Physical and mechanical characterization of surface treated bamboo fibers

Abstract

The bamboo fiber has been studied as composite reinforcement for offering lightness and more resistance to the material. Alkalization and acetylation are superficial chemical treatments based on alkaline solution and on a solution based in acid and acetic anhydride, respectively, which modify the fibers composition, introducing functional groups acetyl, turning it hydrophobic. In this project, it was aimed the application of the alkalinization and acetylation treatments, attempting to improve the fibers adhesion to the polymers when in a composite. The fibers were evaluated by moisture content, water absorption tests by immersion, density, infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, tensile tests, and morphological analysis. When acetylated, the bamboo fiber presented lower water absorption (62.98%), gained thermal stability of approximately 50 °C, presented lower crystallinity (62.47%) and, according to SEM images, the fibers has shown an increase of surface roughness, facts that contribute to the best fiber/matrix adhesion in composites. The acetylation decreased the mechanical strength of the fiber, supporting 19,820 MPa, against 27,670 MPa from the natural and 31,730 MPa from the alkaline.

Introduction

With the constant search for low-cost, environmental friendly materials that have good physical, mechanical and thermal properties, researchers have been exploring the possibility of utilizing natural fibers as reinforcements for composite materials in civil construction, aeronautical, automobile, and other industries.

The natural fibers most commonly used as reinforcement are the coconut, sisal, juta, and sugar cane fibers, already explored in the Brazilian literature [1]. However, there was a growing interest in studying the bamboo fiber, since it grows quickly, and as such, can renew faster (it takes up to 3 or 4 years to reach the adulthood). Additionally, it has higher hardness and resistance, as well as lower density, which are important characteristics to produce a good composite material [2], [3], [4], [5].

The bamboo is a plant that belongs to Gramineae family, mostly found and used in Asia, where the largest producers are China and India, being also found in Africa and the American continent. With about 115 genres of bamboo around the world, more than 1500 species are used in diverse applications, from the creation of popular houses in countries like Ecuador and Colombia, to great civil works like bridges and temples in Japan, China, and India [3], [5], [6], [7].

The bamboos consist essentially of an underground rhizome and hollow woody culms with fibers arranged in the form of bundles, mainly in the outermost region endowed with branches and leaves. Morphologically, the bamboo consists of parenchymal tissue, vessels, and fibers [8], [9], [10]. First introduced during the time of the first Portuguese immigrants, the most abundant species in Brazil is the Bambusa vulgaris, and in Brazil, there is an area of more than 30,000 ha of bamboo which form dense clumps with approximately 15 m in height, stemming from 5 to 10 cm in diameter with internodes from 24 to 40 cm in length [6].

Chemically, the bamboo is similar to wood and it is characterized by its relatively high content of lignin, cellulose, and hemicellulose, which represent more than 90% of the total bamboo mass [3], [5], [11], [12].

Adhikari et al. [13] investigated the possibility of developing low-cost towers of bamboo to shorten wind turbines, analyzing the characteristics of the bamboo and utilizing a tower of bamboo 12 m high for a wind turbine of 500 W, making analysis via analytical methods and of finite elements, resulting in a promising potential of reducing costs for smaller wind turbine towers in developed countries.

Francisco [14] utilized bamboo sticks to build barriers of containment for soil erosion, waterproofing bamboo with the use of polypropylene raffia, decreasing the cost and increasing the durability of the barrier.

Some papers have been published on the study of bamboo fiber reinforced composites. Yosoffa et al. [15] developed composites materials using bamboo fiber as reinforcement, obtaining good mechanical properties. Costa et al. [16] used bamboo fibers for the manufacture of polymer matrix laminates, where the laminates presented good mechanical tensile properties, resulting in a material of low cost and low environmental impact. Melo [17] used bamboo fibers as reinforcement in virgin and recycled polypropylene matrix, developing a new material with good properties, reusing polymeric residues.

This work is a part of a study about development of polymeric composite materials, where the natural and treated bamboo fibers were used to reinforcing polyester resin matrix. This way, the bamboo fibers were modified and some characterization was performed in order to compare the mechanical properties of these fibers.