How Does Inline Refractometry Measure Sizing-Agent Concentration?
The refractive index of a process liquid changes systematically as the concentration of dissolved sizing agents increases. The iPR FR² process refractometer measures the refractive index continuously and converts it into a concentration value using a calibration developed for the relevant sizing formulation and process range. Unlike individual laboratory samples, inline refractometry provides a continuous concentration trend throughout ultrafiltration. Operators can observe how the retentate approaches the target concentration, identify deviations immediately, and stop or adjust the process at the required recovery endpoint. Continuous inline measurement supports:- Real-time sizing-agent concentration monitoring
- Reliable recovery endpoint detection
- Immediate identification of concentration deviations
- Reduced dependence on manual sampling
- Consistent retentate quality
- Standardized monitoring across production batches
- Integration into automated process control
Why Is Continuous Concentration Measurement Important in Sizing-Agent Recovery?
During ultrafiltration, operators need to determine when the recovered sizing-agent solution has reached its defined target concentration. If the concentration remains too low:- The process may continue longer than necessary
- Excessive volumes of water may be processed
- The recovered solution may not meet the required reuse concentration
- Membrane and energy use may be inefficient
- Viscosity may increase
- Membrane performance may decrease
- Concentration polarization and fouling may increase
- The concentrate may require additional adjustment
- Process interruptions may occur
Why Is the iPR FR² Suitable for Inline Sizing-Agent Measurement?
The SCHMIDT + HAENSCH iPR FR² full-range inline process refractometer is designed for continuous refractive-index and concentration measurement in industrial processes. Installed directly in a process line, retentate circulation loop, bypass, vessel, or storage tank, the instrument provides real-time concentration data for process control and quality assurance.Continuous Refractive-Index and Concentration Measurement
The iPR FR² continuously monitors concentration changes throughout the ultrafiltration process. Operators can follow the concentration trend directly and determine when the recovered sizing-agent solution has reached the required endpoint.Process-Specific Concentration Calibration
The measured refractive index is converted into a concentration value using a calibration developed for the relevant sizing formulation and concentration range. This allows operators to monitor the process using a meaningful concentration scale instead of refractive-index values alone.Measurement Across the Required Concentration Range
During ultrafiltration, the sizing-agent concentration may increase substantially between the initial wash liquor and the recovered retentate. The full-range measurement capability of the iPR FR² supports continuous monitoring throughout the concentration process.Measurement at Elevated Process Temperatures
Sizing-agent recovery can take place at elevated temperatures. The iPR FR² is designed for integration into demanding industrial processes and can be configured according to the required process-temperature range. Continuous measurement under process conditions also avoids delays and temperature changes associated with removing samples for laboratory analysis.Integration into PLC and Process-Control Systems
Analog and digital interfaces allow the concentration signal to be transferred to a PLC, DCS, or other plant-control system. The measurement data can be used for:- Process visualization
- Concentration alarms
- Recovery endpoint detection
- Trend monitoring
- Automated process control
- Documentation of batch performance
Robust Process Installation and Prism Cleaning
The iPR FR² can be integrated into pipes, circulation loops, bypass lines, tanks, and other process locations. Its robust industrial design supports reliable operation in textile-processing environments. Appropriate installation and cleaning options help prevent deposits from affecting the measuring surface and support stable long-term measurement.How Does Ultrafiltration Recover Starch, CMC, and PVA?
Sizing agents such as starch, CMC, and PVA are applied to yarns before weaving to increase strength, reduce friction, and minimize thread breakage. After weaving, the sizing agents are removed from the fabric during washing and desizing. The resulting wash liquor contains dissolved sizing polymers, water, and other process components. During ultrafiltration, water and low-molecular-weight substances pass through the membrane as permeate, while larger sizing polymers are retained in the retentate. As the process continues, the retentate concentration increases until the recovered solution reaches the required level for adjustment or reuse. The permeate water can also be returned to the washing process when it meets the plant’s quality requirements. In established recovery systems, wash liquors may contain approximately 20–30 g/L of sizing agents and may be concentrated to approximately 150–350 g/L. Actual values depend on the sizing formulation, membrane system, and plant configuration. PVA recovery by ultrafiltration follows the same general principle and can also be applied to processes using starch, CMC, or consistent sizing-agent blends. Where the recovered concentrate remains at an elevated temperature, retained process heat can reduce the energy required before reuse. Permeate recycling can also reduce fresh-water demand and the energy required to heat incoming process water.Can Inline Refractometry Measure Starch, CMC, and PVA Solutions?
The iPR FR² can monitor solutions containing starch, CMC, PVA, or consistent mixtures of these sizing agents using a calibration developed for the relevant formulation and concentration range. The refractometer measures the total concentration represented by the calibrated process scale. It does not separately determine the individual concentrations of starch, CMC, and PVA within a mixed formulation. For reliable concentration measurement, the composition of the process liquid must remain sufficiently consistent with the calibration. If the formulation changes significantly, the calibration should be reviewed and adjusted accordingly.Where Should the Inline Refractometer Be Installed in the Ultrafiltration Process?
The most suitable installation point depends on the plant design and the required control task.Retentate Circulation Loop
Installation in the retentate circulation loop, typically on the pressure side of the circulation pump, enables continuous monitoring of the increasing sizing-agent concentration. This is the most relevant measurement position for following the concentration trend and identifying the recovery endpoint.Ultrafiltration Feed Line
Measurement in the feed line determines the initial sizing-agent concentration entering the ultrafiltration system. This provides a reference value for evaluating the concentration increase and overall process performance.Concentrate Outlet or Storage Tank
Measurement at the concentrate outlet or in the storage tank verifies the final concentration before the recovered sizing agent is adjusted or returned to production.Sizing-Agent Mixing Tank
Measurement during mixing confirms that the recovered material has been adjusted to the concentration required by the sizing formulation.Which Process Variables Affect Refractometric Concentration Measurement?
Reliable inline concentration measurement requires representative contact between the process liquid and the measuring prism. Important process variables include:- Sizing-agent formulation
- Concentration range
- Process temperature
- Water and solvent composition
- Dissolved auxiliaries
- Air bubbles
- Deposits on the measuring surface
- Accumulation of fibers or solids
How Does Continuous Concentration Measurement Improve Ultrafiltration Control?
Continuous measurement with the iPR FR² gives textile manufacturers direct control over concentration development during ultrafiltration. Real-time concentration data helps operators:- Identify the required recovery endpoint
- Avoid unnecessary processing time
- Maintain consistent retentate concentration
- Reduce manual sampling and laboratory workload
- Detect process deviations immediately
- Improve membrane utilization
- Support sizing-agent and water reuse
- Improve batch-to-batch consistency
- Integrate concentration control into automated plant workflows
By measuring sizing-agent concentration directly in the
ultrafiltration process, the iPR FR² provides the real-time information
required to control the recovery endpoint and verify the concentrate
before reuse.
