Why Starch Concentration Changes in a Paper Mill

Starch solutions are not necessarily stable from the moment they are prepared. Concentration can change during cooking, dilution, storage, and circulation through the paper machine.

A typical surface-sizing process involves preparing cooked starch, diluting it to the desired concentration, and sending it to a storage tank or directly to the size press. At the size press, some of the liquid is absorbed by the paper while the remainder returns to the circulation system. Because the paper absorbs water and sizing material at different rates, the concentration of the recirculating solution can change over time. Water is then added as needed to restore the desired dilution.

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Several conditions can contribute to concentration changes:

• Water addition: Excess dilution lowers the concentration of dissolved starch and other solids.

• Evaporation: Water loss can increase the concentration of the remaining solution.

• Starch cooking: Inadequate or inconsistent cooking can affect the properties of the starch solution.

• Carryover and contamination: Other process chemicals or materials can alter the optical measurement.

• Temperature changes: Refractive index varies with temperature, making consistent temperature control or compensation important.

A refractometer provides a fast way to detect a change in the optical concentration of a sample. Rather than waiting for a laboratory analysis, an operator can take a reading at several points in the process and compare it with the mill's established operating target.

The Best BOSS Refractometer Range for Paper-Mill Starch

BOSS 0–18 Brix Refractometer

Recommended starting range

For low-concentration starch and sizing solutions, the BOSS 0–18 Brix range is the most logical BOSS scale to evaluate first.

For a paper mill investigating handheld refractometry, the BOSS 0–18 Brix refractometer is the best starting point among the BOSS ranges for a typical low-solids sizing application. A published paper-sizing application note identifies approximately 0–15% starch as a typical measurement range for sizing liquids. That makes a low-range instrument such as the BOSS 0–18 Brix a more sensible candidate for initial evaluation than a high-range instrument.

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There is an important qualification: the BOSS 0–18 Brix scale is a Brix scale, not a factory-certified paper-starch scale. Its suitability for a particular mill must be established through testing against known starch concentrations.

Why the 0–18 range makes sense

A refractometer is most useful when the expected readings fall within a practical portion of its scale. If a mill's sizing solution produces readings near the lower or middle part of a 0–18 Brix instrument, the operator can use the instrument to identify repeatable changes in concentration.

For example, suppose a paper mill prepares a starch solution and establishes that its properly diluted process solution normally produces a reading of 8.4° Brix. After several hours of circulation, the operator observes a reading of 9.1° Brix. That change could indicate increased concentration from water loss or a change in the mixture.

The reading does not prove that the starch concentration has increased by 0.7 percentage points. Instead, it signals that the solution's optical concentration has changed. The operator can investigate the cause and, if the mill's calibration confirms the relationship, make an appropriate dilution adjustment.

The BOSS 0–18 Brix model is therefore best positioned as a rapid process-checking and concentration-trending instrument, provided the mill validates the reading against its own starch formulation.

How to Use a BOSS Refractometer to Monitor Starch

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A practical monitoring procedure can be established with a few straightforward steps.

1. Prepare a representative sample

Collect a sample from the starch preparation tank, storage tank, or size-press circulation line. The sample should represent the liquid the mill wants to monitor.

If the sample contains fibers, suspended particles, foam, or other material that could interfere with the optical reading, the mill should establish an appropriate sampling and preparation procedure. A handheld refractometer is not automatically suitable for measuring a thick pulp suspension simply because it measures refractive index.

The sampling location matters. A sample from a freshly prepared starch tank could have a different concentration from a sample taken after the sizing liquid has circulated through the machine.

2. Check the instrument with a reference

Before collecting process data, verify the refractometer with an appropriate reference fluid according to the instrument's instructions.

Distilled water is commonly used as a zero reference for Brix refractometers, but the correct calibration procedure depends on the specific BOSS model. A reference check confirms that the instrument is behaving consistently. It does not establish that a Brix reading equals the actual starch percentage.

3. Measure the sample

Place the required amount of sample on the prism, close the cover if the model uses one, and take the reading according to the operating instructions.

Record the reading along with:

• Sample location.

• Date and time.

• Sample temperature.

• Starch type and formulation.

• Tank or machine operating condition.

• Any dilution or water addition made before sampling.

Recording the temperature is particularly useful when comparing readings from different parts of the mill. Temperature can affect refractive index, and the relationship between temperature and concentration must be considered when establishing a reliable process method.

4. Compare the reading with the established target

The mill should have a target reading or acceptable operating band based on its own formulation and production requirements.

A simple record might look like this:

These values are illustrative examples, not a recommended operating specification for a particular paper grade.

The mill should not make automatic chemical adjustments based on an arbitrary Brix number. The correct target must come from the actual starch formulation, laboratory measurements, and the paper machine's operating requirements.

Creating a Starch Calibration Curve

The most important step in using a BOSS Brix refractometer for starch is creating a calibration curve.

A calibration curve connects the refractometer's optical reading to the actual concentration of the material being tested. For a paper mill, the curve should be developed using the starch type and formulation that the mill intends to monitor.

For example, the mill could prepare several known concentrations of its starch solution:

The numbers in the first column represent the concentrations the laboratory prepares. The readings in the second column must be obtained through actual testing.

The mill can then plot the results and determine whether the relationship is sufficiently consistent for routine process monitoring. If the relationship is nonlinear, the calibration should account for that rather than assuming a straight line.

The calibration should also be repeated or checked when the formulation changes. Corn starch, potato starch, wheat starch, modified starch, and starch formulations containing additives can behave differently. A calibration developed for one mixture should not automatically be applied to another.

Brix versus actual starch percentage

Consider a hypothetical calibration in which a paper mill finds that a reading of 8.5° Brix corresponds to 7.2% starch in its particular solution.

That relationship is useful only for the tested formulation and operating conditions. It does not mean that 8.5° Brix universally equals 7.2% starch.

If the mill changes the starch supplier, adds a different sizing chemical, changes the cooking procedure, or alters the solution temperature, it should verify whether the existing calibration remains valid.

This distinction is especially important for SEO and technical product marketing. A product listing should not claim that a BOSS Brix refractometer directly measures paper-mill starch percentage unless the instrument has a validated starch-specific scale for that application.

Where Refractometry Fits in the Paper-Making Process

Starch cooking

Starch cooking is the preparation stage where starch is heated and processed to achieve the required properties for the paper machine. Consistent cooking conditions help produce consistent sizing behavior.

Industrial paper mills often use inline process refractometers to monitor the concentration of cooked starch. Vaisala, for example, describes refractometer-based measurement for controlling cooked starch concentration and helping maintain consistent total solids during batch preparation.

A BOSS handheld instrument could be useful as a portable verification tool alongside a larger process measurement system. An operator could compare a handheld reading with the mill's established process measurement or use it to investigate a suspected concentration change.

Size press and blade coater

The size press and blade coater are especially relevant applications because the concentration of sizing liquid affects the amount of material delivered to the paper.

A sizing liquid is commonly pumped from a preparation or storage tank into the circulation system. Some of the liquid is applied to the paper, while excess material returns to the tank. Since water and sizing material are not necessarily absorbed at the same rate, the circulating concentration can change.

Routine refractometer measurements can help identify changes before they become a larger production problem. The instrument does not replace paper testing, but it can provide an additional process-control measurement.

Pulp suspension and brownstock washing

Paper mills also use refractometry for other liquid-concentration applications, including black liquor and brownstock washing. These are different applications from starch control.

In brownstock washing, refractometers can be used to monitor dissolved solids in process liquor. The objective is to improve washing efficiency and help control chemical recovery.

A BOSS handheld Brix refractometer should not be assumed to be the correct instrument for black liquor, caustic solutions, or other highly alkaline mill liquors. Those applications require a properly selected instrument, validated method, and consideration of the chemical environment.

Limitations of a Handheld BOSS Brix Refractometer

A BOSS 0–18 Brix refractometer is a reasonable candidate for investigating low-range starch sizing solutions, but it has limitations.

It does not directly measure starch molecules. Refractometry responds to the optical properties of the sample. If the solution contains several dissolved substances, the reading reflects the combined optical behavior of the mixture.

It does not measure pulp consistency automatically. A thick suspension of fibers and water is different from a clear or relatively homogeneous starch solution. High-consistency pulp may not provide enough liquid for a reliable optical measurement, and suspended material can complicate sampling and interpretation.

It is not a substitute for laboratory starch analysis. Standardized laboratory methods, including iodine-based analytical methods, can be used to quantify starch under defined testing conditions. These methods require appropriate sample preparation and calibration.

Temperature and contamination matter. The mill should use consistent sampling procedures, clean the prism thoroughly, and account for temperature effects. If the formulation changes, the calibration should be reviewed.

For continuous, automated control of a production line, a dedicated inline process refractometer could be more appropriate than a handheld instrument. Industrial inline systems are designed for continuous concentration monitoring and can connect to process control systems.

Why National Industrial Supply Is a Useful Resource

National Industrial Supply carries BOSS refractometers along with other refractometer brands, including Atago, Misco, Hanna, Milwaukee Instruments, and Vee-Gee. The company provides a range of optical and concentration-measurement instruments for industrial, laboratory, and field applications.

For a paper mill considering the BOSS 0–18 Brix refractometer, the most useful first step is to discuss the actual process solution with a refractometer supplier.

Before selecting an instrument, the mill should be prepared to provide:

1. The type of starch being used.

2. The expected starch concentration or total solids range.

3. Whether the solution is cooked starch, surface-sizing liquid, or a coating formulation.

4. The presence of additives such as CMC, PVA, salts, or other chemicals.

5. Whether the desired measurement is a quick handheld check or continuous inline control.

6. The expected sample temperature and appearance.

This information helps determine whether a BOSS Brix instrument is appropriate for the application or whether a refractive-index instrument, custom concentration scale, or dedicated inline process refractometer would be a better choice.

Final Recommendation

For a paper pulp mill interested in using a handheld refractometer to monitor starch-containing sizing liquids, the BOSS 0–18 Brix refractometer is the best BOSS range to investigate first because it is aligned with the general low-concentration range associated with many paper-sizing applications.

The instrument should be marketed accurately as a tool for checking and trending the concentration of starch-containing solutions, not as a universal direct starch analyzer. The strongest technical approach is to establish a mill-specific calibration curve, compare refractometer readings with laboratory starch measurements, and use the resulting relationship to guide routine process checks.

A refractometer can provide a quick, convenient measurement that helps a paper mill identify concentration changes, investigate dilution problems, and maintain more consistent sizing conditions. The value comes from pairing the right measurement range with a validated method and an understanding of the particular starch formulation.

Contact National Industrial Supply

National Industrial Supply

Industrial refractometers and concentration measurement instruments

www.nisupply.com 

Sales: (951) 308-9269

Email: nisupply@gmail.com

30777 Rancho California Rd #891420

Temecula, CA 92589