European Polymer Journal 39 (2003) 2129–2134

www.elsevier.com/locate/europolj

Mechanical properties and morphological structuresof short glass fiber reinforced PP/EPDM composite

Weizhi Wang, Longxiang Tang, Baojun Qu *

Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei, 230026 Anhui, PR China

Received 20 June 2003; received in revised form 6 July 2003; accepted 14 July 2003

Abstract

The mechanical properties and crystal morphological structures of short glass fiber (SGF) reinforced dynamically

photo-irradiated polypropylene (PP)/ethylene–propylene–diene terpolymer (EPDM) composites were studied by me-

chanical tests, wide-angle X-ray diffraction (WAXD), optical microscopy, scanning electron microscopy (SEM), dif-

ferential scanning calorimetry (DSC), and thermogravimetric analyzer (TGA). The mechanical properties of PP/EPDM

composites, especially the tensile strength were greatly strengthened by dynamically photo-irradiation and the incor-

poration of SGF. The results from the WAXD, SEM, DSC, and TGA measurements reveal: (i) the formation of b-typecrystal of PP in the PP/EPDM/SGF composite; (ii) the fiber length in dynamically photo-irradiated PP/EPDM/SGF

composites are general longer than that in corresponding unirradiated samples. The size of EPDM phase in the photo-

irradiated composites reduces obviously whereas the droplet number increases; (iii) photo-irradiation improves the

interface adhesion between SGF and polymer matrix; (iv) the melting and crystallization temperatures of the photo-

irradiated composites are not affected greatly by increasing the SGF content; (v) the thermal analysis results show that

the incorporation of SGF into PP/EPDM plays an important role for increasing its thermal stability.

� 2003 Elsevier Ltd. All rights reserved.

Keywords: Glass fibers; Polypropylene; Composites; Mechanical properties; Morphological structure

1. Introduction

Polypropylene (PP) used as a thermoplastic is widely

used in many fields, such as building materials, furni-

ture, automobile and toy industries. However, the poor

impact resistance, especially at low temperature con-

siderably limits its application. Therefore, PP is usually

modified with elastomers, such as ethylene–propylene–

diene terpolymer (EPDM), to improve its impact

strength [1–4]. However, the improvement of toughness

of PP/rubber blend always follows by the decrease of

stiffness. In recent years, short glass fiber (SGF), glass

ball, calcium carbonate, talc, and montmorillonite re-

* Corresponding author. Tel.: +86-551-3606467; fax: +86-

551-3607245.

E-mail address: qubj@ustc.edu.cn (B. Qu).

0014-3057/$ - see front matter � 2003 Elsevier Ltd. All rights reserv

doi:10.1016/S0014-3057(03)00157-5

inforced composites have been widely studied and de-

veloped rapidly [5–8], which provide an alternation to

increase the stiffness of polymer composites. However,

the poor interface adhesion between fillers and matrix

will obviously lead to the reduction in tensile ductility

and impact toughness. These difficulties make the effi-

ciency for improving toughness and stiffness of PP/rub-

ber/SGF ternary composite decrease. In order to solve

this problem, many researchers focus on the glass fiber

surface modification technique or the approaches of

adding compatilizers [9–15]. Although the toughness can

be improved in some degree from these methods, the

complicated treatment and rigorous condition greatly

confine the preparation of composites in mass with low

cost.

In the present paper, we combine the dynamically

photo-crosslinking technology [16] with SGF reinforce-

ment to prepare crosslinked PP/EPDM/SGF ternary

ed.

2130 W. Wang et al. / European Polymer Journal 39 (2003) 2129–2134

composite. Their mechanical properties and crystal

morphological structures were investigated by mechan-

ical tests, wide-angle X-ray diffraction (WAXD), optical

microscopy, scanning electron microscopy (SEM), dif-

ferential scanning calorimetry (DSC), and thermo-

gravimetric analyzer (TGA).

2. Experimental

2.1. Materials

PP (F401, MFR¼ 2.7) was supplied by Yangzi Pet-

rochemical Co. Ltd., China. EPDM 4770 containing

70 wt% ethylene and 5 wt% diene was supplied by Du-

Pont Dow Elastomer Co. Ltd., USA. 2-Ethylidene-5-

norbornene was used as a diene. The short glass fiber

(diameter, 10–20 lm) was supplied by Shanghai Chem-

istry Co., China. Benzil dimethyl ketal (BDK) as a

photo-initiator and hindered amine Tinuvin 144 as a

photo-stabilizer were obtained from Ciba-Geigy Co.,

Switzerland. Triallyl isocyanurate (TAIC) used as a

crosslinking agent was obtained from Anhui Institute of

Chemical Engineering, China. All chemicals were used

as received without purification.

2.2. Sample preparation and measurements

The dynamically photo-irradiated PP/EPDM/SGF

composites were prepared as following steps: PP was

firstly mixed with EPDM (PP:EPDM¼ 8:2, wt%), a

given amount of SGF, 1 wt% BDK and 4 wt% TAIC

(based on EPDM content) for 7 min at 180 �C using a

double roller mixer. And then, a 2 kW Philips HPM 15

lamp was applied to irradiate the composite at 15 cm

distance from the lamp for 90 s while mechanically

blending. The dynamically photo-irradiated PP/EPDM/

SGF composite was continuously mixed for another

Table 1

Mechanical properties, gel content, and MFR of PP/EPDM and PP/

Sample code Component weight (g) Tensile

strength

(MPa)

Elong

(%)PP EPDM SGF

PP 100 – – 34.0 1140

PP/EPDM 80 20 – 22.5 650

PP/EPDM/

10%SGF

72 18 10 31.5 183

PP/EPDM/

30%SGF

56 14 30 34.7 118

PP/EPDMir 80 20 – 25.0 200

PP/EPDMir/

10%SGF

72 18 10 36.2 146

PP/EPDMir/

30%SGF

56 14 30 40.2 96

5 min. Finally the samples for measurements were ob-

tained by injection. The unirradiated PP/EPDM/SGF

composite as a control sample was prepared with the

above similar steps except for UV-irradiation. PP/

EPDMir and PP/EPDMir/SGF represent for the dynam-

ically photo-irradiated composites without and with the

addition of SGF, respectively. The composition of those

composites is listed in Table 1.

The tensile properties were measured with a Univer-

sal Testing Machine (DCS5000, SHIMADZU, Japan) at

25± 2 �C. The crosshead speed was 50 mm/min. The

dumb-bell shaped specimens were prepared according to

ASTM D412-87. The notched Izod impact strength was

measured by an Izod impact tester (made in Chengde,

China). The size of rectangular specimens was 80· 10· 4mm3 with a 45� V-shaped notch (tip radius 0.25 mm,

depth 2 mm). The average value from five specimens was

used for the data plot. The melt flow rate (MFR) was

measured at 230 �C under a load of 2.16 kg according to

ASTM D-1238.

The gel content of a sample was determined by

extracting the photo-irradiated sample in the basket

for 48 h with boiling xylene stabilized by 0.2 wt%

(based on the solvent content) antioxidant Tinuvin 144

and with N2 bubbling to prevent oxidation. The dy-

namically photo-irradiated sample was cut into thin

slices and put into a basket made of 200-mesh stainless

steel net. The solvent was renewed after the first 24 h

of extraction. After the extraction, the basket was

washed with acetone. After being dried in a vacuum

desiccator at about 70 �C to constant weight, the in-

soluble residue (w1) was weighed. The EPDM average

gel content (wt%) in the test was calculated as the

value of w1 � wSGF=wEPDM (wSGF and wEPDM present

the weight of SGF and EPDM in PP/EPDM/SGF

composite, respectively). Usually, five samples were

analyzed to determine the average gel content for a

given set of experimental conditions.

EPDM/SGF composites

ation Tensile

strength

(GPa)

Impact

strength

(kJ/m2, 25 �C)

Gel

content

(%)

MFR

(g/10 min)

1.30 2.3 – 3.5

0.65 8.7 – 2.5

0.88 7.8 – 1.3

1.41 5.1 – 0.8

0.69 10.8 92 1.8

0.94 9.6 90 1.0

1.48 6.2 90 0.6

W. Wang et al. / European Polymer Journal 39 (2003) 2129–2134 2131

The WAXD patterns were recorded at room tem-

perature with a D/Max-rA rotating anode X-ray dif-

fractometer (Rigaku Electrical Machine Co., Japan)

equipped with a CuKa tube and Ni filter. The diffraction

patterns were determined over a range of diffraction

angle 2h ¼ 10–40� at 40 kV and 50 mA. The fibers col-

lected after burning in a muffle furnace were observed by

a Nikon-YS2 optical microscope (Nikon, Japan). The

SEM images were obtained by a Philips-XL30 scanning

electron microscopy (Philips, Holland). The samples

were previously etched by xylene and coated with a

conductive gold layer. The DSC data were obtained in a

nitrogen atmosphere at a heating rate of 10 �C/min using

a Perkin–Elmer differential scanning calorimeter (model

DSC 2). The degree of crystallization of PP in nano-

composite was evaluated from the relative ratio of the

values of fusion heat of the blend to the fusion heat of

PP (DHPP ¼ 209 J/g) [17]. Thermal stability was deter-

mined with a Perkin–Elmer TGA-7 thermogravimetric

analyzer over a temperature range of 30–800 �C at a

heating rate of 10 �C/min.

3. Results and discussion

3.1. Mechanical properties

The tensile strength (TS), elongation at break, and

notched Izod impact strength (NIIS) of PP/EPDM

samples containing different amount of SGF before and

after photo-irradiation are summarized in Table 1. It has

been found that the TS value of 22.5 MPa for PP/EPDM

is smaller than that of 34.0 MPa for PP sample, because

of the incorporation of flexible component EPDM in PP

matrix. When blended 10% and 30% SGF into PP/

EPDM, the TS increases to 31.5 and 34.7 MPa, re-

spectively. Those results indicate that the stiffness of

composites can be improved by the addition of SGF

efficiently. After photo-irradiation, the TS further in-

creases to 36.2 and 40.2 MPa for the composites con-

taining 10% and 30% SGF, respectively, which indicates

that photo-irradiation can greatly enhance the stiffness

of composites incorporated with SGF. The elongation

data show that the rigid SGF incorporation decreases

the elongation from 650% for PP/EPDM to 183% for PP/

EPDM/10%SGF, and 118% for PP/EPDM/30%SGF.

Moreover, photo-irradiation makes the elongation at

break decreasing more obviously than the unirradiated

samples. The elongation of photo-irradiated samples

with 10 and 30 wt% SGF addition decreases from 183%

and 118% to 146% and 96%, respectively. However,

after blended EPDM rubber into PP matrix, the NIIS

increases to 8.7 kJ/m2 from 2.3 kJ/m2 of PP. On the

other hand, the NIIS of samples without SGF addition

is higher than that for corresponding samples with SGF

addition, which implies that the incorporation of SGF in

order to improve matrix stiffness is always at the expense

of tensile ductility. However, after photo-irradiation, the

NIIS increases from 7.8 and 5.1 kJ/m2 for PP/EPDM/

10%SGF and PP/EPDM/30%SGF, respectively, to 9.6

and 6.2 kJ/m2 for the corresponding photo-irradiated

samples. This result also is proved by the tensile mod-

ulus data as listed in Table 1. Gel content and melt flow

rate data present EPDM phase products crosslinked

structure after photo-irradiation. These can be suggested

that photo-irradiation significantly improves the inter-

face adhesion of different phases by photo-grafting re-

action to form grafted copolymer, such as SGF grafted

PP, SGF grafted EPDM, and PP grafted EPDM. The

interface adhesion plays a decisive role in determining

the mechanical properties of the resultant composites,

ensuring effective stress transfer from the matrix to the

SGF phase during impact or tensile deformation, which

gives rise to enhanced tensile and impact properties of

composites.

3.2. Crystal structure of PP

The WAXD spectra of unirradiated and photo-irra-

diated PP/EPDM, PP/EPDM/10%SGF, PP/EPDM/

30%SGF composites are shown in Fig. 1. It shows that

the 2h peaks of all samples at 14.1�, 16.8�, 18.5� and

21.2� due to the 110, 040, 130 and the overlapping 131,

041 and 111 planes are characteristics of a-type mono-

clinic crystal structure of PP. It proves that these sam-

ples contain a-type crystal. However, compared with PP/

EPDM curve, it can be obviously found that a new peak

at 16.2� appears for other five curves. This new peak has

been assigned to the (3 0 0) reflection of b-type hexago-

nal crystal structure of PP. Moreover, the b phase

fraction in the crystalline part of samples can be assessed

from the ratio of the height of main (3 0 0) b reflection to

the sum of the heights of four main crystalline reflec-

tions, i.e. (1 1 0), (0 4 0) and (1 3 0) from the a phase plus

(3 0 0) from the b phase, as proposed by Turner-Jones

[18]. The calculated results of b phase fraction for PP/

EPDM, PP/EPDMir, PP/EPDMir/10%SGF, PP/EPDM/

10%SGF, PP/EPDMir/30%SGF, and PP/EPDM/

30%SGF samples are 0%, 26.3%, 25.3%, 23.8%, 24.5%,

and 22.2%, respectively. It shows that the b phase

fraction in unirradiated samples is less than that in the

corresponding photo-irradiated samples, as the photo-

irradiated products act as a nucleating agent in PP

matrix. However, the incorporation of SGF decreases

the b-type crystal content in both unirradiated and

photo-irradiated samples, which leads to the reduction

of the impact strength of composites because the b-typehexagonal crystal has higher ductility and strength than

a-type monoclinic crystal with little loss of stiffness [19].

These results are also proved by the above mechanical

measurements.

12 14 16 18 20 22 24 26 28

PP/EPDM/30%SGFPP/EPDMir /30%SGF

PP/EPDM/10%SGF

PP/EPDMir /10%SGF

PP/EPDMir

PP/EPDM

16.2° (111)

(040)(131)

(130)

(040)(110)

2θ(°)

Fig. 1. WAXD spectra of unirradiated and photo-irradiated

PP/EPDM, PP/EPDM/10%SGF, PP/EPDM/30%SGF com-

posites.

2132 W. Wang et al. / European Polymer Journal 39 (2003) 2129–2134

3.3. Morphological structures

The SEM micrographs of the impact surfaces of

unirradiated and photo-irradiated PP/EPDM/30%SGF

Fig. 2. SEM images of composites: (a) and (c) for PP/EPD

samples are shown as photo (a) and photo (b) in Fig. 2,

respectively. The impact surfaces determined are per-

pendicular to the flow direction. The photo (a) shows the

clean surface of SGF, which implies that no adhesion

exists between SGF and PP/EPDM matrix. However,

the photo (b) for photo-irradiated sample shows the

SGF is packed closely by the polymer matrix and some

polymer matrix may link to the surface of SGF. The

dynamically UV irradiation not only improves the in-

terface adhesion for SGF but also makes the EPDM

crosslink. Photo (c) and photo (d) show the EPDM

component in the unirradiated and photo-irradiated

blends. It can be observed from photo (c) that the dense

black voids exist in the micrograph, which are EPDM

droplets that had been etched by xylene. After photo-

irradiation, the size and number of black voids in

photo (d) become smaller and less compared with that in

photo (c). It can be explained that the crosslinked

EPDM particles can not be etched by xylene due to the

gelled network nature. Consequently, the crosslinked

EPDM component can improve the stiffness of its

composite.

The fiber length distributions in photo-irradiated and

unirradiated PP/EPDM/30%SGF samples are shown in

Fig. 3. The blending and injection process reduce the

length of glass fiber as expected. However, it is very in-

teresting to be found that there is a difference between the

photo-irradiated and unirradiated samples. In photo-ir-

radiated sample, SGF is closely packed by the polymer

matrix as a jacket which prevents SGF from fracture.

M/30%SGF; (b) and (d) for PP/EPDMir/30%SGF.

0.0 0.2 0.4 0.6 0.8 1.00

5

10

15

20

25

30

35

uncrosslinked photocrosslinked

Num

ber f

ract

ion

(%)

Fiber length (mm)

Fig. 3. Number fraction vs fiber length distribution of unirra-

diated and photo-irradiated PP/EPDM/30%SGF composites.

0 100 200 300 400 500 600 700 800 900

0

20

40

60

80

100 PP/EPDM PP/EPDM/10%SGF PP/EPDMir /10%SGF

Wei

ght (

%)

Temperature (°C)

Fig. 4. TGA curves of PP/EPDM, PP/EPDM/10%SGF, and

PP/EPDMir/10%SGF composites.

W. Wang et al. / European Polymer Journal 39 (2003) 2129–2134 2133

Therefore, the maximum value of fiber length distribu-

tion for photo-irradiated sample located at 0.5 mm is

higher than that for unirradiated sample at 0.3 mm.

3.4. Thermal behavior

Table 2 lists the data from DSC curves for PP, dy-

namically photo-irradiated PP/EPDM and PP/EPDM/

SGF composites in the temperature range of 30–200 �C.It can be seen that the melting points slightly decrease

with the EPDM incorporation and increasing the SGF

content in the PP/EPDM/SGF samples, when compared

with that of PP. This is due to the fact that the non-

crystallizable component EPDM and solid SGF inhibit

the crystal growth of PP, which thus leads to the for-

mation of small and unperfected PP crystals. The data of

crystallinity also give another evidence for the nega-

tive effects of EPDM and SGF to the crystallinity of

composites. The crystal structure mainly provides the

stiffness of a composite. On the other hand, the crys-

tallization temperatures increase slightly with increasing

the SGF content in the composites. This result can be

explained by that SGF acts as a heterogeneous nucle-

ation agent for PP, although the total content of crystal

decreases. The above thermal analysis data are in accord

with the results obtained from WAXD.

Table 2

Melting behavior and crystallinity of PP, dynamically photo-irradiate

Sample code Heat of fusion

(DH ), J/g

Meltin

(Tm), �

PP 84.1 169.1

PP/EPDMir 70.0 168.4

PP/EPDMir/5%SGF 46.7 166.8

PP/EPDMir/10%SGF 37.7 165.4

PP/EPDMir/20%SGF 37.1 165.2

PP/EPDMir/30%SGF 36.0 165.0

Fig. 4 shows the thermogravimetric analysis curves

for PP/EPDM, PP/EPDM/10%SGF, and PP/EPDMir/

10%SGF composites in the temperature range of 20–800

�C. The curve of PP/EPDM sample shows that the initial

degradation temperature, degradation temperature, and

total weight loss are 238, 386 �C, and 98.9% respectively,

compared with 294, 446 �C, and 89.3% for PP/EPDM/

10%SGF sample. However, it was found that photo-

irradiation has a small influence on the thermal behavior

of PP/EPDMir/10%SGF. Therefore, the incorporation

of SGF into the composite plays an important role for

improving the thermal stability of a composite.

4. Conclusion

The SGF and photo-irradiation can considerably

improve the mechanical properties of PP/EPDM blends,

especially for the tensile strength and notched Izod im-

pact strength. The WAXD measurements substantiated

the formation of b-type crystal of PP, which partly en-

hances the impact strength of dynamically photo-irra-

diated PP/EPDM/SGF composites. The SEM images

demonstrated that photo-irradiation process increases

the interface adhesion of SGF and matrix, whereas de-

creases the aggregation of EPDM particles and thus in-

creases the sites for dissipation of shock or impact energy

d PP/EPDM, and PP/EPDM/SGF composites

g temperature

C

Crystallization tem-

perature (Tc), �CCrystallinity,

%

118.1 40.2

119.5 33.5

121.1 22.3

121.6 17.9

121.9 17.8

122.8 17.2

2134 W. Wang et al. / European Polymer Journal 39 (2003) 2129–2134

in photo-irradiated PP/EPDM/SGF composites. The

melting and crystallization temperatures of the photo-

irradiated composites are not affected greatly by in-

creasing the SGF content. The thermal analysis results

show that the incorporation of SGF into PP/EPDM

plays an important role for increasing its thermal sta-

bility.

Acknowledgement

Contract grant sponsor: National Natural Science

Foundation of China (no. 50073022).

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