Synthetic polymers and resins are central to modern society. They make beverage containers leakproof, automotive parts heat-resistant, and advanced medical implants biocompatible. Despite the vast array of structures and properties, all polymers have their genesis in a polymerisation reaction. These reactions transform simple molecules (monomers) into complex chains (polymers) to create materials with useful and unique properties. However, controlling polymer reactions at manufacturing scale has many challenges.
One of the most important challenges is identifying the reaction endpoint – the point when polymer chains reach the optimal length and complexity for their intended application. Polymerisation reactions are highly exothermic, fast, and sensitive to trace impurities. Traditional methods of endpoint detection often lack accuracy and precision, resulting in costly errors and inefficiencies.
By monitoring a reaction’s progress in real-time, in-line viscometers provide accurate endpoint detection.
Key Polymerisation Reactions Driving Industrial Applications
Polymerisation reactions fall into two main categories. Both produce long molecular chains, but the chains grow using different mechanisms and have different reaction characteristics. Addition reactions add a single monomer to a growing chain, as in polyethylene (PE) production. Condensation reactions join two different monomers, releasing a small molecule like water or HCl in the process, as seen in production of formaldehyde-based resins and epoxy resins.
Formaldehyde-based resins have versatile properties and extensive applications. Urea-formaldehyde (UF) is used to produce textiles, paper, moulded products, and wood-based composites. Melamine-formaldehyde (MF) resins have good heat and chemical resistance and are popular in wood laminates, automotive surface coatings, and fire-resistant protective clothing. Phenol-formol (PF) resins have high weathering resistance and adhesive strength, useful for fiberglass, exterior plywood, and heat-resistant products.
Why is Identifying the End Point Important?
Reaction duration influences polymer molecular weight, composition, and structural and physicochemical properties. Stopping the reaction too early or too late may result in an out-of-spec product.
For formaldehyde-based resins, the endpoint reaction determines the amount of crosslinking and thus crucial properties like chemical resistance and dimensional stability.
Besides product quality, endpoint detection affects process efficiency and safety. Polymerisation is exothermic, and over-running can lead to dangerous overheating. Reactions left too long can solidify within the reaction vessel, requiring labour-intensive manual removal.
Using Viscosity to Measure the End of a Polymerisation Reaction
As a polymerisation reaction progresses, growing molecular chains increase the reaction mixture’s viscosity. While it is a complex property, viscosity correlates with the degree of polymerisation and allows for real-time monitoring of polymer chain growth, crosslinking, and reaction completion. It is also compatible with aqueous environments, important for emulsion polymerisation reactions. Knowing molecular weight allows estimation of the polymer’s melting point, crystallinity, tensile strength and polymer grade.
Other measurement techniques such as light scattering (DLS) can also be used to characterise polymer properties, however for large-scale industrial production, inline viscosity measurement is often preferred due to its practicality and robustness.
The Challenge with Offline Measurements
In polymer production, reaching the endpoint often means achieving a target viscosity. The reaction’s progress is tracked until this target is met, then the process is terminated. Termination methods include cooling, flushing with water, or alkali quenching.
Most manufacturers rely on offline, manual methods to determine reaction completion. These include opening the manway to visually assess viscosity, making particle size measurements or other fluid analyses. As the reaction proceeds and viscosity increases, manual sampling becomes increasingly more difficult and less reliable.
Offline methods provide only snapshots of the ongoing reaction. If sampling takes 15 minutes, results are already well outdated as soon as they become available. This lag causes missed endpoints and inconsistent batch quality, and means multi-step polymerisation reactions become even more difficult.
In addition, manual sampling of hot, pressurised reactors poses safety risks. Human error and variability also become an issue, as batch results can vary based on operator skill and experience. All these factors lead to higher production costs.
Inline Viscosity: A Real-Time Solution
Real-time automated monitoring is the only way to address these challenges and guarantee accurate endpoint detection. Hydramotion’s viscometers measure viscosity using a stainless-steel sensor element submerged within the reaction mixture. The sensor vibrates microscopically and measures the energy absorbed by the polymerising liquid to calculate viscosity. This method provides real-time data for precise reaction tracking.
These direct, automated measurements eliminate the sampling errors, inconsistencies, and safety risks inherent in manual sampling. They are unaffected by variations in the process environment (like vibrations and noise) and product properties (like flow rate, suspended particles or bubbles). Because they measure viscosity of all reactants, they paint an accurate picture of the whole reaction’s progress, in contrast to manual measurements which are heavily affected by localised differences within the vessel.
Hydramotion viscometers are highly accurate and robust with negligible maintenance, translating to a low total cost of ownership.
Real-World Success Stories
Inline Viscometers Eliminate Batch Failures Through Endpoint Detection
A major resin manufacturer experienced frequent missed endpoints for formaldehyde resin production, with high failure costs. Hydramotion supplied a custom XL7 viscometer with optimised design and coating that could withstand harsh and abrasive process conditions. Results were dramatic: the batch failure rate dropped to zero, resulting in substantial cost savings. This optimised viscometer was depolyed as part of a global rollout initiative and quickly became the gold standard for formaldehyde resin production.
Inline Viscometers Streamline PET Flake Recycling
A PET recycling facility struggled with energy efficiency and consistency in their glycolysis depolymerisation process because of variability in post-consumer recyclable materials. Hydramotion’s XL7 High Temperature viscometer operates at temperatures up to 450°C without special cooling and is resistant to flow rate variations and harsh environments, making it ideal for this challenging application.
After installing the XL7-HT they were able to observe the variability in real time and adjust the process conditions accordingly. Batch processing time was also reduced by up to 2 hours thanks to more precise endpoint detection, resulting in significantly lower energy consumption. The time saved meant the facility could run more batches per day whilst also achieving a greater batch-to-batch consistency.
Are Inline Viscometers Right for You?
If you’re facing inconsistent product quality, high batch failure rates, excessive energy consumption, or concerns about manual sampling, Hydramotion’s inline viscometers may be the ideal solution for your polymerisation or depolymerisation process.
- Real-time tracking of reaction progress for precise endpoint detection
- Measure viscosity with high accuracy and repeatability, regardless of process conditions and product properties
- Eliminate time delays and human error associated with manual sampling
- Cut production costs by preventing over-runs, improving consistency and reducing failure rates
Hydramotion offers a full range of viscometers designed specifically for polymer applications, from lab-scale to full production. With real-time viscosity data, you can take control of your reactions, optimise processes and produce higher-quality polymers with greater efficiency.