RESUMEN
Biomass-derived isosorbide (ISB) is a promising alternative to petroleum-based monomers in industrial plastics. In this study, ISB-based thermoplastic polyurethanes (ISB-TPUs) were prepared using ISB as a biomass chain extender, and the effects of the preparation route on the structural and physical properties of the resultant polymers were investigated. Prepolymer methods were more suitable for obtaining the desired molecular weights (MWs) and physical properties of ISB-TPUs than the one-shot method. The presence of the solvent and catalyst in the prepolymer step had significant effects on the structural and physical properties of the resultant polymer. Among several prepolymer conditions, the solvent- and catalyst-free methods were the most suitable for preparing commercial-level ISB-TPUs, with number- and weight-average MWs (M n and M w ) of 32,881 and 90,929 g mol-1, respectively, and a tensile modulus (E) and ultimate tensile strength (UTS) of 12.0 and 40.2 MPa, respectively. In comparison, the presence of a catalyst in the prepolymer step resulted in lower MWs and mechanical properties (81,033 g mol-1 and 18.3 MPa of M w and UTS, respectively). The co-existence of the catalyst/solvent led to a further decline in the properties of ISB-TPUs (26,506 and 10.0 MPa of M w and UTS, respectively). ISB-TPU prepared via the solvent- and catalyst-free methods exhibited remarkable elastic recovery when subjected to up to 1000% strain in mechanical cycling tests. Rheological characterization confirmed the thermo-reversible phase change (thermoplasticity) of the polymer. Supplementary Information: The online version contains supplementary material available at 10.1007/s13233-023-00125-w.
RESUMEN
Although biodegradable plastics are gradually emerging as an effective solution to alleviate the burgeoning plastic pollution, their performance is currently trivial for commercialization. A proposed two-pronged strategy to overcome this limitation includes (1) preparation of the nanocomposites from biorenewable nano-fillers to preserve their biodegradability and (2) tailoring their properties to meet the diverse demands in various applications. Herein, we report the preparation of biodegradable nanocomposites composed of poly(butylene succinate) (PBS) and cellulose nanocrystals (CNCs) (loading of 0.2-3.0 wt%) and propose a rheological strategy to tailor their performances. Depending on the shear frequencies, the rheological evaluation revealed two percolation thresholds at approximately 0.8 and 1.5 wt%. At high shear frequencies, the disappearance of the first threshold (0.8 wt%) and the sole persistence of the second one (1.5 wt%) indicated the collapse of the immature network of partially interconnected CNCs. The tensile and hydrolytic properties of the nanocomposites were found to undergo drastic changes at the thresholds. The tensile strength increased by 17% (from 33.3 to 39.2 MPa) up to 0.8 wt% CNC loading. However, the reinforcing efficiency of CNC decreases sharply with further incorporation, reaching nearly zero at 1.5 wt%. On the other hand, hydrolytic degradation of the nanocomposites was rapidly accelerated above 1.5 wt% CNC loading. Therefore, a thorough understanding of the rheological properties of nanocomposites is essential for the design and development of materials with tailored properties.
RESUMEN
The activities and consequences of workplace bullying and harassment have been widely explored in the literature but mainly studied within the scope of individuals or at the team level. Taking a holistic approach, we associate the concept of bullying with firm-level performance as well as stakeholders' responses in the market. In this paper, we examine whether and how market investors react to the news of corporate harassment by top officials of publicly listed firms in Korea. Using a standard event study methodology and multiple regression analysis with matched sample, we find significantly negative stock price reactions to news of corporate bullying. We also find that the impact is more salient if emotional bullying is involved and discuss both the theoretical and practical implications of these findings.