What is Hot Melt Polyurethane Used for
Hot melt polyurethane, or short of hot melt PUR, is not a single material with a fixed composition. Rather, it is a range of chemicals sharing similar chemistry. It is a polymer composed of units of organic chains joined by urethane or carbamate links. Most polyurethanes are thermosetting polymers and do not melt when heated, thermoplastic polyurethanes which do melt have also been made available.
Polyurethane polymers are formed by the reaction of isocyanate and a polyol. Both the isocyanates and polyols used contain two or more functional groups per molecule, usually.
Whatever the exact composition, polyurethanes have some things in common. They are sticky. Polyurethane glues will work on just about all normal materials, porous or not. Wood, metals, rubbers, cured epoxy, leather, tile and glass, many plastics, concrete and brick, the list goes on.
Polyurethane based adhesives can set solid and relatively inflexible, or can remain rubbery and flexible. Boat owners will have heard of hot melt polyurethanes sold as sealant and somewhat removable adhesives. These are commonly available as sealants and high quality bedding materials that can be painted, unlike silicone sealant.
Most hot melt polyurethane adhesives set more solidly without being brittle. They can be sanded, and a true form will cut through the glue without dulling the blade as epoxy might.
Then, what are the advantages of hot melt polyurethane glue? There are a list of them:
1. It stick to most things and can glue different materials together. It is successful in bonding non porous materials such as metal to wood, or mirrors to walls.
2. Some compositions have a nice work time of 20 or so minutes. This allows for leisurely working and clamping time.
3. Depending on the glue, it can set quite quickly after clamping and allow the user to continue work as the glue completes its curing.
4. A major advantage over many adhesives is its ability to set in high moisture conditions. In fact, it needs moisture to set and will cure faster in conditions where other glues, such as epoxy, cannot be used.
5. It is waterproof. However, hot melt polyurethanes are generally not recommended for long term immersion in water or use below the waterline unless protected by paints or other protection.
6. It requires no mixing or measuring and can be used directly from the bottle.
7. It is available in several different viscosities and packaging. It is available in caulking tubes with filler which makes it stay and not sag, squeeze bottles, tubes, etc.
8. Polyurethane is available as a hot melt glue that sets and holds parts together without the need for clamping. Once the glue has cooled and set, it continues to cure for several days to attain its full strength.
9. If properly applied and cured, how melt polyurethane makes a strong bond.
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