Water content
Water content is the amount of water present in a material, expressed as a percentage of its mass or in parts per million, and determines how a plastic, an oil or a foodstuff is processed, how long it lasts and how it behaves in service.
As part of our materials and product testing services, we determine the water present in raw materials, pellets, parts, oils and finished products. We choose the method according to the matrix and the expected level (loss on drying, Karl Fischer or thermogravimetry) and interpret the result against the specification, as part of the quality control and testing of each process.
In demanding industrial environments, very small amounts of water are enough to hydrolyze a polyester during injection molding, lower the dielectric strength of an insulating oil or shorten the shelf life of a hydrolysis-sensitive active ingredient. Measuring that water with the right method helps prevent batch rejections and drying decisions made blind.
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What is water content?
What is it?
Water determination quantifies the mass of water a sample contains relative to its total mass, as a percentage or in mg/kg. It is used to check that a raw material meets its specification, to decide whether a material is ready to be processed and to explain defects that appear in production or in service when water exceeds the limit the material can tolerate. It is a common incoming inspection parameter for plastics, chemicals, pharmaceuticals and food.
Water is held in different ways depending on the material. It can be free on the surface or in pores, absorbed by the polar groups of a hygroscopic polymer, or chemically bound as water of hydration in salts and active ingredients. Each form is released at a different temperature and responds differently to each technique, which is why two methods can give different values on the same sample. One result is only comparable with another if both state the method used.
Besides the percentage of water, a complete study repeats the measurement to establish its spread, checks whether other volatiles interfere and, when the material requires it, follows mass loss against temperature to tell surface water from bound water. The value can then be compared with the material specification, with the moisture limit set by the process or with another batch from the same supplier.
Water determination at INFINITIA
We start from the question the result has to answer: accept a batch, adjust a drying step or explain a defect. With it we define the method, the number of replicates, the extraction temperature and the acceptance criterion before measuring, so that the data supports a concrete decision.
We prepare and measure samples so that they neither gain nor lose water along the way, using sealed containers and minimal exposure times. In hygroscopic materials water is a cause of defects worth confirming or ruling out early, as in the evaluation of polycarbonate injection conditions, where the moisture of the plastic was one of the causes analyzed.
We interpret the result together with the rest of the material data: the datasheet, the drying conditions, the batch history and, if there is a failure, the appearance of the part. A value within specification does not close the case if the defect points to hydrolysis or to later moisture pickup.
We deliver a technical report with the method, test conditions, results per replicate and their interpretation against the agreed criterion. If water explains the problem, the report shows at what point in the process it enters or remains and which control should be added to prevent it from happening again.
Benefits of measuring water in materials for process and quality
Benefits
Measuring water before processing or accepting a material helps prevent defects that cost far more later: bubbles and splay in molded parts, loss of strength through hydrolysis, caking of powders or unwanted reactions in sensitive formulations. The data makes it possible to correct the drying step or reject the batch in time.
It allows suppliers to be compared on an objective criterion. Setting a water limit in the purchase specification and checking it at incoming inspection gives quality managers verifiable data to accept or claim a batch. It is especially useful for recycled or variable-origin materials: retained moisture was one of the properties determined when studying the reuse of PA66 and ABS industrial waste as 3D printing filament.
It reduces energy use and process scrap. Knowing the actual water in pellets or powders makes it possible to adjust drying times and temperatures instead of overdrying, which wastes energy and can degrade the material, or underdrying, which produces rejected parts.
It increases reliability in service. In insulating oils, electrolytes, adhesives or active ingredients, water triggers corrosion, loss of dielectric properties or chemical degradation. Controlling it at the source reduces the risk of failures that would only appear months later, once the product is already with the customer.
Water and moisture determination methods
Types
Water determination applies to almost any solid, liquid or powdered material, but there is no universal method. Each technique measures a different fraction of the water and has its own range, interferences and sample preparation requirements.
The selection criterion combines the expected water level, the presence of other volatiles, the thermal stability of the material and the standard or specification that sets the method. When the result will be compared with a supplier’s data, it is best to use the same technique.
Loss on drying in an oven or moisture balance
Loss on drying measures the difference in mass of a sample before and after heating it at a fixed temperature to constant mass, in an oven or in a moisture analyzer balance. It is a simple and robust method for medium and high contents in thermally stable materials such as minerals, fillers, wood or many food products.
Its limitation is that it does not distinguish water from other compounds that evaporate at the same temperature, such as residual solvents, monomers or plasticizers. If the material contains them, the result is closer to the volatile substances content than to the actual water, and it should be confirmed with a specific method. It can also overestimate water if the material starts to decompose.
Volumetric Karl Fischer titration
Karl Fischer titration, described by the chemist Karl Fischer in 1935, is based on a water-specific reaction: the iodine in the reagent reacts with water in the presence of sulfur dioxide, a base and an alcohol, and the end point is detected with a platinum electrode. In the volumetric version the reagent is dosed with a burette, which makes it suitable for medium and high contents in solids and liquids.
| Method | Water-specific | Suitable level | Typical sample |
|---|---|---|---|
| Loss on drying | No | Medium and high | Stable solids |
| Volumetric Karl Fischer | Yes | Medium and high | Solids and liquids |
| Coulometric Karl Fischer | Yes | Traces | Liquids |
| Karl Fischer oven | Yes | Low and traces | Plastics and salts |
| Thermogravimetry (TGA) | Separates steps | Medium and high | Small samples |
| NIR spectroscopy | Indirect | Calibration-dependent | In-line control |
ASTM E203 describes it as a general guide for determining free water and water of hydration in organic and inorganic compounds. It can measure water in the presence of many other volatiles, but some substances interfere with the reaction (certain ketones and aldehydes, or oxidizing and reducing compounds) and require special reagents or an oven method.
Coulometric Karl Fischer for trace water
In the coulometric variant the iodine is generated by electrolysis inside the cell, and the amount of water is calculated from the electric charge consumed. This makes it possible to quantify traces in the mg/kg range in liquids such as solvents, oils, fuels or electrolytes. As a rule of thumb, below about 500 mg/kg it is more accurate than the volumetric method.
For petroleum products, lubricating oils and additives, ASTM D6304 sets out the procedure, including the evaporator variant for viscous samples. It is a reference technique in the testing of lubricants and industrial oils, where water is one of the contaminants that decide whether an oil stays in service.
Karl Fischer oven method for plastics and solids
When the sample does not dissolve, reacts with the reagent or releases water slowly, it is heated in an oven and a dry carrier gas sweeps the water vapor into the Karl Fischer cell. This keeps the matrix out of contact with the reagent, and only the water released at the selected temperature is measured.
It is a common method for plastic pellets and parts. ISO 15512 covers several procedures for determining water in plastics in the form of powder, pellets and finished articles, including vaporization in a tube oven followed by Karl Fischer titration. The temperature is chosen to release the water without degrading the polymer.
Thermogravimetric analysis (TGA)
Thermogravimetric analysis continuously records the mass of a small sample while it is heated under a controlled program in an inert atmosphere. The resulting curve shows the temperature range in which the material loses mass, so surface moisture, bound water, solvents and decomposition appear as separate steps when they do not overlap.
It does not identify which compound is lost in each step, so it is combined with Karl Fischer or with evolved gas analysis when confirmation is needed. It is useful for setting the temperature of an oven method, detecting water of hydration in salts and fillers, or comparing batches when very little sample is available.
NIR spectroscopy and other indirect techniques
Near-infrared (NIR) spectroscopy detects the absorption bands of water and estimates its content in seconds without destroying the sample, which makes it useful for in-line control. Other indirect techniques, such as refractometry in solutions or gas chromatography with a thermal conductivity detector in solvents, cover specific cases.
Indirect techniques need calibration with standards or against a reference method, usually Karl Fischer or loss on drying, using samples of the same material. Their value lies in measuring many samples quickly and detecting deviations, while acceptance or root cause decisions rely on the reference method.
Industries where measuring water in materials prevents defects and rejections
Sectors
Water in a material is a critical parameter wherever a polymer is melted, a reagent is dosed, a powder is compressed or an oil provides insulation. Each industry has its own matrix, tolerable water level and method set by the specification.
In all of them the water value is used at three points: when receiving raw materials, when adjusting the process and when investigating a defect. Measuring it with the same method at all three reduces disagreements between supplier, processor and customer.
Water content in plastics and rubber: pellet drying and injection molding defects
Polyamides, polycarbonate, PET and PBT absorb water from the air. If they enter the injection molding machine wet, silver streaks and bubbles appear and, in polyesters and polycarbonate, hydrolysis reduces the strength of the part.
- Pellet moisture: checked after the dryer and in the hopper, because the material can pick up water on the way.
- Overdrying: excessive times or temperatures oxidize and yellow some polymers, such as polyamides.
- Polyamide parts: their equilibrium water changes stiffness and dimensions, so it is measured before testing them.
Measuring water in both pellets and parts helps separate a material defect from a process defect, as explained in the article on injection molding defects.
Water content in the chemical industry: solvents, reagents and sensitive formulations
In the chemical industry water acts as an unwanted reagent. Isocyanates react with it and release carbon dioxide, organometallic catalysts are deactivated, and some technical solvents must be supplied with a maximum water level in mg/kg.
- Polyurethane foams and adhesives: water in polyols and fillers causes bubbles and alters crosslinking.
- Solvents and raw materials: the supplier’s certificate is checked against an independent titration at incoming inspection.
- Salts and hydrates: distinguishing water of crystallization from surface moisture avoids dosing and purity errors.
Karl Fischer titration, direct or with an oven, provides water-specific data for accepting raw materials and setting process limits in moisture-sensitive reactions.
Water content in health and pharma: stability of active ingredients and excipients
In pharmaceuticals water affects the chemical stability of hydrolysis-sensitive active ingredients, the crystal form of some hydrates and the behavior of powders during blending, compression or capsule filling.
- Hygroscopic excipients: they gain water during storage and change powder flow and tablet hardness.
- Gelatin capsules: an out-of-range moisture level makes them brittle or soft.
- Packaging and stability: measurements over time show whether the packaging provides enough protection against moisture.
Pharmacopoeias include Karl Fischer and loss on drying methods; choosing the right one and validating it for each product is the first step toward reliable moisture control.
Water content in agriculture and food: preservation, texture and yield
In food, water determines preservation, texture and process yield. Flours, cereals, nuts, milk powder and animal feed have moisture limits that affect price, storage and safety.
- Grain and flour intake: excess moisture promotes mold growth during storage.
- Dehydrated products: residual water decides whether the product cakes, loses crispness or meets its specification.
- Process yield: knowing the water going in and coming out makes it possible to adjust drying and calculate the mass balance.
Loss on drying is the usual method for many food products, and Karl Fischer is reserved for low-moisture matrices or those with sugars and fats that change during drying.
Water content in energy: insulating oils, lubricants and batteries
In energy, water degrades insulation and working fluids. In transformers it lowers the dielectric strength of the oil and accelerates the aging of the insulating paper; in turbines and gearboxes it reduces lubricant film thickness and promotes corrosion.
- Transformer oils: dissolved water is measured in mg/kg and makes it possible to track the condition of the insulation over time.
- In-service lubricants: water ingress points to sealing failures or condensation in the circuit.
- Battery electrolytes and electrodes: trace water reacts with lithium salts and forms compounds that degrade the cell.
Coulometric Karl Fischer measures these trace levels and, together with used oil analysis, helps decide whether a fluid should be dried, filtered or replaced.
Water content in electrical and electronics: insulation, potting and components
In electrical and electronic equipment, water absorbed by insulating materials, potting resins and printed circuit board laminates lowers insulation resistance and, during soldering, evaporates suddenly and can delaminate or crack components.
- Insulating materials: comparing the water retained by materials from different suppliers after humid conditioning guides qualification.
- Potting resins and compounds: moisture in the components before curing affects adhesion and can cause bubbles.
- Moisture-sensitive components: water absorbed before assembly can explain cracks and delamination after reflow.
Measuring water in these materials before and after conditioning makes it possible to set pre-drying times and storage criteria that reduce failures in assembly and in service.
Water measurement as a basis for process and purchasing decisions
Value
Water determination adds value when the method, the sample and the acceptance criterion are defined before measuring. The result is then traceable and comparable across batches and suppliers, and it can support a purchase specification, a process adjustment or a claim to a supplier.
Measuring water systematically moves moisture control from the end of the line to the beginning. Instead of discovering the problem in a rejected part or a field complaint, it is detected when the raw material arrives or at the dryer outlet, when correcting it only means adjusting one parameter. With data series from several batches, specification limits can also be set on the actual behavior of the material, which is more reliable than generic catalog values.
In regulated industries such as pharmaceuticals, food or electrical equipment, moisture is part of specifications and technical files, and the method used must be justifiable. We apply standardized methods where they exist and, when the sample does not fit any of them, we define and document a custom method with its temperature, sample size and repeatability, so the result can be reproduced later, by us or by another testing provider.
If you have a batch that is not behaving as expected, a drying step that does not quite work or a supplier who claims to meet the specification, send us samples in an airtight container together with the datasheet, the water limit you work with and the drying or storage conditions. If you are not sure which method to apply, we will define it with you before measuring. We return a technical report with the method applied, the results per replicate and a concrete recommendation on the batch or the process.
Frequently asked questions about water content
FAQs
What does water content not reveal about a material?
The value shows how much water the sample contains at the moment of measurement, but not how much it will absorb in service or how fast. A dry hygroscopic plastic at incoming inspection can pick up water within hours if stored open, and a porous material can have little water and a large absorption capacity.
That behavior is assessed with water absorption tests by immersion or by exposure to controlled humidity, which are common in construction material testing, for example. Combining both data points, the water present and the capacity to absorb it, makes it possible to define how to store a material and when to process it.
Why do loss on drying and Karl Fischer give different values?
Because they measure different fractions, and the difference is useful information. When Karl Fischer gives more water than drying, part of the water is usually bound (water of crystallization in salts or hydrates) and is not released at oven temperature, while the reagent reaches it by dissolving the sample.
When the opposite happens, the sample is losing more than water (solvents, monomers or decomposition products). Thermogravimetric analysis shows at what temperature each fraction is released and helps decide which method best reflects the water that matters for the process or for the customer’s specification.
What is the difference between water content and water activity?
The percentage of water measures how much is present; water activity measures how much is available to react or to support microbial growth. It is expressed from 0 to 1 as the ratio between the vapor pressure of water in the product and that of pure water at the same temperature.
Two products with the same percentage of water can have very different activities, because sugars, salts or proteins hold part of the water. That is why both are measured in food and in some pharmaceutical products: content for the mass balance and the specification, and activity for microbiological stability and shelf life.
What does it mean to express water on a wet basis or a dry basis?
On a wet basis, water is referred to the total mass of the sample; on a dry basis, to the mass of the material once dried. For low contents the difference is small, but it grows with the water level: a sample with 20% on a wet basis has 25% on a dry basis.
Wood, for example, is usually expressed on a dry basis, which can exceed 100% in freshly cut pieces, while plastics, powders or oils are expressed on a wet basis. Before comparing a result with a specification or a supplier certificate, it is worth confirming which basis each value uses.
How precise is the measurement and how many replicates are needed?
Precision depends on the method and the amount of sample: ISO 15512 for plastics, for example, places the detection limit between 0.1% and 0.001% depending on the procedure. To this instrumental precision must be added the variability of the sample itself, which in pellets, powders or large parts can exceed that of the method.
That is why several replicates are run per sample, at least two or three, with several subsamples when the batch is large or heterogeneous. The report lists each replicate and its spread, so it can be judged whether a difference between batches is real or within the noise of the measurement.
Can water be measured in a finished part and not just in the raw material?
Yes, and it is the measurement that links a defect to the material. Representative portions are cut from the part, prepared quickly so their moisture does not change and analyzed, usually by the Karl Fischer oven method, which releases the water without having to dissolve the polymer.
If the distribution of water matters, the surface layer and the core are separated and measured individually. A gradient from the surface toward the core shows that the part has absorbed water from the environment after manufacture, which is common in polyamides, and helps define storage and packaging conditions.
Can service humidity conditions be reproduced in a test?
Yes. Samples are conditioned in a chamber at the temperature and relative humidity of the service environment until their mass stabilizes, and the water they have reached at that equilibrium is then measured. Repeating the process at several humidity levels gives the sorption isotherm of the material, which relates ambient humidity to the water it holds.
These conditioned samples can then be tested for mechanical, electrical or dimensional properties in their real service state. This anticipates how a part will change between the factory, the warehouse and the customer, and sets representative test conditions instead of always testing dry.
Can water determination be used to validate a drying process?
Yes. Samples of the material are taken at intervals during drying and the water in each one is measured, which gives the drying curve: how long it takes to reach the set limit and from what point it no longer drops. This confirms whether the working time and temperature are sufficient.
The curve should be repeated with the wettest material that may reach the plant and at the actual line throughput, because a dryer that works with dry material or low consumption can fall short in the worst case. The result makes it possible to set minimum drying times and a routine control point.
How much does water determination cost and what does it depend on?
The cost depends mainly on the number of samples, the method and whether an applicable standard procedure exists or a custom one has to be developed. A routine determination with a standardized method is the most economical option; the cost increases with replicates, with the preparation the sample requires and with the development of a specific method.
The scope of the report and the need to combine techniques, such as Karl Fischer and thermogravimetry, to explain a defect also play a part. For a firm quote, send us the type of material, the number of samples, the expected water level and the specification you need to meet, and we will prepare a proposal.
How long does it take to get results?
Typical lead times range from one to four weeks, depending on the number of samples, the method and whether a specific procedure has to be developed. A determination with a standardized method on a few samples falls at the lower end of that range; a study that combines techniques or conditions samples at several humidity levels, at the upper end.
If the result is holding up a batch or a line, an urgent 24 to 72 hour service can be considered depending on the case. Tell us the date you need the data and send the samples already prepared and well sealed, because shipping and receiving time also counts.
Why does the material meet the water specification while the part keeps failing?
Because the value on the certificate does not always match the material that reaches the machine. It may have been measured at origin, with another method or on another basis, and before processing the material goes through transport, storage and handling, where it can pick up water if the packaging is not airtight.
It may also be that water has already done its damage, such as hydrolysis during processing that cannot be detected by measuring water in the part, or that the cause lies elsewhere. In those cases the next step is a failure analysis that compares good and defective parts and measures, for example, the viscosity or molecular weight of the polymer.
Which samples should I send and how should I prepare them?
Send the sample in an airtight glass or low-permeability plastic container, filled almost completely to reduce the air inside, and close it immediately after sampling. Avoid paper bags or open sacks, because the sample will gain or lose water before it arrives. The amount needed depends on the method, and we will tell you when preparing the proposal.
Label it with the batch, the date and the sampling point (incoming inspection, dryer outlet, hopper or part), and include the datasheet and the water limit you need to meet. If you suspect a defect, also send good and defective parts from the same batch so they can be compared.