Overview
ISO 9184-5:1990 is an international standard that specifies the Lofton-Merritt staining test for fibre furnish analysis in paper, board, and pulps. This test is a modification of the Wisbar staining method and is designed to identify and differentiate various types of wood pulps by their fibre composition using microscopic examination. The standard provides detailed guidance on the preparation, use, and colour reactions of the Lofton-Merritt stain, which is essential for both qualitative and quantitative analysis of softwood and hardwood chemical pulps, kraft, sulfite, and semi-chemical pulps. This part of ISO 9184 must be used alongside ISO 9184-1 (General method) and, where appropriate, ISO 9184-2’s staining tests.
Key Topics
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Scope and Application
The Lofton-Merritt test is applicable to:
- Unbleached and bleached softwood chemical pulps
- Unbleached kraft and sulfite softwood pulps
- Unbleached semi-chemical kraft and sulfite pulps
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Principle of the Test
Fibres are stained using a prepared mixture containing fuchsine, malachite green, and hydrochloric acid. Different pulps exhibit distinctive colour reactions when stained, enabling identification under microscopy.
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Reagent Preparation
Key reagents include:
- Fuchsine solution (~1%)
- Malachite green solution (~2%)
- Hydrochloric acid solution (~0.5%)
These are carefully mixed in specific volumes to create the Lofton-Merritt stain. Proper laboratory safety and use of analytical-grade reagents are emphasized.
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Colour Reactions and Interpretation
The standard includes a detailed colour chart correlating pulp type with stain colour:
- Softwood chemical pulp: greenish or greyish-blue
- Unbleached kraft pulp: red-violet
- Unbleached sulfite pulp: colourless, with distinct violet staining on bordered pits
- Bleached kraft and sulfite pulp: light pink or colourless
- Mechanical pulp: bright blue
This facilitates accurate visual differentiation between pulp types.
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Test Procedure
The method involves boiling fibre samples with the stain, rinsing, and preparing microscope slides. Fibres are then examined at 40x to 120x magnification, identified, and counted according to ISO 9184-1.
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Expression of Results
Results must be documented and reported as per ISO 9184-1 guidelines to ensure standardization and comparability across laboratories.
Applications
The Lofton-Merritt staining test is widely used in:
- Pulp and paper industries for quality control and fibre analysis
- Research laboratories studying pulp composition and properties
- Paper recycling operations to identify and sort pulp types
- Regulatory compliance to verify pulp composition in products meeting environmental or industry standards
This staining test assists in evaluating raw material sources, understanding fibre blends in paper products, and ensuring consistent paper quality by distinguishing between pulp types.
Related Standards
- ISO 9184-1:1990 – General method for fibre furnish analysis, providing overarching instructions for sample preparation, counting, and reporting
- ISO 9184-2 – Staining guide detailing staining characteristics of different fibres
- ISO 9184-3 – Herzberg staining test methodology
- ISO 9184-4 – Graff 'T' staining test
- ISO 9184-6 and 9184-7 – Methods involving weight factors by fibre coarseness and comparison techniques
Together, these parts form a comprehensive framework for fibre furnish analysis in paper, board, and pulps, enabling accurate, reproducible identification and quantification of fibre types.
Keywords: ISO 9184-5, Lofton-Merritt staining test, fibre furnish analysis, paper pulp testing, softwood chemical pulp, kraft pulp, sulfite pulp, semi-chemical pulp, paper industry standards, pulp fibre differentiation, microscopy in pulp analysis, stain colour reactions, ISO fibre analysis standards.