santoprene sterilization study

7/24/2019 Santoprene Sterilization Study

1/13

Page 1 of 13

Sterilization Study of

Santoprene Thermoplastic VulcanizateTechnical Literature - TL00708

Introduction

Santoprene thermoplastic vulcanizate (TPV) is a fully crosslinked thermoplastic elastomer (TPE) whichhas many unique properties over thermoset rubbers and other thermoplastic elastomers. Examples ofthese advantages are:

Low compression set Thermoplastic processing

Wide hardness range

Available Grades

The current medical grades available are:

Colorable Black

281-55MED 8281-65MED 181-55MED

8281-35MED 8281-75MED 181-57W180

8281-45MED 8281-90MED

8281-55MED

Product data sheets for these grades can be found at www.santoprene.com.

From these unique properties, product designers often incorporate Santoprene TPV in medical devicessuch as syringe plungers, gaskets, grips and bumpers. When in such devices, these materials will likelybe exposed to one of the following sterilization processes:

Ethylene oxide (EtO)

Gamma radiation

Autoclave

A key consideration in a medical device is to understand the affects sterilization has on the physicalproperties of Santoprene TPV.

Scope

To better understand how sterilization affects the properties of Santoprene TPV, several grades that spanthe available hardness were submitted to EtO, gamma radiation and autoclave sterilization, and tested forrelevant properties. This technical document reviews the results from this testing.

For reference, the retention of a property is calculated by the following equation:


2/13

Page 2 of 13

% Retention = (Property after Aging) / (Property Unaged) * 100

Addi tional Note: This product, including the product name, shall not be used or tested in any medical

application without the prior written acknowledgement of ExxonMobil Chemical as to the intended use.

Ethylene Oxide Sterilization

EtO sterilization is a popular method for one time use medical disposables that are also only sterilizedonce. The key property to monitor for this type of sterilization is the retention of residuals (measured inmgs/day) for EtO and ethylene chlorohydrins (ECHs). For this study:

The grades evaluated were 181-57W180, 281-45MED, 281-64MED and 281-87MED.

Plaques of each grade were submitted to two EtO sterilization cycles. Two cycles were usedto represent the maximum exposure incurred in typical medical device manufacturing.Exposing a device to a second cycle arises when the first cycle prematurely ends. Exposureto the second cycle ensures the device was exposed to at least one complete cycle. Cycles

beyond two are not expected. Test procedures and allowable residual limits are specified per ISO 10993-7 October 1995.

The procedure for the residual analysis was per ISO 17025. The following additional steps

were employed:

1. Test specimens were frozen after sterilization and thawed prior to testing to accurately

control aeration time.2. Residuals were extracted in an eluate by placing the plaques in 20 ml of purified water at

37C for 24 hours.3. Residual levels in the eluate were determined by gas chromatography.

Residual levels were measured at one and four days of aeration.

Results can be found in Table I. Results were:

EtO: After one day post sterilization, EtO residuals for all grades were well below themaximum allowable limit of 20 mgs/day (per ISO 10993-7)and not detectable after fourdays.

ECH: After one day post sterilization, ECH residuals for all grades were less than half themaximum allowable limit of 12 mgs/day (per ISO 10993-7) and below 1.8 mgs/day afterfour days.

In summary, all grades in this testing exhausted both EtO and ECH residuals well below the maximumallowable limits after only one day of aeration.

Autoclave

Autoclaving is a common technique used for sterilizing devices by the individual medical careprofessional (e.g.,doctors office, hospital, etc.) for durable medical instruments (scalpels, tongs, pliers,etc.). Autoclaving sterilizes a device by exposing it to super-heated steam (steam heated to temperaturesabove 100C and pressures above one atmosphere) for a specific duration (usually a minimum of fiveminutes at peak temperature and pressure). To evaluate the effect autoclave sterilization has onSantoprene TPV, plaques were submitted to two different sets of autoclave exposures. The first set wasfor five autoclave exposures. The second set was for 250 autoclave exposures, with samplesincrementally pulled and tested at 50, 100 and 250 cycles.


3/13

Page 3 of 13

Autoclave - 0 Cycles

The first study (five autoclave exposures) exposed plaques of 281-45MED, 281-64MED, 281-87MED,

8281-45MED, 8281-65MED and 8281-90MED.

Autoclave parameters for each of these exposures were:Exposure Temperature: 132C (270F)Exposure Time: 30 minutesExposure Pressure: 28.6 psigContainment: Plaques were placed in plastic bags

Parameters measured in the testing were:

% Retention of Hardness ISO 868

% Retention of Ultimate Tensile Strength ISO 37

% Retention of Tensile Stress at 100% Elongation ISO 37

% Retention of Ultimate Elongation ISO 37

Results can be found in Graph 1 (a-d).

Five cycles of autoclaving showed less than 20% effect on ultimate tensile strength and tensile stress at100% elongation and less than 30% reduction of % elongation for all grades.

Autoclave - 250 Cycles

The second study exposed plaques of 281-64MED, 281-73MED and 281-87MED to 250 autoclavecycles.

Autoclave parameters in this testing were:Exposure Temperature: 132C (270F)Time at Temperature: 6 minutesTime between Exposures: 30 minutesContainment: Plaques were directly exposed to the steam (no bags)

Results can be found in Graph 2 (a-d).

Properties measured in this testing were:

% Retention of Ultimate Tensile Strength ASTM D412

% Retention of Tensile Stress at 100% Elongation ASTM D412

% Retention of Ultimate Elongation ASTM D412

% Retention of Hardness ASTM D2240

Two hundred-fifty cycles of autoclaving had little effect on hardness and ultimate tensile strength. Thetensile stress at 100% elongation could only be measured for 281-87MED. This is due to the elongationof 281-73MED and 281-64MED going below 100% after 50 cycles. For the 250 cycles of autoclaving, themajority of changes in physical properties occurred in the first 50 cycles.

Gamma Sterilization

Gamma sterilization is a method that sterilizes devices by exposing them to controlled dosages of gammaradiation. Gamma sterilization has the advantage of 1) short turn around times, and 2) low cost when


4/13

Page 4 of 13

performed in volume. From these advantages, this method is gaining popularity for many one time usemedical disposables.

Historically, much of the medical industry expressed the amount a device was gamma irradiated in theunits of MegaRads (Mrads). Today, the amount a device is exposed to gamma irradiation is expressed inthe international standard of KiloGray (KGy). Ten KGy = one Mrads (example: 25 KGy = 2.5 Mrads).

A typical irradiation for a medical device for one cycle is 10 to 25 KGy. Should a problem arise duringsterilization, the devices may be exposed to a second cycle of up to an additional 25 KGy. Such asecond cycle ensures the device was exposed to at least one full cycle. It should be noted the effects ofgamma irradiation are cumulative. This means that if the first gamma cycle is 25 KGy and a second cycleof 25 KGy is performed, then the total effect on the device and its materials is the same as the devicebeing exposed to one dose of 50 KGy. For this testing, dosages as high as 70 KGy were evaluated,which is an excessive overexposure for any medical device. From this, all data above 50 KGy should beviewed only for reference.

The Santoprene TPV grades selected for this testing were 281-45MED, 281-64MED, 281-87MED, 8281-45MED, 8281-65MED and 8281-90MED.

Parameters measured in testing were:

% Retention of Ultimate Tensile Strength ISO 37

% Retention of Tensile Stress at 100% Elongation ISO 37

% Retention of Ultimate Elongation ISO 37

Changes in Color TPE-0135

Changes in Compression Set ISO 815Note: Because of limited samples, compression set testing was only conducted on the following

grades: 281-45MED, 281-64MED and 8281-65MED.

Results can be found in Graph 3 (a-f).

All grades showed a gradual change in tensile properties and color for gamma sterilization under 50 KGy.In compression set testing, the 281-45MED and 281-64MED showed little effect from gamma irradiation.The 8281-65MED showed a significant loss (or increase) in compression set. From this, it is suggestedthat the 8281-XXMED grades may possibly not be suitable for sealing applications that are exposed to 25KGys or more gamma irradiation.

Summary

Santoprene TPV exhibits excellent retention of physical properties after repeated heat histories. The

Santoprene TPV grades in the above testing showed excellent performance when sterilized with EtO.

Santoprene TPVs released all measured residuals quickly and to levels well below requirements.

From five cycles of autoclaving in the above testing, Santoprene TPV showed less than 30% change in

properties. From 250 cycles of autoclaving in the above testing, most change in physical properties

occurred in the first 50 cycles and was under 30% for the entire test.

For gamma sterilization, all grades in this study showed a gradual change in properties and color whenirradiated to 50 KGys. 281-XXMED grades showed better property retention in compression set than8281-XXMED. 8281-XXMED may not be suitable grades for sealing applications requiring 25 KGys ormore irradiation.


5/13

Page 5 of 13

Table I

Ethylene Oxide Sterilization - EtO Residuals

Materialsmgs/day

1 Day 4 Days

Allowable Limit per ISO 10993-7 20 20

Santoprene 181-57W180 TPV


6/13

Page 6 of 13

Graph 1-a

Graph 1-b

% Retention of Ultimate Tensile Strength after 5 Autoclave Cycles

0%

20%

40%

60%

80%

100%

120%

281-45MED 281-64MED 281-87MED 8281-45MED 8281-65MED 8281-90MED

%R

etentio

nofUltimateTensileStrength

% Retention o f Tensile Modu lus at 100% Elongation after 5 AutoclaveCycles

0%

20%

40%

60%

80%

100%

120%


%R

etentionofTensileModulusat100%E

longation


7/13

Page 7 of 13

Graph 1-c

Graph 1-d

% Retention o f Elongation after 5 Autoclave Cycles

0%

20%

40%

60%

80%

100%

120%


%Re

tentionofElongation

% Retention o f Hardness after 5 Autoclaves

0%

20%

40%

60%

80%

100%

120%

281-45 MED 281-64 MED 281-87 MED 8281-45 MED 8281-65 MED 8281-90 MED

%R

et

entionofHardness


8/13

Page 8 of 13

Graph 2-a

Graph 2-b

% Retention of Hardness vs . Autoclave Cycle

0

20

40

60

80

100

120

140

0 50 100 150 200 250 300

Number of Autoclave Cycles

%R

etentionofHardness

281-87MED 281-73MED 281-64MED

% Retention o f Ultimate Tensile Strength vs. Autoclave Cycle

0

20

40

60

80

100

120

140

0 50 100 150 200 250 300


%R

etentionofUltimateTensile

Strength

281-87MED 281-73MED 281-64MED


9/13

Page 9 of 13

Graph 2-c

Note: The only grade % retention of tensile stress @ 100% elongation could be calculated for was 281-87MED, due to281-64MED and 281-73MED not having a 100% elongation after 50 cycles.

Graph 2-d

% Retention o f Tensile Modu lus at 100% Elongation vs. Autoclave

Cycle

0

20

40

60

80

100

120

140

0 50 100 150 200 250 300


%

RetentionofTensileModulusat

100%Elongation

281-87MED

% Retention of Elongation vs . Autoclave Cycle

0

20

40

60

80

100

120

140

0 50 100 150 200 250 300


%RetentionofElongation

281-87MED 281-73MED 281-64MED


10/13

Page 10 of 13

Graph 3-a

Graph 3-b

% Retention of Ultimate Tensile Strength vs. Levels of Gamma

Exposure

0%

20%

40%

60%

80%

100%

120%

0 10 20 30 40 50 60 70 80

KGy Gamma

%Reten

tionofUltimateTensileStrength


% Retention o f Tensile Modulus at 100% Elongation vs. Lev els ofGamma Exposure

0%

20%

40%

60%

80%

100%

120%

0 10 20 30 40 50 60 70 80

KGy Gamma

%RetentionofSecant

Modulusat100%



11/13

Page 11 of 13

Graph 3-c

Graph 3-d

% Retention of Elongation vs. Levels of GammaExposure

0%

20%

40%

60%

80%

100%

120%

0 10 20 30 40 50 60 70 80

KGy

%R

etentionofElongation


Color L v s. Levels of Gamma Exposure

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80

KGy

LHunterColorUnits

281-45MED 281 -64MED 281 -87MED 8281-45MED 8281-65MED 8281-90MED


12/13

Page 12 of 13

Graph 3-e

Graph 3-f

Color B v s. Levels of Gamma Exposure

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80

KGy

BHunterColorUnits


% Compression Set after 168 hours at 100C vs. Lev els of

Gamma Exposure

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80

KGy

%CompresionSet

281-45 MED 281-64 MED 8281-65 MED


13/13

Page 13 of 13

Contact your ExxonMobil Chemical representativefor more in formation.

santoprene.com

2008 ExxonMobil. ExxonMobil, the ExxonMobil logo, the interlocking X device andother product or service names used herein are trademarks of ExxonMobil, unlessindicated otherwise. This document may not be distributed, displayed, copied or alteredwithout ExxonMobil's prior written authorization. To the extent ExxonMobil authorizesdistributing, displaying and/or copying of this document, the user may do so only if thedocument is unaltered and complete, including all of its headers, footers, disclaimers andother information. You may not copy this document to or reproduce it in whole or in parton a website. ExxonMobil does not guarantee the typical (or other) values. Any dataincluded herein is based upon analysis of representative samples and not the actualproduct shipped. The information in this document relates only to the named product ormaterials when not in combination with any other product or materials. We based theinformation on data believed to be reliable on the date compiled, but we do not represent,

warrant, or otherwise guarantee, expressly or impliedly, the merchantability, fitness for aparticular purpose, freedom from patent infringement, suitability, accuracy, reliability, orcompleteness of this information or the products, materials or processes described. Theuser is solely responsible for all determinations regarding any use of material or productand any process in its territories of interest. We expressly disclaim liability for any loss,damage or injury directly or indirectly suffered or incurred as a result of or related toanyone using or relying on any of the information in this document. This document is notan endorsement of any non-ExxonMobil product or process, and we expressly disclaimany contrary implication. The terms we, our, "ExxonMobil Chemical" and "ExxonMobil"are each used for convenience, and may include any one or more of ExxonMobilChemical Company, Exxon Mobil Corporation, or any affiliate either directly or indirectlystewarded.

S0608-636E98

santoprene sterilization study

Documents