〉〉 Fusion of Core Technologies

Crystal Orientation Analysis of Injection-Molded Polypropylene
by Micro-Beam Wide Angle X-ray Diffraction
Yukihiro Ikura*1, Suzune Ito*1, Hirokazu Sasaki*2

Toward the injection molding specimens which are made of Polypropylene
Grafted with Maleic Anhydride melt-blended in polypropylene, we performed
the analysis of the crystal orientation in the local region of the specimens with the micro-beamwide angle X-ray diffraction measurement which has a high resolution of Super Photon ring8 GeV (SPring-8) and is considered with the physical property. As a result, the skin layer of themolding becomes thinner with the influence of the fluidity variation caused by an increase of anadditive amount of the polypropylene grafted with maleic anhydride into the polypropylene,
however it is found that this addition doesn’t have considerable effects on the tensile strengthand modulus of the molding.

ABSTRACTINTRODUCTION
1.1. INTRODUCTION
Recently many developments of plastic materials suchas glass fiber reinforced polypropylene (PP) are performed for the purpose of weight reduction in automobiles. In such developments, the addition of polypropylene grafted with maleic anhydride (Mah-PP) have beenused extensively to improve mechanical properties
between the PP and the filler to be added such as glass
fiber as the reinforced fiber1). Usage of the Mah-PP is
also known as one technique of strength improvementsof cellulose reinforced plastic material which raised theattention recently 2). Mah-PP usually has a lower molecular weight and viscosity than PP, therefore, if Mah-PP is
added to PP, there is a possibility of changes in the fluidity such as Melt Mass-Flow Rate (MFR) and in the crystallization rate of a molding, and it is figured that changes
will occur in the degree of the crystallinity and the crystal
orientation and also in the physical properties.
The injection molding is widely applied for, as themolding method of resin, from making dumbbell-likespecimens in laboratories to manufacturing of large
moldings. The injection molding is a manufacturing method that is injecting a molten resin into a mold. When themolten resin is injected into a mold, the surface of the
dissolved resin which gets in contact with the mold iscooled rapidly and a skin layer is formed. Since thermal
conductivity of the inner region of the plastic is extremely
small comparing with that of the metal mold, the innerpart of the molding isn’t cooled rapidly, therefore it forms
a core layer.
*1*2

Laboratories for Fusion of Core Technologies, R&D Division
Advanced Technologies R&D Laboratories, R&D Division

However there are few examples of detailed analysis
about variations of crystal condition and others in theinjection molding of the PP blended Mah-PP. Therefore, inthis study, as a core technology for analysis, on the injection molded specimen consist of a neat PP melt-blended
with the Mah-PP, by observing wide angle X-ray profiles of
local region in the injection molding using micro-beam
X-ray of SPring-8,which has a high resolution, we analyzed the degree of crystallinity and crystal orientation in
the thickness direction of the molding, as factors whichhave influence on the mechanical properties.

THEEXPERIMENTS
EXPERIMENTS
2.2. THE
2.1

Micro-beam Measurement Using Synchrotron
Radiation Facility
For the X-ray equipment in the laboratory system, there isa limitation to focus to a beam generally which has adiameter of hundreds micrometers, therefore it is difficult
to obtain information from a local region of few micrometers. On the other hand, for the industrial products, the inplane distribution analysis of products structure with spatial resolution of few micrometer order is often required.
The synchrotron radiation facilities such as SPring-8
implement micro-beam in several beam lines to meetsuch industry’s requirements. BL24XU of SPring-8 administered by Hyogo Prefecture brings off to focus with the
X-ray to smaller than 10micrometer. Using this microbeam, Small Angle X-ray Scattering (SAXS) measurement, Wide Angle X-ray Diffraction (WAXD) measurement,
or X-ray Absorption Fine Structure (XAFS) analysis can berealized. In this study, from those analysis methods, wetook the micro-beam wide angle X-ray diffraction toattempt the crystalline orientation analysis on the PP.
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Crystal Orientation Analysis of Injection-Molded Polypropylene by Micro-Beam Wide Angle X-ray Diffraction

2.2

Micro-beam Wide Angle X-ray Diffraction
Measurement and Crystalline Orientation
Analysis of PP by Using Synchrotron Radiation
Facility
Micro-beam wide angle X-ray diffraction measurement
was done by using BL24XU of SPring-8 with 96 mm ofcamera length. The photograph of the equipment isshown in Figure 1. The measurement condition is that
X-ray of 8.2×7.0 μm2 (FWHM) beam size and 0.12 nm
wavelength (10 keV) and PILATUS3-X-300K (487×689
pixels, pixel size 172 μm2 ) is used as a detector and theexposure time is set as 5 sec. The measurement is performed scanning at 40 points in the Normal direction (ND)on the Machine direction-Normal direction (MD-ND) planefrom the surface to the middle of the thickness of thespecimen which is a 1 mm (approx.)-specimen (Figure 2)
cut out from the parallel part of 2 mm-thick tensile test
specimen.

a possibility to overestimate the degree of orientation in
the c-axis because the orientation information derived
from a-axis and c-axis appear at once in the equatorial
direction if the (040)-plane is used for the analysis, andalso the diffraction peak which belongs to β-crystal’s(300)-plane is observed in the slightly inner side of the(040) at some measured locations therefore it is difficult toseparate them when the orientation is analyzed.

(110)
a axis orientation

(040)

(110)
c axis orientation

(130)

(110)
a axis orientation(111)_(131 )(041)

Figure 3 2D-WAXD pattern of surface region of MD-ND plane
for a PP injection-molded sample.

Figure 1 Schematic photograph of micro-beam-WAXD
equipment.

MD (Machine Direction)
TD

MD

Scanning
Pitch: 25 µm
40Points(Transverse Direction)

ND(Normal Direction)

The 2D-WAXD pattern of the Figure 3 is shown in
Figure 4 as the 1D-WAXD pattern. In the 1D-WAXD pattern of the Figure 4, as “h” is the peak height, “p” is thepeak location, “w” is the half-value width and “x” is theangle, we applied curve fitting by using Lorentz function
L(x) shown below.

ND

Intensity (a.u.)

According to the diffraction peak position, the crystal
structure of the PP obtained from this X-ray diffraction
measurement mainly belongs to an α-form. The α-crystalof the PP is monoclinic phase and each lattice parameterare a=0.665nm, b=2.096nm, c=0.650nm and β=99.20° 3).
A representative 2D-WAXD pattern in the skin layer of the
PP is shown in Figure 3. The diffraction peaks in the
Figure 3 belong each from the center in order to (110)plane, (040)-plane, (130)-plane and (111)-plane. This time,the (110)-plane is used for the orientation analysis on the
PP. The reasons are that sufficient diffraction intensity canbe obtained with the diffraction of the (110)-plane, there is

Measured
Calculated(110)

Figure 2 Schematic diagram of the dumbbell specimen MD-ND
plane.

_(131 )(111) (041)

(040)
(130)
βform
(300)

5

10

15

20

2theta (degree)
Figure 4 1D-WAXD pattern of surface region of MD-ND plane
for PP injection-molded sample.

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Crystal Orientation Analysis of Injection-Molded Polypropylene by Micro-Beam Wide Angle X-ray Diffraction

As the result, the peak location “p” of (110) plane is2θ =11.3°. Therefore, we used an angle range of 2θ =10.8° - 11.8° for the orientation analysis and made 1dimension profile of azimuthal angle (Φ) direction. This 1dimension profile is shown in Figure 5.

c axis orientationa axis orientation

Intensity (a.u)

a axis orientation

0

45

90

135

180

Azimuthal angle φ (degree)
Figure 5 Azimuthal intensity distribution of (110)-plane of a PP
crystal.

We used the orientation function ƒ in the following forthe analysis of orientation degree.

3 mass% by using a twin screw extruder. Each blend pellets are obtained by water-cooling and pelletizing fromthe twin screw extruder.
2.4 The Injection Molding
Dumbbell specimens of each blend pellets which support
the standard of JIS No.5 are molded by using electric
injection molding machine “ROBOSHOT” α-S301A of
FANUC CORPORATION. The cylinder temperature is
200°C and mold temperature is 40°C.
2.5 The Measurement of Melt Viscosity
Melt Mass Flow Rate (MFR) is measured for each blendpellets under the condition of 230°C cylinder temperatureand 2.16 kg load by Melt Flow Index Tester of YASUDASEIKI SEISAKUSHO, LTD.
2.6 The Measurement of Melt Crystallization
Behavior
Differential Scanning Calorimetry (DSC) measurement ismeasured by Thermal Analyzer TA-60A of Shimadzu
Corporation. The injection molding specimens for eachcomposition are cut out into approx. 10 mg, filled in analuminum pan, sufficiently dissolved at the temperature
up to 200°C and then the exothermic peak temperaturecaused by crystallization is measured while cooling themat the cooling rate of 10°C/min.

RESULTAND
ANDCONSIDERATIONCONSIDERATION
3.3. RESULT
3.1

The Effect of the Mah-PP Addition to the Fluidity
and Crystallization Behavior
The DSC thermograph of each blend pellets is shown in
Figure 6. As many as the Mah-PP is added, the crystallization temperature shifts to higher temperature and thetendency such that crystallization rate becomes faster isconfirmed.

Where, I(Φ) is the intensity profile in the azimuthal angle
direction of (110)-plane.

PP/Mah-PP (3 mass%)
PP/Mah-PP (1 mass%)
Neat PP← Endotherm.

As shown in Figure 5, in the skin layer of the PP, bothorientation information of the a-axis orientation (15° and161°) and the c-axis orientation (90°) are observed atonce in the azimuthal angle direction. The higher-order
structure is known that it becomes parent-daughter
lamellar structure which is parent lamellar with molecular
chain arrayed and growing crystal in the flow direction,accompanied by a daughter lamellar with a-axis arraying
in the flow direction and growing crystal 5). In this study,
the purpose is to obtain the orientation information ofc-axis as the molecular chain, therefore the orientation
components of a-axis and c-axis are eliminated by peak
resolution and the orientation function f with only the orientation component of c-axis is obtained.
2.3 The Manufacturing of Composition for the
Evaluation
Homo-PP (Melt Mass Flow Rate: MFR approx.15 g/10 min)and commercially available Mah-PP are melt-blended as
the concentration of the Mah-PP becomes 0, 1 and

75

100

125

150

175

200

Temperature (℃)
Figure 6 DSC thermograph of cooling curve for neat PP and
PP/Mah-PP blends.

The result of MFR measurement is shown in Table 1.
MFR becomes lager as many as Mah-PP are added. Thatis, it is considered that the viscosity decreases as manyas Mah-PP are added.
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Crystal Orientation Analysis of Injection-Molded Polypropylene by Micro-Beam Wide Angle X-ray Diffraction

Table 1

Crystallization temperature and MFR of neat PP and
PP/Mah-PP blends.

Mah-PP content[mass%]

Crystallization temperature[℃]

MFR[g/10min]

0

127.8

15.0

1

128.9

17.1

3

129.7

17.9

Fujiyama et al. had a fundamental consideration about
the relations among the relaxation time, the crystallization
time and the quantity of molecular chain with crystal oriented (=thickness of the skin layer), and they showed thatthe longer the relaxation time and the longer the crystallization time, the thicker the skin layer 4). Considering theresult of this section, the addition of Mah-PP causes MFR
to increase, viscosity to decrease and relaxation time toshorten. On the other hand, the crystallization temperature shifts to higher range and the time to start crystallizing becomes shorter. This result shows that each of thetwo effecting factors to the thickness of skin layer, considered by Fujiyama et al., have effects on both thicken-〉〉 Fusion of Core Technologies

ing and thinning of the skin layer. In the next section, we
will subsequently discuss about the thickness of the skinlayer by using micro-beam WAXD measurement.
3.2 The X-ray Structure Analysis of Injection
Molding Specimen With Mah-PP Added
Figure 7 shows the WAXD patterns obtained at several
positions on the MD-ND plane of the injection molding
specimens with variable amount of Mah-PP addition.
The orientated diffraction profile patterns are obtainedat the position of 25 μm from the surface of all molded
specimens. On the other hand, we confirmed the tendency that the intensity is not quite large. It is considered thatis because degree of crystallinity becomes relatively
lower with rapid cooling by the mold. Subsequently thehigh-orientated WAXD patterns can be obtained at theposition of 225 μm from the surface of all injection molded specimens regardless of the amount of Mah-PP addition. On the other hand, at the inner side within the position of 475 μm from the surface, WAXD patterns are likeisotropic, therefore it suggests that low-oriented corelayer is formed in those thickness area.

←Surface(a) 25 µm

(110)
Plane

225 µm475 µm

725 µm

975 µm(b) 25 µm

225 µm475 µm

725 µm

975 µm(c) 25 µm

225 µm475 µm

725 µm

975 µm↓MD

Figure 7 2D-WAXD profiles at each position from the surface of the molded sample of (a) neat PP, (b) PP/Mah-PP(1 mass%) and (c) PP/Mah-PP (3 mass%).

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Crystal Orientation Analysis of Injection-Molded Polypropylene by Micro-Beam Wide Angle X-ray Diffraction

Next, to clarify the border between the skin layer andthe core layer, the degree of orientation “fc” toward MDof c-axis is calculated from the intensity distribution in theazimuth angle direction of the PP crystal’s (110) reflection
obtained at each of the measurement points, and the distribution of the PP crystal orientation function in the ND
direction on the MD-ND plane is calculated. The results
are shown in Figure 8.

1

Neat PP
PP/Mah-PP (1 mass%)

0.8

PP/Mah-PP (3 mass%)

fc ( - )

0.6
0.4
0.2

with the Mah-PP addition, contribute to, however thedetails of how such configuration occurs still remains
unknown.
Next, averaging diffraction profile patterns in the direction of azimuthal angle, the degree of crystallinity estimated from the 2θ vs intensity-curve is shown in Figure 9. It
is found that, comparing with neat PP, the degree of crystallinity becomes slightly higher in the surface layer andthe core layer with adding the Mah-PP. As described in
the Section 3.1, this is estimated that is because crystallization speed becomes faster. From the results so far, theorientation function and the degree of crystallinity in the
direction of the thickness on the injection molding specimens can be analyzed in detail, and it is found that theskin layer becomes thinner with Mah-PP adding. There is
the possibility that the thinning of skin layer causes
decrease in the tensile modulus, therefore we discuss
about the results of mechanical properties in the next
section.

0

0

200

400

600

800

1000

Distance from surface (µm)

Figure 8 Orientation functions of c-axis of various samples as afunction of distance from the surface.

It is found that while all molded specimens have relatively high-degree of orientation at the surface, thedegree of orientation at the position of 100 µm from thesurface slightly decreases because of the Mah-PP addition.
Next, we study the thickness of the skin layer from theorientation function in the thickness direction. Drastic
decrease of orientation function is observed between
325 µm to 350 µm with the neat PP, therefore it is considered that there is a border of skin layer and core layer
within this range. On the other hand, with the Mah-PP
addition, the range where the orientation function drastically decreases shifts to the range within 275-300 µm
with 1 mass% addition and within 225-275 µm with
3 mass% addition. That means that the high-oriented
skin layer becomes thinner with the Mah-PP addition. It
can be said that, with the Mah-PP addition, shortening
relaxation time caused by viscosity decrease has more
effect to the thinning of the skin layer than the effect of
crystallization described in Section 3.1.
Focusing on the orientation degree in the core layer, theorientation degrees are negative values in the core layerof all molding specimens. It is considered that there isslight a-axis orientation in the core layer. On the other
hand, it is confirmed the tendency that c-axis orientation
function becomes slightly higher in the core layer when
the Mah-PP addition is large. This is estimated that crystallization behavior and the variation of relaxation time,

Crystallinity by WAXD (%)

-0.2

80

70

60

Neat PP50

PP/Mah-PP (1 mass%)
PP/Mah-PP (3 mass%)
40

0

200

400

600

800

1000

Distance from surface (µm)
Figure 9 The degree of crystallinity for various samples as afunction of the distance from surface.

The Measurements of the Strength and theTensile Modulus of Injection Molding Specimens
With the Mah-PP Addition
Table 2 shows the results of the tensile test. It is alreadydescribed in Section 3.2 about the thinning of the skinlayer thickness with the Mah-PP addition, however thetensile strength and the tensile modulus didn’t changemuch even if the amount of the Mah-PP addition isincreased. For the PP fiber, relationship between the orientation function and the tensile modulus of PP has beenstudied many times from long time ago. Shimizu et al.
elucidated the relations among the drawn speed, the tensile modulus, orientation function and the birefringence of
the PP fiber 6), 7). They show that, between the tensile
modulus and birefringence, at threshold level, the effectof the tensile modulus increment in large slope isobtained toward the increase of birefringence in the highbirefringence region, however the slope of the tensile
3.3

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Crystal Orientation Analysis of Injection-Molded Polypropylene by Micro-Beam Wide Angle X-ray Diffraction

modulus increment is small toward increment of birefringence in the low-birefringence region. From the literatures, it can be considered that birefringence and the orientation function are in a proportional relation.
Table 2Tensile modulus and strength of neat PP an PP/MahPP blends.

Mah-PP content[mass%]

Tensile modulus[GPa]

Tensile strength
[MPa]

0

2.1

40.8

1

2.0

39.4

3

2.1

39.5

From the results of this measurements for the mechanical properties, even though there is slight effect of thinning to thin the skin layer, it can be estimated that, theeffect of low- degree orientation core layer which forms alarge part of specimen’s volume is larger than the effectof regions which have orientation degree sufficient tocontribute to the elasticity degree, and it leads to no-large
difference between bulk tensile modulus of the moldings.
On the other hand, since the thickness of skin layer has
a possibility to affect the occurring warpages in use, it isconsidered that attention to the properties is required in
the case of fiber reinforced PP composite as the original
purpose of the Mah-PP adding. In the case of fiber reinforced, it is necessary to consider effects of variations of
fluidity and crystallization behavior caused by the fiber
addition, therefore it is necessary to verify continuously if
the results of this time can be applicable or not to thematerials which are filer added or fiber reinforced composite.

〉〉 Fusion of Core Technologies

es associated with residual stress occurring, therefore
attention is required.
Recently, according to high value addition of materials,
importance of core analysis technology such as structural
analysis and simulation in developments is increasing
more than ever. Therefore there are reports 8) about simulation technique, corresponding to more than 10 2 °C/secof the cooling rate of a skin layer in the injected molding,by utilizing equipment such as a high-speed DSC, performing high-speed crystallization analysis and associating crystallinity and oriented crystallization in the direct
flow. And also an observation technique for filler dispersion and orientation under non-destruction, such as X-ray
CT, and a flow analysis technique by computer aided
engineering (CAE) are developed 9).
We will continue to strengthen the core analysis technique by combining this time analysis technique of crystalline orientation with those existing techniques, and utilize those techniques to the designing of plastic products.
ACKNOWLEDGEMENTS
The experiments at SPring-8 described in this study are
the issues no.2016A3270, 2016B3270, 2017A3270 and
017B3270 and performed on the beamline BL24XU.
We express our sincere thanks to all people involved forproviding the most cutting edge equipment and supporting system to solve technological problems in the industries.

REFERENCES

CONCLUSION
4.4. CONCLUSION
On the injection molding specimen consisting of neat PP
melt-blended with Mah-PP, by observing wide angle
X-ray profiles of local region in the injection molding
specimen using micro-beam WAXD of SPring-8,which
has a high resolution, we analyzed the degree of crystallinity and crystal orientation which occur in the molding
specimen, and examined details of the degree of crystallinity and the orientation function in the thickness direction of the molding, as factors which has influence on themechanical properties, and confirmed correlation withphysical properties.
From the result, we could analyze the crystal orientationin the MD-ND plane of the injection molding specimen by
micro-beam WAXD, and analyze the skin layer becomesthinner which is effected by the fluidity caused from theincrement of the Mah-PP addition.
On the other hand, it is found that the Mah-PP addition
has not large effect on the tensile strength and modulus,
however there is possibility that variation of the skin layer’s thickness of the molding effects to the long-term
properties including the occurrence of sinks and warpag-

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