Effects of Pigments on the Processing and Crystallization Properties of Polypropylene
Polypropylene is a kind of commonly used plastic,and many products need the addition of color pigments during processing.For a long time,there has been little research focusing on the impact of color pigments on polymer performances.This study selected four color pigments with different chemical structures to investigate their effects on the processing viscosity,crystallinity,thermal oxidative resistance,and impact properties of polypropylene.The experimental results show that the morphologies of the color pigments significantly affect the flow properties of polypropylene.The addition of color pigments notably increases the steady-state shear viscosity of polypropylene.The rod-like yellow pigment raises the steady-state shear viscosity of PP to 6 400 Pa·s,which is four times that of the polypropylene resin.After the color pigment addition,the PP crystallization temperature increases and the half-crystallization time decreases,indicating that the pigment acts as the nucleating agent.The green pigment has the most pronounced effects on the crystallization temperature,elevating the crystallization temperature by 5-10 ℃.Under the cooling conditions of 40 ℃/min,the half-crystallization times of all samples are similar,approximately 0.4 min.The red and yellow pigments contain keto groups in their chemical structures,which provides the antioxidant effects and could extend the oxidation induction period of PP.Compared to the other color pigments,the green pigment could refine the grain size of PP and improve PP notch impact strength at room temperature.
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