desarrollo de peliculas de empacado a partir de bioplastico de acido polilactico con plastificantes

7/24/2019 Desarrollo de Peliculas de Empacado a Partir de Bioplastico de Acido Polilactico Con Plastificantes

1/20

621

PACCON2011 (Pure and Applied Chemistry International Conference 2011)

Development of Packaging Film from Bioplastic Polylactic Acid (PLA)

with Plasticizers

P. Boonfaung, P. Wasutchanon, and A. Somwangthanaroj*

Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok, 10330, Thailand

*Corresponding Author E-mail: [email protected]

Abstract: Nowadays, plastics are extensively used in

almost daily activities such as the plastic packaging bags

produced from polyethylene and polypropylene.

However, the products from these polymers cause

environmental problem. To replace the conventional

plastics with biodegradable plastic such as polylactic acid

(PLA) can solve this problem. PLA is a biodegradable

material showing good transparency and high tensile

strength. However, its application is still limited because

of its brittleness and rigidity. The packaging film

produced from PLA can be improved by the addition of

plasticizers which will enhance ductility and flexibility of

the packaging films. The aim of this research is to find

the suitable plasticizers from Polypropylene glycol (PPG),

Poly(ethylene glycol-ran-propylene glycol) (PEPG),

Dioctyl phthalate (DOP), Tributyl citrate (TBC) andAdipic acid. PLA were melt-mixed with plasticizers at

different ratio varied from 3% to 7% by weight by twin

screw extruder and the blown films were obtained. The

thermal and mechanical properties of neat PLA and

plasticized PLA were characterized. Plasticized PLA

exhibited lower glass transition temperature than neat

PLA. In addition, a phase separation was observed with

the 5 wt% plasticized PLA. PPG was a good plasticizer

for PLA in which the tensile strength and Youngsmodulus of the plasticized PLA decreased, whereas its

elongation at break increased dramatically.

Introduction

PLA has attracted both industries andresearch institutions. It is one of the biopolymer whoseproperties are comparable with the commercial plasticsuch as poly(ethylene terephthalate) (PET) [1]. PLA

production is derived from annually renewableresources such as corn starch, cassava starch or

sugarcanes. PLA exhibits good properties such as

biodegradability, heat resistance, transparency, goodmechanical properties and processability [2-5], causingit to be used in many packaging applications. Theimportant requirement for packaging materials is hightensile strength, ductility, flexibility, transparency and

good barrier properties [3]. However, PLA is stilllimited for its application because of its price,brittleness, rigidity and low crystallization rate [1,2].Therefore, plasticizers are used to increase theflexibility of PLA for packaging applications such as,packaging films, wrap films, stretch films andagricultural mulch films [4].

Effort has been made to improve the

processability, flexibility and ductility of PLA byblending with plasticizer. The choice of plasticizers to

be used as modifiers for PLA is limited by the

requirement of the application. Only non toxicsubstances approved for food contact which can be

considered as plasticizing agents in food packagingmaterials. For a low molecular weight plasticizer animportant demand is miscible with PLA and stable atthe elevated temperature used during processing, thuscreating a homogeneous blend. Plasticized PLA shouldbe stable all the time because the migration of the

plasticizer to the surface could be a source ofcontamination of the food or beverage in contact with

the packaging or may possibly regain the initialbrittleness of pure PLA [3].

The main objective of this study is to improveand modify packaging film produced from PLA by theaddition of plasticizers which will enhance ductilityand flexibility of the packaging films. The study is

mainly focused on the miscibility of PLA andplasticizer, and thermal properties of the plasticizedPLA which will inform us the suitable plasticizersfrom Polypropylene glycol (PPG), Poly(ethyleneglycol-ran-propylene glycol) (PEPG), Dioctylphthalate (DOP), Tributyl citrate (TBC) and Adipicacid.

Materials and Methods

MaterialsThe PLA was supplied by Nature Works, USA. Theselected grade, PLA 2002D, is a semi crystallineextrusion material. PPG, PEPG, DOP and adipic acidwere obtained from Sigma-Aldrich chemical, USA.

TBC was obtained from ACROS organics, USA.Blown film preparation

PLA was dried in an oven for 24 h at 60oC. PLA and

plasticizers were compounded into pellets with twinscrew extruder (Thermo Hakke Reomix, Germany)attached to rod capillary die, cooling bath and pelleizer.After that, the plasticized PLA pellets were dried in anoven for 24 h at 60 oC. The mixing ratio between PLAand plasticizer were 97/3, 95/5 and 93/7 w/w. The

plasticized PLA blown films were then produced withtwin-screw extruder attached to blown film die in

which thickness of films is 0.0700.002 mm.Characterization of blown films

Thermal properties

Differential scanning calorimeter (DSC)

measurements were performed by using a differentialscanning calorimeter ( TA Instruments 2910). All ofthe blown films (5-10 mg) were tested at a heating rate


2/20

622


of 10oC/ min in a nitrogen atmosphere from 30 to 200

oC. Using eq 1, the percent of crystallinity of all the

blown films were estimated according to the enthalpyobtained from the DSC curves.

100x

xH

HHX

o

cm

c

(1)

where Hmand Hc are the enthalpies of the meltingand cold crystallization of blending PLA, and H0 (93J/g) is the melting enthalpy of 100% crystalline PLA

[6]. A parameter , the weight fraction of the matrix,is introduced to eliminate the weight contribution ofplasticizer [2].Mechanical testing measurements

Tensile testing of the blown films wasperformed according to ASTM D 882 by usingUniversal Testing Machine (Instron 5567, NY, USA),

equipped with a 1 kN load cell at a crosshead rate of12.5 mm/min. All tested specimens were required in

rectangular shape with the width of 10 mm and thelength of 100 mm.

Results and Discussion

Thermal properties of blown filmsThe DSC results of neat PLA and plasticized

PLA films are summarized in Figures 1 and Table 1.The plasticizers decreased the glass transitiontemperature (Tg) of neat PLA from 63.03

oC to 58.93-56.93 oC, 54.36-51.96 oC, and 55.90-47.20 oC by

adding 3, 5, and 7 wt% of plasticizers, respectively.

Furthermore, the cold crystallization temperature (Tc)is decreased when plasticizer is added. Especially, 7 wt%plasticized PLA film, Tc of PLA dramaticallydecreases from 124.48

oC to 91.74-116.92

oC. The

decreasing of Tgand Tcwere enhanced with a higherplasticizer content as a result from the enhanced chainmobility [5]. The melting behavior in blends changedwith an increase of the plasticizer content in a similar

way freely of a plasticizer type [6]. Figures 1 c) showsthat the DSC thermograms of 7 wt% plasticized PLAfilm exhibits two separate peaks of meltingtemperature (Tm) because of the occurring of phaseseparation [6,7].

It can be observed that Tc and Tm ofplasticized PLA occurred clearly peak becauseplasticizers acted as nucleating agent [8]. These also

caused the crystallizability and enthalpy of plasticizedPLA film increased.

Mechanical properties of PLA films

Tensile strength and Youngs modulus ofblown films in both machine direction (MD) andtransverse direction (TD), are illustrated in Figure 2a,2b, and 3a, 3b, respectively. By adding plasticizer intoPLA matrix can decrease rigidity and increase ductility

of PLA films. Therefore, the addition of plasticizer

causes the decrease of tensile strength and Youngsmodulus because the plasticizer penetrates between thepolymer chains and decreases the intermolecular

forces which cause the lower polymer chain cohesion[5].

Figure 1. DSC thermograms recorded duringheating at a rate of 10 oC/min for neat PLA and a) 3

wt% b) 5 wt% and c) 7 wt% plasticized PLA blownfilms.

40 60 80 100 120 140 160 180 200

a)

Temperature (oC)

Pure PLA

Adipic

PPG

DOP

TBC

PEPG

40 60 80 100 120 140 160 180 200

Temperature (oC)

PEPG

TBC

DOP

PPG

Adipic

Pure PLA

b)

40 60 80 100 120 140 160 180 200

c)

Temperature (oC)

PEPG

TBC

DOP

PPG

Adipic

Pure PLA


3/20

623


Table 1. Thermal properties and the crystallinity of neat PLA and the plasticized PLA with 3, 5 and 7 wt% ofplasticizers

Plasticizer typePlasticizer

content (wt %)Tg(

oC) Tc(

oC) Hc(J/g) Tm(

oC)

Hm

(J/g)Xc(%)

None 0 63.03 124.48 2.01 153.44 3.09 1.16

Adipic 3 56.93 102.23 29.17 151.17 31.04 2.075 51.94 91.81 34.26 146.84 42.13 8.91

7 55.90 91.74 26.01 151.67 45.87 22.96

PPG 3 57.01 121.59 12.32 149.16 14.07 1.94

5 53.24 113.33 22.96 147.06 25.27 2.61

7 49.83 105.07 24.09 155.62 29.11 5.80

DOP 3 58.93 120.29 23.24 150.78 24.25 1.12

5 52.63 122.75 16.54 149.44 17.80 1.43

7 48.94 116.72 18.79 147.53 20.34 1.79

TBC 3 57.97 121.55 21.99 151.46 22.99 1.11

5 54.36 116.92 24.02 149.38 25.39 1.32

7 47.20 109.93 30.49 153.25 31.71 1.41

PEPG 3 57.38 122.64 4.12 148.93 5.15 1.145 52.88 109.23 24.08 156.25 26.59 2.84

7 49.18 101.03 28.97 156.22 31.74 5.52

Tg, glass transition temperature; Tc, cold crystallization temperature; Tm, melting temperature; Hc, enthalpy of thecold crystallization; Hmthe melting enthalpy; Xc, crystallinity.

The tensile strength and Youngs modulus ofneat PLA film are 58, 2886 MPa in MD and 48, 2844MPa in TD, respectively. Tensile strength and

Youngs modulus of PLA plasticized with 7 wt% PPGwere decreased to be 37, 2115 MPa in MD and 25,2150 MPa in TD, respectively. Thus PPG extremelyaffects the tensile strength and Youngs modulus of

the films. In addition, it was also found that PLAadded with 7 wt% of adipic acid showed the increasein the tensile strength and Youngs modulus because

adipic acid increases degree of crystallinity of PLA.The elongation at break of neat PLA is 3.3%

in MD and 2.2% in TD as shown in Figure 4a and 4b,respectively. It was found that PLA added with PPGexhibited the highest elongation at break. However,low contents of plasticizer hardly affect the elongationat break of PLA, i.e., 3wt% plasticized PLA. Theincrease of PPG content to 5 wt% increases the

elongation at break to about 130% in MD and 6.5% inTD. Moreover, the elongation at break reached 350%

in MD and 140% in TD for the PPG content of 7 wt%in which an increase of elongation at break resultsfrom the PPG having segments comprising apoly(alkylene ether) and higher molecular weight thanother plasticizers [4] which can be miscible well withPLA. The plasticizers increase the ability of PLA to beplastic deformation which is reflected in the increase

of elongation at break. However, the DSC resultsreveal that 7 wt% plasticized PLA causes phaseseparation. Therefore, the optimal plasticizer contentfor this study is 5 wt%.

Figure 2. Tensile strength of PLA and plasticizedPLA a) Machine direction (MD)and, b) Transverse

direction (TD)

30

35

40

45

50

55

60

65

0 1 2 3 4 5 6 7 8

a) AdipicPPGDOPTBCPEPG

Plasticizers (wt%)

20

25

30

35

40

45

50

55

0 1 2 3 4 5 6 7 8

b) AdipicPPGDOPTBCPEPG

Plasticizers (wt%)


4/20

624


Figure 3. Youngs modulus of PLA and plasticized

PLA a) MD and b) TD

Figure 4. Elongation at break of PLA and plasticizedPLA a) MD and b) TD

ConclusionDSC results indicated that all plasticizers

were compatible with PLA at 5 wt%. Tg and, Tmof theplasticized PLA films shifted to lower temperaturewhile increasing plasticizer content. In addition, theDSC peak of plasticized PLA appeared clearly which

would be due to the increase in degree ofcrystallization. Tensile tests indicated that PPG is asuitable plasticizer for PLA which can be observed

from an increase of elongation at break approximately39 times in MD and 3 times in TD. Furthermore, avalue of tensile strength still suffices for application inpackaging field (value up to 24 MPa).

AcknowledgementsThe authors would like to acknowledge TRF-

Master research grants (MAG Window II) Co-fundingannual 2552 and Mahachai plastics factory forfinancial supports.

References[1] M. A. Huneault, and H. Li, Polymer (2007), p. 270-

280.[2] S.L. Yang, Z. H. Wu, B. Meng, and W. Yang, Journal

of Applied Polymer Science, 2009: p. 1136-1145.[3] N. Ljungberg, and B. Wesslen, Polymer, 2003. 44: p.

7679-7688.[4] US patent 7,632,897B2, Matsumoto et al., issued 2009-

12-15.[5] Y. Lemmouchi, M. Murariu, A. M. D. Santos, A. J.

Amass, E.Schacht, and P. Dubois, European Polymer,

2009. 45: p. 28392848.[6] Z. Kulinski, E. Piorkowska, K. Gadzinowska, and M.

Stasiak,.Biomacromolecules, 2006: p. 2128-2135.

[7]

E. Piorkowska, Z. Kulinski, A. Galeski, and R.Masirek,.Polymer, 2006. 47: p. 7178-7188.

[8] Z. Jia, J. Tan, C. Han, Y. Yang, and L. Dong, Journalof Applied Polymer Science, 2009: p. 1105-1117.

1750

2000

2250

2500

2750

3000

3250

0 1 2 3 4 5 6 7 8

a) AdipicPPGDOPTBCPEPG

Plasticizers (wt%)

1750

2000

2250

2500

2750

3000

3250

0 1 2 3 4 5 6 7 8

b) AdipicPPGDOPTBCPEPG

Plasticizers (wt%)

0

50

100

150

200

250

300

350

400

0 1 2 3 4 5 6 7 8

a)

AdipicPPGDOPTBCPEPG

Plasticizers (wt%)

0

50

100

150

0 1 2 3 4 5 6 7 8

b)

AdipicPPGDOPTBCPEPG

Plasticizers (wt%)


5/20

625


Toughening of Poly(Lactic Acid) Film Blended by Natural Rubber

J. Mangmeemak1, P. Tangboriboonrat2, N. Rattanasom3and A. Somwangthanaroj1*

1Department of Chemical Engineering, Faculty of Engineering,

Chulalongkorn University, Phayathai Road, Bangkok, Thailand

103302Department of Chemistry, Faculty of Science, Mahidol

University, Rama VI Road, Bangkok, Thailand

104003Department of Chemistry, Faculty of Science, Mahidol

University Salaya, Nakhon Pathom, Thailand73170

*E-mail: [email protected]

Abstract: Poly(lactic acid) (PLA) film was melt-blended

via twin-screw extruder with two kinds of rubber

component which are unvulcanized and vulcanized

natural rubber by peroxide, in order to toughen PLA at

3 and 5 wt%. All of the blended samples showedimmiscible texture which could be due to the difference

in polarity between PLA and natural rubber. Thus high

polarity polymer would be more suitable for toughening

PLA than the non-polar one. The blended films showed

that domain size of rubber was larger than 0.85 m. The

tensile strength and tensile modulus decreased with

increasing both types of rubber content. However, the

elongation at break and the energy at break increased

with increasing both types of rubber content. Adding 5

wt% of natural rubber increased elongation at break

and energy at break by 5 and 2.5 times respectively,

compared with neat PLA film.

Introduction

At Present, the environmental problem from the

waste of plastic packaging have increased every year

due to its light weight, easy to process and good

properties for various application. However, these

packaging produced from petrochemical based

polymers such as polyethylene (PE), polypropylene

(PP) and polystyrene (PS) which are non-

biodegradable and can lie around for 500-1000 years

without degrading [1, 2]. To solve this problem, the

biobased polymers such as PLA, PHA, PCL are

selected to use as packaging material because

biodegradable plastics made from renewable natural

resources can be biodegraded in 0.5-2 years[1, 2]

Replacing the use of petrochemical plastic with

bioplasticwith comparable properties can reduce the

use of fossil fuel such as crude oil, gas and coal which

increases the CO2level in the air.

Poly (lactic acid) (PLA) is the linear thermoplastic

aliphatic polyester produced by either ring-opening

polymerization of lactide or condensationpolymerization of lactic acid monomers that are

produced from renewable resources such as corn via a

fermentation process. Because PLA exhibits

comparable properties as petrochemical based

polymers with high mechanical properties,

biodegradability, eco-friendly, and processibility as

well as biocompatibility, it can be used an alternative

plastic for general applications. However, application

of PLA is limited due to its stiffness and brittleness at

room-temperature.[3, 4] Therefore, the properties of

PLA must be improved by adding toughening agent in

which many researchers try to improve the toughness

of PLA through blending method with plasticizers

such as, Poly(-caprolactone)(PCL)[6], Poly(butylenes

adipate-co-terephthalate (PBAT)[7], poly(ethylene

glycol)s (PEGs)with molecular weight range of 400-

10,000 g/mol, Acetyl tri-n-butyl citrate (ATBC) [8],

oligomeric lactic acid (OLA)[9], citrate ester[10],

triacetine[11], poly(propylene glycol) (PPG)[12].

These plasticizers decrease glass transition

temperature (Tg) while increasing percent elongation

at break of PLA. However, the modulus and yield

strength of plastics were decreased.

Natural rubber is one of the toughening agents that

can be used to improve the properties of several kinds

of polymer. It is a milky colloid produced by plants

(Hevea brasiliensis). Natural rubber shows high

elasticity, high tear resistance, high impact strength,and biodegradable.[13, 14] Mathew et al. found that

by adding 70 wt% of natural rubber can increase

percent elongation at break of polystyrene about 100-

140 times.[15] Also PLA was melt-blended with four

kinds of rubber components: ethylene-propylene

copolymer (EPM), ethylene-acrylic rubber (AEM),

acrylonitrile-butadiene rubber (NBR) and isoprene

rubber (IR) Ishida et al found that the samples were

distinct phase separation with all types of rubber.

However, impact strength increased about 2 folds by

using 20 wt% of NBR[16].


6/20

626


The objective of this research is to improve the

toughness of PLA film by using natural rubber as the

toughening agent. Both unvulcanized NR and

vulcanized NR are used in order to investigate the

effect of vulcanization in NR on the mechanical and

thermal properties of PLA/NR film.


Materials

PLA grade 2002D pellets were supplied by

NatureWorksTM. It has a specific gravity of 1.24 and

melt index around 5-7 g/10min (210/2.16 Kg).

Commercial high-ammonia natural rubber latex (N.Y.

Rubber Co., Thailand) (60% dry rubber content) was

filtered through a 250-mesh aluminium screen.

Vulcanizing ingredients i.e. tert-Butyl hydroperoxide(t-BuHP; Fluka, purum), sodium dodecyl sulphate

solution (SDS; Fluka, gel permeation

chromatography), tetraethylene pentamine (TEPA),

and toluene (Fluka, commercial) were used as

received.

Methods

Preparation of peroxide-prevulcanized NR latex

The formulation used for peroxide-

prevulcanization of NR latex are given in Table 1.[17,18] t-BuHP (1.82g) was mixed with distilled water

(16.8g) when SDS solution (1.88g) was poured, while

stirring, into the NR latex (250g) in glass reaction

vessel at room temperature. TEPA (1.75g) and

distilled water (16.8g) were then added into the

mixture prior heating at 60oC in a water bath while

stirring at 20020 rpm. At the end of the reaction

about 3 hour, the prevulcanized latex was cooled

rapidly to room temperature to prevent further

vulcanization and a portion (about 5 g) of sample was

taken, cast on a Petri dish and dried at room

temperature for 1 week to determine the cross-link

density of the vulcanized rubber. The dried rubber was

cut into a square piece of known weight (about 0.2 g)

and its cross-link density was then determined by

immersing it in toluene (40 ml) to equilibrium-swell.

The swelling ratio of the rubber was calculated as

previously described.[18, 19] and NR latex was casted

on glass plate about 1-2 week to form NR sheet.

Table1. Formulations used for peroxide-

prevulcanization of NR latex.[17, 18]

Ingredients Parts by wet weight (g)

Concentrated NR latex 250

Tert-Butyl hydroperoxide

solution (70% w/v)

1.82

Sodium dodecyl sulphate

solution (20% w/v)

1.88

Tetraethylene pentamine

(10% w/v)

1.75

Distilled water 33.60

Preparation of PLA/NR film

PLA was dried in an oven at 60 oC for 24 h before

using. NR sheet was cut into small pieces. PLA blend

with NR were prepared by using an internal mixer

(Brabender 350s) at 180oC with rotor speed of 50

rpm, and was then sheeted by using two-roll mill

before cutting into small pieces. The samples were

pelletized by using a twin-screw extruder (thermo

Hakke Reomix, Germany) at temperature of 180 oC.

The samples were dried in an oven at 60oC overnight

and were re-extruded using blown film die of twin-

screw extruder with similar thermal profiles.


Characterization of Rubber

Dry rubber content (DRC) and total solid

content (TSC) of NR latex are 59.86% (about 60%)

and 60.46% (about 61%) respectively, and the

impurity is about 1% (i.e. protein content). The

particle size was measured by a laser particle size

analyzer (Mastersizer 2000, Malvern). The number of

particle size of NR latex was ranged from 0.07-1.6 m

where the number average particle size was 0.85 m.

The obtained data is agreed with other literature.[19]The %swell ratio of NR and VNR (at 3h) is 3825

and2908, respectively.

The thermal properties of samples are tested by

means of DSC. As shown in Fig 1, the glass transition

(Tg) and melting temperatures (Tm) of neat PLA are

60-65oC and 150-160

oC respectively. Incorporating

NR and VNR into PLA matrix insignificantly

decreases the Tg of the blends indicating that the

immiscible PLA-rubber blend was occurred.[16]


7/20

627


Figure 1. DSC profiles of neat PLA and PLA/rubber

blends.

Mechanical testing

The effects of natural rubber on the mechanical

properties of PLA are shown in Fig 2. As shown in

Fig 2(a), the elongation at break in machine direction(MD) for PLA/NR blends increased with the rubber

content. However, the elongation at break of PLA/NR

in transverse direction (TD) was slightly decreased.

On the other hand, the elongation at break in MD and

TD of PLA/VNR blends slightly increased. Adding 5

wt% of NR and VNR increased the elongation at

break in MD about 8 and 2 times compared with neat

PLA. VNR is crosslinked rubber which is stiffer than

NR, the mobility of the polymer chains is thus high

which affects the elasticity of PLA matrix. On the

other hand, the elongation at break in TD of the blendsshows the same intend with that in MD at 3 wt%.

However, the difference at 5 wt% that the elongation

at break of PLA/NR is decreased but PLA/VNR is

slightly increased. The difference in the change of

elongation could be caused by the area of plastic

deformation zone, where the materials showed

whitening. The results are similar with data of Ishida.

He found that the elongation at break of IR rubber,

synthesized rubber with the same structure as natural

rubber, is higher than that of other rubbers in his

research.[16] Thus, the elongation at break is

depending on the type of rubber and the rubber

content.

To improve toughness of PLA matrix as shown in

Fig 2(b), the energy at break in MD and TD of NR is

increased with the rubber content in which these

results show similar trend as the elongation at break

previously mentioned. Adding 5 wt% of NR in PLA in

MD shows the highest toughness of film. However,

the energy at break of VNR is low. The energy at

break implies the toughness of polymers. Thus, this

data indicates that the NR can improve the toughness

for PLA film.

(a)

(b)

(c)

(d)

Figure 2.a) percent elongation at break b) Energy at

break, c) Tensile Strength, d) Tensile Modulus of

PLA/NR and PLA/VNR blends in both MD and TD

*MD = Machine direction;*TD = Transverse direction

0

20

40

60

80

100120

140

0 1 2 3 4 5 6

Toughness(mJ)

Rubber content(%wt)

NR(MD)NR(TD)VNR(MD)VNR(TD)

0

10

20

30

40

50

60

70

0 1 2 3 4 5 6

Tensilestrength(M

Pa)

Rubber content (wt%)

NR(MD)

NR(TD)

0

500

1000

1500

2000

2500

3000

3500

0 1 2 3 4 5 6

TensileModulus(MPa)

Rubber content (wt%)

NR(MD)NR(TD)VNR(MD)VNR(TD)


8/20

628


Fig 2(c,d) shows that the tensile strength and

tensile modulus in MD and TD of the both types of

PLA blends decreased with an increasing rubber

content because rubber shows high elasticity which

decreased the strength of polymer. Tensile strength

and tensile modulus of PLA/NR is lower than those ofPLA/VNR, because VNR is crosslinked rubber thus it

is stronger than NR (uncrosslinked rubber) in which

the effect of crosslinking is clearly shown when the

rubber content is higher than 5wt%.

Conclusions

The Tg of PLA/NR and PLA/VNR blend systems

were insignificantly decreased indicating that the

systems of blends were immiscible due to the

difference in polarity between PLA and rubber.The results obtained from mechanical test showed

that the elongation at break and the energy at break in

MD of PLA/NR blends increased with the rubber

content. However, the elongation at break and the

energy at break in TD of PLA/NR blends were

slightly decreased. The elongation at break in MD of

NR blends at 3 and 5 wt% are about 5-7 folds

compared with that of neat PLA, respectively, which

is higher than that of VNR blend. However, tensile

strength and tensile modulus in MD as well as in TD

of both rubber blends are decreased with increasingthe rubber content.

Thus, rubber can improve the toughness of PLA

film which depends on the type of rubber, the

compatibilizer, and rubber content.

Acknowledgment

The authors would like to acknowledge TRF-

Master research grants (MAG Window II) Co-funding

annual 2553 for financial supports

References

[1] B. Eling, S. Gogolewski, and A. Pennings,Polymer. 23(1982), pp. 1587-1593.

[2] M. Pluta,Polymer. 45(2004), pp. 8239-8251.

[3] R.M. Rasal, A.V. Janorkar, and D.E. Hirt,Progress in Polymer Science. 35 (2010),

pp.338-356.[4] T.N. Li, L.S. Turng, S.Q. Gong, and K. Erlacher,

Polymer Engineering and Science. 46(2006),pp. 1419-1427.

[5] K.S. Anderson, S.H. Lim, and M.A. Hillmyer,Journal of Applied Polymer Science. 89 (2003),pp. 3757-3768.

[6] M.E. Broz, D.L. VanderHart, and N.R.

Washburn,Biomaterials. 24(2003), pp. 4181-4190.

[7] F. Signori, M.B. Coltelli, and S. Bronco,Polymer Degradation and Stability. 94

(2009),pp. 74-82.[8] M. Baiardo, G. Frisoni, M. Scandola, M.

Rimelen, D. Lips, and K. Ruffieux,JournalApplied Polymer Science. 90(2003), pp. 1731-

1738.[9] O. Martin, and L.Avrous,Polymer. 42 (2001),pp. 6209-6219.

[10] N. Ljungberg, and B. Wesslen,Polymer. 44(25)

(2003), pp. 7679-7688.[11] N. Ljungberg, T. Andersson, and B. Wesslen,

Journal Applied Polymer Science. 88(14)

(2003), pp. 3239-3247.

[12] E. Piorkowska, Z. Kulinski, A. Galeski, and R.Masirek,Polymer. 47(20)(2006), pp. 7178-7188.

[13] J. Sakdapipanich,Natural Rubber of Technology.1 ed, 2010, Bangkok, pp.107.

[14] P. Saeoui, Rubber, 1 ed, 2005, MTEC, Bangkok,pp. 150.

[15] A.P. Mathew, S. Packirisamy, H.J. Radusch, and

S.Thomas,European Polymer Journal.37(9)(2001), pp. 1921-1934.

[16] S. Ishida, R. Nagasaki, K. Chino, T. Dong, and

Y. Inoue,Journal Applied Polymer Science. 113(2009), pp. 558-566.

[17] D.J. Hourston, D.J. and J. Romaine,JournalApplied Polymer Science. 39(1990), pp. 1587

-1594.[18] P. Tangboriboorat, and C. Lerthittrakul, Colloid

and Polymer Science. 280(2002), pp. 1097-1103.

[19] P. Tangboriboonrat, P. and C. Tiyapiboonchaiya,

Journal of Applied Polymer Science. 71(8)(1999), pp. 1333-1345.


9/20

629


Preparation of High Surface Area Nano-Ceria

by Colloidal Emulsion Aphrons Method

S. Sunisa*, J. Somnuk and B. Virote

Department of Chemical Engineering, Faculty of Engineer,King Mongkuts University of Technology Thonburi, Tungkru, Bangkok, Thailand 10140

*Corresponding Author: [email protected]

Abstract: Nano-sized CeO2particles were synthesized by

colloidal emulsion aphrons (CEAs). The effect of cerium

source, surfactant type and the calcination temperature

on the particles were investigated. The synthesized

samples were characterized using XRD, BET, TGA and

TEM. It was found that all of cerium sources and

surfactants produced crystalline CeO2nanoparticle aftercalcined at 400C. The particle size and specific surface

area were in the range of 4-7 nm and 138.8 - 154.8 m 2/g,

respectively. The surface tension of cerium source has the

effect on the particle size. The size control of CeO 2

particle could be interpreted in term of the adsorption of

the surfactant on the cerium ion surface. The increasing

of calcination temperature caused enhancement of

crystallinity and growth of particles size but decreasing

the specific surface area. Finally, methane steam

reforming on synthesized CeO2 were studied. It was

found that the conversion of CH4 was 18.9 %. The

quantities of carbon deposited on the CeO2 surface was

0.05 mmol/g.

Introduction

Nanomaterials has generated a lot of interest due totheir unique physical and chemical properties that aresingnificantly different from those bulk materials.Reducing the particles size to a few nanometer, whilekeeping its chemical composition fixed, can changethe fundamental properties of a material [1].

During the past decade, the most importantapplication of CeO2 is apply as catalyst in a widevariety of reactions involving support materials ofthree-way catalysts for reducing harmful automotiveexhaust emission concentrations. As a catalyst and asupport material, CeO2should have high surface area,high purity in the fine particulate form and should bestable under reaction condition [2-4]. There are veryimportant in order to improve the activity of thecatalyst.

Several processing routes including precipitation,flux method, hydrothermal, spray pyrolysis, sol-gelmethod and mechanochemical [5-10] have beeninvestigated to synthesize nano-sized CeO2 powders.Compared to other methods, the colloidal emulsionaphrons has several advantages in producing particleswith a spherical shape, narrow size distribution,reducing the cost of producing powders of high purityand having a lower aggregation than the others [11-14]. However, its performance in different application

areas is directly determined by its physicochemicalproperties.

Colloidal emulsion aphrons (CEAs) are consideredas the micrometer-sized water-in-oil (W/O) emulsioncores encapsulated by a soapy shell consisting ofmulti-layer surfactant molecules. In this dispersion, the

emulsion core sizes are mainly 10100 m and that ofthe inner phase droplets are 15m. CEAs can also beused as a microreactor to synthesize fine powdermaterials [11,15]. The structure of the CEAs aphronshows in Fig. 1.

In the present study, the synthesis of CeO2nanoparticles was studied by CEAs method. Theeffects of cerium sources, surfactant type and thecalcination temperature on the particles wereinvestigated. Finally, methane steam reforming onsynthesized CeO2were studied.


- Preparation of nano-sized CeO2An internal phase of W/O emulsion was N2H4H2O

solubilized in the organic membrane phase comprisingn-hexane and surfactant. The mixed solution wasstirred for 30 min then the W/O emulsion wasobtained. The W/O emulsion was added to thecolloidal gas aphrons (CGAs) under vigorouslystirring condition. The CGAs was prepared by addingTween80 into deionized waterand were mixing with a

homogenizer. After stirring for 1 h, the colloidalemulsion aphrons (CEAs) was obtained then anexternal water phase containing (NH4)2Ce(NO3)6 and

Figure 1. Proposed structure of the CEAs [11].


10/20

630


deionized water was addes into CEAs, the mixedsolution was vigorously stirred for 30 min. Afterstirring, the mixed solution was turned into dark brownthen were placed into centrifuge to separate theprecipitate from the solution. The precipitate werewashed with ethanol followed by centrifugation in

order to completely remove both residual externalphase and organic membrane phase. The precipitatewas dried at 100C for 1 h and finally was calcined at500C for 1 h, CeO2powder was obtained. The effectof cerium source, sort of surfactant and the calcinationtemperature were studied. The structure of studiedsurfactant are presented in Figure 2.

The crystalline phase of CeO2 obtained frompreparation was identified by X-ray diffraction (XRD,Bruker: D8 Discover) analysis using CuK radiation( = 1.5406 ). The crystallite size of CeO2 wascalculated from the line broadening of the (111)diffraction line according to the Scherrer equation.

The particle morphology and the size of CeO2 wasobserved by transmission electron microscopy (TEM,Jeol Model JEM-2100). The thermal analysis wasperformed by thermo-gravimetrically (Shimadzu TA-50 thermal analyzer) at the heating rate of 10C/minfrom room temperature to 1000C in air atmosphere.The specific surface area was measured by BETsurface area analysis (Quantachrome: Autosorb-1).

- Methane steam reforming

An experimental reactor system [16] consists ofthree main sections: feed, reaction and analysissections. The feed gases including the component ofinterest (CH4, H2O, H2 or O2) were introduced in thereactor section, where an 8 mm internal diameter and40 cm length quartz reactor was mounted verticallyinside a furnace. The CeO2 (prepared by using(NH4)2Ce(NO3)6 as cerium source and PE4LE assurfactant) was loaded in the quartz reactor, which waspacked with a small amount of quartz wool to preventthe catalyst from moving. A Type-K thermocouplewas placed into the annular space between the reactorand the furnace. This thermocouple was mounted on

the reactor in close contact with the catalyst bed tominimize the temperature difference between thecatalyst bed and the thermocouple. After the reactions,

the exit gas mixture was transferred via trace-heatedlines to the analysis section, which consists of aPorapak Q column Shimadzu 14B gas chromatographyand a mass spectrometer. The gas chromatography wasapplied in order to investigate the steady statecondition of the experiments, whereas the mass

spectrometer was used for the transient carbonformation.


-The effect of cerium source

Figure 3. shows the XRD patterns of the thesynthesized particles prepared by CEAs method usingdifferent cerium sources. All the reflection can beindexed to pure crystalline CeO2 and no impuritypeaks are observed in the patterns. The peaks are closeto the ones of the face centered cubic fluorite structureof CeO2.

Figure 4. shows the TEM micrographs of CeO2prepared by CEAs method using different ceriumsource. It is evident from the figure that the. particleswere small in size and uniform in shape. The averageparticle size of CeO2 obtained from (NH4)2Ce(NO3)6,Ce(NO3)36H2O and CeCl37H2O as a cerium sourceare 4.7, 5.4 and 5.9 nm, respectively. The smallestparticle size obtained from (NH4)2Ce(NO3)6might be

explained by the lowest surface tension. Anexperiment was carried out by dropping the sameconcentration solution of all cerium sources on a glasssurface, it was found that a droplet of CeCl37H2Oshowed less flat shape than the others which meansCeCl37H2O has higher surface tension. Ceriumcompound that has low surface tension, can disperse tosmall droplets in emulsion easily [17], as a result, thesmall particles were produced. The surface area ofCeO2 prepared by (NH4)2Ce(NO3)6, Ce(NO3)36H2Oand CeCl37H2O were 139.9, 138.8 and 139.5 m

2/g,respectively. The results show that the surface areaswere nearly the same, On the other hand, the surfacearea obtained from (NH4)2Ce(NO3)6 was higher thanthe others.

Figure 2. The chemical structure of surfactants.

20 30 40 50 60 70 802-Theta (degree)

RelativeIntensity(a.u.)

(a)

(b)

(c)

(111)

(200)

(220)(311)

Figure 3. XRD patterns of CeO2 using different ceriumsource (a) NH4)2Ce(NO3)6, (b) Ce(NO3)36H2O and (c)CeCl37H2OAOT

PE4LE

CTAB


11/20

631


The thermal analysis was carried out in order toevaluate the chemical composition of the CeO2 andelucidate the transformation of crystalline CeO2. Thethermo-gravimetric analyses of CeO2 prepared bydifferent cerium source are given in Fig. 5. TGAprofile of CeO2 obtained from all cerium sourcesshows decomposition in two distinct states. The initialweight losses appear at around 70 -180C. Which arecorresponding to a mass loss of adsorbed water andcrystal water. The second stages appear at 180-300Cwhich represented decomposition of surfactant to otherorganic compounds. The total weight loss of CeO2obtained from (NH4)2Ce(NO3)6, Ce(NO3)36H2O andCeCl37H2O were 44.97, 48.80 and 52.63%,respectively.

All of TGA profile showed that there were noweight losses at the temperature higher than 400Cindicating the crystalline CeO2 formation as the finalproduct. Therefore, CeO2 obtained from three ceriumsources was calcined at 500C are purity confirmed byTGA analysis.

-The effect of surfactant type

Figure 6. shows the TEM micrographs of CeO2prepared by different surfactant. The average particle

size of CeO2in the case of PE4LE and CTAB were 5.9and 5.1 nm, respectively, while the size in the case ofAOT was as small as 4.1 nm. It was considered thatthe cerium ion has positive charge and that AOTstrongly adsorbed on the surface but CTAB may notadsorbed on surface. A certain repellent action exists

between the hydrophilic group of CTAB and ceriumcation at grain surface, which makes the stabilizingeffect of CTAB on grain become weaker [18]. Whennonionic surfactant (PE4LE) is used, the crystallitesize of CeO2are bigger than the other. This result canbe considered as the reason that the stabilizing effectof nonionic surfactant on water droplets and particlesmainly derives from its hydrogen bond with water[19]. This action is weaker than that of ion bond.

-The effect of calcinations temperature

Fig.7. shows the TEM micrographs of CeO2prepared by CEAs method carried out at differentcalcinations temperature in the range of 300-800C.The average particle size of CeO2 obtained from thecalcinations temperature of 300, 500, 600 and 800Care 4.3, 5.4, 7.6 and 14.9 nm, respectively. The

average particle size of CeO2 increases sharply withthe rising of calcinations temperature.The reason can be explained as with the increase of

calcination temperature, the growth rate of particlesincreases more rapidly than the nucleation rate does,and the aggregation trend of particles becomesstronger.

-The stability and activity toward methane

reformingThe synthesized CeO2was studied in the methane

steam reforming at 900C. The inlet component wereCH4/H2O/H2 in helium with the inlet ratio of

1.0/3.0/0.2. The main products from the reactor overCeO2 were H2 and CO with some CO2, indicating acontribution from the water-gas shift, and the reversemethanation at this high-temperature. The conversion

Figure 4. TEM micrographs of CeO2 using differentcerium source (a) NH4)2Ce(NO3)6, (b) Ce(NO3)36H2O

and (c) CeCl37H2O

Figure 6. TEM micrographs of CeO2 using differentsurfactant (a) AOT, (b) PE4LE and (c) CTAB

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

Temperature ( C)

Weight(%)

(NH4)3Ce(NO3)6

CeCl3 7H2O

Ce(NO3)3 6H2O

(NH4)3Ce(NO3)6

CeCl3 7H2O

Ce(NO3)36H2O

Figure 5. Thermo-gravimetric analysis of CeO2preparedby different cerium sources.

(a) (b)

(c)

(a) (b)

(c)


12/20

632


of CH4 with time for CeO2 catalysts are shown inFigure 7. In the figure, the steam reforming activity ofCeO2significantly declined with time. At steady state,It was found that the conversion of CH4 was 18.5%(Higher than steam reforming reactivity of CeO2prepared by the precipitation based catalysts [20]), the

H2yield was 68.9%, the H2/CO ratio was 4.19 and thequantities of carbon deposited on the CeO2surface was0.05 mmol/g (less than steam reforming reactivity ofAl2O3 based catalysts [21]). The explanations for thesteam reforming reactivity of CeO2 based catalystswith high resistance toward carbon deposition aremainly due to the high oxygen storage capacitymaterial. CeO2contains a high concentration of highlymobile oxygen vacancies and; thus, acts as a localsource or sink for oxygen on its surface. The majorweakness of CeO2 was its low specific surface areaand also high size reduction due to the thermalsintering impact; consequently, the reforming

reactivity over CeO2 was much lower than theconventional metallic catalysts.

Conclusions

Nano-sized was successfully prepared by CEAsmethod. The results from XRD, TGA, TEM and BETmeasurement indicated that the obtained particles werecubic fluorite structure of CeO2 nanoparticles. Thesurface tension of cerium source has the effect on theparticle size. The size control of CeO2 particle couldbe interpreted in term of the adsorption of thesurfactant on the cerium ion surface. Calcinations inhigher temperature make the average size of productsincrease. The synthesized CeO2was tested by methanesteam reforming resulting in the low steam reforming

reactivity but high resistance towards carbondeposition.

Acknowledgement

The financial supported by grant from under theprogram Strategic Scholarships for Frontier ResearchNetwork for the Ph.D. Program Thai Doctoral degreefrom the Office of the Higher Education Commission,

Thailand. The author would like to thank Assoc. Prof.Dr. Navadol Laosiripojana for contributing histhoughts on the section of reforming process.

References

[1]A. Hadi and I.I. Yaacob,Mater. Lett. 61(2007), pp. 93-96.

[2]

G.C. Bond, Heterogeneous Catalysis: Principle andApplications. Oxford Science (1987)

[3]

N. Laosiripojana and S. Assabamrungrat,Appl. Catal. B:Environ. 66(2006), pp. 29-39.

[4]

V. Bedekar, A.K Patra, D. Sen, S. Mazumder and A.K.Tyagi,J. Alloys Compd. 453(2008), pp. 347-351.

[5]

H. I. Chen and H. Y. Chang, Ceram. Inter.31(2005),pp. 795-802.[6]F. Bondioli, A.B. Corradi, C. Leonelli and T.

Manfredini,Mater. Res. Bull. 34(1999), pp. 2159-2166.[7]X. Lu, X. Li, F. Chen, C. Ni and Z. Chen, J. Alloys

Compd. 476(2009), pp. 958-962.[8]

H. S. Kang, Y. C. Kang, H. Y. Koo, S. H. Ju, D. Y. Kim,S. K. Hong, J. R. Sohn, K. Y. Jung and S. B. Park,Mater. Sci. Eng. B.127 (2006), pp. 99-104.

[9]Y.X. Li, X. Z. Zhou, Y. Wang and X. Z. You, Mater.Lett.58(2003), pp. 245-249.

[10]N. Phonthammachai, M. Rumruangwong, E. Gulari,A.M. Jamieson, S. Jitkarnka and S. Wongkasemjit,Colloids Surf. A: Physicochem. Eng. Asp. 247(2004),pp. 61-68.

[11]

T. Deng, Y. Dai and J. Wang, Colloids Surf. A:Physicochem. Eng. Asp.266(2005), pp. 97-105.

[12]Y. Dai, T. Deng, S. Jia, L. Jin and F. Lu, J. Memb. Sci.281 (2006), pp. 685-691.

[13]Y. Dai, T. Deng and F. Lu, Inter. J. Pharm. 311(2006),pp. 165-171.

[14]J.S. Lee, , J.S. Lee and S.C. Choii, Mater. Lett.59(2005), pp. 395-398.

[15]

F. Sebba, Foams and Biliquid Foams-Aphrons.Wiley.New York (1987).

[16]

N. Laosiripojana and S. Assabumrungrat, Appl. Catal.B: Environ. 60(2005), pp. 107-116.

[17]

M.J. Rosen, Surfactants and Interfacial Phenomena.Wiley-Interscience. New York (2004).

[18]

M. Kisida, T. Hanaoka, W. Y. Kim, H. Nagata and K.Wakabayashi,App. Surf. Sci. 121(1997), pp. 347-350.

[19]Y. He, B. Yang and G. Cheng, Mater. Lett.57(2003),pp. 1880-1884.

[20]T. Palikanon, N. Laosiripojana, S. Assabumrungrat andS. Charojrochkul, Songklanakarin J. Sci. Technol. 28(2006), pp. 1237-1249.

[21]

A. Shotipruk, S. Assabumrungrat, P. Pavasant and N.Laosiripojana, Chem. Eng. Sci. 64(2009), pp. 459-466.

Figure 7. TEM micrographs of CeO2 at differentcalcinations temperature (a) 300C, (b) 500C (c) 600 Cand (c) 800C

(a) (b)

(c) (d)


13/20

633


Characterization of Pt-Co/C Electrocatalyst for Oxygen Reduction Reaction

Prepared by Electrodeposition Method

N. Chaisubanan1 and N. Tantavichet1,2*

1Fuels Research Center, Department of Chemical Technology, Faculty of Science, Chulalongkorn University, Bangkok,Thailand 10330

2National Center of Excellence for Petroleum, Petrochemicals and Advance Materials, Chulalongkorn University, Bangkok,Thailand 10330


Abstract: Platinum alloy electrocatalysts have high

potential to be used in proton exchange membrane fuel

cells (PEMFCs) due to their high activities for oxygen

reduction reaction (ORR). In this work, the Pt-Co/C

electrocatalysts were prepared by electrodeposition

method. The surface morphologies of PtCo alloy

deposits were examined using scanning electronmicroscopy (SEM) whereas the energy-dispersive

spectroscopy (EDS) was used to analyse the

compositions of PtCo alloy deposits. The active areas

were determined by cyclic voltammetry based on charge

integration under the hydrogen desorption peak. Effect

of type of applied current and electrodeposition

parameters on the morphology of Pt-Co/C

electrocatalyst were investigated. The results showed that

the Pt-Co/C electrocatalyst prepared using pulse

reverse electrodeposition provided the smallest

platinum particle size and uniform distribution with

the good particle dispersion compared to those prepared

using direct and pulse current electrodeposition.

Moreover, the catalyst prepared using pulse reverse

electrodeposition had a low catalyst loading and the

Pt-Co composition of the catalyst where the prepared

catalysts have the Pt:Co composition around 90:10.

Introduction

In fuel cell technologies, proton exchangemembrane fuel cells (PEMFCs), with the advantagesof low operating temperature (60100 C) and thefast start-up, are promising candidates for applicationin portable power sources, electric vehicles andtransportation applications. Platinum alloys as

cathode catalysts have attracted wide attention as a

candidate to achieve high performance, to increasepower density, and to reduce a component cost ofPEMFCs. Co has been previously been studied inorder to increase catalyst activity and stability for usein PEMFCs [1].

The deposition of precious metals eitherchemically or electrochemically plays an important

role in the development of technologies where thesemetals are used. Particularly this is true in the area ofelectrodeposition as each method with differentoperating parameters such as temperature, pH andcurrent density. It is low temperature and non-vacuum technique and easily applied on different

scales, from micrometric to macroscopic areas [2]. It

also allows for a good control of the amount ofelectrocatalyst, and can be used to deposit films orparticles of metals, alloys and compound.

This research studies the preparation of the Pt-Co alloy catalyst on the electrode by theelectrodeposition technique using direct current

(DC), pulse current (PC) and pulse reverse current(PRC) electrodeposition.

A typical direct current electrodepositionschematic is shown in Figure 1. where the currentdensity is the only controlled parameter to achievethe desired deposit properties.

As shown in Figure2. the pulse electrodepositionmethod has three independent variables to control the

deposition namelyON time, OFF time and current density. The dutycycle which is the ratio between on time andcycle time (the summation of on-time and off-time) can influence the formation of nuclei and

growth of existing crystals.

i(mAcm

-2)

t (sec)

Figure 1. Schematic of direct current electrodeposition.

i(mAcm-2)

t (sec)

Figure 2. Schematic of pulse electrodeposition.

ton toff

tcycle


14/20

634


When a pulse with reverse current is used (PRC),even more parameters could be used to modulate the

composition and morphology of PtCo alloy depositsis possible for cobalt componentin PtCo alloys to beremoved preferentially when converting current fromcathodic to anodic, which may result in the deposition

of high-cobalt-containing PtCo alloys [4]. The basicwaveform of the pulse reverse electrodeposition is

shown in Fig. 3. Symbols marked in the schematicdiagram, Ic, Ia, Iav, T, tc, and ta, stand for cathodiccurrent density (Ic ), anodic current density (Ia),average current density (Iav), cycle time (T), cathodictime (tc) and anodic time (ta), respectively.

The prepared Pt-Co catalysts were characterized bya scanning electron microscopy (SEM), X-raydiffraction (XRD) and the energy-dispersive

spectroscopy (EDX), respectively.

The active areas of Pt was determined by cyclicvoltammetry based on charge integration under thehydrogen desorption peak.


- Preparation of carbon substrate layer forelectrodeposition

The supported catalyst layer is divided into

two sub-layers are hydrophobic sublayer and

hydrophilic sublayer. The first step, to preparehydrophobic sublayer, a mixture of DI water, PTFE(60. wt%) (Aldrich), isopropanol (Fluka) and carbonblack (Vulcan XC-72) was painted on a carboncloth (5 cm2). Then, the carbon cloth was dried at300 C for 2 hr. This sub-layer was prepared tohave a total loading of 1.9 mg cm-2 (with a carbon

black to PTFE ratio of 30:70). The hydrophilic layerwas prepared by painting a mixture of Nafion andglycerol on the electrode from the previous step,and then drying at 80 C for 2 h.

- Electrodeposition of catalyst layer

The electrodeposition of catalyst layer on thepretreated electrode was conducted in a2-compartment electrochemical cell containing asolution of 0.01M H2PtCl6.6H2O and 0.1MCoSO4.7H2O in 0.5 M H2SO4 . An electrode wasplaced on the opposite face as titanium gauze was

used as a counter electrode , and silver/silver chloride(0.197V vs NHE) was used as reference electrode.

An Autolab PGSTAT 10 potentiostat (Eco Chemie)was used to perform current electrodeposition. Duringthe electrodeposition the plating solution was stirredby magnetic stirrer at 300 rpm. The detailedpreparation conditions were summarized in Table1. After electrodeposition all electrodes were rinsedthoroughly with de-ionizedwater and dried at 110 Cin a vacuum oven.

Figure 3. Schematic of pulse reverse electrodeposition.

ic

ia

tc

ta

tc cle

iavi(mA

cm

-2)

t (sec)

DC PC PRC

Currentdensity 10 mA cm-2 Average current 10 mA cm-2 Cathodic current 200 mA cm-2

Total time 200 sec. density density

Chargedensity 2 C cm-2 Pulse current 200 mA cm-2 Anodic current 200 mA cm-2

density density

Duty cycle 5 % Cathodic time 0.05 sec.

On time 0.05 sec. Anodic time 0.025 sec.

Off time 0.95 sec. Total time 30 sec.

Total time 200 sec. Charge density 2 C cm-2

Charge density 2 C cm-2 Charge ratio2:1

Frequency 1 Hz (Cc: Ca)

Table 1.The electrodeposition parameters


15/20


16/20

636


catalyst for electrodes, which is normalized to themetal loading of the Pt-Co alloy catalyst. The

electroactive areas measured for electrodepositedelectrodes on substrates are given in Table 2.

Figure 6. illustrates that the hydrogendesorption peaks of the Pt-Co catalyst electrodes was

substantially affected by type of applied current.The Pt-Co catalyst prepared by the pulse reverse

current electrodeposition has the smallest and welldispersed catalyst particles so it has hight activesurface area where catalysts prepared by directcurrent electrodeposition has larger particles whichleads to lower active surface areas.

ConclusionsAccording to this study, it can be concluded that

the current applied during the electrodepositionwas found not to affect the composition butaffects the deposited amounts , structure and grainsize of Pt-Co alloy electrodeposition. Depositionusing the pulse reverse current yields the smallestparticles, the highest electrochemical active area, andthe lowest amount of metal. Overall, electrodeposition

gives the Pt-Co atomic ratio of approximately 90:10.

Acknowledgements

The authors are gratefully acknowledge thefunding support from National Center of Excellence

for Petroleum, Petrochemicals and Advanced

Materials

(NCE-PPAM).The authors would like tothank the support of Department of ChemicalTechnology, Faculty of Science, ChulalongkornUniversity

References

[1] B. F.Elise, R.Hector, C.Mercado,Journal of

Hydrogen Energy, 35:3280-3286 (2010).[2] A.J. Martn, A.M. Chaparro, L. Daz,Journal of Power

Sources,169 (2007) 6570.

[3] N. Rajalakshmi, K.S. Dhathathreyan, Journal ofhydrogen energy, 33 (2008) 5672 5677.

[4] J.Y. Fei, G.D. Wilcox, Electrochimica Acta, 50 (2005)26932698.

[5] S. Yupa, T. Nisit,Journal of Applied Electrochemistry,39 :123-134(2009) .

[6] Y. Ra, J. Lee, I. Kim, S. Bong, H. Kim,Journal of

Power Sources, 187 (2009) 363370.[7] L. Jingjing, Y. Feng, C. Ling, W. Tongtao, L. Jiangling,

W. Xindong,Journal of Power Source, 186 (2009)

320 327.

Figure 6. Cyclic voltammograms (20mVs1) of of the

PtCo catalyst electrodes prepared by (a) DC ; (b) PC

and (c) PRC electrodeposition

(a)(b)

(c)


17/20

637


Synthesis and Characterization of Porphyrin-Based Metal-Organic

Frameworks for Gas Adsorption

S. Laokroekkiat1, B. Pulpoka2* and D. Nuntasri2

1Program of Petrochemistry and Polymer Science, Faculty of Science, Chulalongkorn University, Bangkok, Thailand 103302Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok, Thailand 10330


Abstract: Metal-Organic Frameworks (MOFs) are solid

structures which compose of metal cluster and

carboxylate/bipyridyl linker providing a plentiful of

pores. MOFs are used to store several gases, such as

carbon dioxide and hydrogen or as heterogeneous

catalyst. This research concerns solvothermal synthesis

of porphyrin-based MOFs containing meso-tetra(4-

carboxyphenyl)porphyrin or triply-fused di(4-carboxyphenyl)diporphyrin as organic linker. The

synthesis of MOFs for H2 or CO2 storage material has

two steps. The first one is a synthesis of organic linkers

which were characterized by spectroscopic techniques

(NMR, FT-IR and elemental analysis). The second step

concerns a construction of porphyrin-based MOFs from

meso-tetra(4-carboxyphenyl)porphyrin by using

dimethylformamide as solvent. The obtained MOF was

characterized by spectroscopic techniques (XRD, SEM)

and nitrogen adsorption data (surface area and pore

volume) were determined. The porphyrin-based MOF

obtained exists as nanocrystal with a size of about 50 nm.

The BET nitrogen adsorption study revealed that

porphyrin-based MOF has a mean pore diameter of

0.6326 nm. classified to micropore.

Introduction

Fuel cell technology is one of the most interestingapproaches to replace gasoline and diesel engines. Thisdevice can generate the electric power by chemical

reaction between hydrogen and oxygen. However,hydrogen storage for fuel cell is the key factor for

development this technology. Many researchers seekfor highly efficient and practical hydrogen storagemethods. There are two major types of hydrogenstorage which are chemisorption and physisorptionmethodologies. The chemisorption uses metal hydridesas a source of hydrogen gas while the physisorptionnormally employ metal-organic framework (MOF)

materials to absorb hydrogen gas. The goal is to designthe light weight material that can store hydrogen atambient condition.

Metal-organic frameworks [1]

are the inter-penetrating network containing high porosity and largespecific surface areas. MOFs are solid structures whichcompose of metal clusters and organic linkers such ascarboxylate and bipyridyl[2]. Two compositions of

MOFs play an important role in directing the topologyand properties of framework.

Porphyrin is one of the most popularsupramolecular molecule which is flat and rigid

structure. Porphyrins contain a lot -electron whichcan polarize molecular hydrogen resulting to thehigher property to store gas. The gas storage capacity

of MOFs depends on metal cluster, pore size andsurface area. By keeping these factors in mind, fused

porphyrin arrays[3]

containing extensive delocalized -

conjugation are being synthesized to use as organiclinker for construction of new MOFs. This arrayPorphyrin-based MOFs[4,5]may capture other gases forexample carbon dioxide or carbon monoxide thereforethey may be used as catalyst[6] and in other

applications.This research concerns solvothermal synthesis of

porphyrin-based MOFs containing meso-tetra(4-carboxyphenyl)porphyrin or triply-fused di(4-carboxyphenyl)diporphyrin as organic linker. Thesynthesis of MOFs includes two steps. The first step isa synthesis of organic linkers, free base and their zinccomplexes. The second step concerns a construction of

porphyrin-based MOFs from meso-tetra(4-carboxyphenyl)porphyrin by using dimethylformamideas solvent. The construction of MOF based on triply-fused di(4-carboxyphenyl)diporphyrin and M(NO3)2/M(OAc)2 (M= Zn, Cu) with or without 4,4-bipyridine (as pillar) by using dimethylformamide orpyridine as solvent is a going project. The molecule

4,4-bipyridine as a spacer between the porphyrinplane may reduce the stacking of triply-fused di(4-

carboxyphenyl)diporphyrin in the framework.


All reagents were analytical grade and purchasedfrom Sigma-Aldrich, Merck and Tokyo ChemicalIndustry and used as received without furtherpurification except pyrrole which was distilled before

use.1H NMR spectra were obtained in CDCl3at 400

MHz (Varian, USA). Chemical shifts () were reported

in parts per million (ppm). Coupling constant (J) arereported in Hertz (Hz). Mass spectra were obtainedusing matrix-assisted laser desorption ionization mass

spectrometry (MALDI-MS) by using -hydroxycyanocinnamic acid (CCA) as a matrix. All UV-visibleabsorption spectra were recorded by Varian Cary 50

Probe UV-Vis spectrophotometer at 25C with a

Julabo F33 temperature controller. XRD pattern wasobtained by X-Ray Diffractometer, Rigaku DMAX


18/20

638


2200 Ultima+/Cu lamp. IR spectrum was obtained byFourier Transform Infrared Spectroscopy, Nicolet

Impact 412. Elemental analysis was obtained byCHNS/O Analyzer, Perkin Elmer PE2400 Series II.SEM image was obtained by Scanning ElectronMicroscope, JEOL 6480LV. Nitrogen adsorption

analysis was obtained by Surface area analyzer,BELSORP- mini instrument.

Synthesis of meso-tetra(4-carboxyphenyl)porphyrin(1)

[7] :4-Carboxybenzaldehyde (2.803 g, 18.7 mmol) and

propionic acid (90 mL) was stirred in a two-neckedround-bottomed flask and gently heated until 4-carboxybenzaldehyde was completely soluble. 1.26mL (18.2 mmol) of freshly distilled pyrrole was added

in the solution by syringe.The mixture was heated atreflux for 6 hours. After cooling at room temperature,meso-tetra(4-carboxyphenyl) porphyrin (1) was

precipitated by methanol. The purple solid was filteredand washed with acetone to obtained the desiredproduct (1) (0.757 g, 20 %) 1H NMR (400 MHz,DMSO-d6) : -2.98 (s, 2H, NH), 8.31 (d, J= 8.1, 8H,Ar-H), 8.34 (d,J= 8.1, 8H, Ar-H), 8.81 (s, 8H, -H).

Synthesis of dipyrromethane (2)[8] :A mixture of paraformaldehyde (0.3 g, 10 mmol)

and freshly distilled pyrrole (14 mL, 202 mmol) wasstirred in a round bottom flask and bubbled withnitrogen gas for 15 minutes. The mixture was heated at

55C to obtain a clear solution, then trifluoroaceticacid (0.15 mL, 2 mmol) was added. The solution was

stirred for 25 minutes at 55C. At the point that nostarting aldehyde was evident by TLC analysis(hexane/ethyl acetate/triethylamine; 80:20:1), themixture was diluted with CH2Cl2 (20 mL), washedwith aqueous 0.1 M NaOH (40 mL) and then washed

with water. The organic layer was dried withanhydrous Na2SO4. The solvent and unreacted pyrrolewere removed by rotary evaporator to yield a darkbrown oil. Column chromatography (silica gel,cyclohexane/ EtOAc/triethylamine; 80:20:1) yielded apale white solid (440 mg, 30%) of the pure

dipyrromethane (2). TLC (silica gel) was monitoredwith visualization using bromine vapor. Compound 2

turned bright pink, and the higher oligomers had lowerRf).

1H NMR (400 MHz, CDCl3) : 3.93 (s, 2H, CH),6.06 (s, 2H, pyrrole-H ), 6.18-6.20 (q, J=2.8, 2H,pyrrole-H), 6.61 (s, 2 H, pyrrole-H), 7.64 (s (br), 2 H,pyrrole-NH).

Synthesis of 5-(4-Carbomethoxyphenyl)dipyrromethane (3)[9]:

A mixture of methyl 4-formylbenzoate (1.77 g,10.8 mmol) and freshly distilled pyrrole (15 mL, 216mmol) was stirred in a round bottom flask withbubbling with nitrogen gas for 15 minutes, thentrifluoroacetic acid (0.17 mL, 2.2 mmol) was added.

The solution was stirred at room temperature for 25minutes. At which point, no starting aldehyde was

evident by TLC analysis (hexane/ethyl acetate/

triethylamine; 80:20:1). The mixture was diluted withCH2Cl2 (20 mL), washed with aqueous 0.1 M NaOH

(40 mL) and then washed with water. The organiclayer was dried with anhydrous Na2SO4. The solventand unreacted pyrrole was removed by rotaryevaporator to yield dark brown oil. Column

chromatography (silica gel, cyclohexane/ EtOAc/triethylamine; 80:20:1) yielded a yellow pale solid

(1,260 mg, 42%) of the pure dipyrromethane (3). TLC(silica gel) was monitored with visualization usingbromine vapor. Compound 3 turned bright pink, andthe higher oligomers had lower Rf).

1H NMR (400MHz, CDCl3) : 3.91 (s, 3H, -OCH3), 5.52 (s, 1H,meso-H ), 5.89 (s, 2H, pyrrole-H), 6.17 (q, J=2.8, 2H,pyrrole-H), 6.72 (d, J=1.2, 2 H, pyrrole-H), 7.29 (d,J=8, 2H, Ar-H), 7.98 (d (br), J=8, 4H, pyrrole-NH andAr-H)

Synthesis of 5-(4-methoxycarbonylphenyl)-10,20-

diphenylporphyrin (4):5-(4-Carbomethoxyphenyl) dipyrromethane (3)

(840 mg, 3 mmol) was dissolved with toluene (30 mL)in a two-necked round-bottomed flask under nitrogen

atmosphere. The solution was heated at 60C to obtaina clear solution and charged with solutions ofdipyrromethane (2) (440 mg, 3 mmol) in toluene (20mL) and benzaldehyde (0.6 mL, 6 mmol) in toluene(20 mL). Propionic acid (70 mL) was added into thesolution which turned the solution to dark color. Thereaction was heated at reflux (120C) for 3 hours inthe open air. The solvents were removed under reduce

pressure and the crude obtained was rinsed with

CH2Cl2. The residual propionic acid was removed bysaturated NaHCO3 solution and then washed withwater. The organic phase was separated, dried withanhydrous Na2SO4and evaporated to dryness in vacuo.Column chromatography (silica gel, cyclohexane/

CH2Cl2; 80:20) yielded a purple solid (40 mg, 2.2 %)of the porphyrin derivative (4).

1H-NMR (400 MHz,

CDCl3) : -3.05 (s, 2H, NH), 4.11 (s, 3H, -OCH3),7.77-7.80 (m, 6H, Ar-H), 8.25 (d, J=4, 4H, Ar-H),8.30 (d,J=8, 2H, Ar-H), 8.43 (d,J=8, 2H, Ar-H), 8.82(d,J=4, 2H, -H), 8.93 (d, J=4, 2H, -H), 9.04 (d, J=4,2H, -H), 9.36 (d,J=8, 2H, -H), 10.25 (s, 1H, meso-H) MS(MALDI-TOF) calcd for [C40H28N4O2]

+ m/z

596.221, found 597.173 [M+H]+

Synthesis of Zinc-5-(4-methoxycarbonylphenyl)-10,20-diphenylporphyrin (5)[10] :

A saturated solution of Zn(OAc)2 .2H2O (147 mg,0.67 mmol) in MeOH (20 mL) was added to a solutionof free-base porphyrin derivative (4) (40 mg, 0.067mmol) in CHCl3 (40 mL), and the mixture was heatedat reflux for 8 hours. After the complete metalation

confirmed by TLC, the mixture was washed withwater and the organic layer was dried with anhydrousNa2SO4to yield a reddish purple solid (43 mg, 100%)of Zinc porphyrin complex (5) 1H-NMR (400 MHz,CDCl3) : 4.11 (s, 3H, -OCH3), 7.76-7.81 (m, 6H, Ar-H), 8.23 (d,J=7.2, 4H, Ar-H), 8.29 (d,J=8, 2H, Ar-H),8.39 (d, J=8.4, 2H, Ar-H), 8.91 (d, J=4.8, 2H, -H),


19/20

639


9.00 (d, J=4.8, 2H, -H), 9.07 (d, J=4.4, 2H, -H), 9.36(d, J=4.4, 2H, -H), 10.20 (s, 1H,meso-H)

Synthesis of triply-fuse-di-Zinc-5-(4-methoxy-carbonylphenyl)-10,20-diphenylporphyrin (6)[3]:

Zinc Porphyrin complex (5) (20 mg, 0.03 mmol)

was dissolved in dry CH2Cl2 (30 mL) in a round-bottomed flask. The solution was cooled to

-78C by a dry ice-acetone bath, and PIFA([bis(trifluoroacetoxy)iodo]benzene) (32 mg, 0.074mmol) was added. Then, the cooling bath wasremoved, and the mixture was stirred at ambient

temperature for 2 hours. A suspension of NaBH4(11.4mg, 0.3 mmol) in methanol (5 mL) was added, andstirred for 0.5 hour. The reaction mixture was pouredinto water and extracted with CH2Cl2. The organiclayer was washed with saturated NaHCO3solution andwater and dried with anhydrous Na2SO4. Columnchromatography (silica gel, MeOH/CH2Cl2; 1:99)

yielded a blue-violet solid (9 mg, 30%) of the triply-fused diporphyrin derivative (6)

1H-NMR (400 MHz,

CDCl3) : 7.16 (s, 12H, -H), 7.18 (s, 20H, Ar-H), 7.23(s, 8H, -H ),4.10 (s, 6H, -OCH3)MS(MALDI-TOF)calcd for [C80H46N8O2Zn2]

+ 1314.09 m/z, found

1314.392

Figure 1. Scheme for synthesis of triply-fuse-di-Zinc-5-(4-methoxy-carbonylphenyl)-10,20-diphenyl-porphyrin (6)

Synthesis of meso-tetra(4-carboxyphenyl)-porphyrin MOF [11]:

A round-bottomed flask containing meso-tetra(4-carboxyphenyl)porphyrin(1)(0.200 g, 0.25 mmol) andZn(NO3)2. 6H2O (0.162 g, 0.54 mmol) were chargedfreshly distilled DMF (20 mL). The mixture was

stirred at room temperature for 1 hr. 6 Drops of 30%H2O2 were added dropwise and follwed by

triethylamine (TEA) (0.28 mL, 2 mmol). The mixturewas further stirred at room temperature until purplesolid was observed and extended stirring for 1 hr. Thesolid was filtered and washed with DMF. meso-tetra(4-carboxyphenyl)-porphyrin MOF obtained wasdried in vacuo at 140-150C for 6-7 hours to obtaineda dark purple porphyrin-based MOF (0.234 g, 83%)

FT-IR (KBr pellet) /cm-1: 3420, 1654, 1601, 1400.

Anal. Calcd for C192H96O37N16 Zn20.2tcpp: C, 56.70;H, 2.45; N, 5.51. Found: C, 56.91; H, 4.08; N, 4.96.

XRD 2-(deg.): 5.44, 7.06, 8.34


The synthesis of meso-tetra(4-carboxyphenyl)porphyrin (1) gave a reasonable yield (20%) andobtained as a purple solid which its spectroscopic datawere in good agreement with its structure. However,the synthesis of the triply-fused diporphyrin derivative

6 is quite complex. In the synthesis of 5-(4-methoxycarbonylphenyl)-10,20-diphenylporphyrin (4),

there was different reactivity between twodipyrromethane (2and 3). 5-(4-Carbomethoxyphenyl)dipyrromethane (3) was a better nucleophile than

dipyrromethane (2) due to aromatic substituent, thus itis easy to attack aldehyde(benzaldehyde) to obtain5,15-(4-methoxycarbonylphenyl)-10,20-diphenylporphyrin which was a major byproduct and 5,15-

diphenylporphyrin was a minor byproduct. Thus thedesired porphyrin product (4) was trace amount (2%

yield).Another pathway for synthesis porphyrin

derivative (4) (not show in the scheme) wasbromination using N-bromosuccinimide at the mesoposition of 5,15-diphenylporphyrin to obtain mono-brominated porphyrin, then followed by Suzuki

coupling reaction using boronic acid and palladiumcatalyst. However, there was low percent yield (10%)for synthesis mono-brominated porphyrin. In the caseof di-brominated porphyrin was 70% yield.

The synthesis of triply-fused diporphyrinderivative (6) relied on the process of synthesis and thecenter metal of porphyrin due to radical mechanism.Cooling the reactionwas required to stabilize the

radical of catalyst (PIFA) and porphyrin that couldreduce the polymeric residue. Free base porphyrincould not be promoted triply-fused diporphyrinbecause the phenyl iodide radical of catalyst wouldcombine with a inner NH proton of porphyrin whichwas weaker bond than CH proton of meso- and -position. That would obtain the porphyrin (5) reactantnot the desired triply-fused diporphyrin (6).

NH

O

H H NH

COOCH3

CHOTFA TFA

NH

NH

NH

NH

O

H3CO

2 3

benzaldehydepropionicacid/toluene reflux, air

NO

H3CO

N

N NM

4: M = 2 H5: M = Z n

Zn(OAc)2.2H2Odry CH2Cl2, RT

NO

H3CO

N

N NZn

N O

OCH3

N

NNZn

PIFA

6


20/20

640


The color of porphyrin (5) was reddish purple andtriply-fused diporphyrin (6) was blue-purple. The

observed color change implied that triply-fusedporphyrin was a stable molecule because it absorbedred region. UV-visible spectrophotometry techniquewas used to prove this hypothesis.

Figure 3. UV-vis absorption spectra of porphyrin 5andtriply-fused diporphyrin 6 in CH2Cl2.

Figure 3 displayed the UV-vis absorption spectraof porphyrin 5 and triply-fused diporphyrin 6 inCH2Cl2. The absorption spectrum of porphyrin 5showed two major bands at 414 (soret band) and 544(Q-band) nm, which may correspond to bands I and II

of the triply-fused diporphyrin 6. Compound 6exhibited bands at 418 (band I) and 561-579 (band II)

nm. Bands II was was relatively more broad andcomplicated and red-shifted to bands I. That may beascribed to the increased conjugation which theelectron was extensively delocalized upon increasingconnection between the two units of the porphyrin.

Figure 4. SEM image magnified 30,000 times of meso-tetra(4-carboxyphenyl)-porphyrin MOF.

The SEM image in figure 4 shows that themorphology of meso-tetra(4-carboxyphenyl)porphyrin

MOFwas amorphous with a particle size of around 50nm. Then, this porphyrin-based MOF is classified as a

nanocrystal MOF. According to nitrogen absorption(BET) analysis at 77 K, the absorption isotherm ofmeso-tetra(4-carboxyphenyl)-porphyrin MOF wasclassified as Type I isotherm. Besides this, it wasfound that the surface area of porphyrin-based MOFwas 331.26 m2/g with mean pore diameter of 0.6326(t-plot) nm and micropore volume at p/p0=0.990 of

0.1219 cm3/g identified as micropore.

Conclusions

The porphyrin-based MOF was successfullysynthesized and it showed medium surface area withmicropore even though the organic linker, meso-

tetra(4-carboxyphenyl)-porphyrin, is bigger moleculecompared to telephthalic acid. The meso-meso, - ,- triply-fused diporphyrin derivative was preparedin order to increase the pore size as well aspolarizability of porphyrin-based MOF.

Acknowledgements

We would like to thank the center of Excellence ofPetroleum, Petrochemicals and Advance Material, theCenter of Innovative Nanotechnology ChulalongkornUniversity, the Supramolecular Chemistry ResearchUnit and Graduate School of ChulalongkornUniversity for partial financial support of this research.

References

[1] U. Mueller, M. Schubert, F. Teich, H. Puetter, K.

Schierle-Arndt and J. Pastre, MetalOrganicFrameworks-Prospective Industrial Applications, J.Mater. Chem. 16(2006), pp. 626636.

[2] M.J. Rosseinsky,Recent Developments in Metal OrganicFramework Chemistry: Design, Discovery, PermanentPorosity and Flexibility, Microporous MesoporousMater. 73(2004), pp. 15-30 .

[3]Q. Ouyang, Y.-Z. Zhu, C.-H. Zhang, K.-Q. Yan, Y.-C. Liand J.-Y. Zheng, An Efficient PIFA-Mediated Synthesisof Fused Diporphyrin and Triply-Singly InterlacedlyLinked Porphyrin Array, Org. Lett.11( 2009), pp. 5266-5269.

[4] T. Ohmura, A. Usuki, K. Fukumori, T. Ohta, M. Ito andK. Tatsumi, New Porphyrin-Based Metal-OrganicFramework with High Porosity: 2-D Infinite 22.2-Square-Grid Coordination Network, Inorg. Chem. 45(2006), pp. 7988-7990.

[5] E.-Y. Choi, P.M. Barron, R.W. Novotny, H.-T. Son, C.Hu and W. Choe, Pillared Porphyrin HomologousSeries: Intergrowth in Metal-Organic Frameworks,Inorg. Chem. 48(2009), pp. 426-428.

[6] F.X.L. Xamena, A. Abad, A. Corma and H. Garcia,

MOFs as Catalysts : Activity, Reusability and Shape-Selectivity of a Pd-containing MOF, J. Catalysis. 250(2007), pp. 294298.

[7] S. Minghao, W. Di, W. Jingyuan and L. Yaoxian, Thesynthesis and characterization of tetra(4-carboxyphenyl)porphyrin and it metal complexes,J. A.m. Chem.Soc.44(2003), pp. 762-763.

[8] J.K. Laha, S. Dhanalekshmi, M. Taniguchi, A. Ambroise

and J.S. Lindsey, A Scalable Synthesis of Meso-Substituted Dipyrromethanes, Org. Proc. Res. Dev. 7(2003), pp. 799812.

[9] J.-W. Ka and C.-H. Lee, The Synthesis of 5,10-Disubstituted Tripyrromethane, Tetrahedron Lett. 41(2000), pp. 4609-4613.

[10] T. Ikeda, N. Aratani, S. Easwaramoorthi, D. Kim andA. Osuka, Meso-Doubly Linked Zn(II) PorphyrinTrimers: Distinct Anti-Versus-Syn Effects on TheirPhotophysical Properties, Org. Lett. 11 (2009), pp.3080-3083.

[11] D.W. Smithenry, S.R. Wilson and K.S. Suslick, ARobust Microporous Zinc Porphyrin Framework Solid,Inorg. Chem. 42(2003), pp. 7719-7721.

56

desarrollo de peliculas de empacado a partir de bioplastico de acido polilactico con plastificantes

Documents