ISO 9184-7:1994

Overview

ISO 9184-7:1994 (Paper, board and pulps - Fibre furnish analysis - Part 7) specifies two standard methods to determine the fibre weight factor used in furnish analysis. The weight factor is a dimensionless ratio of the mass per unit length of a given fibre to that of a reference fibre (the reference mass per unit length is 0.180 mg/m). The part applies to pulps from unmixed wood species that contain no more than 5% of fibres with a substantially different weight factor.

Key Topics

• Two accepted methods

  • Comparison method: mix the unknown pulp with a known reference pulp in defined mass ratios and count fibres microscopically to calculate the sample weight factor.
  • Fibre coarseness method: calculate the weight factor directly from measured fibre coarseness using the standard equation f = 5.55 · e_r (where e_r is fibre coarseness in mg/m).

• Procedure highlights

  • Prepare mixtures with about 20%, 40%, 60% and 80% by mass of the sample (balance is reference pulp).
  • Prepare two slides per mixture and count fibres crossing the eyepiece centre mark; typically ~300 fibres per slide (≈600 fibres per mixture).
  • Use a stain that differentiates reference pulp and sample (see ISO 9184-2 guidance).
  • Report weight factor as a dimensionless value to two decimal places.

• Quality checks and precision

  • Condition samples before weighing and allow slides to dry as indicated in ISO 9184-1.
  • If the four mixture results vary widely (minimum < 80% of maximum), repeat counts or redo the test; discard and restart if repeatability is not achieved.

Applications

• Routine furnish analysis in pulp and paper laboratories to support pulp blending, grade verification and process quality control.
• Determining species-specific contributions in paper and board production where accurate mass-per-length conversion is required for formulation and billing.
• Use in research and development when validating new stains, reference pulps or when comparing analytical methods for fibre characterization.

Related Standards

• ISO 9184-1: General method for fibre furnish analysis
• ISO 9184-2: Staining guide
• ISO 9184-6: Determination of fibre coarseness

Practical value: ISO 9184-7 provides reproducible, standardized approaches-comparison or calculation-to derive reliable weight factors, enabling consistent furnish composition reporting and improved quality control across laboratories.