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Microbial Challenges for Long-lived
Adhesive and Sealant Formulations
Don Satchell, Ph.D.
Technical Director
Situ Biosciences LLC
Wheeling, IL
1Microbial Challenges for Long-Lived Adhesive & Sealant Formulations – ASC 2016
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Topics
• Adhesive and Sealant
Application Challenges
• Microbes &
Environmental conditions
• Antimicrobials,
Formulations, Testing
and Performance
Microbial Challenges for Long-Lived Adhesive & Sealant Formulations – ASC 2016
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Challenges for Adhesives & Sealants
By their nature, adhesive and sealants are commonly used in conditions
favoring microbial growth.
• High humidity and exposure to moisture
o Bathrooms, Windows, Flooring, Siding Stagnant high humidity
Environments,
• Environmental exposure
• Sunlight (UV in particular)
• Water/rain
• Freeze and thaw and dew point cycles
Microbial Challenges for Long-Lived Adhesive & Sealant Formulations – ASC 2016
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Microbes Perspectives & Environmental Conditions
Nutrients:
• Environmental contaminants (organics in dust, etc.)
• Organics in the PRODUCT (olefins, urethanes, latex,
plasticizers, mineral slurries, surfactants…etc.
Microbial Challenges for Long-Lived Adhesive & Sealant Formulations – ASC 2016
Water alone is not sufficient for microbial growth
Environmental conditions and nutrients must be present allow
for microbial proliferation
Generally - Standard environmental conditions that allow for
microbial growth are the same conditions we cohabitate
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Antimicrobials and Product Formulations
Antimicrobials used in adhesive and sealant formulations can perform
differently depending on:
How the additive is incorporated into the product formulation
The intended use instructions for the product.
Product Testing can vary for a variety of reasons:
• Layers of material
• Curing time
• Test substrate
• Volume
• Nutrient Load
• Mixing
• Durability Testing prior to resistance testing
Microbial Challenges for Long-Lived Adhesive & Sealant Formulations – ASC 2016
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Microbial Testing Methods (Fungal):An example: ASTM G21: a Standard Method for Determining
Resistance of Synthetic Materials to Fungi
Strengths
• Standard inocula that can accommodate a range of fungal types
• (A. niger, P. funiculosum, C. globosum, T. virens and A.
pullulans)
• Standard replicates allow a comprehensive level of analysis
• Historical perspective on product quality/performance
Challenges
• Representation to a ‘standard’ condition
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Fungal Resistance Testing
On the rating scale of 0-4 (4 being the worst)
this sample received a score of 2 with
approximately 20% coverage by fungal
mycelia and spore; all growth was along the
perimeter edge.
Microbial Challenges for Long-Lived Adhesive & Sealant Formulations – ASC 2016
This sample also received a score of
2 with <30% coverage by mycelia
and spore
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Assessment of Antimicrobials in Adhesives
Microbial Challenges for Long-Lived Adhesive & Sealant Formulations – ASC 2016
Score of 1; <10% coverage by
mycelia and sporeScore of 4; >90% coverage by mycelia
and spore
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Bacterial Resistance Testing
ASTM E1428: Standard Method for Evaluating Performance of
Antimicrobials Against Staining by Streptomyce Species
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Properly Formulated Materials will resist fungal growth
Microbial Challenges for Long-Lived Adhesive & Sealant Formulations – ASC 2016
• Low aqueous solubility will provide the best
environmental durability
• pH stability
• Broad spectrum efficacy
• Chemical compatibility with the substrate
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Common Antimicrobial Additives for Adhesives
Dichloropheynoxy-phenol -
Triclosan
Diiodomethyl- p - tolysulfone -
Amical
Quaternary ammonium trimethoxysilane -
Quatsilane
Zinc pyrithione - Zinc Omadine
Isothiazolinones
Microbial Challenges for Long-Lived Adhesive & Sealant Formulations – ASC 2016
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ConclusionsMicrobial control strategies for product
environments
• Manage the environment to minimize
microbial challenges
• Manage the formulation to minimize
microbial impact
• Combination strategies work best,
but are potentially costly and
complicated
• Managing microbes requires
application and formulation insight
Microbial Challenges for Long-Lived Adhesive & Sealant Formulations – ASC 2016