## 3 Results and Discussion
### Mechanical Properties
Mean values and standard deviation. Different superscripts indicate statistically significant differences (_p_< 0.05). Figure 6: Mechanical properties of all prepared WFF biocomposites with coffee silverskin particles and extracts. Mean values and standard deviation. Different superscripts indicate statistically significant differences (_p_< 0.05). Estimating Young's modulus from the stress-strain curve has limitations due to equipment accuracy, slippage, and loss of accuracy at large deformations. To provide more accurate estimations, Figure 7 shows tensile stress-strain% curves for selective samples, followed by a comparison of our films with well-known materials. The % elongation values for LDPE according to the literature are 20-100% and 100-700% for HDPE. The values of the WFF and the films with extracts are higher than those of LDPE and are in the range of those of HDPE. The values of all the films showed much lower values than the tensile stress and Young's modulus of LDPE (7-17 MPa, 102-240 MPa) and HDPE (18 MPa, 960-1000 MPa) [56]. It is widely recognized that the level of moisture present in the samples significantly influences the mechanical characteristics of the materials, and it is possible that this factor had an impact in this instance. However, the significant decrease in Young's modulus with the addition of 1% coffee silverskin extract and the substantial increase with the addition of 2.5% CS particles can be attributed to various factors affecting the microstructure and mechanical behavior of the membranes. The samples with extracts may contain polyphenols and other water-soluble compounds that act as plasticizers, reducing the rigidity of the polymer material and leading to a decrease in Young's modulus. This results in a more flexible and less stiff material. Furthermore, the particles can act as reinforcing agents, enhancing the mechanical properties of the polymer through mechanisms such as dispersion strengthening and secondary phase reinforcement, resulting in an increase in stiffness and Young's modulus. The films of wheat flour and coffee silverskin particles produced in this work presented superior mechanical properties than the extruded films produced only with wheat flour by [PERSON] et al. (tensile stress of 0.7-1.4 MPa and tensile strain of 36-72%) [57]. Similar values of tensile stress and lower values of tensile strain, in comparison with films with CS extracts, were observed by [PERSON] et al. for extruded films with wheat flour (tensile stress ranged from 0.72 to 1.75 MPa and tensile strain ranged from 38.33 to 115.82%) [7]. Wheat flour by-product films containing glycerol and sorbitol exhibited lower values of tensile stress than the WFF-Xss films and values similar to films with CS extracts (ranging from 0.10 to 2.82 MPa), with tensile strain analogous to the WFF-Xss films (ranging from 25.84% to 56.71%) [43]. Similarly, biodegradable thermoplastics derived from wheat flour with varying concentrations of glycerol displayed lower Young's modulus (16-276 MPa), tensile stress (0.9-4.9 MPa), and tensile strain (14-44%) [58]. The incorporation of oregano oil microparticles in wheat flour/PBAT active films during production resulted in comparable tensile stress (3.01-3.87 MPa), increased tensile strain (296.67-351.65%), and reduced Young's modulus, comparable to films with CS  
Figure 7: Tensile stress–strain curves for selected samples. extracts (15.20-19.16 MPa) [45]. [PERSON] et al. [59] found that the addition of spent coffee grounds into thermoplastic wheat flour led to an increase in tensile strength and a decrease in the swelling degree of biocomposites.