J. Magn. Soc. Jpn., 41, 66-69 (2017)
LetterEffect of Amorphous Region on Magnetic Orientation ofPoly(lactic acid)
Blend Films with Different Molecular Weight
Rei Nakayama, Hiroki Ikake*, Kimio Kurita*, Shigeru Shimizu*, Satoshi Kurumi*, Kaoru Suzuki*, Kohki
Takahashi** and Hiroyuki Nojiri**
Graduate School of Science and Technology, Nihon Univ., 1-8-14 Kanda Surugadai, Chiyoda-ku, Tokyo 101-8308, Japan*

College of Science and Technology, Nihon Univ., 1-8-14 Kanda Surugadai, Chiyoda-ku, Tokyo 101-8308, Japan**

Institute for Materials Research, Tohoku Univ., 2-1-1 Katahira, Aobaku, Sendai, Miyagi, JapanThe magnetic-field-induced blend films, poly(L-lactide)(PLLA10) (Mn = 1.0 × 105) and poly(DL-lactide) (Mw = 1.0 ×
104 (PDLLA1) and 1.0 × 105 (PDLLA10)) were prepared in isothermal process under the magnetic-field 10 T. The
effects of amorphous region, i.e., molecular weight of PDLLA effect on crystallization and orientation of PLLA in thefilms were investigated using wide-angle X-ray diffraction and polarizing microscopy. The crystallinity of each films
showed 60% at crystallization growth time tc = 30 hrs irrespective of PDLLA molecular weight. The degree oforientation of PLLA10/PDLLA10 film increased with increasing tc. We concluded that the blending with amorphous
high-molecular-weigh PDLLA and crystallization in an applied high magnetic field is effective to achieve the PLLA
film that has higher crystallinity and orientation.
Key words: magnetic-induced-orientation film, poly(L-lactide), poly(DL-lactide), amorphous, blend film, highmagnetic field
1. Introduction
Recently, biomass plastics are interest for saving
petroleum resources and reduction of carbon dioxide. Itis especially expected that the biomass plastics
produced from plant-derived raw materials. For
example, poly(lactic acid)(PLA) is well-known biomass
plastic which are produced from renewable resources
and used in many field such as biomedical, packaging
and ecological fields.
There has been an extensive effort to investigate for
PLA such as crystal structure, crystal growth, melting
behavior, and applications.1) Many researchers havestudied stereocomplex consist of blend of PLLA andpoly(D-lactic acid)(PDLA) as a solution to improve thethermal and physical properties of PLLA.2) 3) However,
PDLA is the high cost as industrial raw material.
Another approach such as the orientation control is
proposed to improve the properties of PLLA.
Orientation control of PLLA is an important subject
because the physical properties of PLLA are strongly
affected by the orientation. By using mechanicalorientation, one obtains materials with ordered polymer
crystals. This method is often used in industry, however
there is a fear of deformation. PLLA is known to be
miscible with PDLLA and develop PLLA crystal inPDLLA.4) 5) We previously reported that themagnetic-induced oriented films of PLLA/PDLLA,
which PDLLA has lower molecular weight than that ofPLLA.6)
Crystallization of PLLA has been developed in PDLLA
and shown the high degree of orientation.
In this work, the influence of molecular weight ofamorphous PDLLA in the PLLA/PDLLA blend films on66

the crystallization and orientation behaviors of PLLA
was investigated.
2. Experimental
2.1 Materials
PLLA of Mn = 1.0 × 105 (PLLA10), and PDLLA of Mw= 1.0 × 104 (PDLLA1) and Mw = 1.0 × 105 (PDLLA10)
were purchased from Sigma-Aldrich Co. The opticalpurity was determined by the specific optical rotation
measurement of PLA sample [α]sample using P-2300
polarimeter (JASCO Corporation, Japan) with awavelength of 589.3 nm (D-line of the sodium lamp) at
25 °C.

OP% =[α ] sample
× 100[α ] PLLA(1)where [α]PLLA is the specific rotation of PLLA with 100%of L stereoisomer and value of -156° was used.7) The€
percentage optical purity of PLLA10, PDLLA1 andPDLLA10 were 98.3, 0.4 and 0.5%, respectively. This
result shows both PDLLA10 and PDLLA1 areconsisting of racemic lactate units and are completely
noncrystallizable polymers.
2.2 Preparation of PLLA/PDLLA solution-castfilms
Twokindsofsolution-cast
blendfilms,
PLLA10/PDLLA1 film and PLLA10/PDLLA10 film,
were prepared. Concentration of 10 wt% of PLLA10chloroform solution and 10 wt% of PDLLA1 orPDLLA10 chloroform solution were mixed and stirred
for 2 hrs, and the solution was put in petri dish and wasJournal of the Magnetics Society of Japan Vol.41, No.3, 2017

stood for 24 hrs. PLLA/PDLLA films were dried at
70 °C for 2 hrs in vacuum oven. The thickness of eachfilms was 100 ± 20µm.
2.3 Preparation of PLLA/PDLLA oriented films
under high magnetic fieldPreparation of PLLA/PDLLA oriented films in amagnetic field was carried out at Institute for Materials
Research, Tohoku University. The temperature
program for the crystallization of PLLA in the blend
films was illustrated in Figure 1. The films were heatedfrom room temperature to the annealing temperature
185°C at a rate of 3°C/min and held constant for 10 min.
Then, films were cooled to 140°C (isothermalcrystallizationtemperature)
forisothermal
crystallization time tc = 0, 2, 15 and 30 hrs. Themagnetic field of 10 T was applied throughout thewhole thermal process.

respectively. 8) 9) 10) The intensity of these diffraction
peaks
increasedgraduallywithincreasing
crystallization time. However, refraction peaks of
110/200 and 203 of the PLLA10/PDLLA10 film for tc = 2hrs have been not detected.

Fig.2 WAXD patterns of PLLA10/PDLLA1 films.

Fig.1 Thermal process for PLLA10/PDLLA1
and PLLA10/PDLLA10 films. Throughout
the whole thermal process, the magnetic fieldof 10 T was applied.
2.4 Measurements
WAXD measurement was carried out using X'Pert
PRO MPD(PANalytical, Japan) operated at 45 kV and40 mA to generate Ni-filtered CuKα X-ray beam.
Scanning speed was 0.01°/s and measurement range
was 3 – 60° at room temperature. Crystals growth in
the films was observed by polarization microscope(BX53-33P-OC-1, Olympus, Japan).
3. Results and discussion
3.1 Crystallization of oriented films
In Figures 2 and 3, WAXD pattern of
PLLA10/PDLLA1 and PLLA10/PDLLA10 films after
annealing at 140°C for different periods was shown.
PLLA shows the two dominant diffraction peaks at
16.7° and 19.1° of α-form crystal. These diffraction
peaks are assigned to the 110/200 and 203 reflections,Fig.3 WAXD patterns of PLLA10/PDLLA10 films.
The relationship between tc and the degree ofcrystallization Xc was shown in Figure 4. From the peakareas of WAXD patterns, Xc was calculated by thefollowing equation,

XC % =SPLLA
× 100
SPLLA + SPDLLA(2)

where SPLLA and SPDLLA are PLLA and PDLLA€Journal of the Magnetics Society of Japan Vol.41, No.3, 201767

diffraction peaks areas.11) Xc of neat PLLA film which
prepared in the same condition also was shown forcomparison. From the figure, it is clear that theinduction period of PLLA crystallization of blend films
are longer than that of neat PLLA10 film. The
induction period of PLLA10/PDLLA1 is short incomparison with PLLA10/PDLLA10. This could beinterpreted that the mobility of PLLA10 chains arelarge
becausethemeltviscosityof
low-molecular-weight PDLLA1 are lower than that ofPDLLA10. The crystallization rate of both blend films isfaster than that of neat PLLA after the induction period.
The value of Xc of all films, however, attained about
60% for tc = 30 hrs.

neat PLLA films are constant for all range of tc, i.e., thisshows that applied magnetic field has no effect on theorientation of these films.

Fig. 5 The degree of orientation fc by WAXD
measurementof
PLLA10/PDLLA1
andPLLA10/PDLLA10 films.

Fig. 4 The degree of crystallinity Xc by WAXD
measurementof
PLLA10/PDLLA1
andPLLA10/PDLLA10 films.

3.3 Isothermal crystalline behavior of orientedfilms
Figure 6 shows a polarizing optical micrograph of (A)PLLA10/PDLLA1, (B) PLLA10/PDLLA10, and (C) neat
PLLA films. Optical micrographs were taken atdifferent crystal growth time ranging from 0 to 30 hrs.
These films show the formation of spherulite that wasgrown isothermally at 140°C, and its content increase
with increasing tc. As is seen in Figure 6(C), thespherulite radius of neat PLLA10 increased with

3.2 Magnetic orientation of oriented films
The c-axis of PLLA crystal in the PLLA/PDLLA film
was oriented in the parallel direction to the magneticfield.6) The degree of orientation was defined as theazimuthal angle of reflected intensity of 110/200 planes.
The degree of the magnetic-field-induced orientation fc
was calculated by the following equations,2
 2 I( ) cos2 sin d(3)cos= 0 2I( ) sin d03 cos2
fc =21(4)where φ is the azimuthal angle and I(φ) is theazimuthal intensity. Figure 5 shows fc against tc of
blend films and neat PLLA film.
In the case of PLLA10/PDLLA10 film, fc increased withincreasing tc. In contrast, a fc of PLLA10/PDLLA1 and68

Fig.6 Polarized photomicrographs of films.
(A): PLLA10/PDLLA1 and (B): PLLA10/PDLLA10
at tc = 0, 2, 15 and 30 hrs. (C): neat PLLA10 at tc =0, 2, 12 and 30 hrs.

Journal of the Magnetics Society of Japan Vol.41, No.3, 2017

increasing tc, and the behavior agrees with theliterature.12) On the other hand, the crystallization
behavior of blend films could be explained by following.
Increasing of spherulites in both blend films is due totrapping amorphous PDLLA in the spherulite ofPLLA.5) 12) For tc = 0 hr, the photomicrographsdemonstrate small crystallites grew spherically fromsingle nuclei. For tc = 2 hrs, numbers of small
crystallites increase in PLLA10/PDLLA1 film, but afaintly increase in PLLA10/PDLLA10 film. For tc > 15hrs, it is clear that the spherulites contents in eachfilms increased with increasing crystal growth time. Fortc = 30 hrs, PLLA10/PDLLA1 film shows large opticaltextures in Figure 6(A).
Comparisonwithspherulite
structureofPLLA10/PDLLA1 and PLLA10/PDLLA10, the latter ismore disordered than the former. Formation of theselarge spherulites observed in PLLA10/PDLLA1 can beexplained by the homogeneous crystallization. Incontrast, PLLA10/PDLLA10 film shows small opticaltexture(Figure 6(B)). This is due to heterogeneous
nucleation, i.e., the locally orientated domain.
4. Conclusions
We have investigated the magnetic-field-induced
PLLA in amorphous PDLLA oriented films without
nucleating agents in a 10 T magnetic field. The
dependence of molecular weight of PDLLA oncrystallization of PLLA in the blend films was notobserved in the crystallization in the magnetic field.
However, orientation behavior is quite different
between PLLA10/PDLLA1 and PLLA10/PDLLA10 films.
That is, trapping of low-molecular-weight PDLLA in thespherulite of PLLA10 show disturb the orientation ofPLLA crystal. On the other hand, trapping
high-molecular-weight
PDLLA
promotehigherorientation film. Hence, the blending with amorphous
high-molecular-weigh PDLLA and crystallization in an
applied magnetic field is effective to achieve the PLLA
film that has higher crystallinity and orientation.
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Received Dec. 08, 2016; Accepted Jan. 05, 2017

Journal of the Magnetics Society of Japan Vol.41, No.3, 201769