Multiscale Natural Fiber-Reinforced Thermoplastic Composites Towards Enhanced Mechanical Performance
Topic(s) : Material science
Co-authors :
Dina ESTEVES (PORTUGAL), Luís NOBRE (PORTUGAL), Carlos MOTA , Joao BESSA , Fernando CUNHA , Raul FANGUEIROAbstract :
In recent years, fiber-reinforced composite materials play a very important role in advanced defence equipment, wind energy, marine and aerospace sectors, among others. A considerable interest in natural fibers as flax, hemp and jute, exist on account of the growing environmental and ecological concerns. Still, natural fiber-reinforced composites often present lower performance than the alternatives containing synthetic fibers specifically in what concerns lower mechanical and chemical properties. When incorporated in a polymer matrix, natural fibers typically exhibit a hydrophilic behavior, due to the presence of hydroxyl groups in the lignocellulosic content, leading to compatibility issues with thermoplastic matrix that is traditionally hydrophobic. According to Alao et al., the adhesion between the matrix and the pretreated fibers can be greatly improved by chemical treatments, considering different solutions of sodium bicarbonate (NaHCO3), at 2, 6 and 9 wt.%, at different times intervals (24, 48, 72 and 96 hours) [1]. For higher concentrations, the impact of the treatments on the mechanical performance of samples was found to be improved in comparison with the non‐treated counterparts. Worthy of emphasis is that this chemical treatment present itself as a sustainable solution, not harmful to the environment, since the residual elements had a neutral pH. Regarding the matrix modification and conforming moreover to Stanley and al., advocate for the use of the novel reactive methylmethacrylate (MMA) thermoplastic resin, namely Elium®, which can lead to a competitive and sustainable solution against traditional epoxy-based composites, allowing that the final products and systems can be recycled [2].
In this study, composites materials were developed using thermoplastic resin Elium®, with incorporation of nanocellulose, dispersed in the matrix at different concentrations (1, 2.5 and 5 wt.%). Natural fibers, such as flax, were chemically treated by immersion in an aqueous solution with a concentration of 9 wt.% of NaHCO3, for different periods (24, 48, 72 and 96 hours), at room temperature. After this treatment, flax fibers were washed with distilled water and dried in an oven at 50 ºC, for 18 hours. Then, the thermoplastic matrix composites were developed via incorporation of intercalated layers of flax fibers and the final composites were produced using the compression molding technique. After that, the samples were evaluated, regarding mechanical performance, morphology, and degree of fiber surface tension by contact angle.
The incorporation of nanocellulose in the thermoplastic resin improved the fiber/matrix interface and, consequently, flexural and tensile strengths. The chemical treatment of flax fibers, with a concentration of 9 wt.% of NaHCO3, can lead to a significant improvement of flexural strength due to the removal of impurities and introduction of hydroxyl groups, which improve adhesion to the thermoplastic matrix.
In this study, composites materials were developed using thermoplastic resin Elium®, with incorporation of nanocellulose, dispersed in the matrix at different concentrations (1, 2.5 and 5 wt.%). Natural fibers, such as flax, were chemically treated by immersion in an aqueous solution with a concentration of 9 wt.% of NaHCO3, for different periods (24, 48, 72 and 96 hours), at room temperature. After this treatment, flax fibers were washed with distilled water and dried in an oven at 50 ºC, for 18 hours. Then, the thermoplastic matrix composites were developed via incorporation of intercalated layers of flax fibers and the final composites were produced using the compression molding technique. After that, the samples were evaluated, regarding mechanical performance, morphology, and degree of fiber surface tension by contact angle.
The incorporation of nanocellulose in the thermoplastic resin improved the fiber/matrix interface and, consequently, flexural and tensile strengths. The chemical treatment of flax fibers, with a concentration of 9 wt.% of NaHCO3, can lead to a significant improvement of flexural strength due to the removal of impurities and introduction of hydroxyl groups, which improve adhesion to the thermoplastic matrix.