Influence of dynamic crosslinking on the morphology, crystallization, and dynamic mechanical properties of PA6,12/EVA blends

Soybean-Based Polyol as a Substitute of Fossil-Based Polyol on the Synthesis of Thermoplastic Polyurethanes: The Effect of Its Content on Morphological and Physicochemical Properties

Thermoplastic polyurethanes (TPUs) are remarkably versatile polymers due to the wide range of raw materials available for their synthesis, resulting in physicochemical characteristics that can be tailored according to the specific requirements of their final applications. In this study, a renewable bio-based polyol obtained from soybean oil is used for the synthesis of TPU via reactive extrusion, and the influence of the bio-based polyol on the multi-phase structure and properties of the TPU is studied. As raw materials, 4,4'-diphenylmethane (MDI), 1,4-butanediol, a fossil-based polyester polyol, and a bio-based polyol are used. The fossil-based to soybean-based polyol ratios studied are 100/0, 99/1, 95/5, 90/10, 80/20, and 50/50% by weight, respectively. The TPUs were characterized by size exclusion chromatography (SEC), gel content analysis, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), dynamic mechanical analysis (DMA), and contact angle measurements. The results reveal that incorporating the renewable polyol enhances the compatibility between the rigid and flexible segments of the TPU. However, due to its high functionality, the addition of soybean-based polyol can promote cross-linking. This phenomenon reduces the density of hydrogen bonds within the material, also reducing polarity and restricting macromolecular mobility, as corroborated by higher glass transition temperature (Tg) values. Remarkably, the addition of small amounts of the bio-based polyol (up to 5 wt.% of the total polyol content) results in high-molecular-weight TPUs with lower polarity, combined with suitable processability and mechanical properties, thus broadening the range of applications and improving their sustainability.

Effects of nano-silica on the crystallization, structure, and mechanical properties of crosslinked ethylene-octene copolymer/nano-silica composites

Nano-silica (SiO2) has been widely used to fill rubbers (crosslinked) and usual polyolefin elastomers (POEs). SiO2 filled POE with crystalline structure can also be crosslinked. Crystallization, structure, and mechanical properties of crosslinked POE/SiO2 composites can be affected by SiO2. In this paper, crosslinked POE/SiO2 composites were obtained through two different methods: dynamic crosslinking in molten state and static crosslinking. For the non-crosslinked and static crosslinked composites, SiO2 had a more significant effect on the nucleation in non-crosslinked POE than in static crosslinked POE. For the dynamic crosslinked composite, SiO2 and crosslinking points hindered the mobility of POE chains and suppressed the POE crystallization, resulting in smaller and fewer crystals. Dynamic mechanical analysis showed that the SiO2 and POE were compatible, as evidenced by the lower tan(δ) value in SiO2-filled samples. The latter was more consistent with the higher tensile strength and elongation at break for the non-crosslinked and static crosslinked composites than for the non-filled samples. However, the dynamic crosslinked composite exhibited the worst elongation at break, resulting from the lowest number of crystals and shortened molecular chains due to the shearing that occurred during crosslinking process. The SiO2 had no observable effect on the permanent deformation of samples.