Photon Factory Activity Report 2019 #37 (2020)
BL-10C/2018G026

Effects of Loading Amount of Plasticizers on
Improved Crystallization of Poly(L-lactic acid)Pham Thi Ngoc DIEP1, Hideaki TAKAGI2, Nobutaka SHIMIZU2, Noriyuki IGARASHI2,Sono SASAKI1 and Shinichi SAKURAI1,*
1
Department of Biobased Materials Science, Kyoto Institute of Technology, Matsugasaki, Kyoto,606-8585, Japan2
Photon Factory, Institute of Materials Structure Science,High Energy Research Organization, 1-1 Oho, Tsukuba, 305-0801, Japan
1 Introduction
Poly(L-lactic acid) (PLLA) is one of the mostpopularly utilized biobased polymers, as it is derived
from renewable sources (sugar, carbohydrate, etc).
Although PLLA bears environmentally benign
characteristics, there are crucial faults of PLLA such as
slow crystallization and insufficient crystallinity which
can be finally attained even after the fully thermalannealing.
To improve crystallizability of PLLA,
nucleation agents have been utilized. Although typical
nucleation agents work at the solid state, we havereported that a special plasticizer (organic acidmonoglyceride; OMG) can partly improve thecrystallizability of PLLA [1,2]. The results are significant
because plasticizers are believed to delay crystallizationof polymers by reducing the thermodynamical driving
force of crystallization. We speculated that the loweringof the activation energy for the PLLA crystallization may
be the main effect of the plasticizer [3]. In this study, we
confirmed that the enhanced crystallization of PLLA canbe also attained by using a general plasticizer which is
dioctyl phthalate (DOP). To identify the effects ofloading amount of plasticizers on improved
crystallization of PLLA, we conducted time-resolved
small- and wide-angle X-ray scattering (SWAXS) tofollow the isothermal crystallization of PLLA/plasticizerspecimens.
2 Experimental
The PLLA samples used in this study are obtained fromNatureWorks LLC. As shown in Table 1, one of thembears 1.4% D content (PLLA4032D) and the other 0.5%
D content (PLLA2500HP), which enabled us to study theeffects of the optical impurity on the crystallization ofPLLA with or without the presence of plasticizers. The
other characteristics and code names are listed together inTable 1.
Two kinds of plasticizers were used; OMG and DOP.
The OMG contains an organic acid as a succinic acid anda saturated fatty acid as a stearic acid, and it is a productof Taiyo Kagaku Co,. Ltd. with the commercial name ofChirabazol D which is a “100% plant-derived” fatty acid
ester surfactant developed based on technology of theTaiyo Kagaku Co., Ltd. The OMG has a molecularweight of 500 and the melting temperature of Tm = 67 ̊C(measured by DSC). DOP (purity: 99%) was purchased

Table 1: Sample characteristics

from Nacalai Tesque, Kyoto, Japan. The specimen codenames are PLLA neat and PLLA/plasticizer(x) with “x”
corresponding to the weight % of plasticizer amountloaded in the specimen of PLLA (D0.5 or D1.4).
All the specimens were prepared by a solution casting
method. PLLA pellets were dried in a vacuum oven at 50
̊C for 24 h before preparation of a solution. A given
amount of PLLA and plasticizer were weighed anddissolved in chloroform (purchased from Nacalai Tesque)with the PLLA concentration of 5% (w/v). Then, thesolution was poured in the Petri dish for the solvent
evaporation under ambient condition at room temperature.
The amount of PLLA solution was calculated so as tohave the film thickness of 200 µm after complete
evaporation of the solvent. The films were further driedin a vacuum oven at 50 ̊C for 24 h for further
measurements.
We conducted SWAXS measurements to study isothermal
crystallization kinetics.
The time-resolved SWAXS
measurements were conducted upon T-jump from themelt (200 ̊C) and rapidly cooling down to Tc = 100 ̊C for
the D0.5/OMG and D1.4/OMG specimens or to Tc = 110
̊C for the D0.5/DOP and D1.4/DOP specimens, with anexposure time of 5s using PILATUS3 200K for WAXS
and PILATUS3 2 M for SAXS (DECTRIS Ltd., Baden,Switzerland) as a two-dimensional detector at BL-10C ofthe Photon Factory in High Energy Accelerator Research
Organization, Tsukuba, Japan. The sample to-WAXS andSAXS detector distances are 40 mm and 2 m, respectively.
The X-ray wavelength was 0.150 nm.

3 Results and Discussion
Fig.1 shows temporal changes in the one-dimensional
WAXS (1d-WAXS) profiles upon temperature jump (Tjump) from 200 ̊C to 110 ̊C for (a) D1.4 neat, (b)D1.4/DOP(1.0), and (c) D1.4/DOP(2.0) specimens.
These profiles were obtained by conducting a sector
average. Here, q denotes the magnitude of the scatteringvector as defined by q = (4π/λ) sin (θ/2) with λ and θPhoton Factory Activity Report 2019 #37 (2020)
being the wavelength of the X-ray and the scattering
angle, respectively. The 1d-WAXS profiles at t = 25 s forall specimens show only amorphous halo peaks where t is
the elapsed time from T-jump from 200 ̊C. As time goeson, the crystalline peak appears and the number of peaks
also increases. At t = 100 s, the (200/110) reflection peakis clearly observed for the D1.4/DOP(1.0) andD1.4/DOP(2.0) specimens while this peak is not clear for
the D1.4 neat specimen, indicating that the DOP canenhance the crystallization of PLLA. In order to evaluate
the crystallinity from the results of WAXS, the peakdecomposition of the 1d-WAXS profiles was conductedto distinguish the crystalline peaks from the amorphous
halo peak. The area of the crystalline peaks and theamorphous halo peak was used to calculate the apparent
degree of crystallinity [φ(t)]. φ(t) is plotted as a functionof t in Fig. 2 for the case of DOP loading (isothermalcrystallization at 110 ̊C) as well as OMG loading(isothermal crystallization at 100 ̊C). Note here that theφ(t) is just apparent crystallinity because the WAXS does
not completely cover the whole q range of the crystalline
peaks of PLLA. However, comparison of φ(t) values
between the different PLLA specimens with different
plasticizer loading amounts is possible because of thesame chemical structure of PLLA with the negligibly
small amount of plasticizer and D moieties.
Overall, we may be able to recognize that OMG
improved crystallization of PLLA from the plots of Fig. 2.
As for the DOP loading, it is important to examine its
ability as an agent for improved crystallization of PLLA.
For this purpose, we evaluated the crystallization halftime (t1/2), the induction period, and the ultimate degree ofcrystallinity (the degree of crystallinity finally attained)from the results shown in Fig. 2. Note that t1/2 wasevaluated as the time when the 50% of the ultimate

crystallinity was attained. Thus-evaluated t1/2 is shown inFig. 3(a) as a function of the OMG content for the OMG
loading, and it is shown in Fig. 3(b) as a function of theDOP content for the DOP loading. Since the inverse of
t1/2 can be a measure of the crystallization rate, it is clearlyobserved in Fig. 3 that the OMG and DOP accelerated thecrystallization of PLLA. However, for the case of the 2%
OMG loading is not so effective as expected. Although
the crystallization temperature for the OMG loading isdifferent from that for DOP loading, the results of theOMG loading may suggest that there is an appropriate
amount of loading for the best effect of improved
crystallization of PLLA. For the case of the DOP loading,the appropriate amount will be somewhat larger than thatfor the OMG loading (about 2% of DOP). This is due tothe effect that too much amount of loading the plasticizer
decreases Tm̊ (the equilibrium melting temperature)
which in turn decreases the thermodynamic driving forceof crystallization. Anyhow, the fact that we can recognize
the improved crystallization of PLLA in Fig. 3 by thevery small amount of loading of plasticizers (0.5 ~ 1.0%
with the negligibly small lowering of Tg (1.7 ~ 4.0 ̊C) issurprising because generally speaking the plasticizers are
believed to depress the crystallizability of polymers. The
depression of the thermodynamic driving force ofcrystallization is simply the case of the large amountloading (2%), of which improving effects of thecrystallization behaviors of PLLA is not so clear as isshown in Fig. 3. The fact that only 1% or several % ofloading plasticizers can improve crystallization is a very
important and valuable finding, although the mechanismof the improved crystallization is still unknown at present[1,3]. It is needless to say that t1/2 always longer for theD1.4 specimens than those for the D0.5 specimens
because of the larger D content which depresses theFig. 1 Temporal changes in the 1d-WAXS profiles upon T-jump from 200 ̊C to 110 ̊C for (a) D1.4 neat, (b)D1.4/DOP(1.0), and (c) D1.4/DOP(2.0) specimens.

Photon Factory Activity Report 2019 #37 (2020)
the effect of loading DOP is unclear or even negative. The
reason may lie in a presumably attractive interaction
between the phenylene ring in DOP and the lone pair ofelectrons existing at the oxygen atom in the main chain ofPLLA. Such attraction (too much favorable interaction)
may degrade the ultimate crystallinity even though thecrystallization rate is enhanced by DOP.

Fig. 2 Apparent crystallinity as a function of time, asevaluated from the results of the isothermal
crystallization WAXS measurements at 100 ̊C for (a)D0.5/OMG, and (b) D1.4/OMG specimens and at
110 ̊C for (c) D0.5/DOP, and (d) D1.4/DOP
specimens.

References[1] P. T. N. Diep, M. Mochizuki, M. Doi, H. Takagi, N.
Shimizu, N. Igarashi, S. Sasaki, S. Sakurai, Polymer
Journal, 51, 283 (2019).
[2] P. T. N. Diep, H. Takagi, N. Shimizu, N. Igarashi, S.
Sasaki, S. Sakurai, J. Fiber Sci. Technol., 75, 99(2019).
[3] A. K. Pandey, P. T. N. Diep, R. Patwa, V. Katiyar, S.
Sasaki, S. Sakurai, in Advances in Sustainable
Polymers
Synthesis,Fabrication
andCharacterization (Editers: V. Katiyar, A. Kumar, N.
Mulchandani), Springer Nature Singapore, Chapter 14(2019). DOI: 10.1007/978-981-15-1251-3
Research Achievements
1. Pham Thi Ngoc Diep, JFST Best Paper Awards of
the Society of Fiber Science and Technology, Japan(J. Fiber Sci. Technol., 75(8), 99-111 (2019).)* shin@kit.ac.jp

Fig. 3 Crystallization haft time t1/2 as a function of (a)OMG content for PLLA/OMG specimens
isothermally crystallized at 100 ̊C and as a functionof (b) DOP content for PLLA/DOP specimens
isothermally crystallized at 110 ̊C.
crystallizability of PLLA due to the effect as an impurity.
Fig. 4 shows the plots of the ultimate crystallinity,
which is the crystallinity value attained in the final stageof crystallization (from the plots shown in Fig. 2 showing
a constant value in the final stage) against the content ofplasticizer for PLLA/OMG specimens isothermally
crystallized at 100 ̊C or for PLLA/DOP specimens
isothermally crystallized at 110 ̊C. For the case of theOMG loading, the ultimate crystallinity is increased as afunction of OMG content, although at 2% loading forD0.5 is decreased as compared to the case of 1% loading
which is similar tendency as observed in Fig. 3(a). On
the other hand, the ultimate crystallinity is almost
constant for the D1.4/DOP specimens or it decreases as afunction of the DOP content for the D0.5/DOP specimens.
Thus, there are opposed effects of the plasticizers on theultimate crystallinity as the effect of loading OMG on theimprovement of the ultimate crystallinity is clear whileFig. 4 Plots of the ultimate crystallinity, which is thecrystallinity value attained in the final stage ofcrystallization (from the plots shown in Fig. 2
showing a constant value in the final stage) against
the content of plasticizer for PLLA/OMG specimens
isothermally crystallized at 100 ̊C or for PLLA/DOP
specimens isothermally crystallized at 110 ̊C.