Two-component Polyol

Two-component, polyol-cured 25.4 6 Isophthalic polyester (vinyl toluene ... 

Injection moulding can be applied to two-component thermosets in a process known as Reaction Injection Moulding. The two liquid components are mixed and then injected into a closed mould. In the case of epoxies and polyurethanes, heat is produced on mixing due to the exothermic reaction between the two components (polyol and isocyanates in the case of polyurethanes), so no external source of heat is required. 

Two-component, polyol-cured Two-part solventless, polybutylene-based Silicones... 

Polyurethane adhesives are known for excellent adhesion, flexibihty, toughness, high cohesive strength, and fast cure rates. Polyurethane adhesives rely on the curing of multifunctional isocyanate-terrninated prepolymers with moisture or on the reaction with the substrate, eg, wood and ceUulosic fibers. Two-component adhesives consist of an isocyanate prepolymer, which is cured with low equivalent weight diols, polyols, diamines, or polyamines. Such systems can be used neat or as solution. The two components are kept separately before apphcation. Two-component polyurethane systems are also used as hot-melt adhesives. 

The first urethane reaction in Fig. 1 is used in two major ways in adhesives. In one case, a two-component adhesive usually employs a polyol and polyisocyanate with catalyst. This can react at room temperature to form the polyurethane. The second use of this reaction is to make an isocyanate-terminated prepolymer. Reacting a stoichiometric excess of isocyanate with polyol can produce an isocyanate-terminated prepolymer. A prepolymer is often made with an NCO/OH ratio of 2.0, as shown below, but the isocyanate ratio can range from 1.4 to over 8.0, depending upon the application ... 

Blocked isocyanate, for our purposes, will refer to the reaction product of a diisocyanate or isocyanate-terminated prepolymer in which the isocyanate functionality has been reacted with a blocking agent . Once blocked , the diisocyanate can be added to polyols or certain chain extenders, and these materials will not react at room temperature. The concept is shown in the sixth item of Fig. 1. An adhesive formulated with a blocked isocyanate is basically a two-component adhesive that does not react until heated to the activation temperature. When an adhesive is made with a blocked isocyanate together with hydroxyl-containing curatives, the adhesive has a good long shelf life at room temperature. However, once heated... 

The soft segments made from asymmetrical (amorphous) polyols are important for two-component structural adhesives and one-component moisture-curing adhesives. These materials are applied and usually cured at room temperature. 

With the exception of fillers, the raw materials used in two-component urethanes are all liquids. The two components have an isocyanate side and a polyol side. The raw materials are combined in various ways in order to produce with liquids that are combined at a 1 1 volume ratio, preferably, thus keeping the dispensing equipment as simple as possible. Fixed ratios of 3 2 or 1 2 are also commonly used. Ratios other than these are possible, but require the use of a... 

Open times of two-component urethanes can vary widely, depending on the level of catalyst. Reaction times can vary from 90 s to over 8 h. Dibutyltin dilaurate is the most common catalyst employed to catalyze the urethane reaction. This is normally added to the polyol side. A tertiary amine may also be added in small amounts. Tin catalysts do not catalyze the amine/isocyanate reaction very well. Acids, such as 2-ethyl hexanoic acid, may be employed to catalyze the amine/isocyanate reaction where needed. 

Two-component systems consist of (1) polyol or polyamine, and (2) isocyanate. The hardening starts with the mixing of the two components. Due to the low viscosities of the two components, they can be used without addition of solvents. The mass ratio between the two components determines the properties of the bond line. Linear polyols and a lower surplus of isocyanates give flexible bond lines, whereas branched polyols and higher amounts of isocyanates lead to hard and brittle bond lines. The pot life of the two-component systems is determined by the reactivity of the two components, the temperature and the addition of catalysts. The pot life can vary between 0.5 and 24 h. The cure at room temperature is completed within 3 to 20 h. 

Most polyurethane formulations are two-component systems, meaning they are made from two basic constituents which are mixed together and react to form the final polymer. The two components are an isocyanate (or isocyanate blend) and a polyol (or polyol blend). The isocyanate is often referred to as the A side and the polyol the B side , although some use the opposite convention. 

One component contained the isocyanate and epoxy resin, and the other component contained the polyols, chain extenders, catalysts, fillers, and plasticizers. The two components were then mixed together for 30 seconds (at room temperature) using a high speed mechanical stirrer at 2000 rpm. The mixture was then quickly poured into a pre-heated mold and pressed on a laboratory platen press at 100 C. The sample was removed from the press and demolded 30 minutes after it gelled. The gel time was approximately 3-6 minutes. The post curing condition was for 5 hours at 120 0. 

Second-generation solventless polyurethane adhesives Two-component second-generation adhesive systems are the most widely used of the 100% solids products. These two-part adhesives comprise an isocyanate terminated prepolymer based on the reaction product normally of MDI and polyols (polyether or polyester) in the presence of excess isocyanate, and a polyol (polyether or polyester based). 

Pitch-polyurethane coatings are two-component materials containing polyol as the base resin and an isocyanate curing agent. They cure satisfactorily at temperatures as low as 0°C (BSC, undated). 

Two-component polyurethane adhesives are the condensation product of a polyol with an organic isocyanate. The first component contains a prepolymer of the polyol, and polyisocyanate is the second component. These two components are thoroughly mixed before application. 

In most cases semi-rigid urethane foams are produced by using two-component systems, that is component A (polyisocyanate component) and component B (blend of the remaining ingredients, i.e., polyol, blowing agent, catalyst and surfactant). 

The evaluation of panel physicals was carried out as follows The fiber glass reinforcement was preblended into the B-component (polyol side) on a high shear mixer and the slurry was charged to the machine. The panels were postcured for one hour at 250°F and conditioned in the Instron Lab for at least 12 hours before testing. Tests were performed according to ASTM standards (4). Specimens for each test were cut both parallel and perpendicular to the direction of the flow in the mold five specimens per direction were cut from each of two panels (a template was used to ensure good run-to-run comparison). 

Two of the three binder systems used by the foundry industry are two-component, room-temperature curing adhesives. All systems use polymeric MDI as the isocyanate component. All of the cross-linkable components are polyols. The first polyol introduced into the industry was an alkyd oil resin consisting of linseed oil, pentaerythritol and isophthalic acid. The system... 

In order to simplify the procedure of using too many components, a masterbatch , that is a mixture of the components that do not react with each other, (e.g., oligo-polyol, water, chain extender, catalysts, etc.), is made before foaming. Then it is possible to use only two components one is the polyolic component (called component A or formulated polyol, containing a mixture of all raw materials except for the isocyanate, in the proportions needed) and the second component is the isocyanate (called component B or isocyanate component). The polyurethane that results is a consequence of the very efficient contact between the isocyanate component and the polyolic component. Usually, in rigid PU foams only two components are used. In flexible foams, the polyolic component is divided into two components, especially in order to avoid the contact of some hydrolysable component with water, (e.g., stannous octoate). The gravimetric ratio between the components is verified before the foaming process and if necessary, it is corrected. 

The earliest commercial urethane coatings were based on polyester-polyisocyanate systems that exhibited excellent abrasion resistance, toughness, and a wide range of mechanical strength properties. Most urethane coating systems in this country were first based on tolylene diisocyanate (TDI), while in Europe many systems based on 4,4 -methylene bis(phenyl isocyanate) (MDI) were developed. In order to avoid the use of free TDI, adducts of polyols such as trimethyolpropane or 1,2,6-hexanetriol with TDI were introduced, particularly for two-component coatings (1., 2). 

Two-Package Polyol Urethane Coatings (ASTM Type 5). Two-package polyol urethane coatings consist of isocyanate-terminated adducts of polymers that are cured by reaction with di- or polyfunctional hydroxyl-containing materials. The latter may consist of low- to medium-weight polyols with a polyester, polyether, polyether urethane, or castor oil backbone. When the two components (OH- and NC0-) are mixed together, they have only a limited pot life. Therefore, the components are mixed prior to application. Catalysts may be used to speed up the cure either for room temperature or oven cure. 

Initially, two-component, PVC/TPU blends were proposed [B. F. Goodrich Co., 1960], but soon, PVC/TPU blends with a modifier, e.g., ABS [Waugaman et al., 1963] NBR or PA [Kepes, 1959] were disclosed. Blending was also carried out by mixing PVC with polyols and isocyanates then polymerizing these two [Dainichiseika Color Chemicals, 1983]. Commercial PVC/TPU (with NBR) are represented by Duralex . The materials are usually formulated for extrusion, e.g., for wire and cable insulation, hoses and packaging. 

Through the synthesis of poly(urethane-imide) films and their carbonization, carbon films were obtained whose macropore structure could be controlled by changing the molecular structure of polyurethane prepolymer [164-166]. Poly(urethane-imide) films were prepared by blending poly(amide acid), which was synthesized from pyromellitic dianhydride (PMDA) and 4,4 -oxydianiline (ODA), and phenol-terminated polyurethane pjrejwlymers, which were synthesized through the reaction of polyester polyol with either hexamethylene diisocyanate (HDI), tolylene-2,4-diisocyanate (TDI) or 4,4 -diphenyknethane-diisocyanate (MDI). The reaction schemes of two components, poly(imide) (PI) and poly(urethane) (PU), are shown in Fig. 46a). 

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