- Email: [email protected]
Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l -poly-(lactide)-flax blends
G Model
ARTICLE IN PRESS
INDCRO-7529; No. of Pages 7
Industrial Crops and Products xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop
Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends Alain Bourmaud ∗ , Yves-Marie Corre, Christophe Baley Laboratoire d’Ingénierie et Matériaux de Bretagne (UBS), Université Européenne de Bretagne, Centre de Recherche Christiaan Huygens, Rue Saint Maudé, 56321 Lorient, France
a r t i c l e
i n f o
Article history: Received 4 June 2014 Received in revised form 29 August 2014 Accepted 16 September 2014 Available online xxx Keywords: Poly-(butylene-succinate) Flax fiber Mechanical properties l-Poly-(lactide) Nanoindentation
a b s t r a c t To take advantage of the mechanical performance of plant fibers and avoid their degradation, it is necessary to develop biocomposites by working on the least aggressive process conditions possible. The use of thermoplastic polymers with low processing temperatures is one possible way. In this study, tests were performed on poly-(butylene-succinate) (PBS) flax composite, extruded and injected at 140 ◦ C. They have a good level of tensile or impact properties compared to poly-(propylene) (PP) or l-poly-(lactide) (PLLA) based biocomposites. Nanoindentation measurements were performed in situ on the composites. Despite the low Young’s modulus of PBS, it was shown that the use of a moderate process temperature limits the downward stiffness of the flax cell walls. Finally, it was demonstrated that the PBS could be associated with PLLA for making flax fiber reinforced biocomposites. The introduction of PBS, with adjustable volume fractions, improves elongation at break and impacts on the behavior of PLLA–flax composites, whilst retaining high performance mechanical properties. Thus, it is possible to elaborate fully biodegradable composites with the desired mechanical properties. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Nowadays, the depletion of our natural resources as well as the increasing impact of our society on our environment necessitates the modification of composite material design. Thus, for many industrial products, plant fibers could be used to substitute synthetic fibers in composite material reinforcement. In Europe, the most relevant are flax or hemp fibers due to their highperformance specific mechanical properties (Assarar et al., 2011; Baley, 2002; Bourmaud et al., 2010; Misnon et al., 2014; Muralidhar, 2013; Placet, 2009), their environmental and ecological benefits (Azwa et al., 2013; Joshi et al., 2004; Le Duigou et al., 2011; Pervaiz and Sain, 2003) and their low cost. In industrial development, plant fibers are generally associated to petrochemical matrixes like polyolefin in order to substitute glass fiber. Nevertheless, it is possible to increase the environmental interest of these new composites by using some biobased or biodegradable polymers. In this way, and despite its low toughness, many works focused on the association of plant fibers with PLLA (Bax and Müssig, 2008; Le Duigou et al., 2013; Oksman et al., 2003) or poly-(hydroxybutirate) (PHB) (Barkoula et al., 2010; Bledzki and
∗ Corresponding author. Tel.: +33 2 97 87 45 05; fax: +33 2 97 87 45 88. E-mail address: [email protected] (A. Bourmaud).
Jaszkiewicz, 2010; Le Duigou et al., 2012) highlighted the potential of bio-sandwich PLLA–flax materials in terms of environmental impact. Due to the low degradation temperature of the plant fibers (Bourmaud and Baley, 2010; Velde and Baetens, 2001), the choice of the matrix is a preponderant parameter in order to preserve the fiber performances. Temperatures that are too high, or aggressive processes (Bourmaud and Baley, 2010) could cause an alteration of the plant cell wall structure and of their mechanical properties (Baley et al., 2012). In this way, the use of a low process temperature polymer has a real interest, and, due to its low melting point (Liang et al., 2010) and its biodegradability (Kim et al., 2006; Liu et al., 2009b; Teramoto et al., 2004), the poly-(butylene succinate) (PBS) is a potential candidate to be associated with plant fibers. Recently, many authors worked on the elaboration of vegetal fiber PBS composites. For example, Teramoto et al. (2004) proved the biodegradability of PBS-abaca composites; Dorez et al. (2013) evidenced the interest of a high fiber loading rate to improve the fire barrier properties of PBS-plant fiber composites. Other explorative works showed the technical or environmental suitability of PBS-sisal (Feng et al., 2011, 2013), jute (Liu et al., 2009a,b) or cotton (Bin et al., 2011; Qu et al., 2011) biocomposites. To explore the impact of the process on the mechanical properties of the cell walls, nanoindentation could be carried out, in situ, on the biocomposites. In this way, it is possible to obtain the
http://dx.doi.org/10.1016/j.indcrop.2014.09.033 0926-6690/© 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: Bourmaud, A., et al., Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.09.033
G Model INDCRO-7529; No. of Pages 7
ARTICLE IN PRESS A. Bourmaud et al. / Industrial Crops and Products xxx (2014) xxx–xxx
2
stiffness and hardness of fibers of the composite at the micron or sub-micron scale without any extraction or damage to the material. An attractive feature of this technique is that the measurements are made without requiring burning, chemical or mechanical modifications to isolate individual fibers as required in single-fiber tensile tests. In a previous study (Bourmaud and Baley, 2010), we showed the significant negative impact of injection molding, compared to film stacking, on PLLA flax composites fibers mechanical properties. Despite a significant discrepancy between the Young’s modulus and the apparent nanoindentation modulus (Gindl et al., 2008), due to the inclination of the indenter pyramid with regard to the principal material axes, nanoindentation is an appropriate technique for the comparison of vegetal fiber stiffness. The aim of this work is to estimate the suitability of the use of a PBS matrix for biocomposite elaboration. Firstly, the tensile, impact, thermal and morphological properties of PBS–flax fiber biocomposites were investigated in order to estimate the potential of PBS as a matrix. In a second part of the study, to estimate the impact of the process on the cell walls’ integrity, we measured the Young’s modulus and hardness of flax fibers in the biocomposite before and after processing by using nanoindentation. Finally, the incorporation of PBS into PLLA–flax composites was explored in order to elaborate fully biodegradable composites with improved elongation and impact resistances.
2. Experimental details 2.1. Materials The PBS used in this study is Bionolle 1020 MD supplied by Showa Denko (Tokyo, Japan) with a Melt Flow Index (MFI) of 20–34 g/10 min (at 140 ◦ C and 2.16 kg) and a density of 1.23 g/cm3 . In addition, and to compare the composite’s mechanical properties or to elaborate PLLA–PBS–flax composites, we used injection grade PP (PPC 10642 from Total Petrochemical) and PLLA (7001D from Nature Works). The PP or PLLA MFI and density are 44 g/10 min (at 190 ◦ C and 2.16 kg) and 0.92 g/cm3 or 5–15 g/10 min (at 190 ◦ C and 2.16 kg) and 1.24 g/cm3 , respectively. To be treated under the same conditions as that for PBS and PLLA, we did not use a compatibilizer for the PP–flax blend. The flax fiber (Linum usitassinum) used in this study is from the Marilyn variety and comes from a 2003 harvest cultivated in Normandy (France). The flax fibers selected are representative and have known and reproducible properties (Lefeuvre et al., 2013). Their production information are detailed in previous work (Lefeuvre et al., 2013). The extracted fibers are cut at 1 mm. The average length and aspect ratio of the elementary fibers was estimated to be 1068 ± 139 m and 33.3 ± 12.1, respectively, as determined by optical microscopy for 250 fibers after inclusion into epoxy resin and polishing of the section (Fig. 1). The aspect ratio is the most significant parameter of the mechanical properties of the composite for short fiber reinforced polymers (Kelly and Tyson, 1965). Generally, the aspect ratio has to be superior to 10, which is considered as the minimum aspect ratio value for good strength transmission for any reinforcement (Jiang et al., 2007; Mutje et al., 2007). In our case 92.3% of fibers have an aspect ratio superior to this value. This result exhibits a good individualization of our fibers, probably due to an appropriate retting step, and the high quality of the cutting process.
Fig. 1. Flax fiber length (A) and aspect ratio (B) dispersion.
As observed in Fig. 1, the cutting process used leads to a performing length dispersion highlighted by a narrow distribution. The mechanical properties of the flax fibers used in the present work were studied in a previous work (Bourmaud et al., 2013); they are shown in Table 1. 2.2. Compounding and processing Flax fibers were dried under vacuum at 60 ◦ C for 12 h prior to the extrusion step. Compounding was achieved in a single screw extruder at 20 rpm and with the following temperature profile: 130/135/140 and 140 ◦ C in the nozzle for the PBS–flax fiber 25.5%-vol compounds. The extrusion temperatures for the PLLA–flax 25.7%-vol, for the PLLA–PBS-25.5%-vol and PP–flax 25.6%-vol blends were 190/190/190 and 190 ◦ C in the nozzle. Compounded pellets were also dried under vacuum at 60 ◦ C for 48 h. Injection molding was then carried out on a Battenfeld machine. All parameters were kept constant during the injection molding process. The temperature profile was kept as follows: 130/135/140
Table 1 Mechanical properties of flax fibers. Materials
Number of fibers
Diameter (m)
Young’s modulus (GPa)
Strength at break (MPa)
Elongation at break (%)
Marylin flax fibers
90
15.5 ± 2.7
53.8 ± 14.3
1215 ± 500
2.24 ± 0.59
Please cite this article in press as: Bourmaud, A., et al., Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.09.033
G Model
ARTICLE IN PRESS
INDCRO-7529; No. of Pages 7
A. Bourmaud et al. / Industrial Crops and Products xxx (2014) xxx–xxx
and 140 ◦ C in the nozzle for the PBS and PBS–flax composites and 190/190/190 and 190 ◦ C in the nozzle for the virgin PP and PLLA, PP–flax, PLLA–PBS–flax and PLLA–flax compounds. The mold temperature was maintained at 30 ◦ C for all the compounds. The compounds were injected into a mold designed to produce ISO-527 normalized specimens. To be sure of the fiber volume rate in our samples, density measurements were carried out after injection molding. We calculated the fiber rate by a classical mixing rule, by knowing the fiber and matrix density. We found 25.3 ± 0.4%, 25.5 ± 0.3% and 25.7 ± 0.2% for the PBS–flax, PP–flax and PLLA–flax composites, respectively. The materials for nanoindentation tests were then cut into injected specimens. The reference virgin fibers were embedded into a thermoset epoxy resin which exhibits a low reticulation temperature (40 ◦ C). As far as the nanoindentation technique is concerned, sample preparation is very important because accurate results are obtained only if the indentations are deeper than the surface topography of the specimen. Meticulous polishing can significantly reduce the uncertainty in determining the surface properties. Hence, all surfaces to be indented were polished to a 1-m particle size polishing solution finish. The average surface roughness, Ra, was measured with a profilometer at 0.1 m. 2.3. Composites mechanical testing The static tensile tests were carried out using a MTS Synergie RT1000 (MTS, Eden Prairie, Minnesota, USA) testing apparatus in a laboratory where the temperature was 23 ◦ C and the humidity was 48% (ISO 527) according to ASTM: D638. The loading speed was 1 mm min−1 . A MTS Extensometer was used with a nominal length of 25 mm. The tests were carried out at least five times for each specimen and the results were averaged arithmetically.
2.4. Charpy impact
3
The degree of crystallinity (c ) was estimated using Eq. (1) where H100% crystalline PBS = 200 J/g (Miyata and Masuko, 1998; Papageorgiou and Bikiaris, 2005). c =
Hm H100%
(1)
2.6. Scanning Electron Microscopy (SEM) pictures The fibers were sputter-coated with a thin layer of gold in an Edwards Sputter Coater and then observed with a Jeol JSM 6460LV Scanning Electron Microscope. 2.7. Nanoindentation experiments The cross section of an injected specimen was used for this study. The samples were mounted on aluminum cylinders using Superglue© for indentation tests (Nanoindenter XP, MTS Nano Instruments) at room temperature (23 ± 1 ◦ C) with a continuous stiffness measurement (CSM) technique. An oscillating force at controlled frequency and amplitude was superimposed onto a nominal applied force so that the material responded with a displacement phase and amplitude (Li and Bhushan, 2002). The Young’s modulus was estimated from the experimental curves as previously described (Bourmaud and Pimbert, 2008). A three-side pyramid (Berkovich) diamond indenter was used, whose area function was calibrated by using a standard silica sample. After the indenter made contact with the surface, it was driven into the material with constant strain rate of 0.05 s−1 to a depth of 120 nm; the load was held at maximum value for 60 s; then, the indenter was withdrawn at the same rate as loading until 10% of the maximum load was reached. A 3 nm amplitude and 70 Hz oscillation was chosen for the CSM parameters. Indents were made in the S2 layer of around 50 fibers. The modulus and hardness calculated are average values from 80 to 120 nm. 3. Results and discussion
Notched Charpy impact and Izod tests were performed using a Tinuis Olsen machine at an ambient temperature. Specimens for the Charpy test were cut from tensile specimens using ISO 179 (80 mm × 10 mm × 4 mm). The tests were carried out at least 10 times for each type of specimen and the results were averaged arithmetically.
2.5. Calorimetric measurements Calorimetric data were obtained using a Mettler-Toledo DSC 822 (Mettler Toledo, Viroflay, France). The calibration was done with indium and zinc. Aluminum pans were used and the sample mass was approximately 10 mg. The samples were first melted to 180 ◦ C (1st run) and kept at this temperature for 2 min, then cooled to a temperature of −60 ◦ C and heated up again to 180 ◦ C (2nd run). Temperature and heat of phase transitions were determined, respectively, from the maxima and areas of the crystallization and melting peaks.
3.1. Mechanical properties of a PBS-flax composite Table 2 shows the tensile mechanical properties of PBS–flax fiber composites compared to PP and PLLA–flax fiber composites for similar volume fractions. For the PBS–flax composite, an important increase in tensile modulus with the addition of vegetal fibers can also be observed (+465.5%). In fiber-reinforced composites, the tensile modulus is mainly governed by the mechanical properties of the fibers. This tendency has been observed, at lower levels, by different authors in the literature. Liang et al. (2010) investigated the reinforcement of PBS with kenaf fibers; they illustrated an increase in modulus from around 670 to 1700 MPa with a kenaf fiber content ranging from 0 to 30%-wt (25.5%-vol). Similar results are exhibited by Lee and Wang (2006) on PBS-bamboo composites with an improvement of the Young’s modulus from 500 to 1200 MPa with the same weight fraction (30%-wt). In our case, the significant improvement of the stiffness is probably due to the conjugated effect of the high
Table 2 Tensile and impact properties of PBS–flax fiber composites compared to PP and PLLA–flax fiber composites. Materials
Young’s modulus (MPa)
Virgin PBS PBS – flax fiber 25.5%-vol Virgin PP PP – flax fiber 25.6%-vol Virgin PLA PLA – flax fiber 25.7%-vol
643 3636 1772 5787 3760 7437
± ± ± ± ± ±
29 179 17 143 56 21
Strength at break (MPa) 39.7 38.6 20.1 21.2 55.2 55.4
± ± ± ± ± ±
0.8 0.1 0.4 0.4 0.9 1.2
Strain at break (%) 264 3.9 11.5 3.0 2.8 1.4
± ± ± ± ± ±
8 0.1 4.4 0.2 0.4 0.1
Impact energy at failure (kJ/m2 ) – 17.8 ± – 11.6 ± 19.5 ± 9.1 ±
1.1 0.9 2.4 0.8
Please cite this article in press as: Bourmaud, A., et al., Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.09.033
G Model INDCRO-7529; No. of Pages 7 4
ARTICLE IN PRESS A. Bourmaud et al. / Industrial Crops and Products xxx (2014) xxx–xxx
Fig. 2. SEM observations of the PBS–flax composite.
stiffness of the flax fibers (53.8 ± 14.3 GPa) compared to kenaf (Ochi, 2008) or bamboo (Defoirdt et al., 2010) fibers and of the low rigidity of the virgin PBS which is highly improved by the incorporation of flax fibers. Whatever the matrix used, unchanged values of the strength at max could be observed for the virgin matrix and plant fiber composites. These results are well correlated with the literature results for PLLA–flax (Le Duigou et al., 2008). In the case of the PP–flax composite and compared with previous studies (Ausias et al., 2013; Bourmaud et al., 2013), the strength value seems to be low, but, in our case, we do not use a compatibilizer, in order to be consistent with the PLLA–flax and PBS–flax composites. Moreover, the fiber orientation in injected composites is not perfect with a significant skin-core effect (Bourmaud et al., 2013). In addition, the PBS–flax composite exhibits a more significant elongation at break (3.9 ± 0.1%) compared to those of PP–flax or PLLA–flax. The plant fiber composite benefits from the significant elongation of the pure matrix, while having high stiffness and strength at break. These results are corroborated by the impact energy at failure of the composites. The PBS–flax composite exhibits high Charpy impact energy (17.8 ± 1.1 kJ/m2 ) due to the softness of the PBS matrix. The functional mechanical properties of the PBS–flax composite, conjugated with high impact energy, could enable this biocomposite to be a good candidate for replacing glass reinforced materials for automotive parts elaboration. In order to better understand the high mechanical properties of the PBS–flax composites, a morphological analysis, using SEM observations, has been carried out. Fig. 2 shows SEM images of tensile fracture surfaces of PBS–flax composite (Fig. 2A–C) and of a polished cross section in order to estimate the quality of the fiber individualization in the composite (Fig. 2D). Fig. 2A and B evidence a good adhesion between the PBS matrix and the flax fiber, there is no decohesion or debonding and
the flax fibers are well linked to the matrix with reduced pullout phenomena. We can also see the breaking of fibers during tensile tests (Fig. 2C) showing the quality of the adhesion between matrix and fibers. Moreover, Fig. 2D exhibits a good dispersion of the flax fibers into the PBS matrix; we observe the presence of many elementary fibers, evidencing the quality of the compounding step for dividing the bundles. In a previous work (Bourmaud et al., 2013), we highlighted the rule of bundles; they can cause premature breakage by creating privileged damage areas. Conversely, a good dispersion has a direct influence on the composites’ mechanical properties and at best enables it to benefit from plant reinforcement properties (Coroller et al., 2013). In order to better understand the origin of the good mechanical properties of the PBS–flax composite, the next section will be dedicated to the estimation of the impact of the process on the flax fiber’s mechanical properties. 3.2. Thermal properties of virgin PBS and PBS–flax composite Table 3 presents the calorimetric properties of virgin PBS and PBS–flax 25.5%-vol. The melting and crystallization behavior of the different samples was studied. The addition of vegetal fibers to PBS results in
Table 3 Thermal properties of PBS and PBS–flax composites. Materials ◦
Glass temperature ( c) Melting temperature (◦ C) Crystallization temperature (◦ C) Heat of crystallization (J/g) Reduced crystallinity (%)
Virgin PBS
PBS–flax 25.5%-vol
Evolution
−38.4 117.8 64.4 85.29 42.65
−35.1 111.4 69.8 59.16 42.26
+3.3 ◦ C −6.4 ◦ C +5.4 ◦ C −30.6% −0.39%
Please cite this article in press as: Bourmaud, A., et al., Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.09.033
G Model INDCRO-7529; No. of Pages 7
ARTICLE IN PRESS A. Bourmaud et al. / Industrial Crops and Products xxx (2014) xxx–xxx
5
Fig. 4. Evolution of Young’s modulus estimated by nanoindentation for virgin and into PBS or PLLA processed flax fibers.
Fig. 3. AFM picture of indents in a flax cell wall.
a slight increase in Tc . Nevertheless the percentage of crystallinity is unchanged. The incorporation of flax fibers causes an acceleration of the crystallization process but their nucleating ability is not demonstrated in our case. The increase of the crystallization temperature with the addition of vegetal fiber is a well-known phenomenon highlighted by many authors (Bourmaud and Baley, 2007; Joseph et al., 2003; Pracella et al., 2006). The glass temperature and melting temperature are slightly modified with the incorporation of flax fiber; the melting temperature decrease could be explained by an improvement of the shear rate during the compounding process in the presence of fibers. It could cause a decrease of the polymer chains and consequently an increase in their mobility. These results illustrate the interest of using PBS as a matrix for biocomposites; its crystallinity is not modified with the incorporation of flax fibers and the slight decrease in its melting temperature could allow a reduction of the compounding temperature in order to better preserve the fiber’s integrity. 3.3. Impact of the process on the flax fiber’s mechanical properties estimated by nanoindentation Fig. 3 presents an Atomic Force Microscopy (AFM) picture of 6 indents on a flax cell wall and Fig. 4 shows the average curves of the Young’s modulus vs. indentation depth for virgin Marylin fibers and for flax cell walls after processing into PLLA and PBS. In Fig. 3, we can clearly see two areas, the first one is attributed to the heterogeneity and roughness of the sample, the second one, after around 50 nm, evidences a good stabilization of the Young’s modulus. In our case, the indentations have been carried out in the middle of the cell wall; due to it being a significant part of the fiber section (around 80%), the nanoindentation results are more specifically associated to the mechanical properties of the secondary wall and especially to the S2 layer. All the indent positions were checked, and those located near the edges of the fibers have not been taken into account. A Poisson’s ratio of 0.35 (Baiardo et al., 2004) was used in all modulus calculations. The values are averaged on an indentation depth of 80–120 nm and for the virgin flax fibers, we have obtained a modulus of 18.9 ± 1.3 GPa. These results are comparable with the literature values. In previous works of our team (Bourmaud
and Baley, 2010, 2012; Bourmaud and Pimbert, 2008), we found a nanoindentation longitudinal modulus of 17.97 ± 1.61, 18.4 ± 1.9 and 19.8 ± 0.7 GPa for flax fibers. There are few studies showing nanoindentation on flax fibers; however several authors have worked on cellulose or wood fibers. Good correlation is obtained with cellulose Young’s modulus (18.2 ± 1.7 GPa) exhibited by Gindl et al. (2008) or with wood transversal Young’s modulus (between 12.7 and 17.9 GPa) (Tze et al., 2007). The variations between varieties could be caused by variations in the microfibrillar angle (MFA) of the crystalline cellulose or by the cellulose/matrix volume ratio as evidenced by Tze et al. (2007). The average longitudinal modulus of flax fibers from nanoindentation experiments is low compared to the modulus obtained by several authors on Hermes fibers (Baley, 2002; Charlet et al., 2007) with conventional tensile tests (from 46.9 to 59.1 GPa), but the scales and the solicitation modes are very different. Gindl et al. (2008) and Gindl and Schöberl (2004) indicated that the longitudinal modulus of wood cell walls obtained by nanoindentation is considerably lower than the tensile Young’s modulus or model calculations. Because of the inclination on the faces of the Berkovich-type indenter, the wall is loaded at an angle of approximately 25◦ . Consequently, the resulting three-dimensional stress is not only governed by the longitudinal modulus, but is also affected by the transverse modulus, resulting in an underestimation of the longitudinal modulus. As evidenced by Baley et al. (2006), flax fibers are too highly anisotropic, and their transversal modulus is estimated to be 8 GPa. This tendency is confirmed by the nanoindentation results obtained with other vegetal fibers. We have obtained a transversal modulus of 5.0 ± 1.5 GPa and 3.9 ± 0.9 GPa, respectively, for hemp and sisal fibers (Bourmaud and Baley, 2009). After a compounding step and injection molding, a significant decrease in mechanical properties can be observed (Table 4). After injection molding with a PLLA matrix, the modulus and hardness Table 4 Longitudinal Young’s modulus and hardness of Hermes fibers before and after processing. Materials
Number of indents
Longitudinal modulus, EL (GPa)
Hardness, H (MPa)
Virgin Marylin fibers Marylin fibers after injection molding in PLA Marylin fibers after injection molding in PBS
57 63
18.9 ± 1.3 10.2 ± 1.3
517 ± 68 293 ± 39
48
13.2 ± 1.4
345 ± 63
Please cite this article in press as: Bourmaud, A., et al., Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.09.033
G Model INDCRO-7529; No. of Pages 7 6
ARTICLE IN PRESS A. Bourmaud et al. / Industrial Crops and Products xxx (2014) xxx–xxx
4. Conclusions
Fig. 5. Evolution of the PLLA/PBS/flax composites mechanical properties with the PLLA volume fraction into the polymeric matrix. The flax fiber volume fraction is fixed at 25.5%.
decreases are 46.0% and 43.3%, respectively, and 30.2% and 33.3% for the fibers in a PBS matrix. This drop in mechanical properties could be caused by the process parameters and especially by the combined effect of shear rate and temperature (Baley et al., 2004; Bourmaud and Baley, 2010). 3.4. Use of PBS as a plasticizer for PLLA–flax composites The results presented in previous sections have demonstrated the advantages of using PBS as a matrix of thermoplastic biocomposites reinforced with flax fibers. This polymer, thanks to its moderate process temperature, can at best preserve the plant cell walls and limit the loss of their mechanical properties. Also, its crystallinity is not affected by the addition of flax fibers. Furthermore, the PBS mechanical properties are significantly improved by adding flax fibers and, in certain respects, they can be compared to those of composites or PP–PLLA–flax. These good mechanical properties open the way for mixtures combining PBS, PLLA and flax fibers. The stiffness of PLLA, associated with good elongation of PBS, could help to develop composites with intermediate mechanical performances which are fully biodegradable. Fig. 5 shows the mechanical properties of PBS/PLLA/flax composites where a different volumetric rate of PLLA and PBS was used. The volume fraction of fibers is constant; it is fixed at 25.5% in order to be consistent with previous experiments. We observed a significant and regular increase in the composite’s stiffness when the volume fraction of PLLA is increasing in the formulations. After stabilization for the low volume fractions, the strength at break is enhanced from 50%-vol of PLLA. In contrast, and as expected, the elongation at break decreases almost linearly with the increase in the PLLA fraction in the composites. This parameter can be seen as a major weakness of the PLLA–flax composite. Thus, the incorporation of PBS can be used to increase this elongation while retaining satisfactory mechanical properties. For example, it is possible for a mixture comprising equal parts of PLLA and PBS, to significantly increase the elongation of the composite (2.2 ± 0.1% compared to 1.4 ± 0.1% for virgin PLLA) which then becomes similar to that of flax fibers. In the same way, compared to the virgin PLLA, the impact energy at failure of the composites is enhanced (12.2 ± 0.6 kJ/m2 compared to 9.1 ± 0.8 kJ/m2 for the pure PLLA) due to the softness of the PBS matrix. The improved elongation at break of the matrix at best benefits the composite capacity to absorb energy during stress. In addition, these mixtures with the iso polymer fraction have a high rigidity (6690 ± 51 MPa) and a sufficient stress (40.1 ± 0.9 MPa) for many industrial applications. Finally, the plasticizing effect of PBS on the PLLA allows the development of efficient and fully biodegradable composites.
During this work, we studied the use of PBS as a matrix for flax fiber reinforced composites. Uploading of flax fiber PBS allows a significant increase in the mechanical properties of the polymer without changing its degree of crystallinity. Given the low Young’s modulus of PBS, the rigidity obtained with a fiber volume fraction of about 25% is smaller than the PP–flax (−37%) but the achieved strength is higher (+82%). Moreover, due to the large extension of PBS, the elongation at break and impact strength of a PBS–flax composite are greatly improved compared to those of PP–flax or PLLA–flax. Nanoindentation tests performed on the composite after injection molding showed that the use of a moderate process temperature (140 ◦ C) limits the decrease of the mechanical properties of the plant cell walls compared with transformations at 190 ◦ C. Finally, we introduced varying volume fractions of PBS in a PLLA–flax composite. For example, a composite with 25.5%vol of flax fibers and having an equal part of PBS and PLLA, has a stiffness of 6690 ± 51 MPa, a strength at break of 40.1 ± 0.9 MPa, an elongation at break of 2.2 ± 0.1 MPa and an impact strength of 12.6 ± 0.8 kJ/m2 . This good performance opens the way for new fully biodegradable biocomposites with homogeneous mechanical performances. In forthcoming works, it would be relevant to focus on the microstructure or morphology of PBS–PLLA–flax blends as well as on the PBS–flax interface to more comprehensively understand the composite mechanical behavior. In order to investigate the end of the life of these promising composites, a study of their recyclability or biodegradability will be carried out next. Acknowledgements The authors would like to thank CTLN® for supplying fibers, the French Ministry of Research and Innovating Technologies, Région Bretagne and the European Community for their financial support. References Assarar, M., Scida, D., El Mahi, A., Poilâne, C., Ayad, R., 2011. Influence of water ageing on mechanical properties and damage events of two reinforced composite materials: flax-fibres and glass-fibres. Mater. Des. 32, 788–795. Ausias, G., Bourmaud, A., Coroller, G., Baley, C., 2013. Study of the fibre morphology stability in polypropylene–flax composites. Polym. Degrad. Stabil. 98, 1216–1224. Azwa, Z.N., Yousif, B.F., Manalo, A.C., Karunasena, W., 2013. A review on the degradability of polymeric composites based on natural fibres. Mater. Des. 47, 424–442. Baiardo, M., Zini, E., Scandola, M., 2004. Flax fibre–polyester composites. Compos. A: Appl. Sci. Manuf. 35, 703–710. Baley, C., 2002. Analysis of the flax fibres tensile behaviour and analysis of the tensile stiffness increase. Compos. A: Appl. Sci. Manuf. 33, 939–948. Baley, C., Le Duigou, A., Bourmaud, A., Davies, P., 2012. Influence of drying on the mechanical behaviour of flax fibres and their unidirectional composites. Compos. A: Appl. Sci. Manuf. 43, 1226–1233. Baley, C., Perrot, Y., Busnel, F., Guezenoc, H., Davies, P., 2006. Transverse tensile behaviour of unidirectional plies reinforced with flax fibres. Mater. Lett. 60, 2984–2987. Baley, C., Pillin, I., Grohens, Y., 2004. État de l’art sur les matériaux composites biodégradables. Revue des Composites et des Matériaux Avancés 2, 135–166. Barkoula, N.M., Garkhail, S.K., Peijs, T., 2010. Biodegradable composites based on flax/polyhydroxybutyrate and its copolymer with hydroxyvalerate. Ind. Crops Prod. 31, 34–42. Bax, B., Müssig, J., 2008. Impact and tensile properties of PLA/Cordenka and PLA/flax composites. Compos. Sci. Technol. 68, 1601–1607. Bin, T., Qu, J.-P., Liu, L.-M., Feng, Y.-H., Hu, S.-X., Yin, X.-C., 2011. Non-isothermal crystallization kinetics and dynamic mechanical thermal properties of poly(butylene succinate) composites reinforced with cotton stalk bast fibers. Thermochim. Acta 525, 141–149. Bledzki, A.K., Jaszkiewicz, A., 2010. Mechanical performance of biocomposites based on PLA and PHBV reinforced with natural fibres – a comparative study to PP. Compos. Sci. Technol. 70, 1687–1696. Bourmaud, A., Ausias, G., Lebrun, G., Tachon, M.L., Baley, C., 2013. Observation of the structure of a composite polypropylene/flax and damage mechanisms under stress. Ind. Crops Prod. 43, 225–236.
Please cite this article in press as: Bourmaud, A., et al., Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.09.033
G Model INDCRO-7529; No. of Pages 7
ARTICLE IN PRESS A. Bourmaud et al. / Industrial Crops and Products xxx (2014) xxx–xxx
Bourmaud, A., Baley, C., 2007. Investigations on the recycling of hemp and sisal fibre reinforced polypropylene composites. Polym. Degrad. Stabil. 92, 1034–1045. Bourmaud, A., Baley, C., 2009. Rigidity analysis of polypropylene/vegetal fibre composites after recycling. Polym. Degrad. Stabil. 94, 297–305. Bourmaud, A., Baley, C., 2010. Effects of thermo mechanical processing on the mechanical properties of biocomposite flax fibers evaluated by nanoindentation. Polym. Degrad. Stabil. 95, 1488–1494. Bourmaud, A., Baley, C., 2012. Nanoindentation contribution to mechanical characterization of vegetal fibers. Compos. B: Eng. 43, 2861–2866. Bourmaud, A., Morvan, C., Baley, C., 2010. Importance of fiber preparation to optimize the surface and mechanical properties of unitary flax fiber. Ind. Crops Prod. 32, 662–667. Bourmaud, A., Pimbert, S., 2008. Investigations on mechanical properties of poly(propylene) and poly(lactic acid) reinforced by miscanthus fibers. Compos. A: Appl. Sci. Manuf. 39, 1444–1454. Charlet, K., Baley, C., Morvan, C., Jernot, J.P., Gomina, M., Bréard, J., 2007. Characteristics of Hermès flax fibres as a function of their location in the stem and properties of the derived unidirectional composites. Compos. A: Appl. Sci. Manuf. 38, 1912–1921. Coroller, G., Lefeuvre, A., Le Duigou, A., Bourmaud, A., Ausias, G., Gaudry, T., Baley, C., 2013. Effect of flax fibres individualisation on tensile failure of flax/epoxy unidirectional. Compos. A: Appl. Sci. Manuf. 51, 62–70. Defoirdt, N., Biswas, S., Vriese, L.D., Tran, L.Q.N., Acker, J.V., Ahsan, Q., Gorbatikh, L., Vuure, A.V., Verpoest, I., 2010. Assessment of the tensile properties of coir, bamboo and jute fibre. Compos. A: Appl. Sci. Manuf. 41, 588–595. Dorez, G., Taguet, A., Ferry, L., Lopez-Cuesta, J.M., 2013. Thermal and fire behavior of natural fibers/PBS biocomposites. Polym. Degrad. Stabil. 98, 87–95. Feng, Y.-H., Li, Y.-J., Xu, B.-P., Zhang, D.-W., Qu, J.-P., He, H.-Z., 2013. Effect of fiber morphology on rheological properties of plant fiber reinforced poly(butylene succinate) composites. Compos. B: Eng. 44, 193–199. Feng, Y.-H., Zhang, D.-W., Qu, J.-P., He, H.-Z., Xu, B.-P., 2011. Rheological properties of sisal fiber/poly(butylene succinate) composites. Polym. Test. 30, 124–130. Gindl, W., Reifferscheid, M., Adusumalli, R.-B., Weber, H., Röder, T., Sixta, H., Schöberl, T., 2008. Anisotropy of the modulus of elasticity in regenerated cellulose fibres related to molecular orientation. Polymer 49, 792–799. Gindl, W., Schöberl, T., 2004. The significance of the elastic modulus of wood cell walls obtained from nanoindentation measurements. Compos. A: Appl. Sci. Manuf. 35, 1345–1349. Jiang, B., Liu, C., Zhang, C., Wang, B., Wang, Z., 2007. The effect of non-symmetric distribution of fiber orientation and aspect ratio on elastic properties of composites. Compos. B: Eng. 38, 24–34. Joseph, P.V., Joseph, K., Thomas, S., Pillai, C.K.S., Prasad, V.S., Groeninckx, G., Sarkissova, M., 2003. The thermal and crystallisation studies of short sisal fibre reinforced polypropylene composites. Compos. A: Appl. Sci. Manuf. 34, 253–266. Joshi, S.V., Drzal, L.T., Mohanty, A.K., Arora, S., 2004. Are natural fiber composites environmentally superior to glass fiber reinforced composites? Compos. A: Appl. Sci. Manuf. 35, 371–376. Kelly, A., Tyson, W.R., 1965. Tensile properties of fibre-reinforced metals: copper/tungsten and copper/molybdenum. J. Mech. Phys. Sol. 13, 329–338. Kim, H.-S., Kim, H.-J., Lee, J.-W., Choi, I.-G., 2006. Biodegradability of bio-flour filled biodegradable poly(butylene succinate) bio-composites in natural and compost soil. Polym. Degrad. Stabil. 91, 1117–1127. Le Duigou, A., Davies, P., Baley, C., 2011. Environmental impact analysis of the production of flax fibres to be used as composite material reinforcement. J. Biobased Mater. Bioenergy 5, 1–13. Le Duigou, A., Davies, P., Baley, C., 2013. Exploring durability of interfaces in flax fibre/epoxy micro-composites. Compos. A: Appl. Sci. Manuf. 48, 121–128.
7
Le Duigou, A., Deux, J.-M., Davies, P., Baley, C., 2012. PLLA/Flax Mat/Balsa BioSandwich – environmental impact and simplified life cycle analysis. Appl. Compos. Mater. 19, 363–378. Le Duigou, A., Pillin, I., Bourmaud, A., Davies, P., Baley, C., 2008. Effect of recycling on mechanical behaviour of biocompostable flax/poly(l-lactide) composites. Compos. A: Appl. Sci. Manuf. 39, 1471–1478. Lee, S.-H., Wang, S., 2006. Biodegradable polymers/bamboo fiber biocomposite with bio-based coupling agent. Compos. A: Appl. Sci. Manuf. 37, 80–91. Lefeuvre, A., Bourmaud, A., Lebrun, L., Morvan, C., Baley, C., 2013. A study of the yearly reproducibility of flax fiber tensile properties. Ind. Crops Prod. 50, 400–407. Li, X., Bhushan, B., 2002. A review of nanoindentation continuous stiffness measurement technique and its applications. Materials Characterization 48 (1), 11–36. Liang, Z., Pan, P., Zhu, B., Dong, T., Inoue, Y., 2010. Mechanical and thermal properties of poly(butylene succinate)/plant fiber biodegradable composite. J. Appl. Polym. Sci. 115, 3559–3567. Liu, L., Yu, J., Cheng, L., Qu, W., 2009a. Mechanical properties of poly(butylene succinate) (PBS) biocomposites reinforced with surface modified jute fibre. Compos. A: Appl. Sci. Manuf. 40, 669–674. Liu, L., Yu, J., Cheng, L., Yang, X., 2009b. Biodegradability of poly(butylene succinate) (PBS) composite reinforced with jute fibre. Polym. Degrad. Stabil. 94, 90–94. Misnon, M.I., Islam, M.M., Epaarachchi, J.A., Lau, K.-T., 2014. Potentiality of utilising natural textile materials for engineering composites applications. Mater. Des. 59, 359–368. Miyata, T., Masuko, T., 1998. Crystallization behaviour of poly(tetramethylene succinate). Polymer 39, 1399–1404. Muralidhar, B.A., 2013. Study of flax hybrid preforms reinforced epoxy composites. Mater. Des. 52, 835–840. Mutje, P., Lopez, A., Vallejos, M.E., Lopez, J.P., Vilaseca, F., 2007. Full exploitation of Cannabis sativa as reinforcement/filler of thermoplastic composite materials. Compos. A: Appl. Sci. Manuf. 38, 369–377. Ochi, S., 2008. Mechanical properties of kenaf fibers and kenaf/PLA composites. Mech. Mater. 40, 446–452. Oksman, K., Skrifvars, M., Selin, J.F., 2003. Natural fibres as reinforcement in polylactic acid (PLA) composites. Compos. Sci. Technol. 63, 1317–1324. Papageorgiou, G.Z., Bikiaris, D.N., 2005. Crystallization and melting behavior of three biodegradable poly(alkylene succinates): a comparative study. Polymer 46, 12081–12092. Pervaiz, M., Sain, M.M., 2003. Carbon storage potential in natural fiber composites. Res. Conserv. Recycl. 39, 325–340. Placet, V., 2009. Characterization of the thermo-mechanical behaviour of Hemp fibres intended for the manufacturing of high performance composites. Compos. A: Appl. Sci. Manuf. 40, 1111–1118. Pracella, M., Chionna, D., Anguillesi, I., Kulinski, Z., Piorkowska, E., 2006. Functionalization, compatibilization and properties of polypropylene composites with Hemp fibres. Compos. Sci. Technol. 66, 2218–2230. Qu, J.-P., Tan, B., Feng, Y.-H., Hu, S.-X., 2011. Mechanical properties of poly(butylene succinate) reinforced with continuously steam-exploded cotton stalk bast. Polym. Plast. Tech. Eng. 50, 1405–1411. Teramoto, N., Urata, K., Ozawa, K., Shibata, M., 2004. Biodegradation of aliphatic polyester composites reinforced by abaca fiber. Polym. Degrad. Stabil. 86, 401–409. Tze, W.T.Y., Wang, S., Rials, T.G., Pharr, G.M., Kelley, S.S., 2007. Nanoindentation of wood cell walls: continuous stiffness and hardness measurements. Compos. A: Appl. Sci. Manuf. 38, 945–953. Velde, K.V.D., Baetens, E., 2001. Thermal and mechanical properties of flax fibres as potential composite reinforcement. Macromol. Mater. Eng. 286, 342–349.
Please cite this article in press as: Bourmaud, A., et al., Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.09.033
ARTICLE IN PRESS
INDCRO-7529; No. of Pages 7
Industrial Crops and Products xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop
Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends Alain Bourmaud ∗ , Yves-Marie Corre, Christophe Baley Laboratoire d’Ingénierie et Matériaux de Bretagne (UBS), Université Européenne de Bretagne, Centre de Recherche Christiaan Huygens, Rue Saint Maudé, 56321 Lorient, France
a r t i c l e
i n f o
Article history: Received 4 June 2014 Received in revised form 29 August 2014 Accepted 16 September 2014 Available online xxx Keywords: Poly-(butylene-succinate) Flax fiber Mechanical properties l-Poly-(lactide) Nanoindentation
a b s t r a c t To take advantage of the mechanical performance of plant fibers and avoid their degradation, it is necessary to develop biocomposites by working on the least aggressive process conditions possible. The use of thermoplastic polymers with low processing temperatures is one possible way. In this study, tests were performed on poly-(butylene-succinate) (PBS) flax composite, extruded and injected at 140 ◦ C. They have a good level of tensile or impact properties compared to poly-(propylene) (PP) or l-poly-(lactide) (PLLA) based biocomposites. Nanoindentation measurements were performed in situ on the composites. Despite the low Young’s modulus of PBS, it was shown that the use of a moderate process temperature limits the downward stiffness of the flax cell walls. Finally, it was demonstrated that the PBS could be associated with PLLA for making flax fiber reinforced biocomposites. The introduction of PBS, with adjustable volume fractions, improves elongation at break and impacts on the behavior of PLLA–flax composites, whilst retaining high performance mechanical properties. Thus, it is possible to elaborate fully biodegradable composites with the desired mechanical properties. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Nowadays, the depletion of our natural resources as well as the increasing impact of our society on our environment necessitates the modification of composite material design. Thus, for many industrial products, plant fibers could be used to substitute synthetic fibers in composite material reinforcement. In Europe, the most relevant are flax or hemp fibers due to their highperformance specific mechanical properties (Assarar et al., 2011; Baley, 2002; Bourmaud et al., 2010; Misnon et al., 2014; Muralidhar, 2013; Placet, 2009), their environmental and ecological benefits (Azwa et al., 2013; Joshi et al., 2004; Le Duigou et al., 2011; Pervaiz and Sain, 2003) and their low cost. In industrial development, plant fibers are generally associated to petrochemical matrixes like polyolefin in order to substitute glass fiber. Nevertheless, it is possible to increase the environmental interest of these new composites by using some biobased or biodegradable polymers. In this way, and despite its low toughness, many works focused on the association of plant fibers with PLLA (Bax and Müssig, 2008; Le Duigou et al., 2013; Oksman et al., 2003) or poly-(hydroxybutirate) (PHB) (Barkoula et al., 2010; Bledzki and
∗ Corresponding author. Tel.: +33 2 97 87 45 05; fax: +33 2 97 87 45 88. E-mail address: [email protected] (A. Bourmaud).
Jaszkiewicz, 2010; Le Duigou et al., 2012) highlighted the potential of bio-sandwich PLLA–flax materials in terms of environmental impact. Due to the low degradation temperature of the plant fibers (Bourmaud and Baley, 2010; Velde and Baetens, 2001), the choice of the matrix is a preponderant parameter in order to preserve the fiber performances. Temperatures that are too high, or aggressive processes (Bourmaud and Baley, 2010) could cause an alteration of the plant cell wall structure and of their mechanical properties (Baley et al., 2012). In this way, the use of a low process temperature polymer has a real interest, and, due to its low melting point (Liang et al., 2010) and its biodegradability (Kim et al., 2006; Liu et al., 2009b; Teramoto et al., 2004), the poly-(butylene succinate) (PBS) is a potential candidate to be associated with plant fibers. Recently, many authors worked on the elaboration of vegetal fiber PBS composites. For example, Teramoto et al. (2004) proved the biodegradability of PBS-abaca composites; Dorez et al. (2013) evidenced the interest of a high fiber loading rate to improve the fire barrier properties of PBS-plant fiber composites. Other explorative works showed the technical or environmental suitability of PBS-sisal (Feng et al., 2011, 2013), jute (Liu et al., 2009a,b) or cotton (Bin et al., 2011; Qu et al., 2011) biocomposites. To explore the impact of the process on the mechanical properties of the cell walls, nanoindentation could be carried out, in situ, on the biocomposites. In this way, it is possible to obtain the
http://dx.doi.org/10.1016/j.indcrop.2014.09.033 0926-6690/© 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: Bourmaud, A., et al., Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.09.033
G Model INDCRO-7529; No. of Pages 7
ARTICLE IN PRESS A. Bourmaud et al. / Industrial Crops and Products xxx (2014) xxx–xxx
2
stiffness and hardness of fibers of the composite at the micron or sub-micron scale without any extraction or damage to the material. An attractive feature of this technique is that the measurements are made without requiring burning, chemical or mechanical modifications to isolate individual fibers as required in single-fiber tensile tests. In a previous study (Bourmaud and Baley, 2010), we showed the significant negative impact of injection molding, compared to film stacking, on PLLA flax composites fibers mechanical properties. Despite a significant discrepancy between the Young’s modulus and the apparent nanoindentation modulus (Gindl et al., 2008), due to the inclination of the indenter pyramid with regard to the principal material axes, nanoindentation is an appropriate technique for the comparison of vegetal fiber stiffness. The aim of this work is to estimate the suitability of the use of a PBS matrix for biocomposite elaboration. Firstly, the tensile, impact, thermal and morphological properties of PBS–flax fiber biocomposites were investigated in order to estimate the potential of PBS as a matrix. In a second part of the study, to estimate the impact of the process on the cell walls’ integrity, we measured the Young’s modulus and hardness of flax fibers in the biocomposite before and after processing by using nanoindentation. Finally, the incorporation of PBS into PLLA–flax composites was explored in order to elaborate fully biodegradable composites with improved elongation and impact resistances.
2. Experimental details 2.1. Materials The PBS used in this study is Bionolle 1020 MD supplied by Showa Denko (Tokyo, Japan) with a Melt Flow Index (MFI) of 20–34 g/10 min (at 140 ◦ C and 2.16 kg) and a density of 1.23 g/cm3 . In addition, and to compare the composite’s mechanical properties or to elaborate PLLA–PBS–flax composites, we used injection grade PP (PPC 10642 from Total Petrochemical) and PLLA (7001D from Nature Works). The PP or PLLA MFI and density are 44 g/10 min (at 190 ◦ C and 2.16 kg) and 0.92 g/cm3 or 5–15 g/10 min (at 190 ◦ C and 2.16 kg) and 1.24 g/cm3 , respectively. To be treated under the same conditions as that for PBS and PLLA, we did not use a compatibilizer for the PP–flax blend. The flax fiber (Linum usitassinum) used in this study is from the Marilyn variety and comes from a 2003 harvest cultivated in Normandy (France). The flax fibers selected are representative and have known and reproducible properties (Lefeuvre et al., 2013). Their production information are detailed in previous work (Lefeuvre et al., 2013). The extracted fibers are cut at 1 mm. The average length and aspect ratio of the elementary fibers was estimated to be 1068 ± 139 m and 33.3 ± 12.1, respectively, as determined by optical microscopy for 250 fibers after inclusion into epoxy resin and polishing of the section (Fig. 1). The aspect ratio is the most significant parameter of the mechanical properties of the composite for short fiber reinforced polymers (Kelly and Tyson, 1965). Generally, the aspect ratio has to be superior to 10, which is considered as the minimum aspect ratio value for good strength transmission for any reinforcement (Jiang et al., 2007; Mutje et al., 2007). In our case 92.3% of fibers have an aspect ratio superior to this value. This result exhibits a good individualization of our fibers, probably due to an appropriate retting step, and the high quality of the cutting process.
Fig. 1. Flax fiber length (A) and aspect ratio (B) dispersion.
As observed in Fig. 1, the cutting process used leads to a performing length dispersion highlighted by a narrow distribution. The mechanical properties of the flax fibers used in the present work were studied in a previous work (Bourmaud et al., 2013); they are shown in Table 1. 2.2. Compounding and processing Flax fibers were dried under vacuum at 60 ◦ C for 12 h prior to the extrusion step. Compounding was achieved in a single screw extruder at 20 rpm and with the following temperature profile: 130/135/140 and 140 ◦ C in the nozzle for the PBS–flax fiber 25.5%-vol compounds. The extrusion temperatures for the PLLA–flax 25.7%-vol, for the PLLA–PBS-25.5%-vol and PP–flax 25.6%-vol blends were 190/190/190 and 190 ◦ C in the nozzle. Compounded pellets were also dried under vacuum at 60 ◦ C for 48 h. Injection molding was then carried out on a Battenfeld machine. All parameters were kept constant during the injection molding process. The temperature profile was kept as follows: 130/135/140
Table 1 Mechanical properties of flax fibers. Materials
Number of fibers
Diameter (m)
Young’s modulus (GPa)
Strength at break (MPa)
Elongation at break (%)
Marylin flax fibers
90
15.5 ± 2.7
53.8 ± 14.3
1215 ± 500
2.24 ± 0.59
Please cite this article in press as: Bourmaud, A., et al., Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.09.033
G Model
ARTICLE IN PRESS
INDCRO-7529; No. of Pages 7
A. Bourmaud et al. / Industrial Crops and Products xxx (2014) xxx–xxx
and 140 ◦ C in the nozzle for the PBS and PBS–flax composites and 190/190/190 and 190 ◦ C in the nozzle for the virgin PP and PLLA, PP–flax, PLLA–PBS–flax and PLLA–flax compounds. The mold temperature was maintained at 30 ◦ C for all the compounds. The compounds were injected into a mold designed to produce ISO-527 normalized specimens. To be sure of the fiber volume rate in our samples, density measurements were carried out after injection molding. We calculated the fiber rate by a classical mixing rule, by knowing the fiber and matrix density. We found 25.3 ± 0.4%, 25.5 ± 0.3% and 25.7 ± 0.2% for the PBS–flax, PP–flax and PLLA–flax composites, respectively. The materials for nanoindentation tests were then cut into injected specimens. The reference virgin fibers were embedded into a thermoset epoxy resin which exhibits a low reticulation temperature (40 ◦ C). As far as the nanoindentation technique is concerned, sample preparation is very important because accurate results are obtained only if the indentations are deeper than the surface topography of the specimen. Meticulous polishing can significantly reduce the uncertainty in determining the surface properties. Hence, all surfaces to be indented were polished to a 1-m particle size polishing solution finish. The average surface roughness, Ra, was measured with a profilometer at 0.1 m. 2.3. Composites mechanical testing The static tensile tests were carried out using a MTS Synergie RT1000 (MTS, Eden Prairie, Minnesota, USA) testing apparatus in a laboratory where the temperature was 23 ◦ C and the humidity was 48% (ISO 527) according to ASTM: D638. The loading speed was 1 mm min−1 . A MTS Extensometer was used with a nominal length of 25 mm. The tests were carried out at least five times for each specimen and the results were averaged arithmetically.
2.4. Charpy impact
3
The degree of crystallinity (c ) was estimated using Eq. (1) where H100% crystalline PBS = 200 J/g (Miyata and Masuko, 1998; Papageorgiou and Bikiaris, 2005). c =
Hm H100%
(1)
2.6. Scanning Electron Microscopy (SEM) pictures The fibers were sputter-coated with a thin layer of gold in an Edwards Sputter Coater and then observed with a Jeol JSM 6460LV Scanning Electron Microscope. 2.7. Nanoindentation experiments The cross section of an injected specimen was used for this study. The samples were mounted on aluminum cylinders using Superglue© for indentation tests (Nanoindenter XP, MTS Nano Instruments) at room temperature (23 ± 1 ◦ C) with a continuous stiffness measurement (CSM) technique. An oscillating force at controlled frequency and amplitude was superimposed onto a nominal applied force so that the material responded with a displacement phase and amplitude (Li and Bhushan, 2002). The Young’s modulus was estimated from the experimental curves as previously described (Bourmaud and Pimbert, 2008). A three-side pyramid (Berkovich) diamond indenter was used, whose area function was calibrated by using a standard silica sample. After the indenter made contact with the surface, it was driven into the material with constant strain rate of 0.05 s−1 to a depth of 120 nm; the load was held at maximum value for 60 s; then, the indenter was withdrawn at the same rate as loading until 10% of the maximum load was reached. A 3 nm amplitude and 70 Hz oscillation was chosen for the CSM parameters. Indents were made in the S2 layer of around 50 fibers. The modulus and hardness calculated are average values from 80 to 120 nm. 3. Results and discussion
Notched Charpy impact and Izod tests were performed using a Tinuis Olsen machine at an ambient temperature. Specimens for the Charpy test were cut from tensile specimens using ISO 179 (80 mm × 10 mm × 4 mm). The tests were carried out at least 10 times for each type of specimen and the results were averaged arithmetically.
2.5. Calorimetric measurements Calorimetric data were obtained using a Mettler-Toledo DSC 822 (Mettler Toledo, Viroflay, France). The calibration was done with indium and zinc. Aluminum pans were used and the sample mass was approximately 10 mg. The samples were first melted to 180 ◦ C (1st run) and kept at this temperature for 2 min, then cooled to a temperature of −60 ◦ C and heated up again to 180 ◦ C (2nd run). Temperature and heat of phase transitions were determined, respectively, from the maxima and areas of the crystallization and melting peaks.
3.1. Mechanical properties of a PBS-flax composite Table 2 shows the tensile mechanical properties of PBS–flax fiber composites compared to PP and PLLA–flax fiber composites for similar volume fractions. For the PBS–flax composite, an important increase in tensile modulus with the addition of vegetal fibers can also be observed (+465.5%). In fiber-reinforced composites, the tensile modulus is mainly governed by the mechanical properties of the fibers. This tendency has been observed, at lower levels, by different authors in the literature. Liang et al. (2010) investigated the reinforcement of PBS with kenaf fibers; they illustrated an increase in modulus from around 670 to 1700 MPa with a kenaf fiber content ranging from 0 to 30%-wt (25.5%-vol). Similar results are exhibited by Lee and Wang (2006) on PBS-bamboo composites with an improvement of the Young’s modulus from 500 to 1200 MPa with the same weight fraction (30%-wt). In our case, the significant improvement of the stiffness is probably due to the conjugated effect of the high
Table 2 Tensile and impact properties of PBS–flax fiber composites compared to PP and PLLA–flax fiber composites. Materials
Young’s modulus (MPa)
Virgin PBS PBS – flax fiber 25.5%-vol Virgin PP PP – flax fiber 25.6%-vol Virgin PLA PLA – flax fiber 25.7%-vol
643 3636 1772 5787 3760 7437
± ± ± ± ± ±
29 179 17 143 56 21
Strength at break (MPa) 39.7 38.6 20.1 21.2 55.2 55.4
± ± ± ± ± ±
0.8 0.1 0.4 0.4 0.9 1.2
Strain at break (%) 264 3.9 11.5 3.0 2.8 1.4
± ± ± ± ± ±
8 0.1 4.4 0.2 0.4 0.1
Impact energy at failure (kJ/m2 ) – 17.8 ± – 11.6 ± 19.5 ± 9.1 ±
1.1 0.9 2.4 0.8
Please cite this article in press as: Bourmaud, A., et al., Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.09.033
G Model INDCRO-7529; No. of Pages 7 4
ARTICLE IN PRESS A. Bourmaud et al. / Industrial Crops and Products xxx (2014) xxx–xxx
Fig. 2. SEM observations of the PBS–flax composite.
stiffness of the flax fibers (53.8 ± 14.3 GPa) compared to kenaf (Ochi, 2008) or bamboo (Defoirdt et al., 2010) fibers and of the low rigidity of the virgin PBS which is highly improved by the incorporation of flax fibers. Whatever the matrix used, unchanged values of the strength at max could be observed for the virgin matrix and plant fiber composites. These results are well correlated with the literature results for PLLA–flax (Le Duigou et al., 2008). In the case of the PP–flax composite and compared with previous studies (Ausias et al., 2013; Bourmaud et al., 2013), the strength value seems to be low, but, in our case, we do not use a compatibilizer, in order to be consistent with the PLLA–flax and PBS–flax composites. Moreover, the fiber orientation in injected composites is not perfect with a significant skin-core effect (Bourmaud et al., 2013). In addition, the PBS–flax composite exhibits a more significant elongation at break (3.9 ± 0.1%) compared to those of PP–flax or PLLA–flax. The plant fiber composite benefits from the significant elongation of the pure matrix, while having high stiffness and strength at break. These results are corroborated by the impact energy at failure of the composites. The PBS–flax composite exhibits high Charpy impact energy (17.8 ± 1.1 kJ/m2 ) due to the softness of the PBS matrix. The functional mechanical properties of the PBS–flax composite, conjugated with high impact energy, could enable this biocomposite to be a good candidate for replacing glass reinforced materials for automotive parts elaboration. In order to better understand the high mechanical properties of the PBS–flax composites, a morphological analysis, using SEM observations, has been carried out. Fig. 2 shows SEM images of tensile fracture surfaces of PBS–flax composite (Fig. 2A–C) and of a polished cross section in order to estimate the quality of the fiber individualization in the composite (Fig. 2D). Fig. 2A and B evidence a good adhesion between the PBS matrix and the flax fiber, there is no decohesion or debonding and
the flax fibers are well linked to the matrix with reduced pullout phenomena. We can also see the breaking of fibers during tensile tests (Fig. 2C) showing the quality of the adhesion between matrix and fibers. Moreover, Fig. 2D exhibits a good dispersion of the flax fibers into the PBS matrix; we observe the presence of many elementary fibers, evidencing the quality of the compounding step for dividing the bundles. In a previous work (Bourmaud et al., 2013), we highlighted the rule of bundles; they can cause premature breakage by creating privileged damage areas. Conversely, a good dispersion has a direct influence on the composites’ mechanical properties and at best enables it to benefit from plant reinforcement properties (Coroller et al., 2013). In order to better understand the origin of the good mechanical properties of the PBS–flax composite, the next section will be dedicated to the estimation of the impact of the process on the flax fiber’s mechanical properties. 3.2. Thermal properties of virgin PBS and PBS–flax composite Table 3 presents the calorimetric properties of virgin PBS and PBS–flax 25.5%-vol. The melting and crystallization behavior of the different samples was studied. The addition of vegetal fibers to PBS results in
Table 3 Thermal properties of PBS and PBS–flax composites. Materials ◦
Glass temperature ( c) Melting temperature (◦ C) Crystallization temperature (◦ C) Heat of crystallization (J/g) Reduced crystallinity (%)
Virgin PBS
PBS–flax 25.5%-vol
Evolution
−38.4 117.8 64.4 85.29 42.65
−35.1 111.4 69.8 59.16 42.26
+3.3 ◦ C −6.4 ◦ C +5.4 ◦ C −30.6% −0.39%
Please cite this article in press as: Bourmaud, A., et al., Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.09.033
G Model INDCRO-7529; No. of Pages 7
ARTICLE IN PRESS A. Bourmaud et al. / Industrial Crops and Products xxx (2014) xxx–xxx
5
Fig. 4. Evolution of Young’s modulus estimated by nanoindentation for virgin and into PBS or PLLA processed flax fibers.
Fig. 3. AFM picture of indents in a flax cell wall.
a slight increase in Tc . Nevertheless the percentage of crystallinity is unchanged. The incorporation of flax fibers causes an acceleration of the crystallization process but their nucleating ability is not demonstrated in our case. The increase of the crystallization temperature with the addition of vegetal fiber is a well-known phenomenon highlighted by many authors (Bourmaud and Baley, 2007; Joseph et al., 2003; Pracella et al., 2006). The glass temperature and melting temperature are slightly modified with the incorporation of flax fiber; the melting temperature decrease could be explained by an improvement of the shear rate during the compounding process in the presence of fibers. It could cause a decrease of the polymer chains and consequently an increase in their mobility. These results illustrate the interest of using PBS as a matrix for biocomposites; its crystallinity is not modified with the incorporation of flax fibers and the slight decrease in its melting temperature could allow a reduction of the compounding temperature in order to better preserve the fiber’s integrity. 3.3. Impact of the process on the flax fiber’s mechanical properties estimated by nanoindentation Fig. 3 presents an Atomic Force Microscopy (AFM) picture of 6 indents on a flax cell wall and Fig. 4 shows the average curves of the Young’s modulus vs. indentation depth for virgin Marylin fibers and for flax cell walls after processing into PLLA and PBS. In Fig. 3, we can clearly see two areas, the first one is attributed to the heterogeneity and roughness of the sample, the second one, after around 50 nm, evidences a good stabilization of the Young’s modulus. In our case, the indentations have been carried out in the middle of the cell wall; due to it being a significant part of the fiber section (around 80%), the nanoindentation results are more specifically associated to the mechanical properties of the secondary wall and especially to the S2 layer. All the indent positions were checked, and those located near the edges of the fibers have not been taken into account. A Poisson’s ratio of 0.35 (Baiardo et al., 2004) was used in all modulus calculations. The values are averaged on an indentation depth of 80–120 nm and for the virgin flax fibers, we have obtained a modulus of 18.9 ± 1.3 GPa. These results are comparable with the literature values. In previous works of our team (Bourmaud
and Baley, 2010, 2012; Bourmaud and Pimbert, 2008), we found a nanoindentation longitudinal modulus of 17.97 ± 1.61, 18.4 ± 1.9 and 19.8 ± 0.7 GPa for flax fibers. There are few studies showing nanoindentation on flax fibers; however several authors have worked on cellulose or wood fibers. Good correlation is obtained with cellulose Young’s modulus (18.2 ± 1.7 GPa) exhibited by Gindl et al. (2008) or with wood transversal Young’s modulus (between 12.7 and 17.9 GPa) (Tze et al., 2007). The variations between varieties could be caused by variations in the microfibrillar angle (MFA) of the crystalline cellulose or by the cellulose/matrix volume ratio as evidenced by Tze et al. (2007). The average longitudinal modulus of flax fibers from nanoindentation experiments is low compared to the modulus obtained by several authors on Hermes fibers (Baley, 2002; Charlet et al., 2007) with conventional tensile tests (from 46.9 to 59.1 GPa), but the scales and the solicitation modes are very different. Gindl et al. (2008) and Gindl and Schöberl (2004) indicated that the longitudinal modulus of wood cell walls obtained by nanoindentation is considerably lower than the tensile Young’s modulus or model calculations. Because of the inclination on the faces of the Berkovich-type indenter, the wall is loaded at an angle of approximately 25◦ . Consequently, the resulting three-dimensional stress is not only governed by the longitudinal modulus, but is also affected by the transverse modulus, resulting in an underestimation of the longitudinal modulus. As evidenced by Baley et al. (2006), flax fibers are too highly anisotropic, and their transversal modulus is estimated to be 8 GPa. This tendency is confirmed by the nanoindentation results obtained with other vegetal fibers. We have obtained a transversal modulus of 5.0 ± 1.5 GPa and 3.9 ± 0.9 GPa, respectively, for hemp and sisal fibers (Bourmaud and Baley, 2009). After a compounding step and injection molding, a significant decrease in mechanical properties can be observed (Table 4). After injection molding with a PLLA matrix, the modulus and hardness Table 4 Longitudinal Young’s modulus and hardness of Hermes fibers before and after processing. Materials
Number of indents
Longitudinal modulus, EL (GPa)
Hardness, H (MPa)
Virgin Marylin fibers Marylin fibers after injection molding in PLA Marylin fibers after injection molding in PBS
57 63
18.9 ± 1.3 10.2 ± 1.3
517 ± 68 293 ± 39
48
13.2 ± 1.4
345 ± 63
Please cite this article in press as: Bourmaud, A., et al., Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.09.033
G Model INDCRO-7529; No. of Pages 7 6
ARTICLE IN PRESS A. Bourmaud et al. / Industrial Crops and Products xxx (2014) xxx–xxx
4. Conclusions
Fig. 5. Evolution of the PLLA/PBS/flax composites mechanical properties with the PLLA volume fraction into the polymeric matrix. The flax fiber volume fraction is fixed at 25.5%.
decreases are 46.0% and 43.3%, respectively, and 30.2% and 33.3% for the fibers in a PBS matrix. This drop in mechanical properties could be caused by the process parameters and especially by the combined effect of shear rate and temperature (Baley et al., 2004; Bourmaud and Baley, 2010). 3.4. Use of PBS as a plasticizer for PLLA–flax composites The results presented in previous sections have demonstrated the advantages of using PBS as a matrix of thermoplastic biocomposites reinforced with flax fibers. This polymer, thanks to its moderate process temperature, can at best preserve the plant cell walls and limit the loss of their mechanical properties. Also, its crystallinity is not affected by the addition of flax fibers. Furthermore, the PBS mechanical properties are significantly improved by adding flax fibers and, in certain respects, they can be compared to those of composites or PP–PLLA–flax. These good mechanical properties open the way for mixtures combining PBS, PLLA and flax fibers. The stiffness of PLLA, associated with good elongation of PBS, could help to develop composites with intermediate mechanical performances which are fully biodegradable. Fig. 5 shows the mechanical properties of PBS/PLLA/flax composites where a different volumetric rate of PLLA and PBS was used. The volume fraction of fibers is constant; it is fixed at 25.5% in order to be consistent with previous experiments. We observed a significant and regular increase in the composite’s stiffness when the volume fraction of PLLA is increasing in the formulations. After stabilization for the low volume fractions, the strength at break is enhanced from 50%-vol of PLLA. In contrast, and as expected, the elongation at break decreases almost linearly with the increase in the PLLA fraction in the composites. This parameter can be seen as a major weakness of the PLLA–flax composite. Thus, the incorporation of PBS can be used to increase this elongation while retaining satisfactory mechanical properties. For example, it is possible for a mixture comprising equal parts of PLLA and PBS, to significantly increase the elongation of the composite (2.2 ± 0.1% compared to 1.4 ± 0.1% for virgin PLLA) which then becomes similar to that of flax fibers. In the same way, compared to the virgin PLLA, the impact energy at failure of the composites is enhanced (12.2 ± 0.6 kJ/m2 compared to 9.1 ± 0.8 kJ/m2 for the pure PLLA) due to the softness of the PBS matrix. The improved elongation at break of the matrix at best benefits the composite capacity to absorb energy during stress. In addition, these mixtures with the iso polymer fraction have a high rigidity (6690 ± 51 MPa) and a sufficient stress (40.1 ± 0.9 MPa) for many industrial applications. Finally, the plasticizing effect of PBS on the PLLA allows the development of efficient and fully biodegradable composites.
During this work, we studied the use of PBS as a matrix for flax fiber reinforced composites. Uploading of flax fiber PBS allows a significant increase in the mechanical properties of the polymer without changing its degree of crystallinity. Given the low Young’s modulus of PBS, the rigidity obtained with a fiber volume fraction of about 25% is smaller than the PP–flax (−37%) but the achieved strength is higher (+82%). Moreover, due to the large extension of PBS, the elongation at break and impact strength of a PBS–flax composite are greatly improved compared to those of PP–flax or PLLA–flax. Nanoindentation tests performed on the composite after injection molding showed that the use of a moderate process temperature (140 ◦ C) limits the decrease of the mechanical properties of the plant cell walls compared with transformations at 190 ◦ C. Finally, we introduced varying volume fractions of PBS in a PLLA–flax composite. For example, a composite with 25.5%vol of flax fibers and having an equal part of PBS and PLLA, has a stiffness of 6690 ± 51 MPa, a strength at break of 40.1 ± 0.9 MPa, an elongation at break of 2.2 ± 0.1 MPa and an impact strength of 12.6 ± 0.8 kJ/m2 . This good performance opens the way for new fully biodegradable biocomposites with homogeneous mechanical performances. In forthcoming works, it would be relevant to focus on the microstructure or morphology of PBS–PLLA–flax blends as well as on the PBS–flax interface to more comprehensively understand the composite mechanical behavior. In order to investigate the end of the life of these promising composites, a study of their recyclability or biodegradability will be carried out next. Acknowledgements The authors would like to thank CTLN® for supplying fibers, the French Ministry of Research and Innovating Technologies, Région Bretagne and the European Community for their financial support. References Assarar, M., Scida, D., El Mahi, A., Poilâne, C., Ayad, R., 2011. Influence of water ageing on mechanical properties and damage events of two reinforced composite materials: flax-fibres and glass-fibres. Mater. Des. 32, 788–795. Ausias, G., Bourmaud, A., Coroller, G., Baley, C., 2013. Study of the fibre morphology stability in polypropylene–flax composites. Polym. Degrad. Stabil. 98, 1216–1224. Azwa, Z.N., Yousif, B.F., Manalo, A.C., Karunasena, W., 2013. A review on the degradability of polymeric composites based on natural fibres. Mater. Des. 47, 424–442. Baiardo, M., Zini, E., Scandola, M., 2004. Flax fibre–polyester composites. Compos. A: Appl. Sci. Manuf. 35, 703–710. Baley, C., 2002. Analysis of the flax fibres tensile behaviour and analysis of the tensile stiffness increase. Compos. A: Appl. Sci. Manuf. 33, 939–948. Baley, C., Le Duigou, A., Bourmaud, A., Davies, P., 2012. Influence of drying on the mechanical behaviour of flax fibres and their unidirectional composites. Compos. A: Appl. Sci. Manuf. 43, 1226–1233. Baley, C., Perrot, Y., Busnel, F., Guezenoc, H., Davies, P., 2006. Transverse tensile behaviour of unidirectional plies reinforced with flax fibres. Mater. Lett. 60, 2984–2987. Baley, C., Pillin, I., Grohens, Y., 2004. État de l’art sur les matériaux composites biodégradables. Revue des Composites et des Matériaux Avancés 2, 135–166. Barkoula, N.M., Garkhail, S.K., Peijs, T., 2010. Biodegradable composites based on flax/polyhydroxybutyrate and its copolymer with hydroxyvalerate. Ind. Crops Prod. 31, 34–42. Bax, B., Müssig, J., 2008. Impact and tensile properties of PLA/Cordenka and PLA/flax composites. Compos. Sci. Technol. 68, 1601–1607. Bin, T., Qu, J.-P., Liu, L.-M., Feng, Y.-H., Hu, S.-X., Yin, X.-C., 2011. Non-isothermal crystallization kinetics and dynamic mechanical thermal properties of poly(butylene succinate) composites reinforced with cotton stalk bast fibers. Thermochim. Acta 525, 141–149. Bledzki, A.K., Jaszkiewicz, A., 2010. Mechanical performance of biocomposites based on PLA and PHBV reinforced with natural fibres – a comparative study to PP. Compos. Sci. Technol. 70, 1687–1696. Bourmaud, A., Ausias, G., Lebrun, G., Tachon, M.L., Baley, C., 2013. Observation of the structure of a composite polypropylene/flax and damage mechanisms under stress. Ind. Crops Prod. 43, 225–236.
Please cite this article in press as: Bourmaud, A., et al., Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.09.033
G Model INDCRO-7529; No. of Pages 7
ARTICLE IN PRESS A. Bourmaud et al. / Industrial Crops and Products xxx (2014) xxx–xxx
Bourmaud, A., Baley, C., 2007. Investigations on the recycling of hemp and sisal fibre reinforced polypropylene composites. Polym. Degrad. Stabil. 92, 1034–1045. Bourmaud, A., Baley, C., 2009. Rigidity analysis of polypropylene/vegetal fibre composites after recycling. Polym. Degrad. Stabil. 94, 297–305. Bourmaud, A., Baley, C., 2010. Effects of thermo mechanical processing on the mechanical properties of biocomposite flax fibers evaluated by nanoindentation. Polym. Degrad. Stabil. 95, 1488–1494. Bourmaud, A., Baley, C., 2012. Nanoindentation contribution to mechanical characterization of vegetal fibers. Compos. B: Eng. 43, 2861–2866. Bourmaud, A., Morvan, C., Baley, C., 2010. Importance of fiber preparation to optimize the surface and mechanical properties of unitary flax fiber. Ind. Crops Prod. 32, 662–667. Bourmaud, A., Pimbert, S., 2008. Investigations on mechanical properties of poly(propylene) and poly(lactic acid) reinforced by miscanthus fibers. Compos. A: Appl. Sci. Manuf. 39, 1444–1454. Charlet, K., Baley, C., Morvan, C., Jernot, J.P., Gomina, M., Bréard, J., 2007. Characteristics of Hermès flax fibres as a function of their location in the stem and properties of the derived unidirectional composites. Compos. A: Appl. Sci. Manuf. 38, 1912–1921. Coroller, G., Lefeuvre, A., Le Duigou, A., Bourmaud, A., Ausias, G., Gaudry, T., Baley, C., 2013. Effect of flax fibres individualisation on tensile failure of flax/epoxy unidirectional. Compos. A: Appl. Sci. Manuf. 51, 62–70. Defoirdt, N., Biswas, S., Vriese, L.D., Tran, L.Q.N., Acker, J.V., Ahsan, Q., Gorbatikh, L., Vuure, A.V., Verpoest, I., 2010. Assessment of the tensile properties of coir, bamboo and jute fibre. Compos. A: Appl. Sci. Manuf. 41, 588–595. Dorez, G., Taguet, A., Ferry, L., Lopez-Cuesta, J.M., 2013. Thermal and fire behavior of natural fibers/PBS biocomposites. Polym. Degrad. Stabil. 98, 87–95. Feng, Y.-H., Li, Y.-J., Xu, B.-P., Zhang, D.-W., Qu, J.-P., He, H.-Z., 2013. Effect of fiber morphology on rheological properties of plant fiber reinforced poly(butylene succinate) composites. Compos. B: Eng. 44, 193–199. Feng, Y.-H., Zhang, D.-W., Qu, J.-P., He, H.-Z., Xu, B.-P., 2011. Rheological properties of sisal fiber/poly(butylene succinate) composites. Polym. Test. 30, 124–130. Gindl, W., Reifferscheid, M., Adusumalli, R.-B., Weber, H., Röder, T., Sixta, H., Schöberl, T., 2008. Anisotropy of the modulus of elasticity in regenerated cellulose fibres related to molecular orientation. Polymer 49, 792–799. Gindl, W., Schöberl, T., 2004. The significance of the elastic modulus of wood cell walls obtained from nanoindentation measurements. Compos. A: Appl. Sci. Manuf. 35, 1345–1349. Jiang, B., Liu, C., Zhang, C., Wang, B., Wang, Z., 2007. The effect of non-symmetric distribution of fiber orientation and aspect ratio on elastic properties of composites. Compos. B: Eng. 38, 24–34. Joseph, P.V., Joseph, K., Thomas, S., Pillai, C.K.S., Prasad, V.S., Groeninckx, G., Sarkissova, M., 2003. The thermal and crystallisation studies of short sisal fibre reinforced polypropylene composites. Compos. A: Appl. Sci. Manuf. 34, 253–266. Joshi, S.V., Drzal, L.T., Mohanty, A.K., Arora, S., 2004. Are natural fiber composites environmentally superior to glass fiber reinforced composites? Compos. A: Appl. Sci. Manuf. 35, 371–376. Kelly, A., Tyson, W.R., 1965. Tensile properties of fibre-reinforced metals: copper/tungsten and copper/molybdenum. J. Mech. Phys. Sol. 13, 329–338. Kim, H.-S., Kim, H.-J., Lee, J.-W., Choi, I.-G., 2006. Biodegradability of bio-flour filled biodegradable poly(butylene succinate) bio-composites in natural and compost soil. Polym. Degrad. Stabil. 91, 1117–1127. Le Duigou, A., Davies, P., Baley, C., 2011. Environmental impact analysis of the production of flax fibres to be used as composite material reinforcement. J. Biobased Mater. Bioenergy 5, 1–13. Le Duigou, A., Davies, P., Baley, C., 2013. Exploring durability of interfaces in flax fibre/epoxy micro-composites. Compos. A: Appl. Sci. Manuf. 48, 121–128.
7
Le Duigou, A., Deux, J.-M., Davies, P., Baley, C., 2012. PLLA/Flax Mat/Balsa BioSandwich – environmental impact and simplified life cycle analysis. Appl. Compos. Mater. 19, 363–378. Le Duigou, A., Pillin, I., Bourmaud, A., Davies, P., Baley, C., 2008. Effect of recycling on mechanical behaviour of biocompostable flax/poly(l-lactide) composites. Compos. A: Appl. Sci. Manuf. 39, 1471–1478. Lee, S.-H., Wang, S., 2006. Biodegradable polymers/bamboo fiber biocomposite with bio-based coupling agent. Compos. A: Appl. Sci. Manuf. 37, 80–91. Lefeuvre, A., Bourmaud, A., Lebrun, L., Morvan, C., Baley, C., 2013. A study of the yearly reproducibility of flax fiber tensile properties. Ind. Crops Prod. 50, 400–407. Li, X., Bhushan, B., 2002. A review of nanoindentation continuous stiffness measurement technique and its applications. Materials Characterization 48 (1), 11–36. Liang, Z., Pan, P., Zhu, B., Dong, T., Inoue, Y., 2010. Mechanical and thermal properties of poly(butylene succinate)/plant fiber biodegradable composite. J. Appl. Polym. Sci. 115, 3559–3567. Liu, L., Yu, J., Cheng, L., Qu, W., 2009a. Mechanical properties of poly(butylene succinate) (PBS) biocomposites reinforced with surface modified jute fibre. Compos. A: Appl. Sci. Manuf. 40, 669–674. Liu, L., Yu, J., Cheng, L., Yang, X., 2009b. Biodegradability of poly(butylene succinate) (PBS) composite reinforced with jute fibre. Polym. Degrad. Stabil. 94, 90–94. Misnon, M.I., Islam, M.M., Epaarachchi, J.A., Lau, K.-T., 2014. Potentiality of utilising natural textile materials for engineering composites applications. Mater. Des. 59, 359–368. Miyata, T., Masuko, T., 1998. Crystallization behaviour of poly(tetramethylene succinate). Polymer 39, 1399–1404. Muralidhar, B.A., 2013. Study of flax hybrid preforms reinforced epoxy composites. Mater. Des. 52, 835–840. Mutje, P., Lopez, A., Vallejos, M.E., Lopez, J.P., Vilaseca, F., 2007. Full exploitation of Cannabis sativa as reinforcement/filler of thermoplastic composite materials. Compos. A: Appl. Sci. Manuf. 38, 369–377. Ochi, S., 2008. Mechanical properties of kenaf fibers and kenaf/PLA composites. Mech. Mater. 40, 446–452. Oksman, K., Skrifvars, M., Selin, J.F., 2003. Natural fibres as reinforcement in polylactic acid (PLA) composites. Compos. Sci. Technol. 63, 1317–1324. Papageorgiou, G.Z., Bikiaris, D.N., 2005. Crystallization and melting behavior of three biodegradable poly(alkylene succinates): a comparative study. Polymer 46, 12081–12092. Pervaiz, M., Sain, M.M., 2003. Carbon storage potential in natural fiber composites. Res. Conserv. Recycl. 39, 325–340. Placet, V., 2009. Characterization of the thermo-mechanical behaviour of Hemp fibres intended for the manufacturing of high performance composites. Compos. A: Appl. Sci. Manuf. 40, 1111–1118. Pracella, M., Chionna, D., Anguillesi, I., Kulinski, Z., Piorkowska, E., 2006. Functionalization, compatibilization and properties of polypropylene composites with Hemp fibres. Compos. Sci. Technol. 66, 2218–2230. Qu, J.-P., Tan, B., Feng, Y.-H., Hu, S.-X., 2011. Mechanical properties of poly(butylene succinate) reinforced with continuously steam-exploded cotton stalk bast. Polym. Plast. Tech. Eng. 50, 1405–1411. Teramoto, N., Urata, K., Ozawa, K., Shibata, M., 2004. Biodegradation of aliphatic polyester composites reinforced by abaca fiber. Polym. Degrad. Stabil. 86, 401–409. Tze, W.T.Y., Wang, S., Rials, T.G., Pharr, G.M., Kelley, S.S., 2007. Nanoindentation of wood cell walls: continuous stiffness and hardness measurements. Compos. A: Appl. Sci. Manuf. 38, 945–953. Velde, K.V.D., Baetens, E., 2001. Thermal and mechanical properties of flax fibres as potential composite reinforcement. Macromol. Mater. Eng. 286, 342–349.
Please cite this article in press as: Bourmaud, A., et al., Fully biodegradable composites: Use of poly-(butylene-succinate) as a matrix and to plasticize l-poly-(lactide)-flax blends. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.09.033