Volume 9, January 2014

01| 2014

Magazine for the Polymer Industry

S. Kuwahara, M. Gründken,

R. Böhm

Polymer development for sustainable product design

Kuraray Liquid Rubber (KLR) is a reactive plasticizer based on isoprene and/or butadiene. KLR is colourless, transparent and almost odorless. Also KLR has very low VOC values. Applications: Rubber goods, Adhesives, Sealants, Coatings and others.

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30 RFP 1/2014 – Volume 9

Liquid rubber

Shigenao Kuwahara

shigenao.kuwahara@kuraray.eu

Marcel Gründken, Ralph Böhm

Kuraray Europe GmbH, Hattersheim am Main,

Germany

1. Introduction

Plasticizers are one of the key components of the rubber and adhesives industry. They are used to lower hardness, improve process-ability and reduce raw material cost. On the other hand, mechanical properties can dete-riorate with increasing plasticizer content. In addition, plasticizers often cause changes in properties with time and staining due to vol-atilization or bleeding. Phthalate plasticiz-ers and aromatic oils are or possibly will be regulated due to environmental and human health issues. KLR are plasticizers that are co-vulcanizable with solid rubbers. Therefore it is very unlikely that KLR will be subject to these bleeding or volatilization issues. As a result, we expect KLR have a growth poten-tial as environmentally friendly plasticizers.

2. Characteristics of Kuraray Liquid Rubber (KLR)

KLR is a low molecular weight poly-diene. The molecular weight is designed

between a typical solid rubber and plasti-cizer as shown in figure 1. KLR, therefore have characteristics of both rubbers and plasticizers, namely vulcanizability with solid rubbers and excellent plasticizing ef-fects. We call our liquid rubber a “reactive plasticizer” due to these properties. KLR is available in homopolymer (standard grade), copolymer and modified types (hydrogen-ated, carboxylated, and methacrylated). These polymers consist of isoprene, buta-diene and styrene (fig. 2).

3. Effect in NR/carbon black compounds

Typical properties of KLR are shown in table 1. The polymers were mixed with nat-ural rubber, carbon black and vulcanizing agents with a Banbury mixer and laboratory

Polymer development for sustainable product designAdvantages of liquid rubber in tire compounds

S. Kuwahara, M. Gründken, R. Böhm

Kuraray has developed a series of liquid rubbers with molecular weights rang-ing from 5,000 to 70,000. The polymers, which consist of isoprene, butadiene and styrene, can be used by rubber processors to achieve improvements in properties and processing. They are designed to have a plasticizing effect and offer vulcaniz-ability with solid rubbers. These properties allow the materials to act as “reactive plasticizers” or “co-vulcanizable plasticizers”. Liquid rubbers can be used for a wide range of applications including rubber goods (tires, belts), adhesives (solution, hot melt, latex, UV curable), automotive/construction sealants and others (printing plate, coating). The main application of Kuraray Liquid Rubber (KLR) is in rubber goods, particularly in tire compounds. KLR can be used for various parts of the tire, including tread, carcass, side wall, and bead filler.

MW

100

1,000

10,000

100,000

1,000,000

Liquid rubbers

NR, SBR

Process oilLiquid polybutene

Rubber

Plasticizer

Isoprene

KurarayLiquid Rubbers

Standard

Hydrogenated

Standard

NR, IR modifier, tires, PSA

Cross-link type sealants

SBS modifier, Hot melt PSA

SIS modifier, Hot melt PSA

SBS modifier, flexo plateButadiene

LIR-15*, LIR-30,LIR-50

LIR-290

LIR-310

LIR-390

LIR-700

LIR-403, LIR-410

Styrene/butadienerandom

LBR-307, LBR-305LBR-352*, LBR-353*

L-SBR-820L-SBR-841*

Ip/St copolymer

Ip/Bd copolymer

Emulsification

Carboxylated

Standard

EPDM, IIR modifier, PSA

NR, SBR latex modifier

SBR modifier tire

UV curable adhesivesUC-102 ,UC-203Methacrylated

*Commercialization in progress

Fig. 1: Molecular weight of liquid rubber

Fig. 2: Grade line of KLR

RFP 1/2014 – Volume 9 31

roll mill in two formulations (NR/CB/plasti-cizer = 100/50/10 and 100/50/6).

Mooney viscosity values are shown in figure 3. The plasticizing effect of KLR was equivalent to TDAE in natural rubber formu-lations. Furthermore, low molecular weight KLR showed a better level of plasticizing ef-fect in comparison to TDAE and all KLR for-mulations maintained tensile strength and elongation with TDAE formulations.

Properties of DIN abrasion are shown in figure 3. LBR formulations showed a better level of wear resistance compared with TDAE.

3.1 Performance in tires

Tire labeling has been introduced in the EU in November 2012, and has also been adopted by countries outside Europe such as Japan and South Korea. Key indicators are fuel efficiency, noise and break safety. Scientists connected these properties with physical detectable properties such as tan δ and storage modulus E’. As the tire ro-tates under the weight of the vehicle, it experiences repeated cycles of deforma-tion and recovery, and it dissipates energy as heat. This phenomenon, called hysteresis loss and is the main cause of energy loss

associated with rolling resistance. On the other hand, the tire is also deformed dur-ing braking and sliding on the rough road surface, and accordingly dissipates ener-gy. This hysteresis loss relates to frictional force between the tire and road surface.

Hysteresis loss is attributed to the viscoelastic characteristics of the rubber com-position. The loss tangents (tan δ) at -20, 0, 25 and 60 °C have been used to indicate ice, wet, dry traction, and rolling resistance properties respectively when the measurement is carried out at 10 Hz condition (fig. 4).

Storage modulus (E’) is measured with a high torque dynamic mechanical analysis unit, Eplexor (Gabo Qualimeter Testanlagen GmbH) under conditions of static strain of 0.5 % and dynamic strain of 0.1 % (fig. 5). The E’ of the LBR was much lower than that of TDAE because LBR has the lower Tg. Therefore, LBR is expected to keep softness of vulcanized natural rubber compositions at lower temperature and improve ice trac-tion control.

Liquid rubber Structure MnMelt viscosity at 38 °C / Pa·s

Glass transition temperature / °C

LIR-30 IR 28,000 70 –63

LIR-50 IR 54,000 500 –63

LBR-300* BR 44,000 225 –95

LBR-305 BR 26,000 40 –95

LBR-307 BR 8,000 1.5 –95

L-SBR-820 SBR 8,300 350 –14

L-SBR-841* SBR 10,000 130 / 60 °C –6

*Commercialization in progress

40

45

50

55

60

65

0 20,000 40,000 60,000

Molecular weight / Mn

Moo

ney

visc

osit

y / M

L1+

4

None

TDAE

LBR

LIRL-SBR

28

30

32

34

520 540 560 580 600

Elongation / %

Tens

ile s

tren

gth

/ MPa

None

TDAE

L-SBR

High Mw

LIRHigh Mw

LBR

L-SBR-841

115 125 135 145 155 165

TDAE

LIR-50

LBR-307

LBR-300

Wear volume / mm3

-80 -60 -40 -20 20 40 60 800

10

1

0,1

0,01

Tan

δ

Temperature / °C

10 Hz

Ice

trac

tion

Wet

trac

tion

Dry

trac

tion

Rolli

ng re

sist

ance

10

100

1,000

-50 -40 -30 -20 -10 0Temperature / °C

E' /

Mpa

Good

L-SBR-841TDAELIR-50LBR-307

Tab. 1: Typical properties of KLR

Fig. 3: General properties (NR)

Fig. 4: Viscoelastic characteristics Fig. 5: Storage modulus E‘

32 RFP 1/2014 – Volume 9

Liquid rubber

0.0

2.0

4.0

6.0

8.0

10.0

10 100 1,000 10,000 100,000

Molecular weight / Mn

Tolu

ene

extr

acts

/ w

t%

Control

TDAE

LIRLBRL-SBRControl/TDAE

Figure 6 shows the results of a tolu-ene extraction test for each vulcanized composition in the formulation (NR/CB/plasticizer = 100/50/6). Extracts of high molecular weight KLR formulations were almost the same as the control since they were co-vulcanized with natural rubber. On the other hand, process oils were ex-tracted completely. The extraction test also indicated another advantage of KLR. KLR can maintain the flexibility of vulcanized compositions for long periods because it does not bleed out. This is unlike the behavior of process oil. These properties are suitable for winter tires in which high traction and long term flexibility are re-quired rather than all-season tires which prioritize fuel economy.

4. Effect in SBR/silica compounds

KLR were mixed with SBR, silica and vul-canizing agents with a Banbury mixer and laboratory roll mill in the formulation (SBR/silica/plasticizer = 100/50/10).

Properties of Mooney viscosity are shown in figure 7. The plasticizing effect of KLR was almost equivalent to TDAE in SBR formulations. Especially, LBR showed an excellent level of plasticizing effect and LBR-307 formulations showed better elongation compared with TDAE formula-tions. Properties of DIN abrasion are shown in figure 7. LBR showed a better level of wear resistance compared with TDAE as well as natural rubber and carbon black composition.

4.1 Performance in tires

The tan δ and E’ were measured with the same analysis unit, Eplexor under conditions of static strain of 10 % and dynamic strain of 5 % (fig. 8). The tan δ of the L-SBR at 0 °C was much higher than that of TDAE but L-SBR also increased tan δ at 60 °C slightly because L-SBR has the higher Tg. From these results, L-SBR is expected to improve wet grip although it deteriorates rolling resist-ance a little.

5. Summary

With polymer development for sustainable product design we managed to combine bene-fits from unique technology of liquid polymers as reactive plasticizers. This results in our unique polymer structure with high plasticizing effect. The effect of co-vulcanizability at higher level of molecular weight compared with standard oils like TDAE provides low migration property over all grades and supports better environ-mental protection with longer life durability.

0.22

0.24

0.26

0.28

0.30

0.32

0.34

8 9 10 11E' / MPa

tan

δ

tan

δ

Wetgrip

L-SBR-841

L-SBR-820

TDAE

None

0.12

0.14

0.16

0.18

0.20

0.22

0.24

4 5 6 7E' / MPa

NoneTDAE

Rollingresistance

L-SBR-841L-SBR-820

Fig. 6: Toluene extraction test

Fig. 8: Analysis of viscoelasticity

Fig. 7: General properties (SBR)

22

24

26

28

500 540 580 620 660

Elongation / %

Tens

ile s

tren

gth

/ MPa

None

TDAE

L-SBR-841

LBR-307

80 90 100 110 120 130

TDAE

LIR-50

LBR-307

L-SBR-841

Wear volume / mm3

55

60

65

70

75

80

85

0 20,000 40,000 60,000

Molecular weight / Mn

Moo

ney

visc

osit

y / M

L1+

4

None

TDAE LBR

LIR

L-SBR