Document O3BXq7kG69zGMw2562N4pkyzj

Technical report / A new proprietary additive reduces particulate density that is generated when PVC bums. |n the early days of plastics, the com are at best laboratory tests for compar monly asked question about flammability ing small samples with no direct bearing was; Does it burn? This led to the insti on real-life situations. tution of various small-scale test proce dures whose results were expressed in Hazards in burning plastics terms such as self-extinguishing, slow- burning, or burning. It is now clear that When plastic materials are exposed to too much reliance was placed on the first an active, large-scale fire they usually two classifications as to product safety. soon become part of the flaming mass. Little attention was paid to the hazards In so doing, they are generally consumed of smoke and toxic-gas generation and, by the fire and generate a mixture of in the case of so-called self-extinguish gaseous and particulate products of com ing materials, the fact that most plastics bustion. These can be in the form of along with most other organic materials visible smoke, often very dense, and in will bum in an active fire was ignored. visible gases which may or may not be Now there is general recognition that toxic, but often obscure the vision, and many test methods for flammability do irritate the respiratory tract and the not reveal the facts as they are experi eyes of persons in the vicinity. The pres enced in a general-fire atmosphere and ence of true toxic gases in the products of combustion can result in the death of those exposed and dense smoke may pre Table 1. Density of smoke generated by various materials in the N3S smoke chamber. vent their finding an escape route from the fire area. Various methods are avail able for measuring smoke density in fires; however, at present toxic-gas mea surement tests are in an early stage of Type of combustion development. Rigid PVC generates large quanti ties of smoke during combustion (Table 1). Rigid PVC is inherently flame re tardant so no additional additives are re quired to improve flame retardancy. Prior to discussing the new technol ogy, it may be worthwhile to consider the current state of the art in fiarnaretardant low-smoke products. Table 2 lists some plastics which feature some degree of flame retardancy and lower smoke generation than polyvinyl chlo ride. In each case, smoke reduction was obtained by polymer design. This data illustrates that the optimum blend of flame retardancy (high oxygen index) and reduced smoke (low smoke-density rating) is obtained with chlorinated PVC. Any plastics processor will attest to the fact that chlorinated PVC is not a minor modification of PVC and in fact processes quite differently. Conse quently, it appears that the fabricator or product designer does not have a sim ple choice between alternatives in order to take positive action toward safer lowsmoke products based on current tech nology. This is the background on the development of this new smoke suppres sant technology. Material NonFlaming flaming An action program Red oak 75 Yellow pine 80 Polycarbonate 324 Polystyrene 468 Polyvinyl chloride 525 395 490 36 345 270 Table 2. Polymers with reduced flammability and smoke. Polymer Oxygen index1 Smoke density ratingb Polyvinyl chloride Chlorinated PVC Polycarbonate Polyphenylene oxide Polysulfono 40 50 27 29 30 97 46 ' 74 CS 60 Having recognized the hazards of smoke and toxic gases it became necessary to develop realistic tests for measuring the amounts of each generated in a fire. Various test methods are currently avail able which measure the optical prop erties of smoke as well as one which measures smoke weight*. Systematic studies of toxic-gas measurement are just beginning and significant progress in this area is not anticipated in the near future. Initial attention has been focused on rigid PVC systems and the solid air borne particulate smoke component as measured by both the Arapahoe smoke chamber (ASC) and the National Bu reau of Standards (NBS) smoke cham ber. Rigid polyvinyl chloride (PVC) was chosen for study for three primary rea sons. Rigid PVC is widely used in in terior construction applications where smoke causes a serious life safety haz ard. J. J, Kracklauer Manager, product development and C. J. Sparkes Senior product development chemist Arapahoe Chemicals, Inc, Boulder, Colorado OLI 7523 * ASTM-D-2863 * ASTM-D-2843 Arapahoe smoke chamber (ASC) developed by Arapahoe Chemicals Inc., Boulder, Colo. PLASTICS ENGINEERING JUNE 1974 67