Effects of nucleating agents on physical properties of polypropylene/polylactide blends

Abstract

The effects of three nucleating agents, namely : C.I. Pigment red 122 (quinacridone 122), C.I. Pigment blue 15:3 (phthalocyanine blue 15:3), and 1,2,3,4-bis(3,4-dimethyl-benzylidene sorbitol) or (DMDBS) on nonisothermal polypropylene/polylactide (PP/PLA) blends using 5%wt of poly[propylene-g-(maleic anhydride)], (PP-g-MA) as a compatibilizer were studied. The nucleating agents were charged into the blend during extrusion. The PP/PLA blends were prepared at various ratios of PP and PLA as 90/10, 80/20, and 70/30 whereas the pigment concentration was varied from 0.2%-1%wt. The nucleating agents created good nucleating activity. After the blending, the SEM micrographs showed that the blends with 5%wt PP-g-MA appeared to attain interfacial compatibility between polypropylene and polylactide phases. The XRD patterns exhibited the α-form of crystallinity found in the pigmented blends corresponding to the α-form in PP. When the pigment concentration was increased, the increments of the crystallization temperature, tensile strength, modulus, and elongation at break of the blends were observed compared to the unpigmented blends. It was noted that the C.I. Pigment red 122 (quinacridone 122) blend yielded a slightly higher stability to thermal degradation, while C.I. Pigment blue 15:3 (phthalocyanine 15:3) increased the tensile strength of blends. Dynamic mechanical characterization informed that the pigmented blends achieved both higher storage and loss moduli. A shift in Tg to lower temperature suggested that there was an increase in crystallinity of the pigmented blends.