ORI GIN AL PA PER

Shape memory thermoplastic elastomer from maleatedpolyolefin elastomer and nylon 12 blends

Myung Chan Choi • Ji-Yeon Jung •

Young-Wook Chang

Received: 9 April 2013 / Revised: 26 September 2013 / Accepted: 13 November 2013 /

Published online: 21 November 2013

� Springer-Verlag Berlin Heidelberg 2013

Abstract Semicrystalline maleated polyolefin elastomer (mPOE) and nylon 12

were melt blended in an internal mixer at 200 �C with proportions of 90/10, 80/20,

and 70/30 wt/wt, respectively. Molau test, melt viscosity measurement, differential

scanning calorimetry, dynamic mechanical analysis and tensile testing were con-

ducted to characterize the structure and properties of the blends. The results

revealed that POE-graft-nylon 12 copolymer was formed during the mixing, and the

blends show two melting transitions at 57–60 and 174–178 �C attributed to mPOE

and nylon 12, respectively, which are dependent on the blend composition. The

blends exhibit typical thermoplastic elastomeric behavior and their tensile modulus,

strength and hardness increase with increasing nylon content. It was also observed

that the blends form a physically crosslinked structure until the melting transition of

nylon 12. The blends exhibit excellent thermally triggered shape memory effect,

i.e., almost 100 % shape fixity rate and 100 % shape recovery rate, and the recovery

occurs in a few seconds when the temporarily fixed shaped sample is heated just

above the Tm of mPOE phase in the blends.

Keywords Thermoplastic elastomer � Shape memory effects � Polyolefin

elastomer � Nylon 12 � Blends

Introduction

Thermoplastic elastomers (TPE) are important class of materials due to their

elastomeric properties like vulcanized rubber at normal service temperatures and

M. C. Choi � J.-Y. Jung � Y.-W. Chang

Department of Bionano Technology, Hanyang University, Ansan, Kyunggi-Do, Korea

Y.-W. Chang (&)

Department of Chemical Engineering, Hanyang University, Ansan, Kyunggi-Do, Korea

e-mail: ywchang@hanyang.ac.kr

123

Polym. Bull. (2014) 71:625–635

DOI 10.1007/s00289-013-1081-2

melt processibility at high temperatures like thermoplastics such as polyethylene

and polypropylene [1, 2]. Since TPE is easy to use and easy to recycle, the amount

that is used is increasing every year, and much efforts have been made to develop

the TPEs with high performance and functionalities to meet the demands of variety

of applications.

Blending of a thermoplastic and an elastomer has been regarded as an effective

way to prepare the TPEs [3–11]. The blend-based TPEs, in general, have phase-

separated structure, in which rubber phase provides elastic recoverability upon

mechanical deformation while thermoplastic phase allows the melt processing of the

blends. As compared to segmented or block copolymer type TPEs, the blend-based

TPEs can provide desirable performance properties in a cost-effective way by

proper combinations of commercially available polymers with varying composi-

tions and by the incorporation of suitable additives such as fillers and crosslinking

agents.

Reactive blending of a plastic with a reactive rubber has been extensively studied

to prepare toughened plastics or TPEs, which mainly include the blends of nylons

with functionalized rubbers such as acryl rubber [11], epichlorohydrin rubber [12,

13] and maleated rubbers [14–18]. In these blends, rubber-graft-nylon copolymer is

formed during the mixing via the reaction of amine end group of the nylon with a

functional group existed on the elastomers, which prevents the macrophase

separation of the two polymers and provides synergistic properties to the blends.

Nylon 12, an important semicrystalline engineering plastic, possesses high

strength and toughness, abrasion resistance, dimensional stability and chemical

resistance. Such properties make this polymer very useful in a wide variety of

industrial applications such as machinery, electronic equipment, automobiles, and

the information industries [19]. Multiblock copolymer type TPEs with nylon 12 as a

hard segment has been commercialized as a trade name of Pebax� [20]. But, TPEs

from the blends of nylon 12 and functionalized rubbers have not been reported yet.

In this article, we report that TPEs with a thermally triggered shape memory

effect can be simply prepared by a reactive blending of semicrystalline maleated

polyolefin elastomer (mPOE) with nylon 12. Polymers with shape memory effect,

termed shape memory polymers, are smart material which can recover to its original

shape after being deformed into a temporary shape when it is heated or receives any

other stimuli [21, 22]. The shape memory behavior can often be observed for some

polymer blends [23–26]. But, to the author’s knowledge, the blend-based TPEs

exhibiting shape memory effect have not been reported.

Experimental

Materials and blend preparation

Nylon 12 (Rilsan AESNO TL) was purchased from Arkema Inc. Semicrystalline

maleated polyolefin elastomer (hereafter referred to as mPOE, Amplify TM GR

216) with maleic anhydride content about 1.0 wt% was procured from Dow

Chemical Company.

626 Polym. Bull. (2014) 71:625–635

123

The mPOE/nylon 12 blends with the blend composition of 90/10, 80/20, and

70/30 wt/wt were prepared by a melt blending in a Haake internal mixer at 200 �C

for 10 min (within this time period torque was stabilized) at a rotor speed of 60 rpm.

The mixture was then molded as sheet at 190 �C to obtain test specimens for the

property measurements.

Characterization

The melting temperature (Tm) and heat of fusion (DHm) of the samples were

determined using differential scanning calorimeter (TA Instruments DSC 2010).

Samples (10 mg) were dried completely in a vacuum oven and then used for the

analysis. They were first heated to 220 �C at a rate of 20 �C min-1 under nitrogen

atmosphere and kept for 10 min at this temperature to remove prior thermal history.

The samples were then cooled to -100 �C immediately, and were reheated to

200 �C at a rate of 10 �C min-1 (second scan). The Tm and DHm of the samples

were determined from this second scan.

Melt viscosity of the samples was measured using small amplitude oscillatory

shear rheometer (RMS 800 Instrument, Rheometrics, Inc). The dynamic oscillatory

shear measurement was performed at 190 �C using a set of 25 mm parallel plate and

a sample of 1–2 mm thickness. The frequency sweep was carried out at a frequency

range of 0.1–100 rad/s at a strain 5 %, which is well within the linear viscoelastic

range.

Tensile properties were measured using a universal testing machine (Unites Co,

STM 10 E) at 25 �C at a crosshead speed 50 mm/min according to ASTM D 638. At

least 10 samples were used for the measurement. Tension set was measured to

evaluate the elastic recoverability of the samples by stretching the specimen to

100 % elongation and keeping them in that position for 10 min. The applied stress

was then released and the specimen was kept for 10 min. Tension set was

determined by a following formula:

Tension set %ð Þ ¼ change in length=original lengthð Þ � 100

Dynamic mechanical analysis was performed using a dynamic mechanical analyzer

(TA Instrument 2980). Samples were subjected to a cyclic tensile strain with an

amplitude 0.2 % at a frequency of 1 Hz. The temperature was increased at a heating

rate 10 �C/min over the range from -100 to 200 �C

The phase morphology of the blends was observed by scanning the fracture

surface using field-emission SEM (JEOL JSM-630F) at an accelerating voltage of

15 kV. The sample was prepared by fracturing the compression-molded specimen

cryogenically. The fractured surface was sputter-coated with gold.

Results and discussion

Thermal characterization of the mPOE/nylon 12 blends was carried out using DSC

measurements. The second heating thermograms for pure mPOE, pure nylon 12 and

the mPOE/nylon 12 blends are shown in Fig. 1, and melting temperature(Tm), heat

Polym. Bull. (2014) 71:625–635 627

123

of fusion (DHm), and associated degree of crystallinity (vc) obtained from the DSC

thermograms are listed in Table 1.

The degree of crystallinity of mPOE and nylon 12 in the blends was calculated using

the heat of fusion per gram of each polymers determined from DSC measurements and

the heat of fusion corresponding to 100 % crystalline LDPE (293 J/g) [27] and 100 %

crystalline nylon 12 (209 J/g) [28], respectively. As observed from the thermograms,

all of the blends show two endothermic peaks. The first melting peak at about 60 �C is

attributed to mPOE and the second one at about 175 �C to nylon 12.

The presence of two melting transitions in the blends indicates that the blends

form a phase-separated structure. In addition, the Tm and vc of the each component

in the blends decrease with blend composition, as illustrated in Table 1. The

lowering of Tm and vc of the crystalline components in the blends with respect to the

pure polymers is generally observed when there are thermodynamically favorable

interactions between the component polymers in the blends [27, 29]. In the blends of

-150 -100 -50 0 50 100 150 200 250

endo

Hea

t Flo

w(m

W)

e

xo

(i)

(ii)

(iii)

(iv)

(v)

(i) neat mPOE

(ii) mPOE/nylon 12 (90/10)

(iii) mPOE/nylon 12 (80/20)

(iv) mPOE/nylon 12 (70/30)

(v) neat nylon 12

Temperature (°C)

Fig. 1 DSC thermograms of neat mPOE, neat nylon 12, and mPOE/nylon 12 blends

Table 1 Thermal characteristics of samples

Samples Tm of

mPOE (�C)

DHm of

mPOE (J/g)

vc of

mPOEa (%)

Tm of nylon

12 (�C)

DHm of nylon

12 (J/g)

vc of nylon

12a (%)

Neat mPOE 62.6 26.9 9.2 – – –

Neat nylon 12 – – 178.3 47.2 22.6

mPOE/nylon 12

90/10 60.3 21.7 8.2 174.3 4.1 19.6

80/20 58.3 17.8 7.6 175.5 8.7 20.8

70/30 57.2 14.0 6.8 176.5 13.6 21.7

a vc = 100 9 (DHm�/DHm�)/w, where DHm� is the heat of melting for 100 % crystalline POE (293 J/g)

[27], 100 % crystalline nylon 12 (209 J/g) [28] and w is the weight fraction of each component in the

blends

628 Polym. Bull. (2014) 71:625–635

123

mPOE with nylon 12, POE-graft-nylon 12 can be formed during the melt mixing via

the reaction between the maleic anhydride of mPOE and amine group at the end of

the nylon 12 chain, which has been generally observed in blends of various nylons

with maleated polymers [15–18, 23]. Such a graft copolymer formation depresses

the crystallization of each component in the blends.

The formation of POE-g-nylon 12 graft copolymers obtained during the melt-

blending process was confirmed by Molau test, which was well accepted as a good

method to verify the presence of graft copolymers of the components in the reactive

blend systems [30, 31]. Since POE is the major component in our samples, toluene

was chosen as the testing agent. Simple mixture of mPOE and nylon 12 was

prepared by mixing the mPOE and nylon 12 in an internal mixer for less than 1 min

(which is not sufficient time to form graft copolymer during the blending) and the

mixture was dissolved in toluene. In this case, the POE was seen to dissolve into

toluene within 3–5 h and forms a transparent solution, while nylon 12 precipitated

in the form of white flakes because toluene is not a good solvent for the nylon 12

(Fig. 2a). When the same experiment was repeated for the mPOE/nylon 12 blend

prepared by mixing them for 10 min, a light milky-white emulsion was obtained

and this emulsion was stable (Fig. 2b). This indicates that POE-graft-nylon 12

copolymer was formed by the melt blending of mPOE and nylon 12.

Such a graft copolymer formation was also confirmed from the complex viscosity

measurement of the samples, as shown in Fig. 3. As is observed, the mPOE/nylon

12 blends showed higher complex viscosity than neat mPOE and neat nylon 12 over

all frequency range. The intermolecular bonding between the component polymers

in the mPOE/nylon 12 blends may restrict the movement of the polymer chains, thus

increasing the complex viscosity [14].

Stress–strain curves of the neat mPOE and mPOE/nylon 12 blends are shown in

Fig. 4, and the tensile properties are summarized in Table 2 along with the tension set

Fig. 2 Molau test. a Simplemixture of mPOE and nylon 12and b mPOE/nylon 12 blend

Polym. Bull. (2014) 71:625–635 629

123

values. It can be seen that the tensile modulus and tensile strength of the blends increase

with increasing nylon content. The elongation at break decreases with increasing nylon

content in the blends, and it is 650 % for mPOE/nylon 12 (70/30) blend.

Tension set was measured to evaluate the elastic recoverability of the samples. It

can be seen that the tension set increases with nylon content in the blends, but all the

blends show the tension set value less than 15 %, indicating that the blends studied

here, have good elastic recoverability.

The temperature dependence on dynamic storage modulus of pure mPOE and

mPOE/nylon 12 blends is shown in Fig. 5. The storage moduli for the blends are

higher than those of the neat mPOE over the whole temperature range examined

here, and the modulus increases with increasing nylon content in the blends. It can

Frequency(ω, rad/s)

0.01 0.1 1 10 100 1000

Com

plex

Vis

cosi

ty(η

∗, P

a s)

1e+1

1e+2

1e+3

1e+4

1e+5

1e+6

mPOE/nylon 12 (90/10)mPOE/nylon 12 (80/20)mPOE/nylon 12 (70/30)neat mPOEneat nylon 12

Fig. 3 Frequency dependence of complex viscosity (g*) of neat mPOE, neat nylon 12 and mPOE/nylon12 blends

Strain (%)

0 200 400 600 800 1000 1200

Str

ess

(MP

a)

0

2

4

6

8

10

12

14

16

neat mPOEmPOE/nylon 12 (90/10)mPOE/nylon 12 (80/20)mPOE/nylon 12 (70/30)

Fig. 4 Tensile stress–strain curves of neat mPOE and mPOE/nylon 12 blends

630 Polym. Bull. (2014) 71:625–635

123

be seen that there is a certain drop in the modulus at about 60 �C for all samples

which is associated with the melting of crystalline domain of the mPOE. Above the

melting transition of mPOE, the modulus keeps quite stable up to Tm of the nylon 12

for the blends. This indicates that the mPOE/nylon 12 blends form a physically

networked structure before the melting transition of nylon 12 occurs, in which nylon

12 domains act as physical crosslinks.

Field-emission SEM micrographs of cryogenically fractured surfaces of mPOE/

nylon 12 blends are shown in Fig. 6. Randomly dispersed particles were observed

and the particle size increases with increasing nylon content in the blends. Average

particle sizes are about 130, 200, and 600 nm in diameter for the mPOE/nylon

12 = 90/10, 80/20, 70/30 blends, respectively. The elemental composition of these

particles in the mPOE/nylon 12 (90/10) blend is given via an energy-dispersive

X-ray (EDX) spectrum (Fig. 6a), which shows high nitrogen content, confirming

that the dispersed particles are nylon 12 aggregates. This result clearly indicates that

the mPOE/nylon 12 blends have a phase-separated structure with nylon submicron

domains in the POE matrix and the nylon domains can act as physical crosslink

points.

Table 2 Tensile properties of neat mPOE and mPOE/nylon 12 blends

Samples 50 % tensile

modulus (MPa)

300 % tensile

modulus (MPa)

Elongation at

break (%)

Tensile

strength (MPa)

Tension

set (%)

Neat mPOE 2.2 ± 0.1 3.4 ± 0.1 1,230 ± 50 11.6 ± 1.0 8

mPOE/nylon 12

90/10 2.4 ± 0.1 3.9 ± 0.2 1,000 ± 50 12.1 ± 1.0 9

80/20 2.8 ± 0.2 5.3 ± 0.3 830 ± 30 13.2 ± 1.2 12

70/30 3.4 ± 0.2 7.7 ± 0.4 650 ± 20 14.1 ± 1.2 14

-150 -100 -50 0 50 100 150 200

Sto

rage

mod

ulus

(M

Pa)

0.01

0.1

1

10

100

1000

10000

neat mPOE mPOE/nylon 12 (90/10)mPOE/nylon 12 (80/20)mPOE/nylon 12 (70/30)

Temperature (°C)

Fig. 5 Variation of dynamic storage modulus with temperature for neat mPOE and mPOE/nylon 12blends

Polym. Bull. (2014) 71:625–635 631

123

We observed shape memory effects in the mPOE/nylon 12 blends, as

demonstrated in Fig. 7. Each sample was stretched to 100 % at 70 �C (which is

just above Tm of mPOE) and then cooled to 0 �C to obtain a temporarily fixed

sample. It was observed that, for all the blend samples, the temporarily deformed

shape is fixed well as deformed upon the cooling (100 % shape retention) and the

temporarily fixed sample recover to its original shape when it is heated just above

Tm of mPOE (100 % shape recovery ratio). The final shape recovery ratio (R) can be

evaluated by following equation:

R %ð Þ ¼ Ld�Lfð Þ= Ld�Loð Þ½ � � 100 %ð Þ

where Lo, Ld, and Lf are the original gauge length, the deformed length, and the final

recovery length of sample, respectively.

For the polymer to exhibit shape memory behavior, it must have two separated

phase, namely, stationary phases and reversible phase, where the stationary phase

with highest thermal transition stabilize the permanent shape and the reversible

phase serves as switch [21]. The mPOE/nylon 12 blends fulfill this structural

requirement, in which semicrystalline mPOE phase act as a reversible phase and

nylon 12 acts as a stationary phase. When the blend sample is stretched to a certain

level above the Tm of mPOE and then cooled, the sample can be fixed in its

Fig. 6 SEM micrographs and EDX spectrum of cryogenically fractured surfaces of mPOE/nylon 12blends: a 90/10, b 80/20 c 70/30

632 Polym. Bull. (2014) 71:625–635

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deformed state due to crystallization of mPOE. When the temporarily fixed sample

is heated above the Tm of mPOE, the crystalline domains of mPOE are melted and

the sample can be recovered elastically to its original shape. It is to be noted again

that formation of crosslinked structure is an important factor for the shape memory

effect of a polymer. As observed in SEM analysis, all the blends examined in this

study have a well phase-separated structure with dispersed nylon domains

130–600 nm in diameter at 10–30 wt% nylon 12 in the blends. The nylon domains

are covalently bonded to rubber phase, and thus the blends can form physically

crosslinked structure in which the nylon domains act as crosslink points even in the

blend with a low nylon content (mPOE/nylon 12 = 90/10). This leads to high shape

recovery of the blend.

The mPOE/nylon 12 blends can be contrasted with maleated HDPE (mHDPE)/

nylon 6 blends reported earlier [23]. The graft copolymers formed from the

mHDPE/nylon 6 blends showed shape memory effect but they are not elastomeric

because mHDPE is not a rubber. On the contrary, the mPOE/nylon 12 blends

reported in the present paper showed elastomeric behavior with shape memory

effects and melt processibility. Further, switching temperature of the shape recovery

to occur in this blend can be tuned around 60 �C (corresponding to Tm of mPOE

phase), while the temperatures for mHDPE/nylon 6 blends are higher than 100 �C.

Conclusions

This paper demonstrates that a thermoplastic elastomer with shape memory effects

could be prepared from reactive blending of maleated polyolefin elastomer (mPOE)

possessing a small degree of crystallinity with nylon 12. POE-graft-nylon 12

copolymer was formed during the melt mixing and exhibits elastomeric behavior

Fig. 7 Shape recovery process of mPOE/nylon 12 blend samples. (The recovery process was conductedat 70 �C)

Polym. Bull. (2014) 71:625–635 633

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with melt processibility when the nylon content is up to 30 wt% in the blend.

Thermally triggered shape memory effect was observed for the blends that are

attributed to the presence of semicrystalline mPOE phase acting as a reversible

phase and to a physically crosslinked structure of the blends. This shape memory

TPE may have diverse applications such as ergonomic grips, sports shields, and

toys.

Acknowledgments This work was supported by the research fund of Hanyang University, ERICA

Campus, Republic of Korea (HY-2012-P).

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