Hybrid antioxidant based on exfoliated layered double hydroxides nanosheets with improved thermal stabilizing effects for polypropylene

Abstract

An antioxidant (AO) agent, 3-(3,5-ditertbutyl-4-hydroxyphenyl) propionate anions (DBHP), intercalated between layered double hydroxides (DBHP-LDH) was prepared by coprecipitation method and then a part was delaminated in toluene to form exfoliated DBHP-LDH nanosheets. Both types of DBHP-LDH compositions, powder and exfoliated nanosheets were characterized by XRD, SEM and TEM, and subsequently incorporated into polypropylene (PP) as AO filler to improve the thermal stability of PP. The addition of DBHP-LDH affected the crystallization and melting behaviour as well as transmittance of PP, giving rise to its crystallinity improved but its transparency reduced. It was found that by incorporating either DBHP-LDH powder or exfoliated DBHP-LDH nanosheets the thermal decomposition temperatures and thermal aging resistance of PP were enhanced. Interestingly, between the two hybrid systems, it is however the exfoliated DBHP-LDH nanosheets that showed a better stabilizing effect for PP. This is attributed to the better dispersion regarding the exfoliated DBHP-LDH nanosheets, thus providing a more efficient radical scavenging capability. Even with its pronounced interface between PP chains and highly exposed nanosheets, about 30 % of DBHP was released from the exfoliated DBHP-LDH/PP compared to about 20 % DBHP migrated out of the conventional DBHP-LDH/PP films after 132 h test. This shows that the organic AO agent is well tethered to hydroxyl-bearing LDH nanosheets, thus opening new route to design functionalized filler for polymer from exfoliated LDH hybrid layers.