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Composites are particularly susceptible to microbes

patio furniture

Did you ever wonder why some of your outdoor plastic furniture – especially white or the lighter colors – gets dark gray or greenish stains on it that won’t wipe off? Well, that’s because the stains are caused by plastics’ susceptibility to bacteria, fungi and algae. It is a problem that gets worse during the summer months when the humidity is high and temperatures are warm, something that these microbes love and that causes them to thrive.PVC – particularly flexible PVC – which many of your outdoor furniture products are made from, is especially susceptible to attack from these microbes and accounts for the greatest usage of antimicrobial additives, polyurethane foam is the second largest consumer, with polyolefins, acrylics and nylons also using antimicrobials but in lesser quantities.Not only do the microbes cause staining, but can impact the chemical and physical properties of the plastics as well making the products brittle and subject to failure.

The various additives used in PVC such as the plasticizers, starch fillers, oils and lubricants make PVC more vulnerable to microbe growth.That’s bad news for Wood-Plastic Composites (WPC) used in fencing, decking and railing too. The acceptance of these products has grown rapidly due to the promotion of these products as “maintenance free.” Most manufacturers call them “low maintenance” because they are also susceptible to fungi due to the high levels of cellulosic fibers in the plastic materials. Any of these WPCs that contain 50% or higher wood fiber filler can be adversely affected by moisture. Some WPC manufacturers “cap” their products, which means they extrude the WPC decking and railing with an overlay or “cap” of virgin plastic to keep the cellulosic fibers from being exposed to moisture.There are a number of antimicrobials that can be used to protect products, especially PVC products, from attack by microbes.  Oxybisphenoxarsine (OBPA) is an organometallic compound and is the most commonly used antimicrobial additive for plastics, according to the Freedonia Group’s* report on antimicrobial additives.

The antimicrobial mechanism of action for OBPA is enzyme inhibition. Enzymes regulating cellular respiration, energy production, and cellular growth are destroyed. Protein destruction, and the subsequent production of free radicals, is the actual cause of cell death. However, there are concerns about this additive’s arsenic content and OBPA was recently withdrawn from the European market, notes The Freedonia Group.The other leading antimicrobial type is organosulfur compounds such as Isothiazolones, which The Freedonia Group says will see better than average growth through 2017. They are the product of choice for the rapidly-expanding WPC market. Also, they contain no arsenic, which may make them an attractive option for companies increasingly concerned about their environmental image.So while you’re enjoying your outdoor time this summer, you can know that many of these new additives will be protecting your patio furniture from the destructive microbes that believe your plastic is just another tasty treat! *The Freedonia Group’s reports on a variety of markets and topics can be found at

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