Water Based Polyurethane (PUD) Shoe Glue

The first binder (adhesive) was tree alburnum/extracts obtained from natural sources and was used to make clay vessels. After natural adhesives, the first synthetic adhesive came into existence in 1942 through Dr. Harry Coover's discovery of cyanoacrylate. Different adhesive systems followed over time.

The adhesives used today can be grouped as follows;

•Solvent-Based Adhesives •Solvent-Free, Two-Component Adhesives •Solvent-Free, One-Component Adhesives •Solvent-Free, One-Component, Hot Melt Adhesives •Water-Based Adhesives When we look at adhesive usage specifically in the shoe sector, we see that solvent-based adhesives are in the forefront. They are obtained by dissolving polymeric materials such as polychloroprene, polyurethane and styrene copolymer in suitable solvents. These products provide adhesion by removal of the solvent they contain. Taking the example of bonding the shoe upper to the sole, binder is applied separately to the shoe upper and the sole. Then it is dried at 140°C-180°C through an oven. The shoe upper and the sole, out from the oven, are adhered and pressed immediately against one another before the binder cools. After that, the adhesive, which cools down, sticks strongly. Looking at this process technically, a kind of solvent which has two different vaporization rates is used to provide gradual removal of solvent as well as in all coating and binding systems. Furthermore, these sticking applications are performed by manual labor. Therefore, there is always a risk in the environment no matter how much investment is made for workers' health. As PURIN Polyurethane, from 2018 we have started producing Water-Based Polyurethane (PUD) in Turkey. We add new products to the PUD product groups day by day and increase our production volume in this area. Since we have considered PUD technology as the future of polyurethane, we started our R&D work in this area long ago and began domestic production with investments in this area.

To explain PUD production simply;

The biggest obstacle in polyurethane synthesis is the water substance in raw materials. Therefore, at moisture levels over 300-400 ppm the synthesis cannot proceed and it is necessary to remove the moisture from the environment with a suitable drying agent. Otherwise, because of the reaction of isocyanates with water, the molecule extension process of polymer cannot proceed and it ends. We can interpret that molecular weight of polymer directly affects the product performance. Therefore; if we do not extend the molecule, the product will be waste. On the other hand, when we synthesize the product in a suitable environment, exposure with water in the application area is another problem. Swellings will occur in the product because of the CO2 gas as a result of the exposure of prepolymer-based products with water and the product will end up with low performance. Non-reactive polyurethane products, on the other hand, are coagulated after exposure to water. PUD technology answers the question of how a synthesis is made in water, whereas water has such a negative effect on polyurethane synthesis and afterwards.

Products can be synthesized in 5 different stages with PUD technology;

Prepolymer Synthesis Stage: At this stage, prepolymer synthesis is carried out at proper stoichiometric ratios with polyol, isocyanate, chain extender and hydrophilic monomer and cosolvent (e.g. acetone). Of course, the raw materials to be used depend entirely on the application area, desired properties and performance. For example, when there is a need for hydrolysis resistance, that is, non-degradation in aqueous areas is needed, polyether or polycarbonate-based polyols must be used instead of polyester-based polyols. Higher molecular weight polyols and long chain isocyanates must be used where high elasticity is desired.

Neutralization Stage:

The hydrophilic monomer used in the prepolymer stage is the most important raw material in PUD technology. This monomer provides the coherence of water with the polyurethane chain. However, this monomer has an acidic structure and will not work directly by using in the synthesis. To activate this monomer, it should be neutralized with an appropriate base.

Dispersion Stage:

The polyurethane chain can be dispersed in water after neutralization. The product is changed into water-soluble prepolymer form by adding water to the prepolymer under the mixer. After this critical stage, synthesis will proceed in aqueous area.

Chain Extension Stage:

At this stage, molecular weight extension is carried out on the polyurethane prepolymer, which is in water, with diamine compounds. After achieving the desired molecular weight, the product is ready however there is a cosolvent in the system which needs to be removed.

Solvent Recovery Stage:

As the last step; cosolvent (acetone) in the completed product is absorbed out from the product by vacuuming and heating. The end product is formed in this way. Thus, water-based polyurethane resin synthesis is carried out by PUD technology. Suitable raw material choice for application and performance is made based on our experience and technical research before resin synthesis. We determine our optimum production method with the product analysis afterwards. After the PUD resin synthesis conducted under control of the Synthesis R&D department, the Application R&D department carries out studies for sectorial applications by making the required modifications on the obtained resin.

Using PUD binder,

•Provides odor-free, clean and healthy working environment, •Provides higher adhesion performance, •Provides easy working with low viscosity, •Provides minimization in energy cost, •Reduces the working stages, •Increases production pace. As PURIN, we will provide you better service on PUD product groups than the sector like in all of our product groups; •Developing technical projects and providing the most suitable product, •Providing technical support through our leading expert R&D experienced team on every process (e.g. product selection, application and afterwards), •Fast supply to entire Turkey and regional countries from our factory in Kocaeli, •Providing cost advantage with reasonable price as a local PUD producer. Binders, which are acquired with business development for the shoe sector, increase your production pace and provide minimization in your working processes. İbrahim Kecin Chemist, M. Sc. General Manager PURIN Polyurethane     Ayşenur Dede R&D Manager PURIN Polyurethane