Silane Impact on Color Stability of a Silane Modified...

Silane Impact on Color

Stability of a Silane Modified

Polyether (SMP) Sealant

Dr. Tim Biggs

October 2016

Outline

• Study Objective

- Evonik Silanes Background

• Project Design

- Silanes Evaluated

- Preparation of SMP Sealant

- Preparation of Test Coupons

- Weathering Conditions

• Results

- Analysis of Weathered Samples

- Conclusions

ASC October 2016 Page | 2

Study Objective:

What options do formulators have for low yellowing sealants?

• Traditional aminosilane adhesion promoters cause yellowing over time

• Conventional wisdom is, only hindered aminosilane adhesion promoters

with dimethyl branching adjacent to nitrogen significantly reduces yellowing

• This limits formulations to one type of adhesion promoter and restricts

formulation design

Compare Evonik low yellowing silane adhesion promoters to hindered

aminosilanes in an opaque SMP sealant

• Compare in Various Weathering Scenarios

• Examine Visual Color Change

• Test Color Change via Colorimetry Analysis


Organofunctional Silanes are

Bifunctional Molecules…

Y (CH2)nSi (OR)3

n = 0,3

R = CH3, C2H5, (CH2)2OCH3

Y = Organofunctional group

Y (CH2)n

Si OR

OR

ORhydrolyzablenon hydrolyzable

Organofunctional group can

react with polymers, resins…

Silicon functional group

can react with inorganic

fillers, metals, glass…


Five Generations of Functional

Silanes Developed by Evonik

Time

Traditional

Silanes

Dynasylan®

VTMO

Technology

1970 2010

Water - Borne

Silanes

Dynasylan®

HYDROSIL

2627

2909

Low VOC

Oligomeric

Silanes

Dynasylan®

40

9896

1146

Special

Silanes

Dynasylan®

11894148

1124

SIVO®

Technology

Unique Silanes

Dynasylan®


E 1 SilaneProprietary silane for critical substrates

Technologies

• MS-Polymer

• Silane modified polymers (SMP)

• RTV-1/-2 silicones

Applications

• Construction

• Transportation

• Industrial Assembly

• DIY

Benefits

• Better adhesion on critical substrates (PVC, PET)

• Higher cohesion

• Higher flexibility

• Less tendency towards yellowing


0

50

100

150

200

250

300

PC PMMA PET

Standard

SIVO 203

AF AF

E 1 Silane presented excellent adhesion on plastics !

Filled Sealant with 1 % Adhesion Promoter

E 1 Silane:Adhesion on Critical Polymer Substrates


E 1 Silane

E 1 Silane showed highest flexibility in SMP sealant !

E 1 Silane:“High-Elastic” Bonding


0

20

40

60

80

100

120

140

Standard E 3 Silane

E 1 Silane

Filled Sealant with 0.5 % Adhesion Promoter

0

1

2

3

4

5

E 2 Silane Standard

E 2 Silane:Unique silane co-oligomer

• Diamino/Alkyl Co-oligomer

• Improved water resistance at interface

• Reacts like a silane monomer

• Reduced VOCA = diamino, B = alkyl

OR = methoxy

R O Si

A

OR´

O Si O R

B

OR´a b

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

3 7 14 21 28

Storage in water [days]

Wa

ter

up

tak

e

[%]

Dynasylan® DAMO-T

Dynasylan® 1146

Excellent

Acceptable

Very Poor

Sealant Aged in Water: Water Uptake and Adhesion

Dry

Adhesion

Wet

Adhesion

Standard

E 2 Silane

Hindered Aminosilane

Theoretical Low Yellowing Mechanism:

• Dimethyl groups adjacent or near amine reduce or prevent formation of radicals

• Radicals lead to the formation of azo compounds

• Azo Compounds are highly colored

Selected a Typical Commercial Hindered Aminosilane:


Formulation Details

Parts [wt. %] Raw material

30.0 – 40.0 Hybrid Polymer

15.0 – 20.0 Plasticizer

0.5 – 1.0 Moisture Scavenger

45.0 – 55.0 CaCO3

1.5 Silane Adhesion Promoter

0.06 Tin Catalyst

Formulation Details:SMP Sealant


Sealant Batch Preparation:Pigment Grind Equipment

Planetary Mixer Centrifugal Mixer


Preparation of Test Coupons:Sealant patches on aluminum panels

Aluminum Panels were used as the testing substrate. Adequate cleaning and

substrate preparation is critical:

• Wipe the aluminum panel with isopropanol

• Prepare Alkaline Solution

• Turn on stirring to the speed 6 or 7

• Heat the solution to 140-150°F

• Dip the panel in the solution for 3 min until

a break free water surface is noticed

• Take out the panel and immediately put in

the water and shake it

• Wash with DI water and air-blow dry

Aluminum Panels: dimensions: 3 in x 6 in x 0.032 in)



Preparation of Test Coupons:Patches and Curing

After cleaning, the sealant was

applied to panels with a PTFE frame

Samples were placed in a humidity

chamber (50% moisture & 23°C) for a

curing time of 21 days

Simulating Long-term Exposure: Weathering Chamber and Test Cycles

Test Coupons were exposed to UV-light,

heat, and water:

• Equipment: QUV

• UV-Lights: UV-A 340, chosen to simulate lights

contained in sunlight radiation between 295-365

nm

• Simulated long-term weather exposure by

applying cycles of high temperatures and UV

light, as well as condensation of water

• During weathering cycle, UV radiation happens

at a higher temperature (60°C) and

condensation happens at a slightly lower

temperature (50°C). During condensation mode

the UV light is turned off.

UVH2O


Sample Exposure Conditions


Condition 1

• UV Light

• Oxygen

• Moisture

Condition 2

• Oxygen

• Moisture

Condition 3

• UV Light

Condition 4

• No Exposure

Colorimetry Analysis:Determining the degree of yellowing

Surface Colorimeter:

• Measures the amount of light reflected in three wavelength ranges across the visible

spectrum. In our case we measured the yellowness of our samples.

• These measurements were performed after 21 days of curing and then periodically after

combinations of UV-light / water / oxygen exposure.

• For this project, yellowness is measured using the standard E313 index. The more yellow

the sample gets, the larger the number.


Samples After 21 Days:UV, Oxygen and Moisture Exposure

Condition 1


0 days

10 days

21 days

0

1

2

3

4

5

6

7

8

9

10

UV H2O O2 UV H2O O2 UV H2O O2 UV H2O O2

Blank E 1 Silane E 2 Silane Hindered Silane

Yello

wn

ess

E31

3

0 days 10 days 21 days

Samples After 21 Days:UV, Oxygen and Moisture Exposure



Samples After 21 Days:Oxygen and Moisture Exposure

Condition 2


0 days

10 days

21 days

0

1

2

3

4

5

6

7

8

9

10

O2 O2 O2 O2




Samples After 21 Days:Oxygen and Moisture Exposure


Samples After 21 Days:UV Exposure

Condition 3


0 days

10 days

21 days

0

5

10

15

20

25

30

35

UV UV UV UV


UV



Samples After 21 Days:UV Exposure


Samples After 21 Days:No Exposure

Condition 4


0 days

10 days

21 days

0

1

2

3

4

5

6

7

8

9

10

None None None None



Samples After 21 Days:No Exposure



Amine Oxide

Colorless

Discoloration in Sealants:Azo vs Amine Oxide

Analysis of Results:

• Yellowing of adhesives and sealants may be caused azo compounds.

• The absence of oxygen causes an even worse discoloration, possibly due to

oxygen forming colorless amine oxides instead of azo compounds.

Yellow

Azo Compound


Benefit of Oligomeric Silanes:Steric or Shielding Effect

R O Si

A

OR´

O Si O R

B

OR´a b >

E 2 Silane


Analysis of Results:

• Steric bulk reduces yellowing of adhesive and sealants

• E 2 Silane alkyl groups and oligomeric structure provides the highest degree

of steric bulk and shield the amine from Azo formation.

• Hindered aminesilanes offer shielding as well, but not the magnitude of E 2

Silane.

Conclusion


Key Points Learned:

• E 2 Silane performed significantly better than the Hindered Silane when exposed to

UV light in vacuum

• Under all other conditions, the three silanes gave similar low yellowing results.

• Hindered silanes do not out-perform E 1 Silane and E 2 Silane under typical sealant

conditions.

• Multiple types of advanced silanes can be used to formulate adhesives and

sealants with low yellowing potential.

0

5

10

15

20

25

30

35

None UV O2 UVH2OO2

None UV O2 UVH2OO2

None UV O2 UVH2OO2

None UV O2 UVH2OO2


Yello

wn

ess

E31

3

21 days

Tim BiggsResource Efficiency

Head of Applied Technology

2 Turner Place

Piscataway, NJ 08876

phone: 732-718-1219

[email protected]

Chelsea StantonResource Efficiency

Marketing Adhesives & Sealants

299 Jefferson Road

Parsippany, NJ

phone: 973-929-8551

[email protected]


Evonik Contacts for Questions

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