THE PROPERTIES OF REINFORCED POLYPROPYLENE

KOMISJA BUDOWY MASZYN PAN – ODDZIAŁ W POZNANIU
Vol. 28 nr 3
Archiwum Technologii Maszyn i Automatyzacji
2008
∗
ZOLTÁN BUDAI∗, ZSOLT TIBA , GYÖRGY DEÁK∗∗
THE PROPERTIES OF REINFORCED
POLYPROPYLENE COMPOSITES HAVING
DIFFERENT DISTRIBUTED FIBERS
The paper deals with reinforcing of polypropylene copolymers with homopolymer fibers.
There are several methods to produce reinforced polypropylene composites. One of them is to feed
homopolymer fibers into the molten plastic in the mixing chamber and after that specimens can be
cut away from this copolymers. An other method of producing specimens is that oriented homopolymer fibers are pressed between two semifinished polipropylene copolymer plates. Specimens
produced in this ways were tested by authors with tensile-testing instrument and the influence of
the different distribution of fibers on the mechanical properties of copolymer has been evaluated.
Key words: polypropylene homopolymer fiber, randomly distributed fibers, oriented fibers
1. INTRODUCTION
In several Eastern European countries the economy is quickly growing, plastic demand, especially that of polypropylene, is rising with very high rate. In
Hungary TVK Co. Ltd. (Tiszaújváros) is the only polyethylene, polypropylene
producer. They produce polypropylene homopolymer, random copolymers and
block/copolymers with ethylene.
The production and usage of polypropylene is dynamically growing, because
of the excellent properties wide applicability and relatively low cost of PP (almost as good as PVC). Recently much attention has been paid to the modification of properties of PP by making composites [1–5]. The main aim of these
blending is to improve the impact strength especially at low temperatures. Because of the easier dispose of PP compared to PVC, the medical equipment users
often ask how plasticized PVC can be replaced with PP.
Our aim was to investigate the possibility of the use of PP fiber to produce
composites with PP matrices. We planed to make PP composites containing
∗ Coll. Prof. Dr. hab PhD – University of Debrecen Centre for Agricultural Sciences and
Engineering Faculty of Engineering.
∗∗ Dr. – University of Debrecen Faculty of Science Department of Applied Chemistry.
126
Z. Budai, Z. Tiba, G. Deák
randomly mixed short PP fibers and we also wanted to make PP composites
containing oriented PP fibers. The homopolymer fibre is a trimming at the production of clingfilm getting from the manufacturer in the given size and form.
2. EXPERIMENTAL
We used PP fiber (ribbon) 20-115×3×0.07 mm H284F type. This polymer has
a softening point of 150oC. All the matrices used have a softening point of 130oC
(of course it is less than melting point), so there is a 20oC gap in the softening
range. The Table 1. shows the softening point and the MFI of the fiber and the
matrices. If the temperature of R889 type polipropylene copolymer during the
production is raising above 150oC the homopolymer fiber would melt in the
matrice. The kneading torque was not measured.
All polymers are made by TVK Co., Hungary.
Table 1
The softening points and the melt flow indices of the fiber and the matrices
Temperatura mięknienia oraz wskaźniki ciekłego włókna i matryc
PP type
Softening point
MFI (230oC, 21.6 N)
R 359
R 451 F
R 654
R 889
H 284 F
130oC
130oC
130oC
130oC
150oC
11 g/10 min
6.5 g/10 min
2.0 g/10 min
0.4 g/10 min
18 g/10 min
3. METHODS
The preparation of mixed PP composites were made in a Brabender typemixing chamber at 140°C for 5 min. The matrix was melted and the fiber was
introduced into the mixing chamber for about 1–5 minutes. The mixing chamber
was stopped, sample was taken from which plates were pressed while the sample
was hot. Next day the dumbbell specimen were cut out and tested.
The preparation of oriented fiber containing composites were the following:
Thin plates were made from the matrix and the fibers were fixed on the surface
with the use of a soldering iron then plate-fiber-plate sandwiches were pressed
together at 140°C for 10 minutes. The pressing temperatures of all the plates
were 140°C.
Specimens were cut out for testing.
The Figure 1. shows the dumbbell specimen having two oriented fibers.
The properties of reinforced polypropylene…
127
Fig. 1. Specimen with two oriented fibers (the measures are in mm)
Rys. 1. Próbka z dwoma zorientowanymi włóknami (wymiary w milimetrach)
4. INSTRUMENTS
A Brabender type of mixing chamber was used for mixing together the matrices and the fiber.
A Fontijne type table press was used for molding plates and the mechanical
testing was done by using a computer controlled Instron 4200 mechanical testing
instrument.
5. RESULTS AND DISCUSSION
Mechanical properties of the starting materials can be seen in Table 2. Other
properties of the fibre (e.g. shrinkage ability) were not tested which can significant influence the thermal stability of the composite.
Table 2
Mechanical Properties of the Starting Materials
Właściwości mechaniczne użytych do badań materiałów
Polymer
Stress at yield
[MPa]
Strain at yield
[%]
Modulus
[MPa]
R 359
R 451 F
R 654
R 889
H 284 F plate
H 284 F fiber
26
26
27
29
34
479
10
13
13
13
10
21
1000
850
800
1120
1400
3500
The polymers used for matrices have stress at yield lower than 30 MPa, but
the fiber has a higher value. So we hoped that the fiber could improve the mechanical properties of matrices.
128
Z. Budai, Z. Tiba, G. Deák
A typical stress-stain curve of the randomly mixed PP composite can be seen
in Figure 2. The yielding point is at about 10% of strain and the composite
breaks soon after yielding. Slight improvement of mechanical properties can be
observed only.
Fig. 2. A Typical Stress-Strain Curve for the Composite Having Randomly Distributed PP Fibers
Rys. 2. Typowe krzywe rozciągania kompozytu z losowo rozłożonymi włóknami PP
The Figure 3. shows the dependence of stress at yield versus fiber content.
The trend-line shows none or just a slight increase with increasing fiber content.
40
Stress at Yield [MPa]
35
30
25
R 359
R 452 F
20
R 654
15
10
5
0
0
10
20
30
40
50
60
Fiber Content [%]
Fig. 3. Stress at Yield vs Fiber Content (Randomly distributed fibers)
Rys. 3. Naprężenia przy granicy plastyczności w zależności od składu losowo rozłożonych włókien
The properties of reinforced polypropylene…
129
The Figure 4. shows the dependence of strain at yield on fiber content of
composites. The strain at yield decreases with the increasing fiber content of the
composites.
6
Strain at Yield [%]
5
4
R 359
R 451 F
3
R 654
2
1
0
0
10
20
30
40
50
60
Fiber Content [%]
Fig. 4. Strain at Yield vs Fiber Content (Randomly distributed fibers)
Rys. 4. Odkształcenie przy granicy plastyczności w zależności od składu losowo rozłożonych włókien
Figure 5. shows several typical stress-strain curves for the composites having
oriented fibers. The line 0% shows the behavior of the native polymer. When we
added 4% of oriented fiber a good increase in stress at yield can be observed.
Additional 4% of oriented fiber (altogether 8%) doubles the strength of the polymer composite. We found that we can predict the stress at yield value of composite with the use of the addition rule and the stress at yield value of pure starting materials. Figure 6 and 7 show the dependence of the stress and strain at
yield on the fiber content. Stress and strain at yield increase with the increasing
fiber content.
Fig. 5. Typical Stress-Strain Curves for the Composites Having Oriented Fibers
Rys. 5. Typowe wykresy rozciągania kompozytu o zorientowanych włóknach
130
Z. Budai, Z. Tiba, G. Deák
Stress at yield [MPa]
70
60
50
359
451
40
654
889
30
20
10
0
0
1
2
3
4
5
6
7
8
9
10
Fiber Content [%]
Fig. 6. Stress at Yield vs Fiber Content (Oriented fibers)
Rys. 6. Naprężenia przy granicy plastyczności w zależności od składu zorientowanych włókien
Strain at Yield [%]
30
25
359
20
451
15
654
889
10
5
0
0
1
2
3
4
5
6
7
8
9
10
Fiber content [%]
Fig. 7. Strain at Yield vs Fiber Content (Oriented fibers)
Rys. 7. Odkształcenia przy granicy plastyczności w zależności od składu zorientowanych włókien
6. SUMMARY
The mechanical properties of composites were investigated. The composites
were made from a polypropylene homopolymer fiber and several random polypropylene co- and polyethylene homopolymers.
Although very small difference exists in softening behavior of the matrix and
the fiber (130 and 150ºC) we were able to ensure the temperature difference and
in this way we could keep the fiber in its original form.
The PP fiber and PP-copolymer composites show an increasing stress at yield
by increasing the fiber content.
A significant increase in stress at yield was observed by increasing the
oriented fiber content.
The properties of reinforced polypropylene…
131
REFERENCES
[1] Calimberti M., Giannini U., Albizzati E. et al., J. Mol. Catal. A: Chem., 1995, 101, 1–10.
[2] Chung T.C., Lu H.L., Li C.L., Polymer Int., 1995, 37, 197–205.
[3] Lu Yan, Zhu Meifang, Zhang Yu, Chen Yanmo, Petrochem. Techn.&Application., 1999,
17(3), s. 138–141.
[4] Peckstadt J.-P., Chem. Fibers Int., 1997, 47(5), 342.
[5] Saheb D.N., Jog J.P., Advences in Polymer Technology, 1999, 18, 351.
[6] Xu G., Lin S., Macromol. Sci. – Rev., Macromol. Chem. Phys., Part C, 1994, 34, 555–606.
Praca wpłynęła do Redakcji 31.03.2008
Recenzent: prof. dr hab. inż. Tomasz Sterzyński
WŁAŚCIWOŚCI KOMPOZYTÓW POLIPROPYLENOWYCH
O RÓŻNIE ROZŁOŻONYCH WŁÓKNACH
S t r e s z c z e n i e
Artykuł dotyczy wzmacniania kopolimerów polipropylenowych włóknami homopolimerowymi. Istnieje kilka metod wytwarzania wzmocnionych kompozytów polipropylenowych. Jedną
z nich jest dodawanie homopolimerowych włókien w stanie ciekłym do komory mieszania, po
czym wycina się próbki z kopolimeru. Inna metoda wytwarzania próbek polega na tym, że zorientowane włókna homopolimerowe są prasowane między dwoma półwykończonymi płytkami kopolimeru polipropylenowego. Próbki wytwarzane w ten sposób były testowane przez autorów na
maszynie wytrzymałościowej, co pozwoliło na ocenę wpływu różnego rozłożenia włókien na
właściwości mechaniczne kopolimeru.
Słowa kluczowe: homopolimerowe włókno polipropylenowe, losowo rozłożone włókna,
włókna zorientowane