Importance of standard dissociation steps
In the physical strength testing process of paper, fiber dissociation is the first step in the preparation of standard sheets, and it is also the cornerstone for determining the accuracy and comparability of subsequent strength data such as tensile resistance and bursting resistance. If the dissociation step is not standardized, the initial state of the fiber has deviated from the standard, and all subsequent precise mechanical tests will be based on the deviated sample, and the scientific value and guiding significance of the results will be greatly reduced. Therefore, mastering and strictly implementing the standard dissociation steps is the primary prerequisite to ensure the reliability of the entire paper strength testing system.
Dissociation principle
The goal of fiber dissociation is to fully disperse and swell the fiber bundles without significantly damaging the shape and strength of the fibers themselves, so as to form a uniform fiber suspension. The process mainly relies on the combined interaction of mechanical shear forces and water, and its key control parameters include dissociation concentration, dissociation time, dissociation speed, and water quality. The dissociation process can be understood as the application of energy input to the fiber network, and its dispersion effect E is related to the input energy I, the initial binding state of the fiber S, and the medium condition M, which can be conceptually expressed as:
E = f(I, S, M)
where the input energy I is a function of the dissociation time t and the dissociation speed ω. Improper energy input, such as too long or too high a speed, can cause the fibers to break off excessively, artificially reducing the strength performance of the final paper.
The operation steps are explained in detail
The following steps comprehensively refer to the standard methods of pulp laboratory dissociation at home and abroad, and are suitable for most plant fiber raw materials.
Step 1: Sample preparation and wetting. Weigh a slurry sample equivalent to the specified gram mass (such as 2.0 grams) and soak and swell with an appropriate amount of distilled or deionized water, usually for no less than 30 minutes, to ensure that the moisture penetrates fully into the fiber.
Step 2: Initial dispersion. The swollen slurry is transferred to the inner cavity of the fiber dissociator and water at the specified temperature (usually 20±1°C) is added to the specified scale to accurately reach the standard value (e.g., 1.57%). Close the lid and start the device for preliminary low-speed dispersion, which lasts about 1-2 minutes.
Step 3: Standard dissociation. Adjust the dissociator to a standard speed (e.g., 3000 rpm or according to specific standards) to begin formal dissociation. Strict timing, the total dissociation time needs to be precisely controlled (e.g., 10 minutes or as specified). Stop as soon as the time arrives.
Step 4: Suspension transfer and cleaning. Completely transfer the dissociated fiber suspension to the storage container, and rinse the inner wall of the dissociator and the rotor several times with a small amount of water to collect and merge all the fibers to ensure no loss. The final suspension should be set aside and should be used for the preparation of handwritten tablets within the specified time.
Common operational misunderstandings
| Operational misunderstandings | results that may result from |
| Dissociation concentrations are inaccurate | The shear force of the fiber changes, and the dispersion uniformity becomes worse. |
| Dissociation takes too long | The fibers are over-cut and the length decreases, resulting in reduced paper strength. |
| The dissociation speed is not standard | The input energy deviation affects the fiber dispersion and damage degree. |
| Use non-standard water quality | Ions in water affect the ζ potential of the fibers and change the flocculation behavior. |
| Leave it for too long after dissociation | The fibers were re-flocculated, and the quantitative distribution of the handwritten sheets was uneven. |
cascading effects on subsequent strength tests
The fiber suspension prepared by non-standard dissociation steps had deviated from the reference in terms of fiber length distribution, damage degree and dispersion state. The structure and strength of the internal fiber bonding network made of this are inherently insufficient. When performing tensile strength testing, it may be manifested as a systematic low strength value or an increase in data dispersion. The burst resistance test may cause abnormal rupture due to uneven stress distribution. These deviations can obscure true process or raw material differences, making testing meaningless to guide production or R&D.
Conclusion
Standardization of fiber dissociation steps is the fundamental guarantee for accurate, reproducible and comparable data for laboratory paper physical strength testing. It is not a simple "beating" preparatory action, but a scientific process that requires precise control of parameters. Only by strictly following the standards from this first step can the subsequent strength test data be credible and provide a solid experimental basis for product quality control, process optimization and new material research and development.
References
ISO 5263-1: Pulp - Wet dissociation in the laboratory - Part 1: Dissociation of chemical pulps.
TAPPI T205 sp-06: Pulp slices that form paper pages for physical testing.
GB/T 24325: Pulp - Laboratory pulping - Valley pulping machine method.