The use of natural fibers in cementitious composites has been gaining prominence in engineering. The natural lignocellulosic fibers (NLFs) used in these composites have advantages such as reduced density, reduced fragmentation and concrete cracking, thus improving flexural performance and durability. Coconut-fiber is one of those natural fibers and its use presents technical, ecological, social and economic benefits, as it is improperly disposed of, representing a large waste of natural resources, in addition to causing environmental pollution. Thus, composites reinforced with natural fibers are promising materials for the construction industry, as in addition to meeting the sustainability of buildings, there will also be a reduction in urban solid waste generated and gains for structures with the use of environmentally friendly materials that meet to active efforts and with greater durability. This work aims to evaluate the tensile behavior of green coconut-fibers subjected to different drying temperatures through chemical, thermal (TG\/DSC), morphological, visual and mechanical analysis. Drying temperatures of 70\u00a0\u00b0C, 100\u00a0\u00b0C and 130\u00a0\u00b0C were analyzed and the results indicated that the drying temperature at 70\u00a0\u00b0C was satisfactory, providing fiber-reinforced composites with good tensile strength, combined with good ductility.<\/p>\n\n\n\n
In Brazil, the total generation of urban solid waste in 2021 was approximately 82 million tons, equivalent to 390 kg\/person\/year1<\/a><\/sup>. Of the urban solid waste generated, attention should be paid to the green coconut, a tropical fruit whose production record in Brazil was approximately 2.65 million tons in 20162<\/a><\/sup>. It is recorded that 70% of the garbage collected on Brazilian beaches is composed of coconut husks, and that factors such as proliferation of vectors and long period for decomposition contribute to the reduction of the useful life of landfills in which coconut husks are discarded3<\/a>,4<\/a><\/sup><\/p>\n\n\n\n Although Brazil is a large consumer of coconuts, only part of it is used for food2<\/a><\/sup>. The pulp of the green coconut is edible, but consumption of the fruit in natura<\/em> is often limited to water. This results in the disposal of thousands of tons a month, representing a huge waste of natural resources. Thus, the use of green coconut residue, especially its husk fibers, has technical, ecological, social and economic benefits.<\/p>\n\n\n\n Natural fibers are ecological and low-cost materials, considered new, effective, alternative materials and their field of use is quite wide, from applications in tapestry, ornamental pieces to the textile industry. Specifically in civil construction, natural fibers are used in cement matrices in the production of roofing and cladding elements, particle board sheets, green roofs, reinforcement and rehabilitation of masonry walls and housing components5<\/a><\/sup>.<\/p>\n\n\n\n As for the addition of 0.5% by volume of green coconut-fibers in cementitious matrices, there was an increase in compressive strength of around 15% and tensile strength of 20%, when compared to conventional concrete3<\/a><\/sup>. On the other hand, considering the compressive strength with the addition of 4% by volume of coconut-fiber to the concrete, this resistance was reduced by around 50%, while in the flexural resistance there was an increase of 50%6<\/a>,6<\/a>,7<\/a>,8<\/a>,9<\/a>,10<\/a>,11<\/a>,12<\/a>,14<\/a><\/sup>. In addition to dispersed fiber, there are studies to reinforce concrete walls using ropes composed of coconut-fibers in order to increase the stability of structures against earthquakes15<\/a><\/sup>. Other studies used coir-fibers in concrete to improve its properties under impact load, reducing concrete spalling and cracking16<\/a><\/sup> Rumbayan et al.17<\/a><\/sup> found that 0.25% coconut-fiber provided an improvement of approximately 19% in compressive and flexural strength in 28 days. It was found in this study that the greater the amount of coconut-fiber in the concrete, the lower the tensile strength and that with the presence of fibers in the concrete there is lower workability.<\/p>\n\n\n\n Various natural fibers are used in cementitious composites such as oil palm broom fibers, a\u00e7a\u00ed, bamboo, curau\u00e1, etc. Oil palm broom fibers when subjected to treatments show improvements in their performance, for example using treatment with an alkaline concentration of 6% NaOH at room temperature for 48 hours showed improvements in tensile strength and in elastic modulus of up to 60% and 65%, respectively. Already considering silane treatment, Momoh et al.18<\/a><\/sup> found that the ideal recommendation is 3% silane for 24 h at room temperature, which resulted in up to 60% improvement in tensile strength and a reduction of 11 % in water absorption. Hot water treatment for 30 min at 100 \u00b0C resulted in a 40% increase in tensile strength. A\u00e7a\u00ed fiber has a tensile strength of 17.8 MPa whereas curau\u00e1 fiber already has a tensile strength of 488 to 752 MPa.<\/p>\n\n\n\n As most natural lignocellulosic fibers (NLFs), the coconut-fibers are highly hygroscopic and their use, when wet, strongly affects the properties of these materials17<\/a><\/sup>. As its mechanical properties are dependent on the moisture content and considering its use as reinforcement in composites, this moisture content must be reduced through the drying process. In general, artificial drying with ovens or dryers is used19<\/a><\/sup>. Therefore, the objective of this study is to analyze the tensile behavior of green coconut-fibers subjected to different drying temperatures (70\u00a0\u00b0C, 100\u00a0\u00b0C and 130\u00a0\u00b0C) in comparison with natural fibers (without drying process). It is therefore expected that it will be possible to define the most suitable drying temperature for the application of green coconut-fibers in cementitious composites.<\/p>\n\n\n\n