Epoxy/amine networks for coating 316L stainless steel ... · PDF fileEpoxy/amine networks for...

European International Journal of Science and Technology ISSN: 2304-9693 www.eijst.org.uk

78

Epoxy/amine networks for coating 316L stainless steel: Preparation,

surface characterization, adhesive properties and water absorption

Filiberto González Garciaa*

, Alexandre Z.Simõesb, L. Rogerio O. Hein

b, Elson Longo da Silva

c

aInstitute of Pabsortionhysics and Chemistry, Federal University ofItajubá, Av. BPS. No. 1303, 37500-903,

Itajubá, MG, Brazil.

bFacultyofEngineeringGuaratingueta,Paulista StateUniversity, Ave. Dr. Ariberto Pereira da Cunha 333,

Guaratinguetá, 12516-410, São Paulo, SP, Brazil.

cPaulistaStateUniversity, InstituteofChemistry, Rua Francisco Degni, 55, Quitandinha,

14801907 - Araraquara, SP, Brazil.

*Corresponding Author Email: [email protected]

Sponsoring information:This work was financially supported by the Brazilian research funding agencies

FAPEMIG (Fundação do Amparo à Pesquisa do Estado de Minas Gerais, Brazil, processes APQ.01736-11

and APQ.00073-13) and CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnológico, Brazil).

Abstract: 316L stainless steel (SS) is widely used in the metallic stents manufacturing and in general is

considered to be a biocompatible material, but it is prone to corrosion in contact with biological

environments. We examined possible surface coating by using inert polymeric with antithrombotic

properties and low cytotoxicity. Thickness and roughness of the surface coating, adhesive properties and

water absorption of three epoxy thermosetting polymers were studied. Diglycidyl ether of bisphenol A

(DGEBA) epoxy monomer modified with reactive diluent and cured with 4,4’-diamino-3,3’-

dimethyldicyclohexylmethane (3DCM), isophorone diamine (IPD) and 4-methylpiperidina (4MPip)were

evaluated. Only the DGEBA/4MPip system formed a coating on polished and silanizated metal plates and

exhibits the better adhesive strength and low water adsorption. We conclude that the DGEBA/4MPip system

exhibits greater ability to form coatings surface on 316L SS with better adhesive properties and lower water

absortion.

Keywords: Surface coating; 316L stainless steel; epoxy/amine networks; adhesive properties; water

adsorption.

European International Journal of Science and Technology Vol. 4 No. 7 September, 2015

79

1. INTRODUCTION

The percutaneous transluminal coronary angioplasty (PTCA) was introduced in the management of coronary

artery disease symptoms (Sheiban et al., 2008).Grüntzig and Myler performed the first coronary angioplasty

during coronary artery bypass graft surgery in 1977 (Newsome et al., 2008; Erbel et al., 2002). PTCA is

today the most frequent interventions in medicine and constitutes an important economic factor. PTCA is a

minimally invasive procedure to open up blocked coronary arteries, allowing blood to circulate unobstructed

to the heart muscle. This involves steering a balloon catheter to the blockage site and inflating it to compress

the deposit that obstructs the artery and to re-establish the blood flow. The most important complication

associated to this therapy is restenosis that is re-narrowing of the vessel, which occurs in 30 – 40% of

coronary lesions within 6 months (Serruys et al., 1994).To improve the clinical outcome of PTCA, bare

metallic stents have been used. Stents are small metal scaffolds that are placed on the balloon and then

expanded into the damaged artery at stenosissite. It is known that the use of these devices has reduced the

restenosis rate to 20 – 30%, they often increase the incidence of inflammation, thrombosis, and

fibromuscular proliferation (Mani et al., 2007).

316L stainless steel(SS) is widely used in the metallic stents manufacturing and in general is

considered to be a biocompatible material, but it is prone to corrosion in contact with biological

environments and causes the gradual release of metal ions, such as chromium, iron and nickel in the

surrounding tissue. This may trigger local immune response and inflammatory reaction, which in turn may

induce intimal proliferation (Kajzer et al., 2008; Köster et al., 2000). In cardiovascular stenting application,

a thin stainless steel wire could also lose its mechanical integrity as a result of corrosion. To improve the

performance of cardiovascular stents different types of protective coating based on stainless steel are being

developed. For example; inorganic coating such as two oxides (TiO and ZrO) and diamond-like carbon have

been studied by in vitro and in vivo essays exhibiting good biological properties (Mikhalovska et al., 2011).

Another possibility is a plasma-activated coating for metallic coronary stents that is durable, with stands

crimping and expansion, has low thrombogenicity and can covalently bind proteins, linker-free. It is know

that the enhancement of endothelial cell interactions in vitro has the potential to promote biointegration of

stents (Waterhouse et al., 2012).To improve the strength and corrosion resistance of 316L SS the cold spray

technique was used. In this work the stainless steel mixed with cobalt chromium alloy L605 powders has

been cold sprayed onto mild steel substrate (AL-Mangour et al., 2013).

Multiples investigations have been devoted to polymers and copolymers coating of bare metallic

stents. Polymer properties can be tailored by specific physico-chemical characteristics. For example a new

copolymer acrylic was investigated for stent coating which contain trifusal covalently attached to the

polymer backbone. This polymer is a powerful platelet aggregation inhibitor which has been used in the

development of stent coating with inherent anti aggregating modulation of platelets, as well as support for

the release of a antiproliferative drug to prevent restenosis (Rodríguez et al. 2010). The metallic surface

(alloy 316L) deposited by plasma from biological environment has lead to an ultra-thin, stable, cohesive and

adhesive plasma polymerized allylamine coating with high selective towards primary amine groups. The

coatings satisfy the adhesion and cohesion properties to be stable upon desionised water immersion and to

resist to stent expansion (Gallino et al., 2010).A new nanocomposite polymer based on polyhedral

oligomeric silsesquioxanes (POSS) and poly(carbonate-urea)urethane (PCU), which is an antithrombogenic

and a non-biodegradable polymer with in situ endothelialization properties has also been investigated. This

nanocomposite coated with nitinol(NiTi) surface can enhance surface resistance and improve

biocompatibility (Bakhshi et al., 2011). Copolymers of poly(e-caprolactone) (PCL), poly(ethylene glycol)

(PEG), and carboxyl-PCL(cPCL) were also employed as potential coronary stent coating materials with two

primary human coronary artery cell types: smooth muscle cells (HCASMC) and endothelial cells (HCAEC)


80

and the copolymer with 4%PEG–96%PCL–0%cPCL was identified as the most appropriate coatingmaterial

(Crowder et al., 2012).Amphiphilic copolymers based on the copolymerization of hydrophilic and

hydrophobic moieties offer versatility in various biomedical material applications. Copolymer of dextran-

graft-poly (butyl methacrylate) was synthesized and characterized as coating for metallic endovascular stents

(alloy 316L). The resulting coating is smooth and uniform with neither cracks nor detachment after stent

expansion. Interestingly, surfaces coated with the copolymer greatly improve in vitro adhesion and growth

of endothelial cells (Dekaoui et al., 2012). However, an epoxy thermosetting polymer has never been

studying for coating 316L SS (e.g., stent material). The use of inertpolymeric coatings is attractive for bare

metallic coronary stents. This argument is supported by studies with human blood compatibility and Chinese

hamsters ovary cells which possess anti thrombotic properties (González Garcia et al., 2009; 2015) and no

signs of cytotoxicity (González Garcia et al., 2009).Moreover, epoxy thermosetting polymers its interest for

coating applications (Omrani et al., 2011; 2013) and have good adhesive properties to various metals,

including stainless steel (de Morais et al., 2007).However, this property decreases in water physiological

environment (humidity or water) over time as a result of water absortion by the polymeric matrix (Oudad et

al., 2012; González Garcia et al., 2011; Colombini et al., 2002).Another problem is related to the rigidity of

suchpolymers (Pascault et al., 2002; Clayton, 1988). However, a suitable selection of the monomers and

additives can be obtained in a wide range of biological properties, mechanical properties, adhesive strength

and water absortion. The study of these properties is in progress in our laboratories.

In this work, we examined the possibility of coating the surface of 316 Lstainless steel based

thermosete poxy polymers such asdiglycidyletherof bisphenol A modified with diepoxy aliphatic diluent

cured with cycloaliphatic amines. Optical microscope (OM) was used to examining the polished surface

plate, silanized and coated after cure process. The adhesive strength of epoxy formulation on 316LSS

adherend was evaluated in terms single lap shear using 316L SS adherends. Finally, the water absortion of

the thermosetting polymers was obtained by immersion at the physiological temperature (37 °C).

2. MATERIALS AND METHODS

2.1 Materials

The formulations used in this study are based on the diglycidyl ether of bisphenol A (DGEBA, DER 331

Dow Chemical Co. Ltda) with an equivalent weight of epoxy groups of 185.5 as determined by acid

titration, modified with 30 phr of diepoxy aliphatic diluent (1,4-butanediol diglycidyl ether, DGEBD), 30 g

of DGEBD per 100 g of DGEBA. The epoxy monomer was vacuum dried at 80 °C before use. The

cycloaliphatic amines used were4-methylpiperidine (4MPip, 96% Aldrich), 4,4'-diamino-3,3'-dimethyl-

dicyclohexylmethane (3DCM, 99% Aldrich) and isophorone diamine (IPD, 99% Aldrich) with an equivalent

weight of amine hydrogen groups 42.6 for IPD and 59.6 for 3DCM determined by potentiometric titration,

respectively (González Garcia et al., 2007). The cycloaliphatic amines were used as received.

2.2 Surface treatment and silanization

The 316L SS used was a commercial stainless steel VI 138 (specialty alloy, ASTM – F138) from Villares

Metals, Brazil. This metallic substrate was supplied with shape plates of side 1.0mlong, 10.0 mm wide and

1.2 mm thick with unpolished surfaces. Plates were used as carrier instead of real stents due the high costs.

The composition of such alloy is given in Table 1. In order to increase its adhesive properties, the metallic

adherend surfaces were prepared. The applied surface treatment consisted of the following steps: (1) Before

any application the plates were ultrasonically cleaned in acetone at room temperature for 5 min then dipped

in acetone at 60 °C for 5 minutes and dried by dabbing with absorbent paper and dry nitrogen flow. (2) The

surface of the plate was mechanically polished to a mirror like finish using 230, 300, 400, 500, 600, 1200


81

silicon carbide disks followed by 0.30 µm and 0.05 µm alumina oxide polishing (suspension in solution). To

remove polishing residuals, samples were cleaned with distillated water between each polishing step.

Samples were then dried by dabbing with absorbent paper. (3) The surface of the plates were silanizated: the

method consisted in a silane solution (0.12 % v/v) of 3-aminopropyl-trimethoxysilane (ATPS, 97% Aldrich)

prepared with 25%/75% v/v mixture of ethanol and distilled water according to the methodology reported in

the literature[Chovelon et al., 1995). The polished and silanizated metal plates were stored in a vacuum at

room temperature.

Table 1. Chemical composition in % (wt) of the specialty alloy IV 138 by Villares Metals supply.

C Mn Si Cr Ni Mo P S Cu N

0.025

max.

1.80 0.40 17.50 14.00 2.80 0.025

max.

0.003

max.

0.10

max.

0.10

max.

2.3 Viscosity and contact angle

On the surface of the plate treated, one drop of the epoxy formulation freshly prepared was deposited using

micropipette and the contact angle measured at room temperature. The used equipment was Kruss, model

FMMK2 Easy drop equipped with camera and software. Viscosity of epoxy formulations was measured

using a Rheometric, Physica Anton Paar (model MCM 301) at 25 °C with conical plates of 24.74 mm of

diameter and angle 1.012°.

2.4 Coating and curing

Three different epoxy matrixes based on diglycidyl ether of bisphenol A (DGEBA).The first one was cured

with 4-methylpiperidina. The second one and the third one were cured with 4,4’-diamino-3,3’-

dimethyldicyclohexylmethane and isophorone diamine, respectively. The first formulation was cured with 4-

methylpiperidine (4MPip) using 5 phr (5 g of 4MPip per 100g of DGEBA) with the following thermal cycle:

30 minutes at 60 ºC and later during 16 hours at 120 °C. The second and the third one were prepared by

carefully weighting the monomers at the stoichiometric proportion (epoxy/amine hydrogen e/a= 1). The

cured schedule was4 hours at 60 ºC for these two systems and for the formulations based on 3DCM and IPD

were post-cured at 180 ºC and 160 ºC during 2 hours, respectively. All mixtures were stirred for 2 minutes

and degased under vacuum over for 5 minutes at room temperature to remove trapped air. The silanized

metal plates surfaces were coated by immersion in the monomers mixtureat60 ºC. After immersion, the

metal plates were cured according to the schedule for each system and slowly cool down to room

temperature. After that, it was stored at room temperature in a vacuum system.

2.5 FTIR spectroscopy

Fourier transform infrared (FTIR) measurements of cured coatings were performed with the Perkin Elmer,

Spectrum 100 spectrometer equipped with universal ATR sampling accessory with a diamond crystal.

Spectra were recorded with a resolution of 4 cm-1

and at least 32 scans with the wave number range from

650 – 4000 cm-1

.

2.6 Differential scanning calorimetry (DSC)

The glass transition temperature (Tg) and the residual enthalpy (∆HR) of the cured coatings were investigated

in a differential scanning calorimetry (DSC) (Shimadzu, DSC 60). Samples of around 10.0 mg were

weighting in standard 40 µL aluminum pan and heat from 30 °C to 145 °C with a heating rate of 10 °C min-1

European International Journal of Scien

in nitrogen atmosphere with 50 mL min-

the initial changes on heat capacity (onse

2.7 Optically microscopy

The thickness and roughness of the po

metallic plates surface coated were o

technique was performed and allowed t

dimensional images using a opening hol

the focal plane. The optical microscope u

2.8 Preparation of lap shear specimens

The adhesive behavior was evaluated fo

adhesion test was carried out according t

1. In order to increase its adhesive pro

surface treatment which consists of th

acetone at room temperature for 5 min t

with absorbent paper and dry nitrogen f

bath at 60 °C for 10 minutes, rinsed with

method consisted in silane solution (0.1

25/75% (v/v) mixture of ethanol 95%

literature (Chovelon et al., 1995). Speci

applications, specific metallic mold was

by the design of the mold. After surface

shear joint. Each epoxy formulation wa

epoxy formulation was applied uniforml

specific metallic molds. The applied con

with uniform adhesive thickness, (0.2±

the tensile axis, chocks in the extremes

room temperature (22 ± 2) °C and relativ

Fig. 1.Dimensions of the adhesives joint

ence and Technology ISSN: 2304-9693

-1nitrogen flow rate. The glass transition tempera

set value).

polymer coating was determined byoptical mic

observed at ambient temperature. Confocal m

d to increase the contrast microscopic image and

ole pinhole, which leads to a high image definitio

e used in confocal mode was the Leica DCM3D.

ens

for mechanical tests using single-lap shear joint.

g to ASTM D1002. The geometry of adhesive join

roperties, the metallic adherend surfaces were p

the following steps: (1) Specimens were ultras

n then dipped in acetone at 60 °C for 5 minutes a

n flow. (2) The metal surface was chemical treate

ith distillated water and blown dry with nitrogen.

.12% v/v) of 3-aminopropyl-trimethoxysilane (A

and distilled water according to the methodo

cimens were stored in a glass dryer with silica g

as designed for adhesive joint. The layer thickne

ace treatment, metallic pieces were assembled for

as prepared and cured as mentioned in item coa

ly on both surfaces of the adherend with the sam

ontact pressure was kept constant, which allows

0.02) mm. To reduce the deviation of the adhe

es of the specimens were used. These specimens

tive humidity of (50 ± 5) % during 24 hours befor

ints of single lap shear using steel adherend (meas

www.eijst.org.uk

erature (Tg), is taken at

icroscopy (OM). The

l microscopy imaging

nd constructing three-

tion in thicker samples

t. For this purpose, the

oint is shown in Figure

prepared by applying

rasonically cleaned in

and dried by dabbing

ated in a sulfochromic

en. (3) The silanization

(ATPS) prepared with

dology reported in the

a gel. For the adhesive

ness can be controlled

for adhesive single-lap

oating and curing. The

mple introduced in the

s obtaining specimens

hesive layer, respect to

ns were maintained at

ore testing.

asured in mm).

User

Typewritten Text

User

Typewritten Text

82


83

2.9 Testing of the adhesive specimens

The adhesive strength of the single-lap shear joints was measured at room temperature in a same universal

testing machine under a 5 kN load cell. A crosshead speed of 3.0 mm/min was employed. The lap shear

strength was expressed in MPa. The adhesion tests were carried out at (22 ± 2) °C and relative humidity of

(50 ± 5) %. The average values were taken from at least eight specimens.

2.10 Water absorption

Test specimens (10.0 ± 0.2) mm long, (15.0 ± 0.2) mm wide and (3.2 ± 0.2) mm thick, were used for water

absorption tests, following the recommendations of ASTM D570 standard of test specimens for sheet

materials. The samples were removed from distillated water at (37.0 ± 0.2) °C, carefully wipped with a filter

paper and weighting on analytical balance to ± 0.01 mg. Three specimens were used per each epoxy

polymer. The mass water absorbed Ct (%) by the specimens was calculated with the following expression

(Equation 1):

��%� = � ��

�� ∗ 100 (1)

where: wt is the mass of the specimens at time t, w0 is the mass of the dry specimen. The average standard

deviation corresponds to the value less than 0.05% on the Ct (%) scale.

3. RESULTS AND DISCUSSION

3.1 Coating and curing

In this work we examined possible surface coating of 316L SS by using inert polymeric with antithrombotic

properties and low cytotoxicity. For this purpose metal plates were used. The plates were submitted to a

conventional mechanical polish method to simulate the surface of the stent and silanization treatment with

APTS to improve adhesive strength between metal substrate and polymeric coating. In previous work

(González Garcia et al., 2009; 2015),the epoxy/amine systems based on diglycidyl ether of bisphenol A

(DGEBA) and diglycidyl ether of glycerol (DGEG) epoxy monomers cured with cycloaliphatic amines

demonstrated that these epoxy thermosetting exhibit better blood compatibility and low cytotoxicity.

Therefore, three cycloaliphatic amines as curing agents were chosen.

After the immersion of the plates in the mixture of monomers, a thin film coating was formed on the

plates surface. At room temperature, the thin film is released from the steel and large drops in the center of

the plate were formed. This effect inhibits films formation based on DGEBA/IPD and DGEBA/3DCM

systems which indicates that the viscosity is an important factor to achieve the formation of a coating on the

surface of the plates. As shown in Table 2 the DGEBA/4MPip system exhibits the low viscosity and contact

angle. After curing schedule only the DGEBA/4MPip system formed a thin coating on the metal plates. The

other two formulations formed droplets which didn’t spread uniformly on the plates surface. Only the

DGEBA/4MPip system formed a thin coating on surface polished and silanizated metal plates.

Also, is possible to ensure the influence of the viscosity and consider the gelation and vitrification

during cure schedule. For the DGEBA/4MPip system, the cure schedule of 30 minutes at 60 °C and 120 °C

for 16 hours causes appreciably decrease on viscosity of the monomers mixture. Under these conditions, the

formation of a thin coating of the formulation on the surface of the metal plates is enhanced occurring during

the gelation and the vitrification processes. For the DGEBA/3DCM and DGEBA/IPD systems in the first

curing stage at 60 °C for 2 hours the viscosity of the monomers is low. Thus it appears that the cure schedule

have no significant contribution on the formation of thin coating layer on the surface of the plates.


Table 2. Viscosity and contact angle of

Epoxy formulations V

DGEBA/3DCM 0.

DGEBA/IPD 0.

DGEBA/4MPip 0.

3.2 FTIR spectroscopy

The FTIR spectrums of the coated pla

literature for diglycidyl ether of bisphen

(Lee & Neville, 1967). For instance, ab

groups, and bands at 2911, 2865 and

vibration to APTS, respectively. Bands

1508 cm-1

. The bands around 1236 and

bands at 1432, 1380, 1360 and 1294 an

between APTS silanol groups and 316L

vibration mode, respectively while the b

absortion band around 915 cm-1

attribu

suggest that all networks are completely

Fig. 2.FTIR spectra of DGEBA/4MPip (

3.3 DSC Measurements

DSC results of the DGEBA/3DCM netw

These results were obtained from both

considered in the first scan. The same Tg

that the networks are fully cured or th

maximum Tg value. Similar results wer

present in Table 3.

ence and Technology ISSN: 2304-9693

of the epoxy/amine system.

Viscosity (Pa s) Contact angle (°)

0.51 48.6 ± 2.4

0.44 36.6 ± 3.5

0.42 32.1 ± 1.5

plates are shown in Figure 2. Typical absortio

enol A bonded to an amine group in aliphatic co

absortionb and at around 3387 cm-1

is associated

d 2853 cm-1

belong to C–H stretching vibration

ds associated with the aromatic ring appear aro

and 1031 cm-1

is associated with C-O-C ether g

and 1432cm-1

can be assigned to the siloxane lin

6L SS hydroxyl groups (Wang et al., 2007) and

band at 827 cm-1

is assigned to the 1.4 substitut

ibuted to epoxy group vibration mode was evid

ly cross linked and there are no huge differences a

p (

____), DGEBA/IPD (

_ _ _) and DGEBA/3DCM (

_

etwork are presented in Figure 3. The Tg value o

th first and second scans and no residual enthal

g value from both scans and the absence of an ex

the same, we can infer that the three epoxy s

ere obtained for the other system. DSC results o

www.eijst.org.uk

ion bands reported in

compound were noted

ed with –OH hydroxyl

ional sp3 and skeleton

round 1605, 1580 and

r group. The absortion

linkage due to reaction

d methyl symmetrical

ution. Furthermore, no

idenced. FTIR spectra

s among them.

_ _ _) networks.

obtained was 125 °C.

alpy (∆HR) have been

exothermic peak prove

systems attaining the

of the all systems are

User

Typewritten Text

84


Fig. 3.DSC scans for cured system DGE

Table 3. Glass transitions temperatu

networks determined by DSC.

Networks First sc

DGEBA/4MPip 55.5

DGEBA/IPD 100.2

DGEBA/3DCM (30 phr) 125.0

3.4 Optically microscopy

Figure 4 and Table 4 show tree-dimensi

the coating surfaces from the 316L SS

roughness increased from 0.32 µm to 1.

surface coating metal plates. The silaniz

of coating surface was 1.97 µm. The su

smoother than the surface of the s

DGEBA/4MPip (Figure 4c), the rough

behaviors can be related to ATPS covale

groups and 316L SS hydroxyl groups

monomers mixture epoxy groups.

Table 4. Thickness (µm) and roughnes

Metallic surface Po

Thickness (µm)

Roughness (µm )

ence and Technology Vol. 4 No. 7

EBA/3DCM.

ature (Tg) of DGEBA/4MPip, DGEBA/IPD a

scan (T °C) Second scan (T °C)

55.3

100.3

125.1

sional OM images and the roughness of the poli

with DGEBA/4MPip system, respectively. Th

1.75 µm and 1.54 µm, respectively after the poli

izated surface is rougher than the coating surface

surface roughness of the polished 316L SS surf

silanized one (Figure 4b). After coating th

ghness slightly becomes smoother to that the s

lently linked to 316L stainless steel by reaction be

ps and subsequent reaction between APTS am

ess (µm) obtained from optical microscopy.

Polished Polished and

silanized

Co

DGE

- 1.39 1.

0.32 1.75 1.

September, 2015

and DGEBA/3DCM

lished, silanizated and

he root-mean-squared

lished, silanizated and

ace being the thickness

urface (Figure 4a) was

the surface with the

silanized one. These

between APTS silanol

amine groups and the

Coatedwith

EBA/4MPip

1.97

1.54

User

Typewritten Text

85


86

(a) (b)

(c)

Fig, 4.OM images of (a) polished surfaces SS, (b) after silanizated surface SS, (c) after coating surface SS

with DGEBA/4MPip system.

3.5 Adhesive properties

The adhesive properties were evaluated in terms of single lap shear using 316 SS adherends chemical

treated. The glass transition temperature (Tg) and the adhesive properties values of three epoxy formulations

obtained from single lap shear joints tests is shown in Table 5. The Tg of the epoxy networks also presents

large influence on the adhesive behavior of the adhesive joints.

Table 5. Glass transition temperature (Tg) and adhesives properties of different epoxy adhesives

obtained from single lap shear tests.

Epoxy networks Tg(°C) Adhesive strength in lap shear

joints (MPa)

DGEBA/3DCM 125.0 14.6 ± 0.5

DGEBA/IPD 100.2 15.5 ± 0.4

DGEBA/4MPip 55.5 17.2 ± 0.4


87

The DGEBA/4MPip system has the lower glass transition temperature and as expected exhibits the

best adhesive properties. It is well known that low Tg values are results of lower cross linking density

(Pascault et al., 2002). This explained the adhesive behavior because is know that the lower crosslink

density improve the ability of the adhesive and thus increase the lap shear strength (Colombini et al., 2002;

Hu & Huang, 2005). Also, it is known that the viscosity influencing for adhesive strength of the joints

(Montions et al., 2007). The lower viscosity is an important factor to achieve surface coatings with adhesive

strength. The performance of adhesive properties is related to different structure of the epoxy networks by

changing the chemical structural of curing agent. This comes from the fact that the networks involved are

“closed” networks (Pascault et al., 2002), resulting from a single step polymerization mechanism and also

that stoichiometric ratio of monomers are reacted until attaining the maximum Tg value. In particular, the

DGEBA/4MPip system presents two different curing processes. The first one by step-growth

polymerizations were carried out for epoxy cross linking, and the second one by homo polymerization of

epoxy groups by anions mechanism allowing into generating polyether chains with flexible structure

(González Garcia et al., 2002). In those circumstances, the flexible epoxy network chains exhibit lower

crosslink and smaller value of Tg. From these results, we can infer the relationship between adhesive

behaviors with the chemical structure of the curing agent in the networks structure.

3.6 Water absorption

Solvent transport in organic polymer matrices is usually depicted as a two-step mechanism. The first step is

the solution of the solvent in the superficial polymer layer. This process, which can be considered almost

instantaneous in the case of water, creates a concentration gradient. The second step is the solvent diffusion

in the direction of the concentration gradient. This process may be described by a differential mass balance

(often called Fick’s second law) (Pascault et al. 2002, Apostol, 1974), which, in the one-dimensional case,

may be written as (Equation 2):

∆�

��= �

��

�� (2)

where: D is the diffusion coefficient and x the coordinate along the sample’s (L) thickness. For a membrane

shape sample (Apostol, 1974) the resolution of this differential equation gives (Equation 3):

�

�∞= 1 − ∑

�

�� ∞

�� exp [�# ��/��

%�)] (3)

At short times, typically when C ≤ 0.5 C∞, this function can be well approximated by (Equation 4):

�

�∞= 1 −

�

��&

�'()�

*+� � (4)

where: Ct is the mass of water absorbed at time t, C∞ is the amount of water absorbed at saturation, L is the

thickness of the freestanding specimen and D is the diffusion coefficient.

It is thus usual to plot ln (1- Ct/C∞) vs. ln t. The linearity of the curve in its initial part can be

considered as validity criteria for the Fick’s law. The slope of the linear allows us to determine the diffusion

coefficient. To obtain the saturation value (C∞) and diffusion time (tD) it usual to plot weight gain vs. time.

In this plot the diffusion time, tD defined as the duration of the transient, can be arbitrary taken at the

intersection between the tangent at the origin and the asymptote and the saturation value (C∞) as considered


88

as the maximum value of the weight gain. This point corresponds to the value where the absortion reaches a

stable value.

Figure 5 shows the experimental data for the weight gain vs. time curves. All epoxy polymers show

an almost linear relationship between the weight gain and the immersion time at the beginning of the

absorption process. This behavior is well described by Equation 4, showing that the initial stage of water

absorption behavior is governed by the Fick’s law. Therefore, the water concentration gradient is the driving

force that leads to water absorption in these epoxy polymers.

Fig. 5.The gain weight vs. time curve showing the water sorption behavior of the different epoxy adhesives.

The obtained values for C∞, D and tD are listed in Table 6. It can be highlighted that the diffusion

coefficient obtained is consistent with the values cited for other epoxy polymers (Pascault et al., 2002; Berry

et al., 2007; Maggana et al., 1999; Moy &Karasz, 1980). The diffusion coefficient, saturation value and

diffusion time for each epoxy network changed depend on the curing agent employed. The diffusion

coefficient (D) and saturation (C∞) values of the DGEBA/4MPip network is always lower than that of the

others epoxy networks. However, the diffusion time (tD) value is the largest. On the other hand, the

DGEBA/3DCM and DGEBA/IPD networks show the same diffusion coefficient (C), water saturation (C∞)

and diffusion time (tD) values. However, the structure-diffusivity relationships are not clearly established. It

is known that the curing agent affects the water absortion (Abdelkader&While, 2005). But reports based on

the diffusion kinetic suggest that in aliphatic diepoxide cured by aromatic diamine, the diffusion rate of

water is controlled by the strength of the polymer-water hydrogen bond (Tcharkhchi et al., 2000). In this

way, the DGEBA/4MPip network has a little hydrogen bond concentration (González Garcia et al., 2011)

because this network is formed by steps-growth polymerization and homopolymerization by anionic

mechanics as mentioned before. This structural characteristic makes difficult the diffusion rate of water. For

the DGEBA/3DCM and DGEBA/IPD polymers the hydrogen bond concentration are similar, but the first

network present more rigid structure leading to a relative lower diffusion coefficient (C), water saturation

(C∞) and time of diffusion (tD) values. This make the diffusion rate of the water in the DGEBA/3DCM

network more complicated.


89

Table 6. Diffusion coefficient (D, mm2/s), saturation value (C∞, %) and diffusion time tD, days)

obtained from experimental weight gain vs. time curve of DGEBA/3DCM, DGEBA/IPD and

DGEBA/4MPip systems.

Epoxy networks DGEBA/3DCM DGEBA/IPD DGEBA/4MPip

C∞ (%) 1.497 1.522 1.227

D (mm2/s) 1.17 x 10-6

9.43 x 10-6

9.55 x 10-7

tD(days) 57.56 54.12 61.04

4. CONCLUSIONS

This study demonstrated that the cure schedule of the epoxy systems achieve high conversion. Only

DGEBA/4MPip system formed a thin coating on surface polished and silanizated of 316L stainless steel.

This epoxy system show slow viscosity and contact angle that could be applied to stents with complicated

shapes. In addition, this system shows better adhesive properties and exhibit low water absortion.

Accordingly, we believe that DGEBA/4MPip system can be potentially employed for coating in bare

metallic coronary stents.

5. REFERENCES

Abdelkader, A.F.,& While, J.R. (2005) Water absortion in epoxy resins: The effects of the crosslinking

agent and curing temperature. Journal of Applied Polymer Science, 98, 2544-2549.

AL-Mangour, B., Mongrain, R., Irissou, E.,& Yue, S. (2013) Improving the strenght and corrosion

resistance of 316L stailess steel for biomedical application using cold spray. Surface and Coatings

Thecnology, 216, 297-307.

Apostol, T.M. (1974) Mathematic Analysis. (2nd ed.). Addison-Wesley (Chapter 4).

Bakhshi, R., Darbyshire, A., Evans, J.E., You, Z., Lu, J.,& Seifalian, A.M. (2011) Polymeric coating of

surface modified nitinol stent with POSS-nanocomposite polymer. Colloids and Surface B: Biointerface, 86,

93-105.

Berry, N.G., d’Almeida, J.R.M., Barcia, F. L.,& Soares, B.G. (2007) Effect of water absorption on the

thermal-mechanical properties of HTPB modified DGEBA-based epoxy systems. Polymer Testing, 26, 262-

267.

Chovelon, J.M., Aarch, L.E.L., Charbonnier, M.,& Romand, M. (1995) Silanization of stailess steel

surfaces: Influence of application parameter. The Journal of Adhesion, 50, 43-58.

Clayton, A.M. (1998) Epoxy Resins.Chemistry and Technology. (2nd ed.).New York:Marcel Dekker,

(Chapter 6)

Colombini, D., Martinez-Vega, J.J.,& Merle, G. (2002) Dynamical mechanical investigations of the

effects of water sorption and physical ageing on an epoxy resin system. Polymer, 43, 4479-4485.

Crowder, S.W., Gupta, M.K., Hofmeister, L.H., Zachman, A.L.,& Sung, H.J. (2012) Modular polymer

design to regulate phenotype and oxidate response of human coronary artery cells for potential stent coating

aplications. Acta Biomaterialia, 8, 559-569.

De Morais, A.B., Pereira, A.B., Teixeira, J.P.,& Cavaleiro, N.C. (2007) Strength of epoxy adhesive-

bonded stainless-steel joints. International Journal of Adhesion and Adhesives, 27, 679-686.


90

Dekaoui, S.M., Labbé, A., Chevallier, P., Holvoet, S., Roques, C.,& Avramoglou, T. (2012) A new

dextran-graft-polybutylmethacrylate copolymer coated on 316L metallic stent enhances endothelial cell

coverage. Acta Biomaterialia, 8, 3509-3515.

Erbel, R., Konorza, T., Haude, M., Dagres, N.,&Baumgrat, D. (2002) Future of interventional cardiology

in the treatment of coronary artery disease.Herz, 27, 471-480.

Gallino, E., Massey, S., Tatoulian, M.,& Mantovani, D. (2010) Plasma polymerized allylamine films

deposited on 316L stainless steel for cardivascular stent coating. Surface and Coatings Thecnology, 205,

2461-2468.

González Garcia, F., de Queiroz, A.A.A., Higa O.Z.,& Baratéla, F.J.C. (2015) Epoxy/aliphatic amine

networks with perspectives in cardiovascular applications. In vitro biological properties. Sumit to Revista

Matéria (in portuguese).

González Garcia, F., Leyva, M.E., de Queiroz, A.A.A.,& Higa, O.Z. (2009) Epoxy networks for medicine

applications: Mechanical properties and in vitro biological properties. Journal of Applied Polymer Science,

112, 1215-1225.

González Garcia, F., Leyva, M.E., de Queiroz, A.A.A.,& Simões, A.Z. (2011) Durability of adhesives

based on different epoxy/aliphatic amine networks. International Journal of Adhesion and Adhesives, 31,

177-181.

González Garcia, F., Silva, P.M., Soares, B.G.,&Rieumont, J. (2007) Combined analytical techniques for

the determination of the amine hydrogen equivalent weight in aliphatic amine epoxy hardeners. Polymer

Testing, 26, 95-101.

González Garcia, F., Soares, B.G.,& Williams, R.J.J. (2002) Poly(ethylene-co-vinyl acetate)-graft-

poly(methyl metacrylate) (EVA-graft-PMMA) as modifier of epoxy resins. Polymer International, 51, 1340-

1347.

Hu, X.,& Huang, P. (2005) Influence of polyether chain and sinergetic effect of mixed resins with

different functionality on adhesion properties of epoxy adhesives. International Journal of Adhesion and

Adhesives, 25, 296-300.

Kajzer, W., Krause, A., Walke, W.,&Marcianiak, J. (2008) Corrosion behaviour of AISI 316L steel in

artificial body fluids. Journal of Achievements in Materials and Manufacturing Engineering, 31, 247-253.

Köster, R., Vieluf, D., Kiehn, M., Sommerauer, M., Kähler, J., Baldus, S., Meinertz, T.,&Hamm, C.W.

(2000) Nickel and molybdenum contact allergies in patients with coronary in-stent restenosis. The Lancet,

356, 1895-1897.

Lee, H.,& Neville, K. (1967) Characterization of epoxy-resin curing-agent systems. In: H. Lee, & K.

Neville (Eds) Handbook of Epoxy Resins (pp. 1-66). New York:McGraw-Hill.

Maggana, C.,& Pissis, P. (1999) Water sorption and diffusion studies in an epoxy resin system. Journal of

Polymer Science Part B: Polymer Physics, 37, 1165-1182.

Mani, G., Feldman, M.D., Patel, D.,&Agrawa, D.C. (2007) Coronary stents: A materials perspective.

Biomaterials, 28, 1689-1710.

Mikhalovska, L., Chorna, N., Lazarenko, O., Haworth, P., Sudre, A.,& Mikhalovsky, S. (2011) Inorganic

coatings for cardiovascular stents: In vitro and in vivo studies. Journal of Biomedical Materials Research

Part B: Applied Biomaterials, 96B, 333-341.

Montions, P., Nassiet, V., Petit, J.A.,& Adrian, D. (2007) Viscosity effect on epoxy-diamine/metal

interphases – Part II: Mechanical resistance and durability. International Journal of Adhesion and Adhesives,

27, 145-155.

Moy, P., & Karasz, F.E. (1980) Epoxy-water interactions. Polymer Engineering & Science, 20, 315-319.


91

Newsome, L.T., Kutcher, M.A.,& Royster, R.L. (2008) Coronary artery stents: Part I. Evolution of

percutaneous coronary intervention. Anesthesia & Analgesia, 107, 552-569.

Omrani, A., Rostami A., Ravari, F.,& Ehsani, M. (2013) The relationship between composition and

electrical properties of brass covered by nanocomposite coating of glycerol diglycidyl ether: An EIS and

DMTA study. Progress in Organic Coatings, 76, 360-366.

Omrani, A., Rostami, A.A., Ravari, F.,& Mashak, A. (2011) Curing behavior and structure of a novel

composite from glycerol diglycidyl ether and 3,3-dimethylglutaric anhydride. Thermochimica Acta, 519, 9-

15.

Oudad, W., Madani, K., Bouiadjra, B.B., Belhouari, M., Cohendoz, S., Touzain, S.,& Feaugas, X. (2012)

Effect of humidity absortion by the adhesive on the performances of bonded composite repairs in aircraft

structure. Composites Part B: Engineering, 43, 3419-3424.

Pascault, J.P., Sautereau, H., Verdu, J.,& Williams, R.J.J. (2002) ThermosettingPolymers.(1s.ed.). New

York: Marcel Dekker, (Chapters3, 10 and 14).

Rodríguez, G., Fernádez-Gutiérrez, M., Parra, J., López-Bravo, A., Honduvilla, N.G., Buján, J., Molina,

M., Duocastella, L.,& San Román, J. (2010) Bioactive polymeric system with platelet antiaggregatig activity

for the coating of vascular devices. Biomacromolecules, 11, 2740-2747.

Serruys, P.W., de Jaegere, P., Kiemeneij, F., Macaya, C., Rutsch, W., Heyndrickx, G., Emanuelsson, H.,

Marco, J., Legrand, V., Materne, P., Belardi, J., Sigwart, U., Colombo, A., Goy, J. J., Van den Heuvel, P.,

Delcan, J.,& Morel, M.A. (1994) A comparison of balloon-expandable-stent implantation with balloon

angioplasty in patients with coronary artery disease. The New England Journal of Medicine, 331, 489-495.

Sheiban, I., Villata, G., Bollati, M., Sillano, D., Lotrionte, M.,&Biondi-Zoccai, G. (2008) Next-

generation drug-eluting stents in coronary artery disease: Focus on envirolimus-eluting stent (Xience V).

Vascular Health and Risk Management, 4, 31-38.

Tcharkhchi, A., Bronnec, P.Y.,& Verdu, J. (2000) Water absortion characteristics of diglycidyl ether of

butane diol-3,5-diethyl-2,4-diaminotoluene networks. Polymer, 41, 5777-5785.

Wang, S.F., Lin, M.L., Shieh, Y.N., Wan, Y.R.,& Wan, S.J. (2007) Organic modification of synthesized

clay-magadiite. Ceramic International, 33, 681-685.

Waterhouse, A., Wise, S.G., Yin, Y., Wu, B., James, B., Zreiqat, H., McKenzie, D.R., Bao S., Weiss,

A.S., Ng, M.K.C.,& Bilek, M.M.M. (2012) In vivo biocompatibility of plasma-activated, coronary stent

coating. Biomaterials, 33, 7984-7992.

Epoxy/amine networks for coating 316L stainless steel ... · PDF fileEpoxy/amine networks for...

Documents

Transcript of Epoxy/amine networks for coating 316L stainless steel ... · PDF fileEpoxy/amine networks for...