Kennedy Sichamba 1* and Vanessa Chanda 2
2 Former student, Copperbelt University, School of Natural Resources, Kitwe, Zambia
nessachandacmv@gmail.com
Abstract
Elephant grass (Pennisetum purpureum) and thatching grass (Hyparhenia rufa) are common grass species in Zambia. Elephant grass is a perennial plant, growing in uncultivated wetlands and is mainly used for making mats and baskets, while thatching grass grows in open
woodlands, and used for thatching houses in rural communities or burned out as a weed.
Chemical composition, kraft pulp yield, and burst strength of paper handsheets of the grasses were determined in order to evaluate their suitability for pulp and paper making. The grasses were first air dried for a week and then cut in 2cm pieces before analysis. Determination of chemical composition was conducted following the standard ASTM procedures with minor modifications. Kraft pulp was produced by cooking air dried grass material in 18% alkali solution containing sodium hydroxide and sodium sulfide, with 25% sulfidity. Pulp yield was expressed as percentage of the ratio of dry pulp to dry grass material. The pulp was bleached using hydrogen peroxide, sodium hypochlorite and sodium hydroxide to improve its brightness. The Bursting strength of paper handsheets was determined following the standard TAPPI T403 procedure. The cellulose, hemicelluloses, acid insoluble lignin and ash content of elephant grass and thatching grass were, respectively, 64.8%, 19.8%, 8.3%, 3.5% and 54.5%, 33.1%, 7.8, 2.9%.
The high holloceluloses and relatively lower lignin content suggest that both grasses can easily be pulped. The Pulp yields (51% and 65%,) were comparable to commercial pulp species such as switch grass and wood. The burst strength values were lower than other species previously studied. The handsheets were able to hold ink and glue quiet well. The results of this study suggest that both elephant and thatching grasses could be an alternative raw material for making pulp, paper and paper products, though addition research would be required to determine the optimal pulping conditions, to validate the findings of this study, and to investigate other pulp and paper properties. Paper from these grasses could be used to fabricate paper shopping bags to replace or reduce the use of environmentally harmful plastic bags in the country.
Key words: elephant grass, thatching grass, chemical composition, kraft pulp, handsheets Introduction
Paper consists of a web of fibers obtained from plants, bonded together primarily by hydrogen bonds. Any plant material can be used to make paper provided that it is readily available and produces high amount of fibers which are conformable and able develop strong hydrogen bonds (Smook 2002). Chemical content (cellulose, hemicelluloses, lignin and ash) is also an important yardstick of plant materials’ suitability for pulping and paper making. Usually, the higher the amounts of celluloses and hemicelluloses in a plant material, the more the pulp yield and the better the quality of fibers (Khali 2006). In addition, lower lignin content indicates that fibers can be extracted from the plant material more easily. Wood from trees is the principle raw material used in pulp and paper making since it is readily available and produces good quality fibers. However, using trees has a lot of challenges. Because of its' complex structure, wood requires a lot of chemicals to process; trees take long to mature; high deforestation rate is threatening the future of wood raw materials; and wood faces competition from other uses such as energy and construction. Because of these factors, recent research has focused on identifying alternative non-wood raw materials for paper making.
Because of their availability, several grass species have been investigated for their potential for pulp and paper making, and the results are promising. Work on suitability of elephant grass for paper making in South Africa showed that is it suitable for making paper, because both the pulp yield and paper strength properties were comparable to commercial plant species (Madakadze et al. 2010). To extract the fibers, the grass materials were cooked in 14% alkali solution
containing sodium hydroxide and sodium sulfide at 160oC for two hours. The pulp yield was 50% (compared to 48% for switch grass, a commercial species), while the burst index was above 5.85 KPa.m-2g-1, suggesting that the grass was suitable for making high strength paper. Similar results were obtained from elephant grass growing in India (Reddy et.al. 2014). The pulp yield was 58% while the burst index was 4.98 KPa m2g-1. An earlier study by Madakadze et al. (1999) also found several warm seasonal grasses (switch grasses, big bluestem, cord grass, and sand reed) in Canada to be suitable raw materials for paper making. The pulp yield ranged from 44%
- 51%, and the burst index was above 5.0. KPa.m-2g-1 for all species. Jahan (2016) also found that umbrella palm grass (cyperus flabettiformic) is suitable for paper making. Both the pulp yield (55%) and the burst index (4.4 kPa.m 2 /g ) were similar to other grass species, although the α-cellulose content (32.2%) was lower, and the lignin content (24.0%) was higher than most grasses.
The aim of this study was to evaluate the pulp and paper making properties of elephant grass (Pennisetum purpureum) and thatching grass (Hyparhenia Rufa) growing in Zambia. The grasses are readily available in the country. Elephant grass is a perennial plant, grows in uncultivated wetlands and is sometimes used for making mats and baskets. Thatching grass on the other
Materials & Methods Chemical Composition
Subsamples of the raw materials were analyzed for ash, lignin, hemicelluloses and α-cellulose.
The air-dried grass materials were first grinded to pass through a 40-mesh screen according to TAPPI T 257 (“Sampling and Preparing Wood for Analysis”). The Ash content was determined according to ASTM D-1102 “Standard test method for ash content in wood and wood-based materials” (ASTM International, 1984), while the acid insoluble lignin content was analyzed according to ASTM D-1106 “Standard test method for lignin in wood” (ASTM International, 1984). Alpha cellulose and Hemicelluloses content were determined following the procedure by Rowel (2005).
Pulping Procedure
To extract fibers, the grass materials were cooked in 18% alkali solution containing sodium hydroxide and sodium sulfide at 25% sulphidity, with an initial liquid to material ratio of five.
About 180g (7.7% moisture content) of the grass material was weighed in a beaker, to which 25.3g of NaOH, 8.4g of Na2S and 937ml of water were added. The material was cooked for 8 hours at about 100oC while stirring with a glass rod. Additional water was added as required.
After cooking, the fibers were thoroughly washed with water to remove the excess chemicals and then refined using a domestic blender for about five minutes. Refining collapses the fibers to improve their conformability. Refined pulp was then screened to remove uncooked
materials. The fibers were then bleached to improve their brightness, by cooking in hydrogen peroxide, sodium hypochlorite and sodium hydroxide in series. Bleaching conditions used for each chemical followed those recommended by Biermann (1996), and are shown in table 1 below.
Table 1. Bleaching Conditions
Conditions Sodium Hypochlorite Hydrogen Peroxide Sodium hydroxide
Chemical addition 2% 2% 2%
Consistency 5% 10% 10%
Temperature 35oC 75 oC 95 oC
Time 1.5 hours 2 hours 1.5 hours
Ph 10 10 12
Hand sheet Making and Strength Test
To make paper handsheets, about 3.5g of air-dried pulp was thoroughly mixed with 1 liter of water in a blender to make pulp slurry. To form the mat, the slurry was poured on a mould which was placed in water and thereafter raised to allow the pulp settle on the mould as the water drains. The mat was then consolidated by gently pressing it between a cloth. The mat was then hot pressed under a cotton cloth using a hot-pressing iron to form the paper. Paper hand sheets were then prepared for determination of burst strength. Bursting strength test was performed using a Bursting tester (Mullen tester) according to TAPPI T403“Bursting Strength of Paper” (Tappi International, 1997). Greeting cards, business cards, envelopes and miniature
bags were then made from the handsheets to demonstrate the ink and glue holding capabilities of the paper.
Results and Discussion Chemical Composition
Cellulose, hemicelluloses, acid insoluble lignin and ash content of elephant and thatching grasses are shown in the table 2 below. The cellulose content of elephant grass (64.8%) was higher than that of thatching grass (54.5%), but the cellulose composition of both grasses were however higher than that of most hardwoods and softwoods, which range from 45% to 50%
(Smook 2002), as well as that of switchgrass (41.2%), a commercial specie used for pulp
production, (Madakadze et al. 2010). Cellulose content of elephant grass observed in this study was significantly higher than that of elephant grass growing in South Africa (45.6%) reported by Madakadze et al. (2010). The difference could be explained by differences in species, age and the harvesting season, as well as the extraction methods. The high cellulose content of the grasses was consistent with the lower lignin content (7.8 – 8.3%), and it suggests that the grasses can produce good quality pulp. The lignin content of the grasses was much lower than that of both softwoods and hardwoods (20-35%) as well as switch grass (23.89%) as reported by Madakadze et al. (2010). The low lignin content shows that fibers can be extracted from the grass using less delignification chemicals with mild conditions. The average ash content was lower than most grasses, suggesting that the grass could also be processed commercially with less difficult. These figures suggest that elephant grass and thatching glass could potentially be used for producing good quality pulp, but further research work is necessary to verify these findings.
Table 2. Chemical Composition of elephant grass and thatching grass (% ± SD) Elephant grass Thatching grass
Cellulose 64.8±0.75 54.5 ± 0.50
Hemicellulose 19.8±0.79 33.1 ± 0.83 Holocellulose 84.6±0.577 87.6 ± 0.58 Acid insoluble lignin 8.3±0.045 7.8 ± 0.15
Ash 3.52±0.03 2.96 ± 0.05
Pulp Yield
Pulp yield of elephant grass (51%) was lower than that of thatching grass (65%). Elephant pulp yield was comparable to the yield of most of softwoods and hardwoods (45-50%), and other grasses previously studied such as elephant grass (50%) and switchgrass (48%) as reported by Madakadze et al. (2010). But Reddy et al. (2014) reported elephant grass pulp yield of 58%, slightly higher than the yield obtained from the current study. The difference was probably due
attributed to incomplete extraction and screening. Open air cooking was used to extract the fibers, at much lower temperatures (below 110oC), and the pulp was not thoroughly screened to remove uncooked materials due to limited equipment. However, the higher pulp yield was consistent with high cellulose and hemicelluloses content of the grasses. Species chemical composition is one of the principal factors that affect the chemical pulp yield. Results of this study suggest that both elephant grass and thatching grass could potentially be used to produce pulp. However, follow-up work should be done to extract fibers at optimum
conditions, followed by sufficient screening to verify these results. Further work should also be done on several other species of elephant and thatching grasses growing in Zambia.
Burst strength
Paper hand sheets of elephant grass had an average burst index of 1.96 kPa.m2.g-1 while that of thatching grass had an average burst index of 1.94. kPa.m2.g-1. Both were much lower than other grasses studied previously like elephant grass growing in Southern Africa (over 5.85 kPa.m2.g-1) (Madakadze et. al (2010), elephant grass growing in India (4.98 kPam2.g-1) (Reddy et al. (2014) and switchgrass (Madakadze et al.2010). Incomplete defibration and screening leading to weaker interbiber bonding due to uncooked materials in pulp, might have
contributed to the lower bursting strength of paper observed in this study. Bleaching improved the paper brightness (Figure 1a), and elephant grass pulp was brighter than thatching grass pulp, probably due to higher cellulose content of elephant grass. The paper was able to hold ink and glue reasonably well, as seen from the products - shopping bags and envelope - which were crafted (figure 1b), suggesting that paper from thatching grass could be used to manufacture products like paper shopping bags and envelopes, where glue is applied.
Figure 1. (a) Brightness changes during bleaching, (b) Paper hand sheets fabricated from thatching grass fibers, and a shopping bag.
Summary and Conclusions
Results of this preliminary study suggest that elephant grass and thatching grass could potentially be used for producing pulp and paper. The holocellulose content was high while lignin content was relatively lower. The pulp yield was comparable to some of the species used commercially. The low bursting strength could be improved by adding chemical additives.
Additional work would be needed to determine the optimal pulping conditions, and to test the physical, mechanical and chemical properties of both pulp and paper from these grasses. The abundance and fast growth are additional advantages these plant materials possess as
a b
alternative raw materials for making paper. Paper produced from the resources could be used to make paper shopping bags (as illustrated in this study) or other fiber-based products.
References
ASTM International, 1984. ASTM Standards D 1106, “Standard test method for lignin in wood”.
ASTM International, 1984. ASTM Standards D 1102, “Standard test method for ash in wood and wood based materials”.
Biermann,J.C (1996) Handbook of Pulping and Paper Making. Second eddition. Academic Press, California, USA.
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Reddy O.K, Maheswari U.C, Shukla M. et al. (2014). Preparation, Chemical Composition, Characterization, and Properties of Napier Grass Paper Sheets. Separation Science and Technology, Volume 49, pp. 1527-1534.
Rowell R. M (2005). Handbook of Wood Chemistry and Wood Composites. CRC Press, New York, USA.
Smook G.A (2002). Handbook for pulp and paper technologists, 3rd ed., Vancouver, Canada, Angus Wilde Publications.
TAPPI International, 1997. Tappi Standard T403. “Bursting Strength of Paper”.
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Biography
Numerical Study of Sorption Behavior of Piano Soundboard
1 Department of Wood Science and Technology, Faculty of Forestry and Wood Technology, Mendel University in Brno, Czech Republic
2 PETROF, spol. s r. o., Czech Republic
Abstract
Wooden musical instruments are strongly influenced by moisture content. Moisture induce the changes of tuning, defects and resonance properties of pianos. Minimization of wood hygroscopicity ensures the shape stability and stable acoustic properties of the soundboard during the changes of ambient climatic conditions (relative air humidity, temperature). Complex physical model of piano soundboard provides a reliable tool to describe the sorption properties of piano soundboard and possibilities to improve the resistance to moisture influence by thermal modification of wood. The main goal of modelling is shortening the development of the appropriate modification process.
The numerical model of thermally treated and untreated wood was designed, implemented into the FEM based computational software and validated on small samples (44 × 450 × 12 mm). The sorption properties of treated and untreated resonance spruce wood (Picea abies (L.) Karst) were
experimentally evaluated. All the samples were conditioned in the laboratory chamber to 7 states of the equilibrium moisture content (EMC). The duration of attaining the EMC (sorption dynamics), dimensional changes and the weight changes (density) were recorded and used for the validation of numerical model.
The model of moisture diffusion is based on the partial differential equation which stems from the transient form of Fick’s law. No significant influences of the temperature field on the diffusion were found, so all the tasks were solved isothermally. Validated numerical model was applied on the
geometries of real piano soundboards with respect to the wood fiber deflection. The longitudinal, radial and tangential diffusion coefficients were considered as a function of actual moisture content. The results show that the thermally modified soundboard reaches the EMC 3 times slower than untreated soundboard, what is caused mainly by the change of the diffusion coefficients. The influences of the moisture transfer coefficient value were also investigated to detect the influence of the surface layer varnishing. Its influence was found to be very significant – by reducing the coefficient in one order of magnitude (from 1E-7 to 1E-8 m·s-1), the time of reaching the EMC is 3 times longer. The numerical evaluation of piano soundboard showed the influence of individual parameters on its sorption behavior
and helped to reveal the key factors that need to be addressed during the development of thermally modified soundboards.
Biography
Papermaking Fines a Potential Wood-component for New Materials Outside the Paper Industry
Armin Winter, University of Life Science, Vienna, Austria
armin.winter@boku.ac.at
Abstract
In times of climate change and the development of country-specific bio-economy strategies, the demand for wood-based raw materials will rise. This research project aims to increase the utilization of the individual wood components. For example, the paper industry produces different types of paper fibres with different mechanical and chemical properties during the production process. Depending on the paper product, different fibre fractions can have both positive and negative effects. One of these fractions are the so-called primary fines and these fines have a great impact on the behaviour of pulp, on its processing, and on the characteristics of the resulting products. This fraction is produced during pulp digestion and is characterised by a short fibre length and a high lignin content. According to the standard, these are fibres that can be separated through a 200 mesh screen (76 µm plate). In order to make the subsequent bleaching process more efficient and cost-effective, this fraction should be separated and used for products outside the paper industry. Here, alternative ways of utilization are shown, such as oil-absorbing sponges, reinforcing fibers for biopolymers, high-density products for boards and additionally as starting material for nanocellulose. In order to put the potential of the primary fines into context, the resulting products will be compared with common reinforcing fibers such as microfibrillated cellulose fibres (MFC). Can the primary fines bring the same improvements as MFC fibers? In general, the energy consumption for fractionation is considerably lower compared to mechanical defibrillation. Additionally, the major challenge of establishing alternative utilization methods is shown, which is related to the processing properties of the resulting primary fines fraction.
Biography