(552e) Improvement of Hdpe and Ipp Blend Properties through Small Molecule Self-Assembly

Polyethylene (PE) and Polypropylene (PP) constitute a significant portion of post-consumer plastic waste. Because of their similar physical properties, it is very challenging to sort and separate them in the recycling process. Thus, melt blending of PE and PP could be an efficient way to avoid having to separate them. However, the major issue is that they are thermodynamically incompatible, which results in low-quality end products. In this work, a novel approach is used by utilizing the self-assembly mechanism of a sorbitol derivative acting as a nucleating agent to enhance the thermal and mechanical properties of high-density polyethylene (HDPE) and isotactic polypropylene (iPP) blends. One of the unique characteristics of the sorbitol derivatives is that after melting, during the cooling process, they form a fibril network structure.

In this study, two different mixing orders are used to study the effect of the sorbitol derivative’s localization on its performance as well as on the crystallization behavior of the HDPE/iPP blends. Differential scanning calorimetry (DSC) thermograms of the HDPE/iPP/sorbitol, with and without MDBS at various blend ratios, demonstrated that sorbitol derivatives induce distinct and separate crystallization behavior in HDPE and iPP blends. DSC results further indicate that sorbitol derivatives act as a nucleating agent in iPP and increase the crystallization temperature of the iPP, even when mixed first with PE.

Additionally, x-ray diffraction results show that sorbitol derivatives interact differently with HDPE and iPP. When sorbitol derivatives are mixed first with HDPE, a synergistic crystallization effect is observed. However, when sorbitol derivatives are mixed first with iPP, and then the HDPE is added into the system, it disrupts the crystallinity of the iPP/ sorbitol derivatives.

Moreover, mechanical measurements indicate that incorporating MDBS into the HDPE and iPP blends across all the samples improves both the Young’s modulus and yield strength. The presence of sorbitol derivatives and the iPP content play important roles in enhancing the Young’s modulus and yield strength.