Polyurethanes are not just engineered to optimize a single performance parameter. Instead, formulators must address multiple parameters that can include flexibility, durability, and the maintenance of properties at high and low temperatures. In addition, formulators are also tasked with modifying the performance of polyurethane articles to improve hydrolysis, chemical, oil and solvent resistance; toughness, abrasion, and cut-chip resistance; UV and oxidation resistance; and a long service life.
Our various polycaprolactone polyol grades at Gantrade have been designed to allow formulators to maximize a wide cross-section of these parameters within a polyurethane formulation. This FAQ provides a roadmap for selection of the appropriate polycaprolactone polyol to meet the specific requirements for a polyurethane application.
When compared with adipate-based polyester polyols in polyurethane elastomers, caprolactone polyols demonstrate the following performance advantages:
Formulators can further enhance these general property sets by the proper selection of the polycaprolactone diol used to produce polyurethanes requiring demanding performance attributes and service life.
Polycaprolactone polyols are a special class of aliphatic polyester polyols. The polycaprolactone polyols are created by a ring-opening polymerization process (ROP) onto a diol (or triol) “initiator” under mild conditions without the involvement of acidic moieties, as depicted in the chemistry below. The polycaprolactone polyols can be produced with very low acid values (increases hydrolytic stability); perfect end-termination functionality (excellent reactivity and high MWs); narrow molecular weight distributions (low viscosity, etc.) and using a wide variety of “initiator” molecules that allow the design of customized features.
Take a look at the list below to see just some of the “initiator” diols (R-[-OH]f] that are used, as well as key characteristics of the resulting polycaprolactone polyols in a polyurethane elastomer.
The molecular features of the various initiator types manifest themselves in polyurethane characteristics such as crystallization tendencies, dynamic properties, strength, and durability. Some initiators, like NPG and DEG, afford liquid polyols at lower molecular weights.
Placcel N diols were developed with very narrow degrees of polydispersity. The significant reduction in polydispersity results in superior dynamic properties, excellent elastic recovery and resiliency properties, high transparency, and light transmission, and other attributes.
The superior dynamic properties are especially useful in polyurethane high-speed wheels and roller applications, to name a few. The greater transparency afforded by the narrow MWD polyols is beneficial in transparent interlayer film, Paint Protective Film (PPF), safety glazing, and surface protection film applications where excellent durability, abrasion and scratch resistance, oil and solvent resistance and UV resistance are required.
The Placcel T series of very low acid value polycaprolactone polyols offers polyurethanes with greater hydrolysis resistance than even the standard grades of polycaprolactone polyols. An example is shown in the low acid values of Placcel 220T with an acid value of 0.01 vs. 0.06 KOHmg/g for a standard grade Placcel 220 (note that conventional polyester polyols show acid values of 0.50 and above). The improvements in hydrolysis resistance for the T series manifests itself in the tensile strength retention values for Placcel 220NT when compared with Placcel 220N, PTMEG 2000, a 2000 MW HDO adipate, and a polycarbonate diol (PCD). The PCD reference is known to exhibit the highest retention of wet properties in a polyurethane formulation.
The low acid values also result in higher reactivities with isocyanates, especially MDIs, since acidity often reduces the activity of catalysts that may be incorporated. Daicel has developed low acidity grades that also exhibit lower reactivity with isocyanates, without compromising the benefits of low acidity.
The degree of phase separation of the hard and soft segments in a polyurethane increases with the polyol molecular weight. This increase results in a reduction of the Tg for higher molecular weight polyols (MWs), but for the caprolactone polyols, crystallinity and “cold hardening” increase at higher MWs.
The polycaprolactone polyols soft segment mainly affects the elastomeric and dynamic properties and low temperature performance. The hard segment influences the hardness, tear, cut and chip resistance.
At equivalent hardness values, the lower molecular weight polyols show superior transparency, high tear strength, and high elastic recovery. The higher MW polyols exhibit better low temperature performance, higher elongations and reduced compression set values. The table below compares the properties for three different MW grades of polycaprolactone polyols in TPUs.
The Placcel 200 series diols exhibit superior UV, oxidative, and thermal resistance versus polyether polyols, greater water resistance, and a broader service temperature profile than adipate-based polyester diols. The physical properties of these diols range from liquids, to pastes to hard waxes.
Increasing the functionality to three hydroxyl groups affords polyurethanes with a greater crosslink density, higher stiffness and hardness, enhanced thermal and chemical resistance, and improvements in physical properties.
The superior dynamic properties are especially useful in polyurethane high-speed wheels and roller applications. The inherent oil and chemical resistance, hydrolysis resistance, and toughness of the polycaprolactones are useful in TPUs for the oil, mining, and automotive industries, as well as in conveyor belts and hydraulic and pneumatic seals. The greater transparency is beneficial in transparent interlayer film, paint-protective film (PPF), safety glazing, and surface protection film applications where excellent durability, abrasion and scratch resistance, oil and solvent resistance, and UV resistance are required.
Gantrade’s urethane platform of specialty polyols, chain extenders, curatives, and isocyanates provide a broad range of possibilities to achieve your high-performance polyurethane requirements. Our team’s wealth of technical knowledge and expertise, along with our uncompromising standards for customer service, ensure that you will receive the best polyurethane solutions for your applications. Our customers have relied on our technical acumen and responsive service for over 45 years. Contact Gantrade today to learn more.