Materials
The following materials were used in the work: polycarbonate granules with a size of 0.5 × 0.2 cm brand Makrolon 2407 Bayer Material Science (the properties are shown in Table 1); ethylene glycol (GOST 10164-75); lithium hydroxide (GOST 8595-83); potassium hydroxide (GOST 24363-80); potassium carbonate (GOST R 55053 − 2012); sodium carbonate (GOST 83 − 79); cesium carbonate (GOST 30333 − 2007); bisphenol A from Sisco Research Laboratories; ethylene carbonate from Acros Organics; technical acetone (GOST 2768-84); distilled water.
Table 1
Characteristics of Makrolon 2407 Bayer Material Science PC
Index | Value |
Granule size, cm | 0.5х0.2 |
Tensile modulus, MPa | 2400 |
Stress at the yield point, MPa | 66 |
Nominal elongation at break, % | > 50 |
Casting shrinkage (longitudinal), % | 0,7 |
Elongation at the yield point, % | 6 |
Melt flow rate (at 300°C and 1.2 kg), cm3/10min | 19 |
Casting shrinkage (transverse), % | 0.7 |
Electrical strength kV/mm, not less than | 34 |
Dielectric constant at a frequency of 106 Hz, no more | 3 |
Vicat softening temperature, °C, not less than | 143 |
Density, kg/m3 | 1200 |
Impact force, kJ/m2 | 65 |
Tensile strength, MPa | 65 |
Bending strength, MPa | 80 |
Molecular weight | 50,000 |
Methods
Methods of PC glycolysis
A weighed portion of EG and catalyst was placed in a 100-ml three-neck reactor and heated to the required temperature. Then, a sample of the initial PC was loaded into the hot reaction mass. A heating plate (model IKA C-MAG HS 7) was used for heating, and a thermocouple (model IKA ETS-D5) was used to keep the reaction mixture's temperature consistent throughout the procedure. Utilizing a magnetic anchor, stirring was done. The speed of the stirring was limited to 200–250 rpm.
Method of separation of the reaction mixture
The remains of unreacted PC were separated from the reaction mass obtained at the first stage by filtration, washed with water and acetone, then dried in an oven at 80°C, and weighed. The homogeneous reaction mass was unloaded into a separating funnel. Thereafter, 100 ml of water was added thereto. The funnel was shaken. The mixture was divided into two layers. The bottom layer is a light brown oily liquid (BPA, BPA and ethylene glycol ethers), the top layer is water and ethylene glycol with a possible admixture of BPA. The separated oily layer was qualitatively analyzed by NMR spectroscopy.
Method for obtaining BPA esters and ethylene glycol/ethylene carbonate
To assess the reactivity of BPA with ethylene carbonate and ethylene glycol, a direct reaction of BPA with the corresponding reagent was carried out.
A three-necked reactor was filled with a weighed amount of recrystallized BPA ethylene glycol or ethylene carbonate (stoichiometric ratio) and heated to 160°C before the addition of 0.6 ml of K2CO3 catalyst solution (0.1%mol. from BPA). The synthesis took place for three hours at 160°C while being stirred. HPLC was used to evaluate the reaction mass that resulted.
Analysis Methods
PC conversion (X(PC)) was determined according to Eq. (1):
$$X\left(PC\right)= \frac{m\left({PC}_{0}\right)-m\left({PC}_{1.}\right)}{m\left({PC}_{0}\right)} \times 100\%$$
1
where \(m\left({PC}_{0}\right)\) - the initial PC mass, g; \(m\left({PC}_{1}\right)\) - the mass of unreacted PC, g.
The mass of unreacted PC was determined by dividing its mass in grams by the molecular weight of the polymer unit, which was 254.29 g/mol.
The method of nuclear magnetic resonance (NMR) was used for the qualitative analysis of the products of the alkaline glycolysis of PC, which were an oily liquid. 13C-NMR and H1-NMR spectra were obtained on a Bruker AVANCE-III200 spectrometer at room temperature using standard Bruker pulse programs. The samples were prepared in standard 7'' 5-mm NMR ampoules in a solution of deuterated chloroform (purity not less than 99.9%), with a concentration of 5–6%wt.
High-performance liquid chromatography (HPLC) was used to assess the quantitative concentration of BPA and BPA esters produced during glycolysis. The approach states that initially, smaller molecules depart the column because they do not fully occupy the pores of the sorbent, and that as molecule size rises, so does the amount of time that substances are retained in the column.
In this study, the analysis was performed on a BISCHOFF HPLC system with NanoSpher Eco C8 250 mm × 4.6 mm × 5 µm (pore size 50Å) and NanoSpher Eco C18
300 mm × 4 mm × 10 µm (pore size 100Å) chromatographic columns connected in series, UV detector (wavelength 254 nm) and a computer with MultiChrom GPC software. The sample was dissolved in acetonitrile (TU 2636-017-29483781-2014). BPA was used as a standard. Analysis conditions: eluent – acetonitrile (TU 2636-017-29483781-2014); eluent flow rate – 0.5 ml/min; Tthermostat - +20℃; sample concentration − 0.01% mass; analysis time − 25 min.
A JEOL 1610LV scanning electron microscope was used to examine the structure of a PC particles that had partially reacted. Images were captured digitally at a 1,000x magnification. It was possible to calculate the surface area using the ImageJ application. The darkest portion of the image's histogram's range (from 0 to 60) was used to compute the area by adding all the pixels that represent that level of gray.
To study the structure of a PC plate, we used a Biomed-3 optical microscope and a Levenhuk C-Series camera model. A digital image was obtained at 4x magnification using the "Top View" program.