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

Abstract

This work reports the development and characterization of green composites based on polylactide (PLA) containing fillers and additives obtained from by-products or waste-streams from the linen processing industry. Flaxseed flour (FSF) was first produced by the mechanical milling of golden flaxseeds. The resultant FSF particles were melt-compounded at 30 wt% with PLA in a twin-screw extruder. Two multi-functionalized oils derived from linseed, namely epoxidized linseed oil (ELO) and maleinized linseed oil (MLO), were also incorporated during melt mixing at 2.5 and 5 parts per hundred resin (phr) of composite. The melt-compounded pellets were thereafter shaped into pieces by injection molding and characterized. Results showed that the addition of both multi-functionalized linseed oils successfully increased ductility, toughness, and thermal stability of the green composite pieces whereas water diffusion was reduced. The improvement achieved was related to both a plasticizing effect and, more interestingly, an enhancement of the interfacial adhesion between the biopolymer and the lignocellulosic particles by the reactive vegetable oils. The most optimal performance was attained for the MLO-containing green composite pieces, even at the lowest content, which was ascribed to the higher solubility of MLO with the PLA matrix. Therefore, the present study demonstrates the potential use of by-products or waste from flax (Linum usitatissimum L.) to obtain renewable raw materials of suitable quality to develop green composites with high performance for market applications such as rigid food packaging and food-contact disposable articles in the frame of the Circular Economy and Bioeconomy.

Torrefaction of Coffee Husk Flour for the Development of Injection-Molded Green Composite Pieces of Polylactide with High Sustainability

“…Valorization of food processing by-products and agricultural waste is acquiring increasing importance due to the high interest in the development of novel sustainable materials as part of the Circular Bioeconomy framework [1,2]. Agro-food wastes, such as flax fibers [3,4], rice husk [5], jute fibers [6,7], almond husk [8,9], walnut husk [10], orange peel [11], coconut fibers [12] or sisal fibers [13], represent examples of recently explored fillers to be incorporated into biopolymer matrices. The resultant green composites can successfully show technological advantages over conventional petroleum derived polymer composites, including cost reduction, lower density, no toxicity, balanced mechanical properties and, more importantly, lower environmental impact [14,15].…”

Evaluation of Different Compatibilization Strategies to Improve the Performance of Injection-Molded Green Composite Pieces Made of Polylactide Reinforced with Short Flaxseed Fibers

“…One can also observe that all the compatibilizers suppressed the double-melting peak phenomenon and PLA melted in a single peak in the 151-154 • C range. This result suggests that all the crystalline structures presented similar lamellae thicknesses, being lower than that of PLA in the pieces without compatibilizer due to the effect of those on the PLA chains [53]. The degree of crystallinity of PLA in the green composite pieces slightly increased when the fibers were silanized or processed with the reactive compatibilizers.…”

“…It was supplied in pellets, having a melt flow rate (MFR) of 15-30 g/10 min measured at 210 • C and 2.16 kg and a true density of 1.24 g/cm 3 . This resin is suitable for injection molding and it has been previously screened for preparing green composites due to its high fluidity [19,23,53,54]. Schwarzwälder Textil-Werke Heinrich Kautzmann GmbH (Schenkenzell, Germany) delivered FF as NATURAL FIBRE.…”

“…For temperatures above 600 • C, thermal degradation continued but no significant weight losses were detected, indicating that the entire organic component were already pyrolyzed. The residual mass at the end of the analysis was over 20%, which can be related to the high mineral content present in flax [53].…”

“…Both main thermal stability values, that is, T 5% and T deg1 , were reduced by approximately 55 • C and 33 • C, respectively. The lower thermal stability of green composites has mainly been explained in terms of the low thermal stability of the lignocellulosic fillers and also to the remaining moisture, which is extremely difficult to remove [53]. Moreover, FF increased the intensity of the second degradation peak centered at~410 • C, which can be related to the passive pyrolysis of the lignocellulosic fillers.…”