Butyl glycol and propylheptyl alcohol in water-borne paint

Importance of the Topic

Effective control of co-solvents and plasticizers such as butyl glycol and propylheptyl alcohol in waterborne paints is essential to maintain consistent rheological properties, drying times, film appearance and adhesion. Conventional wet-chemical assays are time-consuming and labor-intensive, whereas visible–near infrared (Vis-NIR) spectroscopy offers a rapid, multi-parameter alternative suitable for inline or at-line quality control.

Study Objectives and Overview

The main goal of this application note was to demonstrate the feasibility of Vis-NIR spectroscopy combined with chemometric modeling to quantify butyl glycol and propylheptyl alcohol in two types of water-based paint (light gray and black). The study compares spectral predictions with reference laboratory values to validate accuracy and precision.

Methodology

Paint samples spiked with known concentrations of butyl glycol and propylheptyl alcohol were continuously stirred in a beaker to ensure homogeneity of pigments and solvents. Spectral data were recorded in transflection mode over the full Vis-NIR range (400–2500 nm). Data pretreatment employed a first derivative (segment size 20 nm, gap 1 nm) to enhance spectral features. Partial Least Squares (PLS) regression models were developed separately for each additive in light gray and black paint matrices. External validation with an independent sample set assessed model robustness.

Used Instrumentation

• NIRS XDS SmartProbe Analyzer (Metrohm code 29211610) equipped with transflection probe
• Vision Software 4.0.3 (Metrohm code 66069102) for chemometric model development

Main Results and Discussion

The PLS models delivered strong linear correlations (R² > 0.97) and low prediction errors for both additives in each paint type:

• Butyl glycol in black paint: R² = 0.9904, SEC = 0.0093 %, SEV = 0.0095 %, PRESS = 0.0804
• Butyl glycol in light gray paint: R² = 0.9732, SEC = 0.0216 %, SEV = 0.0882 %, PRESS = 0.0545
• Propylheptyl alcohol in black paint: R² = 0.9957, SEC = 0.0068 %, SEV = 0.0969 %, PRESS = 0.0846
• Propylheptyl alcohol in light gray paint: R² = 0.9975, SEC = 0.0072 %, SEV = 0.0704 %, PRESS = 0.0346

External validation residuals remained within ±0.1 %, confirming model accuracy across independent samples.

Benefits and Practical Applications

Vis-NIR spectroscopy provides:

• Rapid, reagent-free quantification in under one minute per sample
• Simultaneous determination of multiple additives in complex paint matrices
• Minimal sample preparation and operator training
• Potential for at-line or inline process monitoring in paint production

Future Trends and Opportunities

Advancements may include integration of Vis-NIR sensors into continuous production lines, development of universal calibration transfers between instruments, and application of machine learning algorithms for improved predictive performance. Expansion to other critical paint additives and real-time monitoring platforms will further enhance quality assurance workflows.

Conclusion

The demonstrated Vis-NIR method achieves fast, reliable quantification of butyl glycol and propylheptyl alcohol in water-borne paints, offering an efficient alternative to conventional laboratory assays for quality control in paint manufacturing.