Determination of Emulsion Coating Content in Glass Fiber Fabric: Test Methods, Standards, and Qualit

Emulsion-coated glass fiber fabric is a key reinforcement and facing material in thermal insulation, waterproofing, and wall covering systems, where the coating content (resin or binder pickup) directly controls strength, flexibility, and long-term durability. Accurate determination of coating content—typically performed by ignition loss, solvent extraction, or gravimetric difference methods in accordance with ISO, ASTM, and GB standards—is essential for incoming material inspection and process quality control. This article explains the applicable standards, sampling procedures, calculation formulas, and practical considerations for reliable coating content measurement.

Technical Overview

Emulsion-coated glass fiber fabric is a woven textile produced from continuous or staple glass fibers—commonly E-glass, C-glass, or ECR-glass—that has been impregnated with an aqueous polymer emulsion such as acrylic, polyvinyl acetate (PVAc), silane coupling agent systems, or specialty silicone emulsions. After drying and curing, the emulsion binder forms a thin polymeric film that bonds the filaments and yarns, improving fabric integrity, abrasion resistance, drape, printability, and compatibility with downstream adhesives or bituminous coatings.

Coating content, also referred to as resin content, binder content, or loss on ignition (LOI), is defined as the mass fraction of organic coating relative to the total dry mass of the coated fabric, expressed as a percentage. It is one of the most critical quality attributes of the material: insufficient coating leads to loose selvages, fiber shedding, and poor mechanical performance, while excessive coating increases cost, reduces porosity, and may cause brittleness or adhesion problems. Depending on the application, typical coating contents range from approximately 3% to 10% for lightly sized scrims and from 10% to 30% for heavily coated wall covering and membrane fabrics.

Because the coating is applied during fabric manufacture and can vary across the fabric width and along the roll length, coating content determination requires standardized sampling, conditioning, and analytical procedures. ISO, ASTM, and GB standards organizations have established recognized methods, and testing is routinely carried out both in manufacturers' internal laboratories and by accredited third-party laboratories for independent verification.

Testing Samples

Typical Sample Types

Coating content determination is applicable to a wide range of emulsion-coated glass fiber products, including plain and leno woven scrims for insulation facings, lightweight glass wall fabric, bitumen membrane carriers, filtration fabrics, and surface finishing mats. Both roll goods and cut panels can be evaluated, provided the material is representative of the production lot and has not been contaminated by dust, oil, or moisture.

Specimen Preparation and Conditioning

Specimens are usually cut to a minimum of 100 mm × 100 mm (0.01 m²), or a circular disc of equivalent area, with an individual dry mass of at least 1 g where practicable. A minimum of three to five specimens should be taken, distributed diagonally across the full fabric width—including selvage, quarter-width, and center positions—to capture cross-direction coating variation. Loose fibers and creel debris must be removed, and specimens should be marked and weighed individually.

Prior to testing, specimens are conditioned to equilibrium in a standard atmosphere in accordance with ISO 139 or ASTM D1776 (commonly 23 ± 2 °C and 50 ± 5% relative humidity), or oven-dried at 105 ± 2 °C to constant mass when results are required on a dry basis. Dry-basis testing is strongly recommended for emulsion-coated fabrics because polymer emulsions and glass sizes are moderately hygroscopic, and uncorrected moisture can bias results by several tenths of a percent.

Testing Items

The core testing program for emulsion-coated glass fiber fabric typically includes the following measurable parameters:

• Coating (binder/resin) content, expressed as mass percentage of the dry coated fabric
• Combustible matter content in accordance with ISO 1887 or GB/T 9914.2
• Loss on ignition (ignition loss) in accordance with ASTM D2584 or the calcination principles of ISO 1172
• Dry basis weight (mass per unit area) in accordance with ISO 3374 or GB/T 7689.3, for the gravimetric difference method
• Moisture content, determined by drying at 105 ± 2 °C to constant mass
• Ash or inorganic residue content, relevant when the emulsion formulation contains mineral fillers or pigments

Testing Methods

Ignition (Burn-Off) Method

The ignition method is the most widely used and internationally standardized approach. Each conditioned, weighed specimen (initial dry mass m1) is placed in a pre-weighed crucible or dish and introduced into a muffle furnace maintained at 625 ± 20 °C, the reference temperature specified in ISO 1887, GB/T 9914.2, and ISO 1172. The specimen is held at temperature for 20 to 40 minutes, or until successive weighings confirm constant mass, during which all organic binder is completely oxidized while the glass substrate remains stable. The residue is cooled to ambient temperature in a desiccator and reweighed (residue mass m2). The coating content is calculated as: Coating content (%) = (m1 − m2) / m1 × 100. Combustion fumes should be extracted through a suitable hood, and specimens must never be inserted into a furnace already at full temperature without pre-charring, as rapid ignition can cause spattering and mass loss.

Solvent Extraction Method

When the emulsion binder is a soluble thermoplastic—such as PVAc or many acrylic systems—or when the glass composition is sensitive to elevated temperature, the coating can be removed by Soxhlet reflux extraction using a suitable solvent such as acetone, ethanol, or a formulation-specific solvent blend. The specimen is extracted for a defined period (commonly 4 to 8 hours), then dried at 105 °C to constant mass and reweighed. The mass loss corresponds to the extracted binder fraction. This method avoids thermal effects on boron-rich glass but requires solvent selection studies to confirm complete binder recovery and safety controls for flammable solvent handling.

Gravimetric Difference Method

For production control, the coating content can be derived from basis weight measurements. The dry mass per unit area of the coated fabric (G1) is determined per ISO 3374 or GB/T 7689.3, and the mass per unit area of the corresponding uncoated base fabric (G0) is either measured before coating on the same production run or obtained from the qualified base fabric specification. The coating content is then calculated as: Coating content (%) = (G1 − G0) / G1 × 100. This method is rapid and non-destructive but depends on accurate knowledge of the base fabric grammage and uniform textile thickness.

Reporting and Evaluation of Results

A complete test report should identify the standard applied, glass type and emulsion class, specimen dimensions and number, conditioning procedure, ignition temperature and dwell time, individual and mean coating content values, standard deviation, and any deviations such as visible filler residue. Cross-width uniformity is commonly evaluated by comparing selvage, quarter, and center specimens; a practical acceptance criterion for many specifications is a nominal coating content within ±1% absolute, or ±10% relative, of the declared value.

Applications

Coating content determination supports quality assurance across the principal end uses of emulsion-coated glass fiber fabric, including:

• Facing scrims and reinforcement layers for FSK, ASJ, and PSK thermal insulation jacketing systems, where coating level governs scrim integrity and facing lamination strength
• Carrier fabrics for bituminous and polymer waterproofing membranes, ensuring consistent impregnation and dimensional stability
• Textured glass wall fabric and wall coverings, where coating uniformity affects paintability, fire classification, and surface appearance
• Gypsum board and cement board facing mats, controlling dusting, porosity, and board bond strength
• Industrial filtration and dust collection fabrics, balancing stiffness, cleaning behavior, and airflow resistance
• Surface finishing mats and veils for fiber reinforced plastic (FRP) composites, where binder content influences resin uptake and surface quality
• Thermal wrapping, electrical insulation tapes, and heat-shield substrates requiring controlled burn-off characteristics

In supply contracts, certification of coating content by accredited third-party laboratories is frequently used to verify manufacturer declarations, resolve quality disputes, and support conformity assessment of construction products.

FAQ

What is the difference between coating content and combustible matter content?

Combustible matter content, per ISO 1887, measures everything removed by ignition—organic binder, processing sizes, and any carbonaceous contaminants. For a pure polymer emulsion coating on clean glass fabric, the two values are practically identical; when the emulsion contains inorganic fillers, pigments, or flame retardants, the combustible matter result will be lower than the true total coating mass, since those inorganic components remain in the ash.

Which method is most appropriate for routine quality control?

The ignition method at 625 ± 20 °C is the default choice for E-glass and most C-glass fabrics because it is fast, standardized, and equipment requirements are modest. Solvent extraction is preferred for temperature-sensitive or filler-rich systems, and the gravimetric difference method suits rapid in-line production monitoring when base fabric grammage is well controlled.

Why is the ignition temperature limited to approximately 625 °C?

Borosilicate and high-boron C-glass compositions can begin to lose volatile components, notably boron oxide, at higher temperatures, which would falsely inflate the measured binder content. The 625 ± 20 °C window ensures complete organic combustion while keeping the glass substrate thermally stable, which is why ISO 1172, ISO 1887, and GB/T 9914.2 converge on this temperature.

What happens if the emulsion contains inorganic fillers or pigments?

Ignition will not remove mineral fillers, so the measured loss on ignition understates total coating mass. In such cases, the filler loading should be determined separately—for example by ashing the neat emulsion film—and the calculation corrected, or solvent extraction should be used with a solvent validated to dissolve the full binder formulation.

How many specimens are required and how is sampling performed?

A minimum of three to five specimens of at least 100 mm × 100 mm is recommended, taken diagonally across the full fabric width to reflect coating migration and edge effects. Rolls should be sampled at least one meter from the roll end, and results are reported as individual values together with the mean and standard deviation.

Can moisture content distort the results?

Yes. Emulsion binders and glass sizes absorb ambient moisture, which inflates the initial mass and reduces the calculated coating content. Oven drying at 105 ± 2 °C to constant mass, followed by cooling and weighing in a desiccator, eliminates this bias and improves repeatability.

How quickly can results be obtained?

A standard ignition test, including drying, ignition, cooling, and weighing, is typically completed within two to three hours for a small specimen set, allowing same-shift feedback for coating bath adjustments in production environments.