Life assessment of rubber articles in fuels

108 Pages·2013·8.49 MB·English

Examensarbete 30 hp
Juni 2013
Life assessment of rubber articles
in fuels
Emmy Selldén

Abstract
Life assessment of rubber articles in fuels
Emmy Selldén

Teknisk- naturvetenskaplig fakultet
UTH-enheten The choice of rubber material for use in sealings and hoses in the fuel system is of
great importance. If a wrong type of rubber is used, premature failure during service
Besöksadress: may occur. This impacts the environmental performance, the safety during driving,
Ångströmlaboratoriet
uptime and economy of the transport. In this diploma work, rubbers for use in sealing
Lägerhyddsvägen 1
Hus 4, Plan 0 and hoses in the fuel system have been evaluated to assess which materials have the
potential to be used under long-term use in contact with commercial fuels.
Postadress:
Box 536
Three commercial fuel hoses, nitrile rubber (NBR), hydrogenated nitrile rubber
751 21 Uppsala
(HNBR), ethylene-acrylic rubber (AEM) and fluorocarbon rubber (FKM) of varying

Telefon: types and compositions have been evaluated in diesel with 7% RME (rapeseed methyl
018 – 471 30 03 ester), 100% biodiesel of RME and ethanol fuel. Tests were performed by immersing
the materials in fuel and measure the compression set and changes in properties like
Telefax:
volume, hardness, tensile strength and elongation at break.
018 – 471 30 00

Hemsida: The results showed that one NBR material, one AEM and all FKM are potential

http://www.teknat.uu.se/student materials for long term use in diesel with 7% RME. All types of NBR and two types of
FKM (terpolymers, peroxide cured) may be used in ethanol fuel. NBR and HNBR
were the only rubbers evaluated in biodiesel. NBR and HNBR with an ACN content
of ~30% might be used in 100% RME at lower temperatures for shorter periods. The
aging resistance in air was good for HNBR, AEM and FKM but poor for NBR.
Handledare: Maria Conde
Ämnesgranskare: Jöns Hilborn
Examinator: Karin Larsson
ISSN: 1650-8297, UPTEC K 13012
Sponsor: Scania CV AB
Svensk sammanfattning
(Swedish summary)
I lastbilens och bussens bränslesystem finns det packningar, tätningar och slangar av
gummimaterial. Gummi är ett material som består av så kallade polymerer, d.v.s. långa
kedjor mer repeterande enheter, som är sammanbundna till varandra i vissa
gemensamma punkter. Typ av polymer som används, men också andra tillsatser i
gummit, påverkar gummits egenskaper. Vissa typer lämpar sig bättre när det är kallt,
andra när det är mycket varmt. En del klarar av att användas i kontakt med kemikalier
medans andra bryts ned.
I bränslesystemet kommer gummit i kontakt med bränsle vilket gör att det är viktigt att
det gummit man använder klarar av att användas i bränslet. Ett felaktigt materialval kan
innebära att komponenten drabbas av förtidigt mekaniskt brott vilket medför en
säkerhetsrisk och innebär att fordonet inte kan köras lika länge som tänkt, vilket också
påverkar ekonomin.
I takt med att koldioxidutsläppen ökar och tillgången på olja minskar, utvecklas nya
bränslealternativ till diesel. Två sådana alternativ är biodiesel och etanol. Biodiesel
utvinns från växtolja och fett medans etanol kan utvinnas ur socker, stärkelse och
cellulosa från växter. Att byta från ett bränsle till ett annat innebär dock problem när det
kommer till materialval. Skillnader i kemisk sammansättning hos de olika bränslena gör
att gummit påverkas olika beroende på bränsle.
I det här examensarbetet har tester av ett antal gummi utförts i olika sorters bränsle för
att göra en bedömning av vilka sorters gummi lämpar sig för användning under lång tid i
tunga fordon. Det har gjorts genom att sänka ner prover i olika bränslen vid förhöjda
temperaturer. En förhöjd temperatur gör att kemiska reaktioner, såsom åldring och
absorption av media, går snabbare, vilket gör att man på några veckor vid en hög
temperatur kan uppskatta bränslets påverkan under en lång tid vid lägre temperatur.
Eftersom att gummikomponenterna även utsätts för luft i verkligheten, har även
exponeringar i luft vid förhöjd temperatur utförts. De exponerade materialen har
utvärderats med avseende på volymsvällning, ändring i hårdhet och mekaniska
egenskaper samt sättning. Det sistnämnda är en mycket relevant egenskap för att
bedöma risken för läckage.
Resultaten visar att typ av gummi påverkar och att vissa gummityper lämpar sig bättre
än andra i olika bränslen. Fluorgummi visade sig till exempel fungera bra i både diesel
med 7 % biodiesel och etanolbränsle. Även luft hade smärre inverkan på dessa material.
Nitrilgummimaterialen uppvisade stora skillnader i diesel med 7 % biodiesel, beroende
på sammansättning. Alla sorters nitrilgummi klarade sig däremot bra i etanolbränsle,
men dåligt i luft. En specialvariant av nitrilgummi kan också komma att användas i
diesel med 7 % biodiesel. En typ av etenakrylgummi svällde mycket i etanolbränsle, men
klarar i övrigt av både varm luft och diesel med inblandning av 7 % biodiesel.
I
Acknowledgments
I would like to thank all the people at Scania that have helped me during my diploma
work, especially my supervisor Maria Conde for great support during the whole process.
I would also like to thank Martin Bellander for good advice and Christian Sjöstedt for
help in the lab and for good music during lab sessions. Thank you Jenny Johansson and
Karin Agrenius, at SP Technical Research Institute of Sweden, for help during the project
and for letting me visit you in Borås. Thank you Erica Forslund at Trelleborg Ersmark AB
for providing the samples and for technical support.
Great thanks to the whole team at UTMC, Materials Technology at Scania, you have all
been very kind and helpful. Finally I would like to thank my friends and family for
supporting me.

Emmy Selldén
II
Contents
Svensk sammanfattning ................................................................................................................................. I
Acknowledgments .......................................................................................................................................... II
Acronyms and glossary of rubbers ........................................................................................................... V
1 Introduction .............................................................................................................................................. 1
1.1 Background ...................................................................................................................................... 1
1.2 Aim and goals .................................................................................................................................. 2
2 Theory ......................................................................................................................................................... 3
2.1 Rubber materials ............................................................................................................................ 3
2.1.1 Description of some elastomers used in rubber ....................................................... 3
2.1.2 Additives ................................................................................................................................... 7
2.2 Fuels .................................................................................................................................................... 8
2.3 Degradation of rubber and interaction with fluids ........................................................ 10
2.4 Accelerated tests ......................................................................................................................... 12
2.4.1 Arrhenius equation ............................................................................................................ 12
2.4.2 Fluid resistance tests ........................................................................................................ 13
2.5 Previous research ....................................................................................................................... 14
3 Methods ................................................................................................................................................... 16
3.1 Rubber components analyzed ................................................................................................ 16
3.2 Fuels used ...................................................................................................................................... 18
3.3 Choice of time and temperature for exposures ............................................................... 18
3.4 Sample preparation .................................................................................................................... 19
3.5 Aging in air and exposure in fuels ........................................................................................ 19
3.6 Analysis of samples .................................................................................................................... 21
3.6.1 Volume change .................................................................................................................... 21
3.6.2 Change in hardness ............................................................................................................ 22
3.6.3 Tensile testing ..................................................................................................................... 23
3.6.4 Compression set ................................................................................................................. 24
3.6.5 FTIR ......................................................................................................................................... 25
4 Results and discussion ....................................................................................................................... 27
4.1 Visual observations .................................................................................................................... 28
4.2 FTIR analysis ................................................................................................................................. 30
4.3 NBR materials ............................................................................................................................... 34
III
4.4 HNBR materials ........................................................................................................................... 38
4.5 AEM materials .............................................................................................................................. 41
4.6 FKM materials .............................................................................................................................. 44
4.7 Hoses ................................................................................................................................................ 48
4.8 Comparison between polymer types .................................................................................. 51
4.9 Testing in B100 ............................................................................................................................ 52
4.10 Reflections ..................................................................................................................................... 52
5 Conclusions ............................................................................................................................................ 53
6 Further work ......................................................................................................................................... 54
7 References .............................................................................................................................................. 55
Appendix A: FTIR spectra .......................................................................................................................... 58
Appendix B: Color graded tables for properties after fuel exposure and aging in air ....... 94
Appendix C: Bar charts for hoses ........................................................................................................... 98

IV
Acronyms and glossary of rubbers
Nomenclature of rubbers according to Swedish standard SS-ISO 1629
ACN Acrylonitrile
AEM Copolymer of ethyl acrylate (or other acrylates) and ethylene. Ethylene-acrylic rubber
AR Aramid Reinforcement
ASTM American Society for Testing of Materials
ATR Attenuated Total Reflectance
B100 100% biodiesel
B7 Diesel with 7% RME
CO Polychloromethyloxirane. Epichlorohydrin rubber.
CPE Chlorinated Polyethylene Rubber
CR Chloroprene Rubber
CS Compression set
DLO Diffusion Limited Oxidation
ECO Copolymer of ethylene oxide and chloromethyloxirane. Known as epichlorohydrin
copolymer or rubber
ED95 Ethanol fuel of 95% ethanol and 5% additives
FAME Fatty Acid Methyl Esters
FKM Fluoro rubber having substituent fluoro, perfluoroalkyl or perfluoroalkoxy groups on
the polymer chain
FPM Same as FKM
FTIR Fourier Transform Infrared Spectroscopy
GECO Terpolymer of epichlorohydrin-ethylene oxide-allyl glycidyl ether
HNBR Hydrogenated acrylonitrile-butadiene rubber
IRHD International Rubber Hardness Degree
NBR Acrylonitrile-butadiene rubber, known as nitrile rubber
PVC Poly Vinyl Chloride
RME Rapeseed Methyl Ester
SIS Swedish standards institute
SS Swedish Standard

V
1 Introduction
This diploma work has been performed at Scania CV AB, a manufacturer of heavy trucks,
buses and industrial and marine engines. Material selection is an important part when
developing new components. In this part, a background to the use of rubber components
in contact with fuel will be given, followed by aim and goals for the project.
1.1 Background
The main applications of rubber materials in heavy vehicles are in components for
sealing, vibration damping, fluid transportation and in interior details. In particular,
tightness of seals and hoses for fluid transport are of great importance for the
environmental performance, the driving safety, uptime and economy of the transport.
Fuel hoses are used in several parts of the fuel system in low and medium pressure
applications. They are used in the tank area in the fuel filler system and in the engine as
feed hoses to direct the fuel towards the fuel injector. Rubber hoses are also used to
connect the tank and engine compartment and consist of feed hoses that transport fuel
to the engine and as return hoses that transport unreacted fuel back to the tank. Fuel
hoses consist typically of several layers of materials. The inner rubber layer is in direct
contact with the fuel. Behind the inner layer, reinforcement is used. Depending on
temperature it can, for example, be polyester, cotton or aramid. Outermost is an external
rubber layer that faces the outer environment and it should be able to resist weather,
fuel, high external temperature, ozone, coolant, vibrations etc. Depending on the
materials used for the inner and outer layer, an intermediate layer might be used. The
intermediate layer gives less permeation and gives better adhesion between the layers
and the reinforcement [1].
Sealings are used to prevent leakage and exclude contaminants. Several materials can be
used like metal and rubber. Rubber has low hardness which allows for lower sealing
pressures and it has elasticity making it possible to maintain the pressure [2]. Rubber is
therefore common in sealings and gaskets. Many types of sealings and gaskets are
available on the market. Commonly used are radial, axial and O-ring sealings. Radial
sealings consist of several components, where one is a gasket cuff made of rubber. It is
used to prevent the transportation of fluid between two parts where, for example, one
part is stationary and the other is rotating. Axial sealings are commonly used to exclude
external contamination. O-rings are circular sealings used for both radial and axial
sealing. The O-ring is placed in a groove between two parts. When subjected to a load, it
deforms and seals [2]. One example of an important gasket is the cylinder head gasket
between the engine block and the cylinder heads in the engine. This gasket comes in
contact with oil, unreacted fuel and degraded fuel.
The temperature in the fuel system varies and there are areas that are colder and
warmer. For example, the fuel transport for injection in the engine transports cold fuel
1
and the temperature is rarely over 60⁰C. For transportation of unreacted fuel, the
temperature is higher.
To reduce repair cost and to ensure safety it is wished that rubber articles have a life-
time close to the truck life.
To estimate how good rubber components will perform in fuel, accelerated tests are
commonly performed according to Swedish standard SS-ISO 1817 or American standard
ASTM D471, these tests are normally short, for example 70h [3]. There is a need to
perform these tests at longer times, about 1000h, in real fuels to better estimate how
good different rubber components will perform during long time in service. In this
diploma work, three fuel hoses and thirteen rubbers will be examined in air and some in
commercial fuels. The rubber components are three types of nitrile rubber (NBR), two
types of hydrogenated nitrile rubber (HNBR), four types of ethylene-acrylic rubber
(AEM) and four types of fluorocarbon rubber (FKM). NBR and HNBR are used in lower
temperature applications while AEM and FKM are used at higher temperatures.
1.2 Aim and goals
This study aims to obtain relevant data to predict the long-term properties of rubber
components used in applications in commercial fuels such as diesel with 7% RME
(rapeseed methyl ester), biodiesel and ethanol fuel. This information will help to give
safer recommendations on the life assessment of different rubber materials in fuels.
The questions to be answered are:
 Which of the chosen rubber materials have the potential to be used in fuel
applications, for long-term use, in commercial fuels like diesel with 7% RME,
biodiesel and ethanol fuel?
 How does polymer type and differences in composition of the different rubber
components impact on aging and fuel resistance?

2