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Industrial Crops and Products 34 (2011) 865– 872

Contents lists available at ScienceDirect

Industrial Crops and Products

journa l h o me page: www.elsev ier .com/ locate / indcrop

pgrading of hemp core for papermaking purposes by means ofrganosolv process

. Barberàa, M.A. Pèlacha,∗, I. Pérezb, J. Puiga, P. Mutjéa

Grupo LEPAMAP, Departamento de Ingeniería Química, Agraria y Tecnología Agroalimentaria, Universitat de Girona, Campus Montilivi, Edifici P-I, 17071 Girona, SpainDepartamento de Ciencias Experimentales, Universidad Pablo Olavide, Carretera de Utrera km 2, Sevilla, Spain

r t i c l e i n f o

rticle history:eceived 5 November 2010eceived in revised form 4 February 2011ccepted 9 February 2011vailable online 9 March 2011

a b s t r a c t

Non-wood raw materials for paper production have been maintained constant during last decade. InEurope, fibres from non-wood resources proceed mainly from flax and hemp crops. Hemp core is con-sidered a by-product of the process, mainly used in equestrian sector. The application of these fibres forpapermaking process gives a significant added value to the sector.

New technologies in cooking processes like organosolv pulping gives advantages compared with tra-

eywords:on-wood resourcesemp corerganosolv cookingulp characterisationapermaking ability

ditional Kraft cooking. Hemp fibres obtained by means of organosolv process have been compared witheucalyptus Kraft pulp to determine if physical and mechanical properties of final pulps are similar.

Efficiency of the organosolv cooking experiments was evaluated by means of yield, percentage ofuncooked sample, kappa number and viscosity.

To analyze the suitability of pulp samples for papermaking applications, different evaluation of mechan-ical properties as morphological characterization were done. Controlling cooking conditions of hemp core,similar properties of eucalyptus Kraft fibres are obtained.

. Introduction

The use of non-wood raw materials has been maintained con-tant around 5% of the total pulp for paper production worldwideuring last decade. But since 2001, there has been an increase of8% in the total amount of non-wood pulp for paper productionchieving during 2007 the value of 18.36 million tonnes. At Euro-ean level, the percentage of contribution of non-wood fibres forulp production has been lower (∼1.3%) due to the higher uses ofecovered paper and lower surface of agricultural fields (FAO, 2009;EPI, 2010).

Production of pulp from non-wood resources has many advan-ages such as easiest pulpability, excellent fibres for specialityapers and higher quality bleached pulp. It can be used as an effec-ive substitute to avoid decreasing forest wood resources. Countriesike China and India, with a shortage of wood for their increasingemands of cellulosic fibres, have in non-wood pulps and recoveredaper its raw material for paper industry. Therefore, the utilization

f these pulps may help to solve the fibre shortage anticipated torise in the future and also help to diminish the rural depopulationiving an added value to fields (Navaee-Ardeh et al., 2004; Rousut al., 2002).

∗ Corresponding author. Tel.: +34 972418455; fax: +34 972418399.E-mail address: angels.pelach@udg.edu (M.A. Pèlach).

926-6690/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.indcrop.2011.02.005

© 2011 Elsevier B.V. All rights reserved.

In Europe, fibres from non-wood resources proceed mainlyfrom flax and hemp crops. The European Union takes a relativelyimportant share of world flax and hemp production with about500,000 ha and 15,000 ha, respectively, representing a share of20% for flax production and 29% from hemp production world-wide, according to FAO. In a published report from the Commissionof the European Parliament about the flax and hemp sector (EUReport, 2008) it is detailed than one ha of hemp produces in aver-age 5.8 tonnes of hemp straw. This industrial hemp straw refers tothe stalk of the plant. This stalk can be separated, or decorticated,into two main components: fibres and hurds or core fibres, as Fig. 1shows. Fibre refers mainly to the long strands of material that comefrom the outer rings of hemp straw presenting lengths between 200and 600 �m and a diameter in the order of 10–30 �m. Core fibresor hurds refer to the inner material of the straw. The yield in totalfibres of one hectare of hemp crop is not too high, around 26–28%whereas the yield in hemp core is 3.2 tonne per ha, i.e. a 55% versustotal hemp (EU, 2008; Vallejos et al., 2006).

Applications have been discovered for using hemp in everythingfrom food products to textiles to structural materials. Conse-quently, the viability of industrial hemp as an agricultural crop

is strongly linked to these markets and products for which hempcan feasibly be used to produce. Valued added quality papers liketeabags and coffee filters (Dutt et al., 2007), wax match paper (Duttet al., 2002), cigarette papers (Jeyasingam, 1994), electrical insu-lation papers (Dutt et al., 2003), glassine and grease proof papers,

866 L. Barberà et al. / Industrial Crops and Products 34 (2011) 865– 872

emp s

cim

mfi1t

mmBlbclrhoidmis

ctuhchtR

--

Fig. 1. Hemp straw processing to obtain h

ondenser papers (Dutt et al., 2004), are one of the main markets forndustrial hemp fibre (75%) with additional outlets for composite

aterials (20%) and insulation material (5%).High level of wet strength and shorter fibres from abaca make it

ost effective in teabags (Thompson et al., 1998). Industrial hempbre is closest in strength and fibre length to flax fibre (Werf et al.,994). This is fortunate since flax fibre is the largest component ofhe specialty fibre market.

Hemp core is considered a by-product of the process and isainly used for the equestrian sector (83%) and also for small ani-als (10%) and poultry breeds (2%) providing additional incomes.

uilding sector also uses a percentage of hemp core (5%) as insu-ation material for the preparation of panels or as an additive forricks. The use of this hemp core to obtain fibres with added valueould help hemp sector to stabilise in the long run. However, aack of suitable technology and logistic constraints are the mainestrictions to the extended use of these nonwood materials likeemp cores. The use of conventional technology has resulted inverwhelming environmental problems. The most common pulp-ng technology for wood pulps (alkaline route) causes problemsuring the delignification process. The silicon present in the rawaterial dissolves into the cooking liquor, which lets to difficulties

n the recovery of cooking chemicals. So far, the costs of alkali andilicon recovery are high (Rousu et al., 2002).

New technologies in pulping facilities like tornado pulper orhemical pulping processes have to be improved to produce indus-rial hemp pulp at competitive prices. “Tornado” like pulpers aresed to defibre hemp and other non-wood raw materials (cotton,emp, flax, leather and synthetic fibres) without pre-treatment orhemicals. Organosolv process to replace standard alkaline pulpingas also been under study. The use of organosolv process comparedo kraft one has different advantages (Jiménez et al., 2004, 2008;

odríguez et al., 2008):

Reduction of small- and mid-scale production costs. Facilitate the efficient recovery of solvents and by-products.

trands or fibres, and hemp core or hurds.

- Use less water, energy and chemicals.- Less polluting and the bleaching effluents are easier to treat.- Useful for all types of wood and non-wood plants.- Similar pulp properties, higher yields and lower lignin contents.- Organosolv pulp is brighter and easier to bleach and refine.

The greatest disadvantages of organosolv processes is that theyusually require high pressures (solvents of low boiling point, i.e.ethanol), which require special equipments and raises operatingcosts. This makes the use of solvents with a high boiling pointlike ethanolamine, a potentially interesting alternative: however,it supposes a more expensive solvent recuperation because thedistillation occurs at higher temperature. The separation of the sol-vent from the degradation products is an essential part of recovery(Jiménez et al., 2007; Rodríguez et al., 2008).

The objectives of studies intended to promote sustainable devel-opment in the use of hemp fibres and hemp core as raw materialfor paper industry have to be centred in:

- Efficient utilization of nonwood materials (hemp core representaround 55% of hemp straw).

- Effluent-, sulphur- and chlorine-free operation.- High quality pulp.- Profitable in small scale because mills have remained relatively

small due to logistic constraints.

Achieving these objectives, hemp fibres could compete with vir-gin and recycled fibres for the production of office papers (Rousu

et al., 2002).

The present study aims to optimise pulping conditions forhemp core of Cannabis sativa by means of organosolv pulping pro-cess using ethanolamine that could be considered environmentallykind.

ps and Products 34 (2011) 865– 872 867

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Table 1Results from chemical characterization of raw material and comparison with otherreferenced values.

Analysis Hemp core Kenaf corea Hardwooda Publishedhemp corea

�-Cellulose (%) 42.5 34 38–49 39–49Hemicellulose (%) 22.2 19.3 (18–24) 19–26 16–23Lignin (%) 24.8 17.5 (15–21) 23–30 16–23

L. Barberà et al. / Industrial Cro

. Materials and methods

.1. Raw material

Hemp core of Cannabis sativa was provided by Agrofibra, S.L.rom Puigreig (Barcelona, Spain) as chopped pieces of 10 mm oress long. The hemp core was disintegrated into powder (TAPPI T64 cm-97 “Preparation of wood for chemical analysis”) and theraction passed through a sieve of 40 mesh and retained in a sievef 60 mesh was used for �-cellulose and hemicellulose (TAPPI

203 cm-99 “Alpha-, Beta-, and Gamma-Cellulose in Pulp”), acidnsoluble lignin (TAPPI T 222 om-02 “Acid-insoluble lignin in woodnd pulp”) and ash content (TAPPI T 211 om-02 “Ash in wood, pulp,aper, and paperboard: combustion at 525 ◦C”) determinations.

.2. Pulping conditions

Organosolv experiments were performed in a 25-L stainlessteel rotator digester with a heat exchanger system and pres-ure control. Pulping conditions of industrial hemp core werearied over the following ranges: 30–90 min, 155–185 ◦C, 40–60%thanolamine. Pulping conditions that were maintained constantsere: liquor to wood ratio: 6:1 and digester pressure at Tmax:

–7 bar.These conditions were previously tested by other authors

Jiménez et al., 2007) in vine shoots pulping using ethanolamine.After completion of cooking, the cooked hemp core pulps were

efibred in a hydrapulper and screened through a Somerville vibra-ory flat screen with 0.15 mm slot size, and the screened pulp wasashed, pressed, crumbled and stored at 4 ◦C. The pulps were eval-ated for kappa number (TAPPI T 236 om-06 “Kappa number ofulp”), pulp yield, screening rejects, and viscosity (TAPPIT 230 om-8 “Viscosity of pulp: capillary viscometer method”).

Morphological characteristics of hemp core pulp like fibreength, width and fines percentage were determined with a MorFiompact device analyzer (Techpap). The pulp was disintegratedn a standard disintegrator and laboratory handsheets of 60 g/m2

ere prepared using a sheet former, pressed and air-dried undertmospheric conditions (TAPPI T205 sp-06 “Forming handsheetsor physical tests of pulp”). Laboratory handsheets were precondi-ioned at 23 ± 1 ◦C at a relative humidity of 50 ± 2% and evaluatedor Scott index (TAPPI T 569 pm-00 “Internal bond strength: Scottype”), tensile breaking properties (TAPPI T 494 om-01 “Tensileroperties of paper and paperboard: Using constant rate of elonga-ion apparatus”), tearing resistance (TAPPI T 414 om-04 “Internalearing resistance of paper: Elmendorf-Type Method”), burstingtrength (TAPPI T 403 om-02 “Bursting strength of paper) and airesistance by means of Gurley method (TAPPI T 460 om-02 “Airesistance of paper: Gurley Method”). These results were comparedith a typical Eucalyptus Kraft pulp.

.3. Experimental design

To be able to relate the dependent and independent variablesith the minimum possible number of experiments, a 2n cen-

ral composite factor design was used. This design enabled theonstruction of first and second-order interaction terms of a poly-omial design and the identification of statistical significance of theariables used. The total number of experiments required (N) was

ound from the equation:

= 2k + 2 × k + 1 (1)

here k denotes the number of independent variables.Solving this equation for k = 3, a total of 16 experiments were

lanned. Independent variables were normalized using the follow-

Ash (%) 3.3 2.5 (2–4) 1 3–4.5Holocellulose 70.6 79.5–80.5

a Hurter (2006).

ing equation

xn = 2x − x

(xmax − xmin)(2)

where x is the absolute value of the independent variable con-cerned, x is the average value of the variable and xmax and xminare its maximum and minimum values respectively. In the presentstudy normalized variables were:

−1 0 1

Time (Xt , min) 30 60 90Temperature (XT, ◦C) 155 170 185Ethanolamine (E, %) 40 50 60

Experimental results were fitted to the following second-orderpolynomial:

Z = a0 +k∑

i=1

biXni +k∑

i=1

ciX2m +

k∑

i=1

dijXniXnj (i < j) (3)

where Z denotes the response variables, Xni the normalized valuesof the independent variables (time, temperature and ethanolamineconcentration), and a, b, c and d are constants.

Normalization of independent variables provides better esti-mates for the regression coefficients by reducing correlationbetween linear and quadratic interaction terms.

3. Results

Results from chemical characterization of the raw material usedin the study, i.e., hemp core, are presented in Table 1 and com-pared with referenced values of kenaf core, hardwood fibres andpublished hemp core values (Hurter, 2006).

Results presented show that, hemp core material selected hassimilar chemical composition than hardwood fibres. Hemp coreability to deliver chemical cellulose, defined as �-cellulose, to finalfibrous suspensions is higher than kenaf and really good comparedto hardwood. As it was confirmed previously by de Groot (De Grootet al., 1999), hemp woody core is chemically related to hardwood.

When analysing hemicelluloses values, there are no real differ-ences between them. Hemicelluloses are important for the paperindustry because they are needed for final good pulp quality. Itspresence aids swelling of the pulp, bonding between fibres, burst-ing strength, tensile strength, tear resistance, folding endurance,opacity and specific surface of the pulp sheet. Experimental valuesof lignin from hemp core samples are also within the range of hard-wood pulp. Chemical characterization allowed continuing with theobjective of upgrading these fibres for papermaking uses.

Organosolv cooking of hemp core samples using ethanolaminewere conducted according to experimental design described inmethodology. Table 2 shows the relation of experiments with the

corresponding normalized values for the independent variablesand characteristic results of cooked samples (yield, rejects, kappanumber, viscosity and fibre length). Yield presented in Table 2 con-siders fibrous suspension able to produce paper, i.e. it is a screenedyield. It does not take into consideration rejects or uncooked mate-

868 L. Barberà et al. / Industrial Crops and Products 34 (2011) 865– 872

Table 2Operating conditions of experimental design and results of pulp characterisation in the ethanolamine hemp core pulping.

Time (Xt , min) Temperature (XT, ◦C) Ethanolamine (XE, %) Yield (%) Rejects (%) Kappa number Viscosity (cm3/g) LLw (�m)

1 1 1 53.17 0.79 25.26 256 450−1 −1 −1 28.16 62.57 113.36 764 690

0 0 0 56.11 15.14 66.26 535 5900 0 1 63.44 13.7 58.48 377 6150 0 −1 54.00 17.65 71.44 413 5950 −1 0 43.56 39.16 90.80 767 6351 1 −1 55.37 0.98 39.33 275 510

−1 1 1 59.37 6.69 55.95 498 535−1 0 0 52.32 31.65 82.49 759 680

1 −1 1 42.98 42.94 82.19 243 655−1 1 −1 55.57 9.63 74.05 639 595

1 −1 −1 36.99 48.68 70.81 278 655.47 61.21 91.56 463 730.17 10.17 68.36 607 595.30 0.99 41.11 780 480

rbbt

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rtort

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−1 −1 1 271 0 0 570 1 0 64

ial that was calculated using the Sommerville-type equipment,ased on TAPPI T275 standard. There is an inverse relationshipetween screened yield and rejects, therefore, cooking conditionshan will favour yield, contradict rejects.

A multiple non-linear regression analysis using JMP softwareversion 8.0) was performed on all the results related with organo-olv hemp core pulp characterization. A backward stepwise methodas applied over all interactions to take into consideration only

he terms with a Snedecor’s F-values less than 4. The equationsbtained are presented in Table 3. This table also contents statis-ical values as r2, Snedecor’s F, highest p values and the optimummaximum or minimum) values for the dependent variables andhe normalized independent variables needed to achieve them. Theesponse surface methodology (Myers and Montgomery, 1995) waspplied to equations in order to determine the optimum (maximumr minimum) values for the dependent variables over the rangestudied for the process variables.

Equations presented in Table 3 reproduce the experimentalesults for the different dependent variables, as a function ofhe independent ones. Quadratic correlation coefficients (r2) ofbtained equations for the characterization of pulp samples areeally good (>0.90) and the variations obtained were always lowerhan 5% except the viscosity that gave too high values of variation.

The described statistical method applied to yield’s equation inrder to determine the highest value over the range studied, gave aaximum yield of 63.3% obtained for a short time and a high tem-

erature (normalised values of −0.04 and 0.75, respectively) andndependent of ethanolamine concentration. Similar yield results63.9%) were obtained by Jiménez et al. (2007) when treatingine shoots with ethanolamine, however at lowest temperatures155 ◦C).

Surface representation of proposed yield equation (Fig. 2) byeans of Sigmaplot 8.0 confirmed the importance of temperature

nd time as independent variables. The greatest changes in yieldesulted from variation of the temperature, whereas the smallestnes were due to ethanolamine concentration, with an insignificantnfluence on yield variation. It is a usual behaviour than yield is

ore sensitive to changes in temperature than in reaction time orrganosolv concentration (Jiménez et al., 2004).

As it was mentioned before, there is an inverse relationshipetween screened yield and rejects, therefore, independent vari-bles that influence yield would be the same for the reject analysis.s it is observed in Table 3, this is confirmed. Time and temperature

re the variables that influence uncooked material or rejects fromrganosolv hemp core samples. Minimum value obtained with pre-icted equation reaches negative values.

Delignification process, expressed as kappa number, increasedith increasing temperature and reached a predicted minimum

Fig. 2. Surface representation of yield (%) in function of temperature (◦C) and time(min) within the normalized range.

level of 28.6 at higher temperature, time and ethanolamine concen-tration, as it can be observed in Table 3. More extreme conditionspromoted delignification and thus enhanced the dissolution oflignin. From initial value of acid insoluble lignin (24.8%) determinedas TAPPI T222, it can be considered than in optimum conditions, a85% of this lignin is removed during digestion. Poorer conditionsremoved only a 43% of total lignin.

The same hemp core raw material was treated in previous works(Cerdán, 2008) using chemical process (i.e., Kraft) and semichem-ical one (i.e., soda–anthraquinone). Yield obtained ranged from 72to 40% for chemical treatment and from 79 to 43% for semichemicalone. Kappa number ranged from 72 to 15 for chemical treatmentand from 168 to 21 for semichemical one. Comparing all these treat-ments, it can be concluded that organosolv treatment for hemp corepulps is adequate in terms of pulp characterisation.

Viscosity is a measure of polymerization degree based on dis-solving the lignin-free pulp in a solvent, typically a standardsolution of cupriethylenediamine. By measuring the viscosity, onecan estimate the extent of degradation of cellulose and undissolvedhemicelluloses than can affect fibre strength and may also influencepapermaking properties. Viscosity of obtained organosolv hemp

core pulps varied from 243 to 780 cm3/g, i.e., from low to reallyhigh viscosity values. Optimum value predicted by the polynomialequation is even greater (813 cm3/g). Temperature is not a sig-nificant variable on viscosity variation while cooking liquor and

L. Barberà et al. / Industrial Crops and Products 34 (2011) 865– 872 869

Table 3Obtained equations to predict pulp characterization variables (yield, rejects, kappa, viscosity and length) into the range of cooking conditions used.

r2 F p Optimum value Variation (%) Normalized values of the independent variables lead tooptimum values of dependent variables.

Time (Xt , min) Temperature (XT, ◦C) Ethanolamine (XE, %)

Yield (%) = 59.21 + 2.28 · Xt +10.86 · XT − 3.84 · Xt · XT −6.50 · X2

t − 7.31 · X2T

0.94 33.3 <0.0001 63.3 2.3 −0.04 0.75 –

Rejects (%) = 14.75 − 6.82 · Xt −23.55 · XT + 7.47 · X2

t +6.64 · X2

T

0.97 108.5 <0.0001 0.0 2.8 0.46 +1 –

Kappa = 68.61 − 13.15·Xt −21.30·XT − 5.56·XE

0.91 41.5 <0.0001 28.6 4.9 1 1 1

Viscosity = 663.83 − 146.4 · Xt −53.2 · XE − 243.23 · X2

E

0.82 18.1 <0.0001 813.1 45.9 −1 – −0.10

LL = 596.6 − 36.5 · X − 0.96 49.5 <0.0001 732 11.3 −1 −1 −1

trntimfNia

earsp

oc

L

bsa

TM

w t

79.5 · XT − 14 · XE +42.7 · X2

t − 37.3 · X2T

ime are reactive. The reactions between the cooking liquor andeactive lignocellulosic components dissolve some of these compo-ents resulting in openings that allow the chemicals to penetratehe hemp structure. As the pulping process proceeds, this resultsn further decomposition of hemp core components and transfor-

ation of the hemp structure. The pulping reactions start to spreadrom the initial reactive sites of the hemp as confirmed by Dang andguyen (2006). The pronounced differences suggest that the peel-

ng reactions, which are responsible for the loss of pulp viscosity,re more sensitive to the time and organosolv reagent.

Values of kappa number and viscosity for a typical unbleacheducalyptus Kraft pulp obtained in the same rotator digester using

proportion of active alkali of 15% were 23.8 and 753.6 cm3/g,espectively. It means that organosolv hemp core pulp is notignificantly different from a hardwood pulp obtained in a Kraftrocess.

The information related with morphological characterizationf pulps presented in Table 2 is length weighted in length (LL

w),alculated as follows:

Lw =

∑ni · L2

i∑

ni · Li

This is the most common definition of fibre length distributionecause the plain arithmetic average is not applicable when theample contains a high proportion of fines (∼24%) and short fibress expected in pulps from non-wood raw material.

able 4echanical characterisation of handsheets from hemp core pulp obtained at different eth

Time (Xt , min) Temperature(XT, ◦C)

Ethanolamine(XE, %)

Breakinglength (m)

1 1 1 5295

−1 −1 −1 4865

0 0 0 4910

0 0 1 5256

0 0 −1 4763

0 −1 0 4808

1 1 −1 4139

−1 1 1 5153

−1 0 0 4387

1 −1 1 4474

−1 1 −1 3865

1 −1 −1 4419

−1 −1 1 5986

1 0 0 5107

0 1 0 4311

The weighted length (LLw) variation obtained with the differ-

ent experiments using a MorFI compact device, is into the rangeof 450–730 �m, in accordance with published values of averagelength (510 �m) of an industrial hemp core (Hurter, 2006). All inde-pendent variables are present in LL

w predicted equation (Table 3)with a robust statistical analysis. This equation leads to a maximumvalue of fibre length of 732 �m achieved at the lowest cooking con-ditions, i.e. low temperature, time and ethanolamine concentration.This maximum fibre length is slightly lower from that obtained bythe eucalyptus kraft pulp, i.e., 870 �m.

Summarising, chemical and morphological properties oforganosolv hemp core pulp are comparable to a typical eucalyp-tus Kraft pulp with the exception of some lengths of organosolvhemp core pulps.

To analyze the suitability for papermaking applications ofthe organosolv hemp core pulp obtained at different conditions,mechanical properties should be evaluated. The most impor-tant strength properties of paper and board would include:tensile strength analysed by means of breaking length; inter-nal bond strength analysed by means of Scott index; tearingstrength; bursting strength analysed by means of Müllen indexand porosity or air resistance analysed by means of Gurley

method. Table 4 summarizes the values obtained on correspondinghandsheets.

The same multiple non-linear regression analysis applied beforeis used with these mechanical properties. Obtained equations andstatistical parameters are presented in Table 5 and reproduce the

anolamine cooking conditions.

Scott index(J/m2)

Tear index(100 gf m2/g)

Müllen index(1000(kg/cm2)/(g/cm2))

Porosity (s)

527.7 31.5 31.23 274478.6 30.5 18.63 288447.0 33.2 19.44 206436.8 31.4 19.44 302459.8 31.3 19.10 226514.1 31.0 17.02 282276.9 35.4 26.17 44448.0 33.9 19.68 326507.5 33.5 17.88 192454.8 31.3 20.49 384308.6 32.0 16.26 99448.4 28.1 17.03 210542.4 28.3 20.67 420472.9 31.7 19.95 308405.9 30.8 20.17 258

870 L. Barberà et al. / Industrial Crops and Products 34 (2011) 865– 872

Table 5Obtained equations to predict mechanical properties (breaking length, scott index, tear index, burst index and porosity) into the range of cooking conditions used.

r2 F p Optimum value Variation (%) Normalized values of the independent variables lead tooptimum values of dependent variables

Time (Xt , min) Temperature(XT, ◦C)

Ethanolamine(XE, %)

Breakinglength = 4790.5 − 82.2·Xt −178.9·XT + 411.3·XE

+ 296.75·Xt·XT

0.68 5.9 0.0086 5759 243 −1 −1 +1

Scottindex = 448.53−47.12·XT

+ 43.74·XE + 40.0·XT ·XE

0.72 10.13 0.0013 499.4 30.9 – −1 +1

Tearindex = 31.69 + 1.44·XT

0.38 8.71 0.0105 33.13 1.2 – 1 –

Müllen index =18.98 + 2.18 · Xt +1.97 · XT + 1.43 · XE +2.91Xt · XT + 1.89 · X2

E

0.92 22.0 <0.0001 29.35 0.7 1 1 1

efcsvMctssotv

epietvccnr

wabtnt

ipb(an

ppsdi

Porosity = 251.56 − 58.3·XT

+ 83.9·XE

0.77 21.2 <0.0001 (394)max

(109.4)min

xperimental results for the different dependent variables, as aunction of the independent ones. Quadratic correlation coeffi-ients (r2) of obtained equations for the characterization of pulpamples are good (≥0.70) except for tear index (r2 = 0.38). Theariations obtained were lower than 5% only for tear index andüllen index. The higher variations presented by breaking length

an be explained by the standard deviation of the analysis itselfhat was higher than 300. The same situation was presented bytandard deviation of Scott that in this case, corresponds to theame variation of statistical analysis (i.e. 31). The porosity was thenly parameter that variation was not well explained in function ofhe residuals obtained, based on the variation of real and predictedalues.

The relative influences of the independent variables are differ-nt among physical characteristics analysed. From the equationresented in Table 5 describing the variation of breaking length

t can be assumed that the variable with the highest effect isthanolamine concentration, followed by the interaction betweenime and temperature. For the Scott index, the most significantariable is the temperature, followed by the ethanolamine con-entration and their interaction. If the equation analysed is thatorresponding to tear index, it can be deduced that the only sig-ificant variable is the temperature even tough the variation in theesponse is not totally attributed to the model (lowest r2).

Table 5 also contains proposed equations for Müllen index fromhich one can be inferred that the variables with highest effect

re time, temperature and ethanolamine concentration, followedy the interaction between time and temperature. For porosity,aking into consideration that was evaluated as the time that aireeded to pass the handsheet, the most significant variables arehe ethanolamine concentration and temperature.

Breaking length and porosity increased more markedly onncreasing the ethanolamine concentration while increasing tem-erature affected them negatively. Scott index showed the sameehaviour. Processing time only affected positively burst indexexpressed as Müllen one). However, when assessing pulp char-cterisation cooking time was a significant variable for Kappaumber, viscosity and weighted length.

To proceed with the goodness of the results, Eucalyptus Kraft

ulp, recycled liner and recycled fluting were used as referenceulps. This is because the optimum pulp quality depends on thepecific product requirements. Fluting and liner are used to pro-uce corrugated board, a competitive packaging material. Fluting

s equivalent to corrugated medium, the paperboard grade that is

39.6 – −1 1

1 −1

used in corrugated board as the “wave” between the two liners.Because corrugating medium is a bulk product, price is very impor-tant for raw materials and the upgrading of nonwood pulps hasa niche in this market. Strength is an important property to ana-lyze. Table 6 contains their corresponding mechanical propertiesobtained using the same standards and equipments, and the rangeof experimental values from ethanolamine hemp core cooking’s.

Ranges of variation of breaking length, Scott index and Müllenindex values are considerable high for an organosolv papercompared with all other pulp handsheets. These results are inaccordance with published organosolv experiments (Gonzálezet al., 2008). Tear index values for the ethanolamine pulp are lowerthan other pulps analysed. Porosity values obtained are out of rangewhen comparing with Eucalyptus Kraft pulp or pulps obtained fromrecycled Kraft liner or corrugated medium (i.e. fluting).

Summarising, it can be inferred that physical properties areacceptable for a big range of industrial papers some examples ofwhich are shown in this paper.

Therefore, to upgrade hemp core pulps, is important to decidewhich type of paper is the objective and to which additionaltreatments will be submitted (i.e. refining process). If the papertarget requires higher brightness, lower kappa numbers have to beobtained. If the paper target requires important strength proper-ties, then mechanical parameters have to be evaluated to decidecooking conditions. The same conclusion could be taken if poros-ity is an important parameter. In this sense, three different set ofoperation conditions are proposed in order to optimise certain vari-ables without affecting too much on the others, using the obtainedequations. These conditions are listed in Table 7.

Pulping conditions more suitable for obtaining sheets with goodphysical properties (set of conditions a) require operation at hightemperature and concentration of ethanolamine (60% and 185 ◦C,respectively), as well as a cooking time of 85 min. Under these con-ditions all the physical properties of handsheets differ by less than10% of its optimal value, being the deviation from the optimal valueof performance only of 10.31%. However, the intrinsic properties ofpulps (viscosity and fibre length) as well as porosity are far fromoptimal values.

Pulping conditions corresponding to set b (Table 7) are recom-

mended if the goal of the process is to obtain pulps with optimumyield, viscosity and fibre length, to further undergo a refining pro-cess. Ethanolamine concentration of 44% for 36 min at 174.5 ◦Care ideal conditions for optimal values of the variables mentionedabove do not differ from 15%. Among the physical properties of

L. Barberà et al. / Industrial Crops and Products 34 (2011) 865– 872 871

Table 6Mechanical properties of handsheets made with Eucalyptus Kraft pulp, recycled liner and fluting, compared with the range of experimental values.

Ethanolamine hemp core pulp Eucalyptus kraft pulp Recycled kraft liner Recycled fluting

Breaking length (m) 3865–5986 2246 2984 3536Scott index (J/m2) 277–542 70.8 150 171.2Tear index (100 gf m2/g) 28–35 52.4 62 92.9Müllen index (kPa m2/g) 16–31 10.5 16.2 17.7Porosity (s) 44–420 1 8 27

Table 7Different sets of recommended operation conditions with values of dependent variables and percentage of deviation with respect to optimum.

Condition Normalized values of the independent variables lead tooptimum values of dependent variables

Variable Value Deviation with respect tooptimum (%)

Ethanolamine Time Temperature

a 1 0.85 1 Yield (%) 56.74 10.3Rejects (%) 0 0Kappa 30.57 6.9Viscosity 243 70.1LL

w 466 36.4Breaking length 5205 9.6Scott index 485.1 2.9Tear index 33.1 0Müllen index 28.6 2.6Porosity 277 (29.6)max/(153.5)min

b −0.6 −0.8 0.3 Yield (%) 56.75 10.3Rejects (%) 18.52 –Kappa 76.08 166Viscosity 725 10.8LL

w 634 13.3Breaking length 4485 22.1Scott index 400.9 19.7Tear index 32.1 3.0Müllen index 16.95 42.3Porosity 184 (53.3)max/(68)min

c 0.13 −1 0.4 Yield (%) 55.14 12.8Rejects (%) 20.68 –Kappa 72.52 153.6Viscosity 799 1.7LL

w 636 13.1Breaking length 4736 17.8

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andsheets obtained, only the Tear index remained acceptable dif-ering by only 3% from optimal value.

Finally, the proposed operation conditions are intermediateetween those indicated above, getting a loss of physical proper-ies not very high, and preserving fibre properties (set of conditions). As seen in Table 7, working with a concentration of 51%thanolamine for 30 min at 176 ◦C, you can get the properties stud-ed, differ by less than 15% of its optimal value (17.8% for breakingength) with the exception of Kappa, Müllen index and porosity.

Under these conditions (set c) final yield would be 55.14%, butonsidering that rejects (20.68%) in a continuous process are recir-ulated and reintroduced to the process, this yield would be higher.t should be noted that the proposal of cooking at shorter times andower temperatures have greatest interest from the point of viewf operational costs.

. Conclusions

Upgrading of hemp core based on ethanolamine organosolv pro-ess was achieved in this study. Handsheets obtained from this

rocess have physical properties similar or even better than hard-ood Kraft pulps.

Mathematical models obtained reproduce results in anrganosolv cooking process with acceptable errors. The most rec-mmended operating conditions for high yields are 60 min at 185 ◦C

Scott index 437.5 12.4Tear index 32.3 2.6Müllen index 16.64 43.3Porosity 239 (39.3)max/(118.7)min

using a 60% of ethanolamine. To improve physical properties isnecessary to increase cooking time. If working conditions are deter-mined at 51% of ethanolamine for 30 min at 176 ◦C, a balancebetween physical properties of paper and fibre characteristics isobtained.

Acknowledgments

Authors wish to thanks Spanish Ministry of Education andScience (MEC) for the grant obtained to develop this study(CTM2007-66793-C03-01/TECNO).

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