Peroxide-Induced Synthesis of Maleic Anhydride-Grafted Poly(butylene succinate) and Its Compatibilizing Effect on Poly(butylene succinate)/Pistachio Shell Flour Composites.

Sandra Rojas-Lema,Jordi Arevalo,Sergio Torres-Giner,Jaume Gomez-Caturla,Daniel Garcia-Garcia

doi:10.3390/molecules26195927

Sandra Rojas-Lema, Jordi Arevalo + Show 3 more

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https://doi.org/10.3390/molecules26195927

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Abstract

Framing the Circular Bioeconomy, the use of reactive compatibilizers was applied in order to increase the interfacial adhesion and, hence, the physical properties and applications of green composites based on biopolymers and food waste derived lignocellulosic fillers. In this study, poly(butylene succinate) grafted with maleic anhydride (PBS-g-MAH) was successfully synthetized by a reactive melt-mixing process using poly(butylene succinate) (PBS) and maleic anhydride (MAH) that was induced with dicumyl peroxide (DCP) as a radical initiator and based on the formation of macroradicals derived from the hydrogen abstraction of the biopolymer backbone. Then, PBS-g-MAH was used as reactive compatibilizer for PBS filled with different contents of pistachio shell flour (PSF) during melt extrusion. As confirmed by Fourier transform infrared (FTIR), PBS-g-MAH acted as a bridge between the two composite phases since it was readily soluble in PBS and could successfully form new esters by reaction of its multiple MAH groups with the hydroxyl (–OH) groups present in cellulose or lignin of PSF and the end ones in PBS. The resultant compatibilized green composites were, thereafter, shaped by injection molding into 4-mm thick pieces with a wood-like color. Results showed significant increases in the mechanical and thermomechanical rigidity and hardness, meanwhile variations on the thermal stability were negligible. The enhancement observed was related to the good dispersion and the improved filler-matrix interfacial interactions achieved by PBS-g-MAH and also to the PSF nucleating effect that increased the PBS’s crystallinity. Furthermore, water uptake of the pieces progressively increased as a function of the filler content, whereas the disintegration in controlled compost soil was limited due to their large thickness.

Highlights

The rising concern toward environmental issues has stimulated research efforts in the perspective of reducing plastic waste given the fact that, in recent decades, the disposal and non-biodegradability of petroleum derived plastics have caused serious water and land pollution issues
The particle surfaces displayed high porosity, as it can be inferred from Figure 1b, showing a field emission scanning electron microscopy (FESEM) micrograph of the lignocellulosic particles taken at higher magnification
The present study demonstrates the high potential of pistachio shells, a residue of the agricultural and food industries, to be manufactured in the form of flour for serving as a reinforcing filler in combination with biodegradable polymers to yield green composites in the frame of the Circular Bioeconomy

Summary

Introduction

The rising concern toward environmental issues has stimulated research efforts in the perspective of reducing plastic waste given the fact that, in recent decades, the disposal and non-biodegradability of petroleum derived plastics have caused serious water and land pollution issues In this context, fully or partially bio-based and biodegradable polymers currently represent the most promising options to replace petrochemical polymers. PBS presents good processability and balanced mechanical and thermal properties, closely comparable to some polyolefins [4,5] It shows tensile and impact strengths similar to those of polypropylene (PP), whereas its glass transition temperature (Tg) and melting temperature (Tm) are approximately −32 and 115 ◦C, respectively, resulting in a thermal profile similar than low-density polyethylene (LDPE) [6]. PBS is still currently considered an expensive biopolymer, with prices in the 3–6 USD/kg range, which is considered to be the main limitation for applications of products fully based on this biopolyester [11]

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