The effect of the compounding method on the morphology and on the properties of poly(lactic acid) (PLA)-hydrotalcite (HT) composites was studied. Moreover, the influence of two different kinds of HT-organically modified (OM-HT) and unmodified (U-HT)-and their concentration was evaluated. The composites were prepared using either a single screw extruder (SSE), a counter rotating twin-screw compounder (TSC) or a corotating twin-screw extruder (TSE). The prepared materials were characterized by scanning electron microscopy, gel permeation chromatography (GPC) analysis, mechanical and rheological measurements. The results indicated that the best morphology, i.e., particles dimension and distribution, is exhibited by materials prepared by TSE while the worse ones by the samples processed by SSE. The viscosity of all the materials containing the HT is lower in comparison with the viscosity exhibited by the neat matrix, in particular, when the OM-HT is used. These results were correlated to degradation phenomena occurring during the processing of the materials as revealed by the results of GPC analysis. The addition of HT caused only a slight increase of elastic modulus of filled materials even when 5% of filler was incorporated. However, in full agreement with morphological analyses, the best performances were exhibited by materials prepared by TSE while the worse ones by the samples processed by SSE. POLYM. ENG. SCI., 54:1804-1810
In this work, the mechanical and the self-healing behaviors of an ethylene-co-methacrylic acid ionomer were investigated
in different testing conditions. The self-healing capability was explored by ballistic impact tests at low-velocity, midvelocity, and
hypervelocity bullet speed; different experimental conditions such as sample thickness and bullet diameter were examined; in all impact tests, spherical projectiles were used. These experiments, in particular those at low and midspeed, allowed to define a critical ratio between sample thickness and bullet diameter below which full repair was not observed. After ballistic damage, the healing efficiency was evaluated by applying a pressure gradient through tested samples. Subsequently, morphology analysis of the affected areas was made observing all tested samples by scanning electron microscope. This analysis revealed different characteristic features of the damaged zones affected at different projectile speed. Stress–strain curves in uniaxial tension performed at different temperatures and
strain rates revealed yield strength and postyield behavior significantly affected by these two parameters. A rise of temperature during high strain rate tests in the viscoplastic deformation region was also detected. This behavior has a strong influence on the self-repair-ing mechanism exhibited by the studied material during high-energy impact tests
The development of self‐healing materials, based on polymer blends, is an important issue either from a scientific or a technological point of view. The application of such materials can be remarkably extended if healing effects can be maintained even in polymers that are modified in order to tune their physical and mechanical behavior. In this research the self‐healing behavior of blends made of ionomers (sodium and zinc salts of poly(ethyelene‐co‐methacrylic acid)—EMNa and EMZn) with functionalized elastomers (epoxidized natural rubber with different epoxidation levels—ENR50 and ENR25, polyisoprene—PISP) of different compositions is investigated. The role of processing conditions, phase morphology, functionalization level, polymers compatibility over self‐healing response are discussed. Rubber functionality and phase dispersion are recognized as crucial factors affecting the healing efficiency of blends. Results of ballistic tests, DSC thermal analysis, FTIR spectroscopy, optical and electron (SEM and TEM) microscopy observations, rheological and mechanical tests are presented as supporting evidences.
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