Overview
ISO 5351:2010 - Pulps: Determination of limiting viscosity number in cupri-ethylenediamine (CED) solution specifies a standardized laboratory method to estimate the limiting viscosity number [η] of pulp dissolved in a dilute cupri-ethylenediamine (CED) solvent. The method is primarily applicable to CED‑soluble bleached chemical pulps but can be used for any pulp that dissolves completely in CED. Results are used to infer average cellulose molecular mass and the degree of polymerization (DP), giving an indication of cellulose degradation from pulping or bleaching.
Key technical topics and requirements
- Principle: Measure efflux times of solvent and pulp solution through capillary‑tube viscometers at 25 °C and calculate the limiting viscosity number using Martin’s formula.
- Reagent: CED solution, c = (1.00 ± 0.02) mol·L⁻¹ (saturated with Cu(OH)2). Handle with care (ethylenediamine allergenicity; environmental disposal).
- Apparatus:
- Two capillary viscometers (water‑jacketed): a calibration viscometer (capillary ≈ 0.58 ± 0.02 mm) and a test viscometer (capillary ≈ 0.80 ± 0.05 mm).
- Constant‑temperature bath maintained at (25 ± 0.1) °C.
- Dissolving bottles, copper wire, balance (±0.1 mg), timing device (0.1 s).
- Controlled shear rate: The procedure targets a shear rate G = (200 ± 30) s⁻¹ to minimize non‑Newtonian effects; product [η] × ρ is chosen to be 3.0 ± 0.4 (viscosity ratio η/η0 ≈ 6–10).
- Calibration & procedure: Calibrate viscometers with water, glycerol solution and 0.5 mol·L⁻¹ CED; prepare test solutions with precise mass concentration; measure efflux times and compute viscosity ratio, viscosity number and limiting viscosity number.
- Accuracy and scope limitations: Results are primarily valid for samples with low non‑cellulosic content. Viscosity results for pulps with >0.5% lignin are not acceptable for technical specifications; interpret data cautiously if non‑cellulosic substances are present.
Practical applications and users
- Quality control and routine testing in pulp and paper laboratories
- Monitoring cellulose degradation during pulping and bleaching
- Research on degree of polymerization (DP) and molecular weight effects
- Process engineers tracking pulp quality and chemical effects
- Industrial producers of bleached chemical pulp
Related standards and annexes
- Normative references: ISO 638 (dry matter by oven) and ISO 7213 (sampling for testing)
- ISO 5351 includes annexes for CED preparation and analysis (Annex A), tables for viscosity calculations (Annex B) and DP estimation (Annex C).
Keywords: ISO 5351:2010, limiting viscosity number, cupri‑ethylenediamine, CED, pulp viscosity, viscometer, degree of polymerization, pulp testing, paper laboratory.
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