ISO 15361

Introducing ISO 15361 – Industrial Physics

ISO 15361 is the international standard for determining the zero‑span tensile strength of pulp. This method measures the intrinsic strength of individual fibers by eliminating the influence of fiber length and bonding, giving mills and laboratories a direct, highly sensitive indicator of fiber integrity.

Zero‑span tensile strength is one of the most reliable predictors of runnability, sheet formation, and overall pulp quality. It helps producers detect process drift early, evaluate incoming fiber, and understand how refining, bleaching, or contamination affects fiber performance long before issues appear on the paper machine.

What ISO 15361 Covers

ISO 15361 outlines procedures for measuring wet and dry zero‑span tensile strength using specialized clamping and loading systems. Key elements include:

• Preparing handsheet or strip samples
• Clamping fibers at zero span to isolate intrinsic fiber strength
• Measuring tensile force under wet and/or dry conditions
• Calculating fiber‑strength values for QC and process control
• Ensuring consistent sample conditioning and test parameters

The method applies to:

• Pulp evaluation and benchmarking
• Refining and process‑control studies
• Recycled‑fiber assessment
• Wet‑end chemistry and fiber‑treatment analysis
• R&D and quality‑control laboratories

ISO 15361 provides a direct, standardized measure of fiber strength — essential for predicting sheet performance and maintaining stable production.

Where ISO 15361 Is Used

This standard is widely used across pulp, paper, and fiber‑based industries:

• Pulp mills and integrated paper mills
• Recycled‑fiber operations
• Tissue, packaging, and printing‑paper producers
• Independent and mill‑based laboratories
• R&D, optimization, and troubleshooting teams

It supports both routine QC testing and deeper fiber‑quality investigations.

Why Zero‑Span Testing Matters

Understanding fiber strength is essential for:

• Preventing web breaks and production losses
• Detecting process drift before quality declines
• Evaluating refining, bleaching, and fiber‑mix impacts
• Benchmarking incoming pulp quality
• Improving sheet bonding, formation, and runnability

Zero‑span testing gives mills early warning when fiber integrity begins to slip — long before issues show up on the machine.

Testing solutions for ISO 15361

One product from the Industrial Physics portfolio aligns directly with ISO 15361’s focus on zero‑span tensile testing:

Technidyne Pulmac Automated Z‑Span™ Fiber Strength Tester

The Automated Z‑Span™ Tester measures fiber strength before quality slips. Load handsheet or strip samples onto the feed tray, and the system automatically runs up to 24 wet and/or dry zero‑span tests in a single sequence. Results appear on the touchscreen within minutes and export directly to a PC database for trending and record keeping.

The Z‑Span™ Tester generates fiber‑quality numbers sensitive to fiber strength, fiber length, bonding potential, and fiber alignment — the variables that determine whether your sheet holds together on the machine. Routine testing helps mills detect process changes early, adjust before quality drops, and avoid costly web breaks.

Industrial Physics also offers deep knowledge resources on pulp evaluation, including guidance on standard methods such as TAPPI T 275 and broader pulp‑quality insights to help you maximize the performance of your Z‑Span™ system.

Your Global Test and Measurement Partner for ISO 15361

Industrial Physics supports pulp and paper producers with the tools and expertise needed to evaluate fiber strength in line with ISO 15361. From automated zero‑span testing to fiber screening, contaminant detection, and handsheet preparation, we help ensure your fiber is strong, stable, and ready for production.