Polyvinyl alcohol polymer matrix

The polyvinyl alcohol polymer matrix used in this research was obtained from Sigma-Aldrich Chemical Company (Darmstadt, Germany). Series of experiments were performed using samples with different PVA molecular weights: 30–70 kDa (degree of hydrolysis 87.0–90.0, melting point 250 °C), 89–98 kDa (degree of hydrolysis 99.0, melting point 250 °C), 125 kDa (Mowiol 20–98, degree of hydrolysis 98.0–98.8, melting point 200 °C), 130 kDa (polyvinyl alcohol 18–88, degree of hydrolysis 86.7–88.7, melting point 200 °C), and 145 kDa (Mowiol 28–99, melting point 230 °C). For each PVA molecular weight, three polymer concentrations in an aqueous solution for electrospinning were obtained (6, 8, and 10 wt.%). Laboratory distilled water (conductivity 1 µS/cm) was used to prepare the PVA solutions.

The polyvinyl alcohol polymer matrix used in this research was obtained from Sigma-Aldrich Chemical Company (Darmstadt, Germany). The series of samples using different PVA molecular weights Mowiol 20–98 (Mw = ~125 kDa, degree of hydrolysis 98.0–98.8) and polyvinyl alcohol 18–88 (Mw = ~130 kDa, degree of hydrolysis 86.7–88.7) were performed; the melting point was 200 °C and the density was 1.269 g/cm³. The total flavonoids content was determined according to [23 (link)], using zirconium oxychloride (98%, Mw = 322.25, Sigma-Aldrich) and methanol (99.9%, Mw = 32.04%, Sigma-Aldrich). The ethyl alcohol (96.4–96.6%, Mw = 46.07, SIA Kalsnavas Elevators, Jaunkalsnava, Latvia) used to prepare the laboratory-made propolis extracts. The extract from Riga Pharmaceutic Factory (Riga, Latvia) contains 70% ethyl alcohol extract. Various types of propolis and its extracts were used (Table 7). The stages of the solution-mixing process are designated as marked (Figure 3). Laboratory distilled water (conductivity 1 µS/cm) was used to prepare PVA solutions and propolis extracts.