The effect of epoxidized natural rubber on the structure and properties of Stereocomplex polylactide

Abstract

Polylactic acid (PLA), as a sustainable polymer known for its biodegradability and biocompatibility, suffers from a slow crystallization rate that limits its processing and application potential. Blending poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) leads to the formation of stereocomplex crystals (SC-PLA), which enhances heat resistance, crystallization rate, and mechanical strength. This study systematically investigates the effects of epoxidized natural rubber (ENR) and natural rubber (NR) on the crystallization behavior, thermal stability, and rheological properties of PLLA/PDLA blends, aiming to expand the functional versatility of PLA-based materials.

Experimental results demonstrate that ENR significantly promotes the formation of stereocomplex crystals. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses reveal that distinct SC crystallization occurs when the ENR content reaches 10 wt% or higher, while NR shows negligible impact. Polarized optical microscopy (POM) further confirms that ENR accelerates crystal growth and raises the onset crystallization temperature. Rheological tests indicate that the addition of 5 wt% ENR facilitates the formation of a stereocomplex crystal network, with higher ENR content increasing the blend’s viscosity, elasticity, and viscoelasticity. Water contact angle measurements suggest that around 10 wt% ENR provides the optimal balance between polarity enhancement and interfacial compatibility.

Non-isothermal crystallization kinetics and activation energy analyses show that ENR reduces the energy barrier for SC formation, thereby promoting crystallization. However, thermogravimetric analysis (TGA) results show a decrease in thermal stability upon ENR incorporation—for instance, the T10% of the sample with 20 wt% ENR is about 21°C lower than that of the ENR-free blend. These findings establish ENR as an effective compatibilizer and crystallization accelerator for PLLA/PDLA blends, offering both theoretical insights and practical guidance for the development of high-performance PLA materials with improved processability and functionality.

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