Comparative study regarding the tribological behaviour of [608135]

Comparative study regarding the tribological behaviour of
lysine and isoleucine modified epoxy matrix

Iuliana Bălan1, Radu Bosoancă1,2, Ana Că pățină1, Iulia Graur1,2, Claudia
Ungureanu1

1 Research amd Development Center for Thermoset Composites”Dunărea de Jos”
University, Galati, ROMÂNIA
2Diagnose and Measurement Group , Galați, ROMÂNIA

[anonimizat]
Abstract . The aim of this study is to point out the effect of L -lysine and L -isoleucine used as
modifying agents for epoxy resins. The amino acids are largely used to turn the usual polymers
in bio -compatible materials but they effect also other significant proprieties of formed
materials. The general study developed in Polymer Composite Laboratory is focused on
analysis of 14 amino acids used as mod ifying agents but the two above mentioned showed a
special behaviour namely they re -crystalized during the polymerization of the matrix. The
friction coefficient was obtained through the calculation of friction torque measured with a
loaded cell sensor . As far as we know, there is no report on the tribological proprieties of
amino acids modified epoxy resins.

1. Introduction
Epoxy resins have long been receiving a lot of scientific and technical interests. They are a family of
thermosetting materials wide ly used as adhesives, coatings and matrices in polymer composites
because of the low viscosity of the formulations, good insulating properties of the final material even
at high temperatures and good chemical and thermal resistance [1].The most common epox y monomer
is diglycidylether of bisphenol A (known as DGEBA). DGEBA -based resins are synthesized via the
addition of epichlorohydrine and bisphenol A so oligomers with a relatively narrow distribution of

polymerization degrees are obtained [2]. Because of the high adhesive strength and low cost, epoxy –
type resins have been primary matrix resins of the adhesives, and various types of curing agents, such
as nitrogen – (amines and polyamides), oxygen – (anhydrides), and sulphur – (mercaptans) containing
agents, have been used for crosslinked adhesives. However, these systems do have some
environmental problems that have been especially noted in recent years. One problem is that the
systems usually generate dense smoke and toxic decomposition products during com bustion. Another
environmental problem of epoxy resins is that all the curing agents are toxic before curing.
The curing agents, such as aromatic and aliphatic amines, which are most commonly employed for
epoxy curing, are known to be toxic, and to reduce the toxicity, adduct types of amines are sometimes
employed. Recently was demonstrated the feasibility of using an amino acid as a novel ecofriendly
curing agent. Therefore, the development of environmentally friendly epoxy systems is a great
importance fo r designing green and biocompatible materials in many applications. L -lysine is one of
the essential amino acids used in a wide range of applications. In this study an amino acid was used for
the preparation of polymeric materials.
The more important epox y hardeners are the amines and their derivatives, because are less
reactive but with higher mechanical properties than those of aliphatic amines. However, these
aromatic amines can be also toxic and there is a need for biobased and nonharmful amine hardene rs.
Unfortunately, there are very few biobased amines; some have been prepared such as isosorbide
diamine but through complex chemistries. More simple is the hydrolysis and decarboxylation of
amino acids which can lead to diamines, mostly aliphatic diamin es. One example is lysine, which can
be an interesting platform chemical and which can be converted into a number of industrial monomers,
including 1,5 -diaminopentan.
Li at al., [3] reported that lysine was used as a novel curing agent for a cycloaliphatic -type
epoxy. Also, the reaction between L -lysine amino acid and bisphenol A epoxies was not been widely
investigated yet. Yong Lv et al. [4] studied the curing kinetics of a diglycidyl ether of bisphenol A
with a methanol etherified amino resin [5].The che mical reactivity of the epoxies enables using a wide
variety of molecules as curing agents depending on the process and required properties. The amino
acids are largely used to turn the usual polymers in bio -compatible materials but they effect also other
significant proprieties of formed materials.
The fundamental understanding of synergy in tribological performance [6] among various
functional fillers is essential for successful applications [7]. The tribological behaviour of epoxy
matrix can be significa ntly improved by addition of suitable filler materials as lysine and isoleucine.
Besides the type, the shape and size of the materials added also influence the tribological properties
[8].

2. Experimental section
Three epoxy systems were chosen mostly becaus e of their different bisphenol A content namely
Epiphen RE4020 -DE 4020 (Bostik), Epoxy Resin C (R&G Gmbh Waldenbuch), and Epoxy Resin
HT-2 (R&G Gmbh Waldenbuch). L -lysine and L -isoleucine obtained from Sigma -Aldrich were the
chosen filler. All the systems are slow resins with a gel time between 20 and 45 minutes time which
allows the manoeuvres required by moulding. All these systems were modified by mixing the main
component (the resin) with various amounts of amino acids such as finally their weight ratio s into the
formed materials to be 1%, 3%, and 5%. L -isoleucine was used as received. L -lysine is not miscible
with epoxy resin, it cannot be incorporated into epoxy as such. For this reason, L -Lysine was
dispersed in methanol and ethanol (1%, 3% and 5% of epoxy resin). Thereafter, the epoxy resin was
added. Methanol and ethanol were evaporated at 500C on a magnetic heating stirrer and curing agent
for each resin was added. For each pair of substances and for each concentration first of all the
mixtures wer e homogenised by mechanical stirring at 300 rotation/min for 15 minutes. After curing,
three thermal treatments were applied: 8 hours at 600C, 2 hours at 800C and 1 hour at 900C. Coefficient
of friction of of lysine and isoleucine modified epoxy matrix was measured using pin -on-disc

tribometer TRM 1000 from Wazau at the Polymer Composites Laboratory of Dunărea de Jos
University of Galați . The samples of 8mm diameter were tested. A steel disc was used as a
counterpart. Sliding was performed under ambient at a sliding velocity of 1m/s, 1.5m/s and 2m/s and
nominal load of 10N, 15N and 20N for 1000 m.

3. Results and discussion
In each representation three curves are shown. As seen from figures below tribological behavior of L –
isoleu cine and L -lysine in C, E and H epoxy resins are compared according to their concentration in
those resins. As we can see from Fig.1, the friction coefficient under dry friction condition remains
almost constant for 10N applied force for all concentration of L -isoleucine and L -lysine. I t should be
noted that 3% of L -lysine in C epoxy resin has the weakest tribological behavior. The results in Fig.2
and Fig.3 confirm that the materials friction coefficient is not dependent on the applied force.

Fig.1.Friction coefficient for L -isoleucine and L -lysine in C epoxy resin for all concentrations

Fig.2.Friction coefficient for L-isoleucine and L -lysine in E epoxy resin for all concentrations

Fig.3.Friction coefficient for L-isoleucine and L-lysine in HT epoxy resin for all concentrations

4. Conclusion
From the results of this investigation, the following conclusions can be made. Friction coefficient is
are very much affected by sliding distance and applied force, excepting the HT epoxy resin filled with
3% of L -lysine where the friction coefficient remains constant at 10N and 15N. For 5% of L -lysine in
HT epoxy resin the friction coefficient remains also constant at 10N. The minimum friction coefficient
µ= 0.4 is obtained for 5% of L -lysine i n HT epoxy at 10N. The friction coefficient for L -isoleucine
increases for all concentrations of amino -acids and for all three types of epoxy resins.

Acknowledgments
The authors would like to acknowledge the financial contribution of the Project 12 P01 024 21 (C11)
/31.08.2012 (code SMIS 50414).

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