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Anatomical characterization of black wattle wood for the pulp and paper production

Caracterização anatômica do lenho de acácia-negra para produção de celulose e papel

ABSTRACT:

The growing worldwide demand in the pulp market has fostered research that evaluates alternative fiber sources with specific characteristics that attend the needs of the consumer market, with a view to add value to the final product and reduce production costs. Acacia mearnsii De Wild wood is a by-product of the extraction of tannin from the trunk bark, used for firewood, charcoal and pellets. However, its wood is still poorly studied, especially its anatomical characteristics, which can provide important information about its industrial potential. This study evaluated the anatomical characteristics of Acacia mearnsii wood for the production of pulp and paper. Ten trees at approximately seven years old were cut down, five from the seed production area (SPA) and five from the clonal population area (CPA). From each tree, one trunk disc was sectioned at the diameter at breast height (DBH), resulting in 10 (ten) wood samples. From each disc, a sapwood specimen was made oriented in the tangential longitudinal, radial longitudinal and transversal planes, for later obtaining the anatomical cuts and the macerates. The anatomical description of the wood followed the recommendations of the International Association of Wood Anatomists-IAWA. From the dimensions of the fibers, their quality evaluation ratios for the production of pulp and paper were calculated. Results obtained from the anatomical characterization allowed to conclude that the Acacia mearnsii woods from SPA and CPA are indicated as a source of raw material for the pulp and paper production.

Key words:
Acacia mearnsii; wood anatomy; fiber morphology

RESUMO:

A crescente demanda mundial do mercado de polpa celulósica tem fomentado pesquisas que avaliem fontes de fibras alternativas com características específicas que atendam às necessidades do mercado consumidor, visando agregar valor ao produto final e reduzir os custos de produção. No estado do Rio Grande do Sul, Brasil, o lenho de Acacia mearnsii De Wild é considerado um subproduto da extração de tanino da casca do tronco, utilizada como lenha, carvão e pellets. No entanto, ainda é pouco estudado, em especial suas características anatômicas, as quais podem fornecer informações importantes sobre suas potencialidades industriais. O presente estudo teve como objetivo avaliar as características anatômicas do lenho de Acacia mearnsii para a produção de celulose e papel. Foram coletadas dez árvores com aproximadamente sete anos de idade, sendo cinco provenientes da área de produção de sementes (APS) e cinco da área de povoamento clonal (APC). De cada árvore, foi seccionado um disco do tronco na altura do DAP, resultando em dez amostras de lenho. De cada disco, foi confeccionado um corpo de prova do alburno, orientado nos planos longitudinal tangencial, longitudinal radial e transversal, para posterior obtenção dos cortes anatômicos e dos macerados. A descrição anatômica do lenho seguiu as recomendações da Associação Internacional de Anatomistas da Madeira-IAWA. A partir das dimensões das fibras, foram calculados os seus índices de avaliação da qualidade para a produção de celulose e papel. Os resultados obtidos da caracterização anatômica permitiram concluir que os lenhos de Acacia mearnsii provenientes de APS e APC são indicados como matérias-primas para a produção de celulose e papel.

Palavras-chave:
Acacia mearnsii; anatomia do lenho; morfologia da fibra

INTRODUCTION:

The growing worldwide demand in the pulp market has fostered research that evaluates alternative fiber sources with specific characteristics that meet the needs of the consumer market, aiming to add value to the final product and reduce production costs. According to the Brazilian Tree Industry statistical report (IBÁ, 2021IBÁ - Brazilian Tree Industry. Brazilian tree industry scenarios, base year 2020. 2021. 5 p. Available at: <https://www.iba.org/datafiles/publicacoes/relatorios/relatorioiba2021-compactado.pdf>.
https://www.iba.org/datafiles/publicacoe...
), in 2020, Brazil was the world’s largest exporter of bleached hardwood pulp and the second largest global producer, adding the short and long fiber segments, with 20.95 million tons.

Several sources of fibrous materials have been studied in recent years aiming to replace wood, the current and main source of fibers in the pulp and paper industries (KAUR et al., 2017KAUR, D.; BHARDWAJ, N.K.; LOHCHAB, R.K. Prospects of rice straw as a raw material for paper making. Waste Management. v.60, p.127-139, 2017. doi: 10.1016/j.wasman.2016.08.001.
https://doi.org/10.1016/j.wasman.2016.08...
; LIU et al., 2018LIU, Z.; WANG, H.; HUI, L. Pulping and papermaking of non-wood fibers. In Pulp and Paper Processing. 2018. doi: 10.5772/intechopen.79017.
https://doi.org/10.5772/intechopen.79017...
; SHARMA et al., 2020aSHARMA, N.; TRIPATHI, S.K.; BHARDWAJ, N.K. Utilization of sarkanda for making pulp and paper using elemental chlorine free and total chlorine free bleaching processes. Industrial Crops and Products, v.149, p.1-8, 2020a. doi: 10.1016/j.indcrop.2020.112316.
https://doi.org/10.1016/j.indcrop.2020.1...
). Despite this, wood remains the main raw material used in pulping processes, because it is obtained from planted forests, which are extremely abundant sources of fibers and which have advanced technologies in the improvement of species, in the cultivation techniques and also, in adaptations to industrial processes, resulting in excellent quality pulps.

According to the IBÁ statistical report (2019)IBÁ - Brazilian Tree Industry. Brazilian tree industry annual report, base year 2018. 2019. 80 p. Available at: <https://www.iba.org/datafiles/publicacoes/relatorios/relatorioiba2019-final.pdf>.
https://www.iba.org/datafiles/publicacoe...
, in 2018 the country had a planted area of 161.9 thousand ha of Acacia spp., mainly in the Rio Grande do Sul State.

The species Acacia mearnsii De Wild (Fabaceae), as known as black wattle, is native from Australia, used mainly for the extraction of tannin from the trunk bark, while wood is considered a by-product, destined for products with little added value, such as firewood, charcoal and pellets, being exported in the form of chips to Asian countries, which are destined mainly for pulp industries (AGEFLOR, 2020AGEFLOR-Gaúcha association of forestry companies. The forest-based sector in Rio Grande do Sul-base year 2019, 2020. 80p. Available at: <http://www.ageflor.com.br/noticias/wp-content/uploads/2020/12/O-Setor-de-Base-Florestal-no-Rio-Grande-do-Sul-2020-ano-base-2019.pdf>.
http://www.ageflor.com.br/noticias/wp-co...
).

Thus, Acacia mearnsii wood is a viable fiber source from an industrial point of view, with technological potential to be commercially explored (CHAN et al., 2015CHAN, J.M.; et al. Acacia mearnsii industry overview: current status, key research and development issues. Southern Forests: a Journal of Forest Science, v.77, n.1, p.19-30, 2015. doi: 10.2989/20702620.2015.1006907.
https://doi.org/10.2989/20702620.2015.10...
).

Acacia mearnsii wood, due to its basic density of approximately 0.544 g/cm3 and low lignin content, can produce pulps with high yield and easy bleachability, being indicated for the production of tissue paper, partly, because it presents anatomical elements with lower mechanical strength when compared to Eucalyptus genus woods (GIESBRECHT et al., 2022GIESBRECHT, B. M.; et al. Performance da madeira de Acacia mearnsii De Wild para polpação kraft. Ciência Florestal, v.32, n.1, p.266-286, 2022. doi: 10.5902/1980509850295.
https://doi.org/10.5902/1980509850295...
; SANTOS et al., 2005SANTOS A.; ANJOS, O.; SIMÕES, R. Evaluation of paper quality produced from fibre of Acacia spp. Silva Lusitana, v.13, n.2, p.249-266, 2005. Available at: <https://ubibliorum.ubi.pt/bitstream/10400.6/581/1/silva-acacia-1.pdf>.
https://ubibliorum.ubi.pt/bitstream/1040...
).

Although, pulp can be manufactured with different fibers, aiming to the production of papers with very different physical and mechanical properties, Acacia mearnsii wood is little used for this purpose in Brazil.

The use of Acacia mearnsii, a widely cultivated species in the Rio Grande do Sul State, together with the possibility of obtaining pulp with quality and specific characteristics that meet the consumer market, will awaken the interest of national industries that export Acacia mearnsii and that use other sources of fiber as raw material for the pulp and paper production, adding value to the plantations of this species.

Thus, this studyevaluate the anatomical characteristics of Acacia mearnsii wood from seed production area (SPA) and from the clonal population area (CPA) for potential application in pulp and paper production.

MATERIALS AND METHODS:

The present study evaluated wood samples of Acacia mearnsii De Wild (Fabaceae) from commercial plantations in Cristal, State of Rio Grande do Sul, Brazil, at the coordinates 30° 59’ 24’’ S and 52° 2’ 17’’ W. Ten representative trees at approximately seven years old were studied, five from the seed production area (SPA). and five from the clonal population area (CPA). The trees were randomly selected from the plantations, observing their vigor and health status (absence of apparent diseases), according to D5536-94 standard, of the American Society for Testing and Materials (ASTM, 2010ASTM - American Society for Testing and Materials. Standard practice for sampling forest trees for determination of clear wood properties: ASTM D5536 - 94. West Conshohocken: Anual Book of ASTM Standard. 2010.).

From each tree, one trunk disc was sectioned at diameter at breast height (DBH), resulting in 10 (ten) wood samples. From each disc, a sapwood specimen was made oriented in the tangential longitudinal, radial longitudinal and transverse planes, for later obtaining the anatomical cuts and the macerates (Figure 1).

Figure 1
Experimental scheme for microscopic anatomical characterization of Acacia mearnsii woods.

The preparation of the anatomical cuts slides followed the standard technique described by BURGER & RICHTER (1991BURGER, M.L.; RICHTER, H.G. Wood anatomy. São Paulo: Nobel, 1991. 154 p.), with the specimen boiling in water (15 hours), sectioned in a sliding microtome (thickness of 20 µm), stained with safranine and astra-blue, dehydration in increasing alcoholic series (50%, 70%, 90%, absolute alcohol), diaphanization using xylol and mounting of permanent slides with “Entellan”. Dissociation of woody tissue was performed by the nitric-acetic acid maceration method (FREUND, 1970FREUND, H. Handbook of microscopy in technology. Frankfurt: Umsham Verlag, 1970. 375 p.). The other steps for mounting of macerated permanent slides followed the standard technique described by BURGER & RICHTER (1991).

After making anatomical cuts and macerates slides, observations were performed under an optical microscope for description and measurements of morphological parameters, following the recommendations of the International Association of Wood Anatomists-IAWA (WHEELER et al., 1989WHEELER, E.A.; BAAS, P.; GASSON, P.E.IAWA list of microscopic features for hardwood identification. IAWA Bulletin, v.10, n.3, p.218-359, 1989.). The determination of the percentage of different tissues that make up the wood followed the methodology proposed by MARCHIORI (1980MARCHIORI, J.N.C. Anatomical study of the secondary xylem of some species of Acacia and Mimosa genus, native from the Rio Grande do Sul state, Brazil. 1980. 186 s. Dissertation (Masters in Forest Engineering) - Postgraduate Program in Forest Engineering, Federal University of Paraná, Curitiba. 1980.). From the measurement of the lumen diameter, width, length and wall thickness of the fibers, fiber quality evaluation ratios for the production of pulp and paper were calculated from the equations 1, 2, 3, 4 (FOELKEL & BARRICHELO, 1975FOELKEL, C.E.B.; BARRICHELO, L.E.G. Relationships between wood characteristics and pulp and paper properties. O Papel, v.36, n.9, p. 49-53, 1975. Available at: <https://www.celso-foelkel.com.br/artigos/ABTCP/1975_Caracteristicas_Madeira+Celulose+Papel.pdf>.
https://www.celso-foelkel.com.br/artigos...
):

Runkel ratio= 2 ×wall thickness (μm)lumen diameter (μm)(1)

Flexibility ratio %= lumen diameter μmfiber width μm ×100(2)

Slenderness ratio= fiber length (mm)fiber width μm÷1000 (3)

Wall fraction %= 2 x wall thickness μmfiber width μm×100 (4)

The results for each variable of the anatomical characterization of Acacia mearnsii woods from seed production area (SPA) and clonal planting area (CPA) were submitted to descriptive statistics, to calculate the number of observations, minimum, maximum, average and standard deviation, using the statistical program R (R CORE TEAM, 2020R CORE TEAM. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. 2020. Available at: <http://www.r-project.org/index.html>.
http://www.r-project.org/index.html...
).

RESULTS AND DISCUSSION:

Microscopic description of Acacia mearnsii woods

Figure 2 (A, C, E) shows photomicrographs of Acacia mearnsii wood from the SPA, whose microscopic anatomical description is presented below:

Figure 2 -
Photomicrographs of Acacia mearnsii wood from the seed production area (SPA) and the clonal population area (CPA). Source: authors. Where: A (SPA) and B (CPA) - Cross section: diffuse porosity, solitary and radial multiple pores. C (SPA) and D (CPA) - Radial section: homogeneous radial tissue composed entirely of procumbent cells (arrow). E (SPA) and F (CPA) - Tangential section: multiserial rays with more than 3 cells wide (arrow).

Vessels: few (13 ± 2.2 (10 - 17) pores/mm2) with diffuse porosity, radial multiple pores of 2 - 5 (49%), solitary (40%), and multiple clusters of 3 - 6 (11%), circular or oval (113 ± 22 (60 - 160) µm), thin to thick walls (5.8 ± 1.2 (3.8 - 7.5) µm) (Figure 2A). Short vascular elements (323 ± 72 (200 - 460) µm), with simple perforation plates, oblique or transverse to the vessel, short appendices (34 ± 22 (10 - 100) µm), usually at one end. Small and rounded intervessel pits (6.3 ± 0.6 (5.2 - 7.2) µm), alternate, vestured, sometimes, coalescent, with slit-like aperture included. Vessel-ray pits, similar tointervessel pits, but smaller (4.7 ± 0.4 (4.2 - 5.2) µm). Spiral thickenings, absent. Contents, present. Tylosis, absent.

Axial parenchyma: little abundant; scarce paratracheal, unilateral. Contents, uncommon (Figure 2A). Rare fusiform cells 338 ± 60 (275 - 400) µm high. Parenchymal series 346 ± 87 (175 - 487) µm high, with 2.5 ± 0.7 (2 - 4) cells.

Rays: numerous (6 ± 0.9 (4 - 7) rays/mm), homogeneous, composed entirely of procumbent cells (Figure 2C). Predominant biseriates (48%) of 330 ± 162 (143 - 812) µm and 11 - 66 cells high, triseriates (41%), less commonly tetraseriates (4%); uniseriates (7%), 113 ± 58 (55 - 313) µm and 4 - 19 cells high. Aggregate rays, fused rays and content, absent. Surrounding cells, radial cells with disjoint walls and perforated cells, absent.

Fibers: libriform, 1.160 ± 0.205 (0.800 - 1.520) mm length, 21 ± 3.7 (15 - 28) µm width, and thin to thick walls 3.5 ± 0.6 (2.5 - 4 .4) µm, occupying approximately three fourths of the wood volume (Figure 2A). Gelatinous fibers, present; spiral thickenings, septate fibers and tracheids, absent.

Other characters: cambium variants, laticiferous and tannin tubes, intercellular channels, oil cells, mucilaginous cells, stratification, and medullary macules, absent. Crystals, present.

Figure 2 (B, D, F) shows photomicrographs of Acacia mearnsii wood from the CPA, whose microscopic anatomical description is presented below:

Vessels: numerous (22 ± 5.6 (13 - 38) pores/mm2) with diffuse porosity. Radial multiple pores of 2-8 (44%), solitary (39%), and multiple clusters of 3-10 (17%), circular or oval (123 ± 28 (70 - 163) µm) and thin to thick walls (5 ±1.2 (2.5 - 7.5) µm) (Figure 2B). Medium vascular elements (358 ± 52 (250 - 450) µm), with simple perforation plates, oblique or transverse to the vessel; short appendices (57 ± 41 (10 - 100) µm), usually at one end. Small and rounded intervessel pits (5.5 ± 0.4 (5.2 - 6.2) µm), alternate, vestured, sometimes coalescent, with slit-like aperture included. Vessel-ray pits, similar tointervessel pits, but smaller (4.3 ± 0.6 (3.1 - 5.2) µm). Spiral thickenings, absent. Contents, present. Tylosis, absent.

Axial parenchyma: little abundant, scarce paratracheal, unilateral. Contents, uncommon (Figure 2B). Parenchymal series 295 ± 70 (200 - 450) µm high, with 2.7 ± 0.9 (2 - 5) cells. Rare prismatic crystals.

Rays: numerous (7 ± 0.9 (5 - 8) rays/mm), with cells 21 ± 4.2 (15 - 25) µm wide; homogeneous, composed entirely of procumbent cells (Figure 2D). Predominant biseriates (75%), 228 ± 82 (88 - 438) µm and 5 - 29 cells high, less commonly triseriate (9%); uniseriate (16%), 81 ± 36 (50 - 188) µm and 3 - 13 cells high. Aggregate rays, fused rays and content, absent. Surrounding cells, radial cells with disjoint walls and perforated cells, absent.

Fibers: libriform, 1.042 ± 0.167 (0.700 - 1.420) mm long, 17 ± 3.8 (11 - 25) µm wide, and thin to thick walls 3.2 ± 0.6 (2.5 - 5) µm, occupying approximately two thirds of the wood volume (Figure 2B). Gelatinous fibers, present; spiral thickenings, septate and tracheid fibers, absent.

The anatomical description is close to that described by MARCHIORI & SANTOS (2011MARCHIORI, J.N.C.; SANTOS, S.R. dos. The segregation of Acacia (Tourn.) Mill. genus, according to wood anatomy of native and cultivated species in the Rio Grande do Sul state, Brazil. Balduinia. n. 30, p. 25-36, 2011.), for Acacia mearnsii wood. Xylem histometry, i.e., the proportional relationship and the distribution of the tissues that make up the wood, is in accordance with the description by FOELKEL (2008FOELKEL, C.E.B. The eucalypts and the leguminous. Part 1: Acacia mearnsii. 2008. Celsius Degree. 2008. 87 p. Available at: <https://www.eucalyptus.com.br/ capitulos/PT08_leguminosas.pdf>.
https://www.eucalyptus.com.br/ capitulos...
).

Morphological characterization of Acacia mearnsii wood

The dimensions of wood anatomical elements become important in the process of producing pulp for several reasons, ranging from the entry of white liquor into the wood, with the requirement that its capillaries be available and well distributed (FOELKEL, 2008FOELKEL, C.E.B. The eucalypts and the leguminous. Part 1: Acacia mearnsii. 2008. Celsius Degree. 2008. 87 p. Available at: <https://www.eucalyptus.com.br/ capitulos/PT08_leguminosas.pdf>.
https://www.eucalyptus.com.br/ capitulos...
), until the paper properties (FLORSHEIN et al., 2009; NIGOSKI et al., 2012).

The vessel length of Acacia mearnsii woods from SPA and CPA were 323 and 358 µm, respectively. These results are in the range of average values (between 200 and 600 µm) found for eucalypt vessel length used for pulp production (FOELKEL, 2007FOELKEL, C.E.B. Eucalypt vessel elements and pulps. Celsius Degree. 2007. 56 p. Available at: <https://www.eucalyptus.com.br/capitulos/PT04_vasos.pdf>.
https://www.eucalyptus.com.br/capitulos/...
).

The vessel diameters were 113.0 and 122.8 µm and the abundance were 13.0 and 22.0 vessels/mm², for Acacia mearnsii woods from SPA and CPA, respectively. These values are within the ranges cited by FOELKEL (2007FOELKEL, C.E.B. Eucalypt vessel elements and pulps. Celsius Degree. 2007. 56 p. Available at: <https://www.eucalyptus.com.br/capitulos/PT04_vasos.pdf>.
https://www.eucalyptus.com.br/capitulos/...
), for eucalypts used in the manufacture of pulp, where vessel diameters ranged from 60 to 250 µm and frequencies from 3 to 25 vessels per mm². The vessels, with their different dimensions and distributions in the wood, can affect the impregnation stage, because they are anatomical elements that contribute to the penetration and diffusion of the cooking liquor into the interior of the wood (ALVES et al., 2011ALVES, I.C.N.; et al. Technological characterization of Eucalyptus benthamiiwood for kraft pulp production. Ciência Florestal, v.21, n.1, p.167-174, 2011. doi: 10.5902/198050982759.
https://doi.org/10.5902/198050982759....
).

It is important to emphasize that; although, the vessels contribute to the impregnation of chips and, consequently, improve the pulping performance, a high fraction of vessels may be undesirable, because it implies in lower density wood, providing lower productivity at the mill and higher wood consumption (ALVES et al., 2011ALVES, I.C.N.; et al. Technological characterization of Eucalyptus benthamiiwood for kraft pulp production. Ciência Florestal, v.21, n.1, p.167-174, 2011. doi: 10.5902/198050982759.
https://doi.org/10.5902/198050982759....
). For pulps that will be destined for the production of printing and writing papers, QUEIROZ et al. (2004QUEIROZ, S.C.S.; et al. Effect of wood basic density on kraft pulp quality of hybrid Eucalyptus grandis W. Hill ex Maiden x Eucalyptus urophylla S.T. Blake clones. Brazilian Journal of Forest Science, v.28, n.6, p.901-909, 2004. doi: 10.1590/S0100-67622004000600016.
https://doi.org/10.1590/S0100-6762200400...
) mentioned that these vessels can be yanked from paper surface during printing, by a process called vessel-picking. This phenomenon is due to vessels adhering to the paper surface, which are easily yanked at the time of printing, resulting in an unprinted area and dirt in the printer (QUEIROZ et al., 2004).

The proportions of axial parenchyma of Acacia mearnsii woods from SPA and CPA were 3.16 and 3.83%, respectively. Due to their dimensional characteristics, these cells interfere unfavorably in the inter-fiber bonds, damaging the paper strength (BARRICHELO & BRITO, 1976BARRICHELO, L.E.G.; BRITO, J.O. Eucalypt species wood as raw material for the pulp and paper industry. Dissemination series - Forestry Research and Development Project (Brazil)-PRODEPEF, Brasília, n.13, 1976. 145 p.). However, the values obtained for the woods in this study are lower when compared to those found for the Eucalyptus genus (OLIVEIRA et al., 2012OLIVEIRA, J.G. de L.; et al.Quantitative parameters of eucalypt wood anatomy grown in different locations. Brazilian Journal of Forest Science, v.36, n.3, p.559-567, 2012. doi: 10.1590/S0100-67622012000300018.
https://doi.org/10.1590/S0100-6762201200...
).

In addition to the vessels, the proportion of radial parenchyma and its distribution can influence the entry of white liquor into the wood (FOELKEL, 2007FOELKEL, C.E.B. Eucalypt vessel elements and pulps. Celsius Degree. 2007. 56 p. Available at: <https://www.eucalyptus.com.br/capitulos/PT04_vasos.pdf>.
https://www.eucalyptus.com.br/capitulos/...
). The values reported for the proportions of radial parenchyma of Acacia mearnsii woods from SPA and CPA were 10 and 11%, respectively, which is close to the values found by RAMOS et al. (2011RAMOS, L.M.A.; et al.Radial variation of wood anatomical characters of Eucalyptus grandis W. Hill Ex Maiden and age of transition between adult and juvenile wood. Scientia Forestalis, v.39, n.92, p.411-418, 2011. Available at: <https://www.ipef.br/publicacoes/scientia/nr92/cap03.pdf>.
https://www.ipef.br/publicacoes/scientia...
) for Eucalyptus grandis wood (11 to 13%). Conversely, FOELKEL (2008) reported that Acacia mearnsii wood contains a lower proportion of radial parenchyma (5 to 7%) when compared to the Eucalyptus genus.

The abundant presence of parenchymal cells does not favor pulp refining, because they are anatomical elements that produce many fines during this process (LI & HE, 2009LI, X.; HE, B. Effect of beating levels on the morphology of vessel cell in bleached acaciakraft pulp. Paper Science Technology.v.28, n.6, p.31-33, 2009.). In addition, the parenchyma cells, when present in the pulp, increased the adhesion of the sheet to the rolls in the paper machine, increasing the frequency of breaks of the formed sheet (SPERANZA et al., 2009SPERANZA, M.; et al. Sterols and lignin in Eucalyptus globulus Labill. wood: Spatial distribution and fungal removal as revealed by microscopy and chemical analyses. Holzforschung, v.63, n.3, p.362-370, 2009. doi: 10.1515/HF.2009.041.
https://doi.org/10.1515/HF.2009.041....
).

Fiber characteristics, mainly morphology and anatomy, have a great impact on the strength properties of the paper sheet (SHARMA et al., 2020bSHARMA, N.; et al. Morphological and anatomical characterization of bleached soda, soda-AQ and kraft pulps from essential oil isolated citronella grass. Materialstoday: Proceedings, v.32, n.3, p.280-286, 2020b. doi: 10.1016/j.matpr.2020.01.373.
https://doi.org/10.1016/j.matpr.2020.01....
). The proportions of fibers in Acacia mearnsii woods from SPA and CPA were 74 and 67%, respectively, being considered high (CHOWDHURY et al., 2013CHOWDHURY, M.Q.; et al. Anatomical property variation in Acacia auriculiformis growing in Bangladesh. International Wood Products Journal, v.4, n.2, p.75-80, 2013.doi: 10.1179/2042645313Y.0000000032.
https://doi.org/10.1179/2042645313Y.0000...
), indicating that these woods would produce pulps with high yield.

Fiber lengths of Acacia mearnsii woods from SPA and CPA were 1.16 and 1.04 mm, respectively, being considered average, because they comply between the range from 0.9 to 1.6 mm (METCALFE & CHALK, 1983METCALFE, C.R.; CHALK, L. Anatomy of the dicotyledons. v.2: Wood structure and conclusion of the general introduction. 2 ed. Oxford: Clarendon Press, 1983. 330 p.). These results are close to those found by SEGURA (2012SEGURA, T.E.S. Evaluation of woods from Eucalyptus grandis x Eucalyptus urophylla and Acacia mearnsii for the kraft pulp production through conventional and Lo-Solids® processes. 2012. 99 s. Dissertation (Masters in Forest Resources) - Luiz de Queiroz College of Agriculture, Federal University of São Paulo, Piracicaba. 2012.) and MARCHIORI (1990MARCHIORI, J.N.C. Wood anatomy of Acacia genus, native and cultivated in the Rio Grande do Sul state, Brazil. 1990. 226 s. Thesis (Doctorate in Forest Engineering) - Postgraduate Program in Forest Engineering, Federal University of Paraná, Curitiba. 1990.) for fiber lengths of Acaciamearnsii, i.e., 0.94 mm and from 0.95 to 1.52 mm, respectively. The fiber length influences the tensile strength, tear strength, formation and uniformity of the paper sheet (SHARMA et al., 2020bSHARMA, N.; et al. Morphological and anatomical characterization of bleached soda, soda-AQ and kraft pulps from essential oil isolated citronella grass. Materialstoday: Proceedings, v.32, n.3, p.280-286, 2020b. doi: 10.1016/j.matpr.2020.01.373.
https://doi.org/10.1016/j.matpr.2020.01....
).

The values for fiber cell wall thickness of Acacia mearnsii woods from SPA and CPA were 3.4 and 3.2 μm, respectively, allowing them to be classified as thick-walled fibers, because they comply between the range from 3 to 5 μm, according to the classification proposed by MANIMEKALAI et al. (2002MANIMEKALAI, V.; PAVICHANDRAN, P.; BALASUBRAMANIAN, A. Fibres of Sorghum bicolor (L.) Moench and their potential use in paper and board making. Phitomorphology, v.52, n.1, p.55-59, 2002. Available at: <https://www.researchgate.net/publication/295577852_Fibres_of_Sorghum_bicolor_L_Moench_and_their_potential_use_in_paper_and_board_making>.
https://www.researchgate.net/publication...
). These results are close to those reported by MARCHIORI (1990MARCHIORI, J.N.C. Wood anatomy of Acacia genus, native and cultivated in the Rio Grande do Sul state, Brazil. 1990. 226 s. Thesis (Doctorate in Forest Engineering) - Postgraduate Program in Forest Engineering, Federal University of Paraná, Curitiba. 1990.) and SEGURA (2012SEGURA, T.E.S. Evaluation of woods from Eucalyptus grandis x Eucalyptus urophylla and Acacia mearnsii for the kraft pulp production through conventional and Lo-Solids® processes. 2012. 99 s. Dissertation (Masters in Forest Resources) - Luiz de Queiroz College of Agriculture, Federal University of São Paulo, Piracicaba. 2012.) for Acacia mearnsii woods, i.e. 3.3 μm and smaller than 4.2 μm, respectively. However, they are smaller than those found for Eucalyptus woods by FERREIRA et al. (2006FERREIRA, C.R.; et al.Technological evaluation of eucalypt clones: part 1 - wood quality for kraft pulp production. Scientia Forestalis, v.70, p.161-170, 2006. Available at: <https://www.ipef.br/publicacoes/scientia/nr70/cap16.pdf>.
https://www.ipef.br/publicacoes/scientia...
) and GOMIDE et al. (2005GOMIDE, J.L.; et al. Technological characterization of the new generation of Eucalyptus clones in Brazil for kraft pulp production. Brazilian Journal of Forest Science, v.29, n.1, p.129-137, 2005. doi: 10.1590/S0100-67622005000100014.
https://doi.org/10.1590/S0100-6762200500...
), i.e. 4.83 μm and 4.8 to 5.2 μm, respectively.

Fiber lumen diameters of Acacia mearnsii woods from CPA (10.8 μm) and SPA (13.6 μm) were close to those evaluated by SEGURA (2012SEGURA, T.E.S. Evaluation of woods from Eucalyptus grandis x Eucalyptus urophylla and Acacia mearnsii for the kraft pulp production through conventional and Lo-Solids® processes. 2012. 99 s. Dissertation (Masters in Forest Resources) - Luiz de Queiroz College of Agriculture, Federal University of São Paulo, Piracicaba. 2012.) for Acacia mearnsii wood and also by ALZATE (2004) and FERREIRA et al. (2006FERREIRA, C.R.; et al.Technological evaluation of eucalypt clones: part 1 - wood quality for kraft pulp production. Scientia Forestalis, v.70, p.161-170, 2006. Available at: <https://www.ipef.br/publicacoes/scientia/nr70/cap16.pdf>.
https://www.ipef.br/publicacoes/scientia...
), for Eucalyptus sp. woods. These lumen diameter and fiber wall thickness dimensions indicate that the woods used in this study will favor the liquor impregnation step in the wood, resulting in greater uniformity and yield cooking (FOELKEL, 2007FOELKEL, C.E.B. Eucalypt vessel elements and pulps. Celsius Degree. 2007. 56 p. Available at: <https://www.eucalyptus.com.br/capitulos/PT04_vasos.pdf>.
https://www.eucalyptus.com.br/capitulos/...
).

Fiber quality ratios for pulp and paper production

Although, all the cellular elements making up the wood are important, the indication of a species for pulp and paper production must meet the requirements determined by the ratios derived from the fibers, whose results for Acacia mernsii wood fibers from SPA and CPA are presented in table 1.

Table 1
Fiber quality ratios of Acacia mearnsii woods from seed production area (SPA) and clonal planting area (CPA) for pulp and paper production.

The smaller the Runkel ratio value in relation to the unit, the greater the pulp strength, and the better the bounds between the fibers in the paper (FOELKEL & BARRICHELO, 1975FOELKEL, C.E.B.; BARRICHELO, L.E.G. Relationships between wood characteristics and pulp and paper properties. O Papel, v.36, n.9, p. 49-53, 1975. Available at: <https://www.celso-foelkel.com.br/artigos/ABTCP/1975_Caracteristicas_Madeira+Celulose+Papel.pdf>.
https://www.celso-foelkel.com.br/artigos...
). Acacia mearnsii woods from SPA and CPA are within category III (between 0.5 and 1.0) for the Runkel ratio, being considered good for paper (RUNKEL,1952RUNKEL, R.O.H. Pulp from tropical wood. TAAP, v.35, n.4, p.174-178, 1952.).

According to FLORSHEIM et al. (2009FLORSHEIM, S.M.B.; et al. Variation in the dimensions of the anatomical elements of seven-year-old Eucalyptus dunnii wood. Forest Institute Magazine, v.21, n.1, p.79-91, 2009. Available at: <https://smastr16.blob.core.windows.net/iflorestal/ifref/RIF21-1/RIF21-1_79-91.pdf>.
https://smastr16.blob.core.windows.net/i...
) and NISGOSKI et al. (2012NISGOSKI, S.; MUÑIZ, G.I.B.; TRIANOSKI, R.; MATOS, J.L.M.M.; VENSON. I. Anatomical characteristics of wood and strength indexes of Schizolobiumparahyba (Vell.) Blake from experimental plantation. Scientia Forestalis, v.40, n.94, p.203-211, 2012.), the higher the value of the flexibility coefficient, the more flexible and the less susceptible to break the fiber will be; consequently, producing papers with greater tensile and burst strength. The flexibility coefficients of Acacia mearnsii woods from PSA (66.3%) and CPA (62.6%) are in the range from 50 to 75%, according to the classification presented by NISGOSKI (2005), indicating good contact surface and bond between the fibers in the paper structure. The values observed for the fiber flexibility coefficients of Acacia mearnsii woods in this study were higher than those of Eucalyptus sp., verified by FERREIRA et al. (2006FERREIRA, C.R.; et al.Technological evaluation of eucalypt clones: part 1 - wood quality for kraft pulp production. Scientia Forestalis, v.70, p.161-170, 2006. Available at: <https://www.ipef.br/publicacoes/scientia/nr70/cap16.pdf>.
https://www.ipef.br/publicacoes/scientia...
), FLORSHEIM et al. (2009) and COSTA (2011COSTA, J.A. Quality of Eucalyptus grandis wood grown in the Federal District for kraft pulp production. 2011. 76 s. Dissertation (Masters in Forest Science) - Faculty of Technology, University of Brasília, Brasília. 2011.).

Fiber slenderness ratio is directly related to the paper tear and double folds strength (FOELKEL & BARRICHELO, 1975FOELKEL, C.E.B.; BARRICHELO, L.E.G. Relationships between wood characteristics and pulp and paper properties. O Papel, v.36, n.9, p. 49-53, 1975. Available at: <https://www.celso-foelkel.com.br/artigos/ABTCP/1975_Caracteristicas_Madeira+Celulose+Papel.pdf>.
https://www.celso-foelkel.com.br/artigos...
). ROCHA & POTIGUARA (2007ROCHA, C.B.R.; POTIGUARA, R.C.V. Leaf fibers morphometry of Astrocaryum murumuru var. murumuru Mart. (Arecaceae). Acta Amazônica, v.37, p.511-516, 2007. doi: 10.1590/S0044-59672007000400005.
https://doi.org/10.1590/S0044-5967200700...
), and BENITES et al. (2015BENITES, P.K.R.M.; et al. Anatomical characterization of eight forest species fibers from Cerrado of Mato Grosso do Sul for paper production. Brazilian Journal of Wood Science, v.6, n.2, p.88-93. 2015. doi: 10.12953/2177-6830/rcm.v6n2p88-93.
https://doi.org/10.12953/2177-6830/rcm.v...
) mentioned that this value must be greater than 50 for paper production, which was found for Acacia mearnsii wood from CPA (60.4) and SPA (56.6) in this study.

For NISGOSKI et al. (2012NISGOSKI, S.; MUÑIZ, G.I.B.; TRIANOSKI, R.; MATOS, J.L.M.M.; VENSON. I. Anatomical characteristics of wood and strength indexes of Schizolobiumparahyba (Vell.) Blake from experimental plantation. Scientia Forestalis, v.40, n.94, p.203-211, 2012.), high wall fraction values indicate that the fibers are rigid, reducing the number and the strength of bonds between fibers in paper production, damaging its strength. The wall fraction values for Acacia mearnsii woods from SPA (33.7%) and CPA (37.4%) are below 40%, a limit established for the fiber wall fraction aiming paper manufacturing (FOELKEL & BARRICHELO, 1975FOELKEL, C.E.B.; BARRICHELO, L.E.G. Relationships between wood characteristics and pulp and paper properties. O Papel, v.36, n.9, p. 49-53, 1975. Available at: <https://www.celso-foelkel.com.br/artigos/ABTCP/1975_Caracteristicas_Madeira+Celulose+Papel.pdf>.
https://www.celso-foelkel.com.br/artigos...
). The values reported in this study were lower than 42.25%, found by BUSNARDO et al. (1986BUSNARDO, C.A.; GONZAGA, J.V.; SANSIGOLO, C.A. Characterization of wood and kraft pulp quality produced from healthy and attacked by gummosis Acacia mearnsii trees. Guaíba: Riocell S.A. 1986. 38 p. (Technical report)) for fiber wall fraction of Acacia mearnsii wood.

CONCLUSION:

The results obtained from the anatomical characterization of Acacia mearnsii woods allowed the following conclusions: The values of Runkel ratio, flexibility coefficient, slenderness ratio and wall fraction are within the acceptable range for pulp and paper production. The Acacia mearnsii wood from SPA and CPA are indicated as a source of raw material for the pulp and paper production.

ACKNOWLEDGEMENTS

We would like to thank the Brazilian Federal Agencies: “Coordenação de Aperfeiçoamento de Pessoal de Nível Superior” (CAPES), Brazil - Finance Code 001, and “Conselho Nacional de Desenvolvimento Científico e Tecnológico” (CNPq), Brazil, for funding the research.

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  • 0
    CR-2021-0865.R3

Edited by

Editors: Leandro Souza da Silva(0000-0002-1636-6643) Rômulo Trevisan(0000-0002-8535-0119)

Publication Dates

  • Publication in this collection
    13 Feb 2023
  • Date of issue
    2023

History

  • Received
    07 Dec 2021
  • Accepted
    17 Oct 2022
  • Reviewed
    19 Dec 2022
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