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The polysaccharides composition of bleached and unbleached pulp and paper is an important parameter for the characterization of their chemical and physical properties (Sundberg et.al 2003, Willfor et.al 2005a,b 2009) The alkaline delignification/pulping process involves a number of complicated reactions. The initial reaction between alkaline pulping liquor and polysaccharides is a salvation of the hydroxyl group by the hydroxyl ions and water. At the same time, the carboxyl group of the uronic acid is neutralized and the carboxylate groups are solvated, the salvation results in considerable swelling of the cell wall, which facilitates the penetration and diffusion of the pulping liquor (Stone 1957) and subsequently dissolves out the easily accessible low molecular weight polysaccharides. The lignocellulosic material contains a considerable amount of xylan, e.g hardwood and agricultural residues. The alkaline hydrolysis of the acetyl group also occurs at the early stage of pulping probably immediately when in contact with pulping liquor. In the alkaline pulping the chemical degradation of the polysaccharide chain has been shown partly an alkaline hydrolysis of glycoside bonds (Corbett and Richards,1957) and partly a reaction starting at the aldehydic end groups and proceeding as a successive “ peeling off” of the terminal units under formation of iso-saccharinic and other hydroxyl acids(Kenner 1957). The peeling off proceeds until a rearrangement of the polysaccharide terminal unit to a meta saccharinic acid configuration or until the degradation reached to monomer substituted in the 2 positions, the later is the case with xylan, which is frequently substituted by methyl glucouronic acid units in the 2 positions. This is one of the reasons why xylan is fairly hot alkali resistant. However alkaline hydrolysis of the glycosidic bond at 170 oC always forms new starting points for peeling-off reactions. Thereby monosidic bonds have been found to be considerably more resistant than are glucosidic, galactosidic, and xylosidic bonds (Lindberg 1958). There are differences in the rate of hydrolysis of polysaccharides due to differences in the reactivity rate of the glycosidic linkages. The type of monosaccharide, anomer linkage neighboring activating and deactivating groups, and their positions and the hydrogen bond are major influencing factors ( Yoneda et.al 2016, will for et.al 2005). Apart from these chemical differences in the behavior of the various polysaccharides in the alkaline pulping crystalline of cellulose being to a considerable extent is less accessible to degradation than amorphous Hemi cellulose. The later, however, degraded to liner fragments with definite crystallization tendency. The behavior of xylan during the alkaline pulping indicates that xylan loses some of its bulkier substituents at a fairly early stage where after somewhat degraded xylan is adsorbed in the fiber walls in a less accessible state that in the native form, possibly by an inter crystallization with the cellulose at the microfibril surfaces. However, the alkaline hydrolysis of acetyl groups and removal of uronic acid groups are the prerequisite for the re-precipitation of xylan as these form irregularities in the straight chain configuration of polysaccharide

Chemically wood is comprised mainly of three macromolecular species cellulose, hemicelluloses, and lignin. Pulps contain hemicelluloses along with cellulose with traces of lignin. Knowledge about the polysaccharide composition is very important in material characterization (Swiatek et.al 2020, Willfor et.al 2005a,b 2009, Sundberg et.al 2003). Polysaccharide composition is determined by acid hydrolysis and qualitative and quantitative analysis of monomers by different analytical methods (Nitsos et al 2019, Haykiri-Acma et al 2019, Black and Fore 1996). Cleavage of the glycosidic bonds of the polysaccharides occurs during hydrolysis and releases the monomers of polysaccharides. Acid hydrolysis is mostly preferred by means of sulphuric acid, trifluoroacetic acid, etc.( Vedovatto et al 2021, Bose et.al 2009, Galant et.al 2015, Sundberg et. al 1996, Marques et.al 2010). The main advantage of acid hydrolysis is the high conversion, shown in the complete solubilization of the starting raw material and commonly called “ total hydrolysis”. Substrates that are resistant to hydrolysis because of high crystallinity or poly uronic acid are reliably converted.

Experimental

Polysaccharides composition of wood, unbleached and oxygen-treated pulp of Anthocephulus indicus :  Holocellulose was isolated by the standard method (Wise et.al) and subjected to acid hydrolysis

Total hydrolysis of holocellulose ( Seamen et.al,1954, Bose et.al 2009)

Holocellulose (0.10 g) was weighed and transferred to a test tube and 72 % sulphuric acid (W/W) (1ml) was added. The test tube was placed in a water bath at 20^oC and the mixture was stirred occasionally with a glass rod to promote dissolution. After 1 hour the hydrolysate was poured into a beaker (100ml) was diluted with distilled water to 28ml. The beaker was covered with a glass plate was autoclaved at 120^oC for 1 hour. The resulting solution was cooled and diluted to 80ml. This solution was neutralized by adding a suitable quantity of anion exchange resin (IR-45,20-50 mesh). After washing the resin with distilled water (1.25 ml), the resulting solution was evaporated to dryness in a vacuum evaporator. Finally, water was added to give a volume of 5 ml.

Reduction and acetylation ( Steward et.al 1973)

To the above solution, sodium borohydride (20mg)was added and the solution was allowed to stand for 4 hours. The sodium ions were by adding a small amount of cation exchange resin ( Dowex 50,50-100 mesh). After standing for 5 minutes the solution was filtered through a sintered crucible and the resin was washed with water: ethanol (1:1 V/V) mixtures (5 X 3ml). The filtrate and washing were collected and evaporated under a vacuum to dryness. Alditols (reduced product), thus obtained were refluxed for 4 hours with a mixture containing equal amounts of acetic anhydride and pyridine (2ml). The acetylated sample was poured into ice-cold water and alditol acetates were isolated with methylene chloride (2X10ml) methylene chloride was evaporated to get a concentrated solution of alditol acetates thus obtained, which was chromatographed.

Gas-liquid chromatography of hydrolysis products

Analysis was performed on a Perkin Elmer model 3920B chromatograph equipped with a glass column and a flame ionization detector. To facilitate the identification of individual mono sugar.  CO-GC of individual mono sugar was performed and peak enhancement was noted besides comparing the retention time of individual sugar with those of the reference sample. The relative percentage of each sugar was calculated on peak area bases.

Acid hydrolysis of holocelloluse of Anthocephalus indicus wood, unbleached pulp producing using 12 5 and 14% alkali during pulping corresponding to kappa number 36.49 and 24.76, and oxygen-treated pulps were carried out. Rhamnose, arabinose, xylose, mannose, galactose, and glucose were identified by gas chromatography. In each case, the relative percentage of glucose was exceptionally high as compared to another constituent (Table- 1). It is expected that a major portion of the glucose might have been generated from the cellulose while hemicelluloses may have contributed for a small portion.

The relative percentage of xylose was higher except for glucose as compared to other neutral sugar. It was 21.42 % for wood, 14.62 %, and 13.57% for unbleached pulps produced using 12 5 and 14% alkali during pulping and it was 12.63 % and 11.20 % for respective oxygen-treated pulps. These data reveal that the main hemicelluloses of Anthocephalus indicus was xylan, presence of other monomers viz. Rhamnose, arabinose, mannose, galactose, and glucose indicated the presence of other hemicelluloses in minor quantities along with a substantial amount of cellulose.

Comparison of Sugar Composition of Wood, unbleached pulps, and Oxygen treated pulps 

Results recorded for the sugar composition of Anthocephalus indicus wood holocellulose revealed that wood contains a comparatively higher amount of xylose (21.42%) as compared to 14.62 % and 13.57% for unbleached pulps producing using 12 % and 14% alkali during pulping. It was further decreased to 12.63 % and 11.20 % for respective oxygen-treated pulps, suggesting that during the course of pulping the hemicelluloses , xylose might have undergone chemical degradation leading to a decrease in relative percentage. xylose in pulp and further degradation during oxygen treatment. The relative percentage of rhamnose 0.54, 0.25, 0.20, traces and traces, arabinose 1.05, 0.40, 0.27, traces and traces mannose 2.14, 1.55, 1.50,1.48 and1.42, galactose 2.37, 1.89, 1.80, 1.72 and 1.50 and glucose 72.48, 81.29, 82.66, 84.07 and 85.55 for wood dust,  unbleached pulps producing using 12 % and 14% alkali during pulping and their oxygen treated pulps respectively. The descending trend in the relative percentage of these mono sugar except glucose which exhibited ascending trend indicated that almost all the hemicelluloses suffered degradation during pulping and subsequent oxygen treatment stage. Ascending trend exhibited by the glucose may be attributed to the more resistant nature of cellulose during pulping and subsequent oxygen treatment stage as compared to hemicelluloses.

A perusal of data for the ratio of xylose to other of mono sugar revealed that the xylose to rabinose ratio was increased while xylose to mannose and xylose to galactose ratio was decreased on pulping and subsequent oxygen treatment ( Table-2). These results indicated that perhaps rahaminose and arabinose-containing hemicelluloses are more labile to degradation during pulping and subsequent oxygen treatment stages as compared to main hemicelluloses xylan. While hemicelluloses containing mannose and galactose are comparatively more resistant to alkaline degradation and even in the subsequent oxygen treatment stage. The decreasing trend in xylose to glucose may be due to the more resistant nature of cellulose during pulping and subsequent oxygen treatment stage.

Table  1 Sugar composition of  Anthocephalus indicus wood, unbleached and oxygen-treated pulps

S. No	Particular	Relative retention time, min	Wood dust	Unbleached Pulp		Oxygen treated Pulp
				12% Alkali	14% Alkali	12% Alkali	14% Alkali
1	Rhamnose	0.25	0.54	.025	0.20	traces	traces
2	Arabinose	0.74	1.05	0.40	0.27	traces	traces
3	Xylose	1.00	21.42	14.62	13.57	12.63	11.20
4	Mannose	1.79	2.14	1.55	1.50	1.48	1.42
5	Galactose	2.05	2.37	1.89	1.80	1.72	1.50
6	Glucose	2.34	72.48	81.29	88.66	84.17	85.88

Table  2  Ratio of Xylose to other mono-sugar

S. No	Particular	Wood dust	Unbleached Pulp		Oxygen treated Pulp
			12% Alkali	14% Alkali	12% Alkali	14% Alkali
1	Xylose : Rhamnose	39.66: 1	58.48:1	67.85:1	-	-
2	Xylose : Arabinose	20.40: 1	36.55:1	50.26:1	-	-
3	Xylose : Mannose	10.01: 1	9.43: 1	9.05: 1	7.99: 1	7.89: 1
4	Xylose : Galactose	9.04: 1	7.74: 1	7.54: 1	7.46: 1	7.46: 1
5	Xylose : Glucose	0.30: 1	0.18: 1	0.17: 1	0.15: 1	0.13: 1

1. Black GE, Fox A. Recent progress in the analysis of sugar monomers from complex matrices using chromatography in conjunction with mass spectrometry or stand-alone tandem mass spectrometry. J Chromatogr A. 1996;720(1–2):51–60. 2. Bose SK, Barber VA, Alves EF, Kiemle DJ, Stipanovic AJ, Francis RC. An improved method for the hydrolysis of hardwood carbohydrates to monomers. Carbohydr Polym. 2009;78(3):396–401. 3. Corbett W.M and Richards G.N (1957) Svensk papperslidin 60:791 4. H. Haykiri-Acma, S. Yaman (2019) “Effects of dilute phosphoric acid treatment on structure and burning characteristics of lignocellulosic biomass” J. Energy Resour. Technol. Trans. ASME, 141 (8) 5. Galant AL, Kaufman RC, Wilson JD. Glucose: detection and analysis. Food Chem. 2015;188:149–160 6. Kenner J (1957) J.chem Soc; 3019 7. Lindberg B (1958) Acta chem. Scand 12:340 8. C.K. Nitsos, P.A. Lazaridis, A. Mach-Aigner, K.A. Matis, K.S. Triantafyllidis “Enhancing lignocellulosic biomass hydrolysis by hydrothermal pretreatment, extraction of surface lignin, wet milling and production of cellulolytic enzymes” ChemSusChem, 12 (6) (2019), pp. 1179-1195 9. K. Swiatek, S. Gaag, A. Klier, A. Kruse, J. Sauer, D. Steinbach. "Acid hydrolysis of lignocellulosic biomass: sugars and furfurals formation". Catalyst vol. 10, no. 437, pp. 1–18, 2020. 10. Sundberg A, Sundberg K, Lillandt C, Holmbom B. Determination of hemicelluloses and pectins in wood and pulp fibres by acid methanolysis and gas chromatography. Nordic Pulp Pap Res J. 1996;11(4):216–226. 11. Sundberg A, Pranovich AV, Holmbom B. Chemical characterization of various types of mechanical pulp fines. Anglais. 2003;29(5):6. 12. Stone J.E (1957) Tappi 40:239 13. F. Vedovatto, G. Ugalde, C. Bonatto, S.F. Bazoti, M.A.Mazutti H.Treichel, G.L. Zabot, M.V. Tres “Subcritical water hydrolysis of soybean residues for obtaining fermentable sugars” J. Supercrit. Fluids, 167 (2021) 14. Willför S, Sundberg A, Pranovich A, Holmbom B. Polysaccharides in some industrially important hardwood species. Wood Sci Technol. 2005; 15. Willför S, Pranovich A, Tamminen T, Puls J, Laine C, Suurnäkki A, Saake B, Uotila K, Simolin H, Hemming J, Holmbom B. Carbohydrate analysis of plant materials with uronic acid-containing polysaccharides-A comparison between different hydrolysis and subsequent chromatographic analytical techniques. Ind Crops Prod. 2009;29(2–3):571–580. 16. Yoneda Y, Hettegger H, Rosenau T, Kawada T. Additive tendency of substituent effects onto rate constant of acidic hydrolysis of methyl 4-O-methyl-beta-D-glucopyranoside. Chem Select. 2016;1(18):5715–5720. 17. Marques G, Gutiérrez A, del Río JC, Evtuguin DV. Acetylated heteroxylan from Agave sisalana and its behavior in alkaline pulping and TCF/ECF bleaching. Carbohydr Polym. 2010;81(3):517–523.