The 3nd International Conference on [600300]

The 3nd International Conference on
DIAGNOSIS AND PREDICTION
IN MECHANIC AL ENGINEERING SYSTEMS
DIPRE 12

1
The 3nd International Conference on
DIAGNOSIS AND PREDICTIONIN MECHANICAL ENGINEERING SYSTEMS
May 31 – June 1, 2012, Galați, Romania

INFLUENCE OF ADDING MICRO GLASS BEADS
IN A PBT MATRIX ON T HE MECHANICAL PROPER TIES

Mihail BOTAN , Constantin GEORGESCU, Lorena DELEANU

“Dunarea de Jos ” Univ ersity of Galati, ROMANIA

[anonimizat] , [anonimizat]

ABSTRACT
This pa per presents the influence of the adding materials (micros glass spheres) in a
matrix of PBT on several mechanical properties: elasticity modulus, stress at break ,
elongation at break , energy at break.
The mechanical properties of these composites depend on the glass beads
concentration. The additivation of polybuthylen therephtalate with glass beads increases the
values of the elasticity modulus , but reduces quite drastically the elongation at break. The
authors pointed out, by SEM investigation, the part icular aspects of fracture surfaces: a
ductile process at sample margins and a brittle one in the middle of the composite.

Keywords: PBT, glass beads, composite , elasticity modulus, stress at break, elongation
at break, energy at break

1. INTRODUCTION

It is a basic problem with the tests that the result
will vary with the test piece geometry and the test
conditions and it may not be easy to extrapolate to
different conditions [ 7-9].
Even if there are many standards relat ed to
short -term tensile testing , they endeavor to quantify a
number of specific characteristics , which relate to the
strength and deformation of a material. Knowledge
of these characteristics can supply the designers with
the potential performances of a material and a reliable
basis of com paring materials [ 8, 19 ].
The term „short term mechanical tests‟ is used as
a convenience to describe mechanical properties
where the effects of long times and cycling are
ignored. This group of tests includes hardness,
tensile, compression, shear, flexing , impact and tear.
The material properties require to be rated for
generating design data, for quality controlling, for
predicting their durability and, unfortunately but
necessarily for investigating failures. The polymers
have a complex behavio r, thus, m ore than any
material, they have to be evaluated in a useful way
by particular or adequately adapted method s [8]. Polymeric materials are non -linear and their
stress -strain characteristic is not linear and hence
their modulus is not a constant [1, 2, 8, 9 ].
The use of PBT as an engineering material is a
consequence of a balance of good properties rather
than of a few outstanding ones. It does not possess
the toughness of polycarbonate (PC), the abrasion
resistance of an aliphatic polyamide, the heat
resista nce of a polysulphone, polypheny1ene sulphide
(PPS) or polyketone, the low water absorption of a
modified poly( p-phenylene oxide) (PPO).
However, PBT , when it is suitably modified by,
for example, glass fiber or fire retardants, some very
useful compounds can be produced. The particular
characteristics of PBT pointed out by the suppliers
[9, 26, 27 ] include:
– high softening temperatures (especially for
composites with glass or carbon fibers , challenging
the use of PC and modified PPOs);
– high rigidity, exceed ed only by PPS among
the engineering thermoplastics;
– good electrical insulation properties for an
engineering thermoplastic as compared to PC,
modified PPOs, PPS and the polyether imides;
– low friction and good abrasion resistance;

INFLUENCE OF ADDING MICRO GLASS BEADS
IN A PBT MATRIX O N THE MECHANICAL PRO PERTIES

2
The 3rd International Conference on
DIAGNOSIS AND PREDICTION IN MECHANICAL ENGINEERING SYSTEMS
May 31 – June 1, 2012, Galat i, Romania – good impact strength at low temperatures and
excellent creep rupture strength;
– low water absorption and good chemical
resistance, including resistance to stress cracking;
– good dimensional stability, a consequence of
the low water absorption but also because of a low
coeffi cient of thermal expansion;
– good moldability (easy flow and rapid setting ).
A large number of PBT grades is available,
including unreinforced, glass – and carbon -fiber
reinforced, mineral filler reinforced, impact
modified, elastomer modified, flame retar dant and
various combinations of the foregoing [ 9, 15, 16, 24,
27, 28 ].

2. THE GLASS BEADS A S ADDING
MATERIAL IN A POLYME RIC MATRIX

C type glass is adequate for using in chemically
aggressive environments, especially acids. This
outstanding chemical resista nce is a consequence of
its composition, typically as following: at least 60%
SiO 2, Li and Na oxides , Yn and Ca oxides and also
rare earth oxides with small amounts of Al2O3, B2O3,
Fe2O3, TiO 2, MnO and SnO 2 [17, 18]. Adding this
type of reinforcing materia l influences the
technological properties [5, 6, 10, 25 ] the mechanical
ones [3, 4, 11 -13, 22 ] and the tribological ones [14,
20].
In 2010, Akiyama et al. [ 2] reported a modifying
tendency of the mechanical properties of the
composites with ceramic particl es (average diameter
of 150 m) a little more greater than the glass beads
introduced in PBT for this study and more ragged as
compared to the almost spherical shape of the glass
beads (Fig. 5). Adding 60% of ceramic particles in
PBT makes the elastic modu lus to increase to 7500
MPa, 2.5 times greater than pure PBT, but the tensile
at break decreases with 10…12% and Vickers
hardness has a double value .

a) b) c)
Fig. 1. Damaging m odels of the interface in
composites with spherical particles [21] Medadd and Fisa [ 21] have proposed a
damaging model of the interface when samples were
load with tensile forces (Fig. 1) that proved to be
suitable to explain the PBT + glass beads composite
behavior in a qualitative way. Break at traction of a
composite with spherical part icles depends very
much on the chemical and mechanical nature of the
interfaces between the polymer and the hard
particles :
a) the r esistance interface is not damaged under
loading and the break is initial ly developed in the
composite matrix ;
b) an interface partially damaged, usually
dependent on the elasticity modulus, the volume
fraction of the adding material without damaged
interfaces and the complementary volume fraction of
the adding material that is characterized by a
damaged interface (the ration between these two
interface categories being very hard to be estimated) ;
c) a wick defective interface that is easy to be
destroyed when applying the load .
The difficulty is that the sample made of such a
composite is loaded, all the above -described
processes could occur, with different contribution to
the final fracture.
Several research works reported that even if the
glass beads bearing different treatment, the
mechanical properties do not had significant
modifications (Fig. 1.7) [21].

a) untreated b) treated by silan (SiH 4)
Fig. 2. Aspects of the tensile fracture surface for a
composite PS+10% GB [M12]

Dekkers and Heikens [ 12, 13] noticed that, for
polymeric composites, the band forming mechanism
at traction is fundamentally different, depending on
the treatment applied to glass beads . After analyzing
the stresses, they concluded that the bands '
gene ration had occurred in the zones characterized
by maximum values for the main shear stress and by
maximum values of the strain energy (Fig. 3) .

INFLUENCE OF ADDING MICRO GLASS BEADS
IN A PBT MATRIX ON T HE MECHANICAL PROPER TIES

3
The 3rd International Conference on
DIAGNOSIS AND PREDICTION IN MECHANICAL ENGINEERING SYSTEMS
May 31 – June 1, 2012, Galat i, Romania

a) a good adherence
between matrix and glass
beads , using -
aminopropil silan a) without adherence
between glass bead and
the polymer matrix, as
obtained with silicon oil
Fig. 3. Tensile fracture zones of the composite
PC + GB [13]

3. TESTING METHODOLOGY MATERIALS

The s amples were obtained by extruding the
mixtures of granulated PBT and glass beads (Fig. 5),
in thre e mass concentrations (Table 1), at ICEFS
Savinesti, Romania. The p olymer had been dried up
at a temperature of 100șC within two hours. There
were obtained bone samples with the geometry and
dimensions given in Figure 4 and a thermal treatment
was applied to the bone samples, as recommended by
the producer [ 27].
The initial distance between the gauge marks on
the central part of the test specimen was of 115 mm,
the rate of separation of the grips of the testing
machine during test 5 mm/min (the s peed of tes ting)
and the it was calculated the t ensile Stress
(engineering), that is the tensile force per unit area of
the original cross section within the gauge length,
carried by the specimen at any given moment.
The here -presented results include data for at
least 5 tensile tests and it was calculated the average
value for each mechanical characteristics and there
also were presented the scattering intervals for each
one. Stress was calculated with reference to the
initial values of the cross section, thus, there are
given the engineering stress -strain curves for each
material.

Fig. 4 . The bone sample Type 1A ISO 527 -2
Table 1. The tested materials
Material
symbol Composition ( %wt)
PBT neat polymer ,
grade Crastin 6130 NC010 [10]
GB10 10% GB glass bead + 1.5…2 % PA + 1%
black carbon ,
for technological reason GB20 20% GB
GB30 30% GB

Fig. 5. The glass beads before being mixed with PBT

The traction tests were done with the help of the
universal testing machine TESTOMETRIC M350 –
5AT, having a force c ell of 5 kN, as recommended
by EN ISO 527 -2 [25], in the Laboratory of
Polymeric Materials Research (Faculty of
Mechanical Engineering, "Dunarea de Jos"
University of Galati).
The values for the mechanical properties were
calculated as the average of five tests that the authors
consider to have no anomalous features and in
accordance with the literature [9, 24, 27, 28 ].

3. EXPERIMENTAL RESULTS

For PBT, the stress -strain curves (Fig. 7a) have
the same aspect as presented in [4, 5, 16, 24 ]; it was
noticed a typical creep zone for the thermoplastic
polymers , as this polymer could be included in the
class of t ough materials with a yield stress l ower than
the failure s tress [ 8]. The composites have the shape
of the stress -strain curves typical for brittle mat erials
(Fig. 7b, c and d).
The authors applied Einsteins's model for having
a dependency of the mechanical properties on the
mass concentration of glass beads ,
Ec = E m (1 + V f), (1)

INFLUENCE OF ADDING MICRO GLASS BEADS
IN A PBT MATRIX O N THE MECHANICAL PRO PERTIES

4
The 3rd International Conference on
DIAGNOSIS AND PREDICTION IN MECHANICAL ENGINEERING SYSTEMS
May 31 – June 1, 2012, Galat i, Romania where Em is the elasticity m odulus of the matrix and
Vf is the volumic frac tion of the adding material. For
the composite with 10% GB, the value of the
elasticity modulus as experimentally determined is
greater with 10.8% as compared to the value given
by Eq. ( 1) and for the composit e with 20% GB, the
experimentally obtained value is greater with 21.3%
as compared to the theoretical value given by the
same model of mixture. The elasticity modulus and
the density for glass beads were taken from literature
[13, 21]: Ef=70000 MPa, ρf = 1.6 g/cm3.
Analyzing Fig. 3.4, the following remarks may
be done :
– the elasticity modulus of these composites with
PBT matrix increases almost linearly with the massic
concentration of GB ;
– stress at break for the composite with 10% GB
is just 10% higher than the polymer but the
composites with 10% GB and 20% GB have lower
values, 85% and 63%, respectively from the values
exhibits by the polymer (Fig. 6b) ;
– elongation at break decreases with ~72% for
PBT + 10% GB and with ~ 92% for the composite PBT + 20% GB, as compared to the value obtained
for PBT .
The composites have reduced elongation at
break (Table 2 and Fig. 6c) and all the samples did
not present the typical bottle neck shape
characterizing the polymer.
There is a clear tendency of decreasing the value
for the strength limit only for the composite with
20% and 30% GB, respectively.

Table 2. The average values of several mechanical
properties for the tested materials
Characteristic Material
PBT GB10 GB20 GB30
Elasticity
modulus, E
[N/mm2] 1923. 458 2358. 356 2848. 581 4087. 458
Stress at break,
σr [N/mm2] 41.571 40.265 36.543 25.795
Elongation at
break , εr [mm] 9.404 2.609 0.763 0.411
Energy at break,
[N·m] 17.665 2.207 0.701 0.294

a) Elasticity modulus b) stress at break c) elongation at break
Fig. 6. The average values and the scattering ranges for the discussed mechanical characteristics
of the tested materials

Strain (%)Stress (N/mm2)
0 1 2 3 4 5 6 7 8 9 100102030405060
0 1 2 3 4 5 6 7 8 9 100102030405060
PBT
Test 1
Test 2
Test 3
Test 4
Test 5

a) the set of five samples, after being tested a) the set of five samples, after being tested
Fig. 7 . The stress -strain curve (left) for PBT and the tested samples (right)

INFLUENCE OF ADDING MICRO GLASS BEADS
IN A PBT MATRIX ON T HE MECHANICAL PROPER TIES

5
The 3rd International Conference on
DIAGNOSIS AND PREDICTION IN MECHANICAL ENGINEERING SYSTEMS
May 31 – June 1, 2012, Galat i, Romania
Strain (%)Stress (N/mm2)
0 1 2 301020304050
GB_10
Test 1
Test 2
Test 3
Test 4
Test 5
a) PBT + 10% GB
Strain (%)Stress (N/mm2)
0 1 2 301020304050
GB_20
Test 1
Test 2
Test 3
Test 4
Test 5

b) PBT + 20% GB
Strain (%)Stress (N/mm2)
0 1 2 301020304050 GB_30
Test 1
Test 2
Test 3
Test 4
Test 5

c) PBT + 30% GB
Fig. 8. The stress -strain curves for the composite PBT+GB ( left) and the sets of the samples after break ( right )

Table 2. Data upon the mathematical models attached to the experimental data

Material
symbol Relation Correlation
coefficient Standard error
about the line
PBT y = –0.741 + 50. 492 x + 57.331 x2 – 124.096 x3 + 89.270 x4 –
– 34.749 x5 + 8.185 x6 – 1.201 x7 + 0.107 x8 – 0.005 x9 + 0.0001 x10 0.999 0.376
dd
xbxcbay

(Fig. 4)
a =2.886, b =0.1674, c =50.597, d =2.255 0.996 0.667
GB10 y=-0.356+82.17 1x – 36.466×2 0.999 0.304
GB20 y=-0.871+ 93.729x – 57.723×2 0.999 0.396
GB30 y = 1.513x+ 119.147 – 88.929×2 0.993 0.701

INFLUENCE OF ADDING MICRO GLASS BEADS
IN A PBT MATRIX O N THE MECHANICAL PRO PERTIES

6
The 3rd International Conference on
DIAGNOSIS AND PREDICTION IN MECHANICAL ENGINEERING SYSTEMS
May 31 – June 1, 2012, Galat i, Romania
SEM images show that the damaging process of
the interface has an intermittent nature (Fig. 8b
reveals a bigger glass bea d that was discontinuously
detached from the matrix). For the tested composites,
the 1% PA, even small, could influence the interface
resistance, having a greater ductility and adherence
to the glass beads as compared to PBT .
Analyzing the SEM images from small scale to
larger ones, one may notice the existence of two
types of surface aspect. At the sample margins the
fracture surface has a ductile nature but towards the
center of the sample the aspect becomes brittle (Figs.
7 and 8).

a) The ductile (at the sample margin – right) and
brittle (left) aspects of the fracture section

b) Intermittent detaching of the glass beads in
the middle of the fracture section

Fig. 9. Typical aspects of the fracture section for the
samples made of the composite PBT + 10% GB

a) The zone of ductile fracture

b) The middle zone of the fracture, with brittle aspect

Fig. 10. Typical aspects for tensile break surface of
the composite PBT + 20% GB

CONCLUSIONS

The additivation of polybuthylen therephtalate
with glass beads incr eases the values of the elasticity
modulus but reduces quite drastically the elongation
at break. The obtained results point out the
importance of testing the polymers and their
composites.
The authors elaborated mathematical models for
each tested materi al. The mat hematical models could
be useful in analyses w ith finite elements in first step
evaluation of a design.

INFLUENCE OF ADDING MICRO GLASS BEADS
IN A PBT MATRIX ON T HE MECHANICAL PROPER TIES

7
The 3rd International Conference on
DIAGNOSIS AND PREDICTION IN MECHANICAL ENGINEERING SYSTEMS
May 31 – June 1, 2012, Galat i, Romania REFERENCES

1. Agbossou A., Bergeret A., Benzarti K., Alberola N.,
1993, Modelling of the viscoelastic behaviour of amorphous
thermoplastic/gla ss beads composites based on the evaluation
of the complex Poisson's ratio of the polymer matrix, Journal
of Materials Science , pp. 1963 -1972.
2. Akiyama, M., Yamaguchi, T., Matsumoto, K. ,
Hokkirigawa, K., 2010, Polymer Composites Filled with
RB Ceramics Part icles as Low Friction and High Wear
Resistant Filler. Tribology online , Vol. 5, No. 1, January ,
pp. 19 -25.
3. Arencon D., Velasco J.I. , Realinho V., Antunes M.,
Maspoch M.L., 2007, Essential work of fracture analysis of
glass microsphere -filled polypropylene and
polypropylene/poly (ethylene terephthalate -co-isophthalate)
blend -matrix composites, Polymer Testing , 26, pp. 761 -769.
4. Bai S. -L., 2000, The role of the interfacial strength in
glass bead filled HDPE, Journal of Materials Science Letters ,
19, pp. 1587 -158.
5. Banik K., Mennig G., 2006, Influence of the Injection
Molding Process on the Creep Behavior of Semicrystalline
PBT During Aging Below its Glass Transition Temperature,
Mechanics of Time -Dependent Materials , 9, pp. 247 -257.
6. Bessmertnyi V.S., Krokhin V.P., Lyashko A.A.,
Drizhd N.A., Shekhovtsova Zh. E., 2001, Production of
Glass Microspheres Using the Plasma -Spraying Method,
Glass and Ceramics , vol.58, nos.7 -8.
7. Brandrup, J., Immergut, E.H. & Grulke E.A. (Ed.),
2003, Polymer Handbook 4th Edition , Wiley -Interscience,
England
8. Brown, R., 2002, Handbook of Polymer Testing – Short –
Term Mechanical Tests , Rapra Technology, U.K.
9. Brydson, J.A. 1999, Plastics Materials, 7th Edition ,
Butterworth -Heinemann, Oxford.
10. Bula K., Jesionowski T., Krysztafkiewicz A., Janik J.,
2007, The effect of filler surface modification and processing
conditions on distribution behaviour of silica nanofillers in
polyesters, Colloid Polym Sci , 285, pp.1267 -1273.
11. Crowson R.J., Arridge R. G. C., 1977, The elastic
properties in bulk and shear o f a glass bead -reinforced epoxy
resin composite, J. of Materials Science , 12, pp. 2154 -2164 .
12. Dekkers M. E. J., Heikens D., 1985, Crazing and shear
deformation in glass bead -filled glassy polymers, Journal of
Materials Science , 20, pp. 3873 -3880 .
13. Dekkers M. E. J., Heikens D., 1984, Shear band
formation in polycarbonate -glass bead composites, Journal of
Materials Science ,19, pp. 3271 -3275.
14. Deleanu L., Andrei G., Maftei L., Georgescu C.,
Cantaragiu A., 2011, Wear maps for a class of composites
with polyamide m atrix and micro glass spheres, J. of the
Balkan Tribological Association , vol. 17, n o 3, pp. 371-379.
15. Deshmukh G.S., Peshwe D.R., Pathak S.U., Ekhe
J.D., 2011, A study on effect of mineral additions on the mechanical, thermal, and structural properties of poly(butylene
terephthalate) (PBT) composites, J Polym Res , 18, pp. 1081 –
1090 .
16. Deshmukh G.S., Peshwe D.R., Pathak S.U., Ekhe
J.D., 2011, Evaluation of mechanical and thermal properties
of Poly (butylene terephthalate) (PBT) composites reinforced
with wolla stonite, Transactions of The Indian Institute of
Metals , vol. 64, issues 1 & 2, February -April, pp. 127 -132.
17. Kolesov Yu. I., Kudryavtsev M. Yu., Mikhailenko N.
Yu., 2001, Science for Glass Production Types and
Compositions of Glass for Production of Contin uous Glass
Fiber (Review), Glass and Ceramics , vol. 58, nos. 5 -6.
18. Lahiri J., Paul A., Effect of interface on the mechanical
behaviour of glass bead -filled PVC, Journal of Materials
Science , 20, pp. 2253 -2259, 1985.
19. Le Blanc J., 2010, Filled Polymers. Scien ce and
Industrial Applications, Taylot & Francis Group .
20. Maftei L., 2010, Contribuții la studiul comportării
tribologice a compozitelor cu poliamidă și microsfere de sticlă,
PhD, "Dunarea de Jos" University , Galati, 2010.
21. Meddad A., Fisa B., 1997, Filler –matrix debonding in
glass bead -filled polystyrene, Journal of Materials Sci ence, 32
pp. 1177 -1185.
22. Sánchez -Soto M., Gordillo A., Maspoch M. LL.,
Velasco J.I., Santana O.O., Martínez A.B., 2002, Glass bead
filled polystyrene composites: morphology and fracture,
Polymer Bulletin , 47, 587 -594.
23. Tsui C.P., Chen D.Z., Tang C.Y., Uskok ovic P.S., Fan
J.P., Xie X.L., 2006, Prediction for debonding damage
process and effective elastic properties of glass -bead-filled
modified polyphenylene oxide, Composites Science and
Technology , 66, pp. 1521 -1531 .
24. Vincent L., Connolly S. N., Dolan F., Willcocks P.H.,
Pendlebury R., 2006, Deter mination and Comparison of the
Plane Stress Essential Work of Fracture of Three Polyesters
PET, PPT and PBT, Journal of Thermal Analysis and
Calorimetry, Vol. 86, 1, pp. 147 -154.
25. Yang W., Liu Z. -Y., Shan G. -F., Li Z. -M., Xie B. -H.,
Yang M. -B., 2005, Study on the melt flow behavior of glass
bead filled polypropylene, Polymer Testing , 24, pp. 490-497.
26. *** DuPont Engineering Polymers. Blow Moulding
of Technical Components, Available from:
http://www2.dupont.com/Plastics/en_US/assets/downloads
/processing/BM_PM_e. pdf Accessed: 2012 -01-12
27. *** DuPont. Crastin® PBT. thermoplastic polyester
resin Crastin® 6130 NC010, Available from:
http://plastics.dupont.com/plastics/dsheets/crastin/CRASTI
N6130NC010.pdf Accessed: 2012 -01-12
28. *** Polybutylene Terephthalate (PBT), on-line:
http://www.rtpcompany.com/info/guide/descriptions/1000.
htm Accessed: 2012 -01-23.
29. *** SR EN ISO 527 -2:2000 Materiale plastice.
Determinarea proprietăților de tracțiune. Partea 2: Condiții de
încercare a materialelor plastice pentru injecție și extrudare.