Gum Rosin as a Size Control Agent of Poly(Butylene Adipate-Co-Terephthalate) (PBAT) Domains to Increase the Toughness of Packaging Formulations Based on Polylactic Acid (PLA)

Miguel Aldas,José Miguel Ferri,Dana Luca Motoc,Juan López-Martínez,Laura Peponi,Marina Patricia Arrieta

doi:10.3390/polym13121913

Abstract

Gum rosin (GR) was used as a natural additive to improve the compatibility between polylactic acid, PLA, and poly(butylene adipate-co-terephthalate, PBAT, blended with 20 wt.% of PBAT (PLA/PBAT). The PBAT was used as a soft component to increase the ductility of PLA and its fracture toughness. The coalescence of the PBAT domains was possible due to the plasticization effect of the GR component. These domains contributed to increasing the toughness of the final material due to the variation and control of the PBAT domains’ size and consequently, reducing the stress concentration points. The GR was used in contents of 5, 10, 15, and 20 phr. Consequently, the flexural properties were improved and the impact resistance increased up to 80% in PLA/PBAT_15GR with respect to the PLA/PBAT formulation. Field emission scanning electron microscope (FESEM) images allowed observing that the size of PBAT domains of 2–3 µm was optimal to reduce the impact stress. Differential scanning calorimetry (DSC) analysis showed a reduction of up to 8 °C on the PLA melting temperature and up to 5.3 °C of the PLA glass transition temperature in the PLA/PBAT_20GR formulation, which indicates an improvement in the processability of PLA. Finally, transparent films with improved oxygen barrier performance and increased hydrophobicity were obtained suggesting the potential interest of these blends for the food packaging industry.

Highlights

Polylactic acid (PLA) is one of the most widely consumed biodegradable and compostable polymers
PLA-poly(butylene adipate-co-terephthalate) (PBAT) blends were melt-blended and compatibilized through the incorporation of gum rosin. An improvement in both tensile and impact toughness was observed when adding gum rosin (GR) to the formulation composed of a PLA matrix with 20 wt.% of PBAT as a ‘soft’ component. Such increment is due to the coalescent effect of the PBAT domains into the PLA matrix due to the plasticizing effect of GR
The flexural modulus was improved and the tensile strength increased by 80% compared to the PLA/PBAT formulation

Summary

Introduction

Polylactic acid (PLA) is one of the most widely consumed biodegradable and compostable polymers. The PLA processing method with the more favorable industrial viability is its physical mixing or blending [11,12]. The modification of biodegradable polymers through physical blending with another biodegradable polymer shows many advantages since it offers the opportunity to create a new material with desired properties. It is relatively simple and cost-effective to blend polymeric materials in the melt state, based on available processing technologies commonly used at the industrial level (i.e., extrusion, injection molding, film-forming, etc.) [13]. Many biodegradable polymer formulations have been obtained by blending polymeric matrices to modulate their mechanical, thermal, rheological, and morphological behavior. In most of the scientific works reported up to now, poor miscibility or total immiscibility between components of the blend was observed and the expected synergism to improve the overall properties was not achieved

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