Solid content testing in accordance with Chinese national standards (GB) is a fundamental quality control procedure for coatings, adhesives, polymer emulsions, and printing inks, quantifying the non-volatile fraction of a product through gravimetric oven-drying methods such as GB/T 1725, GB/T 2793, and GB/T 11175. Accurate solids data underpin formulation control, VOC compliance with mandatory Chinese limit standards, and fair commercial settlement between manufacturers and buyers. This article explains the applicable GB standards, sample types, testing items, procedural details, and frequently asked questions related to GB-based solid content determination.
Technical Overview
Solid content, also referred to as non-volatile matter content or total solids, expresses the mass percentage of a liquid or paste-form product that remains after water and organic solvents have been evaporated under controlled heating conditions. Because solid content directly determines film-forming capability, spreading rate, formulation cost, and volatile organic compound (VOC) emissions, it is one of the most frequently specified quality parameters for liquid chemical products in the Chinese market.
Chinese national standards (GB standards) establish gravimetric determination methods for solid content across different product categories. Although the specific temperature and drying time vary by standard and product type, the core principle is identical: a weighed test portion is heated in a conditioned dish until volatile components are removed, and the mass of the dry residue is used to calculate the solid fraction. The principal GB standards include:
- GB/T 1725-2007, Paints, varnishes and plastics - Determination of non-volatile-matter content, harmonized with ISO 3251, applicable to coatings, resins, and plastics.
- GB/T 2793-1995, Determination of non-volatile matter content of adhesives, applicable to water-based, solvent-based, and reactive adhesives.
- GB/T 11175-2002, Test methods for synthetic resin emulsions, applicable to acrylic, styrene-acrylic, vinyl acetate, and other polymer dispersions.
- GB/T 14074-2017, Wood adhesives - Terminology and test methods, covering urea-formaldehyde, phenol-formaldehyde, and related aminoplast adhesives.
- GB/T 8298, Concentrated natural rubber latex - Determination of total solids content, aligned with ISO 124.
For comparison and international trade, the gravimetric results obtained under these GB methods are generally consistent with those obtained under ISO 3251 and ASTM D2369, provided that equivalent heating conditions are agreed upon by the interested parties.
Testing Samples
Accredited third-party laboratories performing GB-based solid content testing typically accept the following categories of samples. Representative sampling in accordance with standards such as GB/T 3186 for liquid paints is essential, since stratification or bubble entrapment can bias results significantly.
Coatings and Paints
Waterborne and solvent-borne architectural coatings, industrial protective coatings, wood coatings, automotive refinish coatings, powder coating binders, and resin solutions. Non-volatile matter determination for these products follows GB/T 1725-2007.
Adhesives and Sealants
Water-based emulsion adhesives, solvent-based contact adhesives, hot-melt adhesives, polyurethane adhesives, and formaldehyde-based wood adhesives. Testing is performed to GB/T 2793-1995 or GB/T 14074-2017 depending on the product family.
Polymer Emulsions and Dispersions
Styrene-butadiene latex, pure acrylic emulsion, vinyl acetate-ethylene copolymer dispersions, epoxy emulsions, and other synthetic resin emulsions used as raw materials for coatings, textiles, and paper, tested to GB/T 11175-2002.
Printing Inks
Waterborne and solvent-borne liquid inks, energy-curable ink systems, and ink binders, for which non-volatile matter data support VOC compliance and print consistency evaluations.
Other Liquid Chemical Products
Textile finishing agents, paper coating chemicals, leather finishing agents, detergent and cleaning formulations, agricultural emulsifiable concentrates, and natural rubber latex, each tested under the applicable product-specific GB method.
Testing Items
GB-based solid content testing programs commonly cover the following measurable items, which may be requested individually or as a combined analytical package:
- Total solid content (non-volatile matter content), expressed as mass percentage.
- Volatile matter content, calculated as the complement of the solid content.
- Water content by Karl Fischer titration to GB/T 6283, used to separate water from organic volatiles in VOC calculations.
- Density of the liquid product, tested to GB/T 6750 or equivalent, to support conversion between mass solids and volume solids.
- VOC content, determined or calculated in accordance with GB/T 23985, GB/T 23986, or GB/T 34682, using solid content as an input value.
- Volume solids of coatings by dry film density measurement to GB/T 9272, used to estimate theoretical spreading rate.
Testing Methods
Oven-Drying Gravimetric Method
The primary GB method is the oven-drying gravimetric procedure. A clean weighing dish of aluminum, glass, or stainless steel is dried, cooled in a desiccator, and weighed on an analytical balance with a resolution of 0.1 mg. A test portion, typically between 0.2 g and 1.0 g depending on the standard and expected solids level, is distributed evenly over the base of the dish and weighed immediately to minimize evaporation losses. The dish is then placed in a forced-convection oven controlled within plus or minus 2 degrees Celsius of the specified temperature and heated for the prescribed duration, or to constant mass for standards that require it.
After heating, the dish is cooled to ambient temperature in a desiccator over desiccant and weighed again. The solid content is calculated as:
Solid content (%) = (m2 - m0) / (m1 - m0) x 100, where m0 is the mass of the empty dish, m1 is the mass of the dish plus the test portion before heating, and m2 is the mass of the dish plus the dry residue after heating. Duplicate determinations are performed, and the reported result is the arithmetic mean. Results should agree within the repeatability limits defined by the governing standard, which for most coatings and emulsions corresponds to an absolute difference of less than 0.5 percentage points.
Temperature and Time Parameters
Heating conditions must match the product and the governing standard:
- 105 degrees Celsius plus or minus 2 degrees Celsius is the default condition for most waterborne coatings, adhesives, and emulsions, with a typical holding time of 30 to 60 minutes.
- Elevated temperatures such as 125 or 150 degrees Celsius may be agreed between interested parties for solvent-borne products to shorten drying time, provided no thermal decomposition occurs.
- Adhesive standards based on constant-mass criteria require repeated weighing cycles until the change between successive weighings falls below the specified threshold.
- Vacuum-oven drying at reduced temperature is reserved for heat-sensitive materials such as certain polymer dispersions to prevent degradation of the residue.
Equipment and Quality Control
Essential equipment includes an analytical balance readable to 0.1 mg, a calibrated forced-convection oven with temperature uniformity within plus or minus 2 degrees Celsius, a desiccator with fresh desiccant, and conditioned disposable dishes. Accredited laboratories operating to ISO/IEC 17025 verify the balance and oven against calibrated references at defined intervals, run certified reference materials or in-house control samples alongside client samples, and document all weighing steps to ensure traceability.
Complementary Rapid Methods
For in-process quality control, infrared or halogen drying balances provide solids results within minutes and are widely used as fast screening tools. However, because their heating profile differs from a conventional oven, GB standard methods remain the referee procedure for disputes, type testing, and regulatory VOC submissions.
Applications
GB-based solid content testing results are used across the entire product lifecycle:
- Manufacturing quality control, verifying batch-to-batch consistency of emulsions, coatings, and adhesives against internal or contractual specifications.
- Regulatory VOC compliance, since solid content and water content are direct inputs to VOC calculations under mandatory limit standards such as GB 18581, GB 18582, GB 24409, GB 30981, GB 33372, and GB 38507.
- Formulation research and development, quantifying how binder loading, filler addition, and solvent levels affect the non-volatile fraction.
- Incoming material inspection, allowing downstream manufacturers to confirm that purchased raw materials meet declared solids specifications.
- Commercial settlement and customs purposes, where the price or duty basis of a product is tied to its non-volatile content.
- Comparison and benchmarking of products, since solids data normalize performance metrics such as hardness, coverage, and bond strength.
FAQ
What is the difference between solid content and non-volatile matter?
The two terms are used interchangeably in GB standards. Both describe the mass fraction of material remaining after volatile components, mainly water and organic solvents, are evaporated under specified heating conditions. The result is always conditional on the test temperature and time, which is why the applicable standard must be cited in the test report.
Which GB standard applies to my product?
Coatings, resins, and plastics are tested to GB/T 1725-2007; adhesives to GB/T 2793-1995 or GB/T 14074-2017 for wood adhesives; synthetic resin emulsions to GB/T 11175-2002; and natural rubber latex to GB/T 8298. Product-specific standards take precedence where they exist, and accredited third-party laboratories can confirm the correct method during technical review of the sample.
How much sample is required and how is it prepared?
A single determination normally consumes 1 gram or less, but laboratories typically request 50 to 100 grams of homogeneous sample to allow duplicate testing, moisture measurement, and repeat analysis if required. The sample should be mixed thoroughly without entraining air, and solvent-bearing samples should be sealed in airtight containers to prevent solvent loss before testing.
How accurate are the results?
With a 0.1 mg balance and properly controlled oven conditions, the repeatability of duplicate determinations is generally better than 0.5 percentage points in absolute terms for products in the common 20 to 70 percent solids range. Uncertainty increases for very low solids samples due to the small residue mass, so a larger test portion is recommended in such cases.
How does solid content relate to VOC compliance?
For most products, VOC content is derived from the relationship VOC = 100 - non-volatile matter - water content. Because solid content is measured gravimetrically and water content is measured by Karl Fischer titration to GB/T 6283, an accurate solids value is a prerequisite for demonstrating compliance with the mandatory Chinese VOC limit standards.
What is included in a typical test report and how long does testing take?
A compliant report identifies the applied GB standard, the heating temperature and time, sample identification, individual and mean results, and the dates of testing. Routine solid content determinations are usually completed within three to five working days, and reports issued by laboratories accredited to ISO/IEC 17025 are widely accepted for regulatory submission and commercial disputes.