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Following the ban in Europe on the use of OBPA, a common antifungal agent, new antimicrobial products have had to be developed to protect areas such as roofs. Incorporated into the product during PVC manufacturing, the chemistry operates by preventing microtubule structures from forming – terminating cell division – and by disrupting enzyme activity, which blocks energy production pathways and, ultimately, leads to cell death
Roof membranes are particularly susceptible to the growth of fungi – such as moulds and mildews – since they often combine warm and damp conditions with poor ventilation and low accessibility. Fungi reproduce through air-dispersed spores that are invisible to the naked eye, which can then settle and propagate on almost any surface. Uncontrolled proliferation of these organisms may eventually cause visible and structural damage to roofing materials, including staining, discolouration, odours and reduced physical strength. This degradation can potentially create an unpleasant environment for building occupants and elicit considerable safety concerns, shortening the usable lifetimes of materials and requiring them to be frequently maintained or replaced.
PVC is a popular and highly versatile building material due to its exceptional physical properties, fire resistance characteristics and excellent cost-performance ratio, with 70% of all PVC produced being used within the construction industry. Unfortunately, PVC roofing membranes are at particular risk of fungal attack, as they contain plasticisers that provide micro-organisms with a nutrient-rich food source. In addition, membranes also inherently prevent airflow, which encourages condensation to build up inside the roof space, contributing to the creation of an ideal environment for microbial growth.
Pioneering metal-free antimicrobial chemistries provide roofing membranes with excellent antifungal protection without stimulating the environmental concerns associated with toxic alternatives.
Addressing a growing problem
The structural risks associated with mould and mildew, coupled with the cost and inconvenience of replacing damaged roofing materials, have sparked interest in preventative antimicrobial technologies that could extend the usable lifetime of these products, as well as contributing to a more sustainable construction industry. These chemistries can be built into roofing membranes, including PVC polymers, during the manufacturing process to provide around-the-clock protection against the growth of damaging microbes, including moulds and mildews. This helps to prevent the colour changes, odours and reduced performance caused by uncontrolled fungal proliferation, extending the usable lifetimes of roofing materials for greater safety and sustainability.
Historically, arsenic-based 10,100-oxybisphenoxyarsine (OBPA) was a common antifungal agent used to protect a range of materials against fungal growth. However, the safety of this compound was recently called into question, as it was discovered to be highly toxic to a range of organisms. Studies have also shown that OBPA readily leaches into water sources, causing harm to aquatic life. To make matters worse, this arsenic-based compound is also a recognised carcinogen, posing a risk to human and animal health. Consequently, OBPA was totally banned in the EU in 2016, and was also added to the REACH restricted substances list, meaning that goods imported into the EU also cannot contain this compound. This ban left a significant gap in the antimicrobial space, causing roofing manufacturers to seek safer alternative technologies with improved toxicology profiles and broader consumer acceptance.
Breakthrough solutions for improved sustainability
Innovators have responded to this pressing need by developing new antimicrobial products with a reduced environmental impact. One of these revolutionary technologies is MicroGuard™ from Microban International, which is effective against a variety of fungal species. MicroGuard is a metal-free, globally-compliant antifungal alternative to the antimicrobial agents currently used in PVC manufacturing. The chemistry operates by preventing microtubule structures from forming – terminating cell division – and by disrupting enzyme activity, which blocks energy production pathways and, ultimately, leads to cell death. MicroGuard can be easily incorporated into PVC roofing membranes at the point of manufacture, without affecting the appearance or function of the final goods. The active agent then becomes an intrinsic component of the roofing material, actively inhibiting fungal growth 24/7 for the expected lifetime of the membrane. In addition, MicroGuard does not wear off or leach out into the environment over time, further reducing ecological concerns for enhanced sustainability.
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Proven antifungal efficacy for greater peace of mind
The performance of a MicroGuard liquid formulation was assessed using the AATCC 30-III test method against Aspergillus niger (A. niger), and the ASTM G21 test method against a mixture of five different fungal species. In the AATCC 30-III test, PVC plaques were placed onto nutritive agar plates, inoculated with a high concentration of A. niger spores, and incubated for seven days at 28±1°C and high humidity – optimal conditions for fungal proliferation. The extent of growth on the plaques was then rated on a scale of 0 to 2, where:
0: No Growth
1: Microscopic growth (visible under a microscope)
2: Macroscopic growth (visible to the naked eye)
During the ASTM G21 test, PVC plaques were placed onto a non-nutritive agar, inoculated with a mixture of five different organisms, and incubated for 28 days at 28°C and high humidity. Without added nutrition, fungi must use the substrate material as their food source to survive, so this test method enables the evaluation of a specimen’s ability to resist fungal attack at the point of its final application. After the full exposure time, the plaques were examined under a microscope, and rated on a scale of 0 to 4 according to the percentage of the plaque surface covered by fungal growth, where:
0: No Growth
1: Traces of Growth (<10 %)
2: Light Growth (10-30 %)
3: Medium Growth (30-60 %)
4: Heavy Growth (60-100 %)
All plaques treated with MicroGuard received a score of 0 in both the AATCC 30-III and ASTM G21 tests. In contrast, the untreated PVC samples received a score of 2 and 4 during the AATCC 30-III and ASTM G21 tests, respectively, indicating heavy fungal growth on the plaques that did not contain MicroGuard.
Building a more sustainable future
Pioneering metal-free antimicrobial chemistries – such as MicroGuard – provide roofing membranes with excellent antifungal protection without stimulating the environmental concerns associated with toxic alternatives. This novel solution is helping manufacturers to develop roofing materials with enhanced longevity and structural integrity, while simultaneously reassuring contractors and building users of the safety and sustainability of their surroundings.
