Effect of native starch on processing and vulcanizing properties of rubber blends
Annals of Warsaw University of Life Sciences - SGGW
Forestry and Wood Technology № 83, 2013: 317-321
(Ann. WULS - SGGW, For. and Wood Technol. 83, 2013)
Effect of native starch on processing and vulcanizing properties of rubber
blends
JÁN ORAVEC1), JOZEF PREŤO1), PETER JURKOVIČ1), JÁN MATYAŠOVSKÝ1),
IVAN CHODÁK2), ANDREA ORAVCOVÁ2)
1)
2)
VIPO, a.s., 958 01 Partizánske, Slovakia
SAV UP, Dúbravská cesta 9, 842 36 Bratislava, Slovakia
Abstract: Effect of native starch on processing and vulcanizing properties of rubber blends. Research and
development in the rubber industry in the last decades pay attention to application of biodegradable and natural
renewable bio-based fillers such as starch and lignin. Native corn starch as filler in the rubber model blends
accelerated crosslinking reaction and improved physical and mechanical properties of vulcanizates.
Keywords: starch, lignin, rubber blends, filler
INTRODUCTION
Fillers belong to important components of rubber blends because they modify
rheological properties of raw-rubber blend as well as physical properties of vulcanizates.
Research and development in the rubber industry in the last decades pay attention to
application of biodegradable and natural renewable bio-based fillers such as starch and lignin1.
The surfaces of starch contain a large amount of hydroxyl groups as the silica.
Starch/plasticizer composites have been suggested for use in elastomer composition for
various purposes, including tires2-4. Other biopolymers, such as lignin have been tested for use
as modifying components in rubber blends as filler with anti-degradation abilities5, substituent
of polymer matrix and also as modifier of some mechanical properties6.
EXPERIMENTAL
The model blends, consisting of a natural rubber or styrene butadiene rubber polymer
(NR or SBR), a bio-filler (native corn starch to 20 phr), and vulcanizing system (ZnO,
stearine, CBS, S) were evaluated (the effect on vulcanizing process, physical properties and
processing properties) and compared with the real blends consisting of all common rubber
blend components. The processing properties were evaluated using Extrusiongraph Brabender
L/D = 25; dye = 5 mm.
RESULTS AND DISCUSSION
In our present work the basic exploration of native corn starch as fillers in model as
well as in real rubber blends is reported.
Tab. 1 Vulcanizing and viscosity properties of model blends
NR based blends
Starch Ts2
Tc90
(phr) [min] [min]
0
3.01 5,65
5
2.53 4,74
10
2.39 4,67
15
2.45 4,66
20
2.50 4,64
Mmax
ML
[dNm] 1+4@100°C
14,3
31,7
14,9
32,6
15,5
32,9
16,7
34,1
17,7
34
SBR based blends
Starch Ts2
Tc90
(phr) [min] [min]
0
3.13 7,46
5
2.51 6,32
10
2.56 5,69
15
2.51 6,03
20
2.33
5,7
317
Mmax
ML
[dNm] 1+4@100°C
16,1
35,5
18,1
34,5
18,1
35,9
20,3
37
20
38,8
At first we used the model blends consisting of polymer (NR or SBR) native corn
starch and vulcanizing system (ZnO, stearine, N-Cyclohexyl-benzothiazole-2-sulphenamide,
S). The miscibility, processability and effect on vulcanizing and physical properties were
evaluated.
Fig. 1 Physical and mechanical properties of model blends.
It was found that in the model blends the starch as a filler affected the crosslinking
reaction. The values of optimum curing time Tc90 decreased and values of torque were
increased in both rubber blends. The physical properties such as tensile strength, tear strength
and elongation were also increased. This is caused by the reinforcing effect of the applied
filler into model blends and its principal compatibility with the tested polymers.
Tab. 2 Processing properties of model blends
NR based blends
Starch Weight
(phr) [g/min]
0
6.58
5
7.19
10
7.75
15
8.06
20
8.29
[mm]
8.59
8.26
8.39
8.10
7.88
M
[Nm]
30.0
38.3
40.5
44.6
45.1
SBR based blends
Density
[g/cm3]
0,9507
0.9634
0.9715
0.9837
0.9876
Starch Weight
(phr) [g/min]
0
5
10
15
20
5.98
6.01
6.18
6.45
6.24
[mm]
M
Density
[Nm] [g/cm3]
9.28
9.29
9.20
8.93
8.77
37.1
32.5
31.5
33.4
33.5
0.9659
0.9842
0.9961
1.0101
1.0134
The processing properties were also improved. The weight of the extruded material
under stead flow was increased and growing of extruded string diameter F was decreased with
increasing amount of a bio-filler. Densities of blends with increasing amount of starch filler
increased also, because model blends were not filled with any filler.
The corn starch was tested in the real rubber blends. Unmodified native corn starch
was applied as substitution of part of silica filler. Measured results showed slight or fairly
large effect on observed properties, depending on the proportion of substituted filler or raw
rubber. The vulcanizing characteristics such as scorch time Ts2, optimum curing time Tc90 of
NR real blend were lower, what means acceleration of crosslinking reaction and achieve the
optimum vulcanization took shorter time.
318
Tab. 3 Vulcanizing and viscosity properties of real blends.
NR based blends
Starch Ts2
Tc90
(phr) [min] [min]
0
2.82
6,8
5
2.6
5,93
10
2.38 5,24
15
2.26 5,12
20
2.15 4,87
Mmax
ML
[dNm] 1+4@100°C
8,7
39,6
8,6
24,9
8,1
23,2
8,4
24,8
8,2
21,4
SBR based blends
Starch Ts2
Tc90
(phr) [min] [min]
0
1.17 1,69
5
1.10 1,58
10
1.29 1,73
15
1.33
2
20
1.68 2,68
Mmax
ML
[dNm] 1+4@100°C
5,1
25,9
5,23
26,8
5,52
24,9
5,92
24,7
5,5
23
Contrariwise, the value of Ts2, Tc90 of SBR real blend were higher, what indicates
different effect of starch in crosslinking reaction in SBR based blend. ML value of Mooney
processing viscosity decreases in both cases.
Fig. 2 Physical and mechanical properties of real blends.
The application of the biopolymer to the real rubber blends as substitution of a part of
white fillers, caused a decreases of the tensile strength, elongation and tear strength values
with the increasing amount of native corn starch. At a lower level of the substitution the
declination is not substantial what indicates a practical application especially after
modification of the filler.
Biopolymers have the different effect on the vulcanization process depending on their
chemical nature and their application in rubber blends must be affiliated with modification of
the vulcanization system.
The processing properties of real rubber blends were improved also. The weight of the
extruded material under stead flow in case of NR based blend the increase was higher in
comparison with SBR blends and growing of extruded string diameter F was decreased with
increasing amount of a bio-filler. Also densities of blends with increasing amount of starch
filler increased slightly also, because volume weight of corn starch is higher in comparison
with substituted fillers.
319
Tab. 4 Processing properties of real blends
SBR based blends
NR based blends
Starch Weight
(phr) [g/min]
0
6.58
5
7.19
10
7.75
15
8.06
20
8.29
[mm]
8.59
8.26
8.39
8.10
7.88
M
[Nm]
30.0
38.3
40.5
44.6
45.1
Density
[g/cm3]
0,9507
0.9634
0.9715
0.9837
0.9876
Starch Weight
(phr) [g/min]
0
5.98
5
6.01
10
6.18
15
6.45
20
6.24
[mm]
9.28
9.29
9.20
8 (...truncated)
