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

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.

Upgrading Argan Shell Wastes in Wood Plastic Composites with Biobased Polyethylene Matrix and Different Compatibilizers.

The present study reports on the development of wood plastic composites (WPC) based on micronized argan shell (MAS) as a filler and high-density polyethylene obtained from sugarcane (Bio-HDPE), following the principles proposed by the circular economy in which the aim is to achieve zero waste by the introduction of residues of argan as a filler. The blends were prepared by extrusion and injection molding processes. In order to improve compatibility between the argan particles and the green polyolefin, different compatibilizers and additional filler were used, namely polyethylene grafted maleic anhydride (PE-g-MA 3 wt.-%), maleinized linseed oil (MLO 7.5 phr), halloysite nanotubes (HNTs 7.5 phr), and a combination of MLO and HNTs (3.75 phr each). The mechanical, morphological, thermal, thermomechanical, colorimetric, and wettability properties of each blend were analyzed. The results show that MAS acts as a reinforcing filler, increasing the stiffness of the Bio-HDPE, and that HNTs further increases this reinforcing effect. MLO and PE-g-MA, altogether with HNTs, improve the compatibility between MAS and Bio-HDPE, particularly due to bonds formed between oxygen-based groups present in each compound. Thermal stability was also improved provided by the addition of MAS and HNTs. All in all, reddish-like brown wood plastic composites with improved stiffness, good thermal stability, enhanced compatibility, and good wettability properties were obtained.

Development and Characterization of Weft-Knitted Fabrics of Naturally Occurring Polymer Fibers for Sustainable and Functional Textiles.

This study focuses on the potential uses in textiles of fibers of soy protein (SP) and chitin, which are naturally occurring polymers that can be obtained from agricultural and food processing by-products and wastes. The as-received natural fibers were first subjected to a three-step manufacturing process to develop yarns that were, thereafter, converted into fabrics by weft knitting. Different characterizations in terms of physical properties and comfort parameters were carried out on the natural fibers and compared to waste derived fibers of coir and also conventional cotton and cotton-based fibers, which are widely used in the textile industry. The evaluation of the geometry and mechanical properties revealed that both SP and chitin fibers showed similar fineness and tenacity values than cotton, whereas coir did not achieve the expected properties to develop fabrics. In relation to the moisture content, it was found that the SP fibers outperformed the other natural fibers, which could successfully avoid variations in the mechanical performance of their fabrics as well as impair the growth of microorganisms. In addition, the antimicrobial activity of the natural fibers was assessed against different bacteria and fungi that are typically found on the skin. The obtained results indicated that the fibers of chitin and also SP, being the latter functionalized with biocides during the fiber-formation process, showed a high antimicrobial activity. In particular, reductions of up to 100% and 60% were attained for the bacteria and fungi strains, respectively. Finally, textile comfort was evaluated on the weft-knitted fabrics of the chitin and SP fibers by means of thermal and tactile tests. The comfort analysis indicated that the thermal resistance of both fabrics was similar to that of cotton, whereas their air permeability was higher, particularly for chitin due to its higher fineness, which makes these natural fibers very promising for summer clothes. Both the SP and chitin fabrics also presented relatively similar values of fullness and softness than the pure cotton fabric in terms of body feeling and richness. However, the cotton/polyester fabric was the only one that achieved a good range for uses in winter-autumn cloths. Therefore, the results of this work demonstrate that non-conventional chitin and SP fibers can be considered as potential candidates to replace cotton fibers in fabrics for the textile industry due to their high comfort and improved sustainability. Furthermore, these natural fibers can also serve to develop novel functional textiles with antimicrobial properties.

On the Use of Phenolic Compounds Present in Citrus Fruits and Grapes as Natural Antioxidants for Thermo-Compressed Bio-Based High-Density Polyethylene Films.

This study originally explores the use of naringin (NAR), gallic acid (GA), caffeic acid (CA), and quercetin (QUER) as natural antioxidants for bio-based high-density polyethylene (bio-HDPE). These phenolic compounds are present in various citrus fruits and grapes and can remain in their leaves, peels, pulp, and seeds as by-products or wastes after juice processing. Each natural additive was first melt-mixed at 0.8 parts per hundred resin (phr) of bio-HDPE by extrusion and the resultant pellets were shaped into films by thermo-compression. Although all the phenolic compounds colored the bio-HDPE films, their contact transparency was still preserved. The chemical analyses confirmed the successful inclusion of the phenolic compounds in bio-HDPE, though their interaction with the green polyolefin matrix was low. The mechanical performance of the bio-HDPE films was nearly unaffected by the natural compounds, presenting in all cases a ductile behavior. Interestingly, the phenolic compounds successfully increased the thermo-oxidative stability of bio-HDPE, yielding GA and QUER the highest performance. In particular, using these phenolic compounds, the onset oxidation temperature (OOT) value was improved by 43 and 41.5 °C, respectively. Similarly, the oxidation induction time (OIT) value, determined in isothermal conditions at 210 °C, increased from 4.5 min to approximately 109 and 138 min. Furthermore, the onset degradation temperature in air of bio-HDPE, measured for the 5% of mass loss (T5%), was improved by up to 21 °C after the addition of NAR. Moreover, the GA- and CA-containing bio-HDPE films showed a high antioxidant activity in alcoholic solution due to their favored release capacity, which opens up novel opportunities in active food packaging. The improved antioxidant performance of these phenolic compounds was ascribed to the multiple presence of hydroxyl groups and aromatic heterocyclic rings that provide these molecules with the features to permit the delocalization and the scavenging of free radicals. Therefore, the here-tested phenolic compounds, in particular QUER, can represent a sustainable and cost-effective alternative of synthetic antioxidants in polymer and biopolymer formulations, for which safety and environmental issues have been raised over time.

Microencapsulation of Copper(II) Sulfate in Ionically Cross-Linked Chitosan by Spray Drying for the Development of Irreversible Moisture Indicators in Paper Packaging.

Copper(II) sulfate-loaded chitosan microparticles were herein prepared using ionic cross-linking with sodium tripolyphosphate (STPP) followed by spray drying. The microencapsulation process was optimal using an inlet temperature of 180 °C, a liquid flow-rate of 290 mL/h, an aspiration rate of 90%, and an atomizing gas flow-rate of 667 nL/h. Chitosan particles containing copper(II) sulfate of approximately 4 µm with a shrunken-type morphology were efficiently attained and, thereafter, fixated on a paper substrate either via cross-linking with STPP or using a chitosan hydrogel. The latter method led to the most promising system since it was performed at milder conditions and the original paper quality was preserved. The developed cellulose substrates were reduced and then exposed to different humidity conditions and characterized using colorimetric measurements in order to ascertain their potential as irreversible indicators for moisture detection. The results showed that the papers coated with the copper(II) sulfate-containing chitosan microparticles were successfully able to detect ambient moisture shown by the color changes of the coatings from dark brown to blue, which can be easily seen with the naked eye. Furthermore, the chitosan microparticles yielded no cytotoxicity in an in vitro cell culture experiment. Therefore, the cellulose substrates herein developed hold great promise in paper packaging as on-package colorimetric indicators for monitoring moisture in real time.

Tailoring the Properties of Thermo-Compressed Polylactide Films for Food Packaging Applications by Individual and Combined Additions of Lactic Acid Oligomer and Halloysite Nanotubes.

In this work, films of polylactide (PLA) prepared by extrusion and thermo-compression were plasticized with oligomer of lactic acid (OLA) at contents of 5, 10, and 20 wt%. The PLA sample containing 20 wt% of OLA was also reinforced with 3, 6, and 9 parts per hundred resin (phr) of halloysite nanotubes (HNTs) to increase the mechanical strength and thermal stability of the films. Prior to melt mixing, ultrasound-assisted dispersion of the nanoclays in OLA was carried out at 100 °C to promote the HNTs dispersion in PLA and the resultant films were characterized with the aim to ascertain their potential in food packaging. It was observed that either the individual addition of OLA or combined with 3 phr of HNTs did not significantly affect the optical properties of the PLA films, whereas higher nanoclay contents reduced lightness and induced certain green and blue tonalities. The addition of 20 wt% of OLA increased ductility of the PLA film by nearly 75% and also decreased the glass transition temperature (Tg) by over 18 °C. The incorporation of 3 phr of HNTs into the OLA-containing PLA films delayed thermal degradation by 7 °C and additionally reduced the permeabilities to water and limonene vapors by approximately 8% and 47%, respectively. Interestingly, the highest barrier performance was attained for the unfilled PLA film plasticized with 10 wt% of OLA, which was attributed to a crystallinity increase and an effect of "antiplasticization". However, loadings of 6 and 9 phr of HNTs resulted in the formation of small aggregates that impaired the performance of the blend films. The here-attained results demonstrates that the properties of ternary systems of PLA/OLA/HNTs can be tuned when the plasticizer and nanofiller contents are carefully chosen and the resultant nanocomposite films can be proposed as a bio-sourced alternative for compostable packaging applications.

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

Green composites made of polylactide (PLA) and short flaxseed fibers (FFs) at 20 wt % were successfully compounded by twin-screw extrusion (TSE) and subsequently shaped into pieces by injection molding. The linen waste derived FFs were subjected to an alkalization pretreatment to remove impurities, improve the fiber surface quality, and make the fibers more hydrophobic. The alkali-pretreated FFs successfully reinforced PLA, leading to green composite pieces with higher mechanical strength. However, the pieces also showed lower ductility and toughness and the lignocellulosic fibers easily detached during fracture due to the absence or low interfacial adhesion with the biopolyester matrix. Therefore, four different compatibilization strategies were carried out to enhance the fiber-matrix interfacial adhesion. These routes consisted on the silanization of the alkalized FFs with a glycidyl silane, namely (3-glycidyloxypropyl) trimethoxysilane (GPTMS), and the reactive extrusion (REX) with three compatibilizers, namely a multi-functional epoxy-based styrene-acrylic oligomer (ESAO), a random copolymer of poly(styrene-co-glycidyl methacrylate) (PS-co-GMA), and maleinized linseed oil (MLO). The results showed that all the here-tested compatibilizers improved mechanical strength, ductility, and toughness as well as the thermal stability and thermomechanical properties of the green composite pieces. The highest interfacial adhesion was observed in the green composite pieces containing the silanized fibers. Interestingly, PS-co-GMA and, more intensely, ESAO yielded the pieces with the highest mechanical performance due to the higher reactivity of these additives with both composite components and their chain-extension action, whereas MLO led to the most ductile pieces due to its secondary role as plasticizer for PLA.

Development of Injection-Molded Polylactide Pieces with High Toughness by the Addition of Lactic Acid Oligomer and Characterization of Their Shape Memory Behavior.

This work reports the effect of the addition of an oligomer of lactic acid (OLA), in the 5-20 wt% range, on the processing and properties of polylactide (PLA) pieces prepared by injection molding. The obtained results suggested that the here-tested OLA mainly performs as an impact modifier for PLA, showing a percentage increase in the impact strength of approximately 171% for the injection-molded pieces containing 15 wt% OLA. A slight plasticization was observed by the decrease of the glass transition temperature (Tg) of PLA of up to 12.5 °C. The OLA addition also promoted a reduction of the cold crystallization temperature (Tcc) of more than 10 °C due to an increased motion of the biopolymer chains and the potential nucleating effect of the short oligomer chains. Moreover, the shape memory behavior of the PLA samples was characterized by flexural tests with different deformation angles, that is, 15°, 30°, 60°, and 90°. The obtained results confirmed the extraordinary effect of OLA on the shape memory recovery (Rr) of PLA, which increased linearly as the OLA loading increased. In particular, the OLA-containing PLA samples were able to successfully recover over 95% of their original shape for low deformation angles, while they still reached nearly 70% of recovery for the highest angles. Therefore, the present OLA can be successfully used as a novel additive to improve the toughness and shape memory behavior of compostable packaging articles based on PLA in the new frame of the Circular Economy.