Nicolet 6700 infrared spectrometer

The total polysaccharide content of EPS-160 was measured by the phenol-sulfuric acid (H₂SO₄) method (Yin et al., 2014 (link)). The presence of protein was determined using the Bradford method (Blum et al., 2008 (link)). For monosaccharide composition analysis, 20 mg EPS-160 was hydrolyzed with 2 mL of 2 M trifluoroacetic acid (TFA) at 120°C for 4 h. The hydrolyzate was evaluated by high-performance liquid chromatography (HPLC) (Agilent1200, United States) equipped with a ROA-Organic Acid H⁺(8%) column (Phenomenex, United States) (Zhang et al., 2017 (link)). Functional groups of EPS-160 were identified by measuring from 400 to 4000 cm^–1 wavenumbers in a Nicolet 6700 infrared spectrometer (Thermo Fisher, America). Molecular weights (MWs) of EPS-160 were analyzed by a gel permeation chromatography (GPC) system (LC20, Shimadzu, Japan). The system was equipped with a refractive index (RI) detector (RID-20, Shimadzu, Japan) and a TSK G4000PWXL column (Tosoh, Japan). The MWs was calculated according to the weight-averaged molecular weight.

Attenuated total reflectance Fourier-Transform Infrared Spectroscopy (ATR-FTIR) was used to determine changes in chemical bonding and interactions of post-consumer PP bottles and virgin PP bottles in three repeated measures. A Nicolet 6700 infrared spectrometer (Thermo Scientific, Waltham, MA, USA) with a DTGS detector was used with 32 scans per run and a 2 cm⁻¹ resolution at ambient temperature (22 °C). All spectra were baseline-corrected with OMINIC ^TM 8.3 software (Thermo Fisher, Waltham, MA, USA) [22 (link)]. The diamond window of the ATR assembly was cleaned with an isopropanol wipe after each measurement to ensure no cross-contamination [23 (link)].

To quantify the extracted melanin-like pigment, IR spectra were recorded by Nicolet 6700 infrared spectrometer (Thermo Fisher Scientific, Warsaw, Poland). A small amount of pigment was placed on a diamond window of the spectrometer, and a measurement was done in reflection mode, at a room temperature, by summary of 32 scans with a resolution of 4 cm^-1. The available spectra range was 400–4000 cm^-1. Synthetic melanin (Sigma-Aldrich, Cat. No M8631) was used as a standard.