Restabilization of the aging resistance of compatibilized blends of pre-aged low density polyethylene and high-impact polystyrene (LDPE/HIPS)

Blends of pre-aged low density polyethylene (LDPE) with high-impact polystyrene (HIPS) compatibilized with a 1:1 mixture of styrene-butadiene block copolymer (SBS) and ethylene-propylene-diene statistical terpolymer (EPDM) were upgraded for thermooxidative resistance with N,N'-disubstituted 1,4-phenylenediamine. The impact strength after the oven test was improved. A model experiment confirmed that the efficiency of the phenylenediamine was not lost in the system after a partial sacrificial transformation of PD into the corresponding quinone diimine. The beneficial thermal effect of the upgrading used is a consequence of cooperation between the components of the blend. The system does not protect however against photooxidative stress without a suitable fortification with photostabilizers. The material properties of the upgraded blend upon oxidative stresses were assessed by monitoring of changes in the impact strength, carbonyl index and fracture surfaces on samples aged for various time intervals. It is shown that blends fortified by proper photostabilizers (carbon black or a combination of the UV absorber with photoantioxidant HAS) have sufficient stability for outdoor application.