Introduction
The dry matter content of pulp is a key parameter for evaluating pulp quality and calculating the amount of dry fiber, which directly affects production cost control, process optimization and product performance evaluation. The electric thermostatic temperature drying oven method has become a classic measurement method widely used in laboratories because of its easy operation and reliable results. This paper aims to systematically expound the principles, steps, influencing factors and precautions for the determination of dry matter content of pulp based on electric heating constant temperature drying oven, and to provide technical reference for related testing work.
Principle of determination
Based on the principle of conservation of mass, this method provides a stable and uniform thermal environment through an electric heating constant temperature drying oven, so that the water in the pulp specimen is evaporated by heat. The dry matter content (or absolute dry content) of the pulp is calculated by accurately weighing the mass change of the specimen before and after drying. The dry matter content is usually expressed as a mass fraction, and the calculation formula is as follows:
X = (m₂ / m₁) × 100%
Among them, X is the dry matter content (%), m₁ is the total mass of the sample and container before drying (g), and m₂ is the total mass of the sample and container after drying (g). For accurate results, it is necessary to ensure complete drying and to avoid non-aqueous dispersion during drying.
Instruments and materials
The core instrument is an electric thermostatic drying oven, and its performance needs to meet: the temperature control range is usually 105°C±2°C, the temperature uniformity in the chamber is good, and it is equipped with forced ventilation to accelerate water discharge. Auxiliary equipment includes: analytical balance (sensitivity 0.0001 g), dryer, weighing flask or aluminum box, crucible tongs for drying and timer. The experimental material is the pulp sample to be tested, and the sampling needs to be representative.
Assay steps
The measurement process can be divided into four stages: preparation, drying, weighing and calculation, as follows:
1. Preparation: Place the clean weighing bottle in a drying oven at 105°C to dry until the constant weight, transfer it to the dryer to cool to room temperature and weigh it, and record its quality m₀.
2. Sampling: Quickly weigh an appropriate amount of uniform pulp specimen in the weighing bottle, and immediately weigh the total weight, which is recorded as m₁. The sampling amount is based on the appropriate residual solid mass after drying.
3. Drying: Open the cap of the weighing bottle containing the specimen and place it in a drying oven preheated to 105°C. The drying time is usually 2 to 4 hours, and the specific time is determined by pre-experiments to constant weight. The air circulation in the box should be maintained during the drying process.
4. Cooling and weighing: After drying, use crucible tongs to move the weighing bottle into the dryer, cover the bottle, cool to room temperature and weigh it quickly. Repeat the drying, cooling, and weighing steps until the difference between the two adjacent weighings does not exceed the specified threshold (e.g., 0.001g), and the final mass m₂ is recorded.
5. Calculation: Calculate the dry matter content according to the above formula. It is recommended to measure it in parallel twice, taking the arithmetic mean as the reported result.
Influencing factors
To ensure the accuracy and repeatability of the measurement results, the following points should be paid attention to during operation:
Temperature control: The drying temperature needs to be strictly stabilized at 105°C±2°C. Too high temperature may lead to pyrolysis or oxidation of fibers, resulting in non-aqueous dispersion loss; Too low a temperature can lead to incomplete drying.
Drying time and constant weight judgment: The drying time should be sufficient to ensure that the water evaporates completely, but unnecessarily long heating should be avoided. The criteria for determining constant weight should be clear and indicated in the report.
Sample handling: Pulp samples are easy to absorb moisture, and the sampling and weighing process should be rapid to avoid the influence of environmental humidity. The sample should be laid evenly in the weighing flask to increase the evaporation area.
Cooling and weighing: The dried specimen is extremely hygroscopic, so it must be fully cooled in the dryer, and the weighing action needs to be fast to prevent the absorption of moisture in the air and cause low results.
Instrument maintenance: Regularly verify the temperature uniformity and stability of the drying oven, clean the environment inside the box, and ensure that the ventilation holes are unobstructed.
The results show
The experimental process should record in detail the ambient temperature and humidity, drying temperature, drying time, weighing data and calculation results. The results report should include information such as an overview of the method, the average dry matter content, the single results of parallel assays, and deviations. A typical data record representation is as follows:
| project | Numerical values |
| Weighing bottle mass m₀ (g) | 18.2456 |
| Total mass before drying m₁ (g) | 20.3587 |
| Constant weight mass m₂ (g) after drying | 19.8762 |
| Specimen mass (m₁ - m₀) (g) | 2.1131 |
| Dry matter mass (m₂ - m₀) (g) | 1.6306 |
| Dry matter content X (%) | 77.17 |
Epilogue
The determination of the dry matter content of pulp by using an electric heating constant temperature drying oven is a basic and effective method. Its accuracy is highly dependent on tight control of details such as drying temperature, time, sample handling, and weighing operations. In practical applications, laboratories can fine-tune and verify the steps according to specific pulp types, referring to relevant national standards or industry standards, to ensure that the measurement data can truly reflect the characteristics of the sample, providing a reliable basis for production and research and development.
References
GB/T 462 Paper, cardboard and pulp - Determination of moisture in analytical specimens
TAPPI T412 om-16 Determination of moisture content in pulp, paper and paperboard
ISO 638 Determination of Pulp Dry Matter Content