Tensile and Compressive Properties of PLA-Based Polymeric Blends Depending on PBS, PBAT and TPS Content and Testing Temperature

Environmentally friendly biopolymeric materials can be utilized to replace commonly used plastics, what leads to a noticeable reduction of the pollution level, caused by their processing and exploitation. Nevertheless, in comparison with their non-biodegradable precursors, they suffer from some severe limitations, such as their capability to be untimely decomposed during long-term work, lowered mechanical properties and impaired thermal resistance. Therefore, it is crucial to make efforts to surpass the mentioned constraints by modification of the properties of biodegradable polymers. Among the possible solutions to advance their development a preparation of variously composed biopolymeric blends seems to be a promising route. Poly(lactic acid) (PLA), being widely applied, is one of the most popular biodegradable plastics, characterized with rather high mechanical properties, but with reduced deformability at the same time. To overcome its brittleness, it can be joined together with more ductile additives, namely: polycaprolactone (PCL), poly(propylene carbonate) (PPC), poly (butylene succinate) (PBS), poly(butylene-succinate-co-adipate) (PBSA), poly(butyleneadipate-co-terephthalate) (PBAT), thermoplastic starch (TPS) and polyamide 11(PA11) [1-5]. This work was focused on PLA-based compositions doped with different ratios of PBS, PBAT and TPS to evaluate their mechanical (tensile and compressive) properties in various temperatures (-20°C, 0°C, 20°C, 40°C). Specimens for testing were obtained by preliminary extrusion, subsequent injection molding and final cutting into the intended dimensions. Mechanical properties e.g. tensile strength, elongation at break, Young’s modulus, yield strength and compressive strength for the deformation of 0.4 were investigated. No additional modification step, as for example, addition of compatibilizers was necessary to be involved in the manufacturing method, what significantly simplified this process without impairing the properties exhibited by the obtained blends. Each of the tested plasticizing secondary compounds positively influenced the elongation at break of PLA – increasing it especially in the case of PBAT and TPS. Simultaneously, together with the increasing content of a ductile component, other mechanical properties i.e. tensile and compressive strength were decreased. The stability of the mechanical performance of thus fabricated mixtures was assessed taking into account also the test conditions (strain rate and temperature), aiming to understand its dependence on these parameters. To gain a deeper insight into the potential applicability of the hereby proposed materials also some selected processing parameters were investigated, namely: melt flow ratio (MFR), melt volume ratio (MVR), heat deflection temperatures for 1.8 MPa and 8 MPa (HDT A and HDT C) and Vicat softening temperatures for two loadings of 10 N and 50 N (VST A and VST B). Finally, the DSC test results were used to complement the study, providing information on the softening, glass transition, cold crystallization and crystallization temperatures of the developed mixtures. It can be concluded that the elaborated biodegradable blends provide a desired compromise between the mechanical properties, in terms of both tensile and compressive characteristics, and deformability of durable and brittle PLA and ductile PBS, PBAT and TPS additives. Hereby described biomaterials aim to find their use in energy absorption applications, as for the manufacturing of thin-walled, cellular inserts filling sports helmets, acting as energy absorbers and replacing regularly utilized foamed materials in protection of their users during an accident.<br/><br/><b>Funding:</b> This work was supported by the project BIOKASK ‘‘Development of innovative, replaceable, energy-absorbing structures based on biodegradable plastics for protective helmets” (0223/L-11/2019, LIDER, NCBR).