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

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.

Analysis of Selected Properties of Injection Moulded Sustainable Biocomposites from Poly(butylene succinate) and Wheat Bran

“…The obtained course of change in elongation at break is related to the aforementioned increase in the stiffness of the composition and, at the same time, its brittleness, which is manifested by a significant decrease in deformability. Analogous courses of changes in the maximum deformation of the PBS with the increasing natural filler content can be observed in other works and for other fillers [37,[41][42][43]76]. The nature of the obtained fractures also changed from ductile to brittle, similarly to the case with impact strength.…”

“…As the WB content increases, so does the number of potential material defects that may become points of failure initiation during tension, especially for the hydrophilic WB and PBS matrix with a moderate affinity for water [21,43]. The description of the effect consisting in the decrease in tensile strength of the biocomposites based on the PBS matrix with the increase in natural filler content can be found in many works of other authors [21,[36][37][38][40][41][42][43].…”

“…The filler particles inside the PBS matrix consequently become stress concentration points, resulting in reduced tensile strength [104,105]. natural filler content can be found in many works of other authors [21,[36][37][38][40][41][42][43]. Moreover, during the processing PBS, unlike WB, is subject to the effect of processing shrinkage.…”

“…The increase in stiffness is manifested by lower deformability, deterioration of the elastic and plastic properties, and an increase in brittleness, which clearly affects all the parameters related to the deformation of the samples. This is, of course, a common phenomenon occurring in polymer composites containing filler in powder form, either of natural or mineral origin [37,38,[41][42][43]76].…”

“…The literature includes numerous papers dealing with the manufacturing and properties of biocomposites on a PBS matrix with the addition of various natural fillers. Examples of such fillers are shredded wood shavings [34]; ground bran of cereals (wheat [35] and rice [36]); nut shells (pistachios [37], peanuts [38], and coconut [39]); and seeds (almonds [40]) but also dried pomace (apple [41] and grape [42]) or even wine lees [43]. The composition of all natural fillers of plant origin is based mainly on cellulose, hemicellulose, and lignin, but they differ in structure as well as in the proportion of their main components and the content of additional substances, such as simple and complex sugars, proteins, fats, and water [44][45][46].…”