Solid content testing standards define the gravimetric procedures used to determine the non-volatile matter content of paints, coatings, adhesives, polymer emulsions, and printing inks. By following established methods such as ISO 3251, ASTM D2369, and GB/T 1725, manufacturers can verify formulation consistency, calculate VOC compliance, and control production quality. This article summarizes the applicable standards, sample types, testing items, test procedures, calculation methods, and typical industrial applications of solid content determination.
Technical Overview
Solid content, also known as non-volatile matter content or total solids, expresses the mass percentage of a liquid or paste-like material that remains as residue after volatile components such as water, organic solvents, and other evaporating substances are removed under controlled heating conditions. Together with density, viscosity, and grind fineness, it is one of the core specification parameters for coatings, adhesives, and dispersions, directly governing wet-film thickness, coverage rate, application behavior, formulation cost, and VOC declarations.
The measurement principle is straightforward gravimetry: a known mass of specimen is heated in a preconditioned dish until the volatiles evaporate, the residue is cooled in a desiccator and reweighed, and the mass ratio of residue to original specimen is reported as solid content. Because the measured value is sensitive to drying temperature, heating time, specimen mass, and evaporation surface area, results are only comparable between laboratories when the exact conditions of a published standard method are followed.
The most widely recognized solid content testing standards published by international and national standards organizations include:
- ISO 3251 / EN ISO 3251 - Paints, varnishes and plastics; determination of non-volatile-matter content, including polymer dispersions
- ASTM D2369 - Standard Test Method for Volatile Content of Coatings, commonly mandated in North American coating specifications
- GB/T 1725 - Chinese national standard for determination of non-volatile matter in paints, varnishes, and plastics, technically aligned with ISO 3251
- GB/T 2793 - Determination of non-volatile content of adhesives
- GB/T 6751 - Determination of volatile and non-volatile matter of paints and varnishes
- ASTM D3960 - Standard practice for determining volatile organic compound content of paints and related coatings from solids and water data
Testing Samples
Solid content testing is applicable to a broad range of liquid and paste-form materials. Typical sample categories submitted to accredited third-party laboratories include the following:
Liquid Coatings and Varnishes
Waterborne and solvent-borne architectural paints, industrial coatings, primers, and clear finishes. Specimen masses are typically around 1 g per ISO 3251 or GB/T 1725, or approximately 0.3 g per ASTM D2369, with drying performed at 105 to 110 °C under the prescribed schedules.
Polymer Dispersions and Emulsions
Acrylic, vinyl acetate, styrene-butadiene, and polyurethane dispersions used as binders. Samples should be gently homogenized before subsampling to avoid shear coagulation and to ensure representative results.
Adhesives and Sealants
Waterborne and solvent-borne adhesives, reactive prepolymers, and sealant pastes, generally tested in accordance with GB/T 2793 or a client-specified oven program.
Printing Inks
Liquid inks and energy-curable ink systems, where the drying temperature must be selected carefully to avoid thermal degradation or premature reaction of reactive monomers.
Resin Solutions and Intermediates
Alkyd, acrylic, epoxy, and polyester resin solutions tested for formulation control, incoming inspection, and batch release.
Functional Slurries and Pastes
Lithium-battery electrode slurries, ceramic slurries, textile and papermaking auxiliaries, and other specialty materials, often requiring solvent dispersion and material-specific bake schedules.
For sample submission, approximately 20 to 50 g of each material should be supplied in clean, airtight containers, clearly labeled and protected from premature volatile loss, contamination, and temperature extremes. Homogeneous mixing before subsampling is essential, particularly for pigmented or filled systems prone to settling.
Testing Items
Core test items reported under solid content testing standards typically include:
- Non-volatile matter (solid) content, expressed as percent by mass
- Volatile matter content, calculated as 100 percent minus the solid content
- Mass loss on drying under a specified temperature and time program
- Supporting water content determination, where required for VOC calculations
Testing Methods
Oven Gravimetric Method (ISO 3251 / GB/T 1725)
A glass, metal, or ceramic dish is preconditioned to constant mass and weighed. A specimen of approximately 1 g is weighed into the dish to the nearest 0.1 mg and distributed evenly; waterborne samples may be dispersed with a small amount of water to prevent skin formation, and solvent-borne samples with a suitable volatile solvent. The dish is heated in a ventilated oven, commonly at 105 ± 2 °C for 60 minutes, or under another agreed program such as 150 °C for heat-stable systems. After cooling in a desiccator, the residue is reweighed, and drying cycles are repeated to essentially constant mass where specified.
ASTM D2369 Method
A specimen of 0.3 ± 0.1 g is weighed into a preconditioned shallow aluminum dish and dispersed with an appropriate volatile solvent to maximize the evaporation surface. The assembly is heated at 110 ± 5 °C for 60 ± 2 minutes, cooled in a desiccator, and weighed. The volatile content is calculated, and solid content is obtained as the complementary value. This method is widely referenced for coating VOC determinations in combination with ASTM D3960.
Adhesive Oven Method (GB/T 2793)
A specimen of approximately 1 g is weighed into a low-form weighing bottle and dried at the temperature specified in the relevant product standard, commonly around 105 °C, until essentially constant mass is reached. The method is applied to waterborne, solvent-borne, and hot-melt adhesive materials.
Rapid Moisture Analyzer Method
Infrared and halogen-heated moisture analyzers provide fast, single-instrument results suitable for in-process quality control. Drying temperatures and automatic shutoff criteria must be correlated and validated against the referee oven method for each material, since different energy transfer mechanisms can shift results by several tenths of a percent.
Vacuum and Low-Temperature Drying
For heat-sensitive or oxidation-prone materials such as certain latexes and bio-based binders, drying under reduced pressure at 40 to 60 °C minimizes thermal degradation and avoids bias from decomposition weight loss.
Calculation and Precision
The non-volatile matter content is calculated as w = 100 × (m2 − m0) / (m1 − m0), where m0 is the mass of the empty dish, m1 is the mass of the dish plus specimen before drying, and m2 is the mass of the dish plus residue after drying. Results are reported to 0.1 percent, or to 0.01 percent where tighter specification limits apply, together with the drying temperature and duration used. Repeatability under a single operator is typically within about ±0.5 percent absolute for homogeneous liquids, while reproducibility between laboratories is generally within approximately ±1 percent absolute, depending on the material and the standard applied.
Applications
Solid content data generated under these standards support quality control, commercial settlement, and regulatory compliance across many industries. Accredited third-party laboratories routinely perform these tests as part of product certification, supplier verification, and batch release programs.
- Coating manufacture and incoming material inspection - verifying solids against supplier certificates of analysis and formulation constants
- VOC regulatory compliance - deriving VOC content from solids and water data in accordance with practices such as ASTM D3960 and applicable national emission regulations
- Adhesive and sealant formulation control - solids govern spread rate, open time, curing behavior, and cost efficiency
- Emulsion polymerization plants - monitoring reactor endpoints and batch-to-batch consistency
- Battery and electronics materials - controlling solids stability of electrode slurries, which affects coated mass loading and cell performance
- Commercial and customs purposes - pricing and declaration of materials on a non-volatile solids basis
FAQ
What is the difference between solid content and non-volatile matter?
The two terms are effectively synonymous and describe the residue remaining after heating under the prescribed conditions. ISO and ASTM methods favor the term non-volatile matter, while solid content is the more common industrial usage. The value is operationally defined, meaning it depends on the drying temperature and time specified by the chosen standard.
Which standard should be selected for testing?
Selection depends on the product specification and target market. ISO 3251, EN ISO 3251, or GB/T 1725 are appropriate for paints, varnishes, plastics, and polymer dispersions; ASTM D2369 is typically required by North American coating specifications; GB/T 2793 applies to adhesives. When a purchase agreement cites a specific standard, that method should govern.
What drying temperature and time are used?
Common conditions are 105 ± 2 °C for 60 minutes under ISO 3251 and GB/T 1725, or 110 ± 5 °C for 60 ± 2 minutes under ASTM D2369. Product standards may prescribe alternative programs, such as 150 °C baking for high-temperature-resistant systems, and these must be reported together with the result.
How much sample is required and how long does testing take?
A submission of approximately 20 to 50 g per material is normally sufficient, including material for repeat determinations. The laboratory test itself, including conditioning, drying, cooling, and weighing, is typically completed within a few hours, with same-day or next-day reporting being standard practice.
Can a moisture analyzer replace the standard oven method?
Moisture analyzers are widely used for rapid routine quality control once their drying parameters have been validated against the oven method for the specific material. The standard oven gravimetric procedure remains the referee method for certification, disputes, and formal reporting.
How is solid content related to VOC content?
For waterborne coatings, VOC content is derived from the solid content and water content, for example VOC = 100 − solids − water on a mass basis, with density conversions applied where required. Accurate solid content determination is therefore a prerequisite for reliable VOC compliance declarations under practices such as ASTM D3960 and applicable national regulations.