Using image analysis software to make fast, reliable analysis of pulp contaminants
on-site.

For some time, I have been using image analysis (IA) software that detects and measures light or dark dirt in contrast with cellulose fibers or other media background. These light and dark dirt particles include stickies, pitch, and contaminants in general. Additionally, the IA software measures the size, shape, and shade of these particles.

Qualitative and quantitative measurement of such contaminants in pulp are important tools in determining, implementing, and assessing process control strategies to manage and eliminate their content in production pulp.

To be able to make these measurements, the contaminants must first be separated from the fiber. The following TAPPI methods can be used to do that:

• TAPPI Standard Practice T 274 sp-97: Laboratory Screening of pulp (Master Screen-Type instrument)
• TAPPI Standard Practice T 205: Presoaking and disintegration of pulp.

The Pulmac Master Screen allows a user to make the separation by following a simple procedure. Pulp samples must be diluted to slurry of less than 1% consistency. The slurry consistency must be carefully determined so that a precise oven dry weight of pulp can be drawn with every fiber change. The technique is good with recycled white stock, OCC, and virgin kraft pulp. The white stickies are mainly PSA's (pressure sensitive adhesives) with some high melt point plastics and hot melts.

The second method is the RMD wet method in plants using OCC, which typically contains a high level of stickies (their main components being waxes and hot melts). A brown handsheet previously dried under pressure at temperatures above 200 Co is dipped under a water bath. The water saturates the brown stock everywhere except where the melted thermoplastic stickies have now “waterproofed” the fibers. The result is a dark brown handsheet with light spots where the stickies have melted. After the excess water has been dabbed off, the light areas against a dark background can be measured on a scanner.

The following variables must be carefully controlled:

• Weight of the handsheet
• Pressure on the handsheet during drying
• Time in the handsheet dryer
• Temperature of the dryer.

In a combination of the above methods, a pressure sensitive paper coated with calcium carbonate is placed over a filter paper where stickies have been separated on a Pulmac Master Screen. The two papers are pressed against each other and heated. The stickies melt and the calcium carbonate adheres to them, turning the stickies white. Stickies and shives now have distinct shapes and colors that can be measured using the IA software.

The common attribute of these methods is the use of heat and pressure to cause the stickies to activate.

The Catch
It all sounds very simple. In fact, it sounds so simple that you have to wonder why everyone doesn't rush out and buy the software? After all, image analysis is an exact science dependent on the image of the specimen, the image acquisition, and the preparation of the specimen.

Therein lies “the catch.”

For the applied method to produce reliable, repeatable method results, the following principles must be very carefully respected:

• Integrity - strict adherence to sampling, test, and measurement procedures
• Sampling - drawn sample must be truly representative
• Weight - fiber charge must yield precise weight of pulp fiber
• Equipment - the master screen and its screen plate must be well maintained and operated within specification
• Agitation - fiber charge must be drawn from a well-agitated supply
• Results - sources of measurement error must be controlled.

Not many laboratories or pulp mills have a Pulmac Master Screen and a controlled pressure/temperature heater. I know of a major supplier that takes fiber samples to its laboratory and spends many hours preparing a “fine art” handsheet in pure black and whites. Results are then brought to the paper mill days later.

This reminds me of a submarine race I once attended in London. After the vessels submerged, spectators mulled around several boring hours staring at a calm, empty surface. Finally, after a long period of quiet inactivity, the winner suddenly popped to the surface, followed by second, third, etc.

Obviously, the key to obtaining immediate, reliable results using IA software is sample preparation. You don't really have to have a Pulmac Master Screen or a controlled pressure/temperature heater. If you can develop a simple, consistent, reproducible technique that works for you, I think you will find the IA software very reliable. But careful attention to preparation details is absolutely critical.

I have put the IA software on my laptop computer and travel from site to site with it and a scanner. Being able to make relatively quick (almost instant), reliable analyses of pulp contaminants on-site is an invaluable tool.

About the Author. Pierre Mouyal is president of OmniKlir Inc., an Atlanta-based consultant company specializing in the manufacturing of tissue and market pulp. He can be reached by email at: mouyal@comcast.net

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