Compatibilizing effect of starch-grafted-poly(L-lactide) on the poly(ε-caprolactone)/starch composites

Compatibilizing Effect of Starch-grafted-Poly(L-lactide) onthe Poly(e-caprolactone)/Starch Composites

Li Chen,1 Zhe Zhang,1 Xiuli Zhuang,2 Xuesi Chen,2 Xiabin Jing2

1Department of Chemistry, Northeast Normal University, Changchun 130022, People’s Republic of China2State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Changchun130022, People’s Republic of China

Received 24 September 2008; accepted 2 August 2009DOI 10.1002/app.31269Published online 27 April 2010 in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: The poly(e-caprolactone) (PCL)/starchblends were prepared with a coextruder by using the starchgrafted PLLA copolymer (St-g-PLLA) as compatibilizers.The thermal, mechanical, thermo-mechanical, and morpho-logical characterizations were performed to show the betterperformance of these blends compared with the virginPCL/starch blend without the compatibilizer. Interfacialadhesion between PCL matrix and starch dispersion phasesdominated by the compatibilizing effects of the St-g-PLLAcopolymers was significantly improved. Mechanical andother physical properties were correlated with the compati-bilizing effect of the St-g-PLLA copolymer. With the addi-tion of starch acted as rigid filler, the Young’s modulus ofthe PCL/starch blends with or without compatibilizer all

increased, and the strength and elongation were decreasedcompared with pure PCL. Whereas when St-g-PLLA addedinto the blend, starch and PCL, the properties of the blendswere improved markedly. The 50/50 composite of PCL/starch compatibilized by 10% St-g-PLLA gave a tensilestrength of 16.6 MPa and Young’s modulus of 996 MPa,respectively, vs. 8.0 MPa and 597 MPa, respectively, for thesimple 50/50 blend of PCL/starch. At the same time, thestorage modulus of compatibilized blends improved to2940 MPa. VC 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117:2724–2731, 2010

Key words: PCL/starch blend; Starch-g-PLLA;compatibilizer; interfacial adhesion

INTRODUCTION

In the last decades, biodegradable polymers andblends have been considered as an ultimate solutionto the public environmental problem caused by thedisposal of traditional nondegradable petroleum-based polymers.1,2 However, up to now the biode-gradable polymers cannot be used for wide app-lications because of their limitations on prices ormechanical and physical properties. Starch, a naturebiodegradable polymer from renewable resources, isa potentially useful material for biodegradable plas-tics because of its natural abundance and low cost.But starch itself is not suitable for practical applica-tions because of the brittleness increasing with timeand the strong water absorption. The starch-based

materials produced by conventional melt-processing,such as the thermoplastic starch, usually exhibit verypoor mechanical properties, mainly because of thethermal decomposition of starch before melting, thestrong water absorption, and the poor interfacialadhesion with other components. To solve these prob-lems, various physical or chemical modifications ofthe starch granules have been considered, includingblending3–9 and chemical modifications.10–19

To obtain completely biodegradable materials withsatisfactory mechanical properties, starch is blendedwith biodegradable aliphatic polyesters such aspoly(L-lactide) and poly(e-caprolactone) (PCL). Theblend of starch/PCL is one of the well studied biode-gradable polymer blends, as both materials arecommercially available and widely produced.3,20–23

Koening and Huang3 studied the blends of high-amy-lose and waxy starch granules with PCL. The blendswere found to be mechanically compatible but phaseseparated. Averous et al.20 reported the blend ofwheat thermoplastic starch with PCL. Addition ofPCL to a thermoplastic starch matrix overcomessome weaknesses of pure thermoplastic starch, suchas moisture sensitivity and size stability. Thermaland hydrophobicity studies have shown a fairly lowcompatibility between these two polymers. Hydro-phobic aliphatic polyesters and hydrophilic starchesare thermodynamically immiscible, which leads topoor adhesion between the two components, and

Correspondence to: X. Chen ([email protected]).Contract grant sponsor: Natural Science Foundation for

Young Teacher of Northeast Normal University; contractgrant number: 20050308.

Contract grant sponsor: Jilin Provincial ResearchFoundation for Young Scholar; contract grant number:20090143.

Contract grant sponsor: National Natural ScienceFoundation for Young Scholar of China; contract grantnumber: 50903012.

Journal ofAppliedPolymerScience,Vol. 117, 2724–2731 (2010)VC 2010 Wiley Periodicals, Inc.

show poor and irreproducible performance. Variouscompatibilizers and additives have been evaluated toimprove the interface between starch and the biode-gradable polyesters.24–26 It is confirmed that poly(eth-ylene glycol) (PEG) with proper molecular weight isthe most commonly used compatibilizer and themost investigated for starch-based blends.27 PEGcould stabilize the PCL/starch blends by locating atthe interface and interact with both PCL phase andstarch phase. Choi et al.28 and Bhattacharya and cow-orkers29 used starch-g-PCL as a compatibilizer toenhance the interfacial adhesion between PCL andstarch phases, the properties of the blend wereimproved obviously. Avella30 prepared PCL/high-amylose starch blends in which the low molecularweight PCL modified by reacting its terminal groupswith pyromellitic anhydride was used as a compati-bilizer. Noomhorm and Tokiwa31 studied the influ-ence of poly(dioxolane) (PDXL), a poly(ethyleneoxide-alt-methylene oxide), as compatibilizer on poly(e-caprolactone) (PCL)/tapioca starch (TS) blends.The molecular weight effect of PDXL on the PCL/TSblends showed that mechanical properties of PCL/TS/PDXL blends from low molecular weight (Mn ¼10,000) and high molecular weight (Mn ¼ 200,000)PDXL were rather dependent on TS content.

Our group has prepared the amphiphilic starch-g-poly(L-lacide) (St-g-PLLA),32 which has a core-shellstructure with a hydrophilic core of starch and ashell hydrophobic of PLLA grafts. Previous researchconducted in our laboratory indicated that the St-g-PLLA can be used as a compatibilizer in PLLA/starch blends, which can improve the performanceswithout changing their whole biodegradability.33

The St-g-PLLA proved effective to improve the inter-facial adhesion and the mechanical properties of thecomposites. In this study, we use St-g-PLLA as acompatibilizer to prepare PCL/starch blends and toinvestigate the compatibilizing effect of St-g-PLLAon the mechanical and physical properties of thestarch/ St-g-PLLA/PCL blends.

EXPERIMENTAL

Materials

The corn starch was from Changchun Dacheng CornDevelopment in Jilin province, China. The watercontent in the starch was about 12% in weight meas-ured by water loss at 60�C in a vacuum oven. TwoPCL samples were synthesized in our laboratory,and their molecular weights measured with GPCwere Mn ¼ 71,000 and Mn ¼ 120,700, respectively.

The compatibilizer, St-g-PLLA, was synthesizedand characterized as described in our previous arti-cle31: the starch surfaces were first modified byreacting the hydroxyl groups on the starch withL-lactic acid, and then the St-g-PLLA was synthe-

sized in situ by the ring-opening graft polymeriza-tion of L-lactide (LLA) monomers onto the modifiedsurfaces of the starch granules in the presence ofSn(Oct)2 as a catalyst. After the polymerization reac-tion, the unreacted LLA monomers and PLLAhomopolymer were washed off with ethanol and tol-uene, respectively. In the previous article,33 it wasconcluded that with increase of the PLLA chaingrafting rate, the interfacial tension between starchand PLLA also increased. So in this study, a St-g-PLLA with PLLA grafting rate of 64% (St-g-PLLA64)was selected as the compatibilizer.

PCL/starch blend preparation

The PCL/starch blends with various St-g-PLLA64

contents shown in Table I were prepared by mixingthe three components in an internal mixer (Haake)at 140�C for 15 min. And then, the cooled mixturewas molded into 1–2 mm thick sheets by hot-press-ing at 120�C. PCL/starch blends without compatibil-izer were made undert the same processing condi-tions for comparison.

Thermal analysis of the composites

The thermal characteristics and crystallinity of PCLcomponent in the blend were evaluated by differen-tial scanning calorimetry (DSC) and wide angleX-Ray diffraction (WAXD). The DSC analysis wasperformed at a heating rate of 10�C/min under N2

atmosphere on a Perkin Elmer Pyris 1 instrument.Crystallinity of the PCL in the composites wascalculated from the following formula34:

Crystallity ð%Þ ¼ DHM=136� 100%

where DHM is the melting enthalpy (in J/g) calcu-lated from the fusion peak of DSC (the second heat-ing run). And the value 136(J/g) is the theoreticalenthalpy of completely crystalline PCL.

TABLE IStarch/PCL Blends and Their Thermal Analysis Data

Sample entrySt-g-PLLA64

Content (wt %)Tm

(�C)DHm

(J/g)Xc (%)of PCL

1 2 59.1 65.1 47.92 5 59.3 65.9 48.53 10 60.2 67.4 49.64 20 58.7 63.0 46.3Starch/PCL 0 57.6 56.7 41.7PCL 0 61.5 69.2 50.9

The weight ratio of starch and PCL is 50 : 50 for allblend samples. St-g-PLLA64 was used as compatibilizer. Itscontent is with respect to the total weight of PLLA andstarch.

COMPATIBILIZING EFFECT OF St-g-PLLA 2725

Journal of Applied Polymer Science DOI 10.1002/app

The WAXD analysis was conducted with a Philipsapparatus using a Cu Ka(k ¼ 0.154 nm) source.Measurements of the diffracted intensities weremade in the angular range of 5�–50� (2y) at roomtemperature and at a scan rate of 1�/min.

Phase separation test

To isolate a mixed starch/PCL phase, the selectiveextraction of the components has been carried outon the starch/PCL/10% St-g-PLLA64 and on thestarch/PCL as reference.35 Samples have been sus-pended in chloroform to form emulsions. Then, theemulsion was put in a cylindrical separator funneland left at room temperature for 24 h to let thephase segregate according to a procedure known as‘‘Molau test.’’

Tensile strength

Tensile strength and elongation at break were deter-mined at room temperature on an Instron 1121 testerat a constant deformation rate of 5 mm/min. A min-imum of three specimens were tested, and theresults were averaged. The dumbbell-shaped speci-mens for tensile measurements were cut from thesheets in accordance to ASTM Standard D638 V.

Thermo-mechanical analysis

Thermo-mechanical properties of the differentblends were measured by a dynamic thermo-me-chanical analyzer (Metravib Mak-04 Viscoanalyser).Specimens with dimensions of 20 mm � 4 mm �2 mm were cut from the central part of the sheets.They were tested by applying a bending constraintusing the dual cantilever geometry. The displace-ment amplitude was set to 3 lm. The measurementswere performed at a frequency of 11 Hz. Thetemperature range was from �80 to 60�C at thescanning rate of 3�C/min.

SEM observation

The starch/PCL blend morphology was investigatedby a Model XL 30 ESEM FEG from Micro FEI Philipsafter sputter-coating of gold on the fractured surfaceof the dumbbell specimens.

Contact angle measurements

Contact angle measurements were performed with aKruss DSA10 MK2 (Germany) apparatus. A waterdroplet was dropped on the surface of a small sam-ple cut from a dumbbell specimen. The evolution ofthe droplet shape was recorded by a CCD video

camera and was analyzed to determine the contactangle evolution.

Medium resistance measurements

The medium-resistance measurement of the blendsto 0.5 mol/L acid solution, 0.5 mol/L alkaline solu-tions, and pure water was performed by dispersingthe blend films in corresponding aqueous solutionsat room temperature for 24 h and measuring theweight loss of the films.

RESULTS AND DISCUSSION

The main limitation of the starch/PCL blends is lackof adhesion between the polysaccharide and the syn-thetic polymer matrices owing to their different po-larity. In fact, starch and most of the hydrophobicpolymers are immiscible. The simple blending usu-ally produces a mixture with two separate phases.So, preparing a blend with excellent physico-me-chanical property depends on a proper interfacialtension that generates a small phase size and stronginterfacial adhesion to transmit an applied forceeffectively between the component phases. Compati-bilization is the effective method to improve phaseadhesion and to reduce interfacial energy betweentwo immiscible phases. The compatibilization strat-egy is introduced by the addition of a premadeblock/graft copolymer composed of blocks that areeach miscible with one of the homopolymers. Thesecompatibilizers have turned several incompatibleblends into compatible ones to improve their physi-cal properties. The amphiphilic starch-g-poly(L-lacide) with a core-shell structure, with a core ofhydrophilic starch and a shell of hydrophobic PLLAgrafted, is expected to be a proper compatibilizer instarch/polyester blend.

Thermal analysis of the composites

The thermal properties of St/PCL blends with orwithout compatibilizer were summarized in Table I.The melting temperature (Tm), the fusion enthalpy(DHm) and the crystallinity (Xc ) of PCL in the blendswas determined by DSC. Figure 1 showed the typi-cal DSC curves of St/PCL blends. The pure PCLshowed a Tm at 61.5oC and an Xc of 50.9% , and theSt/PCL (50/50) blend showed a Tm at 57.6oC and anXc of 41.7%. The addition of the starch decreased theTm and Xc of PCL in the blend because the starch asfiller in the continuous PCL phase restricted PCLcrystallization. However, as the compatibilizer St-g-PLLA64 was added into the blends, the values of Tm

and Xc were all higher than that of the virgin St/PCL blends. This difference may be ascribed to thecontribution of the St-g-PLLA filler. It was well

2726 CHEN ET AL.


known that the simple St/PCL blends usuallyshowed depressed thermal properties because of theobvious phase separation and the weak interactionsbetween the two phases. To enhance the interphaseinteractions, PLLA grafted starch is used as a compa-tibilizer in the starch/polyester blends. As shown inTable I, when the content of the compatibilizerincreased from 2 to 15%, Tm and Xc of PCL in theblends increased correspondingly. Sample 3 dis-played the maximum Tm and Xc. When the fillercontent of St-g-PLLA64 reached 20%, the values ofTm and Xs all decreased a lot indicating that furtherincrease of the compatibilizer is not suitable to thephysical properties of the blends.

The crystallizability of the pure PCL, St/PCLblends with or without St-g-PLLA64 could also beconfirmed by WAXD patterns shown in Figure 2.The pure PCL [in Fig. 2(a)] showed two main dif-fraction peaks at 2y ¼ 21.4� and 23.8�, respectively.In Figure 2(b,c), there appeared peaks at 15.2�, 17.1�,and 23.1� attributed to starch crystal in the blends,especially in the blends with St-g-PLLA64 as compa-tibilizer, which enhanced the interphase interactionsbetween PCL and starch. There were no peaksattributed to PLLA, because in the blends the con-tent of PLLA was too low. This result was accordantwith that from DSC.

Phase separation test

By the ‘‘Molau test,’’ it could observed that whenvirgin St/PCL blend was left at room temperaturefor a few minute, a complete phase separation witha supernatant starch phase and a clear CHCl3 solu-tion was reached, whereas in the case of St/PCL/10% St-g-PLLA64 blend the solution was opaque

even after several weeks because of the suspensionof St-g-PLLA64. These phenomena clearly revealedthe emulsifying effect of the St-g-PLLA64. As matterof fact, the interfacial compatibility between starchand PCL was improved by St-g-PLLA64.

Mechanical properties and SEM analysis

Mechanical properties such as tensile modulus (E),yield strength (ry), strength at break (rb), and elon-gation at break (eb) were evaluated from the stress–strain curves (Fig. 3) and the related data are sum-marized in Table II. It was well known that the PCLwas a ductile polymer with large deformations, butit had a relatively low modulus rendering it unableto be used for a high rigidity required applications.As expected, addition of starch fillers into PCL

Figure 1 DSC curves (second heating run) of pure PCL(a), simple St/PCL blend (b), St/PCL with 20% St-g-PLLA(c), with 10% St-g-PLLA (d), with 5% St-g-PLLA (e), with2% St-g-PLLA (f).

Figure 2 X-Ray curves of pure PCL (a), St/PCL/2%St-g-PLLA (b), and simple St/PCL blend (c).

Figure 3 Typical stress-strain curves of PCL (a), simplestarch/PCL blend (b), and starch/PCL with St-g-PLLAcompatibilizer (c).



matrix led to significant reduction of the ry, rb andeb because of the poor filler/matrix interfacial adhe-sion, but improved the blend modulus. The Young’smodulus E of pure PCL was 267 MPa, whereas thatof simple St/PCL was 597 MPa as twice as that ofPCL. After addition of St-g-PLLA compatibilizer intothe blends, the Young’s modulus could reach to 996MPa. The starch phases in the blends with or with-out compatibilizer acted as rigid filler not capable ofbeing deformed in the blends. When the compatibil-

izer was incorporated into the blends, the mechani-cal properties were substantially improved. Concern-ing the mechanical behavior of St/PCL blends withthe compatibilizer, the sample 3 containing 10%comaptibilizer presented a larger increase of elasticmodulus accompanied by higher strength at yield-ing. On the contrary, the elongation at breakdecreased. These results were owing to the betterinterfacial adhesion between the starch and PCL. Inthe region of linear elasticity of the PCL matrix, thePCL chains could not move freely and then resuledin higher rigidity. That is to say, the PLLA graftedstarch really played a role of compatibilizer becauseit was incorporated into both the PCL polyesterphase and the starch phase. It did not only promotea better dispersion of the starch granules in the PCLmatrix but also reinforced the adhesion between thefillers and the matrix hindered the moving of PCLmacromolecules.Generally, the properties of the blends depended

on their morphology (phase structure) and the inter-facial adhesion between starch and synthetic poly-mers. The scanning electron micrographs of uncom-patibilized simple St/PCL blend [Fig. 4(a,c)] and

TABLE IITensile Properties of Starch/PCL Blend Compositions

Sample entrya rb (MPa) eb (%) E ( MPa) r y (MPa)

1 13.7 125 798 7.62 15.2 131 813 8.83 16.6 139 996 9.24 15.1 127 862 8.4Starch/PCL 8.0 516 597 3.9PCL 31.8 1109 267 12.9

a The same samples as in Table I.rb, strength at break; eb, elongation at break; E, tensile

modulus; ry, strength at yielding.

Figure 4 SEM micrographs of the fracture surfaces of the simple St/PCL blend (a), St/PCL/5%St-g-PLLA64 (b), the mag-nified image of simple St/PCL blend (c), and the magnified image of St/PCL/5%St-g-PLLA64 (d).

2728 CHEN ET AL.


compatibilized St-g-PLLA/starch/PCL blend [Fig.4(b,d)] performed on the fractured surfaces of thesamples after the tensile test. It can be seen that thestarch granules in the uncompatibilized blend werenot homogeneously dispersed in the polymer matrixshowing typical characteristics of an immisciblecomposite with poor interfacial adhesion [Fig.4(a,c)]. A clear edge and aperture between the starchgranules and PCL matrix were observed. However,in the blend containing 5 wt % compatibilizer [Fig.4(b,d)], the starch granules were well dispersedwithin the polymer matrix and covered by PCL ma-terial, confirming a good interconnection betweenthe starch granules and PCL matrix. The edge andthe inter-phase between the two phases becomeblurry. Also, these blends showed an improved ten-sile strength, which indicates that the compatibilizerreduced the interfacial energy and thereby produceda finer and more uniform morphology.

Thermo-mechanical analysis

Figure 5 showed the storage modulus (E0), loss mod-ulus (E00), and tan d curves provided by dynamicthermo-mechanical analysis (DMTA) of pure PCL,uncompatibilized and compatibilized starch/PCLblends. In dynamic mechanical studies, changesoccurred close to the Tg of the polymer, with thestorage modulus decreasing rapidly with theincrease of temperature from �80 to 0�C, and theloss modulus and tan d showing maximal values at�60�C. In the transition region, these obviouschanges were called as the primary dispersion (thea-peak). The magnitude of the a-peak in the amor-phous polymer was much higher than in the semi-crystalline polymer, primarily because of the chainsegments of the amorphous polymer in the glasstransition region. For pure PCL, there was a rapiddecrease of the storage modulus with the increase oftemperature at �60�C associated with a loss modu-lus peak and a tan d peak which were consistentwith a glass transition. A second transition isobserved at higher temperatures (maximum of tan dat 60�C), which could be associated with melting ofthe polymer.

For St/PCL blend and St/PCL/St-g-PLLA blend,the storage modulus at �80�C increased from 1900MPa of pure PCL to 2370 MPa and 2940 MPa,respectively. The addition of 50 wt % starch to PCLparticularly increased the storage modulus byenhancing the secondary forces of the St/PCLblends and made the blends more rigid than purePCL by decreasing the polymer chain mobility. Forall DMTA curves of the St/PCL blends with or with-out St-g-PLLA, a tan d peak located at low tempera-ture about �55�C to �57�C was observed. This peakcorresponded to an overlapping of two signals: one

attributed to the glass transition of PCL and onearising from secondary relaxation of starch. The tand value at the a-peak was greater than at the dissipa-tion peaks for lower temperatures and was accompa-nied by the greatest decrease in storage moduluswith increasing temperature. The damping curve forthe dynamic properties of heterogeneous copolymersreflected the border of the transition region betweenimmiscible substances, and this transition was gener-ally broad for such copolymers. As shown in Figure

Figure 5 DMTA curves of PCL and starch/PCL blendswith or without compatibilizer.



5, the intensity of the tan d peak decreased with theincorporation of starch, and the broad transitionregion observed indicated that PCL and starch wereinsoluble in each other. The lower intensity of tan dseen in the blends indicated less movement of themolecular chains in the blends compared with purePCL. It could include that the addition of starchincreased the storage modulus of starch/PCL blendsand decreased the glass transition temperature ofPCL and the melt temperature of polymer blends.At the same time, the compatibilizer St-g-PLLAreduced the interfacial energy resulted in theincreasing of storage modulus of the blends com-pared with simple St/PCL blend.

Contact angle measurements

The contact angle formed between a water dropletand a substrate surface, and the kinetics of spread-ing were related to the hydrophilic character of thematerial. The blends material’s contact angle behav-iors were quantitatively illustrated by the initial con-tact angle just after deposition of a droplet and bythe evolution rate of the contact angle with time.The results were presented in Table III. For the purePCL, the contact angle was 93� because of its hydro-phobic nature. With the addition of the hydrophilicstarch, the contact angle of the starch/PCL blendsdecreased to 51�. When St-g-PLLA compatibilizerwas added to the blend, the value of the contactangle increased and this increase was dependent onthe content of St-g-PLLA. For the simple St/PCLblend without the St-g-PLLA compatibilizer, the evo-lution rate of the water contact angle was morerapid than that with PLLA-g-St, because of thehydrophilic nature of the starch. When the St-g-PLLA was incorporated into the blends, the evolu-tion slope of contact angle at the origin point becameslower with time. In all cases, the introduction ofSt-g-PLLA leaded to a significant improvement ofthe material hydrophobicity. These behaviors pro-vided further evidence for the improved compatibil-ity or the reinforced adhesion between the starch

granules and the PCL matrix in the St-g-PLLA com-patibilized system. Because of the presence of the St-g-PLLA compatibilizer, the hydrophilic starch gran-ules appeared to be hidden in the hydrophobic PCLmatrix.

Medium-resistance

Water resistance was a very important factor forpractical applications of starch-based materials,because starch was usually poor in storage stabilityfor its sensitivity to moisture. The medium-resistan-ces of the starch/PCL blends with or without St-g-PLLA to 0.5 mol/L acid solution, 0.5 mol/L alkalinesolution and pure water were measured at roomtemperature (about 25�C) for 24 h, respectively. Dis-persed in water or an acid solution, the films alwaysgained a certain weights, whereas in an alkalinesolution they lose weights at the beginning stage.The weight increase was because of the wateradsorption by the starch in the blend and theweight-loss is because of the degradation of thestarch catalyzed by the alkali. As shown in Table IV,the stabilities in all three media of the compatibi-lized blends were improved compared with the sim-ple starch/PCL blend. Among them the blend with10% of St-g-PLLA was the best.

CONCLUSION

The thermal, thermo-mechanical, and mechanicalproperties of starch/PCL blends with or withoutSt-g-PLLA as campatibilizer have been investigated.The use of St-g-PLLA as a compatibilizer in starch/PCL blends can improve the performances withoutchanging their whole biodegradability. St-g-PLLA isa good compatibilizer for the blend of hydrophobicPCL and hydrophilic granular corn starch. With theaddition of St-g-PLLA, the tensile modulus of theblends increases because the starch acted as rigid fil-ler, and St-g-PLLA improves interfacial adhesionand mechanical properties of the composites com-pared with the simple starch/PCL blend. At the

TABLE IIIContact Angle Measurements of St/PCL Blends

Sample entrya Initial value (�)b Slope at the origin (�/s)

1 68 �0.252 71 �0.23 72 �0.14 69 �0.1Starch/PCL 51 �1.5PCL 93 �0.05

a Sample entries 1–4 are referred as Table I.b The data were collected by mean of five independent

experiments.

TABLE IVMedium-Resistance of the St/PCL Blends

Sample entry

Weight change (wt %)

In 0.5 mol/LHCl

In 0.5 mol/LNaOH In H2O

1 þ5.2 �16.7 þ5.92 þ4.3 �16.1 þ4.13 þ3.6 �15.4 þ3.44 þ3.8 �15.8 þ3.8Starch/PCL þ18.3 �44.3 þ19.5

The experiments of medium-resistance were carried outat room temperature.

2730 CHEN ET AL.


same time, the storage modulus of the starch/PCLblends also increase. These environmental compati-ble materials are characterized by less cost than theneat PCL and display all required qualities of a dis-posable plastic. Changing the amount of St-g-PLLAcompatibilizer can tailor the properties of the com-posites for specific applications. Compared with thesimple blend, the St-g-PLLA compatibilized starch/PCL blends show stronger water- and medium-resistance. Therefore, this kind of blend is an inter-esting approach to low cost biodegradable materialin order, for instance, to increase the use of environ-mentally friendly materials in packaging industry orin fertilizer control release to be used as fertilizercarriers.

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