jrups
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Abstract: The present work investigates the effect of three different ageing processes (natural, 100% relative humidity and salt spray) on the mechanical performance of two thermoset polymers, epoxy and polyester, commonly used as matrix phase in composite materials. A full factorial design is conducted to evaluate the effect of significant factors and interactions on moisture absorption, tensile and compressive strength and modulus of elasticity of the thermosets. Both polymers reveal a decrease in moisture absorption in the saline environment compared to the completely saturated condition (100% RH). Polyester polymers in harsh environments exhibit higher compressive properties compared to those subjected to natural conditioning. In general, polyester polymers, which are most affected by the positive effect of additional cross-linking, have less moisture absorption and superior mechanical properties compared to epoxy, which is more affected by the negative effect of plasticization. Keywords: Epoxy, polyester, salt spray, mechanical properties, moisture absorption, plasticization. |
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Abstract: Using potassium ethylxanthate as the chain transfer agent, 2,2’-azobis(isobutyronitrile) (AIBN) as the initiator, reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene was carried out. The influences of reaction temperature, reaction time, and the amounts of the initiator and chain transfer agent on the RAFT polymerization were investigated in terms of monomer conversion, average number molecular weight (Mn) and molecular weight distribution (Ð) of the obtained polymer. Monomer conversion and the Mn of the obtained polystyrene (PS) improved with an increase in the reaction temperature, and the polymerization kinetics exhibited a highly linear relationship, indicating a first-order reaction. When the amounts of the initiator and chain transfer agent were increased, it led to a decreased Mn of the produced PS. Meanwhile, the Ð of the PS was in a relatively narrow range (1.42-1.89). The chain-end functionality was further demonstrated by adding methyl methacrylate to the PS. Keywords: Potassium ethylxanthate, Styrene, RAFT, Molecular weight, Chain-end functionality. |
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Abstract: The antifungal activity of the chitosan biopolymer has been extensively studied for several decades. However, the mechanisms of action associated with this process have not been fully clarified yet. To a large extent, this situation is due to the lack of systematization with which, in general terms, the subject has been approached. However, it seems to have begun to change in recent years with the appearance of several papers reviewing the accumulated knowledge on the beneficial effects shown by chitosan in agricultural applications and putting forward it in a more systematic mode. In this work, the most relevant mechanisms of action proposed for chitosan regarding its antifungal activity will be briefly presented, i.e., disruption and changes in the fungal plasma membrane, alteration of gene expression, inhibition of RNA and protein synthesis, Ca2+ channel blocker, to then address the main factors that influence this antifungal activity, observed mainly in studies focused on phytopathogenic species, which have been grouped into three main blocks: those related exclusively to the chitosan molecules, those associated to the fungal itself and those having to do with the environment where the processes take place. Additionally, a brief section addressing some possibilities on which future studies on this topic should focus is also included. Keywords: Action mode, Radial growth inhibition, Membrane disruption, Fungal chitosan, Development stage. |
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Abstract: Non-toxic products with distinguishable characteristics are desirable for use in the packaging sector. Biopolymers fit this criterion and can serve as vehicles for the addition of various compounds, such as enzymes, dyes, antioxidant agents, or monounsaturated fatty acids, to provide useful qualities to a product, such as biodegradability. A biopolymer obtained from fishing industry waste residues can be combined with fatty acids to form films and emulsions with different characteristics to be used in different drug production, packaging, and product protection. This study aimed to use a natural biopolymer, chitosan, in combination with oils from the Mauritia flexuosa L.f., (“buriti”) and Acrocomia aculeata (“macaúba”) species of palm trees to develop films that exhibit excellent biodegradability in soil. The degradation of chitosan films (CF), emulsified chitosan films with buriti oil (CFB), and emulsified chitosan films with macaúba oil (CFM) in soil was investigated, where the CFB samples showed the best protection against moisture and the largest weight reduction over 30, 60, and 90 day testing periods. Further studies are needed to test the practical application of these films, but the results of the CFB sample indicate that these chitosan films imbued with natural oils from the Mauritia flexuosa L.f. and Acrocomia aculeata species have great potential for use in the packaging sector. Keywords: Biopolymer, Soil, Palm oil, Packaging, Mauritia flexuosa L.f., Acrocomia aculeata. |
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Abstract: The aim of this work was to study the interaction of lipases (as an important biopolymer) with models of biomembranes based on the phospholipid and cholesterol. Lipases (triacylglycerolacyl hydrolases) are widely distributed enzymes and well-known by their hydrolytic activity. The study of the lipase interactions with lipid vesicles in aqueous dispersions is of fundamental and practical interest. The pure phosphatidylcholine from egg yolk (ePC) and cholesterol (Chol) were obtained from Sigma-Aldrich. Lipase was obtained from hog pancreas. Measurements of the current and equilibrium surface tension (ST and eST) values were carried out using a BPA-1P device and ADSA program. The particle sizes in the prepared colloidal solutions were determined by the method of dynamic light scattering. An addition of lipase led to some decrease both, of ST and eST for the samples of ePC:Chol (in the ratios from19:1 to 1:1). The mean particle diameter (MPD) and effective particle diameter (EPD) values for the samples of ePC:Chol changed drastically by lipase addition. The EPD/MPD ratios increased from 1.7 to 2.0, from 1.8 to 2.6, from 2.3 to 6.5, from 1.5 to 2.9 for the samples of ePC:Chol at the ratios of 19:1, 14:1, 9:1, 7:1, respectively by lipase concentration increase. This general tendency can be explained by strong interaction of lipase with lipid membrane that leads to the formation of the mixed particles ePC:Chol:lipase with more narrow particle size distribution as compared to the initial EPD/MPD ratio (for the ePC:Chol mixture without lipase) Keywords: Lipase, lipids, surface tension, particle size distribution. |