*2.2.2.2 Crude fiber content*

The determination of the crude fiber content in our powders was determined using performed according to the method described by treating the sample to the boil with sulfuric acid followed by soda. The postharvest by-product obtained is then dried in an oven at 60°C for 24 h, calcined in an oven at 550°C for 4 h with a rate of rise in temperature of 10°C/min and weighed [19].

#### *2.2.2.3 Lignin quantity*

The lignin level was determined by the Klason method reported by Monties [20]. The method consists in observing the power of insolubility in an acidic solvent in a concentrated medium and dissolving all the constituents present in the material. The aim of this analysis was to obtain a raw material rich in woody constituent.

### *2.2.2.4 Reducing sugars quantity*

The reducing sugar content was determined using the DNS (acide 2-hydroxy-3, 5-dinitrobenzoïque) method described by Fischer *et al*. [8]. It begins with an extraction of sugars in a hot acidic medium. In a hot alkaline medium, DNS reacts with reducing sugars and changes from its yellow-oxidized form to its orangereduced form with a maximum absorption at 530 nm.

### *2.2.2.5 Determination of mass loss*

The difference between the mass of the sample before and after the pretreatment represents the mass loss. The sample is dried at105°C before and after pretreatment until a constant mass is obtained.

### *2.2.2.6 Pretreatment of hulls by the organosolv process*

It consists of a batch reactor with a total volume of 100 mL with the useful volume being 80 mL. The experimental protocol was inspired from that described by Nanfack et al. [21]. A mass of 4 g of cocoa shell is mixed with 80 ml of the pretreatment solvent (ethanol-water mixture 52:48 v/v) and loaded into the reactor. The latter is tightly sealed using silicone glue to ensure it is watertight. It is then put in an oven preheated to 200°C. The treatment is stopped by cooling under running water to room temperature. After cooling, the two solid and liquid phases are separated by filtration. The cocoa shell powder thus treated is dried and stored in a glass jar for later use.

#### *2.2.3 Manufacturing method of composite materials*

In this study, fine-sized plastic waste is obtained after shredding with a chisel. Plastic waste is then washed with water and dried at room temperature (25°C) for 3 days.

*Mechanical Properties and Chemical Stability of Bathroom Wall Composites Manufactured… DOI: http://dx.doi.org/10.5772/intechopen.102457*


**Table 2.**

*Formulation of the different composites according to the addition of the powder.*

Composite for PET and cocoa powder: The appropriate with of cocoa powder was added to melt PET in a Haack Rheomix at 225°C. The mixture weighing 200 g was processed for 10 min. The mixture obtained was then hot press at 225°C for 5 min at a pressure of 15 MPa and cooled under pressure. The choice of the temperature of 225° C. was due to the fact that a preliminary sweeping was carried out in order to find the minimum temperature, which makes it possible to develop the composite so as not to alter the powder. From the work of the literature, the melting temperature of PET was around 250° C. Specimens of dimensions 200 × 150 × 8 mm were prepared using a parallelepiped mold. The mold has been polished with a mold release agent to prevent the PET from sticking to it. The process involved melting the grated PET, adding a predetermined proportion of cocoa powder, melt-mixing to form a homogeneous viscous solution, and placing into the prepared mold. Finally, the mold was closed and the samples were cooled to room temperature under a pressure of 15 MPa for 30 min. The specimens of the tiles produced were shaped by sandpaper and used for testing.

Sheets of 3 mm thickness were obtained. The materials were made at different powder concentrations as shown in **Table 2**.

#### **2.3 Mechanical properties and chemical stability of composite**

## *2.3.1 Tensile test*

The tensile test evaluation was performed on the Instron 5567 with a climb speed of 50 mm/min. Preparation of samples for testing was performed according to ASTM D638. At the start of the analysis, the specimen lengthens and the resistance of the specimen increases, which was detected using a load cell; the value was recorded until the composite failed. For this, five samples were tested in order to evaluate the standard deviation [22–25].

#### *2.3.2 Flexural test*

Mechanical strength is the combination of tensile strength and compressive strength. The tests were carried out on a universal testing machine. The specimens were prepared according to the test standard ASTM D790 of dimension 200 × 30 × 8 mm. These samples of composites produced in varying proportions of PET were tested on a support span of 130 mm according to the standard [13].

#### *2.3.3 Impact test*

Charpy impact tests on notched specimens were performed using a model JBS-300 N pendulum impact testing machine. Specimens were prepared according to the ASTM D6110-18 test standard. With a dimension of 50 mm long and a cross section of 24 mm2 , five specimens were tested and one mean value was reported [13].

#### *2.3.4 Water absorption*

The water absorption test was performed on parallelepipedal specimens according to ASTM-C373 [22] where the composite samples were weighed and immersed

in a beaker containing distilled water and the whole boiled, for 2 h, and allowed to cool for 24 h at room temperature. The specimens were then wiped with a paper towel and weighed.
