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Development of polyamide composites with natural fibers for automotive applications

Abstract : The objective of this PhD Thesis is to prepare composites of polyamide with natural fibers, able to withstand high temperatures. The polymeric matrix and treated fibers should be resistant to temperature separately. For this reason, this Thesis is focused in two main topics: chemical treatment of natural fibers and processing of composites of these treated fibers with polyamide 6 and 6.6 matrix. Curauá, jute and flax were the fibers used. To remove low molar mass components, as hemicellulose and lignin, of natural fibers, alkaline-treatment was conducted using a 5.0 wt.% of sodium hydroxide solution. Two treatment techniques at different environments were compared: at room pressure (three successive treatments, at 80 ºC, during 1h each) and high pressure (1.5 MPa and 120 ºC at different time intervals: 15, 30, 45 and 60 minutes). Improvement of thermal properties of natural fibers was observed in both cases by thermogravimetric analysis (TGA) and, looking at the different responses of the three studied fibers to the high pressure alkaline treatment, it was decided to fix 30 minutes of high pressure mercerization for all fibers before performing post-treatments (acetylation and silanization) and preparing composites using polyamide 6 and 6.6 as matrixes. It was employed different fiber contents in both polyamide matrix (10, 20 and 30 wt. %). By tension testings and SEM observations, it was shown improvement of mechanical properties of PA 6 / treated fibers at 70/30 proportion. To reduce the processing temperature of PA 6.6, a combination of 2.5 wt. % of LiCl and 2.5 wt. % of N-butyl benzene sulphonamide (NBBSA) was defined throught experimental design and it was added to pure polyamide 6.6. Moreover, it was found that the highest mechanical properties for composites prepared with polyamide 6.6 matrix was those using 10 wt. % of alkaline-treated + silanized fibers on plasticized polyamide 6.6. It was possible to prepare composites with higher fiber content up to 30 wt. %. However, it is needed an improvement of compounding parameters to enhance fiber dispersion.
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Renato Pereira de Melo. Development of polyamide composites with natural fibers for automotive applications. Materials. Ecole Nationale Supérieure des Mines de Paris; Universidade federal do Rio de Janeiro, 2015. English. ⟨NNT : 2015ENMP0062⟩. ⟨tel-02892103⟩



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