Today, many wood manufacturers supply their own plywood mills, producing tons of resin every year. Once produced, the resins are usually stored in huge tanks for a few days, then transported to the sites responsible for putting the material into product. There, the resins are used to impregnate various types of paper, cardboard, plywood and others. These paper products are destined for various markets, such as building materials, as well as for chemical and even aeronautical projects.
Viscosity and phenolic resin
Phenolic resins are specifically produced for paper sizing and impregnation applications. They are distinguished by their ideal characteristics, including outstanding strength and toughness, which make them particularly suitable for these uses. However, the production of phenolic resins is complex and presents considerable challenges due to the demanding reaction conditions required to obtain the final product. These rigorous conditions require precise control and in-depth technical expertise to guarantee the quality and performance of phenolic resins.
And its constraints…
This is because the various ingredients used in phenolic resin production come from different suppliers, and batches are never exactly the same. Each batch is first weighed before being mixed, then heated in a reactor to begin the production cycle.
Viscosity measurement plays a very important role in:
Determination of the reaction end-point for optimal product specification
Moreover, the heating process involves clearly defined steps, with highly sensitive temperature and viscosity values that must be strictly adhered to. As the reaction process for this resin is exothermic, the contents of the reactor can continue to heat up even if the heating process is stopped. As the rate of reaction increases with temperature, there is a risk of the polymerization running out of control and the hardening of the reactor content. Thanks to its high sensitivity, the MIVI will detect this unexpected event at an early stage, enabling the operator to take appropriate action to avoid this manufacturing accident.
Sofraser viscometers for process control
The optimum solution to this problem is the MIVI viscometer. Its installation is safe and reliable, and reaction control becomes more precise thanks to temperature correlation. This device avoids the stresses associated with resin curing, a problem now solved by Sofraser technology. In addition, production stability and quality are improved, and production efficiency is considerably enhanced. Interruptions due to resin curing are eliminated, reducing production and sales losses.
Sofraser is committed to improving your process with this solution. Our experienced team is ready to answer all your questions about the instrument, its installation and after-sales service.
We are delighted to announce that Sofraser will be exhibiting at Achema 2024 located in Frankfurt, Germany, the must-attend event for process technology and the chemical industry!
Our team will welcome you at stand F1 in hall 11.1 to present our innovations in viscosity measurement and process analysis.
Here’s what you can expect from our stand at Achema 2024:
– 💡 Case studies: Watch case studies, and how they can be integrated into your industrial processes.
– 🧪 Expert advices: Our PhD & engineers will be on hand to discuss your specific challenges and help you find tailor-made solutions.
– 🎁 Contest and prize: Participate to our exclusive contest game and win valuable vibrating leisure experience, so don’t miss this opportunity!
Don’t forget to make a note of these dates and visit us at Achema 2024. We look forward to sharing our innovations with you and discussing the latest industry trends.
In polymer production, the degree of polymerization is strictly dependent on conversion. This very sensitive to impurities and molar imbalance, especially when conversion is high.
Monomer imbalance may prevent the formation of long polymer chains (leading to molecular weight stagnation); and promote the occurrence of undesired secondary reactions (leading to chain branching, gelation and/or chain degradation).
The development and implementation of procedures for online monitoring and control of conversion and weight-average molecular weight (Mw); are highly desirable to avoid gel formation, early Mw stagnation and polymer chain degradation.
Online process measurement tools such as Near-Infrared Process Spectroscopy (NIRS) and Rheology; which includes the measurements of viscosity are both ideal candidates for determining the physical properties of polymers.
Guided Wave and Sofraser have partnered to develop a dual measurement system that can be installed on a single shared flange; which can be installed directly onto the side of a reactor for real-time process control of polymer production.
By having both a NIRS measurement and a dynamic viscosity measurement; process engineers can make informed decisions based on real-time trends of polymer building, monomer reduction and weight-average molecular weight. Additionally, the dual probe configuration allows both measurements to occur under the same localized flow and sample conditions.
In other words, if the viscometer and NIRS probes were installed on separate flanges; in different locations on the reactor, then transient flow within the reactor could introduce a bias between the two techniques.
Overview of Polyurethane Production and the Role of PAT
Polyurethanes, like other similar step-growth polymerizations, are usually produced in two-step processes.
The first step of polymerization
Polymer materials of low average molecular weights (prepolymer); are produced through the reaction of a polyol and a large excess of diisocyanate; typically using a feed molar ration of 2:1. NIR Spectroscopy can measure the number of reactive hydroxyl groups (OH) on the polyol.
The OH number directly impacts the number of urethane linkages; which greatly influences the physical properties of the final polyurethane product. OH Number is, therefore, an important parameter to monitor and control during polyol production.
Additionally, the laboratory method that is commonplace for hydroxyl number determination is both time-consuming; and involves the use of hazardous materials. An In situ NIR transmission probe has faster throughput and reduce occupational exposure; to the hazardous materials required for offline testing.
The second step of polymerization
The polymer chain is extended; though the reaction of the prepolymer with a diol or polyol of low molecular weight (chain extender). Normally, the main objective is the production of polymer resins of large molecular weights at the end of the second reaction stp. To achieve this objective, some secondary objectives should be pursued.
First, monomer conversion and composition should be tightly controlled during the first reaction step. Second, the amount of polyol fed into the reaction vessel during the second step should be rigorously controlled.
These secondary control objectives are required to avoid monomer imbalance, which may lead to the production of polymer of low molecular weight and eventually cause the loss the batch product.
Finally, the evolution of weight average molecular weights should be accurately monitored by process viscometry and spectroscopy. The output of these process monitoring tools can then be used to control the weight average molecular weights and other parameters during the chain extension step of polyurethane synthesis.
Purposed Process Viscometry and Spectroscopy Control Scheme for Polyurethane Synthesis
The control logic shown below can be adapted as needed to meet the specific product requirements. During the first step, process spectroscopy is used to monitor the monomer conversion and weight average molecular weight.
Other parameters such as concentration or ratio of diisocyanates, excess water concentration, or ratio of glycol reaction products can also be measured with process spectroscopy.
During the second step of the reaction, the average polymer molecular weight is monitored by both process spectroscopy and viscometry. Depending on the trend of molecular weight, the reactant feed rate is adjusted or doses based on NIR and MIVI real-time data.
The dual measurement is an optimal mean to control the rate of polymerization towards an in-spec endpoint.
It should also be noted that the precision with which a NIR analyzer, such as the NIRO Full Spectrum Analyzer, can measure the average molecular weight begins to decrease as monomer conversion increases.
An adapted solution
A process viscometer such as the MIVI is therefore used to more precisely measure average molecular weight during the final stages of cross-linking and chain extension.
The onset of gelation can be determined by both process spectroscopy and viscometry. If the NIR determines that monomer conversion is occurring without a change in average molecular weight, then the onset of gelation has likely occurred.
Viscometry can be used as a secondary confirmation of gelation. If gelation is occurring, then the viscometer will measure a sudden perturbation dut to the agglomeration or branching of polymers.
The dual-probe approach enables the process engineer to quickly react to the gelation and begin to add inhibitors to slow the rate of cross-linking. The concentration of inhibitors, such as Hydrochloric Acid, can be measured by process spectroscopy.
Once the reaction trend has returned to normal, the amount of inhibitor can be reduced and the reactant, such as 1.4 Butane Diols, dosing feed rate to increase. The process control scheme allows the process engineer to coach the reaction to the desired molecular weight trajectories and ensure on spec product is produced.
Once the target molecular weight is achieved, the process engineer can transfer the on-spec polyurethane for any post-formation processing such as extrusion.
Conclusion
Bulk polymer production in and of itself is a fairly routine chemical process. However, the drive to optimize production and therefore reduce manufacturing costs necessitates the need for real-time process analysis.
Near-Infrared Process Spectroscopy and Viscometry; which includes the measurement of viscosity are both ideal candidates for determining the physical properties of polymers.
The development of modern process monitoring tools enables direct real-time measurements of the chemical reactions such as monomer conversion, molecular weight, acid number, or even the information of side branches and gels.
The dual probe and subsequent process control scheme can be used to improve batch copolymerization yield.
Designed by Elementale (Texas, USA) this probe was developed in collaboration with Guided Wave and Sofraser.
This information has been sourced, reviewed and adapted from materials provided by Guided Wave.
For more information on this source, please visit Guided Wave
Application of resin viscosity measurement in polymerization
Measuring resin viscosity is an indirect way of measuring the molecular weight of polymers. Phenolic resins have exothermic reactions. They are very sensitive to temperature, and their viscosity value requires continuous observation. If the reaction occurs too quickly, the result is poor polymer quality and possible curing. This causes enormous losses of raw materials and very long downtimes requiring complicated maintenance, additional labor costs and delivery delays. Sometimes even the entire plant has to be replaced at exorbitant cost.
Critical points related to viscosity in a batch polymerization process are:
control of raw materials
detection of the start of the reaction
control of the polymerization rate
measurement of molecular weight
characterization of chain length
detection of the end point of reaction
control of polymer dilution
measurement of concentration
control of final product quality.
The very good sensitivity of MIVI in low viscosities, associated with a high full scale range of the sensor, make it the ideal instrument to control the viscosity of phenolic resin polymerization processes.
The installation of a MIVI sensor on a phenolic resin reactor in a batch plant offered greater safety in production thanks to alarms, and avoided any curing problem. Since then, this plant has not encountered any more problems with the mass setting of the installation. The savings realized after the installation of the MIVI process viscometer in the batch phenolic resin polymerization unit are estimated with a return on investment of about one year.
Polyurethane is one of the most versatile polymers. It appeared at the end of the 1930s and is used as an insulating, coating, adhesive and solid plastic material. Polyurethane can be produced in different forms: flexible and cross-linked foam, elastomer or coating. It is in high demand all over the world and particularly in China.
For online viscosity measurement in distillation and evaporation processes of MDI/TDI
Polyurethanes are produced by reacting an isocyanate, usually TDI (toluene diisocyanate) or MDI (methylene diphenyl diisocyanate) with a polyol (e.g. ethylene or propylene glycol). Depending on the expected end product, additives or other ingredients are incorporated to obtain the desired formulation.
During the manufacturing process, raw materials are pumped from their storage tank to a pressure reactor; where they are heated and stirred, monitoring pressure and temperature.
“Pure” MDI or TDI is produced by the reaction of a diamine (MDA or TDA) with phosgene. The crude diisocyanates are then fractionated in a distillation column to produce purer mixtures of isomers. At the bottom of the column, a mixture of MDI or TDI and tar is sent for recovery through an evaporation and drying process to increase the yield of the MDI/TDI unit.
Viscosity is a crucial parameter for the evaporation of MDI/TDI and can also be beneficial in other manufacturing cycles. Precise control of viscosity and temperature enables the evaporator residue content to be accurately monitored, which in turn provides reliable information on the proper functioning of the process.
The installation of a MIVI viscometer allows a viscosity measurement to be carried out directly on the reactor or on a pipe angle, at the outlet of the evaporator or the distillation tower. The MIVI viscometer allows monitoring of the residue to ensure that sufficient product has been recovered. It also makes it possible to control the final quality of the product.
Classified in polymer product family, starch is used in a large part of industrial production, especially in packaging industry. Starch glue is principally employed for bonding paper products and is used in the manufacture of corrugated board.
Viscosity of starch glue in bonding paper products
Corrugated cardboard is one of the most important application using starches glue. Corrugated board results by the adhesion of a fluted layer of paper between two flat layers. Starch is used as an adhesive in these different liners.
The control of the adhesive viscosity during the process is critical. When the viscosity is out of the acceptable range, it impacts end-product quality and imperfections are important. Adhesives with a sufficient viscosity leads to lower impregnation of grooved blankets and paper, which favors the quality and strength of the adhesive joints.
It should be noted that the rheological behavior of the starch glue is complex. Mainly pseudoplastic and thixotropic, the starch glue requires a precise and versatile viscosity measurement instrument.
A viscometer to maintain end-product quality
The installation of a MIVI sensor on the production line or starch mixing systems provides continuous and stable viscosity values during the laying of the adhesive. The MIVI viscometer and associated electronics guarantee zero default in glue deposit.