果冻传媒

Polymeric materials are essential in our everyday lives due to their many useful properties. Thermoplastics, in particular, stand out for their ability to be reshaped and reused. For his PhD research Hern谩n Ch谩vez Thielemann delved into how the molecular structure of isotactic polypropylene (iPP) affects its mechanical properties. By understanding and optimizing these molecular arrangements, we can create thinner, stronger, and more sustainable materials. This advancement holds significant potential for industries like packaging, automotive, and electronics.

Thermoplastics might be amorphous or semicrystalline, depending on their chain regularity and how easily they can move. In amorphous polymers, the molecules (chains) are not highly ordered, so if we could look at the microscale these would look randomly dispersed. These polymers are normally used below a temperature at which the polymer behaves like a solid (glassy state). Semi-crystalline polymers are named as such because their chains have the ability to achieve highly ordered structures, and since those are ordered in periodic patterns they are described as crystals; crystals are solid under their melting temperature, still due to different reasons there are amorphous domains coexisting with the crystalline ones, giving rise to the name semi-crystalline.

Crystalline-amorphous sandwiches

In his research Hern谩n Ch谩vez Thielemann explored how the arrangement and orientation of molecules affect the behavior of semi-crystalline isotactic polypropylene (iPP). The challenge is the complex nature of iPP, which might solidify into different types of crystals (伪, 尾, and 纬) and include both disordered and oriented phases, amorphous and crystalline, that influence its overall behavior. To study this, a computational model that connects small-scale features to the properties that can be observed at the human scale was developed. The model simulates the material as a collection of crystalline-amorphous sandwiches, called inclusions, and arranged to match the overall structure. Each inclusion uses specific equations to capture the behavior of the crystalline and amorphous phases. Then the contribution of each of the inclusions is considered taking into account its orientation.

Good agreement

Ch谩vez Thielemann first used the inclusion model to describe the large-scale response of 伪-iPP under stretching and compressing forces, showing good agreement with experiments. Then, using simulations of the chains at the molecular level, further insights into the directional elastic properties of 伪- and 尾-iPP are obtained, matching well with existing experimental data and providing new perspectives on the 尾 modification. After that the model was used to understand the crystal deformation behavior of 尾-iPP, building on the previous model for 伪-iPP, and capturing the large-scale mechanical response of the 尾 modification. It effectively describes the material behavior and predicts the time required to reach failure under a certain tensile load.

Consistent response

Finally, the model was used to describe the behavior of an oriented 伪-iPP film, taking into consideration orientation in both phases. The results show a consistent response, accurately capturing variations in the material conditions. This further reveals the role of different phases in the mechanical response of this material.

Title of PhD thesis: . Supervisors: Dr. Hans van Dommelen, and Prof. Leon Govaert.