elaboration of cellulose acetate nanobiocomposites using acidified gelatin-montmorillonite as...

Elaboration of Cellulose Acetate NanobiocompositesUsing Acidified Gelatin-Montmorillonite as Nanofiller:Morphology, Properties, and Biodegradation Studies

Hafida Ferfera-Harrar, Nassima DairiDepartment of Macromolecular Chemistry, Materials Polymer Laboratory, Faculty of Chemistry, University ofSciences and Technology Houari Boumediene USTHB, Algiers, Algeria

Nanobiocomposites were successfully prepared fromcellulose acetate (CA) and a novel organoclay basedon montmorillonite and acidified gelatin as bio-modifier(AGe-MMT), at room temperature via solvent castingprocess. The formation of AGe-MMT was confirmed byFourier transform infrared spectroscopy (FTIR), X-raydiffraction (XRD), differential Scanning Calorimetry(DSC), and thermogravimetric analysis (TGA). Fromboth XRD and transmission electron microscopy (TEM)analyses of these nanohybrids, it was suggested a par-tially exfoliated/intercalated structures, with small claytactoıds remaining. Glass transition (Tg) and melting(Tm) temperatures of the nanobiocomposites, evaluatedby DSC analysis, were slightly affected by clay loadingcompared to neat CA. Significant improvement in theirthermal stabilities was observed from TGA, as evi-denced by the shift of their Tdonset toward highervalues. Otherwise, the optical clarity of these nanohy-brids films, measured by UV–vis spectroscopy, hasshowed a decline in the transmittance in the visibleregion with the increase of clay content, indicating thatclay platelets are not fully exfoliated. The impact ofAGe-MMT on biodegradability of CA under compostwas also studied by gravimetric and Scanning ElectronMicroscopy (SEM). The CA matrix biodegradability wasretarded by both MMT and bio-modifier, except for 5wt% AGe-MMT loading. POLYM. COMPOS., 00:000–000,2013. ª 2013 Society of Plastics Engineers

INTRODUCTION

Most synthetic polymers are produced from petrochemi-

cals and are harmful to nature. Their synthesis produces

hazardous waste and these materials are not easily degrad-

able, causing environmental problems. Nowadays, excessive

levels of plastic waste have caused the concern of scientific

community to develop eco-friendly materials. Plants are

potential sources for a wide variety of polymers which are

renewable and ecologically friendly. The agro-based poly-

mers are edible, biocompatible and biodegradable, which

make them superior to synthetic polymers and useful in

disposable plastics, food, and medicine applications.

In this context, the nanobiocomposites, based on natu-

ral polymer as matrix and layered silicates as nanofillers,

represent an emerging group of hybrid materials. Their

advance has promise in designing eco-friendly nanocom-

posites with enhanced properties (mechanical, thermal,

barrier. . .), at low filler levels, of great interest for several

applications [1–6].

Montmorillonite (MMT), one of the most common

smectite clays, is a promising reinforcing material, natu-

rally abundant and non toxic which can be used as one of

the components for food, medical, cosmetic and health-

care recipients [7, 8].

Cellulose acetate (CA) is a thermoplastic derivative pro-

duced by the esterification of cellulose that is the most abun-

dant polysaccharide in the earth. The CA can be considered

as a good candidate for the preparation of clay-based nano-

biocomposites owing to its biodegradability, excellent opti-

cal clarity and stiffness. It has been widely used in diverse

areas, such as filters, membranes, packing films, adhesives,

coatings for paper and plastic products, textile fibers, electri-

cal isolation, and drug delivery systems [9–12]. To secure

its foothold in the market, it is desirable to optimize its

physical properties, including thermal stability: the elabora-

tion of CA nanocomposites is one way of addressing these

issues and to develop plastic devices and more impermeable

packing films and coatings. CA/organoclay nanocomposites

plasticized with triethyl citrate have already been prepared

to eventually substitute petroleum-based polypropylene/

thermoplastic olefins composites (PP/TPO), which are

required in automotive applications [13–16]. The resulting

materials have exhibited interesting properties mechanical

and vapor permeability behaviors that were associated with

the nanoscale clay dispersion within the polymeric matrix.

The main challenge for preparing nanocomposites is the

nanoscale dispersion of nanoclay in the biopolymer matrix,

which is required for obtaining high performance materials.

To improve the degree of clay dispersion, alkyl ammonium

Correspondence to: H. Ferfera-Harrar; e-mail: [email protected]

DOI 10.1002/pc.22440

Published online in Wiley Online Library (wileyonlinelibrary.com).

VVC 2013 Society of Plastics Engineers

POLYMER COMPOSITES—-2013

salts, and alkyl amines are the most common cationic

intercalants used in the preparation of commercial organo-

modified clay, through cation exchange reaction. However,

these intercalants are mostly toxic and therefore not suita-

ble for bio-applications [17]. For instance, toxicity effect

of clay modified with hexadecyltrimethyl ammonium was

investigated on cells growth, and it was observed that the

increase of nanoclay loading had an adverse effect on

fibroblast skin cell growth [18]. Hence, in the present

report, a biological macromolecule, namely gelatin (Ge)

was selected to prepare the bio-modified nanoclay. Ge, a

typical amphoteric polyelectrolyte, is a denatured deriva-

tive of structural protein collagen with plenty of ��NH2

and –COOH in its molecular chains. Zheng et al. [19–21]

have reported that Ge chains can intercalate into MMT

galleries at different pH values and an intercalated or par-

tially exfoliated gelatin/unmodified MMT hybrid material

was achieved by solution intercalation method.

Besides, an important property of a candidate organo-

clay is its thermal stability. Ideally the nanofiller should

be stable to degradation at the processing temperature of

the polymer. For instance, the onset degradation tempera-

ture of Cloisite 30B is given by the manufacturers as

2208C. Alternative nanoclays with such stabilities are

therefore suitable candidate for study.

On the other hand, the solution casting method is one of

the processes used for the preparation of nanocomposites,

which allows good control the homogeneity of constituents.

Goncalves et al. [22] examined the solvent type effect of on

morphology, thermal and mechanical properties of cellulose

acetate/Naþ-montmorillonite nanocomposites. They con-

cluded that an adequate choice of the solvent must be made

to increase the intercalation/exfoliation level.

With the aim to elaborate entirely green cellulose ace-

tate nanocomposites, we have in a first step of the present

work prepared and characterized a novel organoclay based

on acidified-gelatin and montmorillonite (AGe-MMT).

We then used it as nanofiller to elaborate nanobiocompo-

sites at room temperature by the solution casting method.

To our knowledge, the elaboration of such nanohybrids

has not been reported in the literature so far. In a second

step, we reported on the characterization of the obtained

bio-based materials containing 2, 5, and 8% of AGe-

MMT by different techniques (XRD, TEM, SEM DSC,

and TGA) and compared with the virgin CA matrix. In

this work we focused on studying the effect of clay

loading on the morphology, thermal resistance, optical

properties and biodegradability of these materials.

EXPERIMENTAL

Materials

Cellulose acetate (39.8 wt% acetyl content, Mn 30,000

g/mol and DS 2.45) was supplied by Sigma-Aldrich. Gel-

atin (Type B, extracted from bovine skin, isoelectric point

(IEP): 5.05) was purchased from Sigma Chemical Co.

Montmorillonite (MMT) was extracted using the sedimen-

tation method (size fraction \ 2 lm) [23, 24] from com-

mercial Maghnia bentonite that was kindly supplied by

Algeria Bentonite Company. The unmodified MMT was

homoionized with sodium cations (Na-MMT) and its cat-

ion exchange capacity (CEC) value about 86.16 meq/100

g was determined by conductometric titration [25]. Acetic

acid (analytical grade) was used as received. Deionized

water was used in experiments.

Preparation of Gelatin-Montmorillonite Organoclay

The bio-modified clay, AGe-MMT, was prepared

according to the following procedure: Gelatin powder (1

g) was soaked in 50 ml of deionized water and heated at

708C to obtain a homogeneous solution, followed by the

addition of 0.5 M HCl aqueous solution to adjust the pH

value to 4 (before the isolectric point (IEP) of the gela-

tin). Then, the gelatin solution was added dropwise into a

2 wt% ultrasonically pretreated Na-MMT aqueous suspen-

sion under vigorous mechanical stirring at 708C. Stirringwas maintained for a further 2 h after which time the clay

was harvested by centrifuge. To remove excess modifier,

the organoclay was washed with hot deionized water, cen-

trifuged again and then dried at 608C in a vacuum oven.

Preparation of Films of CA/AGe-MMTNanobiocomposites

Cellulose acetate/AGe-MMT nanohybrids were prepared

at room temperature by solution casting method in acetic

acid/water mixture, which was previously reported to be

an effective solvents mixture for the swelling of the clay

gallery. The preparation conditions were adapted from

those used elsewhere [22]. Typically, a required amount of

organo-modified clay was suspended in the solvent mixture

and stirred at room temperature for 24 h. The organoclay

suspension was ultrasonically pretreated for 30 min and

added dropwise to CA solution (2.75 g in 15 ml of acetic

acid/water mixture). The mixture in suspension was stirred

mechanically for another two days then ultrasonically

treated for 15 min. The mixtures were prepared so as to

give 98/2, 95/5, and 92/8 CA/AGe-MMT weight ratios. In

all cases, the CA content in the solution was maintained at

11 wt% and the water proportion was kept at 23 wt%.

Films were obtained by solution casting on clean glass and

dried in an oven under air at 808C for 4 days.

Characterization

FTIR spectra of natural and bio-modified MMT, CA

and its nanobiocomposites were recorded on a Perkin-

Elmer Spectrum one spectrometer, with a spectral resolu-

tion of 2 cm21 and 62 scans. Samples of CA and its

nanobiocomposites as thin films cast onto KBr disks were

prepared from acetone solutions (2% w/v). The Na-MMT

and AGe-MMT samples were obtained as KBr disks con-

taining 2 wt% of clay.

2 POLYMER COMPOSITES—-2013 DOI 10.1002/pc

X-Ray diffractograms of the unmodified MMT, the

organoclay and their CA nanocomposites were recorded

on a Bruker D8 advance diffractometer using CuKamonochromatic radiation (40 kV, k ¼ 1.5406 A) in 2yrange 1–308 with 0.018/s scan rate.

The morphology of CA/AGe-MMT biocomposites was

examined by transmission electron microscopy (TEM) as

a complementary technique to XRD on a JEM-2000EX

equipped with a MORADA SIS numerical camera at an

acceleration voltage of 200 kV.

Thermogravimetric analysis was performed on a Q500

analyzer, TA Instruments, at a heating rate of 108C/min,

under nitrogen atmosphere.

The glass transition temperatures (Tg) of the gelatin,

CA and corresponding organo-modified bio-based materi-

als were determined by DSC using a Q100, TA instru-

ments. Each sample was heated and subsequently cooled

twice in temperature ranges 30–1608C then 30–2408Cunder nitrogen flow at 108C/min. The Tg’s were deter-

mined at the midpoint of the second scan.

The UV–vis spectra of virgin CA and its nanohybrids films

were obtained with a Perkin-Elmer Lamba-20 spectrophotom-

eter. The films samples were cut into a rectangular piece.

The biodegradability under compost of CA and corre-

sponding nanohybrids was measured by determining the

weight loss during 6 months. All samples films were

uniformly cut into small rectangles (3.5 3 0.8) cm2, accu-

rately weighed and then put into the compost. After com-

post tests, samples were recovered from distilled water,

washed with methanol with an ultrasonic bath for 5 min

and then dried in oven at 608C for 24 h.

Surface changes were observed using an environmental

Scanning Electron Microscope FEI Quanta type 200.

RESULTS AND DISCUSSION

Evidences for MMT Organo-Modification

Figure 1 shows the FTIR spectra of Na-MMT, organo-

modified MMT and gelatin. The spectrum of gelatin

displays characteristic absorption bands of amino acids:

amide A at 3315 cm21 (mN–H coupled with hydrogen

bonding), amide B at 2930 cm-1 (mC–H , mN–H), amide I at

1655 cm21 (mCOO2(asym) ,mN-H), amide II at 1540 cm21

(dN-H(sciss),mC-N), carboxylic group at 1450 cm21 (dC-O-H),amide III at 1240 cm21 (mC-N, dN-H) and at 620 cm21

(dN-H (wagg)) [26–28].

In organoclay spectrum, besides the absorption bands

of MMT [28, 29] (mO-H � 3360 cm21 and dO-H � 1642

cm21 of H2O; mSi-O � 1034 cm21 and dSi-O � 470 cm21

of Si-O-Si; dAl-O � 527 cm21 of Si-O-Al), week addi-

tional bands attributed to gelatin are also observed at

1540 cm21 (amide II), 1450 cm21 (dC-O-H of the carbox-

ylic group) and 600 cm21 (dN-H (wagg)). As well, the band

of the amide I at 1660 cm21 overlaps by that of dO-H of

H2O present into MMT interlayers.

This result confirms the occurrence of clay organo-

modification reaction.

XRD patterns of pristine Na-MMT, MMT-AGe and

gelatin are shown in Fig. 2. Gelatin did not show any dif-

fraction peak in the low angle region while Na-MMT

exhibits a sharp peak at 2y ¼ 6.768 (d001¼1.30 nm). After

the organo-modification reaction, this diffraction peak

shifts towards lower angle value at 2y ¼ 3.558(d001¼2.49 nm) and becomes broad. The increase in the

d-spacing is an evidence of the intercalation of acidified

gelatin chains via cationic exchange reactions. Based on

the studies of Zheng et al. [20, 21, 30] reported on gela-

tin/montmorillonite nanocomposites, the ionized states of

gelatin vary with different pHs of media. The charge

changes as below when pH is higher or lower than IEP.

Therefore, in acidic media (pH \ IEP), gelatin chains

with more -NH3þ can bind with the negative sites onto

MMT sheets through strong static electric interaction and

intercalate into MMT interlayers.

FIG. 1. FTIR spectra of (a) Na-MMT, (b) AGe-MMT, and (c) gelatin.

[Color figure can be viewed in the online issue, which is available at

wileyonlinelibrary.com.]

FIG. 2. XRD patterns of (a) Na-MMT, (b) AGe-MMT, and (c) gelatin.

[Color figure can be viewed in the online issue, which is available at

wileyonlinelibrary.com.]

DOI 10.1002/pc POLYMER COMPOSITES—-2013 3

Figure 3 displays DSC traces of gelatin and AGe-

MMT. The gelatin Tg appears at 2038C, which is

assigned to the devitrification of blocks rich in imino

acids [31], whereas no evident thermal transition was

detected for the AGe-MMT. This behavior may be attrib-

uted to the restriction of the segmental motion of the

charged gelatin chains by the MMT sheets due to high

intercalation level, resulting from favorable statistic inter-

actions between gelatin and clay, in agreement with XRD

results. Also, the MMT sheets can act as physical cross-

linking sites and restrict the movement segments. Conse-

quently, the glass transition become weak and even disap-

pears [32, 33].

Figure 4 exhibits TGA and derivative d(TG) curves of

Na-MMT, AGe-MMT and gelatin. As expected, there is

no weight loss for Na-MMT between 200 and 5008C,while one step weight loss appeared for the organoclay,

in the same temperature range. The observed difference is

obviously attributed to the main degradation stage of the

bio-modifier in the AGe-MMT, as evidenced from gelatin

thermograms. From TGA curves, it can be seen that the

onset decomposition temperature (Tdonset) of AGe-MMT

is 36 8C higher than that of gelatin, and the thermal

decomposition rate is noticeably reduced, suggesting that

intercalation with MMT causes a delay in Ge weight loss

to a certain extent.

The onset and maximal degradation temperatures

(Tdonset, Tdmax) of this organoclay are 305 and 3498C,respectively. Also, it is apparent that the amount of water

evaporated up to 1508C from Na-MMT, which is

adsorbed on the surface of particles and in the interlayers,

is much bigger than that from AGe-MMT and the dehy-

droxylation peak of MMT is shifted to lower temperatures

from 620 to 5708C. This result confirms once again the

modification of MMT with AGe organic cations that

causes decreased in the hydrophilicity of the mineral sur-

face. Hence, the organic content AGe in the MMT is cal-

culated in the temperature range 200–5008C and is about

15 wt%.

It is interesting to note that AGe-MMT has higher ther-

mal stability than those of commercial Cloisite 30B

FIG. 3. DSC thermograms of gelatin and AGe-MMT.

FIG. 4. TGA and d(TG) thermograms of Na-MMT and AGe-MMT and

(c) gelatin. [Color figure can be viewed in the online issue, which is

available at wileyonlinelibrary.com.]

FIG. 5. FTIR spectra of CA and its biocomposites at different clay

loadings. [Color figure can be viewed in the online issue, which is avail-

able at wileyonlinelibrary.com.]


(Tdonset ¼ 2198C), which has been reported to be compat-

ible with CA [34–36], of almost organic content (15.8

wt%) and lower interlayer spacing (d001 ¼ 1.81 nm) [37].

Therefore, this new organoclay can be a good nanofiller

candidate for the development of polymer/clay nanocom-

posites by other procedures such as melt process.

Study of CA/AGe-MMT Nanobiocomposites

Figure 5 displays FTIR spectra of CA and CA/AGe-

MMT nanohybrids with different clay loading. The CA

spectrum shows absorption bands, mainly mO-H of the

hydroxyl group at 3475 cm21, the strong mC¼O(sym) at

1748 cm21 of acetyl group and mC-O band at 1060 cm21

[28, 38].

In composites spectra, the characteristic clay bands, can

be observed in a region not disturbed by CA bands around

839 (dAl-Mg-OH), 706 (silica phase), 558 (dSi-O-Al), and 473

cm21 (dSi-O-Si), excepting for nanohybrid with the higher

clay amount (8 wt%) in which these bands appear

extremely weak. This observation indicates the presence of

all components used to prepare these nanomaterials.

Besides, it can be seen the broadening of the mC¼O band of

CA matrix containing 2 and 5 wt% of AGe-MMT. This

FIG. 6. XRD patterns of CA, AGe-MMT, and its CA/AGe-MMT nano-

biocomposites. [Color figure can be viewed in the online issue, which is

available at wileyonlinelibrary.com.]

FIG. 7. TEM micrographs (a, b) of typical CA/AGe-MMT 5% nanobiocomposite at 500 and 200 nm magnifications.


change may be induced by specific interactions between

the carbonyl groups of CA and the organoclay groups

owing to their compatibility.

The XRD patterns of AGe-MMT, neat CA and its bio-

composites with different clay contents are shown in Fig.

6. As it can be seen, all composites exhibit weak diffrac-

tion peak at lower angle compared to original organoclay.

The movement of the basal reflection of AGe-MMT to

lower angle indicates the formation of an intercalated

nanostructure, while its broadening and intensity decrease

is most likely due to the presence of disordered interca-

lated or intercalated/partially exfoliated mixed structure.

Hence, the nanocomposite formation may be mainly con-

trolled by hydrogen interactions between CA (carbonyl,

hydroxyl) and clay (hydroxyl, carboxylic) groups, in

accord with FTIR study. Besides, the original organoclay

diffraction peak almost disappears at 2 wt% clay content

nanohybrid, while an increase in its intensity is observed

at higher clay loading, suggesting the coexistence of some

aggregates platelets.

XRD is an extremely valuable technique. However, the

results can be ambiguous and cannot be interpreted unless

supporting evidence is offered, generally via representa-

tive microscopic images. Hence, the dispersion of clay

platelets is investigated using TEM as complementary

technique to further explain the morphology of the CA

biocomposites.

Figure 7 illustrates typical TEM micrographs for CA/

AGe-MMT containing 5 wt% clay at high magnifications

(500 or 200 nm scale bar). In agreement with XRD obser-

vation, TEM images confirm the formation of mixed

intercalated/exfoliated nanocomposite structures, as evi-

denced by the presence of some intercalated layered

stacks of relatively small thickness randomly dispersed

within CA matrix coexisting with of disorderly exfoliated

platelets. Some agglomerations internally disordered of

layers are also observed.

It is noteworthy that the presence of exfoliated plate-

lets was not always easily detected in TEM observations,

due to the lower contrast of individual clay layers in the

polymeric matrix.

Thermal properties of CA and its nanobiocomposites

are investigated by DSC and TGA.

In order to analyze the effect of AGe-MMT content on

the thermal stability of CA films, TGA experiments were

conducted under nitrogen flow. TGA and respective deriv-

ative curves of CA and its biocomposites are depicted in

Fig. 8. The Tdonset is an important parameter since it deter-

mines the maximum processing temperature which can be

applied without thermally damage the material. So, Tdonsetis a criterion to evaluate the stability of polymers.

From TGA curves, it can be seen that introducing nano-

clay increase the Tdonset of CA from 2658C, indicating an

improvement in thermal stability of cellulosic films. The

highest Tdonset value 3048C is reached at 5 wt% clay load-

ing, about 398C greater than that of virgin CA. These find-

ings are in agreement with those reported in the literature

for PLA and gelatin nanocomposites [37, 39, 40]. The sig-

nificant increase in Tdonset can be attributed to effects such

as a decrease in permeability due to ‘‘tortuous path’’ effect

of the nanofiller, which delays the permeation of oxygen

and the escape of volatile degradation products [41, 42].

This behavior may also arise from thermodynamic effects

due to the presence of nanofiller, as it has been reported

that the activation energy of the thermal degradation of ep-

oxy-clay nanocomposites increased with organoclay load-

ing to a maximum around 4–6 phr, decreasing rapidly at

higher loadings up to 14 phr [43].

The weight losses of all nanobiocomposites occurs in

single main decomposition step and the maximal degrada-

tion temperatures Tdmax are slightly affected by the

increase of AGe-MMT content within CA matrix. Also,

the char increase observed at 5758C, which acts as insula-

tor and mass transport barrier, confirmed the enhanced

thermal stabilities of these bio-based materials compared

to that of CA matrix. Table 1 summarizes the thermogra-

vimetric data of CA and its nanobiocomposites.

FIG. 8. TGA and d(TG) thermograms of CA and its CA/AGe-MMT

nanobiocomposites. [Color figure can be viewed in the online issue,

which is available at wileyonlinelibrary.com.]


The DSC curves of CA and its nanohybrids films are

shown in Fig. 9. The CA presents, besides the glass tran-

sition temperature (Tg) at 2008C, an exothermic peak

around 2358C, which is ascribed to melting temperature

(Tm) owing to its semicrystalline structure [13, 44]. In

composites curves, the Tg and Tm values are not appreci-

ably affected by clay loading.

One advantage of polymer/clay nanocomposites is that

the optical clarity of the polymer is not affected substan-

tially at lower clay contents. In general, the optical prop-

erty of a well-developed nanocomposite film is not signif-

icantly changed when the clay platelets with about 1 nm

thickness are well dispersed through the polymer matrix,

since such clay platelets with sizes less than the wave-

length of visible light do not hinder light’s passage [45]

so, that well-exfoliated nanocomposites keep good optical

transparency. Figure 10 displays the UV–vis transmission

spectra of nanocomposites films (100 6 15 lm) with dif-

ferent clay loadings. At 700 nm the pure CA lets through

80% of the light. The amount of light being transmitted

through the nanocomposite films is reduced compared

with pure CA. However, the degree of decrease in the

transmittance was strongly dependent on the clay loading

[46, 47]. This result indirectly indicates that the clays pla-

telets are not completely dispersed in the polymer matrix

and there is some heterogeneous distribution of the

agglomerated platelets within the CA matrix, as confirmed

by DRX and TEM characterization. Similar findings were

reported for other systems such as in PLA/clay nanocom-

posites [48, 49].

It is noteworthy that UV and visible light can have a

negative impact on the quality of packed food. So, this

reduction in transmission radiation through these bio-

based materials can be considering an advantage when

using CA in packaging applications.

Despite the numerous studies regarding the CA biode-

gradability in natural or seminatural environment [50–52],

no articles have been reported on the degradation of its

nanocomposites, based on our literature survey. So, the

study of AGe-MMT impact on CA biodegradability is an

interesting aspect of research. Figure 11 illustrate the

FIG. 9. DSC traces of neat CA and CA/AGe-MMT biocomposites at

different clay loadings. [Color figure can be viewed in the online issue,


FIG. 10. UV–vis transmission spectra of neat CA and CA/AGe-MMT

nanobiocomposites. [Color figure can be viewed in the online issue,


TABLE 1. Thermogravimetric parameters of virgin CA and its

nanobiocomposites under nitrogen atmosphere.

Clay

content (wt%) Tdonset (8C) Tdmax (8C)Char

(%) at 5758C

0 (CA) 265 357 13.13

2 298 362 13.41

5 304 364 13.61

8 291 363 17.85

FIG. 11. Mass loss of CA and its nanobiocomposites samples biode-

graded under compost during 6 months. [Color figure can be viewed in

the online issue, which is available at wileyonlinelibrary.com.]


progressive mass losses of CA and corresponding CA/

AGe-MMT nanohybrids films recovered from compost

with time. The tests were conducted for 1, 3, and 6

months. Also, to accurately estimate the effect of cationic

bio-modifier on the biodegradability, nanohybrids were

prepared with 5 and 8 wt% of Na-MMT and their biode-

gradation was compared to those with similar AGe-MMT

content.

As expected, the neat CA film degrades slowly due its

substitution degree (DS) about 2.45, which is considered

rather high [53]. Indeed, Calil et al. [54] explained that at

high DS the hydroxyls groups, which start heterogeneous

hydrolysis reactions after absorbing moisture from the

compost, are reduced. As a result, the biodegradability

process is hindered or even inhibited (DS about 3).

Another factor is related to the hydrophobic character of

the CA which prevents the hydrolysis reactions induce by

microorganisms [55].

Except for the nanocomposite with 5 wt% AGe-MMT,

all histograms exhibit a decrease in mass losses with

increasing clay loading. It is apparent that the biodegrad-

ability of CA is slightly hindered after adding clay. Thus,

the layered silicate acts as a barrier and protects the

FIG. 12. Real pictures of biodegradability of neat CA (a) and its vari-

ous nanohybrids specimens recovered from compost after 6 months. (b)

and (c) 5 and 8 wt% AGe-MMT, respectively; (d) and (e) 5 and 8 wt%

Na-MMT, respectively.

FIG. 13. SEM micrographs of CA and CA/AGe-MMT with 5 wt% loading before (a, c) and after (b, d) compost tests, respectively (magnification

33000).


matrix from the attack of microorganisms. Indeed, this

effect may be related to decrease in the permeability

towards water, which is required for hydrolysis reactions

of the esters groups of CA chains and then reduces the

biodegradation rate [56]. The unexpected enhance in rate

biodegradability of CA observed with 5 wt% AGe-MMT

can be attributed to a better dispersion state of the modi-

fied layered silicates within the matrix, in accordance

with others works on polymer/clay nanocomposites [57–

60]. Overall, the biodegradability of CA matrix is slightly

improved in presence AGe-MMT compared to Na-MMT.

This behavior may be due to the catalytic role of gelatin

bio-modifier on biodegradation process.

The results of various compost burial tests in terms of

changes in external appearance are also illustrated in Fig.

12. It is apparent that all samples are damaged and many

cracks appeared.

This kind of fracture has an advantage for biodegrada-

tion because it is easy to mix with compost and create

much more surface area for further attack by microorgan-

isms. A roughness and a whitening of their surfaces are

also observed. Some authors have attributed this phenom-

enon to the chemical hydrolysis of the polymer [61].

Furthermore, to ascertain the improved biodegradabil-

ity of the biocomposite with 5 wt% of AGe-MMT

compared to virgin CA, SEM micrographs at high magni-

fication (30003) of their films recorded from compost are

displayed in Fig. 13. Before burial, both samples present

homogeneous and smooth surfaces. After 6 months of ex-

posure, their surfaces become rougher and more heteroge-

neous with the appearance of several of cracks, which

reflects their attack by microorganisms. These effects are

more pronounced in the presence of organoclay, where

we observe a more altered surface, with more defects and

cavities of different sizes and shapes, in agreement with

previous gravimetric deductions.

CONCLUSIONS

A novel organoclay based on acidified gelatin and

montmorillonite was prepared and characterized. The ther-

mal stability of this organoclay was found higher than

Cloisite 30B. Using this organoclay as nanofiller, green

cellulose acetate nanocomposites were elaborated. From

XRD patterns together with TEM images, it was sug-

gested the formation of mixed intercalated/partially exfoli-

ated structures, with small clay tactoıds remaining. Better

clay dispersion was observed by TEM for nanohybrid

containing 5 wt% of AGe-MMT, confirmed by the pres-

ence of stacks of relatively small thickness randomly dis-

persed coexisting with some fraction of exfoliated silicate

sheets. The thermal stabilities of these nanohybrids were

greatly enhanced, as evidenced by an increase, in the tem-

perature range of 26-398C, of their onset degradation tem-

peratures compared to the virgin matrix, being the highest

at 5 wt% AGe-MMT loading. It is worth noting the

unchanged Tg and Tm values of the elaborated nanomate-

rials compared to CA. The optical clarity of CA film was

reduced by increasing the organoclay content. Biodegra-

dation results under compost proved that the biodegrad-

ability of CA was retarded after nanocomposites prepara-

tion, excepted for the nanohybrid with 5 wt% AGe-MMT,

in which a catalytic role is observed. This study was a

step in the right way for creating fully renewable CA-

based nanocomposites. The properties we have shown

here will most probably be improved if we are able to

fully exfoliate this organoclay within the matrix.

ACKNOWLEDGMENTS

The authors would like to thank Dr. Omar Arous and

Dr. Zitouni Benabdelghani for assistance in the character-

izations of the elaborated bio-based materials.

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