Composites Science and Technology 68 (2008) 2739–2747

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Composites Science and Technology

journal homepage: www.elsevier .com/ locate/compsci tech

Morphology and mechanical properties of PET by incorporationof amine-polyhedral oligomeric silsesquioxane

Hong-Un Kim a,*, Yun Hyuk Bang a, Soo Myung Choi a, Kwan Han Yoon b

a Tire Reinforcement Team, Production R&D Center, R&D Business Lab., Hyosung Corporation, Kyonggi 431-080, Republic of Koreab Department of Polymer Science and Engineering, Kumoh National Institute of Technology, Gyeongbuk 730-701, Republic of Korea

a r t i c l e i n f o

Article history:Received 21 August 2007Received in revised form 19 March 2008Accepted 28 May 2008Available online 6 June 2008

Keywords:A. Modulus retentionA. NanocompositeB. ReinforcementB. Mechanical propertiesC. Thermal properties

0266-3538/$ - see front matter � 2008 Elsevier Ltd. Adoi:10.1016/j.compscitech.2008.05.020

* Corresponding author. Tel.: +82 31 428 1433; faxE-mail address: hukim@hyosung.com (H.-U. Kim).

a b s t r a c t

Amine-polyhedral oligomeric silsesquioxane(AM-POSS)/poly (ethylene terephthalate) (PET) nanocompos-ites were prepared using in situ polymerization. The thermal decomposition temperatures of the compos-ites, measured at a 5 wt.% weight loss, were 5–10 �C higher than those of PET. There was no significantchange in the other thermal properties. The SEM observations suggest that there was an obvious phase sep-aration in the POSS/PET composites. The nanocomposites that contained 1 wt.% of aminoisobutyl-POSS(AM-POSS-1) showed fine dispersions of POSS (less than 80 nm in diameter), which arose from the stronginterfacial interactions between POSS and PET during the polymerization. The nanocomposite that con-tained liquid aminoisooctyl-POSS (AM-POSS-2) showed both the particles that arose from the reactionand the liquid drops that did not react during the polymerization. The viscosity of the composites increasedwith the addition of POSS, except for the AM-POSS-2/PET composites at high concentrations. In the nano-composite film that contained 1 wt.% of AM-POSS-1 and AM-POSS-2, the tensile strength increased by63% and 35%, respectively, and the modulus, by 300% and 280%, respectively. The storage modulus retentionat 120 �C kept 45% for the AM-POSS-2/PET composite fiber at 1 wt.% loading.

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1. Introduction

Silicon-based organic/inorganic hybrid nanocompounds havebeen studied for the development of new materials with the prop-erties of both organic and inorganic materials. Polyhedral oligo-meric silsesquioxanes (POSS), the formula of which is [RSiO1.5]n,are being studied for the preparation of truly molecularly dispersedcomposites. POSS reagents can be incorporated into polymerchains to modify the local structure and chain mobility of poly-meric materials, which eventually show enhanced properties suchas mechanical, thermal, and other physical properties compared tothose of pristine polymer systems. Unlike silica, silicones, and fill-ers, however, each POSS molecule contains a non-reactive organicsubstituent and one or more covalently bonded reactive function-alities suitable for grafting, polymerizing, or blending with com-mon organic polymers. Furthermore, if the polymerizable Rgroups are selected properly [1–5], the organic components canbe varied to control the cross-linking density about the cube, thesegment distances between the cross-links, the packing of individ-ual cubes with respect to one another, and the stability of the cube-organic bond.

The incorporation of POSS reagents that contain reactive groupsinto organic polymer systems creates the possibility of nanoscale

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reinforcement, with POSS bound to the polymer chain with chem-ical bonds. A number of recent literature describe POSS/polymercovalent composites, including POSS/HDPE [6], POSS/polypropyl-ene [7], POSS/epoxy [8–11], POSS/PMMA [12–15], POSS/polyure-thane [16,17], POSS/PET [18–20] and POSS/polycarbonate [21].Recently, Zheng et al. [8–11,16] reported that the morphology ofthe resulting hybrids was quite dependent on the types of substit-uents R on the POSS monomers, and that the dynamic moduli ofthe hybrids was significantly higher than those of control epoxyand polyurethane. Cohen et al. [13] investigated the thermome-chanical properties of PMMA by blending two types of acrylic-POSS(unmodified and hydrogenated) with PMMA. They found that bothPOSS species have a plasticizing effect on PMMA by lowering theglass transition temperature and decreasing the melt-state visco-elastic moduli measured in a small-amplitude oscillatory shearflow. Schiraldi et al. [19] studied PET composite fibers made withthree types of POSS additives. Significant increases in the tensilemodulus and strength were achieved with non-reactive POSS.The high-temperature moduli of the PET/POSS nanocompositefibers were found to be rather variable, likely due to the modestcompatibility between the filler and the polymers, which can leadto structural anisotropy within the composite.

In this study, monofunctional POSS (aminopropyl isobutyl andaminopropyl isooctyl-POSS) were incorporated into PET with insitu polymerization. The dispersion of the POSS molecules intothe PET matrix through the reaction between the amine group on

2740 H.-U. Kim et al. / Composites Science and Technology 68 (2008) 2739–2747

POSS and the amine group on PET was investigated by analyzingthe morphology and the thermal, rheological, and mechanicalproperties.

2. Experimental

2.1. Materials

Two kinds of amine-POSS-aminopropyl isobutyl (AM-POSS-1)and aminopropyl isooctyl (AM-POSS-2) were used. They were pur-chased from Hybrid Plastics, Inc. (Hattiesburg, MS). AM-POSS-1consisted of white powders and AM-POSS-2, of viscous liquid.The chemical structures of the two AM-POSS’s are shown inFig. 1. Dimethyl terephthalate (DMT) and ethylene glycol (EG) wereobtained from SK Chemicals Co. (Korea) and Daejung Co. (Korea),respectively.

2.2. Preparation of POSS/PET nanocomposites

To prepare the POSS/PET nanocomposites, the POSS moleculeswere dispersed in EG using an ultrasonic homogenizer for betterdispersion. The dispersed EG solution was found to have beenslightly unclear due to POSS. The EG solution with the dispersedPOSS and DMT were mixed in a polymerization vessel at a molarratio of 2:1. A manganese (Mn) catalyst was used for the esterifica-tion, and the reaction was performed at 230 �C for 5 h to obtainmethanol with a similar theoretical value. Thereafter, a smallamount of TMP catalyst as a thermal stabilizing agent was added,after which an antimony (Sb) catalyst was added to perform poly-condensation in a vacuum at 280 �C for 2 h to obtain POSS/PETnanocomposites. The polycondensation time became shorter thanwith pure PET. This was caused by the characteristics of POSS.The POSS/PET nanocomposites that were obtained from the addi-tion of 1, 3, and 5 wt.% of POSS based on the total weight of thepolymers were dried in a vacuum oven at 70 �C, which was thesame as the crystallization temperature, for 24 h. The compositeswere hot-pressed to a thickness of about 200 lm. The film thatwas obtained was cut into a rectangle that was 80 mm long and15 mm wide. The specimens were extended four times in a hotchamber equipped with an Instron instrument. The POSS/PETnanocomposite fiber was prepared with a capillary rheometer(Capillary Rheometer Model 8052, KAYENESS Inc, USA) at 265 �Cand quenching at room temperature. This fiber was sufficientlystretched in an oil bath in a passive mode, washed with carbon tet-rachloride, and then dried at a normal temperature.

2.3. Measurements

The thermal stability of POSS was evaluated as follows. A ther-mogravimetric analysis (TGA) was performed to examine the ther-

Fig. 1. Typical chemical structures of POSS molecules: (a) amin

mal stability of POSS and the POSS/PET nanocomposites. Before theTGA analysis, all the samples were sufficiently dried in a vacuumoven at 40 �C. The mass loss was traced as the samples were heatedat a rate of 10 �C/min from 30 �C to 800 �C under nitrogen.

The thermal behavior of the POSS/PET nanocomposites wasmeasured using DuPont 910 differential scanning calorimetry(DSC). The glass transition, melting, and crystallization tempera-ture were determined at the heating and cooling rate of 20 �C/min.

The dispersion and morphology of the POSS/PET nanocompos-ites were analyzed with field emission scanning electron micros-copy (FE-SEM, JSM-6700F, Jeol Co., Japan). The samples wereprepared at 280 �C through compression molding, and fracturedat cryogenic temperature after immersion in liquid nitrogen.

To study the reaction between POSS and PET, a 500 MHz FT-NMRspectrometer (Bruker AMX-500) was used. The mixed solvents thatwere used were deuterated trifluoroacetic acid/chloroform (70/30,v/v). The inherent viscosity of PET and the POSS/PET nanocompos-ites was measured with a mixed solvent of phenol/tetrachloroeth-ane (60/40, v/v) at 35 �C. The inherent viscosity of the sampleswas 0.55–0.72 dL/g.

The storage modulus and tand of the nanocomposite fiber weremeasured with a dynamic mechanical analyzer (DMA, DMA7e, Per-kin Elmer) that was connected to an intra-cooler cooled by He gas.The measuring temperature range was 30–180 �C at the heatingrate of 5 �C/min. The static force, dynamic force, and frequencywere 50 mN, 30 mN, and 1 Hz, respectively.

The mechanical properties of the nanocomposite films weremeasured using an Instron model 4467 universal instrument. Themeasurements were made at room temperature at a constantcrosshead speed of 2 mm/min. Data were taken as averages of atleast five measurements.

Dynamic rheological measurements were performed using arotational rheometer (PHYSICA Rheo-Lab MC120). The measure-ments were carried out in an oscillatory shear mode using parallelplate geometry. Prior to any measurement, all the samples were al-lowed to relax at the measuring temperature for 2 min, and thensheared at a low shear rate (0.01 s�1) for 3 min under a nitrogenatmosphere. Frequency sweeps were performed from 0.1 to100 rad/s.

Wide-angle X-ray diffraction measurements were performedwith a Rigaku (D/Max-IIIB) X-ray diffractometer, using Ni-filteredCu Ka radiation.

3. Results and discussion

3.1. Characterization of POSS/PET nanocomposites

A series of POSS/PET nanocomposites that contained smallamounts of two AM-POSS was prepared through in situ polymeri-zation. The 1H NMR spectra of PET and the AM-POSS/PET nanocom-

opropyl isobutyl-POSS and (b) aminopropyl isooctyl-POSS.

H.-U. Kim et al. / Composites Science and Technology 68 (2008) 2739–2747 2741

posites are shown in Fig. 2. Two main peaks are shown for PET: onefor the ethylene unit (4.8 ppm) and the other for the aromatic unit(8.1 ppm). In addition to these two peaks, the AM-POSS/PET nano-composites showed a new peak at around 1 ppm. This arose fromthe side R group (isobutyl for AM-POSS-1 and isooctyl for AM-POSS-2) in POSS. This does not prove that the reaction betweenPOSS and PET occurred during the polymerization, as it could haveresulted from the unreacted POSS.

3.2. Thermal properties of POSS/PET/ nanocomposites

Thermal analyses of the POSS/PET nanocomposites were doneusing DSC(DuPont Instruments, DuPont 910). The melting, glasstransition, and crystallization temperatures that were determinedfrom the heating and cooling scans of PET and the POSS/PET nano-

Fig. 2. H NMR spectra of PET and PET/POSS

composites are listed in Table 1. The Tg values of the AM-POSS-1/PET nanocomposite decreased slightly with increases in the POSSconcentration. It was found that the incorporation of smallamounts (less than 3–4 mol.%) of POSS acts as an inert diluent,and actually reduces the glass transition temperature [22]. The5 wt.% of POSS used in this work corresponds to 0.5 mol.%. The Tg

of the AM-POSS-2/PET nanocomposite showed a slight increaseat 1 wt.% loading, however, which indicates the strong interfacialinteraction between AM-POSS-2 and PET that resulted in the pre-vention of the mobility of the PET chain. In higher concentrations,unreacted liquid AM-POSS-2 acts as a plasticizer and causes a de-crease in Tg. The melting temperatures of the composites were veryclose to that of pure PET, and slightly decreased with the POSS con-centration, except for 1 wt.% of the AM-POSS-2/PET nanocompos-ite. The PET crystallization temperature decreased by up to

composites containing 5 wt.% of POSS.

Table 1Thermal properties of PET and PET/POSS composites

PET/POSS samples Tg (�C) Tm (�C) Tcc (�C)a Td (�C)b

PET 75 256 176 400AM-POSS-1 244AM-POSS-1/PET1 wt.% 75 255 173 4093 wt.% 70 252 169 4075 wt.% 67 248 187 405

AM-POSS-2 330AM-POSS-2/PET1 wt.% 77 259 165 4093 wt.% 73 248 189 4075 wt.% 72 252 182 408

a Crystallization peak temperature at a cooling rate of 20 �C/min from melt.b Values measured at 5 wt.% of weight loss.

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3 wt.% of AM-POSS-1 and 1 wt.% of AM-POSS-2, and increased by5 wt.% of AM-POSS-1 and by more than 3 wt.% of AM-POSS-2. Verysmall amounts of the POSS molecules that were incorporated intoPET reacted with PET, which resulted in decreases in the crystalli-zation temperature due to the copolymerization effect. At higher

Fig. 3. FE-SEM micrographs of POSS/PET nanocomposites: (a) AM-POSS-1-1 wt.%, (b) A

concentrations, however, the POSS molecules started to agglomer-ate and acted as nucleating sites, so that the composite crystalliza-tion temperatures increased although the POSS molecules and PETinteracted.

The decomposition temperatures listed in Table 1 indicate amoderate increase in the thermal stability of the nanocomposites.The decomposition temperatures measured at 5% weight loss were5–10 �C higher than those of PET. Schiraldi et al. [23] reported thatwhen trisilanol isooctyl-POSS was heated to the PET processingtemperature of 280 �C under nitrogen, it resulted in the productionof a resinous organosilicate material, but no differences in the ther-mo-mechanical properties of the POSS-polymer composite wereobserved. Therefore, the slight increase in the decomposition tem-perature under nitrogen may have been due to the reaction be-tween the POSS molecules and PET.

3.3. Dispersion of POSS within POSS/PET nanocomposites

Fig. 3 shows the morphologies of the AM-POSS/PET nanocom-posites. The dispersed particles are attributed to the POSS phases.The AM-POSS-1/PET nanocomposites that contained 1 wt.% Fig.3a showed a uniform dispersion of AM-POSS-1, with a size of

M-POSS-1-5 wt.%, (c) AM-POSS-2-1 wt.%, and (d) AM-OISS-2-5 wt.%, respectively.

H.-U. Kim et al. / Composites Science and Technology 68 (2008) 2739–2747 2743

approximately 80 nm. In higher concentrations, as shown in Fig.3b, the AM-POSS-1 molecules tended to agglomerate in the poly-mer matrix due to the POSS-POSS self-assembly. This is interestingto see in Fig. 3c and d. Since AM-POSS-2 is a viscous liquid, the par-ticles in the morphology should not be observed. The AM-POSS-2/PET nanocomposite that contained 1 wt.% showed particles, how-ever, although they were more than 100 nm big. This suggests thatthe particles resulted from the reaction between AM-POSS-2 andPET. In higher concentrations, both unreacted AM-POSS-2, whichcame in the form of liquid drops that were pulled out from thePET matrix, and particles were observed. To confirm the existenceof particles, the X-ray diffraction of the POSS/PET nanocompositeswas measured. The results are shown in Fig. 4. For the AM-POSS-1/PET nanocomposites, a weak diffraction at around 2h = 8� was ob-served in the concentration of more than 3 wt.%, which is a typicalpeak of POSS. Since AM-POSS-2 was a liquid, it should not produce

2

Inte

nsity

(a.u

.)

0 10 20

Inte

nsity

(a.u

.)

0 10 20

a

b

θ

2 θ

Fig. 4. XRD patterns of (a) AM-POSS-1/PET a

an X-ray diffraction peak. Therefore, the peak shown in Fig. 4b im-plies that AM-POSS-2 changed to a solid in the composite, presum-ably through the degradation of amine groups at the hightemperature of polycondensation or through reaction with PET.To check the occurrence of degradation, AM-POSS-2 was heatedin a differential scanning calorimeter pan at 280 �C for 10 min. Itdid not change into a solid from degradation. It is thus surmisedthat the peak at around 2h = 8� resulted from the partial reactionof AM-POSS-2 with PET, even though a phase separation was ob-served in SEM. This is evidence that AM-POSS-2 was chemicallyincorporated into PET to form an AM-POSS-2/PET nanocomposite.

3.4. Complex viscosities of POSS/PET nanocomposites

The frequency dependence of the complex viscosity of the POSS/PET nanocomposites is shown in Fig. 5. The values were measured

PET

AM-POSS-1/PET 1wt%

AM-POSS-1/PET 3wt%

AM-POSS-1/PET 5wt %

30 40

PET

AM -POSS-2/PET 1wt %

AM -POSS-2/PET 3wt %

AM -POSS-2/PET 5wt %

50

30 40 50

nd (b) AM-POSS-2/PET nanocomposites.

Frequency (rad/s)10-1 100 101 102 103

Com

plex

vis

cosi

ty (P

a.s)

101

102

103

104

105

PETAM-POSS-1/PET 1wt%AM-POSS-1/PET 3wt%AM-POSS-1/PET 5wt%

Frequency (rad/s)10-1 100 101 102 103

Com

plex

vis

cosi

ty (P

a.s)

101

102

103

104

105

PETAM-POSS-2/PET 1wt%AM-POSS-2/PET 3wt%AM-POSS-2/PET 5wt%

a

b

Fig. 5. Complex viscosities of (a) PET and AM-POSS-1/PET nanocomposites and (b) PET and AM-POSS-2/PET nanocomposites.

2744 H.-U. Kim et al. / Composites Science and Technology 68 (2008) 2739–2747

at 280 �C. In terms of the AM-POSS-1/PET nanocomposite, theincorporation of AM-POSS-1 led to increases in the complex viscos-ity with increases in the POSS concentration. The relative effectdiminished with increasing frequency, however, due to the shearthinning. For the AM-POSS-2/PET nanocomposites, the viscosityvalue of 1 wt.% nanocomposite was higher than 2 wt.% compositeat a low frequency, and highest in the high-frequency region.Had no reaction occurred in the AM-POSS-2/PET nanocomposites,their viscosity would have been expected to be low due to the slip-page of the matrix, which was composed of the low-viscosity AM-POSS-2 and the highly viscous PET. The viscosities of the AM-POSS-2/PET nanocomposites were higher than those of PET, however,

indicating that a reaction between AM-POSS-2 and PET might haveoccurred. The viscosity value of the AM-POSS-2/PET nanocompos-ites was lower than that of the AM-POSS-1/PET nanocompositesdue to the unreacted AM-POSS-2, which was a liquid.

3.5. Mechanical properties of POSS/PET nanocomposites

The tensile strength and modulus of PET and the POSS/PETnanocomposite films are shown in Fig. 6. The strength of theAM-POSS-1/PET nanocomposites increased by 63% at 1 wt.% andby 6% at 3 wt.%, and decreased by 25% at 5 wt.%, compared to thatof PET. The strength of the AM-POSS-2/PET nanocomposites in-

POSS Content (wt%)

Stre

ngth

(MPa

)

0

10

20

30

40

50

60

70

80

AM-POSS-1/PETAM-POSS-2/PET

0 1 5

POSS Content (wt%)

Mod

ulus

(GPa

)

0

1

2

3

4

5

6

AM-POSS-1/PETAM-POSS-2/PET

0 3

3

1 5

a

b

Fig. 6. (a) Tensile strengths of PET and POSS/PET nanocomposites and (b) tensile moduli of PET and POSS/PET nanocomposites with increasing POSS content.

H.-U. Kim et al. / Composites Science and Technology 68 (2008) 2739–2747 2745

creased by 35% at 1 wt.% and by 9% at 3 wt.%, and decreased by 46%at 5 wt.%. The modulus of the AM-POSS-1/PET nanocomposites in-creased by about 300% at 1 wt.% and 150% at 3 wt.%, and decreasedby 24% at 5 wt.%, compared to that of PET. The modulus of the AM-POSS-2/PET nanocomposites increased by 280% at 1 wt.% and by175% at 3 wt.%, and decreased by 3% at 5 wt.%. The modulus ofthe AM-POSS-1/PET nanocomposite at 5 wt.% significantly de-creased as larger POSS crystallites significantly weakened thematerial. The POSS/PET nanocomposites at 1 wt.% loading of POSSshowed the largest tensile strength and modulus due to the dom-inance of phase-separated crystallites with relatively small diame-ters (d < 80 nm).

As for thermal properties, the AM-POSS-2/PET nanocomposite at1 wt.% loading showed a slight increase in the glass transition andthe melting temperature compared to those of PET. Thus, at this con-

centration, the nanocomposite was expected to have shown anincrease in its modulus at the higher temperature. The dynamic-storage modulus and tand of PET and the AM-POSS-2/PET nanocom-posite fiber were measured using DMA and are shown in Fig. 7. Themeasurements were carried out two times to ensure their reproduc-ibility. As expected, the storage modulus for the filament of theAM-POSS-2/PET nanocomposite at 1 wt.% loading was retained at ahigher temperature than that of PET. This resulted from the interac-tion between AM-POSS-2 and PET. The Tg value at the peak of tand isshown in Fig. 7b. The Tg of AM-POSS-2/PET at 1 wt.% loading in-creased by approximately 30 �C compared to that of pure PET. Schir-aldi et al. [19] reported that the modulus retention at 120 �C is kept at90% for 5 wt.% of TSIO-POSS. There was no mention of reproducibilityin their report, though. The modulus retention in this study wasapproximately 45%, which shows good reproducibility.

Temperature (ºC)0 20 40 60 80 100 120 140 160 180

Stor

age

Mod

ulus

Ret

entio

n (%

)

0

20

40

60

80

100PET,1stPET,2ndAM-POSS-2/PET,1stAM-POSS-2/PET,2nd

Temperature (ºC)

tan

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

PET,1stPET,2ndAM-POSS-2/PET,1stAM-POSS-2/PET,2nd

0 20 40 60 80 100 120 140 160 180

a

b

δ

Fig. 7. Dynamic storage modulus (a) and tand (b) of PET and AM-POSS-2/PET nanocomposites fiber containing 1 wt.% of AM-POSS-2. (Measurements were carried out twotimes.)

2746 H.-U. Kim et al. / Composites Science and Technology 68 (2008) 2739–2747

4. Conclusions

In this study, the POSS/PET nanocomposites that contained ami-noisobutyl POSS (AM-POSS-1) and aminoisooctyl POSS (AM-POSS-2) were prepared using in situ polymerization. The thermal proper-ties of the nanocomposites were no different from those of PET, butthe thermal decomposition temperature of the nanocomposites,measured at a 5 wt.% weight loss, increased by 5–10 �C. Themorphology of the nanocomposites that contained 1 wt.% of AM-POSS-1 indicated fine dispersions of AM-POSS-1, with an approxi-mate size of 80 nm, due to the strong interfacial interactionbetween AM-POSS-1 and PET during the polymerization. At higherconcentrations of AM-POSS-1, aggregates were observed. The mor-phology of the nanocomposites that contained 1 wt.% of AM-POSS-2 showed particles even though AM-POSS-2 was liquid. At higherconcentrations of the unreacted AM-POSS-2, liquid drops were ob-

served. Their morphologies were confirmed with complex viscosityanalysis, which showed low viscosity values compared to the AM-POSS-1/PET nanocomposites. In the nanocomposite film that con-tained 1 wt.% of AM-POSS-1 and AM-POSS-2, the tensile strengthincreased by 63% and 35%, respectively, and the modulus, by300% and 280%, respectively. The storage modulus of the nanocom-posite fiber at 1 wt.% loading of AM-POSS-2 at a high temperaturewas retained, unlike pure PET.

Acknowledgements

This work was supported by Grant No. 10017138 of the Next-generation Advanced Technology Development Project of the Min-istry of Commerce, Industry and Energy and by the Research Fundof Hyosung Corporation.

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