Volatile content determination is a key quality control test for emulsion-coated glass fiber fabric, quantifying the moisture and process volatiles retained in the textile after coating and drying. This article explains the testing principles, sampling requirements, gravimetric oven-drying methodology, calculation formulas and typical applications of volatile matter testing, with reference to recognized standards such as ISO 3344, ISO 1887 and ASTM D751. Understanding volatile content analysis helps manufacturers of glass fiber wallcovering fabric and coated reinforcement mesh ensure consistent drying, stable coating performance and product compliance.
Technical Overview
Emulsion-coated glass fiber fabric is a woven textile produced from continuous glass filament yarns and finished with a polymer emulsion coating, typically acrylic, styrene-acrylic or vinyl-based, applied by impregnation, dipping or knife-over-roll coating. The material combines the high tensile strength, dimensional stability, non-combustibility and chemical inertness of glass fibers with the flexibility, adhesion and surface properties imparted by the organic coating. It is widely used as interior wallcovering fabric, as reinforcement mesh in external thermal insulation composite systems (ETICS/EIFS), and as a substrate in filtration, waterproofing and composite applications.
Volatile content, also called volatile matter, refers to the fraction of the fabric mass lost when a specimen is heated under standardized conditions. This loss consists principally of moisture absorbed by the hygroscopic glass filaments and the coating film, together with residual water and low-boiling volatiles retained in the emulsion after the production dryer. Excessive volatile content indicates incomplete drying and can cause roll blocking, reduced coating cohesion, mold growth during storage, commercial weight discrepancies, and poor printability or adhesion in downstream processing. Volatile content determination is therefore performed routinely as an incoming, in-process and outgoing inspection by manufacturers and by accredited third-party laboratories.
Testing Samples
Emulsion-Coated Glass Fiber Wallcovering Fabric
Plain-woven or leno-woven glass fiber fabric finished with an acrylic or styrene-acrylic emulsion and supplied in roll form for interior wall decoration. Volatile content testing verifies drying completeness before slitting, printing and packaging, and supports conformity with wallcovering product specifications such as the EN wallcovering standard series.
Coated Glass Fiber Mesh for Thermal Insulation Systems
Mesh fabric impregnated with a polymer emulsion for embedding in the base coat of external insulation and finish systems. Residual volatiles influence the effective coating mass per unit area, the flexibility of the mesh and the long-term durability of the system, so volatile content is controlled together with coating content and tensile strength.
Coated Fabric for Converting and Composite Applications
Emulsion-coated fabrics supplied as substrates for lamination, secondary coating, mastic application or pultrusion, where residual moisture and volatiles can generate porosity, blistering or interfacial defects in the finished part.
Testing Items
Depending on the product specification and the purpose of the evaluation, volatile content determination is typically reported alongside the following related characteristics:
- Volatile matter content of the coated fabric, determined by oven drying at 105 °C ± 2 °C
- Moisture content of the fabric in accordance with ISO 3344 (reinforcement products — determination of moisture content)
- Combustible matter (organic coating) content by loss on ignition in accordance with ISO 1887
- Mass per unit area of the coated fabric in accordance with ISO 3374, reported on both as-received and dry bases
- Total volatiles at elevated drying temperatures, for example 160 °C to 180 °C, where specified for particular emulsion systems
Testing Methods
Principle
The test is a gravimetric determination. A conditioned specimen of known mass is heated in a ventilated oven at a specified temperature for a specified time, cooled to ambient temperature in a desiccator, and reweighed. The loss in mass, expressed as a percentage of the original specimen mass, is the volatile content.
Apparatus and Reagents
- Forced-ventilation laboratory oven capable of maintaining 105 °C ± 2 °C, and optionally 160 °C to 180 °C
- Analytical balance with a resolution of 0.1 mg
- Desiccator with fresh silica gel or an equivalent drying agent
- Clean, pre-dried weighing containers or glass watch covers
- Cutting template or shears for preparing specimens, and a ruler accurate to 1 mm
Sampling and Specimen Preparation
- Take samples at least one meter from the end of the roll and from positions distributed across the fabric width to account for cross-width drying variation
- Prepare a minimum of three specimens per sample, each approximately 100 mm × 100 mm or of at least 2 g mass
- Handle specimens with clean gloves or tweezers to prevent contamination, and avoid cutting through heavily coated edges that do not represent the bulk fabric
- Condition specimens in accordance with ISO 291 where the governing specification requires a defined pre-test atmosphere
Procedure
- Dry the weighing container in the oven, cool it in the desiccator and record its mass (m0)
- Place the specimen in the container and weigh to 0.1 mg (m1)
- Heat in the oven at 105 °C ± 2 °C for 1 hour, or until constant mass is reached, defined as a change of no more than 0.1 percent between successive 30-minute drying cycles
- Transfer the covered specimen to the desiccator and cool to room temperature, typically 30 to 60 minutes
- Reweigh the cooled specimen promptly to minimize moisture re-absorption (m2)
Calculation and Expression of Results
The volatile content V is calculated as V = (m1 − m2) / (m1 − m0) × 100, where m0 is the mass of the container, m1 is the mass of the container plus the specimen before drying, and m2 is the mass after drying. The result is reported as the arithmetic mean of all valid specimens, rounded to 0.01 percent, together with the drying temperature and duration. If the specification requires total volatiles of the polymer coating, an elevated drying temperature of 160 °C to 180 °C may be applied, but results are temperature-dependent and must never be compared across different test conditions.
Related Determinations
To distinguish absorbed moisture from coating-derived volatiles, moisture content can be determined separately following ISO 3344, and the combustible organic matter can then be measured by igniting the dried specimen at approximately 625 °C in accordance with ISO 1887. The combination of volatile content, ignition loss and mass per unit area per ISO 3374 provides a complete picture of emulsion pick-up and drying efficiency. General coated-fabric conditioning and test practice follows ASTM D751 and the relevant GB/T 9914 series methods for glass fiber reinforcement products.
Applications
- Production quality control of emulsion drying lines for glass fiber wallcovering and mesh fabric
- Verification of coating mass consistency and emulsion pick-up in ETICS/EIFS reinforcement mesh manufacturing
- Incoming inspection by converters, laminators and printers who require stable, dry substrate surfaces
- Trade and contractual weight verification, since volatile content directly affects the as-delivered mass of the roll
- Research and development of emulsion formulations, drying curves and coating add-on optimization
- Compliance testing against wallcovering, mesh and coated-fabric product specifications by accredited third-party laboratories
FAQ
Why is 105 °C the standard drying temperature?
At 105 °C ± 2 °C, absorbed water and residual emulsion moisture are removed completely and rapidly, while the organic coating and the glass filaments remain thermally stable. Higher temperatures risk beginning to evolve coating decomposition products, which would overstate the volatile content.
What is a typical acceptance limit for volatile content?
Many wallcovering and mesh specifications limit volatile content to below 1 percent of the fabric mass, with some products controlled between 0.5 and 2 percent depending on the coating system. The governing product standard or purchase agreement always defines the applicable limit.
How does volatile content differ from moisture content?
Moisture content per ISO 3344 measures only absorbed water, whereas volatile content measured at elevated temperature also includes residual process volatiles from the emulsion. For fully water-based emulsions dried at 105 °C, the two values are usually very close.
How does volatile content differ from combustible matter content?
Volatile content is the low-temperature mass loss associated with moisture and volatiles, while combustible matter content determined by ignition at about 625 °C per ISO 1887 measures the total organic coating burnt off the glass fabric. The two tests are complementary and are often performed in sequence on the same sample.
How many specimens are required?
A minimum of three specimens taken across the fabric width is recommended so that cross-width drying variation is captured. Additional specimens improve the precision of the mean and are advisable for arbitration testing or borderline results.
Can the test be performed at higher temperatures?
Yes, where a specification defines total volatiles for a heat-resistant coating, drying at 160 °C to 180 °C may be specified. The temperature, time and calculation basis must be reported with the result, because volatile content values are only comparable when determined under identical conditions.