Soda pulping of umbrella palm grass ( cyperus flabettiformic )

Chemical, morphological and anatomical characteristics of Cyperus flabettiformic were evaluated. It is characterized with low α-cellulose (32.2%) and moderate lignin (24.0%) content. Fiber length of C. flabettiformic was shorter (0.94mm) but slender ratio was extremely high (166). Anatomically, this grass is constituted by homogeneous parenchyma cells and the vascular bundles (11.8%). Delignification of C. flabettiformic was carried out by conventional soda pulping under varying alkali charge, time and liquor to material ratio at the boiling temperature. Total pulp yield was 55.0% with kappa number 15.5 at the cooking conditions of 12% alkali charge, 2 h of cooking and liquor to material ratio 10:1. Multivariate data analysis was used to evaluate the influence of alkali charge, cooking time and liquor ratio on pulp yield and kappa number. Alkali charge had a significant effect on pulp yield and kappa number. PLSR model showed better prediction efficiencies for pulp yield and PCR model performed better prediction for kappa number. Initial drainage resistance and papermaking properties of C. flabettiformic pulp were higher than other nonwood.


INTRODUCTION
Globally paper and board consumption is increased by 0.9% in 2014. 1 Its growth is even higher in wood resources scarce countries.Therefore, it is important to find alternative fibrous resources like industrial crops, agricultural wastes and recycle fibers.Furthermore, the valorization of agricultural residues is potential interest in such countries like Bangladesh.
Paper pulp from non-woody crops is mainly produced in developing countries and the raw materials which are most widely used are straw, bagasse and bamboo.Many studies have been carried out on the pulping of agricultural wastes like cotton stalks, corn stalks, rice straw, wheat straw etc. [2][3][4][5] Some non-wood plants can give more pulp per hectare per year than wood. 6. flabettiformic is a grass-like plant, commonly call umbrella plant.Globally this is cultivated as an ornamental plant.This is a fast-growing monocotyledonous plant with stems 100 to 150cm tall and up to 1cm wide as seen in Bangladesh (Fig. 1).Tanaka and Agata 7 showed that C. flabettiformic plant produced 4.63 kg/m 2 biomass and is considered as a highly productive herb.The biomass yield is higher than that of kenaf (Hibiscus cannabinus), which has been identified as a fast growing annual crop with a high fiber yield. 8here is no industrial application found of this grass.Kantawanichkul et al., 9 treated domestic wastewater by C. flabettiformis.It was found that this plant is suitable for wastewater treatment by vertical-flow constructed wetlands in tropical areas under hydraulic and organic loading rates within 121 mm/d and 198 kgCOD/ha.d,respectively.For the first time Tanaka and Agata 7 studied C. flabettiformis for pulping.But the chemical, morphological and morphological characteristics of the raw material were not evaluated.
The natural problem of grass in pulping is the high content of small parenchyma cells, generating fines in the pulp, which creates secondary fines during the refining.This behavior limits the utilization of grasses as pulping raw materials.Another drawback of grass is collection, which limits to build up full-size pulp mill based on grass.Recently, Bangladesh government has issued an order to use biodegradable bag.So, interest is growing to setup handmade paper industry for manufacturing paper bag.Different types of grass are grown in the different region of Bangladesh.The quantity of these grasses is too low in respect to set up a pulp mill.Also drainage resistance of these grasses is very high.Therefore, a few cottage pulp mills could be set up for the manufacture of handmade paper.Most of the grasses are easier to delignify than wood and non-wood.Establishment of handmade paper industry based of C. flabettiformis may reduce poverty in the rural area.
The objective of the work is to evaluate C. flabettiformis in terms of chemical, morphological and anatomical characteristics in respect to pulping.Pulping of C. flabettiformis is also carried out by varying cooking time, alkali charge and material to liquor ratio.As the purpose of this study is to produce handmade paper in the rural area, therefore, all cooking experiments are done at atmospheric pressure.Finally papermaking properties were evaluated.

Materials
C. flabettiformis was collected from Sothern region of Bangladesh and sun dried.It was cut to 2-3 cm in length, and ground (40/60 mesh) in a Wiley mill for chemical analysis.The moisture content of C. flabettiformis was determined for the subsequent experiments.

Morphological properties
For the measurement of fiber length, C. flabettiformis was macerated in a solution containing 1:1 HNO 3 and KClO 3 .A drop of macerated sample was taken on a slide and fiber length was measured under a digital microscope (Labomed, USA).Fiber width was determined from the cross section photograph taken in an image analyzer using software.

Pulping
Pulping of C. flabettiformis was done in an electrically heated open digester with constant stirring device.The pulping was carried out under the following conditions: -Alkali charge: 6, 8, 10 and 12% as NaOH.
-Liquor to material ratio: 6:1, 8:1, 10:1 and 12:1 -Temperature: boiling During cooking, the constant volume of the liquor inside the digester was maintained by adding hot water.After completing cooking time, pulp was washed with tap water till the removal of all chemicals, and screened on flat vibratory screener (Yasuda, Japan).The screened pulp yield, total pulp yield and screened reject were determined gravimetrically as percentage of o.d.raw material.

Statistical analysis
Multivariate Analysis techniques, namely Principal Component Analysis (PCA), Multivariate Linear Regression (MLR), Principal Component Regression (PCR) and Partial Least Square Regression (PLSR) have been used in the study besides descriptive univariate and bivariate analysis of data.Here for computation, The Unscrambler of its version 9.7 (CAMO Press AS) has been used.

Evaluation of pulps
C. flabettiformis pulps were disintegrated in a standard disintegrator.The handsheets of about 60 g/m 2 were made in a Rapid Kothen Sheet Making Machine according to German Standard Methods number 106.The sheets were tested for tensile, (T 494 om-96), burst (T 403 om-97), and tear strength (T 414 om-98) according to TAPPI Standard Test Methods.

Chemical characteristics
Table 1 shows chemical properties of C. flabelliformic and compared with lemon grass-a common grass in Bangladesh.Both cold and hot water solubilities of C. flabelliformic were higher than lemon grass as shown in Table 1.The cold water treatment removes a part of extraneous components like tannins, gums, sugars, inorganic matter and colored compounds present in lignocellulosic biomass whereas hot water treatment removes, in addition, starches.The higher water solubility adversely affects the pulp yield. 10 Acetone solubility of C. flabelliformic was 1.5%, which was much lower than lemon grass (4.3%).Acetone solubles content also adversely affects the paper machine runnability.High extractive contents in lignocelluloses are undesirable for pulping, bleaching and papermaking.It also affects the quality of paper because of shadow marking and paper manufactured from such type of fibrous material might show reduced water absorbency. 10One percent NaOH solubility of C. flabelliformic was 49.6%, which was higher compared to lemon grass (30.6%).The higher NaOH solubility of C. flabelliformic was possibility due to the presence of low molar mass of carbohydrates and other alkali soluble materials.Higher one percent NaOH solubility of the material indicated that milder cooking conditions may results satisfactory separation of cell wall to produce pulp of acceptable quality.
] From a chemical composition point of view, raw materials with 34% or higher cellulose content are considered as suitable for pulp and paper production.But in this study, this grass is considered for handmade paper production.In this consideration α-cellulose content is acceptable.Lignin is undesirable polymer for paper production and the removal of lignin during pulping requires the high amount of energy and chemicals.Lower lignin content of raw materials makes them suitable for delignification at milder pulping conditions (lower temperatures and chemical charges) to reach a desirable kappa number.Lignin content in C. flabelliformic was much higher than the lemon grass (24.0%vs 17.4%).
Ash content of C. flabelliformic was found much lower compared to lemon grass (1.5% vs 7.05%) (Table 1).The mineral components of lignocellulosic biomass represented as ash content.Higher ash content is undesirable during chemical recovery in the process.It is well established that transition metals such as Mn, Fe and Cu negatively affects pulp bleachability (hydrogen peroxide and oxygen) and bleaching selectivity. 15

Morphological characteristics
The role of morphological characteristics fiber length, fiber width and slenderness ratio of C. flabelliformic presented in Table 1.Fiber length for C. flabelliformic was 0.94 mm which was shorter compared to other grasses such as bamboo (1.91 mm), lemon grass (1.09 mm) and sofia grass (0.87 mm). 10,16 iber diameter for C. flabelliformic 8.4 µm, which was less than bamboo (16.8 μm), lemon grass (16.3 μm) and sofia grass (14.7 μm) respectively.7] The fibre diameter and cell wall thickness controlled the fibre flexibility.The thickness of cell wall affects most of the paper properties such as tensile strength, burst strength and folding endurance.The paper made of thick-walled fibers has low tensile strength, burst strength and folding endurance.The laboratory handsheets would be bulky, coarse-surfaced and had higher void volume.7] Slenderness ratio (fibre length/fibre diameter) affects the paper properties positively.As shown in Table 1, C. flabelliformic showed higher slenderness ratio (111.7)compared to lemon grass (66.9) and sofia grass (59.2).Generally, it is considered that if the slenderness ratio for the fiber is less than 70 then pulp would have poor strength. 17

Anatomy
The anatomical structure of C. flabelliformic was studied on transverse sections (Fig. 2).It is observed from the light microscopy that the plant constituted by homogeneous parenchyma cells and the vascular bundles.The stalks of C. flabelliformic have a large number of small cells originated mostly from parenchyma cells with poor papermaking characteristics, between fiber bundles (Fig. 2).The average content of parenchyma of hardwood and softwood are 20% and 7%, respectively 18 and wheat straw is 68%. 19The proportion of vascular bundles was 11.8% only, which is close to wheat straw and bamboo but different from hardwood. 18Each vascular bundle is surrounded by a large number of fibers.The fibers are the important cells for pulping and papermaking properties.Thus, in comparison with other non-wood C. flabelliformic is poorer raw materials for papermaking.Paper machine running is not a issue in handmade paper.So little or no problem will be faced in considering C. flabelliformicas raw material for handmade paper.

Pulp yield and kappa number
Soda pulping of C. flabelliformic was carried out with varying cooking time, alkali charge and material to liquor ratio at the boiling temperature and results are shown in Table 2.As expected screened pulp yield increased and total pulp yield and kappa number decreased with increasing cooking time and alkali charge.At the constant material to liquor ratio of 10 and 2 h of cooking, total pulp yield decreased from 70.7 to 61.2% and screened pulp yield increased from 30.2% to 52.5% with increasing alkali charge from 6% to 12%, while kappa number decreased from 23.1 to 15.5.It is observed from the Fig. 3 that kappa number sharply decreased from the alkali charge of 10% to 12%.Alkali charge is one of the major factors which affect the degree of delignifpooreication and carbohydrates degradation significantly in the soda pulping.On the basis of lignin content in C. flabelliformic, kappa number was unexpectedly low and delignification was easier.This is may be loosely anatomically bonded metrics.At the alkali charge of 12% C. flabelliformic was completely defibrated.So 12% alkali charge was considered as an optimum alkali charge for C. flabelliformic pulping at atmospheric pressure.In an earlier study, pulp yield from C. flabelliformic was 58.0% with kappa number 61 at the cooking conditions of 10% alkali charge for 2 h cooking at 100 o C. 7 This pulp yield was similar to our result but kappa number was higher.This can be explained by the fact that pulp was not screened in previous study, consequently shives contributed kappa number.At the cooking time of 2 h, the screened pulp yield with kappa number was 52.5% and 15.5, respectively, at the liquor to material ratio of 10 and 12 % alkali charge, further increase in cooking time decreased the screened pulp yield.
The increase in liquor to material ratio from 6 to 12 at the conditions of 12% alkali charge and 2 h of cooking improved the screened pulp yield from 51.4% to 55.4% while kappa number dropped from 21.1 to 13.8.The screened reject also decreased from 10.3% to 0.3%.Improved screened pulp yield and reject in higher liquor ratio can be explained by easy penetration cooking chemicals into the raw material.Although liquor ratio 12 was better, liquor ratio 10 was considered as optimum.

Statistical analysis
As shown in Table 3, there is a strong and positive correlation between total pulp yield and Kappa number (0.911).Alkali percentage, time and liquor to material ratio ration were negatively correlated with pulp yield, and the relation with alkali percentage is strong (-0.848).Similar type of association can be observed with Kappa Number.That means, alkali charge was a significant effect for pulp yield and kappa number.

Principal Component Analysis (PCA)
From Principal Component Analysis (PCA), Fig 4(a).shows that first Principal Component (PC1) express 90% of the variation whereas PC2 express 5% of the total variations.Score plot in Fig. 4(a) shows the samples are independently scattered without following any pattern.
Correlation loadings in Fig. 4(b) explained that pulp yield and Kappa number are strongly and positively correlated variables, whereas the time and liquor to material ratio are negatively correlated to paper yield percentage and Kappa number.From the influence plot, Fig. 4(c), we can see that no outlier in the samples considered in the study.Explained variance plot in Fig. 4(d) predicts that highest explained variance in found with 4 PCs, (slightly more than 90%), but the explained variance in the models using 1 PC contains similar explained variance (80-90%).

Prediction models
Three prediction models have been developed for prediction of pulp yield and Kappa Number on the basis of Alkali charge (%), cooking time (h) and liquor to material ratio, and their prediction efficiencies have been compared.The models were Multivariate Linear Regression (MLR), Principal Component Regression and Partial Least Squares Regression (PLSR).In order to develop the models 70% samples have been used for calibration and rests of them are for validating the models.For pulp yield, PLSR shows better prediction efficiencies than that of MLR and PCR with R 2 value 92% and 84% for prediction and validation set respectively.For Kappa number prediction, PCR performs better that other two methods for both prediction and validation data (Table 4).

Physical properties
The strength properties of unbleached C. flabelliformic pulp were determined in the unbeaten state and results are given in Table 5.Our main objective of this study was to utilize C. flabelliformic as a source of raw materials for handmade paper.Therefore, pulp beating was avoided.Pulp obtained at the conditions of 12% alkali charge, 10 liquor to material ratio and 2 h of cooking was selected for papermaking properties.In the unbeaten state drainage resistance of C. flabelliformic pulp was very high (47).This high drainage resistance can be explained by high parenchyma in the raw material (Fig. 2).In the unbeaten state papermaking properties were very good.Improved papermaking properties in the unbeaten state can be explained by higher density of pulp sheet (Table 5).The fines of chemical pulps have a strong tendency to intensify the interaction between fibers. 20This is mainly due to the increased density of the network.Tensile index was 59.9 N.m/g, which was higher than the pati-a grass grown in Bangladesh.Tear index of C. flabelliformic pulp was 11.4 mN.m 2 /g.The papermaking properties were close to pati-a grass grown in Bangladesh. 21Papermaking properties of C. flabelliformic was better than rice straw pulp. 22Finally it can be said that C. flabelliformic pulp in the unbeaten state is quite good, which support to use in good quality handmade paper.Fiber length for C. flabelliformic was shorter (0.94 mm) but the slender ratio was extremely high.One percent alkali solubility of C. flabelliformic was 49.6%, which indicated milder cooking conditions may be needed to satisfactorily extract fibers.The α-cellulose content in C. flabelliformic was 32.2%, significantly lower than wood.Soda pulping of C. flabelliformic was carried out in the lab, and multivariate data analyses were performed to evaluate the influence of alkali charge, cooking time and liquor ratio on pulp yield and kappa number.Alkali charge had a significant effect on pulp yield and kappa number.PLSR model showed better prediction efficiencies for pulp yield and PCR model performed better prediction for kappa number.Initial drainage resistance and papermaking properties of C. flabettiformic pulp were quite acceptable.

Fig. 3
Fig. 3 Effect of alkali charge on the pulping of C. flabettiformis

Fig. 4
Fig. 4 Principal component analyses of the pulping results

Table 1
Chemical and morphological characteristics of C.

Table 2 .
Soda pulping of C. flabelliformic at atmospheric pressure

Table 3 .
Correlation of among the dependent and independent variables ** Correlation is significant at 1% level of significance

Table 4 .
Comparison of calibration model for pulp yield and kappa number

Table 5 .
Papermaking properties of C. flabelliformic pulp