**2.3. Preparation of the biocomposites**

an extensive variety of polymer matrices like polyethylene [2, 3], polypropylene [4], polystyrene [5], polyester resins [6], and natural rubber [7]. Clear effects have been seen in the improvement of mechanical performance. For example, usually Young's modulus and tensile and flexural strength increase when natural fibers are compounded in percentages from 10 to 40%, which make the composites stiffer than its matrix counterpart [8]. Also, improvement in impact strength has been observed [9]. These findings give to the natural fibers a real opportunity to replace to some extent the use of fiberglass, aramid, and other synthetic fibers usually used for polymer reinforcement since, on top of their reinforcement ability, natural fibers are also cheap and have a much lower density than fiberglass, as previously stated in literatures [10–12]. However, the interest in utilization of natural fibers in biocomposites goes beyond their advantages for formulating new and mechanically improved materials. Interest is also driven by a global concern about the impact of plastics in the environment and a growing consciousness of the need for establishing a circular economy where residues like biomass and lignocellulosic can be valued and used as new raw material for industrial processes [13, 14]. In that regard it makes sense to use the agroforestry residues of extensive

of using them for energy production through combustion. An example of the potential of lignocellulosic materials is the region of Valle del Cauca in the South West of Colombia, which has a large influence of the sugarcane industry. It produces 80% of all Colombian sugar, and also it counts for 50% of all local agricultural production. This industry produces a lot of agroforestry residues, approximately 6 million tons of sugarcane bagasse a year [15]. The availability and low cost of this residue are thought as competitive advantages for the development of sustainable biocomposites in this region. That is the main reason behind of our resent research: the valorization of sugarcane residues by their use in natural fiber reinforced polymer composites (NFPC). In regard to the use of sugarcane bagasse, some studies have reported its use as reinforcement for polypropylene, polyester, recycled PET, PVC, HIPS, and HDPE and as agents and/or compatibilizing treatments such as aluminates and mercerization (NaOH treatment) and the use of ethylene and methyl acrylate as copolymers and benzyl chloride [16–19]. However, to the best of our knowledge, there have been no reports of the use of silanes as compatibilizing agents in sugarcane bagasse microfibers, in order to improve their adhesion to polymer matrices. In this chapter, polypropylene bagasse (PP bagasse) biocomposites prepared through extrusion, injection, and thermocompression molding will be evaluated. The morphology as well as the mechanical, thermal, and thermomechanical properties of the biocomposites will be investigated with the aim to understand the effect of the chemical treatments of the bagasse fibers on the polypropylene (PP) matrix properties.

Sugarcane bagasse was obtained from a local sugar mill and kindly provided by Sucromiles S.A. Hexadecyltrimethoxysilane and sodium hydroxide were analytical-grade reagents from Aldrich (Wisconsin, USA). Absolute ethanol was a product from Merck (PA, USA). Polypropylene

homopolymer 01H41 was obtained from Essentia (Cartagena, Colombia).

process, like the fabrication of composites, instead

crops in a way that results in a neutral CO2

132 Characterizations of Some Composite Materials

**2. Materials and methods**

**2.1. Materials**

Biocomposites were compounded in a counter-rotating twin screw extruder Thermo Scientific HAAKE™ Polylab. In all cases fibers were physically premixed with polypropylene pellets in a plastic bag using 20% of fiber in weight. About 500 g of fiber-polypropylene mix was introduced in the extruder at 70 rpm. A temperature gradient from 140 to 170°C from the feeder to the melting zone was used. The outcoming cord of composite from the extruder was pelletized using a rotating cutter which produced pellets of about 5 mm long.

After the pelletization process, the PP and PP-bagasse biocomposite samples were dried in an oven at 85°C followed by injection molding process at 180°C. A BOY XS (BOY Machines, Inc., USA) microinjection molding machine was used to prepare samples (3\*12.7\*60 mm) for flexural and impact tests. An injection pressure of 68 bar and a back pressure of 18 bar were used.

Also, sheets of the different samples were obtained using a hot-plate press and a forced water circulation cooling system (LabPro 400, Fontijne Presses). To shape the specimens, stainless steel molds were used. The molding was conducted at a temperature of 185°C, with a pressure of 50 kN and a 15 minute cycle. Finally, the sheets were demolded and adjusted to the required dimensions for DMA tests (1.7\*12.7\*60 mm) using a computer numerical control router. **Figure 1** shows the injected specimens of PP and a PP-bagasse biocomposite.

and, in others, as viscous fluids. As such, its mechanical properties also depend on time, stress, and temperature. The present study of the viscoelastic performance was carried out in a DMA RSA-G2 with ACS-3 Air Chiller System. In order to identify the viscoelastic behavior

Biocomposites from Colombian Sugarcane Bagasse with Polypropylene: Mechanical, Thermal…

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135

To begin the study of the viscoelastic response of biocomposites, the linear viscoelastic region for the PP matrix was identified. To find this region, strain sweeps were carried out at a defined temperature. The geometry used to perform these tests was three-point bending. A strain sweep test takes successive measurements with an increase in the strain. For these experiments, the RSA-G2 was programmed with a strain between 0.001 and 1%; the

After finding the linear viscoelastic zone, temperature ramp tests were performed to observe the behavior of the PP matrix at different temperatures. These tests were performed between

Scanning electronic microscopy (SEM) of biocomposites was carried out on the cryogenic fracture surfaces of the specimens using a Quanta FEG 250 microscope operating at a voltage of 10 kV. The samples were previously sputter-coated with gold to increase their electric conductivity. The cross-sectional diameters of the dispersed phase were measured using ImageJ 1.8v (Wayne Rasband, National institutes of health, USA). Determinations were performed in different areas

Flexural and impact properties of the materials were subjected to analysis of variance (ANOVA), and the Tukey's test was applied at the 0.05 level of significance. All statistical analyses were performed using Minitab Statistical Software Release 12 (Pennsylvania, USA).

In order to produce and tune a lignocellulosic material to improve the mechanical performance of natural fiber reinforced polymer composites (NFPC), it is very important to conceptualize adhesion as one of the most important factors to achieve such challenge [20, 21]. Adhesion on the polymer-fiber interface is said to follow one of the four common mechanisms: mechanical interlocking, electrostatic interactions, molecular entanglement, or chemical bonding [22]. Many commercial polymer-coupling additives like maleic and acrylate grafted thermoplastics work as adhesion enhancers in polyolefins by generating chemical bonds with the free

**3.1. Preparation of bagasse microfibers for biocomposite fabrication**

frequency was constant at 1 Hz. Measurements were made at 0, 30, and 60°C.

of biocomposites, the following test modes were used:

−60°C and 170°C, at 1 Hz, 3°C/min, and 0.01% of strain.

*2.4.4.1. Strain sweep tests*

*2.4.4.2. Temperature ramp tests*

*2.4.5. Morphology*

of the SEM images.

*2.4.6. Statistical analysis*

**3. Results and discussion**

**Figure 1.** Injected specimens of PP and a PP-bagasse biocomposite.
