Image Analysis Methods to Determine Fiber Properties

Image Analysis Methods to Determine Fiber Properties

Paper physics has gone to peaks in terms of understanding the pulp and developing pulp or fiber properties analysis is a step in determining the fibers status in the process it is undergoing. Image analysis methods are well known and adapted ways to determine accurate fiber properties in a short time.


Bauer-McNett classification – a preferred method
The Bauer-McNett classification is a much used method for characterising both chemical and mechanical pulps, although it is more suitable for the latter, because the fibre length distribution is usually broader than in chemical pulps and thus the fibres will be distributed more evenly in each fraction. It has been shown (Lindholm 1980, Koran 1994) that these fractions serve well to predict most of the properties of a given mechanical pulp. Hence it is a suitable method for the analysis of pulp fractionation.

The Bauer-McNett apparatus are to classify pulp primarily according to fibre length, while other factors such as width and fibre flexibility have only minor effects. The analogy between pressure screening and Bauer-McNett classification is obvious. The analysis as such has been shown to be repeatable at same labs, but its reproducibility between laboratories and tests has been found to be poor. The repeatability, expressed as the coefficient of variation, has been reported to be of the order of 1% for each fraction. The poor reproducibility is attributable to dimensional and constructional anomalies in the apparatus, and the differences between the results of analyses performed with different apparatuses have been shown to be so great that attempts at developing Bauer-McNett analysis into a standard method have been abandoned.

Pulp properties are determined by the analysis includes:

  • » Fiber Length, Kink, Curl and Coarseness Evaluation
  • » PFI Milling and Beater Studies
  • » Drainage and Freeness Testing
  • » Somerville, Pulmac, and Valley Flat Screening


While the pulp sheet properties analysis includes:

  • » Tear, Tensile, Burst, Tensile Stiffness, Fold, and Bulk
  • » Zero Span Tensile, Internal Bond, Smoothness & Porosity, Edgewise Compression
  • » Brightness, and Opacity


The capabilities include analysis of Kraft, Sulfite, Recycled Fiber, Thermo-Mechanical, and Chemi-Thermo-Mechanical Pulps.
Many models are invented to make the fiber properties insights more in-depth. Over these years, not only there was an evolution of different types of fibers, lot advancements came in the models, methods, theories and technologies.

Chemical and structural analysis of fiber and core tissues
A standard approved in 2005 was with exact proportion by weight of ground fiber and shive, a model was developed using near infrared spectroscopy and a series of mixtures were determined. This model is based on shive material, the presence of cuticularized epidermis, having a high level of wax and cuticle along with aromatics, may dictate another model, or modification, in further refinements of the method.
The future standards in the properties are some of those commonly required for typical fiber applications. While the standards for fiber strength and length are two others that require future action.

Feature-based transfer learning to train a novel cotton imaging system
A research on the application of cotton imaging system to train a novel target system, goal is to measure a cotton fiber property named maturity using image analysis. The research also worked on feature-based supervised domain adaptation approach named G2DA which performs mapping using the generalized discriminant analysis. After domain adaptation is complete, model estimation is performed easily using traditional machine learning algorithms. Specifically, RANSAC-based regression is performed to learn a maturity function for the target system. This function is then used to estimate the maturity of any newly scanned fiber. Validation studies performed show good results for our overall approach.

The major gauges that determine the fiber properties are:
Fibre Volume Fraction Measurement
These Two standard approaches are generally adopted while examining fiber fraction in a composite laminate. So, standard methods have been available by burning small composite samples and resulting in complete oxidation of the resin that ultimately determines the fibre fraction

Void Measurement
The assessment of the void content of a composite laminate requires information of overall void volume fraction, void size distribution and void location. While, the correlation quoted used void content figures that are obtained by destructive means like resin burn off or acid digestion. Hence, these measurements are essential and laborious point by point measurements resulting an average value over a finite volume of material whilst they can give some guidance as to the variation of void content across the slab, they say nothing about the uniformity of the mechanical test sample.

Image analysis role in the fiber properties measuring process
Many optical techniques were used to define fibre volume fraction, void content and the distribution. The process involves shining a strong light through a sample and observing any shadows formed by voids. For example, the Quantimet 800 image analyser was used to provide a rapid measure of void content in any particular sample and the system consisted of a scanning device and an analyzer. This allows analysis of an image directly or with an epidiascope using micrographs. The technicality of the analyzer is


  • » 512* 480 pixel CCD camera works at high resolutions of up to 2.1 microns per pixel
  • » Image frame passes to the controller and converted to a binary signal
  • » In 50 milliseconds, up to four image frames could be derived from every exposure


L&W Pulp Tester
The L&W Pulp Tester measurements conforms to establish international standards, and together with the latest and fastest technique. Being a major help in achieving optimal process settings for high production rate of uniform paper quality and good runnability. The system is built up of modules like; fibre morphology with standard fibre length, coarseness, standard optical properties, ERIC 950, NIR, Canadian Standard Freeness/Schopper-Riegler, a new module that measures shives optically and with better statistics than ever before (20 g) and a modeling tool for statistical analysis.

Uniform pulp quality by testing pulp…
The paper quality depends on fibre properties. So, the fibre properties measuring through modern automatic technology gives advantage with image analysis technology. An automatic sampling and pulp quality analysis determines frequent testing possible and guarantee uniform pulp quality to the manufacturer. Benefits


  • » Size distribution of the fibres with respect to length and width are important for the runnability of pulp and for the quality of the paper
  • » Measuring fibre deformations
  • » Optical properties like brightness, colour, etc are other important and well known properties
  • » Quality problems will be detected earlier
  • » Repeatability
  • » Prediction of strength parameters from fibre data
  • » Coarseness online improves strength predictions from fibre morphology
  • » Determination of Viscosity


The standard, traditional and old laboratory test methods are now combined with the new age technology and smart / artificial intelligence. Now the industry is in the age of 3 dimensional (3D) analyses. The 3D micrograph of a fiber-fiber bond between two contacting fibers can be extracted from X-ray microtomography image of a model paper. Here, the fiber centrelines were determined and the bond surface would be calculated.

Hence, using the X-ray synchrotron microtomography imaging kind ofequipment helps to aim the proposing method of getting 3D information on paper fibrous microstructures. Therefore, these techniques are useful for better understanding the links between the manufacturing conditions, the resulting microstructural and mechanical properties of the paper fibrous networks, together with the morphology of fibres and fibre-fibre bonds.

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