂O₃ introduced by sodium feldspar significantly improves the tensile strength of glass fiber. A 2023 study showed that the tensile strength of fibers with a high Al₂O₃ content can reach 3.5 GPa, which is 20% higher than the low Al₂O₃ formula. In contrast, although the CaO in limestone enhances corrosion resistance, it has limited effect in high-strength requirements (such as in the aerospace field). The comprehensiveness of sodium feldspar in performance makes it more competitive.
Environmental advantages, reduced carbon footprint
The decomposition of limestone releases about 440 kg CO₂ per ton, while sodium feldspar, as a natural mineral, does not need to be decomposed, and carbon emissions are greatly reduced. It is estimated that replacing part of the limestone with sodium feldspar can reduce CO₂ emissions by 5%-8% per ton of glass fiber production. This advantage is particularly prominent in the context of the increasingly urgent goal of carbon neutrality. Although borax has similar environmental protection potential, its purification process consumes more energy and its overall environmental benefits are not as good as sodium feldspar.
According to the 2024 data of the International Glass Fiber Association (GFIA), the global glass fiber production exceeds 9 million tons, of which E glass accounts for 60%. The proportion of sodium feldspar in E glass increased from 12% in 2019 to 18% in 2024, while the proportion of limestone dropped from 15% to 13%, showing the industry’s inclination towards efficient raw materials. Borax is more used in the field of borosilicate fibers, which accounts for about 10%, and its market share is limited by its much higher cost than sodium feldspar.
In addition, the stable supply and price advantage of sodium feldspar further enhance its attractiveness. Compared with the low cost of limestone, its processing and environmental protection costs make its comprehensive benefits inferior to sodium feldspar.
Sodium Feldspar and borax each have their own strengths, but in the competition with limestone, sodium feldspar wins with its energy efficiency, versatility and environmental advantages and becomes the new favorite of the industry. As a leading supplier, Henan Ankai New Materials Co., Ltd. helps sodium feldspar account for 25% by 2030, promoting the green upgrade of the glass fiber industry. Although borax is unique among specialty fibers, the rise of sodium feldspar injects new vitality.
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