*3.5. Preparation of Polymer Composite Films and Characterisation*

To prepare the film forming solution, lyophilized PSC collagen was suspended at 0.1 (*w*/*v*) in 4% aqueous commercial vinegar solution with continuous stirring overnight at 4 ◦C.

The film-forming solution of chitosan extracted from shrimp waste (mean degree of deacetylation = 80%), was solubilised in a 4% aqueous commercial vinegar solution (1%, *w*:*v*) with an overnight continuous homogenisation at room temperature.

Once both polymer solutions were prepared, different films were prepared: pure CO, CH and mixture of collagen-chitosan solution with different ratios C50 (50% collagen, 50% chitosan), and C75 (25% collagen, 75% chitosan). For a homogeneous suspension, the collagen-chitosan solution was stirred continuously for at least 30 min at room temperature; the solution was then poured into Petri dishes and dried at room temperature. Finally, the dried films were peeled off manually and stored at maintained at 55% relative humidity in a desiccator before analysis.

#### 3.5.1. Thickness

The thickness of films was measured using a Thickness Tester (Thwing-Albert Instrument, ProGage, NJ, USA). Different locations on each film sample were used for determination of thickness.

#### 3.5.2. Mechanical Properties

The film's stress-strain properties (tensile strength TS and elongation at break point EAB) were measured in accordance to ISO 527-1 [85]. The test was performed using the universal testing machine (Lloyd Instruments Ltd, LRX plus Series, West Sussex, UK).

Films were cut to width 15 mm and conditioned at 23 ± 2 ◦C and ~50 ± 10% RH 25 ± 0.5 ◦C for 24 h before measurement. Initial grip separation distance was set to 30 mm and mechanical crosshead speed to 100 mm/min.
