Thermo-Mechanical and Morphological Properties of Polymer Composites Reinforced by Natural Fibers Derived from Wet Blue Leather Wastes: A Comparative Study

The present work investigated the possibility to use wet blue (WB) leather wastes as natural reinforcing fibers within different polymer matrices. After their preparation and characterization, WB fibers were melt-mixed at 10 wt.% with poly(lactic acid) (PLA), polyamide 12 (PA12), thermoplastic elastomer (TPE), and thermoplastic polyurethane (TPU), and the obtained samples were subjected to rheological, thermal, thermo-mechanical, and viscoelastic analyses. In parallel, morphological properties such as fiber distribution and dispersion, fiber–matrix adhesion, and fiber exfoliation phenomena were analyzed through a scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS) to evaluate the relationship between the compounding process, mechanical responses, and morphological parameters. The PLA-based composite exhibited the best results since the Young modulus (+18%), tensile strength (+1.5%), impact (+10%), and creep (+5%) resistance were simultaneously enhanced by the addition of WB fibers, which were well dispersed and distributed in and significantly branched and interlocked with the polymer matrix. PA12- and TPU-based formulations showed a positive behavior (around +47% of the Young modulus and +40% of creep resistance) even if the not-optimal fiber–matrix adhesion and/or the poor de-fibration of WB slightly lowered the tensile strength and elongation at break. Finally, the TPE-based sample exhibited the worst performance because of the poor affinity between hydrophilic WB fibers and the hydrophobic polymer matrix

Studio delle proprietà di resine epossidiche reticolate con indurenti amminici da fonte rinnovabile

Le resine epossidiche più diffuse industrialmente sono a base di diglicidil etere del bisfenolo A (DGEBA) e vengono reticolate con indurenti di tipo amminico; tali sostanze però hanno impatti negativi sulla salute umana e sull’ambiente. Il pensiero alla base di questo progetto, nasce dalla possibilità di utilizzare indurenti amminici derivanti da fonte rinnovabile per la formulazione e produzione di nuovi sistemi di resine epossidiche. Dopo test preliminari su vari composti, è stato utilizzato come nuovo indurente bio-based l’adenina, ed in particolare è stato studiato il suo comportamento con una resina epossidica a base di DGEBA. Questa formulazione è stata utilizzata per validare l’uso di adenina come indurente. Successivamente il DGEBA è stato sostituito con una resina commerciale da infusione per lavorare in condizioni più simili al reale. Questi due sistemi sono stati caratterizzati tramite analisi termogravimetrica (TGA), calorimetrica a scansione differenziale (DSC in modalità dinamica e isoterma) e analisi dinamico-meccanica (DMA). I risultati ottenuti hanno fornito importanti informazioni su questa nuova classe di indurenti amminici da fonte rinnovabile decisamente promettenti

Recycling of Chrome-Tanned Leather and Its Utilization as Polymeric Materials and in Polymer-Based Composites: A Review

Tanneries generate large amounts of solid and liquid wastes, which contain harmful chemical compounds in the environment, such as chromium, that is used in the tanning process. Until now, they have been almost completely dumped in landfills. Thus, finding eco-sustainable and innovative alternatives for the management and disposal of these wastes is becoming a huge challenge for tanneries and researchers around the world. In particular, the scientific and industrial communities have started using wastes to produce new materials exploiting the characteristics of leather, which are strongly connected with the macromolecular structure of its main component, collagen. None of the reviews on leather waste management actually present in the scientific literature report in detail the use of leather to make composite materials and the mechanical properties of the materials obtained, which are of fundamental importance for an effective industrial exploitation of leather scraps. This comprehensive review reports for the first time the state of the art of the strategies related to the recovery and valorization of both hydrolyzed collagen and leather waste for the realization of composite materials, reporting in detail the properties and the industrial applications of the materials obtained. In the conclusion section, the authors provide practical implications for industry in relation to sustainability and identify research gaps that can guide future authors and industries in their work

Wine By-Products as Raw Materials for the Production of Biopolymers and of Natural Reinforcing Fillers: A Critical Review

The plastic industry is today facing a green revolution; however, biopolymers, produced in low amounts, expensive, and food competitive do not represent an efficient solution. The use of wine waste as second-generation feedstock for the synthesis of polymer building blocks or as reinforcing fillers could represent a solution to reduce biopolymer costs and to boost the biopolymer presence in the market. The present critical review reports the state of the art of the scientific studies concerning the use of wine by-products as substrate for the synthesis of polymer building blocks and as reinforcing fillers for polymers. The review has been mainly focused on the most used bio-based and biodegradable polymers present in the market (i.e., poly(lactic acid), poly(butylene succinate), and poly(hydroxyalkanoates)). The results present in the literature have been reviewed and elaborated in order to suggest new possibilities of development based on the chemical and physical characteristics of wine by-products

Indentation and impact response of conventional, auxetic, and shear thickening gel infused auxetic closed cell foam

Auxetic closed cell foams, and highly viscoelastic foams, both show potential to improve impact protection. Specifically, auxetics adapt to the shape of impacting bodies, while highly viscoelastic foams stiffen during severe impacts. So, we made auxetic closed cell foam sheets, including those that were infused with (highly viscoelastic) shear thickening gel. We then undertook comparative quasistatic and impact (drop) tests. Quasisatic tests included compression, tension and indentation. Impact tests were with a flat faced impactor at energies of 1, 3 and 5 J, and a 50 mm diameter hemisphere at 1 and 3 J. Poisson's ratios of the foams were obtained by optical fullfield strain measurement. An analytical model was used to separate the contribution of the various measured orthotropic properties during the hemispherical impact and indentation tests. The Poisson's ratios of the converted foams (both with and without shear thickening gel) were close to zero or marginally negative when measured through thickness. Planar values of Poisson's ratio (measured in tension) were as low as −0.6. Through thickness Young's moduli of the converted foams were 0.5 MPa, and planar moduli were ~12 times higher. The auxetic foams outperformed the unconverted ones during the more severe impacts, exhibiting about half the peak force during the 3 J hemispherical impacts (2.5 vs. 5 kN). The reduction in peak force was related to a measured doubling in indentation resistance for the auxetic foam. The analytical model suggests that 7 to 15% of the measured doubling in indentation resistance was due to (negative) Poisson's ratio. Infusing the auxetic foams with shear thickening gel caused, at best, a marginal reduction in peak impact force, attributed to low and non-uniform levels of infusion