Methods of Characterizing and Inhibiting the Occurrence of Pink Stain in Polyurethane Substrates

摘要

The use of antimicrobial additives in polyurethane foam formulations is quite common. Regulatory changes in the laws that govern the use of antimicrobials used in polyurethane foam articles can have a significant impact on formulators and end-users. The performance parameters of antimicrobials do vary considerably from product to product. Some are more effective against bacteria and weak against fungus; some can produce large zones of inhibition, while some produce no zone of inhibition at all. The list of available antimicrobials allowed for use in polyurethane products is getting smaller and smaller. For a variety of reasons, technologies previously very common and effective in polyurethane applications are no longer being used by formulators. These include arsenic and tributlytin compounds; both are well known to produce effective large zones of inhibition at relatively low use levels. Of the remaining antimicrobials, most are effective against mold, and less effective against bacteria. None of the remaining antimicrobial candidates produce a large zone of inhibition at typical use-levels. It is this specific occurrence that is currently causing considerable concern, particularly in the marine seat cushion market and other polyurethane and PVC applications. The growth of pink staining bacteria and the ability for these organisms to stain both polyurethane foam and the vinyl covers is characterized by ASTM E-1428. Currently available, non-OBPA or non-TBT antimicrobials are struggling to pass the ASTM E1428 test. In many cases a passing grade is required by the manufacturer and or the end-user. Lonza has studied this phenomenon and is developing meaningful test modifications, resulting in what we believe is a more meaningful and reliable test, especially for absorbent polyurethane foams. INTRODUCTION: REASONS FOR ANTIMICROBIALS IN POLYURETHANES There are three primary reasons for adding an antimicrobial to any polyurethane: 1.) Product Protection: 1.1 Polymer type and formulation will dictate susceptibility of finished product to the growth of microorganisms Polyester Polyurethanes 1.2 Protecting product from its own ingredients: 1.3 Polyester-based polyurethanes in particular will support microbial growth and result in product degradation (Figure 1). 2.1 Degradation is a result of enzymatic hydrolysis of the ester linkage in the polyurethane polymer resulting in loss of flexibility, discoloration, and cracking.