Structural Adhesives - PART 4, POLYURETHANE

Quick recap – structural adhesives are used in high strength, permanent applications and are able to withstand considerable distress and will not fail at the bonded joint. There are 3 main types: Epoxies, Polyesters and Polyurethanes. Epoxies are high strength and versatile. Unsaturated polyesters are used in the stone industry and are fast curing and low cost. Let us now discuss the third, Polyurethanes.

Polyurethane is any polymer consisting of a chain of organic units joined by urethane links. These polymers are formed through polymerization by reacting a monomer containing at least two isocyanate functional groups with another monomer containing at least two hydroxyl (alcohol) groups in the presence of a catalyst. Whew! In other words - it's a high-tech polymer formed by the reaction between two precursor materials. By adjusting the individual properties of the precursors, an almost limitless variety of polyurethanes can be produced. This flexibility in formulation allows one to custom-engineer the polyurethane to meet the unique demands of the project.

There is a large range of polyurethane adhesive products available. Different chemical combinations result in different properties in polyurethanes. The chemical make-up can be altered to produce different levels of stiffness, density and hardness. All this makes polyurethanes versatile over many industries, such as: automotive, aerospace, construction, textile, wood working, book binding and hardscapes. Out of the three: Polyester, Epoxy and Polyurethane – Polyurethanes are the most flexible (ie: least rigid). Polyurethane, as an adhesive, was first developed in 1985 and has gone through many changes to be the product it is today – especially in cure speed. They are available in one-part or two-part systems. The two part systems require a catalyst.

Benefits of Polyurethanes:

• Long open time
• Flexibility
• Resiliency

Specific uses can be:

• Aesthetic repairs to stone surfaces
• Retaining wall capping
• Subfloor construction
• PreFab or modular construction
• Book Binding
• Binding leather soles to leather and synthetic uppers (shoes)

So, what do you think of these structural adhesives? Which do you prefer to work with and why?

Structural Adhesives - Part 3, EPOXY

Let’s quickly recap – structural adhesives are used in high strength, permanent applications and able to withstand considerable magnitude and will not fail at the bonded joint. There are 3 main types Epoxies, Polyesters and Polyurethanes. Unsaturated polyesters are used in the stone industry and are fast curing and low cost.

Epoxy is a copolymer that is formed from two different chemicals - resin and hardener. When these are mixed together, the amine groups react with the epoxide groups to form a bond. This process is called "curing". A strict mix ratio is needed for full cure and cured property retention. If an epoxy is mixed with the incorrect ratio, it may fail.

Epoxies were first introduced commercially in 1946. These high-strength adhesives have a wide range of industry use, such as construction, automotive, aerospace and more. Epoxy adhesives are used where high strength bonds are required.

Epoxies are versatile - as they bond well to many substrates and can be easily modified and developed to suit almost any application. They can be used as adhesives for wood, metal, glass, stone, and some plastics. They can be made flexible or rigid, transparent or colored, fast setting or slow setting.

Epoxies are high strength and have less shrinkage and more chemical resistance than unsaturated polyesters. Epoxies are the structural adhesive that is used primarily in the exterior stone building industry.

Benefits of Epoxies:

• High strength
• Excellent durability
• Extremely versatile

Specific uses can be:

• Anchor Bolts
• Buildings – i.e. stone cladding or dimensional stone
• Boats construction
• Countertops
• Golf clubs
• Surfboards
  

So, do you use Epoxies in your company? Good or Bad - what are your thoughts? Please tell us your thoughts in the comments section, we'd love to hear from you! * * Stay tuned for the final part of our Structural Adhesives postings as we wrap up with Polyurethanes. * *

Structural Adhesives - Part 2, POLYESTER

Let’s begin with Polyester. Polyester is a polymer which contains the ester functional group in their main chain. Depending on the chemical structure polyester can be saturated (thermoplastic) and unsaturated (thermoset).

Translation #1 – saturated/thermoplastic turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently. Saturated polyesters are primarily used in the paint industry for general industrial coating.

Translation #2 - unstaturated/thermoset is material that irreversibly cures. The cure may be done through heat or a chemical reaction. Unsaturated polyesters are used for castings, glass fiber laminates and adhesive systems. It's these adhesive systems that are used in the stone industry – primarily in the stone countertop segment. Unsaturated polyesters are two part systems consisting of a resin and peroxide based catalyst, a strict mix ratio is not required for cure. Unsaturated polyesters have greater shrinkage and less chemical resistance than epoxy adhesives.

Benefits of Unsaturated Polyesters:

• Fast curing
• Low cost
• Perfect for more porous stone, such as Marble

Specific uses with stone can be:

• Interior use
• Laminating Countertop Edges
• Rodding Thin Stone and Countertops
• Countertop Seaming

Have you used Polyesters? If so, what has been your experience with them. If not, why not? * * Stay tuned for the next part of our Structural Adhesives postings as we tackle Epoxy next. * *

Structural Adhesives - Part 1

According to McGraw-Hill Science & Technology Dictionary structural adhesives are capable of bearing loads of considerable magnitude. A structural adhesive will not fail when a bonded joint prepared from the thickness of metal, stone or other material typical for that industry is stressed to its yield point.Structural adhesives are adhesives that are used in high strength-permanent applications. Most often these adhesives are the primary means of attachment in structural applications.

There are many different types of structural adhesives, but, the three main types are Epoxies, Polyesters and Polyurethanes.

In our next few posts, we try to explain the chemical make up, uses, and benefits of these three types of structural adhesives.