Quantification of Cavitation in Neat and Calcium Carbonate-Filled High-Density Polyethylene Subjected to Tension

Abstract

Cavitation-induced deformation mechanisms in neat semiciystalline polymers, i.e.. crazing, and in the derived composites, i.e., particle-matri.x clebonding, are generally activated during the transition between viscoelastic and viscoplastic deformation stages. However, little quantitative information about the void evolution with the drawing level is to date available in the literature. The objective of this work is to quantify cavitation mechanisms in neat and calcium carbonate-filled high-density polyethylene (HDPE) subjected to ten.'iile deformation. Attention was first focused on the properties of the materials that were assessed by means of a thermogravimetric analyzer, a differential scanning calorimeter, a scanning electron microscope (SEM), and a dynamic mechanical analyzer. In a second step, macroscopic aspects of cavitation were studied by quantifying volume variation of the materials subjected to tension using an accurate optical extensonieler (VidéoTraction). Attention was then turned to microscopic features of cavitation through a careful quantification of void density and shape factor by means of a method coupling a SEM with an image analysis procedure. At the two scales of interest, the results demonstrate that (i) the void density generated by crazing in neat HDPE or particle-matri.x debonding in the composites gradually increases with the deformation state, (ii) void density induced by debonding is higher than that generated by crazing, and (Hi) decreasing particles size causes an increase of void density. We also estimated the void shape factor, that is, ratio between the height and the width of the cavities. In all the studied materials, this parameter starts from a value that is below I and increases by a factor of 2 with increasing deformation. Moreover, in the case of the composites, one notes a higher void shape factor compared with the neat material, and particle size does not influence this parameter. The results provided by this paper can be the basis of a physically based model predicting cavitation mechanisms in semicrystalline polymers.

Amplified Toughening Effect of Annealing on Isotactic Polypropylene Realized by Introducing Microvoids

“…For the soft particles or rigid particles toughened polymers, the most universal phenomenon is the cavitation of soft particles or the interfacial debonding between rigid particles and polymer matrix, which releases the high plastic constraint in the matrix. − Rubber cavitation does not consume a considerable amount of energy; however, it induces plastic deformation of the matrix by shear . Therefore, the microvoid toughening concept has been proposed.…”