Phase Morphology, Crystallization Behavior and Mechanical Properties of Poly(L-lactide) Toughened with Biodegradable Polyurethane: Effect of Composition and Hard Segment Ratio

Polyester-based biodegradable polyurethane （PU） with different hard segment ratios was selected to modify the impact toughness of poly（L-lactide） （PLLA）. The influence of blending composition and hard segment ratio of PU on the phase morphology, crystallization behavior and mechanical properties of PLLA/PU blends has been investigated systematically. The results showed that the PU particles were uniformly dispersed in PLLA matrix at a scale from sub- microns to several microns. The glass transition temperature of PU within these blends decreased compared to that of neat PU, but rose slightly with its content and hard segment ratio. The presence of PU retarded the crystallization ability of PLLA, whereas enhanced its elongation at break and impact resistance effectively. As the PU content reaches up to 30 wt%, the phenomenon of brittle-ductile transition occurred, resulting in a rougher fracture surface with the formation of fibril-like structure. Moreover, under the same concentrations, the elongation at break and impact strength of PLLA blends decreased slightly with the increase of hard segment ratio of PU.

A rapid colloidal gold immunochromatographic assay for the diagnosis of coronavirus disease 2019

Coronavirus disease 2019(COVID-19),caused by a severe acute respiratory syndrome coronavirus-2(SARS-CoV-2),which can lead to pneumonia and severe acute respiratory syndrome,continues to spread across the globe.[1]Due to strict precautionary measures,the epidemic situation of COVID-19 has been initially controlled in China.However,the numbers of confirmed positive cases of COVID-19 and deaths are increasing in other countries.In fact,the SARS-CoV-2 is more contagious than severe acute respiratory syndrome coronavirus(SARS-CoV)[2]and Middle East respiratory syndrome coronavirus(MERSCoV).[3]Therefore,the rapid and accurate identification of pathogenic viruses plays a vital role in controlling epidemics.Computed tomography imaging and some hematologic parameters are the initial markers for COVID-19 infection,[4,5]while viral nucleic acid detection by reverse transcription-polymerase chain reaction is used as a gold standard for the clinical diagnosis of suspected cases.