Authors: Coline Roiron
Source: theses.fr (ABES) (preprint, 2022-03-30)
Field: Materials Science — Polymers and Plastics

Contribution à la caractérisation thermomécanique d’un polyéthylène auto-renforcé et de ses « recyclats » : Effet des paramètres du procédé de moulage par compression Reducing energy consumption is an essential issue for today's society. In order to achieve a sustainable energy transition, especially in the field of transportation, new and more demanding regulations are being implemented. The keywords are to increase the proportion of recycled and recyclable materials and lightening structural parts.The use of polymers can be a solution. However, to guarantee good mechanical resistance, the use of self-reinforced composites(SRP) is a lever for action. They are composed of a polymer or a family of polymers in two physical states, one to form the matrix and the second for the reinforcement. They present a low density, interesting mechanical behavior, and increased recyclability. To understand the behavior of a self-reinforced polyethylene and to be able to consider the use of this material for a given application,it is essential to understand the behavior of each of its components. If the behavior of more conventional composites, such as glass or carbon fiber reinforced thermoplastic matrix composites, is well understood, using thermoplastic reinforcements such as UHMWPE (Ultra-High Molecular Weight PolyEthylene) within the composite makes the understanding of the behavior of SRP more complex. The impact of temperature and time on the mechanical response of the reinforcements is then examined in a first step, and the observations are related to microstructural considerations. A test protocol has been proposed and validated before hand. A solid-phase transition is highlighted around 49°C and generates an abrupt behavior change.These UHMWPE reinforcements are integrated into composites. A compression molding process is suggested to process them in a single step from a matrix in granular form. The effect of different process parameters is evaluated to propose an optimal combination.The short and long-term mechanical response in tension and creep is then analyzed, and the interest of the SRPE thus designed is highlighted. Indeed, the benefit of its use is evident, especially at low temperatures. Moreover, the presence of thermoplastic reinforcements seems to introduce additional parameters that affect the behavior of the composites and, in particular, in creep. The precise characterization and the knowledge of the transition temperatures of the latter appeared then determining, mainly since the transitions depend on the microstructure of the reinforcement and thus on the type of stretching and the applied conditions. Finally, the recyclability of the implemented composites is studied since it constitutes a driving force for the development of SRP on the market. Materials science ; Compression molding ; Composite material ; Characterization (materials science) ; Molding (decorative) ; Compression (physics) ; Process (computing) ; Computer science ; Nanotechnology ; Mold Polymer crystallization and properties ; Fiber-reinforced polymer composites ; Material Properties and Applications