Method for Determination of Ash Content in Paper

Overview

Paper ash content refers to the percentage of inorganic matter remaining in the mass of the original sample after high temperature burning. This index is an important parameter for evaluating the content of fillers, coatings and inorganic impurities in paper, and has a significant impact on the physical properties, optical properties and subsequent processing process of paper. The measurement method is based on the principle of high-temperature ashing, and the organic components are completely decomposed and volatilized by controlling the burning temperature and time, so as to accurately determine the residual ash.

Principle of determination

Paper specimens of known quality are placed in a crucible and carbonized and burned under specified temperature conditions, so that the organic substances such as cellulose, hemicellulose, and lignin in the paper are oxidized and decomposed into carbon dioxide and water vapor to escape, while inorganic substances such as calcium carbonate and kaolin remain as ash. The ash content is calculated by weighing the mass change before and after burning. The calculation formula is as follows:

Ash content = (m₃ - m₁) / (m₂ - m₁) × 100%

Among them, m₁ is the crucible mass (g), m₂ is the crucible and the total mass of the sample before calcination (g), and m₃ is the crucible and the total mass of ash after calcination (g).

Instruments and materials

The required instruments and materials should meet the basic experimental requirements to ensure that the measurement process is stable and reliable. The main items are shown in the table below:

Assay steps

First, put the clean porcelain crucible in the muffle furnace, burn it to a constant weight at about 525°C, transfer it to the dryer to cool and weigh. Weigh about 2 g of specimen (to be accurate to 0.0001 g) in a crucible. The crucible is placed on an electric heating plate or Bunsen lamp and slowly heated to carbonize the specimen until it is smoke-free. Then move the crucible into the muffle furnace and burn at 525±25°C for at least 4 hours, or until there are no black carbon particles in the ash. Take out the crucible and place it in a dryer to cool to room temperature before weighing. The burning, cooling, and weighing steps were repeated until the difference between two consecutive weighing did not exceed 0.001 g.

The result is calculated

The ash content is calculated according to the above formula, and the result is kept to two decimal places. The same specimen should be measured in parallel twice, and the arithmetic average value should be taken as the measurement result. If the relative deviation of the two measurement results exceeds 5%, it needs to be re-measured.

Notes:

The carbonization process should be carried out slowly to avoid ash loss caused by violent combustion of the specimen. The temperature of the muffle furnace should be strictly controlled, and too high a temperature may cause the decomposition of some inorganic salts, affecting the accuracy of the results. For paper with low ash content, the sample amount can be appropriately increased to improve the measurement accuracy. A dryer should be used during the experiment to prevent ash moisture absorption.

Scope of application

This method is suitable for the determination of ash content in various cultural papers, packaging papers and cardboards. For special papers that contain volatile inorganic components (such as chloride) or are prone to chemical changes at high temperatures, it may be necessary to adjust the burning temperature or use other auxiliary methods. The results reflect the burning residue of the paper at a specific temperature and are not accurate chemical composition analysis.

References

GB/T 742-2018 Determination of burning residues (ash) of papermaking raw materials, pulp, paper and cardboard

TAPPI T211 om-16 Ash in Wood, Pulp, Paper and Paperboard

ISO 1762:2019 Paper, board and pulps — Determination of residue (ash) on ignition at 525 degrees C