Isotactic polypropylene modified with sorbitol-based derivative and siloxane-silsesquioxane resin

This study details new polypropylene-based materials containing a siloxane-silsesquioxane resin and a sorbitol derivative. Molecular adducts originating from the synergistic interactions of siloxane-silsesquioxane resin (SiOPh) containing phenyl functionalities and 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol, Millad 3988 (DMDBS), strongly influence crystallization of isotactic polypropylene (iPP) as well as its morphology, transparency and mechanical properties. DMDBS is a commonly used clarifying agent for a variety of iPP grades. However, its disadvantage is that when added into iPP during extrusion, it allows only low draw ratios, because it increases crystallization temperature of iPP. Addition of SiOPh allows for control of the nucleation efficiency of the sorbitol derivative and adjust crystallization rate of iPP, to attain transparent formulations suitable for extrusion processes. iPP-based compounds were produced by co-rotating twin screw extrusion and further analyzed by differential scanning calorimetry, wide-angle X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. Moreover, rheological, haze and static tensile measurements were conducted to determine the influence of composition on material properties. It was found that the best combination of properties is achieved when 1 wt% of SiOPh and 0.25 wt% DMDBS are added to iPP. This formulation can significantly change the crystallization behavior of iPP to be tailored for production of highly oriented and transparent products.