Tuning pore size and density of rigid polylactic acid foams through thermally induced phase separation and optimization using response surface methodology.

Rigid polylactic acid (PLA) foams fabricated via thermally induced phase separation (TIPS) utilizing a ternary solution of PLA, Tetrahydrofuran (THF), and water. The PLA gels were stabilized mechanically by the substituting of the THF/water solvent mixture with ethanol as non-solvent and subsequently vacuum dried. A comprehensive characterization of PLA foams was achieved by Scanning Electron Microscopy (SEM), X-ray Diffractometry (XRD) and Brunauer-Emmett-Teller (BET) analyses. The BET area obtained in the PLA foam is up to 18.76 m2/g. The Response Surface Methodology (RSM) was utilized to assess the impacts of four independent variables (polymer concentration, solvent composition, quench temperature, and aging time) on the pore size and density of PLA foam. The experimental findings demonstrated that the fabrication parameters could be fine-tuned to govern the morphology of the pores, comprising their size and density. The optimal values of parameters for cell size were identified by RSM to be 8.96 (wt%), 91.60 (w/w), 5.50 °C, and 3.86 h for the optimum cell size of 37.96 µm (37.78 by Genetic Algorithm). Optimum density by RSM 88.88 mgr/cm3 (88.38 mgr/cm3 by Genetic Algorithm) was obtained at 5.00 (wt%), 89.33 (w/w), 14.40 °C and 2.65 h.

A Comprehensive Study on the Effect of Highly Thermally Conductive Fillers on Improving the Properties of SBR/BR-Filled Nano-Silicon Nitride.

The effect of silicon nitride (Si3N4) as a thermally conductive material on the mechanical, microstructural, and physical properties as well as kinetics of the curing reaction of styrene-butadiene rubber/butadiene rubber (SBR/BR) was investigated in this work. The results showed an improvement in tensile, hardness, and compression features of the composite due to the presence of Si3N4. The properties were enhanced with the filler loading content; somehow, the composite including Si3N4 = 6 parts per hundred (phr) had the most significant performance, an increase of ∼15 and 20% in the maximum strain and toughness of the composite, respectively, an increase of almost 7% in the hardness, and an ∼13% reduction in the compression set. Also, the filler led to an increase in the crosslink density (calculated via the Flory-Rehner equation using swelling test) by 7.12 × 10-5 mol/g, proving the increment of the covalent bonds between the polymer chains during the curing reaction. The kinetic consideration revealed a reduction in the scorch and optimum curing times by ∼40 and ∼25%, respectively. In order to describe the kinetics of curing reaction of SBR/BR-Si3N4, an autocatalytic model based on the Kamal-Sourour model was applied on the rheometry results. The calculated kinetic parameters indicated that the thermally conductive Si3N4 accelerated the curing reaction by ∼40%, particularly at Si3N4 = 6 phr. After 6 phr of Si3N4, agglomeration of the filler particles decreased its performance.

Catalytic effect of high thermal conductive SiC on the kinetics and thermodynamics of vulcanization reaction of SBR/BR-filled nano-SiC.

Nano-silicon carbide (SiC) as a high thermal conductive material with an intrinsic thermal conductivity of ~ 490 W/m K was used to improve the cure characteristics, kinetics, and thermodynamics of curing reaction of styrene-butadiene rubber/butadiene rubber (SBR/BR) compounds. The considerations were carried out by non-isothermal differential scanning calorimetry (DSC). Results revealed that the presence of SiC shifted the peak and end temperatures of the curing peak to lower temperatures. The calculated activation energy of the curing reaction based on the Kissinger approach showed a descent from 409.8 to 93.8 kJ/mol by adding SiC from 0 to 7.5 phr (part per hundred rubber). Moreover, the obtained Gibbs free energy variation and equilibrium constant of the curing reaction proved that the reaction was absolutely forced and irreversible, which can be increasingly characterized as a one-way process. According to the results, SiC accelerated the curing reaction because of the increment of heat transfer into the compound. This phenomenon caused the increment of enthalpy variation of the vulcanization reaction, particularly at the SiC content of 5 phr. The achieved kinetic parameters via fitting an autocatalytic model based on the Sestàk-Berggren model by the Màlek method to describe the kinetics of the curing reaction indicated that the SiC filler had a catalytic effect on the curing reaction of SBR/BR-SiC, particularly after 2.5 phr of the filler.

Comparison of the Effect of the Person-Centered and Family-Centered Training via Telenursing on the Quality of Life in COVID-19 Patients.

Background: Education of the patients with Coronavirus Disease 2019 (COVID-19) and their families is necessary to improve the quality of life. This study investigated the effect of person and family-centered training via telenursing on the quality of life in patients with COVID-19. Methods: This interventional study was performed on 88 patients with COVID-19 18--65 years and 44 family members referred to the Bank Melli Hospital, Tehran, Iran. The samples were randomly assigned into two groups person-centered and family centered. A cyberspace group including patients and their families was created. Four educational sessions planned (15--30-min-every day) and three sessions planned for completing the questionnaires via phone. The data were collected using demographic characteristics form and the 12-item Short-Form Health Survey version 2 before and 6 weeks after the intervention and were analyzed in SPSS 22 using Chi-square test, paired t-test, and independent t-test. Results: The mean scores of quality-of-life increased significantly in the person-centered group from 26.81 ± 5.15 to 34.4 ± 4.39 before and six weeks after intervention, respectively (p < 0.001). The means scores of quality-of-life increased significantly in the family-centered group from 28.11 ± 4.79 to 35.86 ± 3.85 before and 6 weeks after the intervention, respectively. (p < 0.001). Conclusions: The person and family centered methods increase the mean scores of quality-of-life of patients with COVID-19. The family centered method can be more effective to improve the quality of life of these patients.

Microstructure and physical properties of thermoplastic corn starch foams as influenced by polyvinyl alcohol and plasticizer contents.

Thermoplastic starch (TPS) foams was prepared by melt extrusion process and the effects of polyvinyl alcohol (PVA) and glycerol/water plasticizer contents on the physical and cellular properties of these foams were investigated. All TPS/PVA blended foams showed more uniform cellular morphology, lower density and higher cell density than the TPS foam. The density of TPS foam decreased about 70%, and cell density increased up to 60-fold by adding 20% PVA. In addition to the positive effect of the PVA on improving processability and cellular uniformity, it also acted as a polymeric plasticizer and adding it allowed to decrease another low molecular weight plasticizer content in TPS/PVA blends. As a result by statistical analysis significant improvements in expansion ratio (256%), cell density (60 times), and lower moisture absorption (60%) were achieved.

Plasticizing and anti-plasticizing effects of polyvinyl alcohol in blend with thermoplastic starch.

Thermoplastic starch (TPS) and polyvinyl alcohol (PVA) blends were prepared by extrusion method in the presence of water/glycerol and citric acid, and their phase behavior was investigated. Results of scanning electron microscopy (SEM) and X-ray diffractometry (XRD) tests demonstrated the complete plasticization of starch during the melt mixing. PVA crystal phase was not formed in blends with less than 50 wt% PVA. Fourier-transform infrared spectroscopy (FTIR) and dynamic mechanical analysis (DMA) analysis revealed high compatibility between two phases, starch and PVA. Addition of PVA to TPS resulted in the reduction of the glass transition temperature and dynamic moduli and improvement of sample flexibility. However, at 10 wt% PVA, an anti-plasticization effect caused to increase the Tg and storage modulus of the blend.