Thermoplastic Blends Based on Poly(Butylene Succinate-co-Adipate) and Different Collagen Hydrolysates from Tanning Industry: I—Processing and Thermo-mechanical Properties

Abstract

In this study, blends of a biodegradable thermoplastic polyester, poly (butylene succinate-co-adipate) (PBSA) with two different raw hydrolyzed collagens (HCs), derived from the tannery industry, were investigated in terms of processability, rheological, thermal and mechanical properties. HCs, obtained by alkaline (HCa) and enzymatic (HCe) hydrolysis of the solid wastes generated during the shaving of the tanned leather, were used in PBSA/HC blends, up to 20 wt% of HC, produced by melting extrusion and processed by injection molding. All the blends up to 20 wt% HCs resulted suitable for the injection molding obtaining flexible molded specimens with good tensile properties. The different secondary structure of the two HCs influenced the rheology, morphology and mechanical properties of the produced blends. In particular, HCa, due its higher content of oligopeptides and free amino-acids, showed a good compatibility with the polymeric matrix acting as a plasticizer with consequent reduction of melt viscosity with increasing its loading. The molded dog-bones specimens containing 20 wt% HCa showed a value of elongation at break of 810%. While, HCe, due its higher presence of b-sheet structures, behaved as organic filler, showing a poor interfacial interaction with PBSA with consequent decrease of the tensile properties with increasing its loading. The good processability and satisfactory mechanical properties obtained encourage the use of both investigated collagen hydrolysates in the production of thermoplastic blends and relative molded products for applications in agriculture and plant nurseries, such as pots or small containers with fertilizing properties, due the presence of HCs.

Thermoplastic Blends Based on Poly(Butylene Succinate-co-Adipate) and Different Collagen Hydrolysates from Tanning Industry—II: Aerobic Biodegradation in Composting Medium

“…As regard pH, PBSA solution resulted nearly neutral, while both HC solutions showed a sub-acidic reaction, also confirmed in the PBSA/HC blends. Given the HCs origin [12], CNHS analyses proved a relevant content of nitrogen in the pure HCs (about 15%), confirming data provided by the suppliers (Table 1). Consequently, higher nitrogen content resulted in the blends containing higher content of HCs, up to 3.5 wt.% N for PBSA/HCe 80/20 (wt%/wt%) (Table 3).…”

“…In fact, they all showed a biodegradability comparable to that of the reference material (cellulose) in the same period of time (55 days); only the PBSA/HCe 20% blend showed a biodegradability lower than 90% relative to the cellulose reference. The lower biodegradation rate showed by the PBSA/ HCe 20%, compared to neat PBSA and PBSA/HCa blends, can be reasonable attributed to the still present secondary structure of the HCe, as reported by Seggiani et al [12], as well as a negligible content of free amino acids (Table 1), which can make the protein material of the blend less attackable by mesophilic microorganisms operating at such low temperatures.…”

“…As reported in the concomitant study carried out by Seggiani et al [12], PBSA/HC blends were prepared by melting extrusion and provided in different shapes (pellets, dog-bone specimens and films) for running investigations following described. Blends selected for testings were PBSA/HCe (80/20, w/w), PBSA/HCa (95/5) and PBSA/HCa (80/20).…”

“…Dog-bone shaped specimens (length 90 mm, max width 10 mm; min. width 4.8 mm; thickness 1.35 mm, weight 1.2 g), produced by injection molding using PBSA neat and selected PBSA/HCs blends [12], were subjected to the disintegration tests under simulated "industrial" composting conditions. Experiments were carried out using an automatic lab equipment, Composter (Figs.…”

“…In the present study, PBSA/HC blends containing up to 20 wt.% of HCs, obtained by alkaline and enzymatic hydrolysis of tanned leather shavings [12], were investigated in terms of their environmental sustainability. After a preliminary elementary characterization, PBSA/HC blends were assessed for their ultimate aerobic biodegradability under controlled composting conditions, simulating both "industrial" (58 °C) and "home" composting (25 °C).…”