Determination of Volatile Matter and Moisture Content in Materials: Principles, Methods, and Standar

Determination of volatile matter and moisture content is a fundamental physicochemical testing service for evaluating the composition, purity, and processing suitability of polymeric, inorganic, and chemical materials. By applying gravimetric, Karl Fischer, and thermogravimetric techniques in accordance with international standards such as ISO, ASTM, and GB, accredited third-party laboratories can quantify moisture and volatile fractions with high accuracy. This article presents the technical principles, applicable sample types, test items, standard methods, industrial applications, and frequently asked questions related to volatile matter and moisture determination.

Technical Overview

Volatile matter and moisture content are two critical quality parameters that directly influence the performance, processability, shelf life, and safety of industrial materials. Moisture refers specifically to water molecules that are physically adsorbed on or absorbed within a material, whereas volatile matter is a broader gravimetric term covering all mass lost under defined heating conditions, including residual solvents, monomers, plasticizers, oligomers, low-molecular-weight additives, and water. Because the two parameters overlap in definition yet differ in analytical intent, laboratories apply distinct measurement strategies for each.

Moisture determination is typically performed by Karl Fischer titration (volumetric or coulometric), which selectively reacts with water, or by rapid gravimetric drying using halogen or infrared moisture analyzers. Volatile matter determination is generally performed by controlled heating in a ventilated oven, muffle furnace, or thermogravimetric analyzer (TGA), followed by precise weighing of the mass loss. Method selection depends on the matrix, expected concentration range, required accuracy, and applicable product specification.

Excessive moisture or volatile content can cause serious defects: hydrolytic degradation during melt processing of polyesters such as PET and PA, bubbles and voids in injection-molded or extruded parts, reduced dielectric strength in electronic encapsulants, poor adhesion in coatings and adhesives, electrolyte side reactions in lithium battery materials, and inaccurate dosing in pharmaceutical powders. Quantitative determination is therefore essential for incoming material inspection, process control, outgoing quality assurance, and failure analysis.

Testing Samples

Plastics and Polymeric Resins

Thermoplastic pellets, engineering resins (PA6, PA66, PC, PBT, PET, POM), polyolefins (PE, PP), styrenics (PS, ABS), fluoropolymers (PTFE, FEP), and thermosetting molding compounds. Moisture control is especially critical for hygroscopic polyesters and polyamides prior to injection molding or extrusion, in line with ISO 15512 and ASTM D4019.

Rubber and Elastomers

Raw natural rubber, synthetic rubbers (SBR, NBR, EPDM, butyl rubber), rubber compounds, and vulcanizates. Volatile-matter content is commonly determined per ISO 248 and ASTM D5668, using hot-mill or oven procedures.

Chemical Powders and Fillers

Carbon black, silica, calcium carbonate, talc, titanium dioxide, alumina, and other mineral fillers, as well as pigment and dye powders. These materials are tested for moisture and volatiles to ensure consistent dispersion and formulation accuracy.

Adhesives, Sealants, and Coatings

Epoxy, polyurethane, silicone, and acrylic systems in liquid, paste, film, or cured form. Residual solvent and moisture levels affect curing behavior, pot life, bond strength, and VOC compliance.

Battery and Electronic Materials

Cathode and anode active materials, binders, separator films, electrolyte solvents, encapsulation resins, and solder powders, where trace moisture must often be controlled below tens of parts per million.

Fuels, Coal, and Coke

Hard coal, brown coal, coke, and biomass pellets, for which proximate analysis (moisture, ash, volatile matter, fixed carbon) is standardized in ISO 562, ISO 11722, ASTM D3173, ASTM D3175, and GB/T 212.

Pharmaceutical, Food, and Agricultural Materials

Active pharmaceutical ingredients, excipients, lyophilized products, food powders, starches, and grains, tested for water content under pharmacopeial and food-safety frameworks such as loss on drying and Karl Fischer methods.

Testing Items

Typical measurable parameters include:

• Moisture (water) content, expressed as mass fraction or parts per million (ppm)
• Volatile matter content under specified temperature, time, and atmosphere
• Loss on drying (LOD) and total mass loss
• Residual solvent and residual monomer content (combined volatile fraction)
• Thermogravimetric mass-loss profiles as a function of temperature
• Water content by coulometric Karl Fischer for trace-level analysis
• Moisture absorption or saturation values for hygroscopic polymers
• Volatile matter in proximate analysis of coal and solid fuels

Reporting generally includes the measured value, measurement uncertainty, sample conditioning, drying or titration conditions, and the specific standard method applied.

Testing Methods

Oven Drying (Loss on Drying)

The sample is dried to constant mass in a ventilated or vacuum oven at a specified temperature (commonly 105 °C, with material-specific variants), and the moisture or volatile content is calculated from the mass difference. This gravimetric approach is simple, robust, and widely standardized in GB/T 6284, ASTM D2216, and ISO 287 for paper and board. It is best suited for concentrations above approximately 0.1% and for matrices that are thermally stable at the drying temperature.

Karl Fischer Titration (Volumetric and Coulometric)

Karl Fischer titration is the reference technique for selective water determination. Volumetric KF handles water levels from roughly 0.01% to 100%, while coulometric KF extends sensitivity to the microgram and ppm range. Samples may be dissolved directly in the KF cell or heated in a Karl Fischer oven, with the evolved water carried into the titration cell by a dry carrier gas. Key standards include ISO 760, ASTM E203, ASTM D6869, ASTM D4019, ISO 15512, and GB/T 6283. The oven-KF technique is particularly valuable for insoluble or matrix-interfering samples such as polymer pellets and battery powders.

Thermogravimetric Analysis (TGA)

TGA continuously records sample mass while the temperature is ramped under nitrogen, air, or oxygen, producing a mass-loss curve from which moisture, volatiles, and decomposition onset can be resolved. It requires only milligram-scale samples and is governed by ASTM E1131, ASTM E1868, and ISO 11358. TGA is the method of choice when overlapping thermal events must be separated or when only limited sample material is available.

Rapid Moisture Analyzers (Halogen and Infrared Drying)

Benchtop halogen or infrared moisture balances combine radiant heating with an integrated precision balance, delivering results in minutes. They are widely used for in-process quality control of powders, granules, and foodstuffs and are calibrated against oven methods under ASTM D6980-type procedures.

Hot-Mill and Refining Methods for Rubber

For raw rubber, volatile matter is determined by passing the sample through a heated mill or by heating thin sheets in an oven, following ISO 248-1, ASTM D5668, and related national methods. These procedures drive off moisture and other volatiles while preventing degradation.

Azeotropic (Dean-Stark) Distillation

The sample is refluxed with a water-immiscible solvent such as toluene or xylene, and the distilled water is collected and measured in a calibrated trap. This method is suitable for materials containing substantial free water and is referenced in ASTM D95 and GB/T 260.

Standard Reference Portfolio

• ISO 15512 / ASTM D4019 — water content of plastics
• ISO 760 / ASTM E203 / GB/T 6283 — Karl Fischer determination of water
• ISO 248-1 / ASTM D5668 — volatile matter of rubber
• ISO 562 / ASTM D3175 / GB/T 212 — volatile matter of coal and coke
• ISO 11722 / ASTM D3173 / GB/T 211 — moisture in coal analysis samples
• ASTM E1131 / ISO 11358 — thermogravimetric compositional analysis
• GB/T 6284 / ASTM D2216 — determination of water content by drying
• ASTM D95 / GB/T 260 — water by distillation

Applications

Determination of volatile matter and moisture content supports a broad range of industrial and regulatory scenarios:

• Incoming inspection and supplier qualification of polymer resins, rubber bales, fillers, and additives
• Pre-drying verification for injection molding, extrusion, and compounding of PET, PA, PC, and PBT to prevent hydrolysis and silver-streak defects
• Quality control of lithium battery materials, where trace moisture correlates with gas generation, capacity fade, and electrolyte decomposition
• Electronic packaging and encapsulation qualification, ensuring low moisture to avoid delamination during reflow soldering (popcorning)
• Coating, ink, and adhesive formulation control, including residual solvent monitoring for VOC compliance
• Coal, coke, and biomass proximate analysis for fuel valuation and combustion optimization
• Pharmaceutical release testing of water content for stability and microbial-risk control
• Failure analysis and customer complaint investigation related to bubbling, porosity, degraded mechanical properties, or unstable viscosity
• Scientific research supporting new material development, aging studies, and drying-process optimization

FAQ

What is the difference between moisture content and volatile matter content?

Moisture content measures only water, determined selectively by Karl Fischer titration or controlled drying, whereas volatile matter is the total mass lost under specified heating conditions and may include water, solvents, monomers, and other low-molecular-weight substances. A material can therefore show a volatile-matter value higher than its true moisture value.

Which method is most suitable for trace moisture analysis?

Coulometric Karl Fischer titration, ideally combined with a heated evaporation oven, offers the lowest detection limits (down to the ppm level) because the water is transferred to the titration cell without dissolving the sample matrix. It is preferred for battery-grade powders, electrolyte solvents, and engineering plastics.

How are interfering substances handled in Karl Fischer analysis?

Aldehydes, ketones, strong oxidizers, and compounds that react with iodine or methanol can distort results. Laboratories address this by selecting aldehyde-compatible reagents, adjusting the pH, using methanol-free media, or switching to the oven method so that only evolved water reaches the cell.

What sample quantity and conditioning are required?

TGA typically requires 5 to 20 mg, oven drying requires 2 to 10 g, and Karl Fischer requires 0.1 to 2 g depending on the expected water level. Samples should be stored in airtight containers, equilibrated to laboratory temperature before opening, and weighed rapidly to minimize moisture exchange with ambient air.

What accuracy can be expected?

Gravimetric oven methods typically achieve repeatability within about 0.05% absolute for percent-level moisture; volumetric KF reaches approximately 10 ppm precision; and coulometric KF can quantify microgram quantities of water. Measurement uncertainty is influenced by sample homogeneity, weighing precision, and atmospheric humidity control.

How long does a typical determination take?

Rapid moisture analyzers deliver results in 5 to 15 minutes, single-point oven drying usually takes 1 to 4 hours depending on the standard, Karl Fischer titrations are completed within minutes per sample, and full TGA programs range from 30 minutes to several hours when multi-stage profiles are required.

Why does excessive moisture cause defects in plastic processing?

Hygroscopic polymers such as PET and PA undergo hydrolytic chain scission at processing temperatures in the presence of water, reducing molecular weight and mechanical strength. Surface moisture also flashes to steam in the melt or mold, creating silver streaks, bubbles, and voids in finished parts, which is why resin moisture is verified against supplier drying limits before molding.