Preparation and properties of polycarbonate-nano titanium dioxide/polypropylene light diffusing materials based on selective distribution of fillers

Light-diffusing materials could convert point and line light sources into surface light sources, which are widely used in lighting, display, solar photovoltaic, light detectors and other fields. The performance of volumetric light-diffusing materials could be further modulated according to the characteristics and the distribution state of the scattering particles. In this paper, different blending methods were applied for polypropylene (PP), polycarbonate (PC) and modified nano titanium dioxide (nTiO₂) during melt-blending process to achieve different distribution states of nTiO₂. The migration behavior of TiO₂ nanoparticles was analyzed considering kinetic and thermodynamic factors, and the effects of microscopic morphology on the mechanical and light diffusion properties of the composites were specifically investigated. The results showed that: nTiO₂ was mainly distributed in the PP matrix and showed more significant heterogeneous nucleation in the composites when applying the one-step blending method. However, the distribution of nTiO₂ in the PP matrix excessively exacerbated the scattering phenomenon, which resulted in a significant decrease in the light transmittance and comprehensive optical properties of the nTiO₂/PC/PP materials obtained by one-step blending method. In (PC-nTiO₂)/PP composites prepared by the stepwise blending method, nTiO₂ was mainly distributed at the interface and within the PC dispersed phase. The composites showed balanced opticalproperties,meanwhile the distribution of nTiO₂ in the PC phase might trigger multiple scattering, resulting in a larger scattering range. The (PC-nTiO₂)/PP materials produced by the stepwise blending method showed better mechanical properties due to the rigidity of the PC-nTiO₂ dispersed phase and strengthened interfacial interaction between the PP and PC phases raised by the bridging effect of nTiO₂. The distribution state of nTiO₂ also had an impact on the UV resistance of the composites.