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Natural hemp fabric reinforced epoxy resin composites were prepared in flame retarded form.Fabrics were treated in three ways: the first method involved the immersion of preheated fabric into cold phosphoric acid solution (allowing penetration into the capillaries of the fibres) and subsequent neutralization, the second way was a reactive modification carried out with an aminosilane-type coupling agent, while the third treatment combined the sol-gel surface coating with the first method. The introduction of P-content into the reinforcing fibres resulted in decreased flammability of not only the hemp fabrics, but also of the flame retardancy of epoxy composites, comprising it changed advantageously. By applying aminetype phosphorus-containing curing agent (TEDAP) in combination with the treated fabrics, V-0 UL-94 rating was achieved. Composites of unexpectedly improved static and dynamic mechanical properties could be prepared only when the simple phosphorous fibre treatment and reactive flame retardancy was combined. . This problem can be solved or moderated by using flame retarded biofibres combined with matrix containing flame retardant additive, by which way the polymer concentration of the matrix and thus its strength can maintained [16,17,18].In this work the idea of flame retarded reinforcement was adapted to epoxy resin composites, by combining it with P-containing crosslinking agent as reactive flame retardant in the matrix.Hemp fabrics were selected for forming flame retarded reinforcement and a P-containing amine [19,20] was applied as curing agent in the FR matrix composites. Materials and methods MaterialsThe epoxy Fabric treatmentTwill woven hemp fabrics (HF) were washed with water to remove dust and impurities and then dried in oven at 70 °C for 12 h. The fibres were treated in three ways in order to render them flame retardant. In the first case, the so-called thermotex procedure [21] was applied.The high-temperature treatment of the fabrics allows better absorption of the treating solution to the capillaries of the fabric. For this purpose, the fabrics were preheated at 120 °C for 2 h, and then immersed in cold 17 mass% phosphoric acid solution for 5 min. The ratio of fabric to phosphoric acid solution was 1 g to 10 ml. As the acid may induce long-term degradation in cellulose fibre structure, it was neutralized by immersing the fabrics in 5% ammonium hydroxide solution. The excess of the treating and neutralizing solutions were removed by pressing the fabrics by a foulard. After treatment, the fabrics were dried in air. The amount of the absorbed phosphorus was determined by the mass increase of the treated fibres and by elemental analysis using energy-dispersive X-ray spectroscopy (see section 2.3.3). The mass increase of the THF fibres was 8 mass%, which means the absorption of 1.7 mass% of P (1.65 mass% by elemental analysis).In the other case, sol-gel treatment of the fabrics was carried out using Geniosil GF-9 aminetype silane. The fabrics were immersed in 10 mass% toluene solution...

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