A preliminary investigation into the suitability of Kawui wood ( Vernonia arborea ) for pulp and paper

Abstract

The anatomical and chemical properties of a lesser known species, Kawui wood, were investigated Two trees were examined based on IAWA, ASTM and SNI. A completely randomised design was used with radial direction of the trunk (sapwood and heartwood) as the factor, in three replications. It indicated the highest to lowest cell proportions are fibres, rays, vessels and parenchyma. The highest proportion of rays was in the sapwood, while the fibre was in the heartwood. However, the average fibre length in the sapwood was higher than the heartwood, while the lumen diameter showed the reverse. Holocellulose, α-cellulose, lignin, extractives, and ash content of the sapwood was higher than the heartwood. Based on its anatomical and chemical properties, Kawui wood can be included in grade II–IV, which is suitable for medium quality pulp and paper production.

Keywords

Kawui lesser known species anatomy chemical pulp and paper

Introduction

Since 1994, the industrial timber plantations have been designed to meet the needs of the pulp and paper industries. It includes the fast growing, Australian native tree genus, Eucalyptus. In fact, Eucalyptus is currently the greatest contributor to the world's pulp and paper production, including in Indonesia (Fatimah et al. 2013). In 1998, Eucalyptus pellita was initially cultivated in Central Kalimantan, mainly for this purpose. Central Kalimantan, particularly its peat swamp forest, is known for their rich biodiversity. Meranti, Ramin, Jelutung kapur, and Bangkirai are among trees that have high economic value. Nevertheless, some of them have been classified as protected or endangered species, e.g. Jelutung and Ramin. Noor and Heyde (2007) claimed that at least 2500 flora species are native of peat lands. Yet past forest mismanagement only prioritised massive production instead of a continuous cycle, leading to higher plant extinction rates. In addition to commercial timbers, a number of non-commercial or lesser known species have not been exploited. However, it requires studies on the basic properties of wood to determine their potential utilisation. Wood structure, physical properties, mechanical properties and chemical properties are factors widely used as the basis for wood utilisation and quality measurement (Vidaurre et al. 2018).

Hampangen Education and Research Forest (Hutan Pendidikan dan Penelitian Hampangen, HPPH) of Universitas Palangka Raya, Indonesia was established for the purpose of forestry with special Educational Functions. The total area of HPPH is 5000 ha. A preliminary study estimated that approximately 80 flora species from 27 families were found in HPPH. Moreover, the species diversity at the pole and tree level was high (H′ > 3). The species are both commercial and non-commercial types. One of the non-commercial or lesser known species is Kawui. The list of timber in Central Kalimantan published by the Forestry Department, Directorate General of Forestry, Directorate of Forestry Program Development in 1983 merely informed the local name of Kawui tree. Dendrologists have identified that Kawui belongs to Asteracea family with the name of species Vernonia arborea (author Buch. Ham). A preliminary survey identified that the presence of this species is fairly high. It can be classified as ‘moderate’ in which there are at least 10 trees within a radius of 50 m. Henrikson et al. (2009) stated that the anatomical properties of wood, i.e. cell length, cell wall thickness, cell diameter and lumen diameter, and chemical properties of wood, i.e. the proportion of fibres, rays, vessels and parenchyma cells greatly affect pulp and paper production. Therefore, it is considered important to conduct research on Kawui wood in order to obtain information about the anatomical and chemical properties of wood for pulp and paper production.

This study aimed to obtain information relating to the basic properties of Kawui wood including the anatomical and chemical structure of wood. It is expected that such information will be useful for determining the optimal use of this wood. In addition, this study also aimed to explore the potential of non-commercial or lesser known species as an alternative to meet the need for the pulp and paper industries.

Research methodology

The present study was conducted from 9 September–9 December 2019. Wood anatomy was examined at the Wood Anatomy Lab., Faculty of Forestry, Universitas Mulawarman, Samarinda, Indonesia. The chemical properties were examined at the Laboratory of Biomaterial Chemical Conversion, Faculty of Forestry, Universitas Gadjah Mada, Yogyakarta. The samples investigated were two Kawui trees of 34.74 and 28.34 cm in diameter (at breast height). The distance between them was about 100 m. The coordinate of the first tree was 1° 5′ 44″ S and 113° 45′ 34″ E, while the second tree was 1° 52′ 51″ S and 113° 30′ 23″ E. The criteria for the samples were that those trees must have upright, healthy growth rate and no signs of physical damage. The sample size was determined by considering the research method, by cutting down trees and collecting parts of trunks for the replicate samples. This method was carried out by Lukmandaru (2018) using one sample of E. pellita tree, and by Ohshima et al. (2019) using two trees of both E. camaldulensis and E. globulus. Other materials were distilled water, alcohol, benzene, acetic acid, sodium chlorite, acetone, sulphuric acid and sodium hydroxide for wood chemical testing. The equipment included aluminium foil, desiccators, plastic wrap, scales, chain saws, calipers, ribbon saws and circular saws, chipper, sandpaper, markers, gauges, and calculator. Other tools were required during wood chemical testing, including furnace, porcelain cups, flasks, measuring cups, erlenmeyer flasks, water baths, and burettes.

The study used a completely randomised design (CRD) for examining the anatomical properties of Kawui wood with two treatments, i.e. sapwood and heartwood, in three replications. An Analysis of Variance was performed to analyse the data, and a significant difference between the treatments was followed by Honest Significant Difference (HSD) test. The wood chemical properties were the average of two measurements (in duplo), after which a descriptive analysis was performed.

The dissection of trunks and specimen preparation was done based on the established procedure and research design. The anatomical properties were examined according to IAWA standard while the chemical properties were examined according to the ASTM (D1107-96, D1110-84 and 1102-02) and SNI (0492:2008 and 14-1031-89).

Measuring fibre dimensions

Before testing, maceration was conducted. The sample was cut into 9–10 matchsticks and immersed in a test tube containing a solution of 30% hydrogen peroxide (H₂O₂) and 60% acetic acid (CH₃COOH) in a 1: 1 ratio. The tube was put into a measuring cup filled with water, boiled over low and stable heat for approximately 5 h until the samples were white and soft. Subsequently, the samples were shaken to separate the fibres and rinsed with distilled water. They were immersed in 50% alcohol to stabilise the fibre dimension. For the measurement, fibres were transported to a microscope slide using tweezers, and then covered with cover glass. Fibre dimensions, including fibre length, fibre diameter, lumen diameter and cell wall thickness, were observed under a microscope.

Measuring the proportion of fibre

A sample of dimension 2 cm x 2 cm x 2 cm was boiled in a mixture of water and 87% glycerin for approximately 1 h. It was cut into three different planes, i.e. tangential, radial and transverse, using a microtome to a thickness of 20–30 µm. The sliced sections were stained with aniline blue, dehydrated with a series of alcohol, placed on an object glass and covered with glass. The specimens were observed using the microscope equipped with a camera. Vessel diameter measurement was carried out in the transverse section. The number of vessels per mm² was calculated using a dot grid that was converted into on-screen microscope (1 × 1mm).

Measurement of the vessel diameter, length and width of ray was carried out on the tangential section using the microscopic magnification. The result was converted with a value of 8.116 µm. The percentage of wood cells was obtained by subtracting the area of a dot grid on the microscope, the dot grid area was 21 × 21 dots, or a total of 441 dots (100%) with a magnification of 100x. The vessel percentage and parenchyma percentage were obtained from the transverse section, while the rays were from the tangential section. Calculation of the percentage of vessels, rays and axial parenchyma use the formula as follows: (1) (2)

Measurement of fibre length was done using an Olympus BH2 microscope with a magnification of 100x and a conversion value of 14.92 µm. Fibre diameter and lumen diameter were measured using magnification of 400x and a conversion value of 3.70 µm. Cell wall thickness is the subtraction of fibre diameter from lumen diameter and divided by two. Derived values are obtained by comparing the values of cell dimensions, hence they have no single unit, except Muhlstep ratio that has percentage (%) since the value is multiplied by 100%. According to Vademicum (1976), the derived values of fibre dimensions are calculated using the formula as follows: (3) (4) (5) (6) (7)

Testing wood chemical properties

The examination of the chemical properties of wood is based on several parameters. They include ethanol-toluene content using ASTM D1107-96; solubility in hot water using ASTM D1110-84 standard; holocellulose, α-cellulose and lignin contents using SNI 0492: 2008; ash content using ASTM D-1102-02; and silica content using SNI 14-1031-89 standard.

Results and discussion

The anatomical properties of Kawui wood

The anatomical properties of Kawui wood, namely the mean of cell proportion of Kawui trees, are presented in Table 1.

Table 1

Mean of cell proportion of Kawui wood.

Mean	Trunk cross section	Parameter
		Cell Proportion
		Vessels (%)	Rays (%)	Parenchyma cells (%)	Fibre cells (%)
First tree	Sapwood	11.04	14.98	4.55	69.43
First tree	Heartwood	12.38	14.84	5.32	67.46
	Mean	11.71	14.91	4.94	68.45
Second tree	Sapwood	13.99	18.45	4.76	62.8
	Heartwood	11.37	12.01	4.76	71.86
	Mean	12.68	15.23	4.76	67.33
Eucalyptus pellita ^a		7.5–24.44	7.96–26.11	11.48–32.78	∼

^aIkhtiyarullatifah (2014).

Table 1 indicates the difference between the proportion of cells of heartwood and sapwood. In the first tree, the proportion of vessels and parenchyma cells in the heartwood is higher than the sapwood, while the proportion of rays and fibre cell in the heartwood is lower than the sapwood. The variation of cells proportion occurs since the wood formation varies in each developmental phase. Wood formation depends on cambial activity in which it produces wood inwards and the bark outwards. Physiologically active wood cells form sapwood and when the cells die, it is called heartwood. Growth is influenced by genetic and environmental factors, as well as the availability of resources, i.e. carbohydrates, hormones, water and nutrients in meristematic tissues (Zobel and dan Van Buijtnenen 1989; Salisburry and dan Ross 1995; Kozlowski and dan Stephen 1997). Indrayanti (2015) confirmed the effect of changes in temperature and rainfall on cell proportion and cell dimensions in Jelutung (Dyera lowii (Hook)). Such conditions affect the basic properties of wood. Casey (1960) suggested that growth conditions influence the properties of wood, causing variation in the pulp quality. Several studies have reported variations in the properties of wood. Supartini and Kholik (2010) confirmed variation in the cell proportion of sapwood and heartwood of Shorea parvistipulata, in which the percentage of vessels from the heartwood toward the sapwood increases, while the percentage of rays, parenchyma cells and fibres decreases. Meanwhile, Siska et al. (2012) found out that in Pupu Pelanduk, the percentage of those cells increase from heartwood to sapwood. This finding confirms Ohshima et al. (2004) on the difference of the variation of radial position (heartwood-sapwood) on parenchyma percentage. In the second tree, the proportion of both vessels and rays on the sapwood is higher than the heartwood. Meanwhile, the proportion of parenchyma cell is equal but fibre cell on the heartwood is higher than the sapwood. The proportion of vessels between two trees is different. It decreases from heartwood to sapwood in the first tree, while the second tree shows contrary result. According to Ohshima et al. (2005), vessels affect the roughness level of the paper surface. The different proportion of fibre found in the samples was also reported by Chowdhury et al. (2013) on a study of Acacia auriculiformis A. Cunn. (ex Benth), in which the proportion of fibre increases from heartwood to sapwood. On the contrary, Denne and Hale (1999) revealed the proportion of fibre in Nothofaguis nervosa (rauli) decreases from heartwood to sapwood. The comparison between the cell proportions of Kawui wood and E. pellita (as derived from Ikhtiyarullatifah (2014)) is presented in Table 1. It shows the proportion of vessels in Kawui wood is lower than the rays, but both are in the range of the proportion of vessels and rays in E. pellita. Meanwhile, the proportion of fibre cells in Kawui is higher than that in E. pellita. In general, regardless of the position on the trunk, fibre cells have the highest proportion in the tree samples. Srivaro et al. (2018) stated that fibre cells generally have a higher proportion than parenchyma cells. The present study confirms this finding in which, in Kawui wood, parenchyma cells have the lowest proportion compared to other cells. Furthermore, fibre cells have the longest length since they have the role of supporting the trunk of the tree. Generally, the proportion of fibre cells is about 50%, while the present study shows that Kawui wood has approximately 62–69%, which is higher than that of E. pellita as reported by Ikhtiyarullatifah (2014). The results of the analysis of variance of cell proportion are presented in Table 2.

Table 2

Analysis of variance of cell proportion of Kawui wood.

Sample	Measurement		df	Sum of squares	Mean square	F _ratio	F_table 5%
First tree	Vessels	Std. error	38	1174.24	30.9	0.507 tn	4.098
	Rays			601.13	15.819	0.012 tn
	Parenchyma cell			96.812	2.548	2.336 tn
	Fibre cell			2.149.463	56.565	0.689 tn
Second tree	Vessels	Std. error	38	836.57	22.015	3.1116 tn	4.098
	Rays			529.293	13.929	29780**
	Parenchyma cell			65.780	1.731	0.00004 tn
	Fibre cell			1.867.743	49.151	16.689**

Note: Ftab = Ftabel.

**Significant at 5%.

Table 2 shows that in the first tree, there is no significant difference among the parameters. Meanwhile, in the second tree, there is a significant difference between the proportions of rays and fibre cells. The results of further tests on both parameters, showed that the highest proportion of rays was found in sapwood, while the highest proportion of fibre cells was found in heartwood. The difference of means test of the proportion of rays and fibre cells is presented in Table 3.

Table 3

Difference of means test of the proportion of rays and fibre cell of Kawui.

Parameter	Trunk cross section		p-value
Parameter	Sapwood	Heartwood	5%
Proportion of vessels in second tree	18.45a	12.01b	2.411
Proportion of fibre cells in second tree	62.80a	71.86b	4.53

Based on the results of analysis of variance on the mean of the cell proportion, the rays and fibre cells have different proportions based on their position on the trunk. The variation in the ray proportion is due to its relationship with tree maturity process as marked by the difference in size between the cells near the pith and mature cells.

In addition to chemical properties, physical properties of paper made from hardwood pulp are influenced by its fibre characteristics (Nugroho et al. 2012). The characteristics include fibre dimensions and its derived values. The dimensions of Kawui wood are presented in Table 4.

Table 4

Mean of cell dimension and standard for pulp and paper production.

Mean	Trunk cross section	Parameter
		Cell dimension
		Length of cell	Cell diameter	Lumen diameter	Cell wall thickness
		(µm)	(µm)	(µm)	(µm)
First tree	Sapwood	1161.52	25.25	15.91	4.77
First tree	Heartwood	1070.51	28.49	18.41	5.04
	Mean	1116.02	26.86	17.16	4.91
	Class	Medium	High	High	Thin
Second tree	Sapwood	1181.66	25.99	15.54	5.23
	Heartwood	971.29	30.99	19.89	5.51
	Mean	1076.48	28.49	17.72	5.37
	Class	Medium	High	High	Thin
E. pellita ^a	Mean	1020	13.25	6.94	3.15
	Class	Medium	Medium	Medium	Thin

Notes: Remarks µ = micrometer; Standard of the dimension of pulp and paper material (Vademicum 1976).

^aLukmandaru (2016).

Table 4 shows the mean of Kawui wood, which has a propensity to decline from heartwood to sapwood (both on the first and second tree), respectively from fibre diameter, lumen diameter to cell wall thickness. On the contrary, the length of fibre shows a decline from sapwood to heartwood. This finding on fibre diameter confirms Chowdhury et al. (2013), in which the fibre diameter of Acacia auriculiformis A. Cunn (ex Benth) gradually decreases from heartwood to sapwood. In contrast, Quilhó et al. (2006) found the fibre length of Eucalyptus grandis has an increasing trend from heartwood to sapwood. Shashikala and Vijendra (2009) revealed the significant differences of the cell dimension of Eucalyptus citriodora (Hook) from pith outward (heartwood to sapwood). The mean of fibre length and fibre diameter of Kawui wood can be classified as ‘medium.’ However, there is a significant difference between the ‘thick’ lumen diameter of Kawui wood and that of ‘medium’ lumen diameter of E. pellita (Lukmandaru 2016). Subsequently, the cell wall thickness of Kawui wood is in the same category to E. pellita, which is ‘thin.’ Quilhó et al. (2006) claimed that the assessment of fibre is important because of one of the primary key factors for evaluating the success of pulpwood resource is the assessment of fibre characteristics. The result of Analysis of Variance of cell dimensions is presented in Table 5.

Table 5

Analysis of variance of cell dimensions of Kawui wood.

Sample	Measurement		df	Sum of squares	Mean square	F _ratio	F _tabel
Sample	Measurement		df	Sum of squares	Mean square		5%
First tree	Length of fibre	Std. Error	38	985322.708	25.929.545	3.194 tn	4.098
	Fibre diameter			702.810	18.495	5.667*
	Lumen diameter			601.504	15.829	3.941 tn
	Cell wall thickness			21.813	0.574	1.342
Second tree	Length of fibre	Std. Error	38	15.914,134	4189.294	10.568**	4.098
	Fibre diameter			1143.763	30.099	8.306**
	Lumen diameter			816.794	21.495	8.783**
	Cell wall thickness			31.181	0.978	0.781 tn

*Significant at 5% level of significance.

**Significant at 1% level of significance.

The analysis results show the significant difference in fibre diameter between the heartwood and sapwood in the first tree. In the second tree, the fibre length, fibre diameter and lumen diameter between sapwood and heartwood also show a very significant difference. Supartini and Kholik (2010) found that in the radial direction, the fibre quality of Shorea parvistipulata is uniform. Pulp made from long fibre also has a high capacity to hold bonds between fibre. Fibre diameter and fibre length are closely related in pulp and paper production. The present study reveals Kawui wood has medium length, thin-walled and wide lumen diameter. According to Vademicum (1976), fibre with such classification is flattened after the grinding process and has high bonding strength, plasticity, slenderness and flexibility. In general, small diameter and thin-walled fibre generally has better quality as pulp and paper material. The difference of means test indicates the cell diameter in the heartwood of the first tree is higher than that in the sapwood. Meanwhile, of the second tree, there is an insignificant difference between the cell diameters of sapwood and heartwood. Nevertheless, the length of fibre in the sapwood is longer than that of the heartwood, whereas the lumen diameter of the heartwood is wider than that of the sapwood.

The suitability of wood as pulp and paper production must meet the requirements determined by the fibre derived indexes, i.e. Runkel ratio, slenderness ratio, Muhlstep ratio, rigidity coefficient and flexibility coefficient. The fibre dimension derived indexes of Kawui wood and the standard indexes for pulp and paper production are presented in Table 6. Fibre with Runkel ratio less than 1 produces high quality pulp and paper. The value is obtained from the ratio of twice the cell wall thickness to the lumen diameter. The thicker the cell wall, the higher the Runkel ratio is. Meanwhile, the lower the Runkel ratio, the higher the wood quality for pulp and paper production. Thin cell wall/fibre produces flexible and high bonding strength. Ona et al. (2001) argued that cell wall thickness has a very significant effect on the quality of pulp made from Eucalyptus camaldulensis and Eucalyptus globulus. The derived values of fibre dimension of Kawui wood indicate various results in association with the requirement of pulp production. Similarly, Lukmandaru (2016) also found such variation in E. pellita. The Runkel ratio of Kawui wood (Table 6) is lower than E. pellita. Based on the standard of fibre derived index for pulp–paper production, the Runkel ratio of Kawui wood is classified Grade III or medium quality, while E. pellita is included in Grade IV or less. The slenderness ratio of a wood also indicates the pulp–paper quality. This ratio is related to the slippery level. The greater the slenderness ratio, the more slippery the paper is. The present study reveals, based on its slenderness ratio, Kawui wood is included in Grade III–IV, which is lower than the ratio of E. pellita (classified in Grade II).

Table 6

Derived values of fibre dimension of Kawui wood and the standard for pulp and paper production.

Sample	Trunk cross section	Runkel ratio	Slenderness ratio	Muhlstep ratio	Coefficient of rigidity	Coefficient of flexibility
First tree	Sapwood	0.600	46.001	60.297	0.189	0.630	Total
First tree	Heartwood	0.548	37.575	58.244	0.177	0.646
	Mean	0.574	41.788	59.271	0.183	0.638
	Grade	III	III	II	III	II	II–III
	Score	50	50	75	50	75	300
Second tree	Sapwood	0.673	45.466	64.249	0.201	0.598
	Heartwood	0.554	31.342	58.807	0.178	0.642
	Mean	0.554	37.784	58.807	0.178	0.642
	Grade	III	IV	II	III	II	II–IV
	Score	50	25	75	50	75	275
E. pellita ^a	Mean	0,97	78,21	60,297	0,238	0,524
	Grade	IV	II	II	IV	II	II–IV
	Score	25	75	75	25	75	275

^aLukmandaru (2016).

The plasticity of pulp and paper is determined by the value of Muhlstep ratio. This value determines the smoothness and flatness of the produced paper. The greater the value of Muhlstep ratio, the higher the plasticity of the paper as indicated by its tear resistance. The present study reveals the Muhlstep ratio of Kawui wood is lower than E. pellita, although both are classified in Grade II. It indicates Kawui wood has medium smoothness and tear resistance. Subsequently, paper with a low coefficient of rigidity has higher bonding strength when subject to forces/loads. The lower the coefficient of rigidity, the better the produced paper is. Based on its coefficient of rigidity, Kawui wood is classified in Grade III, which is higher E. pellita (Grade IV). Another parameter essential for pulp/paper production is the coefficient of flexibility. A higher flexibility value indicates a better paper quality. Fibres serve to enhance the elasticity of paper. Based on its coefficient of flexibility, Kawui wood is classified into Grade II, which is similar to E. pellita. According to Chowdhury et al. (2013), the anatomical properties of wood are essential information for wood utilisation. The anatomical properties of Kawui wood indicate its prospect as an alternative for pulp and paper production. Moreover, it has better properties than E. pellita. In overall, the findings of the present study show that paper made from Kawui wood has medium quality for pulp and paper production.

Wood chemical properties

The results of testing the chemical properties of Kawui wood are presented in Table 7. It shows the comparison between chemical compositions of Kawui and E. pellita (as derived from Lukmandaru (2018)). E. pellita was selected in this comparison because it is widely used in pulp and paper production in Indonesia. In addition, the classification of wood chemical composition of broad-leaved trees (Vademicum 1976) is also included in this comparison. Therefore, the chemical composition of Kawui in pulp and paper production can be determined.

Table 7

Mean of chemical composition of Kawui, E. pellita and chemical composition classification for pulp and paper.

	Kawui		E. pellita ^a		Classification of wood chemical composition for pulp and paper^b
Parameter	%		%
Position	Sapwood	Heartwood	Sapwood	Heartwood	Low (L)	Medium (M)
• Solubility in Hot water (%)	0.53 M	0.67 M	2.29 M	3.39 M	<0.2	2–4
• Ethanol-toluene soluble extractives (%)	2.82 M	1.95 M	8.09 H	7.91 H	<0.2	2–4
• Ash content (%)	1.02 H	0.68 H	0.38 M	0.26 M	<0.2	0.2-0.6
• Lignin (%)	24.25 H	31.29 H	31.07 H	35.81 H	<21	21–24
• Holocellulose (%)	68.94 H	69.12 H	72.04 H	65.71 H	<18	18–33
• α-cellulose (%)	40.87 M	42.57 M	38.47 L	35.57 L	<40	40–45

^aLukmandaru (2018).

^bVademicum (1976).

Sjostrom (1995) suggests extractives, i.e. resin acids are usually stored in resin ducts, fats and waxes are stored in the parenchyma cells of the rays, while phenols are mainly stored in heartwood. The present study reveals that the solubility in hot water of sapwood is lower than that of heartwood. The yield is also lower than the toluene–ethanol soluble extractives of both sapwood and heartwood. The measurement of hot-water-soluble extractives includes polar compounds found in cavities, i.e. starch, tannin, latex, and sugar. Meanwhile, the measurement of ethanol-toluene soluble content of wood includes non-polar compounds, i.e. waxes, fats, resins, oils, tannins and other ether-insoluble components. The high ethanol-toluene soluble extractives in Kawui wood are allegedly related to its high content of non-polar compounds. Nevertheless, these extractive values of Kawui wood are lower than those of E. pellita (Lukmandaru 2018), including hot-water-soluble extractives and ethanol-toluene soluble extractives of both sapwood and heartwood. In addition, the value of hot-water-soluble extractives of Kawui wood is also lower than that of E. Pellita obtained from PT. Koriintiga Central Kalimantan, which ranges from 6.67 to 8.17% (Sirait 2019). Based on the classification of wood chemical composition for pulp and paper, the extractives of Kawui wood is included as ‘medium.’ The measurement of extractive content is very significant for estimating the quality of the produced pulp and paper. In addition to causing black spots on paper, woods with high extractives require high amount of chemicals for the bleaching process. As a result, the yield of pulp will be lower.

The percentage of holocellulose in the sapwood and heartwood of Kawui is insignificantly different, which is 0.18% higher in heartwood. It is lower than E. pellita as reported by Lukmandaru (2018), Fatimah et al. (2013) of 72.89–79.91%, Sirait (2019) of 87.07–89.20%, and Arizandi et al. (2019) of 64.87–75.75% in sapwood and 67.00–74.14% in heartwood. However, both Kawui and E. pellita are included in high holocellulose content. The α-cellulose content of Kawui wood increases from sapwood to heartwood, both are classified ‘medium.’ Moreover, the α-cellulose of Kawui is higher than E. pellita (Lukmandaru 2018), in which both sapwood and heartwood are included ‘low.’ Holocellulose and α-cellulose contents indicate the yield of pulp (Pari and dan Hartoyo 1990; Supartini 2009). The higher the cellulose content, the higher the yield of pulp is, and the higher the affinity of the solution, the brighter the yield of pulp is. Therefore, the higher the cellulose content, the higher the quality of the pulp and paper.

The lignin content of Kawui wood is included ‘high,’ as it reaches above 24%. This result is similar to the high lignin content of E. pellita (Lukmandaru 2018), in which E. pellita has higher lignin content than Kawui. It adversely affects the pulping process and later, the quality of paper yield. High lignin content requires high alkaline consumption during pulping process, leading to high kappa numbers (Syafii and Siregar 2006). Likewise, Pari and dan Hartoyo (1990) stated that high lignin content complicates the grinding process, causing unfavourable characteristics of paper, i.e. rigid, yellow in colour and low in quality. To address these problems, a high amount of bleach will be used during the production. It automatically has an impact on production costs.

The ash content of Kawui wood is included in ‘high’ category, as it is above 0.6%. It is also much higher than the ash content of E. pellita (Lukmandaru 2018), which is included in the medium category. According to Pari and Hartoyo, the ash content influences the production process before pulping process, i.e. wood chipping. High ash content adversely affects the durability of wood saw blades.

Conclusion

The observations of wood anatomy, i.e. fibre proportions, fibre dimensions and fibre derived values, indicate the quality of Kawui wood is classified in Grade II–IV. Meanwhile, the chemical composition of Kawui, i.e. extractive, holocellulose, α-cellulose, lignin and ash contents, are in the medium-high category. In overall, Kawui wood is suitable for medium quality pulp and paper production.

Recommendation

Despite of its classification as a lesser known species, the prospective and potential of Kawui wood as an alternative material for commercial wood is reliable. Nevertheless, further studies are required to investigate the silvicultural systems of Kawui wood, including its growth rate. In addition, feasibility analysis of Kawui-based products will be valuable to obtain detailed and comprehensive data about this wood.

Footnotes

Acknowledgements

The authors would like to express gratitude to Institute of Research and Community Services (LPPM) of Universitas Palangka Raya for the support under the scheme of the 2018 Dana DIPA PNPB, No. 042.01.2.400956/2019 of 20 June 2019 based on the Research Agreement No. 741/UN24.13/PL/2019.

Disclosure statement

No potential conflict of interest was reported by the author(s).

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