The emergence of new technologies, in line with the demand for innovation and sustainability, has brought the use of lignocellulosic biomasses as an alternative raw material for non-woody fiber. Therefore, the need arose to implement the use of cellulosic biomass on an industrial scale in the most diverse sectors of the forest production chain. Among some motivating factors are the need to complement the production of wood raw material, the optimization of processes, the possible reduction of costs, competition between different forest sectors and the edaphoclimatic conditions of the planting sites.
On the world stage, Brazil is the second largest producer and largest exporter of cellulosic pulp obtained through wood delignification (IBÁ 2019). For this purpose, Eucalyptus and Pinus species are the most used worldwide. This segment currently represents about 1.3% of the Brazilian national GDP and 6.9% of the industrial GDP, and is therefore considered a sector that maximizes the country's economy. Although Brazil has a planted area of eucalyptus that exceeds 5.6 million hectares, there are factors that increase the need to obtain alternative sources of production, such as the trends of increasing wood processing costs and competition with other industrial sectors (Borges et al. 2018).
The average productivity of bamboo biomass can vary between 20 to 90 t/ha (曹明勇 2016). Brazil has 1.5 million hectares of native and planted bamboo forests with 258 different species. The genera Bambusa and Dendrocalamus have good agricultural productivity, 25t/ha on average (Guarnetti 2013).
Bamboo emerges as a possibility for use as an alternative lignocellulosic raw material in Brazil because it is a crop with high occurrence in Brazilian soil, short harvest cycles, good adaptability even in poorly fertile soils and high productivity per hectare (Reubens 2010; Xuhe 2003). In Brazil, according to the List of Species of Brazilian Flora, there are 258 species of bamboo and, according to data measured by the Ecological-Economic Zoning (ZEE) of Acre, this state has drawn attention for having the largest native bamboo forest in the world, presenting about 180 thousand square kilometers of forests with the presence of the plant. The use of bamboo for the production of conventional cellulosic pulp is already a reality in the Asian market. In Brazil, the company Itapajé used Bambusa vulgaris for the production of paperboard, however, the industrial application is still incipient in western countries.
Bamboo fibers have intermediate values of fiber length and wall thickness in relation to the Pinus spp. and the Eucalyptus spp. It may be used to production of short fiber pulp and long fiber pulp simultaneously (Júnior et al. 2019) This characteristic makes bamboo a good material for pulping, paper and dissolving pulp. Dissolving pulp is a chemically refined, bleached 90% pure cellulose compound with low hemicellulose and lignin content (Chen et al. 2016).End uses include such as cellophane and rayon, cellulose esters, cellulose ethers, and grafted or crosslinked cellulose derivatives.
Bamboo may be used as a potential resource for dissolving pulp production. However, its hemicellulose content is higher than that of traditional wood species. Therefore, it is challenging to use bamboo for dissolving pulp production.
Dissolving pulp quality mainly depends on the pulping process, in addition to the properties of the raw material. Currently, the pre-hydrolysis Kraft pulping process is one of the primary methods for producing dissolving pulp due to its high efficiency in lignin and hemicellulose removals (Chen et al. 2016). In addition, compared to wood, bamboo contains a higher silica content. Silica generates problems during pulping and bioconversion processes, causing complications in effluent streams. Therefore, the low silica content in raw materials is of great importance in expanding the use of bamboo.
The production of dissolving pulp is expanding in Brazil. Currently, the largest consumption of this product is concentrated in the Asian continent, representing about 77% of world demand and, due to the high capacity of forestry production, an investment of 7.5 billion reais is estimated for new projects for the production of wood. dissolving pulp in Brazil, which can generate thousands of jobs directly and indirectly (FIEP 2016).
A clear example of the expansion of the sector in the country is the association between the companies Lenzing and Duratex, creating LD Celulose Co., which will be inaugurated in 2022, in Minas Gerais.
The overall fiber yield for the production of dissolving pulp is rarely above 35% (Batalha et al. 2012), pulps must contain a high content of alpha-cellulose (95 to 98%) and relatively low contents of hemicelluloses (< 4%) and lignin (< 0.05%). The intrinsic viscosity of dissolving pulp viscose grade should be in the range of 400 to 600 mL/g (Duan et al. 2015; Strunk et al. 2012).
The PHK procedure features a combination of acidic (pre-hydrolysis) and alkaline (kraft cooking) conditions. The pre-hydrolysis step causes the depolymerization of hemicelluloses, allowing a greater degree of delignification in kraft cooking (Sixta 2006). Finally, the brown pulp is sent to the bleaching stages, in order to achieve the desired purity.
Therefore, the interest in studying the applicability of bamboo as an alternative source for the production of soluble pulp is justified, identifying the viability of the process, species that are chemically more favorable to kraft cooking and technological solutions that remedy the challenges of working with this culture.