In this paper, we produced ethylene vinyl acetate copolymer (EVA)-filled poly(lactic acid) (PLA) blends by extrusion and injection moulding. We annealed the injection-moulded specimens at 80 °C, ...100 °C, 120 °C and 140 °C to produce various crystal structures in PLA. Then we investigated the cross-effect between the crystal structure of PLA and the presence of EVA on the mechanical, impact, calorimetric, thermomechanical and heat deflection temperature properties of the blends. We found a synergistic toughening effect between the crystal structure of PLA that developed during annealing and the presence of dispersed EVA particles in the PLA matrix. The blend had a very high impact strength of over 65 kJ m
−2
, which is three times higher than the impact strength of acrylonitrile butadiene styrene copolymer (~ 20 kJ m
−2
), and thus it is very promising for technical applications.
The widely used plastic products which became a part of our everyday life are produced almost entirely from crude oil. There are various estimates on oil resources, but there is an increasing need to ...use other, preferably renewable resources to produce plastic products. Although plastics from renewable resources, bio-based, and inherently biodegradable plastics, or so-called bioplastics/biopolymers, are already on the market, their properties are not always adequate compared to those of “ordinary” petroleum-based plastics, which the bioplastic is supposed to replace. One of the most promising bioplastics nowadays is Poly(lactic acid) (PLA). Despite the great potential of PLA to replace petroleum-based engineering plastics, such as Acrylonitrile Butadiene Styrene (ABS), Polypropylene (PP), and others, the inherent brittleness and low Heat Deflection Temperature (HDT) hinders the widespread application of PLA. Many methods have been developed to improve the properties of PLA, but its widespread industrial application is still rather an exception than the rule. The current study aims to survey the progress in the modification of the properties of PLA. We focused on the most effective additives to improve the properties of injection molded PLA products, which we selected from a comprehensive literature review. Most of the modification possibilities presented in this review can also be used for other processing technologies, but in the discussion, we focused on their use in injection molding.
•Oligomeric Lactic Acid is one of the most suitable plasticizers for PLA.•Impact of EVA or NR filled PLA enormously increases when PLA phase is crystallized.•The usage of compatibilizer is essential when blending various biopolymers.•Improving HDT of PLA parts can be done using PPC or IMC method and effective nucleator (heterogeneous or stereocomplex).•There is great potential in injection molding of long natural fiber reinforced PLA.
We selected the thirteen most effective nucleating agents for Poly(lactic acid) (PLA) from the literature, and synthesized and compounded them with two different PLA grades: 3001D (1.4% D-lactide ...content) and 3100HP (0.5% D-lactide content, considered PLLA). We determined the crystallinity and crystallization of PLA with different nucleating agents in identical conditions (same nucleating agent content, same cooling rate) with the help of differential scanning calorimetry. We compared the efficiency of each nucleating agent and found that for both PLA grades, Zinc PhenylPhosphonate was the most effective. However, even when nucleated PLA was injection molded into a cold mold (25 °C), it still could not fully crystallize during cooling and the heat deflection temperature did not increase significantly. The maximum achieved crystallinity, in this case, was between 32.4 and 35.7%. On the contrary, when a 90 °C “hot mold” and in-mold crystallization together were applied, the specimens achieved full crystallization during the injection molding cycle (crystallinity was between 44.5 and 50.0%), and the heat deflection temperature increased to an average of 88.8 °C. We also examined the mechanical properties of the nucleated PLA and found that the usage of nucleating agents together with a hot mold improved tensile strength, tensile modulus, and Charpy impact strength but decreased elongation at break.
Al99.5 and AlSi12 matrix syntactic foams were produced by pressure infiltration of Globocer grade ceramic hollow spheres. The produced aluminium matrix syntactic foams (AMSFs) were investigated by ...compressive tests, dynamic mechanical analysis (DMA), finite element methods (DMA) and elasticity based analytical calculations. The aim of the investigations was (i) to map the compressive properties of the AMSFs, (ii) to determine and compare the effective Young's modulus of the AMSFs determined by compressive tests, DMA, FEM and analytical calculations and (iii) to determine the low frequency damping capability of the AMSFs. The compressive tests showed pronounced differences between the two matrix materials, characterized by higher compressive strength, compressive strain and absorbed mechanical energy in the case of AlSi12 matrix, however, the energy absorption efficiency due to the different failure mechanism of AMSFs (homogeneous densification in the case of Al99.5 and cleavage in the case of AlSi12 matrix, respectively). The DMA tests confirmed the effective Young's moduli values, measured by compression and proved higher damping capability in the case of AlSi12 matrix. FEM and analytical calculations also confirmed the measured effective Young's moduli within a reasonable error band.
•d-Amino acid separation methods used for biological samples are overviewed.•Quantitative performance of the methods is critically reviewed.•d-Amino acid levels, especially d-aspartate, d-serine and ...d-alanine in various biological samples are summarized.
It is widely accepted that some of the free d-amino acids play important biological role. d-Aspartate and d-serine formed in the central nervous system of higher vertebrates have neurotransmitter/neuromodulator function. Together with d-alanine they are distributed in various tissues and biological fluids. Studying their physiological and pathological significance requires their sensitive and accurate determination in biological samples.
The various separation and detection methods used for their analysis are overviewed in the present paper. Our focus is mainly the quantitative performance and the analysis of real biospecimens.
The era of MAO-B inhibitors dates back more than 50 years. It began with Kálmán Magyar’s outstanding discovery of the selective inhibitor, selegiline. This compound is still regarded as the gold ...standard of MAO-B inhibition, although newer drugs have also been introduced to the field. It was revealed early on that selective, even irreversible inhibition of MAO-B is free from the severe side effect of the non-selective MAO inhibitors, the potentiation of tyramine, resulting in the so-called ‘cheese effect’. Since MAO-B is involved mainly in the degradation of dopamine, the inhibitors lack any antidepressant effect; however, they became first-line medications for the therapy of Parkinson’s disease based on their dopamine-sparing activity. Extensive studies with selegiline indicated its complex pharmacological activity profile with MAO-B-independent mechanisms involved. Some of these beneficial effects, such as neuroprotective and antiapoptotic properties, were connected to its propargylamine structure. The second MAO-B inhibitor approved for the treatment of Parkinson’s disease, rasagiline also possesses this structural element and shows similar pharmacological characteristics. The preclinical studies performed with selegiline and rasagiline are summarized in this review.
We demonstrated the applicability of integrated Fibre Bragg Grating (FBG) sensors in the case of flax fabric reinforced epoxy matrix composites produced by resin transfer moulding (RTM). FBG sensors ...were integrated between the reinforcing layers of the composites. We verified the robustness of FBG-based strain measurement by comparing it to strain gauge strain measurement, optical fine strain measurement and deflection measurement from crosshead displacement during four-point flexural tests. After the extensive characterization of the static properties of the composite material, fatigue tests were performed in the same setup on the specimens with integrated FBG sensors. We demonstrated that with the integrated optical fibres, the cyclic creep strain of the composites could be monitored, which could be used as a criterion to predict the fatigue failure of the composites. The proposed technique can provide an effective and robust way for periodic condition monitoring of composite structures, especially in natural fibre reinforced composites, where creep is more pronounced than in the case of synthetic fibre reinforced composites.
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Monoamine oxidase B (MAO-B) inhibitors have an established role in the treatment of Parkinson’s disease as monotherapy or adjuvant to levodopa. Two major recognitions were required for their ...introduction into this therapeutic field. The first was the elucidation of the novel pharmacological properties of selegiline as a selective MAO-B inhibitor by Knoll and Magyar and the original idea of Riederer and Youdim, supported by Birkmayer, to explore its effect in parkinsonian patients with on–off phases. In the 1960s, MAO inhibitors were mainly studied as potential antidepressants, but Birkmayer found that combined use of levodopa and various MAO inhibitors improved akinesia in Parkinson’s disease. However, the serious side effects of the first non-selective MAO inhibitors prevented their further use. Later studies demonstrated that MAO-B, mainly located in glial cells, is important for dopamine metabolism in the brain. Recently, cell and molecular studies revealed interesting properties of selegiline opening new possibilities for neuroprotective mechanisms and a disease-modifying effect of MAO-B inhibitors.
•Capillary electrophoresis method was developed to analyze underivatized gangliosides.•Conditions for the separation of GM3, GM1, GD1a, GD1b, GT1b and GQ1b were optimized.•Effect of borate and ...cyclodextrins on the separation was examined.•The optimized method was validated for the quantification of neural gangliosides.•Ganglioside patterns in rat cerebral and cerebellar synaptosomes were compared.
Gangliosides are sialic acid containing glycosphingolipids of the plasma membrane with diverse biological functions. They are most abundant in neural tissues where their dysregulation has been suggested to be involved in various pathological conditions. Due to their importance, efficient analytical methods are needed to determine individual gangliosides in biological samples. Here we report a capillary electrophoresis method, optimized and validated for the simultaneous quantification of major neural gangliosides GM1, GD1a, GD1b, GT1b and GQ1b in their underivatized form. The most abundant extraneural monosialogangloside, GM3 can also be separated by this method. Micelles of the highly amphiphilic gangliosides were disrupted with cyclodextrins (CyDs) in the aqueous separation buffer. Among the tested CyDs, the best resolution was observed using 20 mM randomly methylated alpha-CyD in alkaline sodium borate buffer enabling the separation of all studied gangliosides. The method was applied for the quantification of gangliosides in rat cerebral and cerebellar synaptosomes.
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