poly (lactic acid) interface adhesion

Composites: Part B xxx (2014) xxx–xxx

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Composites: Part B journal homepage: www.elsevier.com/locate/compositesb

The effect of surface modifications on sisal fiber properties and sisal/poly (lactic acid) interface adhesion A. Orue, A. Jauregi, C. Peña-Rodriguez, J. Labidi, A. Eceiza, A. Arbelaiz ⇑ ‘Materials + Technologies’ Group, Chemical & Environmental Engineering Dep., Polytechnic College of San Sebastian, University of the Basque Country UPV/EHU, Pza. Europa 1, 20018 Donostia-San Sebastián, Spain

a r t i c l e

i n f o

Article history: Received 15 July 2014 Received in revised form 31 October 2014 Accepted 11 December 2014 Available online xxxx Keywords: A. Fibers B. Fiber/matrix bond B. Mechanical properties D. Mechanical testing

a b s t r a c t The main aims of this work were to study the effect of surface modifications on sisal fiber properties as well as on fiber/poly (lactic acid) (PLA) interface adhesion. For this purpose, alkali, silane and combination of both treatments were applied to sisal fiber. The effects of treatments on fiber thermal stability, fiber wettability, morphology, tensile properties and on fiber/PLA interfacial shear strength (IFSS) were studied. After treatments IFSS values improved at least 120%, however, tensile strength of sisal fibers decreased. Alkali treatment removed some non-cellulosic components (hemicelluloses, lignin) as confirmed by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The removal of non-cellulosic materials led to fibrillated and rough morphology as observed by optical microscopy (OM). FTIR spectrum of silane treated fibers showed a band related to silane amino group and contact angle measurements confirmed that fibers became more hydrophobic. All treatments used improved fiber/PLA adhesion. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction Environmental awareness and scarcity of fossil resources have caused an interest in the development of composite materials based on renewable resources with comparable properties to synthetic polymers in order to reduce petroleum consumption and pollution [1–4]. For example, PLA which is obtained from renewable agricultural raw materials is commercially available and fully biodegradable polymer [1,3]. PLA is one of the most promising biodegradable polymers for industrial plastic applications due to its high mechanical properties and good processability [3]. However, PLA polymer has some drawbacks such as brittleness, low impact strength and low ability in resisting thermal deformation [1,3]. To overcome all these disadvantages, natural fibers can be used as reinforcement [2–4]. They are abundant around the word and they exhibit many advantages, for example, the biodegradability, acceptable specific mechanical properties due to their low density and its easy processability [2–4]. However, the main disadvantages of lignocellulosic fibers are the low compatibility and poor interfacial adhesion with polymeric matrices [3,4]. Poor fiber/polymer

⇑ Corresponding author. Tel.: +34 943018585; fax: +34 943017200. E-mail address: [email protected] (A. Arbelaiz).

interfacial adhesion leads to an inefficient stress transfer under load, resulting in low mechanical strength. Therefore, fiber surface has to be modified and several methods to modify the natural fiber surface were proposed in the literature [5–12]. In this study the effects of alkali, silane and combination of both treatments on sisal fiber tensile properties and on sisal fiber/PLA interfacial shear strength were investigated. Untreated and treated sisal fibers were characterized using different techniques (FTIR, TGA, contact angle measurements and optical microscopy). 2. Experimental 2.1. Materials PLA (Ingeo™, 2003D) was provided in pellet form by Nature Works LLC (Minnetonka, USA). According to the supplier, the Disomer content of PLA was 4%, with a melt flow index of 6 g/ 10 min at 210 °C and a density of 1.24 g/cm3. The sisal fibers used in this work were kindly supplied by Celulosa de Levante S.A. (Tortosa, Spain). Sodium hydroxide pellets supplied by Panreac (Castellar del Vallés, Barcelona, Spain) and 3-(2-aminoethylamino) propyltrimethoxysilane (supplied by Sigma–Aldrich (San Luis, USA)) were used as fiber surface modifiers. Other reagent employed was glacial acetic acid supplied by Panreac.

http://dx.doi.org/10.1016/j.compositesb.2014.12.022 1359-8368/Ó 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Orue A et al. The effect of surface modifications on sisal fiber properties and sisal/poly (lactic acid) interface adhesion. Composites: Part B (2014), http://dx.doi.org/10.1016/j.compositesb.2014.12.022

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2.2. Fiber surface treatments 2.2.1. Alkali treatment In order to swell raw sisal fibers, they were treated with 2 wt% NaOH solution for 12 h at room temperature using a fiber/NaOH solution ratio of 1:20 (w/v). After this, fibers were treated with 7.5 wt% NaOH solution under reflux for 90 min to remove more lignin amount and separate fiber bundles into smaller fibers. Finally, fibers were washed to pH 6 and dried at 100 °C for 12 h [13]. 2.2.2. Silane treatment To improve the accessibility of silane chemical agent to the hydroxyl groups of cellulose, firstly sisal fibers were sonicated for 3 h. Sonicated fibers were soaked in silane aqueous solution (2% v/v) under continuous stirring for 3 h. The pH of solution was adjusted to 3–4 with glacial acetic acid and fiber and silane ratio used was 1:2 (w/v). Wet fibers were kept in air for 3 days before to dry at 100 °C for 12 h. 2.2.3. Alkali and silane treatment When a combination of both treatments was applied to sisal fibers, alkali treated sisal fibers were further modified by silane chemical agent. Alkali and silane treatments conditions were the same used previously. 3. Characterization of fibers 3.1. Fourier transform infrared spectroscopy Attenuated total reflection-Fourier transform infrared (ATRFTIR) spectroscopy was used to analyze the characteristic functional groups of natural fibers and also to investigate changes in treated fibers. Measurements were performed with a Nexus spectrometer (Nicolet, Madison, Wisconsin, USA) equipped with a MKII Golden Gate accessory (Specac, UK), which uses diamond crystal at a nominal incident angle of 45° with a ZnSe lens. Single beam spectra of the samples were obtained after averaging 32 scans in the range from 600 to 4000 cm1 with a resolution of 4 cm1. 3.2. Optical microscopy Optical images of untreated and treated fibers surfaces were taken using an Eclipse E600 microscopy (Nikon, Tokyo, Japan) with software analysis of Soft Imaging SystemÒ.

Table 1 Total, dispersive and polar surface energy components of test liquids. Liquid

cL (dyne cm1)

cdL (dyne cm1)

cpL (dyne cm1)

Ethylene-glycol Diiodomethane HPLC water

48.0 50.8 72.8

29.0 48.5 21.8

19.0 2.3 51.0

Surface energy values were calculated by using Owens–Wendt formula [14,15] as shown in Eq. (1):

j 0:5  p p 0:5 k ð1 þ cos hÞcL ¼ 2 cdL cdS þ cL cL

ð1Þ

where h is the contact angle of the fibers with the test liquid, cdL ; cpL and cL are dispersive, polar and total surface energy of the test liquid, respectively, and cdS ; cpS are dispersive and polar components of the surface energy of fibers, respectively. Plotting cL ð1þ  0:5  0:5 versus cpL =cdL cos hÞ= 2 cdL the polar and dispersive components of fibers were determined by the slope and intercept of the resulting graph, respectively [16]. 3.5. Fiber bundle tensile test Tensile tests of untreated and treated fibers were performed using a Minimat 2000 tester (Rheometric Scientific, Piscataway, USA) at a testing speed of 1 mm/min. Fiber bundles were mounted and glued on a paper tab with a drop of glue before measurement. The paper tab with the sample was mounted in the grips and then the middle portion of the papers was cut by means of scissors, so that only the fiber carried the load [17]. Clamping length used was of 5 mm and at least 10 specimens were tested. Fiber diameter was measured by optical microscopy and the minimum diameter value measured at three different locations along the fiber length was taken for calculating the cross section area. The cross section of natural fibers is polygonal and has a cavity inside fiber, the lumen. However, the fiber cross section area was calculated assuming that fibers have a round cross section without lumen. Taking into account these assumptions, the cross section area of natural fibers could vary along the fiber length more than 70%. Mechanical properties obtained should be analyzed with caution due to the assumptions used and the high dispersion of cross section area values. The strength values were fitted to a two parameters Weibull distribution function (Eq. (2)):

  a r 

3.3. Thermogravimetric analysis

FðrÞ ¼ exp

To study the thermal stability of untreated and treated sisal fibers, thermogravimetric analysis was carried out using a TGA/ SDTA 851 (Mettler Toledo, L’Hospitalet de Llobegrat, Barcelona, Spain). Samples between 5 and 10 mg were placed in ceramic crucibles and tests were carried out in nitrogen atmosphere between 30 and 600 °C at a rate of 10 °C/min.

where the cumulative probability of failure is related to the applied stress (r) and the parameters a and ro are the shape and scale parameter, respectively.

3.4. Contact angle and surface energy measurements Contact angles of untreated and treated sisal fibers were measured with OCA 20 (Data Physics Instruments, Germany). Three different test liquids, HPLC water, ethylene-glycol and diiodomethane were used and their dispersive, polar and total surface energy components are given in Table 1. A controlled amount of sisal fibers was compressed in a mould to obtain disc geometry and a droplet of liquid was deposited on the surface and contact angle was measured. Five samples were used to measure contact angles and the average values and standard deviation were calculated.

ro

ð2Þ

3.6. Pull-out test Force and displacement values of pull-out samples were acquired with a Minimat 2000 tester (Rheometric Scientific, Piscataway, USA).The maximum force (Fmax) was used to calculate the apparent interfacial shear strength between fiber and matrix according to the Kelly/Tyson formula [14,17,18] as shown by Eq. (3):

s¼

F max pDL

ð3Þ

where D and L are fiber diameter and embedded length, respectively. Interfacial shear strength (IFSS) values were obtained using the assumption that the shear stress at the interface was uniformly

Please cite this article in press as: Orue A et al. The effect of surface modifications on sisal fiber properties and sisal/poly (lactic acid) interface adhesion. Composites: Part B (2014), http://dx.doi.org/10.1016/j.compositesb.2014.12.022

A. Orue et al. / Composites: Part B xxx (2014) xxx–xxx

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distributed along the embedded length. The strength values were fitted to a two parameters Weibull distribution function. At least 10 specimens were tested for each fiber treatment and the typical sisal fiber/PLA pull-out test specimen is shown in Fig. 1. 4. Results 4.1. Fourier transform infrared spectroscopy FTIR spectra of untreated and treated sisal fibers are shown in Fig. 2. Untreated fibers showed a broad band at 3500–3200 cm1 related to O–H stretching vibration of the hydroxyl groups in cellulose molecules. The bands between 2900 and 2700 cm1 were related to the C–H stretching vibration of alkyl groups in aliphatic bonds of cellulose, lignin and hemicelluloses. The band around 1740 cm1 was ascribed to the acetyl and ester groups of hemicelluloses and aromatic components of lignin. The band around 1640 cm1 was related to the O–H bending of water absorbed into cellulose fiber structure and absorption bands at 1602 cm1 and 1505 cm1 were associated with C–C in plane symmetrical stretching vibration of aromatic rings present in lignin. The band at 1430 cm1 was associated to the CH2 symmetric bending present in cellulose. The band at 1250 cm1 was related to the C–O stretching vibration of hemicelluloses component and aryl–alkyl ether compounds present in lignin. Bands observed around 1170– 1050 cm1 and 890 cm1 were associated with the C–O stretching and C–H deformation vibrations of the pyranose ring skeletal of cellulose [19–21]. After alkali treatment, the chemical composition of fibers changed since the prominent bands of the raw fiber around 1740 and 1250 cm1 were disappeared almost completely indicating that alkali treatment removed hemicelluloses and a portion of lignin. Valadez-Gonzalez et al. [5] and Zhou et al. [6] studied the effect of alkali treatment on sisal fibers and they also observed that after alkali treatment the bands which appeared approximately at 1740 and 1250 cm1 disappeared. Liu et al. [7] observed the same changes in FTIR spectra for native grass fibers treated with an alkali solution. Silane treated fibers showed (b and d spectra) a new absorption band around 1560 cm1 related to – NH2 bending vibration of organosilane agent indicating that the silane was successfully grafted on the fiber. The band around 1560 cm1 was more appreciable when fibers were previously alkali treated. Similar result was observed by Koga et al. [8] after treating cellulose paper with 3-aminopropyl-trimethoxy-silane. Zhou et al. [6] for sisal fibers treated with two different aminosilanes observed new bands at 1570 and 1484 cm1.

Fig. 2. FTIR spectra of sisal fibers after different surface treatments: (a) untreated, (b) silane, (c) NaOH and (d) NaOH + silane.

4.2. Thermogravimetric analysis TGA and derivative TGA curves of untreated and treated sisal fibers are shown in Fig. 3a–b. Untreated and alkali treated fibers showed around at 100 °C a weight loss of about 4% related to surface water evaporation [19,22]. However, when fibers were treated with silane chemical agent, the evaporation of water was not so obvious which may indicate that after silane treatment fibers became less hydrophilic. Fibers without alkali treatment showed

(a)

(b)

Fig. 1. A typical sisal fiber/PLA pull-out test specimen.

Fig. 3. (a) TGA and (b) derivative TGA curves of untreated and treated sisal fibers.

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two decomposition peaks at 298 °C and 355 °C corresponding to the thermal depolymerization of hemicelluloses and cellulose decomposition, respectively [6]. However, in alkali treated fibers, the loss related to hemicelluloses was not observed confirming that hemicelluloses were removed, in agreement with FTIR spectra obtained. The removal of hemicelluloses and a fraction of lignin resulted in a better thermal stability of alkali treated fibers. Other authors [6,9] observed similar results for sisal fibers after treated with an alkali solution. Fibers treated with silane chemical agent showed higher percentage of char which could be related to the degradation of grafted silane. Similar result was observed by Joseph et al. [10] for banana fibers treated with triethoxyvinil-silane and aminopropylsilane. Rachini et al. [11] observed higher percentage of char for hemp fibers treated with two different silane chemical agents and they also attributed to the presence of grafted silane.

4.3. Optical microscopy Fig. 4a–d shows optical images for untreated and treated sisal fibers. Except for alkali treated fibers, no apparent changes were observed in fiber surface morphology. After alkali treatment, fiber surface roughness was considerably increased and created fibers with smaller diameters probably due to the removal of hemicelluloses and lignin. Fernandes et al. [23] observed that alkali treatment led to fibrillation of the sisal fiber bundles, reducing the diameter and increasing the roughness. Bogoeva-Gaceva et al. [24] mentioned that alkali treatment reduced the diameter of natural fiber and increased the aspect ratio by removing the impurities of the fibers. Untreated sisal fibers showed diameter values between 154 and 220 lm while the diameter of alkali treated fibers was smaller ranging from 109 to 132 lm and showed fibrils with diameters around 10–20 lm. Fernandes et al. [23] observed that after alkali treatment sisal fiber diameter values decreased from 117– 234 to 85–197 lm. Mwaikambo and Ansell [25] observed similar changes in the morphology of hemp, sisal and jute fibers after dif-

ferent alkali treatments. Joseph et al. [10] observed by Scanning Electron Microscopy the fibrillation of banana fibers after the alkali treatment and they suggested that the removal of alkali soluble hemicelluloses resulted in fibrillation of banana fibers. 4.4. Contact angle and surface energy Contact angle values of PLA, untreated and treated sisal fibers are reported in Table 2. After treating fibers with silane and with a combination of NaOH + silane treatments, higher contact angles were obtained. Le Moigne et al. [26] treated flax fibers with 3-glycidyl-oxypropyl-trimethoxy-silane and they observed a decrease of hydrophilic character of flax fibers. Park et al. [27] studied the contact angle values for lignocellulosic fibers treated with a combination of NaOH and silane chemical agent using the Wilhelmy plate technique. They observed that the contact angle became higher after dipping fibers with silane chemical agent. Doan et al. [28] measured the contact angle of untreated and treated jute fibers using a tensiometer and they observed an increase in the hydrophobicity after silane treatment of alkali treated fibers. Total surface energy cs, dispersive component cds and polar component cps values are reported in Table 3. After silane treatment the cps =cs value decreased as a result of polarity reduction which was in agreement with water evaporation observed in TGA analysis. Doan et al. [28] observed a similar reduction in cps =cs value when they modified jute fibers with a combination of alkali and silane treatments. On the other hand, comparing untreated and alkali treated fibers, no big differences in total surface energy, dispersive component and polar component were observed. These results were in agreement with water evaporation observed in TGA analysis. 4.5. Fiber bundles tensile test measurements Tensile strength values as a function of fiber surface treatments were plotted by means of two parameters Weibull probability dis-

Fig. 4. Optical microscopy images of sisal fibers after different surface treatments: (a) untreated, (b) silane, (c) NaOH and (d) NaOH + silane.

Please cite this article in press as: Orue A et al. The effect of surface modifications on sisal fiber properties and sisal/poly (lactic acid) interface adhesion. Composites: Part B (2014), http://dx.doi.org/10.1016/j.compositesb.2014.12.022

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A. Orue et al. / Composites: Part B xxx (2014) xxx–xxx Table 2 Contact angle values for PLA polymer, untreated and treated sisal fibers with different test liquids. System

PLA Untreated Silane NaOH NaOH + silane

Contact angle (°) Ethylene-glycol

Diiodomethane

Water

60.0 ± 1.8 68.2 ± 7.2 77.0 ± 2.8 64.8 ± 2.0 70.0 ± 4.4

48.0 ± 1.5 42.7 ± 2.5 50.4 ± 4.8 45.4 ± 4.8 53.1 ± 4.1

75.2 ± 1.6 70.6 ± 2.4 86.7 ± 9.9 74.6 ± 4.5 89.6 ± 7.6

Table 3 Total, dispersive and polar surface energy components for PLA polymer, untreated and treated sisal fibers. System

cS (mJ/m2)

cdS (mJ/m2)

cpS (mJ/m2)

cps =cs

PLA Untreated Silane NaOH NaOH + silane

34.6 34.7 28.9 34.2 30.0

26.9 25.3 25.8 26.6 27.6

7.7 9.4 3.1 7.6 2.4

0.26 0.27 0.11 0.22 0.10

Table 4 Tensile properties of sisal fibers after different fiber surface treatments. Treatment

ro (MPa)

a

Et (GPa)

ebreak (%)

Untreated Silane NaOH NaOH + silane

366 341 352 212

2.9 1.9 2.9 1.4

9.5 ± 3.4 6.4 ± 3.9 5.0 ± 3 9 5.0 ± 3.7

3.9 ± 1.3 4.3 ± 1.0 6.1 ± 2 8 5.4 ± 2.2

fibers, Ray and Sarkar [34] observed that fibers treated with 5 wt% NaOH for 8 h showed the highest mechanical properties. The values reported in Table 4 for alkali treated samples suggested that alkali treatment conditions used in this study could depolymerize the native cellulose I molecular structure, producing short length crystallites [25]. However, as observed by optical microscopy, alkali treatment conditions used produced a fibrillated surface that could improve fiber/polymer adhesion. The combination of alkali and silane treatments reduced considerably fibers properties due to the combined effect of both treatments.

4.6. Pull-out tests tribution function (Fig. 5) and provided a good adjustment to experimental strength values. Tensile properties of untreated and treated sisal fibers are reported in Table 4. Although the variability of tensile values was very large, tensile strength and Young modulus values obtained for untreated fibers were 366 MPa and 9.5 GPa, respectively. These values were similar to those reported in the literature [23,29,30]. The variability in mechanical properties was probably related to the variability in microstructure of natural fibers and the possible damage suffered by the fibers during the extraction process [29,31]. All treatments decreased the tensile strength values of sisal fibers. However, alkali treated fibers showed an improvement in the deformation at break values. For silane treatment, the acid medium used could catalyze the cleavage of b-1,4-glycosidic bonds between two anhydroglucose units and cellulose chain reduction might be the reason for lower mechanical properties [14]. Similar tendency was observed by Rong et al. [30] for sisal fibers treated with silane chemical agent. The effects of alkali treatment on the properties of natural fibers depend on the alkali treatment conditions (concentration, temperature and time) [32]. Sydenstricker et al. [33] observed for sisal fibers that 2 wt% NaOH treatment provided the highest fiber tensile strength which decreased at higher concentrations. For jute

Fig. 6 shows typical pull-out test curves and in Table 5 are reported the scale (so) and shape parameter (a) values obtained using two parameters Weibull probability distribution function for untreated fiber/PLA and treated fiber/PLA systems. A two parameters Weibull distribution function provided a good adjustment to experimental interfacial shear strength values (Fig. 7). The IFSS value obtained for untreated fiber/PLA system was 2.4 MPa. After treatments, so value increased and the highest interfacial shear strength value of 6.0 MPa was obtained after alkali treatment. This improvement can be explained by the increase of contact surface area between fiber and PLA polymer which improved the mechanical interlocking. Alkali treatment removed non-cellulosic materials from fibers as observed by FTIR and TGA techniques and increased fiber surface roughness. Moreover, after alkali treatment, fiber bundles can be opened creating fibers with smaller diameter, as observed by optical microscopy, and more surface area. Another reason of adhesion improvement could be due to the removal of the non-cellulosic materials which increase the exposure of cellulose OH groups and might create more hydrogen bonds with PLA [35]. Pickering et al. [36] mentioned that the increase in IFSS values for alkali treated fibers could be due to the removal of non-cellulosic material allowing stronger bonding

Fig. 5. Tensile strength data fitted to a two parameter Weibull probability distribution as a function of fiber surface treatment.

Fig. 6. Pull-out test curves for untreated and treated sisal/PLA system.

Please cite this article in press as: Orue A et al. The effect of surface modifications on sisal fiber properties and sisal/poly (lactic acid) interface adhesion. Composites: Part B (2014), http://dx.doi.org/10.1016/j.compositesb.2014.12.022

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Table 5 Sisal fiber/PLA interfacial shear strength (so) values after different fiber surface treatments. Treatment

so (MPa)

a

Untreated Silane NaOH NaOH + silane

2.4 5.3 6.0 5.8

1.3 2.2 2.6 2.3

the presence of amino group was confirmed by FTIR analysis corroborating that the silane chemical agent was successfully grafted on the fiber. Silane treated fibers showed a polarity reduction which was in agreement with the amount of weight loss by water evaporation observed in TGA thermograms. All treatments decreased the tensile strength values of sisal fibers, especially when the combination of NaOH + silane treatment was used. After treating fibers, the IFSS value improved at least 120%. Alkali treatment gave more surface area which can promote mechanical interlocking adhesion with PLA polymer. For silane treatment, the increase of IFSS value observed could be due to the chemical bonding between PLA and fibers through silane agent. However, IFSS values obtained suggested that PLA/fiber adhesion was still weak. Taking into account tensile properties of fibers and fiber/PLA interfacial shear strength values, it is clear that the treatment conditions have to optimize in order to obtain a fibrillated surface with the highest tensile strength. Acknowledgements Authors are grateful for the financial support from the Basque Country Government in the frame of Consolidated Groups (IT-776-13). Technical and human support provided by SGIker Macrobehaviour-Mesostructure-Nanotechnologie (UPV/ EHU, MINECO, GV/EJ, ERDF and ESF) is also gratefully acknowledged. Also, the authors would like to thank Unai Unsuain for helping in tensile properties measurements.

Fig. 7. Apparent interfacial shear strength data fitted to a two parameters Weibull probability distribution as a function of fiber surface treatment.

between PLA and cellulose at the interface. For silane treatment, the increase of IFSS value may be attributed to the chemical bond between PLA matrix and amino groups linked to the fiber surface. Therefore, stress could be transferred from PLA chains, through fiber bonded silane agent, to the fiber. Sawpan et al. [37] studied the effect of different treatments on the interfacial shear strength of hemp fiber reinforced PLA composites. They observed that IFSS value for untreated hemp fibers/PLA system was 5.55 MPa and when fibers were treated with an alkali solution, the highest IFSS value was obtained (11.41 MPa) following by a combination of alkali and silane treatments (9.87 MPa) and silane treatment (8.22 MPa). In this work the same improvement order in IFSS value was obtained by chemical modifications. In the hypothetical case of a strong interfacial bond and assuming that s is limited by the shear strength of the matrix, and also assuming isotropy of the matrix, the IFFS might be estimated by Eq. (4) [14],

r s ¼ pmffiffiffi

3

ð4Þ

where rm is the matrix strength. IFSS value estimated for a strong interfacial fiber/matrix bond should be around 34 MPa. Although, all treatments improved the so values at least 120%, the values reported in Table 5 are far away from a strong interfacial fiber/ matrix bond which means that values obtained are related to a weak adhesion. 5. Conclusions Different treatments used modified sisal fibers properties as well as sisal fiber/PLA adhesion. Alkali treatment removed some non-cellulosic components as confirmed by FTIR and TGA. Alkali treatment led to fibrillation of the sisal fiber bundles into smaller fibers and surface roughness of the fibers was considerably increased compared to untreated ones. In silane treated sisal fibers

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Please cite this article in press as: Orue A et al. The effect of surface modifications on sisal fiber properties and sisal/poly (lactic acid) interface adhesion. Composites: Part B (2014), http://dx.doi.org/10.1016/j.compositesb.2014.12.022