Method principle
The 105°C oven method is based on the basic principle that the moisture in the paper can completely evaporate at a certain temperature, and the solid components of the paper maintain stable physical and chemical properties at this temperature. The specimen was dried in an oven at (105±2)°C to a constant weight, and the moisture content of the paper was calculated by the change of the quality of the specimen before and after drying. The calculation formula is as follows:
Moisture (%) = (m₁ - m₂) / m₁ × 100
Among them, m₁ represents the mass of the specimen before drying (g), and m₂ represents the mass of the specimen after drying (g). This method is a classic benchmark method for paper moisture determination, and its results are often used as a basis for evaluating the accuracy of other rapid moisture measurement methods.
Instruments
The core instrument required for the experiment is the blast drying oven, and its temperature uniformity needs to meet the requirements of (105±2)°C. Other aids include analytical balances (0.0001 g sensitivity), desiccants, weighing bottles, and dry and clean glass containers. Specimen preparation should follow relevant standards, avoid obvious defects on the entire page, and cut representative specimens. It should be placed in a closed container immediately after sampling to prevent the influence of environmental humidity.
Procedure:
The operation process can be divided into three stages: pre-drying preparation, drying process and post-drying weighing, each stage has technical details that need to be strictly controlled.
Preparation before drying:First, put the clean weighing bottle in the oven, dry it to a constant weight at 105°C, move it into the dryer to cool to room temperature and weigh it. The prepared paper specimens are then quickly placed in a constant-weight weighing bottle, immediately capped and accurately weighed for their total mass. This process should be done quickly to reduce moisture absorption by the specimen in the air.
Drying process control:Open the cap of the weighing bottle containing the specimen and place it in a blast drying oven that has been preheated to 105°C. During the drying process, the temperature in the oven should be maintained steadily within the range of (105±2)°C, and air circulation should be maintained to allow moisture to escape sufficiently. Drying time should be sufficient to ensure complete evaporation of moisture, usually by reference to standard specifications or to constant weight.
Weighing and constant weight determination after drying:Once the specified drying time is reached, the weighing cap is closed and transferred to the dryer to cool to room temperature. Weigh quickly after cooling. The constant weight is determined by the difference between two consecutive weighings that does not exceed a specific percentage of the original mass of the specimen (e.g., 0.1%). If the constant weight is not reached, the drying, cooling and weighing steps need to be repeated.
Influencing factors
The accuracy and repeatability of the measurement results are affected by many factors, and they need to be controlled systematically in the experiment.
| Temperature control | Too high a temperature may cause thermal decomposition of fibers, and too low a temperature will cause incomplete evaporation of water. It is essential to ensure that the oven temperature is uniform and stable. |
| Drying time | Insufficient time leads to low results, while too long time leads to inefficiencies and may introduce risk. It should be baked to a constant weight. |
| Specimen processing | The representativeness of the sample, the size of the sample and whether it is immediately sealed and stored directly affect the authenticity of the initial moisture data. |
| Weighing operation | Weighing flasks and specimens are highly hygroscopic during cooling and transfer. The operation needs to be skilled and fast, and the silicone in the dryer should be effective. |
| Ambient humidity | High humidity in the laboratory environment can significantly interfere with cooling and weighing processes. It is recommended to operate under stable conditions of relative humidity. |
The result is calculated
Calculate the moisture content according to the above formula. At least two parallel assays are usually required and results are reported as arithmetic averages. The calculation result is kept to one decimal place. The allowable deviation between parallel measurements should be within the range specified by the method standard, and if there is an exceedance, the experiment should be re-tested. The experimental record should include specimen identification, weighing data, drying temperature and time, calculation results and operators.
Notes:
Experimenters should wear insulated gloves to operate high-temperature ovens and weighing bottles to prevent burns. High-temperature utensils taken out of the oven should be placed smoothly on the insulation pad, and then moved to the dryer after cooling slightly to prevent the dryer from exploding. The laboratory should be well ventilated. Discarded paper specimens should be disposed of in accordance with laboratory solid waste management regulations.
This method is suitable for the determination of moisture in most paper products such as cultural paper, packaging paper and cardboard. However, this method may not be suitable for papers containing additives that volatilize or decompose at 105°C, such as certain coatings, inks, or chemical additives, and the results may contain mass loss of volatile substances, thus overestimating the true moisture value. In such cases, consider using other assay methods or modifying test conditions.
References
GB/T 462-2008 Paper, cardboard and pulp - Determination of moisture in analytical specimens
TAPPI T412 om-21 Moisture in Pulp, Paper and Paperboard
ISO 287:2017 Paper and board — Determination of moisture content — Oven-drying method