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What is Polyurethane? A Materials Case

By sensXPERT

What is Polyurethane? A Materials Case

Polyurethane is an adaptable class of polymers that is used to combat difficulties or challenges in a myriad of industrial and consumer products. The material’s versatility allows it to insulate sensitive components, provide consumer comfort, and resist harsh environmental conditions. Polyurethane can also be molded into numerous sizes and shapes.  

In this week’s article, we outline what polyurethane is, the properties exhibited by the materials, the applications in which this material is applied, and provide a materials case on polyurethane conducted by sensXPERT’s applications specialists. 

Polyurethane Encapsulating Pipe

What is Polyurethane? 

This versatile class of polymers is formed through a reaction between isocyanates and polyols. Polyurethanes, or PUs, can be rigid and hard or flexible and soft depending on the chemical formulation and production process. PUs have a vast range of properties that make them popular in numerous applications.  

During formation, polyurethanes commonly undergo a reaction called polyurethane polymerization. In the formation process, isocyanates react with polyols to form urethane linkages, and material suppliers can adjust this reaction to influence the hardness, flexibility, or other properties of the final polyurethane material.  

Material suppliers produce polyurethanes that exhibit various properties, some of which include the following: 

  • Durability 
  • Versatility 
  • Water Resistance 
  • Chemical Resistance 

Accordingly, there are several types of polyurethanes that are chosen for different applications: 

  • Flexible foams: used in comfort applications such as cushions, car seats, and mattresses 
  • Rigid foams: can be used as insulation in construction or appliances 
  • Coatings: provide protective coatings for surfaces such as metal, concrete, or wood 
  • Adhesives and Sealants: used in bonding or sealing applications 
  • Elastomers: display rubber-like properties and used in applications such as wheels, seals, or tires 

Besides the above-mentioned applications, polyurethane is often used in electromobility and electronics manufacturing to insulate components against harmful influences.  

What is Potting? 

Potting is a process wielded in manufacturing to encapsulate or embed components or devices in protective materials. Potting is conducted to provide mechanical support, environmental protection, and, in some cases, insulation for enclosed items. This process is typically carried out to safeguard components from environmental factors such as moisture, vibrations, thermal stress, and more.  

Potting is concerned with the pouring or dispensing of a potting material around components in an open mold or enclosure.  

This process is not to be confused with closed mold encapsulation processes, which involve placing electronic components inside of a closed mold or cavity and injecting encapsulation material to completely surround the components. 

You can read more about electronics encapsulation by downloading our free white paper on ‘A Guide to Electronics Encapsulation: Optimizing Closed Mold Encapsulation Processes

A Materials Case: Potting Polyurethane 

Depending on the type, polyurethane reacts extremely quickly at room temperature. In this case, sensXPERT’s applications specialists conducted material trials on rigid foam polyurethane to determine the material’s behavior throughout its reaction process.  

More specifically, the rigid foam PU is a foam with gas bubbles that, once cured, cannot be deformed. This material is desirable for several applications because the gas bubbles ensure that the final component’s overall weight will be lighter than if compact materials were used. 

The sensXPERT specialists conducted the trials with the aim of understanding the most effective ways of using the Digital Mold sensor technology to characterize polyurethane behavior in a potting process.  

To begin with, the specialists selected a couple of processing temperatures to examine whether polyurethane displays different molecular behavior when subjected to different temperatures. Additionally, sensXPERT’s material specialists monitored the effects on the measurements when adding a thin film – teflon foil, to be specific – between our sensor technology and the polyurethane.  

Trial Results

The polyurethane material study led to several findings. Regarding the impact of placing a thin film between sensXPERT’s dielectric sensors and the polyurethane, our specialists concluded that there are no detrimental effects on the measurements. 

Figure 1 illustrates the curing progression of polyurethane at 45°C with a teflon foil film. These results are noteworthy, as, due to polyurethane’s adhesive properties, some manufacturers may want to use a thin film to prevent the material from sticking to their molds, which does not hamper the dielectric sensors from conducting real-time material measurements. 

Polyurethane cure curve
Figure 1: PU curing at 45°C with a teflon foil between sensor and material

Additionally, results of the material study concluded that as the material is heated, molecular mobility increases and viscosity decreases. This influence is more pronounced at higher temperatures, as is visible in figure 2 with a greater drop in ion and rheological viscosity at 45°C (green line). At a certain point, the curing reaction begins and there is an initial balance between the drop in viscosity and curing with the curing reaction eventually overtaking the drop in viscosity.  

Another conclusion by our specialists is that polyurethane curing reactions are quicker at higher temperatures. 

Polyurethane cure at 45 degrees and 30 degrees
Figure 2: Comparison of PU curing at 30°C and 45°C

Finally, figure 3 presents the polyurethane’s relative permittivity, which indicates the extent to which a material can be polarized. The measurement technology, in this case, measures dipole mobility and examines the PU’s foaming process. The initial drop in figure 3 represents the start of the material’s foaming reaction.  

The foaming reaction is a crucial one to monitor because the amount and size of the gas bubbles within the foam can heavily impact final component performance. By monitoring the real-time foaming reaction, manufacturers can adjust their process parameters to achieve their desired foaming behavior.  

Polyurethane permittivity at 45 degrees and 30 degrees
Figure 3: PU polarizability at 30°C and 45°C

Overall, our technology ensures that material behavior is sufficiently monitored in real-time to aid manufacturers in achieving their desired degrees of cure and making sure that their final components possess the properties required for their targeted applications.  

By understanding material behavior, manufacturers gain real-time insights on the quality of their final components, without needing to conduct downstream quality assurance testing.  

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