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What is Non-reactive Polyurethane Adhesive

Non-reactive Polyurethane Adhesive
Polyurethane adhesives can be divided into two main classes: non-reactive and reactive. The major application of polyurethane adhesives is to put a thin layer of high molecular weight polyurethane between the two surfaces to be joined and bonded. While reactive polyurethane adhesives are usually supplied as one- or two-components polyurethane resin system, non-reactive polyurethane adhesives are based on high molecular weight polymers, which are applied as solvent-borne, water-borne or as hot-melts.
Firstly, solvent-borne polyurethane adhesives:
  1. By dissolving high molecular weight thermoplastic polyurethanes in solvents, solvent-borne polyurethane adhesives are produced.
  2. To improve the bonding strength and heat resistance, solvent-borne cross-linkers are frequently added to solvent-borne thermoplastic polyurethane adhesives; however this process turns a one-component non-reactive polyurethane adhesive into a two-part reactive adhesive with limited pot-life. Therefore, adding cross-linkers is only necessary in certain applications.
  3. During the process of preparing solvent-borne polyurethane adhesives, typically, about 50% of the solvent required for the final adhesive solution is charged in a closed mixer and thermoplastic polyurethane granules are added in stages, to avoid coagulation, to the stirred mixture. Since the shear forces generated can raise the temperature as high as the boiling point of the solvent, rest of the solvent is added over time to control the viscosity and temperature of the mixture. The dissolution time depends on the process conditions and can be 24 hours using low-temperature equipment or two hours for reflux conditions.
Secondly, for polyurethane hot-melt adhesives:
  1. Polyurethane hot-melt adhesives are also supplied as thermoplastic granules, which can be extruded or melted by heat in holding tanks to form, for examples, glue sticks for hot-melt gun or adhesive films for industrial heat press machine.
  2. Polyurethane hot-melt adhesives can be used to bond paper, board, wood, metals, plastics, and for laminating fabrics to foams.
  3. One of the common ways to use polyurethane hot-melt adhesives is placing polyurethane hot-melt adhesives between substrates, then activating the laminate heat at temperature above the melting point, and then simply giving pressure to the substrates to bond layers together.
Lastly, for water-borne adhesives:
  1. Water-borne polyurethane adhesives are fully reacted, high molecular weight polyurethane dispersed in water that only contains minor amounts of solvent and thus have a very low emission of volatile organic compounds.
  2. The main applications for water-borne polyurethane dispersions, known as PUDs, adhesives are in the construction and packaging industries, footwear industry and in the manufacture of foils and textile laminates. While water-borne polyurethane adhesives have good bonding performance with many materials, including PVC substrates, their adhesion to rubber, or certain surface-treated, or high oil content materials is poor.
  3. Water-borne polyurethane are normally applied by roller or sprayer, and heating is required to speed up the drying process.
Although solvent-borne thermoplastic polyurethane adhesives are easily operated and highly used in the footwear industry, the products are under increasing pressure due to the fact that evaporating solvent and releasing volatile organic compounds into the atmosphere may potentially damage the environment. Therefore, more and more water-borne polyurethane adhesives are used. More information about water-borne polyurethane dispersion can be found on https://www.taiwanpu.com/en/product/PU-Adhesives-and-Hot-Melt

Link to TPUCO products:
Polyurethane Adhesive and Hot-melt:
https://www.taiwanpu.com/en/product/PU-Adhesives-and-Hot-Melt
Shoe adhesive:
https://www.taiwanpu.com/en/product/PU-Adhesives-and-Hot-Melt/Shoe-adhesive
Hot-Melt Thermoplastic Polyurethane:
https://www.taiwanpu.com/en/product/Hot-Melt-TPU
Water-borne Polyurethane Adhesive:
https://www.taiwanpu.com/en/product/Eco-friendly-water-based-polyurethane-adhesive
https://www.taiwanpu.com/en/product/Economical-water-based-PU-adhesive-for-shoes
https://www.taiwanpu.com/en/product/PU-Adhesives-and-Hot-Melt/Polyurethane-dispersion


Reference:
Sonnenschein, Mark. Polyurethanes Science, Technology, Markets, and Trends. John Wiley & Sons, Inc. Hoboken, New Jersey. 2015.