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- W744460441 abstract "The aim of this doctoral thesis is the chemical and physical modification of brittle epoxy resin (EP) using two different modifiers - polyurethanes and montmorillonite nanoclay - with the purpose to improve its mechanical properties. The use of polyurethanes (PUR) is motivated by the versatility of their structure, which can be easily modulated with appropriate substrates. Those utilized in the thesis were synthesized from polyols (polyethylene glycols and polyoxypropylene diols) with different molecular weights, and two diisocyanates: 2,4-toluene diisocyanate (TDI) and 4,4'-diphenylmethane diisocyanate (MDI). It was determined that the short soft segments in polyurethane (polyetylene glycol based PUR) increase the flexural strength of EP, while composites containing polyurethanes with longer soft segments (synthesized from polyoxypropylene diols) are tougher. The addition of MDI based PUR results in a greater improvement of epoxy resin's mechanical properties than in the case of TDI application. Montmorillonite (MMT) is known to significantly improve fracture toughness and strength of polymers even if added in amounts considerably lower than used for (mi)-sized fillers. Epoxy composites containing 1 % MMT demonstrate increased impact strength, whereas 2 % addition of MMT to EP enhances its flexural properties. However, higher MMT concentrations lead to reduction of EP mechanical properties. Hybrid composites containing 1 or 2 % MMT and 5 to 15 % PUR (both MDI and TDI based) exhibit improved mechanical properties in comparison to neat epoxy resin. Moreover, hybrid composites prepared with MDI based PUR show more pronounced enhancement in comparison to those containing TDI, because the increase of fracture toughness and flexural strength is achieved without deterioration of the thermal properties. For optimum strength enhancement the loading level of 1 % MMT and 15 % of MDI-PUR synthesized from polyethylene glycol is intercepted with two mechanisms involved in the improvement: exfoliation of nanoclay depicted with X-ray diffraction, and formation of chemical bonding between hydroxyl groups of epoxy resin with isocyanate groups from polyurethane confirmed with infrared spectroscopy as well as differential scanning calorimetry. Furthermore, polyurethane modifier acts as a compatibilizer for epoxy resin and montmorillonite mixtures and promotes the exfoliation process of the latter. Taking into account all results obtained from mechanical tests and structural analyses, it might be assumed that the obtained EP/PUR/MMT hybrid composites are formed from grafted EP/PUR interpenetrating polymer network and exfoliated montmorillonite acting as nanofiller." @default.
- W744460441 created "2016-06-24" @default.
- W744460441 creator A5051903384 @default.
- W744460441 date "2011-11-25" @default.
- W744460441 modified "2023-09-24" @default.
- W744460441 title "Úprava epoxidových pryskyřic přídavkem polyuretanu a nanojílu" @default.
- W744460441 hasPublicationYear "2011" @default.
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