Mechanistic Insights Into the Role of a Dual Compatibilization Strategy in Improving Mechanical Properties of PLA/TPO(NV) Blends

Abstract

A toughened modification of polylactic acid (PLA) was carried out using a self-made polyolefin elastomer (TPO(NV)) as a toughening agent. In order to enhance the mechanical properties and compatibility of PLA with TPO(NV), TPOGS (TPO grafted with glycidyl methacrylate (GMA) and styrene (St) as a co-grafting monomer) graft copolymer was prepared by melt grafting and used as a compatibilizer, in combination with the small-molecule additive dibutyl itaconate (DBI). PLA/TPOGS/DBI blends with varying DBI contents were prepared, and the synergistic compatibilization effects of the TPOGS and DBI on the PLA/TPO blends were investigated. The impact of the DBI content on the compatibility, crystallization behavior, rheological properties, mechanical properties, and microstructure of the PLA/TPOGS blends was also investigated. The results confirmed that GMA and styrene were successfully grafted onto the TPO elastomer, and the compatibility of the grafted elastomer with PLA was improved. Furthermore, DBI was found to react with the main chains of PLA or TPO(NV) through double bonds, forming chemical links and acting as a “bridge,” which, in synergy with the graft copolymer, further enhanced the compatibility between PLA and TPO(NV). As the DBI content increased, the glass transition temperature (T _g ) difference between PLA and TPO(NV) significantly decreased from 95.06°C (DBI = 2.5 wt%) to 82.53°C (DBI = 12.5 wt%). Due to the plasticizing effect of DBI, the melt flow index of PLA/TPO(NV) gradually increased with the DBI content. The addition of DBI did not affect the crystallization process of the TPO(NV) elastomer, with the crystallization during cooling forming a PP-α crystalline phase, and the degree of crystallinity remained relatively constant, with the crystallization temperature maintained around 104°C. DBI had a stronger influence on the PLA component within PLA/TPOGS/DBI blends, as higher DBI content led to increased PLA crystallinity and a significant shift in the cold crystallization temperature from 122.54°C to 115.05°C. This indicates that the plasticizing effect of DBI primarily impacts the PLA phase within the PLA/TPO(NV) blend. The mechanical properties of PLA/TPOGS/DBI blends initially increased but later decreased as the DBI content continued to increase. At a DBI content of 10 wt%, the notched impact strength and elongation at break reached their highest values, 1.3 times and 7 times higher, respectively, than those of the PLA/TPOGS blend without DBI.