Abstract
The toughening mechanisms of poly(lactic acid; PLA) blended with two different elastomers, namely poly (butylene adipate-co-terephtalate; PBAT) and polyolefin elastomers with grafted glycidyl methacrylate (POE-g-GMA), at 10 and 20 wt.%, were investigated. Tensile and Charpy impact tests showed a general improvement in the performance of the PLA. The morphology of the dispersed phases showed that PBAT is in the form of spheres while POE-g-GMA has a dual sphere/fibre morphology. To correlate the micromechanical deformation mechanism with the macroscopical mechanical behaviour, the analysis of the subcritical crack tip damaged zone of double-notched specimens subjected to a four-point bending test (according to the single-edge double-notch four-point bend (SEDN-4PB) technique) was carried out using several microscopic techniques (SEM, polarized TOM and TEM). The damage was mainly generated by shear yielding deformation although voids associated with dilatational bands were observed.
Highlights
To correlate the micromechanical deformation mechanism with the macroscopical mechanical behaviour, the analysis of the subcritical crack tip damaged zone of double-notched specimens subjected to a four-point bending test (according to the single-edge double-notch four-point bend (SEDN-4PB) technique) was carried out using several microscopic techniques (SEM, polarized transmission optical microscopy (TOM) and Transmission electron microscopy (TEM))
Transmission electron microscopy (TEM) is used to search for damage that occurs below the surface [23], while transmission optical microscopy (TOM) is often used with crossed polars to detect regions of permanent orientation, i.e., plasticity [24]
P blends, as the PBAT content increased, guaranteed an improvement of Charpy impact resistance of up to 50% more compared to pure poly(lactic) acid (PLA)
Summary
Polymers 2021, 13, 4053 the voids are not interconnected but rather the bands are planar arrays of cavitated particles where the matrix between voids is subject to high shear strains and reduced constraints on the plastic flow [19] This idea was found to be effective, demonstrating the cooperation of different micromechanical deformation mechanisms, and it has laid the basis for the development of the rigid filler toughening theory of Argon and Cohen [20,21]. An interesting starting point to study toughening mechanisms is to observe the damage zone around the surviving crack tip, produced by a mechanical test, called the single-edge double-notch four-point bend (SEDN-4PB) technique [29] In this method, one crack will reach its critical stress intensity factor and propagate, while the second one does not propagate. This method, produces a sub-critical propagated crack that can be analyzed by coupling different microscopy techniques [30,31]
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