PA / Polyamide

Polyamides are chemically related to proteins. The term polyamides is used when these materials are synthetically produced and technically usable as thermoplastic plastics.

Chemically, polyamides are polymers whose main chain contains regularly repeating amide bonds. Monomers suitable for producing polyamides include, for example, aminocarboxylic acids and lactams, as well as diamines and dicarboxylic acids.

Their high strength and toughness, along with good chemical resistance, make polyamides suitable as engineering materials.

In fiber production, polyamide is known under the name nylon, and in former West Germany under the brand name Perlon, or in East Germany under the equivalent name Dederon.

Polyamide films, or PA films, are mainly used in multilayer films, where the PA film is responsible for providing high tensile strength.

In the food sector, the aroma barrier and grease resistance of multilayer films containing PA / polyamide are highly valued. Good cold and heat resistance, as well as strong resistance to organic chemicals, are further characteristics that distinguish polyamide films.

Excellent deep-drawing properties make these films easy to process. Their high transparency is appreciated in the packaging industry, both for food products and for non-food applications.

The term cast film refers to polyamide film that has been produced using the casting process. In this process, molten polyamide granulate is cast onto cooled rollers, known as chill rolls. For this reason, the production systems are also called chill-roll systems.

Cast films offer high transparency, and the production process is very fast. By adjusting the roller speed and the temperatures used, material properties such as thickness or deep-drawing capability can be controlled.

As a composite film, cast polyamide film PA 6 is often combined with PE (polyethylene) or other types of polymers to produce flexible, deep-drawable multilayer films. Specific film properties can also be influenced by the combination of the films used.

In addition to the casting process, the blown film process is also used for the production of polyamide films. In this method, a bubble is formed by blowing air into the molten granulate. The take-off speed at which this bubble is drawn determines the thickness of the resulting film.

The blown film process is more difficult and complex than the casting process, but it produces polyamide films with excellent mechanical properties. Elongation capability, puncture resistance, holding strength, and recovery force reach very high levels in the blown film process.

To further optimize these properties, both cast films and blown films can be stretched either monoaxially or biaxially.

Coex film is the technical term for films that are produced directly as multilayer films. In this process, several extruders create different film layers, which are then combined immediately into a single film, for example a PA film together with a polyethylene film.

By using at least two and up to six extruders, films with very specific properties can be manufactured, especially films with high tear resistance.

A well-known everyday example is coex film used for potting soil bags, with a light-proof black inner layer and a printable white outer layer.

Less widely known is the fact that fuel tanks for the automotive industry are also produced in this way, with a diffusion-tight inner layer and a mechanically durable outer layer.

Flexible films are also referred to as thin films and are multilayer packaging films that can be adapted to the respective types of use. In most flexible films, polyamide film is included because it functions as an oxygen barrier.

In addition, the polyamide content ensures good deep-drawing capability of the flexible film.

Composite structures with polyamide for flexible films are possible with polyethylene, polypropylene, or Surlyn, in various layer configurations.

An important field of application for PA films in multilayer films is the food sector. Their excellent gas barrier performance, grease resistance, and aroma barrier properties are key reasons for their use, along with their good mechanical characteristics.

Their strong resistance to organic solvents is another reason for their use in the chemical industry, where multilayer films are used, for example, as vacuum packaging for chemicals.

Technical products can also be effectively protected against corrosion by PA multilayer films.

These films are also needed in construction and materials applications, for instance as roofing underlay films or as release films in the production of fiber-reinforced plastic composite materials.

Numbers and letters following the abbreviation PA distinguish different types of polyamides. For example, the letter T stands for polyamides produced using the monomer terephthalic acid, while I refers to those made with isophthalic acid.

Polyamides derived from aminocarboxylic acids are identified by a number that indicates the specific aminocarboxylic acid used. For instance, the number 6 stands for caprolactam, which is used to produce the most commonly used polyamide, PA 6.

Polyamides derived from diamines and dicarboxylic acids are designated by the abbreviation PA followed by two numbers separated by a dot. For example, PA 6.4 refers to a polyamide manufactured from the diamine hexamethylenediamine and the dicarboxylic acid succinic acid.

This nomenclature may be confusing for non-specialists, but it is understandable and logical for chemists.