Dsc821

Polymers and WPC, especially wood fibers that present low thermal stability, can suffer thermal degradation when subject to high temperature during the extrusion process. Therefore, degradation temperature and melting temperature can be related to the decrease in the molecular mass of the polymer as a result of the thermal degradation [16 (link)].
The thermal degradation temperature was measured using a Thermo Gravimetric Analyzer TGA Q500 (TA instruments, New Castle, DE, USA) under nitrogen flow. The sample was heated at a heating rate of 10 °C/min within the temperature range of 0–900 °C. To ensure complete polymer melting inside the extruder, the melting temperature was measured by using differential scanning calorimetry—DSC821 (Mettler Toledo, OH, USA). The samples were cooled down to −40 °C and held for 3 min. Next, they were heated until 200 °C at a rate of 10 °C/min with a nitrogen flow of 80 mL/min.

The thermal stability of untreated and GA vapour treated collagen disks were determined by DSC using a Mettler Toledo DSC821 instrument. The collagen sponge disks were between 0.8 and 0.9 mg each and were rehydrated in phosphate buffered saline (PBS) prior to analysis. A heating rate of 5°C/min was used. Data were averaged from separate sample determinations, with at least 2 determinations for each condition. The range of values obtained was typically around 1°C for each condition tested.

Thermal characterization was carried out by DSC on a DSC821 from Mettler-Toledo, Inc. (Schwarzenbach, Switzerland). Small samples sizing 6–7 mg were subjected to a dynamic thermal program of three stages: an initial heating from 30 up to 280 °C, a cooling process down to 0 °C, and a second heating cycle from 0 up to 350 °C. The heating and cooling rates were set at 10 °C·min⁻¹ and the atmosphere was nitrogen at a flow-rate of 66 mL·min⁻¹. DSC runs were done in triplicate to obtain reliable results. The main thermal parameters were obtained from the second heating runs to remove the thermal history of the pieces. In addition, the bio-PET crystallinity was also calculated by the expression: $\%{\chi }_c=\frac{(\Delta H_m-\Delta H_{cc)}}{\Delta H_{100\%}·W_p}·100$
where:

%χ_c = Degree of crystallinity (%)

W_p = Weight fraction of bio-PET (%)

ΔH_m = Melting enthalpy (J·g⁻¹)

ΔH_cc = Cold crystallization enthalpy (J·g⁻¹)

ΔH_100% = Melting enthalpy of 100% crystalline PET = 140 J·g⁻¹ [84 (link),85 (link)]

Thermal degradation was evaluated by TGA in a TGA/SDTA851 thermobalance from Mettler-Toledo, Inc. Samples with an average weight of 4–5 mg were subjected to a temperature sweep from 30 up to 700 °C at a constant heating rate of 20 °C·min⁻¹ in air atmosphere (50 mL·min⁻¹). TGA runs were performed in triplicate.