Views: 254 Author: Vickey Publish Time: 2023-12-07 Origin: Site
The goal of this article is to provide users with a quick guide for polyol selection when formulating coatings, adhesives, sealants, and elastomers by directly comparing the salient features of each polyol family.
Determining the essential characteristics for a particular application and the setting in which the components must function is a crucial first step in the correct polyol selection process. For instance, manufacturers use urethane components for their resilience, adaptability, and longevity. Making sure that the original properties won't suffer from severe environmental exposure over time is vitally important. Making the right polyol choice for a given formula can mean the difference between producing a high-quality and low-performing final product.
The hydrolysis of ester-based urethane in hot and humid conditions and the loss of properties that ether-based materials normally exhibit when exposed to either a hot environment or direct sunlight are common examples of negative environmental effects that urethane parts can have and speed up their deterioration.
A thorough grasp of the intrinsic properties of every polyol chemistry is essential for selecting the right material for a given application and preventing modulus, tensile, and tear strength loss from exposure to the environment.
Subsequently, we will discuss each polyol group's fundamental chemistry, the salient features of their physical characteristics, their resistance to chemicals and the environment, and the common uses of these polyols.
Polytetramethylene ether glycols (PTMEG) and polypropylene glycols are the two main families of polyether polyols (PPG).
The best polyol for high-performance polyurethane elastomers is PTMEG. Polyurethanes based on PTMEG demonstrate exceptional resistance to hydrolytic cleavage, excellent mechanical and dynamic properties, high resiliency, good processing characteristics, and good mechanical property retention at low temperatures. The good mechanical properties of the associated polyurethane elastomers can be attributed to low acid values, exact difunctionality, and strain-induced crystallization of the PTMEG soft segments.
PPG polyols exhibit superior resistance to hydrolysis and low-temperature characteristics. Nonetheless, PPG polyols are more susceptible to thermo-oxidative degradation and have worse mechanical properties than PTMEG polyols.
PPG polyols are a great option for room-temperature systems because they are liquid at room temperature.
Because of their low glass transition temperature (Tg), polyethers are impact-resistant and retain their physical characteristics well at low temperatures. When urethane components are required to function in extremely cold conditions, they are the best option.
However, their weak resistance to non-polar, hydrocarbon-based solvents makes polyether polyols unsuitable for applications where the components will come into contact with mineral oils. Their qualities will deteriorate rather quickly in these conditions.
The preferred material for applications where the following characteristics are crucial is PTMEG-based urethanes:
● High resilience with good impingement abrasion.
● Hydrolytic stability in moist and humid environments.
● Excellent dynamic qualities (roll covers, rollers, and wheels).
● Applications in low temperature environments.
● Moreover, PTMEGs are easy to process and mix well due to their comparatively low viscosities.
Dicarboxylic acids and diols react with condensation to form conventional polyester polyols. Segments of polyester may be amorphous or crystalline.
Polyesters are superior to polyethers in terms of tensile strength, cut-and-tear resistance, sliding abrasion resistance, and flex fatigue resistance. Additionally, they show excellent resistance to oxidation, nonpolar solvents, oil, and grease.
Being FDA-compliant, the majority of adipate glycol polyesters are a good choice for prepolymers and urethane articles that are safe to use in applications involving food contact.
When compared to polyethers and polycaprolactones, polyester polyols typically have higher melting temperatures and viscosities, which can cause processing issues. Their use may be restricted at low temperatures due to stiffening and modulus increases, as their Tg is higher than that of polycaprolactones and ethers.
Polyesters have higher acidity levels and a wider molecular weight distribution, which could influence catalyst reactivity. Residual organic acid moieties left by carboxylic acid monomers, such as adipic acid, negatively impact hydrolytic stability.
A unique class of polyester polyols known as polycaprolactone polyols are created by an exclusive addition polymerization process that involves reacting a six-carbon cyclic-ester (lactone) monomer with a low-molecular-weight diol or triol (initiator). Caprolactone polyols and their polyurethane elastomers can have their performance profiles customized through the use of a broad range of glycol initiators.
PCL polyols with very low acid values (which contribute to hydrolytic stability), low polydispersity (which contributes to low viscosities), and perfect primary hydroxy end-functionalities (good stoichiometry control with reactivities that can be adjusted to meet specific application requirements) are made possible by the lower reaction temperatures required and the absence of an organic acid reaction intermediate.
Polycaprolactone polyols are used in applications that require polyurethane elastomers with high durability, broad temperature range performance, good hydrolysis resistance, and excellent elastomeric properties. Urethane applications that require high temperature and oxidative stability, as well as high tensile strength, excellent cut, tear, and flex fatigue resistance, good sliding abrasion resistance, and good chemical resistance to oil, grease, and nonpolar solvents typically choose polycaprolactone polyols.
Compared to adipate-based polyester polyols, caprolactone polyols demonstrate the following performance advantages in polyurethane elastomers:
● Increased ability to withstand hydrolysis.
● Increased resilience to weather and UV stability.
● Improved performance at high temperatures and low temperatures.
● Chemically, it exhibits increased resistance to solvents, fuels, and oils.
● Strength to cut, chip, and tear
● Reduced polydispersity and reduced viscosities.
Polycarbonate diols are aliphatic, linear polyols structurally linked by carbonates. Polycarbonate diols are more hydrolytically stable than polyester polyols because they only soak up small amounts of water and break down at higher temperatures without making an acidic moiety.
The hydrolysis of the soft block of the polyester-based polyurethane is autocatalyzed by acid moieties produced by the hydrolysis of conventional polyesters. Polycarbonate diols represent the next generation of polyurethane elastomer ultimate performance diols. Other polyols cannot match their exceptional durability, consistent performance over time, aging stability, and strong resistance to heat, hydrolysis, weather, and abrasion.
When polycarbonate diols are utilized in polyurethane production, we observe the following characteristics:
● Superior hydrolytic stability, with the exception of base, and minimal water absorption.
● Outstanding stability at high temperatures.
● Chemical resistance is strong.
● UV resistance and weatherability.
● Our product offers superior resistance to environmental stress cracks.
● High gloss retention and minimal yellowing.
● Greater resilience to abrasion, impact, and wear.
● Superior mechanical properties.
Durability of intended characteristics in harsh settings.
In coatings, adhesives, sealants, and elastomers (CASE) formulations, the polyol selection has a major effect on the final product's properties. A variety of polyols have different properties that can affect things like chemical resistance, strength, flexibility, and durability. Key elements impacted by various polyols include:
The polyol's type and molecular weight can affect the CASE material's elasticity and flexibility. Higher-molecular-weight polyols are good for applications that need resilience and flexibility because they tend to impart greater flexibility and elongation properties.
Specific polyols, like polyester polyols, can improve the CASE material's toughness and hardness. These polyols are appropriate for applications requiring strength and durability because they offer better resistance to abrasion and impact.
Different polyols exhibit varying degrees of chemical resistance. For example, polyether polyols are well suited for use in humid or wet environments due to their superior resistance to hydrolysis and stability when exposed to water. Polyester polyols, on the other hand, have a stronger resistance to chemicals like oils and solvents.
Polyol selection can impact the adhesion characteristics of the CASE material. Certain polyols, like acrylic polyols, have the ability to improve adhesion to a variety of substrates, such as wood, plastic, and metal.
The reactivity levels of different polyols can affect the CASE material's processing and curing properties. While slower-reacting polyols, like polyether polyols, allow for longer pot lives and working times, faster-reacting polyols, like polyester polyols, can offer shorter processing times.
The polyol selection may also affect how the CASE material affects the environment. Certain polyols, like bio-based polyols made from renewable resources, provide a more environmentally friendly substitute for traditional petroleum-based polyols.
We hope this post will be useful to you as you think about using various polyols for your CASE products. The purpose of this content is to assist in choosing the right polyol to maximize the performance and processing ease of your coatings, adhesives, sealants, and elastomers.
