Solid Content Analysis Report: Methods, Standards, and Applications

A solid content analysis report provides essential data on the non-volatile fraction of coatings, adhesives, polymers, and chemical formulations, serving as a cornerstone for quality control and regulatory compliance. This technical article explains the testing principles, internationally recognized standards such as ISO 3251, ASTM D2369, and GB/T 1725, sample types, and practical applications of solid content determination in industrial laboratories.

A solid content analysis report provides essential data on the non-volatile fraction of coatings, adhesives, polymers, and chemical formulations, serving as a cornerstone for quality control and regulatory compliance. This technical article explains the testing principles, internationally recognized standards such as ISO 3251, ASTM D2369, and GB/T 1725, sample types, and practical applications of solid content determination in industrial laboratories.

Technical Overview

Solid content, also referred to as non-volatile content or solids by weight, is defined as the mass percentage of residue remaining after a sample has been heated under specified conditions to remove all volatile components, including water, solvents, and other evaporable substances. The solid content analysis report documents the measured value, the test method applied, and the experimental conditions, providing manufacturers with a quantitative basis for formulation control, cost calculation, and batch-to-batch consistency verification.

The significance of solid content determination extends across the entire production chain. For waterborne coatings, the solid-to-water ratio directly influences viscosity, film thickness, drying time, and final mechanical properties. For adhesives and sealants, the non-volatile fraction determines coverage rate, bond line formation, and shrinkage behavior after curing. In addition, solid content data is a required input for calculating volatile organic compound (VOC) emissions in accordance with environmental regulations and ecolabel requirements. Because the result depends on the drying temperature, dwell time, and sample mass, the analysis report must always reference the applicable standard so that values can be compared meaningfully between laboratories.

Testing Samples

Accredited third-party laboratories accept a broad range of liquid, paste-like, and dispersion samples for solid content analysis. Proper sampling and pre-treatment, such as homogenization and moisture-tight sealing, are essential to ensure representative results.

Coatings and Paints

Waterborne and solvent-borne architectural paints, industrial coatings, automotive refinish coatings, powder coating raw materials, and primers. These products typically contain resins, pigments, fillers, additives, and carriers whose proportions must be tightly controlled.

Adhesives and Sealants

Pressure-sensitive adhesives, hot-melt adhesives, water-based emulsion adhesives, silicone sealants, and polyurethane systems. Solid content affects open time, tack, and final bond strength.

Polymer Dispersions and Emulsions

Styrene-butadiene latex, acrylic emulsions, vinyl acetate dispersions, polyurethane dispersions, and epoxy emulsions used as raw materials for downstream formulation. For these materials, solid content is a key purchase specification.

Inks and Printing Materials

Liquid printing inks, inkjet formulations, and coating liquids where the non-volatile fraction determines transfer efficiency, color density, and film formation on substrates.

Other Chemical Products

Cleaning agents, textile auxiliaries, paper chemicals, construction chemicals such as concrete admixtures, and cosmetic or agrochemical suspensions where residual mass after evaporation is a quality parameter.

Testing Items

A comprehensive solid content analysis report typically covers the following measurable parameters:

• Total solid content (non-volatile matter content), expressed as mass fraction in percent
• Volatile content, calculated as 100 percent minus the solid content, representing evaporable substances
• Water content, where applicable, determined separately by coulometric or volumetric Karl Fischer titration
• Residual solvent content for solvent-borne systems, derived from gravimetric data and gas chromatographic confirmation when required
• Density and weight-per-volume solids, used to convert between mass-based and volume-based solid fractions
• Drying loss behavior at multiple temperature setpoints to evaluate thermal sensitivity of the sample
• Repeatability and reproducibility statistics derived from replicate determinations as required by the applicable standard

Testing Methods

Several standardized techniques exist for solid content determination, and the choice depends on the sample matrix, expected volatility range, and required turnaround time. All gravimetric methods share the same basic principle: a weighed quantity of sample is dispersed into a preconditioned dish, heated to evaporate volatiles, cooled in a desiccator, and reweighed. The solid content is calculated from the mass ratio of dry residue to original sample.

Oven Drying Method

The conventional oven method is performed according to ISO 3251, ASTM D2369, and GB/T 1725. A sample of typically 1 to 3 grams is distributed in an aluminum or glass dish, optionally with a lid to prevent splattering, and dried at 105 degrees Celsius for waterborne products or 150 to 160 degrees Celsius for high-solids and solvent-borne systems. Drying continues until constant weight is achieved, usually within 30 to 60 minutes. This method delivers high accuracy and is the reference procedure for most coating and dispersion matrices.

Infrared and Halogen Rapid Drying Method

Infrared moisture analyzers equipped with halogen lamps reduce analysis time to 5 to 15 minutes by applying direct radiant energy to the sample. The method is widely used for in-process quality control after calibration against the oven reference method. Internal halogen balances provide automatic endpoint detection and direct percentage readout.

Vacuum Drying Method

For heat-sensitive materials such as certain polymer dispersions, biochemical formulations, or products containing reactive components, drying is carried out under reduced pressure at lower temperatures. This approach minimizes thermal degradation while still achieving complete volatile removal, in line with procedures described in GB/T 2793 for adhesives.

Microwave Drying Method

Microwave-assisted drying heats the sample volumetrically and is suitable for high-throughput screening of aqueous systems. It requires method-specific calibration because dielectric heating can cause localized overheating in inhomogeneous samples.

Karl Fischer Titration for Selective Water Determination

When the volatile fraction consists predominantly of water, Karl Fischer titration according to ISO 760 or GB/T 6283 provides a selective and precise measurement of moisture content. Combining Karl Fischer water data with total volatile data allows the analyst to distinguish water from organic solvents, which is essential for VOC declaration purposes.

Calculation and Reporting

The solid content is computed as the ratio of residual mass to initial sample mass multiplied by 100. The final report states the standard applied, drying temperature and duration, number of replicates, individual and mean results, and measurement uncertainty. Results from duplicate determinations must agree within the repeatability limits defined by the cited standard, typically a fraction of one percent absolute for well-homogenized samples.

Applications

Solid content analysis reports support decision-making in diverse industrial scenarios:

• Raw material incoming inspection for emulsions, resins, and dispersions purchased against contractual solid content specifications
• Production quality control in coating, adhesive, and ink plants to monitor batch consistency and detect formulation drift
• VOC and hazardous air pollutant calculations required for environmental compliance, ecolabel certification, and product safety data sheets
• Cost and yield optimization, since pricing of polymer dispersions and coatings is conventionally based on delivered solids rather than total wet mass
• Formulation development, where solids adjustment governs application solids, film build, and dilution ratios
• Shelf-life studies and stability testing, tracking changes in volatile balance during accelerated aging
• Customs and trade verification, where declared solid content affects tariff classification of chemical products
• Research and development benchmarking of waterborne versus solvent-borne technologies for sustainability programs

FAQ

What is a normal solid content range for common products?

Typical values vary widely by product category. Waterborne architectural coatings generally fall between 30 and 60 percent solids, polymer dispersions between 40 and 65 percent, high-solids industrial coatings between 60 and 85 percent, and solvent-borne lacquers as low as 20 percent. The analysis report should always be interpreted against the product specification.

Why do different test standards give different solid content values for the same sample?

Drying temperature and duration influence whether low-molecular-weight components, trapped solvents, or thermally labile additives evaporate or decompose. A method drying at 160 degrees Celsius may release volatiles that remain at 105 degrees Celsius. For comparability, always use results obtained under the same standard and conditions.

How much sample is required for a solid content test?

Most gravimetric methods require only 1 to 5 grams per determination, with at least duplicate measurements recommended. Laboratories generally request 20 to 50 grams of homogenized sample to allow repeats, cross-checks, and confirmatory testing.

Can solid content be used to calculate VOC content directly?

Not by itself. VOC content is derived from total volatile matter combined with water content, density, and exempt-compound data. Standards such as ASTM D3960 describe the calculation sequence. A complete solid content analysis report therefore often includes companion water and density measurements to enable compliant VOC reporting.

How long does a typical analysis take?

Rapid infrared or halogen methods deliver results within 15 minutes per sample, while reference oven methods require 1 to 3 hours including conditioning and cooling. Full accredited laboratory reports with replicate determinations are usually issued within three to five working days.

What factors can cause inaccurate results?

Common error sources include skin formation on the sample surface that traps volatiles, splattering during heating, insufficient homogenization, moisture pickup during weighing, and residue loss during handling. Using covered dishes, dispersing the sample in a compatible solvent, and following the specified drying profile minimize these risks.