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Effect of calcium carbonate (CaCO3) particle dispersion on the mechanical properties of polypropylene (PP)/montmorillonite (MMT) composites was investigated. These composites were fabricated by melt-mixing using a twin-screw extruder, and the dumbbell shaped specimen was also fabricated by injection molding. Tensile and notched Izod impact tests were conducted by using dumbbell shaped specimens. The results showed that CaCO3 particle dispersion improved the elongation at break and notched Izod impact strength of PP/organized MMT composites. This mechanism was discussed from MMT dispersion and fracture surface observations using a scanning electron microscopy. It was found that organized MMT was well-dispersed by dispersed CaCO3 particle. The reason was thought to be that localized shear stress near MMT was increased by increase of localized viscosity near MMT due to CaCO3 particle dispersion. Well-dispersed MMT improved the the stability of plastic deformation at quasi-static loading and energy dissipation at impact fracture, resulting in the improvement of the elongation at break and impact strength of PP/MMT composites. In addition, CaCO3 particle dispersion also improved the tensile modulus of PP/MMT composites. This mechanism was discussed from interparticle distance of MMT and CaCO3 calculated by Tyuzyo's equation. From the above results, it was suggested that CaCO3 particle dispersion was an effective way for improvement of mechanical properties and impact strength of PP/MMT composites.

Introduction: We investigated the impact of reduced school scoliosis screenings due to the COVID-19 pandemic on scoliosis management. Methods: The subjects were 104 patients who initially visited the scoliosis outpatient clinic (outpatient clinic group) and 720 participants who underwent school screening (school screening group) from January 2017 to March 2022. We studied the age and radiographic findings at the initial visit in both group. We compared these findings before the COVID-19 pandemic (before March 2020) and after the pandemic began (after April 2020). Results: In the outpatient clinic group, the average age was higher after the pandemic (before the pandemic 12.7±1.5 years vs. after the pandemic 13.4±2.2 years, P=0.0434). The percentage of patients with a Cobb angle of 20-24° at their initial visit, considered borderline for treatment, decreased after the pandemic (before the pandemic 18.2% vs. after the pandemic 7.9%, P=0.0437). In the school screening group, the average number of participants decreased (before the pandemic 159.7 people/year, after the pandemic 120.5 people/year), and the average Cobb angle increased (before the pandemic 11.2±6.9°, after the pandemic 15.3±8.1°, P=0.0002). Conclusion: Due to the COVID-19 pandemic, early detection of scoliosis may have been delayed and the optimal timing for treatment may have been missed. [ABSTRACT FROM AUTHOR]