Volume Change during Creep and Micromechanical Deformation Processes in PLA-PBSA Binary Blends.

Laura Aliotta,Maria-Beatrice Coltelli,Vito Gigante,Andrea Lazzeri

doi:10.3390/polym13142379

Abstract

In this paper, creep measurements were carried out on poly(lactic acid) (PLA) and its blends with poly(butylene succinate-adipate) (PBSA) to investigate the specific micromechanical behavior of these materials, which are promising for replacing fossil-based plastics in several applications. Two different PBSA contents at 15 and 20 wt.% were investigated, and the binary blends were named 85-15 and 80-20, respectively. Measurements of the volume strain, using an optical extensometer, were carried out with a universal testing machine in creep configuration to determine, accompanied by SEM images, the deformation processes occurring in a biopolymeric blend. With the aim of correlating the creep and the dilatation variation, analytical models were applied for the first time in biopolymeric binary blends. By using an Eyring plot, a significant change in the curves was found, and it coincided with the onset of the cavitation/debonding mechanism. Furthermore, starting from the data of the pure PLA matrix, using the Eyring relationship, an apparent stress concentration factor was calculated for PLA-PBSA systems. From this study, it emerged that the introduction of PBSA particles causes an increment in the apparent stress intensity factor, and this can be ascribed to the lower adhesion between the two biopolymers. Furthermore, as also confirmed by SEM analysis, it was found that debonding was the main micromechanical mechanism responsible for the volume variation under creep configuration; it was found that debonding starts earlier (at a lower stress level) for the 85-15 blend.

Highlights

Physical polymeric blends, constituted by a rubbery phase embedded in a more rigid matrix, are a long-lasting route for the preparation of new materials with a modulated balance of properties [1]
The ATR evidence resulted in good agreement with the selected compositions of poly(lactic acid) (PLA)/poly(butylene succinate-adipate) (PBSA) blends
A better knowledge of the micromechanical deformation processes of these new biopolymeric blends is fundamental in order to better exploit their peculiar properties, favoring the replacement of their fossil-based counterparts in several application sectors

Summary

Introduction

Physical polymeric blends, constituted by a rubbery phase embedded in a more rigid matrix, are a long-lasting route for the preparation of new materials with a modulated balance of properties [1]. Improved knowledge of the mechanical behavior of biobased materials is fundamental for better exploiting their peculiar properties and comparing them with fossil-based ones, favoring the replacement of the latter in several application sectors. In this context, it is beneficial to investigate micromechanical deformation processes that occur in physical polymeric blends, knowing that external stresses can be the cause of the starting point of numerous micromechanical deformation processes that play a critical role regarding the failure of pure heterogeneous systems [6]. Higher elastic energy may cause a faster advance of shear bands and, a larger plastic zone form is attained [19]

Methods

Results

Conclusion