What is the shape of plastics? How are the different plastic products we use every day shaped? Which polymer is best suited for my industrial process? If you're racking your brains to find answers to these questions, then this deep dive into the plastic deformation process is just what you need. Ready? Let's dive in!

Transforming plastic takes energy

To reshape an object, you need to apply energy. The more structured and solid this object is, the greater the concentration of energy required to transform it. This principle applies to all things, including plastics. Energy, however, is a vague term because it manifests itself in many different forms. If we were all gifted with super strength, shaping an object to our deside would be quite simple. Instead, most of us didn't even join the gym in January (as we promised!) so we have to think of alternatives. For example, heat is one form in which energy manifests. And it has the power to define modeling, that is, the deformation of plastic.

I explain the plastic deformation to my hairdresser

What we commonly call "plastic" are actually groups of molecular filaments called polymers. To change the arrangement of these filaments, turning them into objects such as caps, chairs or masterbatch, we use heat power through complex machinery found in industrial plants. Basically, it's a bit like when we use hot air from a hair dryer to style hair, giving it a more defined shape. Imagine that heat is like the air that moves hair: just as air acts on the strands, heat acts on the molecules of polymers. This phenomenon represents the basis of the plastic deformation: as the temperature increases, molecules become more active, moving more freely, just like hair moved by the current. This allows the material to dispose more easily, adapting to molding processes.

The process of crystallization

This process of ordering filaments of molecules from a formless state, such as a liquid state, to a more complex and solid state is known as crystallization. The phenomenon involves the arranging of plastic molecules into more regular and ordered crystal-like structures. In other words, the polymer filaments align more uniformly, increasing the strength and improving the mechanical properties of the material. However, it is important to remember that just as hair can be different in nature and therefore require specific treatments for styling, similarly there are also different types of plastics, each with unique characteristics and requirements. Consequently, there are different processes to shape plastic materials according to their specific properties and the needs of the final application.

Messy filaments

Imagine two people walking outside on a windy day. Both have long hair tousled by the wind. The first is perfectly straight-haired and the second has unruly curly hair. When the wind weakens, the straight hair of the first figure falls naturally by gravity and remains unruffled. In contrast, the second person's curly hair still appears somewhat voluminous and messy because it is more congenitally tousled. This parallel, perhaps a bit daring, can be applied to better explain the plastic deformation of polymers of different natures.

The secrets of plastic deformation come to a head

Indeed, some plastics have a stronger predisposition to crystallize (straight hair), becoming rigid and ordered even when subjected to plastic deformation processes using heat (the wind tousling the hair). Others, on the other hand, tend to be more amorphous (curly hair), maintaining a disordered and flexible structure, with a more difficult crystallization. In other words, the heat has the power to keep the molecules separate, the filaments disheveled. However, when this energy dissipates, the polymer molecules tend to come closer together and align. Depending on the peculiar properties of each material, this ordering occurs more or less efficiently and regularly.

Polyolefins vs Styrenics

In practical terms, polyolefins plastics are semi-crystalline polymers with a tendency to crystallize during the process of plastic deformation. The interactions between the positive and negative charges of the elements within the material have an effect similar to that of gravity: molecules have a tendency to align and arrange themselves more neatly, just like straight hair when there is no wind. On the other hand, styrenic plastics are amorphous polymers, lacking a definite crystal structure. Without the energy required to align the molecules, as in the case of a dryer to style hair, these plastics mantain their disordere and flexible nature. It is important to noted that, in general, all polymers show some tendency to crystallize during plastic deformation processes, but this varies greatly depending on the type of plastic and its specific properties.