Enhanced Interfacial Adhesion of Polylactide/Poly(ε-caprolactone)/Walnut Shell Flour Composites by Reactive Extrusion with Maleinized Linseed Oil

Abstract

Novel green composites were prepared by melt compounding a binary blend of polylactide (PLA) and poly(ε-caprolactone) (PCL) at 4/1 (wt/wt) with particles of walnut shell flour (WSF) in the 10–40 wt % range, which were obtained as a waste from the agro-food industry. Maleinized linseed oil (MLO) was added at 5 parts per hundred resin (phr) of composite to counteract the intrinsically low compatibility between the biopolymer blend matrix and the lignocellulosic fillers. Although the incorporation of WSF tended to reduce the mechanical strength and thermal stability of PLA/PCL, the MLO-containing composites filled with up to 20 wt % WSF showed superior ductility and a more balanced thermomechanical response. The morphological analysis revealed that the performance improvement attained was related to a plasticization phenomenon of the biopolymer blend and, more interestingly, to an enhancement of the interfacial adhesion of the green composites achieved by extrusion with the multi-functionalized vegetable oil.

Valorization of Linen Processing By-Products for the Development of Injection-Molded Green Composite Pieces of Polylactide with Improved Performance

“…These morphological characteristics probably result from the crushing process due to the hardness of this type of lignocellulosic particles. A similar morphology has been recently described for other lignocellulosic particles derived from similar crop wastes [12,37]. The size distribution presented in the particle histogram, plotted in Figure 2c, revealed that the particle sizes varied in the range of 1-35 µm whereas the mean size was ~15 µm.…”

“…This new phase can result from the combination of the added MLO with the ejected linseed oil, which potentially favored the interfacial adhesion of the composite and, thus, supports the increase in ductility and impact strength. Previous research studies about green composites based on PLA and lignocellulosic fillers processed with MLO have shown similar morphologies, which correlates well with their enhanced ductility performance [11,12,33]. Figure 5 gathers the DSC thermograms obtained during the second heating scan of the PLA and the PLS/FSF composites.…”

“…It is also worth to mention that the fillers generated an additional degradation peak in the thermal range from 365 • C to 590 • C, which can be related to the thermal decomposition of FSF. The resultant thermal stability impairment has been recently ascribed to the low thermal stability of the lignocellulosic fillers and also to the remaining moisture, which is extremely difficult to remove [12,66]. Moreover, the thermal stability of PLA can also be influenced negatively by the high shear and frictional forces experienced during melt extrusion [12].…”

“…The use of lignocellulosic fillers in biopolymers offers significant processing advantages, biodegradability, non-abrasive, low cost, high specific strength, and a renewable nature [8]. Over the last few years, several articles and applications of green composites have been developed using lignocellulosic fillers derived from food, agricultural, industrial, and marine wastes such as rice husk [9,10], almond shell [11], walnut shell [12], peanut shell [13], coconut fibers [14], orange peel [15], recycled cotton [16], and posidonia oceanica seaweed [17]. In this regard, flax (Linum usitatissimum L.) is one of the most researched plants for industrial purposes.…”

Effect of Almond Shell Waste on Physicochemical Properties of Polyester-Based Biocomposites

“…The micrographs revealed that the particles were irregular in shape and presented a rough surface, more likely resulting from the crushing process due to the high hardness of this type of filler. Some granular features can also be observed, which resemble the original grainy and wavy structure of almond shell [35].…”