Polyurethanes in Practice: Answers to the 10 Most Common Questions from Manufacturers and Processors

Photo: Ömer Haktan Bulut / Unsplash

Polyurethanes are among the most versatile polymers, finding applications from insulating foams and durable coatings to flexible adhesives. However, their processing requires knowledge of key parameters—from the correct component ratio and temperature conditions to the influence of humidity. This article focuses on specific issues that trouble manufacturers and processors: why inadequate adhesion occurs, how to prevent bubbles in the material, or how to optimize processing time. The answers are based on real client inquiries and practical experience with PUR systems.

1. What are the main advantages of polyurethane systems compared to other polymers?

Polyurethanes (PUR) excel in combining mechanical properties, chemical resistance, and processing versatility, making them an ideal choice for a wide range of industrial applications. Key advantages include high tensile strength and abrasion resistance, often surpassing the properties of common thermoplastics such as polyethylene or PVC. PUR systems also offer excellent flexibility – from soft elastomers to rigid structural foams – while maintaining low weight. Another benefit is their resistance to oils, greases, and many solvents, which extends the lifespan of products in demanding conditions.

In terms of processing, polyurethanes are highly adaptable: they can be cast, injected, foamed, or applied as coatings. Thanks to their reaction mechanism (polyaddition polymerization), they achieve rapid curing without the need for high temperatures, reducing energy costs. PUR systems also allow for precise dosing of additives, such as flame retardants, UV stabilizers, or fillers, which expands their application possibilities. Another advantage for manufacturers is the potential for recycling – for example, through mechanical grinding or chemical depolymerization.

2. How to Store and Handle PUR System Components Correctly?

Storing and handling polyol and isocyanate components requires adherence to specific conditions to maintain their reactivity and safety. The basic rule is to keep the storage temperature within the range of 15–25 °C – excessively low temperatures can cause polyol crystallization, while high temperatures accelerate isocyanate degradation. Components must be protected from moisture, which can initiate unwanted reactions and the formation of CO2, leading to foaming or deterioration of the final product’s mechanical properties.

Containers with components must be hermetically sealed and stored separately to prevent contamination. When handling, it is essential to use personal protective equipment (gloves, safety goggles, respirators) and ensure adequate ventilation of the workspace. Isocyanates, particularly MDI and TDI, are classified as hazardous substances under REACH and CLP regulations, so it is necessary to follow safety data sheets and rules for working with volatile organic compounds. It is also recommended to regularly check the expiration of components—most PUR systems have a shelf life of 6–12 months from the date of manufacture.

Photo: Ömer Haktan Bulut / Unsplash

3. How does the mixing ratio of components affect the quality of the final PUR product?

The precise mixing ratio of the polyol and isocyanate components is critical for achieving optimal polyurethane properties. Deviations from the recommended ratio (usually specified by the manufacturer in weight or volume percentages) can lead to insufficient curing, reduced mechanical strength, or increased brittleness. For example, an excess of isocyanate causes excessive hardness and brittleness, while its deficiency results in a soft, sticky material with low chemical resistance.

To ensure accurate dosing, special mixing and metering equipment is used, such as static or dynamic mixers with automatic flow control. For manual mixing, it is crucial to adhere to precise weighing of components and thorough mixing to prevent local inconsistencies. Another important factor is the temperature of the components during mixing—ideally, it should be within the range of 20–25 °C to ensure a homogeneous reaction. For more complex systems with additives (e.g., catalysts or fillers), their influence on the reactivity of the mixture must be taken into account.

4. What are the most common defects in PUR products and how to prevent them?

Typical defects in polyurethane products include bubbles, uneven curing, surface defects (e.g., "orange peel"), or insufficient adhesion to the substrate. Bubbles most commonly arise due to moisture in the components or air trapped during mixing. The solution is thorough degassing of the mixture before application and the use of vacuum degassing for critical applications. Uneven curing can be caused by insufficient mixing or deviations in the component ratio—here, checking the metering equipment and temperature conditions helps.

Surface defects such as "orange peel" are often related to too rapid curing or unsuitable viscosity of the mixture. Adjusting catalysts or thinners can achieve a smoother surface. Adhesion issues to the substrate are addressed by surface pretreatment (degreasing, roughening) and the use of suitable primers. It is also important to follow the technological procedures recommended by the PUR system manufacturer and to perform regular quality tests, such as tensile strength tests or abrasion resistance tests according to standard test methods.

Photo: Ömer Haktan Bulut / Unsplash

5. How to choose the right type of polyols and isocyanates for a specific application?

The selection of polyols and isocyanates is crucial for achieving the desired properties of a polyurethane system, whether it be hardness, elasticity, chemical resistance, or mechanical strength. Polyether-based polyols are suitable for applications requiring flexibility and water resistance, such as in foam materials or elastomers. In contrast, polyester polyols provide better mechanical properties and resistance to oils and solvents, which is appreciated by manufacturers of coatings, adhesives, or technical components.

The type of isocyanate depends on the reaction type and desired reactivity. Aromatic isocyanates, such as MDI or TDI, are cost-effective and provide high strength but may yellow under UV radiation. For applications requiring light stability, aliphatic isocyanates, such as HDI or IPDI, are used instead. It is also important to consider the viscosity of the components – low viscosity facilitates mixing and processing, while higher viscosity can improve the mechanical properties of the final product.

6. Which additives improve the processability and properties of PUR systems?

Additives play a key role in polyurethane systems, as they enable the optimization of processability, stability, and final material properties. Catalysts, such as amines or organotin compounds, accelerate the reaction between polyols and isocyanates and allow precise adjustment of processing time. For applications requiring a slower reaction, inhibitors are used to extend the gelation time and facilitate material handling.

To improve mechanical properties, fillers such as glass fibers, calcium carbonate, or microspheres are added, which increase strength and reduce shrinkage. To protect the material from aging due to UV radiation or oxidation, stabilizers such as HALS (hindered amine light stabilizers) or antioxidants are used. Blowing agents, whether physical (e.g., pentane) or chemical (water), then determine the structure and density of foam materials. The right combination of additives can significantly expand the application possibilities of PUR systems.

7. What are the ecological and safety aspects of working with PUR systems?

Working with polyurethane systems requires adherence to strict safety and environmental measures, particularly due to the reactivity of isocyanates and volatile organic compounds (VOCs). Isocyanates are classified as hazardous substances under REACH and CLP regulations, as they can cause respiratory sensitization and skin allergies. Therefore, it is essential to use personal protective equipment such as gloves, safety goggles, and respirators, and to ensure adequate ventilation of the workspace.

The ecological aspect concerns not only the safe handling of waste but also reducing VOC emissions and finding alternative raw materials. In recent years, there has been growing interest in bio-based polyols, which are produced from renewable sources such as vegetable oils. These polyols reduce the carbon footprint of PUR systems while maintaining their performance properties. It is also important to follow sustainable processing principles, such as minimizing material residues and recycling waste in accordance with applicable regulations.

Need advice on selection or processing?

Every PUR system requires an individual approach – whether it's the choice of catalysts, stabilizers, or technological conditions. GCG Group provides detailed technical and safety data sheets for every raw material, and our experts will help you select the optimal solution for your application. Contact us – or browse our catalog of over 1,300 products right away.