Comprehensive Guide to Polyurethane Adhesive

Different types of adhesives are used in everyday life and various industries. However, some adhesives possess more interesting and efficient properties that distinguish them from other types. Polyurethane, commonly referred to as PUR adhesive, is one of these exceptional cases, recognized as one of the most widely used types of adhesives due to its numerous advantages. In the following, we will explore polyurethane adhesive, its features, and its applications with “Ana Shimi Araz”.

What is Polyurethane Adhesive?

Polyurethane adhesive is a type of polymer material consisting of organic chains with urethane bonds, often abbreviated as PU or PUR. This adhesive is a synthetic polymer plastic resin used for bonding surfaces. In addition to its adhesive properties, polyurethane has other characteristics that enhance its efficiency in industrial and domestic applications. Polyurethane adhesives have very high resistance to pressure, making them particularly suitable for structures that require high strength.

PUR adhesive hardens as it loses temperature, and room temperature is sufficient for it to dry. When applied to the desired surface, the adhesive reacts chemically with the environment’s temperature, creating a strong bond. Over time, as it cools and loses temperature, its adhesion increases.

Polyurethane adhesive is versatile and can be used on a wide range of materials including wood, metal, plastic, foam, and more. It offers excellent resistance to heat, water, and chemicals. It is also suitable for both indoor and outdoor applications.

The curing of this adhesive occurs through the absorption of moisture from the environment and does not require the presence of air. The adhesive needs moisture to activate its bonding properties. Initially, the adhesive has a paste-like consistency, but once activated, it expands and solidifies into a hard form.

Polyurethane adhesive remains elastic after drying, making it ideal for sealing and waterproofing in areas subject to vibrations and significant movement. Polyurethane adhesives are generally known in the market by various names such as polyurethane mastic, polyurethane glue, PU adhesive, and polyurethane sausage adhesive.

Applications of Polyurethane Adhesive

When reviewing polyurethane adhesive, one must highlight its wide range of applications across various industries. Polyurethane is a versatile adhesive capable of bonding both porous and non-porous materials like wood, glass, ceramics, concrete, and stone. This adhesive is specially designed for bonding dissimilar materials, easily adhering a porous surface like wood to a smooth and polished surface such as metal or glass.

In addition, the expansion during drying is another feature of polyurethane adhesive that allows for various applications, such as filling gaps between tiles, glass, etc.

The primary application of polyurethane adhesive is bonding porous surfaces to non-porous surfaces. The main difference between PU adhesive and PVA (yellow glue) is that PU adhesive can bond two porous surfaces, two non-porous surfaces, or one porous surface to one non-porous surface, while PVA adhesive can only bond porous surfaces together. The multiple uses of polyurethane adhesive can be summarized as follows:

• Wood Industry

Due to the numerous pores in wooden surfaces and their sensitivity to moisture, polyurethane adhesive is considered one of the best options in the woodworking and carpentry industries. Unlike wood glue, polyurethane adhesive does not absorb into the wood’s pores and has high strength and flexibility. This adhesive can bond anything from glass, stone, fabric, etc., to wooden surfaces. Some applications of polyurethane adhesive in the wood industry include the manufacture of furniture, wooden items, decorations, etc.

• Automotive Industry

PU adhesive is highly beneficial in the automotive industry. This adhesive is used for producing composite mold sheets, bonding fiberglass-plastic connections, adhering automotive interior parts and accessories, producing windshields, body color polishing, etc.

The most significant use of polyurethane adhesive is in the installation of automobile glass, also known as windshield adhesive. This polyurethane adhesive has a high resistance, anti-UV properties, and greater adhesion than other types of polyurethane adhesives, specifically designed for sealing and attaching glass to vehicle bodies.

Today, more than 15 kilograms of adhesive are used in an ordinary automobile in advanced automotive manufacturing, enhancing the strength and resistance of vehicles and absorbing vibrations and reducing unwanted noise from the engine and road into the cabin.

• Construction Industry

Polyurethane mastic is one of the most widely used new technologies in the adhesive industry for construction projects, whether they are new constructions or renovation, restoration, and repair projects. This adhesive is available in single-component (polyurethane sausage mastic) or two-component forms, mainly used in horizontal joints and vertical applications without sagging.

Due to their high flexibility, one significant and extensive use of this adhesive is in construction expansion joints. This joint may be vertical, such as the gap between two buildings that we wish to fill with polyurethane adhesive, or horizontal on the floor, like connecting two separate structures with vibrations that may occur.

Sealing the exterior façade of a building is one of the engineering principles and an essential component of construction projects. Polyurethane façade mastic is designed for sealing joints between various façade elements such as structural façades, laminate façades, composite façades, fiber cement façades, exposed concrete, spider structures, skyline, etc., to seal joints and prevent moisture or air infiltration and energy loss.

• Refrigeration Industry

Another use of polyurethane adhesive in the refrigeration industry is for refrigerated trucks and vans. Due to its excellent adhesion to metal, good sealing properties, and hygienic qualities, this adhesive is used for sealing the internal surfaces of refrigerators.

• Shipbuilding Industry

Adhesives and sealants have a long history in shipbuilding and marine industries, protecting against water, chemicals, various weather conditions, and environmental degradation. This adhesive is used for applications such as connecting metal deck seams to the hull, bonding wood to fiberglass, or sealing and waterproofing ship or boat windows.

• Footwear Industry

Apart from its use in making foam, layers, and insoles in shoes, polyurethane adhesive has long been used as shoe glue. Polyurethane adhesive is colorless and offers high strength and cohesion.

• Printing Industry

Characteristics of polyurethane adhesive, including high moisture resistance, flexibility, light color, non-flammability, etc., make this type of adhesive suitable for use in printing and ink industries. Applications include bookbinding and assisting in speeding up the drying process of ink on paper.

• Household Uses

To use polyurethane adhesive, specialized guns should be used. However, this does not mean that this adhesive is only for industrial applications. Given its primary characteristic—bonding dissimilar surfaces together—polyurethane adhesive can have various domestic applications. Adhesion of tiles, sealing, cladding, bonding broken pieces of household items, and mirror work can all be easily accomplished using polyurethane adhesive.

It’s worth mentioning that polyurethane adhesive has other uses, including the production of composites, laminates, sealing water tanks, even drinking water tanks, water and sewage treatment plants, boat building, LNG ship construction, bus manufacturing, rail laying, piping, bonding mechanical components, bonding metal parts in electronics, and more.

Features of the Best Polyurethane Adhesive

But how can one identify and purchase the best polyurethane adhesive? Typically, the highest quality products on the market possess the following characteristics:

• Exceptional adhesive properties to all materials, porous and non-porous surfaces, suitable for varied materials including stone, glass, metal, etc.
• Corrosion-resistant
• Waterproof and moisture-resistant
• Resistant to environmental and climatic factors (UV rays, acid rain, etc.)
• Colorless and paintable
• High flexibility in extreme heat or freezing conditions
• Chemical resistance
• High durability and wear resistance
• No shrinkage and no dripping

Types of Polyurethane Adhesives

Polyurethane adhesives generally come in various types, such as construction adhesives, commonly known as polyurethane mastic, automotive polyurethane adhesive, or multi-purpose polyurethane adhesive that serves both industrial and construction applications.

Another categorization is according to:

Polyurethane adhesives, also referred to as polyurethane glue, are produced in either single-component or two-component varieties.

The single-component type is further divided into two: One type absorbs moisture to acquire its adhesive properties. This model is highly flexible and elastic, with the time required for it to set depending on the moisture level in the environment. The second type of single-component PUR is significantly hard, inflexible, and durable, requiring temperatures between 100 and 200 degrees for shaping.

The two-component type can vary in hardness or flexibility based on the raw materials used and their proportions.

Some other types of polyurethane adhesives available in the market based on application include:

• Standard Polyurethane Adhesive

This is the most common type available. It is often used in carpentry projects as it expands while drying, thus filling gaps and creating a strong bond. This type works effectively with porous materials like wood, foam, and some plastics. Standard polyurethane adhesive tends to set relatively quickly, allowing for faster project completion.

• Fast-setting Polyurethane Adhesive

This type is formulated for quick bonding. It provides a rapid initial bond within a short period, usually within 10 to 15 minutes. Fast-setting polyurethane adhesive is ideal for applications requiring quick assembly or repairs. Thus, it begins to harden more rapidly after use.

• Slow-setting Polyurethane Adhesive

In contrast to the previous model, slow-setting polyurethane adhesive is designed to require more time to harden. This allows users more time to align and adjust their workpieces before the adhesive bond sets. Its setting time typically ranges from 30 minutes to an hour or even longer. This type is useful for complex projects or when bonding large surfaces that require precise positioning.

• Water-resistant Polyurethane Adhesive

As the name implies, water-resistant polyurethane adhesive is moisture resistant, making it suitable for projects requiring excellent water resistance. This type bonds well with materials like wood, metal, and ceramics. It is also suitable for outdoor applications such as outdoor furniture, marine projects, or window installation.

• High-temperature Polyurethane Adhesive

High-temperature polyurethane adhesive is formulated to withstand high temperatures without losing its bond strength. This type can withstand heat up to 200 degrees Fahrenheit (93 degrees Celsius) or higher, which makes it suitable for applications exposed to high heat.

Some of these applications include:

• Bonding heat-resistant materials, such as metal or certain plastics, in industrial environments.

Regardless of the type of polyurethane adhesive you choose, following the manufacturer’s instructions for the best results is essential. Proper surface preparation, application techniques, and setting times are crucial for achieving a strong and durable bond. Always wear protective gloves when using polyurethane adhesive and work in a well-ventilated area.

Types of Polyurethane Adhesives by Packaging

• Pressure Bottles

This model is the most common type of packaging for polyurethane adhesive. Here, the glue is typically supplied in a plastic bottle with a narrow tip nozzle, allowing you to squeeze out the desired amount of adhesive for use.

• Sausage

Polyurethane adhesive can be packaged in sausage-shaped plastic containers. This type of packaging is often used for smaller quantities or for convenient and portable applications.

• Cartridges

Polyurethane adhesive cartridges are generally used with caulking guns. These cartridges have a threaded nozzle that fits into the gun, allowing for controlled application of the adhesive.