Polyurethane (PU) catalyst is a reaction activator that speeds up the hardening of polyurethane-based products. It's used to shorten installation schedules when there are rapid repairs, cool weather, or other issues.
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Polyurethane catalysts serve as agents that accelerate the chemical reactions required to form polyurethane. These reactions typically involve the polymerization of isocyanates and polyols to create flexible or rigid foams, elastomers, and coatings. The role of catalysts is crucial in optimizing reaction rates and ensuring high-quality end products with consistent properties. Without catalysts, the polymerization process would be too slow or inefficient, affecting the quality and cost of production.
There are various types of polyurethane catalysts, each designed to facilitate specific chemical reactions depending on the end product requirements.
Organotin catalysts are among the most commonly used in polyurethane production. These catalysts promote the reaction between isocyanates and polyols, resulting in the formation of polyurethane. They are particularly favored for their ability to speed up the reaction process, providing efficient manufacturing cycles. However, environmental concerns have raised the need for safer and more sustainable alternatives, as some organotin compounds can be toxic.
Amine catalysts are another widely used class of catalysts in polyurethane production. They are particularly effective in producing flexible and rigid polyurethane foams, as they help control the reaction rate and influence the foam structure. Amine catalysts are more environmentally friendly compared to organotin catalysts, making them a popular choice for industries focused on sustainability.
While organotin catalysts offer fast reactions, amine catalysts are increasingly preferred due to their lower toxicity and environmental impact. Amine catalysts also tend to provide more consistent performance, particularly in the production of rigid polyurethane foams, where precision is key.
Polyurethane catalysts facilitate chemical reactions by lowering the activation energy required for the polymerization of isocyanates and polyols. At the molecular level, catalysts interact with the reactants to increase their reactivity, speeding up the reaction and leading to the formation of polyurethane. This activation enables the production of foams, coatings, and other materials with specific properties.
The activation of catalysts involves the formation of intermediate complexes with the isocyanate or polyol, which lowers the energy needed for the reaction to occur. This process accelerates the formation of urethane bonds, essential for creating the final polyurethane product.
Polyurethane catalysts also play a role in chain extension and crosslinking, processes that influence the final properties of the material. Chain extension refers to the lengthening of polymer chains, while crosslinking creates links between these chains, resulting in stronger, more durable materials. The type of catalyst used will determine the extent of these processes, impacting the flexibility, rigidity, and strength of the final product.
Polyurethane catalysts offer several benefits to manufacturers and end-users, making them indispensable in the production of high-performance polyurethane materials.
Polyurethane catalysts significantly reduce reaction times, allowing manufacturers to produce materials more quickly and efficiently. This reduction in processing time can result in cost savings and increased productivity, essential factors for businesses in competitive industries.
By carefully selecting the right catalyst, manufacturers can exert greater control over the final properties of the polyurethane product. Catalysts influence various characteristics such as hardness, density, flexibility, and durability, ensuring that the product meets specific performance standards.
While polyurethane catalysts offer numerous advantages, their environmental impact and safety are essential considerations.
As environmental awareness grows, the demand for greener, more sustainable alternatives to traditional polyurethane catalysts has increased. Bio-based catalysts and those with fewer harmful emissions are being explored as potential solutions. These alternatives not only reduce the environmental footprint but also cater to industries aiming to meet stricter regulatory requirements.
Due to the chemical nature of polyurethane catalysts, safety protocols are critical when handling them in industrial settings. Protective equipment, proper storage conditions, and strict adherence to handling guidelines are necessary to ensure the safety of workers and minimize the risk of accidents.
Polyurethane catalysts find applications in a broad range of industries, from automotive manufacturing to building insulation.
In the automotive sector, polyurethane is used to produce lightweight, durable materials for vehicle interiors, exteriors, and insulation. Catalysts are crucial in controlling the properties of these materials, ensuring they meet safety standards while also offering lightweight solutions for fuel efficiency.
Polyurethane catalysts are extensively used in building and construction, especially in the production of insulation materials and coatings. Rigid polyurethane foams provide excellent thermal resistance, while flexible polyurethane foams are used in cushioning applications such as furniture and mattresses.
Polyurethane insulation foams are highly effective in energy-efficient buildings due to their low thermal conductivity. Catalysts ensure that these foams are produced with the optimal density and durability, making them a top choice for energy-conscious construction projects.
Choosing the right catalyst is essential for achieving the desired properties in the final product.
The selection of a catalyst should be based on the specific requirements of the product, including its flexibility, rigidity, thermal resistance, and strength. Manufacturers must evaluate the performance characteristics of different catalysts to find the optimal match for their needs.
When selecting a supplier, it’s important to consider factors such as the quality, availability, and cost of the catalysts. Working with a trusted supplier ensures consistent product quality and reliable delivery timelines.
Polyurethane catalysts are indispensable in the manufacturing of high-quality polyurethane materials used across various industries. From enhancing reaction times to improving product consistency and sustainability, catalysts play a pivotal role in shaping the properties of polyurethane products. By selecting the right catalyst, manufacturers can optimize their production processes and meet the specific needs of their industries. If you need further assistance or would like to learn more about choosing the right catalyst for your applications, don’t hesitate to contact us. We are a trusted supplier committed to delivering high-quality solutions for your polyurethane manufacturing needs.
How PU catalyst it works?
PU catalyst lowers the activation energy required for a reaction to occur, which allows the reaction to proceed more easily and with less energy.
How to use PU catalyst?
Add 0.5–1.5% of the PU catalyst by weight to the total weight of the polyurethane formula. The amount of catalyst needed depends on the hardening acceleration required, as well as the ambient and substrate temperature and conditions.
How to store PU catalyst?
PU catalyst can be stored for up to 12 months in a dry place in its original packaging.
Safety about PU catalyst
PU catalyst is flammable and harmful if swallowed. It's also fatal if inhaled.
PU catalysts are typically tertiary amines, but other catalysts include metal organics such as tin, bismuth, lead, mercury, zinc, and potassium.
Polyurethane is a popular material used in home furnishings such as furniture, bedding, and carpet underlay.
Polyurethanes are incredibly versatile (Figure 1); they are flexible, have high impact and abrasion resistance, strong bonding properties, are electrically insulating and are relatively low cost compared to other thermoplastics.
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Figure 1. Polyurethanes are versatile materials and can be used to make hard and rigid materials through to soft flexible foams. Common applications for polyurethane include automotive seats, shoes, floor coatings and furniture.
Furniture foams are the dominant application (Figure 2) however uses of polyurethane also include:
Figure 2. Polyurethane consumption worldwide (). Flexible foams for furniture and automotive account for the largest share of polyurethane usage followed by rigid foams for construction and insulation applications.
Polyurethane and its related chemistries were first discovered in by Otto Bayer however it wasn’t until the ’s that they became commercially available. The basic synthesis involves the exothermic condensation reaction of an isocyanate (R’-(N=C=O)n) and a hydroxyl-containing compound, typically a polyol (R-(OH)n) (Figure 3).
The reaction proceeds readily at room temperature, regardless of a catalyst, and is typically completed in a few seconds to several minutes depending on the formulation, in particular the choice of isocyanate. Therefore compared to other polymers such as polyethene or polypropene which are produced then heated and moulded at a later stage, polyurethanes are made directly into the final product via reaction injection moulding (RIM), or applied onto the substrate in the case of adhesives and coatings.
Figure 3. The condensation polymerisation of an isocyanate (R’-(N=C=O)n) and a polyol (R-(OH)n) to form polyurethane.
An important side reaction involves the isocyanate component and water. If moisture is present in the mixture (Figure 4), then the isocyanate will react with this water to form an unstable carbamic acid which then decomposes to form urea and carbon dioxide gas thus resulting in foaming. The selection of an appropriate catalyst can either suppress this reaction or can promote this reaction if foam formation is desired.
Figure 4. Isocyanates are highly reactive with hydroxyl (-OH) groups. When in contact with water, isocyanates react to form carbamic acid which then decays to form an amine and carbon dioxide gas. This gas is responsible for foaming and is often used in the production of PU foams for furniture or construction applications.
Polyurethanes are typically supplied as two-component formulations; a part A containing the polyol, catalyst, and any additives, and a part B compromising of the isocyanate.
The majority of polyols used in polyurethane production are hydroxyl-terminated polyethers though hydroxyl-terminated polyesters are also used. The choice of polyol ultimately controls the degree of cross-linking and therefore the flexibility so formulators must consider not only the size of the molecule, the degree of branching but also the number of reactive hydroxyl groups present.
If a polyol containing two hydroxyl groups (a diol) is reacted with TDI or MDI, then a linear polymer is produced. Polyols with a greater number of reactive hydroxyls result in a higher level of crosslinking and a more rigid final product.
The most commonly used isocyanates for polyurethane production are the aromatic diisocyanates toluene diisocyanate (TDI) and methylene diphenyl diisocyanate (MDI) which form the basis for >90% of all polyurethanes (Figure 5).
TDI is a mixture of two isomers and is primarily used in the production of low-density flexible foams whereas MDI is a more complex mixture of three isomers and is used to make rigid foams and adhesives.
Figure 5. Chemical structures of the aromatic isocyanates toluene diisocyanate (TDI) and methylene diphenyl isocyanate (MDI). TDI and MDI account for 90% of all isocyanate usage globally and are mostly used to produce flexible and rigid foams.
Less reactive are the aliphatic isocyanates (Figure 6) however these are important for coatings applications due to their excellent UV and colour stability. Aliphatic isocyanates account for <5% of isocyanate usage worldwide and include hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI).
Figure 6. Chemical structures of the aliphatic isocyanates hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI). HDI and IPDI mostly find use in coatings applications and account for <5% of isocyanate usage.
Blocked isocyanates are a relatively new development whereby the reactive NCO- groups are further reacted with groups such as dimethyl malonate (DEM), dimethyl pyrazole (DMP) or methylethyl ketoxime (MEKO) to produce inert and non-hazardous materials. These materials can be selectively unblocked at elevated temperatures (+100°C) thus opening up a greater variety of applications such as usage in 1K or waterbased formulations, or for lower free isocyanate levels.
Catalysts play an important role in the production of polyurethane as not only do they increase the reaction rate and control gelling time, they also assist with balancing the side reactions including the water reaction and therefore control gas-formation and foaming.
Broadly speaking, the catalysts used for polyurethane manufacture fall into two categories: amines or organometallic catalysts including organotin, bismuth and zinc.
Amine catalysts are derived from ammonia (NH3) by substituting one (primary) or two (secondary) or three (tertiary) of the hydrogen atoms with an alkyl group. Their catalytic activity is determined by both the structure and the bascity with increased steric hinderance of the nitrogen atom resulting in decreased activity and increased bascity increasing activity. Tertiary amines are predominantly used in the manufacture of foam as whilst they drive urethane formation, they also promote the water reaction leading to CO2 gas generation.
Mercury catalysts such as phenylmercuric acetate, propionate, and neodecanoate are highly efficient at driving urethane formation and characteristically result in a long pot life in combination with rapid back-end cure. However despite their excellent performance, mercury catalysts are less common due to their poor toxicological status.
Outside of amine catalysts, organotin catalysts are the most widely used in polyurethane production with grades such as TIB KAT® 218 (dibutyltin dilaurate DBTL), TIB KAT® 216 (dioctyltin dilaurate DOTL), and TIB KAT® 318 (dioctyltin carboxylate) widely used in CASE applications (coatings, adhesives, sealants, and elastomers).
TIB KAT® 218 (DBTL) is the workhorse grade (Figure 7) and strongly drives the urethane reaction however in some instances longer ligand dioctyltins such as TIB KAT® 216 (DOTL) or TIB KAT® 318 are preferred due to more favourable labelling.
Other grades such as TIB KAT® 223 or TIB KAT® 214 can provide varying curing profiles such as a rapid cure in the case of TIB KAT® 223 or a “mercury-like” curing profile with TIB KAT® 214.
Figure 7. Mechanism of polyurethane catalysis using TIB KAT® 218 (dibutyltin dilaurate DBTL). DBTL acts as a Lewis acid and accepts the non-bonding electrons from the oxygen on the isocyanate molecule to initiate the reaction.
Bismuth and zinc catalysts are growing in popularity due to their low toxicity and both TIB KAT® 716 (bismuth) and TIB KAT® 616 (zinc) are used in CASE applications as they are strongly selective towards the urethane reaction.
Bismuth, in particular, can mimic DBTL performance and in some instances offers a shorter pot life than organotins. However, bismuth typically requires higher dosage levels than organotins and is sensitive to hydrolysis; even low moisture levels can have a detrimental effect on activity.
Zinc on the other hand results in increased pot life with a good through cure and is especially useful when curing at elevated temperatures (>60 °C).
Other catalysts such as aluminium, titanium and zirconium complexes are being used in some instances though are not widespread as have lower activity and can require much higher dosages. They can also be more selective towards primary alcohols in a polyol mixture leading to poorer and breakable polyurethane material.
Catalyst Advantages DisadvantagesAmine
(e.g. DABCO, DMDEE)
Can have a strong odour.
Can affect colour.
Mercury
(e.g. phenylmercury propionate)
Table 1: Advantages and disadvantages of amine and metallic catalysts for polyurethane production.
Depending on the final application, polyurethane formulators will also include other additives in the formulation including, but not limited to:
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