Crosslinking of PVC formulations treated with UV light

Typical wire and cable formulations of plasticized Poly(vinyl chloride) were prepared with three different stabilizer systems: Ca/Zn (21 or 1:1) and dibasic lead phthalate. The mixtures contained trimethylolpropane trimethacrylate (TMPTMA) as crosslinking agent and a UV photoinitiator (Irgacure 819). Mixtures were dry-blended, then roll-milled and to finally hot-pressed at 180 degrees C to obtain sheets of 1 and 1.5 mm thickness. Small specimens (3 x 3 cm) were irradiated with UV light for up to 10 days while monitoring changes at different time intervals. The presence of TMPTMA in the samples, as expected, influenced the storage modulus (E') and gel content percentage, specifically for the thinner samples. These results indicated that UV irradiation produced surface crosslinking. The samples with crosslinking agent also reached higher carbonyl index values. The Ca/Zn formulations showed higher mechanical properties with respect to the Pb ones, thus suggesting that during the stabilization period of the Ca/Zn mixtures, an effective crosslinking was promoted. Irregular behavior was observed during the last days of treatment for both types of formulations, thereby suggesting an optimum irradiation time for this procedure.