Calcium Carbonates for Sealants
Redefining Performance
Kalena Stovall, PhD
Imerys Carbonates
October 19, 2016
Calcium Carbonates in Sealants
Caulks and sealants use high levels of calcium
carbonate for desired performance and cost reduction
Reactive sealants often need very low moisture content for
processing and shelf stability
Specialty engineered carbonates are incorporated to control
rheology and mechanical properties
Higher brightness calcium carbonates offer better color match
and surface finish
Typical carbonates in caulks and sealants
Water-borne caulks: medium PSD GCC
Reactive sealants: fine PCCs and GCCs, treated carbonates
10/19/2016Calcium Carbonates for Adhesives, Caulks &
Sealants
GCC and PCC Manufacturing
Ground Calcium Carbonate (GCC)
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Sealants
2.5” and smaller pebbles 1 mm and smaller (0.4 µm)
particles
Crush,
Pulverize,
Grind
Precipitated Calcium Carbonate (PCC)
Big rock Pebble Powder
Final powders made by wet or dry grinding
Calcite, only
Purity impacted by nature and processing
Chemically prepared in aqueous solution
Multiple polymorphs and crystal shapes
Finer PSD options than GCC
Purer calcium carbonate than most GCCs
Higher surface area than GCC
Ultrafine PCC
Polymorphs: Vaterite,
Aragonite, Calcite
Can surface treat either product (with fatty acid or other)
All Calcium Carbonates Are Not the Same..
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Sealants
Typical Differentiation Properties between PCC and GCC
Particle or granular size
Morphology / aspect ratio
Brightness
Surface functionality
Chemical purity
Moisture content
Surface area
Porosity
Oil absorption
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Sealants
Silicone and modified
silicones
Polyurethane and
silane-terminated
Water-borne Acrylics
Polysulfide
Butyl
Cost
Manufacturing cycle
Package stability
Application
Adhesion
Tensile properties
Chemical resistance
0
10
20
30
40
50
60
70
80
90
100
0.1 1 10 100
% p
as
s
Particle Diameter (µm)
3 µm untreated GCC
3 µm fatty acid treated GCC 1
3 µm fatty acid treated GCC 2
3 µm GCC treated withengineered treatment
Particle Size Distribution: More than d50 Matters (Example 3 µm GCCs)
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Sealants
Treated GCC 1 and untreated GCC contain more fines may be higher surface area GCC may
have higher viscosity sealant
Fines can be viewed two ways:
1. Overall steepness of the curve more steep = less fines = likely lower viscosity/ faster extrusion rate
2. % of particles passing at 1 µm
0
10
20
30
40
50
60
70
80
90
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0.1 1 10 100
% p
as
s
Particle Diameter (µm)
Treated PCC, PPS: 0.06 µm
Treated PCC, PPS: 0.06 µm
Treated PCC, PPS: 0.07 µm
Treated PCC, PPS: 0.1 µm
Particle Size Distribution: More than d50 Matters (Example PCCs)
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Sealants
PSD curve and primary particle size (PPS) in PCCs should be considered together available surface area
sealant rheology, mechanical properties
Inflections of particle sizes in a single batch particle packing in sealant and sealant viscosity
Calcium Carbonate Differentiation Study
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Sealants
Calcium Carbonate Differentiation – Looking Beyond PSD
Known: PSD and moisture content can influence sealant performance
Manufacturers use untreated and treated GCC, PCC or both to optimize sealant properties
Curiosity/ Hunch: Surface area and surface treatment impact sealant:
Processing time
Rheology
Mechanical properties
To probe this, tested GCCs of varying surface area and surface treatment in a SPUR construction
sealant
Fixed GCC PSD at 3 microns, and examined:
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Sealants
GCC Surface Treatment Surface Area
Untreated Naked surface High surface area
Classically treated Excess carboxylic acid* Low surface area
Classically treated Excess carboxylic acid* Low surface area
Engineered product No excess treatment Medium surface area
*Classical carbonate treatment to obtain a monolayer of fatty acid
coverage typically yields an excess of unreacted carboxylic acid
SPUR Sealant Formulation
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Sealants
Component Wt %
SPUR+ 1015LM prepolymer 22.2
Plasticizer (DIDP) 18.5
Moisture scavenger (Silquest A-171* silane) 1.0
Calcium Carbonate (PCC) 30.0
Calcium Carbonate (GCC) 25.5
UV Stabilizers 0.5
Thixatropic Agent (SiO2) 0.2
Colorant (TiO2) 1.2
Adhesion Promoter (Silquest* A-1110 silane) 0.6
Catalyst (dibutyltin dilaurate) 0.3
SPUR Sealant Formulation GCCs and PCCs Tested
Product PPS, µm Treatment
level, wt %
Surface
Area, m2/g
GCC A 3 0 4.9
GCC B 3 1.0 2.5
GCC C 3.5 0.9 3.5
GCC D 3.2 2.5 1.8
PCC 1 0.07 2.6 24.5
PCC 2 0.06 2.7 19.5
PCC 3 0.07 2.8 22.6
PPS = primary particle size
Calcium Carbonate Influence on Silylated Polyurethane (SPUR)
Sealant Pre-Batch Processing Time
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Sealants
Calcium Carbonate Influence on SPUR Sealant Pre-Batch Processing/
Drying Time
Pre-batched GCC and PCC with DIDP, TiO2 and anti-oxidant package
GCC and PCC not pre-dried
Compounded in mixer with high speed disperser blade (1000 rpm) and scraper
blades (60 rpm)
Mixed under vacuum at 93C until 800 ppm reached
Time to reach 800 ppm tracked
Moisture level checked using volumetric Karl Fisher titration
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100
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350
0
500
1000
1500
2000
2500
1 2 3 4
Tim
e to
Red
uce
Moi
stur
e to
800
ppm
(m
ins)
Sea
lant
Initi
al M
oist
ure
(ppm
)
Se…
Calcium Carbonate Influence on Pre-Batch Processing/ Drying Time
Pre-batch processing target: 800 ppm moisture
Surface area is not the clear influencer
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Sealants
GCC surface area (m2/g):
PCC surface area (m2/g):
2.5 2.5 3.5
19 19.5 1818
4.9
GCC D
PCC 3GCC B
PCC 2
GCC C
PCC 1
GCC A
PCC 1
100
150
200
250
300
350
0
500
1000
1500
2000
2500
1 2 3 4
Tim
e to
Red
uce
Moi
stur
e to
800
ppm
(m
ins)
Sea
lant
Initi
al M
oist
ure
(ppm
)
Se…
Calcium Carbonate Treatment Influences Pre-Batch Processing/
Drying Time
Pre-batch processing target: 800 ppm moisture
Engineered treatment reduces processing/drying time compared to traditionally treated carbonates
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Sealants
GCC D
PCC 3
GCC treatment: Fatty Acid Fatty AcidNone
GCC B
PCC 2
GCC C
PCC 1
GCC A
PCC 1
Unreacted Treatment (wt%): n/a 0.40
Engineered Treatment
0
Calcium Carbonate Influence on SPUR Sealant Rheology & Mechanical
Properties
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Sealants
SPUR Sealant Rheology
Sealant based on SPUR+ 1015LM prepolymer compounded with GCC and PCC
Rheology:
Extrusion rate/ gunnability (ASTM C1183)
Slump (ASTM D2202)
Brookfield viscosity
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Sealants
Extrusion rate
Semco nozzle, cartridge, instrument
40 psi, 0.318 mm nozzle tipSlump
Mixing / Compounding
0
50
100
150
200
250
1 2 3 4
Ext
rusi
on
Rat
e (g
/min
)
2.5 2.5 3.5
19 19.5 1818
4.9
Influence on Extrusion Rate
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Sealants
373k cP 329k cP 290k cP390k cP Brookfield Viscosity
GCC D
PCC 3
GCC surface area (m2/g):
PCC surface area (m2/g):
GCC B
PCC 2GCC C
PCC 1
GCC A
PCC 1
GCC treatment: Fatty Acid Fatty AcidNone Engineered
Treatment
In general, higher GCC surface area higher Brookfield viscosity and lower extrusion rate
Having no unreacted treatment may influence rheology differently
SPUR Sealant Mechanical Properties
SPUR sealant cured for 2 weeks at 23C and 50% RH
Mechanical Properties:
Tensile (ASTM D412)
Tear (ASTM D624)
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Tensile Testing
Tear, Die B
0
100
200
300
400
500
600
700
1 2 3 4
% Elongation @ Break
Tensile @ Break, psi
2.5 3.5
19.5 1818
4.9 2.5
19
Influence on Mechanical Properties (Medium Modulus Sealant)
Increase elongation for similar tensile behavior using treated GCC
As-good-as or better tensile performance with untreated GCC versus treated GCC
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Sealants
GCC D
PCC 3
GCC surface area (m2/g):
PCC surface area (m2/g):
GCC treatment: Fatty Acid Fatty AcidNone Engineered
Treatment
GCC B
PCC 2
GCC C
PCC 1
GCC A
PCC 1
Summary
Surface area and surface treatment DO impact sealant processing time, rheology, and
mechanical properties
Specifically,
‒Surface treatment Processing time
‒Surface area Rheology
‒Surface treatment Mechanical properties and rheology
Engineered product provides:
Lower processing and drying time
Good mechanical properties
Rheology modification
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Sealants
Thank you for your attentionFor more information, visit: www.imerys-carbonates.com