Industry News

Flame Retardants in Coated Fiberglass Fabrics

Author : Heaterk

Update time : 2025-02-05 16:35:08

In the industrial textiles sector, coated fiberglass fabrics are widely applied as heat resistant fabric solutions, serving as insulation, flame resistance, and high-temperature barriers. Contrary to common assumptions, whether it is high-performance silicone coated fabric or vermiculite coated fabric, a certain proportion of fire retardant additives is almost always included—ensuring durability under extremely harsh conditions and making them more inherently flame retardant.

By being treated with flame retardants, this heat resistant fabric coating can enhance flame retardant properties and extend the critical window for evacuation or firefighting. Contrary to popular belief, in most real-world scenarios, the overall flame resistance of these coated fabrics depends more heavily on the ratio of these additives than many realize.

Types of Flame Retardants

Flame retardants are generally classified by their chemical composition and mode of action. Below are the primary categories used in fire resistant fabric and inherently flame retardant textile applications, which demand robust flame resistance for safety-critical environments such as building materials or industrial PPE.

Halogen-Based Flame Retardants

Halogen-based flame retardants typically rely on brominated or chlorinated compounds, forming radicals that disrupt the flame propagation. For applications requiring high flame retardant properties in flammable fabrics, halogen-based additives can deliver substantial fire retardant performance but may generate toxic or corrosive by-products under an open flame.

Inorganic Flame Retardants

Inorganic flame retardants, including aluminum hydroxide (ATH) or magnesium hydroxide (MDH), act by releasing water or inert gases upon decomposition. This method involves endothermic cooling of the substrate, which greatly benefits inherently flame retardant coatings requiring additional flame resistance. However, the relatively high loadings needed can affect mechanical flexibility in flame retardant fabrics.

Phosphorus-Based Flame Retardants

Phosphorus-based solutions, such as TCPP or DOPO derivatives, facilitate char formation and can be treated with flame retardants that create an intumescent barrier. These additives often yield strong flame retardant properties while reducing smoke and toxic gas emissions. Consequently, many fire retardant coatings leverage phosphorus-based chemistries to balance cost, efficacy, and environmental considerations.

Nitrogen-Based Flame Retardants

Nitrogen-based flame retardants—such as melamine cyanurate—work synergistically with phosphorus to form robust char layers. This synergy is especially beneficial in inherently flame retardant textiles that rely on an intumescent process to hinder catching fire. Overall, nitrogen-based systems can enhance the fire retardant threshold, making these coated fabrics more reliable under continuous open flame exposure.

Silicone-Based Flame Retardants

Silicone-based flame retardants, including polysiloxanes, decompose to form a silica layer, acting as a thermal insulator. While their flame retardant properties are sometimes less pronounced than halogen or phosphorus systems, they emit fewer toxic by-products and maintain good mechanical flexibility, making them attractive for flammable fabrics that need repeated usage in harsh environments.

Impact of Flame Retardants on Coated Fiberglass Fabrics

Coated fiberglass fabrics already exhibit inherently flame retardant qualities due to the glass fibers. When these materials are treated with flame retardants in the coating matrix, their ability to withstand open flame conditions improves significantly.

Silicone coated glass fabric with flame retardant

The table below summarizes typical loadings, LOI (Limiting Oxygen Index) changes, and mechanical effects across different flame retardant types.

Flame Retardant Type	Typical Coating Systems	Typical Loading	LOI Before / After ¹	Mechanical Impact
Halogen-Based	PVC, PU, Silicone	5–20 wt% (by total coating)	~22→32 (Baseline to Treated)	Can reduce tensile strength by 5–15%. May slightly stiffen fabric. Some coatings show discoloration above 300 °C (572 °F).
(e.g., decabromodiphenyl ethane)		or 5–15 phr²	(22 °C→32 °C)
Inorganic	Silicone, Acrylic	30–60 phr (often 20–40 wt%)	~24→35 (Depending on filler loading)	High loadings (≥40 wt%) can decrease elongation by 10–20%. Increases coating thickness and weight.
(e.g., ATH, MDH)
Phosphorus-Based	PU, Acrylic, Epoxy	5–20 wt%	~22→30 (Enhanced char formation)	Generally ±5% effect on tensile strength. Helps reduce dripping in vertical burn tests (UL 94 V-0 or V-1).
(e.g., TCPP)
Nitrogen-Based	PU, Acrylic (w/ P synergy)	5–15 wt%	~23→29 (Often used in intumescent systems)	Minimal impact on stiffness. In synergy with phosphorus, can improve char yield and lower smoke release.
(e.g., melamine polyphosphate)
Silicone-Based	Silicone resin over fiberglass	3–10 wt%	~23→28 (Primarily reduces smoke)	Minimal mechanical impact. Often preserves flexibility and reduces toxic by-products.
(e.g., polysiloxanes)

¹ LOI values measured per ASTM D2863 (approximate range based on typical formulations).
² phr = parts per hundred resin (commonly used in rubber/plastics).

By selecting the right additives, manufacturers can create fire retardant coatings that offer excellent flame retardant properties while preserving mechanical strength. However, higher filler loadings or halogen-based approaches may lead to stiffer fabric and potential environmental concerns. Overall, fiberglass fabrics treated with flame retardants in silicone, acrylic, or polyurethane systems can reach LOI values above 30, limiting the chance of an open flame igniting the material.

Negative Impacts of Flame Retardants on Textile Performance

Despite the benefits in preventing fabrics burn and reducing catching fire, flame retardants can lead to:

Mechanical Property Degradation
High filler loadings (≥40 wt% inorganic fillers) often lower the tensile and tear strength of coated fabrics by up to 15–20%. Excessive halogen-based additives can also stiffen the coating, reducing flexibility.
Thermal Stability Limits
Some halogen compounds degrade or decompose at elevated temperatures (>300 °C / 572 °F), leading to off-gassing, discoloration, or reduced flame resistance over time.
Environmental and Health Concerns
Halogenated additives may release corrosive fumes during combustion. Regulatory bodies like REACH (EU) and TSCA (U.S.) often limit their usage, prompting a shift toward low-smoke, low-toxicity systems.
Processing Challenges
High-viscosity or heavily filled formulations can be difficult to apply with standard methods (knife-over-roll, dip coating), affecting product uniformity and possibly requiring specialized equipment.

Other Factors Affecting Flame Retardant Performance

While flame retardants are central to improving fire safety, several additional variables influence how well coated fiberglass fabrics perform under fire.

Coating Thickness and Application Method

Coating thickness and processing have a profound influence on both fire protection and mechanical properties. Knife coating offers precise control, typically yielding thicknesses of 0.2–0.5 mm (8–20 mils) for industrial-grade fabrics. This uniformity ensures consistent flame-retardant distribution and predictable LOI values. In contrast, dip coating can lead to uneven coverage if parameters like line speed, viscosity, or solvent ratios are not carefully optimized.

Thicker coatings often deliver superior thermal insulation and facilitate higher filler loadings. It is not uncommon for industrial insulation fabrics to gain +150 g/m² (+4.4 oz/yd²) after coating, improving barrier properties yet adding weight—an important consideration in lighter applications such as personal protective equipment.

Fiberglass Substrate Properties

The inherent strength and weave density of the fiberglass fabric significantly influence performance under open flame. S-Glass yarns, for instance, withstand higher temperatures than E-Glass, making them useful in more demanding industrial or aerospace settings. Additionally, tighter weaves tend to retain char residues better, further hindering the spread of flames. However, denser fabrics naturally absorb more coating, raising total weight and possibly necessitating additional flame retardant to maintain uniform coverage.

Durability and Post-Treatment Care

Flame-retardant performance is also contingent on long-term durability. In high-wear or outdoor installations, coatings can degrade through abrasion, washing, or UV exposure. Testing protocols like ASTM D573 for heat aging or ISO 4892 for UV weathering help confirm that the flame retardant properties remain stable throughout the product’s lifespan. When the environment is especially harsh, periodic top-coat refreshes might be necessary, adding a logistical factor for procurement managers.

Synergistic Additives and Formulation Balance

In many formulations, a single flame retardant is supplemented by synergistic additives, such as zinc borate or molybdenum compounds, to reduce smoke density. Flow promoters or dispersants can also be added to achieve uniform filler distribution. Striking the right formulation balance is critical—over-reliance on any single mechanism can drive up cost or compromise mechanical performance. Well-designed multi-additive systems can attain LOI values above 35–40, cut peak heat release rates by half, and preserve 80–90% of the baseline tensile strength in inherently flame retardant fiberglass fabrics.

In coated fiberglass fabrics, flame resistance is integral for safety, prolonging evacuation times and mitigating property damage. By carefully selecting flame retardant chemistry, application methods, and substrate characteristics, manufacturers can meet rigorous U.S. and international fire safety standards (e.g., UL 94, NFPA 701, ASTM E84, EN 13501-1). Buyers and procurement managers should evaluate coating thickness, weave density, durability, and synergistic formulations to ensure the best performance-to-cost ratio. As regulatory landscapes evolve, the industry will continue shifting toward halogen-free and low-smoke, low-toxicity solutions, shaping the future of treated with flame retardants textiles.