Amazon Natural Fibers: History
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The Amazon rainforest, spanning multiple countries in South America, is the world’s largest equatorial expanse, housing a vast array of relatively unknown plant and animal species. Encompassing the planet’s greatest flora, the Amazon offers a tremendous variety of plants from which natural lignocellulosic fibers (NLFs) can be extracted. In this century, NLFs, which have long been utilized by indigenous populations of the Amazon, have garnered interest as potential reinforcements for composites, whether polymer- or cement-based, in various technical applications such as packaging, construction, automotive products, and ballistic armor. A comparison with synthetic materials like glass, carbon, and aramid fibers, as well as other established NLFs, highlights the cost and specific property advantages of Amazon natural fibers (ANFs). 

  • natural lignocellulosic fibers
  • NLFs
  • Amazon rainforest
  • composite materials
  • engineering applications
  • sustainability

1. Natural Lignocellulosic Fibers

Fibers can be classified into natural or artificial fibers. In recent decades, there has been an increase in the use of natural fibers as a replacement for artificial fibers due to advantages such as low cost, low density, and reduced tool wear. Additionally, natural fibers exhibit similar or even superior properties in various applications [40,41]. The extensive utilization of natural fibers as reinforcement in composites has driven research in a wide range of fibers. There are three main types of natural fibers based on their origins: plant fibers, mineral fibers, and animal fibers. However, animal fibers such as hair and silk [42,43,44] and mineral fibers like asbestos and basalt [45,46,47,48,49] are not as widely used as reinforcement compared to plant fibers [50,51,52]. On the other hand, several plant fibers have been extensively employed in biocomposites for automotive, maritime, aerospace, and construction applications [53,54,55,56,57,58,59,60,61]. Plant fibers can also be classified based on the region of the plant from which they are extracted, categorized as bast, fruit, grass, seed, leaf, stalk, and wood fibers [62,63]. Figure 1 illustrates the classification of plant fibers according to their extraction source.
Figure 1. Classification of natural fibers based on the part of the plant of origin.
Natural fibers have satisfactory mechanical performance when used as reinforcement agents in composite materials [64]. Although they have lower tensile strength compared to synthetic fibers, they offer several significant advantages. Additionally, natural fibers are typically rigid and do not fracture during processing, exhibiting specific strength and stiffness comparable to glass fibers. They also have lower density and competitive Young’s modulus or elasticity [65]. The performance of polymer composites reinforced with natural fibers depends on various factors, including chemical composition, cell dimensions, microfibril angle, defects, structure, and the physical and mechanical properties of the fiber, as well as the interaction between the fiber and the polymer [66].
Natural fibers can be considered as natural composites, primarily composed of crystalline cellulose fibrils incorporated in an amorphous lignin matrix. These cellulose fibrils are aligned along the length of the fiber, and the effectiveness of natural fiber as reinforcement is related to the nature of cellulose and its crystallinity [67].
Natural fibers are composed of hollow cellulose fibrils interconnected by a matrix of lignin and hemicellulose [69]. The cell wall of a fiber is not uniform and consists of a complex layered structure. Each fibril has a thin primary wall, which is the first layer deposited during cell growth, surrounding a secondary wall. The secondary wall is composed of three layers, with the thick middle layer determining the mechanical properties of the fiber. This middle layer is formed by a series of helically twisted cellulose microfibrils, composed of long cellulose molecules [67].
These fibrils have a diameter ranging from 10 to 30 nm and are composed of 30 to 100 cellulose molecules in an extended chain conformation, providing mechanical strength to the fiber. The amorphous phase in a cell wall consists of hemicellulose, lignin, and in some cases, pectin. Hemicellulose molecules are linked by hydrogen bonds to cellulose and act as a cement matrix between cellulose microfibrils, forming the cellulose–hemicellulose network, which is considered the main structural component of the fiber cell. The hydrophobic network of lignin affects the properties of other networks, acting as a coupling agent and increasing the stiffness of the cellulose/hemicellulose composite [70].

2. Amazon Natural Fibers

The Amazon region is globally recognized for its immense natural and cultural diversity. Located in South America, the Amazon spans eight countries: Brazil, Bolivia, Colombia, Ecuador, Guyana, Peru, Venezuela, and Suriname. However, the majority of its expanse is located in Brazil. The Amazon stands out for harboring the greatest fauna and flora on the planet, representing approximately 20% of the world’s biodiversity [164]. Figure 2 illustrates a map of South America, highlighting the Brazilian Amazon region.
Figure 2. Map of South America, highlighting Brazil and its main biomes: Amazon, colored in green; Cerrado, colored in orange; Pantanal, colored in red; and the Legal Amazon Region, highlighted with green dashed lines. Reprinted from ref. [165]. Licensed under CC BY 4.0.
The Amazon rainforest is rich in plant species that produce high-quality fibers used for a variety of purposes. Among the most well-known fibers are ubim, jute, buriti, piassava, and tucum. Each of these fibers has unique characteristics and interesting properties that make them valuable for different applications.
These natural fibers from the Amazon are widely used by local communities, both for traditional crafts such as baskets, mats, and nets, and for the construction of rural dwellings. Additionally, these fibers generate interest in the global market, being used in the textile industry, paper production, furniture manufacturing, and the creation of sustainable products.
This section will discuss some plant fibers from the Amazon region that have applications in engineering composites. Among the countless plants from which fiber can be extracted, whether from leaves, stems, fruits, or roots, 10 fibers have been selected herein.

2.1. Açaí

The açaí palm, scientifically known as Euterpe oleraceae Mart., is a palm tree belonging to the Arecaceae family and is widely cultivated in the Brazilian Amazon region. This plant is prominently featured due to its economic significance in regional fruit cultivation, particularly in the state of Pará, where the production and commercialization of açaí pulp generate a significant market [166]. The fruit holds considerable nutritional value and is a fundamental part of the diet in the states of Pará and Amapá. Its composition is characterized by high levels of lipids, proteins, fibers, and anthocyanins [167]. The primary cultivation areas for this species are located in the estuary region of the Amazon River, considered its center of origin. In this area, dense and diverse populations inhabit periodically flooded lands due to tides [168].
The açaí fruit has a rounded shape, and approximately 70% of the fruit consists of residues, with only 3% of these residues being composed of lignocellulosic fibers. Although these residues can be used in bioenergy production, it is advisable to separate the fibers from the seeds since burning these components together can result in charcoal with varied chemical composition and thermal behavior, potentially altering the physical and mechanical properties of a specific material in which açaí fiber has been used [174].
The fibers from the açaí mesocarp are by-products of pulp extraction and adhere to the fruit’s seed [174]. These fibers are lignocellulosic in nature and have an elliptical shape with an average thickness of 130 μm and a length of about 18 mm. They have a slightly higher density than water, approximately 1.11 g/cm3. Generally, açaí fibers are underutilized due to their toxic residues, leading to various environmental issues, and the extracted fiber yield is low [175,176,177].
Despite açaí being well-known, primarily for consumption, the properties of its fiber are relatively unexplored. Nevertheless, there are studies in the literature that examine the fiber’s properties and its application in composite materials. Castro et al. [178] conducted a study on the production of composites using two distinct polymeric matrices, namely, polypropylene (PP) and high-impact polystyrene (HIPS), both derived from recycling processes. In this study, pressed açaí fibers were employed as reinforcement agents in the composites. The manufacturing of the composites took place through the hot compression method, and their properties were subsequently evaluated through tensile, compression, and impact tests. The tensile test results revealed significantly superior performance for the PP/açaí composite compared to the HIPS/açaí composite. Furthermore, the PP/açaí composite demonstrated higher impact resistance when contrasted with the HIPS/açaí composite. Notably, the HIPS/açaí composite exhibited superior properties only in terms of compression resistance, indicating an overall inferior mechanical behavior. This phenomenon is attributed to the low interfacial adhesion present in the HIPS/açaí composite. Thus, this study emphasizes the importance of the choice of polymeric matrix and the quality of the interface between components in determining the mechanical properties of composites.

2.2. Babassu

The babassu, belonging to the Arecaceae family and the Attalea genus, has the Brazilian species Attalea speciosa, a palm tree that can reach up to 20 m in height, as illustrated in Figure 3a. Its fruit contains oleaginous and edible seeds, with a high number of coconuts per cluster (between 150 and 250) and an average of four clusters per palm tree [181]. The fruits, as shown in Figure 3b, are ellipsoidal, measuring 8 to 15 cm in length and 5 to 7 cm in diameter, weighing between 90 and 280 g [182,183]. In Brazil, there are numerous babassu groves distributed from the southern Amazon region to the northeast, with occurrences also in Bolivia for the Attalea speciosa species [184].
In the states of Maranhão, Piauí, and Tocantins, the largest expanses of babassu forests in Brazil are found, forming homogeneous, dense, and naturally dark clusters due to the proximity of the large babassu palm trees [185]. This region is recognized as the world’s largest concentration of oil-producing plants and the primary source of extractive plant production, known as the “Mata dos Cocais” [186].
Figure 3. Babassu (Attalea speciosa Mart ex Spreng.): (a) palm tree; (b) babassu fruit; (c) fiber extracted from the fruit. Figures reprinted from ref. [187]. Licensed under CC BY-NC 4.0.
The production of babassu nuts is of significant importance for generating income for thousands of families that rely on babassu nut harvesting, with estimates suggesting that over 300,000 women depend on this activity. After maturation, the babassu nut falls to the ground, where it is harvested by workers. It is also collected by climbing the palm tree. When collected, it is transported in straw baskets, typically on the backs of animals. When not possible, the nut cracking is carried out at the base of the palm tree. The fruits are broken in a rudimentary manner, usually by women, using a machete as a cutting tool and a wooden bar for mechanical action. The babassu nut is a fruit that can be fully utilized [188].
Unlike other plants that yield natural fibers, babassu has a distinctive characteristic: the practicality of utilizing almost all parts of the plant. Its trunk is used for structural support in the construction of houses in these regions, and the leaves are used for roofing houses, fences, and in the fabrication of small utensils such as baskets and fans. From the babassu nut, almonds are extracted and used in the production of oil known as “azeite”. The mesocarp is used to prepare flour with medicinal properties, and the husk is employed in charcoal production. These products are used in the daily lives of families [189]. It is possible to obtain more than 60 products from babassu, many manufactured from the nut, such as oil, “azeite”, milk, for both fresh consumption and industries like food, cleaning materials, personal hygiene, cosmetics, as well as charcoal, fertilizers, and other by-products [190,191,192].
Babaçu fibers are manually obtained, extracted from both the coconut and the palm tree trunk. However, the most common extraction method is from the coconut. Chaves et al. [193] conducted the extraction of babaçu fibers with the aim of characterizing their properties for potential application in composites. Throughout the study, the authors followed a sequence of steps to obtain the fibers. Initially, the babaçu coconut is left to dry for 48 h for dehydration. Subsequently, the coconut shell is placed in a container for washing, where it remains for a period of 7 days. This phase is crucial to facilitate the extraction of fibers in the subsequent defibration process. Figure 4 illustrates the steps of fiber extraction carried out by the authors.
Figure 4. Steps of babassu fiber extraction: (a) babassu coconut in drying process for 48 h; (b) washing babassu; (c) babassu after washing, ready for defibrillation; (d) manual defibrillation process; (e) extracted babassu fibers. Reprinted from ref. [193]. Licensed under CC BY-NC-ND 4.0.
The babassu palm already has a significant history of applications, as mentioned earlier, including the use of its fibers in composites for engineering applications. In addition to the analysis of the properties of the fiber in isolation [193,194,195], the investigation of composite materials using this fiber as a reinforcing agent enables its application in various engineering fields while maintaining a sustainable approach to plastic materials.

2.3. Buriti

The fiber from the Buriti palm (Mauritia Flexuosa) originates from a plant that is widely found in different regions of Brazil, with the main occurrence in the Amazon. Although buriti is also found in the Brazilian central region, as well as in the states of Bahia, Ceará, Maranhão, Minas Gerais, and Piauí, it is found predominantly in regions with a tropical climate, with an annual average temperature of between 26 °C and 30 °C and a rainfall of between 200 mm and 400 mm [199,200].
Buriti palm trees (Figure 5a) display some notable characteristics, reaching significant heights of up to 40 m, with a stem diameter between 50 and 60 cm. The leaves, which are over 15 cm long, remain attached to the stem after death, before eventually falling off. These leaves are widely used to make handicrafts and as roofing material in community dwellings. The fruit of the Buriti palm tree has horny scales with a reddish-brown hue, while the inner pulp displays an orange color. This pulp proves to be versatile, serving as human food, bait for hunting, a source of oil, and with potential medicinal applications. This diversity of uses highlights the ecological and socioeconomic significance of this species in local communities [201].
Figure 5. Buriti (Mauritia flexuosa.): (a) palm tree; (b) bundle of fibers extracted from the leaf; (c) fabric produced from the extracted fibers with an inset for viewing the weave from an SEM micrograph. Reprinted from ref. [202]. Licensed under CC BY-NC-ND 4.0.
Products derived from buriti have gained high market value, and the practice of destructive harvesting of palm trees is a growing concern. The felling of palm trees to collect fruit in the Peruvian Amazon has been documented as a threat since the late 1980s [203]. Other products, such as young leaves and oil extracted from the buriti palm, are rapidly gaining economic value, presenting potential challenges of overexploitation [204]. Considering that a buriti palm produces, on average, one leaf per month [205], the intensive collection of young leaves, as opposed to the collection of fallen fruit and extraction of mature leaves for subsistence, can result in significant negative impacts on the sustainability of the buriti palm. In addition to its commercial value, buriti plays a vital role in indigenous communities, being one of the most relevant plant species for their subsistence needs, such as food, shelter, building material, and ornaments [206].
The extraction of buriti fiber (Figure 5b,c) is carried out in an artisanal manner, where residents of rural areas climb the trees, remove the green leaves, and cut the fibers, which can be obtained from both the leaves (known as linen) and the petiole [207]. The petiole, or stem of the leaf, can reach up to 3m long and its fibers have a high cellulose content (77.8%) and a low lignin content (24.0%). These fibers, extracted from the epidermis of the petiole, are useful for making mats and curtains [208]. However, a deep understanding of the inherent physical and chemical properties and characteristics of buriti fiber is essential to anticipate the behavior of this material when used as reinforcement in polymer matrix composites. Based on the properties and characteristics exhibited by buriti fibers, several researchers suggest their application as reinforcement in polymer matrix composites [209,210,211,212].
The buriti fibers exhibit a comparatively low density ranging from 0.63 to 1.12 g/cm3, coupled with a moderate tensile strength within the range of 129 to 254 MPa. This characteristic renders them suitable as reinforcement for polymer composites characterized by lower density yet relatively weaker strength [213].

2.4. Carnauba

The Carnauba tree, illustated in Figure 6a, is classified as a palm of the Arecaceae family and has xerophytic characteristics. Its scientific name is Copernícia prunífera and it originated in Brazil. The term “carnauba” comes from the indigenous language and means “the tree that scratches”, an allusion to the 44 thorns distributed along the stem. In addition to its primary name, the plant is also known by variations such as carnaúva, carnaba, carandaúba, and carnaíba. The genus Copernicia comprises approximately 28 species, distributed in regions of India and South America. On the South American continent, species such as Copernícia tectorum (found in Venezuela and Colombia), Copernícia alba (found in Bolivia, Argentina, and Paraguay), and Copernícia prunífera are predominant in Brazil [218].
Figure 6. Carnauba (Copernícia prunífera): (a) carnauba tree; (b) leaf stalks of carnauba tree; (c) leaf stalks of carnauba tree; (d) carnauba fibers extracted from leaf stalks. Adapted from ref. [219]. Licensed under CC BY 4.0.
It is estimated that the carnauba tree can reach a height between 10 and 15 m, with a productive life expectancy of around 200 years. Demonstrating remarkable resistance, this species adapts effectively to adverse climatic phenomena, such as severe droughts and floods. Its ideal habitat includes floodplains and riverbanks, and the plant thrives at altitudes ranging from 45 m above sea level to around 500 m. Natural propagation takes place predominantly in its native environment, especially in sandy, moist soils. The palm has opaque green leaves, arranged in a spiral around the stem, concentrated in the crown of the plant [220].
Every part of the carnauba palm finds utility; its roots are employed for medicinal purposes, the fruits serve as a significant component in animal nutrition, and the trunk constitutes a valuable source of timber for civil construction. Carnauba wax, derived from the palm, is extensively utilized in the manufacturing of lubricants and anti-corrosive agents. Additionally, the leaves of the carnauba palm find application in various domains, including house roofing, handicraft production, and the extraction of fibers [218,220].
Carnauba fiber exhibits highly promising outcomes for its application as reinforcement in epoxy matrix composites or within a biodegradable polyhydroxybutyrate (PHB) matrix. Noteworthy mechanical properties of carnauba fibers include significant elongation (1.7–2.6%), impressive tensile strength (205–264 MPa), and a substantial Young’s modulus (8.2–9.2 GPa) [219].

2.5. Curaua

Curauá (Ananas Erectifolius) is a hydrophilic species native to the Amazon region, from which lignocellulosic fibers are extracted, known for their excellent mechanical properties [228]. In the Amazon, curauá fibers are widely recognized in the Amazon River basin region, particularly in the western part of the state of Pará, where the first commercial plantations of this plant were pioneeringly established [229,230].
Distinctive characteristics of curauá include hard, flat, and erect leaves, with an average length of 1–1.5 m, a width of approximately 40 mm, and a thickness of 5 mm. Each curauá plant exhibits a remarkable leaf production, averaging 50–60 per year, weighing about 150 g each [231]. This yield results in an annual production of 3–9 tons of dry fibers per hectare, notably relying on natural irrigation from rainfall throughout the year [230,232].
Beyond its economic significance, curauá fibers play a crucial role in the traditional practices of indigenous peoples. Indigenous communities use these fibers to craft ropes, hammocks, and fishing lines, requiring materials with high strength and deformability [233]. This application underscores the versatility of curauá fibers, combining remarkable mechanical properties with a sustainable origin. Figure 7 illustrates the curauá plant and the fiber resulting from the extraction of the plant’s leaves.
Figure 7. Curauá (Ananas Erectifolius): (a) curauá plant; (b) bundle of manually extracted fibers; (c) SEM micrograph of a cross-section of a curauá fiber. Reprinted from ref. [234]. Licensed under CC BY-NC-ND 4.0.
Curauá fibers are obtained from the leaves of the plant, which are manually cut. These leaves undergo a process called decortication, in which rudimentary machines equipped with rotating cutting blades remove the mucilage, extracting the fibers. Subsequently, the extracted fibers undergo a mercerization process in tanks, lasting 36 h, followed by washing to remove mucilage residues. Finally, the fibers are dried in an oven at 50 °C for 5 h or in the open air for 2 days before being baled. Each curauá leaf produces between 3 and 8% of dry fibers. The majority of curauá fiber production is still carried out by small farmers in the city of Santarém and the state of Amazonas, characterizing a traditional process without the use of advanced technology and appropriate safety measures [229,231].
Since the early 2000s, the production of curauá fibers has experienced exponential growth, driven by their use in automotive components. Renowned companies such as Volkswagen and Mercedes Benz have played a crucial role in this advancement, adopting curauá fibers as reinforcement in polypropylene matrix composites [235]. This substitution of glass fibers has become particularly notable in the manufacturing of automotive parts, including bumpers, interior panels, trunk lids, and various other components. The success of this transition is evident in the successful integration of curauá fibers in the construction of vehicle parts, notably in Volkswagen’s VW Fox and VW Polo models [236,237]. This significant milestone has further propelled research into the application of curauá fibers not only in the automotive sector but also in various areas such as construction [238,239,240], ballistic armor [241,242,243,244], and biodegradable packaging [245,246,247], among other applications.

2.6. Guaruman

The guaruman plant (Ischnoshiphon Koern) is frequently found along the riverbanks in the Amazon region, especially in the Salgado Paeaense area in the state of Pará. Extracted from this region, these plants play a crucial role as raw material for handicrafts [250]. The Amazon is renowned for its vast diversity of native plant species, which play fundamental roles in food, medicine, construction, and fiber production. In the specific context of guaruman, this plant holds significant importance in the culture of riverside caboclos and various indigenous tribes. It is widely used in crafting, particularly in the creation of the famous straw weaving, a highly popular practice in the Para region [250,251].
Guaruman, also known as arumã, belongs to the Marantaceae family and is typically found in flooded várzea areas along riverbanks [252]. Barcarena, in the state of Pará, and more specifically, the Utinga-Açu community, are the main hubs for artisanal production of products made from guaruman fibers. The extraction process involves processing the guaruman stem, resulting in flexible, durable fibers with a distinctive golden hue, as illustrated in Figure 8 [250].
Figure 8. Guaruman (Ischnoshiphon Koern): (a) guaruman plant; (b) as-received, mechanically divided splints from the stalk; (c) manual separation of fibers from the splint; (d) bunch of the final isolated fibers (d). Adapted from ref. [253]. Licensed under CC BY-NC-ND 4.0.
The crafting of handicrafts from these fibers often constitutes the main source of economic sustenance for the surrounding riverside communities. Similar to other non-timber materials used in artisanal production, the goal is always to transform these resources into higher value-added goods [250,252]. Research focused on the development of new products from guaruman not only contributes to the technological innovation of the country but also addresses the specific needs of the regional population that relies on the trade of these fibers.
Guaruman fiber is underexplored concerning the assessment of its properties, encompassing both the individual characteristics and properties of the fiber, as well as its application as reinforcement in composites. The lack of dissemination, coupled with the potential difficulty in obtaining the plant, may constrain studies on this fiber. However, although rare, some works have been identified in the literature. Reis et al. [253] conducted an analysis of the characteristics and properties of guaruman fibers, comparing them with commonly studied natural fibers.

2.7. Periquiteira

The Periquiteira (Cochlospermum orinocense), also known as tree cotton, Envira-Branca, or Buxixão, is a plant from the Bixaceae family. This plant is characterized by being a medium-sized tree, ranging from 12 to 28 m in height, with a straight cylindrical trunk that can measure 40 to 75 cm and remain unbranched for up to half of the tree’s height. Its bark is whitish, with vertical fissures and fiber detachment, with 60 cm of cataphylls [255,256].
The wood has a coarse texture, a straight grain, is tasteless but slightly fragrant when fresh, lightweight, smooth, with low resistance to decay and attack by wood-eating insects, and it grows best in a sunny position. It is a fast-growing tree [256,257].
The occurrence of the Periquiteira is in Brazil, specifically in the Amazon Rainforest, but it also extends to countries in South America such as Peru, Colombia, Venezuela, and the Guianas. It mainly grows in more open areas of advanced secondary growth, in upland areas not subject to periodic flooding, plain areas, and highlands, usually on dry clay at altitudes of up to 450 m in Peru [256]. In Brazil, the Periquiteira is found in the states of Roraima, Rondônia, Amapá, Pará, Amazonas, Acre, Maranhão, and Mato Grosso [257].

2.8. Piassava

Piaçava is a palm tree native to Brazil, belonging to the Arecaceae family. Its popular name comes from the indigenous Tupi language, meaning “Fibrous Plant”. The different species of Piaçava are found mainly in the states of Acre (Aphandria natalia), Figure 9a and Bahia (Attalea funifera), and Amazonas (Leopoldinia piassaba). This palm is capable of growing in low-fertility soils that are unsuitable for many crops [260].
Figure 9. Piassava (Attalea funifera): (a) piassava palm tree; (b) piassava fibers extracted from leaf; (c) SEM micrograph of piassava fiber surface. Adapted from ref. [261]. Licensed under CC BY 4.0.
Among the species of Piassava, Bahia is the largest fiber producer in the country, representing 95% of the national production, followed by the Piassava from Amazonas and Acre. These species of Piassava differ in the characteristics of their fibers [119,262]. The fiber from Bahia is the most commercialized due to its long, rigid, and waterproof fibers that maintain their elasticity even when wet. On the other hand, the fibers from Amazonas are softer, more flexible, and elastic. These fibers are commonly used in the manufacturing of brushes, brooms, ropes, crafts, and also in the composition of rustic coverings [260].
The extraction of Piassava fibers is carried out through extractivism, with different systems in the producing states. In Bahia, there are associations of collectors in the communities, which generates income and, at the same time, preserves the ecosystem in the Atlantic Forest [262,263]. In Amazonas, on the other hand, extractivism occurs through aviation, where the boss provides advanced food and goods in exchange for the services of the collectors. This type of extractivism does not benefit the collectors, often leaving them in a situation similar to slavery [264].
The collection of Piassava plant fibers is conditioned by the water level, which means that during dry periods, collectors are isolated without the opportunity to receive supplies and goods since the rivers are not navigable. Piassavas can be classified in two ways: by height and by the presence or absence of previous cutting [265]. The cutting method varies according to the size of the palm tree. As for height, Piassavas are classified as follows: new Piassava (up to 2 m), garrote (2 to 4 m), garrotão (4 to 6 m), and giant or old (over 6 m). Regarding the type of cutting, they can be non-extractable (poor or fiberless), mamaipoca (already cut, ready for recutting), or virgin (never cut) [266]. Piassava fibers originate from the base of the palm leaves and are collected manually. In this process, they are untangled, arranged, cut, and then tied together for commercialization, generating the fibers as illustrated in Figure 9b,c [267,268,269].
Piassava fibers have been widely used due to the high production of this palm tree, which can yield around 8 to 10 kg of fibers per tree. These fibers have various applications, ranging from crafts, utensils, and ropes, to engineering, as reinforcement in composites. As a result, numerous research studies are conducted annually using this fiber.

2.9. Tucum

The tucum, scientifically named Astrocaryum vulgare (Figure 10a), is a palm tree typical of the Amazon region. This plant has several scientific names, such as Astrocaryum chambira Burret and Astrocaryum aculeatum G. The fruits of the tucum are called tucumã and are widely used in local cuisine. In addition, the palm has a thorny trunk and can be used as a living fence to protect crops in short-cycle forestry of pioneer species. The purpose of this fence is to protect the seedlings from herbivory by animals [276].
Figure 10. Tucum: (a) tucum palm tree; (b) tucum fruits; (c) tucum leaves exhibiting a thorny characteristic to ward off predators; (d) tucum fibers extracted from the leaf. Adapted from ref. [277].
Their fruits (Figure 10b) are up to 6 cm long and vary between 4 and 5 cm in diameter, with a rounded shape, a greenish color, and a sour taste. When ripe, the fruit is black in color and tastes sweet [278].
Tucum fibers are taken from the palm’s leaves (Figure 10c), which are very resistant and have the following characteristics: sheath and petiole covered in flat, yellowish spines; sheath 1.1 m long; petiole 2.6 m long; rachis 4.8 m long; 160 spines per side, linear or linear-lanceolate, irregularly arranged and arranged in different planes; with small spines on the margins, midribs subterminal; midribs 1.51–1.63 m long and 4–4.5 cm wide [278,279].
Tucum fiber, illustrated in Figure 10d, is obtained after the palm leaves have been removed and dried. This fiber contains a considerable amount of cellulose, over 80%, and has been an important source of income for communities in the region, being widely used in handicrafts. For several indigenous communities in the northwestern Amazon region, tucum fiber is of significant value. The fibers obtained from the unexpanded leaves are used to make a wide variety of products, such as hammocks, bags, and fishing nets [203,280,281,282,283]. Harvesting and processing these fibers is part of Aboriginal traditions and represents important moments of social interaction [284].
In recent years, products made from tucum fibers have become very popular with tourists and in craft shops. The tucum palm has become an important cash crop for indigenous families. However, frequent extraction, often carried out in a destructive manner, has depleted the natural populations of tucum in some areas of the Amazon [282,285].

2.10. Ubim

Ubim is a palm from the Arecaceae family, also known by its scientific name Geonoma baculífera [289]. The word ubim comes from the indigenous language, specifically the Tupi u’bi. The palm is also known by other names, such as Geonoma estevaniana Burret, Gynestum baculiferum Poit., Geonoma acutiflora Mart [290].
The Arecaceae family includes the genus geonoma, which is made up of small palms that generally grow in the understory. This genus is one of the largest in the Americas and is home to 15 species that are widely distributed across the continent, especially in tropical regions [291]. The species of Geonoma are commonly found in areas with high levels of rainfall, and are one of the most prevalent plant species in these environments. Palms of the genus Geonoma have a preference for riparian forest vegetation that occurs along watercourses, as well as open vegetation [292].
Ubim is a small cespitose palm with multiple, smooth stems and elongated, unbranched fibers. Its height varies between 1 and 4 m, with a diameter of 1 to 3 cm. The stem can be erect or partially creeping, and the plant has seven to twelve leaves, sparsely branched inflorescences, and globose or ovoid fruits. This species is typically found in the understory of forests with high rainfall, riparian forests, floodplains and igapós. The ubim is adapted to humid environments, is considered shade-tolerant, and generally grows in places with low incidence of direct light [289].
The occurrence of the ubim covers Central and South America, with records in the Guianas, Peru, Bolivia, and Venezuela. In Brazil, this plant can be found in the states of Amazonas, Acre, Amapá, Pará, Maranhão, and Piauí [294,295]. This species is widely used in the Amazon by extractivist communities who depend on the sustainable exploitation of various native species to meet their needs for construction materials for rural buildings. The leaves of the ubim, when intertwined along a stick, form ubim “cloths”, which are used as a covering in the constructions of these communities. This is a traditional practice, especially among those who live close to the border between Brazil and Bolivia. In Bolivia, ubim is commercially exploited, which indicates that the species may also have commercial potential on the Brazilian side [296].
In addition to its use in construction, ubim also has ecological importance for some indigenous and riverside communities. Ubim fibers are used to make baskets, mats, and other handicrafts. In addition, this plant has potential for ornamental purposes in gardens and interiors.
Ubim is widely used in the Amazon and Acre regions; however, the plant’s potential application depends on the development of the market, which currently lacks a regular and abundant supply of the product. It also faces the apparent lack of awareness of its existence on the part of consumers in the city of Rio Branco, in the state of Acre, which represents the largest potential market for this product in the region [296]. In addition to the potential of ubim daughters, ubim fiber has yet to be widely applied as a reinforcing material in industrialized products and engineering applications. Unlike better-known fibers such as sisal, bamboo, curaua, coconut, jute, and others, there are practically no scientific reports studying the properties of ubim fiber and its application.

This entry is adapted from the peer-reviewed paper 10.3390/eng5010009

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