Polylactide-Based Renewable Green Composites from Agricultural

1654

Biomacromolecules 2010, 11, 1654–1660

Polylactide-Based Renewable Green Composites from Agricultural Residues and Their Hybrids Calistor Nyambo,† Amar K. Mohanty,†,‡ and Manjusri Misra*,†,‡ Department of Plant Agriculture, Bioproducts Discovery and Development Centre (BDDC), University of Guelph, Guelph, Ontario N1G 2W1, Canada, and School of Engineering, Thornbrough Building, University of Guelph, Guelph, Ontario N1G 2W1, Canada Received March 22, 2010; Revised Manuscript Received May 1, 2010

Agricultural natural fibers like jute, kenaf, sisal, flax, and industrial hemp have been extensively studied in green composites. The continuous supply of biofibers in high volumes to automotive part makers has raised concerns. Because extrusion followed by injection molding drastically reduces the aspect ratio of biofibers, the mechanical performance of injection molded agricultural residue and agricultural fiber-based composites are comparable. Here, the use of inexpensive agricultural residues and their hybrids that are 8-10 times cheaper than agricultural fibers is demonstrated to be a better way of getting sustainable materials with better performance. Green renewable composites from polylactide (PLA), agricultural residues (wheat straw, corn stover, soy stalks, and their hybrids) were successfully prepared through twin-screw extrusion, followed by injection molding. The effect on mechanical properties of varying the wheat straw amount from 10 to 40 wt % in PLA-wheat straw composites was studied. Tensile moduli were compared with theoretical calculations from the rule of mixture (ROM). Combination of agricultural residues as hybrids is proved to reduce the supply chain concerns for injection molded green composites. Densities of the green composites were found to be lower than those of conventional glass fiber composites.

Introduction The use of natural fibers and biobased polymers as sustainable materials is of increasing interest because of their potential to substitute certain petroleum-derived composites. Recently, there has been increasing concerns regarding shortages of landfills, persistence of nonbiodegradable petroleum-based polymers in the environment, and the dependence on finite and depleting nonrenewable petroleum resource. Green composites, which are a combination of bioplastics and natural fibers, have emerged as promising alternatives to conventional polyolefin/glass fiber composites because they offer a wide variety of advantages, such as low density, renewability, biodegradability, and better cost versus a certain required performance. Polylactide (PLA) is one of the most readily available thermoplastic polyester that is derived from renewable resources such as corn, beet, and sugar.1 PLA is 100% biodegradable, can be recycled over 7-10 times and has a high tensile strength of 70 MPa and tensile modulus of 3 GPa.2 Commercial application of pure PLA is limited because of its inherent weakness, such as low impact strength, low HDT, poor gas barrier, and high brittleness. More research effort is being directed toward finding methods of addressing the weakness of PLA without compromising its biodegradability.3-5 Many researchers have studied PLA composites with various types of fibers and this has been reviewed by Plackett et al.6 and Oksman et al.7 The effect in PLA of various types of fibers such as abaca leaves,8 jute,9 sugar beet pulp,10 kenaf,11 green coconut,12 hemp,13 wood,14 oat, and cocoa shells15 has been extensively studied and is well understood. However, no report of PLA composites reinforced with agricultural residues like wheat straw, corn stover, and soy stalks has been found. * To whom correspondence should be addressed. Tel.: +1-519-824-4120, ext. 58935. Fax: +1-519-763-8933. E-mail: [email protected]. † BDDC. ‡ School of Engineering.

Panthapulakkal and Sain16 have studied the mechanical properties of injection molded wheat straw and corn stem reinforced polypropylene (PP) composites. They observed increases in tensile and flexural properties (modulus and strength) when the composites were compatibilized with 5% maleated polypropylene, than when fungi-treated or untreated wheat straw and cornstalks were used. The enhancement in strength was attributed to improved interfacial adhesion between matrix and filler in composites containing maleated polypropylene. The aim of this paper is to investigate the physicomechanical effect of wheat straw, soy stalk, and corn stover alone or in combination (as hybrid) in PLA. These underutilized agricultural byproducts are enormously produced worldwide and contain cellulose-based fibers. Finding value-added uses of these undervalued field crop residues together with biobased polymers may help maintain a carbon dioxide balance, give an incentive to farmers, and has the potential of reducing problems associated with emissions produced during incarceration of polyolefin composites.17 Moreover, the incorporation of inexpensive agricultural residues, which are 8-10 times cheaper than agricultural fibers, into bioplastics is a key strategy that may help create cheap sustainable injection molded composites. Driven by its corporate desire for “going green”, Ford Motor Company recently introduced a wheat straw reinforced polypropylene composite in the interior of the 2010 Ford Flex. There is a concern for automotive parts manufacturers on the supply chain of natural fibers. Because agricultural residues (i.e., wheat straw, soy stalk, and corn stover) contain comparable amounts of cellulose-based fibers, we hypothesized that their combinations (as hybrid) in composites may (i) probe synergism of the fibers in the PLA, and (ii) reduce concerns of automotive parts manufactures because this may provide an alternative formulation in the event that one type of fiber goes out of supply. In this study, the green composites were prepared by extrusion followed by injection molding and were characterized by

10.1021/bm1003114  2010 American Chemical Society Published on Web 05/26/2010

Polylactide-Based Renewable Green Composites

density, differential scanning calorimetry (DSC), heat deflection temperature (HDT), scanning electron microscopy, dynamic mechanical analysis (DMA), and mechanical testing (i.e., tensile, flexural, and impact analysis).

Experimental Section Materials. Wheat straw, corn stover, and soy stalks were obtained from Elora Farms in Guelph, Canada. Chemical compositions, that is, cellulose, hemicellulose, ash, and lignin content of these agricultural residues are described in the literature.18 The polylactide (PLLA; Biomer L 9000, Mw ) 200000 g/mol, Mn ) 101000 g/mol, 2% D-lactide), referred hereafter as PLA, was procured from Biomer, Krailling, Germany. Testing and Characterization. Density. Densities of the PLA composites were measured in an electronic densimeter Alfa Mirage model MD-300 S by weighing the mass of the composites in water and air. Differential Scanning Calorimetry, DSC. The glass transition (Tg), crystallization (Tc), and melting (Tm) temperatures were determined using a TA Instrument, DSC Q200, under a nitrogen flow of 50 mL/ min. Samples for DSC analysis were obtained from composites that had been extruded followed by injection molding. Approximately 10 mg samples were heated in a sealed aluminum pan at a ramp rate of 10 °C/min, cooled at a rate of 10 °C/min, and subsequently heated at 10 °C in heat/cool/heat mode. Enthalpies of melting (∆Hm) and crystallization (∆Hc) were evaluated using TA Universal software by integrating the area of the melting and crystallization peaks. The Tg was taken as the deflection of the DSC curve from baseline in the third heating cycle. Dynamic Mechanical Analysis, DMA. Dynamic mechanical properties (storage modulus, loss modulus, and tan δ as a function of temperature) were determined in a TA Instruments, DMA Q800, operated in multifrequency strain mode, using a single cantilever clamp, following the standard ASTM D4065. A heating rate of 3 °C/min from 15 to 115 °C, strain of frequency 1 Hz, and amplitude 15 µm were used during testing. Heat Deflection Temperature, HDT. A dynamic mechanical analyzer (TA Instruments DMA Q800), operated in the DMA controlled force mode, with three point bending clamps, was used to determine the heat deflection temperature according to ASTM D648, under a load of 0.455 MPa. The heating rate was 2 °C/min and data was collected from 15 to 120 °C. Scanning Electron Microscopy, SEM. Fractured samples from tensile testing were sputter-coated with gold/palladium using an Emitech K550 instrument under a flow of argon and observed using a Hitachi S-570 scanning electron microscope (SEM) at an accelerated voltage of 10 kV. Mechanical Testing. Tensile and flexural properties were measured using the Instron Instrument Model 3382 according to ASTM standards D638 and D790, respectively. The crosshead speed for tensile testing was 5 and 1.40 mm/min for flexural testing. Notched Izod impact strengths of the composites were carried out with a TMI 43-02 impact tester machine, following the ASTM D256 standard. Notches were cut on the impact samples using TMI notching cutter, and a 5 ft-lb pendulum was used to impact the samples. Fabrication of the Green Composites. Dry wheat straw, corn stover, and soy stalk fibers were ground in a Fritsch-Universal Cutting Mill Pulverisette 19 and sieved through a mesh of size 0.25 mm. The PLA and the fibers were dried in an oven at 80 °C for 4 h. Drying of fibers to remove water is an important step that prevents formation of voids, and it is a common practice to dry biobased polymers because these are known to degrade by hydrolysis during processing.19 A total of 30 wt % of the dried fibers and 70 wt % PLA were extruded in a DSM Micro 15 cc twin screw compounder (rpm ) 100, time ) 3 min, and temperature ) 180 °C for all three processing zones). A reference sample of unmodified PLA without any fiber and a hybrid composite consisting of PLA combined with 10 wt % of soy stalks, corn stover,

Biomacromolecules, Vol. 11, No. 6, 2010

1655

Table 1. Densities of PLA and Its Composites

formulation PLA PLA + 30% soy stalks PLA + 30% corn stover PLA + 30% wheat straw PLA + 30% hybrid (i.e., 10% corn stover + 10% wheat straw + 10% soy stalks)

density (g/cm3)

calculated density of fibera (g/cm3)

( ( ( ( (

1.424 1.420 1.405 1.411

1.254 1.305 1.304 1.299 1.301

0.002 0.005 0.009 0.013 0.005

a Calculated using the rule of mixture, i.e., Fc ) VfFf + VmFm, where Vf, Vm and Ff, Fm are the volume fractions and densities of the fiber and matrix, respectively.

and wheat straw were prepared using the same procedure. Testing specimens were prepared by injection molding in a DSM Micro 12 cc molder. The molten composites obtained were transferred from the extruder to the injection molder using a cylinder preheated at 180 °C.

Results and Discussion Density of the PLA Composites. One of the advantages of using natural fibers over glass fiber is their low density of 1.3-1.5 g/cm3 compared to 2.6 g/cm3 for E-glass.17 Such low densities may offer a weight saving advantage, especially in applications that require light components, such as in automotive interior leading to improved fuel efficiency.20 Density data for the PLA green composites are summarized in Table 1. The composites show densities around 1.3 g/cm3. Neat PLA gave a lower density than the composites and there is no significant difference in the densities of the different types of fibers. Calculated fiber densities obtained using the rule of mixture gave values around 1.4 g/cm3 for all the different types of the fibers and these are lower than that of glass fiber. The calculated fiber densities are comparable to those reported in literature for agricultural natural fibers, for example, sisal (1.3-1.45 g/cm3), jute (1.3-1.45 g/cm3), and flax (1.5 g/cm3).32 Crystallization and Melting Behavior of the Composites. The crystallization and melting behavior of the composites were studied using differential scanning calorimetry (DSC). DSC data is summarized in Table 2. The degree of crystallinity (χ) was calculated using the equation presented below.21

χ)

∆Hm 0 f · ∆Hm

× 100%

where f is the weight fraction of PLA in the composite; ∆Hm is the enthalpy of melting, and ∆H0m is the enthalpy of melting of 100% pure PLA taken as 93.7 J/g.22 Neat unprocessed PLA showed a glass transition, Tg, at 60 °C and a broad melting peak, Tm, at 170 °C. A crystallization peak was observed after extrusion and injection molding of the neat PLA and its composites. The appearance of an exotherm peak during heating might have occurred due to changes in molecular structure of the PLA during processing or due to a nonequilibrium process such as cooling after processing. Changing the cooling rate from 10 to 5 °C and 50 °C per min did not result in significant changes in the crystallization enthalpies of the processed PLA, suggestive of the low influence of cooling on the crystallization temperature and enthalpies in the green composites. The dependence of molecular weight of PLA upon composite formation was studied and the data is reported elsewhere.23 It

1656


Nyambo et al.

Table 2. Differential Scanning Calorimetry (DSC) Dataa formulation PLA PLA PLA PLA PLA PLA

unprocessed extruded/injection + 30% soy stalks + 30% corn stover + 30% wheat straw + 30% hybrid

Tg (°C)

Tc (°C)

∆Hc (J/g)

∆Hm (J/g)

Tm (°C)

χ (%)

61 ( 0 61 ( 1 61 ( 0 61 ( 0 60 ( 0 60 ( 0

none 110 ( 0 100 ( 0 106 ( 1 97 ( 1 98 ( 1

none 28 ( 1 11 ( 1 21 ( 0 17 ( 1 16 ( 1

1(0 46 ( 2 37 ( 2 31 ( 2 34 ( 1 33 ( 1

170 ( 0 171 ( 0 171 ( 0 171 ( 1 170 ( 0 170 ( 0

1 49 56 48 51 50

a Tg, glass transition temperature; Tc, crystallization temperature; Tm, melting temperature; ∆Hc, enthalpy of crystallization; ∆Hm, enthalpy of melting; and χ, degree crystallinity.

was observed that processing (extrusion followed by injection) of the PLA and addition of fibers reduces the molecular weight by about 20 and 30%, respectively. Bioplastics, including PLA, are known to be heat sensitive and thermally degrade during processing, and this results in changes in the molecular structure of the polymer.24 Such changes in molecular weight occurring during processing and due to the presence of fibers are known to affect the crystallization behavior of PLA and have been reported in the literature.10,15 Addition of the fibers alone or in combination did not affect the Tg and Tm but led to a reduction in enthalpies of melting (∆Hm) and crystallization (∆Hc). A decrease in the temperature of crystallization, Tc, was observed, possibly suggesting some nucleation activity of the fibers, and the degree of crystallinity in the composites was also increased (Table 2). This observation is consistent with the literature, in which the addition of agricultural residue fibers (sugar beet pulp) as fillers nucleated PLA and increased the degree of crystallinity.15 Dynamic Mechanical Analysis (DMA) Properties. Viscoelastic properties of the composites were studied using dynamical mechanical analysis (DMA). The temperature dependence of storage, loss, and tan δ are presented in Figure 1a, b, and c, respectively. The storage modulus is significantly enhanced in the composites at room temperature than in neat PLA, indicating improved stiffness. This is in agreement with the tensile and flexural data (Figures 4 and 6) and suggests that the fibers have strong influence on the elastic properties of the composites. A decrease in the storage modulus was observed with increasing temperature due to softening of the composites, and a sharp decrease in storage modulus occurred between 50-60 °C, corresponding to the glass transition. The loss modulus also increased around the Tg in composites, as shown in Figure 1b, and this is in agreement with the storage modulus data. The plots of tan δ versus temperature presented in Figure 1c are useful for detecting molecular transitions, and the peak of tan δ is often interpreted as the Tg. It is clear that the tan δ peaks for PLA and its composites are around 60 °C and are not significantly shifted in composites, indicating that there the presence of the fibers did not affect the Tg, which is in agreement with the DSC data (Table 2). Moreover, the tan δ peaks are reduced in intensity for the composites than in neat PLA, and this may suggest that the addition of the fibers hinders mobility of the PLA chains.25 It is also possible that changes in the degree of crystallinity and molecular characteristics during processing, as observed in the DSC study, may also lead to a reduced intensity of the tan δ peaks. Heat Deflection Temperature, HDT. The heat deflection temperature, HDT, defined as the temperature at which a material deflects 0.25 mm under a load of 0.455 or 1.82 MPa, is an important benchmark for composite application. Table 3 summarizes the HDT data for PLA and its composites obtained under a load of 0.455 MPa. It can clearly be seen that the addition of wheat straw, corn stover, and soy stalks, alone or in combination, did not alter the HDT of PLA. The observed

Figure 1. Temperature dependence of (a) storage modulus, (b) loss modulus, and (c) tan δ for the PLA and its composites

values are around the glass temperature, Tg. This is reasonable because it is generally known that the HDT of a low crystalline polymer is close to its Tg, while that of a highly crystalline polymer is in the vicinity of Tm. Huda et al.14 reported that the addition of wood fiber to PLA does not bring about an increase in the HDT. In contrast, Kawamoto et al.,26 observed a 2-fold increase in the HDT of PLA after addition of 1 wt % of dibenzoylhydrazide compounds. The authors attributed the increase in HDT to the fact that the dibenzoylhydrazide acted as effective nucleating agent that increased the degree of crystallinity. Here, the addition 30 wt % of agricultural residues (corn stover, wheat straw, soy stalks, and their hybrids) to PLA did not give rise to any enhancement in HDT, even though the degree of crystallinity was increased in the composites.


Figure 2. Tensile data for PLA with various amounts of wheat straw


1657

Figure 6. Flexural data for PLA with corn stover, wheat straw, soy stalks, and hybrid fibers. Table 3. Heat Deflection Temperature Data

Figure 3. Correlation analysis of experimental tensile data with the rule of mixture (ROM).

Figure 4. Tensile data for PLA with corn stover, wheat straw, soy stalks, and hybrid fibers.

Figure 5. Stress-strain curves for PLA with corn stover, wheat straw, soy stalks, and hybrid fibers.

Mechanical Properties of the Composites. Tensile testing data is presented in Figures 2 and 4. Rashaed et al.27 studied the effect on tensile strength of varying amounts of jute fiber in polypropylene and observed a decrease in the tensile strength above 10% loading of fiber. The authors attributed the decrease

formulation

HDT (°C)

PLA PLA + 30% soy stalks PLA + 30% corn stover PLA + 30% wheat straw PLA + 30% hybrid (i.e., 10% corn stover + 10% wheat straw + 10% soy stalks)

56 ( 0 57 ( 0 57 ( 0 57 ( 1 56 ( 1

in tensile strength to poor adhesion between the fibers and the matrix and to the fact that gathering of the fibers tends to occur at higher fiber loadings, and this may lead to poor dispersion. This reported observation is consistent to what is observed in this study (Figures 2 and 4) in which the addition of wheat straw from 10 to 40 wt % resulted in a systematic decrease in tensile strength, possibly due to poor interfacial adhesion of the fiber and matrix. Generally, an increase in tensile modulus or stiffness is commonly observed when fibers are used as reinforcement in composites. Here, a linear increase in tensile modulus is observed when the amount of wheat straw is varied from 10 to 40 wt %, and this observation agrees very well with that reported by Shibata et al.,8 in which the modulus was found to increase linearly with varying amounts of abaca fiber in PLA. There is no significant difference in the tensile properties of the composites prepared with different types of fibers at 30% loading, as shown in Figure 4. The tensile strength decreases when different types of fibers are used alone or in combination. This decrease in strength may suggest that there is no effective transfer of stress from all the different types of fiber to the matrix. The tensile data show that the mechanical performance of the hybrid composite is similar to that of composites with individual fibers. This observation is important for commercial injection molding application, because these agricultural residues may be substituted or combined without compromising mechanical performance, that is, in the event that manufacturers face problems related to supply chain like fiber shortages. Stress-strain curves of the composites are presented in Figure 5. The stress-stress curves are similar in shape for the composites compared to neat PLA and reveal that the addition of the fibers to PLA reduces the % elongation at break and tensile strength. Toughness, defined as the amount of energy a material can absorb before it fractures (i.e., area under the stress-strain curve), is decreased upon addition of the fibers to PLA. Changes in the molecular structure and crystallinity of the PLA may affect mechanical properties of a composite. It is generally accepted that the modulus may increase with an increasing level of crystallinity. Here, the composites show increased stiffness, reduced toughness, and elongation mainly due to the presence of a high amount of the rigid fiber fillers.

1658


Nyambo et al.

Figure 7. Scanning electron microscopy images (SEM) at (a) high and (b) low magnification for PLA + 30% soy stalks, (c) high and (d) low magnification for PLA + corn stover, (e) high and (f) low magnification for PLA + wheat straw and low (g) and high magnification for PLA + 30% hybrid composite (i.e., 10% corn stover + 10% wheat straw + 10% soy stalks). The scale bars for high and low magnification are 50 and 200 µm, as indicated on the scale bars in the images.

Mechanical properties of the neat processed PLA were comparable with the technical data provided by the manufacturer, suggesting less influence of processing on the mechanical properties of PLA. The flexural data is presented in Figure 6. A decrease or increase in tensile strength/modulus can often be correlated with a decrease or increase in flexural strength/ modulus, respectively. It has been reported that an increase in

flexural modulus also corresponds to an increase in tensile modulus in polypropylene/kenaf/baggase composites.28 The flexural data obtained is consistent with the tensile data, showing a decrease in flexural strength and an increase in flexural modulus. The rule of mixture (ROM) presented in the equation below was used to predict the modulus of the wheat straw composites.


Figure 8. Impact analysis data for PLA with corn stover, wheat straw, soy stalks, and hybrid fibers.


1659

fracture in the wheat straw composites (Figure 7f). This is reasonable because no compatibilizer was added and no surface modification of the fibers was performed to improve interfacial adhesion. Poor adhesion of the fiber to the matrix and fiber breakages are some of the major factors that have been reported to be the main cause of failure in natural fiber composites.31 Surface modifications of fibers by alkaline treatment, silane coupling, acetylation, or use of compatibilizer are some of the methods that have been developed to improve interfacial adhesion of the fiber and matrix.32 Here the major objective of the study was to investigate the effect of combinations of agriculture residues without surface modification. It is unlikely that the observed voids on the surface of the tensile fractures in the SEM images are due to the presence of water, because all the materials were completely dried for 4 h at 80 °C in a vacuum oven, but might have been formed as a result of fiber pullout during testing.

This rule is generally applied to short and randomly distributed fiber reinforced composites.13

Conclusions Ec ) kVfEf + VmEm where Ec, Ef, and Em are the elastic modulus of the composite, fiber (wheat straw, 9.3 GPa29), and matrix (neat PLA), respectively; k is a factor used to fit the data (contribution of the fiber length and orientation), while Vf and Vm are the volume fractions of the fiber and matrix, respectively, calculated using the density of PLA (1.25 g/cm3) and that of wheat straw (1.4 g/cm3 from the density results in Table 1). As seen in Figure 3, both the theoretical and the experimental data show an increase in modulus with an increase in the amount of wheat straw. The theoretical calculations from ROM give higher values of modulus when k ) 1 but show good agreement to experimental data when the fiber efficiency factor (k) is 0.90. This data is reasonable considering the fact that fiber orientation is assumed to be random in the ROM. Similar conclusions have been reported in the literature.30 Figure 8 presents the Izod notched impact data. The impact strength, which is the ability of the material to withstand fracture or the amount of energy required to propagate a crack, is reduced by the addition of the fibers. One possible explanation for these impact results could be due to the observed reduction in toughness (area under the stress-strain) curves and the % elongation at break. There is no significant difference in the impact strength of the composites with individual fibers or as a hybrid. The reduced impact strength may be improved by the addition of impact modifiers. Similar observations have been reported by Panthapulakkal and Sain,16 in which the addition of milled wheat straw and corn stem to polypropylene led to a reduction in impact strength. The authors also observed improvements in impact strength when the composites where compatibilized with maleated polypropylene and concluded that the presence of weak interfaces between the fiber and matrix may also contribute to crack propagation. Morphology of the PLA Composites. The morphology of the tensile fractures was studied using scanning electron microscopy (SEM), and the images at low and high magnification are presented in Figure 7a-h. The SEM images show moderate dispersion of the fiber at high magnification and platelike structures at low magnification. These images have evidence of voids and fiber pullout that may have contributed to the observed reduction in tensile, flexural, and impact strength. Besides, there is clear evidence of fiber debonding due to poor adhesion in the corn stalk composites (Figure 5d) and fiber

Green renewable composites based on PLA and 30 wt % of corn stover, wheat straws, soy stalks, and hybrid fibers were successfully prepared using twin screw extrusion followed by injection molding. The addition of the fibers improved the tensile modulus and led to a decrease in the tensile strength. Subsequent incorporation of wheat straw in PLA at various loadings from 10 to 40 wt % resulted in a systematic increase in tensile modulus. A linear correlation between tensile strength and % wt loading of wheat straw was observed and this was in strong agreement with theoretical predications from the rule of mixture (ROM). The density of the composites was around 1.3 g/cm3 and no significant changes in Tg were observed in DSC. DMA analysis of the composites revealed that the addition of the fibers increases the storage modulus, loss modulus and reduces the tan δ. The enhancement in storage modulus was attributed to the stiffening effect of the fibers, while the reduction in tan δ was probably due to the hindrance in mobility of the PLA chains or changes in molecular characteristics of PLA after the addition of the fibers. SEM on tensile fractures revealed poor adhesion of the fibers and this might have led to the observed decrease in strength (tensile, flexural, and impact) of the composites. There was no significant difference in the physicomechanical properties of the composites with individual fiber or with hybrid fibers. This is an important observation because it suggests that these agricultural residues can be substituted or be combined with each other for commercial applications without sacrificing mechanical performance, thus, providing a solution for addressing concerns related to supply chain problems. The prepared green composites are promising because they are renewable, biodegradable, and are better alternatives for nonrenewable petroleum-based composites on the basis of cost versus mechanical performance. Acknowledgment. Financial support from 2008 Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), University of Guelph Bioproducts program, NSERC- Discovery grant program individual (A.K.M.) is greatly appreciated. The authors gratefully thank Alexandra Smith for helping with SEM and Elora Farms for kindly providing the agriculture residues (corn stover, wheat straw, and soy stalks).

References and Notes (1) Henton, D. E.; Gruber, P.; Lunt, J.; Randall, J. In Natural Fibers, Biopolymers and Biocomposite; Mohanty, A. K., Drzal, L. T.,

1660

(2) (3) (4) (5) (6)

(7)

(8) (9) (10) (11) (12) (13) (14) (15) (16) (17)


Manjusri, M., Eds.; CRC Press, Francis & Taylor Group: Boca Raton, FL, 2005; p 527. Zenkiewicz, M.; Richert, J.; Rytlewski, P.; Moraczewski, K.; Stepczyn˜ska, M.; Karasiewicz, T. Polym. Test. 2009, 28, 412–418. Bhardwaj, R.; Mohanty, A. K. Biomacromolecules 2007, 8, 2476– 2484. Zhang, J. F.; Sun, X. Biomacromolecules 2004, 5, 1446–1451. Jiang, L.; Wolcott, M. P.; Zhang, J. Biomacromolecules 2006, 7, 199– 207. Plackett, D.; Sodergard, A. In Natural Fibers, Biopolymers and Biocomposites; Mohanty, A. K., Drzal, L. T., Manjusri, M., Eds.; CRC Press, Francis & Taylor Group: Boca Raton, FL, 2005; p 579. Oksman, K.; Selin, J. F. In Natural Fibers, Plastics and Composites; Wallenberger, F. T., Weston, N. E., Eds.; Kluwer Academic: Dordrecht, The Netherlands, 2004; p 149. Shibata, M.; Ozawa, K.; Teramoto, N.; Yosomiya, R.; Takeishi, H. Macromol. Mater. Eng. 2003, 288, 35–43. Plackett, D.; Andersen, T. L.; Pedersen, W. B.; Nielsen, L. Compos. Sci. Technol. 2003, 63, 1287–1296. Mohamed, A. A.; Finkenstadt, V. L.; Palmquist, D. E. J. Appl. Polym. Sci. 2008, 107, 898–908. Huda, M. S.; Drzal, L. T.; Mohanty, A. K.; Misra, M. Compos. Sci. Technol. 2008, 68, 424–432. Wu, C.-S. Polym. Degrad. Stab. 2009, 94, 1076–1084. Hu, R.; Lim, J.-K. J. Compos. Mater. 2007, 41, 1655–1669. Huda, M. S.; Drzal, L. T.; Misra, M.; Mohanty, A. K. J. Appl. Polym. Sci. 2006, 102, 4856–4869. Lezak, E.; Kulinski, Z.; Masirek, R.; Piorkowska, E.; Pracella, M.; Gadzinowska, K. Macromol. Biosci. 2008, 8, 1190–1200. Panthapulakkal, S.; Sain, M. J. Polym. EnViron. 2006, 14, 265–272. Joshi, S. V.; Drzal, L. T.; Mohanty, A. K.; Arora, S. Composites, Part A 2005, 35, 371–376.

Nyambo et al. (18) DOE (U.S. Department of Energy) Biomass Feedstock Composition and Property Database; DOE, Biomass Program; Department of Energy: Washington, DC, 2006; http://www.eere.energy.gov/biomass/ progs/search1.cgi. (19) Hiljanen-Vainio, M.; Varpomaa, P.; Seppala, J.; Tormala, P. Macromol. Chem. Phys. 1996, 197, 1503–1523. (20) Ashori, A. Bioresour. Technol. 2008, 99, 4661–4667. (21) Kong, Y.; Hay, J. N. Polymer 2002, 43, 3873–3878. (22) Fischer, E. W.; Sterzel, H. J.; Wegner, G. Kolloid Z. Z. Polym. 1973, 251, 980–990. (23) Pradhan, P.; Reddy, M.; Diebel, W.; Erickson, L.; Misra, M.; Mohanty, A. K. Comparative compostability and biodegradation studies of various components of green composites and their blends in simulated aerobic composting bioreactor. Proceedings from International Conference on Advancements in Polymeric Materials, February, 2010. Available on CD from http://www.apmcipet.com. (24) Jamshidi, K.; Hyon, S. H.; Ikada, Y. Polymer 1980, 29, 2229–2234. (25) Pothana, L. A.; Oommennb, Z. Compos. Sci. Technol. 2003, 63, 283–293. (26) Kawamoto, N.; Sakai, A.; Horikoshi, T.; Urushihara, T.; Tobita, E. J. Appl. Polym. Sci. 2007, 103, 244–250. (27) Rashed, H. M. M. A.; Islam, M. A.; Rizvi, F. B. J. NaVal Architecture Mar. Eng. 2006, 3, 1–6. (28) Shibata, S.; Cao, Y.; Fukumoto, I. J. Appl. Polym. Sci. 2006, 100, 911–917. (29) White, N. M.; Ansell, M. P. J. Mater. Sci. 1983, 18, 1549–1556. (30) Liu, W.; Mohanty, A. K.; Manjusri, M.; Drzal, L. T.; Kurian, J. V.; Miller, R. W.; Strickland, N. Ind. Eng. Chem. Res. 2005, 44, 857– 862. (31) Wollerdorfer, M.; Bader, H. Ind. Crops Prod. 1998, 8, 105–112. (32) Mohanty, A. K.; Misra, M.; Drzal, L. T. Compos. Interfaces 2001, 5, 313–343.

BM1003114

Polylactide-Based Renewable Green Composites from Agricultural

Recommend Documents