Polyurethane Resins

Polyurethane foams are versatile materials used as structural building components, molded parts, flexible cushion materials, and adhesive/sealants. They are a part of our everyday life. Polyurethane foams represent a wide class of materials that can be formulated with specific characteristics for a particular end use. When specially formulated, they can be extremely effective sealants.

What is the Chemistry of Polyurethane Foam?

Polyurethane foam is produced through an exothermic reaction between an isocyanate and a hydroxyl-containing compound, typically a polyol. The polyol structure influences the amount of cross-linking and flexibility in the finished resin or foam. Often, there is a secondary reaction with water that drives additional properties. The water and isocyanate release carbon dioxide which generates foam and cures into a polymer structure. Important modifiers of the reaction are the catalyst and gelling agent. These determine the speed of the reaction and can act to balance the water reaction as well.

How Does Polyurethane Foam Work? The Chemical Reaction Explained

Polyurethane is substantially made of two raw materials — isocyanate and polyol, which are derived from crude oil. After mixing those two process-ready liquid components of the system and various auxiliary materials, such as catalysts, foaming agents, and stabilizers, a chemical reaction starts. Polyurethane foam is the result of a chemical reaction when its two components are mixed. The basics of the reaction are the expansion and gel phase. During the initial reaction phase, a small amount of CO₂ gas is released and trapped in the liquid mixture. This creates small bubbles. As these bubbles multiply and expand, the mixture also expands or rises. The more the liquid foams in this initial reaction phase, the less dense the material. The resin then cures and hardens around the bubbles, creating a uniform matrix of cells. This cellular structure is strong. When the cells remain closed, the structure is watertight and airtight. They provide perfect adhesion to both vertical and horizontal surfaces, and it has porous structure. Porous materials have hollow cavities inside. Porosity is a property that tells us about the volume and quantity of pores with certain diameter. Polyurethane foam is also characterized by a short treatment time and, after curing, it retains its chemical neutrality. Polyurethanes demonstrates good thermal parameters — it is resistant to a wide range of temperatures (from –200°C to +135°C). Average thermal conductivity coefficient of polyurethane foam is 0.026 W/m2 The components of the polyurethane foam must be well mixed to initiate the reaction. This can be done mechanically with a mixer.

Pot Life for Polyurethane Adhesives

Pot Life of the adhesive is loosely defined as the amount of time required for the polyurethane adhesive to double in viscosity. Full cure is generally 24 hours or more. In most cases, the critical piece of information, is not the full cure but the handling strength. Handling strength indicates is the amount of time before you can move or pack assemblies. Ensure you have sufficient strength before putting any stress on the bond. The pot life will provide some indication of how quickly the two component polyurethane sets and also indicates the length of time possible between mixing and use. Two component polyurethanes are used in thin films for bonding metals, plastics and composites. They are also great for potting components. Thick layers of adhesive or potted sections may cure more quickly than adhesive squeezed into a thin layer. This is because of heat generated by exothermic reaction. Chemfil Offers a range of Two component Polyurethane systems. A few systems suitable for Filter Industry are offered as : – Semi-rigid Two Component Cold Curing Polyurethane systems for metal to media bonding – Foam Type Air Sealant Gasket Type – Two Component Cold Curing Polyurethane systems

PU Soft Air filter Gasket Application

PU Metal to media bonding application

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