ORIGINAL PAPER

Gas Barrier and Biodegradable Properties of Poly(L-lactide)Nanocomposites Compounded with Polyhedral OligomericSilsesquioxane Grafted Organic Montmorillonite

Qifang Li • Dan Bi • Guang-Xin Chen

� Springer Science+Business Media New York 2014

Abstract A novel organic montmorillonite (OMMT) was

prepared by reacting the aminopropyllsobutyl polyhedral

oligomeric silsesquioxane (POSS) with the OMMT that

had already been modified by cationic surfactants. The

layer spacing of OMMT increased from 1.68 to 3.43 nm

after being intercalated by POSS. Poly(L-lactide) (PLLA)

based nanocomposites with montmorillonites were pro-

duced by melt compounding. The PLLA nanocomposites

with POSS modified OMMT were comprised of a random

dispersion of intercalated/exfoliated aggregates of layered

silicates throughout the PLLA matrix. The incorporation of

POSS modified OMMT resulted in a significant increase in

decomposition temperature for 5 % weight loss in com-

parison with the virgin PLLA. Gas permeation analysis

showed that the increase of the montmorillonite concen-

tration in the polymer matrix led to an expected decrease in

permeation values. Gas barrier properties of the nano-

composites were compared with those predicted by phe-

nomenological models such as the Nielsen model and

Cussler model. Incorporation of the POSS on OMMT

improved significantly mechanical properties of PLLA.

The biodegradability of the neat PLLA and corresponding

nanocomposite was studied under compost, and the rate of

biodegradation of PLLA increased after nanocomposite

preparation.

Keywords Montmorillonite � Polyhedral oligomeric

silsesquioxane � Poly(L-lactide) � Nanocomposites

Introduction

Over the past decade, organic/inorganic nanohybrid is a

subject of great interest because it offers unique hybrid

properties difficult to obtain from individual components.

Of particular interest among different organic/inorganic

nanohybrids are polymer/layered silicate nanocomposites,

which constitute a relatively new class of materials that has

attracted growing scientific and technological interest due

to their unique properties, which make them candidates for

a number of potential applications [1–4]. Montmorillonite

is one of the most commonly used layered silicates in

polymer nanocomposites, due to its low cost, high surface

area, high aspect ratio, and low toxicity [5]. With a charged

nuture, pristine montmorillonites are hydrophilic and thus

incompatible with hydrophobic polymers, and it is neces-

sary to reduce the polarity in order to enhance their com-

patibility with most polymer matrixes. Therefore, the two

main objectives of surface modification on montmorillonite

are: (1) to expand the interlayer space, allowing large

polymer molecules to enter into the montmorillonite gal-

leries, and (2) to improve the miscibility of montmoril-

lonite with polymers to achieve a good dispersion of

layered structure within the polymer matrix [6]. At present,

montmorillonite surfaces are often treated with surfactants

containing long alkyl chains that help to expand the

interlayer space of the montmorillonites to facilitate their

exfoliation in polymers [7].

Polyhedral oligomeric silsesquioxane (POSS) reagents,

monomers, and polymers are emerging as a new chemical

technology for nano-reinforced organic–inorganic hybrids

Q. Li � D. Bi � G.-X. Chen (&)

Key Laboratory of Carbon Fiber and Functional Polymers,

Ministry of Education, Beijing University of Chemical

Technology, Beijing 100029, People’s Republic of China

e-mail: gxchen@mail.buct.edu.cn

Q. Li

College of Material Science and Engineering, Beijing University

of Chemical Technology, Beijing 100029, People’s Republic of

China

123

J Polym Environ

DOI 10.1007/s10924-014-0653-z

[8, 9] and the polymers incorporating POSS monomers are

becoming the focus of many studies [10, 11] in view of

their excellent mechanical properties, thermal stability,

simplicity in processing and flame retardation etc. Typical

POSS monomers possess the structure of cube-octameric

frameworks with eight organic corner groups, one or more

of which are reactive or polymerizable. The POSS cage is

thermally stable, and its bulkiness may help the expansion

of the montmorillonite interlayer space so that the amount

of such hybrid surfactants required to achieve a large

expansion of the interlayer space may be fairly small. Also,

POSS can be used as the intercalating agents of layered

silicates to prepare nanocomposites combining the two

types of nanoreinforcement agents [12]. Some POSS-

modified montmorillonites have been prepared in recent

years with the aim to be dispersed into polymers to yield

polymer/montmorillonite nanocomposites. These studies

were principally motivated by the high thermal stability of

POSS that allows the POSS-modified montmorillonite

minerals to withstand the high temperatures required for

processing some thermoplastics. The high thermal stability

of POSS has to be compared with the onset temperature

around 170–190 �C of nonoxidative decomposition of

alkyl quaternary ammonium salts [13]. POSS ammonium

surfactants with isooctyl substituents were used to prepare

polypropylene/montmorillonite [14] and poly (butylene

terephthalate)/montmorillonite [15] nanocomposites.

In most studies on POSS modified montmorillonites,

POSS is used as a substitute for onium ions in montmo-

rillonite modification. The POSS derivatives containing

short alkyl chains with amine groups behave like a sur-

factant and the POSS modified montmorillonites are syn-

thesized via ion-exchange reaction. Although POSS-based

surfactants hold sound promise in lessening the degrada-

tion, there is also a great concern that the inherent tendency

for POSS compounds to aggregate or crystallize [16, 17]

may hinder the exfoliation of POSS-modified clay in

polymer matrices, thus limiting the properties of the

nanocomposites.

In our previous research, we introduced the concept of

‘‘twice functionalization’’ to modify the montmorillonite,

with organic agent to swell the montmorillonite and func-

tional agent to react with the polymer matrix to further

improve the interfacial interaction [18–22]. In present

work, we present the synthesis of POSS modified organic

montmorillonites (OMMTs) that had already been modified

by cationic surfactants and thereafter, the POSS-modified

organic montmorillonite (POMMT) was employed to pre-

pare the nanocomposites of poly(L-lactide) (PLLA). By

using some extending range of mathematical models, we

investigate the improved barrier properties of the nano-

composite barrier membranes in relation to the large sur-

face area and high aspect ratio of the montmorillonite, so as

to identify both the benefits and limitations of nanocom-

posite barrier materials.

Experimental

Materials

The OMMT, I.24TL-montmorillonite, was purchased from

Nanocor Co., USA, and was purified by dissolution in

ethanol at 70 �C for 4 h to remove any contaminants. The

structure of the organic modifier is HOOC–(CH2)17–NH3?.

The POSS used to modify OMMT was commercial pro-

ducts, e.g. aminopropyllsobutyl POSS (APB-POSS), pur-

chased from Hybrid Plastic Co. USA. The PLLA was

manufactured by Weihua Co. (Shenzhen, China) with a

weight-average molecular weight of 2.4 9 105. All of

reagents (purity [ 99.5 %) were purchased from Beijing

Chemical Factory and used as received.

Preparation of POMMT

The typical procedure of preparing POMMT is described as

follows: the mixture of I.24TL-montmorillonite (5 g) and

excess thionyl chloride was heated and stirred vigorously

in an oil bath with reflux at 80 �C for 24 h. The product

was then filtered and repeatedly washed with hexane at

room temperature to obtain the acyl-chloride functional-

ized OMMT (OMMT-COCl), a kind of gray powder. Then

the OMMT-COCl was mixed with 10 g of APB-POSS and

excess re-steamed THF. The mixture was heated and stir-

red vigorously in an oil bath with reflux at 75 �C for 24 h,

then filtered and repeatedly washed with re-steamed THF

to yield the POMMT. The POMMT was dried in a vacuum

oven at 50 �C for 24 h in order to remove the residual

solvents. The chemical reaction between the OMMT and

APB-POSS is shown below:

J Polym Environ

123

Preparation of PLLA Based Nanocomposites

The nanocomposites of the PLLA/montmorillonites were

prepared by melt compounding PLLA with montmorillo-

nites, using HAAKE torque rheometer at 190 �C under

60 rpm for 5 min. The resulting products were hot pressed

at 190 �C for 1 min under 4 atm to prepare sheets with a

thickness of approximately 0.5 mm which were then

quickly cooled prior to various characterizations.

Characterization

The morphology of the nanocomposites was analyzed by TEM

(JEOL 2000FX) with an acceleration voltage of 120 kV. All

the ultrathin sections (\100 nm) were microtomed with a

Super Nova 655001 instrument (Leica, Switzerland) with a

diamond knife and were then subjected to TEM observation

without staining. The basal spacings of the montmorillonites

and the PLLA/montmorillonites nanocomposites were mea-

sured with an X-ray diffractometer (Brucker AXS, D8) with

CuKa radiation at 45 kV and 50 mA. The diffraction patterns

were collected in the range 1�\2h\10� at a scanning rate of

1�/min-1. Thermal gravimetric analysis (TGA) was performed

on a Setaram TGA 92 Thermobalance, by heating the samples

at 10 �C/min from ambient temperature to 900 �C under

nitrogen atmosphere.

Gas permeability of pure PLLA and PLLA/montmoril-

lonite nanocomposites was measured in an automatic

tightness tester which was homemade according to the

standard of ISO 2782. Ultra high purity nitrogen was used

for purging and analyses. The film specimens were cut into

a circular shape with a diameter of 8 cm, and then tested at

40 �C and under 0.57 MPa. The membranes were placed in

a stainless steel cell with chambers of known volume on

each side. The nitrogen permeation rate was then calcu-

lated by multiplying the measured transmission rate by the

average sample thickness. Each sample was measured at

five points oriented in a cross pattern over the testing area,

and the results were averaged. To confirm the reproduc-

ibility of the data, more than one sample was used to test

the nanocomposites systems. The permeation rates of the

film specimens were evaluated by using the following

formula:

P ¼ Vðm3Þ � dðmÞsðm2Þ � tðsÞ � pðPaÞ ð1Þ

where V is the volume of the penetrated gas, d is the

thickness of the film specimen, s is the area of the pene-

trated gas, t is the time of penetration, p is the differential

pressure of both sides of the film.

Dumbbell-shaped tensile specimens were prepared from

the hot pressed sheets of PLLA/OMMT and PLLA/APB-

POMMT as well as PLLA. The specimens were subjected

to uniaxial elongation at room temperature. All experi-

ments were carried out with a UTM, Hounsfield test

equipment at a cross head speed of 20 mm/min.

Animal fodder was used as the substrate in composting

process. The composition of fiber, fat and protein in the

animal fodder was similar to food garbage. The composting

process lasted about 1 month. All the samples were pow-

dered at a cryogenic condition for the biodegradation test.

Biodegradation of the nanocomposites was conducted in

the laboratory-scale compost according to ASTM D5209-

92 and ASTM D5338-92. The air flow rate was controlled

at 40 ml/min. A mixture of mature compost (200 g, wet

weight) and the plastics (5 %, on a dry basis) was intro-

duced and incubated at 58 �C. The moisture content of the

compost was maintained at 65 %. CO2 produced from the

compost was absorbed by a 0.4 N potassium hydroxide and

2 N barium chloride mixture solution, and was quantified

by titrating the solution with 0.2 N HCl.

Results and Discussion

Morphology and Structure

Figure 1 shows the FT-IR spectra of OMMT and APB-

POMMT. It can be perceived from Fig. 1 that the peak at

1,112 cm-1, which is assigned to the stretching of Si–O–Si

from POSS cage, confirming the chemical reaction

between the APB-POSS monomers with the end carboxyl

groups of OMMT.

Figure 2 shows the XRD patterns of the OMMT and the

POMMTs. Bragg equation is used to calculate the d (001)

spacing values of the samples and characterize the layered

4000 3000 2000 1000

(b)

Wave number (cm-1)

(a) OMMT(b) APB-POMMT

(a)

Fig. 1 FT-IR spectra of the OMMT and the APB-POMMT

J Polym Environ

123

structure of the POMMTs. As shown in Fig. 2, the

d-spacing of the OMMT was expanded from 1.68 to

3.43 nm after being modified by APB-POSS, indicating

that the APB-POSS was grafted to the organic modifier and

hence the intercalation between the OMMT layers.

The XRD patterns of the PLLA nanocomposites with

2 wt% of OMMT and APB-POMMT are shown in Fig. 3

where the peak appearing at 2h = 3.92� reveals the for-

mation of partially intercalated nanocomposites by 2 wt%

of OMMT (d spacing = 2.25 nm). However, a complete

disappearance of the reflection peak was observed in the

PLLA nanocomposite with 2 wt% of APB-POMMT,

which indicates a disordered structure, but does not provide

enough evidence whether the montmorillonite platelets

were fully exfoliated and evenly dispersed throughout the

PLLA matrix. Apart from measuring the d spacing by

XRD, TEM is required to determine the actual distribution

of platelets within the polymer matrix, so as to complete

characterizing the formation of the nanocomposite.

TEM analysis allows direct visualization of the mor-

phology and dispersion of the nanoparticles and platelets

within the polymer matrix. Figure 4 shows the TEM ima-

ges of the microstructures of the PLLA/OMMT and PLLA/

APB-POMMT nanocomposites, where the dark line rep-

resents individual silicate layers and the brighter area

stands for the PLLA matrix. Figure 4a shows that the

OMMT layers do not fill the full volume, suggesting that

the platelet tactoids of the OMMT were dispersed in the

PLLA matrix at a sub-micro-sized scale. A close obser-

vation of an area of platelet tactoid reveals the individual

platelets of montmorillonite clearly separated by the

polymer matrix. The measured distance between the two

adjacent lines, i.e., the interlayer spacing of the intercalated

tactoids (about 2.2 nm), obtained from the TEM observa-

tions, is consistent with that from the XRD data (2h is

about 4� shown in Fig. 3). In contrast, TEM image of

PLLA/APB-POMMT shown in Fig. 4b demonstrates the

presence of individual layers as well as a few packets of

silicate consisting of about two layers. Therefore, a higher

degree of exfoliation of the silicate layers is obtained for

the PLLA/APB-POMMT nanocomposite than for the

PLLA/OMMT nanocomposite. This is consistent with the

fact that the XRD pattern of the PLLA/APB-POMMT is

absent. The absence of the XRD peak in Fig. 3b attributed

to the higher interlayer spacing of APB-POMMT and the

enhanced interaction between the organic modifier of APB-

POMMT and the PLLA chains. TEM micrograph shows

that the APB-POMMT resulted in better dispersion and

exfoliation in the PLLA matrix compared with the OMMT.

2θ (ο)

APB-POMMT

OMMT

MMT

2 4 6 8 10

10 20 30 40

Si Si

Si Si

Si Si

Si Si

O

O

O

OO

O

OO O

OO

O

NH 2

2θ ((ο)

APB-POSS

Fig. 2 XRD patterns of the MMT, OMMT, APB-POMMT and APB-

POSS

2 4 6 8 10

(b)

2θ (o)

(a) PLLA/OMMT(b) PLLA/APB-POMMT

(a)

Fig. 3 XRD patterns of the PLLA nanocomposites with a 2 wt% of

OMMT and b 2 wt% APB-POMMT

J Polym Environ

123

Thermal Properties

Figure 5 shows the thermal degradation behavior of the

OMMT, POMMT and POSS in nitrogen. The slower

weight loss of POSS compared with OMMT and POMMT

before 250 �C is observed. Two decomposition steps for

the OMMT (Fig. 5a) are attributed to the decomposition of

physically absorbed water and water molecules around the

exchangeable sites in the OMMT before 200 �C and the

dehydroxylation of the structure water of the OMMT

between 525 and 700 �C, respectively [23, 24]. The ther-

mal degradation between 200 and 525 �C is attributed to

the decomposition of attached organic surfactant on the

surface of OMMT. The APB-POMMT exhibits thermal

stability in nitrogen which is about 72 �C higher than the

OMMT. The embedding of the APB-POMMT leads to a

remarkable thermal stabilization of the molecular

compound. The decomposition peak appears at about

443 �C is mainly due to the decomposition of the POSS

bounded surfactant, which caused a relatively high phase-

transformation temperature compared with the free sur-

factant. The higher thermal stability of the APB-POMMT

than the OMMT maybe lies in the rigidity of the molecular

structure of the bounded POSS. The OMMTs with high

decomposition temperature is very important for the melt

compounding process of polymer nanocomposites as the

processing temperatures for most engineering plastics are

around 200 �C. The low decomposition temperatures of

OMMTs would lead to the degradation of the surfactants

during the processing [25].

Figure 6 shows the TGA curves of PLLA and its

nanocomposites. Both of the PLLA/montmorillonite

nanocomposites display higher decomposition tempera-

tures than that of the virgin PLLA. The nanocomposite

prepared from the APB-POMMT displays a 32.5 �C

increase in the decomposition temperature for 5 % weight

loss, and the PLLA/OMMT nanocomposite 21.1 �C,

compared with the virgin PLLA. Therefore, the PLLA/

APB-POMMT nanocomposite is the most thermally stable

one among these three samples. The thermal stability of the

polymer/montmorillonite nanocomposites can be affected

by polymer matrix, fillers, and the interaction between

them. Such behaviour was explained by the decomposition

temperature of montmorillonites and the relative extent of

exfoliation. Indeed, the enhanced decomposition tempera-

ture of APB-POMMT and the exfoliated individual plate-

lets together increased the thermal stability of the

nanocomposites [26].

Gas Permeation

Figure 7 shows the effect of the concentration of the APB-

POMMT in the PLLA nanocomposites on gas permeability.

Fig. 4 TEM images of a PLLA/OMMT and b PLLA/APB-POMMT

nanocomposites. The content of the montmorillonites was 2 wt%

200 400 600 8000

20

40

60

80

100

50 100 150 200 250 30090

92

94

96

98

100

102

104

c

Wei

ght L

oss

(%)

Temperature (°C)

ab

c

(a) OMMT(b) APB-POMMT(c) APB-POSS

Wei

ght L

oss

(%)

Temperature (°C)

a

b

Fig. 5 TGA traces of a OMMT, b APB-POMMT and c APB-POSS

J Polym Environ

123

As seen in Fig. 7, increasing the montmorillonite concen-

tration in the polymer matrix leads to an expected decrease

in permeation values. For example, the N2 permeation

obtained for the pristine PLLA membrane is

0.593 9 10-17 m2s-1 Pa-1, and the addition of 10 wt%

APB-POMMT in the matrix decreases the N2 permeation

value to 0.203 9 10-17 m2s-1 Pa-1. This represents a 66 %

decrease in permeability in comparison with the pristine

polymer sample. It has been known that the exfoliated

morphology increases the effective surface area of the

montmorillonite in the matrix, and consequently increases

the tortuous pathway for the permeating gas molecules.

These results suggest that the APB-POSS increases the

dispersion of OMMT particles in the PLLA matrix sub-

stantially, which in turn generates more tortuous pathways

for permeating gas molecules. At low organoclay loadings,

tactoids are surrounded by significant quantities of neat

polymer, and while the platelets themselves are able to slow

permeating species, the surrounding polymer nevertheless

allows for substantial permeation. As the organoclay content

is increased, the tactoids begin to overlap more and more

significantly, forming a layered structure with the polymer

dispersed throughout, which contributes more effectively to

the tortuous path effect that is often credited as the main

source of the improvement seen with the addition of

nanoclays [27].

A number of models have been applied to describe the

permeation behavior of nanolayer-based nanocomposites.

They are based on ideal conditions, such as complete ex-

foliation of the flake platelets, perfect alignment of the

flakes in a perpendicular direction to the flow of the per-

meating molecules [28], and the assumption that the type

of polymer used as the matrix has no effect on the effective

ration of permeabilities. The mathematical representation

of the Nielsen model and the Cussler model are presented

in Table 1, where, P and P0 are the permeabilities of the

composite film and the pristine polymer, respectively, U is

the volume fraction of the filler and a is the aspect ratio of

half the width to the thickness of the impermeable flakes.

These models can predict the ratio of the permeation of the

200 250 300 350 4000

20

40

60

80

100

(c)(b)

Wei

ght L

oss

(%)

Temperature (°C)

(a) PLLA(b) PLLA/OMMT(c) PLLA/APB-POMMT

(a)

Fig. 6 TGA curves of the PLLA and the PLLA/montmorillonite

nanocomposites under a nitrogen atmosphere. The content of the

montmorillonites was 2 wt%

0% 2% 5% 10%0.0

0.2

0.4

0.6

Perm

eabi

lity

coef

fici

ent P

(m

2s-1

Pa-1

)*10

-17

APB-POMMT Loading (wt%)

Fig. 7 Effect of the APB-POMMT concentration in its PLLA

nanocomposites on gas permeability of N2

Table 1 Published formulas for the barrier models

Model Formulas Array/orientation

(cross-section)

Nielsen [31] P0(1-U)/

P = 1?aU/2

Regular array, oriented

Cussler-random

array [32]

P0(1-U)/

P = (1 ? aU/3)2Random array, oriented

0.00 0.05 0.10 0.15 0.200.0

0.2

0.4

0.6

0.8

1.0

a=20

a=10

P/P

0

Volume Faction (φ)

a=4

Fig. 8 Nielsen phenomenological model plot of N2 permeability

J Polym Environ

123

pristine polymer to that of the nanocomposite membrane as

a function of montmorillonite content and aspect ratio. All

of the models use aspect ratio as an adjustable parameter

and the results can be seen in Figs. 8 and 9. At the same

time, all of the experimental gas permeation data obtained

from the pristine PLLA and the PLLA/APB-POMMT

nanocomposites are shown in Figs. 8 and 9 for fitting.

As shown in Figs. 8 and 9, the models are able to match

the data over at least some part of the composition range

explored here. In particular, Fig. 9 shows N2 permeation

data fitted with the Cussler model (Cussler-random array).

The adjusted aspect ratio, a, obtained by fitting N2 per-

meation of the samples was about ten. One likely reason

for the discrepancies observed, however, is that while the

models account for platelet aspect ratio, they do not

account for platelet orientation and instead assume perfect

alignment perpendicular to the direction of gas flow.

Biodegradability and Mechanical Properties

The biodegradability of PLLA and its nanocomposites was

investigated by the weight loss in the compost. The weight

changes of the PLLA/montmorillonite nanocomposites in

the compost at 58 �C are shown in Fig. 10. Obviously, the

biodegradability of PLLA is significantly enhanced after

nanocomposite preparation with both OMMT and APB-

POMMT. At the same time, weight changes of nanocom-

posites increase with increasing time and the PLLA/APB-

POMMT nanocomposite showed a higher weitht change

than that of PLLA/OMMT sample.

The degradation of biodegradable polyester in compost

is a complex process involving four main phenomena,

namely, water absorption, ester cleavage and formation of

oligomer fragments, solubilization of oligomer fragments,

and finally diffusion of soluble oligomers by bacteria.

Therefore, the factor that increases the hydrolysis tendency

of PLLA ultimately controls the degradation of PLLA [29].

As reported by M. Okamoto et al. [30] the presence of

terminal hydroxylated edge groups of the silicate layers is

one of the responsible factors for the degradation.

Compared with the PLLA/APB-POMMT and PLLA/

OMMT nanocomposites, the exfoliated and intercalated

silicate layers in former case are dispersed much more

homogeneous than that of latter one in the PLLA matrix

(from TEM image), indicating the absorbed water is also

homogeneously dispersed in PLLA/APB-POMMT. When

the hydroxyl groups start heterogeneous hydrolysis of the

PLLA matrix after absorbing water from compost, the

degree of hydrolysis of PLLA/APB-POMMT is higher than

that of PLLA/OMMT. This is the reason why PLLA/APB-

POMMT showed a greater degradation from compost than

that of PLLA/OMMT.

The improved mechanical properties are expected to be

the result of a higher degree of exfoliation. According to

Table 2, the addition of OMMT to PLLA increased the

tensile modulus, which suggests that OMMT acted as

reinforcing filler due to its high aspect ratio and platelet

structure. However, the tensile strength and particularly the

elongation at break of the PLLA/OMMT nanocomposites

decreases precipitously as the OMMT content is increased.

The enhancement of the tensile modulus of the PLLA/

APB-POMMT nanocomposites is more prominent than

those with OMMT. Table 2 demonstrates that not only the

tensile modulus but also tensile strength of the PLLA/APB-

POMMT nanocomposites increased as the APB-POMMT

content is increased to 10 wt%. The higher degree of ex-

foliation and the improved tensile properties of the PLLA/

0.00 0.05 0.10 0.15 0.200.0

0.2

0.4

0.6

0.8

1.0

a=20

a=10

a=4

P/P

0

Volume Faction (φ)

Fig. 9 Cussler phenomenological model plot of N2 permeability

(Cussler-random array)

0 5 10 15 20 25 30

0

10

20

30

40

50

60

PLLA PLLA/OMMT PLLA/APB-POMMT

Bio

degr

adat

ion

(wt%

)

Composting time (days)

Fig. 10 Biodegradation of a PLLA, b PLLA/OMMT, and c PLLA/

APB-POMMT nanocomposites

J Polym Environ

123

APB-POMMT nanocomposites are believed to be associ-

ated with the enhanced interaction between the APB-

POMMT and the PLLA.

Conclusions

A method was successfully developed to prepare POSS

modified OMMT, where the amino-POSS was grafted to

the carboxyl-ended surfactant in the gallery of OMMT. The

incorporation of 2 wt% of APB-POMMT into the PLLA

resulted in a significant increase of the thermal stability.

Gas permeation analysis showed that increasing the

montmorillonite concentration in the polymer matrix lea-

ded to a decrease in permeation values. The exfoliation of

the APB-POMMT to the PLLA matrix provided a 66 %

decrease in gas permeability of up to 10 wt% montmoril-

lonite for N2 in comparison with the pristine PLLA. Phe-

nomenological models of effective gas permeabilities in

nanocomposites, such as the Nielsen model and the Cussler

model, though able to fit the experimental data, are still too

idealized to explain the influence of aspect ratio on effec-

tive permeabilities of the PLLA/OMMT nanocomposites.

The rate of biodegradation of PLLA under compost

increased after nanocomposite preparation and the PLLA/

APB-POMMT showed a greater degradation from compost

than that of PLLA/OMMT. The tensile modulus and

strength of PLLA/APB-POMMT were much higher than

those of PLLA/OMMT. Increased interfacial interaction

between APB-POMMT and PLLA was thought to be

responsible for the higher degree of exfoliation of the

montmorillonite platelets and in turn for the enhanced

mechanical properties.

Acknowledgments The authors gratefully acknowledge financial

support of this work coming from Natural Science Foundation of

China (NSFC) (No. 51173009).

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Table 2 Tesile properties of pure PLLA and its nanocomposites

Samples Modulus

(MPa)

Elongation at

break (%)

Strength

(MPa)

PLLA 1,506.5 5.5 48.7

PLLA/OMMT-2 % 1,598.6 3.4 47.8

PLLA/OMMT-5 % 1,755.2 2.1 39.3

PLLA/OMMT-10 % 1,904.1 1.2 35.5

PLLA/APB-POMMT-2 % 1,675.9 5.3 52.4

PLLA/APB-POMMT-5 % 1,912.5 4.9 56.8

PLLA/APB-POMMT-10 % 2,186.8 4.1 58.7

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