A comparative study of branched and linear dialkyl phthalate plasticizer surface levels and their effects on adhesive bonds in flexible PVC

A method has been developed to quantitatively measure the surface plasticizer levels present on test plaques made from a plasticized PVC compound. The plaque fabrication conditions have been chosen so that the plaque closely models an extruded flexible PVC profile. The analysis method utilized sorption of the surface plasticizer on fumed silica, followed by methanol extraction and liquid chromatographic identification and quantitation of the plasticizer. Typical results are presented for a model compound plasticized with either di-2-ethylhexyl phthalate (DOP) or a mixture containing predominantly linear C₇, C₉, and C₁₁ dialkyl phthalates (DHNUP). The effect of compound work level, as measured by Banbury drop temperature and final processing temperature, has also been studied. These results show that, for the model compound studied, the average surface level of DHNUP is always greater than that of DOP. The DOP levels are essentially independent of compound work level. The DHNUP levels generally increase with increasing mold temperatures. Finally, this data has been correlated with a study of the lifetime of a Neoprene-based adhesive bond to DOP-and DHNUP-plasticized flexible PVC in a 100°C oven. These studies clearly show that a one-to-one substitution of DOP for DHNUP will increase the time to adhesive bond failure by a factor of at least 10 with this particular adhesive system and model compound.