Biometric characteristics of bamboo and other natural fibers.
This chapter explores the characteristic potentials of alkaline sulfite anthraquinone and methanol (ASAM) pulping of bamboo culms (Gigantochloa scortechinii) in the industrial production of pulp and paper for packaging. The biometric characterization results of the bamboo culms show that bamboo has fiber length of 1980–4000 μm, Runkel ratio of 0.86, and flexibility ratio of 50.19, while the chemical compositions of the bamboo contain 47.67% cellulose, 68.33% holocellulose, 26% lignin, and 3.69% solvent extractive, which give good paper quality fiber and also falls within the range of wood from softwoods species. The study revealed that the optimum ASAM pulping parameters was at 16% NaOH and 90 min cooking time, resulting in Kappa number of 14.17 and pulp yield of 49.06%, while the paper tensile index of 20.86 Nm/g, tear index of 22.64 mN.m2/g, and brightness of 39.32% were obtained. The biometric and chemical characterizations of the ASAM pulped bamboo have shown that ASAM pulped bamboo produces high-quality pulp and paper suitable for packaging and printing paper. Hence, the use of bamboo materials can reduce the burden on the forest, due to the increasing demand for paper and paper products, while supporting the natural biodiversity.
- alkaline sulfite anthraquinone and methanol
- pulp and paper
Despite the global digital revolution and consequence to the variation in the global regional market shares with respect to the production capacity and consumption pattern, the pulp and paper industry has experienced dramatic growth in the recent years. The recent trend of packaging that is gaining consumer’s attraction is the emergence of paper and paperboard packaging due to its effective solutions in food and beverages, healthcare, manufacturing, personal care and other industries . The demand of innovative and convenient packaging features is synonymous to the changing lifestyle of people. Conversely, the growth of the pulp and paper industries has been hindered since the major raw material for pulp and paper manufacturing is wood, which is drastically depleting. The industries are saddled with various challenges from ecological protocols, energy consumption and economic survival; therefore, modified technologies that are environmentally benign and economically viable are being sought to enhance the survival of the industries through the twenty-first century and beyond. Various researchers have reported the replacement of wood with non-wood as the immediate panacea to the challenges in the pulp and paper industries. In the array of these non-woods is bamboo, which is a fast-growing monocotyledon plant found in temperate, subtropical and tropical areas with diverse groups of plant in the grass family with 75 genera and 1250 species of bamboo worldwide . Conventionally, bamboo has gained commercial usage in the field of construction (poultry cages, shade blinds,), furniture and handicrafts (vegetable baskets, incense sticks, tooth picks, chopsticks, skewers, barbeque sticks and joss paper) .
1.1. Socio-economic benefits of bamboo
Traditionally, being one of the oldest materials used worldwide with wide applicability, bamboo industry is a flourishing business especially at the small-scale level. Since the engine that drives the growth of any economy is the small-scale industries, bamboo business plays a very significant role in the overall growth of an economy. Statistics revealed that of all forests in the world, bamboos occupy approximately 36 million hectares at the rate of present expansion of 3.2% of total forest area . Bamboo can be divided into four regions based on supply chain in various continents of the world and this include Asia-Pacific bamboo region (India, China, Indonesia, Myanmar and Malaysia) [5, 6], which contributes about 65% global supply of bamboo. This is closely followed by American bamboo region (North American and Latin American countries) which contributes about 28% and African bamboo region which contributes about 7% supply. Asia-Pacific bamboo region is expected to continue to dominate the global bamboo market both in terms of value and volume by 2027. Consequently, the cumulative average growth rate (CAGR) of bamboo is projected at 11.8% CAGR. Hence by the end of 2027, nearly three-fourth of global bamboo revenue will be accounted by the region . This projection is based on the versatility of bamboo entrepreneurship, which ramifies wood and furniture (timber substitute, plywood, mat boards, flooring, furniture, outdoor decking), construction (scaffolding, housing, roads), food (bamboo shoots), pulp and paper, textile, agriculture, charcoal and handicrafts, regarded as being one of the key instruments in uplifting the socio-economic status of the poor and underprivileged people in a community. Being the largest consumer of lignocellulose biomass, pulp, paper and paper packaging industries are expected to benefit from this wide availability of bamboo.
2. Suitability of bamboo for pulp and paper
Amid the collection of non-wood natural fibers, bamboo has gained wide applicability in pulp and paper industry. Several reports on the potential of bamboo revealed its potential as a better raw material for pulp and paper packaging because of its long fiber, since the fiber length is an important factor in paper making. The fiber length is similar with what is obtained in softwood fiber properties, hence making bamboo as an ideal replacement in pulp and paper manufacture. For instance, the fiber length has impacts on the physical and mechanical properties of paper such as tear strength and folding endurance. These spectra of properties make bamboo very economical in terms of management and can easily be transported to the pulp and paper mills .
The large lumen width and fiber diameter characteristic of bamboo contribute positively to the effective beating process . Like other wood species bamboo fibers have many similar benefits than wood such as: (1) bamboo can be chipped in a similar manner to wood, (2) bamboo is a low-cost crop due to low maintenance, (3) bamboo chips can be blended with wood chips and (4) bamboo is a fast-growing fiber source. Almost all studies suggested that papers made from bamboo are relatively stronger than those made from softwood. Successful development of bamboo pulping requires a technology which is able to exploit the full potential of this raw material. Specifically, this means that selectivity in pulping and bleaching has to be on a high level resulting in pulps with high yield and good strength properties.
2.1. Biometric characteristics of
Table 1 shows the biometric characterization of the studied bamboo (
|Biometric parameters||Type of fibers|
|FL (μm)||1980 ± 3.3||1890||840||810||19|
|FD (μm)||17.27 ± 3.7||3.45||10.1||16.75||10|
|LD (μm)||8.66 ± 2.3||6.78||4.4||4.12||4.5|
|CWT (μm)||0.86 ± 0.20||3.93||0.87||0.49||0.9|
|Runkel ratio||50.14 ± 3.6||20.29||53.15||67.05||52.63|
|Flexibility ratio||114.64 ± 3.6||111.2||44.21||32.42||152.63|
|Slenderness ratio||This study|||||||||
Many studies have reported that the fiber length of bamboo is generally greater than hardwood and is similar to softwood . Fiber length may actually be a detriment to good strength properties, as in the case of certain non-wood fibers, such as bamboo, bagasse and cotton. In such a case, fibers are longer than 2 μm . The long fibers are covered with fibrils, fines, and the large fibrils effectively serve to bridge the gaps between the naturally rough surfaces of adjacent fibers. In this way, long fibers have an effect on the strength of a bond and especially its toughness, which is characteristic of the bonds between natural paper making fibers and which is completely lacking with bonds between smooth viscose fibers. On the other hand, water drains from long fiber pulps more rapidly, and this is a point in their favor. Therefore, for pulp and paper production, species with higher fiber lengths are preferred since a better fiber net can be achieved, resulting in a paper with high resistance. The biometric characteristic of
The average fiber diameter of
2.2. Chemical compositions
The chemical compositions of
|Composition %||Natural fibers|
|Holocellulose||68.33 ± 3.7||70.50||70.90||74.46|
|Cellulose||47. 67 ± 3.4||43.30||48.20||44.31|
|Lignin||26. 00 ± 2.3||24. 50||17.20||25.20|
|Solvent extraction||3.64 ± 3.2||3.90||3.50||3.40|
|1% NaOH||19.82 ± 3.5||25.10||49.20||10.26|
|HWS||5.53 ± 1.2||6.50||16. 20||2. 81|
|CWS||4. 61 ± 1.4||—||10.70||1.47|
|Ash||1.98 ± 0.33||1.40||16.60||0.32|
|Silica||1.56 ± 0.25||—||14.90||—|
The mechanical properties of final paper are related to the amount of hemicellulose and cellulose contents of raw materials. In addition, polysaccharides such as cellulose and hemicellulose have a positive effect on pulp yield of alkaline pulping process . Raw material with more than 34% of cellulose content can be used for pulp and paper production . The cellulose content of
The lignin content of
3. Pulping of bamboo (
Traditionally, kraft pulping has been the most commonly reported pulping milieu for bamboo species . This is due to its strong bundle sheathes, impenetrable epidermis, a complete absence of ray cells and limited area of conducting tissues. As good as this pulping technique is, it is saddled with a lot of environmental legislative issues. The present paradigm shift in the pulp and paper making toward environmental benign pulping has informed the search for better pulping method for bamboo species.
3.1. Drawbacks of the conventional commercial pulping technique
The conventional commercial pulping procedures of annual plants include both kraft and soda pulping. The major drawback of these pulping protocols is that in the case of alkaline cooking liquors, apart from the delignification process, significant decomposition of carbohydrates portion of the lignocellulose biomass is observed by peeling-off reactions and alkaline hydrolysis. Optimum alkaline cooking condition is pertinent as excess alkaline loading could result in lowering of the ISO brightness due to the concept of alkaline darkening. Furthermore, sodium hydroxide easily dissolves phenolic lignin structures; besides, lignin undergoes condensation reactions under strong alkaline conditions which reduce the reactivity of residual lignin. In the like manner, strong alkaline cooking liquors dissolve high silica content of annual plants and precipitates evaporation problems in soda recovery boilers and in the causticizing plant .
In contrast, conventional kraft pulping has been used commercially for paper packaging from annual plants such as wood and some bamboo species, due to good paper properties. Kraft pulping has been found suitable for all ranges of fiber sources. It gives paper of high tensile strength and also high efficiency of the recovery of cooking chemicals . In non-phenolic lignin moieties only β-ethers are cleaved. This has also an impact on bleaching. Among the disadvantages of kraft pulping process, low yield pulp, high consumption of bleaching chemicals, emission of obnoxious odor from the pulping process and large mill size require a tremendous capital investment.
Compared to soda pulps, soda/anthraquinone (soda/AQ) pulps have slightly better bleaching ability, higher yield and sometimes better strength. Similarly, alkali sulfite pulping had been known to give good strength properties and significantly higher yields than kraft process . The addition of anthraquinone helped to reduce Kappa number from the unbleached pulp.
In order to overcome the abovementioned challenges, Patt and Kordsachia  discovered that the addition of methanol or ethanol extended delignification to levels below kraft or sulfite pulps. They named their process as alkali-sulfite-anthraquinone methanol (ASAM). Unlike the conventional pulping protocols, ASAM pulping process has dual advantages of paper properties and higher pulp brightness. In addition, ASAM pulping results in pulp with high pulp yield, low Kappa number and high paper strength. Furthermore, the obnoxious odor from methyl mercaptan that is generated during kraft pulping is completely absent in ASAM pulping.
3.2. Mechanism of alkaline sulfite anthraquinone and methanol (ASAM)
Alkaline sulfite anthraquinone with methanol pulping known as the ASAM process was developed by Patt and Kordsachia in 1986 as an alternative cooking process option for soda and kraft pulping processes. According to the authors, the chemical materials that make up the ASAM process are sodium sulfite (Na2SO3), sodium hydroxide (NaOH), anthraquinone (AQ) and methanol (CH3OH). These materials play a unique role in the pulping milieu because, sodium sulfite and sodium hydroxide are the major ingredients of the alkaline sulfite process while the anthraquinone and methanol act as catalysts to enhance the chemical penetration delignification of the lignocellulose biomass. Table 3 shows the characteristics of cooking parameters in the ASAM pulping process, while Table 4 gives a summary of the key role of each chemical constituent in ASAM blend.
|Total alkali (NaOH)||20–25 o.d|
|Alkali ratio (Na2SO3/NaOH) or (Na2CO3/NaOH)||80/20–70/30|
|Methanol||10–15 by vol|
|Cooking time at maximum temperature||120–180 min|
|Total alkali (NaOH)||Accelerant delignification|
Increases the cooking PH
|Alkali ratio (Na2SO3/NaOH) or (Na2CO3/NaOH)||Sodium hydroxide accelerant delignification in comparison with sodium carbonate|
Sodium sulfite changed lignin to solvable material
Sodium carbonate generates pulp with the strongest tensile index, highest pulp yield, and highest brightness than sodium hydroxide
|Anthraquinone (AQ)||Enhances the delignification rate|
Act as effective stabilizer in both wood and non-wood polysaccharides
|Methanol||Enhances chemical penetration into the woody chips|
Methanol improves the solubility of the AQ
|Raw material||Pulping parameters||Total yield||Kappa no.||Tensile index (Nm/g)||Burst index (kPa.m2/g)||Tear index (mN.m2/g)||Brightness (%)||Reference|
|Bamboo (||NaOH: 16%; AQ: 0.1%|
T: 90 min; Temp: 170°C
|NaOH: 17%; AQ: 0.1%|
T: 120 min; Temp: 175°C
|Whole jute plant||NaOH: 22%; AQ: 0.1%|
T: 60 min; Temp: 170°C
|NaOH: 22.5%; AQ: 0.1%|
T: 135 min; Temp: 180°C
|0.1%; Methanol: 10%|
T: 120 min; Temp: 170°C
|NaOH: 25%; AQ: 0.1%|
T: 90 min; Temp: 170°C
|NaOH: 17%; AQ: 0.1%|
T: 120 min; Temp: 180°C
The mechanism of ASAM pulping process can be viewed with respect to the cooking parameters.
3.2.1. Effect of sodium hydroxide addition in ASAM pulping
Sodium sulfite and sodium hydroxide are two major active constituents in ASAM pulping process playing the dual role of delignification and increasing pulp brightness. Several research trials toward the effect of replacement of sodium hydroxide with sodium carbonate or sodium peroxide in the ASAM pulping process have been reported. The advantage of sodium hydroxide in ASAM pulping is that NaOH tends to accelerant delignification than sodium carbonate; furthermore, by applying NaOH as a source of alkali charge, the initial pH of the white cooking liquor enhances leading to the dissolution of more lignin and carbohydrates (hemicellulose) .
Apart from the substitution of sodium hydroxide with sodium carbonate in ASAM pulping, attempt has been made with the use of sodium peroxide. It was reported that sodium carbonate substitution gave better pulp products due to the fact that the sodium carbonate-substituted ASAM mixture gave pulp with the stronger tensile index, higher pulp yield and higher brightness  due to greater delignification process. This results from the fact that solution of acid soluble lignin contributed to lignin dissolution. The relatively low pH of spent liquor at high temperature results in the partial cleavage of α-ether bonds in lignin [40, 41]. On the other hand, the use of alkaline sodium sulfite as an additive in the ASAM process produces a low Kappa number, high pulp yield and high brightness. In addition, the production cost is also significantly reduced and the total alkalinity consumption becomes less .
3.2.2. Effect of anthraquinone (AQ) addition
The addition of anthraquinone (AQ) in white cooking liquor increases the delignification rate due to the rate of decrease in the lignin content of wood or non-wood as the alkali consumption during the alkaline pulping process progresses. This can be divided into three phases: (1) initial reaction, (2) bulk delignification and (3) residual delignification.
In the initial reaction phase, alkali is consumed in deacetylation reaction, in neutralization of wood or non-wood acids and in dissolution of readily soluble wood or non-wood carbohydrate components (hemicellulose, tannins, etc.); hence, very little actual delignification occurs. More lignin is eliminated in the period of bulk delignification phase. This elimination occurs much more quickly than the third stage (residual delignification) [41, 42]. As a result, the proportion of lignin removal in polysaccharides happens slowly. Thus, this is only true when a sufficient amount of alkali charge is available. Thereupon, by adding AQ to the cooking liquid, more alkalinity can be stored for the bulk delignification volume and more lignin can be removed [38, 42]. On the other hand, AQ has the role of an effective stabilizer in both wood and non-wood polysaccharides. AQ is effective at extremely lower dosage levels of 0.05–0.1% on oven-dry wood, giving good results in most cases .
3.2.3. Effect of methanol addition
The addition of methanol at the initial pulping stage enhances chemical penetration into the woody chips by increasing the solubility of lignin, subsequently, producing a uniform (homogeneous) chemical performance in the cooking time and also suppresses the dissociation of the inorganic pulping chemicals. The trapped air from the woody cells could be removed by raising the pressure of the digester, thus accelerating the penetration of chemicals into the wood cells [44, 45].
In ASAM pulping, it is important to ensure that alkali has penetrated into the center of the chip prior to rising the temperature above 140°C, since undesirable lignin condensation reactions can occur at high temperatures in the absence of alkali [46, 47]. The use of methanol is preferred over ethanol in ASAM pulping protocol because of the lower boiling point that results in lower energy consumption for recovery. In addition, compared to ethanol, methanol has less viscosity, polarity and surface tension. The low surface tension and increased pressure, together with the ability of methanol to dissolve resins, have a positive impact on the penetration of chemicals into the chips [48, 49].
Apart from enhancing chemical penetration during pulping, Sridach  discovered that methanol also improves the cellulose stability in the ASAM pulping, hence producing pulp with higher viscosity. This was achieved by suppressing, stopping the reaction or slowing down the transformation of the cellulose aldehydic functional groups into keto groups that initiate the peeling reaction. Due to the use of methanol in the cooking liquor, more penetration of chemicals into the chips occurs. Raising pressure of the digester and more air removal of chips are the two main ways of improving the penetration of chemical materials into wood or non-wood chips. Therefore, adding methanol while an ASAM cooking liquor is in the process of penetrating the chips leads to a higher pressure of the digester. As a result, the entrapped air of the chips is displaced, and chemical materials can penetrate into both wood and non-wood chips. Consequently, more delignification happens and fibers can be easily separated .
3.2.4. Advantages of ASAM pulping
In comparison with kraft pulping process, the ASAM pulping process has a higher digester pressure of 1.3–1.4 MPa and the cooking temperature of 5–10° . Several studies have considered the application of ASAM in the cooking process of both hard and soft wood. Moradbak et al.  reported that E
Several reports have shown some of the unique advantages of ASAM pulping process. These include (i) prevention of air pollution, (ii) high delignification rate, (iii) high brightness of pulp, (iv) high pulp yield and (v) ease of pulp bleaching .
3.2.5. Reactivity of ASAM pulping
A review of the reactivity of alkaline sulfite anthraquinone and methanol (ASAM) pulping process shows that the information available is relatively scarce, fragmented and yet to gain adequate commercial applications. Previous studies have focused on either sodium-anthraquinone (Soda/AQ) pulping or alkaline sulfite-anthraquinone (AS/AQ) pulping. In pulping process, the parameters that are of most significance with respect to delignification and polysaccharide removal are alkali charge and cooking time [42, 47]. In addition, ASAM pulping process has better selectivity in comparison to kraft or soda pulping processes in terms of delignification, which leads to low Kappa number and high viscosity. Few studies have considered the application of ASAM in the cooking process of both hard and soft wood. Table 5 gives the summary of the reported pulping of lignocellulose biomass using ASAM pulping process on different lignocellulose biomass compared with the ASAM pulped bamboo (
The tear, tensile and burst indices of unbleached bamboo ASAM paper were within the range of 26.33–18.64 mN.m2/g, 24.8–17.87 Nm/g and 10.83–9.27 kPa.m2/g, respectively, which is suitable for packaging paper. The study revealed that the optimum ASAM pulping parameters were at 16% NaOH and 90 min cooking time, resulting in paper having tensile index of 20.86 Nm/g, tear index of 22.64 mN.m2/g and brightness of 39.32%. Another advantage of this pulping process is to produce pulp with a low proportion of rejected material. Aldonic acid, which is present as a result of isolation from pulp hydrolyzates, indicates that stabilization takes place through conversion of the end group to the acid out of an oxidation reaction [42, 60]. Therefore, according to role of AQ and methanol in ASAM pulping process, one can expect high yields of ASAM bamboo unbleached pulp.
The study determined the technical feasibility of bamboo culms (
The authors are thankful to the Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia (UPM), and the Higher Institution Centre of Excellence (HICoE) Ministry of Higher Education Malaysia, Grant No. 6369107. Additional thanks are extended to the School of Industrial Technology, Universiti Sains Malaysia (USM) and the Federal Institute of Industrial Research Oshoidi Nigeria for technical support.