The plastic industry has created an important space for itself in the field of soles and footwear which until a few decades ago were exclusive to leather and other minor materials.
The creation of new recipes, the chemical and technological progress on the systems, has allowed plastic polymers to create a valid alternative to traditional soles to be used in footwear subjected to heavy wear, with a protective value for the foot, thermal insulation, flexibility and impermeability.
In addition to the growth of new formulations made with virgin polymers, the recycled polymer market is offering different alternatives through sustainable products especially in the field of PVC and ABS.
The plastic materials that are mostly used in the footwear sector are:
Let's see in detail the features and applications:
Although ABS is not a commonly used polymer in footwear, it is often used in safety footwear, as a protective element for the toe of the shoe. The tip, in fact, is often made of recycled ABS, from post industrial waste, whose recipe is adapted to give the tip strength to shocks and flexibility.
TR or Thermoplastic Rubber
With this material it is possible to manufacture soles to be applied or inserted into the shoe by direct injection.
Thermoplastic rubbers are compounds whose fundamental component is styrene-butadiene-styrene (SBS) added with oils, polystyrene, mineral fillers, pigments, antioxidants, etc. .
Through a correct formulation of the recipe of the material, the soles do not have problems with resistance to cold and can maintain excellent flexibility at temperatures much lower than 0 ° C.
PVC, Plasticized Polyvinyl Chloride
PVC is one of the most popular plastic materials in the world, not only in the footwear sector, but is also used for the creation of doormats, carpets, wires, pipes , water reeds and many other products.
In the waterproof footwear sector, such as boots, soles, sandals, slippers and accessories, PVC has found a wide use as a material in continuous technological development, having reached a good level of environmental efficiency today and ensuring good safety in all phases of its life cycle.
In fact, in the footwear market, there are important volumes of products made of recycled PVC that allow the construction of sustainable soles and footwear, therefore recycled and recyclable.
TPU, Thermoplastic Polyurethane
TPU is a chemical compound made up of polyurethane elastomers treated with the techniques of thermoplastic materials.
Its realization goes through the isocyanate addition process, in a certain temperature range, recreating the elastic characteristics of the rubber. Thermoplastic polyurethanes are used for different types of soles intended for certain segments of footwear such as sport, work and leisure.
The formulas that characterize the materials for TPU soles change according to the type of use of the same and consequently of the shoe.
PUR, Bi-Component Polyurethane
Polyol and Isocyanate, in liquid form, which are part of the Polyethers and Polyesters families, are two chemical elements that characterize the formation of Bicomponent Polyurethane .
The difference between these two classes is based on the structure of the foam that will be created, in fact, using the polyether a compact surface skin is created and, inside, the sole will have open cells, while using polyester a structure with closed cells will be created.
Eva, Ethyl vinyl Acetate
Ethylene and Vinyl Acetate are the two main components of the polymer called EVA, a polymer used for the construction of soft and resistant soles. The sole, however, is not constituted only by the two components that form the main polymer but, through the correct calibration of these elements and of crosslinkers, fillers, expanding agents, and more, the performance characteristics of the final product are determined.
The main characteristics are lightness, flexibility, elasticity and a good propensity to keep the original shape.
The evolution of fashion, technical needs and the general costs of the finished product have allowed the creation of materials composed of different but similar polymers.
Polyurethane materials, rubber and EVA are the main polymers that are used with the aim of creating different combinations in terms of aesthetic appearance, costs and of technical use, surprisingly widening the offer on the market.
Characteristics of finished products
The study and realization of new polymer recipes, for the creation of new commercial opportunities, must not make us forget that the footwear and the soles themselves must respond to well-defined characteristics for the end customer.
There are specific regulations that must be respected in the construction of a product for the footwear sector, in which it is requested that the articles be subjected to behavior tests. Let's see the main ones:
Automatic translation. We apologize for any inaccuracies. Original article in Italian.