Could oleaginous flax fibers be used as reinforcement for polymers?

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Industrial Crops and Products 34 (2011) 1556– 1563

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Industrial Crops and Products

jo ur nal homep age: www.elsev ier .com/ locate / indcrop

ould oleaginous flax fibers be used as reinforcement for polymers?

sabelle Pillina,∗, Antoine Kervoelena, Alain Bourmauda, Jérémy Goimardb, Nicolas Montrelaya,hristophe Baleya

Université de Bretagne Sud, Laboratoire d’Ingénierie des MATériaux de Bretagne, Rue de St Maudé, BP 92116, 56321 Lorient Cedex, FranceValorex, La Messayais, 35210 Combourtillé, France

r t i c l e i n f o

rticle history:eceived 27 April 2011eceived in revised form 16 May 2011ccepted 17 May 2011vailable online 12 June 2011

eywords:laxiberarietyechanical properties

a b s t r a c t

Many works deal with the mechanical properties of flax fibers cultivated for textile applications and todayused for the reinforcement of polymers. Nevertheless, quantities of oleaginous flax fiber are obtainedeach year and not promoted. The aim of this work is to study the mechanical properties of single linseedflax fiber as a function of variety, culture year, dew-retting degree and agronomic factors. Five varietiesof oleaginous flax have been characterized by tensile tests on elementary fibers and compared to fourvarieties of textile flax. These tensile experiments have been carried out on with the same equipment,experimental protocol and environmental conditions.

The results show that interesting mechanical properties were obtained with the oleaginous variety andare close of those of textile varieties, such as Agatha or Electra. Considering the diameters and specificproperties of these oleaginous fibers, we evidenced that they are good candidates for the substitution of

gronomic factor glass fibers in composite materials. To increase the development of flax fibers, it is important to have abetter control of the spread of their mechanical properties. This point could be observed with the Everestvariety cultivated for 4 years and no conclusion could be made.

We have evidenced that the retting degree has no influence on the diameters and mechanical propertiesof the fibers; the same conclusion is obtained with agronomic factors such as seeding rate and plant height.

. Introduction

Natural fibers have received much attention for the last decade.hey are now considered as a serious alternative to glass fiber foreinforcement in polymer matrix composites. Many works dealith the mechanical properties of flax fibers cultivated for textile

pplications and today used for the reinforcement of thermosetsAndersons et al., 2005; Baley, 2002; Mohanty et al., 2000).

Many factors can influence the structure and the chemical com-osition of the natural fiber such as the variety, growth conditions,aturity, retting degree and the location in the stem. The fiber

roperties can be influenced by the treatment processes, but theuality and quantity of raw material is controlled by the variety,lant density and harvesting.

Some of the literature deals with the mechanical properties ofingle fibers for textile flax, such as Ariane (Baley, 2002), Hermes

∗ Corresponding author. Tel.: +33 2 97 87 45 05; fax: +33 2 97 87 45 88.E-mail address: isabelle.pilin@univ-ubs.fr (I. Pillin).

is also cultivated for its seeds with high omega 3 content, how-ever use its stem has not been developed. Diederischsen and Ulrich(Diederichsen and Ulrich, 2009) studied the variability in stem fibercontent for fiber flax or linseed flax from 55 countries. The linseedflax gives interesting stem fiber content from 16.3% to 27.3% whichis close to that of textile flax fiber (15.8–33.6%).

Charlet et al. (2007, 2009) have investigated the influence ofthe location in the stem on the mechanical properties of Hermèsand Agatha flax fibers; these studies pointed out that middle fibersexhibit the best mechanical properties which can be explained bythe growing of these fibers during the rapid elongation stage of thestems inducing a high cellulose content.

Retting is important to separate the single fibers from the bun-dles. Three different methods can be used: dew-retting, enzymaticand/or chemical retting with temperature control or water treat-ments. Baley et al. (2005) showed that drying flax fibers inducesa decrease in tensile strength, and after water absorption of thesedried fibers, the mechanical properties cannot be recovered.

Li and Pickering (2008) have shown that enzymatic treatments

and Products 34 (2011) 1556– 1563 1557

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Table 1Variety, year and retting degree of studied oleaginous flax fiber.

Variety Year Retting degree

Hivernal 2006 Normal (R3)

Alaska 2006Low (R1)Normal (R3)

Niagara 2006 Normal (R3)

Everest

2005 Normal (R3)2006 Normal (R3)2007 Normal (R3)

I. Pillin et al. / Industrial Crops

hat the quality of flax fiber obtained after soft and friendly waterreatments (72 h at 23 ◦C) can be very interesting in terms of theirppearance, cleanliness, extraction facility and mechanical prop-rty.

The retting degree can be characterized by several techniques.allesen (1996) quantified the quality of retting with the increase inellulose content by chemical analysis. Meijer et al. (1995) showedhat the pectin content decreases from 30 g/kg in the stem to 8 g/kgfter 40 days in field retting, whereas the same content is reachedfter 150 h for water retting at 34 ◦C. Velde and Baetens (2001)uantified the retting degree by ATG measurements: the first lossf weight is attributed to the release of water, the second one iselated to the degradation of cellulosic substances (between 50%nd 65%) and the third one at the highest temperature correspondso the degradation of the non-cellulosic substances (between 20%nd 30%). They showed that the mechanical properties of singlebers are not modified by the retting degree.

The dispersion of the results is an important point in the char-cterization of elementary vegetal fibers; tensile values on vegetalbers are characterized by a broad distribution. However, we haveo keep in mind that plant fibers are natural products which do notave, in essence, repeatable properties and which exhibit manyefaults, particularly after elementary fiber extraction which canreate kink bands (Baley, 2004).

Norton et al. (2006) studied the influence of agronomic practicen the yield, fineness and strength of several varieties in 2002 and003. It was clearly shown that a low-nitrogen treatment and a dryeason induce finer fibers. Using statistical analysis, they noticedhat the fiber yield is related to fiber fineness, with the coarser fibersorresponding to higher yields.

A study carried out on five hemp varieties showed that a highereed rate leads to higher fiber yields (Bennett et al., 2006). Anothertudy on two hemp varieties gave opposite results with a betterber yield when the seed rate was lower; the fiber diameter waslso reduced when the seed rate was high. Nevertheless, a dry sea-on gives a finer fiber as is described in Amaducci et al. (2008) andennett et al. (2006).

The aim of this paper is to study the tensile mechanical proper-ies of elementary linseed flax fiber and the diameter of flax fiberfter stripping as a function of variety, culture year and dew-rettingegree. These properties were compared to those of textile flaxbers. The results obtained for all the samples are discussed inerms of repeatability and compared with the intrinsic mechanicalroperties of glass fibers.

. Materials and methods

.1. Material

Several flax fibers were provided by the “Chambre d’Agricultureu Morbihan” (Chamber of Agriculture of Morbihan in Brittany,rance) after 4 years of flax cultures (2005–2008). These flaxes haveeen cultivated on the same geographic area and lands in a temper-te region (West of France). The varieties of oleaginous flax studiedere Oliver, Hivernal, Alaska, Niagara and Everest. These varietiesere sowed and harvested during winter months, in opposition to

he summer culture, usually practiced for the textile flax. For eachear, several parameters which could impact on the properties ofhe fibers were noticed, such as the date of sowing, the chemi-al culture treatments and the height of the plants. The flax wasore or less dew-retted noted R3 and R1 respectively. R3 corre-

ponds to a classical retting degree whereas R1 corresponds to a

2008 Normal (R3)

Oliver 2006 Normal (R3)

properties were measured in the middle of the stem. The studiedvarieties, culture year and retting degree are given in Table 1.

2.2. Scanning electron microscopy (SEM) pictures

The fibers were sputter-coated with a thin layer of gold in anEdwards Sputter Coater and then observed with a Jeol JSM 6460LVscanning electron microscope.Diameter fiber measurements

The average diameters of flax fibers were determined on at least400 fibers using a Leica optical microscope (Leica Microsystems)with a software program IM 500. They were obtained after theinclusion of flax fibers into an epoxy thermoset resin and after cut-ting the sample in a transverse direction. In order to reduce theerror on the fiber diameter measurements, an epoxy resin hav-ing shrinkage inferior to 1% was used, so the external pressureon fiber is minimized. Unidirectional composites, having a lengthabout 200 mm, were prepared. In this case, the fibers are entire andthe lumen is not accessible to epoxy resin. Using this method, noepoxy resin into the lumen or swelling of section by an impregna-tion of cell wall by epoxy resin was never observed in our case. Forone variety, we verified that the average diameter is similar even ifseveral resins were used.

A meticulous polishing of the sections was carried out to a 1-�mparticle size polishing solution finish.

2.4. Tensile tests

The mechanical properties (Young’s modulus, ultimate strengthand failure strain) of single fibers were obtained from tensile tests.Due to the short fiber length (between 10 and 50 mm), a gaugelength of 10 mm is chosen. Before testing, the fiber is glued on apaper frame and its diameter is determined from the average ofoptical measurements in three different spots. Then, the frame isclamped on a universal MTS Synergie RT100 type tensile machineequipped with a 2 N capacity load cell, and the edges of the frameare cut. The fiber is loaded at a constant crosshead displacementof 1 mm/min. The mechanical properties are determined in accor-dance with the NFT 25-704 standard which takes into account thecompliance of the loading frame. For each series, 100 flax fiberswere glued. During optical measurements, about 20–50 flax fiberscould be suppressed because of the presence of 2 or 3 fibers onthe same frame or due to the presence of defaults. Indeed, Baley(2004) showed that these defaults can be created during handlingextraction of single flax fiber.

The Young’s moduli were calculated on the linear part of thecurve stress–strain.

2.5. Thermogravimetric analysis

The retting degree was measured using ATG measurementsas described by Velde and Baetens (Velde and Baetens, 2001).

1558 I. Pillin et al. / Industrial Crops and Products 34 (2011) 1556– 1563

2006 R

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ing the diameter for each single fiber. For example, in Figs. 4–6, werepresent the mechanical characteristics for the Niagara (2006 R3)variety as a function of fiber diameter, Young’s modulus, stress andstrain at break are shown. The average diameter of the tested fibers

Fig. 1. SEM pictures of flax fibers. From left top to right bottom: Alaska

xperiments were performed using a Mettler Toledo apparatus.he heating rate was 3 ◦C min−1 under air atmosphere from 25 ◦Co 600 ◦C. Around 40 mg of each kind of fiber was used. Weighthanges and derivative weight changes were plotted against tem-erature.

. Results and discussion

.1. Observation by SEM of several linseed flaxes

Fig. 1 shows SEM pictures for Alaska and Everest stripped flaxbers after 2 degrees of retting and 2 culture years. In Fig. 1a and, the dew-retting degree of the Alaska variety can be observed.t can be easily seen that a low-retting degree gives bundles andbers with pectic cements, whereas a higher retting degree leadso relatively clean and separate fibers.

We can notice that a high retting degree leads to an easier extrac-ion of single fibers from bundles and induces a decrease in the riskf damage (creation of kink bands) (Baley, 2004).

Fig. 1c and d represents the Everest fiber cultivated in 2005 and006. No difference can be observed, similar to the Alaska 2006 R3Fig. 1b) and Everest (Fig. 1c and d), the fibers are clean and welleparated. Nevertheless, some bundles could be observed for thebers with a normal dew-retting degree.

.2. Measurements of fiber diameters

Before measuring mechanical properties, it is necessary toetermine precisely the morphological dispersion of diameters ofhe stripped fibers selected in the middle of the stems. Thus, we

easure the diameter of the fibers in the bundle for each vari-ty with a classical retting degree (R3). In Fig. 2, the percentagef fiber is plotted against the average diameter for the Alaska vari-ty cultivated in 2006. The average diameter obtained is 13.8 �m±4.7).

Table 2 lists the average diameters for each variety. We canlearly see that the average diameters of the stripped fibers areery close (13.3–15.3 �m) and are close to those of flax fibers, suchs the Agatha, Electra or Hermes varieties.

1 (a), Alaska 2006 R3 (b), Everest 2005 R3 (c), and Everest 2006 R3 (d).

3.3. Tensile properties of several linseed flax fibers

The tensile stress–strain curves of the different oleaginous flaxfibers are shown in Fig. 3. The behavior of oleaginous flax fiberis similar to that of the textile: a non-linear region is observedin the earlier stage of the loading, for the small deformations(0–0.5%). This behavior can be explained by the reorganisation ofthe cellulose microfibrils in the direction of the fiber axis and shear(Baley, 2002) during the tensile solicitation. These microfibrils havea micro fibrillar angle (MAF) of 10◦ (Bledzki and Gassan, 1999;Wang et al., 2001). For higher deformations, a linear region of thestress–strain curve is observed which is characteristic of a Hookeanbehavior. The Young’s modulus is measured by the slope of thislinear region.

For each variety, about 50–80 single fibers were tested afteroptical observation, checking the integrity of the fiber and measur-

Fig. 2. Percentage of flax fibers as a function of diameter for flax Alaska 2006.

I. Pillin et al. / Industrial Crops and Products 34 (2011) 1556– 1563 1559

Table 2Average diameter of oleaginous and textile flax fibers in the stems for several varieties.

Fiber number observed Average diameter (�m) Reference Sort of flax

Hivernal 2006 416 13.3 (±5.2) This work OleaginousAlaska 2006 405 13.8 (±4.7) This work OleaginousNiagara 2006 436 15.3 (±5.2) This work OleaginousEverest 2006 409 14.2 (±4.7) This work OleaginousOliver 2006 411 15.3 (±4.5) This work Oleaginous

Agatha 800 13.6 (±4.1) Charlet et al. (2009) TextileHermes 236 15.7 (±3.9) Charlet et al. (2007) TextileAriane 353 17.8 (±5.2) Baley (2002) TextileElectra 252 15.4 (±4.9) Bourmaud et al. (2010) Textile

43210Strain (%)

Hivern alEverestOliverNiagaraAlaska

30252015105

in sugars observed at different growth stages indicate important

ig. 3. tensile strength–strain curves for the different varieties of flax fibers 20063.

s 15.8 �m (±4.1) which is close to the diameter of the strippedbers (13.8 ± 4.7 �m).

In Figs. 4 and 5, it can be clearly seen that the Young’s modulusnd the strength decrease with the diameter of the fiber. Theseesults are in accordance with those obtained for textile fibersAndersons et al., 2005; Baley, 2002; Bourmaud and Baley, 2009;ourmaud et al., 2010; Charlet et al., 2007, 2009; Duval et al., 2011).

The dependence of strength on fiber size has already beennderlined in the literature (Andersons et al., 2005; Zafeiropoulosnd Baillie, 2007): the larger the fiber, the higher its probability of

This decrease of the Young’s modulus and breaking strength ofhe fiber could be partly explained by the presence of the lumen in

30252015105

Diameter (µm)

Fig. 4. Young’s modulus as a function of fiber diameter for Niagara 2006 R3.

Diameter (µm)

Fig. 5. Stress at break as a function of fiber diameter for Niagara 2006 R3.

the fiber center, the size of which increases with the fiber diameter;this lumen is not usually taken into consideration when calculatingthe cross-section due to its difficult determination. The decrease ofthe mechanical properties with the fiber diameter could also beexplained by outside parameters, such as inconstant fiber growingconditions (temperature, hygrometry, sunshine time or soil qual-ity). These growing conditions can be subjected to many variationsduring fiber development.

As highlighted by Morvan et al. (2003), the significant variations

remodelling with structural impacts on the physical properties offibers. Also, the chemical composition of non-cellulosic polysac-charides, as well as fiber morphology depends on the fiber position

302520151050.0

Diameter (µm)

Fig. 6. Strain at break as a function of fiber diameter for Niagara 2006 R3.

Table 3Measured mean values and standard deviation of diameter of tested fibers Ø, Young’s modulus E, tensile strength � and strain at break ε.

Number of fibers Ø of tested fibers (�m) E (MPa) � (MPa) ε (%) Reference

Hivernal 2006 (R3) 57 12.9 (±3.3) 71.7 (±23.2) 1111 (±544) 1.7 (±0.6) This workAlaska 2006 (R3) 66 15.8 (±4.1) 49.5 (±13.2) 733 (±271) 1.7 (±0.6) This workNiagara 2006 (R3) 71 15.6 (±2.3) 45.6 (±16.7) 741 (±400) 1.7 (±0.6) This workEverest 2006 (R3) 76 21.2 (±6.6) 48.0 (±20.3) 863 (±447) 2.1 (±0.8) This workOliver 2006 (R3) 76 13.7 (±3.7) 55.5 (±20.9) 899 (±461) 1.7 (±0.6) This work

Agatha 45 21.3 (±6.3) 57.0 (±29.0) 865 (±413) 1.8 (±0.7) Charlet et al. (2009)68.254.151.1

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Hermes 37 19.6 (±6.7)

Ariane 77 23.0 (±5.7)

Electra 45 15.8 (±4.5)

long the stem and more importantly on the flax variety. Thesemportant differences in the biochemical structure could have areat deal of impact on the mechanical properties of the fibers.

In Fig. 6, no tendency of strain at break with the fiber diameteran be observed, which is representative of all the oleaginous flaxbers tested. This phenomenon has been already noticed in severaltudies (Alix et al., 2009; Baley et al., 2005; Charlet et al., 2007,009).

Table 3 gives the diameter and the mechanical properties of thebers as a function of the variety of the flax plant. To compare thesealues, it is important to notice that all these tensile experimentsave been done on the same tensile machine and with the samerotocol. First, it can be noticed that the diameters of the testedbers are close to those measured in the morphological analysisxcept for the Everest variety R3 (21.2 �m for tested fibers against4.2 �m for stripped fibers). This could be explained by the diffi-ulty of extracting the fibers in the stem as a function of the variety.

The Young’s moduli of the different varieties vary from 48.0 MPao 71.7 MPa and are close to the textile flax (from 51.1 to 89.0 MPa)Baley, 2002; Charlet et al., 2007, 2009). The main difference is theensile strength: the values for linseed flax are significantly infe-ior to those of textile flax fibers, except for the Hivernal varietyhich provides the best mechanical properties of the several testedbers. Its modulus is superior to those of textile flax fibers and itsensile strength is comprised between those of the Agatha and theermes/Ariane varieties.

Nevertheless, some differences can be noticed between theiameter measured in the stem and the diameter of the flax fiberested. In order to homogenise the results, we specify in Table 4 the

echanical properties of a subset of fibers, the diameters of whichre around the mean values obtained from the morphological anal-sis (mean diameter ± 2.5 �m).

The mean mechanical properties of linseed flax fibers arelightly modified when the fibers are selected as a function of

diameter near the diameter obtained from the morphologicalnalysis. The Hivernal variety again has the better mechanical prop-

able 4verage mechanical properties of flax fibers whose diameters are close to the mean value

Number of fibers Average diameter (�m) Ø (�m) interva

Hivernal 2006 (R3) 23 13.3 (±5.2) 10.8–15.8

Alaska 2006 (R3) 37 13.8 (±4.7) 11.3–16.3

Niagara 2006 (R3) 40 15.3 (±5.2) 12.8–17.8

Everest 2006 (R3) 19 14.2 (±4.7) 11.7–16.7

Oliver 2006 (R3) 32 15.3 (±4.5) 12.8–17.8

Agatha 7 13.6 (±4.1) 11.1–16.1

Hermes 9 15.7 (±3.9) 13.2–18.2

Ariane 22 17.8 (±5.2) 15.0–20.0

Electra 31 15.4 (±4.9) 12.9–17.9

(±35.8) 1454 (±835) 2.3 (±0.6) Charlet et al. (2007) (±15.1) 1339 (±486) 3.3 (±0.8) Baley (2002) (±15.0) 808 (±442) 1.6 (±0.4) Bourmaud et al. (2010)

not representative of an entire plant. Indeed, even if the mechanicalproperties for the Hermes variety are very interesting, the stan-dard deviations of modulus and strength are very high which canbe explained by a low specimen test number.

In Table 4, we can also observe that the mechanical properties(Young’s modulus and stress at break) cannot be correlated to theaverage diameter of the flax fiber for one variety. Even if the Hiver-nal variety has the best mechanical properties and the smallest fiberdiameter, the Niagara and Oliver varieties, which have the samefiber diameters, have different mechanical properties. As describedbelow, the Young’s modulus and strength increase when the diam-eter of fiber decreases for one variety. But, for one variety to anotherone, it cannot be put in evidence a correlation between diameterof fibers and mechanical properties. The same observation can benoted for the textile fibers with the higher mechanical properties,the Hermes variety, for example, has a fiber diameter of 15.7 �m,whereas the diameter of the Agatha variety is 13.6 �m.

Other parameters, such as cellulose fraction, polymerizationdegree, microfibrillar angle, pectin or hemicellulose content, caninfluence the mechanical properties. These parameters are directlyinfluenced by weathering conditions, geographical area and soilcomposition.

3.4. Influence of retting degree

Two degrees of retting were studied for the Alaska variety culti-vated in 2006. In order to quantify retting degrees, we realized TGAanalyses as described in Velde and Baetens (2001). We obtainedclassical curves with three mass losses (Fig. 7). The first one isrelated to the release of water (≈50 ◦C), the second one to the cellu-losic substances (mainly hemicelluloses and cellulose) degradation(≈330 ◦C) and the third one to the degradation of non cellulosic sub-stances (including lignin, sugar, mallards derivatives, etc.) at about430 ◦C.

Table 5 shows the thermogravimetric analysis (TGA) resultsobtained for the Alaska fiber. The moisture percentage is approx-

s obtained by morphological analysis (±2.5�m).

l E (MPa) � (MPa) ε (%) Reference

67.5 (±23.7) 1119 (±490) 1.9 (±0.5) This work53.1 (±12.2) 754 (±311) 1.6 (±0.6) This work44.1 (±17.2) 647 (±296) 1.8 (±0.6) This work57.2 (±24.6) 1086 (±462) 2.3 (±0.7) This work55.2 (±20.3) 956 (±536) 1.7 (±0.7) This work

71.0 (±25.0) 1381 (±419) 2.1 (±0.8) Charlet et al. (2009)76.7 (±40.8) 1795 (±1127) 2.0 (±0.7) Charlet et al. (2007)58.6 (±14.2) 1496 (±325) 3.4 (±1.0) Baley (2002)55.3 (±25.7) 934 (±593) 2.0 (±0.5) Bourmaud et al. (2010)

I. Pillin et al. / Industrial Crops and Products 34 (2011) 1556– 1563 1561

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Fig. 7. Thermogravimetric be

precise sorption method (Alix et al., 2009) has shown that fibersrom green flax (not submitted to retting) display at low waterctivity very strong interactions with water, thus the diffusion coef-cient exhibit a minimal value.

The mass changes in the second peak increased with the rettingegree. The most retted fibers contain the highest percentage ofellulose due to the removing of pectin during retting. In our case,he mass change in the second peak is 63.2% in comparison to 60.8%or the low retting degree fibers. These values are well correlatedith the literature and they confirm the elimination of a significant

mount of pectins during retting.The size of the third peak is inversely proportional to the ret-

ing degree and it is an indication of the amount of remaining nonolysaccharidic matter (such as phenolics) (Sharma et al., 1996;elde and Baetens, 2001). Our results are in accordance with pub-

ished results with a lower mass loss for the higher retted fibers.

etting degrees for the fibers with diameters close to those obtainedith morphological analysis indicating a good quality of handlinguring unitary fiber extraction. A slight decrease of the fiber diam-

able 5hermo gravimetric analysis on Alaska 2006 flax fibers.

Materials First peak Second peak

Weight loss (%) Temperature (◦C) Mass loss (%)

Alaska R1 7.5 51.0 60.8

Alaska R3 7.4 42.9 63.2

able 6laska 2006 R1 and R3. Mean values and standard deviation of fiber diameter in the stem

Average diameter (�m) Tested fibers Ø (�

Alaska 2006. R1 15.3 (±5.4) 20

Alaska 2006. R3 13.8 (±4.7) 37

r of Alaska 2006 R3 flax fiber.

eter can be noticed after retting probably induced by the removingof surface pectins or middle lamella fragments. A previous study(Bourmaud et al., 2010) shows the opposite after a water treat-ment. This phenomenon could be explained by some release of theentanglement of the pectic network within the primary wall of thefibers after the removal of middle lamella enriched in calcium-HGA.Young’s modulus and strength is slightly higher for high rettedfibers. Nevertheless, the mechanical properties are close, what-ever the retting degree, if we look the standard deviations. Theseresults correlate well with those published by Velde and Baetens(2001). They studied three retting degrees on a bundle (accord-ing to ISO4923) and showed that there is no tendency for Young’smodulus or elongation at break, and the strengths are very close,whatever the retting degree.

3.5. Influence of culture year on the reproducibility of the

In this part, we study the influence of the culture year on thefiber properties. An Everest linseed flax was cultivated for 4 years

Third peak

Temperature (◦C) Mass loss (%) Temperature (◦C)

327.6 28.4 427.1329.3 27.3 436.5

Ø, tested fibers Ø, Young’s modulus E, tensile strength � and strain at break ε.

m) interval E (MPa) � (MPa) ε (%)

12.8–17.8 46.3 (±12.1) 691 (±253) 1.8 (±0.6)11.3–16.3 53.1 (±12.2) 754 (±311) 1.6 (±0.6)

Table 7Comparison of cultural techniques between 2005 and 2008 for Everest variety and fiber diameter after stripping.

Year Sowing Seeding rate(g/m2)

Harvest Seed yield(Quintal/ha)

Plant Height(cm)

Stemnumber/m2

Fiber numberobserved

Averagediameter (�m)

2005 06/10 400 14/07 9.3 80 431 423 16.9 ± −4.92006 28/09 450 24/07 28.0 65 425 409 14.2 ± −4.82007 03/10 350 19/07 17.8 68 203 403 14.3 ± −5.12008 03/10 400 21/07 28.0 78 370 413 15.4 ± −5.1

Table 8Mean values and standard deviation of diameter of tested fibers Ø, Young’s modulus E, tensile strength � and strain at break ε. Everest 2005, 2006, 2007, 2008.

Number of fibers Average diameter (�m) Ø (�m) interval E (GPa) � (MPa) ε (%)

Everest 2005 9 16.9 (±4.9) 14.5–19.5 41.0 (±12.5) 663 (±307) 1.8 (±0.4)Everest 2006 19 14.2 (±4.8) 11.7–16.7 57.2 (±24.6) 1086 (±462) 2.3 (±0.7)

11.8–16.8 51.8 (±15.6) 685 (±222) 1.7 (±0.6)12.9–17.9 75.0 (±21.6) 1232 (±554) 2.1 (±0.8)

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Hiverna

Alaska

Niagara

Oliver

Everes

Agatha

Hermes

Ariane

Electra

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at break which could be due to differences in the cellulose rate ofthe different flax varieties. Alix et al. (2008) showed that the Oliverlinseed variety contains 770 mg/g of fiber of cellulose comparedto 840 mg/g for the Hermes textile variety. Nevertheless, these

liver 20

Agatha

Hermes

Ariane

Electra

Glass f

Everest 2007 25 14.3 (±5.1)

Everest 2008 30 15.4 (±5.1)

2005, 2006, 2007 and 2008) using equivalent agronomic factors.he results were discussed as a function of seed rate, plant height,nd yield. These several factors are given in Table 7.

The average fiber diameters can be noted as being similar forulture years 2006–2008; the 2005 Everest variety has an averageiameter slightly higher than those of the other culture years. Thisesult seems to correlate to very low yields of seed obtained in005. For the four years, the plant heights are practically similar,et slightly lower for 2007.

The development of the stem is probably different each year. Itepends on meteorological and soil conditions. These outside fac-ors induce different fiber morphologies which, of course, spreadnto the mechanical properties. In order to develop the reinforce-

ent of polymers with vegetal fibers, it is important to control theeproducibility of the fiber morphologies and of their mechanicalroperties. We need to produce fibers with reproducible averageroperties and quantities.

Table 8 specifies the mechanical properties of flax fibers for eachear for the fibers with diameters close to those measured in thetem (±2.5). In 2005, Young’s modulus and tensile strength areeak. These results can be attributed to the high average diame-

ers as mechanical properties and average diameter are correlateds described in Baley (2002). Fibers obtained in 2008 give the bestesults and are close to the textile fibers (Table 4).

The comparison between the parameters in Table 7 andechanical properties in Table 8 can lead us to several conclusions.

he seeding rates are very close for the cultures of all four years andeem to have no influence on the quality of flax fibers.

In 2005, the very weak yields lead to a high diameter and poorechanical properties. In 2007, the yields are lower than in 2006

nd 2008, but higher than in 2005 and Young’s modulus and ten-ile strength are comprised between those of 2005 and 2006/2008.hese observations are the result of growth conditions of the planthich depends on agronomic factors such as meteorological and

ulture conditions. The culture conditions, such as nitrogen fer-ilizers, herbicide, and regulator height, can be controlled but theunshine, rainfall and temperature are external factors which can-ot be controlled especially during the growth of the stem (fromarch to May). These results show the difficulty to obtain fibersith reproducible mechanical properties.

In Figs. 8 and 9 are plotted the specific mechanical properties forach tested sample and compared to specific properties of textileax and glass fibers. A specific Young’s modulus and stress at breakere calculated by dividing each value by the density (1.54 for flax

As discussed previously, it can be noted that oleaginous fibersxhibit mechanical properties slightly lower than those of textileaxes. This phenomenon is much more pronounced for the stress

Fig. 8. Specific Young’s modulus for each flax sample in comparison with textile flaxand glass fiber. The solid line represents the average Young’s modulus for oleaginousflax and the dash lines its standard deviation.

Hiv A A Nia O Ev Ev Ev Ev

Fig. 9. Specific stress at break for each flax sample in comparison with textile flaxand glass fiber. The solid line represents the average stress at break for oleaginousflax and dash lines its standard deviation.

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I. Pillin et al. / Industrial Crops

echanical properties are very competitive compared to those oflass fiber (36 GPa against 29 GPa for the specific Young’s modu-us and close to 600 MPa against 800 MPa for the specific stress atreak) proving that oleaginous flax fibers could be good candidatesor substitution to glass fiber for polymer reinforcement. Moreover,heir performances are very interesting compared to other vegetalbers already used in composite reinforcement, such as hemp orisal (Bourmaud and Baley, 2009).

. Conclusion

In this paper, we studied the mechanical properties of elemen-ary linseed flax fibers by tensile tests. We characterized around00 fibers, 5 varieties, and 2 retting conditions for a particular vari-ty and 4 growing years for another one. All the tested fibers haveeen removed from stems which came from the same geographicrea.

We have shown that the Hivernal and Oliver varieties haventeresting tensile moduli and strengths at break, but the average

echanical properties of linseed varieties are slightly inferior tohose of textile varieties. Nevertheless, we can notice that, despite

moderate stress at break, the specific Young’s modulus of linseedax fibers is better than the specific Young’s modulus of glass fibers.hanks to these satisfactory mechanical properties, oleaginousax fibers could be considered as good candidates for substitu-ion to glass fibers in polymer matrix reinforcement. Besides their

echanical advantages, these fibers exhibit an economical inter-st due to the fact that linseed flax is especially cultivated for itsmega-3 seed (used for cattle feed); thus, the fibers could be con-idered as a co product which can induce a new revenue for thearmers without any competition with farming surfaces used foruman food.

The tensile experiments showed that, for a specified year, dif-erences in mechanical properties exist between several oleaginousax varieties. Nevertheless, the reproducibility study carried out for

years on the Everest variety evidences that it is impossible to con-lude on this point. The seeding rate or plant height has no influencen the mechanical properties, whereas low yields lead to flax withigh diameter fiber and poor mechanical properties. Using similarulture conditions, the morphological and mechanical properties ofbers are obtained, which show that the meteorological conditionsave a strong impact on the stem growth and quality of fiber.

To conclude, with an accurate selection of flax varieties and goodeteorological and environmental conditions, oleaginous fibersith interesting mechanical properties can be obtained. The stem

fter seed harvest can be developed and used for the reinforcementf polymers. Despite the mechanical and economical advantages ofhe linseed flax fibers, the obtaining of high quality fibers dependsn the structuring and the organization of the profession; as forhe textile industry, the different steps between the field and thebers, i.e. dew-retting, pulling out, harvest, scutching or carding,ave to be optimized and controlled to obtain the best possiblebers.

This study could be continued by an important work on under-tanding the reproducibility of mechanical properties. Conditionsf extraction from retting to carding should permit us to have aetter understanding of the role of each step. Biochemical analy-es of fiber cell walls could be interesting to understand the main

roducts 34 (2011) 1556– 1563 1563

Acknowledgments

The authors would like to acknowledge ADEME (Agence del’Environnement et de la Maîtrise de l’Energie).

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Could oleaginous flax fibers be used as reinforcement for polymers?

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